KR101100299B1 - Hydrophilic non-woven fabric comprising homogeneous mixture of polypropylene and hydrophilic polymer and method for preparing same - Google Patents

Abstract

The present invention comprises the steps of (a) dissolving polypropylene in a mixed solvent and mixing with a hydrophilic polymer to form a mixed polymer solution; (b) electrospinning the mixed polymer solution to form a nonwoven fabric; And (c) provides a method for producing a hydrophilic nonwoven comprising stabilizing the formed nonwoven fabric.

The present invention also provides a hydrophilic nonwoven fabric comprising a homogeneous mixture of polypropylene and a hydrophilic polymer, and a separator for a secondary battery including the same.

The hydrophilic nonwoven fabric comprising a homogeneous mixture of the polypropylene and the hydrophilic polymer of the present invention can be used in applications such as separators for secondary batteries because of its simple manufacturing process and excellent wettability.

Nonwovens, Separators, Hydrophilic Polymers

Description

HYDROPHILIC NON-WOVEN FABRIC COMPRISING HOMOGENEOUS MIXTURE OF POLYPROPYLENE AND HYDROPHILIC POLYMER AND METHOD FOR PREPARING SAME}

The present invention relates to a hydrophilic nonwoven fabric comprising polypropylene and a process for producing the same. More specifically, the present invention relates to a hydrophilic nonwoven fabric in which polypropylene and a hydrophilic polymer are homogeneously mixed, a separator including the same, and a method of manufacturing the same.

Since the Galvanic cell was invented by Volta in 1800, about 200 years later, hybrid electric vehicles as well as small devices such as mobile phones, notebook PCs, PDAs, electric appliances, camcorders and digital cameras; HEV), Plug-in Hybrid Electric Vehicle (PHEV), Fuel Cell, Robot, etc. The importance of high performance secondary batteries is increasing and the demand is growing rapidly.

Nickel-metal hydride cells (Ni-MH cells), a variation of nickel-hydrogen batteries, are secondary batteries using nickel oxyhydroxide (NiOOH) for the positive electrode and hydrogen storage alloy for the negative electrode. The energy density per unit volume is 2-3 times higher than that of nickel-cadmium batteries, and is widely used in emergency power (UPS), solar street lights, and plug-in hybrid vehicles.

As a separator for Ni-MH secondary batteries, the use of polyolefin-based polymer membranes and nonwoven fabrics excellent in alkali resistance and oxidizing property without decomposing in the electrolyte alkali is increasing. The most widely used polymer separator is a single olefin or an olefin composite such as polyethylene, polypropylene, etc., which is manufactured as a nonwoven fabric or a polymer membrane. However, a separator made of only polyolefin has to have a hydrophilic treatment (surface treatment) by any method because the separator is not compatible with the electrolyte due to the water repellency of the material and thus cannot be used as a separator for batteries.

In general, as the hydrophilization treatment, sulfonation treatment, fluorination treatment using fluorine gas, graft polymerization treatment of vinyl monomer, surfactant treatment and the like are frequently used. Such a method has port hydrophilicity and is known to be good in battery characteristics. However, such a hydrophilization treatment process has a disadvantage that it is complicated, time-consuming and expensive.

For example, sulfonation treatment may be used with fuming sulfuric acid, sulfuric acid, sulfur trioxide, chlorosulfuric acid, or sulfyl chloride. Among these, sulfonation with fuming sulfuric acid is highly reactive and can be sulfonated relatively easily. It is used a lot. Representative sulfonation treatment process uses a fuming sulfuric acid, so it has to go through a multi-step process, such as unwoven fabric produced, generated gas sealing, acid neutralization, cleaning, drying, winding, and has a cumbersome disadvantage in that it requires attention to process management.

On the other hand, as another treatment method, there is a method of imparting hydrophilicity by corona discharge and an ion exchange resin binder, and a process of imparting functionality and hydrophilicity to a surface is also attempted. However, these methods have been difficult in actual battery applications due to the problem that the port hydrophilicity is not maintained continuously. In order to overcome this problem, studies through changes in the surface treatment process, the surface treatment material and the composition have been conducted.

1 is a schematic diagram of a sulfonation treatment apparatus and a process using fuming sulfuric acid which is a typical hydrophilization treatment process. Conventional techniques for hydrophilizing polyolefin membranes through sulfonation treatment devices are usually divided into five stages: 1) prepared membrane unwinding 2) gas sealing 3) acid neutralization 4) washing and drying 5) hydrophilized membrane winding It requires a sequential process. The sulfonated hydrophilization treatment is caused by the use of polyolefin-based polymers to produce a separation membrane by electrospinning or forming a polymer membrane, and then additionally undergoes hydrophilization treatment through sulfonation treatment. Different processes such as gas sealing, acid neutralization, washing, and drying are required, which makes the manufacturing process complicated. In addition, the nonwoven fabric manufacturing process and the hydrophilization treatment process cannot be a continuous manufacturing process, which requires a lot of time and manpower when manufacturing the finished product. As a result, the manufacturing cost of the nonwoven fabric separator also increases, and as the size of the electrode increases, the burden for this becomes more problematic.

Electrospinning is a method of spontaneously spinning in the form of fibers using a low viscosity polymer by electrostatic force to obtain the product. Electrospinning has the important feature of making nanometer fibers using materials with diameters in micrometers. Thus, from about ten years ago, this technique has been of interest and is used to make nanofibers with a diameter of 20 nm to 1 μm.

In electrospinning, high voltage is used to obtain a filled polymer jet solution or melt. This filled polymer jet solution or melt is dried or solidified to obtain polymer fibers. One electrode spin coats a solution or melt to adhere to the surface of another collector. The subject of the electrical domain is that the polymer solution adheres to the end of the capillary tube by its tension.

Spinning methods include melt spinning and solution spinning. In solution spinning, when the polymer solution is spun in filament form, wet spinning and solvent are not used, and the solvent is hot. Dry spinning, which is removed by air or inert gas, is generally commercialized.

The present invention is to provide a hydrophilic nonwoven fabric comprising polypropylene useful as a secondary battery separator such as a NiMH battery and a manufacturing method thereof.

As a result of improving the polyolefin-based nonwoven membrane production process, the present inventors have conducted research on a process capable of imparting hydrophilicity to a hydrophobic polyolefin. As a result, the substituted polypropylene is mixed with a hydrophilic polymer to be dissolved using a solvent. Solution electrospinning has completed the present invention by discovering that a nonwoven fabric having a property that can be used as a separator without a conventional hydrophilization treatment can be produced.

Accordingly, the present invention comprises the steps of (a) dissolving polypropylene in a mixed solvent and mixing with a hydrophilic polymer to form a mixed polymer solution; (b) electrospinning the mixed polymer solution to form a nonwoven fabric; And (c) provides a method for producing a hydrophilic nonwoven comprising stabilizing the formed nonwoven fabric.

The present invention also provides a hydrophilic nonwoven fabric comprising a homogeneous mixture of polypropylene and a hydrophilic polymer, and a separator for a secondary battery comprising the same.

Hereinafter, the present invention will be described in more detail with reference to embodiments and drawings.

In one embodiment of the invention (a) dissolving the polypropylene in a mixed solvent and mixed with a hydrophilic polymer to form a mixed polymer solution; (b) electrospinning the mixed polymer solution to form a nonwoven fabric; And (c) provides a method for producing a hydrophilic nonwoven comprising stabilizing the formed nonwoven fabric.

Polypropylene is a polyolefin-based synthetic polymer used in a variety of fields from general household goods to industrial parts because of its high crystallinity and excellent mechanical and thermal properties. In particular, since 1990, nonwoven fabrics made of polypropylene having excellent alkali resistance and chemical resistance have increased in usage as separators for nickel-hydrogen secondary batteries.

On the other hand, polypropylene is known to be difficult to manufacture nanofibers by electrospinning because it is excellent in chemical resistance and difficult to dissolve in a solvent. However, in the method of the present invention, in order to dissolve in a solvent in order to perform solution spinning of polypropylene, it can be used by dissolving in a solvent such as toluene, tetrahydrofuran (THF) using polypropylene partially substituted with Cl. . Dissolved polypropylene through this process can be mixed with the hydrophilic polymer to be capable of spinning and forming nanofibers, and the formed nanofibers have a large surface area per volume, which is good in hydrophilicity and wettability, so that non-woven fabrics that do not require hydrophilic treatment are required. It is possible.

The mixed solvent used for dissolving polypropylene is not limited. Any solvent capable of dissolving so as to be spinable at room temperature for the solution spinning of polypropylene can be used. Preferably the mixed solvent used in the process of the invention is a mixture of at least one good solvent and at least one poor solvent for polypropylene. Good solvents contribute to the solution of polypropylene and poor solvents improve spinning properties.

In one embodiment of the present invention, the good solvent may be selected from toluene, chloroform, tetrahydrofuran (THF) and benzene, and the poor solvent is N, N-dimethylformamide (DMF), alcohols such as ethanol, acetone, Methylcarbonate, water. Preferably, polypropylene is used by dissolving in a mixed solvent of toluene and N, N-dimethylformamide (DMF).

In one embodiment of the invention, polypropylene partially substituted with Cl is soluble in toluene but not in DMF. The polypropylene solution dissolved in toluene does not form a fibrous phase during electrospinning, but the nanofibers prepared by adding DMF to toluene increase in diameter as the amount of DMF increases as shown in FIG. 6. In addition, it can be seen that the distribution of the fiber diameter increases as the amount of DMF increases (data not shown). Table 1 below is a result of measuring the physical properties of the polypropylene electrospinning solution prepared while changing the toluene to DMF composition ratio on the solvent according to the above embodiment. DMF does not dissolve polypropylene but improves electrospinning characteristics such as increasing the viscosity, conductivity and surface tension of the solution as DMF is added.

The solvent for dissolving the polypropylene should include a poor solvent to improve the spinning properties, the content is preferably about 5% to 50% by volume in the solvent. If the poor solvent is more than 50% by volume in the solvent, polypropylene is not dissolved in the mixed solvent and precipitates, making it difficult to manufacture nonwoven fabrics by electrospinning. On the contrary, when the content of the poor solvent is too small, the spinning property is poor. The solution spinning of polypropylene itself is difficult.

The kind of hydrophilic polymer mixed in the polypropylene solution to form the mixed polymer solution of the present invention is not particularly limited. Any hydrophilic polymer of a similar class that can be mixed with a polypropylene solution to form a homogeneous mixed fiber through electrospinning can be used. Preferably, the hydrophilic polymer used in the nonwoven fabric manufacturing method of the present invention may be selected from the group consisting of polypropylene glycol, polyethylene glycol, poly (acrylic acid), poly (ethylene oxide), and poly (vinyl acetate). More preferably the hydrophilic polymer is polypropylene glycol.

The electrospinning step of the present invention is generally carried out using any method used to solution spinning meta to nanofiber nonwovens using synthetic polymers. When a polymer solution or polymer melt in a syringe is placed at the tip of the spinneret, a voltage of several tens of kV is applied to form droplets at the capillary tip by surface tension, and as the voltage increases, charges are induced on the fluid surface. Drops are disturbed. At this time, a single jet is injected above the threshold voltage beyond the surface tension of the liquid, and the instability of the fluid is increased in the electric field, and a series of fiber formation phenomena such as bending and cracking of the polymer occurs, which becomes nanoscale and forms a nonwoven fabric on the collecting plate. .

The main factors affecting the shape of the resulting electrospun nanofibers are the voltage during electrospinning, the tip to collector distance (TCD), the solution properties such as concentration or viscosity, surface tension, solution Variables such as feed rate (flow rate). On the other hand, it is also greatly affected by the working environment, such as external temperature or humidity.

The nonwoven fabric produced by electrospinning is subjected to post treatment for solvent removal and final product stabilization purposes. It is a general process to fix the prepared nonwoven fabric to a support and then vacuum dry it, and it may be preferably performed at a temperature of about 70 ℃.

In another embodiment of the present invention, the method of manufacturing a hydrophilic nonwoven fabric of the embodiment, the hydrophilic nonwoven fabric characterized in that the hydrophilic polymer is mixed by varying the content of the hydrophilic polymer mixed in the polypropylene solution between 0.5% to 20% by weight It provides a manufacturing method. Depending on the use and need, the hydrophilic polymer content in the mixed polymer solution may be increased to increase the hydrophilicity of the nonwoven fabric, and conversely, control may be made to reduce the hydrophilicity by decreasing the content. (See Figure 4)

In another embodiment of the present invention, in the method of manufacturing the hydrophilic nonwoven fabric of the above embodiment, the hydrophilic polymer content mixed in the polypropylene solution is changed between 0.5% by weight to 20% by weight, characterized in that to control the fiber thickness of the nonwoven fabric Provided is a method for producing a hydrophilic nonwoven fabric. Considering the materials used and the environment in which the final product is used, non-woven fabrics made of coarse fibers can be produced by increasing the hydrophilic polymer content in the mixed polymer solution according to the use and the need, and, on the contrary, reducing the content It is possible to control such as manufacturing a non-woven made of. (See Fig. 3)

In another embodiment of the present invention, a hydrophilic nonwoven fabric is provided that comprises a homogeneous mixture of polypropylene and a hydrophilic polymer. In the hydrophilic nonwoven fabric according to the present invention, the components of the fibers constituting the nonwoven fabric itself contain a hydrophilic polymer, so that the hydrophilic treatment is performed by a separate hydrophilic treatment, a fluorination treatment using fluorine gas, a graft polymerization treatment of a vinyl monomer, and an interface. It is structurally different from the nonwoven fabric at the time of performing an active agent treatment.

In this embodiment the hydrophilic polymer may be preferably selected from the group consisting of polypropylene glycol, poly (acrylic acid), poly (ethylene oxide), poly (vinyl acetate).

Another embodiment of the present invention provides a separator for a secondary battery comprising the hydrophilic nonwoven fabric of the present invention according to the above embodiment. The hydrophilic nonwoven fabric according to the present invention may be used as a separator for batteries without any separate treatment per se, and may be further subjected to further treatment depending on the use.

The type of secondary battery in which the separator including the nonwoven fabric of the present invention can be used is not particularly limited. Preferably the secondary battery is a nickel-metal hydride (Ni-MH) battery. The Ni-MH secondary battery prepared using the nonwoven fabric of the present invention as a separator exhibits excellent charge and discharge characteristics.

Unlike the hydrophilization process used in the conventional polyolefin-based nonwoven fabric manufacturing method, the present invention does not go through the process step of satisfying the cumbersome conditions by mixing and liquefying a polypropylene and a hydrophilic polymer as a support and electrospinning in one step 1) Hydrophilic nonwovens can be made through a simple process that is summarized as forming mixed polymer solutions, 2) electrospinning, and 3) stabilization (vacuum drying). As a result, the desired effect in the surface treatment performed in order to impart the most important characteristics in terms of battery performance in most battery separator manufacturing techniques can be realized by integrating the separator manufacturing step. As a result, in manufacturing the hydrophilic nonwoven fabric, there is a technical advantage in the process simplification by reducing the process step and the process equipment, thereby reducing the manufacturing cost.

In addition, in the conventional process, the post-treatment is frequently exposed to the opportunity of contamination during the process of neutralizing, cleaning, and drying the hydrophilic material, whereas the present invention uses the present invention to remove the solvent simply and effectively through vacuum drying. The material can be removed easily.

In addition, there is an additional advantage that can control the degree of hydrophilization and fiber diameter by adjusting the content of the hydrophilic polymer when forming a mixed polymer solution. According to the electrospinning conditions, the diameter of the fiber is freely controlled and the degree of hydrophilicity is controlled according to the content of the hydrophilic material, thereby simultaneously exhibiting the effect of increasing the performance of the separator.

The hydrophilic nonwoven fabric comprising a homogeneous mixture of the polypropylene and the hydrophilic polymer of the present invention can be used as a separator for secondary batteries due to its simple manufacturing process and excellent wettability.

Specific embodiments of the present invention will be described through the following examples.

The terminology used herein is not to be construed as being limited to a general and dictionary meaning, and the concept of a specific term may be defined within an appropriate range in order to explain the present invention in the best manner. Various equivalent or modified embodiments that are within the scope of the invention disclosed herein are also apparent to those skilled in the art in view of the present specification or the prior art in the art. The embodiments described below are only described for illustrative purposes, and the scope of the present invention is limited only by the claims.

<Examples>

Example 1 Preparation of Hydrophilic Nonwovens

(1) Preparation of polymer mixed solution

Molecular weight 150 kD polypropylene substituted with Cl group containing 32% by weight chlorine completely dissolved in a mixed solvent of toluene and N, N-dimethylformamide (DMF), and then 0% by weight of polypropylene glycol, respectively. , 7 wt%, 14 wt%, and 20 wt% were added to prepare a polymer solution containing polypropylene glycol of various compositions.

(2) electrospinning process

Insert the prepared electrospinning liquid into the syringe and use a high voltage generator (Model NT-PS-35K, NTSEE) to connect the positive electrode to the syringe needle and the negative electrode to the collector to apply high voltage. After the non-woven membrane was prepared by electrospinning. The nonwoven fabric produced by electrospinning is made by attaching aluminum foil to the current collector to facilitate the collection of the fibers after being spun. The applied voltage was 18 kV, the TCD (tip to collector distance) was 17 cm, the injection speed of the polymer solution and the rotation speed of the focusing body were set to 0.2 ml / min and 300 rpm, followed by electrospinning. The concentration of the polymer solution used was carried out at 12.5% by weight.

(3) post-treatment

Post-treatment was performed as a stabilization step of the prepared nonwoven fabric. The polypropylene / polypropylene glycol (PP / PPG) mixed nonwoven separator prepared by the above method was fixed to a support, followed by vacuum drying at 70 ° C. for 24 hours.

Figure 1 shows an overview of the process for producing a hydrophilic nonwoven separator comprising a homogeneous mixture of polypropylene and polypropylene glycol.

Example 2: Evaluation of Nonwoven Membrane

(1) Evaluation of physical properties of nonwovens

Experiments were conducted to evaluate the process conditions and characteristics of the nonwoven fabric membranes produced by the present invention. An SEM image of the fibers constituting the hydrophilic nonwoven fabric prepared according to the present invention is shown in FIG. 3. As the amount of polypropylene glycol increases, the average fiber diameter of the prepared nonwoven fabric also increases, and it can be seen that it is measured from 1.1 μm to 2.5 μm (see FIG. 3).

 The thickness of the hydrophilic nonwoven fabric prepared according to Example 1 was measured to be about 80 to 90 μm, and the tensile strength was found to be 7.7 to 12.0 MPa depending on the content of polyethyleneglycol, and thus the level of the nonwoven fabric commercially available for secondary battery separators. Tensile strength (9.8 MPa in the same experimental condition in the control group) was shown. Also, as the amount of polyethylene glycol added increased, the liquid retention (wetting) of 14 to 55% electrolyte was shown.

(2) Evaluation of Interface Characteristics of Membrane

In order to evaluate the interfacial properties of the prepared hydrophilic nonwoven fabric membrane, the prepared nonwoven fabric was embedded in a nickel plate electrode and immersed in 6M KOH electrolyte at 45 ° C. for 24 hours, and then impedance was measured using an electrochemical impedance analyzer. As can be seen from the results shown in FIG. 4, as the polyethylene glycol content was increased, the interface resistance decreased. This indicates that as the content of polyethylene glycol, a hydrophilic polymer, increases, the liquid-resistance (wetting) of the electrolyte increases, thereby reducing the interface resistance, and the performance of the nonwoven membrane is improved due to the decrease in the interface resistance. As a control separator, a nonwoven membrane WFS3885 manufactured by NKK Corporation was used.

Example 3: Evaluation of the electrochemical characteristics of the secondary battery using the prepared separator

Charge / discharge characteristics of the battery prepared were evaluated using the nonwoven fabric prepared according to Example 1 as a separator.

Ni-MH cell application experiment of the hydrophilic nonwoven fabric was conducted by configuring a half cell using an electrode having a capacity of 710.6 mAh / g. Electrochemical characterization was performed by charging and discharging at 0.1 C to activate and then evaluating the capacity of the battery by charging and discharging at 0.1 C and 0.2 C / 0.2D. The cut-off voltage at discharge was 1V.

  FIG. 5 shows a charge / discharge curve after assembling a Ni-MH secondary battery including a hydrophilic nonwoven fabric (polyethylene glycol content 7 wt%) prepared according to Example 1 at room temperature and 45 ° C. for 12 hours. . The battery prepared as shown in Figure 5 can be seen to exhibit excellent charge and discharge characteristics.

1 is a schematic diagram illustrating a manufacturing process of a commercialized polypropylene nonwoven separator product manufactured according to a technique using a sulfonated hydrophilization treatment step;

FIG. 2 is a schematic diagram illustrating a process of preparing a hydrophilic nonwoven separator comprising a polypropylene / polypropylene glycol homogeneous mixture prepared according to the present invention.

3 is a photograph showing an SEM image of the fibers constituting the hydrophilic nonwoven fabric prepared according to the present invention. The unit scale is 10 μm and the polypropylene glycol content is (a) 0% by weight (b) 7% by weight, (c) 14% by weight and (d) 20% by weight, respectively.

Figure 4 is a graph showing the impedance measurement results of the hydrophilic nonwoven membrane prepared by the present invention and the conventional commercially available nonwoven membrane (control).

Figure 5 shows the charge and discharge curve of the Ni-MH secondary battery prepared using the separator of the present invention.

6 is a photograph showing an SEM image of a nonwoven fabric prepared by dissolving polypropylene using solvents of various compositions. Magnification x 5000, toluene / DMF volume ratio are (A) 90/10 (B) 80/20 (C) 70/30 (D) 60/40 and (E) 50/50, respectively.

Claims (8)

(a) dissolving polypropylene in a mixed solvent to mix with a hydrophilic polymer to form a mixed polymer solution; (b) electrospinning the mixed polymer solution to form a nonwoven fabric; And (C) a method for producing a hydrophilic nonwoven fabric comprising the step of stabilizing the formed nonwoven fabric. The method of claim 1, wherein the hydrophilic polymer is selected from the group consisting of polypropylene glycol, polyethylene glycol, poly (acrylic acid), poly (ethylene oxide), and poly (vinyl acetate). The method for producing a hydrophilic nonwoven fabric according to claim 1 or 2, wherein the hydrophilic polymer is controlled to vary between 0.5 wt% and 20 wt%. The method for producing a hydrophilic nonwoven fabric according to claim 1 or 2, wherein the hydrophilic polymer is varied between 0.5 wt% and 20 wt% to control the fiber thickness of the nonwoven fabric. The method of claim 1 or 2, wherein the mixed solvent comprises at least one good solvent and at least one poor solvent for chlorinated polypropylene. 6. The method of claim 5 wherein the at least one good solvent is toluene and the at least one poor solvent is N, N-dimethylformamide (DMF). delete delete

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