A polyvinylidene fluoride resin and preparation method thereof

Abstract

The present invention relates to the field of polymer technology, and specifically to a polyvinylidene fluoride resin and a preparation method thereof, comprising the following steps: Step S1: adding water, a dispersant, an initiator, and a vinylidene fluoride monomer to a closed reactor; Step S2: heating the closed reactor to a reaction temperature, intermittently adding a polar comonomer solution to the closed reactor, and controlling the pressure in the closed reactor to fluctuate between a first pressure and a second pressure, thereby producing the polyvinylidene fluoride resin. Combining the intermittent addition of the polar comonomer with a pressure-swing reaction process enables the simultaneous preparation of homoblocks and copolymer blocks, improving polymerization uniformity and achieving a polyvinylidene fluoride resin with both excellent thermal stability and high adhesion properties.

Description

Technical Field

[0001] The present invention relates to the field of polymer technology, in particular to a polyvinylidene fluoride resin and a preparation method thereof. Background Art

[0002] Polyvinylidene fluoride (PVDF) resin refers to vinylidene fluoride (VDF) homopolymer or a copolymer of VDF and other small amounts of vinyl monomers. Its repeating unit is —CH2—CF2—. PVDF resin combines the characteristics of fluororesins and general-purpose resins, offering excellent overall performance. It is a high-performance thermoplastic known for its exceptional chemical resistance, thermal stability, and physical durability.

[0003] Polyvinylidene fluoride resin has the following properties: (1) Chemical resistance: PVDF exhibits excellent resistance to a variety of chemicals, acids, and solvents; (2) Thermal stability: PVDF has a high melting point and good thermal stability, and can maintain its performance in high temperature environments; (3) Electrical insulation: PVDF is known for its excellent electrical insulation properties and is commonly used in electrical and electronic applications; (4) Mechanical strength: PVDF has good mechanical strength and toughness, and can withstand mechanical stress and impact; (5) UV resistance: PVDF has good resistance to ultraviolet (UV) radiation and is suitable for outdoor applications. Polyvinylidene fluoride resin is widely used in the chemical industry, electronic and electrical, membrane technology, medical equipment, and lithium batteries.

[0004] To improve the bond strength of polyvinylidene fluoride (PVDF), Solvay's Chinese patent document CN101679563A discloses a linear semicrystalline copolymer. The polymerization process involves copolymerizing a vinylidene fluoride monomer with a hydrophilic (meth)acrylic acid monomer. While this patent enhances the bond strength of PVDF resins by introducing a polar comonomer, the resulting copolymer exhibits poor thermal stability and limited improvement in bond strength. Alternatively, the industry has also incorporated a copolymerized resin formed by copolymerizing vinylidene fluoride monomers with a hydrophilic (meth)acrylic acid monomer into a homopolymer resin. However, the resulting resin composition suffers from uneven distribution of the polar comonomer, resulting in low bond strength and poor thermal stability. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defects of low bonding strength and poor thermal stability of polyvinylidene fluoride resin in the prior art, thereby providing a polyvinylidene fluoride resin and a preparation method thereof.

[0006] To this end, the present application provides a method for preparing a polyvinylidene fluoride resin, comprising the following steps:

[0007] Step S1: adding water, dispersant, initiator and vinylidene fluoride monomer into a closed reactor;

[0008] Step S2: heating the closed reactor to a reaction temperature, intermittently adding a polar comonomer solution into the closed reactor to control the pressure in the closed reactor to fluctuate between a first pressure and a second pressure, thereby preparing a polyvinylidene fluoride resin; wherein the first pressure is M1, the second pressure is M2, wherein 9 MPa≤M1≤14 MPa, the difference between the first pressure and the second pressure is M1-M2, and 0.1 MPa≤M1-M2≤1.2 MPa, and the polar comonomer has a structural formula shown in the following formula (I):

[0009] R1R2C=CR3—COOR4 (I); wherein R1, R2, and R3 are the same or different, and R1, R2, and R3 are independently selected from H or a linear or branched C1-C20 hydrocarbon group; and R4 is selected from H, a linear or branched C1-C20 hydrocarbon group, or a hydroxyl-substituted linear or branched C1-C20 hydrocarbon group.

[0010] Furthermore, R1, R2, and R3 are the same or different, and R1, R2, and R3 are independently selected from H or a linear or branched C1-C3 alkyl group; R4 is selected from H, a linear or branched C1-C8 alkyl group, or a linear or branched C1-C8 alkyl group substituted with a hydroxyl group.

[0011] Furthermore, R1 and R2 are both H, R3 is selected from H or methyl; R4 is selected from H, hydroxy-substituted ethyl, butyl or octyl.

[0012] Furthermore, the polar comonomer is selected from one or more of acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, and butyl acrylate.

[0013] Furthermore, in step S2, the total amount of the polar comonomer added is 0.2wt%-5wt% of the mass of the vinylidene fluoride monomer; and / or the mass percentage of the polar comonomer in the polar comonomer solution is 0.4wt%-8wt%; and / or the solvent of the polar comonomer solution includes water.

[0014] Furthermore, the dispersant is selected from one or more of hydroxypropyl methylcellulose, hydroxyethyl methylcellulose, polyvinyl alcohol, and polyethylene glycol; and / or the initiator is selected from one or more of diethyl peroxydicarbonate, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, benzoyl peroxide, and tert-butyl peroxypivalate; and / or the amount of the dispersant added is 0.04wt%-0.4wt% of the mass of the vinylidene fluoride monomer; and / or the amount of the initiator added is 0.05wt%-0.42wt% of the mass of the vinylidene fluoride monomer; and / or the mass of water is 1-3 times the mass of the vinylidene fluoride monomer.

[0015] Furthermore, in the step S1, the reactor further comprises the step of adding a fluorine-containing comonomer and / or a chain transfer agent.

[0016] Furthermore, the fluorine-containing comonomer is selected from fluorine-containing olefins; and / or the chain transfer agent is selected from one or more of ethyl acetate, dimethyl carbonate, ethyl methyl carbonate, acetone, and methyl propionate; and / or the amount of the fluorine-containing comonomer added is 0.05wt%-0.42wt% of the mass of the vinylidene fluoride monomer; and / or the amount of the chain transfer agent added is 0-3wt% of the mass of the vinylidene fluoride monomer.

[0017] Furthermore, the fluorine-containing comonomer is selected from one or more of vinyl fluoride, trifluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene, hexafluoropropylene, hexafluoroisobutylene, perfluorobutylethylene, and pentafluoropropylene.

[0018] Furthermore, in step S2, the intermittent method of adding the polar comonomer solution to the closed reactor specifically includes adding the polar comonomer solution to the closed reactor, stopping the addition when the pressure in the closed reactor increases to a first pressure, causing the pressure in the closed reactor to decrease due to polymerization reaction of the materials, and adding the polar comonomer solution again when the pressure in the closed reactor decreases to a second pressure; and then repeating the above steps until the addition of the polar comonomer solution is complete and the reaction is terminated;

[0019] and / or, 8MPa≤M2≤13MPa;

[0020] And / or, in step S2, the reaction temperature is 45-60°C;

[0021] And / or, after the reaction is completed, the method further includes washing, filtering and drying the reactants.

[0022] Furthermore, the washing temperature is 50-80°C.

[0023] Furthermore, the drying temperature is 80-100°C.

[0024] The closed reactor can be a conventional reactor in the art, such as a high-pressure reactor.

[0025] The reaction begins when the closed reactor is heated to the reaction temperature.

[0026] The present application also provides a polyvinylidene fluoride resin prepared by any of the above-mentioned preparation methods.

[0027] The technical solution of the present invention has the following advantages:

[0028] 1. The preparation method of polyvinylidene fluoride resin provided in the present application comprises the following steps: step S1: adding water, a dispersant, an initiator and a vinylidene fluoride monomer into a closed reactor; step S2: heating the closed reactor to the reaction temperature, and using an intermittent method to add a polar comonomer solution into the closed reactor to control the pressure in the closed reactor to change back and forth between a first pressure and a second pressure to obtain a polyvinylidene fluoride resin; wherein the first pressure is M1, and the second pressure is M2, wherein 9≤M1≤14MPa, and the difference between the first pressure and the second pressure is M1-M2, 0.1MPa≤M1-M2≤1.2MPa; by using an intermittent method to add a polar comonomer solution to achieve polyvinylidene fluoride resin The monomers are copolymerized under variable pressure. During the polymerization process, a polar comonomer solution represented by general formula (I) is intermittently fed into the reactor so that the reaction pressure fluctuates back and forth within the above-mentioned specific range. During the stage of adding the polar comonomer solution, the vinylidene fluoride main chain connects the polar comonomer units to form copolymer blocks, thereby improving the bonding strength of the resin. During the stage of stopping the addition of the polar comonomer solution, more vinylidene fluoride homoblocks are prepared, thereby improving the thermal stability of the resin. Therefore, the possibility of simultaneously preparing homoblocks and copolymer blocks by combining the intermittent feeding of the polar comonomer with the variable pressure reaction process is achieved, which not only improves the uniform distribution of the polar comonomer and the bonding strength of the polyvinylidene fluoride resin, but also significantly improves the thermal stability of the polyvinylidene fluoride resin.

[0029] In addition, the study found that when the difference M1-M2 between the first pressure and the second pressure is too small, the polar comonomer solution will be added too frequently, the product modification degree will be too large, and the thermal stability of the product will be insufficient. When M1-M2 is too large, the polymerization will be mainly homopolymerization, and the product modification will be insufficient, resulting in the adhesion performance failing to meet the requirements. In addition, when the first pressure M1 is too small, the reaction pressure will be too low and the monomer concentration will be insufficient, which will lead to limited molecular chain growth, low product molecular weight, and the adhesion strength and thermal stability failing to meet the requirements. If M1 is too large, the reaction pressure will be too high, the monomer concentration will be too high, and the reaction rate will be faster. Similarly, it is impossible to produce a product with a moderate molecular weight, and the adhesion strength and thermal stability will fail to meet the requirements. In this application, the first pressure is controlled between 9MPa-14MPa, and the difference M1-M2 between the first pressure and the second pressure is controlled between 0.1MPa-1.2MPa to make the feeding period of the polar monomer moderate, thereby preparing a better relative amount of homopolymer molecules and modified molecules, and the product has both high bonding strength and good thermal stability, and excellent overall performance. DETAILED DESCRIPTION

[0030] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0031] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0032] 1. Main sources of raw materials

[0033] Vinylidene fluoride: Wanhua Chemical Group Co., Ltd., industrial products;

[0034] Polyvinyl alcohol (alcoholysis degree 80%): Yingzhan Chemical, industrial products;

[0035] Hydroxypropyl methylcellulose: Merck Chemical, analytical grade;

[0036] Benzoyl peroxide: Aladdin, analytical grade;

[0037] Diethyl peroxydicarbonate: Aladdin, analytical grade;

[0038] Ethyl acetate: Sigma, analytical grade;

[0039] Dimethyl carbonate: Sigma, analytical grade;

[0040] Acrylic acid: Wanhua Chemical Group Co., Ltd., industrial product;

[0041] Hydroxyethyl acrylate: Inochem, industrial product;

[0042] Hexafluoropropylene: Hunan Yuanchuang Company, industrial product;

[0043] Chlorotrifluoroethylene: Hunan Yuanchuang Company, industrial product.

[0044] 2. Main test methods

[0045] The following performance tests were performed on the polyvinylidene fluoride resins produced in each embodiment or comparative example:

[0046] (1) Bond strength

[0047] The bonding strength of polyvinylidene fluoride resin after being prepared into an electrode was measured according to ISO4624 standard (adhesion pull-off test). The electrode preparation process is as follows: At room temperature, 1g of polyvinylidene fluoride resin produced in the embodiment or comparative example was dissolved in 50g of NMP under mechanical stirring. 2g of conductive carbon black and 30g of lithium cobalt oxide (LiCoO2) were added under stirring and mixed thoroughly to ensure uniformity. The mixture was then degassed under vacuum and spread on aluminum foil with a spatula. Finally, the aluminum foil spread with the electrode material mixture was placed in a vacuum oven, heated to 60°C, and dried for 12 hours to finally prepare an electrode sheet. The bonding strength of the electrode material on the electrode sheet was measured using an INSTRON tensile testing machine.

[0048] (2) Thermal stability

[0049] Approximately 200g of polyvinylidene fluoride resin powder was extruded and pelletized using a twin-screw extruder, maintaining a barrel temperature of 200°C at all sections and a screw speed of 50 rpm to produce polymer pellets. An appropriate amount of the polymer pellets was then molded into 4mm thick plates, which were then heated in an oven at 250°C for 1 hour. The plates were then tested using a Hunter Lab CQX3576 yellowness meter, using the yellowness index (YID1925) to indicate the degree of yellowing. A lower YID indicates better thermal stability.

[0050] (3) Random distribution

[0051] The fraction of randomly distributed second monomer units represents the percentage between the average number (%) of second monomer sequences (the sequence being comprised between two repeating units derived from the first monomer) and the total average number (%) of second monomer units:

[0052]

[0053] The first monomer is a vinylidene fluoride monomer. The second monomer is a polar comonomer.

[0054] When each second monomer repeat unit is isolated, ie, contained between two repeat units of the first monomer, the average number of second monomer sequences is equal to the average total number of second monomer units, and the fraction of randomly distributed second monomer units is 100%.

[0055] The total average number of second monomer units in the polymer can be determined by acid-base titration of the carboxyl groups. A 0.5 g sample of polymer is weighed and placed in acetone at 70-80°C. 5 mL of water is added dropwise with thorough stirring to prevent polymer precipitation. The mixture is then titrated with 0.1 N NaOH solution until completely neutralized, with an endpoint of approximately -270 mV. Based on the measured acid equivalent weight, the second monomer content is determined, and the total average number of second monomer units (i.e., the mole % of second monomer units) is further determined.

[0056] The average number (%) of the second monomer sequence can be obtained by 19 F-NMR determination. A signal associated with the CF2 portion of the vinylidene fluoride unit adjacent to the isolated second monomer unit (in bold in the following chemical formula) was found to correspond to a peak at -94.8 ppm. Based on the ratio of the intensity of the polar monomer signal to all peaks in this spectrum, the average number of second monomer sequences per 100 first monomer units (i.e., the mol% of second monomer sequences) was determined. Ultimately, the ratio of the randomly distributed second monomer unit fraction as the mol% of the second monomer sequence to the mol% of the second monomer units was determined.

[0057] Example 1

[0058] This embodiment provides a method for preparing a polyvinylidene fluoride resin, comprising the following steps:

[0059] (1) Add 22.4 g of polar comonomer acrylic acid to 950 g of deionized water and mix well to prepare an acrylic acid solution for later use. Add 2100 g of deionized water to a 5 L autoclave with a stirrer. After stirring, add 2.8 g of dispersant hydroxypropyl methylcellulose, 16.8 g of chain transfer agent ethyl acetate, 3.5 g of initiator diethyl peroxydicarbonate, 60.2 g of fluorinated comonomer hexafluoropropylene, and then add 1400 g of vinylidene fluoride monomer to the autoclave to obtain a mixed solution.

[0060] (2) The temperature of the reactor was raised to 53°C. After the reaction started, acrylic acid solution was added to the reactor. When the pressure in the reactor reached 13.2 MPa (the first pressure, denoted as M1), the addition was stopped. The reaction was continued, and the pressure in the reactor decreased. When the pressure in the reactor dropped to 12.2 MPa (the second pressure, denoted as M2), acrylic acid solution was added again. The above steps of adding acrylic acid solution and stopping the addition were repeated to make the pressure in the reactor fluctuate between 12.2 MPa and 13.2 MPa until all the acrylic acid solution prepared in step (1) was added. The reaction was completed. The reactor was cooled and discharged. The reaction product was washed at 65°C with deionized water as a detergent. After washing, the reaction product was filtered and placed in a 95°C oven. After drying, the polyvinylidene fluoride resin product was obtained.

[0061] Example 2

[0062] This embodiment provides a method for preparing a polyvinylidene fluoride resin, comprising the following steps:

[0063] (1) Add 63 g of polar comonomer hydroxyethyl acrylate to 950 g of deionized water and mix well to prepare a hydroxyethyl acrylate solution for later use. Add 1540 g of deionized water to a 5 L autoclave with a stirrer. After stirring, add 0.84 g of dispersant hydroxypropyl methylcellulose, 5.6 g of chain transfer agent ethyl acetate, 5.74 g of initiator benzoyl peroxide, 109.2 g of fluorinated comonomer hexafluoropropylene, and then add 1400 g of vinylidene fluoride monomer to the autoclave to obtain a mixed solution.

[0064] (2) The temperature of the reactor was raised to 47°C. After the reaction started, hydroxyethyl acrylate solution was added to the reactor. When the pressure in the reactor reached 9.8 MPa, the addition was stopped and the reaction was continued. The pressure in the reactor dropped. When the pressure in the reactor dropped to 9.5 MPa, hydroxyethyl acrylate solution was added again. The above steps of adding hydroxyethyl acrylate solution and stopping the addition were repeated to make the reaction pressure fluctuate between 9.5 MPa and 9.8 MPa. When all the hydroxyethyl acrylate solution was added, the reaction was terminated. The reactor was cooled and discharged. The reaction product was washed with deionized water at 52°C. After washing, the reaction product was filtered and placed in a 92°C oven. After drying, the polyvinylidene fluoride resin product was obtained.

[0065] Example 3

[0066] This embodiment provides a method for preparing a polyvinylidene fluoride resin, comprising the following steps:

[0067] (1) Add 4.2 g of polar comonomer acrylic acid to 950 g of deionized water and mix well to prepare an acrylic acid solution for later use. Add 2380 g of deionized water to a 5 L autoclave with a stirrer. After stirring, add 5.3 g of dispersant polyvinyl alcohol (80% alcoholysis degree), 36.4 g of chain transfer agent ethyl acetate, 0.98 g of initiator diethyl peroxydicarbonate, 25.2 g of fluorinated comonomer chlorotrifluoroethylene, and 1400 g of vinylidene fluoride monomer to the autoclave to obtain a mixed solution.

[0068] (2) The temperature of the reactor was raised to 58°C. After the reaction started, acrylic acid solution was added to the reactor. When the pressure in the reactor reached 13.6 MPa, the addition was stopped and the reaction was continued. The pressure in the reactor dropped. When the pressure in the reactor dropped to 12.4 MPa, acrylic acid solution was added again. The above steps of adding acrylic acid solution and stopping the addition were repeated to make the reaction pressure fluctuate between 12.4 MPa and 13.6 MPa. After all the acrylic acid solution was added, the reaction was terminated. The reactor was cooled and the material was discharged. The reaction product was washed at 78°C with deionized water as a detergent. After washing, the reaction product was filtered and placed in an 83°C oven. After drying, the polyvinylidene fluoride resin product was obtained.

[0069] Example 4

[0070] This embodiment provides a method for preparing a polyvinylidene fluoride resin, comprising the following steps:

[0071] (1) Add 30.8 g of polar comonomer hydroxyethyl acrylate to 950 g of deionized water and mix well to prepare a hydroxyethyl acrylate solution for later use. Add 2240 g of deionized water to a 5 L autoclave with a stirrer. After stirring, add 2.4 g of dispersant hydroxypropyl methylcellulose, 21 g of chain transfer agent dimethyl carbonate, 2.5 g of initiator diethyl peroxydicarbonate, 50.4 g of fluorinated comonomer trifluorochloroethylene, and 1400 g of vinylidene fluoride monomer to the autoclave to obtain a mixed solution.

[0072] (2) The temperature of the reactor was raised to 51°C. After the reaction started, hydroxyethyl acrylate solution was added to the reactor. When the pressure in the reactor reached 12.5 MPa, the addition was stopped and the reaction was continued. The pressure in the reactor dropped. When the pressure in the reactor dropped to 11.9 MPa, the addition was started again. The above steps of adding hydroxyethyl acrylate solution and stopping the addition were repeated to make the reaction pressure fluctuate between 11.9 MPa and 12.5 MPa. After all the hydroxyethyl acrylate solution was added, the reaction was completed. The reactor was cooled and the material was discharged. The reaction product was washed at 60°C with deionized water as a detergent. After washing, the reaction product was filtered and placed in a 95°C oven. After drying, the polyvinylidene fluoride resin product was obtained.

[0073] Example 5

[0074] This embodiment provides a method for preparing polyvinylidene fluoride resin, which is basically the same as that of embodiment 1, except that in step (1), the fluorine-containing comonomer hexafluoropropylene is not added to the mixed solution.

[0075] Example 6

[0076] This embodiment provides a method for preparing a polyvinylidene fluoride resin, which is basically the same as that of Example 1, except that in step (1), butyl acrylate of the same mass is used instead of acrylic acid to prepare a butyl acrylate solution, and in step (2), "adding acrylic acid solution" is replaced by "adding butyl acrylate solution".

[0077] Example 7

[0078] This embodiment provides a method for preparing polyvinylidene fluoride resin, which is basically the same as that of Example 1, except that in step (1), the chain transfer agent ethyl acetate is not added to the mixed solution.

[0079] Comparative Example 1

[0080] This comparative example provides a method for preparing a polyvinylidene fluoride resin, comprising the following steps:

[0081] (1) Add 2100 g of deionized water into a 5 L autoclave with a stirrer. After stirring, add 2.8 g of hydroxypropyl methylcellulose as a dispersant, 16.8 g of ethyl acetate as a chain transfer agent, 22.4 g of acrylic acid as a polar copolymer, 3.5 g of diethyl peroxydicarbonate as an initiator, 60.2 g of hexafluoropropylene as a fluorine-containing copolymer, and 1400 g of vinylidene fluoride monomer to the autoclave to obtain a mixed solution.

[0082] (2) The temperature of the reactor was raised to 53°C. After the reaction started, deionized water was added to the reactor. When the pressure in the reactor reached 13.2 MPa, the addition was stopped. When the pressure in the reactor was lower than 12.2 MPa, deionized water was added again. The above steps of adding deionized water and stopping the addition were repeated to make the pressure in the reactor fluctuate between 12.2 MPa and 13.2 MPa. After all 950 g of deionized water was added, the reaction was completed. The reactor was cooled and discharged. The reaction product was washed at 65°C with deionized water as a detergent. After washing, the reaction product was filtered and placed in a 95°C oven. After drying, the polyvinylidene fluoride resin product was obtained.

[0083] Comparative Example 2

[0084] This comparative example provides a method for preparing a polyvinylidene fluoride resin, comprising the following steps:

[0085] (1) Add 22.4 g of polar comonomer acrylic acid to 950 g of deionized water and mix well to prepare an acrylic acid solution for later use. Add 2100 g of deionized water to a 5 L autoclave with stirring. After starting the stirring, add 2.8 g of dispersant hydroxypropyl methylcellulose, 16.8 g of chain transfer agent ethyl acetate, 3.5 g of initiator diethyl peroxydicarbonate, 60.2 g of fluorinated comonomer hexafluoropropylene, and then add 1400 g of vinylidene fluoride monomer to the autoclave to obtain a mixed solution.

[0086] (2) The temperature of the reactor was raised to 53°C. After the reaction started, acrylic acid solution was added to the reactor to maintain the pressure in the reactor at 13.2 MPa until all the acrylic acid solution prepared in step (1) was added. The reaction was completed. The reactor was cooled and discharged. The reaction product was washed with deionized water at 65°C. After washing, the reaction product was filtered and placed in a 95°C oven for drying to obtain a polyvinylidene fluoride resin product.

[0087] Comparative Example 3

[0088] It is basically the same as Example 1, except that the second pressure in step (2) is adjusted to 11.7 MPa.

[0089] Comparative Example 4

[0090] It is basically the same as Example 1, except that the second pressure in step (2) is adjusted to 13.15 MPa.

[0091] Comparative Example 5

[0092] The process is basically the same as Example 1, except that the first pressure in step (2) is adjusted to 15 MPa and the second pressure is adjusted to 14 MPa.

[0093] Comparative Example 6

[0094] The process is basically the same as Example 1, except that the first pressure in step (2) is adjusted to 8 MPa and the second pressure is adjusted to 7 MPa.

[0095] Comparative Example 7

[0096] 50 g of the polyvinylidene fluoride resin sample prepared in Comparative Example 1 and 50 g of the polyvinylidene fluoride resin sample prepared in Comparative Example 2 were taken and mixed evenly to prepare a physical blend sample.

[0097] The properties of the polyvinylidene fluoride resins obtained in the above examples and comparative examples are shown in Table 1 below:

[0098] Table 1 Performance results of examples and comparative examples

[0099]

[0100] The results show that compared with comparative examples 1-7, the bonding strength and thermal stability of the polyvinylidene fluoride resins prepared in Examples 1-7 of the present application are significantly improved, especially Example 1.

[0101] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing a polyvinylidene fluoride resin, characterized in that: The steps include: Step S1: adding water, dispersant, initiator and vinylidene fluoride monomer into a closed reactor; Step S2: heating the closed reactor to a reaction temperature, intermittently adding a polar comonomer solution into the closed reactor to control the pressure in the closed reactor to fluctuate back and forth between a first pressure and a second pressure, to produce a polyvinylidene fluoride resin; wherein the first pressure is M1, the second pressure is M2, wherein 9.8 MPa≤M1≤14 MPa, the difference between the first pressure and the second pressure is M1-M2, and 0.3 MPa≤M1-M2≤1.2 MPa, and the polar comonomer has a structural formula shown in the following formula (I): R1R2C=CR3—COOR4 (I); wherein R1, R2, and R3 are the same or different, and R1, R2, and R3 are independently selected from H or a linear or branched C1-C20 hydrocarbon group; and R4 is selected from H, a linear or branched C1-C20 hydrocarbon group, or a hydroxyl-substituted linear or branched C1-C20 hydrocarbon group.

2. The method for preparing polyvinylidene fluoride resin according to claim 1, wherein R1, R2, and R3 are the same or different, and R1, R2, and R3 are independently selected from H or a linear or branched C1-C3 alkyl group; R4 is selected from H, a linear or branched C1-C8 alkyl group, or a linear or branched C1-C8 alkyl group substituted with a hydroxyl group.

3. The method for preparing polyvinylidene fluoride resin according to claim 2, wherein R1 and R2 are both H, R3 is selected from H or methyl; R4 is selected from H, hydroxy-substituted ethyl, butyl or octyl.

4. The method for preparing polyvinylidene fluoride resin according to claim 1, wherein The polar comonomer is selected from one or more of acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, and butyl acrylate; and / or, in step S2, the total amount of the polar comonomer added is 0.2wt%-5wt% of the mass of the vinylidene fluoride monomer; and / or, the mass percentage of the polar comonomer in the polar comonomer solution is 0.4wt%-8wt%; and / or, the solvent of the polar comonomer solution includes water.

5. The method for preparing the polyvinylidene fluoride resin according to any one of claims 1 to 4, characterized in that: The dispersant is selected from one or more of hydroxypropyl methylcellulose, hydroxyethyl methylcellulose, polyvinyl alcohol, and polyethylene glycol; and / or the initiator is selected from one or more of diethyl peroxydicarbonate, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, benzoyl peroxide, and tert-butyl peroxypivalate; and / or the amount of the dispersant added is 0.04wt%-0.4wt% of the mass of the vinylidene fluoride monomer; and / or the amount of the initiator added is 0.05wt%-0.42wt% of the mass of the vinylidene fluoride monomer; and / or the mass of water is 1-3 times the mass of the vinylidene fluoride monomer.

6. The method for preparing the polyvinylidene fluoride resin according to any one of claims 1 to 4, characterized in that: In the step S1, the reactor further comprises the step of adding a fluorine-containing comonomer and / or a chain transfer agent.

7. The method for preparing polyvinylidene fluoride resin according to claim 6, wherein: The fluorine-containing comonomer is selected from fluorine-containing olefins; and / or the chain transfer agent is selected from one or more of ethyl acetate, dimethyl carbonate, ethyl methyl carbonate, acetone, and methyl propionate; and / or the amount of the fluorine-containing comonomer added is 0.05wt%-0.42wt% of the mass of the vinylidene fluoride monomer; and / or the amount of the chain transfer agent added is 0-3wt% of the mass of the vinylidene fluoride monomer.

8. The method for preparing polyvinylidene fluoride resin according to claim 7, characterized in that: The fluorine-containing comonomer is selected from one or more of vinyl fluoride, trifluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene, hexafluoropropylene, hexafluoroisobutylene, perfluorobutylethylene, and pentafluoropropylene.

9. The method for preparing the polyvinylidene fluoride resin according to any one of claims 1 to 4, characterized in that: In the step S2, the intermittent method of feeding the polar comonomer solution into the closed reactor specifically includes: Adding a polar comonomer solution to a closed reactor, stopping the addition when the pressure in the closed reactor rises to a first pressure, allowing the material to undergo polymerization reaction to reduce the pressure in the closed reactor, and adding the polar comonomer solution again when the pressure in the closed reactor drops to a second pressure; and repeating the above steps until the addition of the polar comonomer solution is complete and the reaction is terminated; and / or, 8MPa≤M2≤13MPa; And / or, in step S2, the reaction temperature is 45-60°C; And / or, after the reaction is completed, the method further includes washing, filtering and drying the reactants.

10. A polyvinylidene fluoride resin prepared by the preparation method according to any one of claims 1 to 9.

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