A method for producing a polyvinylidene fluoride resin

Abstract

The application discloses a preparation method of polyvinylidene fluoride resin, and the method comprises the following steps: (1) adding a polymerization stabilizer into water and mixing to obtain a polymerization stabilizer solution; (2) adding deionized water, a dispersing agent and an initiator into a reactor, then adding a bottom layer of polyvinylidene fluoride monomer, and then performing a suspension polymerization reaction by heating, and continuously adding the polyvinylidene fluoride monomer into the reactor during the reaction process; (3) after the polyvinylidene fluoride monomer is completely added, maintaining the temperature of the reactor, reducing the pressure in the reactor to 72-85% of the reaction pressure, adding the polymerization stabilizer solution prepared in the step (1) and reducing the temperature; (4) after the temperature in the reactor is reduced to normal temperature, discharging the product, and performing filtering, washing and drying on the product, thereby obtaining high-purity polyvinylidene fluoride resin. The polyvinylidene fluoride resin prepared by the polymerization process has the advantages of narrow molecular weight distribution, excellent basic performances such as heat resistance, and the process is safe and reliable, and has high production efficiency.

Description

Technical Field

[0001] This invention relates to the field of polymers, and more specifically to a process for preparing polyvinylidene fluoride resin. Background Technology

[0002] Polyvinylidene fluoride (PVDF) resin is considered the second largest fluorinated resin after polytetrafluoroethylene (PTFE). It is an important high-quality fluorinated polymer that combines the characteristics of both fluorinated resins and general-purpose resins, such as excellent thermal stability, corrosion resistance, non-flammability, and UV resistance. Compared with other fluorinated resins, represented by PTFE, PVDF resin has the highest tensile strength and compressive strength, as well as superior rigidity, abrasion resistance, and cut resistance. It also has a low melting point and good melt flowability, allowing it to be processed using ordinary plastic processing machinery through molding, extrusion, injection molding, and blow molding. Therefore, PVDF resin is widely used in chemical, electronics, pharmaceutical, construction, and aerospace industries.

[0003] Shandong Huaxia Shenzhou (CN106632770) has invented a method for preparing polyvinylidene fluoride resin with uniform molecular weight and narrow molecular weight distribution. The method involves adding vinylidene fluoride, deionized water, an initial chain transfer agent, and a dispersant to a reaction vessel, evacuating and deoxygenating the vessel, heating it to 20-150℃, and adding vinylidene fluoride monomer until the pressure inside the vessel reaches 1.0-6.0 MPa. An initial initiator is then added, and the polymerization reaction begins. Chain transfer agents and initiators are then added. After the reaction is complete, the resulting polymer emulsion is coagulated, washed, dried, and granulated to obtain the final product.

[0004] Shanghai Sanaifu (CN1257921) discloses a method for preparing a vinylidene fluoride polymer, comprising: (a) providing a dispersion of vinylidene fluoride and optionally one or more comonomers in water, wherein the comonomers are selected from vinyl compounds capable of undergoing free radical or ionic copolymerization with vinylidene fluoride, and the vinyl compounds are at least one fluorine atom, a fluorinated alkyl group, or a fluorinated alkoxy group; (b) adding a chain transfer agent and an organic initiator to initiate the polymerization reaction; (c) further adding an initiator; and (d) stopping the addition of the initiator when the conversion rate of the polymerization reaction reaches 2-65%.

[0005] The two patents mentioned above improve the molecular weight distribution of polyvinylidene fluoride by adjusting the addition process of initiators and chain transfer agents, respectively, but the improvement on the molecular weight distribution is limited.

[0006] Therefore, it is very important to develop a polyvinylidene fluoride resin with a narrow molecular weight distribution and excellent basic properties such as heat resistance. Summary of the Invention

[0007] The purpose of this invention is to provide a polyvinylidene fluoride resin with a narrow molecular weight distribution and excellent basic properties such as heat resistance.

[0008] The molecular weight distribution of polyvinylidene fluoride (PVDF) resin is one of the core indicators. A narrow molecular weight distribution has advantages primarily reflected in its positive impact on material properties, including electrical, mechanical, and adhesive properties. In terms of electrical properties, polymers with narrow molecular weight distributions exhibit higher insulation performance and dielectric constants, making the stability and reliability of PVDF resins crucial for applications in lithium-ion batteries. Regarding mechanical properties, a narrow molecular weight distribution results in a more uniform molecular structure, leading to more uniform melt viscosity, thermal stability, and rheological properties during processing. This uniformity improves the material's processing performance, such as ease of molding, injection molding, and extrusion. In terms of adhesive properties, a uniform molecular weight distribution results in strong intermolecular forces, leading to better adhesion and the formation of robust bonding interfaces with other materials.

[0009] Therefore, polyvinylidene fluoride resin with a narrow molecular weight distribution has significant advantages in improving various properties of materials.

[0010] The inventors have discovered that while the suspension polymerization process of vinylidene fluoride exhibits a good molecular weight distribution during the reaction stage due to its moderate reaction temperature, excessive differences in molecular weight exist at the end of the reaction. Because the polymerization of vinylidene fluoride is a medium-to-high pressure reaction (6-15 MPa), directly discharging the material without cooling after the reaction poses a safety risk due to high-pressure shock. The usual practice is to lower the temperature inside the reactor before discharging. However, during the cooling process, vinylidene fluoride continues to polymerize. At this point, the molecular weight difference of the products below the normal reaction temperature and pressure is significant, resulting in an excessively wide molecular weight distribution of the final polyvinylidene fluoride resin.

[0011] To address this issue, the inventors employ a polymerization stabilizer to proactively terminate the reaction and prevent continued reaction during the cooling phase, thus avoiding the formation of polymers exceeding expectations. This invention selects a non-additional, non-chain-transfer stabilizer to prevent the stabilizer's molecular structure from grafting onto the polyvinylidene fluoride (PVDF) resin backbone, thereby affecting the product's heat resistance and other fundamental properties. Furthermore, the optimal timing for adding the polymerization stabilizer is when the reaction temperature is maintained constant and the pressure inside the reactor drops to 72-85% of the reaction pressure. Adding the stabilizer at higher reaction pressures, where the reaction is still proceeding rapidly, would cause a sudden termination, resulting in a large amount of low-molecular-weight resin. Adding the stabilizer too late at excessively low reaction pressures would lead to a wider molecular weight distribution and negatively impact production efficiency.

[0012] To achieve the above objectives, the present invention provides a method for preparing polyvinylidene fluoride resin, the method comprising the following steps:

[0013] (1) Add the polymerization stabilizer to water and mix thoroughly to obtain a polymerization stabilizer solution;

[0014] (2) Add deionized water, dispersant, and initiator to the reactor, then add vinylidene fluoride monomer as a base layer, and then raise the temperature to carry out suspension polymerization reaction. During the reaction process, vinylidene fluoride monomer is continuously added to the reactor.

[0015] (3) After all the vinylidene fluoride monomers are added, the temperature of the reactor remains constant. When the pressure inside the reactor drops to 72-85% of the reaction pressure, the polymerization stabilizer solution prepared in step (1) is added and the temperature is lowered.

[0016] (4) After the temperature inside the reactor drops to room temperature, the material is discharged, and the product is filtered, washed and dried to obtain high-purity polyvinylidene fluoride resin.

[0017] In some specific embodiments of the present invention, the polymerization stabilizer in step (1) is a non-addition type, non-chain transfer type stabilizer, such as ferric chloride, copper chloride, titanium trichloride, sodium nitrite, sodium sulfide, sodium dimethyl dithiocarbamate, and the amount of polymerization stabilizer added is 90-220 wt% of the mass of the initiator in step (2).

[0018] In some specific embodiments of the present invention, the polymerization stabilizer solution in step (1) contains 2.5-8 wt% solids.

[0019] In some specific embodiments of the present invention, the amount of deionized water added in step (2) is 1.3-1.7 times the total amount of vinylidene fluoride monomer.

[0020] In some specific embodiments of the present invention, the dispersant in step (2) is one of hydroxyethyl cellulose, hydroxypropyl cellulose, sodium carboxymethyl cellulose, and polyvinyl alcohol, and the amount of the dispersant added is 0.08-0.27 wt% of the total amount of vinylidene fluoride monomer.

[0021] In some specific embodiments of the present invention, the initiator in step (2) is one of diisopropyl peroxide, di-n-propyl peroxide, diethyl peroxide, dicyclohexyl peroxide, azobisisobutyronitrile, or benzoyl peroxide, and the amount of the initiator added is 0.07-0.34 wt% of the total amount of vinylidene fluoride monomer.

[0022] In some specific embodiments of the present invention, the suspension polymerization reaction temperature in step (2) is 40-62°C.

[0023] In some specific embodiments of the present invention, the suspension polymerization reaction pressure in step (2) is 6.5-14 MPa.

[0024] In some specific embodiments of the present invention, the reaction process in step (2) involves the addition of vinylidene fluoride for 3-5 hours.

[0025] In some specific embodiments of the present invention, the amount of vinylidene fluoride monomer added in step (3) is 0.6-1.0 times the amount of vinylidene fluoride monomer used as a base layer.

[0026] In some specific embodiments of the present invention, in step (3), the pressure inside the vessel is reduced to a specific pressure, namely, 75-80% of the reaction pressure.

[0027] In some specific embodiments of the present invention, the washing temperature in step (4) is 35-65°C.

[0028] In some specific embodiments of the present invention, the drying temperature in step (4) is 90-105℃ and the drying time is 5-9h.

[0029] The beneficial effects of this invention are as follows:

[0030] This invention provides a novel process for preparing polyvinylidene fluoride (PVDF) resin, which exhibits a narrow molecular weight distribution, excellent heat resistance, and other fundamental properties, while also being safe, reliable, and highly efficient. By adding a polymerization stabilizer at the end of the polymerization process, the molecular weight distribution is improved, preventing the formation of excessively large or small molecular weight products during the cooling process. Furthermore, by selecting a specific polymerization stabilizer, the structural stability of the PVDF resin is ensured, resulting in excellent heat resistance and other fundamental properties. Detailed Implementation

[0031] The method of the present invention will be further illustrated below through specific embodiments, but the present invention is not limited to the listed embodiments, and should also include any other known modifications within the scope of the claims of the present invention.

[0032] The main testing methods are as follows:

[0033] thermal stability

[0034] Weigh approximately 15g of the polymer powder to be tested into a 20ml container and heat it in an oven at 230℃ for 30min. Use a Hunterlab Labscan XE yellow index meter to test it, and use the yellow index YI to characterize the degree of yellowing: the lower the YI index, the better the thermal stability.

[0035] Weight-average molecular weight and molecular weight distribution

[0036] The molecular weight distribution of the polymer was determined using a Shimadzu gel permeation chromatography (GPC) system. The main raw material information is as follows:

[0037] Vinylidene fluoride: Wanhua Chemical Group Co., Ltd., industrial product;

[0038] Sodium carboxymethyl cellulose: Merck Chemicals, analytical grade;

[0039] Polyvinyl alcohol: Sigma, analytical grade;

[0040] Diisopropyl peroxide: Aladdin, analytical grade;

[0041] Di-n-propyl peroxide: Aladdin, analytical grade;

[0042] Ferric chloride: Hongda Chemical, industrial grade;

[0043] Sodium nitrite: Sigma, analytical grade;

[0044] Benzoquinone: Hongrun Chemical, industrial grade.

[0045] Example 1

[0046] 4.04 g of ferric chloride, a polymerization stabilizer, was placed in a beaker. 73.7 g of deionized water was added to the beaker, and the mixture was stirred until homogeneous. A 5L high-pressure reactor was cleaned, evacuated, and purged with nitrogen to remove oxygen. 1995 g of deionized water was added, along with 2.36 g of sodium carboxymethyl cellulose dispersant and 1.05 g of diisopropyl peroxide dicarbonate initiator. Then, 750 g of vinylidene fluoride monomer was added to the reactor. The temperature was raised to 54°C, and polymerization began. Vinylidene fluoride monomer was then added continuously over 4 hours, maintaining the reactor pressure at 11.5 MPa. After adding 562.5g of vinylidene fluoride, the addition was stopped, and the reaction temperature was maintained. The reaction continued in the reactor, consuming vinylidene fluoride monomer, and the pressure in the reactor gradually decreased. When the pressure in the reactor dropped to 8.5MPa, the prepared polymerization stabilizer solution was added to the reactor. After the addition was completed, the reactor began to cool down and discharge the product. The product was washed in deionized water at 45°C. After washing, the slurry was filtered and placed in a 90°C oven to dry for 9 hours to obtain polyvinylidene fluoride resin.

[0047] Example 2

[0048] 0.95g of sodium nitrite, a polymerization stabilizer, was placed in a beaker. 35.5g of deionized water was added to the beaker, and the mixture was stirred until homogeneous. A 5L high-pressure reactor was cleaned, evacuated, and purged with nitrogen to remove oxygen. 1911g of deionized water was added, followed by 1.32g of polyvinyl alcohol (PVA) dispersant and 4.7g of diisopropyl peroxide (DIPC) initiator. Then, 750g of vinylidene fluoride monomer was added to the reactor. The temperature was raised to 41℃, and polymerization began. Vinylidene fluoride monomer was then added continuously over 4.6 hours, maintaining the reactor pressure at 13MPa. After adding 720g of vinylidene fluoride, the addition was stopped, and the reaction temperature was maintained. The reaction continued in the reactor, consuming vinylidene fluoride monomer, and the pressure in the reactor gradually decreased. When the pressure in the reactor dropped to 10.8MPa, the prepared polymerization stabilizer solution was added to the reactor. After the addition was completed, the reactor began to cool down and discharge the product. The product was washed in deionized water at 60°C. After washing, the slurry was filtered and placed in a 96°C oven to dry for 7 hours to obtain polyvinylidene fluoride resin.

[0049] Example 3

[0050] Place 8.42g of ferric chloride, the polymerization stabilizer, in a beaker, add 99.5g of deionized water, mix well, and set aside. Clean the 5L high-pressure reactor, evacuate and purge with nitrogen to remove oxygen, then add 2041g of deionized water, 3.16g of sodium carboxymethyl cellulose dispersant, and 4.0g of di-n-propyl peroxide dicarbonate initiator. Then add 750g of vinylidene fluoride monomer to the reactor, heat to 60℃, and begin polymerization. Continue adding vinylidene fluoride monomer over 3.5 hours, maintaining the reactor pressure at 7MPa. After adding 465g of vinylidene fluoride, the addition was stopped, and the reaction temperature was maintained. The reaction continued in the reactor, consuming vinylidene fluoride monomer, and the pressure in the reactor gradually decreased. When the pressure in the reactor dropped to 5.3MPa, the prepared polymerization stabilizer solution was added to the reactor. After the addition was completed, the reactor began to cool down and discharge the product. The product was washed in deionized water at 36°C. After washing, the slurry was filtered and placed in an oven at 102°C for 6 hours to obtain polyvinylidene fluoride resin.

[0051] Example 4

[0052] 4.28g of the polymerization stabilizer sodium nitrite was placed in a beaker, and 83g of deionized water was added to the beaker. After mixing thoroughly, it was set aside. After cleaning the 5L high-pressure reactor, it was evacuated and purged with nitrogen to remove oxygen. Then, 2172g of deionized water was added, followed by 2.85g of the dispersant polyvinyl alcohol and 2.44g of the initiator diisopropyl peroxide dicarbonate. Then, 750g of vinylidene fluoride monomer was added to the reactor. The temperature was raised to 49℃, and after polymerization began, vinylidene fluoride monomer was added again over a period of 4.2 hours, maintaining the pressure inside the reactor at 10MPa. After adding 607.5g of vinylidene fluoride, the addition was stopped, and the reaction temperature was maintained. The reaction continued in the reactor, consuming vinylidene fluoride monomer. The pressure in the reactor gradually decreased. When the pressure in the reactor dropped to 8MPa, the prepared polymerization stabilizer solution was added to the reactor. After the addition was completed, the reactor began to cool down and discharge the product. The product was washed in deionized water at 52°C. After washing, the slurry was filtered and placed in a 95°C oven to dry for 7 hours to obtain polyvinylidene fluoride resin.

[0053] Comparative Example 1

[0054] After cleaning the 5L high-pressure reactor, it was evacuated and purged with nitrogen to remove oxygen. 1995g of deionized water was added, followed by 2.36g of sodium carboxymethyl cellulose dispersant and 1.05g of diisopropyl peroxide dicarbonate initiator. Then, 750g of vinylidene fluoride monomer was added. The temperature was raised to 54℃, and polymerization began. More vinylidene fluoride monomer was added over 4 hours, maintaining the reactor pressure at 11.5MPa. After adding 562.5g of vinylidene fluoride, the mixture was cooled and discharged. The product was washed in deionized water at 45℃. After washing, the slurry was filtered and dried in a 90℃ oven for 9 hours to obtain polyvinylidene fluoride resin.

[0055] Comparative Example 2

[0056] Place 4.04g of the polymerization stabilizer benzoquinone in a beaker, add 73.7g of deionized water, mix well, and set aside. Clean the 5L high-pressure reactor, evacuate and purge with nitrogen to remove oxygen, then add 1995g of deionized water, 2.36g of dispersant sodium carboxymethyl cellulose, and 1.05g of initiator diisopropyl peroxide. Then add 750g of vinylidene fluoride monomer to the reactor, heat to 54℃, and begin polymerization. Continue adding vinylidene fluoride monomer over 4 hours, maintaining the reactor pressure at 11.5MPa. After adding 562.5g of vinylidene fluoride, the addition was stopped, and the reaction temperature was maintained. The reaction continued in the reactor, consuming vinylidene fluoride monomer, and the pressure in the reactor gradually decreased. When the pressure in the reactor dropped to 8.5MPa, the prepared polymerization stabilizer solution was added to the reactor. After the addition was completed, the reactor began to cool down and discharge the product. The product was washed in deionized water at 45°C. After washing, the slurry was filtered and placed in a 90°C oven to dry for 9 hours to obtain polyvinylidene fluoride resin.

[0057] Comparative Example 3

[0058] 4.04 g of ferric chloride, a polymerization stabilizer, was placed in a beaker, and 73.7 g of deionized water was added. The mixture was then thoroughly mixed and set aside. A 5L high-pressure reactor was cleaned, evacuated, and purged with nitrogen to remove oxygen. 1995 g of deionized water was added, along with 2.36 g of sodium carboxymethyl cellulose dispersant and 1.05 g of diisopropyl peroxide dicarbonate initiator. Then, 750 g of vinylidene fluoride monomer was added to the reactor. The temperature was raised to 54°C, and polymerization began. More vinylidene fluoride monomer was added over 4 hours, maintaining the reactor pressure at 11.5 MPa. After adding 562.5 g of vinylidene fluoride, the addition was stopped. The prepared polymerization stabilizer solution was then added to the reactor. After the addition was complete, the reactor was cooled and the product discharged. The product was washed in deionized water at 45°C. After washing, the slurry was filtered and dried in a 90°C oven for 9 hours to obtain polyvinylidene fluoride resin.

[0059] The properties of the polyvinylidene fluoride resins obtained in the above embodiments and comparative examples are shown in Table 1 below:

[0060] Table 1 Performance parameters of the examples and comparative examples

[0061] Thermal stability YI weight average molecular weight Molecular weight distribution Example 1 12.1 117 1.72 Example 2 11.8 114 1.83 Example 3 11.9 121 1.74 Example 4 12.3 116 1.76 Comparative Example 1 12.5 109 2.44 Comparative Example 2 14.8 118 1.78 Comparative Example 3 12.6 126 2.23

[0062] As can be seen from the table, the polyvinylidene fluoride resin prepared by this invention has a narrow molecular weight distribution and excellent heat resistance.

[0063] Those skilled in the art will understand that modifications or adjustments can be made to the present invention based on the teachings of this specification. These modifications or adjustments should also be within the scope defined by the claims of the present invention.

Claims

1. A method for preparing polyvinylidene fluoride resin, the method comprising the following steps: (1) Add the polymerization stabilizer to water and mix thoroughly to obtain a polymerization stabilizer solution; (2) Add deionized water, dispersant, and initiator to the reactor, then add vinylidene fluoride monomer as a base layer, and then raise the temperature to carry out suspension polymerization reaction. During the reaction process, vinylidene fluoride monomer is continuously added to the reactor. (3) After all the vinylidene fluoride monomers have been added, keep the temperature of the reactor constant. When the pressure inside the reactor drops to 72-85% of the reaction pressure, add the polymerization stabilizer solution prepared in step (1) and cool down. (4) After the temperature inside the reactor drops to room temperature, the material is discharged, filtered, washed and dried to obtain high-purity polyvinylidene fluoride resin. The polymerization stabilizer in step (1) is ferric chloride, copper chloride, titanium trichloride, sodium nitrite, sodium sulfide and sodium dimethyl dithiocarbamate. The amount of polymerization stabilizer added is 90-220 wt% of the mass of the initiator in step (2), and the amount of initiator added is 0.07-0.34 wt% of the total amount of polyvinylidene fluoride monomer.

2. The preparation method according to claim 1, characterized in that, In step (1), the polymer stabilizer solution contains 2.5-8 wt% solids.

3. The preparation method according to claim 1, characterized in that, In step (2), the amount of deionized water added is 1.3-1.7 times the total amount of vinylidene fluoride monomer.

4. The preparation method according to any one of claims 1-3, characterized in that, In step (2), the dispersant is one of hydroxyethyl cellulose, hydroxypropyl cellulose, sodium carboxymethyl cellulose, or polyvinyl alcohol, and the amount of the dispersant added is 0.08-0.27 wt% of the total amount of vinylidene fluoride monomer.

5. The preparation method according to any one of claims 1-3, characterized in that, The initiator in step (2) is one of diisopropyl peroxide, di-n-propyl peroxide, diethyl peroxide, dicyclohexyl peroxide, azobisisobutyronitrile, or benzoyl peroxide.

6. The preparation method according to any one of claims 1-3, characterized in that, The suspension polymerization reaction temperature in step (2) is 40-62℃; and / or the suspension polymerization reaction pressure in step (2) is 6.5-14MPa; and / or the reaction process in step (2) involves the addition of vinylidene fluoride for 3-5 hours.

7. The preparation method according to any one of claims 1-3, characterized in that, In step (3), the amount of vinylidene fluoride monomer added is 0.6-1.0 times the amount of vinylidene fluoride monomer used as a base layer.

8. The preparation method according to any one of claims 1-3, characterized in that, The washing temperature in step (4) is 35-65℃; and / or the drying temperature in step (4) is 90-105℃, and the drying time is 5-9h.