阅读说明：本技术 一种高延伸率聚烯烃微多孔膜及其制备方法、电池 (High-elongation polyolefin microporous membrane, preparation method thereof and battery ) 是由 庄志 孙绪栋 彭锟 宫晓明 李堃 虞少波 王志豪 袁其振 陈强 王思双 欧阳玲萍 于 2021-08-30 设计创作，主要内容包括：本发明涉及锂电池隔膜领域,具体公开了一些高延伸率聚烯烃微多孔膜的制备方法。本发明通过升高摸头和激冷辊的距离、制备过程中采取拉伸-缓慢回缩-不热定型等工艺手段,可以使隔膜在孔隙率、透气度等性能不受影响的情况下,大幅度提升其双向延伸率、拉伸强度和针刺强度性能。随着高端3C消费类电子的发展,如柔性屏,可穿戴设备等,本发明工艺及其制备出的隔膜以及使用该隔膜的电池将具有广阔的应用前景和市场。(The invention relates to the field of lithium battery separators, and particularly discloses a preparation method of polyolefin microporous membranes with high elongation. The invention can greatly improve the performance of the two-way elongation, the tensile strength and the needling strength of the diaphragm under the condition that the performances of porosity, air permeability and the like are not influenced by increasing the distance between the die head and the chill roll and adopting the technological means of stretching, slow retraction, no heat setting and the like in the preparation process. With the development of high-end 3C consumer electronics, such as flexible screens, wearable devices and the like, the process, the diaphragm prepared by the process and the battery using the diaphragm have wide application prospects and markets.)

1. A preparation method of a polyolefin microporous membrane with high elongation is characterized by comprising the following steps:

(1) mixing and heating polymer resin and plasticizer to be molten, extruding through a die head, contacting with a chilling roller, and cooling to form a sheet; wherein the distance between the die head and the chill roll is adjustable;

(2) longitudinally stretching the sheet, controlling the temperature to be 110-130 ℃, controlling the longitudinal stretching ratio to be more than or equal to 10, and slowly retracting by 60-80%;

(3) carrying out first transverse stretching, controlling the temperature to be 110-130 ℃, controlling the first transverse stretching ratio to be more than or equal to 10, and slowly retracting by 60-80%;

(4) and performing second transverse stretching, wherein the temperature is controlled to be less than or equal to 130 ℃, the second transverse stretching multiplying power is controlled to be more than or equal to 5, and the slow retraction is 20-30%.

2. The method for preparing a high-elongation polyolefin microporous membrane according to claim 1, characterized in that:

in the step (2), the longitudinal stretching ratio is more than or equal to 10 at 110-130 ℃, then the slow retraction is carried out by 60-80%, and then the heat setting is not carried out;

in the step (3), the first transverse stretching magnification is more than or equal to 10 at 110-130 ℃, then slowly retracting is carried out for 60-80%, and then heat setting is not carried out;

in the step (4), the second transverse stretching multiplying power is more than or equal to 5 at 120-130 ℃, then the slow retraction is carried out for 20-30%, and then the heat setting is not carried out.

3. The method for preparing a high-elongation polyolefin microporous membrane according to claim 1, characterized in that: the weight average molecular weight of the polymer resin is 4.0-8.0 multiplied by 10⁶The mass ratio of the polyolefin to the plasticizer is 50: 50-60: 40.

4. The method for preparing a high-elongation polyolefin microporous membrane according to claim 1, characterized in that: the polymer resin is composed of one or more polyolefin components.

5. The method for preparing a high-elongation polyolefin microporous membrane according to claim 4, wherein: the polymer resin is a single component polyethylene.

6. A preparation method of a polyolefin microporous membrane with high elongation is characterized by comprising the following steps:

(1) mixing and heating polymer resin and plasticizer to be molten, extruding through a die head, contacting with a chilling roller, and cooling to form a sheet; wherein the distance between the die head and the chill roll is adjustable;

(2) synchronously and bidirectionally stretching the sheet, controlling the temperature to be 110-130 ℃, controlling the stretching ratio to be more than or equal to 10, and slowly retracting to 60-80%;

(3) then transverse stretching is carried out, the temperature is controlled to be less than or equal to 130 ℃, the transverse stretching multiplying power is controlled to be more than or equal to 5, and the slow retraction is 20-30%.

7. The method for preparing a high-elongation polyolefin microporous membrane according to claim 6, wherein:

in the step (2), synchronous biaxial stretching is carried out for 10 times or more at 110-130 ℃, then slow retraction is carried out for 60-80%, and then heat setting is not carried out;

in the step (3), the transverse stretching is carried out for 5 times or more at 120-130 ℃, then the slow retraction is carried out for 20-30 percent, and then the heat setting is not carried out.

8. The method for preparing a high-elongation polyolefin microporous membrane according to claim 6, wherein: the weight average molecular weight of the polymer resin is 4.0-8.0 multiplied by 10⁶The mass ratio of the polyolefin to the plasticizer is 50: 50-60: 40, and the polymer resin is composed of one or more polyolefin components.

9. The method for preparing a high-elongation polyolefin microporous membrane according to claim 8, wherein: the polymer resin is a single component polyethylene.

10. The method for preparing a high-elongation polyolefin microporous membrane according to claim 1 or 6, characterized in that: the distance between the die head and the chill roll is adjustable and is 0.2-2 m.

11. A high-elongation polyolefin microporous film characterized by: the high-elongation polyolefin microporous membrane has an elongation of more than 180% in the MD direction and an elongation of more than 180% in the TD direction.

12. The high-elongation polyolefin microporous film according to claim 11, characterized in that: the polyolefin is a single component polyethylene.

13. The high-elongation polyolefin microporous film according to claim 11, characterized in that: the weight average molecular weight of the polyolefin is 4.0-8.0 x 10⁶。

14. The high-elongation polyolefin microporous film according to claim 11, characterized in that: the high-elongation polyolefin microporous membrane has a single-layer structure.

15. The high-elongation polyolefin microporous film according to claim 11, characterized in that: (the value of (elongation in the longitudinal direction, MD + tensile strength in the longitudinal direction + needling strength + elongation in the TD + tensile strength in the width direction + needling strength)/2 is 5000 or more; wherein the unit of elongation is% and the unit of tensile strength is Kgf/cm²The unit of the needling strength is gf.

16. The high-elongation polyolefin microporous film according to claim 11, characterized in that: the high-elongation polyolefin microporous membrane has an elongation of more than 200% in the MD direction and an elongation of more than 200% in the TD direction.

17. The high-elongation polyolefin microporous film according to claim 11, characterized in that: the high-elongation polyolefin microporous membrane has a needle punching strength of 800 to 2000gf and a tensile strength of 2900 to 7500kgf// cm²。

18. The high-elongation polyolefin microporous membrane according to claim 15, characterized in that: (the value of (elongation in the longitudinal direction, MD tensile strength, needling strength, TD elongation, widthwise tensile strength, needling strength)/2 is 5000 to 7000; wherein the unit of elongation is% and the unit of tensile strength is Kgf/cm²The unit of the needling strength is gf.

19. The high-elongation polyolefin microporous membrane according to claim 17, characterized in that: the high-elongation polyolefin microporous membrane has a needle punching strength of 1400 to 1800gf and a tensile strength of 3000 to 6000kgf// cm²。

20. A battery, characterized by: comprising the high-elongation polyolefin microporous membrane as claimed in any one of claims 11 to 19 as an element for separating positive and negative electrodes.

Technical Field

The invention relates to the field of lithium battery diaphragms, in particular to a high-elongation polyolefin microporous membrane, a preparation method thereof and a battery.

Background

Along with the development of lithium ion batteries in the directions of high energy density, high-rate charge and discharge, long cycle and high safety, the requirements on polyolefin diaphragms are more and more strict, wherein the high tensile strength of the diaphragms can ensure that the diaphragms bear high external stress without breaking to cause short circuit of battery cells. The low elongation rate causes the diaphragm to have external collision or impact and easy stress concentration to cause smaller deformation after stress, the lack of buffer room causes the diaphragm to be directly damaged, and the high elongation rate and the high tensile strength enable the battery to achieve high safety. Meanwhile, at the present of rapid development of flexible screens and wearable devices, further requirements are put forward on the performance of the diaphragm, such as excellent elongation, so as to achieve the folding effect.

At present, factors which influence each other and restrict each other exist in production, so that the preparation of the diaphragm with high elongation and high strength is difficult, the high elongation and the high tensile strength of the diaphragm cannot be simultaneously met, the conventional wet diaphragm strain process is complex, and the yield point does not appear. Resulting in a separator having higher strength but not capable of obtaining a greater elongation.

Disclosure of Invention

In view of the above, the present invention is to provide a polyolefin microporous membrane with high elongation and a method for preparing the same, so as to solve the technical problem.

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

the invention aims to provide a preparation method of a high-elongation polyolefin microporous membrane, which comprises the following steps:

(1) mixing and heating polymer resin and plasticizer to be molten, extruding through a die head, contacting with a chilling roller, and cooling to form a sheet; wherein the distance between the die head and the chill roll is adjustable and is 0.2-2 m;

(2) longitudinally stretching the sheet, controlling the temperature to be 110-130 ℃, controlling the longitudinal stretching magnification to be more than or equal to 10, and then slowly retracting by 60-80%;

(3) carrying out first transverse stretching, controlling the temperature to be 110-130 ℃, controlling the first transverse stretching magnification to be more than or equal to 10, and then slowly retracting by 60-80%;

(4) and carrying out second transverse stretching, controlling the temperature to be less than or equal to 130 ℃, controlling the second transverse stretching multiplying power to be more than or equal to 5, and then slowly retracting by 20-30%.

Further, in the step (2), the longitudinal stretching ratio is more than or equal to 10 at 110-130 ℃, then the slow retraction is carried out by 60-80%, and then the heat setting is not carried out; in the step (3), the first transverse stretching magnification is more than or equal to 10 at 110-130 ℃, then slowly retracting is carried out for 60-80%, and then heat setting is not carried out; in the step (4), the second transverse stretching multiplying power is more than or equal to 5 at 120-130 ℃, then the slow retraction is carried out for 20-30%, and then the heat setting is not carried out.

Further, the weight average molecular weight of the polymer resin is 4.0-8.0 x 10⁶The mass ratio of the polyolefin to the plasticizer is 50: 50-60: 40.

Further, the polymer resin is composed of one or more polyolefin components.

Still further, the polymer resin is a single component polyethylene.

The invention aims to further provide a preparation method of the high-elongation polyolefin microporous membrane, which comprises the following steps:

(1) mixing and heating polymer resin and plasticizer to be molten, extruding through a die head, contacting with a chilling roller, and cooling to form a sheet; wherein the distance between the die head and the chill roll is adjustable and is 0.2 m-2 m;

(2) synchronously and bidirectionally stretching the sheet, controlling the temperature to be 110-130 ℃, controlling the stretching magnification to be more than or equal to 10, and slowly retracting by 60-80%;

(3) then transverse stretching is carried out, the temperature is controlled to be less than or equal to 130 ℃, the transverse stretching multiplying power is more than or equal to 5, and the slow retraction is 20-30%.

Further, in the step (2), the synchronous biaxial stretching ratio is more than or equal to 10 at 110-130 ℃, then the slow retraction is carried out by 60-80%, and then the heat setting is not carried out; in the step (3), the transverse stretching ratio is more than or equal to 5 at 120-130 ℃, then the slow retraction is carried out by 20-30%, and then the heat setting is not carried out.

Further, the distance between the die and the chill roll may preferably be 1m to 2 m.

Further, the weight average molecular weight of the polymer resin is 4.0-8.0 x 10⁶The mass ratio of the polyolefin to the plasticizer is 50: 50-60: 40, and the polymer resin is composed of one or more polyolefin components.

Still further, the polymer resin is a single component polyethylene.

The present invention also provides a high-elongation polyolefin microporous membrane, characterized in that: the high-elongation polyolefin microporous membrane has an elongation of more than 180% in the MD direction and an elongation of more than 180% in the TD direction.

Further, the MD/TD bidirectional elongation of the high-elongation polyolefin microporous membrane is more than 200%. More preferably, the elongation in the MD direction is 260% or more and the elongation in the TD direction is 210% or more.

Further, the polyolefin is a single component polyethylene.

Further, the weight average molecular weight of the polyolefin is 4.0-8.0 x 10⁶。

Further, the high-elongation polyolefin microporous membrane has a single-layer structure.

Further, (elongation in the longitudinal direction, that is, MD direction + tensile strength in the longitudinal direction)The value of + needling strength + width, i.e., elongation in the TD direction + tensile strength in the width direction + needling strength)/2 is 5000 or more; wherein the unit of elongation is% and the unit of tensile strength is Kgf/cm²The unit of the needling strength is gf.

Further, the value of (elongation in the longitudinal direction, i.e., MD direction, tensile strength in the longitudinal direction, needling strength, elongation in the TD direction, i.e., TD direction, tensile strength in the width direction, and needling strength)/2 is 5000 to 7000; the value is 5100-7000; wherein the unit of elongation is% and the unit of tensile strength is Kgf/cm²The unit of the needling strength is gf.

Further, the high-elongation polyolefin microporous membrane has a needle punching strength of 800 to 2000gf and a tensile strength of 2900 to 7500kgf// cm²。

Further, the high-elongation polyolefin microporous membrane has a needle punching strength of 1400 to 1800gf and a tensile strength of 3000 to 6000kgf// cm²。

The present invention also aims to provide a battery using a microporous polyolefin membrane containing any of the above-mentioned high-elongation polyolefin membranes as a member for separating positive and negative electrodes.

Compared with the prior art, the invention can greatly improve the biaxial elongation, the tensile strength and the needling strength performance of the traditional single polyethylene separation film under the condition that the performances such as porosity, air permeability and the like are not influenced by increasing the distance between a touch head and a chill roll and adopting the technological means such as stretching, slow retraction, no heat setting and the like in the preparation process. With the development of high-end 3C consumer electronics, such as flexible screens, wearable devices and the like, the process, the diaphragm prepared by the process and the battery using the diaphragm have wide application prospects and markets.

Drawings

FIG. 1 is a schematic view of a conventional process for molecular linking of cast sheets;

FIG. 2 is a schematic view of molecular linking of the inventive tape casting sheet;

FIG. 3 is a schematic diagram of the conventional process for breaking a stretched molecular chain;

FIG. 4 is a schematic diagram of the ordered arrangement of the stretched molecular chains of the process of the present invention;

FIG. 5 is a schematic view of a die and chill roll according to one embodiment of the present invention;

FIG. 6 is a schematic view of a prior art die and chill roll;

FIG. 7 is a process flow diagram of an embodiment of asynchronous biaxial stretching according to the present invention;

FIG. 8 is a flow chart of a wet process for an asynchronous biaxially oriented lithium battery separator of the prior art;

FIG. 9 is a process flow diagram of a simultaneous biaxial stretching embodiment of the present invention;

FIG. 10 is a flow chart of a prior art wet process for a synchronous biaxially oriented lithium battery separator;

description of the element reference numerals

1. Die head

2. Chill roll

3. Fixed spacing

4. Height adjustable

S1, extrusion

S2, cooling into pieces

S3, MD stretching

S4, TD1 stretching

S5 pore former removal

S6, TD2 stretching

S7, heat setting

S8, MD stretching and slow retraction

S9, TD1 stretching and slow retraction

S10, TD2 stretching and slow retraction

S11, SBS stretching and slow retraction

S12 SBS stretching

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.

Referring to fig. 5 and 7, the embodiment of the present invention provides a method for preparing a high-elongation polyolefin microporous membrane, comprising the steps of:

(1) mixing and heating polymer resin and plasticizer to be molten, extruding the molten polymer resin and plasticizer out of S1 through a die head 1, contacting with a chill roll 2, and cooling to form a sheet S2; wherein, the distance 4 between the die head and the chill roll is adjustable (the height of the chill roll is adjusted up and down, specifically a chill roll bearing is fixed on a stroke track and matched with a cylinder to rise and fall), is 0.2-2 m, and is further preferably 1-2 m, (the melted state of polyolefin and pore former flows out from a lip mouth and is called casting before contacting the chill roll for solid-liquid phase separation, in this state, molecules and molecular chains can freely move at high speed, because the stress is vertical downward gravity, the casting sheet moves downwards, the molecules and the molecular chains are all stretched, tangled and regulated into straight chain parallel arrangement along the moving direction, under the traditional process, the distance is generally 0.05-0.15 m, the time of the diaphragm in the casting sheet is too short, the molecules and the molecular chains move incompletely, when the casting time is over 2m, excessive convergence into columns is easy to generate, when the diaphragm passes through the chill roll, stacking occurs, and the sheet cannot be effectively formed so as to continue processing);

(2) longitudinally stretching the sheet at the temperature of 110-130 ℃ S8, controlling the stretching ratio of longitudinal stretching S8 to be more than or equal to 10, adopting more than or equal to 3-stage stretching (the number of rollers used in the stage) and slowly retracting 60-80%, and adopting more than or equal to 3-stage retracting (the number of rollers used in the stage); (the melting point of the conventional type-selected polyolefin in the industry is mostly about 130-150 ℃, the optimal crystallization temperature is 0.85 times of the melting point, so the temperature type selection is defined as 110-130 ℃, molecular chain links are required to be effectively opened and spread as much as possible along the stretching direction, the stretching ratio is preferably more than or equal to 10, incomplete opening/movement of the molecular chain links caused by over-fast stretching is avoided, more than or equal to 3-stage stretching is selected to effectively improve the opening/movement time of the molecular chain, retraction is defined as 60-80 percent, and more than or equal to 3-stage retraction is adopted to ensure sufficient retraction time of the chain links and gradual retraction, and disordered entanglement caused by over-violent retraction process is avoided.)

(3) Carrying out first transverse stretching S9, controlling the temperature to be 110-130 ℃, controlling the stretching ratio of the first transverse stretching S9 to be more than or equal to 10, and slowly retracting by 60-80%;

(4) and performing second transverse stretching S10 at a temperature of no more than 130 ℃, controlling the stretching ratio of the second transverse stretching S10 at no less than 5, and slowly retracting by 20-30%.

According to the processing characteristics, the molecules are orderly arranged along MD & TD as much as possible, so that a spring type structure with less molecular chain entanglement is generated, when a tensile test is carried out, the spring type molecular structure is orderly extended under tension, and compared with a traditional structure with more molecular chain entanglement, the polyolefin diaphragm integrally shows longer effective displacement and higher elongation before the test is broken.

As shown in FIG. 6, the distance between the position of the traditional die head 1 and the chill roll 2 is generally about 0.05-0.15 m, and the distance 4 between the die head 1 and the chill roll 2 is increased, so that the stretching of fluid is facilitated, the chain bonding of molecules is facilitated, the molecular motion is generated, a long straight chain is formed, the crystallinity is effectively reduced, and the shaping is facilitated.

Further, in the step (2), S8 is longitudinally stretched by 10 times or more at 110-130 ℃, then slowly retracted by 60-80%, and then heat setting is not carried out; in the step (3), S9 is transversely stretched by 10 times or more at 110-130 ℃, slowly retracted by 60-80% and then not heat-set; in the step (4), the second transverse stretching of S10 is performed by 5 times or more at 120-130 ℃, then the slow retraction is performed by 20-30%, and then the heat setting is not performed.

Here, stretching before retraction is to obtain better elongation, and stretching with high rate will make the molecular chain length provide longer breaking stroke during the deformation of the membrane under stress; the slow retraction is beneficial to forming a special spring structure, so that the elongation is better; the absence of heat setting can reduce the occurrence of crystallization and further improve the elongation of the separator.

Here, both of the MD stretching and slow shrinkage S8 and the TD1 stretching and slow shrinkage S9 are preferably 15 times or more, preferably 10 to 15 times, and the TD2 stretching and slow shrinkage S10 are preferably 7 times or more, preferably 5 to 7 times.

Further, as shown in fig. 7, the present invention further includes a porogen removal unit S5, and the porogen removal unit S5 may be disposed after the MD stretching and slow retraction S8 or TD1 stretching and slow retraction S9, or before the MD stretching and slow retraction S8.

Further, the present invention may also include all relevant processes related to the preparation of the separator, such as winding, slitting, etc., as long as the technical effects of the present invention are not affected.

Further, the weight average molecular weight of the polymer resin is 4.0-8.0 x 10⁶The mass ratio of the polyolefin to the plasticizer is 50: 50-60: 40.

Here, it is preferable that the high molecular weight can provide an extremely long molecular chain under a high-rate stretching process, and the longer the molecular chain is, the longer the breaking stroke is, during the material deformation under stress, which is further beneficial to the improvement of the elongation.

Further, the polymer resin is composed of one or more polyolefin components.

Still further, the polymer resin is a single component polyethylene.

Preferably, the single component polyethylene does not comprise additives such as nucleating agents which affect the crystallinity of the polymer, and is further preferably pure polyethylene without other components.

As shown in fig. 5 and 9, the present invention is also directed to a method for preparing a high-elongation polyolefin microporous membrane, comprising the steps of:

(1) mixing and heating polymer resin and plasticizer to be molten, extruding the molten polymer resin and the plasticizer through a die 1, contacting with a chill roll 2, and cooling to form a sheet S2; wherein the distance between the die head 1 and the chill roll 2 can be adjusted by 4, and is 0.15-2 m;

(2) synchronously and bidirectionally stretching the sheet S11, controlling the temperature to be 110-130 ℃, controlling the stretching ratio to be more than or equal to 10, and slowly retracting to 60-80%;

(3) then transversely stretching S10, controlling the temperature to be less than or equal to 130 ℃, controlling the transverse stretching magnification to be more than or equal to 5, and slowly retracting 20-30%;

further, in the step (2), the S11 synchronous biaxial stretching rate is more than or equal to 10 at 110-130 ℃, then slowly retracting is carried out for 60-80%, and then heat setting is not carried out; in the step (3), the S10 transverse stretching rate is more than or equal to 5 at 120-130 ℃, then the slow retraction is carried out for 20-30%, and then the heat setting is not carried out.

Here, stretching before retraction is to obtain better elongation, and stretching with high rate will make the molecular chain length provide longer breaking stroke during the deformation of the membrane under stress; the slow retraction is beneficial to forming a special spring structure, so that the elongation is better; the absence of heat setting can reduce the occurrence of crystallization and further improve the elongation of the separator.

Here, SBS stretching and slow retraction S11 may be preferably 15 times or more, preferably 10 to 15 times, and TD2 stretching and slow retraction S10 may be preferably 7 times or more, preferably 5 to 7 times.

Further, as shown in fig. 9, the present invention further includes a porogen removal unit S5, and the porogen removal unit S5 may be disposed before or after the SBS stretching and slow retracting S11.

Further, the present invention may also include all relevant processes related to the preparation of the separator, such as winding, slitting, etc., as long as the technical effects of the present invention are not affected.

Further, the weight average molecular weight of the polymer resin is 4.0-8.0 x 10⁶The mass ratio of the polyolefin to the plasticizer is 50: 50-60: 40, and the polymer resin is composed of one or more polyolefin components.

Still further, the polymer resin is a single component polyethylene.

Preferably, the single component polyethylene does not comprise additives such as nucleating agents which affect the crystallinity of the polymer, and is further preferably pure polyethylene without other components.

The present invention also provides a high-elongation polyolefin microporous membrane, characterized in that: the high-elongation polyolefin microporous membrane has an elongation of more than 180% in the MD direction and an elongation of more than 180% in the TD direction.

Further, the MD/TD bidirectional elongation of the high-elongation polyolefin microporous membrane is more than 200%. More preferably, the elongation in the MD direction is 260% or more and the elongation in the TD direction is 210% or more.

Further, the polyolefin is a single component polyethylene.

Further, the single component polyethylene does not include additives such as nucleating agents which affect the crystallinity of the polymer, and is more preferably pure polyethylene containing no other component.

Further, the weight average molecular weight of the polyolefin is 4.0-8.0 x 10⁶。

Further, the high-elongation polyolefin microporous membrane has a single-layer structure.

Further, a value of (elongation in the longitudinal direction, that is, MD direction, tensile strength in the longitudinal direction, that is, needling strength, elongation in the width direction, that is, TD direction, that is, tensile strength in the width direction, that is, needling strength)/2 is 5000 or more; wherein the unit of elongation is% and the unit of tensile strength is Kgf/cm²The unit of the needling strength is gf.

Further, the value of (elongation in the longitudinal direction, i.e., MD direction, tensile strength in the longitudinal direction, needling strength, elongation in the TD direction, i.e., TD direction, tensile strength in the width direction, and needling strength)/2 is 5000 to 7000; the value is 5100-7000; wherein the unit of elongation is% and the unit of tensile strength is Kgf/cm²The unit of the needling strength is gf.

Further, the high-elongation polyolefin microporous membrane has a needle punching strength of 800 to 2000gf and a tensile strength of 2900 to 7500kgf// cm²。

Further, the high-elongation polyolefin microporous membrane has a needle punching strength of 1400 to 1800gf and a tensile strength of 3000 to 6000kgf// cm 2.

Further, the thickness of the high-elongation polyolefin microporous membrane is 1-40 mu m; the porosity is 35-50%; the air permeability is 25-400 s/100 ml; the MD thermal shrinkage rate is 1.0-5.0% at 110 ℃/1 hour, and the TD thermal shrinkage rate is 1.0-1.5%.

Furthermore, the porosity of the high-elongation polyolefin microporous membrane is 50-60%; the air permeability is 150-180 s/100 ml; the MD thermal shrinkage rate is 2.0-5.0% at 110 ℃/1h, and the TD thermal shrinkage rate is 1.1-1.5%.

The present invention also aims to provide a battery using a microporous polyolefin membrane containing any of the above-mentioned high-elongation polyolefin membranes as a member for separating positive and negative electrodes.

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

In the following examples and comparative examples, the performance parameters were determined as follows:

1. thickness of

And measuring by using a German Mark film thickness gauge 1216 according to a measuring method of GB/T6672-2001 plastic film and sheet thickness.

2. Degree of air permeability

And (5) measuring stably for 5 seconds by using a Wang's air permeability instrument, and taking a stable value.

3. Thermal shrinkage

The 100mm x 100mm microporous membrane was placed at 110 ℃ for 1H using a high temperature test chamber Espec SEG-021H and measured by an image measuring instrument XTY-5040, and the TD and MD direction lengths were determined using the formula: (before to after Heat treatment)/before Heat treatment X100% conversion

4. Strength of needling

The measurement was carried out using an electronic universal material tester XJ830, 50mm/min traveling speed.

5. Porosity of the material

Intercepting a 100mm multiplied by 100mm sample wafer, weighing using an electronic balance and according to the formula: (1-weight/area of sample piece)/weight X0.957X 100%.

6. Maximum pore diameter

Measured by the bubble point method using a narrow aperture tester.

7. Kinematic viscosity

And (3) 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.

8. Residual oil rate

A10 mm × 10mm diaphragm sample piece is cut, weighed by using an electronic balance, pure water is placed in an Ultrasonic Cleaner 1740T, 300ml of pure dichloromethane in a 500ml beaker is placed, the sample piece is placed, Ultrasonic time is set to be 60s, then the sample piece is placed in an oven at 105 ℃ for drying for 5min, and the sample piece is weighed by using the electronic balance, and the residual oil rate is converted.

Example 1

Mw of 8.0X 10⁶Polyethylene and white oil as raw materials. Feeding 60 mass percent of polyethylene and 40 mass percent of white oil into an extruder according to the flow rate of 240Kg/h for extruding S1, extruding the raw materials at the temperature of 220 ℃ and 100rpm through a T-shaped die at the distance (2m) between the die head and a chill roll, cooling the raw materials by a cold roll with the temperature of 25 ℃ to form a sheet S2, then feeding the sheet S2 into a pore-forming agent removing unit, heating a driving hot roll and a driven hot roll to 90 ℃ through heat conduction oil, stretching the cast sheet with the pore-forming agent removed S5 in the Mechanical Direction (MD) at 130 ℃ by using a stretcher S8, wherein the stretching ratio is 15, then slowly retracting 80% is carried out, heat setting is not carried out, then S9 is stretched in the width direction (TD) at 130 ℃, the stretching ratio is 15, then slowly retracting 80% is carried out, heat setting is not carried out, then S10 is subjected to secondary TD stretching at 120 ℃, the stretching ratio is 7, then slowly retracting 30%, the microporous polyolefin membrane was obtained by winding the microporous polyolefin membrane with a winding roll without heat setting, and having a biaxial elongation of more than 180% in both the MD and TD directions.

Example 2

Mw of 8.0X 10⁶Polyethylene and white oil as raw materials. Feeding 50% polyethylene and 50% white oil by mass percentage into an extruder at a flow rate of 500Kg/h to extrude S1, extruding the raw materials through a T-shaped die head (the distance between the die head and a chill roll is adjusted to be 1.0m) at a temperature of 220 ℃ and 100rpm, cooling the extruded raw materials by a cold roll at a temperature of 25 ℃ to form a sheet S2, then feeding the sheet S2 into a pore-forming agent removing unit, heating a driving hot roll and a driven hot roll to 90 ℃ through heat transfer oil, stretching the cast sheet with the pore-forming agent removed S5 at 110 ℃ in the Mechanical Direction (MD) by using a stretcher at the temperature of S8, wherein the stretching ratio is 10, then slowly retracting 60%, not performing heat setting, then stretching S9 at 110 ℃ in the width direction (TD), wherein the stretching ratio is 10, then slowly retracting 60%, not performing heat setting, then performing S10 secondary stretching at the temperature of 130 ℃, wherein the stretching ratio is 5, then slowly retracting 20%, the microporous polyolefin membrane was obtained by winding the microporous polyolefin membrane with a winding roll without heat setting, and having a biaxial elongation of more than 180% in both the MD and TD directions.

Example 3

Mw is 4.0X 10⁶Polyethylene and white oil as raw materials. Mixing the raw materials in percentage by massFeeding 60% polyethylene and 40% white oil at a flow rate of 240Kg/h into an extruder to extrude S1, extruding through a T-shaped die head (the distance between the die head and a chill roll is 0.2m) at 220 ℃ and 100rpm, cooling by a cold roll at 25 ℃ to form a sheet S2, entering a pore-forming agent removing unit, heating a driving hot roll and a driven hot roll to 90 ℃ by heat transfer oil, stretching the cast sheet with the pore-forming agent removed S5 in the Mechanical Direction (MD) at 130 ℃ by using a stretcher at S8 with a stretching ratio of 10, then slowly retracting 60% without heat setting, then stretching at 110 ℃ by S9 in the width direction (TD) with a stretching ratio of 10, then slowly retracting 60% without heat setting, then stretching at 120 ℃ by using S10 with a secondary TD stretching ratio of 5, then slowly retracting 20%, the microporous polyolefin membrane was wound up by a winding roll without heat setting to obtain a microporous polyolefin membrane having a biaxial elongation of 180 in the MD and TD directions.

Example 4

Mw is 4.0X 10⁶Polyethylene and white oil as raw materials. Feeding 60% of polyethylene and 40% of white oil in percentage by mass into an extruder at a flow rate of 240Kg/h to extrude S1, extruding the raw materials through a T-shaped die head (the distance between the die head and a chill roll is 0.2m) at a temperature of 220 ℃ and 100rpm, cooling the extruded raw materials by a cold roll at a temperature of 25 ℃ to form a sheet S2, then feeding the sheet S2 into a pore-forming agent removing unit, heating a driving hot roll and a driven hot roll to 90 ℃ through heat conduction oil, performing SBS synchronous stretching on the cast sheet with the pore-forming agent removed S5 at a temperature of 130 ℃ by using a stretcher to obtain S11 with a stretching ratio of 10, then performing slow retraction 60% without performing heat setting, performing S10 secondary TD stretching at a temperature of 130 ℃ with a stretching ratio of 5, then performing slow retraction 20% without performing heat setting, and winding by using a winding roll to obtain the polyolefin microporous membrane with a biaxial elongation of 180.

Example 5

Mw of 8.0X 10⁶Polyethylene and white oil as raw materials. 50 percent of polyethylene and 50 percent of white oil in percentage by mass are put into an extruder according to the flow rate of 500Kg/h to be extruded into S1, and the extruded material passes through a T-shaped die head (the distance between the die head and a chill roll is 2m) at the temperature of 220 ℃ and the rpm of 100) Extruding, cooling by a cold roll with the temperature of 25 ℃ to form a sheet S2, entering a pore-forming agent removing unit, heating a driving hot roll and a driven hot roll to 90 ℃ through heat conduction oil, carrying out SBS synchronous stretching on the cast sheet with the pore-forming agent removed S5 at 110 ℃ by using a stretcher to obtain S11, wherein the stretching ratio is 15, then slowly retracting 80%, not carrying out heat setting, then carrying out S10 secondary TD stretching at 120 ℃, wherein the stretching ratio is 7, then slowly retracting 30%, not carrying out heat setting, and coiling by a coiling roll to obtain the polyolefin microporous membrane with the biaxial extension rate of 180.

Comparative example 1

Mw is 4.0X 10⁶Polyethylene and white oil as raw materials. Feeding 60 mass percent of polyethylene and 40 mass percent of white oil into an extruder according to the flow rate of 240Kg/h for extruding S1, extruding through a T-shaped die head (the distance between the die head and a chill roll is 0.15m) at the temperature of 220 ℃ and the rpm of 100, and forming a sheet S2 after the sheet is contacted and cooled by a cold roll at the temperature of 25 ℃. And (3) removing the pore-forming agent in a dichloromethane tank body at 30 ℃ under the heating of a 90 ℃ heat-conducting oil roller. And (3) performing MD stretching S3, and performing stretch setting at 130 ℃ with the stretch ratio of 10. The resulting film was subjected to TD1 stretching S4, and subjected to stretch setting at 110 ℃ at a stretch ratio of 10. The sheet was subjected to TD2 stretching S6 at 120 ℃ at a draw ratio of 5, and then heat-set to S7, and wound up on a take-up roll.

Comparative example 2

Mw is 4.0X 10⁶Polyethylene and white oil as raw materials. Feeding 60% polyethylene and 40% white oil in percentage by mass into an extruder at a flow rate of 240Kg/h to extrude S1, extruding the mixture through a T-shaped die head (the distance between the die head and a chill roll is 2m) at a temperature of 220 ℃ and 100rpm, cooling the mixture by a cold roll at a temperature of 25 ℃ to form a sheet S2, entering a pore-forming agent removing unit, heating a driving hot roll and a driven hot roll to 90 ℃ through heat conduction oil, performing SBS synchronous stretching S12 on the cast sheet with the pore-forming agent removed S5 at a temperature of 130 ℃ by using a stretcher, wherein the stretching magnification is 10, performing S6 secondary TD stretching at a temperature of 130 ℃, wherein the stretching magnification is 5, performing heat setting S7, and coiling the sheet by a coiling roll.

TABLE 1 working process and physical property characteristics of examples and comparative examples

The above matters related to the common general knowledge are not described in detail and can be understood by those skilled in the art.

The present invention is not intended to be limited to the particular embodiments shown and described, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. The technical scope of the present invention is not limited to the content of the specification, and must be determined according to the scope of the claims.