Ethylene-tetrafluoroethylene copolymer emulsion and preparation method thereof

Abstract

The invention relates to the technical field of fluorine-containing polymers, in particular to an ethylene-tetrafluoroethylene copolymer emulsion and a preparation method thereof. The preparation method comprises the step of adding a dispersing agent in the preparation process of the ethylene-tetrafluoroethylene copolymer emulsion, wherein the dispersing agent is a fluorine-containing surfactant containing an olefin structure. The dispersing agent introduced by the method can be used as a dispersing agent for reducing the surface tension of water and improving the gas solubility, and also can participate in polymerization so as to improve the performance of a copolymer, so that the traditional perfluoroalkyl dispersing agent is replaced, and the environment pollution caused by the existence of PFAS in an emulsion is avoided; the adhesive capacity of the ethylene-tetrafluoroethylene copolymer is also improved; and the stability of the ethylene-tetrafluoroethylene copolymer emulsion is enhanced, so that the addition amount of the emulsifier can be reduced in the subsequent concentration stage, and the influence on the performance and appearance of the coating due to residue in the subsequent sintering preparation process of the coating is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of fluorine-containing polymers, and in particular to an ethylene-tetrafluoroethylene copolymer emulsion and a preparation method thereof. Background Art

[0002] Ethylene-tetrafluoroethylene copolymer (ETFE) is a fluoropolymer with special properties formed by the copolymerization of tetrafluoroethylene and ethylene. It not only maintains the excellent electrical insulation, chemical resistance and aging resistance of polytetrafluoroethylene, but also significantly improves the toughness, radiation resistance, mechanical properties and creep resistance of the copolymer by the addition of ethylene, making it widely used in many fields such as pipeline lining, kettle, valve pump, stirring paddle and other chemical corrosion protection, electronic and medical equipment, modern membrane structure building materials, semiconductors, solar backplane membrane and fuel cell diaphragm. At present, various industries mainly use powder electrostatic spraying process to coat ethylene-tetrafluoroethylene copolymer powder on the surface of various large devices, so most of the research on ethylene-tetrafluoroethylene copolymer resin powder is done. However, for small devices, coatings and emulsion coatings required in various fields, it is simpler and more economical to use ethylene-tetrafluoroethylene copolymer emulsion with high solid content and strong adhesion to coat by dipping process.

[0003] At present, there are many methods for preparing ethylene-tetrafluoroethylene copolymer resin powder, but there are very few related patents for its emulsion preparation. Patent application CN103524659A discloses a tetrafluoroethylene-ethylene copolymer emulsion and its preparation method. The method uses aliphatic olefinic acid as a dispersant and a third monomer for preparation. The surface tension of aliphatic olefinic acid is large and it is difficult to initiate polymerization. Although high pressure is used to promote the polymerization reaction in the patent application, the increase in pressure will greatly increase the danger of the entire reaction system; the dispersant is added once, and the obtained emulsion particle size is large, and the application range is limited; the high polymerization reaction temperature is easy to cause ethylene branching, and the obtained copolymer has more alkane chains, and the appearance of the product will turn yellow or black in subsequent processing applications. Patent application CN117946346A discloses a modified ethylene-tetrafluoroethylene copolymer and its preparation method. The preparation method not only uses PFAS-type fluorinated surfactants restricted by relevant regulations, which will cause harm to human health and the living environment, but also the ethylene-tetrafluoroethylene copolymer emulsion prepared by it has a low solid content. Although the solid content of the ethylene-tetrafluoroethylene copolymer emulsion prepared in patent application CN101302262A is relatively high, the PFAS-type perfluorinated dispersant restricted by relevant laws and regulations on environmental pollution is also used in the polymerization. Patent application CN110023402A prepares an ethylene-tetrafluoroethylene copolymer dispersion and their coating. Although there is no non-fluorinated surfactant in the dispersion and the solid content of the dispersion is relatively high, the emulsion prepared by the emulsion has a high emulsifier content, which usually remains in the subsequent sintering process to prepare the coating, directly affecting the performance and appearance of the product. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides an ethylene-tetrafluoroethylene copolymer emulsion and a preparation method thereof.

[0005] In the first aspect, the present invention provides a method for preparing an ethylene-tetrafluoroethylene copolymer emulsion, which includes adding a dispersant during the preparation of the ethylene-tetrafluoroethylene copolymer emulsion, wherein the dispersant is a fluorinated surfactant containing an olefin structure. The method for preparing an ethylene-tetrafluoroethylene copolymer emulsion proposed by the present invention, by introducing a specific dispersant that can participate in the polymerization reaction type, can be used as a dispersant to reduce the surface tension of water and increase the solubility of gas, and can also be used as a third monomer to participate in the polymerization to improve the performance of the copolymer. It not only replaces the traditional perfluoroalkyl dispersant, avoiding the presence of PFAS in the emulsion to pollute the environment; at the same time, the presence of the carboxylic acid structure at the end of the molecule also improves the adhesion ability of the ethylene-tetrafluoroethylene copolymer; it also enhances the stability of the ethylene-tetrafluoroethylene copolymer emulsion, so that the amount of emulsifier added can be reduced in the subsequent concentration stage, avoiding residues in the subsequent sintering process to prepare the coating, affecting the coating performance and appearance.

[0006] Preferably, the dispersant is a fluorinated or perfluorinated olefinic acid.

[0007] More preferably, the dispersant is one of 2,2,3,3,4,4-hexafluoro-5-hexenoic acid, 2,2,3,3-tetrafluoro-4-pentenoic acid, 2,2,3,3,4-pentafluoro-4-pentenoic acid, 2,2,3,3-tetrafluoro-3-[(1,2,2-trifluorovinyl)oxy]propionic acid, and 2,2,3,3,4,4-hexafluoro-4-[(1,2,2-trifluorovinyl)oxy]butyric acid. In the present invention, the preferred type of dispersant is used, which has a better effect, can significantly improve the various properties of the ethylene-tetrafluoroethylene copolymer emulsion, improve the quality of the product, and optimize the production process.

[0008] More preferably, 0.05% to 0.1% of the mass of deionized water is added as a dispersant before the reaction, and then the dispersant is continuously added.

[0009] In the present invention, in order to effectively improve the state of particles in the emulsion, obtain a dispersion with a larger particle size and a narrow distribution range, increase the ultimate film crack thickness of the emulsion, and make the coating processing performance better (such as the particle size range mentioned in patent application CN112552530A is preferably between 0.26um and 0.32um), 0.05% to 0.1% of the mass of deionized water is added to the kettle before the reaction, and then the dispersant is continuously added.

[0010] Preferably, the molar ratio of the amount of the continuously added dispersant to the amount of ethylene and tetrafluoroethylene in the added mixed gas is (0.1-0.5): (45-60): (40-55).

[0011] Preferably, when the solid content of the reaction solution is 38% to 40%, the addition of the dispersant is stopped and the reaction is continued for not less than 30 minutes.

[0012] In the present invention, in order to allow the dispersant to be completely attached to the polymer chain segments without remaining in the emulsion, and at the same time control the surface tension of the reaction medium to stabilize the reaction rate and maintain the stability of the polymerization reaction liquid system, the addition of the dispersant is stopped when the solid content of the reaction liquid is 38% to 40%, and the reaction is terminated after continuing the reaction for no less than 30 minutes.

[0013] According to the present invention, the solid content of the reaction liquid during the reaction is calculated by estimating the weight percentage of the polymerized monomers reacted in the entire system to the weight percentage of the entire system, and the weight of the mixed gas of ethylene and tetrafluoroethylene is estimated by the cumulative pressure drop during the reaction.

[0014] According to a preferred embodiment of the present invention, the method for preparing the ethylene-tetrafluoroethylene copolymer emulsion comprises the following steps: 1) Mix deionized water, part of the dispersant and the chain transfer agent, control the reaction temperature of the system, and introduce the initial mixed gas of ethylene and tetrafluoroethylene to the reaction pressure.

[0015] 2) Add part of the initiator, and continuously add the additional mixed gas of ethylene and tetrafluoroethylene during the reaction to maintain the reaction pressure, and continuously add the remaining dispersant, and continuously add the remaining initiator during the reaction to obtain an ethylene-tetrafluoroethylene copolymer polymerization liquid.

[0016] 3) adding an emulsifier to the ethylene-tetrafluoroethylene copolymer polymerization liquid, and concentrating the mixture under vacuum to obtain an ethylene-tetrafluoroethylene copolymer emulsion.

[0017] Preferably, the reaction pressure is 1.5 MPa to 2.5 MPa, and the reaction temperature is 30° C. to 45° C. More preferably, the reaction pressure is 1.8 MPa to 2.5 MPa, and the reaction temperature is 38° C. to 40° C. Under the preferred reaction conditions, the prepared ethylene-tetrafluoroethylene copolymer emulsion has better effects.

[0018] Preferably, the molar ratio of ethylene to tetrafluoroethylene in the initial mixed gas is 20:80 to 30:70.

[0019] Preferably, the molar ratio of ethylene to tetrafluoroethylene in the added mixed gas is 45:55 to 55:45.

[0020] Preferably, the chain transfer agent is one of diethyl malonate and diethyl oxalate, and the amount of the chain transfer agent is 0.01% to 0.1% of the mass of deionized water.

[0021] Preferably, the initiator is an oxidation-reduction system initiator.

[0022] In the present invention, in order to avoid the polymerization reaction temperature being too high, so that the ethylene monomer produces a branched structure during the polymerization process (an alkane branched structure other than the third monomer is produced on the polymer main chain), which causes the coating to turn black after high-temperature sintering, the initiator used is an oxidation-reduction system initiator.

[0023] Preferably, the oxidant in the oxidation-reduction system initiator is potassium permanganate, and the amount of the oxidant is 0.02% to 0.06% of the mass of deionized water; the reducing agent in the initiator is ammonium oxalate, and the amount of the oxidant is 0.05% to 0.15% of the mass of deionized water.

[0024] In the present invention, in order to increase the molecular weight of ethylene-tetrafluoroethylene copolymer and make it have excellent mechanical properties in later processing applications, the initiator is added in a manner of adding all the reducing agent into the kettle at once before the reaction, and after reaching the reaction temperature, continuously adding an oxidant aqueous solution with a mass fraction of 0.1% to initiate the reaction.

[0025] Preferably, the emulsifier is a secondary alcohol polyoxyethylene ether; preferably, the amount of the secondary alcohol polyoxyethylene ether is 1.0% to 2.0% of the solid mass in the ethylene-tetrafluoroethylene copolymer polymerization liquid (ie, the solid content of the polymerization liquid).

[0026] Preferably, the secondary alcohol polyoxyethylene ether is TMN-10 product of DOW Company.

[0027] In the present invention, in order to ensure the stability of the emulsion and prevent the excessive addition of the emulsifier from affecting subsequent processing, the amount of the secondary alcohol polyoxyethylene ether is 1.0% to 2.0% of the solid mass in the ethylene-tetrafluoroethylene copolymer polymer solution.

[0028] More preferably, the prepared ethylene-tetrafluoroethylene copolymer polymerization liquid is concentrated to a solid content of 59% to 61%.

[0029] In a second aspect, the present invention provides an ethylene-tetrafluoroethylene copolymer emulsion obtained by the above-mentioned preparation method.

[0030] Preferably, the particle size of the ethylene-tetrafluoroethylene copolymer emulsion is in the range of 0.26 μm to 0.31 μm, preferably 0.28 μm to 0.31 μm; the solid content is 59.5% to 60.8%, preferably 59.8% to 60.5%; the stability is >240S, preferably >250S; and the dispersant content is <2ppb, preferably <1ppb.

[0031] In the present invention, the particle size range is between 0.26 μm and 0.31 μm, preferably 0.28 μm to 0.31 μm, such as 0.28 μm, 0.29 μm, 0.30 μm, 0.31 μm, etc., and any range therebetween. The solid content is 59.5% to 60.8%, preferably 59.8% to 60.5%, such as 59.8%, 59.9%, 60.1%, 60.2%, 60.5%, etc., and any range therebetween. The stability is >240S, preferably >250S. The dispersant content is <2 ppb, preferably <1 ppb. The preparation method of the present invention can obtain an emulsion with a better particle size range, which is helpful to improve the processing performance of the coating. At the same time, the appropriate solid content can improve the concentration efficiency. The solid content range of the emulsion before concentration is 38%~40%, and the solid content of the emulsion after concentration can reach 59.5%~60.8%. The emulsion has a longer demulsification time (>250S) at a specific speed, which significantly enhances the stability of the emulsion, reduces the excessive addition of emulsifier, and is helpful for subsequent processing. At the same time, the present invention well controls the dispersant content in the emulsion to be less than 1ppb. The present invention can effectively improve the performance of ethylene-tetrafluoroethylene copolymer emulsion and ensure its comprehensive performance and effect in practical applications.

[0032] The beneficial effects of the present invention are at least as follows: the preparation method of the ethylene-tetrafluoroethylene copolymer emulsion proposed in the present invention can be applied to various industries and fields that use the dipping process, such as various small devices, coatings and paints. The method of the present invention introduces a dispersant that can participate in the polymerization reaction, which can be used as a dispersant to reduce the surface tension of water and increase the solubility of gas, and can also be used as a third monomer to participate in the polymerization to improve the performance of the copolymer. The introduction of the reactive dispersant replaces the traditional perfluoroalkyl dispersant, avoiding the presence of PFAS in the emulsion to pollute the environment; at the same time, the presence of the third monomer also improves the adhesion ability of the ethylene-tetrafluoroethylene copolymer; and enhances the stability of the ethylene-tetrafluoroethylene copolymer emulsion, so that the amount of emulsifier added can be reduced in the subsequent concentration stage, thereby avoiding residues in the subsequent sintering process to prepare the coating, affecting the coating performance and appearance. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] Unless otherwise specified, the raw materials and reagents used in the following examples are all commercially available products or can be prepared by known methods. If no specific techniques or conditions are specified in the examples, they are all conventional methods or the techniques or conditions described in the literature in this field, or according to the product instructions. If the manufacturers of the reagents and instruments are not specified, they are all conventional products that can be purchased through regular channels.

[0035] Example 1 This embodiment provides an ethylene-tetrafluoroethylene copolymer emulsion, and the specific steps of the preparation method are as follows: Into a 20L reactor, 11 kg of deionized water, 8 g of 2,2,3,3,4,4-hexafluoro-5-hexenoic acid, 6 g of diethyl malonate and 11 g of ammonium oxalate were respectively added, the reactor system was evacuated and replaced to an oxygen content of ≤30 ppm, the temperature of the reaction system was raised to 40°C, and an initial mixed gas of ethylene and tetrafluoroethylene (molar ratio = 25:75) was passed into the reactor through a press until the pressure reached 2.0 MPa.

[0036] 600 g of a 0.1% by mass potassium permanganate aqueous solution was slowly added through a metering pump to initiate polymerization, and at the same time, a mixed gas of ethylene and tetrafluoroethylene was introduced through a press to maintain the pressure of the reactor at 2.0 MPa, and 2,2,3,3,4,4-hexafluoro-5-hexenoic acid was continuously added through a metering pump, and the molar ratio of ethylene / tetrafluoroethylene / 2,2,3,3,4,4-hexafluoro-5-hexenoic acid added was 49.6:50:0.4. When the solid content of the reaction system was 38.4%, the addition of 2,2,3,3,4,4-hexafluoro-5-hexenoic acid was stopped, and the reaction was continued for 30 minutes, and then the addition of the mixed monomer and initiator was stopped to terminate the reaction.

[0037] After the polymerization reaction was completed, an emulsifier with a solid content of 1% of the polymerization liquid was added and vacuum concentrated to obtain an ethylene-tetrafluoroethylene copolymer emulsion with a solid content of 60.2%, and the performance was tested.

[0038] Example 2 This embodiment provides an ethylene-tetrafluoroethylene copolymer emulsion and a preparation method thereof. The difference from Embodiment 1 is that the initial mixed gas molar ratio of ethylene and tetrafluoroethylene is 23:77, and the dispersant is replaced by "2,2,3,3,4,4-hexafluoro-5-hexenoic acid" with "2,2,3,3-tetrafluoro-4-pentenoic acid".

[0039] Example 3 This embodiment provides an ethylene-tetrafluoroethylene copolymer emulsion and a preparation method thereof. The difference from Embodiment 1 is that the dispersant is replaced by "2,2,3,3,4,4-hexafluoro-5-hexenoic acid" with "2,2,3,3,4-pentafluoro-4-pentenoic acid"; the molar ratio of ethylene / tetrafluoroethylene / 2,2,3,3,4-pentafluoro-4-pentenoic acid continuously added during the reaction is 49.8:49.8:0.4.

[0040] Example 4 The present embodiment provides an ethylene-tetrafluoroethylene copolymer emulsion and a preparation method thereof. The difference from Example 1 is that the reaction pressure is changed to 1.8 MPa, the dispersant is replaced by "2,2,3,3,4,4-hexafluoro-5-hexenoic acid" with "2,2,3,3-tetrafluoro-3-[(1,2,2-trifluorovinyl)oxy]propionic acid", and the molar ratio of ethylene / tetrafluoroethylene / 2,2,3,3-tetrafluoro-3-[(1,2,2-trifluorovinyl)oxy]propionic acid continuously added during the reaction is 50:49.7:0.3.

[0041] Example 5 The present embodiment provides an ethylene-tetrafluoroethylene copolymer emulsion and a preparation method thereof. The difference from Example 1 is that the reaction pressure is 2.5 MPa, the dispersant is replaced by "2,2,3,3,4,4-hexafluoro-5-hexenoic acid" with "2,2,3,3,4,4-hexafluoro-4-[(1,2,2-trifluorovinyl)oxy]butyric acid", 10 g of 2,2,3,3,4,4-hexafluoro-4-[(1,2,2-trifluorovinyl)oxy]butyric acid is added at one time before the reaction, the molar ratio of ethylene / tetrafluoroethylene / 2,2,3,3,4,4-hexafluoro-4-[(1,2,2-trifluorovinyl)oxy]butyric acid continuously added during the reaction is 50:49.8:0.2, and the amount of emulsifier added is 2.0%.

[0042] Example 6 This embodiment provides an ethylene-tetrafluoroethylene copolymer emulsion and a preparation method thereof, which is different from Embodiment 1 only in that the chain transfer agent is replaced by "8 g diethyl oxalate" from "6 g diethyl malonate".

[0043] Comparative Example 1 This comparative example provides a method for preparing an ethylene-tetrafluoroethylene copolymer emulsion, which is different from Example 1 in that the dispersant is added into the reactor all at once before the reaction.

[0044] Comparative Example 2 This comparative example provides a method for preparing an ethylene-tetrafluoroethylene copolymer emulsion, which is different from Example 1 in that the reaction is terminated immediately after the addition of the dispersant is stopped.

[0045] Comparative Example 3 This comparative example provides a method for preparing an ethylene-tetrafluoroethylene copolymer emulsion, which is different from Example 1 in that the amount of the emulsifier added in the concentration stage is replaced by "50 g" from "80 g".

[0046] Comparative Example 4 This comparative example provides a method for preparing an ethylene-tetrafluoroethylene copolymer emulsion, which is different from Example 1 in that the perfluoro dispersant in patent application CN101302262A is used for preparation.

[0047] Comparative Example 5 This comparative example provides a method for preparing an ethylene-tetrafluoroethylene copolymer emulsion, which is different from Example 1 in that the aliphatic olefinic acid in patent application CN103524659A is used for preparation. Under the reaction pressure conditions of Example 1, no polymerization reaction occurs; and after the pressure is further increased to 2.5 MPa, no reaction occurs.

[0048] Experimental Example 1 The ethylene-tetrafluoroethylene copolymer emulsions obtained in the examples and comparative examples were subjected to performance tests, wherein the stability was determined by the time it took for the emulsion to break at 25°C when the high shear emulsifier was operated at a certain speed (15000 r / min); the solid content was tested according to the method in standard GB / T 2793-1995; the average particle size was tested according to the method in standard GB / T 19077.1-2008; the dispersant content was tested by breaking the emulsion, filtering it, and then measuring the content of the filtrate by liquid chromatography-mass spectrometry according to the determination method in patent application CN115825291A.

[0049] Table 1

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing an ethylene-tetrafluoroethylene copolymer emulsion, characterized in that: The method comprises adding a dispersant during the preparation process of the ethylene-tetrafluoroethylene copolymer emulsion, wherein the dispersant is a fluorine-containing surfactant containing an olefin structure.

2. The method for preparing the ethylene-tetrafluoroethylene copolymer emulsion according to claim 1, characterized in that: The dispersant is one of 2,2,3,3,4,4-hexafluoro-5-hexenoic acid, 2,2,3,3-tetrafluoro-4-pentenoic acid, 2,2,3,3,4-pentafluoro-4-pentenoic acid, 2,2,3,3-tetrafluoro-3-[(1,2,2-trifluorovinyl)oxy]propionic acid, and 2,2,3,3,4,4-hexafluoro-4-[(1,2,2-trifluorovinyl)oxy]butyric acid.

3. The method for preparing the ethylene-tetrafluoroethylene copolymer emulsion according to claim 2, characterized in that: Before the reaction, 0.05% to 0.1% of the mass of deionized water is added as dispersant, and then the dispersant is continuously added; Preferably, the molar ratio of the amount of the continuously added dispersant to the amount of ethylene and tetrafluoroethylene in the added mixed gas is (0.1-0.5): (45-60): (40-55).

4. The method for preparing the ethylene-tetrafluoroethylene copolymer emulsion according to any one of claims 1 to 3, characterized in that: The following steps are involved: 1) Mix deionized water, part of the dispersant and the chain transfer agent, control the reaction temperature of the system, and introduce the initial mixed gas of ethylene and tetrafluoroethylene to the reaction pressure; 2) adding part of the initiator, continuously adding the additional mixed gas of ethylene and tetrafluoroethylene during the reaction to maintain the reaction pressure, and continuously adding the remaining dispersant, continuously adding the remaining initiator during the reaction to obtain an ethylene-tetrafluoroethylene copolymer polymerization liquid; 3) adding an emulsifier to the ethylene-tetrafluoroethylene copolymer polymerization liquid, and concentrating the mixture under vacuum to obtain an ethylene-tetrafluoroethylene copolymer emulsion.

5. The method for preparing the ethylene-tetrafluoroethylene copolymer emulsion according to claim 4, characterized in that: The reaction pressure is 1.5MPa to 2.5MPa; the reaction temperature is 30°C to 45°C; and / or, the molar ratio of ethylene to tetrafluoroethylene in the initial mixed gas is 20:80 to 30:70; And / or, the molar ratio of ethylene to tetrafluoroethylene in the added mixed gas is 45:55 to 55:

45.

6. The method for preparing the ethylene-tetrafluoroethylene copolymer emulsion according to claim 4, characterized in that: The chain transfer agent is one of diethyl malonate and diethyl oxalate; preferably, the amount of the chain transfer agent is 0.01% to 0.1% of the mass of deionized water.

7. The method for preparing the ethylene-tetrafluoroethylene copolymer emulsion according to any one of claims 4 to 6, characterized in that: The initiator is an oxidation-reduction system initiator; Preferably, the oxidant in the oxidation-reduction system initiator is potassium permanganate, and the amount of the oxidant is 0.02% to 0.06% of the mass of deionized water; And / or, the reducing agent in the oxidation-reduction system initiator is ammonium oxalate, and the amount of the reducing agent is 0.05% to 0.15% of the mass of deionized water.

8. The method for preparing the ethylene-tetrafluoroethylene copolymer emulsion according to any one of claims 4 to 6, characterized in that: The emulsifier is secondary alcohol polyoxyethylene ether; preferably, the amount of the secondary alcohol polyoxyethylene ether is 1.0% to 2.0% of the solid mass in the ethylene-tetrafluoroethylene copolymer polymerization liquid.

9. The method for preparing the ethylene-tetrafluoroethylene copolymer emulsion according to any one of claims 4 to 6, characterized in that: The prepared ethylene-tetrafluoroethylene copolymer polymerization liquid is concentrated to a solid content of 59% to 61%.

10. The ethylene-tetrafluoroethylene copolymer emulsion obtained by the preparation method according to any one of claims 1 to 9.

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