阅读说明：本技术 一种聚烯烃微多孔膜及其生产系统、电池隔膜、电化学装置 (Polyolefin microporous membrane and production system thereof, battery diaphragm and electrochemical device ) 是由 程跃 宫晓明 彭锟 虞少波 庄志 于 2020-12-15 设计创作，主要内容包括：本发明涉及电池隔膜领域,具体公开了一种膜厚为2～30μm、穿刺强度为1000～2000gf、MD方向的拉伸强度为3200～5000kgf/cm～2、TD方向的拉伸强度为2800～4800kgf/cm～2、孔隙率为40％～57％、最大孔径33～48nm、气体渗透速率为10～400秒/100ml、阻抗为0.3～0.9Ω/cm～2的聚烯烃微多孔膜以及其生产系统、使用该基膜的涂覆隔膜和电化学装置。本发明聚烯烃微多孔膜均具有出色的性能,它们的厚度、拉伸强度、穿刺强度、透气性、孔隙率以及热收缩率均能满足对微多孔膜的厚度和机械强度有较高要求的应用,非常适合用于动力锂离子电池隔膜领域。(The invention relates to the field of battery separators, and particularly discloses a battery separator with a membrane thickness of 2-30 mu m, a puncture strength of 1000-2000 gf, and a tensile strength of 3200-5000 kgf/cm in the MD direction 2 And a tensile strength in the TD direction of 2800 to 4800kgf/cm 2 The porosity is 40-57%, the maximum aperture is 33-48 nm, the gas permeation rate is 10-400 seconds/100 ml, and the impedance is 0.3-0.9 omega/cm 2 A polyolefin microporous membrane and a production system thereof, a coated separator and an electrochemical device using the base membrane. The polyolefin microporous membrane of the present invention has excellent properties, and the thickness, tensile strength, puncture strength, air permeability, porosity and heat shrinkage of the polyolefin microporous membrane satisfy the requirements for the microporous membraneThe thickness and the mechanical strength have higher requirements, and the lithium ion battery diaphragm is very suitable for the field of power lithium ion battery diaphragms.)

1. A polyolefin microporous membrane characterized by: the film thickness is 2 to 30 μm and the puncture strength is 1000 to 2000 gf.

2. The polyolefin microporous film according to claim 1, characterized in that: a tensile strength in the MD direction of 3200 to 5000kgf/cm²And a tensile strength in the TD direction of 2800 to 4800kgf/cm²。

3. The polyolefin microporous film according to claim 1, characterized in that: an elongation percentage in the MD direction of 47 to 98% and an elongation percentage in the TD direction of 63 to 110%.

4. The polyolefin microporous film according to claim 1, characterized in that: the porosity is 40% -57%, the maximum aperture is 33-48 nm, and the gas permeation rate is 10-400 seconds/100 ml.

5. The polyolefin microporous film according to claim 1, characterized in that: impedance of 0.3-0.9 omega/cm²。

6. The polyolefin microporous film according to claim 1, characterized in that: the polyolefin microporous membrane has a weight average molecular weight of 4.0 to 8.0 x 10⁶The polyethylene composition of (a).

7. A system for producing the polyolefin microporous membrane according to any one of claims 1 to 6, characterized in that: the device sequentially comprises a double-shaft extruder, a casting machine, a pore-forming agent removing unit, a first stretching device, a second stretching device, a heat treatment machine and a coiling machine along the production line direction.

8. The system for producing a polyolefin microporous membrane according to claim 7, characterized in that: the pore-forming agent removing unit comprises a groove body, a driving hot roller, a driven hot roller and a pore-forming agent removing liquid; the groove body is a sealed groove body, and a path through which the polyolefin microporous sheet passes by the casting machine is designed to be an open part.

9. The system for producing a polyolefin microporous membrane according to claim 8, characterized in that: the pore-forming agent removal liquid is positioned in the sealing groove body; the driving hot roller is positioned above the liquid level of the pore-forming agent removing liquid; the driven hot roll is immersed in the pore-forming agent removing liquid.

10. The system for producing a polyolefin microporous membrane according to claim 7, characterized in that: the second stretching device and the heat treating machine are integrated.

11. A battery separator, characterized by: the battery separator comprises the polyolefin microporous membrane according to any one of claims 1 to 6.

12. The battery separator of claim 11, wherein: the diaphragm is one of a ceramic coating diaphragm, a PVDF coating diaphragm and an aramid coating diaphragm.

13. An electrochemical device, characterized in that: comprising the polyolefin microporous membrane according to any one of claims 1 to 6 or the battery separator according to claim 11 or 12 as an element for separating positive and negative electrodes.

Technical Field

The invention relates to the field of battery separators, in particular to a polyolefin microporous membrane and a production system thereof, a battery separator and an electrochemical device.

Background

Polyolefin microporous membranes are generally used for various applications such as battery separators, electrolytic capacitor separators, ultrafiltration membranes, microfiltration membranes, and medical membranes. Both digital lithium ion batteries and power lithium ion batteries tend to be light and thin on the basis of ensuring the performance of a diaphragm. The polyolefin microporous membrane is made thin, and the number of stacked electrode layers can be increased, which is advantageous for increasing the energy density and capacity of a lithium battery, thereby making it possible to realize high output. However, the conventional ultrathin polyolefin microporous membrane has a disadvantage of poor strength, and the conventional ultrathin polyolefin microporous membrane is easily broken when it is wound as a separator film with high tension together with an electrode. Therefore, the prior art still cannot produce an ultrathin high-strength diaphragm with uniform thickness and stable quality.

In Chinese patent application No. CN 102136557A, a preparation method of a lithium ion battery diaphragm is disclosed, the method uses ultra-high molecular polyethylene as a main material to prepare the diaphragm with good strength and the thickness of 20 μm.

In japanese patent jp h0873643A, a method for preparing a lithium ion battery separator is disclosed, which uses polyethylene having a viscosity average molecular weight of 10 ten thousand or more to prepare a separator having a specific thickness, air permeability, porosity and tensile elongation, the thickness of the separator being 20 to 40 μm.

Disclosure of Invention

The formulations and methods disclosed in the above patents and patent applications solve the problem of film strength in the conventional art, but have the drawback that the thickness of the separator is too thick, which cannot meet the requirements of ultra-thinness and high strength. The technical difficulty of the ultrathin high-strength polyolefin microporous membrane is that the performances of the ultrathin membrane, such as thickness, strength, porosity and the like, cannot be considered, and the thickness uniformity of the membrane is poor.

Accordingly, an object of the present invention is to overcome the above-mentioned drawbacks of the prior art and to provide a microporous polyolefin membrane having high porosity, ultra-thinness, high strength, and good thickness uniformity, which is capable of improving battery performance and reducing battery cost.

In order to achieve the purpose, the technical scheme of the invention is realized as follows:

an object of the present invention is to provide a polyolefin microporous membrane having a membrane thickness of 2 to 30 μm and a puncture strength of 1000 to 2000 gf.

Further, the tensile strength in the MD direction is 3200 to 5000kgf/cm²And a tensile strength in the TD direction of 2800 to 4800kgf/cm²。

Further, the elongation in the MD direction is 47-98%, and the elongation in the TD direction is 63-110%.

Furthermore, the porosity is 40% -57%, the maximum aperture is 33-48 nm, and the gas permeation rate is 10-400 seconds/100 ml.

Further, the impedance is 0.3-0.9 omega/cm²。

Further, the polyolefin microporous membrane has a weight-average molecular weight of 4.0 to 8.0X 10⁶The polyethylene composition of (a).

The invention also aims to provide a system for producing any one of the polyolefin microporous membranes, which sequentially comprises a double-shaft extruder, a casting machine, a pore-forming agent removing unit, a first stretching device, a second stretching device, a heat treatment machine and a coiling machine along the direction of a production line.

Further, the pore-forming agent removing unit comprises a groove body, a driving hot roller, a driven hot roller and a pore-forming agent removing liquid; the groove body is a sealed groove body, and a path through which the polyolefin microporous sheet passes by the casting machine is designed to be an open part.

Furthermore, the pore-forming agent removal liquid is positioned in the sealing groove body; the driving hot roller is positioned above the liquid level of the pore-forming agent removing liquid; the driven hot roll is immersed in the pore-forming agent removing liquid.

Further, the second stretching device and the heat treating machine are integrated.

Another object of the present invention is to provide a battery separator comprising any one of the polyolefin microporous films described above.

Further, the diaphragm is one of a ceramic coating diaphragm, a PVDF coating diaphragm and an aramid coating diaphragm.

It is still another object of the present invention to provide an electrochemical device comprising any of the above polyolefin microporous membranes or any of the battery separators as an element for separating positive and negative electrodes.

Compared with the existing microporous membrane, the polyolefin microporous membrane prepared by the method can better meet the application with higher requirements on thickness uniformity, ultra-thinness and high strength of the microporous membrane, and is particularly suitable for the field of power lithium ion battery diaphragms.

Drawings

FIG. 1 is a schematic view of a porogen removal unit in accordance with one embodiment of the present invention;

FIG. 2 is a flow chart of a process for preparing a polyolefin microporous membrane according to the prior art;

FIG. 3 is a flow chart illustrating a process for preparing a microporous polyolefin membrane according to an embodiment of the present invention;

FIG. 4 is a flow chart illustrating a process for preparing a microporous polyolefin membrane according to another embodiment of the present invention;

description of the element reference numerals

1. Driving hot roller

2. Driven hot roller

3. Pore-forming agent removing liquid

4. Extrusion

5. Cooling into tablets

6. MD stretching

7. TD stretch

8. Porogen removal

9. TD Secondary stretching

10. And (3) stretching the SBS.

Detailed Description

The following detailed description of embodiments of the invention refers to the accompanying drawings. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.

The present invention provides a polyolefin microporous membrane having a membrane thickness of 2 to 30 μm and a puncture strength of 1000 to 2000 gf.

Further, the tensile strength in the MD direction is 3200 to 5000kgf/cm²And a tensile strength in the TD direction of 2800 to 4800kgf/cm²。

Further, the elongation in the MD direction is 47-98%, and the elongation in the TD direction is 63-110%.

Furthermore, the porosity is 40% -57%, the maximum aperture is 33-48 nm, and the gas permeation rate is 10-400 seconds/100 ml.

Further, the impedance is 0.3-0.9 omega/cm²。

Further, the polyolefin microporous membrane has a weight-average molecular weight of 4.0 to 8.0X 10⁶The polyethylene composition of (a).

The invention also provides a system for producing any one of the polyolefin microporous membranes, which sequentially comprises a double-shaft extruder, a casting machine, a pore-forming agent removing unit, a first stretching device, a second stretching device, a heat treatment machine and a coiling machine along the direction of a production line.

Further, the pore-forming agent removing unit comprises a groove body, a driving hot roller, a driven hot roller and a pore-forming agent removing liquid; the groove body is a sealed groove body, and a path through which the polyolefin microporous sheet passes by the casting machine is designed to be an open part.

Furthermore, the pore-forming agent removal liquid is positioned in the sealing groove body; the driving hot roller is positioned above the liquid level of the pore-forming agent removing liquid; the driven hot roll is immersed in the pore-forming agent removing liquid.

Further, the second stretching device and the heat treating machine are integrated.

Embodiments of the present invention also provide a battery separator comprising any one of the polyolefin microporous films described above.

Further, the diaphragm is one of a ceramic coating diaphragm, a PVDF coating diaphragm and an aramid coating diaphragm.

Embodiments of the present invention also provide an electrochemical device comprising any of the above polyolefin microporous membranes or any of the battery separators as an element for separating positive and negative electrodes.

The embodiment of the invention also provides a preparation method for preparing the polyolefin microporous membrane to be protected, which sequentially comprises the following steps:

(1) mixing and heating polyolefin resin and a pore-forming agent to a molten mixed solution;

(2) extruding the mixed solution from a die head and cooling to form a casting sheet containing the pore-forming agent;

(3) the casting sheet passes through a boiling pore-forming agent removing unit to remove the pore-forming agent;

(4) stretching the cast sheet from which the pore-forming agent is removed in at least one axial direction to obtain a base film;

(5) stretching and shaping the base film at least along one axial direction again to obtain the polyolefin microporous film;

the boiling pore former removing unit comprises a groove body, a driving hot roller 1, a driven hot roller 2 and a pore former removing liquid 3; the heating temperature of the driving hot roller 1 and the driven hot roller 2 is 50-140 ℃; the polyolefin microporous membrane has a pore-forming agent residual ratio of less than 0.05%, preferably less than 0.02%, more preferably less than 0.01%, and most preferably a pore-forming agent residual amount of 0.

Further, the pore-forming agent accounts for 40-50% of the total mass of the polyolefin resin and the pore-forming agent, and the kinematic viscosity at 60 ℃ is 5-200 mm²/s。

In the present application, there is no particular limitation on the pore-forming agent used as long as it can sufficiently dissolve the polyolefin, and the pore-forming agent may be, for example, but not limited to, one or more of liquid paraffin, mineral oil, and soybean oil. Most preferably, the pore former is liquid paraffin.

Liquid paraffin as pore-forming agent, and polyolefin resin such as polyethylene resin are melt-kneaded and extracted together, and then multi-layer oriented pore structure can be formed in the porous base material, thereby greatly increasing the successive stretching ratio of the gel-like membrane. The higher the stretching ratio and the degree of crystallization, the higher the mechanical strength of the porous substrate. Therefore, the liquid paraffin as the pore-forming agent can improve the tensile strength and puncture strength of the porous film, so that the thinning of the porous film is further realized.

Further, the weight average molecular weight of the polyolefin resin is 4.0-8.0 x 10⁶The polyolefin resin accounts for 50-60% of the total mass of the polyolefin resin and the pore-forming agent.

In the present application, the term "polyolefin" refers to a polymer made by polymerization or copolymerization of one or several olefins, including but not limited to polyolefin resins selected from one or more of polyethylene, polypropylene, polyisopropylene, or polybutylene. More preferably, the polyolefin resin is polyethylene.

Further, the driving heat roller 1 and the driven heat roller 2 are heated by hot oil flowing inside the rollers.

Further, the pore-forming agent removing liquid 3 is an organic solvent miscible with the pore-forming agent. Preferably, the pore-forming agent removing solution is dichloromethane.

Furthermore, the groove body is a sealed groove body, and a path through which the polyolefin microporous sheet passes from the casting machine is designed to be an open part.

As shown in fig. 1, further, the pore-forming agent removing liquid 3 is located in the sealing groove body; the driving hot roller 1 is positioned higher than the liquid level of the pore-forming agent removing liquid 3; the driven heat roller 2 is immersed in the pore-forming agent-removing liquid 3.

The driving heat roller 1 and the driven heat roller 2 are heated to 50 to 140 c by introducing heat transfer oil, and here, a specific method of heating the driving heat roller 1 and the driven heat roller 2 is the same as the method of roller heating in the conventional MD and TD stretching 6, 7, and it is a routine technique of those skilled in the art and a detailed description is not necessary here. At this time, the polyolefin microporous sheet heated by the driving heat roller 1 and the driven heat roller 2 immersed in the pore-forming agent removing solution 3 heat methylene chloride of 0 to 10 ℃ in a normal state to 30 to 39.8 ℃.

During the heating process of the liquid molecules in the pore-forming agent removing liquid 3, the liquid molecules obtain larger kinetic energy through heat transfer and are very active, and the energy generated by the kinetic energy is enough to break loose the acting force among the liquid molecules, so the viscosity of the liquid molecules is reduced; in addition, the increase in temperature accelerates the movement or vibration of the molecules, so that the intermolecular repulsion rises, and in order to achieve equilibrium again, the intermolecular distance increases, and both the attractive and repulsive forces decrease, so that the attractive and repulsive forces again achieve equilibrium, thereby causing the surface tension of the liquid to drop. Therefore, the pore-forming agent removing liquid 3 can enter micro-porous easily, the exchange rate is improved, the successful agent removing efficiency is increased, and the residual rate of the pore-forming agent is lower than 0.05%. Further, different pore-forming agent proportion raw material formulas are prepared, the heating temperatures of the driving hot roller 1 and the driven hot roller 2 are different, the efficiency of successfully removing the pore-forming agent is improved, the residual rate of the pore-forming agent is lower than 0.02 percent and lower than 0.01 percent, and even the residual amount of the pore-forming agent is 0.

Further, the stretching in step (4) is asynchronous biaxial stretching (MD + TD) or Synchronous Biaxial Stretching (SBS).

As shown in fig. 3, when the stretching in step (4) is asynchronous biaxial stretching, after the successful agent is removed by using the pore-forming agent removing unit of the present invention, the roughness of the polyolefin sheet is increased, so that when the MD roll surface is stretched 6, the friction between the roll surface and the polyolefin sheet is increased, and the polyolefin sheet is not easy to slip. Thereby realizing the higher molecular weight (4.0-8.0 multiplied by 10) of the invention⁶) And the cast sheet with the higher powder ratio (50-60%) is stretched 10-35 times along the MD direction and then 10-20 times along the TD direction. More preferably, the stretching ratio is 15 to 25 times in the MD direction and 10 to 15 times in the TD direction.

As shown in fig. 4, when the stretching in step (4) is synchronous biaxial stretching, after the successful agent is removed by the pore-forming agent removing unit of the present invention, the roughness of the polyolefin sheet is increased, so that when the SBS jig is stretched 10, the friction force between the jig and the polyolefin sheet is increased, and the separation is not easy. Thereby realizing the higher molecular weight (4.0-8.0 multiplied by 10) of the invention⁶) And the cast sheet with the formula with higher powder ratio (50-60%) is stretched by 10-20 times. Further preferably, the stretching ratio is 10 to 15.

Further, the stretching ratio of the base film in step (5) to be stretched in at least one axial direction is 2 to 4 times.

After the high-magnification stretching by the different methods, the orientation of the final product diaphragm is increased, so that the mechanical strength (tensile strength and needling strength) of the diaphragm is greatly enhanced, the phenomenon of multi-micropore closed hole/hole dislocation of the sheet caused by slipping is avoided, more straight through holes are formed, more lithium ion channels with high straight through rate are created, and the impedance of the diaphragm is reduced.

The present invention will be described in detail below by way of examples.

In the following examples and comparative examples, the film property test was performed as follows:

film thickness: measuring the width of the finished product at intervals of 10cm along the longitudinal direction by using a Mark thickness tester, and then obtaining the average value of the film thickness;

air permeability value: at room temperature, a 100cc gas passage time through the diaphragm was set using a joker's permeability gauge, and the stable value after 5 seconds was stably measured;

porosity: intercepting a 100mm multiplied by 100mm sample wafer, weighing by using an electronic balance, and combining polyethylene density according to a formula: (1-weight/area of coupon)/weight × 0.957 × 100% conversion;

maximum pore diameter: measuring by bubble point method using nitrogen gas using a narrow pore diameter tester;

tensile strength & elongation at break: using an electronic universal material testing machine XJ830, cutting the specification: measuring the traveling speed of 15mm multiplied by 20cm and 200 mm/min;

the needling strength is as follows: clamping a sample to be tested by using an electronic universal material testing machine XJ830, and measuring at a traveling speed of 50mm/min by using a front end with the diameter of 1mm (0.5 mmR);

heat shrinkage ratio: the 100mm x 100mm microporous membrane was placed at 110 ℃ for 1H using a high temperature test chamber Espec SEG-021H and subjected to length measurement by an image measuring instrument XTY-5040, and the TD and MD direction lengths before and after baking were counted using the formula: (before heat treatment-after heat treatment)/before heat treatment x 100% conversion;

kinematic viscosity: using a kinematic viscosity determinator DSY-004, setting the measurement temperature to be 60 ℃, and carrying out kinematic viscosity measurement after stabilizing for 1 h;

residual oil ratio: cutting 10mm × 10mm diaphragm sample, weighing with electronic balance, placing pure water in Ultrasonic Cleaner 1740T, placing 300ml pure dichloromethane in 500ml beaker, placing sample, setting Ultrasonic time to be 60s, then placing in 105 deg.C oven for drying for 5min, weighing weight before and after cleaning with electronic balance, using formula: (pre-treatment weight-post-treatment weight)/pre-treatment weight x 100% converted residual oil rate;

impedance: and (3) adding sample by using a sample adding device of the battery chamber, adding electrolyte to 2/3 scales of the battery chamber, selecting a resistance testing channel by using an Agilent data acquisition instrument KEYSIGHT 34972A, clicking to operate, and waiting for the equipment to automatically analyze data.

Example 1

First, 50% by mass of polyethylene (Mw 8.0X 10)⁶) And 50% white oil were fed into an extruder at a flow rate of 500kg/h, extruded at 220 ℃ and 100rpm through a T die, and cooled by contact with a chill roll at 35 ℃ to form a cast sheet. And then entering a pore-forming agent removing unit, heating the driving hot roller 1 and the driven hot roller 2 to 140 ℃ through heat conduction oil, further heating the dichloromethane in the groove body to 39.8 ℃, and performing a pore-forming agent removing process. The cast sheet from which the pore-forming agent was removed was stretched 10 times in the Machine Direction (MD)6 at 120 ℃ by a stretcher, then stretched 10 times in the width direction (TD)7 at 100 ℃, and then subjected to TD stretching 2 times at 120 ℃ to fix 9, and then wound up by a winding roll to obtain a polyolefin microporous membrane having a thickness of 30 μm.

Example 2

First, 55% by mass of polyethylene (Mw of 6.0X 10)⁶) And 45% white oil were fed into an extruder at a flow rate of 650kg/h, extruded at 220 ℃ and 100rpm through a T die, and cooled by contact with a chill roll at 35 ℃ to form a cast sheet. And then entering a pore-forming agent removing unit, heating the driving hot roller 1 and the driven hot roller 2 to 100 ℃ through heat conduction oil, and further heating the dichloromethane in the groove body to 35 ℃ to perform a pore-forming agent removing procedure. After removal of the pore-forming agentThe cast sheet was stretched 20 times in the Machine Direction (MD)6 at 120 ℃ by a stretcher, then stretched 15 times in the width direction (TD)7 at 100 ℃, then subjected to TD stretching 9 setting twice at 120 ℃ and wound up by a winding roll to obtain a polyolefin microporous membrane having a thickness of 14 μm.

Example 3

First, 55% by mass of polyethylene (Mw of 6.0X 10)⁶) And 45% white oil were fed into an extruder at a flow rate of 400kg/h, extruded at 220 ℃ and 100rpm through a T die, cooled by contact with a chill roll at 35 ℃ to form a cast sheet. And then entering a pore-forming agent removing unit, heating the driving hot roller 1 and the driven hot roller 2 to 100 ℃ through heat conduction oil, and further heating the dichloromethane in the groove body to 35 ℃ to perform a pore-forming agent removing procedure. The cast sheet from which the pore-forming agent was removed was stretched 20 times in the Machine Direction (MD)6 at 120 ℃ by a stretcher, then stretched 15 times in the width direction (TD)7 at 100 ℃, and then subjected to TD stretching 2 times at 120 ℃ to be 9-set, and then wound up by a winding roll to obtain a polyolefin microporous membrane having a thickness of 9 μm.

Example 4

First, 55% by mass of polyethylene (Mw of 6.0X 10)⁶) And 45% white oil were fed into an extruder at a flow rate of 300kg/h, extruded at 220 ℃ and 100rpm through a T die, cooled by contact with a chill roll at 35 ℃ to form a cast sheet. And then entering a pore-forming agent removing unit, heating the driving hot roller 1 and the driven hot roller 2 to 100 ℃ through heat conduction oil, and further heating the dichloromethane in the groove body to 35 ℃ to perform a pore-forming agent removing procedure. The cast sheet from which the pore-forming agent was removed was stretched 20 times in the Machine Direction (MD)6 at 120 ℃ by a stretcher, then stretched 15 times in the width direction (TD)7 at 100 ℃, and then subjected to TD stretching 2 times at 120 ℃ to fix 9, and then wound up by a winding roll to obtain a polyolefin microporous membrane having a thickness of 7 μm.

Example 5

First, 60% by mass of polyethylene (Mw of 4.0X 10)⁶) And 40% white oil at 500kg/hThe resulting mixture was extruded at a flow rate of 220 ℃ and 100rpm through a T die, and cooled by contact with a chill roll having a temperature of 35 ℃ to form a cast sheet. And then entering a pore-forming agent removing unit, heating the driving hot roller 1 and the driven hot roller 2 to 50 ℃ through heat conduction oil, and further heating the dichloromethane in the groove body to 30 ℃ to carry out a pore-forming agent removing procedure. The cast sheet from which the pore-forming agent was removed was stretched 35 times in the Machine Direction (MD)6 at 120 ℃ by a stretcher, then stretched 20 times in the width direction (TD)7 at 100 ℃, and then subjected to TD stretching 2 times at 120 ℃ to fix 9, and then wound up by a winding roll to obtain a polyolefin microporous membrane having a thickness of 2 μm.

Comparative example 1

Using a conventional process, 20% by weight polyethylene (Mw of 3.5X 10) is first introduced⁶) And 80% white oil at a flow rate of 90kg/h were fed into an extruder and extruded, at 180 ℃ and 80rpm, through a T die, and after cooling by a chill roll at 35 ℃ a cast sheet was formed. The cast sheet was stretched 9 times in the Machine Direction (MD)6 at 110 ℃ by a stretcher, then stretched 8 times in the width direction (TD)7 at 110 ℃, then extracted in a dichloromethane tank at 15 ℃ to remove the pore-forming agent, and then subjected to TD stretching 2 times at 120 ℃ for 9-fold setting, and wound up by a winding roll to obtain a polyolefin microporous membrane having a thickness of 2 μm.

Comparative example 2

Using a conventional process, 20% by weight polyethylene (Mw of 3.5X 10) is first introduced⁶) And 80% white oil at a flow rate of 300kg/h were fed into an extruder and extruded, at 180 ℃ and 80rpm, through a T die, and after cooling by contact with a chill roll at 35 ℃ a cast sheet was formed. The cast sheet was stretched 9 times in the Machine Direction (MD)6 at 110 ℃ by a stretcher, then stretched 8 times in the width direction (TD)7 at 110 ℃, then extracted in a dichloromethane tank at 15 ℃ to remove the pore-forming agent, and then subjected to TD stretching 2 times at 120 ℃ for 9-fold setting, and wound up by a winding roll to obtain a polyolefin microporous membrane with a thickness of 7 μm.

Comparative example 3

Using a conventional process, 20% by weight polyethylene (Mw of 3.5X 10) is first introduced⁶) And 80% white oil at a flow rate of 380kg/h were fed into an extruder and extruded, at 180 ℃ and 80rpm, through a T die, and after cooling by a chill roll at 35 ℃ a cast sheet was formed. The cast sheet was stretched 9 times in the Machine Direction (MD)6 at 110 ℃ by a stretcher, then stretched 8 times in the width direction (TD)7 at 110 ℃, then extracted in a dichloromethane tank at 15 ℃ to remove the pore-forming agent, and then TD stretched 9-shaped twice at 120 ℃ and wound up by a winding roll to obtain a polyolefin microporous membrane having a thickness of 9 μm.

Comparative example 4

Using a conventional process, 20% by weight of polyethylene (Mw of 3.5X 10)⁶) And 80% white oil at a flow rate of 600kg/h were fed into an extruder and extruded, at 180 ℃ and 80rpm, through a T die, and after cooling by a chill roll at 35 ℃ a cast sheet was formed. The cast sheet was stretched 9 times in the Machine Direction (MD)6 at 110 ℃ by a stretcher, then stretched 8 times in the width direction (TD)7 at 110 ℃, then extracted in a dichloromethane tank at 15 ℃ to remove the pore-forming agent, and then subjected to TD stretching 2 times at 120 ℃ for 9-fold setting, and wound up by a winding roll to obtain a polyolefin microporous membrane with a thickness of 14 μm.

Comparative example 5

Using a conventional process, 20% by weight of polyethylene (Mw of 3.5X 10)⁶) And 80% white oil at a flow rate of 800kg/h were fed into an extruder and extruded, at 180 ℃ and 80rpm, through a T die, and after cooling by a chill roll at 35 ℃ a cast sheet was formed. Stretching the cast sheet 6 times in the Machine Direction (MD)6 at 110 deg.C, stretching 8 times in the width direction (TD)7 at 110 deg.C, extracting in dichloromethane tank at 15 deg.C to remove pore-forming agent, performing 2 times TD stretching at 120 deg.C for 9 times, and coiling with a coiling roller to obtain polyolefin micro-poly with thickness of 30 μmAnd (4) a pore membrane.

The results of the performance test of the separators of examples 1 to 5 and comparative examples 1 to 5 are shown in table 1.

Table 1 comparative table of performance of example and comparative example separators

Comparing examples 1 to 5 with comparative examples 1 to 5, it can be seen that the polyolefin microporous membrane of the present invention has a small difference in air permeability, but has excellent porosity and heat shrinkage, and the puncture strength and tensile strength are significantly and substantially enhanced, and the impedance is greatly reduced.

The polyolefin microporous membrane has excellent performance, and the thickness, tensile strength, puncture strength, air permeability, porosity and heat shrinkage rate of the polyolefin microporous membrane can meet the application with higher requirements on the thickness and mechanical strength of the microporous membrane, and is very suitable for the field of power lithium ion battery diaphragms.

The polyolefin microporous membrane prepared by the method can also be applied to various fields such as filtration membranes of humidification membranes, water purification membranes, artificial dialysis membranes, nanofiltration membranes, ultrafiltration membranes, reverse osmosis membranes and the like, cell propagation substrates and the like.

The above description related to the common general knowledge is not described in detail (e.g., the regulation of the thickness of the membrane product by the amount of the charged material is a routine operation in the art), and can be understood by those skilled in the art.

The above-described embodiments are merely illustrative of the principles of the present invention and its efficacy, and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.