Low viscosity self-crosslinking acrylate leather re-tanning agent, preparation method and application thereof

Abstract

The application discloses a low-viscosity self-crosslinking acrylate leather re-tanning agent and a preparation method and application thereof. The re-tanning agent is prepared by polymerization of 55-65 parts of hydrophilic monomers, 35-45 parts of hydrophobic monomers and 19-22 parts of redox initiators in pure water. The hydrophobic monomers include (methyl) acrylate alkyl ester monomers and unsaturated monomers containing epoxy groups. The application adopts a specific mixed dropping polymerization process, limits the reaction temperature to 53-57 DEG C, controls the monomer pH in a narrow range of 6.4-8.4, overcomes the technical bottleneck that the unsaturated monomers containing epoxy groups in the high-carboxyl water phase system are prone to hydrolysis failure, and retains the in-situ self-crosslinking activity. Meanwhile, the initiators are pre-dropped 3-10 minutes before the mixed monomers, a transient high-concentration free radical environment is constructed in the reaction system, the high-hydrophilic components (>55%) are caused to occur strong redox high-frequency nucleation, the polyelectrolyte swelling bridge bonding thickening is fundamentally inhibited, and the latent self-crosslinking stable emulsion with an apparent viscosity of only 300-800 cps is obtained.

Description

Technical Field

[0001] This invention relates to the field of leather chemicals, specifically to a low-viscosity self-crosslinking acrylate leather retanning agent, its preparation method, and its application. Background Technology

[0002] In the leather water treatment process (retanning, filling), synthetic polymer retanning agents are the core auxiliaries that impart fullness, body, and suppleness to the finished leather. Among them, acrylic systems are one of the most widely used and mainstream retanning agent systems. However, in existing technologies, there has been a long-standing technical contradiction between filling performance and penetration efficiency. Currently, in pursuit of a higher filling feel, it is usually necessary to increase the molecular weight of the polymer or the solid content of the system, which inevitably leads to a sharp increase in the apparent viscosity of the product (usually reaching thousands to tens of thousands of cps). This high viscosity causes a penetration threshold limitation, making polymer particles prone to "chromatographic retention effect" on the leather surface, resulting in a non-homogeneous filling phenomenon of "surface accumulation and hollow center". This not only induces "tube wrinkles" on the grain surface, but also hinders the synergistic penetration and uniform distribution of subsequent dyes and chemicals due to the shielding effect, greatly increasing the difficulty of controlling the leather tanning process. In addition, conventional polymer systems mostly lack effective chemical anchoring mechanisms, residing only in the fiber in the form of physical accumulation, resulting in insufficient thermal stability and physical durability. During subsequent vacuum drying, high-temperature embossing, or washing processes, the filler is prone to thermal migration or loss, leading to leather thinning and hardening, and a significant decline in sensory quality. Simultaneously, the high-viscosity medium inhibits the removal efficiency of residual monomers, making it difficult to consistently meet stringent environmental limits.

[0003] Although existing technologies have attempted to achieve self-crosslinking using N-hydroxymethylacrylamide and other methods, formaldehyde release occurs during the crosslinking process. Systems modified with other functional monomers often suffer from poor molecular structure controllability or limitations of the emulsion system, leading to a significant increase in product viscosity and failing to overcome the technical bottleneck of deep penetration. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing polymer retanning agents, such as poor penetration performance due to excessively high viscosity and insufficient filling durability due to the lack of effective chemical anchoring of molecular chains. This invention provides a low-viscosity self-crosslinking acrylic leather retanning agent, its preparation method, and its applications. The product of this invention maintains a high filling feel while possessing excellent deep penetration performance.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a method for preparing a low-viscosity self-crosslinking acrylate leather retanning agent, comprising the following steps: (1) Weigh 55-65 parts of hydrophilic monomer, 35-45 parts of hydrophobic monomer and 20-40 parts of pure water based on a total monomer mass of 100 parts, mix them, and adjust the pH value to 6.0-8.4 with alkaline solution to obtain a mixed monomer solution; the hydrophobic monomer component includes (meth)acrylate alkyl ester monomer and epoxy-containing unsaturated monomer; (2) The first oxidizing agent, the first reducing agent, the second oxidizing agent, and the second reducing agent are water-soluble and are dissolved in pure water to obtain the first oxidizing agent solution, the first reducing agent solution, the second oxidizing agent solution, and the second reducing agent solution, respectively; (3) Add pure water and catalyst to the reactor, introduce nitrogen gas, raise the temperature to 50-60℃, start adding the first oxidant solution and the first reducing agent solution, wait 3-10 min, then start adding the mixed monomer solution obtained in step (1), and then add the three simultaneously, controlling the polymerization reaction temperature to 50-60℃; (4) After the addition is completed, stir at a constant temperature, add the second oxidant solution and the second reducing agent solution to eliminate the residual monomer, cool down and discharge to obtain a low viscosity acrylic polymer emulsion.

[0006] As a preferred embodiment of the present invention, the hydrophilic monomer in step (1) includes at least one of the following: unsaturated monomers containing carboxyl groups, unsaturated monomers containing hydroxyl groups, and unsaturated monomers containing amino groups.

[0007] As a preferred embodiment of the present invention, the carboxyl-containing unsaturated monomer is selected from at least one of acrylic acid, methacrylic acid, itaconic acid, maleic acid, and fumaric acid; preferably acrylic acid.

[0008] As a preferred embodiment of the present invention, the hydroxyl-containing unsaturated monomer is selected from at least one of hydroxyethyl acrylate, hydroxypropyl acrylate, and hydroxyethyl methacrylate; preferably hydroxyethyl acrylate.

[0009] As a preferred embodiment of the present invention, the amino-containing unsaturated monomer is selected from at least one of acrylamide, methacrylamide, and N,N-dimethylacrylamide.

[0010] As a preferred embodiment of the present invention, the hydrophobic monomer includes at least one of (meth)acrylate alkyl ester monomers and epoxy-containing unsaturated monomers; the (meth)acrylate alkyl ester monomer is selected from at least one of (meth)acrylate methyl acrylate, ethyl acrylate, butyl acrylate, isooctyl acrylate, and lauryl acrylate; preferably methyl methacrylate.

[0011] As a preferred embodiment of the present invention, the epoxy-containing unsaturated monomer is selected from at least one of glycidyl methacrylate, glycidyl acrylate, and allyl glycidyl ether; preferably glycidyl methacrylate.

[0012] As a preferred embodiment of the present invention, the amount of pure water added in step (1) is 25-35 parts.

[0013] As a preferred embodiment of the present invention, the pH value in step (1) is preferably 6.4-7.0, more preferably 6.5-6.8.

[0014] As a preferred embodiment of the present invention, in step (2), the first oxidant or the second oxidant is selected from at least one of sodium persulfate, potassium persulfate, ammonium persulfate, and tert-butyl hydroperoxide; the first reducing agent or the second reducing agent is selected from at least one of sodium bisulfite, sodium metabisulfite, sodium dithionite, and sodium isoascorbate. Preferably, the first oxidant or the second oxidant is sodium persulfate; preferably, the first reducing agent or the second reducing agent is sodium metabisulfite.

[0015] As a preferred embodiment of the present invention, in step (2), based on a total monomer mass of 100 parts, the total amount of the first oxidant and the first reducing agent is 18-20 parts, the mass ratio of the first oxidant and the first reducing agent is 2:0.9-1.1, preferably 2:1; the concentration of the first oxidant solution is 30wt%, and the concentration of the first reducing agent solution is 15-16wt%.

[0016] As a preferred embodiment of the present invention, the total amount of the second oxidant and the second reducing agent is 1-2 parts, the mass ratio of the second oxidant and the second reducing agent is 1:2-3, preferably 1:1.7; the concentration of the second oxidant solution is 3-4 wt%, and the concentration of the second reducing agent solution is 5-7 wt%.

[0017] As a preferred embodiment of the present invention, in step (3), the dropping time of the first oxidant solution and the first reducing agent solution is 285 min, and the dropping time of the mixed monomers is 280 min.

[0018] As a preferred embodiment of the present invention, the alkaline solution is selected from at least one of sodium hydroxide, potassium hydroxide, and ammonia water; As a preferred embodiment of the present invention, the alkaline solution in step (1) is preferably a 35% sodium hydroxide aqueous solution.

[0019] As a preferred embodiment of the present invention, the catalyst is selected from at least one of ferrous sulfate, ferrous chloride, ferrous ammonium sulfate, and copper sulfate; the catalyst is preferably ferrous sulfate.

[0020] As a preferred embodiment of the present invention, the amount of catalyst added in step (3) is 0.0003 wt% of the mixed monomers.

[0021] As a preferred embodiment of the present invention, the polymerization reaction temperature in step (3) is 53-57°C, preferably 55°C.

[0022] In a second aspect, the present invention provides a low-viscosity self-crosslinking acrylate leather retanning agent prepared by the above method.

[0023] As a preferred embodiment of the present invention, the low-viscosity self-crosslinking acrylate leather retanning agent has an apparent viscosity of 300-800 cps at 25°C, a pH of 6.5-7.5, and a solid content of 25%-30 wt%.

[0024] In a third aspect, the present invention provides an application of the above-mentioned low-viscosity self-crosslinking acrylate leather retanning agent for leather tanning.

[0025] Compared with the prior art, the present invention has the following beneficial effects: (1) Deep penetration and homogeneous filling performance: This invention selects specific hydrophilic and hydrophobic monomers, controls the polymer molecular weight through a high-proportion redox initiation system, and combines pH value adjustment to maintain the apparent viscosity of the retanning agent at 300-800 cps while maintaining a high hydrophilicity ratio. This invention achieves a filling feel comparable to conventional high-viscosity (thousands of cps) products under low viscosity conditions, effectively reducing the penetration resistance in the retanning process. By avoiding the physical accumulation of high-viscosity media on the particle surface, the risk of tube wrinkling induced under complex working conditions is reduced from the source, improving process safety and agent utilization.

[0026] (2) In-situ anchoring and self-crosslinking enhancement: This invention utilizes epoxy groups to construct a latent self-crosslinking system. Under retanning conditions (pH 3.5-4.5) and drying induction, the epoxy groups open in situ, constructing a three-dimensional network between molecules while simultaneously coupling and anchoring with active groups (-NH2, -OH, -COOH) on collagen fibers. This crosslinking process utilizes the decrease in pH during the process and the evaporation of moisture during drying, leading to an increase in the concentration of cyclic monomers, hydroxyl groups, or amino groups, achieving bulk crosslinking. This dual enhancement mechanism compensates for the limitations of short-chain polymer molecular weight, significantly improving the thickness and resilience of the leather, and effectively preventing the leather from losing thickness and hardening after subsequent high-temperature processing.

[0027] (3) High conversion rate and environmental friendliness: This invention employs a specific low-temperature redox initiation system (reaction temperature 53-57℃), effectively overcoming the technical bottleneck of premature epoxy ring hydrolysis in aqueous phases of traditional high-temperature initiation polymerization (>80℃). It fully preserves the potential crosslinking activity of the epoxy-containing unsaturated monomers in the aqueous medium, thus achieving a perfect balance between waterborne green manufacturing and long-lasting in-situ self-crosslinking performance. Furthermore, the initiator replenishment process in the later stages of polymerization not only ensures extremely high monomer conversion rate and significantly reduces residual monomer content, but also eliminates the need for aldehyde-containing crosslinking agents or thiol chain transfer agents, meeting green manufacturing standards.

[0028] This invention is a self-crosslinking acrylate retanning agent that combines ultra-low viscosity, high penetration efficiency, and environmental friendliness, and is of great value for improving leather quality and simplifying processing. Detailed Implementation

[0029] Unless otherwise stated, all "parts" in this invention refer to parts by weight.

[0030] The described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0031] Unless otherwise specified, all materials and reagents used in the examples and comparative examples are commercially available.

[0032] Example 1 A method for preparing a low-viscosity self-crosslinking acrylic leather retanning agent, the specific steps of which are as follows: (1) Weigh 50g of acrylic acid, 5g of hydroxyethyl acrylate (55 parts of hydrophilic monomers), 33g of methyl methacrylate, 12g of glycidyl methacrylate (45 parts of hydrophobic monomers) and 35g of pure water into a flask and mix them. Adjust the pH to 6.4 with 35% sodium hydroxide solution to obtain a mixed monomer solution. (2) Dissolve 12.35g of sodium persulfate in 28.5g of pure water to prepare a first oxidizing agent solution with a concentration of 30wt%; dissolve 6.2g of sodium metabisulfite in 33g of pure water to prepare a first reducing agent solution with a concentration of 15.8wt%; dissolve 0.5g of sodium persulfate in 15g of pure water to prepare a second oxidizing agent solution with a concentration of 3.2wt%; dissolve 1.2g of sodium metabisulfite in 17g of pure water to prepare a second reducing agent solution with a concentration of 6.6wt%. (3) Add 150g of pure water and 0.0003g of ferrous sulfate to the reactor, purge with nitrogen, and heat to 55℃; begin adding the first oxidizing agent solution and the first reducing agent solution, and after 5min, begin adding the mixed monomer solution from step (1). Control the dropping time of the first oxidizing agent solution and the first reducing agent solution to 285min, the dropping time of the mixed monomer solution to 280min, and maintain the reaction temperature at 55℃; (4) After the addition is complete, stir at a constant temperature of 53-57℃ for 30 minutes; then add the second oxidant solution and the second reducing agent solution, continue to stir at a constant temperature for 30 minutes, and then cool down and discharge. The emulsion obtained in Example 1 had an apparent viscosity of 300 cps, a pH of 6.77, and a solid content of 30.13%.

[0033] Example 2 (1) Weigh 50g of acrylic acid, 5g of hydroxyethyl acrylate (55 parts of hydrophilic monomers), 33g of methyl methacrylate, 12g of glycidyl methacrylate (45 parts of hydrophobic monomers) and 35g of pure water into a flask and mix them. Adjust the pH to 8.4 with 35% sodium hydroxide solution to obtain a mixed monomer solution. (2) Dissolve 13g of sodium persulfate in 30g of pure water to prepare a first oxidizing agent solution with a concentration of 30wt%; dissolve 6.5g of sodium metabisulfite in 35g of pure water to prepare a first reducing agent solution with a concentration of 15.7wt%; dissolve 0.5g of sodium persulfate in 15g of pure water to prepare a second oxidizing agent solution with a concentration of 3.2wt%; dissolve 1.2g of sodium metabisulfite in 17g of pure water to prepare a second reducing agent solution with a concentration of 6.6wt%. (3) Add 150g of pure water and 0.0003g of ferrous sulfate to the reactor, purge with nitrogen, and heat to 55°C; start adding the first oxidant solution and the first reducing agent solution, and start adding the mixed monomer solution from step (1) after 3 minutes; control the adding time of the first oxidant solution and the first reducing agent solution to 285 minutes, the adding time of the mixed monomer solution to 280 minutes, and maintain the reaction temperature at 55°C; (4) After the addition is complete, stir at 55°C for 30 min; then add the second oxidant solution and the second reducing agent solution, continue to stir at 55°C for 30 min, and then cool down and discharge. The emulsion obtained in Example 2 had an apparent viscosity of 490 cps, a pH of 6.83, and a solid content of 28.33%.

[0034] Example 3 A method for preparing a low-viscosity self-crosslinking acrylic leather retanning agent, the specific steps of which are as follows: (1) Weigh 50g of acrylic acid, 5g of hydroxyethyl acrylate (55 parts of hydrophilic monomers), 33g of methyl methacrylate, 12g of glycidyl methacrylate (45 parts of hydrophobic monomers) and 35g of pure water into a flask and mix them. Adjust the pH to 7.0 with 35% sodium hydroxide solution to obtain a mixed monomer solution. (2) Dissolve 13g of sodium persulfate in 30g of pure water to prepare a first oxidizing agent solution with a concentration of 30wt%; dissolve 5.85g of sodium metabisulfite in 31.5g of pure water to prepare a first reducing agent solution with a concentration of 15.7wt%; dissolve 0.5g of sodium persulfate in 15g of pure water to prepare a second oxidizing agent solution with a concentration of 3.2wt%; dissolve 1.2g of sodium metabisulfite in 17g of pure water to prepare a second reducing agent solution with a concentration of 6.6wt%. (3) Add 150g of pure water and 0.0003g of ferrous sulfate to the reactor, purge with nitrogen, and heat to 55℃; begin adding the first oxidizing agent solution and the first reducing agent solution dropwise, and after 3 minutes, begin adding the mixed monomer solution from step (1). Control the dropping time of the first oxidizing agent solution and the first reducing agent solution to 285 minutes, the dropping time of the mixed monomer solution to 280 minutes, and maintain the reaction temperature at 55℃; (4) After the addition is complete, stir at 55°C for 30 minutes; then add the second oxidizing agent solution and the second reducing agent solution, continue to stir at 55°C for 30 minutes, and then cool down and discharge. The emulsion obtained in Example 3 was found to have an apparent viscosity of 770 cps, a pH of 6.86, and a solid content of 26.65%.

[0035] Comparative Example 1 A method for preparing a low-viscosity self-crosslinking acrylic leather retanning agent, the specific steps of which are as follows: (1) Weigh 50g of acrylic acid, 5g of hydroxyethyl acrylate (55 parts of hydrophilic monomers), 33g of methyl methacrylate, 12g of glycidyl methacrylate (45 parts of hydrophobic monomers) and 35g of pure water into a flask and mix them. Adjust the pH to 8.4 with 35% sodium hydroxide solution to obtain a mixed monomer solution. (2) Dissolve 13g of sodium persulfate in 30g of pure water to prepare a first oxidizing agent solution with a concentration of 30%; dissolve 5.85g of sodium metabisulfite in 31.5g of pure water to prepare a first reducing agent solution with a concentration of 15.7wt%; dissolve 0.5g of sodium persulfate in 15g of pure water to prepare a second oxidizing agent solution with a concentration of 3.2wt%; dissolve 1.2g of sodium metabisulfite in 17g of pure water to prepare a second reducing agent solution with a concentration of 6.6wt%. (3) Add 150g of pure water and 0.0003g of ferrous sulfate to the reactor, purge with nitrogen, and heat to 55°C; start adding the first oxidant solution and the first reducing agent solution, and start adding the mixed monomer solution from step (1) after 3 minutes; control the adding time of the first oxidant solution and the first reducing agent solution to 285 minutes, the adding time of the mixed monomer solution to 280 minutes, and maintain the reaction temperature at 55°C; (4) After the addition was completed, the mixture was stirred at a constant temperature of 55°C for 30 minutes; then the second oxidant solution and the second reducing agent solution were added, and the mixture was kept at a constant temperature for another 30 minutes before being cooled and discharged. The emulsion obtained in Comparative Example 1 had an apparent viscosity of 38,000 cps, a pH of 7.16, and a solid content of 25.87%.

[0036] The retanning agents prepared in the various embodiments and comparative examples of the present invention are tested for their various performance indicators and application effects as follows: (1) Apparent viscosity: The NDJ-1 type rotary viscometer was used to measure the viscosity at 25℃. The No. 2 rotor was selected and the speed was set to 30 rpm. If the viscosity of the sample exceeded the range, the corresponding rotor and speed were switched for measurement.

[0037] (2) Solid content: The solid content is determined by referring to the method specified in GB / T 2793-1995. A certain amount of sample is weighed, dried to constant weight, and the mass fraction of non-volatile matter is calculated.

[0038] (3) Sensory performance evaluation (retanning application): Commercially available conventional wet blue leather was selected as the test leather sample, and a comparative experiment with equal feed amount was conducted according to the conventional retanning process in this field. The sensory performance evaluation of the finished leather followed the relevant provisions in GB / T 40000-2021 "Sensory Inspection Requirements for Leather". Three experts conducted a blind evaluation and scored the finished leather on its filling properties, body feel (elasticity and fullness maintenance ability), and grain smoothness and fineness. The score ranged from 1 to 10 points (10 points was the best), and the average value was taken as the evaluation result.

[0039] The retanning agents prepared in Examples 1-3 and Comparative Example 1 were subjected to various performance tests and retanning application experiments. The performance data and sensory evaluation results are summarized in Table 1.

[0040] Table 1: Summary Table of Performance Tests for Low-Viscosity Self-Crosslinking Acrylic Retanning Agents

[0041] As can be seen from the performance data and application evaluation results in Table 1: (1) Synergistic viscosity control effect and criticality of pH and initiator: Comparing Examples 1 and 2, it can be seen that in the pH range of 6.4-8.4, the amount of redox initiator is above the critical value. Even if the total amount of initiator is slightly adjusted by the same ratio of oxidant and reductant, the system can still maintain an extremely low viscosity range of 300-490 cps, indicating that this pH range is an excellent low viscosity control window. Comparing Example 3 and Comparative Example 1, it can be seen that under the same reduction of reductant (10%), the apparent viscosity of Comparative Example 1 (pH 8.4) increased dramatically to 38,000 cps compared with Example 3 (pH 7.0). This proves that in the high pH environment of the present invention, a high dose of reductant is the key to maintaining a high initiation rate and generating a massive number of instantaneous active centers to inhibit excessive molecular chain entanglement. Once the amount is below the critical value, the polymerization kinetic equilibrium is broken, leading to viscosity runaway. This experiment fully confirms that the initiator ratio range of this application can obtain a low viscosity and high-filling acrylic leather retanning agent.

[0042] (2) The technological advantages of "low viscosity and high filling": Examples 1-3 all exhibit significant low viscosity characteristics, and the filling performance and body feel scores remain at a high level, with Example 1 showing the best overall performance. This invention compensates for the filling limitations of low molecular weight systems through an in-situ self-crosslinking mechanism, significantly enhancing the body feel and thickness of leather while ensuring deep penetration, and successfully resolving the contradiction between filling performance and penetration efficiency.

[0043] This invention employs a specific mixed-droplet polymerization process: by limiting the reaction temperature to 53-57℃ and controlling the monomer pH within a narrow range of 6.4-8.4, it overcomes the technical bottleneck of easily hydrolyzing and failing epoxy-containing unsaturated monomers in high-proportion carboxyl aqueous phase systems, thus fully preserving their in-situ self-crosslinking activity. Simultaneously, by pre-dropping the initiator 3-10 minutes before the mixed monomers, a transient high-concentration free radical environment is constructed in the reaction system, promoting strong redox high-frequency nucleation of highly hydrophilic components (>55%), fundamentally inhibiting polyelectrolyte swelling, bridging, and thickening, resulting in a latent self-crosslinking stable emulsion with an apparent viscosity of only 300-800 cps. This invention breaks through the limitations of traditional retanning agents that achieve filling effects through high viscosity, achieving a unity of high penetration and strong filling, and fully complying with environmental standards.

[0044] The embodiments described above are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing a low-viscosity self-crosslinking acrylate leather retanning agent, characterized in that, Includes the following steps: (1) Weigh 55-65 parts of hydrophilic monomer, 35-45 parts of hydrophobic monomer and 20-40 parts of pure water based on a total monomer mass of 100 parts, mix them, and adjust the pH value to 6.0-8.4 with alkaline solution to obtain a mixed monomer solution; the hydrophobic monomer component includes (meth)acrylate alkyl ester monomer and epoxy-containing unsaturated monomer; (2) The first oxidizing agent, the first reducing agent, the second oxidizing agent, and the second reducing agent are water-soluble and are dissolved in pure water to obtain the first oxidizing agent solution, the first reducing agent solution, the second oxidizing agent solution, and the second reducing agent solution, respectively; (3) Add pure water and catalyst to the reactor, introduce nitrogen gas, raise the temperature to 50-60℃, start adding the first oxidant solution and the first reducing agent solution, wait 3-10 min, then start adding the mixed monomer solution obtained in step (1), and then add the three simultaneously, controlling the polymerization reaction temperature to 50-60℃; (4) After the addition is completed, stir at a constant temperature, add the second oxidant solution and the second reducing agent solution to eliminate the residual monomer, cool down and discharge to obtain a low viscosity acrylic polymer emulsion.

2. The preparation method according to claim 1, characterized in that, The hydrophilic monomer includes at least one of carboxyl-containing unsaturated monomers, hydroxyl-containing unsaturated monomers, and amino-containing unsaturated monomers.

3. The preparation method according to claim 2, characterized in that, The carboxyl-containing unsaturated monomer is selected from at least one of acrylic acid, methacrylic acid, itaconic acid, maleic acid, and fumaric acid; the hydroxyl-containing unsaturated monomer is selected from at least one of hydroxyethyl acrylate, hydroxypropyl acrylate, and hydroxyethyl methacrylate; the amino-containing unsaturated monomer is selected from at least one of acrylamide, methacrylamide, and N,N-dimethylacrylamide; the (meth)acrylate alkyl ester monomer is selected from at least one of methyl (meth)acrylate, ethyl acrylate, butyl acrylate, isooctyl acrylate, and lauryl acrylate; the epoxy-containing unsaturated monomer is selected from at least one of glycidyl methacrylate, glycidyl acrylate, and allyl glycidyl ether.

4. The preparation method according to claim 1, characterized in that, The first or second oxidizing agent is selected from at least one of sodium persulfate, potassium persulfate, ammonium persulfate, and tert-butyl hydroperoxide; the first or second reducing agent is selected from at least one of sodium bisulfite, sodium metabisulfite, sodium dithionite, and sodium isoascorbate.

5. The preparation method according to claim 1, characterized in that, In step (2), based on a total monomer mass of 100 parts, the total amount of the first oxidant and the first reducing agent is 18-20 parts, the mass ratio of the first oxidant to the first reducing agent is 2:0.9-1.1, the concentration of the first oxidant solution is 30wt%, and the concentration of the first reducing agent solution is 15-16wt%. The total amount of the second oxidant and the second reducing agent is 1-2 parts, the mass ratio of the second oxidant and the second reducing agent is 1:2-3, the concentration of the second oxidant solution is 3-4 wt%, and the concentration of the second reducing agent solution is 5-7 wt%.

6. The preparation method according to claim 1, characterized in that, The alkaline solution is selected from at least one of sodium hydroxide, potassium hydroxide, and ammonia water; The catalyst is selected from at least one of ferrous sulfate, ferrous chloride, ferrous ammonium sulfate, and copper sulfate.

7. The preparation method according to any one of claims 1-6, characterized in that, The pH value of the mixed monomer solution is 6.4-7.0; the temperature of the polymerization reaction is 53-57℃; and the dropping time of the mixed monomer solution is 260-300 min.

8. A low-viscosity self-crosslinking acrylate leather retanning agent prepared by the method according to any one of claims 1-7.

9. The low-viscosity self-crosslinking acrylate leather retanning agent according to claim 8, characterized in that, The low-viscosity self-crosslinking acrylate leather retanning agent has an apparent viscosity of 300-800 cps at 25°C, a pH of 6.5-7.5, and a solid content of 25-30 wt%.

10. The application of a low-viscosity self-crosslinking acrylate leather retanning agent as described in claim 8 or 9, characterized in that, Used for leather tanning.

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