A high tensile strength fluoropolymer and a method for its preparation

Abstract

The application relates to a fluorine-containing polymer with high tensile strength and a preparation method thereof. The fluorine-containing polymer is prepared by blending modification of a base PVDF resin in a certain proportion, the base PVDF resin is prepared by copolymerization modification of a halogenated vinyl monomer, an unsaturated acid monomer and vinylidene fluoride, and the fluorine-containing polymer is prepared by copolymerization of vinylidene fluoride and an epoxy group-terminated allyl polyether. The prepared fluorine-containing polymer has excellent tensile strength while ensuring good processability and flexibility.

Description

TECHNICAL FIELD

[0001] The present application relates to a fluoropolymer containing 1,1-vinylidene fluoride, other fluorine-containing or non-fluorine-containing comonomers, and an end epoxy group allyl polyether, and a manufacturing method thereof, and blending modification of different components of the fluoropolymer to improve its mechanical properties. BACKGROUND

[0002] Polyvinylidene fluoride (PVDF) is mainly special in the family of fluorine-containing high molecular materials, which has both C-F bond and C-H bond. The C-F bond provides structural stability: excellent mechanical properties, aging resistance, high and low temperature resistance, insulation, chemical resistance, sun resistance and flame resistance. The C-H bond provides solubility and easy processing. Therefore, PVDF resin is particularly suitable for being dissolved by a solvent to be used in the form of a coating or an adhesive glue, such as a coating, a lithium battery separator coating, a photovoltaic backsheet coating, a lithium positive electrode binder (an adhesive glue made with a solvent). In addition, the difference between the melting temperature (170℃) and the decomposition temperature (316℃) of the PVDF resin is more than 100℃, which endows the material with good thermal stability and melt processing property, and a wide processing window. Similar to easy-to-process thermoplastic resins such as polyethylene and polypropylene, PVDF films, separators, rods, pumps, plates, tube membranes, tubes, hoses, valves, pipe fittings, monofilaments and wire insulation layers can be produced by using conventional plastic forming and processing methods such as molding, extrusion, injection molding, blow molding, casting and transfer molding.

[0003] Although polyvinylidene fluoride resin can be used for a long time in the range of -50℃ to 150℃, maintaining good mechanical properties, the mechanical strength and mechanical properties of PVDF are greatly challenged in some special application occasions, such as low-temperature seawater pipelines, high-temperature mechanical processing fittings, and films subjected to curling or tensile stress for a long time. Therefore, it is necessary to improve the mechanical strength of PVDF, especially the tensile strength.

[0004] It is known that the tensile strength and other mechanical properties of products made of PVDF material can be improved by increasing the molecular weight of PVDF. However, high molecular weight PVDF is difficult to melt process or dissolve in organic solvents, which greatly limits the range of use and application fields. Patent CN103351446B discloses a preparation method of high tensile strength polyvinylidene fluoride. By using an organic peroxide as an initiator and a lower alkane as a molecular weight regulator, a high tensile strength PVDF copolymer is prepared by free radical polymerization of vinylidene fluoride (VDF) and other fluorine-containing monomers at low temperature. The obtained polyvinylidene fluoride resin has high crystallinity, high molecular weight and tensile strength greater than 60MPa. However, the high crystallinity and high molecular weight of the polyvinylidene fluoride resin prepared by this method make it difficult to melt process, which limits its application range.

[0005] In addition, copolymerization or graft modification of the molecular segment of vinylidene fluoride can add functional groups that can improve the performance of fluoropolymers to the molecular segment of vinylidene fluoride in various ways to enhance the special performance of fluorinated polymers. The introduction of the second monomer changes the molecular chain structure of PVDF resin, and gives the polymer good mechanical properties. For example, copolymerization of tetrafluoroethylene, hexafluoropropylene, trifluoro-chloroethylene and perfluoro vinyl ether and other perfluoro vinyl monomers can reduce the regularity and crystallinity of polyvinylidene fluoride resin structure, increase the flexibility between molecules, and thus improve the mechanical properties of the resin.

[0006] For example, patents CN111491962B, CN106336476B and CN113260643A use hydrophilic (meth) acrylic monomers and perhalogenated monomers to copolymerize vinylidene fluoride, which significantly improves the mechanical properties such as flexibility, impact strength and elongation at break of the prepared vinylidene fluoride resin, and can be widely used in the field of wire and cable processing. However, due to the reduction of the structural regularity of the polymer molecular chain and the weakening of the force between the molecular chains, the tensile strength of PVDF is not improved, and even has a certain downward trend.

[0007] Patent US4946900A discloses a preparation method of polyvinylidene fluoride copolymerized with trifluorochloroethylene. This method uses stepwise polymerization to connect polyvinylidene fluoride with trifluorochloroethylene copolymer in the form of a chemical bond, thereby improving the flexibility and impact strength of the polymer, but the stepwise polymerization process control is relatively complex, which is not conducive to industrial production. Patent US6201084B discloses a preparation method of polyvinylidene fluoride thermoplastic copolymer. This method uses fluorine-containing dioxole to copolymerize with polyvinylidene fluoride to improve the impact resistance of the polymer, but this method has problems such as complex polymer process and low tensile strength of the polymer.

[0008] Patent CN113851649A discloses a preparation method of a positive electrode slurry. By controlling the addition of different types of binders and the composition of the positive electrode material, an excellent performance electrode sheet is prepared, and good battery performance is obtained. The main invention includes a positive electrode material (controlling particle size D50, free lithium ion content), two types of PVDF binders (limiting intrinsic viscosity, and the dosage ratio of the positive electrode material), and they must satisfy a certain relationship. The intrinsic viscosity of the first binder is 0.4-0.6 L / g, and the second binder is 0.3-0.5 L / g. The large molecular weight PVDF copolymer has a high melt viscosity and poor flowability, and cannot be effectively melt processed and blended. The modification process is more suitable for the field of lithium ion battery binders.

[0009] Patent CN1714465A discloses a preparation method of a battery binder composition, the main invention is that the PVDF polymer containing functional groups + polar polymer containing hydroxyl or / and carbonyl are used as the composition applied to the binder of the positive electrode of the battery. The PVDF modified monomer includes acrylic acid monomer and glycidyl monomer, and the intrinsic viscosity is 0.8-20 dl / g, the polar polymer is one of EVOH, PAA, HEC, PVP and other polar polymers, the two polymers containing polar functional groups are blended as the composition of the battery binder, the adhesion of the positive material to the current collector is improved, and the performance and safety stability of the battery electrode sheet are obtained. However, it is difficult for the two polymers to interact or chemically react with each other to improve the mechanical properties and stability of the polymer itself.

[0010] In addition, due to the super strong electronegativity and anti-interference characteristics of fluorine atoms or fluorine-containing free radicals, it is difficult to directly add functional monomer units to the polymer backbone being polymerized, especially in a random embedded manner. Those skilled in the art can also use post-treatment or blending modification of polyvinylidene fluoride resin to improve the tensile strength and other mechanical properties within a certain range, but the actual effect is not satisfactory, and there are problems such as complex process operation, and the application field and scope are obviously limited. SUMMARY

[0011] The purpose of the present application is to overcome the shortcomings of the prior art, and to provide a high-tensile-strength fluorine-containing polymer and a preparation method thereof. The present application surprisingly found that the basic PVDF resin was prepared by copolymerization modification of halogenated vinyl monomer, unsaturated acid monomer and vinylidene fluoride, and the fluorine-containing polymer was prepared by copolymerization of vinylidene fluoride and epoxy-terminated allyl polyether, and the fluorine-containing polymer was prepared by blending modification of the basic PVDF resin in a certain proportion. The prepared fluorine-containing polymer has excellent tensile strength while ensuring good processability and flexibility.

[0012] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0013] A preparation method of a high-tensile-strength fluorine-containing polymer, comprising the following steps:

[0014] 1) 1,1-vinylidene fluoride, halogenated vinyl monomer and unsaturated acid monomer are copolymerized to prepare a fluorine-containing polymer (A), wherein the tensile strength of the fluorine-containing polymer (A) is not less than 30 MPa, and the melt index is 2.0-10.0 g / 10 min (230℃ / 5.0 kg);

[0015] 2) 1,1-vinylidene fluoride is copolymerized with epoxy-terminated allyl polyether to prepare a fluorine-containing polymer (B), wherein the structural formula of the epoxy-terminated allyl polyether is

[0016] wherein n is an integer less than 20;

[0017] The content of the terminal epoxy allyl polyether in the total mass of the fluoropolymer (B) is 0.01-5%, and the intrinsic viscosity of the fluoropolymer (B) is greater than 1.7 dL / g;

[0018] 3) blending the fluoropolymer (A) with the fluoropolymer (B) in a certain proportion to obtain the desired high tensile strength fluoropolymer with a tensile strength of not less than 50 MPa.

[0019] The terminal epoxy allyl polyether used in the fluoropolymer (B) of the present application is preferably n = 1-10, more preferably allyl glycidyl ether and / or allyl polyether glycidyl ether. It should be noted that during the preparation of the fluoropolymer (B), the terminal epoxy allyl polyether can be added at one time at the bottom of the polymerization kettle, or it can be added into the polymerization reaction system in small amounts, continuously or in batches, alone or together with other additives. The purpose is to ensure that the terminal epoxy allyl polyether reacts with the vinylidene fluoride monomer in the expected way to achieve the desired use effect. Preferably, the amount of the terminal epoxy allyl polyether added is 0.1-2% of the total mass of the fluoropolymer (B).

[0020] The halogenated vinyl monomer used in the fluoropolymer (A) of the present application is selected from one or more of tetrafluoroethylene (TFE), chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), perfluorobutyl ethylene (PFBE), perfluoromethyl vinyl ether (PMVE), perfluoroethyl vinyl ether (PEVE), perfluoropropyl vinyl ether (PPVE), and perfluorobutyl vinyl ether (PBVE). More preferably, it is at least one of chlorotrifluoroethylene, tetrafluoroethylene, and hexafluoropropylene. Preferably, the content of the halogenated vinyl monomer in the total mass of the fluoropolymer (A) is 0.01-10%, preferably 0.1-5%.

[0021] The unsaturated acid monomer used in the fluoropolymer (A) of the present application is selected from at least one of acrylic acid, methacrylic acid, itaconic acid, maleic acid, and cinnamic acid. Further, the content of the unsaturated acid monomer in the total mass of the fluoropolymer (A) is 0.01-5%, preferably 0.1-3%.

[0022] The fluoropolymer (A) of the present application is used as a base resin, in order to ensure that it has excellent mechanical properties such as tensile strength, elongation at break, etc., and also has good melt processing performance, and can be processed into various downstream application materials such as molding, extrusion, injection molding, casting, and blown film. The tensile strength of the prepared fluoropolymer (A) is preferably not less than 40 MPa, and the melt index is preferably 4.0-8.0 g / 10 min (230℃ / 5.0 kg).

[0023] The fluorine-containing polymer (B) in the present application as a functional improvement resin has a large molecular weight in addition to a special modified functional monomer, and the intrinsic viscosity of the fluorine-containing polymer (B) is preferably greater than 2.0 dL / g.

[0024] The high tensile strength fluorine-containing polymer prepared in the present application is obtained by blending the fluorine-containing polymer (A) and the fluorine-containing polymer (B) in a certain proportion, and the blending mode can be physical blending of the two polymer powders or granulation blending by a high-temperature screw extruder, which is mainly determined by the different downstream application modes. The fluorine-containing polymer (A) is used as a base resin as the main content part, and the fluorine-containing polymer (B) is used as a functional improvement resin as the secondary content part, and the blending ratio of the fluorine-containing polymer (A) and the fluorine-containing polymer (B) is preferably 20:1-4:1. Further, the required high tensile strength fluorine-containing polymer is prepared, and the tensile strength thereof is preferably not less than 60 MPa.

[0025] The present application also provides a method for manufacturing a fluorine-containing polymer, and the fluorine-containing polymer in the present application can be prepared by any one of emulsion polymerization or suspension polymerization in an aqueous solution. It should be noted that due to the biological toxicity and environmental pollution problems of the recognized fluorine-containing surfactant, especially perfluorooctanoic acid and its salt, as an alternative solution, the non-fluorine-containing surfactant is preferably used in the emulsion polymerization in the present application, which is generally an anionic or / and non-ionic surfactant selected from one or more of alkyl sulfate, alkyl sulfonate, alkyl benzene sulfonate, alkyl phosphate, alkyl polyoxyethylene ether and its salt, alkyl alcohol (phenol) polyoxyethylene ether and its salt, fatty acid polyoxyethylene ether and its salt, block polyoxyethylene-polyoxypropylene ether and its salt, alkyl polyglucoside, alkyl alcohol amide, etc. However, in order to better and more simply describe the present application, the suspension polymerization method is taken as an example for detailed description below.

[0026] As a preferred solution, a suspension polymerization method for preparing a fluorine-containing polymer comprises the following steps: (a) adding deionized water, polymerization stabilizer, chain transfer agent, etc. in a high-pressure polymerization kettle, stirring and mixing uniformly, and removing oxygen by nitrogen;

[0027] (b) adding an initiator into the high-pressure polymerization kettle, and adding 1,1-vinylidene fluoride, a second monomer, and / or a third monomer, heating and warming, and starting the polymerization reaction;

[0028] (c) continuously adding the remaining polymerization monomers, initiator, and chain transfer agent, and keeping the polymerization temperature and polymerization pressure stable in the required range;

[0029] (d) when the polymerization pressure is less than a certain value at the end of the addition of the polymerization monomers, the polymerization reaction is terminated, and a fluorine-containing polymer dispersion is obtained; and the fluorine-containing polymer resin is obtained by flocculation, washing, filtration, and drying as needed.

[0030] The polymerization reactor described in the present application can be appropriately selected from known polymerization reactors capable of achieving the conditions of the suspension polymerization of the present embodiment, including a high-pressure spherical tank, a high-pressure horizontal tank, and a high-pressure vertical tank. In order to ensure the heat and mass transfer effects of the polymerization reaction, the aspect ratio of the polymerization reactor is as small as possible, preferably L / D is less than 2, and more preferably L / D is less than 1.5. In addition, the stirring mode in the polymerization reactor is also very important for the control of the reaction process and the reaction efficiency, and is selected from one of a three-blade pitched paddle, a four-blade pitched paddle, an anchor paddle, a frame paddle, and a helical ribbon paddle.

[0031] A polymerization stabilizer is used for the purpose of improving the dispersibility of the vinylidene fluoride monomer and other comonomers in water. The polymerization stabilizer is generally a macromolecular dispersant such as a cellulose ether, a polyvinyl alcohol, a polyethylene glycol, a polyacrylic acid, and the like. In the present application, one or more of methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and hydroxypropyl methyl cellulose is preferred. The addition amount of the polymerization stabilizer is preferably 0.1-3% by mass of the polymer, and more preferably 0.1-2% by mass of the polymer.

[0032] A chain transfer agent is used for the purpose of adjusting the molecular weight of the obtained polymer. The chain transfer agent can be appropriately selected from known compounds that can be used to adjust the molecular weight of the vinylidene fluoride monomer. The chain transfer agent is generally selected from, but not limited to, oxygen-containing compounds such as alcohols, carbonates, ketones, esters, and ethers; halogenated hydrocarbons such as chlorinated hydrocarbons, hydrochlorinated hydrocarbons, chlorofluorinated hydrocarbons, and hydrochlorofluorinated hydrocarbons; and alkanes such as ethane and propane. In the present application, one or more of diethyl carbonate, ethyl acetate, and diethyl malonate is preferred.

[0033] A buffer can be optionally included in the polymerization reaction mixture to maintain a controlled pH throughout the polymerization reaction. The pH is generally preferably controlled in the range of about 4-8 to minimize the generation of undesirable color in the product. The buffer can include an organic acid or an inorganic acid or an alkali metal salt thereof, or a base or a salt of the organic or inorganic acid. Preferred buffers in the practice of the present application include phosphate buffers and acetate buffers. Among them, the phosphate buffer is a salt of phosphoric acid or a mixture of multiple salts thereof.

[0034] It should be noted that the presence of oxygen is extremely detrimental to the safety and stability control of the polymerization reaction. Therefore, the polymerization reactor needs to be operated to remove oxygen after the empty tank stage or after the addition of the polymerization reaction aid. Generally, multiple nitrogen replacements are performed under a negative pressure environment, and the oxygen content is preferably controlled to be less than 20 ppm, and more preferably less than 10 ppm.

[0035] The suspension polymerization generally uses an organic peroxide initiator according to the polymerization characteristics, and the present application preferably uses one or more of diacetyl peroxydicarbonate, diethyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxyneodecanoate, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), t-butyl peroxyneopentanoate, t-amyl peroxyneopentanoate, 2,2'-azobis(2,4-dimethylvaleronitrile), t-butyl azo-2-cyanobutane, dibenzoyl peroxide, t-butyl peroxy-2-ethylhexanoate, t-butyl peroxy maleate, t-butyl peroxyisopropylcarbonate, t-butyl peroxyacetate, 2,2'-bis(t-butylperoxy)butane, dicumyl peroxide, t-butyl hydroperoxide, and the like. The amount of the organic peroxide initiator to be added is preferably 0.01 to 2% by mass of the polymer, more preferably 0.1 to 1% by mass of the polymer.

[0036] In the production method of the present embodiment, the pressure in the reactor is sufficiently increased to the polymerization initial temperature by the temperature rise in the reactor to exceed the critical pressure (4.43 MPa) of vinylidene fluoride, and is generally the maximum in the polymerization reaction. Therefore, the vinylidene fluoride in the vinylidene fluoride-containing monomer is mainly used in the polymerization reaction in a supercritical fluid state, and the pressure in the reaction system generally decreases as the vinylidene fluoride-containing monomer is used for polymerization, so it is generally necessary to continuously supply the vinylidene fluoride monomer to maintain the stability of the pressure in the polymerization reactor. If the pressure in the reactor when the above reaction system is heated to the polymerization initial temperature is too high, a pressure-resistant vessel is sometimes required, and if the pressure is too low, the polymerization reaction time becomes long and the productivity is sometimes reduced. From the viewpoint of shortening the reaction time, the pressure in the reactor when the above reaction system is heated to the polymerization initial temperature is preferably 3 MPa or higher, more preferably 4.4 MPa or higher. In addition, for example, from the viewpoint of reducing the cost of the reactor, the pressure is preferably 15 MPa or lower, more preferably 13 MPa or lower. The pressure can be adjusted according to various main factors such as the supply amount of the vinylidene fluoride-containing monomer and the comonomer, the polymerization initial temperature, and the monomer density.

[0037] Meanwhile, the polymerization initial temperature can be appropriately determined within a range of a temperature sufficient to make the vinylidene fluoride in the reactor become a supercritical state. Within this range, if the polymerization initial temperature is too low, the reaction time of the suspension polymerization becomes long, and thus the productivity of the vinylidene fluoride polymer is sometimes reduced, and if the polymerization initial temperature is too high, the pressure of the reaction system of the suspension polymerization increases, and a more pressure-resistant reactor is sometimes required. From the viewpoint of improving the productivity of the vinylidene fluoride polymer, the polymerization initial temperature is preferably 40°C or higher, more preferably 45°C or higher. In addition, from the viewpoint of suppressing the increase in the pressure of the reaction system, the polymerization initial temperature is preferably 100°C or lower, more preferably 70°C.

[0038] In the end point control of the suspension polymerization in the present application, the balance between the decrease in the amount of unreacted monomer and the elongation of the polymerization time (i.e., the productivity of the product polymer) is considered to be appropriately selected. For example, the end point of the suspension polymerization can be determined based on the temperature rise in the reaction system and the change in the pressure accompanying the same in addition to the sampling of the reaction product.

[0039] In the production method of the present embodiment, the vinylidene fluoride polymer is obtained in the form of a powder by subjecting the polymer slurry to dewatering, water washing, and drying after the completion of the suspension polymerization. According to the production method of the present embodiment, the reaction efficiency can be improved and the polymerization time can be shortened. Specifically, the polymerization time from the time point at which the initial polymerization temperature is reached to the completion of the polymerization is preferably within 20 hours, more preferably within 15 hours, after the raw materials are supplied to the reactor.

[0040] In the method of the present application, a small molecular weight melt processable base polymer is first prepared by copolymerization of vinylidene fluoride and epoxy terminated allyl polyether, which has a melt index of 2.0-10.0 g / 10 min (230℃ / 5.0 kg), a molecular weight of about 300,000, and a good tensile strength (>30 MPa), and then a high molecular weight fluorine-containing polymer with modified function is prepared by copolymerization of vinylidene fluoride and epoxy terminated allyl polyether, which has an intrinsic viscosity of >1.7 dl / g, i.e. a molecular weight of >500,000, and contains epoxy functional groups, which can undergo crosslinking reaction during melt processing after blending of the two polymers in a certain proportion, thereby improving the tensile strength of the resin, while also having good processing performance and flexibility.

[0041] The high tensile strength fluorine-containing polymer prepared according to the present application can be melt processed into various plates, films, pipes or cables by injection molding, extrusion or casting, etc., and is widely used in many fields such as aerospace, petrochemical industry, electronic communication and mechanical processing, etc. DETAILED DESCRIPTION

[0042] The present application will be described in more detail by the following examples, but the present application is not limited to these specific embodiments. Those skilled in the art will recognize that the present application encompasses all alternatives, modifications and equivalents as can be included within the scope of the claims.

[0043] The information of the raw materials required for the experiment is as follows:

[0044] Hydroxypropyl methylcellulose: HPMC, Shandong Heda Chemical Co., Ltd., product brand HEADCEL 75HD100

[0045] Diethyl carbonate: DEC, Jinan Plaihua Chemical Co., Ltd.

[0046] Tert-butyl peroxy pivalate: TBPP, Hubei Kanos Technology Co., Ltd.

[0047] Hexafluoropropylene: HFP, Shandong Huaxia Shenzhou New Material Co., Ltd.

[0048] Trifluorochloroethylene: CTFE, Shanghai Sanai Fu New Material Technology Co., Ltd.

[0049] Acrylic acid: AA, Wanhua Chemical Group Co., Ltd.

[0050] Maleic acid: MA, Shandong Hui'an Chemical Co., Ltd.

[0051] Allyl glycidyl ether: AGE, Shandong Jiaying Chemical Technology Co., Ltd.

[0052] Allyl polyether glycidyl ether: KL-11, Liaoning Kelong Fine Chemical Co., Ltd.

[0053] The test methods in the examples and comparative examples are as follows:

[0054] The types of fluorine-containing monomers in the polymer were determined by NMR (Bruker 600MHz liquid nuclear magnetic resonance spectrometer) F spectrum analysis, and the content was calculated; the types of unsaturated acid monomers, end epoxy allyl polyether in the polymer were determined by H spectrum analysis, and the content was calculated.

[0055] The experimental sample was prepared into a tensile strip sample according to the requirements of standard ASTM D638 by an injection molding machine, and the tensile strength was tested.

[0056] The melt index of the experimental sample was tested according to standard ASTM D1238, and the test conditions were an experimental temperature of 230℃ and an experimental pressure of 5kg.

[0057] The intrinsic viscosity was tested according to standard T / FSI 027-2019, the solvent was dimethylacetamide, the test temperature was 30.0℃±0.1℃, a 0.58 dilution type Ubbelohde viscometer was used, and the four-point extrapolation method was used for calculation.

[0058] Preparation Example 1 (Polymer A-1)

[0059] Into a 10-liter high-pressure polymerization vessel, deionized water 4270 g, hydroxypropyl methylcellulose 2.5 g, diethyl carbonate 62.8 g were charged at room temperature, and the contents were mixed uniformly with stirring at 600 rpm. After the oxygen content was reduced to less than 20 ppm by nitrogen replacement under vacuum, tert-butyl peroxypivalate 7.2 g, 1,1- trifluoropropene 2440 g, trifluorochloroethylene 380 g, and maleic acid 1.3 g were added. The temperature was raised to 50°C, and the polymerization was started. The reaction temperature was lowered by circulating water, and after the temperature was stabilized, 0.6% aqueous maleic acid solution 2000 g was continuously added while maintaining the reaction pressure at 9.0 MPa. When the monomer addition was completed, the temperature was maintained at 50°C, and when the reaction pressure decreased to 3.0 MPa, the polymerization was terminated. The obtained polymer dispersion was degassed, washed with water, filtered, and dried at 80°C for 10 hours, thereby obtaining a fluorine-containing polymer resin powder.

[0060] Preparation Example 2 (Polymer A-2)

[0061] Into a 10-liter high-pressure polymerization vessel, deionized water 4270 g, hydroxypropyl methylcellulose 2.5 g, diethyl carbonate 62.8 g were charged at room temperature, and the contents were mixed uniformly with stirring at 600 rpm. After the oxygen content was reduced to less than 20 ppm by nitrogen replacement under vacuum, tert-butyl peroxypivalate 7.2 g, 1,1- trifluoropropene 2440 g, trifluorochloroethylene 380 g, and maleic acid 1.3 g were added. The temperature was raised to 50°C, and the polymerization was started. The reaction temperature was lowered by circulating water, and after the temperature was stabilized, 0.6% aqueous maleic acid solution 2000 g was continuously added while maintaining the reaction pressure at 9.0 MPa. When the monomer addition was completed, the temperature was maintained at 50°C, and when the reaction pressure decreased to 3.0 MPa, the polymerization was terminated. The obtained polymer dispersion was degassed, washed with water, filtered, and dried at 80°C for 10 hours, thereby obtaining a fluorine-containing polymer resin powder.

[0062] Preparation Example 3 (Polymer B-1)

[0063] Into a 10-liter high-pressure polymerization vessel, deionized water 4480 g, hydroxypropyl methylcellulose 2.5 g, diethyl carbonate 25.6 g were charged at room temperature, and the vessel was stirred at 600 rpm. The vessel was deoxygenated by purging with nitrogen gas several times under vacuum (oxygen content < 20 ppm), and then t-butyl peroxy pivalate 11.5 g, 1,1- trifluoroethylene 2560 g, and allyl glycidyl ether 0.8 g were added. The temperature was raised to 50°C, and the polymerization was started. The temperature was lowered by circulating water, and when the temperature was stabilized, 1800 g of 0.64% aqueous solution of allyl glycidyl ether was continuously added. The pressure was maintained at 9.0 MPa. When the addition of the monomers was completed, the temperature was maintained at 50°C, and when the pressure was lowered to 3.0 MPa, the polymerization was completed. The obtained polymer dispersion was degassed, washed with water, filtered, and dried at 80°C for 10 hours, thereby obtaining a fluorine-containing polymer resin powder.

[0064] Preparation Example 4 (Polymer B-2)

[0065] Into a 10-liter high-pressure polymerization vessel, deionized water 4480 g, hydroxypropyl methylcellulose 2.5 g, diethyl carbonate 12.4 g were charged at room temperature, and the vessel was stirred at 600 rpm. The vessel was deoxygenated by purging with nitrogen gas several times under vacuum (oxygen content < 20 ppm), and then t-butyl peroxy pivalate 10.2 g, 1,1- trifluoroethylene 2560 g, and allyl polyether glycidyl ether 1.0 g were added. The temperature was raised to 50°C, and the polymerization was started. The temperature was lowered by circulating water, and when the temperature was stabilized, 1800 g of 1.36% aqueous solution of allyl polyether glycidyl ether was continuously added. The pressure was maintained at 9.0 MPa. When the addition of the monomers was completed, the temperature was maintained at 50°C, and when the pressure was lowered to 3.0 MPa, the polymerization was completed. The obtained polymer dispersion was degassed, washed with water, filtered, and dried at 80°C for 10 hours, thereby obtaining a fluorine-containing polymer resin powder.

[0066] Preparation Example 5 (Polymer B-3)

[0067] Into a 10 liter high pressure polymerization reactor, 4480 g of deionized water and 2.5 g of hydroxypropyl methylcellulose were added at room temperature, and the reactor was stirred at 600 rpm. The reactor was purged with nitrogen several times to remove oxygen (oxygen content < 20 ppm) under vacuum, and then 9.0 g of t-butyl peroxy pivalate, 2560 g of 1,1- trifluoroethylene, and 2.4 g of allyl glycidyl ether were added. The temperature was raised to 50°C, and the polymerization reaction was started. The temperature was lowered by circulating water, and then 1800 g of 2.0% allyl glycidyl ether aqueous solution was continuously added when the reaction temperature was stabilized. The reaction pressure was maintained at 9.0 MPa. When the polymerization monomer addition was completed, the reaction temperature was maintained at 50°C, and the reaction pressure was reduced to 3.0 MPa, and the polymerization reaction was completed. The resulting polymer dispersion was degassed, washed with water, filtered, and then dried at 80°C for 10 hours, thereby obtaining a fluoropolymer resin powder.

[0068] The polymer analysis test data of the above-prepared pre-examples are shown in Table 1 below.

[0069] Table 1 Polymer analysis test data

[0070]

[0071]

[0072] Example

[0073] The powdered products of the polymers A and B prepared in the pre-examples were mixed in the mass ratio according to Table 2 below, and then high-temperature melt extrusion granulation was performed using a twin-screw extruder, and then the tensile strength of the prepared sample was tested according to the standard ASTM D638.

[0074] Table 2 Formulation of examples and tensile strength of products

[0075]

[0076]

[0077] Comparative Example 1

[0078] Into a 10-liter high-pressure polymerization reactor, 4300 g of deionized water, 2.5 g of hydroxypropyl methyl cellulose, and 51.3 g of diethyl carbonate were added at room temperature, and the mixture was stirred at a speed of 600 rpm. The oxygen was removed by purging nitrogen several times under vacuum (oxygen content < 20 ppm), and then 7.2 g of tert-butyl peroxy pivalate and 2510 g of 1,1- trifluoroethylene were added. The temperature was raised to 50°C, and the polymerization reaction was started. When the reaction temperature was stabilized, 2040 g of deionized water was continuously added, and the reaction pressure was maintained at 9.0 MPa. When the addition of deionized water was completed, the reaction temperature was maintained at 50°C, and the reaction pressure was reduced to 3.0 MPa, and the polymerization reaction was completed. The obtained polymer dispersion was degassed, washed with water, filtered, and then dried at 80°C for 10 hours, thereby obtaining a fluoropolymer resin powder. The prepared sample was tested, and the melt index (230°C / 5 kg) was 5.2 g / 10 min, the intrinsic viscosity was 1.1, and the tensile strength was 38.7 MPa.

[0079] Comparative Example 2

[0080] Into a 10-liter high-pressure polymerization reactor, 4510 g of deionized water, 2.5 g of hydroxypropyl methyl cellulose, and 62.8 g of diethyl carbonate were added at room temperature, and the mixture was stirred at a speed of 600 rpm. The oxygen was removed by purging nitrogen several times under vacuum (oxygen content < 20 ppm), and then 7.2 g of tert-butyl peroxy pivalate and 2440 g of 1,1- trifluoroethylene were added. The temperature was raised to 50°C, and the polymerization reaction was started. When the reaction temperature was stabilized, 2000 g of deionized water was continuously added, and the reaction pressure was maintained at 9.0 MPa. When the addition of deionized water was completed, the reaction temperature was maintained at 50°C, and the reaction pressure was reduced to 3.0 MPa, and the polymerization reaction was completed. The obtained polymer dispersion was degassed, washed with water, filtered, and then dried at 80°C for 10 hours, thereby obtaining a fluoropolymer resin powder. The prepared sample was tested, and the melt index (230°C / 5 kg) was 6.9 g / 10 min, the intrinsic viscosity was 1.0, and the tensile strength was 35.4 MPa.

[0081] From the above experimental test results, it can be seen that the tensile strength of the fluoropolymers prepared in the examples is significantly better than the comparative examples. Although the wide range of quantities and parameters described in the present application are approximate values, the numerical values described in the specific examples are reported as accurately as possible, and any numerical value inherently contains certain errors resulting from the standard deviation found in their respective experimental measurements. However, it can still be shown that the present application uses perhalogenated vinyl monomers, (meth) acrylic monomers and vinylidene fluoride to copolymerize and modify the base PVDF resin, and then copolymerize the vinylidene fluoride with the epoxy-terminated allyl polyether to prepare the fluoropolymer, which is blended with the base PVDF resin in a certain proportion to modify the base PVDF resin. The prepared fluoropolymer has excellent tensile strength.

Claims

1. A method for preparing a high tensile strength fluoropolymer, comprising the steps of: 1) copolymerizing 1,1-vinylidene fluoride, a halogenated vinyl monomer and an unsaturated acid monomer to prepare a fluoropolymer A, wherein the tensile strength of the fluoropolymer A is not less than 30 MPa, and the melt index is 2.0-10.0 g / 10 min, the melt index being tested according to the standard ASTM D1238, the test conditions being a test temperature of 230 °C and a test pressure of 5 kg; the halogenated vinyl monomer being selected from one or more of tetrafluoroethylene, trifluorochloroethylene, hexafluoropropylene, perfluorobutyl ethylene, perfluoromethyl ether, perfluoroethyl vinyl ether, perfluoropropyl vinyl ether, perfluorobutyl vinyl ether; the halogenated vinyl monomer being 0.01-10% of the total mass of the fluoropolymer A; the unsaturated acid monomer being 0.01-5% of the total mass of the fluoropolymer A; 2) copolymerizing 1,1-vinylidene fluoride with an epoxy-terminated allyl polyether to prepare a fluoropolymer B, wherein the epoxy-terminated allyl polyether has the structural formula wherein n is an integer less than 20; the epoxy-terminated allyl polyether being 0.01-5% of the total mass of the fluoropolymer B, and the intrinsic viscosity of the fluoropolymer B being greater than 1.7 dL / g; 3) blending the fluoropolymer A and the fluoropolymer B in a ratio of 20:1-4:1 to obtain a high tensile strength fluoropolymer having a tensile strength of not less than 50 MPa.

2. The method of claim 1, wherein, In the epoxy-terminated allyl polyether, n = 1-10.

3. The method of claim 2, wherein, The epoxy-terminated allyl polyether is selected from allyl glycidyl ether and / or allyl polyether glycidyl ether.

4. The method of claim 1, wherein, The epoxy-terminated allyl polyether is added in an amount of 0.1-2% of the total mass of the fluoropolymer B.

5. The method of claim 1, wherein, The halogenated vinyl monomer is 0.1-5% of the total mass of the fluoropolymer A.

6. The method of claim 1, wherein, The unsaturated acid monomer is selected from at least one of acrylic acid, methacrylic acid, itaconic acid, maleic acid, cinnamic acid.

7. The method of claim 1, wherein, The unsaturated acid monomer is 0.1-3% of the total mass of the fluoropolymer A.

8. The method of claim 1, wherein, The tensile strength of the fluoropolymer A is not less than 40 MPa, and the melt index is 4.0-8.0 g / 10 min, the melt index being tested according to the standard ASTM D1238, the test conditions being a test temperature of 230 °C and a test pressure of 5 kg.

9. The method of claim 1, wherein, The intrinsic viscosity of the fluoropolymer B is greater than 2.0 dL / g.

10. The method of claim 1, wherein, The tensile strength of the high tensile strength fluoropolymer is not less than 60 MPa.

11. A high tensile strength fluoropolymer prepared by the method according to any one of claims 1-10.

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