CN109438803B - Polymer isolating membrane and preparation method thereof - Google Patents

Polymer isolating membrane and preparation method thereof Download PDF

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CN109438803B
CN109438803B CN201811139216.0A CN201811139216A CN109438803B CN 109438803 B CN109438803 B CN 109438803B CN 201811139216 A CN201811139216 A CN 201811139216A CN 109438803 B CN109438803 B CN 109438803B
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molecular weight
pore
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polymer
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CN109438803A (en
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程跃
王康
邓洪贵
陈辉
岳齐
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Shanghai Energy New Materials Technology Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
    • C08J5/18—Manufacture of films or sheets
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/403—Manufacturing processes of separators, membranes or diaphragms
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2323/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
    • C08J2323/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
    • C08J2323/04—Homopolymers or copolymers of ethene
    • C08J2323/06—Polyethene
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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Abstract

The polymer isolating film is formed based on the second stretching and retracting process and comprises high molecular weight polyethylene, a pore-forming agent and an antioxidant, wherein the average molecular weight of the high molecular weight polyethylene is 1.0 multiplied by 105～10.0×106Has a density of 0.940g/cm3～0.976g/cm3To (c) to (d); the weight of the pore-forming agent is 100 to 500 parts and the weight of the antioxidant is 0.1 to 10 parts based on 100 parts of the high molecular weight polyethylene; the bidirectional thermal shrinkage rate of the polymer isolating membrane is less than or equal to 3.0 percent, and the bidirectional internal stress shrinkage rate is less than or equal to 15 percent. The method has the advantages that the molecular chain of the film is better relaxed by combining the first biaxial stretching process with the second stretching and shrinking process, the internal stress shrinkage value and the thermal shrinkage rate of the isolating film are effectively reduced, and the safety performance of the isolating film is improved; in addition, the preparation method of the polymer isolation membrane provided by the invention has the advantages of simple processing technology and high efficiency, and can effectively reduce the production cost.

Description

Polymer isolating membrane and preparation method thereof
Technical Field
The invention relates to the field of battery isolation films, in particular to a polymer isolation film with low internal stress and low thermal shrinkage and a preparation method thereof.
Background
The lithium ion battery generally mainly comprises a positive electrode, a negative electrode, a separation film, an electrolyte and a battery shell. In the structure of the lithium ion battery, the isolating membrane is one of the key inner layer assemblies, and mainly has the functions of separating the positive electrode and the negative electrode of the battery, preventing the positive electrode and the negative electrode from being in direct contact and short circuit, enabling electrolyte ions to smoothly pass through the isolating membrane in the charging and discharging process of the battery to form current, closing a migration channel of the electrolyte ions when the working temperature of the battery is abnormally increased, and cutting off the current to ensure the safety of the battery. Therefore, the performance of the isolating membrane determines the interface structure, internal resistance and the like of the battery, the characteristics of the battery such as capacity, cycle and safety performance are directly influenced, and the isolating membrane with excellent performance plays an important role in improving the comprehensive performance of the battery.
The main performance parameters of the battery isolating membrane comprise thickness, porosity, pore size distribution, strength, thermal shrinkage, closed pore temperature, membrane breaking temperature and the like. The battery component needs to pull the isolating membrane in the production and assembly processes, so that the isolating membrane needs to have enough tensile strength; in addition, the polymer isolation film can be subjected to thermal shrinkage under a certain heating condition, and in order to avoid internal short circuit caused by direct contact of a positive electrode and a negative electrode brought by thermal shrinkage, the thermal shrinkage rate of the isolation film is also required to a certain extent. In general, the more significant the polymer molecular chain is stretched, the more easily it shrinks under heat. Therefore, for most separator films, the higher the tensile strength, the higher the thermal shrinkage, and the higher the internal stress. In order to improve the safety of lithium batteries, it is desirable that the tensile strength is high and that the thermal shrinkage is low as well as the internal stress is low as well.
Therefore, it is necessary to provide an isolation film to overcome the problem in the prior art that the safety performance of the isolation film is reduced due to high stress and thermal shrinkage in the isolation film, and a simple and fast isolation film preparation method to improve the production efficiency of the isolation film and save the production cost.
Disclosure of Invention
In view of the above disadvantages of the prior art, an object of the present invention is to provide a polymer isolation film and a preparation method thereof, which are used to solve the problems of the prior art, such as high internal stress and thermal shrinkage of the isolation film, complex processing technology, and low efficiency, thereby reducing the safety performance of the isolation film, reducing the production efficiency, and increasing the production cost.
To achieve the above and other related objects, the present invention provides a polymer separator formed based on a second stretch-retraction process, comprising: polymerA high molecular weight polyethylene having an average molecular weight of 1.0 x 10 and an antioxidant5～10.0×106Has a density of 0.940g/cm3～0.976g/cm3To (c) to (d);
the weight of the antioxidant is between 0.1 and 10 parts based on 100 parts of the high molecular weight polyethylene;
the bidirectional thermal shrinkage rate of the polymer isolating membrane is less than or equal to 3.0%, and the bidirectional internal stress shrinkage rate is less than or equal to 15%.
Optionally, the polymer isolation film has a thickness of between 5 μm and 20 μm.
Optionally, the high molecular weight polyethylene comprises a high molecular weight polyethylene monomer or a mixture of two or more high molecular weight polyethylenes.
Optionally, the antioxidant comprises a composition of one or more of the group consisting of 4, 4-thiobis (6-tert-butyl-m-cresol), dibutylhydroxytoluene, phosphite, tert-butylhydroquinone, N-octadecyl beta- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate, 1, 3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 2-tert-butyl-6-methylphenol, N' -di-beta-naphthylp-phenylenediamine, dilauryl thiodipropionate, tris (nonylphenyl) phosphite, and triphenyl phosphite.
The invention also provides a preparation method of the polymer isolating membrane, which comprises the following steps:
1) mixing high molecular weight polyethylene, a pore-forming agent and an antioxidant, and stirring to form a mixture;
2) dissolving the high molecular weight polyethylene and the antioxidant in the pore-forming agent by adopting a double-screw extrusion process at a certain temperature, and then extruding;
3) casting the mixture extruded in step 2) into a strip;
4) biaxially stretching the strip cast in the step 3) to form a film;
5) extracting to remove the pore-forming agent from the thin film;
6) heat-setting the thin film from which the pore-forming agent is removed;
7) performing second longitudinal stretching and retraction on the film after the heat setting;
8) and rolling the film which is subjected to the secondary longitudinal stretching and retraction to obtain the polymer isolating film.
Optionally, in the step 7), the second longitudinal stretching and retracting process includes a longitudinal stretching process and a longitudinal retracting process;
wherein the longitudinal stretching process comprises one of the following two ways:
a) arranging a plurality of chain clamps for longitudinally fixing the film in a stretching area along the advancing direction of the film, wherein the distance between every two adjacent chain clamps along the advancing direction of the film is sequentially increased;
b) arranging a plurality of rollers for longitudinally fixing the film in a stretching area along the advancing direction of the film, wherein the speed of the rollers is increased in sequence along the advancing direction of the film;
wherein the longitudinal retraction process comprises one of the following two ways:
c) a plurality of chain clamps for longitudinally fixing the film are arranged in the retraction area along the advancing direction of the film, and the distance between every two adjacent chain clamps along the advancing direction of the film is reduced in sequence;
d) and arranging a plurality of rollers for longitudinally fixing the film in a retraction area along the advancing direction of the film, wherein the speed of the rollers is reduced in sequence along the advancing direction of the film.
Optionally, in the step 1), the weight of the pore-forming agent is between 100 and 500 parts based on 100 parts by weight of the high molecular weight polyethylene.
Optionally, the pore former comprises a mixture of natural mineral oil, C6-15Alkane, C8-15Aliphatic carboxylic acid, C8-15Aliphatic Carboxylic acids C1-4Alkyl ester, C2-6Halogenated alkanes, phthalates, trimellitates, adipates, sebacates, maleates, benzoates, epoxidized vegetable oils, benzenesulfonamides, phosphotriesters, glycol ethers, acetylated monoglycerides, citratesA combination of one or more of the group consisting of citrate and diisononyl cyclohexane-1, 2-dicarboxylate.
Optionally, the pore former has a kinematic viscosity at 40 ℃ of between 10mm2/s～100mm2The initial boiling point of the pore-forming agent is above 110 ℃ between s.
Optionally, in the step 4), the ribbon is stretched in a manner of stretching in a longitudinal direction and then stretching in a transverse direction or stretching in the longitudinal direction and the transverse direction simultaneously.
Optionally, in the step 1), at least one of the high molecular weight polyethylene, the pore-forming agent and the antioxidant are mixed and stirred uniformly to form the mixture.
Optionally, in the step 2), the high molecular weight polyethylene and the antioxidant are dissolved in the pore-forming agent at a temperature of 170 ℃ to 200 ℃, and then continuously extruded at a speed of 85 rpm to 115 rpm.
Optionally, in the step 3), the step of casting the mixture extruded in the step 2) into a ribbon comprises: firstly, continuously feeding the mixture extruded in the step 2) into a slot die, then extruding the extruded mixture to a casting cooling roller through the slot die, and casting the mixture into a strip-shaped object under the temperature condition of 20-40 ℃.
Optionally, in the step 6), transversely tightening the film for heat setting for 13-20 seconds at the temperature of 115-145 ℃; and in the step 8), the film is rolled at the speed of 30-70 m/min to obtain the polymer isolating film.
Optionally, the high molecular weight polyethylene has an average molecular weight of 1.0 x 105～10.0×106And the density is between 0.940g/cm3～0.976g/cm3In the meantime.
As mentioned above, the polymer isolating membrane and the preparation method thereof of the invention have the advantages that the first biaxial stretching process is combined with the second stretching and shrinking process, so that the molecular chain of the membrane is relaxed better, the internal stress shrinkage value and the thermal shrinkage rate of the isolating membrane are effectively reduced, and the safety performance of the isolating membrane is improved; in addition, the preparation method of the polymer isolation membrane provided by the invention has the advantages of simple processing technology and high efficiency, and can effectively reduce the production cost.
Drawings
FIG. 1 is a schematic flow chart of a method for preparing a polymer separator according to the present invention.
Fig. 2 is a schematic view showing a second longitudinal stretching retraction process in the method for preparing the polymer release film of the present invention.
Description of the element reference numerals
1 stretch zone
2 zone of retraction
3 chain clip
D distance between adjacent chain clips
S1-S8
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.
Please refer to fig. 1 and fig. 2. It should be noted that the drawings provided in the present embodiment are only for illustrating the basic idea of the present invention, and the components related to the present invention are only shown in the drawings rather than drawn according to the number, shape and size of the components in actual implementation, and the type, quantity and proportion of the components in actual implementation may be changed freely, and the layout of the components may be more complicated.
The invention provides a polymer release film, which is formed based on a second stretching retraction process and comprises the following components: high molecular weight polyethylene, pore-forming agent and antioxidant, wherein the average molecular weight of the high molecular weight polyethylene is 1.0 x 105～10.0×106Has a density of 0.940g/cm3～0.976g/cm3To (c) to (d);
the weight of the pore-forming agent is 100-500 parts and the weight of the antioxidant is 0.1-10 parts based on 100 parts of the high molecular weight polyethylene;
the bidirectional thermal shrinkage rate of the polymer isolating membrane is less than or equal to 3.0%, and the bidirectional internal stress shrinkage rate is less than or equal to 15%.
It should be noted that the high molecular weight polyethylene may be a single high molecular weight polyethylene, or may be a mixture of two or more high molecular weight polyethylenes, so that the molecular weight of the high molecular weight polyethylene is calculated as an average molecular weight.
Preferably, the high molecular weight polyethylene has an average molecular weight of 1.0 × 105～5.0×106More preferably, between 1.0X 105～2.0×106In the meantime.
Preferably, the high molecular weight polyethylene has a density of 0.940g/cm3～0.966g/cm3More preferably, between 0.950g/cm3～0.966g/cm3In the meantime.
Preferably, the weight of the pore-forming agent is between 200 parts and 500 parts, and the weight of the antioxidant is between 0.5 parts and 8 parts, based on 100 parts of the high molecular weight polyethylene.
More preferably, the weight of the pore-forming agent is between 200 and 400 parts and the weight of the antioxidant is between 1 and 6 parts based on 100 parts of the high molecular weight polyethylene.
The thickness of the polymer isolating membrane obtained by the invention is between 5 and 20 mu m. After the film is formed by the first biaxial stretching and is combined with the first stretching and retracting process, the molecular chain of the film is better relaxed, so that the internal stress of the film is reduced, the internal stress shrinkage value and the thermal shrinkage rate of the isolating film are both reduced, and the safety performance of the isolating film can be effectively improved. The bidirectional thermal shrinkage rate of the isolating membrane is less than or equal to 3.0 percent, and the bidirectional internal stress shrinkage rate is less than or equal to 15 percent.
As an example, the antioxidant includes one or more of a composition selected from the group consisting of 4, 4-thiobis (6-tert-butyl-m-cresol), dibutylhydroxytoluene, phosphite, tert-butylhydroquinone, N-octadecyl β - (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate, 1, 3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 2-tert-butyl-6-methylphenol, N' -di- β -naphthylp-phenylenediamine, dilauryl thiodipropionate, tris (nonylphenyl) phosphite, and triphenyl phosphite.
As shown in fig. 1, the present invention further provides a preparation method of a polymer isolation film, the polymer isolation film can be prepared by using the preparation method, and the properties and parameters of the polymer isolation film prepared by using the preparation method refer to the foregoing embodiments, which are not repeated herein, and only the preparation method is described. The preparation method comprises the following steps:
s1, mixing the high molecular weight polyethylene, the pore-forming agent and the antioxidant, and stirring to form a mixture;
s2, adopting a double-screw extrusion process, dissolving the high molecular weight polyethylene and the antioxidant in the pore-forming agent at a certain temperature, and then extruding;
s3, casting the mixture extruded in the step S2 into a ribbon;
s4, biaxially stretching the strip cast in the step S3 to form a film;
s5, extracting to remove the pore-forming agent in the thin film;
s6, heat setting the film with the pore-forming agent removed;
s7, performing second longitudinal stretching and retraction on the film after heat setting;
s8, rolling the film which is contracted by the secondary longitudinal stretching to obtain the polymer isolation film.
According to the preparation method of the polymer isolation membrane, the internal stress shrinkage value and the thermal shrinkage rate of the isolation membrane can be effectively reduced only by adding a second longitudinal stretching and retracting process after the thin film is subjected to heat setting, the processing process is simple and high in efficiency, and the production cost can be effectively reduced.
As an example, the high molecular weight polyethylene has an average molecular weight of 1.0X 105～10.0×106And the density is between 0.940g/cm3～0.976g/cm3In the meantime.
As an example, in step S1, at least one of the high molecular weight polyethylene, the pore former, and the antioxidant are mixed and stirred uniformly to form the mixture.
For example, in step S1, the weight of the pore-forming agent is between 100 and 500 parts based on 100 parts of the high molecular weight polyethylene. Preferably, the weight of the pore-forming agent is between 200 and 500 parts, and more preferably, the weight of the pore-forming agent is between 200 and 400 parts.
As an example, the pore-forming agent comprises a natural mineral oil, C6-15Alkane, C8-15Aliphatic carboxylic acid, C8-15Aliphatic Carboxylic acids C1-4Alkyl ester, C2-6Halogenated alkanes, phthalates, trimellitates, adipates, sebacates, maleates, benzoates, epoxidized vegetable oils, benzenesulfonamides, phosphotriesters, glycol ethers, acetylated monoglycerides, citrates and cyclohexane-1, 2-dicarboxylic acid diisononyl esters.
As an example, the pore former has a kinematic viscosity at 40 ℃ of between 10mm2/s～100mm2The initial boiling point of the pore-forming agent is above 110 ℃ between s.
Preferably, the pore former has a kinematic viscosity at 40 ℃ of between 20mm2/s～80mm2Is between/s. More preferably, the pore former has a kinematic viscosity at 40 ℃ of between 30mm2/s～70mm2Is between/s.
For example, in step S2, the high molecular weight polyethylene and the antioxidant are dissolved in the pore-forming agent at a temperature of 170 to 200 ℃, and then continuously extruded at a speed of 85 to 115 rpm.
As an example, in the step S3, the step of casting the mixture extruded in the step S2 into a ribbon includes: firstly, the mixture extruded in the step S2 is continuously fed into a slot die, and then the extruded mixture is extruded to a casting cooling roller through the slot die and cast into a belt under the temperature condition of 20-40 ℃.
As an example, in step S4, the ribbon is stretched by stretching in the longitudinal direction and then in the transverse direction or by stretching in both the longitudinal and transverse directions.
In step S5, pores are formed in the thin film after the pore-forming agent in the thin film is removed by extraction.
Illustratively, in the step S6, the film is transversely stretched under the temperature condition of 115-145 ℃ for 13-20 seconds.
As an example, in step S7, the second longitudinal stretching and retracting process includes a longitudinal stretching process and a longitudinal retracting process;
wherein the longitudinal stretching process can be realized by any one of the following two ways:
as shown in fig. 2, a) a plurality of chain clips 3 for longitudinally fixing the film are arranged in the stretching region 1 along the advancing direction of the film, in the direction of the arrow in fig. 2, and the distance D between two adjacent chain clips 3 along the advancing direction of the film increases in sequence;
b) and arranging a plurality of rollers for longitudinally fixing the film in a stretching area along the advancing direction of the film, wherein the speed of the rollers is increased in sequence along the advancing direction of the film.
Wherein the longitudinal retraction process can be achieved by any one of the following two ways:
as shown in fig. 2, c) a plurality of chain clamps 3 for longitudinally fixing the film are arranged in the retraction area 2 along the advancing direction of the film, in the direction of the arrow in fig. 2, and the distance D between two adjacent chain clamps 3 along the advancing direction of the film is reduced in sequence;
d) and arranging a plurality of rollers for longitudinally fixing the film in a retraction area along the advancing direction of the film, wherein the speed of the rollers is reduced in sequence along the advancing direction of the film.
Preferably, in the step S7, the second longitudinal stretch retraction process includes:
as shown in fig. 2, a plurality of chain clamps 3 for longitudinally fixing the film are arranged in a stretching area 1 along the advancing direction of the film, in the direction of an arrow in fig. 2, and the distance D between two adjacent chain clamps 3 along the advancing direction of the film is sequentially increased to realize the longitudinal stretching process of the film; a plurality of chain clamps 3 for longitudinally fixing the film are arranged in the retraction area 2 along the advancing direction of the film, namely the arrow direction in figure 2, and the distance D between every two adjacent chain clamps 3 along the advancing direction of the film is reduced in sequence to realize the longitudinal retraction process of the film.
As an example, in the step 8), the film is wound at a speed of 30 m/min to 70 m/min to obtain the polymer separator.
The polymer separator and the production method of the present invention are further described below with reference to examples and comparative examples, wherein the parameters in the examples and comparative examples are measured by the following methods.
1. Thickness of
Method for measuring thickness of plastic film and thin sheet according to GB/T6672-2001 by using German Mark film thickness gauge 1216
And (4) measuring.
2. Thermal shrinkage
Measuring the distance L between two points on the diaphragm under the test environment at normal temperature (23℃)0Placing the sample at 120 +/-1 ℃ for drying
Adding stainless steel in the box, keeping the temperature for 1h, taking out, measuring the distance L1 between two points on the diaphragm when the diaphragm is cooled to a normal-temperature test environment, and calculating the thermal shrinkage rate S according to the following formula: s ═ L0-L1)/L0×100％。
3. Internal stress contraction
In order to represent the internal stress of the diaphragm, a diaphragm sample strip with the width of 4mm and the length of 8mm is cut, the temperature is continuously increased under the condition of constant force of 0.02N, the temperature increasing rate is 5 ℃/min, the temperature increasing cut-off temperature is 180 ℃, the contraction length Ls of the sample strip in the temperature increasing process is observed, the ratio of the length to the original length is the internal stress contraction value, and the larger the value is, the larger the internal stress of the diaphragm is.
Example 1
100 g of the mixture with the density of 0.957g/cm3Has an average molecular weight of 4.0X 105High molecular weight polyethylene, 0.5 g of antioxidant, and then 300 g of a mixture having a kinematic viscosity at 40 ℃ of 50mm2The mineral oil/s is continuously extruded by twin screws at 180 ℃ and 100 r/min, the continuously extruded mixture is extruded to a casting cooling roller through a slit die head, the casting cooling roller is cast into a strip at 30 ℃, the obtained strip is sent to a biaxial stretching machine to be longitudinally stretched and transversely stretched to form a film, then the film enters an extraction tank to be continuously extracted to remove pore-forming agents in the film, the film is transversely tightened and heat-set at 130 ℃ for 15 seconds after extraction, and then the film is further longitudinally stretched and retracted. And reducing the stress in the isolating membrane by longitudinal stretching and retracting, and finally rolling the isolating membrane at the speed of 50 m/min to obtain the low-internal-stress isolating membrane. The specific performance parameters are shown in table 1 through testing:
TABLE 1
Figure BDA0001815387270000081
Example 2
100 g of the mixture with the density of 0.951g/cm3Has an average molecular weight of 15.0X 105High molecular weight polyethylene, 0.5 g of antioxidant, and then 300 g of a mixture having a kinematic viscosity at 40 ℃ of 50mm2The mineral oil/s is continuously extruded by twin screws at 180 ℃ and 100 r/min, the continuously extruded mixture is extruded to a casting cooling roller through a slit die head, the casting cooling roller is cast into a strip at 30 ℃, the obtained strip is sent to a biaxial stretching machine to be longitudinally stretched and transversely stretched to form a film, then the film enters an extraction tank to be continuously extracted to remove pore-forming agents in the film, the film is transversely tightened and heat-set at 130 ℃ for 15 seconds after extraction, and then the film is further longitudinally stretched and retracted. Through the longitudinal directionAnd stretching and retracting to reduce the stress in the isolating membrane, and finally rolling the isolating membrane at the speed of 50 m/min to obtain the low-internal-stress isolating membrane. The specific performance parameters are shown in table 2:
TABLE 2
Figure BDA0001815387270000082
Example 3
100 g of the mixture with the density of 0.957g/cm3Has an average molecular weight of 4.0X 105High molecular weight polyethylene, 0.5 g of antioxidant, and then 300 g of a mixture having a kinematic viscosity at 40 ℃ of 50mm2Mineral oil/s is continuously extruded by twin screws at 180 ℃ and 100 r/min, the continuously extruded mixture is extruded to a casting cooling roller through a slot die head, the casting cooling roller is cast into a strip at 30 ℃, the obtained strip is sent to a biaxial stretcher to be simultaneously stretched longitudinally and transversely to form a film, then the film enters an extraction tank to be continuously extracted to remove a pore-forming agent in the film, the film is transversely tightened and heat-set for 15 seconds at 130 ℃ after extraction, and then the film is further longitudinally stretched and retracted. And reducing the stress in the isolating membrane by longitudinal stretching and retracting, and finally rolling the isolating membrane at the speed of 50 m/min to obtain the low-internal-stress isolating membrane. The specific performance parameters are shown in table 3 through testing:
TABLE 3
Figure BDA0001815387270000091
Example 4
100 g of the mixture with the density of 0.951g/cm3Has an average molecular weight of 15.0X 105High molecular weight polyethylene, 0.5 g of antioxidant, and then 300 g of a mixture having a kinematic viscosity at 40 ℃ of 50mm2Mineral oil/s are continuously extruded together at 180 deg.C and 100 rpm with twin screw, the continuously extruded mixture is extruded through a slot die onto a casting chill roll, cast into a ribbon at 30 deg.C, and the resulting ribbon is fed into a twin screw extruderSimultaneously stretching the film in the longitudinal direction and the transverse direction in a stretching machine to form a film, then continuously extracting the film in an extraction tank to remove pore-forming agents in the film, transversely tightening and heat-setting the film at 130 ℃ for 15 seconds after extraction, and then further stretching and retracting the film in the longitudinal direction. And reducing the stress in the isolating membrane by longitudinal stretching and retracting, and finally rolling the isolating membrane at the speed of 50 m/min to obtain the low-internal-stress isolating membrane. The specific performance parameters are shown in table 4 through testing:
TABLE 4
Figure BDA0001815387270000092
Example 5
100 g of the mixture with the density of 0.957g/cm3Has an average molecular weight of 5.0X 105High molecular weight polyethylene, 0.5 g of antioxidant, and then 300 g of a mixture having a kinematic viscosity at 40 ℃ of 50mm2The mineral oil/s is continuously extruded by twin screws at 180 ℃ and 100 r/min, the continuously extruded mixture is extruded to a casting cooling roller through a slit die head, the casting cooling roller is cast into a strip at 30 ℃, the obtained strip is sent to a biaxial stretching machine to be longitudinally stretched and transversely stretched to form a film, then the film enters an extraction tank to be continuously extracted to remove pore-forming agents in the film, the film is transversely tightened and heat-set at 130 ℃ for 15 seconds after extraction, and then the film is further longitudinally stretched and retracted. In this embodiment, further longitudinal stretching is achieved by the speed difference between the rollers, i.e. the front roller in the forward direction has a greater speed than the rear roller, after which further longitudinal retraction is performed, which is also achieved by the speed difference between the rollers, i.e. the front roller in the forward direction has a slightly smaller speed than the rear roller. And reducing the stress in the isolating membrane and controlling thermal shrinkage by longitudinal stretching and retracting, and finally rolling the isolating membrane at the speed of 50 m/min to obtain the low-internal-stress low-thermal-shrinkage isolating membrane. The specific performance parameters are shown in table 5 by testing:
TABLE 5
Figure BDA0001815387270000101
Example 6
100 g of the mixture with the density of 0.957g/cm3Has an average molecular weight of 5.0X 105High molecular weight polyethylene, 0.5 g of antioxidant, and then 300 g of a mixture having a kinematic viscosity at 40 ℃ of 50mm2The mineral oil/s is continuously extruded by twin screws at 180 ℃ and 100 r/min, the continuously extruded mixture is extruded to a casting cooling roller through a slit die head, the casting cooling roller is cast into a strip at 30 ℃, the obtained strip is sent to a biaxial stretching machine to be longitudinally stretched and transversely stretched to form a film, then the film enters an extraction tank to be continuously extracted to remove pore-forming agents in the film, the film is transversely tightened and heat-set at 130 ℃ for 15 seconds after extraction, and then the film is further longitudinally stretched and retracted. In this embodiment, further longitudinal stretching is achieved by the difference in speed between the rollers, i.e. the front roller in the forward direction has a greater speed than the rear roller, after which further longitudinal retraction is achieved by the difference in distance of the front chain gripper in the forward direction, i.e. the difference in distance of the front chain gripper in the forward direction is smaller than the difference in distance of the subsequent chain gripper. And reducing the stress in the isolating membrane and controlling thermal shrinkage by longitudinal stretching and retracting, and finally rolling the isolating membrane at the speed of 50 m/min to obtain the low-internal-stress low-thermal-shrinkage isolating membrane. The specific performance parameters are shown in table 6:
TABLE 6
Figure BDA0001815387270000111
Example 7
100 g of the mixture with the density of 0.957g/cm3Has an average molecular weight of 5.0X 105High molecular weight polyethylene, 0.5 g of antioxidant, and then 300 g of a mixture having a kinematic viscosity at 40 ℃ of 50mm2Mineral oil/s are continuously extruded together at 180 ℃ at 100 rpm in a twin-screw extruder, and the continuously extruded mixture is extruded through a slot dieCasting a cooling roller, casting the strip-shaped object at the temperature of 30 ℃, sending the obtained strip-shaped object into a biaxial stretching machine, stretching longitudinally and transversely simultaneously to form a film, then entering an extraction tank for continuous extraction to remove a pore-forming agent in the film, stretching and heat-setting the obtained film transversely at the temperature of 130 ℃ for 15 seconds after extraction, and then further stretching and retracting longitudinally. In this embodiment, further longitudinal stretching is achieved by the speed difference between the rollers, i.e. the front roller in the forward direction has a greater speed than the rear roller, after which further longitudinal retraction is performed, which is also achieved by the speed difference between the rollers, i.e. the front roller in the forward direction has a slightly smaller speed than the rear roller. And reducing the stress in the isolating membrane and controlling thermal shrinkage by longitudinal stretching and retracting, and finally rolling the isolating membrane at the speed of 50 m/min to obtain the low-internal-stress low-thermal-shrinkage isolating membrane. The specific performance parameters are shown in table 7 by testing:
TABLE 7
Figure BDA0001815387270000112
Example 8
100 g of the mixture with the density of 0.957g/cm3Has an average molecular weight of 5.0X 105High molecular weight polyethylene, 0.5 g of antioxidant, and then 300 g of a mixture having a kinematic viscosity at 40 ℃ of 50mm2Mineral oil/s is continuously extruded by twin screws at 180 ℃ and 100 r/min, the continuously extruded mixture is extruded to a casting cooling roller through a slot die head, the casting cooling roller is cast into a strip at 30 ℃, the obtained strip is sent to a biaxial stretcher to be simultaneously stretched longitudinally and transversely to form a film, then the film enters an extraction tank to be continuously extracted to remove a pore-forming agent in the film, the film is transversely tightened and heat-set for 15 seconds at 130 ℃ after extraction, and then the film is further longitudinally stretched and retracted. In this embodiment, further longitudinal stretching is achieved by the difference in speed between the rollers, i.e. the front roller in the forward direction has a greater speed than the rear roller, after which further longitudinal retraction is performed, which is carried forward in the longitudinal direction by the chain gripperThe difference in distance of the rows is achieved in that the difference in distance of the front clip in the forward direction is smaller than the difference in distance of the following clips. And reducing the stress in the isolating membrane and controlling thermal shrinkage by longitudinal stretching and retracting, and finally rolling the isolating membrane at the speed of 50 m/min to obtain the low-internal-stress low-thermal-shrinkage isolating membrane. The specific performance parameters are shown in table 8:
TABLE 8
Figure BDA0001815387270000121
Comparative example 1
100 g of the mixture with the density of 0.951g/cm3Has an average molecular weight of 15.0X 105High molecular weight polyethylene, 0.5 g of antioxidant, and then 300 g of a mixture having a kinematic viscosity at 40 ℃ of 50mm2Mineral oil/s is continuously extruded by double screws at 180 ℃ and 100 r/min, the continuously extruded mixture is extruded to a casting cooling roller through a slit die head, the casting cooling roller is cast into a strip at 30 ℃, the obtained strip is sent to a biaxial stretcher to be longitudinally stretched and transversely stretched to form a film, then the film enters an extraction tank to be continuously extracted to remove pore-forming agents in the film, the obtained film is transversely tightened and heat-set at 130 ℃ for 15 seconds after extraction, and finally the isolating film is wound at the speed of 50 m/min to obtain the conventional isolating film. The specific performance parameters are shown in table 9:
TABLE 9
Figure BDA0001815387270000122
Comparative example 2
100 g of the mixture with the density of 0.951g/cm3Has an average molecular weight of 15.0X 105High molecular weight polyethylene, 0.5 g of antioxidant, and then 300 g of a mixture having a kinematic viscosity at 40 ℃ of 50mm2The mineral oil/s are continuously extruded together at 180 ℃ and 100 rpm in a twin-screw extruder, the continuously extruded mixture is extruded through a slot die onto a casting cooling roll at 30 DEGCasting sheets into strips, sending the strips into a biaxial stretching machine, stretching longitudinally and transversely simultaneously to form a film, then sending the film into an extraction tank for continuous extraction to remove pore-forming agents in the film, stretching and heat-setting the film transversely at 130 ℃ for 15 seconds after extraction, and finally rolling the isolating film at the speed of 50 m/min to obtain the conventional isolating film. The specific performance parameters are shown in table 10 after testing:
watch 10
Figure BDA0001815387270000131
Comparative example 3
100 g of the mixture with the density of 0.957g/cm3Has an average molecular weight of 5.0X 105High molecular weight polyethylene, 0.5 g of antioxidant, and then 300 g of a mixture having a kinematic viscosity at 40 ℃ of 50mm2Mineral oil/s is continuously extruded by double screws at 180 ℃ and 100 r/min, the continuously extruded mixture is extruded to a casting cooling roller through a slit die head, the casting cooling roller is cast into a strip at 30 ℃, the obtained strip is sent to a biaxial stretcher to be longitudinally stretched and transversely stretched to form a film, then the film enters an extraction tank to be continuously extracted to remove pore-forming agents in the film, the obtained film is transversely tightened and heat-set at 130 ℃ for 15 seconds after extraction, and finally the isolating film is wound at the speed of 50 m/min to obtain the conventional isolating film. The specific performance parameters are shown in table 11:
TABLE 11
Figure BDA0001815387270000132
Comparative example 4
100 g of the mixture with the density of 0.957g/cm3Has an average molecular weight of 5.0X 105High molecular weight polyethylene, 0.5 g of antioxidant, and then 300 g of a mixture having a kinematic viscosity at 40 ℃ of 50mm2The mineral oil/s are continuously extruded together at 180 ℃ and 100 rpm in a twin-screw extruderExtruding the mixture to a casting cooling roller through a slit die head, casting the mixture into a strip at the temperature of 30 ℃, sending the obtained strip into a biaxial stretching machine, stretching the strip longitudinally and transversely simultaneously to form a film, then entering an extraction tank for continuous extraction to remove a pore-forming agent in the film, stretching the obtained film transversely at the temperature of 130 ℃ for heat setting for 15 seconds after extraction, and finally rolling the isolating film at the speed of 50 m/min to obtain the conventional isolating film. The specific performance parameters are shown in table 12 after testing:
TABLE 12
Figure BDA0001815387270000141
The comparison of the experimental results of the above examples and comparative examples shows that the internal stress shrinkage value and the thermal shrinkage rate of the isolating membrane can be effectively reduced after the film is subjected to the second longitudinal stretching and shrinking process after the heat setting; in addition, no matter the film is formed by asynchronous stretching or synchronous stretching, the higher the molecular weight of the isolating film is, the larger the internal stress shrinkage value is, and after the second longitudinal stretching and shrinking process is adopted, the internal stress shrinkage value is obviously reduced, and the thermal shrinkage rate is well controlled; finally, it can also be seen from the comparison that the second longitudinal stretching and shrinking process more easily reduces the internal stress shrinkage value of the asynchronously stretched separator.
The technical content and technical features of the present invention have been revealed, as mentioned above, that the components of the polymer separator according to the present invention are not limited to the materials and formulations mentioned in the present invention, and other materials and formulations with similar characteristics are also covered by the present invention. It is possible for those skilled in the art to make various alterations and modifications based on the disclosure of the present invention without departing from the spirit thereof. Accordingly, the scope of the present invention should not be limited to the disclosure of the embodiments, but should include various alternatives and modifications without departing from the invention and encompassed by the appended claims.

Claims (12)

1. A polymer isolation film is characterized in that the longitudinal thermal shrinkage rate of the polymer isolation film is between 1.0% and 2.5%, the transverse thermal shrinkage rate of the polymer isolation film is between 0.1% and 1.7%, the longitudinal internal stress shrinkage rate of the polymer isolation film is between 5.0% and 12.0%, the transverse internal stress shrinkage rate of the polymer isolation film is between 0.8% and 5.1%, and the thickness of the polymer isolation film is between 5 mu m and 9 mu m, and the preparation method of the polymer isolation film comprises the following steps:
1) mixing high molecular weight polyethylene, pore-forming agent and antioxidant, and stirring to form mixture, wherein the average molecular weight of the high molecular weight polyethylene is 1.0 × 105~10.0×106Has a density of 0.940g/cm3~0.976g/cm3The weight of the antioxidant is 0.1-10 parts based on 100 parts of the high molecular weight polyethylene;
2) dissolving the high molecular weight polyethylene and the antioxidant in the pore-forming agent by adopting a double-screw extrusion process at a certain temperature, and then extruding;
3) casting the mixture extruded in step 2) into a strip;
4) biaxially stretching the strip cast in the step 3) to form a film;
5) extracting to remove the pore-forming agent from the thin film;
6) heat-setting the thin film from which the pore-forming agent is removed;
7) and performing second longitudinal stretching and retraction on the film after the heat setting, wherein the longitudinal stretching process comprises one of the following two modes: a) arranging a plurality of chain clamps for longitudinally fixing the film in a stretching area along the advancing direction of the film, wherein the distance between every two adjacent chain clamps along the advancing direction of the film is sequentially increased; b) arranging a plurality of rollers for longitudinally fixing the film in a stretching area along the advancing direction of the film, wherein the speed of the rollers is increased in sequence along the advancing direction of the film; the longitudinal retraction process includes one of two ways: c) a plurality of chain clamps for longitudinally fixing the film are arranged in the retraction area along the advancing direction of the film, and the distance between every two adjacent chain clamps along the advancing direction of the film is reduced in sequence; d) arranging a plurality of rollers for longitudinally fixing the film in a retraction area along the advancing direction of the film, wherein the speed of the rollers is reduced in sequence along the advancing direction of the film;
8) and rolling the film which is subjected to the secondary longitudinal stretching and retraction to obtain the polymer isolating film.
2. The polymeric separator of claim 1, wherein: the high molecular weight polyethylene is a single high molecular weight polyethylene or a mixture of two or more high molecular weight polyethylenes.
3. The polymeric separator of claim 1, wherein: the antioxidant comprises one or more of 4, 4-thiobis (6-tert-butyl-m-cresol), dibutyl hydroxy toluene, phosphite, tert-butyl hydroquinone, N-octadecyl beta- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate, 1, 3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 2-tert-butyl-6-methylphenol, N' -di-beta-naphthyl-p-phenylenediamine, dilauryl thiodipropionate, tris (nonylphenyl) phosphite and triphenyl phosphite.
4. A method of making a polymeric separator, the method comprising:
1) mixing high molecular weight polyethylene, pore-forming agent and antioxidant, and stirring to form mixture, wherein the average molecular weight of the high molecular weight polyethylene is 1.0 × 105~10.0×106Has a density of 0.940g/cm3~0.976g/cm3The weight of the antioxidant is 0.1-10 parts based on 100 parts of the high molecular weight polyethylene;
2) dissolving the high molecular weight polyethylene and the antioxidant in the pore-forming agent by adopting a double-screw extrusion process at a certain temperature, and then extruding;
3) casting the mixture extruded in step 2) into a strip;
4) biaxially stretching the strip cast in the step 3) to form a film;
5) extracting to remove the pore-forming agent from the thin film;
6) heat-setting the thin film from which the pore-forming agent is removed;
7) and performing second longitudinal stretching and retraction on the film after the heat setting, wherein the longitudinal stretching process comprises one of the following two modes: a) arranging a plurality of chain clamps for longitudinally fixing the film in a stretching area along the advancing direction of the film, wherein the distance between every two adjacent chain clamps along the advancing direction of the film is sequentially increased; b) arranging a plurality of rollers for longitudinally fixing the film in a stretching area along the advancing direction of the film, wherein the speed of the rollers is increased in sequence along the advancing direction of the film; the longitudinal retraction process includes one of two ways: c) a plurality of chain clamps for longitudinally fixing the film are arranged in the retraction area along the advancing direction of the film, and the distance between every two adjacent chain clamps along the advancing direction of the film is reduced in sequence; d) arranging a plurality of rollers for longitudinally fixing the film in a retraction area along the advancing direction of the film, wherein the speed of the rollers is reduced in sequence along the advancing direction of the film;
8) and rolling the film which is subjected to secondary longitudinal stretching and retraction to obtain the polymer isolation film, wherein the longitudinal thermal shrinkage rate of the polymer isolation film is between 1.0% and 2.5%, the transverse thermal shrinkage rate is between 0.1% and 1.7%, the longitudinal internal stress shrinkage rate is between 5.0% and 12.0%, the transverse internal stress shrinkage rate is between 0.8% and 5.1%, and the thickness is between 5 mu m and 9 mu m.
5. The method for producing a polymer separator according to claim 4, wherein: in the step 1), the weight of the pore-forming agent is 100-500 parts by weight based on 100 parts by weight of the high molecular weight polyethylene.
6. The method of claim 5The method for preparing the polymer isolating membrane is characterized in that: the pore-forming agent comprises natural mineral oil and C6-15Alkane, C8-15Aliphatic carboxylic acid, C8-15Aliphatic Carboxylic acids C1-4Alkyl ester, C2-6Halogenated alkanes, phthalates, trimellitates, adipates, sebacates, maleates, benzoates, epoxidized vegetable oils, benzenesulfonamides, phosphotriesters, glycol ethers, acetylated monoglycerides, citrates and cyclohexane-1, 2-dicarboxylic acid diisononyl esters.
7. The method for producing a polymer separator according to claim 5, wherein: the pore-forming agent has a kinematic viscosity at 40 ℃ of 10mm2/s~100mm2The initial boiling point of the pore-forming agent is above 110 ℃ between s.
8. The method for producing a polymer separator according to claim 4, wherein: in the step 4), the ribbon is stretched in a manner of stretching in a longitudinal direction and then in a transverse direction or stretching in both the longitudinal direction and the transverse direction.
9. The method for producing a polymer separator according to claim 4, wherein: in the step 1), at least one of the high molecular weight polyethylene, the pore-forming agent and the antioxidant is mixed and stirred uniformly to form the mixture.
10. The method for producing a polymer separator according to claim 4, wherein: in the step 2), the high molecular weight polyethylene and the antioxidant are dissolved in the pore-forming agent at the temperature of 170-200 ℃, and then are continuously extruded at the speed of 85-115 rpm.
11. The method of manufacturing a polymer release film according to claim 4, wherein the step of casting the mixture extruded in the step 2) into a ribbon in the step 3) comprises: firstly, continuously feeding the mixture extruded in the step 2) into a slot die head, then extruding the extruded mixture to a casting cooling roller through the slot die head, and casting the mixture into a belt at the temperature of 20-40 ℃.
12. The method for producing a polymer separator according to claim 4, wherein: in the step 6), transversely tightening the film for heat setting for 13-20 seconds at the temperature of 115-145 ℃; and in the step 8), rolling the film at a speed of 30-70 m/min to obtain the polymer isolating film.
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