KR101189758B1 - Method for porous film using microwave and porous film - Google Patents

Abstract

The present invention is a porous film containing a ferroelectric resin, the ferroelectric resin is a fluorinate ethylene propylene copolymer (FEP), perfluoroalkoxy (FA), ethylene tetrafluoroethylene (ETFE), polyvinylidene fluoride ( PVDF), polyethylenechlorotrifluoroethylene (ECTFE), polychlorotrifluoroethylene (PCTFE), and polyvinylidene fluoride-co-hexafluoropropylene (PVdF-co-HFP) Is selected, the ferroelectric resin is arranged in a non-polar alpha-type structure, the size of the pores relates to a porous film of 600nm ~ 6㎛.

Description

Method for manufacturing porous film using microwaves and manufactured porous film {METHOD FOR POROUS FILM USING MICROWAVE AND POROUS FILM}

The present invention relates to a porous film, and more particularly, to a porous film manufacturing method using a microwave and a manufactured porous film.

Microporous membranes are widely used in various fields, and in particular, recently used as a separator of a lithium secondary battery. Of the lithium secondary batteries, particularly, lithium ion batteries use a highly active organic solvent as an electrolyte, and thus, a microporous membrane made of a low polyolefin resin having low reactivity with an organic solvent is mainly used as a separator.

The method for producing a microporous membrane used as a separator of a battery using a polyolefin resin is to prepare a precursor film, annealing the original film, and then stretching to form fine pores, followed by hot setting. )). The method mainly used as a method of manufacturing the original film includes a wet method using a filler or a wax and a solvent and a dry method using no solvent.

The dual dry method is mainly used in that a large-size original film can be manufactured, a production process is relatively easy, a solvent is not used, and thus an excellent manufacturing environment can be obtained and mass production is easy.

The method for producing a microporous membrane by using such a dry method is as follows. U.S. Pat.Nos. 3,679,538 and 3,801,692 disclose that original films having high crystallinity and elasticity are continuously hot stretched through continuous cold stretching to form fine pores, and then heat A method of forming a microporous membrane by heat setting is described.

U.S. Patent Nos. 3,843,761 and 4,238,459 describe a method of initially cold drawing annealing annealed films continuously and then multistage hot drawing. In addition, US Pat. No. 5,013,439 discloses a method for producing membranes having reduced pore size and increased pore density by using a multi-step cold draw process in continuous cold draw and hot draw processes. It is.

This manufacturing process has the advantage of being a clean process without any problems such as solvent contamination because it uses only pure polymer, but the membrane produced by this process has a slight drop in porosity and pore size of the membrane. When used, there is a problem that the passage of electrolyte and ions is not easy.

In the case of the presently disclosed olefin-based membrane, it has low wettability to the organic electrolyte and consequently low ionic conductivity and low properties.

In addition, the membrane prepared by the process is difficult to uniformly control the pore size and shape, and there is a problem in improving the porosity because there is a limit to increase the elongation to maintain the shape of the separator.

In addition, the above-described methods have a complicated problem because the process must be carried out two-step stretching of low-temperature stretching and high-temperature stretching.

The present invention has been proposed to solve the above problems, and an object of the present invention is to provide a porous film manufacturing method and a manufactured porous film using microwave.

Porous film according to an aspect of the present invention, fluorineate ethylene propylene copolymer (FEP), perfluoroalkoxy (FA), ethylene tetrafluoroethylene (ETFE), polyvinylidene fluoride (PVDF), polyethylene chlorotri At least one selected from the group consisting of fluoroethylene (ECTFE), polychlorotrifluoroethylene (PCTFE), and polyvinylidene fluoride-co-hexafluoropropylene (PVdF-co-HFP) In addition, the ferroelectric resin is arranged in a non-polar alpha-type structure, the pore size may be formed of 600nm ~ 6㎛.
Method for manufacturing a porous film according to an aspect of the present invention comprises the steps of: coating a solution containing a ferroelectric resin and a resin for pore forming on a substrate and irradiating microwaves to produce a film; And removing the pore-forming resin contained in the film to form fine pores; wherein the preparing of the film comprises irradiating microwaves such that the ferroelectric resin is arranged in a nonpolar alpha structure.
The ferroelectric resin may be fluorineate ethylene propylene copolymer (FEP), perfluoroalkoxy (FA), ethylenetetrafluoroethylene (ETFE), polyvinylidene fluoride (PVDF), polyethylenechlorotrifluoroethylene (ECTFE), At least one selected from the group consisting of polychlorotrifluoroethylene (PCTFE), and polyvinylidene fluoride-co-hexafluoropropylene (PVdF-co-HFP),

The pore-forming resin is methyl cellulose (MC), ethyl cellulose (EC), hydroxyethyl cellulose (HEC), hydroxyethyl methyl cellulose (HEMC), hydroxypropyl methyl cellulose (HPMC), hydroxypropyl cellulose (HPC). ), Hydroxypropylmethylcellulose (HPMC), microstalin cellulose (MCC), and carboxymethylcellulose (CMC) any one or more selected from the group consisting of can be selected.

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At this time, the mass ratio of the ferroelectric resin and the resin for pore forming may be mixed to have 1.0: 0.2 to 1.0.

In the step of forming the film, the microwave irradiation may irradiate the film with 600 to 800 W of microwave for 1 to 4 minutes.

And the step of forming the fine pores to remove the pore-forming resin by contacting the film to the solution that can be selectively dissolved only the pore-forming resin, it can be irradiated with ultrasound for 10-30 minutes.

In addition, after the step of forming the fine pores may further comprise the step of vacuum drying the film for 3 to 6 hours at a temperature of 70 ~ 80 ℃.

According to the above configuration, the present invention has the advantage that the ferroelectric resin and the resin for pore forming have a high dispersion degree due to microwaves, so that the distribution and size of the pores are uniform.

In addition, the solvent is removed by a microwave in a short time there is an advantage that can shorten the manufacturing time.

1 is a flow chart according to an embodiment of the present invention;
2 is a photograph of a porous film prepared by the first embodiment of the present invention,
3 is a photograph of a porous film prepared by Comparative Example 1,
4 is a photograph of a porous film prepared by a second embodiment of the present invention,
5 is a photograph of a porous film prepared by Comparative Example 2,
6 is an IR (Infrared spectroscopy) graph of the film prepared according to the embodiment of the present invention,
7 is a XRD (X-Ray Diffraction) graph of the porous film prepared according to an embodiment of the present invention,
8 is a XRD (X-Ray Diffraction) graph of the porous film prepared by the drying method,
9 is a graph showing the hardness of the porous film prepared according to an embodiment of the present invention,
10 is a graph measuring the remaining cellulose in the porous film produced by the embodiment of the present invention,
11 is a photograph showing electrolyte permeation of a porous film prepared according to an embodiment of the present invention,
12 is a graph showing the relationship between the ratio of HPC and the impregnation time of the porous film according to an embodiment of the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail.

It is to be understood, however, that the invention is not to be limited to the specific embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Terms including ordinal numbers such as first and second may be used to describe various components, but the components are not limited by the terms.

The terms are used only for the purpose of distinguishing one component from another.

For example, without departing from the scope of the present invention, the second component may be referred to as a first component, and similarly, the first component may also be referred to as a second component.

It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, .

On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

In the present application, the terms "comprises", "having", and the like are used to specify that a feature, a number, a step, an operation, an element, a component, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

In addition, it is to be understood that the accompanying drawings in this application are shown enlarged or reduced for convenience of description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the drawings. Like reference numerals designate like elements throughout, and duplicate descriptions thereof will be omitted.

In the porous film manufacturing method according to an embodiment of the present invention, the first step (S10) of preparing a mixed solution largely mixed with resin and the second step (S20) of forming a film by irradiating microwaves to the mixed solution and the film It includes a third step (S30) for removing the resin for pore formation contained in.

However, the above steps are divided for convenience of description, and the steps may be changed according to embodiments, and it is obvious that each step may be performed at the same time.

First step (S10) is to prepare a solution in which the base resin and the pore-forming resin is dissolved in a solvent, a polymer having a polarity may be selected as the base resin to facilitate dispersion by microwaves.

As the polar polymer, a ferroelectric resin and a resin substituted with fluorine or chlorine may be selected. Preferably, a polyvinylidene fluoro-based polymer may be selected. More preferably, a fluorinate ethylene propylene copolymer (FEP) may be selected. ) Perfluoroalkoxy (FA), ethylene tetrafluoroethylene (ETFE), polyvinylidene fluoride (PVDF), polyethylenechlorotrifluoroethylene (ECTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene At least one selected from the group consisting of fluoride-co-hexafluoropropylene (PVdF-co-HFP).

However, the present invention is not limited thereto, and any polar polymer that reacts to microwaves may be used. For example, perfluoroalkoxy fluororesin (PFA) and polyethylene oxide (PEO, polyethyleneoxide), polypropylene oxide (PPO, polypropyleneoxide), polyethyleneimine (PEI, polyethyleneimine), polyethylene sulfide (PES, polyethylenesulfide), polyvinyl Acetate (PVAc, polyvinylacetate), Polyethylenesuccinate (PESc), Poly (oxymethylene-oligo-oxyethylene) (POO, poly (oxymethylene-oligo-oxyethylene)), Polyacrylonitrile (PAN, polyacrylonitrile), Poly At least one selected from the group consisting of methyl methacrylate (PMMA, polymethylmethacrylate), polyvinylpyrrolidone (PVP, polyvinylpyrrolidone), polyvinyl sulfone (PVS, polyvinylsulfone) and polyphenylene sulfide (PPS).

Among them, polyvinylidene fluoride (PVdF) is an extremely hydrophobic material and has an advantage of maintaining a certain degree of rigidity even when formed into a porous thin film.

The pore-forming resin should be able to be uniformly mixed with the base resin when the solution is prepared, and if the base resin is a resin that does not dissolve and optionally only a pore-forming resin can be dissolved without any limitation on the type Applicable

As the pore-forming resin, a water-soluble polymer may be selected, preferably cellulose may be selected, and more preferably methyl cellulose (MC), ethyl cellulose (EC), hydroxyethyl cellulose (HEC), or hydride. Selected from hydroxyethylmethylcellulose (HEMC), hydroxypropylmethylcellulose (HPMC), hydroxypropyl cellulose (HPC), hydroxypropylmethylcellulose (HPMC), microstalin cellulose (MCC), carboxymethylcellulose (CMC) Any one or more may be selected.

Among these, hydroxypropyl cellulose (HPC) is well soluble in water even at low temperatures has an environmentally friendly advantage.

As the solvent, dimethylacetamide (N, N-dimethylacetamide, DMAc), dimethylformamide (N, N-dimethylformamide, DMF), dimethyl sulfoxide (dimethlsulphoxide, DMSO), methylpyrrolidone (N-methyl-2-pyrrolidone, NMP), triethylphosphate (TEP), acetone, methylethyl ketone and tetrahydrofuran (THF) At least one selected from the group consisting of.

In the first step (S10) to prepare a solution by mixing the base resin and the pore-forming resin in the solvent. In this case, when the mass ratio of the resin for forming a pore is less than 0.2 based on the mass ratio of the base resin, the number of pores is too small and the size is too small to allow the electrolyte to pass through. There is a problem that the pore-forming resin is agglomerated so that the pores are not formed uniformly and the size is too large to peel off the film. Therefore, the base resin and the pore-forming resin are preferably mixed in the solvent in a mass ratio of 1: 0.2 to 1.0.

In addition, the base resin and the pore-forming resin may be dissolved in a solvent to prepare a mixed solution. At this time, it is obvious that the base solution and the pore-forming resin are included in the mixed solution in a mass ratio of 1: 0.2 to 1.0.

Thereafter, in the second step S20, a thin film is formed by coating a mixed solution of the base resin and the pore-forming resin thinly on a substrate, and then irradiating microwaves uniformly on the thinly coated mixed solution.

When irradiating microwaves, microwaves of a frequency at which the base resin can be absorbed may be used. Preferably, microwaves having a frequency of 300 MHz to 300 GHz may be used to heat the reactants, more preferably 600 to 800 W. Microwaves can be used. The method of irradiating microwaves has a shorter reaction time than the method using steam or electric heating.

The base resin and the pore-forming resin increase the kinetic energy by the pendulum motion of the microwave, and rise to a high temperature in a short time, so that the dispersion rate rapidly increases in the solvent and is uniformly spread within the solution.

At this time, the base resin is aligned by the microwaves so that the structure is changed to nonpolar. Particularly in the case of polyvinylidene fluoride (PVdF), when microwaves are irradiated, TGTG 'is an optically and thermodynamically excellent alpha (α) type structure, that is, the arrangement of trans (T) and Ghosh (G) in the three-dimensional structure of the molecular chain. The structure is repeated, resulting in a nonpolar arrangement in which the dipole moments cancel.

At this time, when the base resin is arranged as a non-polar crystal, not only the optical properties such as transparency are improved, but also the film property is improved, which is an advantage as a separator for a lithium secondary battery.

In addition, the solvent is all evaporated after a predetermined time by the microwave. Therefore, when the microwave is irradiated for about 1 to 4 minutes, all of the solvent is removed to form a 4-15 μm thick film composed of a base resin and a pore-forming resin.

Thereafter, in the third step S30, the film is immersed in a solvent in which only the resin for pore forming can be dissolved to remove the pore forming resin from the film. In this case, as the solvent, the base resin may be used without limitation as long as the base resin is not dissolved but only the resin for pore formation is selectively dissolved.

At this time, the microwave or ultrasonic wave may be added for 10 to 30 minutes so that the resin for pore formation fixed in the film is easily dissolved.

Therefore, the pore is formed at the position where the pore-forming resin is formed in the film. As described above, since the pore-forming resin is uniformly formed inside the film by microwaves in the first step, the pores formed at the position are also in the film. It is formed uniformly inside.

Thereafter, the drying step may be further performed to remove the solvent remaining in the film.

Table 1 below is a table relating to the porous film prepared by vacuum drying instead of the porous film prepared according to the embodiment of the present invention.

First Embodiment Second Embodiment Comparative Example 1 Comparative Example 2 PVdF: HPC Mass Ratio 1: 0.4 1: 0.8 1: 0.4 1: 0.8 Drying method microwave microwave Vacuum drying Vacuum drying Uniformity Good Good Bad Bad

Both Examples and Comparative Examples are quartz plates in a state in which a base resin PVdF (hereinafter referred to as PVDF) and a pore-forming resin HPC (hereinafter, referred to as HPC) are dissolved in a solvent DMF. ) And then the solvent was removed. Then, the film was peeled off, and the vial was put together with distilled water to apply ultrasonic waves to remove HPC. However, Examples 1 and 2 were carried out by microwave to remove the solvent, Comparative Examples 1 and 2 were vacuum dried at 170 ℃ for 12 hours to remove the solvent.

Figure 2 is a photograph of the porous film prepared by the first embodiment of the present invention, Figure 3 is a photograph of the porous film prepared by Comparative Example 1.

As shown in FIG. 2, the porous film prepared according to the first embodiment of the present invention can be seen that the pores are uniformly formed in place by removing the uniformly dispersed HPC, and the porous film prepared by Comparative Example 1 of FIG. 3. It can be seen that the film is not uniform in size and distribution of pores. Therefore, it can be seen that the HPC is uniformly dispersed by the microwave.

Figure 4 is a photograph of the porous film prepared by the second embodiment of the present invention, Figure 5 is a photograph of the porous film prepared by Comparative Example 2.

It can be seen that the pores formed in the porous film prepared by the second embodiment are larger than the porous film prepared by the first embodiment. Therefore, as the content of HPC increases, it can be confirmed that a porous film having a large pore size can be prepared.

In addition, the porous film produced by Comparative Example 2 also has a larger pore than Comparative Example 1, it can be seen that the spacing of the pores is not uniform compared to the second embodiment.

6 is an IR (Infrared spectroscopy) graph of a film prepared according to an embodiment of the present invention.

Referring to FIG. 6, the peak of the -OH group was measured in a film made of HPC-only film and a solution of PVdF / HPC (1.0 / 0.4 (mass ratio)) after casting on the crystal plate and peeling the film and removing the HPC. The peak of -OH group was not measured in the film from which HPC was removed.

In addition, it can be seen that the transmittance (transmittance) was measured relatively less in the film from the HPC, which is determined that the infrared wavelength is scattered by the pores and the transmittance is lowered.

7 is an X-ray diffraction (XRD) graph of a porous film prepared according to an embodiment of the present invention.

In general, the peaks of XRD should appear at 17.7 degrees, 18.4 degrees, 19.9 degrees, and 26.7 degrees in alpha-type PVdF films, and the peaks of XRD at 20.8 degrees and 20.7 degrees in beta-type PVdF films.

As can be seen in FIG. 7, the film formed by the microwave treatment method according to the embodiment of the present invention can be seen that the same peak occurs at the alpha type (α) at 17.7 degrees, 18.4 degrees, 19.9 degrees, 26.7 degrees. .

However, it can be seen that the porous film produced by the vacuum drying method does not generate a peak at 26.7 degrees as shown in FIG. 8, and therefore, the alpha-type PVdF film is not produced by the vacuum drying method.

9 is a graph showing the hardness of the porous film prepared according to the embodiment of the present invention.

Referring to FIG. 9, the tensile stress was 16.6 MPa for the porous membrane made by the vacuum drying method, and 12.6 MPa for the porous membrane made according to the microwave irradiation method.

Also, when the mass ratio of PVdF / HPC was 1.0.2 ~ 1.0, Tensile stress was 7.13 MPa for the porous membrane made by vacuum drying method, and 6.67 MPa was hardly different for porous membrane made by microwave irradiation method.

10 is a graph measuring the remaining cellulose in the porous film produced by the embodiment of the present invention.

10 is a porous film of Example 1 and Comparative Example 1 was measured by DSC (Differential Scanning Calorimeter). Since the temperature of Tm of PVdF is 165 ~ 172 ℃, it can be confirmed that all the HPC is removed from the porous membrane made in two ways.

11 is a photograph showing the electrolyte permeability of the porous film prepared according to an embodiment of the present invention.

As a result of impregnating the porous film prepared according to the embodiment of the present invention with an electrolyte for a lithium ion battery (electrolyte (EC / DEC (= 3/7) 1 M LiPF ₆ )), the electrolyte was clearly permeated by the micropores of the film. Can be.

12 is a graph showing the relationship between the ratio of HPC and the impregnation time of the porous film.

Referring to Figure 12 it can be seen that the impregnation time of the porous membrane made by the microwave irradiation method takes less than the porous membrane made by the vacuum drying method. Therefore, it can be seen that the porous membrane made by the microwave irradiation method can be applied as a separator for a secondary battery because it shows excellent impregnation rate and uniformity.

Hereinafter, the present invention is described in more detail in the following non-limiting examples.

20 parts by weight of polyvinylidene fluoride (PVDF) polymer resin was dissolved in 80 parts by weight of DMF solvent in a stirred reactor, and 15 parts by weight of HPC was dissolved in DMF solvent in a stirred reactor by calculating the mass ratio of PVdF and HPC by 1.0 / 0.4. Mixed. The prepared solution was then cast to a quartz plate using a bar coder. In order to remove the solvent, microwaves were irradiated at 700 W for 4 minutes, and the resulting film was peeled off. Then, distilled water and the peeled film were put into a vial, and ultrasonic waves were heated for 30 minutes. And a PVdF porous film was prepared by vacuum drying at 80 ° C. for 6 hours to remove the distilled water remaining in the film.

Porous film prepared in the embodiment of the present invention is composed of alpha-type PVdF, the pores were formed uniformly, the size was formed uniformly in the range of 600nm to 6㎛.

20 parts by weight of polyvinylidene fluoride (PVDF) polymer resin was dissolved in 80 parts by weight of DMF solvent in a stirred reactor, and 15 parts by weight of HPC was dissolved in 75 parts by weight of DMF solvent in a stirred reactor. Calculated as and mixed. Subsequently, the prepared solution was cast on a quartz plate using a bar coder and peeled off a film made by irradiating microwave at 700 W for 4 minutes to remove a solvent. It was. In order to remove the distilled water remaining in the film and vacuum dried at 80 ℃ for 6 hours to prepare a PVdF porous membrane.

In the porous film prepared in the embodiment of the present invention, the porous film is composed of alpha-type PVdF, the pores are uniformly formed, and the size is uniformly formed in the range of 600 nm to 6 μm, the number of pores and The size increased relatively.

20 parts by weight of polyvinylidene fluoride (PVDF) polymer resin was dissolved in 80 parts by weight of DMF solvent in a stirred reactor, and 15 parts by weight of HPC was dissolved in 75 parts by weight of DMF solvent in a stirred reactor, and the two solutions were mass ratio of actual 1.0 / 1.0 of PVdF and HPC. Calculated as and mixed. Subsequently, the prepared solution was cast on a quartz plate using a bar coder and peeled off a film made by irradiating microwave at 700 W for 4 minutes to remove the solvent, and then, distilled water and the peeled film were put into a vial, and ultrasonic waves were applied for 30 minutes. It was. In order to remove the remaining distilled water in the film was vacuum dried at 80 ℃ for 6 hours to prepare a PVdF porous membrane.

S10: First step S20: Second step
S30: third stage

Claims (15)

In a porous film containing a ferroelectric resin,
The ferroelectric resin may be fluorineate ethylene propylene copolymer (FEP), perfluoroalkoxy (FA), ethylenetetrafluoroethylene (ETFE), polyvinylidene fluoride (PVDF), polyethylenechlorotrifluoroethylene (ECTFE), At least one selected from the group consisting of polychlorotrifluoroethylene (PCTFE), and polyvinylidene fluoride-co-hexafluoropropylene (PVdF-co-HFP),
The ferroelectric resin is arranged in a non-polar alpha-type structure, the pore size is 600nm ~ 6㎛ porous film.
In the method of manufacturing a porous film according to claim 1,
Preparing a film by coating a solution containing a ferroelectric resin and a pore-forming resin on a substrate and irradiating microwaves; And
To form a fine pore by removing the pore-forming resin contained in the film; including,
The step of preparing the film is irradiated with microwaves so that the ferroelectric resin is arranged in a non-polar alpha-type structure,
The ferroelectric resin may be fluorineate ethylene propylene copolymer (FEP), perfluoroalkoxy (FA), ethylenetetrafluoroethylene (ETFE), polyvinylidene fluoride (PVDF), polyethylenechlorotrifluoroethylene (ECTFE), At least one selected from the group consisting of polychlorotrifluoroethylene (PCTFE), and polyvinylidene fluoride-co-hexafluoropropylene (PVdF-co-HFP),
The pore-forming resin is methyl cellulose (MC), ethyl cellulose (EC), hydroxyethyl cellulose (HEC), hydroxyethyl methyl cellulose (HEMC), hydroxypropyl methyl cellulose (HPMC), hydroxypropyl cellulose (HPC). ), Hydroxypropyl methyl cellulose (HPMC), micro-stalin cellulose (MCC), and carboxymethyl cellulose (CMC) any one or more selected from the group consisting of porous film production method.
The method of claim 2, wherein the mass ratio of the ferroelectric resin and the resin for pore forming is 1.0: 0.2 to 1.0.
The method of claim 2, wherein the microwave irradiation in the step of producing the film is a porous film manufacturing method for irradiating the film of 600 ~ 800W microwave for 1 to 4 minutes.
The method of claim 2, wherein the forming of the micropores comprises contacting the film with a solution capable of selectively dissolving only the pore-forming resin, thereby removing the pore-forming resin.
The method of claim 5, wherein the forming of the micropores comprises irradiating ultrasonic waves for 10-30 minutes when contacting the solution with the film.
The method of claim 2, further comprising vacuum drying the film for 3 to 6 hours at a temperature of 70 to 80 ° C. after forming the micropores. delete delete delete delete delete delete delete delete

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