Polyurethane and polyvinylidene fluoride hybrid emulsion and preparation method thereof

Abstract

The invention relates to a polyurethane and PVDF hybrid emulsion, which comprises the following raw materials: a polyurethane aqueous dispersion, a vinylidene fluoride monomer, an initiator and a chain transfer agent, the polyurethane aqueous dispersion comprises the following raw materials: polyisocyanate, a polyfunctional polymer, a compound A, a catalyst, a neutralizer and water, the compound A contains more than one hydroxyl and more than one carboxyl, and the total functionality of the compound A is greater than or equal to 3; the preparation method comprises the following steps: introducing a vinylidene fluoride monomer into a closed container filled with a polyurethane aqueous dispersion, carrying out in-situ polymerization under a pressurization condition in the presence of an initiator and a chain transfer agent to obtain polyvinylidene fluoride, and interpenetrating and entangling the polyvinylidene fluoride and polyurethane. The hybrid emulsion provided by the invention integrates chemical corrosion resistance of PVDF (Polyvinylidene Fluoride) and film-forming property of PU (Polyurethane), and has extremely excellent stability. The VDF monomer is a gaseous small molecule, can easily enter the PU polymer, and is subjected to in-situ polymerization around the PU polymer under a pressurized condition to form a PVDF molecular chain to form molecular-level interpenetration and / or entanglement with PU.

Description

Technical Field

[0001] The invention relates to a hybrid emulsion of polyurethane and polyvinylidene fluoride and a preparation method thereof. Background Art

[0002] Polyvinylidene fluoride (PVDF) emulsions are widely used in the coatings industry due to their excellent chemical resistance, especially in building exterior wall coatings and heavy industrial coatings that require extremely high durability. However, the high-temperature baking film-forming process of PVDF emulsions increases the difficulty of processing and may result in insufficient flexibility and cracking after film formation. In contrast, polyurethane emulsions are known for their excellent low-temperature film-forming properties, flexibility and elasticity, although their chemical resistance is poor. The PU / PVDF hybrid emulsion, which is a co-entanglement of polyurethane and PVDF obtained by seed emulsion polymerization / swelling polymerization, can combine the advantages of these two materials at the molecular level and nanoscale, providing a more excellent coating solution for multiple industries. This hybrid emulsion combines the chemical resistance of PVDF and the film-forming properties of PU, indicating a broad application prospect.

[0003] Patent CN118421144A combines polyvinylidene fluoride emulsion with water-based polyurethane emulsion by simple mixing to prepare a hybrid emulsion of polyurethane (PU) and PVDF, which is applied to water-based thermal insulation coatings for the surface protection of railway bridge concrete. However, it is difficult to achieve uniform distribution of the two components in the film-forming process of this hybrid emulsion prepared by blending, and it is difficult to combine and give full play to the advantages of the two materials.

[0004] Patent CN115433512A combines PVDF powder and polyurethane by simple mixing to prepare an oily one-component polyurethane coating for metal corrosion protection. However, this coating contains a large amount of VOC, has high carbon emissions and pollutes the environment.

[0005] In existing reports, most of them adopt the idea of ​​first polymerization and then blending to obtain a mixture of PU raw materials and PVDF raw materials. In view of the low surface energy of fluorinated polymers and the different film-forming and crystallization behaviors of different polymers, such blends are prone to stratification, sedimentation and difficulty in film formation. The present invention introduces VDF monomer after PU polymerization through the seed emulsion polymerization method. VDF monomer is a small gaseous molecule that can easily enter the interior of the PU polymer and form a certain concentration around the PU polymer under certain pressure conditions. After initiating polymerization, PVDF molecular chains can be formed in situ, forming molecular-level interpenetration and entanglement with PU. Summary of the invention

[0006] One of the inventive objectives of the present invention is to provide a hybrid emulsion of polyurethane and PVDF, which has both the chemical corrosion resistance of PVDF and the film-forming property of PU; the hybrid emulsion has a structure with polyurethane as the shell and PVDF as the core. When forming a film, the polyurethane shell can provide excellent moldability; after film formation, the polyurethane phase and the PVDF phase can be evenly distributed on the nanoscale, thereby fully combining and giving play to the advantages of polyurethane and PVDF. Different from the prior art, the hybrid emulsion of the present invention avoids the use of an external emulsifier, thereby avoiding the negative impact of the external emulsifier on its performance after film formation.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] The invention provides a polyurethane and PVDF hybrid emulsion, comprising the following raw materials: polyurethane water dispersion, vinylidene fluoride monomer, initiator, chain transfer agent, the polyurethane water dispersion comprises the following raw materials: polyisocyanate, multifunctional polymer, compound A containing more than one hydroxyl group and more than one carboxyl group and having a total functionality of ≥3, catalyst, neutralizer, water; the multifunctional polymer contains more than two groups capable of reacting with isocyanate; the vinylidene fluoride monomer is introduced into a closed container containing the polyurethane water dispersion, and in situ polymerization is carried out in the presence of an initiator and a chain transfer agent under pressurized conditions to obtain polyvinylidene fluoride, and the polyvinylidene fluoride and the polyurethane form interpenetration and / or entanglement.

[0009] Furthermore, the polyurethane and PVDF hybrid emulsion comprises the following raw materials in parts by weight: 40-60 parts of polyurethane aqueous dispersion, 40-60 parts of vinylidene fluoride monomer, 0.1-1 parts of initiator, and 0.02-0.2 parts of chain transfer agent.

[0010] Furthermore, the pressurization condition is to introduce vinylidene fluoride gas to make the pressure of the closed container 1.5-3MPa, such as 2MPa.

[0011] Furthermore, the polyisocyanate is selected from at least one of aromatic, alicyclic and aliphatic diisocyanates, including but not limited to α,α,α,α-tetramethylxylene diisocyanate (THXDI TM), 3,5,5-trimethyl-1-isocyanato-3-isocyanatomethylcyclohexane, isophorone diisocyanate (IPDI) and its derivatives, tetramethylene diisocyanate, hexamethylene diisocyanate (HDI) and its derivatives, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, isophorone diisocyanate, m-isopropenyl-α,α,-dimethylbenzyl isocyanate (TMI), 4,4'-dicyclohexylmethane diisocyanate (H12MDI), benzene-1,3-bis(1-isocyanato-1-methylethyl), 1,5-naphthalene diisocyanate (NDI), phenylene diisocyanate (PPDI), trans-cyclohexane-1,4-diisocyanate (TMI), toluene diisocyanate (TODI), 4,4'-diphenylmethane diisocyanate, 4,4'-diphenyldimethylmethane diisocyanate, di- and tetra-alkyl diphenylmethane diisocyanates, 4,4'-dibenzyl diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, toluene diisocyanate isomers, 1-methyl-2,4-diisocyanatocyclohexane, 1,6-diisocyanato-2,2,4-trimethylhexane, 1,6-diisocyanato-2,4,4-trimethylhexane.

[0012] Further, the multifunctional polymer is selected from at least one of polyols, polyamines, polythiols, and polyolamines, and the number average molecular weight of the multifunctional polymer is 500-3000 g / mol. Preferably, it is 1000-2000 g / mol. Further, the polyol is selected from at least one of polyether polyols, polyester polyols, and polycarbonate polyols. Preferably, it is a polyether polyol, such as polyethylene glycol, polypropylene glycol, polybutylene glycol, polytetrahydrofuran, and poly(propylene oxide) glycol.

[0013] Furthermore, the compound A containing one or more hydroxyl groups and one or more carboxyl groups and having a total functionality ≥ 3 is at least one selected from di(hydroxymethyl)propionic acid, di(hydroxymethyl)butyric acid, 3-hydroxyglutaric acid, malic acid, tartaric acid, and the like.

[0014] Furthermore, the catalyst is selected from at least one of organic tin, organic bismuth, tertiary amine, morpholine derivatives, and piperazine derivatives. For example, the organic tin is selected from dibutyltin dilaurate, stannous octoate, and dibutyltin dichloride; the tertiary amine is selected from triethylamine, tripropylamine, monoethyldipropylamine, monoethyldibutylamine, diethylmonopropylamine, and diethylmonobutylamine. The amount of the catalyst is 0.1-1wt% of the mass of the polyisocyanate.

[0015] Furthermore, the neutralizing agent is an inorganic base or an organic base, such as sodium hydroxide, potassium hydroxide, tertiary amine, pyridine. The amount of the neutralizing agent is such that the pH value of the polyurethane aqueous dispersion is 7-10.

[0016] Furthermore, the solid content of the polyurethane aqueous dispersion is 30-45wt%, preferably 38-42wt%; wherein the amount of polyisocyanate, multifunctional polymer and compound A is such that the amount of isocyanate group (-NCO) in the polyisocyanate and the total amount of functional groups (hydroxyl, amine, thiol) in the multifunctional polymer and compound A that can react with isocyanate is 2-10. And the ratio of the number of active functional groups of the multifunctional polymer to the number of active functional groups of compound A is 10:1-3. The active functional group is defined as a group that can react with isocyanate, such as hydroxyl, carboxyl, amine, thiol.

[0017] Alternatively, the mass ratio of polyisocyanate, multifunctional polymer and compound A is 150-235:231-305:26-42.

[0018] Further, the initiator is selected from organic initiators and / or inorganic initiators. The organic initiator is selected from diethyl peroxydicarbonate, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di-tert-butyl peroxydicarbonate, di-tert-butyl peroxide, tert-butyl peroxypivalate, dicyclohexyl peroxydicarbonate, diisopropylbenzene peroxide and tert-butyl hydroperoxide or a mixture of two or more thereof. The inorganic initiator is selected from potassium persulfate, sodium persulfate, ammonium persulfate or a mixture of two or more thereof.

[0019] Further, the chain transfer agent is selected from HCFC-123, CFC-11, DEC, DEM, isopropanol, ethyl acetate, methanol, cyclopentane, chloroform, acetone or a mixture of two or more thereof.

[0020] The present invention also provides a method for preparing the above-mentioned polyurethane and PVDF hybrid emulsion, comprising the following steps:

[0021] (S1) mixing polyisocyanate, multifunctional polymer, compound A and catalyst in an inert atmosphere, heating and keeping the temperature to react until the NCO content of the system no longer changes, cooling, adding water and a neutralizing agent, so that the solid content and pH of the obtained polyurethane aqueous dispersion meet the requirements, that is, the pH is 7-10, and the solid content is 30-45wt%, preferably 38-42wt%;

[0022] (S2) In a sealed container, the polyurethane aqueous dispersion, the chain transfer agent, and the initiator are uniformly mixed, and the temperature is raised to above the initiation temperature of the initiator, and the vinylidene fluoride monomer is introduced to pressurize the system to fully react and obtain a polyurethane and PVDF hybrid emulsion.

[0023] Furthermore, in step (S1), the temperature is raised to 80-120°C; in step (S2), the initiation temperature is determined by the initiator, such as 70-130°C, and the pressurization condition is to introduce vinylidene fluoride monomer so that the pressure in the container is 1.5-3MPa, such as 2MPa.

[0024] The hybrid emulsion of polyurethane and PVDF provided by the present invention combines the chemical corrosion resistance of PVDF and the film-forming property of PU, and has extremely excellent stability. The present invention introduces VDF monomer after PU polymerization by a seed emulsion polymerization method. VDF monomer is a small gaseous molecule, which can easily enter the interior of the PU polymer and polymerize in situ around the PU polymer under pressure to form interpenetration and entanglement of PVDF molecular chains and PU at the molecular level. The efficient formation of chain entanglement is an effective means to improve the hybrid mixing of fluorine-containing resin and other resins, which is beneficial to improving the mechanical strength of the polymer composite system. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 These are the TEM image, HAADF-STEM image and energy dispersive spectrum of the hybrid emulsion prepared in Example 1.

[0026] Figure 2 It is the intensity distribution curve of fluorine (F) and nitrogen (N) elements obtained from a single PVDF-PU composite latex nanoparticle in the sample of Example 3. DETAILED DESCRIPTION

[0027] In order to explain the present invention more clearly, the present invention is further described below in conjunction with preferred embodiments. It should be understood by those skilled in the art that the following specific description is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

[0028] In the case of illustrating and explaining the purpose of the present invention through the following examples, the components of the composition are explained in parts by weight as a general standard. Unless otherwise specified, for the sake of simplicity, the "parts" described in the examples of the present invention are all parts by weight.

[0029] Example 1

[0030] (S1) At room temperature, 220 parts of diisocyanate TMXDI, 305 parts of poly(propylene oxide) glycol with a molecular weight of 1000, 42 parts of di(hydroxymethyl)propionic acid and 0.26 parts of dibutyltin dilaurate catalyst are added to a reactor. Stirring is turned on to 200 rpm, and the reaction mixture is heated to 80°C. The reaction mixture is kept in this temperature range until the free NCO no longer changes. The reactor temperature is lowered to 65°C, and then 17 parts of triethylamine are added dropwise to the reactor. The reaction mass is stirred for 15 minutes. 830 parts of deionized water are added dropwise to the reactor within 30 minutes, and stirred for 30 minutes after the addition is completed. The material is cooled to below 35°C to obtain a polyurethane aqueous dispersion.

[0031] (S2) 50 parts of polyurethane aqueous dispersion and 0.02 parts of chain transfer agent isopropanol are added to the reactor successively and stirred for 0.5 hours; after the mixed solution is heated to 80°C, 0.8 parts of initiator ammonium persulfate are added. Then, 50 parts of vinylidene fluoride monomer are introduced, and the pressure of the reactor is controlled at 2MPa. After reacting for 2 hours, a stable polyurethane and polyvinylidene fluoride hybrid emulsion can be obtained.

[0032] Figure 1 The TEM image, HAADF-STEM image and energy dispersive spectrum of the hybrid emulsion obtained in Example 1, wherein (A) is a transmission electron microscope (TEM) image, (B) is a high-angle annular dark field scanning transmission electron microscope (HAADF-STEM) image, and (C) to (E) are element distribution diagrams obtained by energy dispersive spectroscopy (EDS) analysis: (C) is a carbon element distribution diagram, (D) is a fluorine element distribution diagram, and (E) is a nitrogen element distribution diagram. It can be seen that the nitrogen element is contributed by the polyurethane molecular chain, and the fluorine element is contributed by the PVDF molecular chain. It can be seen from the figure that the F element is evenly distributed in the nanoparticles, indicating that PVDF is the main body of the nanoparticles, and the nitrogen element is distributed in the inner and outer layers of the nanoparticles, indicating that the polymerization method can realize the entry of polyurethane molecules into the interior of the PVDF nanoparticles, and at the same time, the nitrogen element is distributed in the outer layer of the nanoparticles at a higher density, indicating that there are more polyurethanes in the shell layer, and such a core-shell structure and the TEM image are mutually confirmed.

[0033] The method provided by the present invention can form a molecular chain-level blending compatibility between PVDF and PU to form a chain entanglement between the two, thereby achieving 1) a decrease in PVDF crystallinity and an improvement in film transparency; and 2) an improvement in the film-forming ability of the fluorine-containing resin and its adhesion.

[0034] Example 2

[0035] (S1) At room temperature, 151 parts of hexamethylene diisocyanate, 231 parts of polyethylene oxide glycol with a molecular weight of 1000, 26 parts of di(hydroxymethyl)propionic acid and 0.2 parts of dibutyltin dilaurate catalyst are added to a reactor. Stirring is turned on to 200 rpm, and the reaction mixture is heated to 80°C. The reaction mixture is maintained in this temperature range until the measured wt% free NCO is between 2.5 and 3.2. The temperature of the reactor is reduced to 65°C, and then 12 parts of triethylamine are added dropwise to the reactor. The reaction mass is stirred for 15 minutes. 611 parts of deionized water are added dropwise to the reactor within 30 minutes, and stirred for 30 minutes after the addition is completed. The material is cooled to below 35°C to obtain a polyurethane aqueous dispersion.

[0036] (S2) 40 parts of the above polyurethane aqueous dispersion and 0.06 part of chain transfer agent isopropanol are added to the reactor and stirred for 0.5 hours; after the mixed solution is heated to 70°C, 1 part of initiator ammonium persulfate is added. Then, 60 parts of vinylidene fluoride monomer are introduced, the pressure is controlled at 2MPa, and the reaction is carried out for 2 hours to obtain a stable hybrid emulsion of polyurethane and polyvinylidene fluoride.

[0037] Example 3

[0038] (S1) At room temperature, add 235 parts of 4,4'-diisocyanate dicyclohexylmethane, 231 parts of poly(ethylene oxide) glycol with a molecular weight of 1000, 32 parts of di(hydroxymethyl)propionic acid and 0.2 parts of dibutyltin dilaurate catalyst to a reactor. Turn on the stirring to 200 rpm and heat the reaction mixture to 80°C. Keep the reaction mixture in this temperature range until the measured wt% free NCO is between 2.5 and 3.2. Reduce the temperature of the reactor to 65°C, and then add 15 parts of triethylamine to the reactor. Stir the reaction mass for 15 minutes. Add 740 parts of deionized water to the reactor within 30 minutes, and stir for 30 minutes after the addition is completed. Cool the material to 35°C to obtain a polyurethane aqueous dispersion.

[0039] (S2) 60 parts of the above polyurethane aqueous dispersion and 0.03 part of chain transfer agent isopropanol are added to the reactor and stirred for 0.5 hours; after the mixed solution is heated to 70°C, 1 part of initiator ammonium persulfate is added. Then, 40 parts of vinylidene fluoride monomer are added, the pressure is controlled at 2MPa, and the reaction is carried out for 2 hours to obtain a stable polyurethane and polyvinylidene fluoride hybrid emulsion. Figure 2It is the intensity distribution curve of fluorine (F) and nitrogen (N) elements obtained from a single PVDF-PU composite latex nanoparticle in the sample of Example 3. The arrow marks inserted along the HAADF-STEM image, F represents the distribution of PVDF, and N represents the distribution of polyurethane. It can be seen that within a single nanoparticle, polyurethane and PVDF are co-distributed in the entire nanoparticle without phase separation, indicating that the molecular chains of the two are fully entangled. After entanglement with the polyurethane molecular chain, the crystallinity of PVDF decreases and the transparency of the film is improved. This method can also increase the surface energy of the fluororesin and improve the adhesion of the film.

[0040] Comparative Example 1

[0041] 50 parts of the polyurethane dispersion in Example 1 and 50 parts of PVDF were mixed uniformly by high-speed stirring.

[0042] Comparative Example 2

[0043] 60 parts of the polyurethane dispersion in Example 3 and 40 parts of PVDF were mixed uniformly by high-speed stirring.

[0044] Comparative Example 3

[0045] The rest is the same as Example 1, except that in step (S2), di(hydroxymethyl)propionic acid is not added.

[0046] Application Examples

[0047] The emulsions of the above examples and comparative examples were subjected to the following performance tests, and the results are shown in Table 1.

[0048] The coating adhesion is tested with reference to the relevant contents in standard GB / T 9286-2021.

[0049] The coating transparency is tested according to the relevant contents in standard JC / T 235-2014.

[0050] The water resistance of the coating is tested in accordance with the relevant contents of standard GB / T 1733-93.

[0051] Table 1 Emulsion performance test

[0052] product Adhesion transparency Water resistance PVDF crystallinity Example 1 Level 0 93 5 days to whiten 40％ Example 2 Level 0 95 7 days to whiten 41％ Example 3 Level 0 96 3 days to whiten 39％ Comparative Example 1 Level 2 76 1 day whitening 47％ Comparative Example 2 Level 1 81 1 day whitening 47％ Comparative Example 3 Level 1 70 2 days to whiten 47％

[0053] As can be seen from Table 1, the performance of the hybrid emulsion of urethane and polyvinylidene fluoride of the present invention is compared from the three aspects of adhesion, transparency and water resistance. Compared with the simple blended emulsion, the hybrid emulsion with a polyurethane shell and a polyvinylidene fluoride core structure has more excellent performance. This is due to the fact that the coating prepared by the hybrid emulsion of this structure can achieve full entanglement of the polyurethane molecular chain and the polyvinylidene fluoride molecular chain, that is, the method can achieve uniform blending of fluororesin and other resins.

[0054] The inventors unexpectedly found that the polyurethane and polyvinylidene fluoride hybrid emulsion prepared by the present invention simultaneously achieves high transparency and significantly improved thermal stability. The high transparency may be due to the fact that PVDF is obtained by in-situ polymerization in a polyurethane aqueous dispersion, the decrease in crystallinity, and the improvement in thermal stability. The atomic polyurethane and PVDF molecular chains form sufficient chain entanglements. Chain entanglements increase the interaction force and cross-point density between polymer chains, which makes the polymer have higher thermal stability in the glassy state.

Claims

1. A polyurethane and PVDF hybrid emulsion, characterized in that: The invention comprises the following raw materials: polyurethane aqueous dispersion, vinylidene fluoride monomer, initiator, and chain transfer agent. The polyurethane aqueous dispersion comprises the following raw materials: polyisocyanate, multifunctional polymer, compound A containing more than one hydroxyl group and more than one carboxyl group and having a total functionality of ≥3, catalyst, neutralizer, and water; the multifunctional polymer contains more than two groups capable of reacting with isocyanate; the vinylidene fluoride monomer is introduced into a closed container containing the polyurethane aqueous dispersion, and in situ polymerization is performed in the presence of an initiator and a chain transfer agent under pressurized conditions to obtain polyvinylidene fluoride, and the polyvinylidene fluoride and the polyurethane form interpenetration and / or entanglement.

2. The polyurethane and PVDF hybrid emulsion according to claim 1, characterized in that: The invention comprises the following raw materials in parts by weight: 40-60 parts of polyurethane water dispersion, 40-60 parts of vinylidene fluoride monomer, 0.1-1 parts of initiator and 0.02-0.2 parts of chain transfer agent.

3. The polyurethane and PVDF hybrid emulsion according to claim 1, characterized in that: The pressurization condition is to introduce vinylidene fluoride gas so that the pressure of the sealed container is 1.5-3MPa, such as 2MPa.

4. The polyurethane and PVDF hybrid emulsion according to claim 1, characterized in that: The polyisocyanate is selected from at least one of aromatic, alicyclic and aliphatic diisocyanates; preferably, the polyisocyanate is selected from α,α,α,α-tetramethylxylene diisocyanate (THXDI TM ), 3,5,5-trimethyl-1-isocyanato-3-isocyanatomethylcyclohexane, isophorone diisocyanate (IPDI) and its derivatives, tetramethylene diisocyanate, hexamethylene diisocyanate (HDI) and its derivatives, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, isophorone diisocyanate, m-isopropenyl-α,α,-dimethylbenzyl isocyanate (TMI), 4,4'-dicyclohexylmethane diisocyanate (H12MDI), benzene-1,3-bis(1-isocyanato-1-methylethyl), 1,5-naphthalene diisocyanate (NDI), p-phenylene diisocyanate At least one of 1,4-diisocyanate (PPDI), trans-cyclohexane-1,4-diisocyanate (TMI), toluene diisocyanate (TODI), 4,4'-diphenylmethane diisocyanate, 4,4'-diphenyldimethylmethane diisocyanate, di- and tetra-alkyl diphenylmethane diisocyanates, 4,4'-dibenzyl diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, toluene diisocyanate isomers, 1-methyl-2,4-diisocyanatocyclohexane, 1,6-diisocyanato-2,2,4-trimethylhexane, and 1,6-diisocyanato-2,4,4-trimethylhexane.

5. The polyurethane and PVDF hybrid emulsion according to claim 1, characterized in that: The multifunctional polymer is selected from at least one of polyols, polyamines, polythiols and polyolamines, and the number average molecular weight of the multifunctional polymer is 500-3000 g / mol, preferably 1000-2000 g / mol; Furthermore, the polyol is selected from at least one of polyether polyol, polyester polyol and polycarbonate polyol; preferably polyether polyol, such as polyethylene glycol, polypropylene glycol, polybutylene glycol, polytetrahydrofuran and poly(propylene oxide) glycol.

6. The polyurethane and PVDF hybrid emulsion according to claim 1, characterized in that: The compound A having one or more hydroxyl groups and one or more carboxyl groups and having a total functionality of ≥3 is selected from at least one of di(hydroxymethyl)propionic acid, di(hydroxymethyl)butyric acid, 3-hydroxyglutaric acid, malic acid, and tartaric acid; and / or The catalyst is selected from at least one of organotin, organobismuth, tertiary amine, morpholine derivatives and piperazine derivatives; and / or The neutralizing agent is an inorganic base or an organic base, such as sodium hydroxide, potassium hydroxide, tertiary amine, pyridine. The neutralizing agent is used in an amount such that the pH of the polyurethane aqueous dispersion is 7-10; Preferably, the organotin is selected from dibutyltin dilaurate, stannous octoate, and dibutyltin dichloride; the tertiary amine is selected from triethylamine, tripropylamine, monoethyldipropylamine, monoethyldibutylamine, diethylmonopropylamine, and diethylmonobutylamine; More preferably, the amount of the catalyst is 0.1-1 wt % based on the mass of the polyisocyanate.

7. The polyurethane and PVDF hybrid emulsion according to claim 1, characterized in that: The solid content of the polyurethane aqueous dispersion is 30-45wt%, preferably 38-42wt%; wherein the amount of polyisocyanate, multifunctional polymer and compound A is such that the amount ratio of the isocyanate group (-NCO) in the polyisocyanate to the total amount of functional groups (hydroxyl, amine, thiol) in the multifunctional polymer and compound A that can react with isocyanate is 2-10. The ratio of the number of active functional groups in the multifunctional polymer to the number of active functional groups in compound A is 10:1-3; Alternatively, the mass ratio of polyisocyanate, multifunctional polymer and compound A is 150-235:231-305:26-42.

8. The polyurethane and PVDF hybrid emulsion according to claim 1, characterized in that: The initiator is selected from organic initiators and / or inorganic initiators. The organic initiator is selected from diethyl peroxydicarbonate, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di-tert-butyl peroxydicarbonate, di-tert-butyl peroxide, tert-butyl peroxypivalate, dicyclohexyl peroxydicarbonate, diisopropylbenzene peroxide and tert-butyl hydroperoxide or a mixture of two or more thereof; the inorganic initiator is selected from potassium persulfate, sodium persulfate, ammonium persulfate or a mixture of two or more thereof; and / or The chain transfer agent is selected from HCFC-123, CFC-11, DEC, DEM, isopropyl alcohol, ethyl acetate, methanol, cyclopentane, chloroform, acetone or a mixture of two or more thereof.

9. The method for preparing the hybrid emulsion of polyurethane and PVDF according to any one of claims 1 to 8, characterized in that: The following steps are involved: (S1) mixing polyisocyanate, multifunctional polymer, compound A and catalyst in an inert atmosphere, heating and keeping the temperature to react until the NCO content of the system no longer changes, cooling, and adding water and a neutralizing agent; (S2) In a sealed container, the polyurethane aqueous dispersion, the chain transfer agent, and the initiator are uniformly mixed, and the temperature is raised to above the initiation temperature of the initiator, and the vinylidene fluoride monomer is introduced to pressurize the system to fully react and obtain a polyurethane and PVDF hybrid emulsion.

10. The preparation method according to claim 9, characterized in that: In step (S1), the temperature is raised to 80-120°C, the amount of neutralizer added is such that the pH is 7-10, and the amount of water added is such that the solid content is 30-45wt%, preferably 38-42wt%; in step (S2), the initiation temperature is 70-130°C, and the pressurization condition is such that the pressure in the container is 1.5-3MPa by introducing vinylidene fluoride monomer.

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