Preparation method of polyvinylidene fluoride resin

Abstract

The invention discloses a preparation method of polyvinylidene fluoride resin. The method comprises the following steps: (1) adding a polymerization stabilizer into water, and fully mixing to obtain a polymerization stabilizer solution; (2) adding deionized water, a dispersing agent and an initiator into the reactor, then adding a bottoming vinylidene fluoride monomer, then heating to carry out suspension polymerization reaction, and continuously supplementing the vinylidene fluoride monomer into the reactor in the reaction process; (3) adding all the vinylidene fluoride monomers, keeping the temperature of the reaction kettle unchanged, adding the polymerization stabilizer solution prepared in the step (1) when the pressure in the kettle is reduced to 72-85% of the reaction pressure, and cooling; and (4) reducing the temperature in the kettle to normal temperature, discharging, and filtering, washing and drying the product to obtain the high-purity polyvinylidene fluoride resin. The polyvinylidene fluoride resin prepared through the polymerization process is narrow in molecular weight distribution and excellent in basic performance such as heat resistance, and meanwhile the process is safe, reliable and high in production efficiency.

Description

Technical Field

[0001] The invention relates to the field of polymers, and in particular to a process for preparing polyvinylidene fluoride resin. Background Art

[0002] Polyvinylidene fluoride resin is considered to be the second largest fluorine-containing resin after polytetrafluoroethylene. It is an important high-quality fluorine-containing polymer that has the characteristics of both fluorine-containing resins and general resins, such as excellent thermal stability, corrosion resistance, non-flammability, UV resistance and other properties. Compared with other fluorine-containing resins represented by polytetrafluoroethylene, polyvinylidene fluoride resin has the highest tensile strength and compressive strength, better rigidity, wear resistance and cut resistance; at the same time, it has a low melting point and good melt fluidity, and can be molded, extruded, injection molded and blow molded with ordinary plastic processing machinery. Therefore, polyvinylidene fluoride resin is widely used in chemical, electronic, medical, construction, aerospace and other fields.

[0003] Shandong Huaxia Shenzhou (CN106632770) invented a method for preparing polyvinylidene fluoride resin with uniform molecular weight and narrow molecular weight distribution. Vinylidene fluoride, deionized water, initial chain transfer agent, and dispersant are added to the reaction kettle, evacuated, deoxygenated, heated to 20-150°C, and the pressure in the kettle is 1.0-6.0MPa by adding vinylidene fluoride monomer, and the initial initiator is added; the polymerization reaction is started, and the chain transfer agent and initiator are added. After the reaction is completed, the obtained polymer emulsion is subjected to coagulation-washing-drying and granulation to obtain the finished product.

[0004] Shanghai San Ai Fu (CN1257921) discloses a method for preparing a vinylidene fluoride polymer, which comprises: (a) providing a dispersion of vinylidene fluoride and one or more optional comonomers in water, wherein the comonomer is selected from a vinyl compound that can undergo free radical or ionic copolymerization with vinylidene fluoride, and the vinyl group has at least one fluorine atom, a fluorine-containing alkyl group or a fluorine-containing alkoxy group connected thereto; (b) adding a chain transfer agent and an organic initiator to initiate a polymerization reaction; (c) further adding an initiator; and (d) stopping adding the initiator when the conversion rate of the polymerization reaction reaches 2-65%.

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

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

[0007] The object of the present invention is to provide a polyvinylidene fluoride resin having a narrow molecular weight distribution and excellent basic properties such as heat resistance.

[0008] The molecular weight distribution of polyvinylidene fluoride resin is one of the core indicators. The advantage of narrow molecular weight distribution is mainly reflected in its positive impact on material properties, including electrical properties, mechanical properties, and bonding properties. In terms of electrical properties, polymer materials with narrow molecular weight distribution have higher insulation properties and dielectric constants. The stability and reliability of polyvinylidene fluoride resin in the lithium battery field are crucial. In terms of mechanical properties, the molecular structure of narrow molecular weight distribution is uniform, and the melt viscosity, thermal stability, rheology and other properties during processing are also more uniform. This uniformity can improve the processing performance of the material, such as easy molding, injection molding and extrusion. In terms of bonding properties, the uniform molecular weight distribution makes the material with strong intermolecular interaction have better bonding properties, and can better combine with other materials to form a strong bonding interface.

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

[0010] The inventors found that the suspension polymerization process of vinylidene fluoride has a good molecular weight distribution in the reaction stage due to the moderate reaction temperature, but there is a large difference in molecular weight at the end of the reaction. Because the polymerization reaction of vinylidene fluoride is a medium-high pressure reaction (6-15MPa), if the material is directly discharged without cooling after the reaction, there is a safety risk of high-pressure shock. The usual operation is to first lower the temperature in the kettle and then discharge the material, but during the cooling process, vinylidene fluoride is still undergoing polymerization reaction. At this time, the molecular weight difference of the product under the normal reaction temperature and pressure is large, so that the molecular weight distribution of the final prepared polyvinylidene fluoride resin is too wide.

[0011] To this end, the present inventors artificially solve the molecular weight difference at the end of the reaction by adding a polymerization stabilizer, actively terminating the reaction to avoid the continued reaction in the cooling stage to produce polymers beyond expectations. The present invention selects a non-addition type and non-chain transfer type stabilizer to prevent the stabilizer molecular structure from being grafted onto the main chain of the polyvinylidene fluoride resin, thereby affecting the basic properties of the product such as heat resistance; at the same time, the best time to add the polymerization stabilizer is to maintain the reaction temperature unchanged, when the pressure in the kettle drops to 72-85% of the reaction pressure, and the reaction is still proceeding rapidly when the reaction pressure is high. If the polymerization stabilizer is added at this time, it will cause a sudden termination and produce more low molecular weight resins; adding the polymerization stabilizer too late when the reaction pressure is too low will result in a wide molecular weight distribution and affect production efficiency.

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

[0013] (1) adding a polymerization stabilizer into water and mixing thoroughly to obtain a polymerization stabilizer solution;

[0014] (2) adding deionized water, a dispersant, and an initiator into the reactor, and then adding a vinylidene fluoride monomer as a base, and then heating to carry out a suspension polymerization reaction, and continuously adding vinylidene fluoride monomer into the reactor during the reaction process;

[0015] (3) After all the vinylidene fluoride monomers are added, the temperature of the reactor is maintained unchanged. When the pressure in 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 in the kettle drops to room temperature, the material is discharged, and the product is filtered, washed, and dried to obtain a 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, cupric chloride, titanium trichloride, sodium nitrite, sodium sulfide, sodium dimethyldithiocarbamate, and the amount of the polymerization stabilizer added is 90-220wt% of the mass of the initiator in step (2).

[0018] In some specific embodiments of the present invention, the solid content of the polymer stabilizer solution in step (1) is 2.5-8 wt %.

[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 the vinylidene fluoride monomer.

[0021] In some specific embodiments of the present invention, the initiator in step (2) is one of diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, diethyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, azobisisobutyronitrile, and dibenzoyl peroxide, and the amount of the initiator added is 0.07-0.34wt% 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 duration of adding vinylidene fluoride during the reaction process in step (2) is 3-5 hours.

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

[0026] In some specific embodiments of the present invention, in step (3), the pressure in the autoclave is reduced to a specific pressure of 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° C. and the drying time is 5-9 h.

[0029] The beneficial effects of the present invention are:

[0030] The present invention provides a novel process for preparing polyvinylidene fluoride resin with narrow molecular weight distribution, excellent basic properties such as heat resistance, safe and reliable process and high production efficiency. By adding a polymerization stabilizer at the end of polymerization, on the one hand, the molecular weight distribution is improved to avoid the generation of products with too large or too small molecular weight during the cooling process, and on the other hand, a specific polymerization stabilizer is selected to ensure that the polyvinylidene fluoride resin has a stable structure and excellent basic properties such as heat resistance. DETAILED DESCRIPTION

[0031] The method of the present invention is further described below by means of specific examples, but the present invention is not limited to the examples listed, and should also include any other known changes within the scope of the claims of the present invention.

[0032] The main test methods are as follows:

[0033] Thermal stability

[0034] About 15 g of the polymer powder to be tested was weighed into a 20 ml container and heated in an oven at 230° C. for 30 min. A Hunterlab Labscan XE yellowness index instrument was used for testing, and the yellowness index YI was used 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 by Shimadzu gel chromatograph (GPC). The main raw material information is as follows:

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

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

[0039] Polyvinyl alcohol: Sigma, analytical grade;

[0040] Diisopropyl peroxydicarbonate: Aladdin, analytical grade;

[0041] Di-n-propyl peroxydicarbonate: 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] Put 4.04g of ferric chloride, a polymerization stabilizer, in a beaker, add 73.7g of deionized water to the beaker, mix well and set aside. After cleaning the 5L high-pressure reactor, evacuate and deoxygenate with nitrogen, add 1995g of deionized water, add 2.36g of sodium carboxymethyl cellulose, a dispersant, and 1.05g of diisopropyl peroxydicarbonate, an initiator, to the reactor, and then add 750g of vinylidene fluoride monomer to the reactor, heat to 54°C, add additional vinylidene fluoride monomer after polymerization begins, and add for 4 hours, maintaining the pressure in the reactor at 11.5MPa. After adding 562.5 g of vinylidene fluoride, the addition was stopped and the reaction temperature was maintained. The reaction in the kettle continued to consume the vinylidene fluoride monomer. The pressure in the kettle gradually decreased. When the pressure in the kettle dropped to 8.5 MPa, the prepared polymerization stabilizer solution was added to the reactor. After the addition was completed, the reactor began to cool down and discharge the material. The product was washed in deionized water at 45°C. After washing, the slurry was filtered and put into a 90°C oven for drying for 9 hours to obtain polyvinylidene fluoride resin.

[0047] Example 2

[0048] Place 0.95g of the polymerization stabilizer sodium nitrite in a beaker, add 35.5g of deionized water to the beaker, mix well and set aside. After cleaning the 5L high-pressure reactor, evacuate and fill with nitrogen to deoxygenate, add 1911g of deionized water, add 1.32g of dispersant polyvinyl alcohol to the reactor, add 4.7g of initiator diisopropyl peroxydicarbonate, and then add 750g of vinylidene fluoride monomer to the reactor, heat to 41°C, add additional vinylidene fluoride monomer after polymerization begins, and add for 4.6 hours, maintaining the pressure in the reactor at 13MPa. After adding 720g of vinylidene fluoride, stop adding and maintain the reaction temperature. The reaction in the kettle continues to consume the vinylidene fluoride monomer. The pressure in the kettle gradually decreases. When the pressure in the kettle drops to 10.8MPa, add the prepared polymerization stabilizer solution to the reactor. After the addition is completed, the reactor begins to cool down and discharge the material. The product is washed in deionized water at 60°C. After washing, the slurry is filtered and put into a 96°C oven for drying for 7 hours to obtain polyvinylidene fluoride resin.

[0049] Example 3

[0050] Put 8.42g of ferric chloride, a polymerization stabilizer, in a beaker, add 99.5g of deionized water to the beaker, mix well and set aside. After cleaning the 5L high-pressure reactor, evacuate and fill with nitrogen to deoxygenate, add 2041g of deionized water, add 3.16g of sodium carboxymethyl cellulose, a dispersant, and 4.0g of di-n-propyl peroxydicarbonate, an initiator, to the reactor, and then add 750g of vinylidene fluoride monomer to the reactor, heat to 60°C, add additional vinylidene fluoride monomer after polymerization begins, and add for 3.5 hours, maintaining the pressure in the reactor at 7MPa. After adding 465g of vinylidene fluoride, the addition was stopped and the reaction temperature was maintained. The reaction in the kettle continued to consume the vinylidene fluoride monomer. The pressure in the kettle gradually decreased. When the pressure in the kettle 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 material. The product was washed in deionized water at 36°C. After washing, the slurry was filtered and put into a 102°C oven for drying for 6 hours to obtain polyvinylidene fluoride resin.

[0051] Example 4

[0052] Put 4.28g of the polymerization stabilizer sodium nitrite in a beaker, add 83g of deionized water to the beaker, mix well and set aside. After cleaning the 5L high-pressure reactor, evacuate and fill with nitrogen to deoxygenate, add 2172g of deionized water, add 2.85g of dispersant polyvinyl alcohol to the reactor, add 2.44g of initiator diisopropyl peroxydicarbonate, and then add 750g of vinylidene fluoride monomer to the reactor, heat to 49°C, add additional vinylidene fluoride monomer after polymerization begins, and add for 4.2h, maintaining the pressure in the reactor at 10MPa. After adding 607.5 g of vinylidene fluoride, the addition was stopped and the reaction temperature was maintained. The reaction in the kettle continued to consume the vinylidene fluoride monomer. The pressure in the kettle gradually decreased. When the pressure in the kettle dropped to 8 MPa, the prepared polymerization stabilizer solution was added to the reactor. After the addition was completed, the reactor began to cool down and discharge the material. The product was washed in deionized water at 52°C. After washing, the slurry was filtered and put into a 95°C oven for drying for 7 hours to obtain polyvinylidene fluoride resin.

[0053] Comparative Example 1

[0054] After cleaning the 5L high-pressure reactor, evacuate and fill with nitrogen to deoxygenate, add 1995g of deionized water, add 2.36g of sodium carboxymethyl cellulose dispersant to the reactor, add 1.05g of diisopropyl peroxydicarbonate initiator, and then add 750g of vinylidene fluoride monomer to the reactor, raise the temperature to 54°C, add additional vinylidene fluoride monomer after polymerization begins, and add for 4 hours, maintaining the pressure in the reactor at 11.5MPa. After adding 562.5g of vinylidene fluoride, start cooling and discharging, wash the product in deionized water at 45°C, filter the slurry after washing, put it into a 90°C oven and dry it for 9 hours to obtain polyvinylidene fluoride resin.

[0055] Comparative Example 2

[0056] Place 4.04g of polymerization stabilizer benzoquinone in a beaker, add 73.7g of deionized water to the beaker, mix well and set aside. After cleaning the 5L high-pressure reactor, evacuate and fill with nitrogen to deoxygenate, add 1995g of deionized water, add 2.36g of dispersant sodium carboxymethyl cellulose to the reactor, add 1.05g of initiator diisopropyl peroxydicarbonate, and then add 750g of vinylidene fluoride monomer to the reactor, heat to 54°C, add additional vinylidene fluoride monomer after polymerization begins, and add for 4 hours, maintaining the pressure in the reactor at 11.5MPa. After adding 562.5 g of vinylidene fluoride, the addition was stopped and the reaction temperature was maintained. The reaction in the kettle continued to consume the vinylidene fluoride monomer. The pressure in the kettle gradually decreased. When the pressure in the kettle dropped to 8.5 MPa, the prepared polymerization stabilizer solution was added to the reactor. After the addition was completed, the reactor began to cool down and discharge the material. The product was washed in deionized water at 45°C. After washing, the slurry was filtered and put into a 90°C oven for drying for 9 hours to obtain polyvinylidene fluoride resin.

[0057] Comparative Example 3

[0058] Place 4.04g of ferric chloride, a polymerization stabilizer, in a beaker, add 73.7g of deionized water to the beaker, mix well and set aside. After cleaning the 5L high-pressure reactor, evacuate and fill with nitrogen to deoxygenate, add 1995g of deionized water, add 2.36g of sodium carboxymethyl cellulose, a dispersant, to the reactor, add 1.05g of diisopropyl peroxydicarbonate, and then add 750g of vinylidene fluoride monomer to the reactor, heat it to 54°C, add vinylidene fluoride monomer after the polymerization begins, and add for 4 hours, maintaining the pressure in the reactor at 11.5MPa. After adding 562.5g of vinylidene fluoride, stop adding, add the prepared polymerization stabilizer solution to the reactor, and after the addition is completed, the reactor begins to cool down and discharge, and the product is washed in deionized water at 45°C. After washing, filter the slurry and put it into a 90°C oven for drying for 9 hours to obtain polyvinylidene fluoride resin.

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

[0060] Table 1 Performance parameters of embodiments 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] It can be seen from the table that the polyvinylidene fluoride resin prepared by the present invention has a narrow molecular weight distribution and excellent heat resistance.

[0063] Those skilled in the art will appreciate that, based on the teachings of this specification, some modifications or adjustments may be made to the present invention, and these modifications or adjustments should also be within the scope defined by the claims of the present invention.

Claims

1. A method for preparing a polyvinylidene fluoride resin, the method comprising the following steps: (1) adding a polymerization stabilizer into water and mixing thoroughly to obtain a polymerization stabilizer solution; (2) adding deionized water, a dispersant, and an initiator into the reactor, and then adding a vinylidene fluoride monomer as a base, and then heating to carry out a suspension polymerization reaction, and continuously adding vinylidene fluoride monomer into the reactor during the reaction process; (3) After all the vinylidene fluoride monomers are added, the temperature of the reactor is maintained unchanged. When the pressure in 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; (4) After the temperature in the kettle drops to room temperature, the material is discharged, and the product is filtered, washed, and dried to obtain a high-purity polyvinylidene fluoride resin.

2. The preparation method according to claim 1, characterized in that The polymerization stabilizer in step (1) is a non-addition type, non-chain transfer type stabilizer, such as ferric chloride, cupric chloride, titanium trichloride, sodium nitrite, sodium sulfide, sodium dimethyl dithiocarbamate, and the amount of the polymerization stabilizer added is the amount of the initiator mass in step (2). 90-220wt% of the amount.

3. The preparation method according to claim 1 or 2, characterized in that: The solid content of the polymer stabilizer solution in step (1) is 2.5-8 wt %.

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

5. The preparation method according to any one of claims 1 to 4, characterized in that: 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 the vinylidene fluoride monomer.

6. The preparation method according to any one of claims 1 to 5, characterized in that: In the step (2), the initiator is one of diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, diethyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, azobisisobutyronitrile and dibenzoyl peroxide, and the amount of the initiator added is 0.07-0.34wt% of the total amount of the vinylidene fluoride monomer.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The suspension polymerization reaction temperature in step (2) is 40-62° C.; and / or the suspension polymerization reaction pressure in step (2) is 6.5- 14MPa; and / or, in the step (2), the duration of adding vinylidene fluoride during the reaction process is 3-5h.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The amount of the additional vinylidene fluoride monomer in step (3) is 0.6-1.0 times the amount of the base vinylidene fluoride monomer.

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