KR20130106070A - Porous support and method for manufacturing same - Google Patents

Abstract

PURPOSE: A porous support is provided to have mechanical properties with directionality while including the assembly of randomly arranged nanofibers, thereby improving unidirectional dimensional stability of a reinforced composite film. CONSTITUTION: A porous support is manufactured by continuously hardening the nanofiber of a polymer precursor manufactured by electrospinning a precursor solution including a polymer precursor for forming a porous support; and a polymer nanofiber randomly aligned. The porous support has a tensile strength ratio of one direction to the vertical direction of 5 or less and an elongation ratio of one direction to the vertical direction of 0.2 or greater.

Description

Porous support and its manufacturing method {POROUS SUPPORT AND METHOD FOR MANUFACTURING SAME}

The present invention relates to a porous support and a method of manufacturing the same that can improve unidirectional dimensional stability when applied to a reinforced composite membrane for fuel cells.

Nanofiber has a wide surface area and excellent porosity, so it is used for various purposes such as water filter, air purification filter, composite material, battery separator, etc., and it can be particularly useful for reinforcement composite membranes used in fuel cells for automobiles. .

A fuel cell is a battery that directly converts chemical energy generated by oxidation of a fuel into electrical energy, and has been in the spotlight as a next-generation energy source due to its high energy efficiency and eco-friendly features with low emission of pollutants. Such a fuel cell generally has a structure in which an anode and a cathode are formed on both sides of an electrolyte membrane.

Representative examples of automotive fuel cells include a hydrogen ion exchange fuel cell using hydrogen gas as a fuel. Since the electrolyte membrane used in the hydrogen ion exchange fuel cell is a passage through which hydrogen ions generated from the anode are transferred to the cathode, it should basically have excellent hydrogen ion conductivity. In addition, the electrolyte membrane should have excellent separation ability to separate hydrogen gas supplied to the anode and oxygen supplied to the cathode, and also have excellent mechanical strength, shape stability, chemical resistance, and low resistance loss at high current density. And other characteristics are required. In particular, fuel cells for automobiles must have excellent heat resistance to prevent the electrolyte membrane from bursting when used at high temperatures for a long time.

Currently used electrolyte membranes for fuel cells include perfluorosulfonic acid resins (Nafion ™) (hereinafter referred to as "nafion resins") as fluorine resins. However, Nafion resins have a weak mechanical strength, so that pinholes are generated when they are used for a long time, thereby lowering energy conversion efficiency. Attempts have been made to increase the film thickness of Nafion resin in order to reinforce mechanical strength, but in this case, there is a problem in that the resistance loss is increased and the economical efficiency is inferior due to the use of expensive materials.

In order to solve this problem and to compensate for the disadvantages of the conventional electrolyte membrane, a reinforced composite membrane has been proposed. The reinforced composite membrane is composed of a porous support for improving dimensional stability, durability, mechanical strength, etc., which are disadvantages of the electrolyte single membrane, together with an ion conductor which is an electrolyte material. Representative products including reinforced composite membranes include PRIIMEA ™, manufactured by Gore. The reinforced composite membrane is characterized in that the mechanical strength is improved by complexing a fluorine-based ion conductor with a porous polytetrafluoroethylene resin. However, the use of a fluorine-based ion conductor and a fluorine-based porous support has a disadvantage in that a cost reduction is required for commercialization of a fuel cell.

Accordingly, inexpensive hydrocarbon-based ion conductors have been developed to replace expensive fluorine-based ion conductors, but hydrocarbon-based ion conductors have a problem in that they are difficult to apply to porous supports including fluorine-based ion conductors.

Accordingly, there is a need for a porous porous support suitable for a hydrocarbon-based ion conductor, and a porous support that can be complexed with not only a hydrocarbon-based ion conductor but also a fluorine-based ion conductor.

Korean Patent Publication Nos. 2011-0084849 and 2011-0120185 disclose reinforcing composite membranes in which a porous support composed of polyimide nanofibers is complexed with an ion conductor.

Korean Patent Publication No. 2011-0084849 (published Jul. 26, 2011) Korean Patent Laid-Open No. 2011-0120185 (published on November 3, 2011)

SUMMARY OF THE INVENTION An object of the present invention is to provide a porous support and a method of manufacturing the same that can improve unidirectional dimensional stability when applied to a reinforced composite membrane for fuel cells.

According to one embodiment of the present invention, the nanofibers of the polymer precursor prepared by electrospinning the precursor solution containing the precursor of the polymer for forming the porous support are zigzag alternately above and below a plurality of rollers under the application of a winding tension of 1 to 15N. It is prepared by continuous curing while transferring to provide a porous support comprising a randomly arranged polymer nanofibers, showing a directional mechanical properties.

The mechanical properties may be tensile strength, elongation or both.

The porous support may have a tensile strength ratio of 5 in one direction and a vertical direction with respect to the one direction.

The porous support may have an elongation ratio of 0.2 in one direction and a vertical direction with respect to the one direction.

The porous support may have 8% or less of dimensional stability in one direction when swelled in water after supporting the ion conductor, and preferably 1% or less.

The porous support may include a hydrocarbon-based polymer that is insoluble in an organic solvent, and may preferably include polyimide.

The porous support may have a porosity of 50 to 90%.

The porous support may have an average thickness of 5 to 50㎛.

According to another embodiment of the present invention, preparing a nanofiber of the polymer precursor by electrospinning the precursor solution containing the precursor of the polymer for forming a porous support; And it provides a method for producing a porous support comprising the step of continuously curing the nanofibers of the polymer precursor alternately zigzag up and down a plurality of rollers under the application of a winding tension of 1 to 15N.

The polymer for forming the porous support may be a hydrocarbon-based polymer that is insoluble in an organic solvent.

The precursor solution may include a precursor of a polymer for forming a porous support at a concentration of 5 to 20% by weight based on the total weight of the precursor solution.

The electrospinning process may be performed by applying an electric field of 850 to 3,500 V / cm.

The curing step may be carried out at 80 to 650 ℃.

Other details of the embodiments of the present invention are included in the following detailed description.

The present invention has the following effects.

First, the porous support according to the present invention includes an array of randomly arranged nanofibers, but exhibits directional mechanical properties, thereby improving unidirectional dimensional stability of the reinforced composite membrane when used as a porous support of the reinforced composite membrane for fuel cells.

Second, the porous support can be thinned to minimize the resistance loss of the reinforced composite membrane when used as a porous support of the reinforced composite membrane for fuel cells.

Third, the porous support is composed of a hydrocarbon-based polymer that is insoluble in organic solvents, so that it does not dissolve in a conventional organic solvent and has a high melting point, and thus has excellent chemical resistance and heat resistance. As a result, it has excellent durability when applied to a reinforced composite membrane for fuel cells. Can be represented.

1 is a schematic diagram schematically showing an apparatus for carrying out a continuous zigzag curing process in the manufacture of a porous support according to the present invention.
FIG. 2 is a scanning electron microscope (SEM) observation photograph of the porous support surface prepared in Example 1. FIG.
3 is a graph showing the results of observing the tensile strength and tensile strength ratio of the porous support prepared in Examples 1 to 3 and Comparative Example 1.
4 is a graph showing the results of observing the elongation and elongation ratio of the porous support prepared in Examples 1 to 3 and Comparative Example 1.

Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, by which the present invention is not limited and the present invention is defined only by the scope of the claims to be described later.

The term "nano," as used herein, refers to nanoscale and includes a size of 1 μm or less.

As used herein, the term "diameter" refers to the length of the short axis passing through the center of the fiber, and the "length" means the length of the long axis passing through the center of the fiber.

In general, since a stack in a fuel cell for a vehicle has a long rectangular shape in the longitudinal direction, when the same dimensional stability is applied to each direction of the reinforced composite membrane, the deformation in the longitudinal direction occurs more and more, depending on the deformation of the electrolyte membrane. There is a problem that the durability and performance of the fuel cell is poor. Therefore, there is a need for a reinforced composite film having better dimensional stability in the longitudinal direction.

On the other hand, in the present invention, a porous support imparting the mechanical property direction by continuously curing while transferring zigzag up and down alternately with a plurality of rollers in a controlled winding tension for random polyimide nanofibers, to prepare a porous support for the fuel cell reinforced composite membrane The present invention was found to be able to improve the unidirectional dimensional stability of the reinforced composite membrane when used as a porous support.

That is, the method of manufacturing a porous support according to an embodiment of the present invention comprises the steps of preparing a nanofiber of a polymer precursor by electrospinning a precursor solution containing a precursor of a polymer for forming a porous support, and the nanoparticles of the prepared polymer precursor Continuously hardening the fibers in alternating zigzag fashion above and below the plurality of rollers under the application of a winding tension of 1 to 15N.

Looking at each step below, step 1 is to electrospin the polymer precursor solution to produce nanofibers of the polymer precursor (hereinafter referred to as "nanofiber precursor").

As the polymer for forming the porous support according to the present invention, a hydrocarbon-based polymer which is insoluble in a conventional organic solvent, exhibits excellent chemical resistance, has hydrophobicity, and is free of morphological changes due to moisture in a high humidity environment. Here, "insoluble" with respect to the organic solvent means a property that does not melt at room temperature.

Specifically, the hydrocarbon-based polymer is nylon, polyimide (PI), polybenzoxazole (polybenzoxazole, PBO), polybenzimidazole (PBI), polyamideimide (PAI), polyethylene terephthalate (polyethyleneterephtalate), polyethylene (PE, PE), polypropylene (PP), copolymers thereof, and mixtures thereof can be used. Among them, heat resistance, chemical resistance, and shape stability can be used. It is preferable to use a better polyimide polymer.

However, since the hydrocarbon-based polymer is insoluble in organic solvents, the porous nanofibers cannot be directly produced through an electrospinning process. In other words, the hydrocarbon polymer which is insoluble in the organic solvent is difficult to prepare the spinning solution because it is insoluble in the organic solvent. Therefore, in the preparation of a porous support including a hydrocarbon-based polymer insoluble in an organic solvent, after forming without dissolving in an organic solvent or using a polymer precursor that is well soluble in an organic solvent, after forming nanofibers of the polymer precursor, It can be prepared through a predetermined reaction.

The polymer precursor may be used without particular limitation as long as it can form the hydrocarbon-based polymer. For example, the porous support including the polyimide is a polyimide precursor that is well soluble in an organic solvent, and then prepares a PAA nanofiber precursor using polyamic acid (PAA) and then performs imidization reaction in a subsequent curing process. It can be prepared through.

The polyamic acid may be prepared according to a conventional manufacturing method, and specifically, may be prepared by mixing diamine in a solvent, adding dianhydride thereto, and then polymerizing it.

Examples of the dianhydride include pyromellyrtic dianhydride (PMDA), 3,3 ', 4,4'-benzophenone tetracarboxylic dianhydride (3,3', 4,4'-benzophenonetetracarboxylic dianhydride, BTDA) ), 4,4'-oxydiphthalic anhydride (ODPA), 3,4,3 ', 4'-biphenyltetracarboxylic anhydride (3,4,3', 4 ') A compound selected from the group consisting of -biphenyltetracarboxylic dianhydride (BPDA), and bis (3,4-dicarboxyphenyl) dimethylsilane dianhydride (SiDA) and mixtures thereof can be used. In addition, the diamine is 4,4'-oxydianiline (4,4'-oxydianiline, ODA), p-phenylene diamine (p-phenylene diamine, p-PDA), o-phenylene diamine (o-phenylene diamine, o-PDA) and mixtures thereof, and may be selected from the group consisting of m-cresol, N-methyl-2-pyrrolidone (NMP) and dimethyl. Dimethylamide (DMF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), acetone, diethyl acetate, tetrahydrofuran (THF), chloroform, γ-butyrolactone and mixtures thereof Solvents may be used.

The precursor solution including the precursor of the porous support-forming polymer may be prepared by dissolving the precursor of the porous support-forming polymer in a conventional organic solvent such as NMP, DMF, DMAc, DMSO, and THF.

At this time, the precursor of the polymer for forming the porous support is preferably included in a concentration of 5 to 20% by weight based on the total weight of the polymer precursor solution. If the concentration of the polymer precursor solution is less than 5% by weight, since spinning does not proceed smoothly, the fiber may not be formed or a fiber having a uniform diameter may not be manufactured, whereas the concentration of the polymer precursor solution is 20 weight. If it exceeds%, as the discharge pressure increases rapidly, spinning may not be performed or processability may be reduced.

Subsequently, the prepared precursor solution is spun using a conventional electrospinning apparatus to prepare a nanofiber precursor.

Specifically, a predetermined amount of the precursor solution is supplied to the spinning unit by using a metering pump in a solution tank in which the spinning solution is stored, and after discharging the precursor solution through the nozzle of the spinning unit, the nanofiber precursor solidified simultaneously with scattering is discharged. Fiber aggregates can be prepared by further concentrating these solidified nanofiber precursors in a collector having a releasing film.

At this time, the intensity of the electric field between the radiator and the collector applied by the high voltage generator is preferably 850 to 3,500V / cm. If the strength of the electric field is less than 850 V / cm, it is difficult to manufacture nanofibers of uniform thickness because the precursor solution is not continuously discharged, and the nanofibers formed after being spun cannot be smoothly focused on the collector. Fabrication of fiber assemblies can be difficult. On the other hand, when the strength of the electric field exceeds 3,500 V / cm, the fiber aggregate having a normal shape cannot be obtained because the nanofibers are not accurately seated in the collector.

Through the spinning process, a nanofiber precursor having a uniform fiber diameter, preferably an average diameter of 0.01 to 5 μm is prepared, and the nanofiber precursors are randomly arranged to form a fiber aggregate, that is, a web.

In step 2, the nanofiber precursor is continuously cured while being alternately transferred zigzag up and down a plurality of rollers under the application of a winding tension of 1 to 15N.

In the production method of the present invention, since the precursor of the polymer is used to form the porous support through electrospinning, the curing process is performed as an additional step for the nanofiber precursor to convert the precursor into the polymer for forming the porous support. do. For example, when the nanofibers or fiber aggregates produced by electrospinning are made of polyimide precursors, they are converted into polyimides through imidization during the curing process.

Accordingly, the temperature during the curing process is preferably adjusted in consideration of the conversion rate of the polymer precursor into the polymer. Specifically, it is preferable that a curing process at 80 to 650 ° C is performed. When the curing temperature is less than 80 ℃, the polymer conversion rate is lowered, and as a result, the heat resistance and chemical resistance of the porous support may be lowered. If the curing temperature exceeds 650 ℃, the physical properties of the porous support due to the decomposition of the polymer There is a risk of deterioration.

1 is a schematic diagram schematically showing an apparatus for carrying out a continuous zigzag curing process in the manufacture of a porous support according to the present invention.

Referring to FIG. 1, a plurality of rolls 11 are placed in a curing apparatus 10 installed up and down to enable zigzag transfer of a nanofiber precursor prepared by electrospinning or a fiber assembly 12 thereof. After that, the rollers are zigzag alternately above and below the plurality of rollers with controlled winding tension.

At this time, the winding tension is preferably 1 to 15N. If the winding tension is less than 1N, the nanofiber precursor may not be transported from the inside of the curing furnace, which is not preferable. If the tension is more than 15N, the shape of the nanofiber precursor or the fiber aggregate thereof is deformed to obtain a uniform thickness and cohesion. As this decreases, the tensile strength may drop, which is not preferable.

In this way, the nanofiber precursor or the fiber aggregate is zigzag-transferred to an optimized winding tension, even though the nanofibers constituting the porous support are fibrous in a random arrangement, the porous support exhibits directional mechanical properties. As a result, the unidirectional dimensional stability of the reinforced composite membrane can be remarkably improved when used as a reinforced composite membrane for fuel cells in which an ion conductor is complexed with a porous support.

Accordingly, according to another embodiment of the present invention, a porous support prepared by the above method is provided.

That is, the porous support includes oriented randomly arranged nanofibers and exhibits directional mechanical properties. The directional mechanical properties mean that the tensile strength and elongation, which usually exhibit mechanical properties, vary depending on the direction.

In order to facilitate the manufacture and to prevent the durability and performance of the fuel cell due to deformation of the electrolyte membrane, it is preferable that the tensile strength and the elongation of the porous support applied to the reinforced composite membrane for the fuel cell have an optimum ratio in a predetermined direction. Specifically, the porous support has a tensile strength ratio of 5 in one direction and a vertical direction with respect to the one direction defined by Equation 1 below.

When the ratio of the tensile strength of the porous support exceeds 5, the variation of the tensile strength with respect to one direction and the vertical direction is large, so that the physical properties are biased in one direction and are easily cut. As a result, it is difficult to apply to the ion conductor supporting process in the preparation of the reinforced composite membrane using a porous support.

In addition, the porous support has an elongation ratio of 0.2 in one direction and a vertical direction with respect to the one direction defined by Equation 2 below.

If the elongation ratio of the porous support is less than 0.2, it is difficult to ensure the dimensional stability of the reinforced composite membrane using the porous support. In particular, large dimensional deformation occurs in one direction, thereby degrading the performance and durability of the fuel cell reinforced composite membrane.

In addition, since the porous support has mechanical properties, the porous support shows excellent dimensional stability when swelled under humidified conditions after supporting the ion conductor on the porous support. Dimensional stability is a physical property evaluated according to the following equation (3) from the change in the length of the humidifying condition after supporting the ion conductor on the porous support, specifically, before and after swelling when swollen in water, specifically, the dimensional stability of one direction is 8% It is below, Preferably it is 1% or less.

The porous support includes an aggregate of nanofibers, ie, webs of nanofibers, in which nanofibers prepared by electrospinning are randomly arranged. At this time, the nanofibers were calculated from the average of 50 fiber diameters by using an electron scanning microscope (Scanning Electron Microscope, JSM6700F, JEOL) in consideration of the porosity and thickness of the nanofiber web, of 40 to 5,000nm It is preferred to have an average diameter. If the average diameter of the nanofibers is less than 40nm, the mechanical strength of the porous support may be lowered. If the average diameter of the nanofibers exceeds 5,000nm, the porosity may be significantly reduced and the thickness may be thickened.

The porous support is made of the nanofibers as described above, may have a porosity of 50% or more. As described above, as having a porosity of 50% or more, the specific surface area of the porous support increases, so that the impregnation of the ion conductor is easy when applied as a reinforced composite membrane, and as a result, excellent ion conductivity can be exhibited. On the other hand, the porous support preferably has a porosity of 90% or less. If the porosity of the porous support exceeds 90% morphological stability is lowered may not proceed smoothly after the process. The porosity may be calculated by the ratio of the air volume to the total volume of the porous support according to Equation 4 below. In this case, the total volume is calculated by measuring the width, length, and thickness of the sample by preparing a rectangular shape, and the air volume can be obtained by subtracting the volume of the polymer inverted from the density after measuring the mass of the sample.

In addition, the porous support may have an average thickness of 5 to 50㎛. When the thickness of the porous support is less than 5 μm, the mechanical strength and dimensional stability may be significantly reduced when applied to the reinforced composite membrane. On the other hand, when the thickness exceeds 50 μm, the resistance loss increases when applied to the reinforced composite membrane, and the weight is reduced. And integration may be degraded. More preferred thickness of the porous support is in the range of 10 to 30 mu m.

The porous support as described above is insoluble in a conventional organic solvent and thus exhibits excellent chemical resistance, facilitates the ion conductor filling process in the pores of the porous support, and has hydrophobicity so that there is no fear of morphological deformation by moisture in a high humidity environment. It is preferable to include a hydrocarbon polymer. The hydrocarbon-based polymer may be nylon, polyimide (PI), polybenzoxazole (polybenzoxazole, PBO), polybenzimidazole (polybenzimidazole, PBI), polyamideimide (PAI), polyethylene terephthalate (polyethyleneterephtalate) ), Polyethylene (polyethylene, PE), polypropylene (polypropylene, PP), copolymers thereof, or mixtures thereof. Among them, polyimide polymers having better heat resistance, chemical resistance, and shape stability are preferable. .

When the porous support comprises polyimide, the porous support preferably has an imidation ratio of 90% or more. The imidation ratio is that the precursor of the polyimide is converted into an imide group by a cyclization reaction through an imidization process such as heat treatment, and can be calculated according to Equation 5 below.

However, the weight of the nanofibers before the solvent treatment is measured using nanofibers left at least 24 hours in a vacuum oven set at a temperature of 30 ℃, the weight of the nanofibers after the solvent treatment is dimethyl nanofibers before the solvent treatment After dipping in formamide organic solvent, stirring at room temperature for 24 hours, washing at least 5 times in distilled water, and then using a nanofiber web obtained after treating for 24 hours in a vacuum oven set at a temperature of 30 ° C. after solvent treatment.

If the imidation ratio is less than 90%, it is difficult to maintain the required physical properties for a long time because the nanofibers may be damaged by the organic solvent. Therefore, the polyimide porous support having an imidation ratio after 90% or more solvent treatment as described above can maintain excellent tensile strength even in a strongly acidic state, which is a driving environment of a fuel cell, and has excellent dissolution resistance to an electrolyte. Since the interface between the electrode and the electrode is not separated, excellent ionic conductivity can be maintained for a long time. In addition, the polyimide porous support having such excellent acid resistance can improve reliability because it can express excellent performance for a long time when used in the electrolyte membrane of a fuel cell driven in a strong acid environment.

The porous support has nanoporous thickness and thickness with excellent porosity and optimized diameter, and is easy to manufacture, and in order to exhibit excellent tensile strength after wet treatment, the polymer constituting the porous support has a weight of 30,000 to 500,000 g / mol. It is preferable to have an average molecular weight. If the weight average molecular weight of the polymer constituting the porous support is less than 30,000 g / mol, the porosity and thickness of the porous support can be easily controlled, but the tensile strength may be lowered after the porosity and the wet treatment. On the other hand, when the weight average molecular weight of the polymer constituting the porous support exceeds 500,000g / mol, heat resistance may be somewhat improved, but the manufacturing process may not proceed smoothly and the porosity may be reduced.

In addition, the porous support may have a weight average molecular weight in the range as described above, and as the polymer precursor is converted into a polymer under optimal curing conditions, it may have a melting point of 400 ℃ or more, preferably 400 to 800 ℃. If the melting point of the porous support is less than 400 ° C., the heat resistance may be easily deformed at high temperatures as the heat resistance thereof is lowered. Accordingly, the fuel cell manufactured using the porous support may degrade performance. In addition, when the heat resistance of the porous support is deteriorated, the shape is deformed by abnormal heat generation, thereby degrading the performance, and in severe cases, may burst and explode.

The porous support as described above is a collection of randomly arranged nanofibers, but by providing the orientation of the mechanical properties can be used to improve the unidirectional dimensional stability of the reinforced composite membrane when used as a porous support of the reinforced composite membrane.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Example  1. Preparation of Porous Support

Polyamic acid (polyamic acid) was dissolved in dimethylformamide solution to prepare 5L of 480 poise spinning solution at 13% by weight. After transferring the prepared spinning solution to the solution tank, it was supplied to the spinning chamber consisting of 20 nozzles and a high voltage of 46kV through a quantitative gear pump to produce a nanofiber precursor. The solution feed amount was 1.5 ml / min.

Subsequently, the nanofiber precursor was thermally cured while transferring the plurality of rollers up and down alternately for 6 minutes in a continuous curing furnace maintained at a temperature of 420 ° C using a curing apparatus as shown in FIG. A porous support composed of nanofibers was prepared. At this time, the winding tension was 10N.

Example  2. Preparation of Porous Support

A polyimide porous support was prepared in the same manner as in Example 1 except that the winding tension during curing for the nanofiber precursor was 1N.

Example  3. Preparation of Porous Support

A polyimide porous support was prepared in the same manner as in Example 1 except that the winding tension of the nanofiber precursor was 15N at the time of curing.

Comparative Example  1. Preparation of Porous Support

A polyimide porous support was prepared in the same manner as in Example 1 except that the winding tension during curing for the nanofiber precursor was 20N.

Comparative Example  2. Preparation of Porous Support

A polyimide porous support was prepared in the same manner as in Example 1 except that only a plurality of rollers were transferred upon curing for the nanofiber precursor.

Test Example   One

The surface of the porous support prepared in Example 1 was observed with a scanning electron microscope (SEM). The results are shown in Fig.

As shown in FIG. 2, it can be seen that nanofibers having a nano level diameter are randomly arranged in the porous support.

The average thickness, thickness variation and porosity of the porous supports prepared in Examples 1 to 3 and Comparative Examples 1 and 2 were measured, and the results are shown in Table 1 below.

The average thickness of the porous support was measured by measuring a sample of 30 × 50 cm ² at a thickness of 1 cm using a thickness gauge (digital indicator 547-401, MITUTOYO Co., Ltd.) and then calculated the average value.

Average thickness
(탆) Thickness deviation
(탆) Porosity
(%) Example 1 22 ± 1 78 Example 2 23 ± 1 80 Example 3 22 ± 1 75 Comparative Example 1 22 ± 1 70 Comparative Example 2 30 ± 7 ND

In Table 1, "ND" means that the porosity is poor due to the large volume change of the support itself, and thus the porosity was not measured.

As shown in Table 1, the porous supports of Examples 1 to 3 and Comparative Example 1 prepared by zigzag transfer of the nanofiber precursors alternately above and below the plurality of rollers showed almost uniform thickness with a thickness variation of ± 1. In the case of the porous support of Comparative Example 2 prepared by transferring the nanofiber precursor only onto a plurality of rollers, the thickness variation was large due to wrinkles caused by shrinkage of the nanofibers in the curing process, and the apparent average thickness also increased.

Test Example  2

Tensile strength (X direction / Y direction) and elongation (X direction) using a universal test machine (Instron 4303, Instron) according to ASTM 638 for the porous support prepared in Examples 1 to 3 and Comparative Example 1 / Y direction) was measured, and the measurement conditions are as follows.

Measuring Speed: 25cm / min

Grip Spacing: 6.35 cm

Temperature and Humidity: 25 ℃ × 50%

The measurement results are shown in Table 2 below, and FIGS. 3 and 4.

In addition, in order to evaluate the effect of improving the dimensional stability of the porous support according to the present invention, using the porous support prepared in Examples 1 to 3 to prepare a reinforced composite membrane, the prepared composite membrane in the following method Dimensional stability was evaluated. The results are shown in Table 2.

In detail, the porous supports prepared in Examples 1 to 3 were impregnated with an ion conductor solution (Nafion 5% by weight) twice for 30 minutes and then left under reduced pressure for 1 hour, and vacuum at 60 ° C. It was dried for 3 hours to prepare a reinforced composite film. The measured value was obtained by measuring the X and Y axis lengths of the changed membrane after putting the reinforced composite membrane cut at 30cm × 50cm into a constant temperature and humidity chamber maintained at a temperature of 80 ° C. and a relative humidity of 90%, which is a general operating environment of a fuel cell. And, the value measured before the humidification treatment was measured by applying the following equation (6).

In Equation 6, La is the length of the reinforced composite film after the humidification treatment, Lb means the length of the reinforced composite film before the humidification treatment.

Seal
Strength ratio The tensile strength
(MPa) Shindobi Elongation (%) Dimensional stability
(%) Swelling dimensions
(cm) X Y X Y X Y X Y Example 1 2.3 37 16 0.4 4.4 11.0 0.1 4.3 50.05 31.29 Example 2 1.6 23 14 0.4 6.1 13.9 0.2 5.1 50.1 31.53 Example 3 4.0 40 10 0.2 3.2 15.0 0.1 7.2 50.05 32.16 Comparative Example 1 6.8 54 8 0.1 2.0 16.2 ND ND ND ND

"ND" in Table 1 means that the physical properties were not measured because the composite film was not prepared.

As shown in Table 2 and Figures 2 and 3, Examples 1 to 3 of the porous support according to the present invention was confirmed that the tensile strength ratio is 5 or less, the elongation ratio is 0.2 or more excellent in the dimensional stability in the X direction. On the other hand, Comparative Example 1 has a tensile strength ratio of 6.8 and an elongation ratio of 0.1, which causes severe variations in mechanical properties in the X and Y directions, and mechanical properties in the vertical direction in one direction are reduced, thus making handling difficult during the ion conductor impregnation process. Membrane manufacturing was difficult.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of right.

10 Curing Equipment
11 rolls
12 Nanofibers of Polymeric Precursors

Claims (15)

The nanofibers of the polymer precursor prepared by electrospinning the precursor solution containing the precursor of the polymer for forming the porous support are continuously cured while being alternately transferred in zigzag up and down a plurality of rollers under the application of a winding tension of 1 to 15 N,
A porous support comprising randomly arranged polymeric nanofibers and exhibiting directional mechanical properties. The method of claim 1,
Porous support that the mechanical properties are tensile strength, elongation or both. The method of claim 1,
The porous support has a tensile strength ratio of 5 or less in one direction and a vertical direction with respect to the one direction. The method of claim 1,
The porous support has an elongation ratio of at least 0.2 in one direction and a vertical direction with respect to the one direction. The method of claim 1,
The porous support is a porous support having dimensional stability of 8% or less in one direction when swelled in water after supporting an ion conductor. The method of claim 1,
The porous support has a dimensional stability of 1% or less in one direction when swelled in water after supporting the ion conductor. The method of claim 1,
The porous support is a porous support comprising a hydrocarbon-based polymer insoluble in an organic solvent. The method of claim 1,
The porous support comprises a polyimide. The method of claim 1,
The porous support is a porous support having a porosity of 50% to 90%. The method of claim 1,
The porous support is one having an average thickness of 5 to 50㎛. Preparing nanofibers of the polymer precursor by electrospinning the precursor solution including the precursor of the polymer for forming the porous support; And
Continuous curing of the nanofibers of the polymer precursor while transferring zigzag up and down alternately a plurality of rollers under the application of a winding tension of 1 to 15N
Method for producing a porous support comprising a. 12. The method of claim 11,
The method for preparing a porous support is a polymer for forming a porous support is a hydrocarbon-based polymer insoluble in an organic solvent. 12. The method of claim 11,
The precursor solution is a method for producing a porous support comprising a precursor of a polymer for forming a porous support in an amount of 5 to 20% by weight based on the total weight of the precursor solution. 12. The method of claim 11,
The electrospinning process is a method of producing a porous support that is carried out by applying an electric field of 850 to 3,500V / cm. 12. The method of claim 11,
The curing process is a method of producing a porous support that is carried out at 80 to 650 ℃.

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