Preparation method of polyvinylidene fluoride resin

Abstract

The invention discloses a preparation method of polyvinylidene fluoride resin, which is characterized in that the polyvinylidene fluoride resin is prepared by using a suspension polymerization process, a dispersion system is a compound type with a polymeric dispersant as a main component and a fluorine-containing emulsifier as an auxiliary component, and a suspension system in which large particles and small particles coexist is formed in a reaction liquid; after the reaction is finished, small particles are demulsified by controlling process conditions to be attached to the surfaces of large particles, so that the specific surface area of the PVDF particles is increased, the contact surface of the PVDF particles and an organic solution is increased when the PVDF particles are dissolved, and the polyvinylidene fluoride resin with excellent solubility is prepared.

Description

Technical Field

[0001] The invention belongs to the field of polymer technology, and in particular relates to a polyvinylidene fluoride resin with excellent solubility. Background Art

[0002] Polyvinylidene fluoride resin (PVDF) is the second largest product in the fluororesin series. It is a thermoplastic resin, a linear crystalline polymer, and the resin is white granular or powdery. Due to the high binding energy of the fluorocarbon chain, it has good heat resistance and corrosion resistance, and can resist corrosion and swelling of oxidants, acids, alkalis, salts, halogens, and aromatic hydrocarbons. It has excellent UV resistance and aging resistance. At the same time, it has excellent processability, hardness, creep resistance, wear resistance, and cutting resistance. Polyvinylidene fluoride resin is widely used in construction, chemical industry, semiconductors, lithium batteries, water treatment and other fields.

[0003] PVDF needs to be dissolved in organic solvents when used in lithium batteries, water treatment membranes, etc. The dissolution rate and effect of PVDF affect its performance, so the solubility of PVDF in organic solvents is crucial.

[0004] In the prior art, CN108003265A discloses a method for improving the solubility of polyvinylidene fluoride resin, which is achieved by increasing the polymerization temperature during the polymerization process when the reaction polymerization pressure drop is less than 0.4MPa / h. The polyvinylidene fluoride resin prepared by the present invention has a dissolution time of less than 30 minutes in DMF or NMP. US8298446B2 discloses a method for preparing a vinylidene fluoride polymer powder having a high molecular weight and excellent solubility in an organic solvent, which is prepared by polymerizing a suspension containing suspended granular monomer droplets at a temperature higher than 30.1°C and a pressure higher than 4.38MPa.

[0005] However, the above method does not change the morphology of PVDF particles, and the solubility improvement is limited. Therefore, further process innovation is needed to solve the problem of unsatisfactory solubility performance of PVDF in the suspension process in the existing technology. Summary of the invention

[0006] The purpose of the present invention is to improve the solubility of PVDF in organic solvents by increasing the specific surface area through the change of PVDF particle morphology. When PVDF particles dissolve in organic solvents, they are greatly affected by the specific surface area. Increasing the specific surface area of ​​PVDF particles can make the contact surface in organic solvents larger, the dissolution rate faster, and the dissolution more complete.

[0007] The present invention uses a polymer dispersant to form large-size particles and a fluorine-containing emulsifier to form small-size PVDF particles. After the polymerization is completed, the temperature is raised to above the gel temperature of the polymer dispersant to make the dispersant ineffective and free into the water. A demulsifier is then added to make the small-size particles unstable and adhere to the surface of the large particles. Finally, a polyvinylidene fluoride resin with a plurality of small-size particles attached to the surface of the large-size PVDF particles is obtained, which can increase the overall specific surface area.

[0008] In order to achieve the above invention object, the present invention adopts the following technical solutions:

[0009] A method for preparing a polyvinylidene fluoride resin comprises the following steps:

[0010] (1) adding water, a polymer dispersant, a fluorinated emulsifier, an initiator and a chain transfer agent to a reaction kettle, and then adding a vinylidene fluoride monomer; reacting to obtain a slurry;

[0011] (2) The slurry obtained in step (1) is heated to a temperature above the cloud point temperature of the polymer dispersant, and then a demulsifier is added, mixed, filtered, washed, and dried.

[0012] As a preferred solution, the gel temperature range of the polymer dispersant in step (1) is: 55°C ≤ gel temperature ≤ 95°C.

[0013] As a preferred solution, the polymer dispersant includes one or more of polyvinyl alcohol (alcoholysis degree 80%), polyvinyl alcohol (alcoholysis degree 75%), hydroxypropyl methylcellulose, hydroxyethyl cellulose, hydroxypropyl cellulose and the like.

[0014] As a preferred solution, the amount of the polymer dispersant is 0.15-0.35 wt % of the amount of vinylidene fluoride.

[0015] As a preferred solution, the number average molecular weight MW of the fluorinated emulsifier in step (1) is ≥500.

[0016] As a preferred embodiment, the fluorinated emulsifier includes one or more of perfluoro-2,5-dimethyl-3,6-dioxanononanoic acid ammonium salt, perfluoroalkyl ethoxymethyl ether, sodium perfluorononenyloxybenzene sulfonate, perfluoroalkylethanol polyoxyethylene ether (FEO-500), perfluoroalkylethanol polyoxyethylene ether phosphate amine salt FEPN, etc.

[0017] As a preferred solution, the amount of the fluorine-containing emulsifier is 0.03-0.14 wt % of the amount of vinylidene fluoride.

[0018] As a preferred embodiment, the initiator in step (1) is one or more of diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, diethyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, and dibenzoyl peroxide.

[0019] As a preferred solution, the amount of the initiator used is 0.03-0.20 wt % of the amount of vinylidene fluoride.

[0020] As a preferred embodiment, the chain transfer agent in step (1) is one or more of ethyl propionate, butyl propionate, dimethyl carbonate, ethyl acetate, and isopropanol.

[0021] As a preferred solution, the amount of the chain transfer agent is 0.6-5.7 wt % of the vinylidene fluoride.

[0022] As a preferred solution, a comonomer may also be added in step (1), suitable examples of which include but are not limited to one or more of perfluoropropyl vinyl ether, chlorotrifluoroethylene, tetrafluoroethylene, hexafluoropropylene, acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, and acrylonitrile.

[0023] As a preferred solution, the amount of the comonomer used is 0.3-4.3 wt % of the amount of vinylidene fluoride.

[0024] As a preferred solution, the reaction temperature in step (1) is 45-54°C.

[0025] As a preferred solution, the demulsifier in step (2) is one or more of aluminum nitrate, calcium chloride, and potassium chloride.

[0026] As a preferred solution, the amount of the demulsifier used is 2.4-6.5wt% of the amount of vinylidene fluoride.

[0027] As a preferred solution, in step (2), the washing temperature is 40-70°C, the drying temperature is 88-106°C, and the drying time is 4-8 hours.

[0028] In the solution of the present invention, the organic solvent for dissolving PVDF is one or more of DMAC, DMF and NMP.

[0029] The beneficial effects of the present invention are as follows: the present invention significantly improves the solubility of PVDF in organic solvents by preparing high specific surface area PVDF product particles. When a polymer dispersant and a fluorinated emulsifier are used together, large and small particles are prepared simultaneously, and under specific conditions, small particles are attached to the surface of large particles. The morphology of the prepared PVDF particles is conducive to dissolution in organic solvents. DETAILED DESCRIPTION

[0030] In order to facilitate the understanding of the present invention, the present invention will be further described below in conjunction with examples. It should be understood that the following examples are only for a better understanding of the present invention and do not mean that the present invention is limited to the following examples.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the invention belongs. The term "and / or" as may be used herein includes any and all combinations of one or more of the associated listed items.

[0032] Main raw material sources

[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] Perfluoro-2,5-dimethyl-3,6-dioxanononanoic acid ammonium salt: Shangfu Technology, industrial products;

[0037] Perfluoroalkyl ethoxymethyl ether: Shangfu Technology, industrial products;

[0038] Diisopropyl peroxydicarbonate: Aladdin, analytical grade;

[0039] Diethyl peroxydicarbonate: Aladdin, analytical grade;

[0040] Ethyl acetate: Sigma, analytical grade;

[0041] Dimethyl carbonate: Sigma, analytical grade;

[0042] Acrylic acid: Wanhua Chemical Group Co., Ltd., industrial products;

[0043] Perfluoropropyl vinyl ether: Beijing Yinuokai, analytical grade;

[0044] Aluminum nitrate: Beijing Yinuokai, industrial products;

[0045] Calcium chloride: Beijing Inokai, industrial product.

[0046] Main test methods

[0047] Take 10g of PVDF particles and add them into a container containing 100g of organic solvent, put the container into a homogenizer to mix, and observe the time when the PVDF particles are completely dissolved and the solvent becomes clear and transparent. Homogenizer: Schnos MIX60GR.

[0048] Example 1

[0049] Add 2500g of deionized water to a 5L reactor with stirring, start stirring, add 3.38g of hydroxypropyl methylcellulose, 0.91g of perfluoro-2,5-dimethyl-3,6-dioxa nonanoic acid ammonium salt, 1.3g of diisopropyl peroxydicarbonate, 33.8g of ethyl acetate, and 29.9g of acrylic acid to the reactor, and finally add 1300g of vinylidene fluoride monomer, raise the temperature of the reactor to 51°C, react for 4 hours, and then cool down. Transfer the prepared slurry to a 10L post-treatment tank, heat the PVDF slurry to 75°C, add 55.9g of demulsifier aluminum nitrate, stir for 30 minutes, and then filter the slurry to obtain demulsified and attached particles, wash the PVDF particles at 55°C, filter the PVDF after washing, add it to a 95°C oven, and dry it for 6 hours to obtain the PVDF product.

[0050] Example 2

[0051] 2500g of deionized water was added to a 5L reactor with stirring, and after stirring was turned on, 2.21g of polyvinyl alcohol (80% alcoholysis degree), 0.52g of perfluoroalkyl ethoxymethyl ether, 2.21g of diisopropyl peroxydicarbonate, 10.4g of dimethyl carbonate, and 5.2g of perfluoropropyl vinyl ether were added to the reactor, and finally 1300g of vinylidene fluoride monomer was added, and the temperature of the reactor was raised to 46°C, and the temperature was lowered after the reaction for 4h. The obtained slurry was transferred to a 10L post-treatment tank, the PVDF slurry was heated to 86°C, 33.8g of demulsifier aluminum nitrate was added, and the slurry was filtered after stirring for 30min to obtain demulsified and attached particles, and the PVDF particles were washed at 42°C. After washing, the PVDF was filtered and added to a 90°C oven, and the PVDF product was obtained after drying for 8h.

[0052] Example 3

[0053] 2500g of deionized water was added to a 5L reactor with stirring. After stirring, 4.29g of hydroxypropyl methylcellulose, 1.56g of perfluoro-2,5-dimethyl-3,6-dioxa nonanoic acid ammonium salt, 0.65g of diethyl peroxydicarbonate, 66.3g of ethyl acetate, and 52g of acrylic acid were added to the reactor. Finally, 1300g of vinylidene fluoride monomer was added, and the reactor temperature was raised to 53°C. After reacting for 4 hours, the temperature was lowered. The obtained slurry was transferred to a 10L post-treatment tank, the PVDF slurry was heated to 75°C, 78g of demulsifier calcium chloride was added, and the slurry was filtered after stirring for 30 minutes to obtain demulsified and attached particles. The PVDF particles were washed at 68°C. After washing, the PVDF was filtered and added to a 105°C oven. After drying for 4 hours, the PVDF product was obtained.

[0054] Comparative Example 1

[0055] 2500g of deionized water was added to a 5L stirred reactor. After stirring, 3.38g of hydroxypropyl methylcellulose, 1.3g of diisopropyl peroxydicarbonate, 33.8g of ethyl acetate, and 29.9g of acrylic acid were added to the reactor. Finally, 1300g of vinylidene fluoride monomer was added. The reactor temperature was raised to 51°C, and the reaction was continued for 4 hours before cooling down. The obtained slurry was transferred to a 10L post-treatment tank, and the PVDF slurry was used to wash the PVDF particles at 55°C. After washing, the PVDF was filtered and added to a 95°C oven. After drying for 6 hours, the PVDF product was obtained.

[0056] Comparative Example 2

[0057] Add 2500g of deionized water to a 5L reactor with stirring, start stirring, add 3.38g of hydroxypropyl methylcellulose, 0.91g of perfluoro-2,5-dimethyl-3,6-dioxa nonanoic acid ammonium salt, 1.3g of diisopropyl peroxydicarbonate, 33.8g of ethyl acetate, and 29.9g of acrylic acid to the reactor, and finally add 1300g of vinylidene fluoride monomer, raise the temperature of the reactor to 51°C, react for 4 hours, and then cool down. Transfer the prepared slurry to a 10L post-processing tank, add 55.9g of demulsifier aluminum nitrate to the post-processing tank, stir for 30 minutes, and then filter the slurry to obtain demulsified and attached treated particles, wash the PVDF particles at 55°C, filter the PVDF after washing, add it to a 95°C oven, and dry it for 6 hours to obtain the PVDF product.

[0058] The properties of the polyvinylidene fluoride resins obtained in the above examples and comparative examples are shown in Table 1 below:

[0059] Table 1 Performance parameters of embodiments and comparative examples

[0060] Particle size (micrometer / D50) Dissolution time (min) Example 1 62 12 Example 2 58 13 Example 3 64 12 Comparative Example 1 60 25 Comparative Example 2 58 20

[0061] It is easy to understand that the above embodiments are only examples for clear explanation and do not mean that the present invention is limited thereto. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the protection scope of the present invention.

Claims

1. A method for preparing a polyvinylidene fluoride resin, comprising the following steps: (1) adding water, a polymer dispersant, a fluorinated emulsifier, an initiator and a chain transfer agent to a reaction kettle, and then adding a vinylidene fluoride monomer; reacting to obtain a slurry; (2) The slurry obtained in step (1) is heated to a temperature above the cloud point temperature of the polymer dispersant, and then a demulsifier is added, mixed, filtered, washed, and dried.

2. The method according to claim 1, characterized in that The gel temperature range of the polymer dispersant in step (1) is: 55°C≤gel temperature≤95°C.

3. The method according to claim 1 or 2, characterized in that: The polymer dispersant includes one or more of polyvinyl alcohol with an alcoholysis degree of 80%, polyvinyl alcohol with an alcoholysis degree of 75%, hydroxypropyl methylcellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose.

4. The method according to any one of claims 1 to 3, characterized in that: The usage of the polymer dispersant is 0.15-0.35wt% of the amount of vinylidene fluoride.

5. The method according to any one of claims 1 to 4, characterized in that: The number average molecular weight MW of the fluorinated emulsifier in step (1) is ≥500.

6. The method according to any one of claims 1 to 5, characterized in that: The fluorine-containing emulsifier includes one or more of perfluoro-2,5-dimethyl-3,6-dioxanonanoic acid ammonium salt, perfluoroalkyl ethoxymethyl ether, sodium perfluorononenyloxybenzene sulfonate, perfluoroalkyl ethanol polyoxyethylene ether FEO-500, and perfluoroalkyl ethanol polyoxyethylene ether phosphate amine salt FEPN.

7. The method according to any one of claims 1 to 6, characterized in that: The amount of the fluorine-containing emulsifier used is 0.03-0.14 wt % of the vinylidene fluoride.

8. The method according to any one of claims 1 to 7, characterized in that: In the step (1), a comonomer is added, and the comonomer comprises one or more of perfluoropropyl vinyl ether, chlorotrifluoroethylene, tetrafluoroethylene, hexafluoropropylene, acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, and acrylonitrile.

9. The method according to any one of claims 1 to 8, characterized in that: The amount of the comonomer used is 0.3-4.3 wt % of the vinylidene fluoride.

10. The method according to any one of claims 1 to 9, characterized in that: In step (2), the demulsifier is one or more of aluminum nitrate, calcium chloride, and potassium chloride; the amount of the demulsifier is 2.4-6.5 wt % of the amount of vinylidene fluoride.