Polyurethane flame-retardant moisture-permeable film and preparation method thereof

Abstract

The invention provides a flame-retardant moisture-permeable polyurethane film and a preparation method thereof. The film is prepared from isocyanate, polyether polyol, dihydric alcohol, a chain extender, a catalyst, a flame retardant, an organic solvent, a dispersing agent, bentonite, kaolin, a silane coupling agent, an antioxidant and a defoaming agent. The halogen and the halogen-free flame retardant are added to form a compound system, efficient flame retardance is achieved, the flame retardant cannot migrate to the surface of the film, and the good hand feeling is kept. Meanwhile, dihydric alcohol is adopted for modification, so that the yellowing resistance, hydrolysis resistance and heat resistance of polyurethane are improved. In addition, the film is endowed with good moisture permeability by introducing the modified bentonite, and the requirements of related fields are met.

Description

Technical Field

[0001] The present invention relates to the technical field of polyurethane, in particular to a polyurethane flame retardant and moisture permeable film and a preparation method thereof. Background Art

[0002] Polyurethane (PU), an important polymer material, is synthesized primarily through the polycondensation reaction between polyols (soft segments) and isocyanates (hard segments). This unique chemical structure endows PU with high elasticity and flexibility, as well as excellent water resistance, oil resistance, and aging resistance. These exceptional properties have led to its widespread application in a variety of fields, including textiles, construction, and automotive.

[0003] However, despite the excellent performance of PU materials, traditional PU has exposed some urgent problems during long-term use. First, traditional PU materials are prone to yellowing, which is particularly noticeable under sunlight and other conditions. This not only affects the material's aesthetics but also has the potential to affect its performance. Second, in humid environments, PU materials are prone to hydrolysis, resulting in a decrease in material performance and a shortened service life. More seriously, pure PU materials are extremely flammable and produce molten droplets during combustion. This not only fails to meet the high flame retardant performance requirements of specific applications, but also poses a safety hazard such as fire during use.

[0004] In response to the above problems, flame retardant modification of PU has become a hot topic of current research. In the process of flame retardant modification of PU, adding flame retardants is a commonly used method. Among them, halogen-free flame retardants and halogen flame retardants are two common choices. Halogen-free flame retardants can significantly improve the flame retardant properties of PU, but usually a higher addition amount is required to achieve the ideal flame retardant effect. However, high content of halogen-free flame retardants often have poor compatibility with the PU matrix, which can easily lead to a decrease in the mechanical properties and thermal stability of the material. Although halogen flame retardants were developed earlier, are widely used and have high flame retardant efficiency, they are often difficult to meet all flame retardant requirements when used alone. Therefore, in practical applications, halogen flame retardants are often used as synergists and compounded with halogen-free flame retardants to achieve more efficient flame retardant effects.

[0005] In summary, the technical problems that need to be solved at present mainly include: how to effectively inhibit the yellowing and hydrolysis of PU materials to extend their service life; how to improve the flame retardant properties of PU materials to meet the high requirements for flame retardant properties in specific fields; and how to minimize the impact on the original mechanical properties and thermal stability of PU materials while ensuring flame retardant properties. Summary of the Invention

[0006] To address the problems existing in the prior art, the present invention provides a flame-retardant and breathable polyurethane film and its preparation method. By adding a halogen and a halogen-free flame retardant to form a composite system, the film achieves efficient flame retardancy without the flame retardant migrating to the film surface, maintaining a good feel. Furthermore, diol modification improves the polyurethane's yellowing resistance, hydrolysis resistance, and heat resistance. Furthermore, the introduction of modified bentonite imparts excellent moisture permeability to the film, meeting the needs of related fields.

[0007] To achieve the above object, the present invention provides the following technical solution: a polyurethane flame retardant and moisture permeable film, the raw materials of which include: isocyanate, polyether polyol, diol, chain extender, catalyst, flame retardant, organic solvent, dispersant, bentonite, kaolin, silane coupling agent, antioxidant, and defoaming agent; The flame retardant is a mixture of antimony trioxide, decabromodiphenylethane and modified silicon dioxide; The bentonite is modified by a silane coupling agent.

[0008] Furthermore, in parts by weight, the raw materials include 20 to 50 parts of isocyanate; 40 to 80 parts of polyether polyol; 5 to 20 parts of diol; 1 to 5 parts of chain extender; 0.5 to 3 parts of catalyst; 10 to 35 parts of flame retardant; 30 to 50 parts of organic solvent; 1 to 3 parts of dispersant; 0.5 to 2 parts of bentonite; 0.2 to 0.5 parts of kaolin; 0.05 to 0.11 parts of silane coupling agent; 0.2 to 0.7 parts of antioxidant; and 0.1 to 0.5 parts of defoaming agent.

[0009] Furthermore, the isocyanate is one of isophorone diisocyanate, 4,4'-diphenylmethylene diisocyanate, and hexamethylene diisocyanate; The polyether polyol is one of polybutylene glycol, polytetramethylene glycol and polypropylene glycol; The diol is one of ethylene glycol, 1,4-cyclohexanedimethanol and 1,2-cyclohexanedimethanol; The chain extender is one of 1,4-butanediol and diethylamino alcohol; The catalyst is one of dibutyltin dilaurate and triethylamine; The organic solvent is one or more of N,N-dimethylformamide, acetone, isopropyl alcohol, N-methylpyrrolidone, toluene, and butanone.

[0010] The dispersant is one of ethylene bisstearamide, polyacrylate, polypropylene alcohol, and polyvinyl ester; The silane coupling agent is one of KH550, KH560, and vinyltriethoxysilane; The antioxidant is one of antioxidant 1010 and antioxidant 168, or a mixture of the two; The defoaming agent is one of polyoxyethylene polyoxypropanolamine ether, polysiloxane, and polyoxypropylene glycerol polyether.

[0011] Furthermore, the isocyanate is 4,4'-diphenylmethyl diisocyanate; The polyether polyol is polytetrahydrofuran diol; The diol 1,4-cyclohexanedimethanol; The chain extender is 1,4-butanediol; The catalyst is dibutyltin dilaurate.

[0012] The organic solvent is NN, dimethylformamide, toluene, and butanone, and the ratio of parts is 1:1:1 to 3:2:1.

[0013] The dispersant is ethylene bisstearamide.

[0014] The silane coupling agent is vinyltriethoxysilane.

[0015] The antioxidant is antioxidant 1010.

[0016] The defoaming agent is polyoxyethylene polyoxypropanolamine ether.

[0017] The present invention also provides a method for preparing a polyurethane flame retardant and moisture permeable film, the specific steps of which are as follows: Under a protective atmosphere, polyether polyol, isocyanate, diol, antioxidant and defoamer are mixed for prepolymerization to obtain a prepolymer; the prepolymer, chain extender and catalyst are mixed for reaction to obtain polyurethane; Mixing a flame retardant and a dispersant, grinding, and drying to obtain a mixture A; The impurity-removed bentonite is mixed with a silane coupling agent for reaction, washed, and dried to obtain modified bentonite; The polyurethane is mixed with an organic solvent to obtain a polyurethane solution, and the mixture A, kaolin, and modified bentonite are added to the polyurethane solution and mixed uniformly to obtain a mixture emulsion B; After defoaming, the mixture emulsion B is formed into a film using a coating machine, and then dried and solidified to obtain a polyurethane flame retardant and moisture permeable film.

[0018] Further, the preparation steps of polyurethane are as follows: Dry the isocyanate and polyether polyol in vacuum at 100-120°C for 1-4 hours; Under a nitrogen environment, slowly add isocyanate, diol, antioxidant, and defoamer to the polyether polyol, and stir the prepolymerization reaction at 60°C to 90°C for 2h to 5h to obtain a prepolymer; The reaction environment is cooled to 50°C to 80°C, a chain extender is added to the prepolymer, and after the chain extension reaction is carried out for 1h to 3h, a catalyst is added and the reaction is continued for 1h to 3h to obtain polyurethane.

[0019] Furthermore, the preparation steps of mixture A are as follows: The flame retardant and dispersant were added to anhydrous ethanol, and the mixture was subjected to high-speed ball milling for 20 min to 60 min, and then dried at 40° C. to 90° C. for 4 h to 8 h to obtain a mixture A.

[0020] Furthermore, the preparation steps of the modified bentonite are as follows: Add bentonite to anhydrous ethanol, stir until completely dispersed, remove impurities by centrifugation, and dry at 40°C to 90°C for 4h to 8h to obtain pure bentonite; Dissolve the silane coupling agent in anhydrous ethanol solution, stir evenly, add 0.5-2 parts of pure bentonite, react at 40℃~60℃ for 1h~5h, and after the reaction is completed, wash with anhydrous ethanol several times, and dry the washed bentonite at 30℃~70℃ to obtain modified bentonite.

[0021] Furthermore, the preparation steps of the polyurethane flame retardant and moisture permeable film are as follows: Add polyurethane to an organic solvent, heat and stir at 60°C to 90°C for 40 minutes to 100 minutes until the polyurethane is completely dissolved to obtain a polyurethane solution; Add mixture A and kaolin to the polyurethane solution, heat and stir at 60°C to 90°C for 50 to 120 minutes, then add modified bentonite and continue heating and stirring for 60 to 180 minutes to obtain mixture emulsion B; The mixture emulsion B was defoamed in a -0.1 MPa environment for 20 min to 60 min. After the defoaming was completed, a film was formed using a coating machine, and the film was dried and solidified to obtain a polyurethane flame retardant and moisture permeable film.

[0022] Furthermore, the steps of preparing the polyurethane flame retardant and moisture permeable film using a coating machine are as follows: The coating machine coats the mixture emulsion B into a film at a speed of 10 mm / s to 20 mm / s. After the film is formed, it is cured and dried at 80°C to 140°C for 2min to 7min in a vacuum environment to obtain a polyurethane flame retardant and moisture permeable film.

[0023] Compared with the prior art, the present invention has at least the following beneficial effects: The present invention provides a polyurethane flame-retardant and breathable film. Halogen and halogen-free flame retardants form a flame retardant compound system, and the flame retardant is mixed with a polyurethane solution to form an emulsion, which can effectively improve the flame retardant properties of the polyurethane film. At the same time, the flame retardant does not migrate to the film surface, allowing the film to have a good flame retardant effect while maintaining a soft feel, improving the user experience of the product. By preparing modified bentonite from bentonite and a silane coupling agent, the polyurethane film not only achieves good breathability, meeting the stringent requirements for waterproof and breathable properties in fields such as sportswear, but also, due to the high chemical stability of the saturated cyclohexane rigid structure in the diol, it inhibits molecular chain motion, slows down photooxidation, and improves yellowing resistance. The aliphatic structure is hydrophobic and can slow the penetration of water molecules into the hard segment, thereby improving hydrolysis resistance. The rigid cyclic structure also restricts segment motion, promotes the formation of hydrogen bonds in the hard segment, and improves heat resistance, resulting in a comprehensive improvement in the overall performance of the polyurethane film.

[0024] The method of the present invention comprises the following steps: the prepolymerization and chain extension reaction of the polyurethane, the mixed crushing and drying of the flame retardant and dispersant, the modification treatment of the bentonite, and finally the mixing of the components to form an emulsion and the preparation of a film. The entire preparation process has a clear process flow, the various steps are closely connected, and the operation is standardized, providing a reliable process guarantee for the preparation of high-quality polyurethane flame-retardant and breathable films. By optimizing the composition and preparation method of the polyurethane polymer, such as carrying out the prepolymerization and chain extension reaction under specific conditions, and rationally treating and mixing the flame retardant, bentonite and other components, the flame retardant properties and bonding strength of the polyurethane film are further improved, while also improving its comprehensive properties such as light transmittance and high-temperature bonding strength, so that the prepared polyurethane flame-retardant and breathable film has better performance in practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a data diagram of the moisture permeability of the PU flame retardant and moisture permeable film of the present invention; Figure 2 This is a contact angle data diagram of the PU flame retardant and moisture permeable film of the present invention; Figure 3 Schematic diagram of the flame retardant mechanism of the present invention. DETAILED DESCRIPTION

[0026] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0027] The present invention provides a polyurethane flame retardant and moisture permeable film, and the polyurethane flame retardant and moisture permeable film is prepared using the following raw materials in parts by weight: Isocyanate, 20-50 parts (e.g., 20 parts, 30 parts, 40 parts, 50 parts); Polyether polyol, 40-80 parts (e.g., 40 parts, 50 parts, 60 parts, 70 parts); 1,4-cyclohexanedimethanol diol, 5 to 20 parts (e.g., 5 parts, 10 parts, 15 parts, 20 parts); Chain extender, 1 to 5 parts (e.g., 1 part, 2 parts, 3 parts, 4 parts, 5 parts); Catalyst, 0.5-3 parts (e.g., 0.5 parts, 1 part, 1.5 parts, 2 parts, 2.5 parts, 3 parts); Flame retardant, 10-35 parts (e.g., 15 parts, 20 parts, 25 parts); Organic solvent, 30-50 parts (e.g., 30 parts, 40 parts, 50 parts); Dispersant, 1 to 3 parts (e.g., 1.5 parts, 2 parts, 2.5 parts, 3 parts); Bentonite, 0.5-2 parts (e.g., 1 part, 1.5 parts, 2 parts); Kaolin, 0.2-0.5 parts (e.g., 0.3 parts, 0.4 parts); Silane coupling agent, 0.05-0.11 parts (e.g., 0.06 parts, 0.07 parts, 0.08 parts, 0.09 parts, 0.1 parts); Antioxidant, 0.2-0.7 parts (e.g., 0.3 parts, 0.4 parts, 0.5 parts, 0.6 parts); Defoaming agent, 0.1-0.5 parts (e.g., 0.2 parts, 0.3 parts, 0.4 parts); The specific preparation method comprises the following steps: Step S1: drying the isocyanate and polyether polyol under vacuum at 100° C. to 120° C. for 1 h to 4 h; Step S2: Weighing dried polyether polyol (40-80 parts) into a four-necked flask, introducing nitrogen, slowly adding isocyanate (20-50 parts), diol (5-20 parts), antioxidant (0.2-0.7 parts), and defoaming agent (0.1-0.5 parts), and stirring the prepolymer at 60°C-90°C for 2-5 hours to obtain a prepolymer; Step S3: Cool the reaction environment to 50°C-80°C, add 1-5 parts of a chain extender to the prepolymer, and allow the chain extension reaction to continue for 1-3 hours. Then, add 0.5-3 parts of a catalyst and continue the reaction for 1-3 hours. If the viscosity is too high during the reaction, add acetone to reduce the viscosity, which is then removed by rotary evaporation to obtain a polyether polyurethane. Step S4: Weigh 10-35 parts of a flame retardant and 1-3 parts of a dispersant, add anhydrous ethanol, and perform high-speed ball milling for 20-60 minutes. Then, dry the mixture in a vacuum drying oven at 40-90° C. for 4-8 hours to obtain a mixture A. Step S5: Weigh bentonite and add it to anhydrous ethanol, stir until completely dispersed to form a suspension, centrifuge to remove impurities, and dry at 40°C to 90°C for 4h to 8h to obtain pure bentonite; take 0.05~0.11 parts of silane coupling agent and dissolve it in the anhydrous ethanol solution, stir evenly, add 0.5~2 parts of pure bentonite, and react at 40°C to 60°C for 1h to 5h to ensure that the silane coupling agent reacts fully with the surface of the pure bentonite. After the reaction is completed, wash with anhydrous ethanol several times, and dry the washed bentonite at 30°C to 70°C to obtain modified bentonite; Step S6: Weigh 20 to 60 parts of the polyether polyurethane obtained in step S3, add 30 to 50 parts of an organic solvent, place in a three-necked flask, heat and stir at 60° C. to 90° C. for 40 to 100 minutes until the polyurethane is completely dissolved, to obtain a polyurethane solution; Step S7: heating the mixture A obtained in step S4 and 0.2-0.5 parts of kaolin with the polyurethane solution obtained in step S6 at 60° C.-90° C. with stirring for 50-120 minutes; after uniform mixing, heating and stirring the mixture with the modified bentonite obtained in step S5 for 60-180 minutes to obtain a mixture emulsion B; Step S8: Defoam the mixture emulsion B obtained in step S7 in a -0.1 MPa vacuum drying oven for 20 min to 60 min. After defoaming, take an appropriate amount of the emulsion and use a coating machine at a speed of 10 mm / s to 20 mm / s. After film formation, cure and dry in a vacuum drying oven at 80~140°C for 2~7 min to obtain a polyurethane flame retardant and moisture permeable film.

[0028] Preferably, the isocyanate is one of isophorone diisocyanate, 4,4'-diphenylmethyl diisocyanate, and hexamethylene diisocyanate; more preferably, 4,4'-diphenylmethyl diisocyanate.

[0029] Preferably, the polyether polyol is one of polybutylene glycol, polytetramethylene glycol, and polypropylene glycol; more preferably, polytetramethylene glycol.

[0030] Preferably, the diol is one of ethylene glycol, 1,4-cyclohexanedimethanol, and 1,2-cyclohexanedimethanol; more preferably, 1,4-cyclohexanedimethanol.

[0031] Preferably, the chain extender is one of 1,4-butanediol and diethylamino alcohol; more preferably, it is 1,4-butanediol.

[0032] Preferably, the catalyst is one of dibutyltin dilaurate and triethylamine; more preferably, dibutyltin dilaurate.

[0033] Preferably, the flame retardant is one or more of antimony trioxide, ammonium polyphosphate, decabromodiphenylethane, aluminum hydroxide, and silicon dioxide; more preferably, it is a mixture of decabromodiphenylethane, antimony trioxide, and modified silicon dioxide; The modified silica is silica modified with a silane coupling agent, and is obtained by adding anhydrous ethanol and silica to the silane coupling agent, stirring the mixture evenly with a magnetic stirrer, and then drying the mixture.

[0034] Preferably, the organic solvent is one or more of N-methylformamide, dimethylformamide, acetone, isopropyl alcohol, N-methylpyrrolidone, toluene, and butanone; more preferably, N-methylformamide, dimethylformamide, toluene, and butanone are selected in a ratio of 1:1:1 to 3:2:1.

[0035] Preferably, the dispersant is one of ethylene bisstearamide, polyacrylate, polypropylene alcohol, and polyvinyl ester; more preferably, it is ethylene bisstearamide.

[0036] Preferably, the silane coupling agent is one of KH550, KH560, and vinyltriethoxysilane; more preferably, vinyltriethoxysilane.

[0037] Preferably, the antioxidant is one of antioxidant 1010 and antioxidant 168 or a mixture of the two; more preferably, antioxidant 1010.

[0038] Preferably, the defoaming agent is one of polyoxyethylene polyoxypropanolamine ether, polysiloxane, and polyoxypropylene glycerol polyether; more preferably, it is polyoxyethylene polyoxypropanolamine ether.

[0039] The present invention forms a flame retardant composite system by adding halogen and halogen-free flame retardants, preparing modified bentonite using bentonite and a silane coupling agent, and then mixing the flame retardant, modified bentonite, and polyurethane solution to form an emulsion. This effectively improves the flame retardancy of polyurethane films, while preventing the flame retardant from migrating to the film surface, thereby maintaining a good feel. Furthermore, the introduction of modified bentonite imparts excellent moisture permeability to the polyurethane film, meeting the demand for waterproof and breathable properties in areas such as sportswear. The diol 1,4-cyclohexanedimethanol (CHDM) is added to the polyurethane resin. The rigid saturated cyclohexane structure in CHDM has high chemical stability, inhibiting molecular chain motion, slowing photooxidation, and improving yellowing resistance. The hydrophobic aliphatic structure in CHDM slows the penetration of water molecules into the hard segments, thereby improving hydrolysis resistance. The rigid cyclic structure restricts segment motion, promotes hydrogen bond formation in the hard segments, and enhances heat resistance. The present invention adopts advanced synthesis methods and equipment to optimize the composition and preparation process of polyurethane resin, further improving the flame retardant properties and bonding strength of polyurethane film; the present invention improves its comprehensive properties, such as light transmittance and high-temperature bonding strength, by optimizing the composition and preparation method of polyurethane polymer.

[0040] The following will provide a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention. The described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Given the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work shall fall within the scope of protection of the present invention.

[0041] Example 1 This embodiment discloses a polyurethane flame retardant and moisture permeable film, the detailed preparation process of which is as follows: Step S1: drying 4,4'-diphenylmethane diisocyanate and polytetrahydrofuran diol in vacuum at 105°C for 2h; Step S2: Weigh 57 parts of dried polytetrahydrofuran diol, add them into a four-necked flask, introduce nitrogen, slowly add 31 parts of 4,4'-diphenylmethyl diisocyanate, 10 parts of 1,4-cyclohexanedimethanol, 0.3 parts of antioxidant 1010, and 0.2 parts of polyoxyethylene polyoxypropanolamine ether, and stir the prepolymerization reaction at 80°C for 4 hours; Step S3: Cool the mixture to 65°C, add 1.2 parts of 1,4-butanediol, and allow the chain to extend for 2.5 hours. Then, add 0.8 parts of dibutyltin dilaurate and continue the reaction for 2.5 hours. If the viscosity is too high during the reaction, add acetone to reduce the viscosity. Remove the excess by rotary evaporation to obtain a polyether polyurethane. Step S4: Weigh 9.375 parts of decabromodiphenylethane, 3.125 parts of antimony trioxide, 1.99 parts of modified silica, 0.28 parts of ethylene bisstearamide compound, slowly add an appropriate amount of anhydrous ethanol solution, high-speed ball milling for 30min, and dry in a vacuum drying oven at 80 ℃ for 6h, and grind the dried compound flame retardant to obtain a mixture A; Step S5: Weigh 0.55 parts of bentonite, add it to an anhydrous ethanol solution, stir for 60 minutes until it is completely dispersed to form a uniform suspension, then centrifuge at 4000 r / min, 15 minutes, 2 to 3 times, and then dry at 80°C for 6 hours to obtain pure bentonite; weigh 0.09 parts of vinyltriethoxysilane, dissolve it in an anhydrous ethanol solution, add the obtained pure bentonite to the vinyltriethoxysilane solution, stir in a water bath at 50°C for 2 hours to ensure that the vinyltriethoxysilane is evenly distributed and fully reacts with the bentonite surface, and after sufficient reaction, dry it in a vacuum drying oven at 60°C for 8 hours to obtain modified bentonite.

[0042] Step S6: Weigh 39 parts of the polyether polyurethane obtained in step S3, 22.5 parts of NN, dimethylformamide, 11.25 parts of toluene, and 11.25 parts of butanone into a three-necked flask, and stir magnetically in an 80°C water bath for 60 minutes until the polyurethane is completely dissolved in the organic solvent; Step S7: Weigh 0.36 parts of kaolin and add it to the solution obtained in step S6. After magnetic stirring in a water bath at 80°C for 60 minutes, add the modified bentonite obtained in step S5 and continue magnetic stirring in a water bath at 80°C for 90 minutes. Step S8: The emulsion obtained in step S7 is placed in a vacuum drying oven at -0.1 MPa for 30 minutes to defoam. After defoaming, an appropriate amount of the emulsion is taken and coated using a film coater at a rate of 15 mm / s. After film formation, the film is cured and dried in a vacuum drying oven at 120°C for 5 minutes to obtain a flame-retardant and moisture-permeable polyurethane film. The magnetic stirring speed should not be too high during the preparation process, as this will generate a large number of bubbles.

[0043] Example 2 This embodiment discloses a polyurethane flame retardant and moisture permeable film, the detailed preparation process of which is as follows: Step S1: drying 4,4'-diphenylmethane diisocyanate and polytetrahydrofuran diol in vacuum at 105°C for 2h; Step S2: Weigh 63 parts of dried polytetrahydrofuran diol, add them into a four-necked flask, introduce nitrogen, add 0.3 parts of antioxidant 1010 and 0.2 parts of polyoxyethylene polyoxypropanolamine ether, slowly add 35 parts of 4,4'-diphenylmethyl diisocyanate, and stir the prepolymerization reaction at 80°C for 4 hours; Step S3: Cool the mixture to 65°C, add 1.2 parts of 1,4-butanediol, and allow the chain to extend for 2.5 hours. Then, add 0.8 parts of dibutyltin dilaurate and continue the reaction for 2.5 hours. If the viscosity is too high during the reaction, add acetone to reduce the viscosity. Remove the excess by rotary evaporation to obtain a polyether polyurethane. Step S4: Weigh 14.025 parts of decabromodiphenylethane, 4.675 parts of antimony trioxide, 2.12 parts of modified silica, 0.4 parts of ethylene bisstearamide compound, slowly add an appropriate amount of anhydrous ethanol solution, high-speed ball milling for 30min, and dry in a vacuum drying oven at 80 ℃ for 6h, and grind the dried compound flame retardant to obtain a mixture A; Step S5: Weigh 0.55 parts of bentonite, add it to an anhydrous ethanol solution, stir for 60 minutes until it is completely dispersed to form a uniform suspension, then centrifuge at 4000 r / min, 15 minutes, 2 to 3 times, and then dry at 80°C for 6 hours to obtain pure bentonite; weigh 0.09 parts of vinyltriethoxysilane, dissolve it in an anhydrous ethanol solution, add the obtained pure bentonite to the vinyltriethoxysilane solution, stir in a water bath at 50°C for 2 hours to ensure that the vinyltriethoxysilane is evenly distributed and fully reacts with the bentonite surface, and after sufficient reaction, dry it in a vacuum drying oven at 60°C for 8 hours to obtain modified bentonite.

[0044] Step S6: Weigh 39 parts of the polyether polyurethane obtained in step S3, 22.5 parts of NN, dimethylformamide, 11.25 parts of toluene, and 11.25 parts of butanone into a three-necked flask, and stir magnetically in an 80°C water bath for 60 minutes until the polyurethane is completely dissolved in the organic solvent; Step S7: Weigh 0.36 parts of kaolin and add it to the solution obtained in step S6. After magnetic stirring in a water bath at 80°C for 60 minutes, add the modified bentonite obtained in step S2 and continue magnetic stirring in a water bath at 80°C for 90 minutes. Step S8: The emulsion obtained in step S7 is placed in a vacuum drying oven at -0.1 MPa for 30 minutes to defoam. After defoaming, an appropriate amount of the emulsion is taken and coated using a film coater at a rate of 15 mm / s. After film formation, the film is cured and dried in a vacuum drying oven at 120°C for 5 minutes to obtain a flame-retardant and moisture-permeable polyurethane film. The magnetic stirring speed should not be too high during the preparation process, as this will generate a large number of bubbles.

[0045] Example 3 This embodiment discloses a polyurethane flame retardant and moisture permeable film, the detailed preparation process of which is as follows: Step S1: drying 4,4'-diphenylmethane diisocyanate and polytetrahydrofuran diol in vacuum at 105°C for 2h; Step S2: Weigh 63 parts of dried polytetrahydrofuran diol, add them into a four-necked flask, introduce nitrogen, add 0.3 parts of antioxidant 1010 and 0.2 parts of polyoxyethylene polyoxypropanolamine ether, slowly add 35 parts of 4,4'-diphenylmethyl diisocyanate, and stir the prepolymerization reaction at 80°C for 4 hours; Step S3: Cool the mixture to 65°C, add 1.2 parts of 1,4-butanediol, and allow the chain to extend for 2.5 hours. Then, add 0.8 parts of dibutyltin dilaurate and continue the reaction for 2.5 hours. If the viscosity is too high during the reaction, add acetone to reduce the viscosity. Remove the excess by rotary evaporation to obtain a polyether polyurethane. Step S4: Weigh 19.125 parts of decabromodiphenylethane, 6.375 parts of antimony trioxide, 2.26 parts of modified silica, 0.56 parts of ethylene bisstearamide compound, slowly add an appropriate amount of anhydrous ethanol solution, high-speed ball milling for 30min, and dry in a vacuum drying oven at 80 ℃ for 6h, grind the dried compound flame retardant to obtain a mixture A; Step S5: Weigh 0.61 parts of bentonite, add it to the anhydrous ethanol solution, stir for 60 minutes until it is completely dispersed to form a uniform suspension, then centrifuge at 4000 r / min, 15 minutes, 2 to 3 times, and then dry at 80°C for 6 hours to obtain pure bentonite; weigh 0.1 parts of vinyltriethoxysilane, dissolve it in the anhydrous ethanol solution, add the obtained pure bentonite to the vinyltriethoxysilane solution, stir in a water bath at 50°C for 2 hours to ensure that the vinyltriethoxysilane is evenly distributed and fully reacts with the bentonite surface, and after sufficient reaction, dry it in a vacuum drying oven at 60°C for 8 hours to obtain modified bentonite.

[0046] Step S6: Weigh 39 parts of the polyether polyurethane obtained in step S3, 22.5 parts of NN, dimethylformamide, 11.25 parts of toluene, and 11.25 parts of butanone into a three-necked flask, and stir magnetically in an 80°C water bath for 60 minutes until the polyurethane is completely dissolved in the organic solvent; Step S7: Weigh 0.4 parts of kaolin and add it to the solution obtained in step S6. After magnetic stirring in a water bath at 80°C for 60 minutes, add the modified bentonite obtained in step S5 and continue magnetic stirring in a water bath at 80°C for 90 minutes. Step S8: The emulsion obtained in step S7 is placed in a vacuum drying oven at -0.1 MPa for 30 minutes to defoam. After defoaming, an appropriate amount of the emulsion is taken and coated using a film coater at a rate of 15 mm / s. After film formation, the film is cured and dried in a vacuum drying oven at 120°C for 5 minutes to obtain a flame-retardant and moisture-permeable polyurethane film. The magnetic stirring speed should not be too high during the preparation process, as this will generate a large number of bubbles.

[0047] Example 4 This embodiment discloses a polyurethane flame retardant and moisture permeable film, the detailed preparation process of which is as follows: Step S1: drying 4,4'-diphenylmethane diisocyanate and polytetrahydrofuran diol in vacuum at 105°C for 2h; Step S2: Weigh 63 parts of dried polytetrahydrofuran diol, add them into a four-necked flask, introduce nitrogen, add 0.3 parts of antioxidant 1010 and 0.2 parts of polyoxyethylene polyoxypropanolamine ether, slowly add 35 parts of 4,4'-diphenylmethyl diisocyanate, and stir the prepolymerization reaction at 80°C for 4 hours; Step S3: Cool the mixture to 65°C, add 1.2 parts of 1,4-butanediol, and allow the chain to extend for 2.5 hours. Then, add 0.8 parts of dibutyltin dilaurate and continue the reaction for 2.5 hours. If the viscosity is too high during the reaction, add acetone to reduce the viscosity. Remove the excess by rotary evaporation to obtain a polyether polyurethane. Step S4: Weigh 24.75 parts of decabromodiphenylethane, 8.25 parts of antimony trioxide, 2.41 parts of modified silica, 0.71 parts of ethylene bisstearamide compound, slowly add an appropriate amount of anhydrous ethanol solution, high-speed ball milling for 30min, and dry in a vacuum drying oven at 80 ℃ for 6h, grind the dried compound flame retardant to obtain a mixture A; Step S5: Weigh 0.66 parts of bentonite, add it to the anhydrous ethanol solution, stir for 60 minutes until it is completely dispersed to form a uniform suspension, then centrifuge at 4000 r / min, 15 minutes, 2 to 3 times, and then dry at 80°C for 6 hours to obtain pure bentonite; weigh 0.108 parts of vinyltriethoxysilane, dissolve it in the anhydrous ethanol solution, add the obtained pure bentonite to the vinyltriethoxysilane solution, stir in a water bath at 50°C for 2 hours to ensure that the vinyltriethoxysilane is evenly distributed and fully reacts with the bentonite surface, and after sufficient reaction, dry it in a vacuum drying oven at 60°C for 8 hours to obtain modified bentonite.

[0048] Step S6: Weigh 39 parts of the polyether polyurethane obtained in step S3, 22.5 parts of NN, dimethylformamide, 11.25 parts of toluene, and 11.25 parts of butanone into a three-necked flask, and stir magnetically in an 80°C water bath for 60 minutes until the polyurethane is completely dissolved in the organic solvent; Step S7: Weigh 0.432 parts of kaolin and add it to the solution obtained in step S6. After magnetic stirring in a water bath at 80°C for 60 minutes, add the modified bentonite obtained in step S5 and continue magnetic stirring in a water bath at 80°C for 90 minutes. Step S8: The emulsion obtained in step S8 is placed in a vacuum drying oven at -0.1 MPa for 30 minutes to defoam. After defoaming, an appropriate amount of the emulsion is taken and coated using a film coater at a rate of 15 mm / s. After film formation, the film is cured and dried in a vacuum drying oven at 120°C for 5 minutes to obtain a flame-retardant and moisture-permeable polyurethane film. The magnetic stirring speed should not be too high during the preparation process, as this will generate a large number of bubbles.

[0049] The vertical burning test results of the PU flame retardant and moisture permeable films prepared in Examples 1 to 4 are shown in the following table:

[0050] Results show that pure PU samples without the addition of a Br-Sb-Si flame retardant are highly flammable and exhibit poor flame retardancy. However, the addition of a Br-Sb-Si synergistic flame retardant significantly improves the flame retardancy, reaching UL-94 V-0. Hydrogen bromide (HBr), a thermal decomposition product of DBDPE, reacts with Sb2O3 to produce H2O, SbBr3, and SbOBr. SbOBr continuously decomposes (an endothermic reaction) to SbBr3. Simultaneously, SiO2 physically migrates to the substrate surface, forming an O-Si-C structure. This, combined with SbBr3, creates a high-density carbonized layer on the substrate, effectively insulating it from heat and oxygen, preventing direct flame contact with the substrate and continuously lowering the temperature surrounding the burning material, thereby improving the flame retardancy.

[0051] Figure 1 The moisture permeability of the PU flame-retardant and moisture-permeable film of the present invention is shown in Figure 2. The presence of the Br-Sb-Si synergistic flame retardant reduces the film's moisture permeability. Both DBDPE and Sb2O3 are hydrophobic. As the synergistic flame retardant content increases, it occupies more space within the PU matrix, forming a dense physical barrier. This extends the diffusion path for water vapor molecules and increases resistance to their escape. This reduces the number of escape routes, resulting in increased water vapor repellency and a decrease in moisture permeability. This makes it more difficult for water vapor molecules to escape into the external environment, thus reducing the moisture permeability.

[0052] Figure 2 The contact angle of the flame-retardant and moisture-permeable PU film of the present invention increases. The contact angle slowly increases with increasing Br-Sb-Si synergistic flame retardant content. Because DBDPE, Sb2O3, and SiO2 all have poor water solubility, increasing the synergistic flame retardant content leads to more flame retardant particles accumulating on the PU film surface, enhancing its water repellency and thus increasing the contact angle.

[0053] Figure 3This is the flame retardant mechanism of the present invention. HBr generated by the thermal decomposition of DBDPE reacts with Sb2O3 to generate H2O, SbBr3, and SbOBr. Among them, H2O can reduce the temperature of the combustion area and further enhance the gas-phase flame retardant effect; SbOBr decomposes into SbBr3 with high stability on the surface of the substrate. This process is an endothermic reaction and can absorb a large amount of heat from the combustion area, effectively reducing the temperature of the combustion area and slowing down the combustion rate of the substrate. SiO2 migrates to the surface of the substrate and forms an O-Si-C structure, which can be cross-linked with SbBr3 (Sb-Br), enhancing the high-temperature stability of the carbon layer. At the same time, SiO2 can adsorb the smoke generated during the combustion process, which has a good smoke suppression effect. The synergistic flame retardant of Br-Sb-SiO2 plays a gas-phase synergistic flame retardant role and a condensed-phase flame retardant role.

[0054] Example 5: Step 1, preparing a prepolymer, comprising: Step 101: vacuum-dry 40 parts of isophorone diisocyanate and 60 parts of polybutylene ether glycol at 110° C. for 2.5 hours; Step 102: Weigh 60 parts of dried polybutylene ether glycol and add them to a four-necked flask, introduce nitrogen, slowly add 40 parts of isophorone diisocyanate, 10 parts of ethylene glycol, 0.5 parts of antioxidant 1010, and 0.3 parts of polyoxyethylene polyoxypropanolamine ether, and stir the prepolymerization reaction at 70° C. for 3.5 hours to obtain a prepolymer; Step 2: Cool the reaction environment to 60° C., add 3 parts of 1,4-butanediol to the prepolymer, and after chain extension reaction for 2 hours, add 1 part of dibutyltin dilaurate and continue the reaction for 2 hours to obtain polyurethane; Step 3, preparing modified bentonite, comprising: Step 301, weighing 20 parts of antimony trioxide and 2 parts of ethylene bisstearamide, adding anhydrous ethanol, high-speed ball milling for 40 minutes, and drying in a vacuum drying oven at 60° C. for 6 hours to obtain a mixture A; Step 302: Weigh bentonite and add it to anhydrous ethanol, stir until it is completely dispersed, centrifuge to remove impurities, and dry it at 60° C. for 6 hours to obtain pure bentonite; Step 303: dissolving 0.08 parts of KH550 in anhydrous ethanol solution, stirring evenly, adding 1 part of pure bentonite, and reacting at 50° C. for 3 hours. After the reaction is completed, washing with anhydrous ethanol several times, and drying the washed bentonite at 50° C. to obtain modified bentonite; Step 4, preparing a polyurethane flame retardant and moisture permeable film, comprising: Step 401: Weigh 40 parts of the polyurethane obtained in step 2, add 40 parts of isopropyl alcohol, place in a three-necked flask, heat and stir at 80° C. for 60 minutes until the polyurethane is completely dissolved, to obtain a polyurethane solution; Step 402: Mix the mixture A obtained in step 301 and 0.3 parts of kaolin with the polyurethane solution obtained in step 401, heating and stirring at 80° C. for 90 minutes; after uniform mixing, continue heating and stirring with the modified bentonite obtained in step 303 for 120 minutes to obtain a mixture emulsion B; Step 403: Defoam the mixture emulsion B obtained in step 402 in a -0.1 MPa vacuum drying oven for 40 minutes. After defoaming, take an appropriate amount of the emulsion and use a coating machine at a speed of 15 mm / s. After film formation, dry it in a vacuum drying oven at 120°C for 5 minutes to obtain a polyurethane flame retardant and moisture permeable film.

[0055] Example 6: Step 1, preparing a prepolymer, comprising: Step 101: vacuum-dry 30 parts of 4,4'-diphenylmethane diisocyanate and 50 parts of polypropylene glycol at 105°C for 3 hours; Step 102: Weigh 50 parts of dried polypropylene glycol and add them to a four-necked flask. Pour nitrogen into the flask, then slowly add 30 parts of 4,4'-diphenylmethane diisocyanate, 15 parts of 1,4-cyclohexanedimethanol, 0.4 parts of antioxidant 1010, and 0.2 parts of polysiloxane. Stir the prepolymerization reaction at 65°C for 4 hours to obtain a prepolymer. Step 2: Cool the reaction environment to 55°C, add 2 parts of diethylamine alcohol to the prepolymer, and after chain extension reaction for 1.5 hours, add 1 part of triethylamine and continue the reaction for 2.5 hours to obtain polyurethane; Step 3, preparing modified bentonite, comprising: Step 301: Weigh 25 parts of ammonium polyphosphate and 1.5 parts of polyacrylate, add anhydrous ethanol, high-speed ball mill for 30 minutes, and dry in a vacuum drying oven at 50° C. for 5 hours to obtain a mixture A; Step 302: Weigh bentonite and add it to anhydrous ethanol, stir until it is completely dispersed, centrifuge to remove impurities, and dry it at 70° C. for 7 hours to obtain pure bentonite; Step 303: dissolving 0.1 parts of vinyltriethoxysilane in an anhydrous ethanol solution, stirring evenly, adding 1.5 parts of pure bentonite, and reacting at 45° C. for 4 hours. After the reaction is completed, washing with anhydrous ethanol several times, and drying the washed bentonite at 40° C. to obtain modified bentonite; Step 4, preparing a polyurethane flame retardant and moisture permeable film, comprising: Step 401: Weigh 35 parts of the polyurethane obtained in step 2, add 45 parts of acetone, place in a three-necked flask, heat and stir at 75° C. for 80 minutes until the polyurethane is completely dissolved, to obtain a polyurethane solution; Step 402: Mixture A obtained in step 301 and 0.4 parts of kaolin are heated and stirred with the polyurethane solution obtained in step 401 at 70° C. for 100 minutes; after uniform mixing, the mixture is heated and stirred with the modified bentonite obtained in step 303 for 150 minutes to obtain a mixture emulsion B; Step 403: Defoam the mixture emulsion B obtained in step 402 in a -0.1 MPa vacuum drying oven for 50 minutes. After defoaming, take an appropriate amount of the emulsion and use a coating machine at a speed of 12 mm / s. After film formation, cure and dry it in a vacuum drying oven at 100°C for 4 minutes to obtain a polyurethane flame retardant and moisture permeable film.

[0056] Example 7: Step 1, preparing a prepolymer, comprising: Step 101, vacuum drying 45 parts of hexamethylene diisocyanate and 70 parts of polytetrahydrofuran diol at 115° C. for 2 hours; Step 102: Weigh 70 parts of dried polytetrahydrofuran diol and add them to a four-necked flask. Pour nitrogen into the flask, slowly add 45 parts of hexamethylene diisocyanate, 10 parts of 1,2-cyclohexanedimethanol, 0.6 parts of antioxidant 168, and 0.4 parts of polyoxypropylene glycerol polyether, and stir the mixture at 85° C. for 3 hours to obtain a prepolymer. Step 2: Cool the reaction environment to 75° C., add 4 parts of diethylamino alcohol to the prepolymer, and after chain extension reaction for 2.5 hours, add 2 parts of dibutyltin dilaurate, and continue the reaction for 1.5 hours to obtain polyurethane; Step 3, preparing modified bentonite, comprising: Step 301: Weigh 15 parts of decabromodiphenylethane and 2 parts of polypropylene alcohol, add anhydrous ethanol, high-speed ball mill for 45 minutes, and dry in a vacuum drying oven at 70° C. for 7 hours to obtain a mixture A; Step 302: Weigh bentonite and add it to anhydrous ethanol, stir until it is completely dispersed, centrifuge to remove impurities, and dry it at 60° C. for 5 hours to obtain pure bentonite; Step 303: dissolving 0.07 parts of KH560 in anhydrous ethanol solution, stirring evenly, adding 0.8 parts of pure bentonite, and reacting at 55° C. for 2 hours. After the reaction is completed, washing with anhydrous ethanol several times, and drying the washed bentonite at 65° C. to obtain modified bentonite; Step 4, preparing a polyurethane flame retardant and moisture permeable film, comprising: Step 401: Weigh 50 parts of the polyurethane obtained in step 2, add 35 parts of N-methylpyrrolidone, place in a three-necked flask, heat and stir at 90° C. for 70 minutes until the polyurethane is completely dissolved, to obtain a polyurethane solution; Step 402: Mix the mixture A obtained in step 301 and 0.5 parts of kaolin with the polyurethane solution obtained in step 401, heating and stirring at 85° C. for 110 minutes; after uniform mixing, continue heating and stirring with the modified bentonite obtained in step 303 for 90 minutes to obtain a mixture emulsion B; Step 403: Defoam the mixture emulsion B obtained in step 402 in a -0.1 MPa vacuum drying oven for 30 minutes. After defoaming, take an appropriate amount of the emulsion and use a coating machine at a speed of 18 mm / s. After film formation, dry it in a vacuum drying oven at 130°C for 6 minutes to obtain a polyurethane flame retardant and moisture permeable film.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A polyurethane flame retardant and moisture permeable film, characterized in that: Raw materials include: isocyanate, polyether polyol, diol, chain extender, catalyst, flame retardant, organic solvent, dispersant, bentonite, kaolin, silane coupling agent, antioxidant, defoaming agent; The flame retardant is a mixture of antimony trioxide, decabromodiphenylethane and modified silicon dioxide; The bentonite is modified by a silane coupling agent.

2. The polyurethane flame retardant and moisture permeable film according to claim 1, characterized in that: The raw materials include, by weight, 20 to 50 parts of isocyanate, 40 to 80 parts of polyether polyol, 5 to 20 parts of diol, 1 to 5 parts of chain extender, 0.5 to 3 parts of catalyst, 10 to 35 parts of flame retardant, and 30 to 50 parts of organic solvent. Dispersant, 1-3 parts; bentonite, 0.5-2 parts; kaolin, 0.2-0.5 parts; silane coupling agent, 0.05-0.11 parts; antioxidant, 0.2-0.7 parts; defoaming agent, 0.1-0.5 parts.

3. The polyurethane flame retardant and moisture permeable film according to claim 1, characterized in that: The isocyanate is one of isophorone diisocyanate, 4,4'-diphenylmethylene diisocyanate, and hexamethylene diisocyanate; The polyether polyol is one of polybutylene glycol, polytetramethylene glycol and polypropylene glycol; The diol is one of ethylene glycol, 1,4-cyclohexanedimethanol and 1,2-cyclohexanedimethanol; The chain extender is one of 1,4-butanediol and diethylamino alcohol; The catalyst is one of dibutyltin dilaurate and triethylamine; The organic solvent is one or more of N,N-dimethylformamide, acetone, isopropyl alcohol, N-methylpyrrolidone, toluene, and butanone; The dispersant is one of ethylene bisstearamide, polyacrylate, polypropylene alcohol, and polyvinyl ester; The silane coupling agent is one of KH550, KH560, and vinyltriethoxysilane; The antioxidant is one of antioxidant 1010 and antioxidant 168, or a mixture of the two; The defoaming agent is one of polyoxyethylene polyoxypropanolamine ether, polysiloxane, and polyoxypropylene glycerol polyether.

4. The polyurethane flame retardant and moisture permeable film according to claim 3, characterized in that: The isocyanate is 4,4'-diphenylmethyl diisocyanate; The polyether polyol is polytetrahydrofuran diol; The diol 1,4-cyclohexanedimethanol; The chain extender is 1,4-butanediol; The catalyst is dibutyltin dilaurate; The organic solvent is NN, dimethylformamide, toluene, butanone, and the ratio is 1:1:1 to 3:2:1; The dispersant is ethylene bisstearamide; The silane coupling agent is vinyltriethoxysilane; The antioxidant is antioxidant 1010; The defoaming agent is polyoxyethylene polyoxypropanolamine ether.

5. The method for preparing a polyurethane flame retardant and moisture permeable film according to any one of claims 1 to 4, characterized in that: The specific steps are as follows: Under a protective atmosphere, polyether polyol, isocyanate, diol, antioxidant and defoamer are mixed for prepolymerization to obtain a prepolymer; the prepolymer, chain extender and catalyst are mixed for reaction to obtain polyurethane; Mixing a flame retardant and a dispersant, grinding, and drying to obtain a mixture A; The impurity-removed bentonite is mixed with a silane coupling agent for reaction, washed, and dried to obtain modified bentonite; The polyurethane is mixed with an organic solvent to obtain a polyurethane solution, and the mixture A, kaolin, and modified bentonite are added to the polyurethane solution and mixed uniformly to obtain a mixture emulsion B; After defoaming, the mixture emulsion B is formed into a film using a coating machine, and then dried and solidified to obtain a polyurethane flame retardant and moisture permeable film.

6. The method for preparing a polyurethane flame retardant and moisture permeable film according to claim 5, characterized in that: The preparation steps of polyurethane are as follows: Dry the isocyanate and polyether polyol in vacuum at 100-120°C for 1-4 hours; Under a nitrogen environment, slowly add isocyanate, diol, antioxidant, and defoamer to the polyether polyol, and stir the prepolymerization reaction at 60°C to 90°C for 2h to 5h to obtain a prepolymer; The reaction environment is cooled to 50°C to 80°C, a chain extender is added to the prepolymer, and after the chain extension reaction is carried out for 1h to 3h, a catalyst is added and the reaction is continued for 1h to 3h to obtain polyurethane.

7. The method for preparing a polyurethane flame retardant and moisture permeable film according to claim 5, characterized in that: The preparation steps of mixture A are as follows: The flame retardant and dispersant were added to anhydrous ethanol, and the mixture was subjected to high-speed ball milling for 20 min to 60 min, and then dried at 40° C. to 90° C. for 4 h to 8 h to obtain a mixture A.

8. The method for preparing a polyurethane flame retardant and moisture permeable film according to claim 5, characterized in that: The preparation steps of modified bentonite are as follows: Add bentonite to anhydrous ethanol, stir until completely dispersed, remove impurities by centrifugation, and dry at 40°C to 90°C for 4h to 8h to obtain pure bentonite; Dissolve the silane coupling agent in anhydrous ethanol solution, stir evenly, add 0.5-2 parts of pure bentonite, react at 40℃~60℃ for 1h~5h, and after the reaction is completed, wash with anhydrous ethanol several times, and dry the washed bentonite at 30℃~70℃ to obtain modified bentonite.

9. The method for preparing a polyurethane flame retardant and moisture permeable film according to claim 5, characterized in that: The preparation steps of polyurethane flame retardant and moisture permeable film are as follows: Add polyurethane to an organic solvent, heat and stir at 60°C to 90°C for 40 minutes to 100 minutes until the polyurethane is completely dissolved to obtain a polyurethane solution; Add mixture A and kaolin to the polyurethane solution, heat and stir at 60°C to 90°C for 50 to 120 minutes, then add modified bentonite and continue heating and stirring for 60 to 180 minutes to obtain mixture emulsion B; The mixture emulsion B was defoamed in a -0.1 MPa environment for 20 min to 60 min. After the defoaming was completed, a film was formed using a coating machine, and the film was dried and solidified to obtain a polyurethane flame retardant and moisture permeable film.

10. The method for preparing a polyurethane flame retardant and moisture permeable film according to claim 5, characterized in that: The steps for preparing polyurethane flame retardant and breathable film using a coating machine are as follows: The coating machine coats the mixture emulsion B into a film at a speed of 10 mm / s to 20 mm / s. After the film is formed, it is cured and dried at 80°C to 140°C for 2min to 7min in a vacuum environment to obtain a polyurethane flame retardant and moisture permeable film.

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