Flame-retardant waterborne polyurethane dispersions and methods for making the same

Abstract

The application discloses a kind of flame-retardant water-based polyurethane dispersions and preparation method thereof, polyol is put into reaction kettle, melt at 70~85 ℃, and dehydration is stirred under vacuum;At 45~60 ℃, isocyanate is added to the reaction kettle, and temperature is raised to 85~90 ℃, and continue to react for 2~4 h;Sulfonated phosphorus-based chain extender and organic solvent B are added, at 60~75 ℃, continue to react for 2~4 h;NCO value is detected, after passing, ion water is added to solution emulsification, and post-chain extender is added, continue to stir for 30~60 min;Material is carried out rotary vacuum evaporation, and organic solvent B is removed, to obtain flame-retardant water-based polyurethane dispersion.The application is synthesized by sulfonation method with phosphorus as the basis sulfonated phosphorus-based chain extender, which can act as chain extender, internal emulsifier also has flame-retardant performance;Water-based polyurethane dispersion prepared using it shows stable dispersion performance, method process is simple, and product performance is excellent.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of synthetic leather, and particularly relates to a sulfonated phosphorus-based chain extender and a preparation method thereof, and a flame-retardant water-based polyurethane dispersion prepared by using the same. BACKGROUND

[0002] The presence of volatile organic components (VOCs) in solvent-based polyurethane resins is an important issue, as volatile organic compounds pose a significant threat to the environment, and inhaling them can cause short-term and long-term adverse effects on human health. In recent years, people have tried to develop and use water-based polyurethane dispersions or solvent-free polyurethane resins, and encouraged the use of low or no VOCs polyurethane resins to prepare synthetic leather to reduce VOCs. Water-based polyurethane dispersions are increasingly used in synthetic leather due to their ease of application, low cost and environmental friendliness.

[0003] Polyurethane resins are not soluble in water by themselves, and water-based polyurethane is grafted with internal emulsifiers in its molecular chain, such as dimethylol propionic acid and dimethylol butyric acid, which are commonly used, and the highly hydrophilic ionized functional groups are formed by the reaction of exposed carboxyl groups with alkaline neutralizing agents, so that the polyurethane can be uniformly dispersed in water. Other ionizable functional groups include sulfonic acid groups (-SO3H), sulfonamide groups (-SO2NH2), and thiol groups (-SH), etc.

[0004] One of the main applications of water-based polyurethane is as a coating for leather, wood and fabric, which are all flammable materials. It is well known that the combustion process requires three basic components: an ignition source, oxygen and fuel, polyurethane is a long chain of hydrocarbons, which decomposes into lower molecular weight compounds during the heating process and can further act as fuel; some polymers also release toxic gases as byproducts of combustion when heated.

[0005] There are two methods to improve the flame retardant properties of polyurethane, additive method and reaction method. In the additive method, the additive is added to the polyurethane resin in bulk form, which is physically mixed with the polymer rather than covalently bonded. Most of these flame retardants are halogen-based additives, which have many disadvantages after mixing, such as easy migration and uneven distribution in polyurethane. In addition, halogen flame retardants release toxic gases when burned, which have the risk of causing cancer. This causes health hazards and environmental pollution problems. Therefore, the use of halogenated compounds as flame retardant materials is subject to several restrictions. Halogen-free phosphorus-containing compounds are considered the most promising flame retardants, mainly because of their high flame retardant efficiency and less toxic gas and smoke generation. Therefore, in recent years, the development of flame-retardant waterborne polyurethane has been very rapid. In the past few years, some research has mainly focused on the synthesis of reactive flame retardants based on organic phosphorus or phosphorus-nitrogen compounds and their use in waterborne. However, research has mainly focused on the improvement of the thermal flame retardant properties of waterborne polyurethane by flame retardants, and there is little comprehensive research on the influence of flame retardants on other important properties of waterborne polyurethane, such as dispersion, physical and mechanical properties. For example: patent document CN103993482B uses aluminum hydroxide, magnesium hydroxide, and ammonium polyphosphate as flame retardants, which are added to polyurethane resin to prepare flame-retardant waterborne polyurethane microfiber synthetic leather base cloth. Patent document CN216373597U uses a post-addition flame retardant method to prepare a waterborne polyurethane synthetic leather with flame retardant function. Patent document CN108715729A uses a post-addition flame retardant method to prepare a flame-retardant, antibacterial waterborne polyurethane coating and adhesive. However, most of these patents improve the flame retardant properties of waterborne polyurethane by adding flame retardants after the reaction, which can easily lead to uneven dispersion of flame retardants in waterborne polyurethane and the defect of easy sedimentation.

[0006] Another method to improve the flame retardant properties of polyurethane is to use polymerizable flame retardant molecules to form a polymer in the backbone of the synthesized polymer, such as phosphorus and sulfur-containing molecules, which can achieve flame retardant effect by forming a layer of carbonized carbon between the burning surface and the atmosphere to isolate the combustible material from the air. For example: patent document CN113278276A mixes phenylphosphoryl dichloride, triethylamine, and tetrahydrofuran, cools to -5-0℃, adds γ-aminopropyltrimethoxysilane, reacts at 0-4℃ for 5-7h, adds methyl methacrylate-β-hydroxypropyl ester, reacts at 0-5℃ for 30-100min, warms to 20-30℃ and reacts for 3-5h, filters, removes the solvent and unreacted triethylamine after the reaction to obtain material A; then uses material A to modify ammonium polyphosphate, and finally uses it in flame-retardant thermoplastic polyurethane elastomer composites. However, this material A cannot be used in waterborne polyurethane dispersions for synthetic leather.

[0007] Patent document CN112142787A discloses an improved synthesis method of N,N-di(6-aminohexyl)phenyl phosphorodiamide-containing flame retardant, dissolves hexamethylene diamine in a solvent, slowly adds a solution of phenyl phosphorodichlorid in drop under stirring, after drop completion, warms up for a certain time, cools down, filters, dissolves the solid in ethanol again, adds 2 times molar amount of triethylamine under stirring, neutralizes, filters, removes solvent from the filtrate and vacuum dries to obtain the product. If this phosphorus-containing aromatic diamine is used for synthesizing flame-retardant water-based polyurethane dispersion, grafting the flame-retardant group into the molecular chain of the polyurethane resin can make the flame-retardant group uniformly distributed in the resin, and the defects of uneven distribution of flame-retardant performance and the phenomenon of migration of the flame retardant causing misting of the synthetic leather do not occur. SUMMARY

[0008] The purpose of the present application is to provide a flame-retardant water-based polyurethane dispersion and a preparation method thereof, grafting a phosphorus-containing group into the molecular chain of the polyurethane, so that the obtained polyurethane dispersion has good internal emulsification and dispersion, and provides good flame retardancy and thermal stability for the final product of synthetic leather polyurethane; and solves the problems of uneven distribution of the added flame retardant in the water-based polyurethane, easy migration, and misting of the synthetic leather surface in the prior art.

[0009] In order to achieve the above-mentioned purpose, the technical scheme of the present application is as follows.

[0010] The first purpose of the present application is to provide a preparation method of a sulfonated phosphorus-based chain extender, characterized in that it comprises the following steps: (1) putting a phosphorus-containing aromatic diamine, methanol and an organic solvent A into a reaction kettle and stirring uniformly; (2) adding fuming sulfuric acid to the reaction kettle dropwise at a temperature of-5-0℃, and stirring and reacting at 15-40℃ for 4-8h; (3) adding a solid base to adjust the PH of the mixture to 7.0-7.4; (4) washing the mixture with ethyl acetate and deionized water in sequence, filtering to obtain a solid, and removing ethyl acetate by rotary evaporation to obtain a yellow-brown solid, i.e. sulfonated diamine;

[0011] The solid base is sodium hydroxide or / and potassium hydroxide;

[0012] The phosphorus-containing aromatic diamine, methanol and fuming sulfuric acid are respectively 10%-20%, 70%-80% and 3%-6% by mass fraction (total is 100%); and the organic solvent A accounts for 50%-75% of the total mass of raw materials;

[0013] The phosphorus-containing aromatic diamine is prepared by the following steps: S1, a small molecule diamine and a deacidifying agent triethylamine are put into a reaction bottle, nitrogen is filled, and an organic solvent A is added to make it fully dissolved; S2, benzene phosphoric dichloride is added dropwise into the reaction bottle at a temperature of-5-0 DEG C, and after being mixed uniformly, the reaction is continuously carried out at 15-40 DEG C for 24-36 h; S3, the obtained mixture is washed with ethyl acetate and deionized water, and the solid is obtained by filtration, and then the ethyl acetate is removed by rotary evaporation to obtain a white solid;

[0014] The small molecule diamine is at least one of ethylenediamine, propylenediamine, 1,4-butylenediamine, pentanediamine, 1,6-hexanediamine and isophorone diamine;

[0015] The mass fractions of the small molecule diamine, triethylamine and benzene phosphoric dichloride are 25%-35%, 10%-20% and 45%-55% respectively; and the organic solvent A accounts for 50%-75% of the total mass of the phosphorus-containing aromatic diamine raw material;

[0016] The organic solvent A described in the above two reactions is one or a combination of four hydrogen furan, N, N-dimethylformamide and acetone.

[0017] A second object of the present application is to provide a preparation method of the flame-retardant water-based polyurethane dispersion, characterized by comprising the following steps:

[0018] (1) a polyol is put into a reaction kettle, melted by heating to 70-85 DEG C, and dehydrated under vacuum stirring; (2) isocyanate is added into the reaction kettle at 45-60 DEG C, and the reaction is continuously carried out at 85-90 DEG C for 2-4 h; (3) the sulfonated phosphorus-based chain extender and an organic solvent B are added at 60-75 DEG C, and the reaction is continuously carried out for 2-4 h; (4) the NCO value is detected, and after passing, ionized water is added for solution emulsification, and a post-chain extender is added, and the stirring is continuously carried out for 30-60 min; (5) the material obtained in step (4) is subjected to rotary vacuum evaporation to remove the organic solvent B, and the flame-retardant water-based polyurethane dispersion is obtained;

[0019] The polyol is one or a combination of polybutylene adipate glycol, polycaprolactone diol, polycarbonate diol and polytetrahydrofuran ether diol with a weight average molecular weight of 500-2000;

[0020] The isocyanate is at least one of 4, 4-diphenyl methane diisocyanate (MDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI) and 4, 4-dicyclohexyl methane diisocyanate;

[0021] The ratio of the NCO value of the isocyanate to the total hydroxyl value of the polyol and the chain extender is (1.2-1.05):1.

[0022] The organic solvent B is acetone or / and butanone; the post-chain extender is a binary amine compound, preferably at least one of ethylenediamine, pentanediamine and hexanediamine; the post-chain extender is added in an amount of 45% to 55%, preferably 50%, of the NCO molar amount determined in the step (4);

[0023] In addition to the organic solvent B, the components in the steps (1) to (5) are respectively 20 to 40% of polyol, 0.8 to 1.6% of sulfonated phosphorus-based chain extender, 12 to 30% of isocyanate, 54 to 56% of deionized water, 0.1 to 0.4% of post-chain extender, and the organic solvent B accounts for 15% to 35% of the total mass of the raw materials.

[0024] The solid content of the flame-retardant water-based polyurethane dispersion provided by the application is 45±1.0%, the viscosity is 100 to 300 mpa.s, and the final flame-retardant water-based polyurethane particle size is 200 to 500 nm.

[0025] The flame-retardant water-based polyurethane dispersion provided by the application is used for preparing flame-retardant polyurethane synthetic leather.

[0026] Compared with the prior art, the application has the following advantages:

[0027] The sulfonated phosphorus-based chain extender synthesized by the sulfonation method in the application can act as a chain extender, an internal emulsifier and has flame-retardant performance; the water-based polyurethane dispersion prepared by using the sulfonated phosphorus-based chain extender exhibits stable dispersion performance, avoids the uneven distribution of the flame-retardant powder in the synthetic leather and the easy migration of the flame-retardant powder to cause the synthetic leather to mist, and affects the quality of the final product, and also avoids the use of halogen-containing flame retardants to release toxic and carcinogenic substances during combustion.

[0028] The sulfonated phosphorus-based chain extender in the application is uniformly distributed in the polyurethane molecular chain, and there is no uneven flame-retardant performance of the synthetic leather; the phosphorus compound is converted into phosphoric acid and water during combustion, the phosphoric acid is further reacted to generate an inorganic polymer layer attached to the surface of the synthetic leather to inhibit further combustion of the synthetic leather, and the generated water helps to further reduce the temperature of the synthetic leather.

[0029] The method of the application has simple process, extremely low cost and energy consumption, excellent product performance, no use of surfactants or other reducing agents and other chemical substances, no waste generated in the production process, is more environmentally friendly and economical, and has good application prospect. DETAILED DESCRIPTION

[0030] The application will be further described in conjunction with specific examples. It should be understood that these examples are only used to illustrate the application and not used to limit the scope of the application. Furthermore, it should be understood that after reading the content of the application, those skilled in the art can make various modifications or changes to the application, and these equivalent forms also fall within the scope defined by the appended claims.

[0031] Example 1

[0032] Preparation of phosphorus-containing aromatic diamine: S1, 29 parts (mass parts, the same below) of ethylenediamine and 17 parts of acid-binding agent triethylamine were put into a reaction bottle, nitrogen was filled, and then 200 parts of tetrahydrofuran was added to dissolve it thoroughly; S2, 54 parts of benzene phosphor dichloride was added dropwise into the reaction kettle, and the temperature of benzene phosphor dichloride was -5℃; after mixing uniformly, the reaction was continued at 15℃ for 24h; S3, the obtained mixture was washed with ethyl acetate and deionized water, and then separated by a separatory funnel to obtain solid, and then ethyl acetate was removed by rotary evaporation to obtain white solid.

[0033] Preparation of sulfonated phosphorus-based chain extender: (1) 17 parts of phosphorus-containing aromatic diamine, 77 parts of methanol and 200 parts of tetrahydrofuran were put into a reaction kettle and stirred uniformly; (2) 6 parts of oleum was added dropwise into the reaction kettle, and the temperature of oleum was -5℃; stirring at 15℃ for 4h; (3) solid sodium hydroxide was added to adjust the PH of the mixture to 7.0; (4) the mixture was washed with ethyl acetate and deionized water in turn, and the solution was filtered to obtain solid by a separatory funnel, and then ethyl acetate was removed by rotary evaporation to obtain yellow-brown solid, i.e. sulfonated diamine.

[0034] Preparation of water-based polyurethane dispersion: (1) 23.8 parts of polybutylene adipate glycol (weight average molecular weight is 500) was put into a reaction kettle, melted by heating to 70℃, and dehydrated under vacuum stirring; (2) 20 parts of isocyanate MDI was added into the reaction kettle at 45℃, and the temperature was raised to 85℃ for continuous reaction for 4h; (3) 0.8 parts of sulfonated phosphorus-based chain extender and 33 parts of acetone were added, and the reaction was continued at 75℃ for 2h; (4) the NCO value was detected to 50%, and after passing, 55 parts of ionized water was added for solution emulsification, and 0.4 parts of post-chain extender ethylenediamine was added, and the stirring was continued for 30min; (5) the material obtained in step (4) was subjected to rotary vacuum evaporation to remove acetone, and the obtained flame-retardant water-based polyurethane dispersion was obtained; the solid content of the flame-retardant water-based polyurethane dispersion was 45.2%, the viscosity was 100mpa.s, and the water-based polyurethane particle size was 490nm.

[0035] Example 2

[0036] Preparation of phosphorus-containing aromatic diamine: S1, 31 parts (mass parts, the same below) of ethylenediamine and 18 parts of acid-binding agent triethylamine were put into a reaction bottle, nitrogen was filled, and then 200 parts of tetrahydrofuran was added to make it fully dissolved; S2, 51 parts of benzene phosphor dichloride was added dropwise into the reaction kettle, and the temperature of benzene phosphor dichloride was -3°C; after mixing uniformly, it was continuously reacted at 25°C for 30h; S3, the obtained mixture was washed with ethyl acetate and deionized water, and then separated by a separatory funnel to obtain solid, and then ethyl acetate was removed by rotary evaporation to obtain white solid.

[0037] Preparation of sulfonated phosphorus-based chain extender: (1) 16.5 parts of phosphorus-containing aromatic diamine, 77.5 parts of methanol and 200 parts of tetrahydrofuran were put into a reaction kettle and stirred uniformly; (2) 6 parts of oleum was added dropwise into the reaction kettle, and the temperature of the oleum was -3°C; it was stirred and reacted at 30°C for 4h; (3) solid sodium hydroxide was added to adjust the PH of the mixture to 7.0; (4) the mixture was sequentially washed with ethyl acetate and deionized water, and the solution was filtered to obtain solid by a separatory funnel, and then ethyl acetate was removed by rotary evaporation to obtain yellow-brown solid, i.e. sulfonated diamine.

[0038] Preparation of aqueous polyurethane dispersion: (1) 21.31 parts of polycaprolactone diol (weight average molecular weight 1000) was put into a reaction kettle, melted by heating to 80°C, and dehydrated under vacuum stirring; (2) 22 parts of isocyanate TDI was added into the reaction kettle at 55°C, and the temperature was raised to 87°C for continuous reaction for 3h; (3) 1.45 parts of sulfonated phosphorus-based chain extender and 35 parts of butanone were added, and the reaction was continued at 70°C for 3h; (4) the NCO value was detected to 50%, and after passing, 55 parts of ionized water was added for solution emulsification, and 0.24 parts of post-chain extender isophorone diamine was added, and the stirring was continued for 45min; (5) the material obtained in step (4) was subjected to rotary vacuum evaporation to remove butanone, to obtain the flame-retardant aqueous polyurethane dispersion; the solid content of the flame-retardant aqueous polyurethane dispersion was 44.8%, the viscosity was 230mpa.s, and the aqueous polyurethane particle size was 370nm.

[0039] Example 3

[0040] Preparation of phosphorus-containing aromatic diamine: S1, 35 parts (mass parts, the same below) of isophorone diamine and 10 parts of acid-binding agent triethylamine were put into a reaction bottle, nitrogen was filled, and then 200 parts of tetrahydrofuran was added to make it fully dissolved; S2, 55 parts of benzene phosphor dichloride was added dropwise into the reaction kettle, and the temperature of benzene phosphor dichloride was 0°C; after mixing uniformly, it was continuously reacted at 40°C for 36h; S3, the obtained mixture was washed with ethyl acetate and deionized water, and then separated by a separatory funnel to obtain solid, and then ethyl acetate was removed by rotary evaporation to obtain white solid.

[0041] Preparation of sulfonated phosphorus-based chain extender: (1) 19 parts of phosphorus-containing aromatic diamine, 78 parts of methanol and 200 parts of tetrahydrofuran were put into a reaction kettle and stirred uniformly; (2) 3 parts of oleum was added dropwise into the reaction kettle, wherein the temperature of the oleum was 0°C; the reaction was stirred at 40°C for 8h; (3) solid sodium hydroxide was added to adjust the pH of the mixture to 7.0; (4) the mixture was washed with ethyl acetate and deionized water in sequence, and the solution was filtered to separate the solid, and then the ethyl acetate was removed by rotary evaporation to obtain a yellow-brown solid, i.e. sulfonated diamine.

[0042] Preparation of the aqueous polyurethane dispersion: (1) 30.4 parts of polytetrahydrofuran ether diol (weight average molecular weight of 2000) was put into a reaction kettle, melted by heating to 85°C, and dehydrated under vacuum stirring; (2) 12.7 parts of isocyanate IPDI was added to the reaction kettle at 60°C, and the temperature was raised to 90°C for continuous reaction for 4h; (3) 1.5 parts of sulfonated phosphorus-based chain extender and 30 parts of butanone were added, and the reaction was continued at 70°C for 4h; (4) the NCO value was detected to be 52%, and after passing, 55 parts of ionized water was added for solution emulsification, and 0.4 parts of post-chain extender hexanediamine was added, and the stirring was continued for 60min; (5) the material obtained in step (4) was subjected to rotary vacuum evaporation to remove butanone, to obtain the flame-retardant aqueous polyurethane dispersion; the solid content of the flame-retardant aqueous polyurethane dispersion was 45.3%, the viscosity was 270mpa.s, and the aqueous polyurethane particle size was 260nm.

[0043] Comparative Example 1

[0044] The flame-retardant aqueous polyurethane dispersion provided by Comparative Example 1 was prepared basically the same as in Example 1, except that: the preparation of the phosphorus-containing aromatic diamine: S1, 25 parts (mass parts, the same below) of ethylenediamine and 17 parts of acid-binding agent triethylamine were put into a reaction bottle, nitrogen was filled, and then 200 parts of tetrahydrofuran was added to make it fully dissolved; S2, 58 parts of phenylphosphonic dichloride was added dropwise into the reaction kettle, wherein the temperature of the phenylphosphonic dichloride was -10°C; after mixing uniformly, the reaction was continued at 10°C for 18h; S3, the obtained mixture was washed with ethyl acetate and deionized water, and then the solid was separated by a separatory funnel, and then the ethyl acetate was removed by rotary evaporation to obtain a white solid. The solid content of the flame-retardant aqueous polyurethane dispersion was 45.2%, the viscosity was 352mpa.s, and the aqueous polyurethane particle size was 183nm.

[0045] Comparative Example 2

[0046] The flame-retardant waterborne polyurethane dispersion provided by Comparative Example 2 was prepared substantially the same as in Example 1, except that the phosphorus-containing aromatic diamine was prepared as follows: S1, 45 parts (mass parts, hereinafter the same) of ethylenediamine and 10 parts of acid-binding agent triethylamine were put into a reaction bottle, nitrogen was filled, and 200 parts of tetrahydrofuran was added to dissolve it thoroughly; S2, 45 parts of benzene phosphor dichloride was added dropwise into the reaction kettle, and the temperature of the benzene phosphor dichloride was 5°C; after mixing uniformly, the reaction was continued at 50°C for 48 h; S3, the obtained mixture was washed with ethyl acetate and deionized water, and then separated by a separatory funnel to obtain solid, and then the ethyl acetate was removed by rotary evaporation to obtain white solid. The solid content of the flame-retardant waterborne polyurethane dispersion was 44.7%, the viscosity was 94 mpa.s, and the particle size of the waterborne polyurethane was 672 nm.

[0047] Comparative Example 3

[0048] The flame-retardant waterborne polyurethane dispersion provided by Comparative Example 3 was prepared substantially the same as in Example 1, except that the sulfonated phosphorus-based chain extender was prepared as follows: (1) 19 parts of phosphorus-containing aromatic diamine, 80 parts of methanol and 200 parts of tetrahydrofuran were put into a reaction kettle and stirred uniformly; (2) 1 part of oleum was added dropwise into the reaction kettle, and the temperature of the oleum was -5°C; the reaction was stirred at 10°C for 3 h; (3) solid sodium hydroxide was added to adjust the PH of the mixture to 7.0; (4) the mixture was washed with ethyl acetate and deionized water in turn, and then the solution was separated by a separatory funnel to obtain solid, and then the ethyl acetate was removed by rotary evaporation to obtain yellow-brown solid, i.e. sulfonated diamine. The solid content of the flame-retardant waterborne polyurethane dispersion was 44.9%, the viscosity was 378 mpa.s, and the particle size of the waterborne polyurethane was 182 nm.

[0049] Comparative Example 4

[0050] The flame-retardant waterborne polyurethane dispersion provided by Comparative Example 4 was prepared substantially the same as in Example 1, except that the sulfonated phosphorus-based chain extender was prepared as follows: (1) 15 parts of phosphorus-containing aromatic diamine, 75 parts of methanol and 200 parts of tetrahydrofuran were put into a reaction kettle and stirred uniformly; (2) 10 parts of oleum was added dropwise into the reaction kettle, and the temperature of the oleum was -5°C; the reaction was stirred at 50°C for 10 h; (3) solid sodium hydroxide was added to adjust the PH of the mixture to 7.0; (4) the mixture was washed with ethyl acetate and deionized water in turn, and then the solution was separated by a separatory funnel to obtain solid, and then the ethyl acetate was removed by rotary evaporation to obtain yellow-brown solid, i.e. sulfonated diamine. The solid content of the flame-retardant waterborne polyurethane dispersion was 45.5%, the viscosity was 72 mpa.s, and the particle size of the waterborne polyurethane was 580 nm.

[0051] The flame-retardant waterborne polyurethane dispersions obtained in Examples 1-3 and Comparative Examples 1-4 were used to prepare polyurethane synthetic leather: color paste, thickening agent and leveling agent were added to the flame-retardant waterborne polyurethane dispersion and stirred to obtain a waterborne polyurethane paste, which was then coated on the surface of a release paper, dried in an oven at 80°C for 3 min, and then coated with a flame-retardant waterborne polyurethane primer, followed by lamination with a flame-retardant base cloth by pressing with a squeeze roller, and drying in an oven at 120°C to obtain the flame-retardant polyurethane synthetic leather. The burning rate of the flame-retardant polyurethane synthetic leather of Examples 1-3 and Comparative Examples 1-4 was determined according to the FMVSS-302 standard, and the results are shown in Table 1.

[0052] Table 1 shows the flame-retardant performance test results of Examples 1-3 and Comparative Examples 1-4

[0053]

[0054] According to the FMVSS-302 standard, a burning rate of 0 is excellent, a burning rate of less than 50 mm / min is good, a burning rate of 50-100 mm / min is fair, and a burning rate of more than 100 mm / min is unqualified. As shown in Table 1, Examples 1-3 have good flame-retardant performance, while Comparative Examples 1-4 have poor flame-retardant performance. This is because the ratio of raw materials used in the preparation of the internal emulsifier has a great influence on the flame-retardant performance of the final product; only when the ratio of raw materials is within an appropriate range can the best flame-retardant performance be achieved.

Claims

1. A process for the preparation of a flame-retardant aqueous polyurethane dispersion, characterized in that, The method comprises the following steps: (1) Put the polyol into a reaction kettle, melt at 70-85℃, and stir to remove water under vacuum; (2) Add isocyanate to the reaction kettle at 45-60℃, heat to 85-90℃, and continue to react for 2-4h; (3) Add sulfonated phosphorus-based chain extender and organic solvent B, and continue to react at 60-75℃ for another 2-4h; (4) Detect the NCO value, add ionized water for solution emulsification after passing, and add a post-chain extender, and continue to stir for 30-60min; the ratio of the NCO value of the isocyanate to the total hydroxyl value of the polyol and the chain extender is (1.2-1.05):1; (5) Perform rotary vacuum evaporation on the material obtained in step (4) to remove the organic solvent B, and obtain the flame-retardant waterborne polyurethane dispersion; In addition to the organic solvent B, the mass fractions of the components in steps (1)-(4) are respectively: polyol 20-40%, sulfonated phosphorus-based chain extender 0.8%-1.6%, isocyanate 12%-30%, deionized water 54%-56%, post-chain extender 0.1%-0.4%, organic solvent 15%-35%, and the sum of all raw materials is 100%. The preparation method of the sulfonated phosphorus-based chain extender comprises: (a) Put the phosphorus-containing aromatic diamine, methanol and organic solvent A into a reaction kettle and stir uniformly; (b) Add fuming sulfuric acid to the reaction kettle dropwise at a temperature of-5-0℃, and stir to react at 15-40℃ for 4-8h; (c) Add solid alkali to adjust the pH of the mixture to 7.0-7.4; (d) Wash the mixture with ethyl acetate and deionized water in sequence, filter to obtain solid, and then remove the ethyl acetate by rotary evaporation to obtain yellow-brown solid sulfonated diamine, i.e. sulfonated phosphorus-based chain extender; the mass fractions of the phosphorus-containing aromatic diamine, methanol and fuming sulfuric acid are respectively: 10%-20%, 70%-80% and 3%-6%, and the sum of all raw materials is 100%; the organic solvent A accounts for 50%-75% of the total mass of the raw materials of the sulfonated phosphorus-based chain extender; The phosphorus-containing aromatic diamine is prepared by the following steps: S1, put the small molecule diamine and acid-binding agent triethylamine into a reaction bottle, fill nitrogen, and then add organic solvent A to make it fully dissolved; S2, add benzene phosphor dichloride to the reaction bottle dropwise at a temperature of-5-0℃, mix uniformly, and then continue to react at 15-40℃ for 24-36h; S3, wash the obtained mixture with ethyl acetate and deionized water, filter to obtain solid, and then remove the ethyl acetate by rotary evaporation to obtain white solid; the mass fractions of the small molecule diamine, triethylamine and benzene phosphor dichloride are respectively: 25%-35%, 10%-20% and 45%-55%, and the sum of all raw materials is 100%; the organic solvent A accounts for 50%-75% of the total mass of the raw materials of the phosphorus-containing aromatic diamine.

2. The method for preparing a flame-retardant waterborne polyurethane dispersion according to claim 1, characterized by, The solid alkali is sodium hydroxide or / and potassium hydroxide.

3. The method of preparing a flame retardant waterborne polyurethane dispersion according to claim 1, characterized in that, The small molecule diamine is at least one of ethylenediamine, propylenediamine, 1,4-butylenediamine, pentanediamine, 1,6-hexanediamine, and isophorone diamine; the organic solvent A is one or more combinations of tetrahydrofuran, N,N-dimethylformamide, and acetone.

4. The method of preparing a flame retardant waterborne polyurethane dispersion according to claim 1, characterized in that, The polyol is one or more combinations of polybutylene adipate glycol with a weight average molecular weight of 500-2000, polycaprolactone diol, polycarbonate diol, and polytetrahydrofuran ether diol; the isocyanate is at least one of 4,4-diphenylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, and 4,4-dicyclohexylmethane diisocyanate; the organic solvent B is acetone or / and butanone; the post-chain extender is a diamine compound; the amount of the post-chain extender added is 45%-55% of the NCO molar amount determined in the step (4).

5. A flame retardant waterborne polyurethane dispersion characterized by, The flame-retardant waterborne polyurethane dispersion prepared by the preparation method according to any one of claims 1-4 has a solid content of 45±1.0%, a viscosity of 100-300 mpa.s, and a particle size of the flame-retardant waterborne polyurethane of 200-500 nm.

6. The flame retardant waterborne polyurethane dispersion according to claim 5, characterized in that, A flame-retardant polyurethane synthetic leather is prepared. A flame-retardant polyurethane synthetic leather is prepared.

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