KR20200062808A - Polyethylene porous separator and manufacturing method thereof - Google Patents

Abstract

Provided are a polyethylene porous separator having physical properties and heat resistance suitable for the porous separator by adding a carbon material to polyethylene, and a manufacturing method thereof. The present invention provides the method of manufacturing the polyethylene porous separator, which includes the steps of: (a) dispersing graphene in a liquid low molecular weight material; (b) mixing the liquid low molecular weight material in which the graphene is dispersed with polyethylene; and (c) removing the liquid low molecular weight substance from the mixture mixed in the step (b), wherein 0.03 to 35 parts by weight of the graphene is included based on 100 parts by weight of the polyethylene.

Description

Polyethylene porous separator and manufacturing method thereof

The present invention relates to a polyethylene porous separator and a method for manufacturing the same, and more particularly, to a polyethylene porous separator having excellent strength by mixing a carbon material with polyethylene used as a porous separator material and a method for manufacturing the same.

Porous membranes are widely used in applications to divide and divide specific components such as secondary battery separators and filtration membranes. Recently, polyolefins are used for film-type porous membranes, which are in increasing demand, and the use of materials is gradually increasing as demand increases. Among them, polyethylene, which can satisfy the required properties even with a thin thickness, has a strong demand growth.

Porous membranes using polyethylene are made by using low molecular weight materials together. First, a high-density polyethylene having a high molecular weight is mixed with a low-molecular substance such as paraffin oil to make a molded article on a sheet, and while stretching the molded article, a low-molecular substance is extracted to form pores. In general, the higher the molecular weight, the better the physical properties, but the polyethylene using this process has very low flowability, so there is a limit to controlling the polyethylene content or increasing the molecular weight. In addition, it can be said that there is a limit to the material change because the shrinkage property of the polymer material increases. In addition, a method of deriving desired characteristics by controlling process temperature, rate ratio, annealing condition, etc. is also used. However, due to the fundamental properties of the polyolefin material, it is difficult to expect more than a certain level of physical properties, and a material such as a metal oxide may be coated on both sides or one side rather than being used alone. However, there are limitations in improving moldability, heat resistance, and heat shrinkage by adjusting the molecular weight of the material, and the coating method may cause problems such as separation of the coating layer, production yield, process complexity, and cost.

Graphene material is a material with very good physical properties, and is very high in strength, stable, and mechanically elastic. In addition, because the weight-to-volume ratio is very large, there is an advantage in that a high amount of properties can be induced only by adding a small amount. However, it is difficult to develop the ideal effect because graphene is difficult to disperse, difficult to use, and difficult to mix with other materials.

Japanese Patent No. 5021461 discloses a microporous membrane obtained by stretching a gel-like molded product including a polyolefin and a solvent, which is a general porous membrane manufacturing method, in order to realize an increase in physical properties by changing the material and process conditions, but the fundamental limitations of the material Exists.

Korean Patent Publication No. 2018-0034290 discloses an electrolyte membrane for a fuel cell including a porous carbonaceous film layer to which graphite is added, but the method for manufacturing a molded product is difficult and complicated by having a fluorine-based ionomer layer on both sides of the film.

Non-patent literature (Pingfu Wei and Shibing Bai, RSC Advanced, 93697-93705) uses a milling method to disperse graphene in polyethylene, but the technique can be used for the method of manufacturing a porous membrane using a high molecular weight material. none.

Therefore, the present invention was devised to solve the above problems, and to provide a polyethylene porous separator having a proper physical property and heat resistance to a porous separator by adding a carbon material to the polyethylene and a method for manufacturing the same.

In order to solve the above problems, the present invention comprises: (a) dispersing graphene in a liquid low molecular substance; (b) mixing the liquid low molecular substance in which the graphene is dispersed in polyethylene; And (c) removing the liquid low-molecular substance from the mixture mixed in the step (b); wherein, the polyethylene porous separator comprising 0.03 to 35 parts by weight of the graphene with respect to 100 parts by weight of the polyethylene Provide a method.

In addition, the liquid low molecular material provides a method for producing a polyethylene porous separator, characterized in that at least one member selected from the group consisting of phthalic acid ester compounds, aromatic ether compounds, and fatty acid compounds having 30 carbon atoms or less.

In addition, step (a) provides a method for producing a polyethylene porous separator characterized in that graphene is dispersed by treating at an ultrasonic frequency of 100 MHz or less.

In addition, the polyethylene of the step (b) provides a polyethylene porous separator manufacturing method characterized in that the high-density polyethylene having a weight average molecular weight of 300,000 ~ 900,000.

It also provides a method for producing a polyethylene porous separator, characterized in that it further comprises the step of molding and stretching the mixture mixed in step (b) between steps (b) and (c).

In addition, the stretching provides a method for producing a polyethylene porous separator characterized in that the mixture mixed in step (b) is stretched 4 to 10 times in the longitudinal and transverse directions at 100 to 140°C.

In addition, it provides a polyethylene porous separator prepared by using the polyethylene porous separator manufacturing method.

In addition, the polyethylene porous separator provides a polyethylene porous separator characterized in that the puncture strength measured by the following measurement method is 500 gf or more and the heat shrinkage is less than 1%.

[Measurement method of puncture strength]

After cutting the porous membrane specimen to a size of 50 x 50 mm, place the specimen on a plate with a hole of 10 mm in diameter and measure the force to be drilled while pressing with a 1 mm probe, after measuring the puncture strength of the specimen three times, the average value Calculated.

[Measurement method of heat shrinkage]

After cutting the porous membrane specimens to 50 x 50 mm size, the specimens were left in an oven at 90°C and 105°C for 1 hour, respectively, and then the degree of shrinkage of each specimen was measured to calculate the average heat shrinkage.

The present invention provides a polyethylene porous separator having a carbon material added to polyethylene in a polyethylene porous separator to produce a polyethylene porous separator, which increases strength and heat resistance, generates less thermal shrinkage, and does not decrease air permeability, and a method for manufacturing the same. You can.

Hereinafter, preferred embodiments of the present invention will be described in detail. In the description of the present invention, when it is determined that a detailed description of related known technologies may obscure the subject matter of the present invention, the detailed description will be omitted. Throughout the specification, when a part “includes” a certain component, this means that other components may be further included instead of excluding other components, unless specifically stated to the contrary.

The present inventors in the polyethylene porous separator, polyethylene, which was previously used as a material for the porous separator, has very low flowability, is difficult to control the content and increase the molecular weight, and also increases the shrinkage characteristics when manufacturing the porous separator. Faced with the fact that there are limitations, and as a result of repeated studies to solve these problems, when preparing a porous membrane by mixing graphene, one of the carbon materials in polyethylene, into a liquid low molecular material exhibiting phase separation properties with polyethylene, The physical properties and heat resistance of the polyethylene porous membrane are increased, and when graphene is dispersed and mixed in a liquid low-molecular substance through a specific process, it has been found that the graphene and the polyethylene are mixed more easily and the present invention has been reached.

Therefore, the present invention comprises the steps of (a) dispersing graphene in a liquid low molecular substance; (b) mixing the liquid low molecular substance in which the graphene is dispersed in polyethylene; And (c) removing the liquid low-molecular substance from the mixture mixed in the step (b); a method for manufacturing a polyethylene porous separator comprising 0.03 to 35 parts by weight of the graphene with respect to 100 parts by weight of the polyethylene. Disclosed.

In the present invention, step (a) is a step of dispersing the graphene in the liquid low-molecular substance so that graphene and polyethylene can be easily mixed, and the liquid low-molecular substance has a phase separation property with the polyethylene. When the polyethylene porous membrane can be easily removed, the porosity of the polyethylene porous separator can be improved due to these characteristics, and the liquid low molecular material is in a liquid state at room temperature, so the polyethylene having a very high molecular weight can also be used for preparing the porous membrane. In addition, additives to be used for preparing a porous membrane may also be used by dispersing in the liquid low molecular material.

The liquid low-molecular substance is a material exhibiting phase separation characteristics with the polyethylene, and may be at least one compound selected from the group consisting of phthalic acid ester compounds, aromatic ether compounds, and fatty acid compounds having 30 carbon atoms or less, preferably 30 carbon atoms. It may be a paraffin oil, which is one type of fatty acids.

In the present invention, the graphene refers to a layer of graphite having a structure in which planes in which carbons are arranged as a honeycomb-shaped hexagonal net are stacked in layers. Is known.

In addition, graphene conducts electricity more than 100 times better than copper, and electron mobility is more than 100 times faster than silicon, which is mainly used as a semiconductor. Its strength is more than 200 times stronger than steel, and it has more than 2 times higher thermal conductivity than diamond, which boasts the best thermal conductivity. In addition, since most of the light passes, it is transparent and has excellent elasticity.

However, graphene has a disadvantage in that it is difficult to express an ideal effect because it is very difficult to use, very difficult to use, and difficult to mix with other materials.

In the present invention, in order to solve the disadvantages of the graphene, the graphene is dispersed in the liquid low-molecular substance and then mixed with polyethylene. The amount of graphene dispersed in the liquid low-molecular substance exhibiting phase separation properties with respect to the polyethylene may be 0.01 to 10 parts by weight based on 100 parts by weight of the total liquid low-molecular substance and polyethylene, preferably 0.03 to 5 parts by weight, , More preferably, it may be 0.05 to 1 part by weight.

When the amount of graphene dispersed in the liquid low-molecular substance is less than 0.01 part by weight based on 100 parts by weight of the total of the liquid low-molecular substance and polyethylene, the puncture strength of the polyethylene porous separator according to the present invention is lowered and heat shrinkage may occur significantly, When the amount of the graphene exceeds 10 parts by weight based on 100 parts by weight of the total liquid low-molecular substance and polyethylene, graphene is not easily dispersed in the liquid low-molecular substance and is agglomerated so that the porosity may be lowered because it is not mixed with the polyethylene.

In addition, in the present invention, ultrasound may be used to disperse the graphene in the liquid low molecular substance, and the frequency of the ultrasound may be 100 MHz or less, preferably 10 to 90 MHz, and more preferably 30 to 70 MHz. Can be

In step (a), the energy of ultrasonic waves is very important to disperse the graphene in the liquid low molecular substance. When the frequency of ultrasonic waves is less than 10 MHz during the ultrasonic treatment, the applied energy is low, so that the graphene is added to the liquid low molecular substance. It may not be evenly distributed, and when the frequency of the ultrasonic wave exceeds 100 MHz, graphene aggregation may occur due to excessive energy supply.

In addition, the time for performing the ultrasonic treatment process may be 1 to 1000 minutes, preferably 10 to 300 minutes, and more preferably 15 to 50 minutes.

If the ultrasonic treatment time is less than 1 minute, the applied energy is small, and the graphene may not be evenly dispersed in the liquid low-molecular substance, and if it exceeds 1000 minutes, the dispersion degree of the graphene over time is not increased, which is economical. May not.

In the present invention, the step (b) is a step of mixing the liquid low-molecular substance in which graphene is dispersed and polyethylene, and the mixing process is not particularly limited, and the liquid low-molecular substance in which the graphene is dispersed and the polyethylene are disposed. In the form of an extruder, it may be carried out at a rate of 40-80 rpm, preferably 50-70 rpm, at 210-250°C, preferably 220-240°C. In step (b), oxidation is performed on the polyethylene to prevent oxidation. The mixing process can be performed after adding the inhibitor.

In addition, in the step (b), high density polyethylene may be used for the physical properties and heat resistance of the porous membrane, and the density of the high density polyethylene may be 0.930 to 0.980 g/cm 3, and the weight average molecular weight is 300,000 to 900,000 days. It may be, preferably from 400,000 to 800,000, most preferably from 500,000 to 700,000. The molecular weight is a range in which the processability and properties and properties of the polyethylene porous separator of the present invention can be optimized.

In the present invention, the mixed mixture may be molded and stretched to easily remove the liquid low-molecular substance after performing the mixing process. The stretching may be performed using a biaxial stretching machine after forming a sheet with a thickness of 0.1 to 2 mm on a hot plate heated to 150 to 170°C. When stretching, the temperature may be 100 to 140°C, preferably 110 to 120°C, and the sheet may be stretched 4 to 10 times, preferably 6 to 8 times, respectively in the longitudinal and transverse directions.

If the temperature at the time of stretching is less than 110° C., unstretched and breakage may occur, and if it exceeds 120° C., voids may not be generated. If the draw ratio is less than 4 times in the longitudinal and transverse directions, as described below It may not be easy to remove the liquid low-molecular substance, and if the stretching ratio exceeds 10 times in the longitudinal and transverse directions, the sheet may be torn during the stretching process, so that it cannot be used as a separator.

In the present invention, step (c) is a step in which pores are formed. Specifically, the porosity of the polyethylene porous separator having pores formed by removing the liquid low-molecular substance from the mixture mixed in step (b) is 30% or more. It may be, preferably 35% or more.

Accordingly, according to the present invention, the porous porous membrane for removing the liquid low-molecular substance contains 0.03 to 35 parts by weight of the graphene, preferably 0.1 to 17 parts by weight, based on 100 parts by weight of the polyethylene, More preferably, it contains 0.2 to 5 parts by weight.

When the graphene is included in the polyethylene porous separator in an amount less than 0.03 parts by weight compared to 100 parts by weight of polyethylene, the puncture strength of the polyethylene porous separator may be lowered and heat shrinkage may occur, and the graphene is polyethylene 100 in the polyethylene porous separator. When included in an amount exceeding 35 parts by weight compared to parts by weight, the graphene may not be easily dispersed and may be aggregated to lower the porosity of the polyethylene porous separator.

In step (c), an organic solvent may be used to remove the liquid low-molecular substance, and specifically methylene chloride, ethanol, methanol, and the like may be used, and preferably methylene chloride may be used.

When the liquid low molecular substance is removed in the step (c), the mixture is dried at room temperature to prepare a polyethylene porous membrane.

Another aspect of the present invention provides a polyethylene porous separator manufactured using the polyethylene porous manufacturing method.

As described above, the polyethylene porous separator manufactured by using the method of manufacturing the polyethylene porous separator according to the present invention is prepared by dispersing graphene in a liquid low-molecular substance and mixing it with a polyethylene resin, so that the molded article and air permeability of polyethylene are similar but have a puncture strength. And reducing the heat shrinkage rate, it is possible to significantly improve the porosity and mechanical properties of the film used as a separator material.

Specifically, the polyethylene porous separator may have a puncture strength measured by the following measuring method of 500 gf or more, preferably 500 to 2,000 gf, more preferably 600 to 1,000 gf, measured by the following measuring method The heat shrinkage may be less than 1%, preferably 0.1 to 0.8%, and most preferably 0.1 to 0.5%.

[Measurement method of puncture strength]

After cutting the porous membrane specimen to a size of 50 x 50 mm, place the specimen on a plate with a hole of 10 mm in diameter and measure the force drilled while pressing with a 1 mm probe, after measuring the puncture strength of the specimen three times, the average value Calculated.

[Measurement method of heat shrinkage]

After cutting the porous membrane specimens to 50 x 50 mm size, the specimens were left in an oven at 90°C and 105°C for 1 hour, respectively, and then the degree of shrinkage of each specimen was measured to calculate the average heat shrinkage.

In addition, the polyethylene porous separator may have an air permeability of 350 s/100 cc or less, preferably 150 to 300 s/100 cc, and more preferably 180 to 250 s/100 cc.

The air permeability of the polyethylene porous separator is a value indicating the permeability of the material. In the battery separator, if the air permeability exceeds 350 s/100 cc, the rapid charge/discharge efficiency may decrease, and if it is less than 150 s/100 cc, correlated puncture strength Can be lowered.

Hereinafter, a specific embodiment according to the present invention will be described.

First, the specifications of the components used in Examples and Comparative Examples of the present invention are as follows.

(1) Paraffin oil: Paraffin oil having a kinematic viscosity at 40°C of 68 cSt and a density of 0.857 g/cc is used.

(2) Polyethylene: A product with a weight average molecular weight of 600,000 is used.

(3) Graphene: Graphene in the form of a nanoplatelet is used (N002-PDR).

(4) Antioxidant: 1010 (Songwon Industrial XONGNOX 1010) 1,000ppm is used.

Examples 1 to 8, Comparative Examples 1 and 2

Prepare 70 parts by weight of paraffin oil with respect to 100 parts by weight of paraffin oil and polyethylene, add graphene of the content shown in Table 1 to the paraffin oil, and then treat it according to the ultrasonic frequency and time according to Table 1 below. Disperse graphene in oil. After dispersion, polyethylene is prepared in 30 parts by weight based on 100 parts by weight of paraffin oil and polyethylene, and 1,000 ppm of antioxidant 1010 is added to the polyethylene to prepare a mixed powder. The paraffin oil in which the graphene is dispersed and the polyethylene powder to which the antioxidant is added are placed in a batch type extruder and mixed at 60° C. under 230° C. conditions. After mixing, the mixture is molded into a sheet having a thickness of 1 mm on a hot plate heated to 160°C, and stretched 7 times in the longitudinal and transverse directions at 114 to 116°C using a biaxial stretching machine. After stretching, the paraffin oil is extracted using methylene chloride, and dried at room temperature to prepare a polyethylene porous separator. The content of the graphene contained in the polyethylene porous separator is shown in Table 1 below.

Comparative example 3

After mixing 70 parts by weight of paraffin oil, 30 parts by weight of polyethylene, 0.5 parts by weight of graphene, and 1010 parts of antioxidant 1010 parts by weight with respect to 100 parts by weight of paraffin oil and polyethylene, and treating them at an ultrasonic frequency of 50 MHz for 20 minutes, the batch extruder Put in and mix at 60 rpm under 230°C. After mixing, the mixture was molded into a sheet having a thickness of 1 mm on a hot plate heated to 160° C., the paraffin oil was extracted using methylene chloride, and dried at room temperature to prepare a polyethylene porous separator. The content of the graphene contained in the polyethylene porous separator is 1.67 parts by weight compared to 100 parts by weight of the polyethylene.

Experimental Example

For the polyethylene porous separators prepared in Examples 1 to 8 and Comparative Examples 1 to 3, thickness, air permeability, porosity, puncture strength and heat shrinkage were measured according to the following measurement methods, and the results are shown in Table 2 below. .

[Experiment method]

1) Thickness: After the thickness of the prepared porous membrane was measured five times, it was calculated using the average value excluding the maximum/minimum values.

2) Air permeability: The average time taken for the separator having a circular area of 1 inch in diameter to permeate 100 cc of air was measured five times, and then the average value excluding the maximum/minimum values was calculated.

3) Porosity: The porosity was derived by calculating the space in the porous membrane. After taking a rectangular specimen and measuring the weight, it was calculated as the ratio of the weight of the resin in the same volume to the weight of the porous membrane.

4) Perforation strength: After cutting the prepared porous membrane to a size of 50×50 mm, the specimen was placed on a hole with a diameter of 10 mm, and the force drilled while pressing with a 1 mm probe was measured. After measuring the puncture strength of each specimen three times, it was calculated using the average value.

5) Heat shrinkage: After cutting the prepared porous membrane to a size of 50×50 mm, the specimens were left in an oven at 90° C. and 105° C. for 1 hour, and then the degree of shrinkage of each specimen was measured to calculate the average heat shrinkage.

Referring to Table 2, when graphene is dispersed using ultrasound (Examples 1 to 6) and when ultrasound is not used (Example 7), graphene is paraffin when ultrasound is not used. It can be seen that the air permeability of the prepared polyethylene porous membrane is very high and the porosity is low because it is not evenly dispersed in the oil, and when a large amount of graphene is contained (Comparative Example 2), graphene is not evenly dispersed in the paraffin oil. It can be seen that the air permeability is very high and the porosity is very low.

Further, when graphene is not included (Comparative Example 1) and graphene is included (Examples 1 to 6), when graphene is not included, the puncture strength is very low and the thermal shrinkage is large. As can be seen, when the frequency of ultrasonic waves is 50 MHz (Examples 1 to 3) and the ultrasonic frequency is 100 MHz or 200 MHz (Examples 5 and 6), the air permeability is high due to the non-uniformity of the porous structure of graphene. You can see that

In addition, when the ultrasonic time is increased (Example 8), it can be seen that the air permeability, porosity, puncture strength, and heat shrinkage rate indicate suitable values for use as a polyethylene porous separator, from which the ultrasonic frequency is graphene dispersion. It can be seen that it has a great influence on.

In addition, when graphene, a liquid low-molecular substance, and polyethylene were simultaneously mixed and subjected to ultrasonic treatment and the stretching process was not performed (Comparative Example 3), air permeability was too high and porosity, puncture strength, and heat shrinkage could not be measured.

As described above, in the case of the polyethylene porous separator according to the present invention, by adding a specific carbon material to the polyethylene and dispersing the carbon material using a specific process, the puncture strength is improved and the heat shrinkage rate is improved compared to the porous separator manufactured using only polyethylene. It is possible to provide a reducing polyethylene porous separator.

The preferred embodiments of the present invention have been described above in detail. The description of the present invention is for illustrative purposes, and those skilled in the art to which the present invention pertains will appreciate that other specific forms can be easily modified without changing the technical spirit or essential features of the present invention.

Claims (8)

(a) dispersing graphene in a liquid low molecular substance;
(b) mixing the liquid low molecular substance in which the graphene is dispersed in polyethylene; And
(c) removing the liquid low molecular substance from the mixture mixed in step (b);
It includes, and the method for producing a polyethylene porous separator comprising 0.03 to 35 parts by weight of the graphene with respect to 100 parts by weight of the polyethylene. According to claim 1,
The liquid low molecular material is a method for producing a polyethylene porous separator, characterized in that at least one member selected from the group consisting of phthalic acid ester compounds, aromatic ether compounds and fatty acid compounds having 30 or less carbon atoms. According to claim 1,
The step (a) is a method of manufacturing a polyethylene porous separator characterized in that graphene is dispersed by treating at an ultrasonic frequency of 100 MHz or less. According to claim 1,
The polyethylene porous membrane manufacturing method of the (b) step is characterized in that the high-density polyethylene having a weight average molecular weight of 300,000 ~ 900,000. According to claim 1,
A method of manufacturing a polyethylene porous separator, further comprising molding and stretching the mixture mixed in step (b) between steps (b) and (c). The method of claim 5,
The stretching is a method for producing a polyethylene porous separator, characterized in that the mixture mixed in step (b) is stretched 4 to 10 times in the longitudinal and transverse directions at 100 to 140°C. A polyethylene porous separator prepared by using the method for manufacturing a polyethylene porous separator according to any one of claims 1 to 6. The method of claim 7,
The polyethylene porous separator is a polyethylene porous separator characterized in that the puncture strength measured by the following measuring method is 500gf or more, and the heat shrinkage is less than 1%.
[Measurement method of puncture strength]
After cutting the porous membrane specimen to a size of 50 x 50 mm, place the specimen on a plate with a hole of 10 mm in diameter and measure the force to be drilled while pressing with a 1 mm probe. Calculated.
[Measurement method of heat shrinkage]
After cutting the porous membrane specimens to 50 x 50 mm size, the specimens were left in an oven at 90 °C and 105 °C for 1 hour, respectively, and then the degree of shrinkage of each specimen was measured to calculate the average heat shrinkage.