Method for preparing polyvinylidene fluoride resin through emulsion polymerization

Abstract

The invention discloses a novel method for preparing polyvinylidene fluoride resin through emulsion polymerization, the novel emulsion polymerization is a miniemulsion polymerization process, fluorine-containing polyether carboxylate is used as an emulsifier, fluorine-containing oligomer is used as a co-stabilizer to realize a miniemulsion polymerization system, and the polymerization system is high in stability and moderate in polymerization rate. Compared with traditional emulsion polymerization, the novel emulsion polymerization process has remarkable technical advantages and industrialization potential, efficient preparation of PVDF can be achieved, and the product has the advantages of being narrow in particle size distribution, high in solid content and the like and is suitable for the fields of high-end coatings, lithium battery binders and the like.

Description

Technical Field

[0001] This invention belongs to the field of polymer technology, specifically relating to a method for preparing polyvinylidene fluoride resin by emulsion polymerization. Background Technology

[0002] Polyvinylidene fluoride (PVDF) resin is an important fluoropolymer with excellent chemical resistance, corrosion resistance, high-temperature resistance, and oxidation resistance. It is widely used in photovoltaics, aerospace, lithium batteries, semiconductors, water treatment, chemicals, and construction. With the rapid development of new energy vehicles and the photovoltaic industry, the demand for PVDF resin is constantly increasing, while higher performance requirements are being placed on it. Especially in the field of lithium battery binders, stringent requirements are being placed on the purity, molecular weight and distribution, and bonding performance of PVDF resin.

[0003] In the prior art, Dongyangguang CN 104558306A discloses a method for preparing polyvinylidene fluoride (PVDF). This method replaces emulsifiers and dispersants by increasing the stirring speed, and includes the following steps: first, a fluorinated organic solvent, PVDF monomer, initiator, and chain transfer agent are added to a reaction vessel containing paraffin and water; the mixture is stirred and heated to 55-110℃ for 3-8 hours, after which the reaction is stopped; and then, after washing, filtration, and drying, high-purity PVDF resin is obtained. Dongyue Shenzhou New Materials CN 101274969A discloses an improved method for preparing fluoropolymers from O / W type microemulsions. Liquid perfluorinated hydrocarbons, emulsifiers, and co-emulsifiers are added to water to form an O / W type microemulsion. By optimizing the polymerization conditions, such as changing the temperature, pressure, and initiator type during the polymerization process, the polymerization rate can be increased, and fluoropolymer microemulsions with good transparency and stability can be prepared. The resulting fluoropolymer particles have a particle size of 10-100 nm and a small number of unstable end groups.

[0004] The aforementioned patents enhance the performance of emulsion polymerization products by optimizing stirring and adding fluorocarbon solvents and co-emulsifiers, thus advancing PVDF emulsion polymerization technology. Further improving the emulsion polymerization process to meet higher customer demands remains a key research focus. Summary of the Invention

[0005] The purpose of this invention is to achieve a fine emulsion polymerization system using fluorinated polyether carboxylates as emulsifiers and fluorinated oligomers as co-stabilizers. This polymerization system exhibits high stability and a moderate polymerization rate. This novel emulsion polymerization process has significant technical advantages and industrialization potential compared to traditional emulsion polymerization. It enables efficient PVDF preparation, producing products with narrow particle size distribution and high solids content, making it suitable for high-end coatings and lithium battery binders.

[0006] The main methods for preparing PVDF resin include emulsion polymerization and suspension polymerization. While emulsion polymerization offers advantages such as fast reaction rate and good stability, it also suffers from problems including low solids content in the polymer emulsion, complex post-processing, and a wide particle size distribution. Suspension polymerization, although capable of producing high-purity PVDF resin, is hampered by long reaction times, dispersant residues, and potential safety hazards.

[0007] The inventors have discovered that fine emulsion polymerization, as an emerging polymerization technology, has potential advantages. Compared with traditional emulsion polymerization, monomers do not need to diffuse to latex particles through the aqueous phase; instead, fine monomer droplets polymerize and nucleate. Fine emulsion polymerization allows for better control of the size and distribution of polymeric particles, increasing the solid content of the emulsion. Simultaneously, fine emulsion polymerization produces products with larger particle sizes, simplifying the demulsification and coagulation process and making product washing easier. Unlike conventional emulsion polymerization, fine emulsion polymerization requires the addition of highly hydrophobic compounds to hinder the diffusion between monomer droplets, i.e., co-stabilizers. Co-stabilizers not only help with monomer dispersion but also facilitate the adsorption of emulsifiers, playing a crucial role in the fine emulsion polymerization system. This invention uses fluorinated oligomers as co-stabilizers, which exhibit good monomer dispersion and emulsion system stability.

[0008] Therefore, the present invention provides a method for preparing polyvinylidene fluoride resin by emulsion polymerization, comprising the following steps:

[0009] (1) Add a certain amount of deionized water to the horizontal polymerization reactor and start stirring. Add emulsifier, stabilizer and chain transfer agent to the reactor, heat to the reaction temperature, and add vinylidene fluoride monomer to the reaction pressure.

[0010] (2) Add an initiator to the reactor to start the polymerization reaction. During the reaction, vinylidene fluoride monomer is continuously added to maintain the pressure inside the reactor. Optionally, the initiator and chain transfer agent can be added continuously or intermittently during the reaction.

[0011] (3) After the reaction is completed, the material is cooled and discharged. The polymer is washed, filtered and dried to finally obtain polyvinylidene fluoride resin product.

[0012] In the present invention, the emulsifier in step (1) is either sodium perfluoropolyether carboxylate or ammonium perfluoropolyether carboxylate, with the general structural formulas CH3-O-[CF(CF3)-CF2-O]M-(CF2-O)N-COONa and CH3-O-[CF(CF3)-CF2-O]M-(CF2-O)N-COONH4, respectively, with an M / N ratio of 0.1-10:1, a number-average molecular weight of 400-900, and the amount of emulsifier added is 0.03-0.7 wt% of the amount of vinylidene fluoride.

[0013] In step (1), the auxiliary stabilizer is one of hexafluoropropylene dimer, hexafluoropropylene trimer, etc., and the amount of the auxiliary stabilizer added is 0.03-0.8 wt% of the amount of vinylidene fluoride.

[0014] In step (1), the chain transfer agent is ethyl acetate, butyl acetate, diethyl malonate, ethyl propionate, diethyl carbonate, etc., and the amount of chain transfer agent added is 0.05-1.1 wt% of the amount of vinylidene fluoride.

[0015] The temperature for heating in step (1) is 65-110℃; the reaction pressure in step (1) is 4.0-7.2MPa.

[0016] In step (2), the initiator is one of ammonium persulfate, potassium persulfate, sodium persulfate, diisopropyl peroxide, di-n-propyl peroxide, benzoyl peroxide, etc., and the amount of the initiator added is 0.01-0.6 wt% of the vinylidene fluoride.

[0017] The reaction time in step (2) is 2-6 hours.

[0018] In step (2), the initiator and chain transfer agent are added continuously or intermittently. The amount of initiator added is 0-0.3% of the amount of vinylidene fluoride, and the amount of chain transfer agent added is 0-0.6% of the amount of vinylidene fluoride. The addition time is 2-6 hours.

[0019] In step (3), the washing is performed using deionized water at a temperature of 40-90℃, the filtration is performed using a plate and frame filter or a centrifuge, and the drying is performed using an oven at a temperature of 85-110℃ for 2-8 hours.

[0020] Compared with existing technologies, this invention provides a method for preparing polyvinylidene fluoride resin through a novel emulsion emulsion polymerization process, which has the following beneficial effects: using fluorinated polyether carboxylates as emulsifiers and fluorinated oligomers as co-stabilizers to achieve a fine emulsion polymerization system, realizing efficient polymerization of vinylidene fluoride monomers, significantly improving polymerization efficiency, and solving the problem of low efficiency in traditional polymerization methods; it can effectively control the size and distribution of polymer particles; the polymerization process is simple, reducing the complexity of post-processing and improving product performance. Detailed Implementation

[0021] To facilitate understanding of the present invention, the following description, in conjunction with embodiments, will further illustrate the invention. It should be understood that the following embodiments are merely for a better understanding of the invention and do not imply that the invention is limited to these embodiments.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The term "and / or" may be used herein to include any and all combinations of one or more of the associated listed items.

[0023] Main raw material sources

[0024] Vinylidene fluoride: Wanhua Chemical Group Co., Ltd., industrial product;

[0025] Sodium perfluoropolyether carboxylate (CME-PN-500): Suzhou Cangmu, industrial product;

[0026] Perfluoropolyether ammonium carboxylate (CME-PA-550): Suzhou Cangmu, industrial product;

[0027] Potassium persulfate: Aladdin, analytical grade;

[0028] Diisopropyl peroxide: Inokai, analytical grade;

[0029] Ethyl acetate: Sigma, analytical grade;

[0030] Diethyl malonate: Sigma, analytical grade;

[0031] Hexafluoropropylene trimer: Langhua Chemical, industrial product;

[0032] Hexafluoropropylene dimer: Langhua Chemical, industrial product;

[0033] Hexadecyl alcohol: Bohr Chemical, analytical grade;

[0034] Hexafluoropropylene: Shandong Luoheng Chemical Co., Ltd., industrial product.

[0035] Main testing methods

[0036] Particle size and particle size distribution: tested using a Dandong Bettersize 3000Plus laser / image particle size and shape analyzer.

[0037] Emulsion solids content: Tested according to GB / T 6284-2006 standard.

[0038] Example 1

[0039] Add 5.1 kg of deionized water and 6.7 g of emulsifier sodium perfluoropolyether carboxylate to a 10 L horizontal reactor and start stirring. Add 8.8 g of stabilizer hexafluoropropylene trimer and 8.0 g of chain transfer agent ethyl acetate. Raise the temperature to 85 °C. Add vinylidene fluoride monomer to the reactor until the reaction pressure reaches 5.2 MPa, and add 5.7 g of initiator potassium persulfate to start the polymerization reaction. During the reaction, add vinylidene fluoride monomer to the reactor to maintain the reaction pressure. Stop adding monomer when the total amount of vinylidene fluoride added (including the bottom layer and the total amount of added monomer) reaches 2.1 kg. The reaction time is about 3 hours. Cool the reactor to end the polymerization reaction. Mechanically demulsify the polymerized product, then wash it with 75 °C deionized water. After filtration using a plate and frame filter, dry the filter cake in a 100 °C oven for 6 hours to obtain the finished polyvinylidene fluoride.

[0040] Example 2

[0041] Add 5.1 kg of deionized water and 1.3 g of emulsifier, perfluoropolyether ammonium carboxylate, to a 10 L horizontal reactor and start stirring. Add 14.9 g of hexafluoropropylene oxide dimer, a stabilizer, and 21 g of diethyl malonate, a chain transfer agent. Raise the temperature to 106 °C. Add vinylidene fluoride monomer to the reactor until the reaction pressure reaches 4.1 MPa, and add 10.5 g of diisopropyl peroxide dicarbonate, an initiator, to begin the polymerization reaction. During the reaction, add vinylidene fluoride monomer to the reactor to maintain the reaction pressure. Stop adding monomer when the total amount of vinylidene fluoride added reaches 2.1 kg. The reaction time is about 2 hours. Cool the reactor to end the polymerization reaction. Mechanically demulsify the polymerized product, then wash it with 45 °C deionized water. After filtration using a plate and frame filter, dry the filter cake in a 110 °C oven for 2 hours to obtain the finished polyvinylidene fluoride.

[0042] Example 3

[0043] Add 5.1 kg of deionized water and 13 g of emulsifier sodium perfluoropolyether carboxylate to a 10 L horizontal reactor and start stirring. Add 1.05 g of hexafluoropropylene trimer as a stabilizer and 1.68 g of diethyl malonate as a chain transfer agent. Raise the temperature to 68 °C. Add vinylidene fluoride monomer to the reactor until the reaction pressure reaches 7 MPa, and add 0.63 g of potassium persulfate as an initiator to start the polymerization reaction. During the reaction, add vinylidene fluoride monomer to the reactor to maintain the reaction pressure. Stop adding monomer when the total amount of vinylidene fluoride added reaches 2.1 kg. The reaction time is about 5 hours. Cool the reactor to end the polymerization reaction. Mechanically demulsify the polymerized product, then wash it with 88 °C deionized water. After filtration using a plate and frame filter, dry the filter cake in a 90 °C oven for 4 hours to obtain the finished polyvinylidene fluoride.

[0044] Example 4

[0045] Add 5.1 kg of deionized water and 8.4 g of emulsifier sodium perfluoropolyether carboxylate to a 10 L horizontal reactor and start stirring. Add 5.25 g of hexafluoropropylene trimer as a stabilizer and 5.88 g of ethyl acetate as a chain transfer agent. Raise the temperature to 80 °C. Add vinylidene fluoride monomer to the reactor until the reaction pressure reaches 5.5 MPa, and add 4.4 g of potassium persulfate as an initiator to start the polymerization reaction. During the reaction, add vinylidene fluoride monomer to the reactor to maintain the reaction pressure. Add the chain transfer agent and initiator every 30 minutes during the reaction, for a total of 5.04 g of chain transfer agent and 3.36 g of initiator. Stop adding monomer when the total amount of vinylidene fluoride added reaches 2.1 kg. The reaction time is about 3 hours. Cool the reactor to end the polymerization reaction. Mechanically demulsify the polymerized product, then wash it with 60 °C deionized water. After filtration using a plate and frame filter, place the filter cake in an 85 °C oven and dry for 8 hours to obtain the finished polyvinylidene fluoride.

[0046] Example 5

[0047] Add 5.1 kg of deionized water and 11.6 g of emulsifier sodium perfluoropolyether carboxylate to a 10 L horizontal reactor and start stirring. Add 9.5 g of hexafluoropropylene trimer as a stabilizer and 15.5 g of ethyl acetate as a chain transfer agent. Raise the temperature to 76 °C. Add vinylidene fluoride monomer to the reactor until the reaction pressure reaches 6.2 MPa, and add 10.9 g of potassium persulfate as an initiator to start the polymerization reaction. During the reaction, add vinylidene fluoride monomer to the reactor to maintain the reaction pressure. Add the chain transfer agent and initiator every 30 min, for a total of 6.5 g of chain transfer agent and 2.5 g of initiator. Stop adding monomer when the total amount of vinylidene fluoride added reaches 2.1 kg. Stop the polymerization reaction after 3.5 h and cool the reactor. Mechanically demulsify the polymerized product, then wash it with 75 °C deionized water. After filtration using a plate and frame filter, dry the filter cake in a 95 °C oven for 3.5 h to obtain the finished polyvinylidene fluoride.

[0048] Comparative Example 1

[0049] Add 5.1 kg of deionized water and 6.7 g of sodium perfluoropolyether carboxylate emulsifier to a 10 L horizontal reactor and start stirring. Add 8.0 g of ethyl acetate chain transfer agent and heat to the reaction temperature of 85 °C. Add vinylidene fluoride monomer to the reactor until the reaction pressure reaches 5.2 MPa, and add 5.7 g of potassium persulfate initiator to start the polymerization reaction. During the reaction, vinylidene fluoride monomer is added to the reactor to maintain the reaction pressure. After 3 hours of reaction, the reactor is cooled to end the polymerization reaction. The polymer product is mechanically demulsified, then washed with 75 °C deionized water, filtered using a plate and frame filter, and the filter cake is dried in a 100 °C oven for 6 hours to obtain the finished polyvinylidene fluoride.

[0050] Comparative Example 2

[0051] Add 5.1 kg of deionized water and 6.7 g of sodium perfluoropolyether carboxylate emulsifier to a 10 L horizontal reactor and start stirring. Add 8.8 g of hexadecyl alcohol as a stabilizer and 8.0 g of ethyl acetate as a chain transfer agent. Raise the temperature to 85 °C. Add vinylidene fluoride monomer to the reactor until the reaction pressure reaches 5.2 MPa, and add 5.7 g of potassium persulfate as an initiator to start the polymerization reaction. During the reaction, add vinylidene fluoride monomer to the reactor to maintain the reaction pressure. After 3 hours of reaction, cool the reactor to end the polymerization reaction. Mechanically demulsify the polymer product, then wash it with 75 °C deionized water. After filtration using a plate and frame filter, dry the filter cake in a 100 °C oven for 6 hours to obtain the finished polyvinylidene fluoride.

[0052] Comparative Example 3

[0053] Add 5.1 kg of deionized water and 6.7 g of emulsifier sodium perfluoropolyether carboxylate to a 10 L horizontal reactor and start stirring. Add 8.0 g of chain transfer agent ethyl acetate and heat to the reaction temperature of 85 °C. Add 8.8 g of hexafluoropropylene to the reactor, then add vinylidene fluoride monomer to the reaction pressure until it reaches 5.2 MPa. Add 5.7 g of initiator potassium persulfate to start the polymerization reaction. During the reaction, add vinylidene fluoride monomer to the reactor to maintain the reaction pressure. When the total amount of vinylidene fluoride added (including the bottom layer and the total amount of added monomer) reaches 2.1 kg, stop adding monomer for 3 hours. Cool the reactor to end the polymerization reaction. Mechanically demulsify the polymerized product, then wash it with 75 °C deionized water. After filtration using a plate and frame filter, dry the filter cake in a 100 °C oven for 6 hours to obtain the finished polyvinylidene fluoride.

[0054] The properties of the polyvinylidene fluoride resins obtained in the above embodiments and comparative examples are shown in Table 1 below:

[0055] Table 1 Performance parameters of the examples and comparative examples

[0056] Emulsion solids content (%) Particle size D50 (μm) Particle size range Example 1 25.2 5.3 0.76 Example 2 24.6 6.2 0.79 Example 3 24.7 5.7 0.77 Example 4 25.3 6.0 0.78 Example 5 24.8 5.8 0.76 Comparative Example 1 21.3 3.2 0.88 Comparative Example 2 21.6 4.5 0.92 Comparative Example 3 21.7 3.6 0.93

[0057] It is readily understood that the above embodiments are merely illustrative examples for clear explanation and do not imply that the invention is limited thereto. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing polyvinylidene fluoride resin by emulsion polymerization, characterized in that, Includes the following steps: (1) Add a certain amount of deionized water to the horizontal polymerization reactor and start stirring. Add emulsifier, stabilizer and chain transfer agent to the reactor, heat to the reaction temperature, and add vinylidene fluoride monomer to the reaction pressure. (2) Add an initiator to the reactor to start the polymerization reaction. During the reaction, vinylidene fluoride monomer is continuously added to maintain the pressure inside the reactor. Optionally, the initiator and chain transfer agent can be added continuously or intermittently during the reaction. (3) After the reaction is completed, the material is cooled and discharged. The polymer is washed, filtered and dried to finally obtain polyvinylidene fluoride resin product.

2. The method as described in claim 1, characterized in that, In step (1), the emulsifier is either sodium perfluoropolyether carboxylate or ammonium perfluoropolyether carboxylate, with the general structural formulas CH3-O-[CF(CF3)-CF2-O]M-(CF2-O)N-COONa and CH3-O-[CF(CF3)-CF2-O]M-(CF2-O)N-COONH4, respectively. The M / N ratio is 0.1-10:1, the number-average molecular weight of the emulsifier is 400-900, and the amount of emulsifier added is 0.03-0.7 wt% of the amount of vinylidene fluoride.

3. The method as described in claim 1 or 2, characterized in that, In step (1), the auxiliary stabilizer is one of hexafluoropropylene dimer, hexafluoropropylene trimer, etc., and the amount of the auxiliary stabilizer added is 0.03-0.8 wt% of the amount of vinylidene fluoride.

4. The method according to any one of claims 1-3, characterized in that, In step (1), the chain transfer agent is ethyl acetate, butyl acetate, diethyl malonate, ethyl propionate, diethyl carbonate, etc., and the amount of chain transfer agent added is 0.05-1.1 wt% of the amount of vinylidene fluoride.

5. The method according to any one of claims 1-4, characterized in that, The temperature for heating in step (1) is 65-110℃; the reaction pressure in step (1) is 4.0-7.2MPa.

6. The method according to any one of claims 1-5, characterized in that, In step (2), the initiator is one of ammonium persulfate, potassium persulfate, sodium persulfate, diisopropyl peroxide, di-n-propyl peroxide, benzoyl peroxide, etc., and the amount of the initiator added is 0.01-0.6 wt% of the amount of vinylidene fluoride; and / or, the reaction time is 2-6 hours.

7. The method according to any one of claims 1-6, characterized in that, In step (2), the initiator and chain transfer agent are added continuously or intermittently. The amount of initiator added is 0-0.3% of the amount of vinylidene fluoride, and the amount of chain transfer agent added is 0-0.6% of the amount of vinylidene fluoride. The addition time is 2-6 hours.

8. The method according to any one of claims 1-7, characterized in that, The washing process in step (3) involves using deionized water at a temperature of 40-90℃, followed by drying in an oven at a temperature of 85-110℃ for 2-8 hours.