A preparation method of polyvinylidene fluoride resin

Abstract

The invention discloses a preparation method of polyvinylidene fluoride resin, the preparation method is to first convert the polarity of acrylic acid, convert the acrylic acid from water-soluble to oil-soluble, and then prepare a pre-emulsion with a vinylidene fluoride monomer, and then drop the pre-emulsion containing acrylic acid and vinylidene fluoride monomer into a reactor maintained by nitrogen for polymerization, and then wash, filter, dry and hydrolyze the polymer product to obtain polyvinylidene fluoride resin. The present invention improves the compatibility of acrylic acid and vinylidene fluoride monomer by polar conversion of acrylic acid, improves the copolymerization uniformity of acrylic acid and vinylidene fluoride monomer, improves the reaction conversion rate and reaction efficiency, and avoids the problem of low molecular weight and wide molecular weight distribution of resin caused by one-pot reaction by nitrogen to maintain the reaction pressure. Finally, a polyvinylidene fluoride resin with high copolymerization uniformity, high molecular weight and narrow molecular weight distribution is obtained, and the preparation method has high reaction conversion rate and safer and more efficient polymerization reaction.

Description

Technical Field

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

[0002] Polyvinylidene fluoride (PVDF) resin refers to vinylidene fluoride (VDF) homopolymer or copolymer of VDF and vinyl monomer. Its repeating unit is -CH2-CF2-, and the alternating arrangement of CH2- and CF2- groups makes PVDF resin have the characteristics of both fluororesin and general resin. Polyvinylidene fluoride resin has good chemical corrosion resistance, high temperature resistance, oxidation resistance, weather resistance, UV resistance, radiation resistance, as well as special properties such as piezoelectricity and thermoelectricity. Therefore, PVDF is widely used in lithium batteries, photovoltaic backplanes, fluorocarbon coatings and other fields.

[0003] Although polyvinylidene fluoride resin has excellent tolerance and stability, the difficulty in preparing acrylic acid copolymerized vinylidene fluoride resin is that acrylic acid is a water-soluble monomer and vinylidene fluoride is an oil-soluble monomer. The two copolymer monomers have poor compatibility and poor reactivity, resulting in unsatisfactory copolymerization uniformity, which leads to no obvious improvement in adhesion and hydrophilicity, and also causes a decrease in thermal stability. At present, the copolymerization process commonly used in the industry is: add vinylidene fluoride monomer to the reactor, add additives and water, heat up to the reaction temperature to start the polymerization reaction, and then continuously add acrylic acid monomer for copolymerization. However, the copolymerization uniformity of the obtained polyvinylidene fluoride resin is not ideal. The problem is that on the one hand, the essence of the poor compatibility between water-soluble acrylic acid and oil-soluble vinylidene fluoride has not changed. On the other hand, all vinylidene fluoride is added at the beginning of the polymerization, and only acrylic acid is added later, resulting in different monomer concentrations before and after the vinylidene fluoride monomer, which affects the consistency of the resin copolymerization reaction before and after.

[0004] Patent CN 101679563A discloses a vinylidene fluoride copolymer, in which a hydrophilic (meth) acrylic acid monomer is copolymerized with vinylidene fluoride to prepare a polyvinylidene fluoride resin. During the polymerization process, an aqueous solution of acrylic acid monomer is continuously added to improve the uniformity of the acrylic acid embedded in the chain segment; however, due to the large differences in reactivity and compatibility, the copolymerization uniformity and polymerization conversion rate are still at a low level.

[0005] Patent CN 111072838A discloses a high-solid content alternating structure polyvinylidene fluoride copolymer dispersion and its preparation method, firstly, acrylic acid pre-emulsion is prepared by using liquid monomers such as acrylic acid monomer and functional monomer, and then high-solid content alternating structure polyvinylidene fluoride copolymer dispersion is prepared by using vinylidene fluoride and pre-emulsion. This method has no essential difference between adding acrylic acid emulsion to the polymerization system and adding acrylic acid monomer, and cannot significantly improve the copolymerization uniformity. At the same time, the method adopts the process of dropping acrylic acid alone, which is not conducive to improving the uniformity of the copolymerization of acrylic acid and vinylidene fluoride monomer.

[0006] In summary, the key point to improve the performance of polyvinylidene fluoride resin lies in how to improve the copolymerization uniformity during the copolymerization process of acrylic acid monomers, so that the acrylic acid monomers can be uniformly embedded in the vinylidene fluoride polymer chain segments, avoiding the concentrated and continuous appearance of acrylic acid monomers, and avoiding the absence of acrylic acid monomers in longer vinylidene fluoride chain segments. The preparation of polyvinylidene fluoride resins with uniform acrylic acid copolymerization and good tolerance and adhesion is the bottleneck of current research. Summary of the invention

[0007] The object of the present invention is to provide a method for preparing polyvinylidene fluoride resin. The method comprises the following steps: firstly converting the polarity of acrylic acid, converting the acrylic acid from water-soluble to oil-soluble, and then preparing a pre-emulsion with a vinylidene fluoride monomer, then dropping the pre-emulsion containing the acrylic acid and the vinylidene fluoride monomer into a reactor maintained at a reaction pressure by nitrogen to carry out a polymerization reaction, and then washing, filtering, drying, and then hydrolyzing the polymerization product to obtain the polyvinylidene fluoride resin.

[0008] The inventors have found that the compatibility of acrylic acid and vinylidene fluoride monomer can be improved by converting water-soluble acrylic acid into oil-soluble one, and the copolymerization uniformity can be improved. The acrylic acid is further esterified with fluorine-containing alcohol, so that the fluorine-containing acrylic acid ester has better compatibility with vinylidene fluoride. After the polyvinylidene fluoride resin is prepared, the acrylic acid ester is hydrolyzed to obtain a water-soluble acrylic acid group, that is, the preparation of polyvinylidene fluoride resin with high copolymerization uniformity is completed through the conversion process of acrylic acid from water-soluble to oily and then to water-soluble.

[0009] The inventors also found that the method of adding vinylidene fluoride to maintain the reaction pressure will lead to inconsistent vinylidene fluoride monomer concentrations, resulting in a large difference in the copolymer structure obtained before and after. At the same time, the acrylic acid monomer is added separately, and it is difficult for acrylic acid to diffuse into the existing vinylidene fluoride oil droplets alone, and the uniformity is poor. The present invention charges nitrogen into the reactor to maintain the reaction pressure so that the vinylidene fluoride monomer is added dropwise to maintain the monomer concentration. It is possible to make it possible to keep the monomer concentration consistent before and after, and also avoid the problem of low molecular weight and wide molecular weight distribution of the resin caused by the one-pot reaction of adding vinylidene fluoride as the bottom. The present invention adopts the method of co-dropping esterified acrylic acid and vinylidene fluoride so that acrylic acid and vinylidene fluoride are evenly mixed and diffused into the particles at the same time for polymerization reaction, so that esterified acrylic acid and vinylidene fluoride have good compatibility, mixing and diffusion uniformity, and copolymerization reaction is carried out under the condition of consistent vinylidene fluoride monomer concentration, and finally obtains a polyvinylidene fluoride resin with high copolymerization uniformity, high molecular weight and narrow molecular weight distribution, and good tolerance and adhesion.

[0010] To achieve the above object, the present invention provides a method for preparing a polyvinylidene fluoride resin, comprising the following steps:

[0011] (1) adding fluorinated acrylate and vinylidene fluoride monomer into a pre-emulsification tank, adding deionized water and emulsifier 1 into the pre-emulsification tank, and stirring at the pre-emulsion temperature to obtain a pre-emulsion;

[0012] (2) adding deionized water, an initiator and an emulsifier 2 into an autoclave, then introducing nitrogen into the autoclave to a reaction pressure, heating the autoclave to a reaction temperature, and then adding a pre-emulsified liquid to carry out a reaction;

[0013] (3) After the reaction is completed, a polymer resin is obtained, which is dissolved in a solvent, then hydrolyzed, and then dried and extruded into granules to obtain a polyvinylidene fluoride resin.

[0014] Preferably, the fluorinated acrylate is obtained by esterification reaction of acrylic acid monomer and fluorinated alcohol substance. After this modification step, the polarity of acrylic acid is transformed from water-soluble to oil-soluble.

[0015] Preferably, the fluorine-containing alcohol substance can be a perfluoroalkyl alcohol, selected from one or more of perfluoro-1-heptanol, perfluoro-1-octanol, 1H,1H-perfluoro-1-nonanol, 1H,1H,2H,2H-perfluoro-1-decanol, 1H,1H-perfluoro-n-decanol, 1H,1H,2H,2H-perfluoro-1-dodecanol, 1H,1H,13H-perfluoro-1-tridecanol, 1,1,2,2-tetrahydroperfluorotetradecanol, 1H,1H-perfluoro-hexadecanol, and 1H,1H-perfluoro-1-octadecyl alcohol; the amount of the fluorine-containing alcohol substance is 100-124 mol% of the molar amount of the acrylic acid monomer.

[0016] In some specific embodiments of the present invention, the catalyst for the esterification reaction is concentrated sulfuric acid, preferably 98% concentrated sulfuric acid, the catalyst is added in an amount of 1.0-12.0 wt % of the mass of the acrylic acid monomer, and the esterification reaction temperature is 75-100°C.

[0017] In some specific embodiments of the present invention, in the process of preparing the pre-emulsion of the fluorine-containing acrylate and vinylidene fluoride in step (1), the amount of deionized water added is 90-140% of the mass of the vinylidene fluoride monomer.

[0018] In some specific embodiments of the present invention, the pre-emulsification temperature of step (1) is 31-40°C. Preferably, in step (1), fluorinated acrylate and vinylidene fluoride are added to the pre-emulsification tank at the same time. The duration of the common dropwise addition of the two is 5-11 hours, preferably 8-10 hours. In some specific embodiments of the present invention, the amount of deionized water added in step (2) is 50-72wt% of the mass of the vinylidene fluoride monomer.

[0019] In some specific embodiments of the present invention, in step (2), the reaction pressure is maintained at the target value by adjusting the amount of nitrogen, and the reaction temperature is maintained at the target value by adjusting the temperature of the jacket oil bath;

[0020] In some specific embodiments of the present invention, the mass of acrylic acid used to prepare the fluorine-containing acrylate is 0.3-4.0 wt % of the mass of the vinylidene fluoride monomer.

[0021] In some specific embodiments of the present invention, the emulsifier 1 in step (1) is one or more of potassium perfluorohexanoate, sodium perfluorohexanoate, ammonium perfluorohexanoate, ammonium perfluorooctanoate, sodium dodecyl sulfate, sodium dodecyl sulfonate or sodium dodecyl carbonate, and the amount of the emulsifier 1 is 0.16-1.2% of the mass of the vinylidene fluoride monomer.

[0022] In some specific embodiments of the present invention, the second emulsifier in step (2) is one or more of potassium perfluorohexanoate, sodium perfluorohexanoate, ammonium perfluorohexanoate, ammonium perfluorooctanoate, sodium dodecyl sulfate, sodium dodecyl sulfonate or sodium dodecyl carbonate, and the added amount is 0.10-1.2 wt% of the mass of the vinylidene fluoride monomer.

[0023] In some specific embodiments of the present invention, the reaction temperature of step (2) is 70-120° C., preferably 75-96° C., and the reaction pressure is 2.8-6.8 MPaG.

[0024] In some specific embodiments of the present invention, the initiator in step (2) is a peroxide initiator or an azo initiator, preferably one or more of ammonium persulfate, sodium persulfate, potassium persulfate, hydrogen peroxide, azobisisobutyronitrile, diisopropyl peroxydicarbonate, di-tert-butyl peroxide, and tert-butyl hydroperoxide, and the amount of the initiator is 1:1 of the mass of the vinylidene fluoride monomer.

[0025] In some specific embodiments of the present invention, the solvent in step (3) is one or more of N-methylpyrrolidone and N,N-dimethylacetamide to obtain a solution with a mass concentration of 8-20%;

[0026] In the step (3), the hydrolysis of the polyvinylidene fluoride resin can be promoted by an acidic catalyst. Preferably, the acidic catalyst is one or more of sulfuric acid, hydrochloric acid, nitric acid, etc., more preferably 20%-

[0027] 40% dilute sulfuric acid, the amount of the acidic catalyst added is 28-55wt% of the mass of the polyvinylidene fluoride resin, the hydrolysis temperature of the polyvinylidene fluoride resin is 70-80°C, and the hydrolysis time is 7-30min.

[0028] The beneficial effects of the present invention are:

[0029] The present invention provides a method for preparing polyvinylidene fluoride resin by co-dropping. The present invention first converts water-soluble acrylic acid monomers into oil-soluble monomers by esterification, thereby essentially solving the problem that acrylic acid and vinylidene fluoride have poor compatibility and are not easy to copolymerize. The present invention adopts fluorine-containing alcohol to esterify acrylic acid, so that the fluorine-containing acrylic acid and vinylidene fluoride have better compatibility, and the prepared polyvinylidene fluoride resin has higher copolymerization uniformity.

[0030] The present invention co-drops vinylidene fluoride monomer and acrylate into a reaction kettle continuously, thereby maintaining a consistent concentration of the vinylidene fluoride monomer, improving the mixing uniformity of the vinylidene fluoride monomer and the acrylate, and enhancing the uniformity of copolymerization. At the same time, nitrogen is used to maintain the reaction pressure instead of the pressure required for the vinylidene fluoride monomer to generate a reaction, making it possible to co-drop the monomers, and also substantially improving the polymerization safety.

[0031] By the method of the present invention, the acrylic acid monomer and the vinylidene fluoride monomer are co-dropped for polymerization reaction after polarity conversion, and finally a polyvinylidene fluoride resin with good tolerance and adhesion is obtained by uniform copolymerization of acrylic acid. The polyvinylidene fluoride resin has high copolymerization uniformity, high molecular weight and narrow molecular weight distribution. The preparation method has high reaction conversion rate and the polymerization reaction is safer and more efficient. DETAILED DESCRIPTION

[0032] 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.

[0033] The main test methods are as follows:

[0034] Bond strength

[0035] The bonding strength of the polymer after being prepared into an electrode is measured according to the IS04624 standard (adhesion pull-off test). The preparation process of the electrode is as follows: At room temperature, 1g of the resin produced in the embodiment or the comparative example is dissolved in 50g of NMP under mechanical stirring. Add 2g of conductive carbon black and 30g of lithium cobalt oxide (LiCoO2) while stirring, and mix thoroughly to ensure uniformity. The mixture is then degassed under vacuum and spread on aluminum foil with a scraper. Finally, the aluminum foil spread with the electrode material mixture is placed in a vacuum oven and heated to 60°C and dried for 12 hours to finally prepare an electrode sheet. Use an INSTRON tensile tester to measure the bonding strength of the electrode material on the electrode sheet.

[0036] Thermal stability

[0037] 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.

[0038] Weight average molecular weight and molecular weight distribution

[0039] The molecular weight distribution of the polymers was measured using Shimadzu gel permeation chromatography (GPC).

[0040] The main raw material information is as follows:

[0041] Vinylidene fluoride: Wanhua Chemical Group Co., Ltd., industrial products;

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

[0043] 1H,1H,2H,2H-Perfluoro-1-dodecanol: Beijing Yinuokai, analytical grade;

[0044] 1H,1H-Perfluoro-hexadecanol: Beijing Yinuokai, analytical grade;

[0045] 1-Decanol: Aladdin, analytical grade;

[0046] Ammonium perfluorooctanoate: Sigma, analytical grade;

[0047] Sodium dodecyl sulfate: Aladdin, analytical grade;

[0048] Sodium persulfate: Aladdin, analytical grade;

[0049] Azobisisobutyronitrile: Aladdin, analytical grade;

[0050] N-Methylpyrrolidone: Sigma, analytical grade;

[0051] 98% concentrated sulfuric acid: Changzhou Qinghong Chemical, industrial products;

[0052] 30% dilute sulfuric acid: Changzhou Qinghong Chemical, industrial product.

[0053] Example 1

[0054] Add 45.1g 1H,1H,2H,2H-perfluoro-1-dodecanol into a 200ml three-necked flask, then add 0.5g 98% concentrated sulfuric acid and 4.8g acrylic acid into the flask, slowly heat the flask to 84 degrees Celsius, and then take out the target product acrylate. Then add the obtained acrylate and 1416g deionized water into a 4L pre-emulsification tank, then add 1200g vinylidene fluoride monomer and 13.2g emulsifier ammonium perfluorooctanoate and heat to 35°C, stir evenly to obtain a pre-emulsified solution of acrylate and vinylidene fluoride.

[0055] The copolymerization reaction is carried out in a 5L high-pressure reactor equipped with a stirrer. The reactor is evacuated and then filled with nitrogen to a positive pressure. 792g of deionized water, 9.6g of ammonium perfluorooctanoate, an emulsifier, and 1.4g of sodium persulfate, an initiator, are added to the reactor, and the temperature is raised to a reaction temperature of 73°C. Nitrogen is introduced into the reactor to maintain the pressure in the reactor at 4.6MPaG, and then the pre-emulsified liquid is continuously added to the reactor for copolymerization, and the total dropwise addition is 10 hours. After the reaction is completed, the reaction product is taken out and dried, and then 10843g of solvent N-methylpyrrolidone is added to the dried product, and 349.4g of 30% dilute sulfuric acid is added, and hydrolysis is carried out at 74°C for 28min. The hydrolyzed product is then dried, extruded and granulated to obtain a finished polyvinylidene fluoride resin.

[0056] Example 2

[0057] 499.3g 1H,1H-perfluoro-hexadecanol was added to a 1L three-necked flask, and then 1.4g 98% concentrated sulfuric acid and 42g acrylic acid were added to the flask, and the flask was slowly heated to 96 degrees Celsius, and then the target product acrylate was taken out. The obtained acrylate and 1128g deionized water were added to a 4L pre-emulsification tank, and then 1200g vinylidene fluoride monomer and 10.2g emulsifier sodium dodecyl sulfate were added and the temperature was raised to 32°C, and the pre-emulsion of acrylate and vinylidene fluoride was obtained after stirring evenly.

[0058] The copolymerization reaction is carried out in a 5L high-pressure reactor equipped with a stirrer. The reactor is evacuated and then filled with nitrogen to a positive pressure. 840g of deionized water, 7.6g of emulsifier sodium dodecyl sulfate, and 5.4g of initiator sodium persulfate are added to the reactor, and the temperature is raised to a reaction temperature of 116°C. Nitrogen is introduced into the reactor to maintain the pressure in the reactor at 3MPaG, and then the pre-emulsified liquid is continuously added to the reactor for copolymerization, and the total dropwise addition is 6h. After the reaction is completed, the reaction product is taken out and dried, and then 9108g of solvent N-methylpyrrolidone is added to the dried product, and 645.8g of 30% dilute sulfuric acid is added, and hydrolysis is carried out at 71°C for 16min. The hydrolyzed product is then dried and extruded and granulated to obtain a finished polyvinylidene fluoride resin.

[0059] Example 3

[0060] 180.2g of perfluoro-1-dodecanol was added to a 1L three-necked flask, and then 0.35g of 98% concentrated sulfuric acid and 20.4g of acrylic acid were added to the flask, and the flask was slowly heated to 78 degrees Celsius, and then the target product acrylate was taken out. The obtained acrylate and 1620g of deionized water were added to a 4L pre-emulsification tank, and then 1200g of vinylidene fluoride monomer and 2.0g of emulsifier sodium dodecyl sulfate were added and the temperature was raised to 39°C, and the pre-emulsion of acrylate and vinylidene fluoride was obtained after stirring evenly.

[0061] The copolymerization reaction is carried out in a 5L high-pressure reactor equipped with a stirrer. The reactor is evacuated and then filled with nitrogen to a positive pressure. 636g of deionized water, 1.44g of emulsifier sodium dodecyl sulfate, and 3.24g of initiator azobisisobutyronitrile are added to the reactor, and the temperature is raised to a reaction temperature of 85°C. Nitrogen is introduced into the reactor to maintain the pressure in the reactor at 6.4MPaG, and then the pre-emulsified liquid is continuously added to the reactor for copolymerization, and the total dropwise addition is 8h. After the reaction is completed, the reaction product is taken out and dried, and then 6407g of solvent N-methylpyrrolidone is added to the dried product, and 500.4g of 30% dilute sulfuric acid is added, and hydrolysis is carried out at 79°C for 8min. The hydrolyzed product is then dried, extruded and granulated to obtain a finished polyvinylidene fluoride resin.

[0062] Comparative Example 1

[0063] 4.8 g of acrylic acid and 1416 g of deionized water were added into a 4 L beaker and mixed evenly to obtain an acrylic acid aqueous solution. The temperature of the acrylic acid aqueous solution was maintained at 35°C.

[0064] The copolymerization reaction was carried out in a 5L high-pressure reactor equipped with a stirrer. The reactor was evacuated and then filled with nitrogen to a positive pressure. 792g of deionized water, 9.6g of ammonium perfluorooctanoate, an emulsifier, and 1.44g of sodium persulfate, an initiator, were added to the reactor. Then, 1200g of vinylidene fluoride monomer was added to the reactor at one time. The temperature was raised to a reaction temperature of 73°C, and then an acrylic acid aqueous solution was continuously added to the reactor for a copolymerization reaction. The addition lasted for 10 hours. After the reaction was completed, the reaction product was taken out and dried to obtain a finished polyvinylidene fluoride resin.

[0065] Comparative Example 2

[0066] 4.8 g of acrylic acid and 1416 g of deionized water were added into a 4 L pre-emulsification tank, and then 1200 g of vinylidene fluoride monomer and 13.2 g of emulsifier ammonium perfluorooctanoate were added and the temperature was raised to 35° C. and stirred evenly to obtain a pre-emulsified liquid of acrylic acid ester and vinylidene fluoride.

[0067] The copolymerization reaction was carried out in a 5L high-pressure reactor equipped with a stirrer. The reactor was evacuated and then filled with nitrogen to a positive pressure. 792g of deionized water, 9.6g of ammonium perfluorooctanoate, an emulsifier, and 1.44g of sodium persulfate, an initiator, were added to the reactor, and the temperature was raised to a reaction temperature of 73°C. Nitrogen was introduced into the reactor to maintain the pressure in the reactor at 4.6MPaG, and then the pre-emulsion was continuously added to the reactor for copolymerization, and the addition was continued for 10 hours. After the reaction was completed, the reaction product was taken out and dried to obtain a finished polyvinylidene fluoride resin.

[0068] Comparative Example 3

[0069] 12.6g of 1-decanol was added to a 20ml test tube, and then 0.5g of 98% concentrated sulfuric acid and 4.8g of acrylic acid were added to the flask, and the test tube was slowly heated to 84 degrees Celsius, and then the target product acrylate was taken out. The obtained acrylate and 1416g of deionized water were added to a 4L pre-emulsification tank, and then 1200g of vinylidene fluoride monomer and 13.2g of emulsifier ammonium perfluorooctanoate were added and the temperature was raised to 35°C, and the pre-emulsion of acrylate and vinylidene fluoride was obtained after stirring evenly.

[0070] The copolymerization reaction is carried out in a 5L high-pressure reactor equipped with a stirrer. The reactor is evacuated and then filled with nitrogen to a positive pressure. 792g of deionized water, 9.6g of ammonium perfluorooctanoate, an emulsifier, and 1.44g of sodium persulfate, an initiator, are added to the reactor, and the temperature is raised to a reaction temperature of 73°C. Nitrogen is introduced into the reactor to maintain the pressure in the reactor at 4.6MPaG, and then the pre-emulsified liquid is continuously added to the reactor for copolymerization, and the total dropwise addition is 10 hours. After the reaction is completed, the reaction product is taken out and dried, and then 10843g of solvent N-methylpyrrolidone is added to the dried product, and 349.4g of 30% dilute sulfuric acid is added, and hydrolysis is carried out at 74°C for 28 minutes. The hydrolyzed product is then dried, extruded and granulated to obtain a finished polyvinylidene fluoride resin.

[0071] The properties of the super absorbent resins obtained in the above examples and comparative examples are shown in Table 1 below:

[0072] Table 1 Performance parameters of embodiments and comparative examples

[0073] Bond strength (N / m) Thermal stability YI Weight average molecular weight Molecular weight distribution Example 1 34.3 11.6 122 1.6 Example 2 34.8 11.4 127 1.7 Example 3 36.3 10.5 133 1.4 Comparative Example 1 22.7 14.4 104 2.7 Comparative Example 2 23.9 14.1 110 2.7 Comparative Example 3 26.5 13.8 113 2.2

[0074] It can be seen from the table that the polyvinylidene fluoride resin obtained by the method for preparing the polyvinylidene fluoride resin by co-dropping in the present invention has better product performance.

[0075] 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, characterized in that: The steps include: (1) adding fluorinated acrylate and vinylidene fluoride monomer into a pre-emulsification tank, adding deionized water and emulsifier 1 into the pre-emulsification tank, and stirring at a pre-emulsification temperature to obtain a pre-emulsion; (2) adding deionized water, an initiator and an emulsifier 2 into an autoclave, then introducing nitrogen into the autoclave to a reaction pressure, heating the autoclave to a reaction temperature, and then adding a pre-emulsified liquid to carry out a reaction; (3) After the reaction is completed, a polymer resin is obtained, which is dissolved in a solvent, then hydrolyzed, and then dried and extruded into granules to obtain a polyvinylidene fluoride resin; The fluorine-containing acrylate is obtained by esterification reaction of acrylic acid monomer and fluorine-containing alcohol substance.

2. The preparation method according to claim 1, characterized in that: The fluorine-containing alcohol substance is selected from one or more of perfluoro-1-heptanol, perfluoro-1-octanol, 1H,1H-perfluoro-1-nonanol, 1H,1H,2H,2H-perfluoro-1-decanol, 1H,1H-perfluoro-n-decanol, 1H,1H,2H,2H-perfluoro-1-dodecanol, 1H,1H,13H-perfluoro-1-tridecanol, 1,1,2,2-tetrahydroperfluorotetradecanol, 1H,1H-perfluoro-hexadecanol, and 1H,1H-perfluoro-1-octadecyl alcohol; The amount of the fluorine-containing alcohol substance is 100-124 mol% of the molar amount of the acrylic acid monomer.

3. The preparation method according to claim 1, characterized in that: The catalyst for the esterification reaction is concentrated sulfuric acid.

4. The preparation method according to claim 3, characterized in that: The concentrated sulfuric acid is concentrated sulfuric acid with a mass fraction of 98wt%.

5. The preparation method according to claim 3, characterized in that: The catalyst is added in an amount of 1.0-12.0 wt% of the acrylic acid monomer, and the esterification reaction temperature is 75-100°C.

6. The preparation method according to claim 1, characterized in that: In the step (1), the amount of deionized water added during the preparation of the pre-emulsion of the fluorinated acrylate and vinylidene fluoride is 90-140% of the mass of the vinylidene fluoride monomer.

7. The preparation method according to claim 1, characterized in that: The pre-emulsification temperature of step (1) is 31-40°C.

8. The preparation method according to claim 1, characterized in that: In the step (1), the fluorine-containing acrylate and vinylidene fluoride are added into the pre-emulsification tank at the same time.

9. The preparation method according to claim 8, characterized in that: The two are added together for 5-11 hours.

10. The preparation method according to claim 9, characterized in that: The two are added together for 8-10 hours.

11. The preparation method according to claim 1, characterized in that: In step (1), the emulsifier 1 is one or more of potassium perfluorohexanoate, sodium perfluorohexanoate, ammonium perfluorohexanoate, ammonium perfluorooctanoate, sodium dodecyl sulfate, and sodium dodecyl sulfonate; The amount of the emulsifier 1 is 0.16-1.2% of the mass of the vinylidene fluoride monomer.

12. The preparation method according to claim 1, characterized in that: The amount of deionized water added in step (2) is 50-72 wt % of the mass of the vinylidene fluoride monomer.

13. The preparation method according to claim 1, characterized in that: In the step (2), the reaction pressure is maintained at the target value by adjusting the amount of nitrogen, and the reaction temperature is maintained at the target value by adjusting the temperature of the jacket oil bath.

14. The preparation method according to claim 1, characterized in that: The mass of acrylic acid used in preparing fluorine-containing acrylate is 0.3-4.0wt% of the mass of vinylidene fluoride monomer.

15. The preparation method according to claim 1, characterized in that: In the step (2), the second emulsifier is one or more of potassium perfluorohexanoate, sodium perfluorohexanoate, ammonium perfluorohexanoate, ammonium perfluorooctanoate, sodium dodecyl sulfate, and sodium dodecyl sulfonate, and the added amount is 0.10-1.2 wt % of the mass of the vinylidene fluoride monomer.

16. The preparation method according to claim 1, characterized in that: The reaction temperature of step (2) is 70-120° C., and the reaction pressure is 2.8-6.8 MPaG.

17. The preparation method according to claim 1, characterized in that: The reaction temperature of step (2) is 75-96°C.

18. The preparation method according to claim 1, characterized in that: The initiator in step (2) is a peroxide initiator or an azo initiator.

19. The preparation method according to claim 1, characterized in that: In step (2), the initiator is one or more of ammonium persulfate, sodium persulfate, potassium persulfate, hydrogen peroxide, azobisisobutyronitrile, diisopropyl peroxydicarbonate, di-tert-butyl peroxide, and tert-butyl hydroperoxide; The amount of the initiator used is 0.1-0.46 wt % of the vinylidene fluoride monomer.

20. The preparation method according to claim 1, characterized in that: In the step (3), the solvent is one or more of N-methylpyrrolidone and N,N-dimethylacetamide, and a solution with a mass concentration of 8-20% is obtained.

21. The preparation method according to claim 1, characterized in that: In the step (3), the hydrolysis of the polyvinylidene fluoride resin is promoted by an acidic catalyst.

22. The preparation method according to claim 21, characterized in that: The acidic catalyst is one or more of sulfuric acid, hydrochloric acid and nitric acid.

23. The preparation method according to claim 22, characterized in that: The acid catalyst is 20%-40% dilute sulfuric acid.

24. The preparation method according to claim 22, characterized in that: The amount of the acid catalyst added is 28-55 wt % of the mass of the polyvinylidene fluoride resin.

25. The preparation method according to claim 1, characterized in that: The hydrolysis temperature of the polyvinylidene fluoride resin is 70-80° C., and the hydrolysis time is 7-30 minutes.