CN102580571B

CN102580571B - Method for preparing ultra high molecular weight polyethylene micro-filtration membrane

Info

Publication number: CN102580571B
Application number: CN201210069559.0A
Authority: CN
Inventors: 刘思俊; 周持兴; 俞炜; 郑泓
Original assignee: Shanghai Jiao Tong University
Current assignee: Shanghai Jiao Tong University
Priority date: 2012-03-15
Filing date: 2012-03-15
Publication date: 2014-04-16
Anticipated expiration: 2032-03-15
Also published as: CN102580571A

Abstract

The invention relates to a method for preparing an ultra high molecular weight polyethylene micro-filtration membrane. The method comprises the following steps of: (1) weighing and mixing 10 to 30 weight parts of ultra high molecular weight polyethylene, 67 to 89.4 weight parts of thinning agent, 0.1 to 2 weight parts of nucleating agent and 0.5 to 1 part of antioxidant, and treating the obtained mixture to obtain a flat membrane by a die pressing process or an extrusion process; (2) orienting the nucleating agent by adopting a shearing process or a stretching process to obtain an oriented flat membrane; (3) removing the thinning agent by using an extracting agent, washing, drying, and thus obtaining a micropore membrane; and (4) drying, annualizing and sizing the micropore membrane, and thus obtaining the ultra high molecular weight polyethylene micro-filtration membrane. Compared with the prior art, the method has the advantages that: the prepared ultra high molecular weight polyethylene micropore membrane has regular form, uniform aperture distribution and high water flux, has predominant mechanical properties, and particularly has high elongation at break in the orientation direction.

Description

A kind of preparation method of ultra high molecular weight polyethylene micro-filtration membrane

Technical field

The invention belongs to membrane separation technique field, relate in particular to a kind of preparation of ultra-high molecular mass polyethylene micropore film, the ultra-high molecular mass polyethylene micropore film making is satisfied with the requirement of the microfiltration membranes material in water treatment procedure.

Background technology

Micro-filtration is a kind of important film separation process, is widely used in the industries such as trade effluent processing, drinking water preparation, food industry, health care, military project.The basic important document of film separation process is filter assemblies, and core is the filter membrane in assembly, and take micropore filtering film that high-molecular organic material makes and assembly as main.According to the mean size of fenestra or trapped particles size, film separation can be divided into various procedures, and wherein the definition pore size of micro-filtration is about 0.1-100um, particulate, protein and bacterium etc. in main trap water.Common diffusion barrier has three kinds of flat sheet membrane, tubular membrane, hollow-fibre membrane.

The method of preparing polymer microporous film is a lot, such as immersion precipitation, phase separation method, pulling method etc.Wherein thermally induced phase separation (TIPS) is important and the method for extensive use, and it is applicable to preparation and can not find at normal temperatures the polymer of good solvent, especially many crystallizations or with the polymer of hydrogen bond; TIPS method is carried out the phase-splitting of induced polymer solution by heat exchange fast simultaneously, controls process conditions and can obtain various pore structure.The summary of TIPS process is: some thermoplasticity, crystalline high polymer and some high boiling diluent are at high temperature first formed to homogeneous phase solution, then reduce system temperature, induction system generation solid-liquid (S-L) or liquid-liquid (L-L) are separated; After extraction removes diluent after system cooling curing, can prepare polymer porous film.Described diluent, refers to for polymeric material it is a kind potential solvent, while being non-solvent but high temperature at normal temperatures, is solvent, i.e. " high temperature is compatible, low temperature phase-splitting ".Diluent kind and content are most important factors in TIPS film-forming process, and final membrane structure and film properties are had to important impact.Often pass through the drafting of the phasor of polymer-diluent, at large study the pore-forming dynamic process of different polymer-diluent systems.

At present, adopt TIPS legal system mainly to concentrate on high density polyethylene (HDPE) (HDPE), polypropylene (PP), Kynoar (PVDF) etc. for polymeric film material.Ultra-high molecular weight polyethylene is due to its excellent mechanical property, biocompatibility and chemical stability, fabulous rub resistance and shock resistance, make the ultra-high molecular mass polyethylene micropore film mechanical strength for preparing large, in sewage disposal, long-term serviceability is stable, is difficult for the overall characteristics such as degraded.Because ultra-high molecular weight polyethylene is elastomeric state when the melting, almost without mobility.The preparation that TIPS method is ultra-high molecular mass polyethylene micropore film provides may.But TIPS method is carried out the phase-splitting of induced polymer solution by heat exchange fast, make the microporous barrier pore-size distribution for preparing inhomogeneous.

Summary of the invention

Object of the present invention is exactly the preparation method that a kind of even aperture distribution, water flux is high, mechanical property is excellent ultra high molecular weight polyethylene micro-filtration membrane are provided in order to overcome the defect that above-mentioned prior art exists.

Object of the present invention can be achieved through the following technical solutions: a kind of preparation method of ultra high molecular weight polyethylene micro-filtration membrane, it is characterized in that, and the method comprises the following steps:

(1) content takes ultra-high molecular weight polyethylene 10-30 weight portion, diluent 67-89.4 weight portion, nucleator 0.1-2 weight portion and the mixing of antioxidant 0.5-1 weight portion by weight, and gained mixture obtains flat sheet membranes by mould pressing process or expressing technique;

(2) adopt and shear technique or drawing process, nucleator is orientated, obtain being orientated flat sheet membranes;

(3) use extractant to remove diluent, after washing, being dried, form microporous barrier;

(4) sizing that microporous barrier is dried and anneals, prepares ultra high molecular weight polyethylene micro-filtration membrane.

The molecular weight of described ultra-high molecular weight polyethylene is 150～5,000,000.

Described nucleator is silica (SiO ₂), titanium dioxide (TiO ₂), CNT (CNT), Graphene, a kind of in 2,4,6-Triaminopyrimidine (TP), malonyl urea (BA) or Sorbitol Nucleator;

Described diluent is selected from one or more in short chain alkanes kind solvent or phthalate solvent;

Described antioxidant is selected from any one or several combination in organic tin antioxidant and/or metal soap antioxidant.

Described Sorbitol Nucleator comprises 1,3:2,4-dibenzal sorbitol (DBS), 1,3:2, bis-pairs of methyl benzylidene sorbitols of 4-(MDBS) or 1,3:2,4-bis-(3,4-dimethyl) benzylidene sorbitol (DMDBS);

Described short chain alkanes kind solvent comprises octane, decane, paraffin oil, solid paraffin or atoleine; Described phthalate solvent comprises phthalic acid ester dimethyl ester, phthalic acid ester diethylester, dibutylphthalate, phthalic acid ester dihexyl, phthalic acid ester dioctyl ester, phthalic acid ester di-isooctyl, phthalic acid ester two isodecyl esters, phthalic acid ester two (the own ester of 2-methyl) or dicyclohexyl phthalate;

Described organic tin antioxidant comprises dibutyl tin laurate, maleic acid dioctyltin, two (butyl maleate) two fourth tin, two (lauryl mercaptan) dibutyl tin, S, S '-bis-(the different pungent tin of sulfo-Glycolic acid) dibutyl tin or Bis(lauroyloxy)dioctyltin; Described metal soap antioxidant comprises calcium stearate, dolomol, lithium stearate, zinc stearate, aluminum stearate, double stearic acid aluminium, calcium laurate, zinc laurate, ricinoleic acid calcium or 2 ethyl hexanoic acid zinc.

The described mould pressing process of step (1) adopts following steps: adopt the direct molten mixture of Haake torque rheometer, again by film laminator compression molding flat sheet membranes, Haake torque rheometer melt mix temperature is 160～180 ℃, and molding temperature is 160～170 ℃.

The described expressing technique of step (1) adopts following steps: by mixture melting in double screw extruder, mix and extrude, obtain noting film liquid, then will note film liquid by T-shaped membrana oralis, curtain coating is molding plate film on metal roller, the processing temperature that twin-screw squeezes machine is 170～200 ℃, and screw speed is 200～400rpm.

The shearing process using following steps that step (2) is described: by torque rheometer, flat sheet membranes is heated to 125～145 ℃ of shear temperature, control shear rate is 10～50s ^-1, strain amplitude is 20～100%, obtains being orientated flat sheet membranes.

The described drawing process of step (2) adopts following steps: by the controlled universal electrical puller system of draft temperature, by flat sheet membranes stretch orientation, draft temperature is 40～100 ℃, and rate of extension is 50～100mm/min, and elongation strain is 100～300%.

The described extractant of step (3) is selected from the one or more combination in absolute ethyl alcohol, glycerine, n-butanol or chloroform.

The described baking temperature dry and annealing sizing of step (4) is 80 ℃, and be 3h drying time, and annealing temperature is 110 ℃, and annealing time is 10h.

In TIPS method, add nucleator for crystalline polymer, its effect has three: one, accelerates the crystalline rate of polymer, is separated, and then affects the dynamic process of film forming thereby control; The 2nd, improve the degree of crystallinity of polymer, contribute to improve the mechanical strength of material and heat resistance etc.; The 3rd, improve grain density, thus the aperture that reduces last microporous barrier.As everyone knows, microporous barrier aperture reduces, and must be accompanied by the increase of water circulation path in film, and water flux reduces.Moreover nano inorganic nucleator is very easily reunited, other disperses to be generally difficult to realize primary particle level, thereby is difficult to embody the property of nano particle.Therefore, mixed polymer/diluent/nucleator, not only cannot improve water flux simply, and is more difficult to realize nucleator fine dispersion.Meanwhile, the incompatible boundary of existence also can cause the deterioration of film article mechanical property.Therefore the dispersion that improves nucleator, prepares the short polymer microporous film of water stream channel and is TIPS legal system for one of key technology of microporous barrier.

The present invention adopts and in diluent and ultra-high molecular weight polyethylene melt, is self-assembled into organic micromolecule compound, CNT and the SiO of nanofiber ₂as nucleator, at a certain temperature, the shearing applying or elongation flow field are orientated nucleator, induction UHMWPE crystallization, and utilize TIPS legal system for ultra-high molecular mass polyethylene micropore film.Nucleator, under hot conditions, can generate homogeneous phase solution in most of diluents and polymer melt.Apply after shearing or elongation flow field, not only improved the dispersion of nucleator, and make nucleator form orientation texture.The nucleator of orientation not only plays the effect of induced crystallization, and makes the vertical nucleator differently-oriented directivity growth of polymer platelet, obtains the polymer microporous film of orientation.Therefore, for the TIPS technique of orientation ultra-high molecular mass polyethylene micropore film, nucleator and processing technology that the present invention selects have following characteristic: (1) selects three kinds of difform nucleators (spherical, bar-shaped and fibrous); (2), for ultra-high molecular weight polyethylene, diluent, nucleator and antioxidant homogeneous phase solution, before polymer crystallization, the flow field applying is orientated nucleator; (3) effectively controlling under the prerequisite of orientation ultra-high molecular mass polyethylene micropore membrane pore structure and film properties, use as far as possible a small amount of nucleator.

Compared with prior art, the present invention adds nucleator in polymer and diluent, then high temperature applies and shears or elongation flow field makes nucleator orientation, not only improved nucleator disperses in polymer/diluent, and the nucleator induction UHMWPE of the orientation crystallization of growing nonparasitically upon another plant, obtain the UHMWPE microporous barrier of apparent height orientation.Do not compare with there is no the UHMWPE microporous barrier of orientation, UHMWPE microporous barrier pore-size distribution after orientation is less, water flux is high, mechanical property is more excellent.Therefore, microporous barrier prepared by the present invention can, for the preparation of food, medicine, ultra-pure water, meet requirement separated, that purify, concentrate and purify.

Accompanying drawing explanation

Fig. 1 is the not orientation UHMWPE microporous barrier surface SEM aspect graph that comparative example 1 obtains;

Fig. 2 is the orientation UHMWPE microporous barrier surface SEM aspect graph that embodiment 1 obtains;

Fig. 3 is the impacts of the different nucleators that obtain of comparative example 1, embodiment 1 and comparative example on UHMWPE microporous barrier water flux;

Fig. 4 is the impacts of the different nucleators that obtain of comparative example 3, embodiment 2, embodiment 4, embodiment 6 on UHMWPE microporous barrier mechanical property.

The specific embodiment

Below in conjunction with the drawings and specific embodiments, the present invention is described in detail.

Comparative example 1

(1) pass through Haake torque rheometer by the antioxidant maleic acid dibutyl tin melting mixing of the atoleine of the DBS of the ultra-high molecular weight polyethylene of 10% weight fraction, 0.1% weight fraction, 89.4% weight fraction, 0.5% weight fraction, obtain ultra-high molecular weight polyethylene mixture.The melt mix temperature of Haake torque rheometer is 160 ℃, and the melting mixing time is 12min, and rotor speed is 80rpm.

(2) then by ultra-high molecular weight polyethylene mixture molding plate film on film laminator.Film thickness is controlled at 200um, and molding temperature is 160 ℃, and clamp time is 5min.

(3) then use absolute ethyl alcohol extraction liquids paraffin, use deionized water cyclic washing, after being dried, form microporous barrier.

(4) finally use the baking oven sizing that microporous barrier is dried and anneals, can obtain ultra high molecular weight polyethylene micro-filtration membrane.Baking temperature is 80 ℃, and be 3 hours drying time, 110 ℃ of annealing temperatures, and annealing time is 10 hours.

Comparative example 2

(1) pass through Haake torque rheometer by the antioxidant maleic acid dibutyl tin melting mixing of the atoleine of the CNT of the ultra-high molecular weight polyethylene of 20% weight fraction, 1% weight fraction, 78% weight fraction, 1% weight fraction, obtain ultra-high molecular weight polyethylene mixture.Melt mix temperature is 170 ℃, and the melting mixing time is 12min, and rotor speed is 80rpm.

(2) by ultra-high molecular weight polyethylene mixture compression molding flat sheet membranes.Film thickness is controlled at 200um, and molding temperature is 170 ℃, and clamp time is 5min, and pressure is 5MPa.

(3) then use absolute ethyl alcohol extraction liquids paraffin, through deionized water, suitably wash, after being dried, form microporous barrier.

Comparative example 3

(1) pass through Haake torque rheometer by the SiO of the ultra-high molecular weight polyethylene of 30% weight fraction, 2% weight fraction ₂, the atoleine of 67% weight fraction is, the antioxidant maleic acid dibutyl tin melting mixing of 1% weight fraction obtains ultra-high molecular weight polyethylene mixture.Melt mix temperature is 170 ℃, and the melting mixing time is 12min, and rotor speed is 80rpm.

Embodiment 1

(1) pass through Haake torque rheometer by the DBS of the ultra-high molecular weight polyethylene of 10% weight fraction, 0.1% weight fraction, the antioxidant maleic acid dibutyl tin melting mixing of the atoleine of 89.4% weight fraction, 0.5% weight fraction, obtains ultra-high molecular weight polyethylene mixture.Melt mix temperature is 170 ℃, and the melting mixing time is 16min, and rotor speed is 80rpm.

(2) by ultra-high molecular weight polyethylene mixture compression molding flat sheet membranes.Film thickness is controlled at 200um, and pressure is 5MPa, and molding temperature is 170 ℃, and clamp time is 6min.

(3) use torque rheometer to apply and shear flow field molding plate film.Shear temperature is 125 ℃, and shear rate is 50s ^-1, strain amplitude is 100%.

(4) then use absolute ethyl alcohol extraction liquids paraffin, through deionized water, suitably wash, after being dried, form microporous barrier.

(5) finally use the baking oven sizing that microporous barrier is dried and anneals, can obtain ultra high molecular weight polyethylene micro-filtration membrane.Baking temperature is 80 ℃, and be 3 hours drying time, 110 ℃ of annealing temperatures, and annealing time is 10 hours.

Embodiment 2

(1) pass through Haake torque rheometer by the antioxidant maleic acid dibutyl tin melting mixing of the atoleine of the DMDBS of the ultra-high molecular weight polyethylene of 30% weight fraction, 1% weight fraction, 68% weight fraction, 1% weight fraction, obtain ultra-high molecular weight polyethylene mixture.Melt mix temperature is 170 ℃, and the melting mixing time is 16min,, rotor speed is 80rpm.

(3) use electronic universal cupping machine to apply elongation flow field to molding plate film.Draft temperature is 40 ℃, and rate of extension is 100mm/min, and elongation strain is 300%.

Embodiment 3

(1) pass through Haake torque rheometer by the CNT of the ultra-high molecular weight polyethylene of 10% weight fraction, 0.5% weight fraction, the antioxidant maleic acid dibutyl tin melting mixing of the atoleine of 89% weight fraction, 0.5% weight fraction, obtains ultra-high molecular weight polyethylene mixture.Melt mix temperature is 170 ℃, and the melting mixing time is 16min, and rotor speed is 80rpm.

(3) use torque rheometer to apply and shear flow field molding plate film.Shear temperature is 130 ℃, and shear rate is 50s ^-1, strain amplitude is 100%.

Embodiment 4

(1) pass through Haake torque rheometer by the antioxidant maleic acid dibutyl tin melting mixing of the atoleine of the CNT of the ultra-high molecular weight polyethylene of 30% weight fraction, 2% weight fraction, 67% weight fraction, 1% weight fraction, obtain ultra-high molecular weight polyethylene mixture.Melt mix temperature is 170 ℃, and the melting mixing time is 16min, and rotor speed is 80rpm.

Embodiment 5

(1) pass through Haake torque rheometer by the SiO of the ultra-high molecular weight polyethylene of 10% weight fraction, 0.5% weight fraction ₂, the antioxidant maleic acid dibutyl tin melting mixing of the atoleine of 89% weight fraction, 0.5% weight fraction, obtains ultra-high molecular weight polyethylene mixture.Melt mix temperature is 170 ℃, and the melting mixing time is 16min, and rotor speed is 80rpm.

Embodiment 6

(1) pass through Haake torque rheometer by the SiO of the ultra-high molecular weight polyethylene of 30% weight fraction, 2% weight fraction ₂, the atoleine of 67% weight fraction is, the antioxidant maleic acid dibutyl tin melting mixing of 1% weight fraction obtains ultra-high molecular weight polyethylene mixture.Melt mix temperature is 170 ℃, and the melting mixing time is 16min, and rotor speed is 80rpm.

Embodiment 7

(1) first utilize the ultra-high molecular weight polyethylene of double screw extruder expressing technique melting mixing 15% weight fraction, the antioxidant maleic acid dibutyl tin of the phthalic acid ester dioctyl ester of the MDBS of 0.5% weight fraction, 84% weight fraction, 0.5% weight fraction obtains noting film liquid.Screw Extrusion temperature is 170～190 ℃, screw speed 350rpm.

(2) make to note film liquid under pressure by a T-type membrana oralis, curtain coating is molding plate film on metal roller.Die temperature is 130～140 ℃, and metal roller temperature is 25～35 ℃.

(4) then use absolute ethyl alcohol extraction phthalic acid ester dioctyl ester, through deionized water, suitably wash, after being dried, form microporous barrier.

Embodiment 8

(1) first utilize the ultra-high molecular weight polyethylene of double screw extruder expressing technique melting mixing 20% weight fraction, the antioxidant maleic acid dibutyl tin of the phthalic acid ester dioctyl ester of the CNT of 1% weight fraction, 78% weight fraction, 1% weight fraction obtains noting film liquid.Screw Extrusion temperature is 170～190 ℃, screw speed 350rpm.

(4) then use absolute ethyl alcohol extraction phthalic acid ester dioctyl ester, after deionized water is suitably washed, is dried, form microporous barrier.

Embodiment 9

(1) first utilize the ultra-high molecular weight polyethylene of double screw extruder expressing technique melting mixing 20% weight fraction, the SiO of 1% weight fraction ₂, the phthalic acid ester dioctyl ester of 78% weight fraction is, the antioxidant maleic acid dibutyl tin of 1% weight fraction obtains noting film liquid.Screw Extrusion temperature is 170～190 ℃, screw speed 350rpm.

Ultra high molecular weight polyethylene micro-filtration membrane of the present invention also can be prepared under the following conditions: adopt the step the same with embodiment 1～9, difference is different shearings or stretching condition, and specific process is in Table 1-2:

Table 1

Table 2

Fig. 1 and 2 is respectively the 10%UHMWPE microporous barrier surface SEM photo that comparative example 1 and embodiment 1 obtain.From photo, can find out, in embodiment 1, due to the orientation induction UHMWPE of the DBS fiber crystallization of growing nonparasitically upon another plant, obtain pore-size distribution anisotropy UHMWPE microporous barrier more uniformly.

Fig. 3 is to 10%UHMWPE, there is no orientation and the impact of orientation on UHMWPE microporous barrier water flux.Obviously can find out by scheming, alignment films water flux has improved 3～4 times.

Fig. 4 is to 30%UHMWPE, there is no orientation and the impact of orientation on UHMWPE microporous barrier differently-oriented directivity mechanical property.For alignment films, along differently-oriented directivity, stress and strain is all improved to some extent.

Claims

1. a preparation method of ultra-high molecular weight polyethylene microfiltration membrane, is characterized in that, the method may further comprise the steps:

(1) Weigh 10-30 parts by weight of ultra-high molecular weight polyethylene, 67-89.4 parts by weight of diluent, 0.1-2 parts by weight of nucleating agent and 0.5-1 part by weight of antioxidant, and mix the obtained mixture through Molding process or extrusion process to obtain flat film;

(2) Using a shearing process to orient the nucleating agent to obtain an oriented flat film;

(3) Use the extractant to remove the diluent, and form a microporous membrane after washing and drying;

(4) Drying and annealing the microporous membrane to prepare the ultra-high molecular weight polyethylene microfiltration membrane;

The shearing process described in step (2) adopts the following steps: heating the flat film to a shearing temperature of 125-145°C through a torque rheometer, controlling the shear rate to be 10-50s ^-1 , and the strain amplitude to be 20-100 %, to obtain an oriented flat film.

2. The method for preparing an ultra-high molecular weight polyethylene microfiltration membrane according to claim 1, wherein the molecular weight of the ultra-high molecular weight polyethylene is 1.5 to 5 million.

3. the preparation method of a kind of ultra-high molecular weight polyethylene microfiltration membrane according to claim 1, is characterized in that, described nucleating agent is silicon dioxide, titanium dioxide, carbon nanotube, graphene, 2,4 , one of 6-triaminopyrimidine, malonylurea or sorbitol nucleating agents;

The diluent is selected from one or more of short-chain alkanes solvents or phthalates solvents;

The antioxidant is selected from any one or a combination of organotin antioxidants and/or metal soap antioxidants.

4. the preparation method of a kind of ultra-high molecular weight polyethylene microfiltration membrane according to claim 3 is characterized in that, described sorbitol nucleating agent comprises 1,3:2,4-dibenzylidene sorbitol , 1,3:2,4-di-p-methylbenzylidene sorbitol or 1,3:2,4-di(3,4-dimethyl)benzylidene sorbitol;

Described short chain alkanes solvent comprises octane, decane, paraffin oil, solid paraffin or liquid paraffin; Described phthalates solvent comprises dimethyl phthalate, phthalic acid Diethyl phthalate, dibutyl phthalate, dihexyl phthalate, dioctyl phthalate, diisooctyl phthalate, phthalate Diisodecyl phthalate, bis(2-methylhexyl) phthalate or dicyclohexyl phthalate;

The organotin antioxidants include dibutyltin dilaurate, di-n-octyltin maleate, bis(monobutylmaleate) dibutyltin, bis(lauryl mercaptan) dibutyltin, S, S' - bis (isooctyltin thioglycolate) dibutyltin or di-n-octyltin dilaurate; the metal soap antioxidants include calcium stearate, magnesium stearate, lithium stearate, stearic acid Zinc, aluminum stearate, aluminum distearate, calcium laurate, zinc laurate, calcium ricinoleate, or zinc 2-ethylhexanoate.

5. The preparation method of a kind of ultra-high molecular weight polyethylene microfiltration membrane according to claim 1, characterized in that, the molding process described in step (1) adopts the following steps: using a Haake torque rheometer to directly melt the mixture , and then molded into a flat film by a film laminator, the melt mixing temperature of Haake torque rheometer is 160-180°C, and the molding temperature is 160-170°C.

6. The preparation method of a kind of ultra-high molecular weight polyethylene microfiltration membrane according to claim 1, characterized in that, the extrusion process described in step (1) adopts the following steps: putting the mixture in a twin-screw extruder Melt, mix and extrude to obtain the film injection liquid, then pass the film injection liquid through the T-shaped mouth film, and cast it on the metal roller to form a flat film. The processing temperature of the twin-screw extruder is 170-200 °C, and the screw speed is 200～400rpm.

7. A method for preparing an ultra-high molecular weight polyethylene microfiltration membrane according to claim 1, wherein the extractant in step (3) is selected from absolute ethanol, glycerin, n-butanol or chloroform one or a combination of several.

8. The preparation method of an ultra-high molecular weight polyethylene microfiltration membrane according to claim 1, characterized in that the drying temperature of the drying and annealing in step (4) is 80°C, and the drying time is 3h. The annealing temperature is 110°C, and the annealing time is 10h.