CN102718907B - Preparation method of ethylene-tetrafluoroethylene copolymer resin - Google Patents

Abstract

The invention relates to a method for preparing ethylene-tetrafluoroethylene copolymer resin by utilizing an inorganic oxidation-reduction system, which solves the technical problems of high initiation temperature of inorganic peroxides and adverse influence on alternating structures, and belongs to the technical field of fluoroplastics. The method is characterized in that an independent gas-mixing tank and a pressurizing system of the gas-mixing tank are arranged, and the gas-mixing tank and a reaction kettle are connected through a check valve, so that gas can only flow from the mixing groove to the reaction kettle in a unidirectional manner; during polymerization reaction, the temperature is reduced to 10 DEG C and is kept constant, the following monomer is added and supplied in the form of mixed gas, and constant pressure is kept in the kettle; and the polymerization reaction adopts an ammonium persulfate-ferrisulphas inorganic redox initiation system. The method has the beneficial effects that the initiation temperature of the inorganic peroxides is lowered, the prepared copolymer resin is in an alternating copolymer structure, radiation-resisting and mechanical performances are improved to a great degree while the good performance of PTFE (Polytetrafluoroethylene) is kept, and the tensile strength can reach 50MPa which is approximately twice as that of the PTFE.

Description

A kind of preparation method of ethylene-tetrafluoroethylene copolymer resins

Technical field

The invention belongs to fluoro-containing plastic and preparation method thereof technical field, relate to a kind of preparation method of ethylene-tetrafluoroethylene copolymer resins, relate in particular to a kind of inorganic oxide reduction system and cause the method for preparing ethylene-tetrafluoroethylene copolymer resins.

Background technology

Ethylene-tetrafluoroethylene (ETFE) copolymer resins is as crystalline high polymer, fusing point is 256～280 DEG C, when burning, can certainly put out, be the most tough fluoroplastics, and its anti-shearing physical strength is high, low-temperature impact-resistant performance, be best in existing fluoroplastics, it is in having kept heat-resisting, the chemical resistance and electrical insulation capability that polytetrafluoroethylene (PTFE) is good, and radiation hardness and mechanical property have significantly to be improved, tensile strength can reach 50MPa, approaches 2 times of PTFE.Use temperature is set as between-65 DEG C to 150 DEG C conventionally.

ETFE is formed by ethene and two kinds of monomer copolymerizations of tetrafluoroethylene, copolymerization structure is divided into block, random, grafting and alternately four kinds, for ETFE, the molecular rigidity of alternating structure and degree of crystallinity are the highest, component mol ratio departs from 50/50 textural defect can affect the crystalline form of polymkeric substance, causes fusing point and second-order transition temperature to decline, especially in the time that ethene ratio is higher, the decomposition temperature of polymkeric substance and the difference of fusing point are less, are unfavorable for forming process.

Domestic about ETFE relevant report in, only relate to processed and applied field, and have no the Patents report that aspect is prepared in polymerization; What external ETFE preparation technology adopted is organic peroxide evocating agent, and its advantage is that shortcoming is that initiator cost is high, deposits and working conditions harshness without doing the processing of molecule tail end base.By contrast, inorganic peroxide (as ammonium persulphate etc.) cost is low and without special solvent, but the kick off temperature of inorganic peroxide in the time of ETFE polymerization need be higher than 60 DEG C, and low temperature is conducive to the formation of alternating structure ETFE in copolyreaction, the kick off temperature of inorganic peroxide is higher, and alternating structure is had to adverse influence.

Summary of the invention

The object of this invention is to provide a kind of inorganic initiator system that adopts, be beneficial to preparation method alternating structure ETFE copolymerization, ethylene-tetrafluoroethylene copolymer resins.

For achieving the above object, the technical scheme of employing is: a kind of preparation method of ethylene-tetrafluoroethylene copolymer resins, is characterized in that step is:

(1) independently gas mixing tank and supercharging system thereof are set, the ethene, the tetrafluoroethylene monomer that in gas mixing tank, are filled with, pressing equimolar amount mixes, the external pump around circuit pipeline of gas mixing tank and supercharging buffering pipeline, between gas mixing tank and polymerization reaction kettle, be connected with vacuum breaker, make the gas can only be by tempering tank to reactor uniflux;

(2) in polymerization reaction kettle, adding mass percent concentration is 1 ‰ ammonium persulfate solution, temperature of reaction is 10 DEG C and does thermostatic control, be filled with tetrafluoroethylene, vinyl monomer, make tetrafluoroethylene: the absolute pressure intrinsic standoff ratio of ethene is 7: 3, in 2 hours, at the uniform velocity adding mass percent concentration is 1% copperas solution again, and add-on (volume ratio) is: ferrous sulfate: ammonium persulphate=3: 20; In the process that adds ferrous sulfate, more (1) step is filled with in polymerization reaction kettle after the mixed gas supercharging in described gas mixing tank, follow-up monomer supplements and adds with mixed gas form, keeps constant voltage in polymerization reaction kettle; Copperas solution adds rear mistake and finishes reaction in 20 minutes, with vacuum pump, residual gas is discharged to reactor, opens still rewinding;

Step (2) gained material spend ionized water repeated washing more than three times, residual initiator is removed, until the filtrate specific conductivity recording is down to below 1 μ S/m; Finally, not dry higher than 150 DEG C of temperature, obtain the ETFE copolymer resins of pressed powder state.

The invention has the beneficial effects as follows: utilize inorganic oxide reduction system, cause and prepare ethylene-tetrafluoroethylene method, not only avoid the harsh problem of expensive and working conditions of organo-peroxide, and the kick off temperature that has solved inorganic peroxide is high, alternating structure is had to the defect of disadvantageous effect.The present invention has reduced the kick off temperature of inorganic peroxide, and the copolymer resins polymer molecular structure formula making is-[CH ₂-CH ₂-CF ₂-CF ₂] _n-, being alternating copolymerization structure, anti-shearing physical strength is high, and low-temperature impact-resistant performance is good, and except having kept PTFE superperformance when, radiation hardness and mechanical property have significantly to be improved, and tensile strength can reach 50MPa, approaches 2 times of PTFE.

Embodiment

Below by embodiment, technical scheme of the present invention is described further, be intended to make those of ordinary skill in the art can understand and implement the present invention.But it should be noted that the present invention is not limited to disclosed most preferred embodiment, based on enlightenment of the present invention, any apparent conversion or be equal to alternatively, also should be considered to fall into protection scope of the present invention.

The present invention design independently gas mixing tank with and supercharging system, the external pump around circuit pipeline of gas mixing tank and supercharging buffering pipe, be connected with vacuum breaker between gas mixing tank and reactor, makes the gas can only be by tempering tank to reactor uniflux.In the time that polyreaction is carried out, follow-up monomer supplements and adds with mixed gas form, keeps constant voltage in still; In polyreaction, adopt ammonium persulphate-ferrous sulfate inorganic oxide reduction initiating system, whole process quantitatively continues the mode that adds and adds.

Each material in embodiment, except indicating especially, is mass percent concentration.Wherein,

Copperas solution mass percent concentration 1%, ammonium persulfate solution mass percent concentration is 1 ‰; Add-on (volume ratio) is: ferrous sulfate: ammonium persulphate=3: 20.Deionized water specific conductivity is 0.7 μ S/m.

Test item has DSC, XRD, ultimate analysis.

Embodiment 1:

A preparation method for ethylene-tetrafluoroethylene copolymer resins, is characterized in that step is:

(1) be 20L gas mixing tank and associated pipe thereof the replacement Treatment of finding time by volume, add tetrafluoroethylene gas to gauge pressure 0.7MPa(be absolute pressure 0.8MPa), add again ethylene gas to gauge pressure 1.5MPa(absolute pressure 1.6MPa, the absolute pressure dividing potential drop of tetrafluoroethylene and ethene all equals 0.8MPa, be that mole number equates), make in groove gas through external pump around circuit pipeline and supercharging buffering pipeline with compression pump, generation circulates;

(2) be the ammonium persulfate solution that adds 5 L 1 ‰ in 10L reactor at volume, make temperature in the kettle be down to 10 DEG C by circulation thermostat, add tetrafluoroethylene gas to gauge pressure 1.37MPa(absolute pressure 1.47MPa), add again ethylene gas to gauge pressure 2.0MPa(absolute pressure 2.1MPa), the absolute pressure dividing potential drop of tetrafluoroethylene and ethene is respectively 1.47MPa and 0.63MPa); At the uniform velocity add step (2) in described reactor the copperas solution of 750ml 1% with volume pump, regulating metering pumping capacity is 375ml/h, by the (1) pump around circuit pipeline sealing of described gas mixing tank of step, open supercharging buffering pipeline, mixed gas is pressurized to gauge pressure 2.0MPa and is maintained at polymerization stage with compression pump, after 20 minutes, finish reaction until copperas solution maintains reaction again after adding, then with vacuum pump, residual gas is discharged to reactor, open still rewinding;

Step is described washing (3), in triplicate more than, residual initiator is removed, be down to below 1 μ S/m until record filtrate specific conductivity.Then dry (not higher than 150 DEG C) 24 hours, obtain the copolymer resins of pressed powder state.

The present embodiment detected result is: fluorine content 59.79%; 278.6 DEG C of fusing points, 23.5 DEG C of melting peak width; 18.660 ° of x-ray diffraction angles are unimodal.

Embodiment 2:

Change gas mixing tank volume in embodiment 1 into 10L, reactor volume changes 2L into, and ammonium persulfate solution volume changes 1 liter into, and copperas solution volume changes 150ml into, and volume pump flow changes 75ml/h into, the other the same as in Example 1 operation.The present embodiment detected result is: fluorine content 58.99%; 277.94 DEG C of fusing points, 21 DEG C of melting peak width; 18.620 ° of x-ray diffraction angles are unimodal.

Embodiment 3:

Change gas mixing tank volume in embodiment 1 into 1000L, reactor volume changes 500L into, and ammonium persulfate solution volume changes 250 liters into, and copperas solution volume changes 3.75L into, and volume pump flow changes 1.875L/h into, the other the same as in Example 1 operation.The present embodiment detected result is: fluorine content 59.34%; 275.66 DEG C of fusing points, 30.3 DEG C of melting peak width; 18.780 ° of x-ray diffraction angles are unimodal.

The content of fluorine element in elemental analysis polymkeric substance, while equating (being that molar ratio equates) by calculating the molecular amounts of two kinds of monomer components, corresponding fluorine content should be 59.375%; XRD characterizes x-ray diffraction angle ,-CH ₂-CF ₂-to be 18.6 ° be the eigenwert of alternating structure, other structure-CF ₂-CF ₂-diffraction angle is 25 ° ,-CH ₂-CH ₂-be respectively 19.8 °, 21.4 °, 23.7 °, 36.1 ° according to crystalline form difference; DSC can characterize polymers fusing point, under the definite prerequisite of molecular structure, can characterize range of molecular weight distributions by melting peak width.

Above-described embodiment completes under different scales equipment, has proved operability and the versatility of technique of the present invention; The actual measurement fluorine content of embodiment 1, embodiment 2, embodiment 3 and the accuracy rate of calculated value reach respectively 99.3%, 99.35%, 99.94%, and the single diffraction angle of X ray is all-CH ₂-CF ₂-eigenwert; Fusing point relative error is no more than 1%, and melting peak width is no more than 30 DEG C, represents that the molecular weight differences opposite sex is very little.Alternating structure and the even molecular weight distribution of ethylene-tetrafluoroethylene copolymer resins of the present invention are proved.

Claims (1)

1. a preparation method for ethylene-tetrafluoroethylene copolymer resins, is characterized in that step is:

(1) independently gas mixing tank and supercharging system thereof are set, the ethene, the tetrafluoroethylene monomer that in gas mixing tank, are filled with, by waiting mole number to mix, the external pump around circuit pipeline of gas mixing tank and supercharging buffering pipeline, between gas mixing tank and polymerization reaction kettle, be connected with vacuum breaker, make the gas can only be by tempering tank to reactor uniflux;

(2) in polymerization reaction kettle, adding mass percent concentration is 1 ‰ ammonium persulfate solution, temperature of reaction is 10 DEG C and does thermostatic control, be filled with tetrafluoroethylene, vinyl monomer, make tetrafluoroethylene: the absolute pressure intrinsic standoff ratio of ethene is 7: 3, in 2 hours, at the uniform velocity adding mass percent concentration is 1% copperas solution again, and add-on volume ratio is: ferrous sulfate: ammonium persulphate=3: 20; In the process that adds ferrous sulfate, (1) step is filled with in polymerization reaction kettle after the mixed gas supercharging in described gas mixing tank, follow-up monomer supplements and adds with mixed gas form, keeps constant voltage in polymerization reaction kettle; Copperas solution adds rear mistake and finishes reaction in 20 minutes, with vacuum pump, residual gas is discharged to reactor, opens still rewinding;

Step (2) gained material spend ionized water repeated washing more than three times, residual initiator is removed, until the filtrate specific conductivity recording is down to below 1 μ S/m; Finally, not dry higher than 150 DEG C of temperature, obtain the ETFE copolymer resins of pressed powder state.