KR20080083805A - Method for preparing polymer film using electric field - Google Patents

Abstract

A method for preparing polymer films is provided to control characteristics of polymer according to the orientation of polymer chains by drying a polymer solution while an electric field is applied to the polymer solution. A method for preparing polymer films includes the steps of: applying a polymer solution(11) containing at least one ionic polymer and a solvent onto a substrate(12); and applying an electric field to a thickness direction of the substrate to evaporate the solvent and solidify the ionic polymer. The ionic polymer contains a sulfonic acid group. The substrate is an electroconductive substrate. The substrate is disposed on any one electrode of the first electrode(13) and the second electrode(14) separated from each other, or is the first electrode or the second electrode.

Description

Polymer film production method using electric field {METHOD FOR PREPARING POLYMER FILM USING ELECTRIC FIELD}

1 illustrates an electric field applying apparatus used in manufacturing a polymer film according to the present invention. (11: ionic polymer solution, 12: substrate, 13, 14: electrode, 15: power source)

2 is a graph showing the performance of a unit battery cell using the electrolyte membrane prepared in Example 1, Comparative Example 1.

3 is a graph showing the performance of a unit battery cell using the electrolyte membrane prepared in Example 3, Comparative Example 3.

The present invention comprises a first step of applying a polymer solution containing at least one ionic polymer and a solvent on a substrate; And a second step of solidifying the ionic polymer while applying an electric field in the thickness direction of the substrate to evaporate the solvent.

The polymer film may be used as an electrolyte membrane for a fuel cell.

A fuel cell is an energy conversion device that converts chemical energy of fuel directly into electrical energy. It has been researched and developed as a next-generation energy source with high energy efficiency and eco-friendly features with low pollutant emission. The polymer electrolyte membrane fuel cell (PEMFC) has been spotlighted as a portable, vehicle, and home power supply for its advantages of low operating temperature, elimination of leakage problems due to the use of solid electrolytes, and fast driving.

An ion exchange membrane (Ion Exchange Membrane), which is used as a solid electrolyte in a fuel cell, exists between two electrodes and transfers hydrogen ions generated from an anode to a cathode. In this case, a polymer membrane in which a sulfonic acid group (-SO ₃ H) is introduced is usually used as an electrolyte.

In general, an electrolyte membrane used in a polymer electrolyte fuel cell may be classified into a perfluorinated polymer electrolyte and a hydrocarbon polymer electrolyte.

The fluorinated polymer electrolyte is chemically stable due to its strong bonding force between carbon and fluorine (CF) and a shielding effect which is characteristic of fluorine atoms, and has excellent mechanical properties. In particular, the fluorinated polymer electrolyte has excellent conductivity as a hydrogen ion exchange membrane. It is commercialized as a polymer membrane of an electrolyte fuel cell. Nafion (perfluorinated sulfonic acid polymer), a product of Du Pont, USA, is based on polytetrafluoroethylene (PTFE) as a representative example of a commercially available hydrogen ion exchange membrane, and has ion conductivity, chemical stability, Due to its excellent ion selectivity, it is currently being most commercialized.

However, the fluorinated polymer electrolyte membrane has a low price due to its high performance, but has low industrial utility due to its high price, high methanol crossover through methanol, and reduced efficiency of the polymer membrane at 80 ° C. or higher. Therefore, research is being actively conducted on hydrocarbon-based polymer electrolyte membranes which can compete in terms of price. In particular, polyetherketone, polyethersulfone-based polyarylene ether polymers have been studied for their application to fuel cells due to their excellent chemical stability and mechanical properties.

On the other hand, US6692857 discloses a technique for preparing a membrane by applying an electric field in a state in which a porous polyethylene film (PE film) and an electrode in a 5% Nafion solution so that Nafion is well filled in the pore of the porous PE. The technique is such that the polymer electrolyte is well filled in the porous membrane by applying an electric field while the electrode plate and the porous membrane are placed in the solution. However, the solvent is electrolyzed by applying an electric field on the solution, and this technique is practically not applicable.

In addition, Korean Patent No. 10-2004-0092332 discloses a technique of improving hydrogen ion conductivity by forming a polymer electrolyte membrane and then applying an electric field to the prepared polymer electrolyte membrane to orient the membrane component. The above technique is a technique in which an ion conducting channel is straightened by orienting a polymer chain which is already solidified by applying a high pressure electric field to a polymer electrolyte membrane which has already been formed.

The present invention is better aligned and packed by an electric field by applying an electric field throughout the entire stage, from the solution state poured onto the substrate to the stage of complete drying, so that the polymer chain is naturally oriented by the electric field in the free state (solution state) and dried. It is intended to provide a packed polymer film.

The present invention comprises a first step of applying a polymer solution containing at least one ionic polymer and a solvent on a substrate; And a second step of solidifying the ionic polymer by applying an electric field in the thickness direction of the substrate to evaporate the solvent, and a polymer film prepared by the method.

Hereinafter, the present invention will be described in detail.

In the present invention, the ionic polymer includes all polymers capable of reacting to an electric field, including an ion conductive polymer, an electrically conductive polymer, and a bipolar polymer. For example, in the case of a fuel cell polymer electrolyte, polymers having a hydrophobic main chain group and a hydrophilic functional group as an ionic polymer include Nafion-based perfluorosulfonic acid (PFSA) or sulfonated hydrocarbon polymer.

Non-limiting examples of ionic polymers include sulfonated poly (arylene ether) s, sulfonated polyimides, and sulfonated polyamides. amide) s], sulfonated polyphosphazenes, sulfonated polystyrenes, sulfonated radiation-grafted FEP-g-polystyrene, sulfonated radiation-grafted ETFE-g-polystyrene, sulfonated radiation Homo copolymer, alternating copolymer, irregular copolymer containing at least one polymer selected from the group consisting of -grafted LDPE-g-polystyrene, sulfonated radiation-grafted PVDF-g-polystyrene, etc. (Random copolymer), Block copolymer (Block copolymer), Multiblock copolymer (Multiblock copolymer), Grafting copolymer (Grafting copolymer) and the like.

In the ionic polymer, ionic sites and nonionic sites are randomly or regularly present, or the ionic polymer may be a block copolymer including an ionic block and a nonionic block. Representative examples of such ionic moieties are sulfonic acid groups. In the polymer electrolyte membrane, sulfonic acid groups are introduced to impart proton (H ⁺ ) conductivity. However, since sulfonic acid groups are hydrophilic, when a large number of sulfonic acid groups are introduced, the water resistance of the polymer membrane is deteriorated, and the mechanical strength and the degree of integration of the polymer membrane are deteriorated due to swelling due to an increase in water content.

On the other hand, according to the existing polymer film manufacturing method, the polymer chains in the film are not oriented in a specific direction in most cases are irregularly arranged in different directions. For example, in the case of a polymer electrolyte membrane for a fuel cell manufactured by a conventional polymer film manufacturing method, the arrangement of functional groups in the membrane is irregular, so that a channel in which hydrogen ions move without forming an optimized structure especially when used as a fuel cell electrolyte membrane is formed. There are drawbacks to this, which takes a long time for initial aging and does not perform as expected.

Therefore, in the present invention, the polymer chain in the film is oriented irregularly so that the ionic sites such as sulfonic acid groups are irregularly arranged in the polymer chain so that the polymer film is dissolved in alcohol such as water or methanol. Ionic and nonionic sites are mixed in one molecule to suppress the inability to maintain the density and to orient the polymer chain in the desired direction to optimize the packing of the polymer chain in the film. The solvent drying step (film forming step) is performed in a state in which an electric field is applied from a state in which the solution of the ionic polymer is poured on the substrate.

When the solvent is removed while applying an electric field to a solution of an ionic polymer in which an ionic moiety and a nonionic moiety coexist by covalent bonds in a molecule, fine phase separation between ionic moieties and nonionic moieties in a molecule Is generated, the ion channel is formed by the group of ionic sites (parts that exhibit hydrogen ion conductivity) by the mutual attraction of the inner-molecules formed by the electric field, and by the group of nonionic sites. The film substrate can be formed to impart mechanical strength and degree of integration. At this time, the ionic end portion is deflected in the direction of movement of the hydrogen ions by the electric field to form a linear ion conduction channel, thereby obtaining a film having an efficient hydrogen migration channel.

In addition, due to the hydrophilicity of ionic moieties such as sulfonic acid groups in ion channels in which local ionic moieties are concentrated, dissociation of polymers under polar solvents such as water, methanol, and ethanol, resulting in lowered mechanical strength, is a group of non-ionic moieties. It can be suppressed by the mechanical strength and the degree of integration exerted by.

When a polymer film is formed while applying an electric field to a polymer solution in which an ionic polymer and a nonionic polymer are mixed, macro phase separation occurs between ionic polymers and nonionic polymers. Mechanical that can be exerted by microphase separation between ionic sites and nonionic sites covalently linked in one molecule, ie a group of nonionic sites can be provided to an ion channel bound within a molecule by covalent bonds. The strength cannot be provided by macro phase separation formed by the electric field when the ionic polymer and the nonionic polymer are mixed, and can be weakened by the interaction with the nonionic polymer that is separated from the macro phase. In addition, due to the presence of the large phase of the nonionic polymer, the ion channel area formed inside the ionic polymer is relatively small.

The minimum mechanical strength of the polymer electrolyte membrane required for driving the fuel cell is about 5% elongation and 10 MPa tensile strength.

The molecular weight of the ionic polymer of the present invention is preferably 4,000 (g / mol) to 400,000 (g / mol). When the molecular weight is less than 4,000 (g / mol), sufficient strength cannot be obtained as an electrolyte membrane, and when the molecular weight is more than 400,000 (g / mol), processing is difficult.

As the solvent in the ionic polymer solution, a common organic solvent, water, or a mixed solution with an organic solvent may be used. Non-limiting examples of organic solvents include dimethylacetamide, dimethylformamide, dimethylsulfoxide, N-methylpyrrolidone, alcohols and the like.

The concentration of the ionic polymer solution is preferably 1 to 40 wt%, preferably 2 to 15 wt%.

The electric field applying device used in manufacturing the polymer film according to the present invention is shown in FIG. 1.

Rather than applying the ionic polymer solution 11 to a non-conductive substrate 12, such as a glass substrate disposed on the voltage application electrode 13, the electrically conductive substrates 12, 13, for example, stainless steel (SUS) and It is preferable to cast the polymer solution directly on the same metal substrate and then apply a voltage to the electrically conductive substrate.

As a result of the experiment, casting the polymer solution on the iron plate was superior in performance than the casting the polymer solution on the glass substrate. It is inferred that the use of the iron plate results in better ion channel formation.

After applying the ionic polymer solution on the substrate it is preferable to perform the solution thickness to 50 ~ 1,000 ㎛ by adjusting the film applicator.

Moreover, the voltage applied to the ionic polymer solution applied on the board | substrate can be 1-200,000V, and it is preferable that it is 10-50,000V.

When the polymer solution is applied on the substrate, only the polymer solution may be applied onto the substrate, or the polymer solution and the porous polymer substrate may be performed.

When only the ionic polymer solution is used, the polymer solution is applied onto the substrate, and the drying process is performed while applying an electric field.

In the case of using a porous polymer substrate together with a polymer solution, (1) a method of first applying a polymer solution onto a substrate and drying, then raising the porous polymer substrate thereon, and again applying and drying the polymer solution thereon, and (2) a substrate It is possible to use a method of directly placing a porous polymer substrate and applying and drying the polymer solution thereon, and (3) applying the coating by dipping the porous polymer substrate into the polymer solution and drying it. At this time, an electric field may be applied at each step or optionally at each film forming step (drying), and each process may be performed repeatedly or in parallel. In this case, as the polymer chain is rearranged by the electric field, the effect of filling the pores of the porous polymer substrate can be expected to be better. In addition, the polymer chain filled as described above can be expected to effectively form a channel in which hydrogen ions are conducted as described above to improve the performance.

Non-limiting examples of porous polymeric substrate materials include polyethylene, polypropylene, polyvinyldifluoroethylene, polyethyleneterephthalate, polyimide, and polyamide. Or mixtures thereof.

The porous polymer substrate has a thickness of 3 µm or more and 1,000 µm or less, preferably 5 µm or more and 50 µm or less, and a porosity of 20% or more and 95% or less, preferably 60% or more and 95% or less. The size is 0.05 µm or more and 20 µm or less, preferably 0.1 µm or more and 2 µm or less.

The state of the polymer in the porous polymer substrate may be a fibrillated phase, a woven fabric, a nonwoven fabric, a sponge, or the like as a non-limiting example.

In addition, the ionic polymer solution of the present invention may further include various additives such as an antioxidant, a heat stabilizer, a lubricant, a tackifier, a plasticizer, a crosslinking agent, an antifoaming agent, a dispersing agent, and the like.

The distance between the first electrode and the second electrode applying the electric field is determined according to the voltage intensity within a range in which the vaporized solvent can be smoothly discharged without touching the polymer solution, and is adjusted in the range of 1 to 1000 mm. Can be.

Membrane film formation from the polymer solution can be carried out while drying under an electric field under drying conditions such as in an oven or on a heating plate. At this time, the drying temperature is from room temperature to 300 ℃, preferably 30 ℃ to 150 ℃.

When the polymer film prepared according to the present invention is used as an electrolyte membrane for a fuel cell, the thickness of the polymer film is preferably 1 μm to 50 μm. In the case of the polymer film with a porous substrate, the thickness is preferably 10 μm to 100 μm.

After the polymer film production step is completed, it is preferable to remove the substrate.

Hereinafter, preferred examples are provided to help understanding of the present invention, but the following examples are merely to illustrate the present invention, and the scope of the present invention is not limited to the following examples.

EXAMPLE

Example 1 Preparation of Nafion Electrolyte Membrane oriented by Electric Field

20% Nafion solution was cast on a 15 mm thick stainless plate. Another metal substrate was spaced apart on the cast stainless plate and an electric field was applied thereto. At this time, the substrate was separated by an insulating material so that an electric leakage phenomenon did not occur. The spacing between the substrates may vary slightly depending on the strength of the electric field, and separation of more than 10 mm is required to facilitate vaporization of the solvent. The solvent was removed while heating to 80 ℃ while applying a voltage of 1 kV. After the heat treatment, the electric field was cut off and the resulting film was separated from the stainless plate. After the acid treatment and washing, the final polymer film was obtained.

Example 2 Preparation of Hydrocarbon-Based Electrolyte Membrane oriented by Electric Field from Sulfonated Block Copolymers

After dissolving 10 g of sulfonated poly (ether ketons) block copolymer prepared by the example shown in Korean Patent Application No. 10-2004-0110487 in 90 g of dimethylacetamide (DMAc) The solution was filtered through a BORU glass filter (pore size 3) to remove dust and the like. The copolymer solution was poured onto a stainless plate, coated with a film applicator, and then coated with a copolymer solution. The stainless plate for the counter electrode was installed at appropriate intervals, and then heated at 50 ° C. under a voltage of 1 kV. Drying on a plate to prepare a reinforced electrolyte membrane of 50 ㎛ thickness. The electrolyte membrane prepared as described above was subjected to acid treatment and washing to obtain a final electrolyte membrane.

Example 3 Preparation of Hydrocarbon-Based Reinforced / Electrolyte Membranes Oriented by an Electric Field from Sulfonated Block Copolymers

Sulfonated Poly (ether ketons) copolymer solution used in Example 2 was poured onto the SUS substrate, and the copolymer solution poured on the substrate with a film applicator was applied. After the plate was installed, the copolymer solution was dried for at least 1 hour on a heating plate at 50 ° C. under a voltage of 1 kV, and the electric field was removed. Subsequently, the polyethylene microporous membrane is spread thereon and attached well thereon, and the copolymer solution is poured thereon again, and the copolymer solution poured on the microporous membrane with a film applicator is applied, and then the copolymer solution is dried under the same conditions as the first 50 μm. A thick reinforced electrolyte membrane was prepared. The electrolyte membrane prepared as described above was subjected to an acid treatment process and a washing process to obtain an electrolyte membrane for the final fuel cell.

Comparative Example 1 Preparation of Nafion Polyelectrolyte Membrane

20% Nafion solution was cast on a 15 mm thick stainless plate. The solvent was removed while heating to 80 ° C. After the heat treatment, the resulting film was separated from the stainless plate. After the acid treatment and washing, the final polymer film was obtained.

Comparative Example 2 Preparation of Electrolyte Membrane from Sulfonated Block Copolymer

The sulfonated poly (ether ketons) block copolymer solution used in Example 2 was poured onto a stainless plate and coated with a film applicator to apply the copolymer solution to the copolymer at 80 ° C. for at least 2 hours. The solution was dried to prepare an electrolyte membrane having a thickness of 50 μm. The electrolyte membrane for the final fuel cell was obtained through an acid treatment process and a washing process on the electrolyte membrane prepared as described above.

Comparative Example 3 Preparation of Reinforced-Electrolyte Membrane from Sulfonated Block Copolymer

Sulfonated Poly (ether ketons) copolymer solution used in Example 2 was poured onto a stainless plate, coated with a film applicator and poured onto the substrate, and then the copolymer solution was poured in an oven at 80 ° C. for at least 2 hours. Dry the copolymer solution, spread the polyethylene microporous membrane well on it, pour the copolymer solution on it again, apply the copolymer solution poured on the microporous membrane with a film applicator, and then apply the copolymer solution under the same conditions as the first time. Drying made a reinforced electrolyte membrane having a thickness of 50 μm. After performing an acid treatment process and a washing process on the electrolyte membrane prepared as described above, an electrolyte membrane for a fuel cell was obtained.

Experimental Example 1 Measurement of Hydrogen Ion Conductivity

The hydrogen ion conductivity of each of the electrolyte membranes prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was measured by the potentio-static two-probe method. First, 1 × 1 (cm2) and 1.5 × 1.5 (cm2) carbon paper electrodes were applied to both sides of the specimen having an area of 2 × 2 (㎠) at a constant pressure, and ultrapure water was flowed to the outside. An AC voltage of 1 MHz to 100 Hz was applied across the electrodes. At this time, the impedance was obtained through an alternating current across the electrode, and the hydrogen ion conductivity of each electrolyte membrane was measured using the impedance.

As shown in Table 1, the electrolyte membranes of Examples 1, 2, and 3 prepared by applying an electric field when the polymer film was formed, were Comparative Examples 1, 2, and 3, respectively, to which the electric field was not applied. The improved hydrogen ion conductivity was confirmed.

line 　 Nafion Hydrocarbon Hydrocarbon Reinforcement Electrolyte Membrane # Example 1 Comparative Example 1 Example 2 Comparative Example 2 Example 3 Comparative Example 3 Hydrogen ion conductivity (S / cm) 80 ℃, rh100% 0.18 0.12 0.20 0.13 0.17 0.11

Experimental Example 2 Cell Performance Analysis

The performance of the electrolyte membranes prepared in Examples 1 and 3 and Comparative Examples 1 and 3 constituted an electrode composite (MEA) unit battery cell was confirmed. The effective area of the electrode was 25 cm ² , the cell temperature was 70 ° C. and Pt / C catalyst of SGL 10BC GDL and DANAKA was used. The loading of platinum catalyst was 0.4mg / cm ² , the flow rate of hydrogen was 200cc / m, the flow rate of air was 1000cc / m, and the cell was operated at atmospheric pressure. The performance evaluation is shown in FIGS. 2 and 3. It was confirmed that the cell performance of Examples 1 and 3 produced by applying an electric field when forming the polymer film was improved compared to that of Comparative Examples 1 and 3.

The present invention, compared to the polymer film manufacturing method that has been prepared by the conventional method, by drying the polymer solution in a state in which the electric field is applied to easily adjust the orientation of the polymer chain to adjust the polymer properties according to the orientation as necessary to give Can be.

Although only described in detail with respect to the described embodiments of the present invention, it will be apparent to those skilled in the art that various modifications and variations are possible within the technical spirit of the present invention, it is natural that such variations and modifications belong to the appended claims. .

Claims (13)

A first step of applying a polymer solution containing at least one ionic polymer and a solvent onto a substrate; And a second step of solidifying the ionic polymer while applying an electric field in the thickness direction of the substrate to evaporate the solvent. The method of claim 1, wherein the ionic polymer contains a sulfonic acid group (-SO ₃ H). The method of claim 1, wherein the substrate is an electrically conductive substrate. The method of claim 1, wherein the substrate is disposed on any one of the first and second electrodes spaced apart from each other, or is a first electrode or a second electrode. The method of claim 1, wherein when the polymer solution is applied to the substrate in the first step, only the polymer solution is coated on the substrate, or the polymer solution and the porous polymer substrate are used. The method of claim 1, wherein the applied voltage ranges from 1 to 200,000 V in the second step. The method of claim 4, wherein a distance between the first electrode and the second electrode is 1 to 1000 mm. The method of claim 1, wherein the ionic polymer is an ion conductive polymer, an electrically conductive polymer, or a bipolar polymer. The method of claim 1, wherein the ionic polymer is a perfluorosulfonic acid (PFSA) polymer or a sulfonated hydrocarbon polymer. The sulfonated hydrocarbon polymer according to claim 9 is a sulfonated polyaryleneether (PAE), a sulfonated polyaryleneetheretherketone (PAEEK), a sulfonated polyaryleneetherethersulfone (PAEES) ), Sulfonated polyazole, sulfonated polyvinylalcohol (PVA), sulfonated poly (phenylene oxide), sulfonated poly (phenylene sulfide), sulfonated poly Sulfone, sulfonated polycarbonate, sulfonated polystyrene, sulfonated polyimide, sulfonated polyamide, sulfonated polyquinoxaline, sulfonated (phosphated) polyphosphazene and sulfonated polybenzimidazole Method for producing a polymer film, characterized in that. A polymer film produced by the method according to any one of claims 1 to 10, wherein the polymer film is characterized in that an ion channel is formed in a thickness direction. The polymer film according to claim 11, which is used as an electrolyte membrane. The polymer film according to claim 11, which is used as an electrolyte membrane of a fuel cell.

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