CN102134342B - Crosslinking polyolefin microporous membrane and preparation method thereof - Google Patents

Abstract

The invention discloses a cross-linked polyolefin microporous membrane and a preparation method thereof. The raw materials used to make the film mainly include: polyolefin, 28.8-48.8 parts by weight; latent solvent, 30-50 parts by weight; peroxide compound, 0.1-2 parts by weight; silane, 1-5 parts by weight; antioxidant, 0.1 parts by weight. In addition, 0 to 20 parts by weight of an ultrafine filler may be further contained. The cross-linked polyolefin microporous membrane of the present invention improves the mechanical strength, heat resistance and resistance to harsh chemical environments such as strong alkali and oxychloride compounds through the crosslinking of polyolefin. In the application process, such as the separator membrane of lithium ion battery or the filter membrane in membrane bioreactor, the service life of polyolefin microporous membrane will be greatly extended.

Description

A kind of cross-linked polyolefin microporous membrane and preparation method thereof

technical field

The invention relates to a cross-linked polyolefin microporous membrane and a preparation method thereof.

Background technique

Polymer microporous membrane refers to a special polymer film that can form through micropores in the thickness direction of the film. Depending on the preparation method, the through-through of the micropores can be straight; but in most cases, the pores have a certain degree of tortuousness. According to different pore sizes, polymer microporous membranes can be divided into microfiltration membranes, ultrafiltration membranes and nanofiltration membranes. The pore size of the microfiltration membrane generally exceeds 0.1um, while the pore size of the nanofiltration membrane generally needs to be below 10nm, and the pore size of the ultrafiltration membrane is in between. Separation membranes such as reverse osmosis membranes, ion exchange membranes, and proton exchange membranes can also be regarded as microporous membranes of certain polymers in a broad sense, but they transport "invisible" ions or protons. In general, micropores cannot be observed in these films under the highest magnification electron microscope.

It should be pointed out that the pore diameter of these micropores may have different changes in the thickness direction: along with the thickness direction, the pore diameter can be roughly constant or gradient (from large to small or small to large), Sometimes even finger-shaped pores are formed, and some composite membranes may have a sudden change in pore size on the interface. Membranes whose pore size changes in the thickness direction are generally called asymmetric membranes.

In particular, when we discuss membrane pore size, we need to explain the methods of observation and characterization. In addition to the most intuitive electron microscope, in different industrial fields, people use a variety of measurement methods to characterize the pore size and distribution of microporous membranes. Such as the specific surface and pore size distribution measuring instrument made by the principle of BET adsorption equation, mercury porosimeter, capillary flow aperture meter, small angle light scattering, cut-off molecular weight and retention rate, retention rate of bacteria or viruses, and Gurley for measuring the speed of gas passage. value and other methods. It is very meaningful to discuss the pore size change and its measurement of the above-mentioned microporous membranes. Because when any microporous membrane performs its separation function, the pore size variation in the thickness direction of the membrane and its fine structure are the most important factors.

Several preparation methods were reviewed in the book "Synthetic Polymeric Membranes" published by Robert E. Kesting in 1971. As of today, the commercial successes are mainly the following: Melt Orientation Stretching (MOS), Diffusion Induced Phase Separation (DIPS) and Thermally Induced Phase Separation Separation into membrane (Thermal Induced Phase Separation, TIPS).

In the melt-draw stretch film forming (MOS) method, common polymer extrusion processing equipment is used, and a steel mouth film is added. When the membrane is a T-shaped die, it can form a flat microporous membrane; the membrane can also be a spinneret commonly used in the textile industry, so that a hollow fiber membrane can be formed. Successful industrial cases generally use semi-crystalline polymers, such as polypropylene (Polypropylene, PP) and polyethylene (Polyethylene, PE). These semi-crystalline polymers crystallize from the melt under stretching conditions to form uniaxially oriented "kebab crystal" structures on the microscopic scale; on the macroscopic scale, these structures sometimes also have so-called "hard elastic". After further stretching the above "hard elastic" mother film, a microporous polymer film can be prepared, as disclosed in US Pat.

In the lyotropic diffusion phase separation film forming method (ie DIPS method), the polymer is first dissolved in a good solvent to form a homogeneous solution of a certain concentration (membrane casting mother liquor), and the mother liquor passes through a steel mouth membrane under pressure (can be It is a slit-shaped membrane or a hollow spinneret. The former forms a film or sheet, and the latter forms a hollow fiber membrane). After forming from the membrane, it enters a gel tank, which uses pure water or low-concentration solutions. Due to the existence of the concentration gradient, the solvent in which the polymer is dissolved rapidly diffuses into the gel tank, causing a drastic change in the concentration of the polymer solution and causing phase separation, that is, the polymer phase is separated from the solvent phase. After the phase separation is completed, the residual solvent is extracted or washed away, and micropores are formed in the place occupied by the original solvent molecules.

In the thermally induced phase separation film forming method (TIPS method), the polymer is first mixed with a selected solvent or plasticizer at high temperature. In order to enhance the mixing effect and continuous production, twin-screw extrusion is generally used commercially. extruder, single-screw extruder, two-stage extruder or continuous internal mixer. The mixture of polymer and solvent passes through a steel die under pressure, and the mixture cools down rapidly after leaving the die. Under the induction of the temperature gradient, the above-mentioned selected solvent changes from a good solvent to a poor solvent and precipitates from the polymer matrix, and the residual solvent is extracted or washed away, and the polymer microporous membrane is successfully prepared. The solvent used in this method is compatible with the polymer at high temperature but insoluble at low temperature. People call it the latent solvent of the polymer.

The basis of the application of polymer microporous membranes lies in its efficient separation function, especially solid-liquid separation and solid-gas separation. In recent years, membrane materials have achieved great success in the water treatment industry, electronics industry, pharmaceutical industry and chemical industry, and are still in the process of rapid development, such as used as a separator for lithium-ion batteries, ultrafiltration and reverse osmosis of water, dialysis , Electrically driven membrane (ion exchange membrane and proton exchange membrane), gas membrane separation, pervaporation, steam permeation, membrane contactor (membrane absorption, membrane adsorption, membrane distillation, membrane crystallization, membrane degassing), membrane chromatography, membrane Catalysis and membrane reactions, etc.

For example, the industry's success in the field of lithium-ion battery separator applications has focused on microporous membranes of polyolefins, such as polyethylene or polypropylene. Such materials have a wide range of sources and are cheap, and polyolefin microporous membranes occupy a monopoly position. In addition, this type of material is also chemically inert and does not react chemically with most polar electrolytes. However, its disadvantages are limited heat resistance and mechanical properties. After exceeding this temperature, the polymer film will melt-down, causing the positive and negative electrodes inside the battery to contact and cause a short circuit, which may sometimes lead to catastrophic results. With the development of the lithium-ion battery industry, the volume of the battery is getting smaller and smaller, and the energy and power density are getting higher and higher, which requires the materials that make up the battery to have better heat resistance, and the polymer separator is a very important component of it. part. It now appears that the melting point of high-density polyethylene is about 140°C, and the melting point of polypropylene is about 165°C, and the temperature resistance is still not enough. Especially at high temperatures, microporous membranes tend to shrink or even collapse.

For another example, due to the large specific surface area, polymer microporous hollow fiber membranes are widely used in microfiltration and ultrafiltration technologies in the field of water treatment. Typical applications such as membrane bioreactor technology for sewage treatment (Membrane Bio-Reactor, MBR). This technology requires that hollow fiber membranes have sufficient strength and have sufficient and superior chemical resistance, such as resistance to strong acids, strong alkalis, chlorine-oxygen compounds, ultraviolet rays and ozone. Polyolefin materials have good resistance to general chemicals, but general to poor resistance to strong alkalis and oxychlorides. All in all, improving the mechanical strength, heat resistance, and resistance to harsh chemical environments in the presence of strong alkalis and chlorine-oxygen compounds of polyolefin microporous membranes is an urgent problem to be solved.

Contents of the invention

The purpose of the present invention is to provide a cross-linked polyolefin microporous membrane and a preparation method thereof.

In order to achieve the above object, the technical solution adopted by the present invention is: the cross-linked polyolefin microporous membrane is characterized in that the raw materials used to make the membrane include:

Polyolefin 28.8～48.8 parts by weight,

Latent solvent 30～50 parts by weight,

Peroxy compound 0.1～2 parts by weight,

Silane 1～5 parts by weight,

Antioxidant 0.1 parts by weight.

The raw material used for making the film in the present invention also includes 0-20 parts by weight of superfine filler.

Further, the polyolefin in the present invention is any one or a combination of polyethylene resins or polypropylene resins.

Further, the latent solvents described in the present invention are phthalates, aliphatic diacid esters, trimellitates, phosphoric acid esters, glycerides, polyols, synthetic oils and paraffins, natural Any one or any combination of oils and environmentally friendly plasticizers.

Further, the silane in the present invention is any one or a combination of vinyl organosilanes.

Further, the ultrafine filler of the present invention is nano-calcium carbonate, ultra-fine calcium carbonate, talc, wollastonite, kaolin, diatomaceous earth, exfoliated nano-montmorillonite, clay, titanium dioxide, precipitated white carbon black, Any one or combination of any of fumed white carbon black, graphene, carbon nanopowder or carbon nanotube, etc., the average particle diameter of the ultrafine filler is 0.5-1 micron.

The preparation method of crosslinked polyolefin microporous membrane of the present invention comprises the following steps:

(1) Use a high-speed mixer to mix all the raw materials evenly, and then use a twin-screw extruder or a continuous internal mixer to transport, plasticize and extrude to obtain a film injection solution. The raw material is 28.8 to 48.8 parts by weight of polyolefin resin , the latent solvent of 30～50 weight parts, the peroxide of 0.1～2 weight part, the silane of 1～5 weight part and the antioxidant of 0.1 weight part, the heating of described twin-screw extruder, continuous internal mixer The temperature is set at 160-240°C;

(2) Then make the injection liquid pass through a T-shaped mouth film, cast on a metal roller to form a flat film; or make the injection liquid pass through a metal spinneret, and form a hollow fiber membrane after being cooled by a gel tank ;

(3) Then stretch the flat film or hollow fiber membrane, the stretching ratio is 1 to 10 times; finally use the extract and the extract to remove the latent solvent and ultrafine filler respectively, and form after washing and drying Polyolefin microporous membrane;

(4) Make the polyolefin microporous membrane continue to pass through the hot water tank to complete the crosslinking under the action of silane hydrolysis, the temperature of the hot water tank is 50-90°C;

(5) Then drying and annealing the polyolefin microporous membrane to prepare a cross-linked polyolefin microporous membrane.

Further, the raw materials in the above step (1) of the present invention also include 0-20 parts by weight of ultrafine fillers.

Further, the average pore diameter of the polyolefin microporous membrane formed in the above step (3) of the present invention is 0.01-1 micron.

Compared with prior art, the beneficial effect of the present invention is:

The cross-linked polyolefin microporous membrane of the present invention improves the mechanical strength, heat resistance and resistance to harsh chemical environments such as strong alkali and oxychloride compounds through the crosslinking of polyolefin. In the application process, such as the separator membrane of lithium ion battery or the filter membrane in membrane bioreactor, the service life of polyolefin microporous membrane will be greatly extended. The present invention uses polyolefin as the base material, and utilizes the method of thermally induced phase separation to prepare microporous membranes; while forming pores or later, vinyl organosilane is grafted on the main chain of polyolefin by reaction processing, and polyolefin The molecular chains are cross-linked after silane hydrolysis, and the cross-linking process does not affect the pore formation of the polymer matrix. Due to the crosslinking, the obtained crosslinked polyolefin microporous membrane has outstanding mechanical strength, chemical resistance and heat resistance. The cross-linked polyolefin microporous membrane has outstanding mechanical strength, chemical resistance and heat resistance; the formed flat membrane can be used as a separator for lithium-ion batteries, and the hollow fiber microporous membrane can be used for sewage treatment, such as membrane biological Separation membranes in reactor technology.

Detailed ways

The following implementation examples are further descriptions of the present invention, but the present invention is not limited to the following examples.

The polyolefin in the raw material used to prepare the crosslinked polyolefin microporous membrane of the present invention can be any one or any combination of several of the following polyethylene resins or polypropylene resins or copolymers: high-density polyethylene, medium-density polyethylene Ethylene, low density polyethylene, linear low density polyethylene, polyethylene with long chain branching, propylene copolymer of polyethylene, butene copolymer of polyethylene, hexene copolymer of polyethylene, octene copolymer of polyethylene Polyethylene elastomer, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-maleic anhydride copolymer, ethylene-maleic anhydride copolymer, ethylene-propylene rubber, etc.

The latent solvent used in the present invention is phthalates, aliphatic diacid esters, trimellitic acid esters, phosphoric acid esters, glycerides, polyols, synthetic oils and paraffins, natural oils and Any one or any combination of environmentally friendly plasticizers. in,

(1) The latent solvents of phthalates can be: dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dihexyl phthalate, phthalate Dioctyl formate, diisooctyl phthalate, diisodecyl phthalate, bis(2-methylhexyl) phthalate, dicyclohexyl phthalate, etc.

(2) The latent solvent of aliphatic diacid esters may be: ethyl sebacate, butyl sebacate, dioctyl adipate, triethyl citrate, etc.

(3) The latent solvent of trimellitate can be: dioctyl trimellitate and the like.

(4) The latent solvent of terephthalic acid esters may be: di-isooctyl terephthalate.

(5) The latent solvent of phosphate esters can be: triethyl phosphate, tributyl phosphate, trioctyl phosphate, etc.

(6) The latent solvent of glycerides can be: propylene glycol dicaprate, propylene glycol dioleate, glycerol monoacetate, glycerol diacetate, glycerol triacetate, N-bis(2 hydroxyethyl ) tallow, sorbitan oleate, sorbitan sesquioleate, sorbitan stearate, etc.

(7) The latent solvent of polyols can be: 2-undecyl alcohol, 1-dodecanol, dibenzylidene sorbitol, diethylene glycol, triethylene glycol, butylene glycol, polyethylene glycol, poly A mixture of ethylene glycol and glycerin, etc.

(8) The latent solvents of synthetic oils and paraffins can be: normal alkanes, liquid paraffin, naphtha, mineral oil, diphenyl ether, decahydronaphthalene, white oil, etc.

(9) The latent solvent of natural oils can be: soybean oil, linseed oil, sunflower oil, sesame oil, oleic acid, linoleic acid, palmitic acid, and mixtures thereof.

(10) The latent solvent of environment-friendly plasticizers can be: epoxy soybean oil, epoxy fatty acid methyl ester, etc.

The silane used in the present invention can be any one or several combinations of the following vinyl organosilanes: triethoxyvinylsilane, trimethoxyvinylsilane, tri(2-methoxyethoxy)ethylene methyl silane, methyl dimethoxy vinyl silane, triisopropoxy silane, trimethoxy propyl methacrylate silane, trimethoxy propyl acrylate silane, etc.

The peroxy compound used in the present invention can be: Luperox 101, Luperox 130, Luperox TBEC and Luperox DI etc. of Arkema Company, or can select Trigonox 117, Trigonox 301, Trigonox T, Trigonox B and Trigonox 145 etc. of Akzo Nobel Company.

The ultrafine fillers involved in the present invention can be nano calcium carbonate, ultrafine calcium carbonate, talcum powder, wollastonite, kaolin, diatomaceous earth, exfoliated nano montmorillonite, pottery clay, titanium dioxide, precipitated white carbon black, gas phase Any one or a combination of any of French silica, graphene, carbon nanopowder and carbon nanotubes, etc., and the average particle diameter of the ultrafine filler is 0.05-1 micron.

The formula of embodiment 1～4 is as follows by weight percentage:

In embodiment 1, the polyolefin used is high-density polyethylene, latent solvent is naphtha, peroxygen compound is peroxygen compound Luperox 101, and silane is trimethoxyvinyl silane, and superfine filler is nano-calcium carbonate, average The particle size is 0.05 microns. The raw material formula of embodiment 1 is as follows (by weight percentage):

High Density Polyethylene 42.9%

Naphtha 30%

Peroxide compound Luperox 101 2%

Trimethoxyvinylsilane 5%

Antioxidant AO168 0.1%

Nano calcium carbonate 20%

In Example 2, the polyolefin used is long-chain branched polyethylene, the latent solvent is dioctyl adipate, the peroxide compound is peroxide compound Luperox TBEC, and the silane is trimethoxymethacrylate propylsilane, ultrafine The filler is ultrafine calcium carbonate with an average particle size of 0.1 microns. The raw material formula of embodiment 2 is as follows (by weight percentage):

Long-chain branched polyethylene 35.9%

Dioctyl adipate 40%

Luperox TBEC 1%

Trimethoxypropyl methacrylate 3%

Antioxidant AO168 0.1%

Superfine Calcium Carbonate 20%

In embodiment 3, the polyolefin used is the combination of high density polyethylene and ultrahigh molecular weight polyethylene, latent solvent is liquid paraffin, peroxide compound is peroxide compound Luperox 130, silane is triisopropoxysilane, superfine The filler is ultrafine calcium carbonate with an average particle size of 1 micron. The raw material formula of embodiment 3 is as follows (by weight percentage):

High Density Polyethylene 14.4%

Ultra-high molecular weight polyethylene 14.4%

Liquid paraffin 50%

Peroxy compound Luperox 130 0.1%

Triisopropoxysilane 1%

Antioxidant AO168 0.1%

Superfine Calcium Carbonate 20%

In Example 4, the polyolefin used is a combination of high-density polyethylene and ultra-high molecular weight polyethylene, the latent solvent is dimethyl phthalate, the peroxide compound is peroxide compound Trigonox 301, and the silane is methyl dimethyl Oxyvinylsilane. The raw material formula of embodiment 4 is as follows (by weight percentage):

High Density Polyethylene 34.4%

Ultra-high molecular weight polyethylene 14.4%

Dimethyl phthalate 50%

Trigonox 301 0.1%

Methyldimethoxyvinylsilane 1%

Antioxidant AO168 0.1%

The cross-linked polyolefin microporous membrane in Example 1 is prepared according to the following steps:

(1) Use a high-speed mixer to mix the raw materials in Example 1 evenly, and the speed of the high-speed mixer is 1000 rpm. Then use the twin-screw extruder to transport, plasticize and extrude to obtain the injection liquid. The twin-screw extrusion temperature is set at 240°C, and the screw speed is 200rpm;

(2) Then make the injection film pass through a T-shaped mouth film, and cast it on a metal roller to form a flat film; the temperature of the T-shaped mouth mold is set to 240 ° C;

(3) Stretching the flat film, the stretching ratio is 5 times; then use the extraction liquid dehydrated alcohol to extract and remove naphtha, use hydrochloric acid to remove nano-calcium carbonate, the mass fraction of hydrochloric acid used is 5% . Then wash with deionized water to remove stains and impurities on the surface of the membrane filament, and then dry in an oven to form a polyolefin microporous membrane. The oven temperature is set at 80°C, and the drying time is 6 hours;

(4) Make the polyolefin microporous membrane continue to pass through the hot water tank to complete the crosslinking under the action of silane hydrolysis, and the temperature of the hot water tank is 50°C;

(5) Finally, an oven is used to dry and anneal the polyolefin microporous membrane to prepare a cross-linked polyolefin microporous membrane. The drying temperature is 80°C, and the drying time is 6h; the annealing temperature is 90°C, and the annealing time is 12h.

The cross-linked polyolefin microporous membrane in Example 2 is prepared according to the following steps:

(1) Use a high-speed mixer to mix the raw materials in Example 2 evenly, and the speed of the high-speed mixer is 1000 rpm. Then use the twin-screw extruder to transport, plasticize and extrude to obtain the injection liquid. The twin-screw extrusion temperature is set at 200°C, and the screw speed is 200rpm;

(2) Then make the injection film pass through a T-shaped mouth film, cast on a metal roller to form a flat film; the temperature of the T-shaped mouth die is set to 200 ° C;

(3) then stretching the flat film, the stretching ratio is 10 times; then use the extraction liquid dehydrated alcohol extraction to remove dioctyl adipate, use hydrochloric acid to remove ultrafine calcium carbonate, the quality of hydrochloric acid used The score is 5%. Then wash with deionized water to remove stains and impurities on the surface of the membrane filament, and then dry in an oven to form a polyolefin microporous membrane. The oven temperature is set at 80°C, and the drying time is 6 hours;

(4) Make the polyolefin microporous membrane continue to pass through the hot water tank to complete the crosslinking under the action of silane hydrolysis, the temperature of the hot water tank is 70°C;

(5) Finally, an oven is used to dry and anneal the polyolefin microporous membrane to prepare a cross-linked polyolefin microporous membrane. The drying temperature is 80°C, and the drying time is 6h; the annealing temperature is 90°C, and the annealing time is 12h.

The cross-linked polyolefin microporous membrane in embodiment 3 is prepared according to the following steps:

(1) Use a high-speed mixer to mix the raw materials in Example 3 evenly, and the speed of the high-speed mixer is 1000 rpm. Then use the twin-screw extruder to transport, plasticize and extrude to obtain the injection liquid. The twin-screw extrusion temperature is set at 160°C, and the screw speed is 200rpm;

(2) Then make the film injection solution pass through a T-shaped mouth film, and cast it on a metal roller to form a flat film; the temperature of the T-shaped mouth mold is set to 160 ° C;

(3) Stretch the flat film, and the stretching ratio is 10 times; then use the extraction solution absolute ethanol to extract and remove the liquid paraffin, and use hydrochloric acid to remove ultrafine calcium carbonate, the mass fraction of hydrochloric acid used is 5% . Then wash with deionized water to remove stains and impurities on the surface of the membrane filament, and then dry in an oven to form a polyolefin microporous membrane. The oven temperature is set at 80°C, and the drying time is 6 hours;

(4) Make the polyolefin microporous membrane continue to pass through the hot water tank to complete the crosslinking under the action of silane hydrolysis, and the temperature of the hot water tank is 90°C;

(5) Finally, an oven is used to dry and anneal the polyolefin microporous membrane to prepare a cross-linked polyolefin microporous membrane. The drying temperature is 80°C, and the drying time is 6h; the annealing temperature is 90°C, and the annealing time is 12h.

Cross-linked polyolefin microporous membrane is prepared according to the following steps in embodiment 4:

(1) Use a high-speed mixer to mix the raw materials in Example 4 evenly, and the speed of the high-speed mixer is 1000 rpm. Then use a continuous internal mixer to mix, plasticize and extrude to obtain a film injection solution. The temperature of the internal mixer is set to 200 ° C, and the screw speed is 200 rpm;

(2) Then make the injection film pass through a metal spinneret, and then enter the cooling water tank (also known as the gel tank) to cool and solidify to form a hollow fiber-shaped film; the temperature of the spinneret is set to 200 ° C;

(3) Stretching the hollow fiber membrane, the stretching ratio is 10 times; then extracting and removing the dimethyl phthalate with the extract liquid absolute ethanol. Then wash with deionized water to remove stains and impurities on the surface of the membrane filament, and then dry in an oven to form a polyolefin microporous membrane. The oven temperature is set at 80°C, and the drying time is 6 hours;

(4) passing the polyolefin microporous membrane through a hot water tank to complete crosslinking under the action of silane hydrolysis, and the temperature of the hot water tank is 90°C;

(5) Finally, an oven is used to dry and anneal the polyolefin microporous membrane to prepare a cross-linked polyolefin hollow fiber microporous membrane. The drying temperature is 80°C, and the drying time is 6h; the annealing temperature is 90°C, and the annealing time is 12h.

The present invention describes as follows to the detection method of polymer microporous membrane:

·Thickness: Measured according to the national standard GB/T-6672-2001 "Mechanical Measurement Method for Thickness Determination of Plastic Films and Sheets". The thickness of the polymer microporous membrane to be measured is generally less than 100um, and the measurement accuracy is 1um. Generally, a common micrometer can be used.

·Gurley value: according to ASTM-D726(B). At room temperature, the time required for 10 mL of air to pass through a 6.45 cm2 (ie 1 square inch) microporous membrane at a water column pressure of 31.0 cm is measured in seconds. The Gurley value is related to the thickness, pore diameter, porosity and tortuosity of the microporous membrane. The Gurley value is easy to measure and can be measured accurately, and its deviation from the characteristic value can reflect the problems of the microporous membrane. The larger the Gurley value, the worse the gas permeability; in the case of lithium-ion battery separators, the greater the resistivity. Handbook of nonwoven filter media(2007)p.248

Pore size, pore size distribution and porosity: Measured according to the national standard GB/T 21650.1-2008 "Determination of pore size distribution and porosity of solid materials by mercury porosimetry and gas adsorption method Part 1: Mercury porosimetry".

Tensile strength: measured according to the national standard GB/T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets". In this disclosure, a distinction is deliberately made between the tensile strength in the direction of stretching and that perpendicular to the direction of stretching.

Melting temperature: use thermal mechanical analysis (Thermal Mechanical Analysis) to measure the change of microporous membrane sample size with temperature. When the TMA curve has obvious plastic changes, record this temperature as the melting temperature of the microporous membrane.

The properties of the cross-linked polyethylene microporous membranes formed in the above examples are shown in Table-1.

Table-1 The performance of the cross-linked polyethylene microporous membrane obtained in the embodiment and the comparison with the comparative example

The comparative example refers to a commercial polypropylene microporous membrane prepared by using the prior art, which is an uncrosslinked polypropylene film. Through the comparison of each example and comparative example, it is shown that the tensile strength, heat resistance stability and chemical resistance of the cross-linked polyethylene microporous membrane in the present invention are significantly improved.

Claims (6)

1. A cross-linked polyolefin microporous membrane is characterized in that the raw materials for making the membrane include: Polyolefin 28.8～48.8 parts by weight, Co-solvent 30～50 parts by weight, Peroxygen compound 0.1～2 parts by weight, Silane 1～5 parts by weight, Antioxidant 0.1 parts by weight, 0-20 parts by weight of superfine filler with an average particle size of 0.05-1 micron; The preparation method of described cross-linked polyolefin microporous membrane comprises the following steps: (1) Use a high-speed mixer to mix the above-mentioned raw materials evenly, and then use a twin-screw extruder or a continuous internal mixer to transport, plasticize and extrude to obtain a film injection solution. The twin-screw extruder and continuous internal mixer The heating temperature is set at 160-240°C; (2) Then let the injection liquid pass through a T-shaped mouth film, cast on a metal roller to form a flat film; or make the injection liquid pass through a metal spinneret, cool down in a gel tank, and form a hollow fiber membrane; (3) Then stretch the flat film or hollow fiber membrane, the stretching ratio is 5 to 10 times; finally use the extract and the extract to remove the co-solvent and ultrafine filler respectively, and form polyolefin after washing and drying Microporous membrane; (4) Make the polyolefin microporous membrane continue to pass through the hot water tank to complete the crosslinking under the action of silane hydrolysis, the temperature of the hot water tank is 50-90°C; (5) Next, dry and anneal the polyolefin microporous membrane to prepare a cross-linked polyolefin microporous membrane. 2. The cross-linked polyolefin microporous membrane according to claim 1, characterized in that: the polyolefin is any one or a combination of polyethylene resin or polypropylene resin. 3. cross-linked polyolefin microporous membrane according to claim 1, is characterized in that: described latent solvent is phthalates, aliphatic diacid esters, trimellitate, phosphoric acid ester Any one or a combination of any of polyols, glycerides, polyols, synthetic oils and paraffins, natural oils, and environmentally friendly plasticizers. 4. The cross-linked polyolefin microporous membrane according to claim 1, characterized in that: the silane is any one or a combination of vinyl organosilanes. 5. The cross-linked polyolefin microporous membrane according to claim 1, characterized in that: the ultrafine filler is nano calcium carbonate, ultrafine calcium carbonate, talcum powder, wollastonite, kaolin, diatomaceous earth, Exfoliated nano-montmorillonite, clay, titanium dioxide, precipitated silica, fumed silica, graphene, carbon nanopowder, carbon nanotubes, or any combination of several. 6 . The cross-linked polyolefin microporous membrane according to claim 1 , characterized in that: the average pore diameter of the polyolefin microporous membrane formed in step (3) is 0.01-1 micron by mercury porosimetry.