A post-treatment method for fluorinated polymer emulsion

Abstract

The present invention discloses a post-processing method for a fluoropolymer emulsion, comprising: (1) filtering the fluoropolymer emulsion and then diluting it to obtain a diluted fluoropolymer emulsion; (2) adding a composite coagulant to the diluted fluoropolymer emulsion at an initial stirring speed of 300-500 rpm, and reducing the stirring speed in stages according to an acoustic wave signal generated during a coagulation process, wherein when the acoustic wave signal increases to 70-80 decibels, the stirring speed is reduced to 200-300 rpm; when the acoustic wave signal decreases to 30-40 decibels, the stirring speed is reduced to 100-200 rpm until the coagulation is completed to obtain a coagulation product; (3) washing the coagulation product to obtain a washed product; and (4) drying the washed product to obtain a fluoropolymer resin. The present invention has the advantages of simple process and good product performance.

Description

Technical Field

[0001] The invention belongs to the field of fluorine-containing polymers, and particularly relates to a post-processing method for a fluorine-containing polymer emulsion. Background Art

[0002] Fluoropolymer resins have excellent electrical insulation, high temperature resistance, chemical resistance, low friction coefficient, and excellent dielectric properties. They can be used in many fields such as cables, pipes, membranes, pump valve linings, etc. The production process of fluoropolymer resins such as THV resin (tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride copolymer) mainly includes polymerization, coagulation, washing, drying, and granulation. Among them, coagulation is the process of separating the fluoropolymer resin emulsion from a single liquid phase of the emulsion into two phases, a solid phase and an aqueous phase, and is an important step in the post-processing process of fluoropolymer resins. Traditional methods for coagulating fluoropolymer dispersions include: physical and chemical methods. In the physical method, a stirring device can be used to subject the dispersion to strong (high) shear force, thereby causing the particles to coagulate (usually using a rotor and stator with a shear rate exceeding 1000 (1 / s)). Another method of physical coagulation is the freeze-thaw method. The dispersion is cooled enough to freeze, which makes the dispersion unstable, so that the coagulates separate from the liquid when thawing. Generally speaking, due to scalability and intensive energy requirements, this technology is not preferred in large-scale production. In the chemical coagulation method, electrolytes or inorganic salts are added to the dispersion, which reduces the stability of the dispersion and causes coagulation.

[0003] For example, CN1910203A discloses a coagulation method and composition for fluoropolymers. The invention provides a method for producing a fully halogenated elastomer, which includes the step of using an onium compound to coagulate a latex containing polymer particles, wherein the polymer particles are basically composed of copolymerized units of one or more fully halogenated comonomers and at least one vulcanization site monomer, wherein the coagulation step is basically carried out in the absence of metal ions and metal salts.

[0004] For example, CN103221479A discloses a method for coagulating fluoropolymer latex, which comprises: providing an amorphous fluoropolymer latex; providing unmodified inorganic nanoparticles; and contacting the amorphous fluoropolymer latex with a sufficient amount of unmodified inorganic nanoparticles to coagulate the amorphous fluoropolymer.

[0005] For example, CN109762081A discloses a continuous coagulation method and pipeline emulsifier for fluoropolymer emulsions. The continuous coagulation method involves continuously feeding a mixture of fluoropolymer emulsion and water into a pipeline emulsifier for continuous demulsification to produce fluoropolymer solids. This continuous coagulation method overcomes the shortcomings of existing coagulation methods, such as the need for additives, increased steam consumption, and poor demulsification effects. It improves emulsion demulsification efficiency, reduces the solids content in the wastewater after demulsification, and mitigates the environmental impact of the wastewater.

[0006] The above existing coagulation methods can simplify the coagulation process, reduce costs, and / or lower the metal ion content during the coagulation of amorphous fluoropolymer latex. However, during the coagulation process, fluoropolymer resins such as THV resins are prone to sticking and agglomerating, resulting in uneven dispersion, affecting the apparent density of the product, and further affecting the oil absorption and discharge performance during processing. Ultimately, the product surface is rough, stress concentration occurs, and the product performance is poor. Clearly, controlling the particle size and uniformity of the coagulated fluoropolymer resin is crucial. Summary of the Invention

[0007] The purpose of the present invention is to provide a post-treatment method for fluorine-containing polymer emulsion with simple process and good product performance in view of the shortcomings of the existing technology.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is: a post-treatment method of a fluoropolymer emulsion, comprising the following steps:

[0009] (1) filtering and diluting the fluoropolymer emulsion to obtain a diluted fluoropolymer emulsion;

[0010] (2) adding a composite coagulant to the diluted fluoropolymer emulsion at an initial stirring speed of 300-500 rpm, and reducing the stirring speed in stages according to the acoustic wave signal generated during the coagulation process. When the acoustic wave signal increases to 70-80 decibels, the stirring speed is reduced to 200-300 rpm; when the acoustic wave signal decreases to 30-40 decibels, the stirring speed is reduced to 100-200 rpm until the coagulation is completed to obtain a coagulation product;

[0011] (3) washing the condensed product obtained in step (2) to obtain a washed product;

[0012] (4) drying the washed product obtained in step (3) to obtain a fluorine-containing polymer resin.

[0013] As a preferred embodiment of the present invention, the fluorine-containing polymer is one of tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymer (THV), polyperfluoroethylene propylene (FEP), polyvinylidene fluoride (PVDF), fusible polytetrafluoroethylene (PFA), and polytetrafluoroethylene (PTFE).

[0014] As a preferred embodiment of the present invention, the solid content of the fluoropolymer emulsion is 25-30 wt% (wt%, mass percentage), and the solid content of the diluted fluoropolymer emulsion is 10-15 wt%.

[0015] As a preferred embodiment of the present invention, the condensation temperature is 25-30°C.

[0016] As a preferred embodiment of the present invention, in step (2), the stirring speed is reduced to 100-200 rpm and then maintained at this speed for 30-60 seconds.

[0017] As a preferred embodiment of the present invention, the composite coagulant is ammonium bicarbonate or a mixture of ammonium carbonate and nano-silicon dioxide, the mass ratio of ammonium bicarbonate or ammonium carbonate to nano-silicon dioxide in the mixture is 1 to 50:1; the mixture is dispersed and dissolved in deionized water at 5-50wt%.

[0018] As a preferred embodiment of the present invention, the median particle size of the nano-silica is 20-100 nm.

[0019] As a preferred embodiment of the present invention, the amount of the compounded coagulant is 0.01-0.1 wt% of the mass of the fluoropolymer emulsion.

[0020] As a preferred embodiment of the present invention, the washing temperature is 10-20° C., and the stirring speed is 100-200 rpm.

[0021] As a preferred embodiment of the present invention, the drying temperature is 160-200° C. and the drying time is 12-24 hours.

[0022] The morphology of the agglomerated particles of the fluoropolymer emulsion is closely related to its processing performance. The present invention optimizes the post-processing process of the fluoropolymer emulsion, strictly controls the temperature, stirring speed and operation time at each stage of the post-processing, particularly adds a compound coagulant during the agglomeration process, and continuously reduces the stirring speed according to the acoustic wave signal generated during the agglomeration process, thereby affecting the morphology, size and distribution of the fluoropolymer emulsion particles. Finally, the particles are washed and dried at low temperature. The obtained fluoropolymer resin particles have a narrow particle size distribution, are full and round, have good fluidity, are not prone to adhesion and agglomeration, have good processing performance, and have excellent finished product appearance and mechanical properties.

[0023] In the present invention, the compound coagulant is a mixture of ammonium bicarbonate or ammonium carbonate and nano-silicon dioxide. Nano-silicon dioxide has a large specific surface area, and even a very small amount can achieve an effective contact area with the fluororesin, effectively increasing the fluidity between particles while also reinforcing and plasticizing the finished product. Ammonium bicarbonate or ammonium carbonate, as a conventional coagulant, synergizes with nano-silicon dioxide to effectively increase the fluidity between coagulants, reduce resin agglomeration, fiberization, and adhesion, and increase the tensile strength and elongation at break of the finished resin product.

[0024] In the present invention, the stirring speed is continuously reduced according to the sound wave signal generated in the coagulation process, and a sound wave recorder is turned on before the coagulation starts. After removing the noise background, the sound wave signal is a smooth line. As the stirring is turned on, the sound wave signal curve gradually rises and stabilizes at about 40-50 decibels. After mixing for a period of time, the sound wave signal gradually increases to about 70-80 decibels, and resin particles are continuously coagulated. At this time, the stirring speed is reduced to 200-300 rpm / min to reduce the shear force of stirring on the resin and avoid the occurrence of resin fiberization caused by high shear. When the sound wave signal reaches a maximum point of about 90-100 decibels, coagulants are quickly precipitated and the sound wave signal begins to decrease. When the sound wave signal decreases to 30-40 decibels, the stirring speed is reduced to 100-200 rpm and maintained at this speed for 30-60 seconds. At this time, the resin is basically completely precipitated, and there is no need for medium or high speed shearing to break the emulsion. The collision probability between the resin particles is further increased by low-speed stirring, so that resin particles with higher regularity are formed and the resin particle size distribution is reduced.

[0025] In the present invention, the washing temperature is 10-20° C. and the stirring speed is 100-200 rpm. Low-temperature washing is adopted because the resin has better fluidity at low temperatures and can avoid the resin from agglomerating during the washing process.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] 1. The process is simple and the treatment effect is good. The present invention optimizes the post-treatment process of the fluoropolymer emulsion, strictly controls the temperature, stirring speed and operation time of each stage of the post-treatment, especially adds a compound coagulant during the coagulation process, and continuously reduces the stirring speed according to the acoustic wave signal generated during the coagulation process, thereby affecting the morphology, size and distribution of the fluoropolymer emulsion particles. Finally, low-temperature washing and drying are performed. The obtained fluoropolymer resin particles have a narrow particle size distribution, are full and round, have good fluidity, are not prone to adhesion and agglomeration, have good processing performance, and the finished product has excellent appearance and mechanical properties.

[0028] 2. The product has excellent performance. The fluoropolymer resin produced is transparent, smooth, and non-porous in appearance and has excellent processing performance. The resin is not easy to agglomerate or fiberize, has good dispersion, high surface density, tensile strength above 26.5 MPa, elongation at break above 480%, and particle size of 500-700 μm accounts for more than 95%. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below with reference to the following examples, but the present invention is not limited to the following examples.

[0030] Example 1

[0031] 50 kg of THV resin dispersion (obtained by free radical dispersion polymerization, the polymer consists of 80 mol% tetrafluoroethylene, 15 mol% hexafluoropropylene and 5 mol% vinylidene fluoride, with a solid content of 28 wt%) was filtered through a 200-mesh filter bag and added to a 200-L coagulation kettle, and diluted with deionized water to a solid content of 15 wt%. The temperature was adjusted to 28°C, stirring was started, and the stirring speed was set to 400 rpm. Then, a dispersion prepared by dispersing 4.66 g of ammonium bicarbonate and 4.66 g of nano-silica in 93.33 g of deionized water was added for coagulation, where the median particle size of the nano-silica was 50 nm. Before the start of coagulation, the acoustic recorder was turned on. After removing the noise background, the acoustic signal was a steady line. As the stirring was turned on, the acoustic signal curve gradually rose. When the acoustic signal gradually increased to 75 decibels, the stirring speed was reduced to 200 rpm. When the acoustic signal reached a maximum point of about 90 decibels, the coagulant was quickly precipitated and the acoustic signal began to decrease. When the acoustic signal dropped to 35 decibels, the stirring speed was reduced to 150 rpm and maintained at this speed for 45 seconds to end the coagulation. Then the temperature in the kettle was reduced to 15°C, and the mixture was washed twice with deionized water at a stirring speed of 150 rpm. After washing, the material was placed on a plate and placed in an oven for drying at 190°C for 18 hours to obtain the treated THV resin.

[0032] Example 2

[0033] 50 kg of THV resin dispersion (obtained by free radical dispersion polymerization, the polymer consists of 80 mol% tetrafluoroethylene, 15 mol% hexafluoropropylene and 5 mol% vinylidene fluoride, with a solid content of 25 wt%) was filtered through a 200-mesh filter bag and added to a 200-L coagulation kettle, and diluted with deionized water to a solid content of 10 wt%. The temperature was adjusted to 25°C, stirring was started, and the stirring speed was set to 300 rpm. Then, a dispersion prepared by dispersing 23.81 g of ammonium bicarbonate and 1.19 g of nano-silica in 125 g of deionized water was added for coagulation, where the median particle size of the nano-silica was 20 nm. Before the start of coagulation, the acoustic recorder was turned on. After removing the noise background, the acoustic signal was a steady line. As the stirring was turned on, the acoustic signal curve gradually rose. When the acoustic signal gradually increased to 70 decibels, the stirring speed was reduced to 250 rpm. When the acoustic signal reached a maximum point of about 90 decibels, the coagulant was quickly precipitated and the acoustic signal began to decrease. When the acoustic signal dropped to 30 decibels, the stirring speed was reduced to 150 rpm and maintained at this speed for 30 seconds to end the coagulation. Then the temperature in the kettle was reduced to 18°C, and the mixture was washed twice with deionized water at a stirring speed of 100 rpm. After washing, the material was placed on a plate and placed in an oven for drying at 200°C for 12 hours to obtain the treated THV resin.

[0034] Example 3

[0035] 50 kg of THV resin dispersion (obtained by free radical dispersion polymerization, the polymer consists of 80 mol% tetrafluoroethylene, 15 mol% hexafluoropropylene and 5 mol% vinylidene fluoride, with a solid content of 30 wt%) was filtered through a 200-mesh filter bag and added to a 200-L coagulation kettle, and diluted with deionized water to a solid content of 12 wt%. The temperature was adjusted to 30°C, stirring was started, and the stirring speed was set to 500 rpm. Then, a dispersion prepared by dispersing 36.29 g of ammonium bicarbonate and 1.21 g of nano-silica in 125 g of deionized water was added for coagulation, where the median particle size of the nano-silica was 80 nm. Before the start of coagulation, the acoustic recorder was turned on. After removing the noise background, the acoustic signal was a smooth line. As the stirring was turned on, the acoustic signal curve gradually rose. When the acoustic signal gradually increased to 80 decibels, the stirring speed was reduced to 300 rpm. When the acoustic signal reached a maximum point of about 90 decibels, the coagulant was quickly precipitated and the acoustic signal began to decrease. When the acoustic signal dropped to 40 decibels, the stirring speed was reduced to 200 rpm and maintained at this speed for 60 seconds to end the coagulation. Then the temperature in the kettle was reduced to 10°C, and the mixture was washed twice with deionized water at a stirring speed of 120 rpm. After washing, the material was placed on a plate and placed in an oven for drying at 180°C for 20 hours to obtain the treated THV resin.

[0036] Example 4

[0037] 50 kg of THV resin dispersion (obtained by free radical dispersion polymerization, the polymer consists of 80 mol% tetrafluoroethylene, 15 mol% hexafluoropropylene and 5 mol% vinylidene fluoride, with a solid content of 27 wt%) was filtered through a 200-mesh filter bag and added to a 200-L coagulation kettle, and diluted with deionized water to a solid content of 13 wt%. The temperature was adjusted to 24°C, stirring was started, and the stirring speed was set to 450 rpm. Then, a dispersion prepared by dispersing 50.9 g of ammonium carbonate and 1.02 g of nano-silica in 103.84 g of deionized water was added for coagulation, where the median particle size of the nano-silica was 100 nm. Before the start of coagulation, the acoustic recorder was turned on. After removing the noise background, the acoustic signal was a steady line. As the stirring was turned on, the acoustic signal curve gradually rose. When the acoustic signal gradually increased to 78 decibels, the stirring speed was reduced to 280 rpm. When the acoustic signal reached a maximum point of about 90 decibels, the coagulant was quickly precipitated and the acoustic signal began to decrease. When the acoustic signal dropped to 38 decibels, the stirring speed was reduced to 180 rpm and maintained at this speed for 40 seconds to end the coagulation. Then the temperature in the kettle was reduced to 20°C, and the mixture was washed twice with deionized water at a stirring speed of 150 rpm. After washing, the material was placed on a plate and placed in an oven for drying at 160°C for 24 hours to obtain the treated THV resin.

[0038] Comparative Example 1

[0039] Take 50 kg of THV resin dispersion (obtained by free radical dispersion polymerization, the polymer consists of 80 mol% tetrafluoroethylene, 15 mol% hexafluoropropylene and 5 mol% vinylidene fluoride, with a solid content of 28%), filter it with a 200-mesh filter bag and add it to a 200-L coagulation kettle, and dilute it with deionized water to a solid content of 15 wt%; adjust the temperature to 28°C, start stirring, set the stirring speed to 400 rpm, and then add 4.66 g of ammonium bicarbonate dispersed in 93.33 g of deionized water. After stirring for 1 hour, all the coagulants are precipitated, the lower layer liquid is released in layers, and the upper layer material is washed twice with deionized water at a speed of 400 rpm and 28°C; after washing, the material is placed on a plate and placed in an oven to dry at 190°C for 18 hours to obtain the treated THV resin.

[0040] The mechanical properties and processing properties of the THV resins obtained in Examples 1 to 4 and Comparative Example 1 were measured. The relevant data are shown in Table 1, where:

[0041] Tensile strength measurement: Dumbbell standard specimens with a width of 5.24 mm and a thickness of 0.6 mm were cut from the THV thermoformed sample with a cutter. The standard specimens were stretched at a tensile speed of 200 mm / min at room temperature using a universal precision material testing machine to measure the maximum tensile strength.

[0042] Elongation at Break: After cooling the hot-pressed resin molded product, a tensile test was performed. The sample was clamped between upper and lower clamps with the chucks adjusted to 24 mm apart. The upper chuck was raised at a speed of 20 mm / min and stopped when the sample broke. The elongation at break was calculated based on the chuck position at that point.

[0043] Elongation at break = (distance between chucks at break / 24 mm) x 100%.

[0044] Determination of the proportion of particles with a diameter of 500 to 700 μm: carried out in accordance with the HG / T2901-1997 standard particle size test method.

[0045] Table 1: Mechanical properties and processing performance test results of THV resin obtained in Examples and Comparative Examples

[0046]

[0047]

[0048] As can be seen from Table 1, the post-treatment method of the fluorine-containing polymer emulsion of the present invention can obtain resin particles with uniform particle size, and the resin has excellent mechanical properties and good processing and application properties after processing.

Claims

1. A post-treatment method for a fluoropolymer emulsion, characterized in that: The following steps are involved: (1) filtering and diluting the fluoropolymer emulsion to obtain a diluted fluoropolymer emulsion; (2) adding a composite coagulant to the diluted fluoropolymer emulsion at an initial stirring speed of 300-500 rpm, wherein the composite coagulant is ammonium bicarbonate or a mixture of ammonium carbonate and nano-silicon dioxide, and reducing the stirring speed in stages according to the acoustic wave signal generated during the coagulation process. When the acoustic wave signal increases to 70-80 decibels, the stirring speed is reduced to 200-300 rpm; when the acoustic wave signal decreases to 30-40 decibels, the stirring speed is reduced to 100-200 rpm, until the coagulation is completed to obtain a coagulation product; (3) washing the condensed product obtained in step (2) to obtain a washed product, wherein the washing temperature is 10-20° C. and the stirring speed is 100-200 rpm; (4) Drying the washed product obtained in step (3) to obtain a fluorine-containing polymer resin.

2. The post-treatment method of fluoropolymer emulsion according to claim 1, characterized in that: The fluorine-containing polymer is one of tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymer, polyperfluoroethylene propylene, polyvinylidene fluoride, fusible polytetrafluoroethylene, and polytetrafluoroethylene.

3. The post-treatment method of fluoropolymer emulsion according to claim 1, characterized in that: The solid content of the fluoropolymer emulsion is 25-30 wt %, and the solid content of the diluted fluoropolymer emulsion is 10-15 wt %.

4. The post-treatment method of fluoropolymer emulsion according to claim 1, characterized in that: The coagulation temperature is 25-30°C.

5. The post-treatment method of fluoropolymer emulsion according to claim 1, characterized in that: In step (2), the stirring speed is reduced to 100-200 rpm and maintained at this speed for 30-60 seconds.

6. The post-treatment method of fluoropolymer emulsion according to claim 1, characterized in that: The mass ratio of ammonium bicarbonate or ammonium carbonate to nano-silicon dioxide in the mixture is 1 to 50:1; and the mixture is dispersed and dissolved in deionized water at 5 to 50 wt%.

7. The post-treatment method of fluoropolymer emulsion according to claim 1, characterized in that: The median particle size of the nano-silicon dioxide is 20-100 nm.

8. The post-treatment method of fluoropolymer emulsion according to claim 1, characterized in that: The dosage of the composite coagulant is 0.01-0.1 wt % of the mass of the fluoropolymer emulsion.

9. The post-treatment method of fluoropolymer emulsion according to claim 1, characterized in that: The drying temperature is 160-200° C. and the drying time is 12-24 hours.

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