Halogen-free flame-retardant polyurethane resin for preparing leather and application thereof

Abstract

The invention discloses halogen-free flame-retardant polyurethane resin for preparing leather and application of the halogen-free flame-retardant polyurethane resin. The method comprises the following steps that raw materials are prepared, and the raw materials comprise polyol, isocyanate, DOPO, MPP, nano-silica, a silane coupling agent, a reactive diluent, a wetting dispersant and a surface migration auxiliary; the preparation method comprises the following steps: adding polyol and isocyanate into a reaction kettle at the temperature of 80 DEG C to react to prepare a polyurethane matrix and a polyurethane prepolymer, detecting the content of NCO% in real time, and when the content of NCO reaches 10%, shunting 20% of the polyurethane prepolymer, and continuing to use the rest as a matrix material; aiming at the problems of poor bonding effect of base cloth and polyurethane resin, substandard resin viscosity and the like in the traditional process, the invention provides the preparation of an enhancer, the enhancement of the bonding degree of the base cloth and the resin, the monitoring of the temperature and the viscosity and the adjustment of the stirring rate, so that the resin viscosity reaches the optimal range; therefore, the quality and the stability of the resin leather can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the field of preparation of urethane resins, and more particularly to a halogen-free flame-retardant polyurethane resin for leather preparation and its application. Background Art

[0002] In the field of leather preparation, polyurethane resins are widely used due to their good properties. However, there are many problems to be solved in the traditional preparation process.

[0003] When using polyurethane resins to prepare leather, the poor bonding effect between the base fabric and the polyurethane resin is a prominent problem. Due to the pores in the base fabric itself, it is difficult for the two to be closely bonded. In previous processes, due to the lack of effective strengthening means, quality problems such as separation of the base fabric and the resin are likely to occur in the leather products, seriously affecting the durability and stability of the products; in addition, the viscosity of the polyurethane resin has a great impact on leather making. In past production practices, due to the difficulty in precisely controlling the resin viscosity, the quality of leather products is often uneven. Leather products in different batches show large fluctuations in hand feeling, appearance, etc. due to differences in resin viscosity.

[0004] In view of the problems in the related art, no effective solution has been proposed yet. Summary of the Invention

[0005] In view of the problems in the related art, the present invention provides a halogen-free flame-retardant polyurethane resin for leather preparation and its application to overcome the above-mentioned technical problems existing in the prior related art.

[0006] To this end, the specific technical solutions adopted by the present invention are as follows:

[0007] A method for preparing a halogen-free flame-retardant polyurethane resin for leather, the method comprising the following steps: S1, preparing raw materials, the raw materials including polyols, isocyanates, DOPO, MPP, nano-silica, silane coupling agents, reactive diluents, wetting and dispersing agents, surface migration aids;

[0008] S2, adding the polyols and isocyanates to a reaction kettle at 80 °C to react to prepare a polyurethane matrix and a polyurethane prepolymer, and detecting the NCO% content in real time. When it reaches 10%, divert 20% of the polyurethane prepolymer, and the remaining part continues to be used as the matrix material;

[0009] S3, adding a wetting and dispersing agent to the diverted polyurethane prepolymer to mix and make a reinforcing agent mixture, and diverting 50% of the reinforcing agent mixture into the matrix material. Finally, add DOPO, MPP, and nano-silica to the matrix material to make a matrix mixture;

[0010] S4, adding the silane coupling agent, reactive diluent, and surface migration aid to the reinforcing agent mixture to make a reinforcing agent;

[0011] S5. Add the strengthening agent to the matrix mixture, mix and stir, monitor the viscosity, establish the curve of the processing parameters and the viscosity, and dynamically adjust the process parameters to make the viscosity of the prepared urethane resin within the optimal range.

[0012] As a preferred embodiment, add the polyol and isocyanate to a reaction kettle at 80 °C to react to prepare the polyurethane matrix and the polyurethane prepolymer. Real-time detect the NCO% content. When it reaches 10%, divert 20% of the polyurethane prepolymer, and the remaining part continues to be used as the matrix material, including the following steps:

[0013] S21. Dehydrate the polyol under vacuum conditions to make the water content of the polyol < 0.05%.

[0014] S22. Raise the temperature of the reaction kettle to 80 ± 2 °C, introduce nitrogen to displace the air, and maintain a slightly positive pressure of 0.05 - 0.1 MPa to prevent moisture from entering.

[0015] S23. Add the dehydrated polyol to the reaction kettle, set the rotation speed to 200 - 400 rpm, start stirring, and then slowly add the isocyanate, and control the temperature not to exceed 85 °C.

[0016] S24. Use an on-line infrared spectrometer to real-time monitor the NCO% content. When the content reaches 10%, pause stirring, divert 20% of the polyurethane prepolymer, and the remaining polyurethane prepolymer continues to be used as the matrix material for stirring.

[0017] As a preferred embodiment, add a wetting and dispersing agent to the diverted polyurethane prepolymer to mix and make a strengthening agent mixture, and divert 50% of the strengthening agent mixture to add to the matrix material. Finally, add DOPO, MPP, and nano-silica to the matrix material to make a matrix mixture, including the following steps:

[0018] S31. Cool the diverted polyurethane prepolymer to 50 - 60 °C, add a wetting and dispersing agent and stir to mix to make a strengthening agent mixture, and divert 50% of the strengthening agent mixture, of which 80% is added to the matrix material and the remaining 20% is added to the nano-silica and pre-mixed into a paste.

[0019] S32. When mixing the strengthening agent mixture with the matrix, control the temperature below 60 °C and stir at 500 rpm for 10 minutes to ensure the compatibility of the prepolymer and the matrix. Then add DOPO, control the temperature at 60 °C and stir at 800 rpm for 615 minutes. Subsequently, add MPP, and raise the stirring speed to 1200 rpm and maintain for 20 minutes. Finally, add the mixture containing nano-silica that has been mixed into a paste and disperse at 2000 rpm for 20 min.

[0020] As a preferred embodiment, the steps of adding a silane coupling agent, a reactive diluent, and a surface migration aid to a reinforcing agent mixture to make a reinforcing agent include the following:

[0021] S41. Control the temperature at 70 °C, slowly add the silane coupling agent, and stir at 1200 rpm for 1 hour;

[0022] S42. Lower the temperature to 50 °C, sequentially add the reactive diluent and the surface migration aid, stir at 600 rpm - 1200 rpm for 30 minutes, and finally defoam at a vacuum of -0.1 MPa for 30 minutes.

[0023] As a preferred embodiment, the steps of adding the reinforcing agent to the matrix mixture, mixing and stirring, monitoring the viscosity, establishing a curve of the processing parameters and the viscosity, and dynamically adjusting the process parameters to make the viscosity of the made urethane resin within the optimal range include the following:

[0024] S51. Set the initial stirring rate, and gradually add the reinforcing agent to the matrix mixture in 10% gradients and stir, with an interval of 2 minutes for each gradient;

[0025] S52. Preset the optimal viscosity range and the optimal temperature range for making leather with polyurethane resin, monitor the resin temperature and viscosity, establish a change curve of the resin viscosity and temperature, obtain the viscosity data of the resin at the optimal temperature for making leather, compare the viscosity data with the optimal viscosity range for making leather, and adjust the stirring rate when the viscosity data exceeds the optimal viscosity range.

[0026] As a preferred embodiment, the steps of presetting the optimal viscosity range and the optimal temperature range for making leather with polyurethane resin, monitoring the resin temperature and viscosity, establishing a change curve of the resin viscosity and temperature, obtaining the viscosity data of the resin at the optimal temperature for making leather, comparing the viscosity data with the optimal viscosity range for making leather, and adjusting the stirring rate when the viscosity data exceeds the optimal viscosity range include the following:

[0027] S521. At a constant stirring speed, obtain the viscosity values corresponding to different temperatures and establish a change curve of the resin viscosity and temperature;

[0028] S522. Through the established change curve of the resin viscosity and temperature, obtain the viscosity data of the resin within the optimal temperature range for making leather;

[0029] S523. Compare the viscosity data with the preset optimal viscosity range. When the viscosity data exceeds the preset optimal viscosity range, calculate the theoretical target stirring speed N according to the current viscosity and temperature curve, and use the PID control algorithm to dynamically correct the stirring speed in combination with the real-time viscosity deviation. The specific formula is:

[0030]

[0031] where η e is the deviation between the current viscosity and the target viscosity, which is the difference between the middle value of the optimal viscosity range and the viscosity data of the resin at the optimal temperature, and K p ·(η e ) is the proportional term, and K p is the proportional gain, and K i ·∫η e dt is the integral term, is the differential term, ∫η e dt is the integral of the viscosity deviation with respect to time, and K i is the integral gain, is the change rate of the viscosity deviation, and K d is the differential gain.

[0032] As a preferred embodiment, the raw materials and proportions of the reinforcing agent and the polyurethane resin include:

[0033] The raw materials of the reinforcing agent are as follows: polyurethane prepolymer: 50% - 55%, silane coupling agent 50% - 55%, reactive diluent 8% - 15%, wetting and dispersing agent 3% - 7%, surface migration aid 0.5% - 2%. Among them, the reactive diluent is 1,4-butanediol, the wetting and dispersing agent is BYK-349, and the surface migration aid is L-75 polyether silicone oil;

[0034] The raw materials of the polyurethane resin are as follows: polyol: 45% - 55%, isocyanate: 12% - 18%, DOPO: 6% - 10%, MPP: 3% - 6%, nano-silica: 1% - 5%, reinforcing agent: 5% - 15%.

[0035] It should be noted that the selection of the proportion components of the reinforcing agent is as shown in Table 1 below:

[0036] Table of the components of each raw material of the polyurethane resin

[0037]

[0038] Table 1

[0039] Mix the raw materials according to the formula and test the following properties after curing. The property table is as shown in Table 2:

[0040] Table of property tests

[0041] Reinforcing agent ratio Tensile strength (MPa) Elongation at break (%) LOI (%) HDT (°C) 5％ 25.3 320 28 85 8％ 28.7 290 30 92 11％ 31.5 260 32 98 14％ 29.8 240 33 95 15％ 27.4 220 34 90

[0042] Table 2

[0043] It can be seen from the experimental data that when the reinforcing agent is 11%, the tensile strength, thermal stability and flame retardancy are all relatively excellent. In addition, due to the different porosity of different base fabrics, the optimal range of the reinforcing agent can be within 5% - 15%.

[0044] An application for preparing halogen-free flame-retardant polyurethane resin for leather, which is prepared by using the above-mentioned one for preparing halogen-free flame-retardant polyurethane resin for leather, and comprises the following steps:

[0045] S1. Uniformly coat the flame-retardant polyurethane resin glue on the surface of the release layer of the release paper, and set the temperature at 80 - 120 °C and bake for 3 - 5 minutes to volatilize the solvent to semi-dryness;

[0046] S2. Compose the semi-dry PU film and the base fabric through a hot pressing roller for 1 - 2 min, while controlling the temperature at 100 - 140 °C and the pressure at 0.5 - 2 MPa;

[0047] S3. Set the temperature at 130 - 150 °C, and heat the composite product for 10 - 20 minutes to ensure complete cross-linking of the PU;

[0048] S4. After cooling to room temperature, peel off the release paper to obtain the textured PU;

[0049] S5. Test the curing degree, peel strength and solvent residue of the prepared PU to verify the performance of the PU. The beneficial effects of the present invention are as follows:

[0050] 1. By preparing the strengthening agent, the present invention can enhance the bonding strength between the base fabric and the polyurethane resin. Since there are pores in the base fabric, when using polyurethane resin to prepare leather, there will be a problem of poor bonding effect between the base fabric and the polyurethane resin. Therefore, by preparing the strengthening agent, a transition layer with both reactive activity and interfacial bonding force can be formed through the synergistic effect of the polyurethane prepolymer and the silane coupling agent. At the same time, the silane coupling agent will chemically bond with the hydroxyl groups on the surface of the base fabric, and the polyurethane prepolymer cross-links with the resin main chain through the -NCO group. In addition, 1,4-butanediol, as a reactive diluent, can adjust the system viscosity and promote penetration, and the BYK-349 wetting and dispersing agent ensures the uniform distribution of nano-silica to enhance the physical anchoring effect. The L-75 polyether silicone oil forms a low surface energy layer through surface migration to reduce the interfacial stress. Therefore, this multi-scale bonding mechanism significantly improves the interfacial bonding strength and the resistance to wet heat aging performance between the resin and the base fabric.

[0051] 2. When using polyol and isocyanate to prepare the matrix material, the present invention can detect the NCO% content in real time. When it reaches 10%, 20% of the polyurethane prepolymer is diverted as the raw material for preparing the strengthening agent, which can effectively simplify the preparation steps and improve the preparation efficiency.

[0052] 3. The viscosity of the polyurethane resin is one of the most influential factors in leather production. Therefore, in the present invention, by monitoring the resin temperature and viscosity and establishing a change curve of the resin viscosity and temperature, the viscosity data of the resin at the preset optimal leather preparation temperature can be obtained. By comparing the viscosity data of the resin with the preset viscosity range, when it exceeds the range, according to the currently established change curve of the resin viscosity and temperature and in combination with the PID control algorithm, the stirring rate parameter is dynamically adjusted so that the finally obtained resin viscosity is within the preset optimal viscosity range. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0054] Figure 1 is a flowchart of a method for preparing a halogen-free flame-retardant polyurethane resin for leather and its application according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0055] To further illustrate the embodiments, the present invention provides drawings. These drawings are part of the disclosure of the present invention. They are mainly used to illustrate the embodiments and can be combined with the relevant descriptions in the specification to explain the operating principles of the embodiments. With reference to these contents, those of ordinary skill in the art should be able to understand other possible implementation manners and the advantages of the present invention. The components in the drawings are not drawn to scale, and similar component symbols are usually used to represent similar components.

[0056] According to an embodiment of the present invention, there is provided a method for preparing a halogen-free flame-retardant polyurethane resin for leather and its application.

[0057] Now, the present invention will be further described in combination with the drawings and specific implementation manners. As Figure 1 shown, a method for preparing a halogen-free flame-retardant polyurethane resin for leather and its application according to an embodiment of the present invention includes the following steps:

[0058] S1. Prepare raw materials, including polyols, isocyanates, DOPO, MPP, nano-silica, silane coupling agents, reactive diluents, wetting and dispersing agents, and surface migration aids;

[0059] S2. Add the polyols and isocyanates to a reaction kettle at 80 °C to react to prepare a polyurethane matrix and a polyurethane prepolymer. Real-time detect the NCO% content. When it reaches 10%, divert 20% of the polyurethane prepolymer, and the remaining part continues to be used as the matrix material;

[0060] Further, polyol and isocyanate are added to a reaction kettle at 80 °C to prepare a polyurethane matrix and a polyurethane prepolymer. The NCO% content is detected in real time. When it reaches 10%, 20% of the polyurethane prepolymer is diverted, and the remaining part continues to be used as the matrix material, including the following steps:

[0061] S21. Dehydrate the polyol under vacuum conditions so that the water content of the polyol is < 0.05%;

[0062] S22. Raise the temperature of the reaction kettle to 80 ± 2 °C, introduce nitrogen to displace the air, and maintain a slightly positive pressure of 0.05 - 0.1 MPa to prevent moisture from entering;

[0063] S23. Add the dehydrated polyol to the reaction kettle, set the rotation speed to 200 - 400 rpm, start stirring, and then slowly add isocyanate while controlling the temperature not to exceed 85 °C;

[0064] S24. Use an on-line infrared spectrometer to monitor the NCO% content in real time. When the content reaches 10%, stop stirring, divert 20% of the polyurethane prepolymer, and continue to stir the remaining polyurethane prepolymer as the matrix material.

[0065] S3. Add a wetting and dispersing agent to the diverted polyurethane prepolymer and mix to form a reinforcing agent mixture. Then divert 50% of the reinforcing agent mixture and add it to the matrix material. Finally, add DOPO, MPP, and nano-silica to the matrix material to form a matrix mixture;

[0066] Further, adding a wetting and dispersing agent to the diverted polyurethane prepolymer and mixing to form a reinforcing agent mixture, diverting 50% of the reinforcing agent mixture and adding it to the matrix material, and finally adding DOPO, MPP, and nano-silica to the matrix material to form a matrix mixture includes the following steps:

[0067] S31. Cool the diverted polyurethane prepolymer to 50 - 60 °C, add a wetting and dispersing agent and stir to mix to form a reinforcing agent mixture, and divert 50% of the reinforcing agent mixture. Among them, 80% is added to the matrix material, and the remaining 20% is added to nano-silica and pre-mixed into a paste;

[0068] S32. When mixing the reinforcing agent mixture with the matrix, control the temperature below 60 °C and stir at 500 rpm for 10 minutes to ensure the compatibility of the prepolymer and the matrix. Then add DOPO, control the temperature at 60 °C and stir at 800 rpm for 615 minutes. Subsequently, add MPP, raise the stirring speed to 1200 rpm, maintain for 20 minutes, and finally add the mixture containing nano-silica and disperse it at 2000 rpm for 20 min.

[0069] S4. Add a silane coupling agent, a reactive diluent, and a surface migration aid to the reinforcing agent mixture to form a reinforcing agent;

[0070] Further, adding a silane coupling agent, a reactive diluent, and a surface migration aid to the reinforcing agent mixture to make the reinforcing agent includes the following steps:

[0071] S41. Control the temperature at 70 °C, slowly add the silane coupling agent, and stir at 1200 rpm for 1 hour;

[0072] S42. Lower the temperature to 50 °C, sequentially add the reactive diluent and the surface migration aid, stir at 600 rpm - 1200 rpm for 30 minutes, and finally defoam at a vacuum degree of -0.1 MPa for 30 minutes. S5. Add the reinforcing agent to the matrix mixture, mix and stir, monitor the viscosity, establish a curve of the processing parameters and the viscosity, and dynamically adjust the process parameters to make the viscosity of the produced urethane resin within the optimal range.

[0073] Further, adding the reinforcing agent to the matrix mixture, mixing and stirring, monitoring the viscosity, establishing a curve of the processing parameters and the viscosity, and dynamically adjusting the process parameters to make the viscosity of the produced urethane resin within the optimal range includes the following steps:

[0074] S51. Set the initial stirring rate, and gradually add the reinforcing agent to the matrix mixture in 10% gradients and stir, with an interval of 2 minutes for each gradient;

[0075] S52. Preset the optimal viscosity range and the optimal temperature range for making leather with polyurethane resin, monitor the resin temperature and viscosity, establish a change curve of the resin viscosity and temperature, obtain the viscosity data of the resin at the optimal temperature for making leather, compare the viscosity data with the optimal viscosity range for making leather, and adjust the stirring rate when the viscosity data exceeds the optimal viscosity range;

[0076] Presetting the optimal viscosity range and the optimal temperature range for making leather with polyurethane resin, monitoring the resin temperature and viscosity, establishing a change curve of the resin viscosity and temperature, obtaining the viscosity data of the resin at the optimal temperature for making leather, comparing the viscosity data with the optimal viscosity range for making leather, and adjusting the stirring rate when the viscosity data exceeds the optimal viscosity range includes the following steps:

[0077] S521. Obtain the viscosity values corresponding to different temperatures at a constant stirring speed, and establish a change curve of the resin viscosity and temperature;

[0078] S522. Obtain the viscosity data of the resin within the optimal temperature range for making leather through the established change curve of the resin viscosity and temperature;

[0079] S523. Compare the viscosity data with the preset optimal viscosity range. When the viscosity data exceeds the preset optimal viscosity range, calculate the theoretical target stirring speed N according to the current viscosity-temperature curve, and use the PID control algorithm to dynamically correct the stirring speed in combination with the real-time viscosity deviation. The specific formula is as follows:

[0080]

[0081] Among them, η e is the deviation between the current viscosity and the target viscosity, which is the difference between the middle value of the optimal viscosity range and the viscosity data of this resin at the optimal temperature. K p ·(η e ) is the proportional term, K p is the proportional gain, K i ·∫η e dt is the integral term, is the differential term, ∫η e dt is the integral of the viscosity deviation with respect to time, K i is the integral gain, is the change rate of the viscosity deviation, K d is the differential gain.

[0082] Furthermore, the raw materials and proportions of the reinforcing agent and polyurethane resin include:

[0083] The raw materials of the reinforcing agent are polyurethane prepolymer: 50% - 55%, silane coupling agent 50% - 55%, reactive diluent 8% - 15%, wetting and dispersing agent 3% - 7%, surface migration aid 0.5% - 2%. Among them, the reactive diluent is 1,4-butanediol, the wetting and dispersing agent is BYK-349, and the surface migration aid is L-75 polyether silicone oil;

[0084] The raw materials of the polyurethane resin are polyol: 45% - 55%, isocyanate: 12% - 18%, DOPO: 6% - 10%, MPP: 3% - 6%, nano-silica: 1% - 5%, reinforcing agent: 5% - 15%

[0085] An application for preparing halogen-free flame-retardant polyurethane resin for leather, characterized in that this application is prepared by using the above-described method for preparing halogen-free flame-retardant polyurethane resin for leather, and includes the following steps:

[0086] S1. Uniformly coat the flame-retardant polyurethane resin glue on the surface of the release layer of the release paper, and set the temperature at 80 - 120 °C and bake for 3 - 5 minutes to volatilize the solvent to semi-dry;

[0087] S2. Compose the semi-dry PU film and the base fabric through a hot pressing roller for 1 - 2 min, while controlling the temperature at 100 - 140 °C and the pressure at 0.5 - 2 MPa;

[0088] S3. Set the temperature to 130 - 150 °C and heat the composite for 10 - 20 minutes to ensure complete cross-linking of the PU.

[0089] S4. After cooling to room temperature, peel off the release paper to obtain textured PU.

[0090] S5. Test the degree of curing, peel strength, and solvent residue of the prepared PU to verify the performance of the PU.

[0091] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A halogen-free flame-retardant polyurethane resin for preparing leather, characterized in that: The method comprises the following steps: S1. Prepare raw materials, including polyol, isocyanate, DOPO, MPP, nano-silica, silane coupling agent, reactive diluent, wetting dispersant, and surface migration aid; S2, adding polyol and isocyanate into a reaction kettle at 80°C to react and prepare a polyurethane matrix and a polyurethane prepolymer, and detecting the NCO% content in real time. When the NCO% content reaches 10%, 20% of the polyurethane prepolymer is diverted, and the remaining part continues to be used as the matrix material; S3, adding a wetting and dispersing agent to the diverted polyurethane prepolymer to prepare a reinforcing agent mixture, and diverting 50% of the reinforcing agent mixture to add to the matrix material, and finally adding DOPO, MPP, and nano-silica to the matrix material to prepare a matrix mixture; S4, adding a silane coupling agent, a reactive diluent, and a surface migration aid to the reinforcing agent mixture to prepare a reinforcing agent; S5. Add the reinforcing agent to the base mixture, mix and stir, monitor the viscosity, establish a curve of processing parameters and viscosity, and dynamically adjust the process parameters to make the viscosity of the prepared urethane resin within the optimal range.

2. The halogen-free flame-retardant polyurethane resin for preparing leather according to claim 1, characterized in that: The method of adding polyol and isocyanate into a reaction kettle at 80° C. to react and prepare a polyurethane matrix and a polyurethane prepolymer, detecting the NCO% content in real time, and when the NCO% content reaches 10%, diverting 20% ​​of the polyurethane prepolymer and continuing to use the remaining part as the matrix material comprises the following steps: S21, dehydrating the polyol under vacuum conditions to make the water content of the polyol less than 0.05%; S22. Raise the temperature of the reactor to 80±2°C, introduce nitrogen to replace the air, and maintain a slight positive pressure of 0.05-0.1MPa to prevent moisture from entering; S23, adding the dehydrated polyol into the reactor, setting the speed to 200-400 rpm, starting stirring, then slowly adding isocyanate, and controlling the temperature not to exceed 85° C.; S24. Use an online infrared spectrometer to monitor the NCO% content in real time. When the content reaches 10%, stop stirring, divert 20% of the polyurethane prepolymer, and continue to stir the remaining polyurethane prepolymer as the base material.

3. The halogen-free flame-retardant polyurethane resin for preparing leather according to claim 1, characterized in that: The method comprises adding a wetting and dispersing agent to the diverted polyurethane prepolymer to prepare a reinforcing agent mixture, diverting 50% of the reinforcing agent mixture to add to a matrix material, and finally adding DOPO, MPP, and nano-silicon dioxide to the matrix material to prepare a matrix mixture, including the following steps: S31, cooling the diverted polyurethane prepolymer to 50-60° C., adding a wetting and dispersing agent, stirring and mixing to form a reinforcing agent mixture, and diverting 50% of the reinforcing agent mixture, of which 80% is added to the matrix material, and the remaining 20% ​​is added to nano-silicon dioxide and pre-mixed into a paste; S32. When mixing the reinforcing agent mixture with the matrix, control the temperature below 60°C and stir at 500 rpm for 10 minutes to ensure that the prepolymer is compatible with the matrix. Then add DOPO, control the temperature to 60°C and stir at 800 rpm for 615 minutes. Then add MPP and increase the stirring speed to 1200 rpm for 20 minutes. Finally, add the mixture containing nano-silica into a paste and disperse it at 2000 rpm for 20 minutes.

4. The halogen-free flame-retardant polyurethane resin for preparing leather according to claim 1, characterized in that: The step of adding the silane coupling agent, the reactive diluent, and the surface migration aid into the reinforcing agent mixture to prepare the reinforcing agent comprises the following steps: S41, controlling the temperature to 70° C., and slowly adding a silane coupling agent, while stirring at 1200 rpm for 1 hour; S42, lowering the temperature to 50°C, and adding a reactive diluent and a surface migration aid in sequence, stirring at 600 rpm-1200 rpm for 30 minutes, and finally degassing at a vacuum degree of -0.1 MPa for 30 minutes.

5. The halogen-free flame-retardant polyurethane resin for preparing leather according to claim 1, characterized in that: The process of adding the reinforcing agent to the matrix mixture, mixing and stirring, monitoring the viscosity, establishing a curve of processing parameters and viscosity, and dynamically adjusting the process parameters to make the viscosity of the prepared urethane resin within an optimal range comprises the following steps: S51, setting an initial stirring rate, and gradually adding the enhancer into the matrix mixture in a 10% gradient and stirring, with an interval of 2 minutes between each gradient; S52. Preset the optimal viscosity range and optimal temperature range for making leather using polyurethane resin, monitor the resin temperature and viscosity, and establish a change curve of resin viscosity and temperature, obtain viscosity data of the resin at the optimal temperature for making leather, compare the viscosity data with the optimal viscosity range for making leather, and adjust the stirring rate when the viscosity data exceeds the optimal viscosity range.

6. The halogen-free flame-retardant polyurethane resin for preparing leather according to claim 5, characterized in that: The method of presetting the optimal viscosity range and the optimal temperature range for making leather using polyurethane resin, monitoring the temperature and viscosity of the resin, and establishing a change curve of the viscosity and temperature of the resin, obtaining the viscosity data of the resin at the optimal temperature for making leather, comparing the viscosity data with the optimal viscosity range for making leather, and adjusting the stirring rate when the viscosity data exceeds the optimal viscosity range comprises the following steps: S521, obtaining viscosity values ​​corresponding to different temperatures at a constant stirring speed, and establishing a variation curve of resin viscosity and temperature; S522, obtaining viscosity data of the resin within an optimal temperature range for making leather by establishing a change curve of resin viscosity and temperature; S523, comparing the viscosity data with the preset optimal viscosity range. When the viscosity data exceeds the preset optimal viscosity range, the theoretical target stirring speed N is calculated according to the current viscosity and temperature curve, and the stirring speed is dynamically corrected by using the PID control algorithm combined with the real-time viscosity deviation. The specific formula is: Among them, η e K is the deviation between the current viscosity and the target viscosity, which is the difference between the middle value of the optimal viscosity range and the viscosity data of the resin at the optimal temperature. p ·(η e ) is a proportional term, K p is the proportional gain, K i ·∫η e dt is the integral term, is the differential term, ∫η e dt is the integral of viscosity deviation over time, K i is the integral gain, is the rate of change of viscosity deviation, K d is the differential gain.

7. The halogen-free flame-retardant polyurethane resin for preparing leather according to claim 5, characterized in that: The raw materials and proportions of the reinforcing agent and polyurethane resin include: The raw materials of the reinforcing agent are: polyurethane prepolymer: 50%-55%, silane coupling agent 50%-55%, reactive diluent 8%-15%, wetting dispersant 3%-7%, surface migration aid 0.5%-2%, wherein the reactive diluent is 1,4-butanediol, the wetting dispersant is BYK-349, and the surface migration aid is L-75 polyether silicone oil; The raw materials of the polyurethane resin are: polyol: 45%-55%, isocyanate: 12%-18%, DOPO: 6%-10%, MPP: 3%-6%, nano-silicon dioxide: 1%-5%, and reinforcing agent: 5%-15%.

8. An application of a halogen-free flame-retardant polyurethane resin for preparing leather, characterized in that: The application is prepared by using a halogen-free flame-retardant polyurethane resin for preparing leather as described in any one of claims 1 to 6, comprising the following steps: S1. Evenly apply the flame retardant polyurethane resin glue on the surface of the release layer of the release paper, and set the temperature to 80-120°C for 3-5 minutes to evaporate the solvent to semi-dryness; S2, compound the semi-dry PU film and the base fabric through a hot pressing roller for 1-2 minutes, while controlling the temperature to 100-140°C and the pressure to 0.5-2MPa; S3. Set the temperature to 130-150℃ and heat the composite product for 10-20 minutes to ensure that the PU is completely cross-linked; S4, after cooling to room temperature, peeling off the release paper to obtain a textured PU; S5. Perform curing degree, peel strength and solvent residue tests on the prepared PU to verify the PU performance.

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