A method for improving membrane coating properties in ion exchange membrane applications, and a woven mesh fabric with improved membrane coating properties in ion exchange membrane applications.

Abstract

To improve the membrane coating characteristics in ion exchange membrane applications using woven mesh fabric as a reinforcing material. [Solution] A woven mesh fabric containing monofilament fibers in the warp and weft of one of the polymers polyphenylene sulfide, polyether ether ketone, and liquid crystal polyester is subjected to at least one heat treatment to fix the mesh openings to a desired size, stabilize the monofilament fibers, and remove surface contaminants. One or more pretreatment steps are carried out, including a plasma pretreatment step and / or a plasma etching step. A plasma coating is deposited on the woven mesh fabric by plasma polymerization incorporating at least one functional group selected from the group consisting of hydroxyl groups, carboxyl groups, amino groups, and sulfonic acid groups. The woven mesh fabric has a filament diameter of 10 μm to 60 μm, a mesh opening of 20 μm or more, and a fabric thickness of 20 μm to 80 μm.

Description

[Technical Field]

[0001] The present invention relates to a method for improving the membrane coating properties in ion exchange membrane applications using a woven mesh fabric as a reinforcing fabric, wherein the woven mesh fabric includes monofilament fibers for the warp and weft. [Background technology]

[0002] Furthermore, the present invention also relates to a woven mesh fabric that improves the membrane coating properties in applications of ion exchange membranes as a reinforcing fabric, wherein the woven mesh fabric comprises monofilament fibers for the warp and weft.

[0003] Considering the hypothesis of anthropogenic climate change, we face significant challenges in the energy and environmental sectors, and exploring alternative energy strategies is crucial to securing future global energy needs.

[0004] Hydrogen serves as an inexpensive and abundant energy source, contributing to a sustainable energy future with zero carbon emissions. In terms of compatibility, it can be produced using renewable energy resources, making it a viable alternative to fossil fuels. Such energy sources are crucial in the transition to more environmentally friendly energy systems and in addressing climate change challenges. Hydrogen has significant application potential across various industrial sectors, contributing to enhanced energy security and reduced reliance on conventional fuels.

[0005] Hydrogen is gaining increasing recognition for its versatility and potential for decarbonization in various industrial and commercial applications. Its primary uses span multiple sectors, including energy, chemistry, and metallurgy, significantly contributing to the transition to a low-carbon economy. Among its many applications, hydrogen is being used in industrial sectors such as petroleum and ammonia production, driven by market demand. It also functions as an energy storage solution in transportation, construction, and heating, as well as in the power sector. While hydrogen offers numerous opportunities, its interactions with metals pose risks and require careful management.

[0006] Hydrogen production technologies for large-scale industrial applications continue to evolve, with several promising methods emerging. Notable technologies include steam reforming, electrochemical hydrogen production, biomass gasification, and marine renewable energy systems. Considering that the environmental impact of hydrogen technology depends on the production process and energy source, water electrolysis is a very promising and preferred approach due to its compatibility with various power generation methods.

[0007] Conventional alkaline electrolysis technology has low efficiency, and proton exchange membranes (PEMs) have been criticized for their cost. In contrast, anion exchange membrane (AEM) water electrolysis devices, using a stack structure with solid polymer membranes, are a promising technology that achieves high volumetric energy density. Compatibility with non-precious metal catalyst electrodes allows for cost reduction in hydrogen production. Cation exchange membranes (CEMs) are also known.

[0008] All of these PEM and AEM processes utilize ion exchange membranes (IEMs), and membrane performance is crucial for ensuring long-term operation in electrochemical separation applications. The main challenge with ion exchange membranes is their low chemical and thermal stability. Therefore, they are composited with polymer substrates, i.e., woven polymer fabrics, as the base or stabilizing layer. Degradation of the polymer substrate during use leads to chain severation, molecular weight reduction, and membrane embrittlement, especially under alkaline conditions. Membrane performance is greatly influenced by the interaction between the supporting structure, which functions as a composite, and the ion-mer polymer.

[0009] Industrial PEM coating processes employ a variety of methods for applying protective and functional coatings to materials, particularly for fuel cell applications. This process is crucial for improving the performance and durability of components used in various industrial applications. To achieve mass production while maintaining the coating's performance characteristics under industrial conditions, a transition from batch processes to continuous processes is essential. This process depends on multiple parameters, and precise control of key parameters such as current and time is necessary to obtain desired coating characteristics, including thickness and adhesion.

[0010] The manufacture of ion exchange membranes (PEM, CEM, or AEM) typically involves polymer synthesis, casting, and functionalization (often coating). Various coating techniques, such as spraying, rolling, and dipping (impregnation), are used to ensure a uniform coating. Typically, ionomer coatings include a combination of polymers and conductive materials such as graphite to enhance conductivity and corrosion resistance. In the impregnation process, the membrane passes through an impregnation chamber to enhance its chemical properties. In subsequent processes, the coated membrane is cured through a tunnel furnace to ensure proper coating adhesion and improved overall membrane properties.

[0011] The ionomer polymer substrate is dissolved or dissolved and directly coated onto a carrier material such as a porous or inert substrate. While the carrier provides mechanical support, the functionalized polymer itself forms an active ion-conducting layer. Ionic groups, such as sulfonic acid groups for PEMs and quaternary ammonium groups for AEMs, are introduced into the polymer to ensure conductivity. The resulting product is a support film, and the carrier is merely a support structure, not a functional component of the film itself.

[0012] Therefore, in this specification, the terms "ion exchange membrane," "membrane," "electrolyte membrane," and "ion exchange matrix" are used interchangeably. Similarly, the terms "membrane coating," "ionomer coating," and "ionomer material" are also used interchangeably.

[0013] Incorporating reinforcing fibers into ion-exchange membranes significantly improves mechanical stability and durability. Multiple studies have demonstrated that these reinforcements reduce mechanical stress and contribute to improved performance under operating conditions.

[0014] Regarding improvements in mechanical and dimensional stability, reinforced films with a woven web layer have been shown to have improved resistance to mechanical failure during operation, preventing failures under normal conditions. Furthermore, when porous polyethylene was used as a support layer in tandem sulfonated polyphenylene films, the tensile strength (up to 453%) and durability were significantly improved, withstanding more than 20,000 cycles in accelerated testing.

[0015] Sulfonated polyether ether ketone (sPEEK) reinforced films have been found to be particularly vulnerable to chemical degradation due to reactions with hydroxyl radicals during the electrolytic process. This interaction causes cationization of the polymer, followed by bond cleavage, which adversely affects the film structure. Mechanical properties are also affected by changes in the humid heat operating conditions of the film assembly. High temperatures exacerbate this problem, leading to microstructural damage and a decrease in mechanical properties. As a result, the lifespan of PEEK reinforced films is significantly shortened. If optimal processing conditions are not obtained during the manufacture of PEEK composites, high porosity and insufficient densification occur, leading to degradation and affecting the overall performance of the composite film.

[0016] Other recent innovations focus on non-fluorinated polymers, special structures, and methods for evaluating film integrity.

[0017] To ensure membrane integrity and overcome challenges, various ion exchange polymers and their backbones are being researched and developed. Examples include polystyrene (PS), polyphenylene oxide (PPO), polysulfone or fluorinated polymers, polyethylene copolymer tetrafluoroethylene (ETFE), polyetherimide (PEI), polyvinyl alcohol (PVA), polyether ether ketone (PEEK), poly(alylene ether ketone), and polycarbazole.

[0018] Meanwhile, researchers have also been studying the degradation mechanisms of reinforced films, particularly in fuel cell applications. This is crucial for improving the durability and performance of these films under harsh environments.

[0019] Monofilament fabrics made of polymers such as PEEK, polyphenylene sulfide (PPS), perfluoroalkoxy alkane (PFA), fluorinated ethylene propylene (FEP), and liquid crystal polyester (LCP) are excellent polymer options because they have distinct geometric properties such as mesh openings, porosity, and fiber diameter, as well as excellent properties such as chemical and temperature stability and high mechanical strength. This fabric can have regular openings that are square or rectangular. By appropriately embedding these fabric mesh cloths, a physically and ionically more stable composite membrane can be obtained.

Summary of the Invention

Problems to be Solved by the Invention

[0020] However, the literature data regarding the proper preparation of the supporting fabric polymer structure, which is a key element for the proper function of membrane reinforcement and optimal consolidation, is extremely sporadic. Conventional fabrics made from these polymers are often not suitable for these applications due to their incompatibility with integration into the ion exchange matrix.

[0021] The development of composite reinforced ion exchange membranes has several technical challenges despite their advantages. The difficulty of properly embedding the fabric into the ion exchange membrane remains a major problem, which reduces the ionic conductivity. Due to the hydrophobic and inert nature of the reinforcement, it acts as an incompatible barrier throughout the composite and becomes an obstacle when the ionomer fills the pores. As a result, various interfacial problems such as bubbles, coating defects, interfacial cracks and fractures occur.

[0022] Therefore, an object of the present invention is to provide a method for improving the membrane coating characteristics in the application of an ion exchange membrane using a fabric mesh cloth as a reinforcing cloth, and to provide a fabric mesh cloth with improved membrane coating characteristics in the application of an ion exchange membrane as a reinforcing cloth.

Means for Solving the Problems

[0023] According to the present invention, this object is achieved, on the one hand, by a method having the features of claim 1 and, on the other hand, by a fabric mesh cloth having the features of claim 17.

[0024] Preferred embodiments of the present invention are described in the respective dependent claims.

[0025] According to the method of the present invention, the fabric mesh cloth comprises monofilaments of warp and weft made of at least one polymer selected from polyphenylene sulfide (PPS), polyether ether ketone (PEEK), perfluoroalkoxy alkane (PFA), fluorinated ethylene propylene (FEP), and liquid crystal polyester (LCP), and one monofilament fiber consists of only one polymer. Other family members of the PPS polymer include polyether sulfone (PESU), polysulfone (PSU), and polyphenyl sulfone (PPSU). Polyaryl ether ketone (PAEK) is also a family member of PEEK.

[0026] According to the present invention, after the fabric mesh cloth is woven, a fixing process is carried out. In this fixing process, the fabric mesh cloth is subjected to at least one heat treatment in a temperature range of 240°C to 350°C to fix the mesh openings to the desired dimensions, stabilize the monofilaments of the fabric mesh cloth, and remove contaminants on the surface of the monofilaments.

[0027] Subsequently, one or more pretreatment steps are carried out. The one or more pretreatment steps include a plasma pretreatment step of further finely cleaning the surface of the fabric mesh cloth by removing, in particular, impurities, firmly adhering dust particles, and organic, inorganic, and microbial contaminants from the surface of the monofilament fibers, and / or a plasma etching step of exposing the fabric mesh cloth to plasma to etch the surface of the monofilament fibers of the fabric mesh cloth to an average roughness of 30 nm to 200 nm.

[0028] Following one or more pretreatment steps, a plasma coating is deposited onto the woven mesh fabric by plasma polymerization incorporating a functional group selected from the group consisting of hydroxyl groups, carboxyl groups, amino groups, and sulfonic acid groups, as a subsequent coating step. All of the one or more pretreatment steps and coating steps are carried out in a plasma chamber equipped with multiple rollers and having a first electrode set and a second electrode set within the plasma chamber, using a roll-to-roll system operating at a radio frequency of approximately 13.56 MHz. The woven mesh fabric is treated on both sides by passing through the plasma zone between the first and second electrode sets.

[0029] According to the present invention, the woven mesh fabric has a filament diameter of 10 μm to 60 μm, a mesh opening of 20 μm or more, and a fabric thickness of 20 μm to 80 μm.

[0030] One of the fundamental concepts of this invention is to provide a substrate structure that is robust against various applications and environmental conditions, and that can reliably fix a film, i.e., a film coating, without affecting the electrolysis process itself.

[0031] In this regard, textiles made of polyphenylene sulfide, polyetheretherketone, and liquid crystal polyester are recognized as particularly suitable as base materials or carrier materials because they can withstand harsh environmental conditions.

[0032] Preferably, only monofilament fibers are used. Not only fabrics having monofilament fibers of one of the above polymers, but also fabrics having monofilament fibers of different polymers, i.e., fabrics having PPS monofilament fibers in the warp direction and PEEK monofilament fibers in the weft direction, can be used. It is also possible to change the type of monofilament fiber in one direction.

[0033] However, in order to manufacture high-performance ion exchange membranes, the surface treatment of the fabric is specified in this invention to provide a good and durable bond between the fabric and the ion exchange membrane. Furthermore, it is recognized that providing the largest possible mesh size is advantageous for this application, but this reduces the stability of the fabric during the ion exchange coating process.

[0034] The inventors recognized that overcoming interfacial problems requires a good chemical bond and sufficient adhesion between the porous woven structure and the ionomer of the ion exchange membrane. Furthermore, the compatibility between the reinforcing material and the ionomer is often limited, which can affect the overall efficiency of the fuel cell and its resistance to harsh chemical environments. To solve this problem, many researchers have attempted to directly functionalize the fibers during the spinning process, but their success has been limited due to constraints on spinnability and the ability to impart functionality to the filament surface. Moreover, functional groups can be affected during the washing and fixing processes of the woven fabric. The inventors discovered that post-processing functionalization of pre-fixed and dimensionally stabilized woven mesh fabric with low-temperature plasma is a simple and scalable technique that solves these problems. Therefore, the idea of ​​the present invention is to design and prepare a precise woven mesh fabric structure that is compatible with post-process membrane coating.

[0035] The fundamental insight of this invention is to identify the influence of the geometric shape and surface properties of textiles on realizing the foundation for an ideal reinforcing material or film coating. The structure and composition of fibers or textiles depend on many factors, including the weave, the type of fiber composition, the fineness of the fibers, and the mesh size (i.e., the number of threads per centimeter). Compared to flat surfaces (films, polymer solids, etc.), textiles have a complex structure and are actually composed of two surfaces: one is the macroscopic surface visible to the naked eye, and the other is the actual internal surface consisting of interfiber spaces and pore size distribution. Ion exchange capacity closely related to fiber structure, such as mesh pore size, fiber diameter, and weave structure (plain weave, twill weave, etc.), has been identified. Plain weave structures with large mesh openings are more effective because they reduce the physical barrier to ion exchange. Furthermore, in addition to plasma treatment parameters and plasma coating properties, capillary action is strongly influenced by the mesh shape, especially the mesh openings (space between two adjacent fibers) and the thread (fiber) diameter.

[0036] In this specification, the term “textile” is used as a synonym for “mesh,” “fiber,” “reinforcing fiber,” “cloth,” or “woven structure” in the present invention, all of which describe inventive monofilament textiles as functional reinforcing materials for ion exchange membranes.

[0037] It has been found that plain weave fabrics with relatively large mesh openings are advantageous for improving the performance of ion exchange membranes. On the other hand, this combination reduces the dimensional stability of the fabric. Therefore, the objective is to fix and dimensionally stabilize the woven mesh fabric by heat treatment. For this purpose, the woven mesh fabric is subjected to at least one heat treatment in the range of 240°C to 350°C, which fixes the monofilament fibers of the woven mesh fabric together and stabilizes its dimensions. That is, individual monofilament fibers are fixed to each other at contact points by the heat treatment. These contact points are located particularly where the weft and warp threads overlap. The woven mesh fabric can be stretched or overfeed in the length direction (warp) and width direction (weft) under appropriate heat settings to adjust the mesh shape (i.e., mesh opening or hole diameter) to a predetermined size. This allows for the desired mesh hole diameter to be obtained and stabilized by optimizing process parameters such as temperature, contact time (material line speed), and stretching or tension adjustment.

[0038] Heat treatment further removes contaminants such as spinning finishes from the filament surface. Spinning finishes are applied during the spinning and weaving of monofilament fibers and monofilament fabrics.

[0039] Considering further pretreatment and coating processes, as well as the effectiveness of the manufactured ion exchange membrane, it is preferable that the woven mesh fabric has a filament diameter of 10 μm to 60 μm, preferably between 20 μm and 50 μm; the mesh opening is 20 μm or larger, preferably between 75 μm and 225 μm; and the fabric thickness is between 20 μm and 80 μm, preferably between 30 μm and 70 μm. The mesh opening shape of the fabric is arbitrary, but regular square or rectangular openings are preferred.

[0040] In principle, a conventional washing process can be optionally used before the heat treatment process. However, the washing process has the disadvantage of not being able to maintain the required mesh pore size because the monofilaments within the fibers are displaced. Therefore, by optimizing the heat treatment, it is possible to make it function as an alternative treatment to wet washing. In addition to saving energy, it is possible to avoid the use of chemicals used in the wet washing process (which are highly harmful to humans and aquatic life).

[0041] The present invention further proposes one or more pretreatment steps based on plasma pretreatment and / or plasma etching, followed by a plasma coating step onto a woven mesh fabric. These steps are techniques for improving surface properties without altering the volumetric properties of the fibers or fabric. These steps are used to enhance surface properties by improving adhesion and strengthening wettability. Wettability plays a crucial role in improving the adhesive strength in ion exchange films by improving the interaction between the fibers and the ion exchange matrix. This is achieved through various mechanisms such as surface modification, chemical interactions, and mechanical interlocking, which together contribute to stronger interfacial adhesion. However, in some ion exchange films, specific functional groups in the plasma coating play a more dominant role than wettability in achieving ultimate film performance.

[0042] Plasma pretreatment aims to further finely clean the surface of woven mesh fabric by removing impurities, firmly attached dust particles, and organic, inorganic, and microbial contaminants from the filament surface. It also activates the molecular groups on the surface of the monofilament fibers.

[0043] In plasma etching, a woven mesh fabric is exposed to plasma, etching its monofilament surface to an average roughness of 30 nm to 200 nm. This roughness provides a surface suitable for the chemical bonding of ion exchange films, creating a fixation effect for the film. Surfaces that have undergone etching and texturing can be characterized by measuring the average surface roughness using an atomic force microscope (AFM).

[0044] In the subsequent coating process, a plasma coating is applied to the woven mesh fabric by plasma polymerization, introducing a functional group selected from the group consisting of hydroxyl groups, carboxyl groups, amino groups, and sulfonic acid groups, at least one of which is selected. This improves the chemical bonding with the film chemistry and also improves wettability by increasing the surface energy. This process generates the functional group, which is then embedded within the coating. These ionic groups further improve the ion exchange capacity of the ion exchange membrane.

[0045] To mitigate adhesion problems in ion exchange or electrolyte membranes, several innovative strategies focused on improving performance and durability are offered. This invention provides a solution involving the modification of the properties of reinforcing / supporting fabric structures for membrane reinforcement. This solution is based on a plasma coating treatment capable of forming a functional surface that promotes stronger bonding and reduces the possibility of delamination. Deposition of an ultrathin layer of plasma polymer onto the surface of a supporting monofilament fabric solves challenges such as reduced contact angles. This hydrophilic property ultimately promotes ion selectivity, mass transport, and moisture management.

[0046] One or more pretreatment and coating steps can be carried out in a plasma chamber equipped with multiple rollers and / or expanders in a roll-to-roll system operating at a high frequency (preferably about 13.56 MHz). The chamber further comprises a first electrode set and a second electrode set positioned within the plasma chamber, and the woven mesh fabric is treated on both sides as it passes through the plasma zone between the first and second electrode sets. The chamber itself can serve as the ground electrode for these processes.

[0047] In a preferred embodiment, the coating process is a plasma chemical vapor deposition (PECVD) process. Specific functionalization of woven mesh fabrics can be achieved through different routes, including wet chemical processes, plasma treatment, PECVD, ion beam implantation, and combinations thereof. While conventional methods other than PECVD can impart permanent chemical functionality, micron-thick coatings negatively impact ion exchange performance within the composite. Conventional wet chemical processes have low functional density and uniformity issues, preventing reductions in coating thickness. Furthermore, conventional coatings lack the multifunctionality and adaptability offered by nanocoatings, potentially limiting their effectiveness in advanced application areas.

[0048] In the field of textile processing, PECVD technology offers significant advantages due to its drying process and environmental friendliness. Furthermore, because it can achieve a wide range of surface chemical reactions using diverse supply gases, it is possible to incorporate a wide variety of chemical functions into the fiber surface and impart various chemical and physical properties. Non-thermal plasma is being widely put into practical use to meet the industrial demand for high-quality, high-productivity, low-cost, and environmentally friendly surface treatment processes.

[0049] Plasma treatment significantly improves the degree of crosslinking in plasma polymerization compared to conventional polymerization. To further explain the plasma polymerization process, already vaporized monomer precursors are introduced into a vacuum plasma chamber. Energy input generates excited electrons during a glow discharge, decomposing molecules into free electrons, ions, radicals, and excited molecules. These free radicals and excited molecules then recombine, condense, and polymerize on the substrate, while the ions and electrons form crosslinks or chemical bonds with the already deposited polymer. Therefore, the properties of the plasma polymer depend not only on the precursor but also on the deposition parameters. This highly controlled polymerization process ensures pinhole-free, crosslinked, dry films in plasma polymerization, avoiding the problems of wet chemical polymerization, such as non-uniform coatings due to solvents and defective coatings in the presence of solvents.

[0050] Unlike conventional polymers, plasma polymer coatings such as the nanocoating of the present invention have the following characteristics: high density of functional groups per unit volume, a highly crosslinked and branched plasma polymer network, an ultrathin coating on the nanometer scale (<100 nm), high adhesion to the substrate, and no change in the bulk properties of the substrate. Retaining functional groups in the plasma polymer generated during plasma polymerization is one of the important challenges in obtaining advanced functionality. This allows for the imparting of new properties to polymer substrate materials, such as high-precision fabrics suitable for post-processing by ion-exchange film coating. Depending on the type and application of the film, different functional groups such as sulfonic acid (SO3), amine (NH2), carboxyl (COOH), and hydroxyl (OH) are embedded in the nanoscale plasma polymer coating. In addition to the strengthening effect, the modified filaments function as ion exchangers. The modified fabric mesh has reduced internal resistance, improved ion conductivity, and improved process efficiency. The proposed functional groups are suitable for long-term coating stability. Furthermore, another advantage is that the functional layer can be formed without requiring additional annealing or post-processing steps. According to the method of the present invention, a mixture of halogen-free precursor monomers and / or hydrocarbons and a reactive gas is plasma polymerized by PECVD to deposit a nanoscale plasma polymer coating on a fabric. Examples of halogen-free precursor monomers and gases include ammonia, acrylic acid, carbon dioxide, 3-allyloxy-1,2-propanediol and / or hydrocarbon precursors.

[0051] The present invention proposes a method for preparing a fabric that imparts reinforcing properties to an ion exchange membrane. These properties are observed in two ways: on the one hand, they improve ion exchange capacity functionally; on the other hand, they reinforce or strengthen the ion exchange membrane physically, improving its mechanical properties and preventing dimensional changes during application.

[0052] At least one functional group is preferably selected to match the ionic groups of the ion exchange membrane and / or to improve its wettability to the ion exchange membrane when the woven mesh fabric is coated. The selection of the ionomer material for the ion exchange membrane and the appropriate functionalization of the reinforcing woven mesh fabric or fibers are critical to the cell performance, and often this performance becomes the main bottleneck. The functionalization of the woven mesh fabric should be compatible with the ionic groups present in the membrane chemistry. Therefore, surface functionalization with specific functional groups should solve the compatibility problem and, as a result, achieve high ion exchange capacity. In fact, cation exchange membranes (CEMs) are—SO3 - ,—COO - It contains negatively charged functional groups such as , which allow cations to pass through while blocking anions. On the other hand, an anion exchange membrane (AEM) is -NR3 + ,―NR2H + These membranes contain positively charged functional groups, such as those that reject cations while allowing anions to pass through. Therefore, ion exchange membranes with reinforced fabrics should be designed to provide superior properties in both ion exchange performance and physical properties specific to each application.

[0053] Preferably, one or more pretreatment steps are carried out under low-pressure plasma conditions in a protective atmosphere, and / or the coating step is a low-pressure plasma polymerization process. These steps may also be low-temperature and low-pressure plasma processes. Low-temperature and / or low-pressure plasma processes are preferred because they place relatively little stress on the woven mesh fabric. In relation to the present invention, the low-pressure plasma is carried out in the range of 0.02 mbar to 0.5 mbar, and the low-temperature plasma is carried out in the range of 20°C to 50°C.

[0054] In preferred embodiments, the plasma pretreatment step is carried out using an inert gas, a reactive gas, or a mixture thereof, and / or the plasma etching step is carried out using an oxygen or fluorine-based etching gas, or a mixture thereof.

[0055] The cleanliness of the woven mesh fabric used as a reinforcing and supporting layer is a crucial factor in ensuring the successful and uniform deposition of ion-exchange polymers for ion-exchange membranes and the overall consistency of adhesion. Plasma pretreatment using inert gases such as argon and helium, reactive gases such as nitrogen, carbon dioxide, and oxygen, and / or mixtures thereof, removes contaminants and impurities from the polymer surface while simultaneously introducing oxygen-containing polar groups directly to the surface. This improves hydrophilicity and negative charge density, significantly enhancing adhesive performance. The combination of adhesion and internal bonding determines the overall integrity of the composite.

[0056] The improved surface roughness of the fiber through the plasma etching process increases the number of anchorable sites for the film coating, resulting in higher adhesion strength. Different plasma process gas mixtures can be used for etching fibrous polymers such as PEEK, PPS, LCP, PSU, PESU, PAEK, PFA, and FEP. When oxygen is mixed with a fluorinated gas such as tetrafluoromethane (CF4) and used in plasma etching, oxyfluoride ions (OF-) are generated. Oxyfluoride ions are powerful etchants for polymer materials. These ions are particularly effective at cleaving carbon-carbon molecular bonds in the polymer backbone and rapidly removing molecules.

[0057] Plasma etching processes require pattern formation in the nanometer to micrometer range with comparable efficiency. Extremely stringent requirements are placed on plasma etching processes regarding etching rate, selectivity, profile control, and surface damage. Key parameters in the plasma-surface interaction vary depending on the material, due to gas mixing ratio, bias voltage, and ion bombardment. The dominant parameter is primarily the ratio of neutral particle flux to ion energy flux.

[0058] One of the main problems with composite reinforced ion exchange membranes (also called ion exchange membranes) is the delamination of the fiber layer due to poor adhesion between the fiber layer and the ion exchange matrix, induced by mechanical stress and operating conditions. To improve adhesion, increasing surface roughness through plasma treatment such as O2 ablation / etching increases the contact area between the membrane coating and the reinforcing substrate. This contributes to improving the mechanical adhesion between the ion exchange polymer and the fabric of the ion exchange membrane. Furthermore, increasing the O2 content of the plasma-treated fabric surface can lead to improved surface polarity and wettability. This can contribute to improved penetration of the ion exchange matrix into the fabric, which acts as a reinforcing layer.

[0059] In the deposition process of plasma coatings by plasma polymerization incorporating functional groups, the use of a reactive gas mixture of nitrogen, carbon dioxide, and / or ammonia with hydrocarbons is preferred. Alternatively, monomer vapor consisting of monomers (e.g., acrylic acid, 3-allyloxy-1,2-propanediol, hydrocarbon precursors) or a mixture of monomers with helium or argon may be used.

[0060] One or more pretreatment steps and the subsequent coating steps may be performed in a single processing step or the two processing steps may be time-offset. A single processing step as defined in this disclosure means that different steps are performed directly and sequentially, preferably within the same reaction chamber. Two or more processing steps mean that there is a time offset between the different processing steps. For example, the fabric is transferred from one processing chamber to another.

[0061] Preferably, the plasma output in the plasma pretreatment step is 5 W / cm² per electrode surface area. 2 Less than, more preferably 3 W / cm² 2 Less than 2 W / cm², more preferably 2 W / cm² 2 It is less than.

[0062] In a preferred embodiment, the plasma output during the plasma etching process is 1 W / cm² per electrode surface area. 2Less than, preferably 1000 mW / cm 2 Less than, more preferably 500 mW / cm 2 Less than that.

[0063] The plasma power in the plasma coating process is 1 W / cm per electrode surface area 2 Less than, preferably 500 mW / cm 2 Less than, more preferably 200 mW / cm 2 It can be less than that.

[0064] The fabric mesh cloth can be singly or doubly calendered by a calendering process.

[0065] To calender the fabric mesh cloth before one or more pre-treatment steps, using a roll-to-roll calender, the fabric mesh cloth can be passed between two rollers at a temperature of 120°C to 200°C, a pressure of 200 N / mm 2 ~450 N / mm 2 and a material speed of 1 m / min to 4 m / min.

[0066] Calendering is a thermo-mechanical finishing process that compresses and smooths the fabric under controlled time, temperature, and pressure conditions. A calender basically consists of two or more rollers stacked vertically, and the fabric passes between these heated and pressurized rollers. Different calendering effects can be obtained on the fabric as follows. - Controlled fabric thickness - Single-sided calendering effect - Double-sided calendering effect - Smoothing / roughening

[0067] ' Depending on the application of the ion exchange membrane, the physical properties of the woven monofilament (thickness, density, pore size, shape, etc.) can be further adjusted by calendering. In this process, parameters such as roller temperature, nip pressure, and residence time (i.e., line speed) must be considered to obtain the desired properties with a predetermined stiffness. Furthermore, the properties of the woven fabric may be affected by the calendering conditions used. For example, air permeability may decrease and the filament shape may flatten.

[0068] In certain embodiments, the woven mesh fabric after the coating process has a water contact angle of 20° to 90°, preferably 40° to 80°, and more preferably 50° to 70°. Furthermore, when sulfonic acid groups and amino groups are incorporated, the water contact angle is preferably 80° to 145°. The water contact angle is measured according to DIN EN ISO 19403:2020-04 for woven fabric P (see Table 1 below) with a fiber diameter (warp or weft) of 38 μm, a mesh opening (warp or weft) of 195 μm, and a fabric thickness of 60 μm. As mentioned above, wettability is an important property of the base fabric in the deposition of ion exchange membranes. The above values ​​have been shown to improve fixation to the base material and consequently improve the efficiency of the ion exchange membrane produced.

[0069] The average roughness after the plasma etching process is preferably between 50 nm and 120 nm. This average roughness provided good properties in the subsequent coating process.

[0070] The thickness of the plasma coating is preferably 10 nm to 200 nm, more preferably 20 nm to 80 nm. In the final application of the electrolytic film, as already explained, it is preferable that the mesh openings of the fabric be as large as possible and the area (specific surface area) be as small as possible. The preferred coating thickness takes this into consideration, as it is sufficiently ultrathin, which increases the total surface area of ​​the film coating and, as a result, increases the ion exchange capacity. It is preferable that the average roughness is greater than the thickness of the plasma coating.

[0071] The processing times for the coating and pretreatment processes can be approximately 4 minutes or less each, and the plasma etching process can be approximately 8 minutes or less. These processing times are sufficient to achieve the desired results for each process, and have little to no effect on the bulk properties of the fabric.

[0072] It has been found beneficial to control the temperature of the electrodes in the electrode set and / or the chamber walls defining the plasma chamber to 30°C to 100°C, preferably 35°C to 80°C. Furthermore, these parameters are sufficient to achieve the desired results in each process without damaging the textile fibers, or causing only minimal damage.

[0073] Based on the method of the present invention, it is possible to manufacture a woven mesh fabric with improved membrane coating properties for use as a reinforcing fabric for ion exchange membrane applications. This woven mesh fabric contains warp and weft monofilaments made of at least one of the polymers polyphenylene sulfide, polyether ether ketone, perfluoroalkoxyalkane, fluorinated ethylene propylene, and liquid crystal polyester, and each monofilament fiber is made of only one of these polymers. This woven mesh fabric has a fiber diameter in the range of 10 μm to 60 μm, a mesh opening of 20 μm or more, and a fabric thickness in the range of 10 μm to 80 μm.

[0074] The monofilament fibers of the woven mesh fabric are heat-treated at 240°C to 350°C after weaving to remove surface contaminants, which fixes them together and stabilizes their dimensions.

[0075] The plasma pretreatment process for the woven mesh fabric includes a plasma pretreatment step that further cleans the surface of the woven mesh fabric by removing impurities, firmly attached dust particles, and organic, inorganic, and microbial contaminants from the surface of the monofilament fibers, and a plasma etching step that etches the surface of the monofilament fibers of the woven mesh fabric to an average roughness of 30 nm to 200 nm by exposing the woven mesh fabric to plasma.

[0076] According to the present invention, a plasma coating is then applied to the woven mesh fabric. Specifically, a plasma coating incorporating at least one functional group selected from the group consisting of hydroxyl groups, carboxyl groups, amino groups, and sulfonic acid groups is deposited on the woven mesh fabric by plasma polymerization. These groups function as ion exchangers, promoting the overall ion exchange efficiency.

[0077] In a preferred embodiment, the woven mesh fabric has a water contact angle of 20° to 90°, preferably 40° to 80°, more preferably 50° to 70°, with respect to incorporated hydroxyl or carboxyl groups, and a water contact angle of 80° to 145°, preferably 110° to 135°, with respect to sulfonic acid and amino groups. The water contact angle is measured according to DIN EN ISO 19403:2020-04.

[0078] The present invention will be further described below using preferred embodiments schematically shown in the attached drawings. [Brief explanation of the drawing]

[0079] [Figure 1] This figure shows an illustration of the fabric before the inventive treatment. [Figure 2] This figure shows a diagram of the fabric after plasma pretreatment. [Figure 3] This is an illustration of the fabric after subsequent plasma etching, and a magnified view thereof. [Figure 4] This is an illustration of the fabric after the subsequent plasma coating process, and a magnified view thereof. [Figure 5] This figure shows an SEM image of a woven mesh fabric. [Figure 6] This figure shows two AFM images of etched PEEK fabric. [Figure 7]This figure shows two SEM images: one of untreated fabric P followed by Nafion coating, and another of fabric P that has been SO3 plasma coated followed by Nafion coating. [Modes for carrying out the invention]

[0080] Figures 1 to 4 show only single monofilament fibers of the polymer material for clarity, but these represent the same fabric before, during, and after the method of the present invention.

[0081] Figure 1 shows the fabric before treatment by the method of the present invention. Undetermined particles are shown as impurities on the surface of monofilament fibers, firmly attached dust particles, and organic, inorganic, and microbial contaminants.

[0082] Figure 2 shows the fabric from Figure 1 after plasma pretreatment. Undetermined particles have been removed. The purpose of this treatment is to clean the fabric surface and facilitate subsequent polymer deposition.

[0083] Figure 3 shows the state of the fabric from Figure 2 after plasma etching. Plasma etching roughens the surface of the substrate or fibers, improving the adhesion of subsequent layers. This roughening can be observed as the formation of nano / micro grooves on the filament surface. The right side of Figure 3 shows a magnified view of the fiber surface, illustrating the non-uniformity and roughness.

[0084] Finally, Figure 4 shows the fabric from Figure 3 after subsequent PECVD treatment. Plasma polymerization formed an ultrathin coating containing at least one functional group selected from hydroxyl, carboxyl, amino, and sulfonic acid groups. Due to the dimensions and roughness of the surface and the ultrathinness of the coating, the fiber remains partially uncoated. This structure has advantages. When applying ion exchange membrane material to a fabric, it chemically bonds with the plasma coating of the fabric, and on the other hand, its relatively high roughness compared to a thin plasma coating allows for mechanical interlocking.

[0085] To further illustrate the present invention, we will now consider different fabrics. Table 1 summarizes the technical properties of plain weave fabrics. This information is interesting for understanding their behavior and the inventive reinforcing weave structure of the ion exchange membrane.

[0086] [Table 1]

[0087] To illustrate these dimensions, Figure 5 shows an SEM image of a woven mesh fabric. The mesh opening (3) (weft or warp) is 195 μm, the filament diameter (4) (weft or warp) is 38 μm, and the thickness is 60 μm, as can be seen in fabric P. The weft direction (1) and warp direction (2) are shown, but in this fabric, these may be reversed.

[0088] Calendaring process To obtain the appropriate thickness for the woven mesh fabric later used as a reinforcing and supporting layer for the ion exchange membrane, fabric P was subjected to calendering. In this process, the fabric is compressed by passing it between two rollers under controlled conditions of time, temperature, and pressure: 160°C, 300 N / mm². 2 Under a line speed of 2 m / min, the process was carried out sequentially in two stages, once on the front side and once on the back side of the fabric. As a result, a reduction in thickness was achieved while maintaining the opening area of ​​the fabric.

[0089] [Table 2]

[0090] Cleaning process Insufficient cleanliness of the fabric reinforcement layer in polymer ion exchange membrane applications can lead to a significant decrease in performance and a shortened service life. Contaminants, particularly cationic species, can displace protons within the membrane, negatively impacting ionic conductivity and overall cell efficiency. In fact, contaminants occupy the active sites of the catalyst layer, reducing the electrochemical surface area and inhibiting the reaction rate. Therefore, high cleanliness is required. As shown in Table 3, PEEK fabric P was subjected to different treatments: heat setting after washing, heat setting only, and low-pressure plasma washing after heat setting. Before treatment, the fabric possesses hydrophilic properties due to the spin finish applied during processing. The treated fabrics were investigated by extraction using 96% ethanol and petroleum ether according to standard DIN EN ISO 11354:2012-06.

[0091] Compared to a two-stage process of washing and heat setting, superior cleanliness was clearly achieved with heat setting alone. Further improvements in fabric cleanliness are possible with an appropriate combination of heat setting and plasma washing. In the plasma washing process, high-energy ions collide with the fiber surface, removing residual fine contaminants. In addition to the fine-cleaning effect, plasma washing promotes the formation of active polar groups on the fabric surface, which was confirmed by a reduction in the water contact angle (Table 3). The contact angle was measured according to DIN EN ISO 19403:2020-04.

[0092] [Table 3]

[0093] Plasma etching Plasma etching is performed using a suitable gas mixture. An example is oxygen and tetrafluoromethane (CF4). When these are mixed during plasma etching, the powerful etchant oxyfluoride ion (OF4) is produced. -) is generated. These ions chemically convert the solid material into volatile micromolecules, which are then removed from the polymer surface. The etched surface was characterized using an atomic force microscope (AFM). Two different power sources (direct bias and remote plasma) were used to increase the root mean square roughness Rq and mean roughness Ra. The direct bias plasma (plasma power 500V) showed the best results in fabric P, with Rq of 130nm and Ra of 105nm.

[0094] The topographic changes caused by the etching process were further investigated using AFM imaging. It was confirmed that the etching conditions resulted in uniform texturing and roughening of the PEEK surface compared to the untreated fabric.

[0095] Figure 6 shows two AFM images of PEEK fabric P, A) untreated and B) etched with a 1300W remote plasma.

[0096] The water contact angle was measured according to DIN EN ISO 19403:2020-04 for two different fabric types etched using direct bias and remote plasma, respectively. In addition to the etching effect, the remote plasma etching process, in particular, introduces chemical functional groups to the filament surface, altering the surface energy. Independent of the fabric type, the water contact angle was significantly reduced, indicating a tendency to achieve high wettability through film coating.

[0097] [Table 5]

[0098] Ion exchange membrane Non-charged, inert fabrics function as a physical barrier in ion-exchange membranes. This physical barrier is effective when the compatibility between the membrane coating and the fabric is good. Therefore, functionalizing the reinforcing material with appropriate ionic groups can significantly improve thermal stability and degradation resistance in the end application. This improvement is mainly due to improved interfacial interactions between the reinforcing material and the polymer matrix, which enhances the uniformity and integrity of the fabric coating within the ion-exchange matrix. As a result, the mechanical and thermal properties of the reinforced ion-exchange membrane are improved.

[0099] Fabric P was subjected to SO3-functionalization treatment and coated with a Nafion film, and its performance was compared with that of uncoated fabric P. Nafion-coated samples A and B were examined using a scanning electron microscope (SEM), as shown in Figure 7. As is clear from photograph A, film coating on the untreated fabric caused defects (holes, cracks) and the formation of bubbles. This is because the polymer had low affinity for the incompatible fabric, resulting in insufficient pore filling. On the other hand, photograph B shows uniform penetration and swelling of the coating material, indicating good adhesion between the functionalized fabric and the Nafion coating and uniform coating application.

[0100] It is clear that functionalizing the reinforcing layer of an ion exchange membrane dramatically improves the strengthening and performance of the composite material (Photo B). On the other hand, on the surface of an untreated woven mesh fabric, the adhesion of the coating is lost, resulting in coating defects and non-uniformity as seen in Photo A.

[0101] Plasma nanocoating offers significant advantages over conventional coatings in improving the interfacial properties of composite materials. These advanced coatings utilize nanoscale effects to enhance mechanical performance, durability, and functionality. From this perspective, three types of fabrics (P, Q, and T) were functionalized with hydroxyl groups and prepared for subsequent ionized coating. As shown in Table 6, the water contact angle decreases sharply after plasma nanocoating. This indicates an increase in the surface energy of the fabric surface, resulting in improved wettability, adhesion, and reactivity.

[0102] [Table 6]

[0103] The durability (self-life) of the coating was evaluated by real-time aging tests and accelerated aging tests (55°C / 20%RH, 10 days) based on the ASTM F1980-16 standard. As shown in Table 7, it was confirmed that the water contact angle remained almost unchanged under both aging conditions.

[0104] [Table 7]

[0105] Based on the present invention, it is possible to provide a method for manufacturing a woven mesh fabric with improved membrane coating properties for use as a reinforcing fabric for ion exchange membrane applications.

Claims

1. A method for improving the membrane coating properties in ion exchange membrane applications, using a woven mesh fabric as a reinforcing fabric, wherein the woven mesh fabric comprises warp and weft monofilament fibers made of at least one polymer from polyphenylene sulfide, polyether ether ketone, perfluoroalkoxyalkane, fluorinated ethylene propylene, and liquid crystal polyester, and each monofilament fiber is made of a single polymer from the above. The aforementioned method, A fixing step is performed after weaving the woven mesh fabric, in which the woven mesh fabric is subjected to at least one heat treatment in a temperature range of 240°C to 350°C to fix the mesh openings to a desired size, stabilize the monofilament fibers of the woven mesh fabric, and remove contaminants from the surface of the monofilament fibers. One or more pre-treatment steps, - A plasma pretreatment step that further cleans the surface of the woven mesh fabric by removing impurities, firmly attached dust particles, and organic, inorganic, and microbial contaminants from the surface of the monofilament fibers, and / or - A plasma etching step in which the woven mesh fabric is exposed to plasma and the surface of the monofilament fibers of the woven mesh fabric is etched to an average roughness of 30 nm to 200 nm, The one or more pretreatment steps including, A coating step in which a plasma coating incorporating at least one functional group selected from the group consisting of hydroxyl groups, carboxyl groups, amino groups, and sulfonic acid groups is deposited onto the woven mesh fabric by plasma polymerization, It has, The one or more pretreatment steps and the subsequent coating steps are carried out in a plasma chamber equipped with multiple rollers in a roll-to-roll system operating at a radio frequency of approximately 13.56 MHz, the plasma chamber having a first electrode set and a second electrode set, and the woven mesh fabric is treated on both sides by passing through the plasma zone between the first and second electrode sets. The woven mesh fabric has a filament diameter of 10 μm to 60 μm, a mesh opening of 20 μm or more, and a fabric thickness of 20 μm to 80 μm.

2. In the method according to claim 1, A method wherein the at least one functional group is selected to match the ionic groups of the ion exchange membrane and / or to improve the wettability of the woven mesh fabric to the ion exchange membrane when the woven mesh fabric is coated.

3. In the method according to claim 1, A method wherein one or more pretreatment steps are carried out under low-pressure plasma conditions in a protective atmosphere, and / or the coating step is a low-pressure plasma polymerization process.

4. In the method according to claim 1, A method wherein the plasma pretreatment step is carried out using an inert gas or a reactive gas or a mixture thereof, and / or the plasma etching step is carried out using an oxygen or fluorine-based etching gas or a mixture thereof.

5. In the method according to claim 1, The coating step of depositing the plasma coating incorporating the at least one functional group by plasma polymerization is as follows: • Reactive gas mixture, or • Monomer vapor consisting of a mixture of monomer and helium or argon How to use it.

6. In the method according to claim 1, A method wherein the one or more pretreatment steps and the subsequent coating steps are carried out in one processing stage or in two processing stages that are offset in time.

7. In the method according to claim 1, The plasma power in the aforementioned plasma pretreatment step is 5 W / cm² per electrode surface area. 2 Less than 3 W / cm² 2 Less than 2 W / Cm 2 A method that is less than.

8. In the method according to claim 1, The plasma output during the aforementioned plasma etching process is 1 W / cm² per electrode surface area. 2 Less than 1000 mW / cm² per electrode surface area 2 Less than, more preferably 500 mW / cm² per electrode surface area 2 A method that is less than.

9. In the method according to claim 1, The plasma output in the coating process is less than 1 W / cm per electrode surface area 2 , preferably less than 500 mW / cm 2 , more preferably less than 200 mW / cm 2 . A method

10. In the method according to claim 1, A method wherein the woven mesh fabric is a calendered mesh fabric.

11. In the method according to claim 1, Prior to the one or more pretreatment steps mentioned above, the woven mesh fabric is subjected to a temperature of 120°C to 200°C and a load of 200 N / mm using a roll-to-roll calendering machine. ２ ~450 N / mm ２ A method of passing the material between two rollers at a pressure and a material speed of 1 m / min to 4 m / min.

12. In the method according to claim 1, The woven mesh fabric after the coating process is - When a hydroxyl group or carboxyl group is incorporated, it has a water contact angle of 20° to 90°, preferably 40° to 80°, more preferably 50° to 70°. - When sulfonic acid groups and amino groups are incorporated, the temperature is 80° to 145°, preferably 110° to 135°. The water contact angle is measured according to DIN EN ISO 19403:2020-04, by method.

13. In the method according to claim 1, A method wherein the average roughness after the plasma etching process is between 50 nm and 120 nm.

14. In the method according to claim 1, A method wherein the thickness of the plasma coating is 10 nm to 200 nm, preferably 20 nm to 80 nm.

15. In the method according to claim 1, A method wherein the processing time for the coating step and the one or more pretreatment steps is approximately 4 minutes or less for each step, and the processing time for the plasma etching step is approximately 8 minutes or less.

16. In the method according to claim 1, A method for controlling the temperature of the electrodes of the first and second electrode sets and / or the chamber wall of the plasma chamber to 30°C to 100°C, preferably 35°C to 80°C.

17. A woven mesh fabric with improved membrane coating properties for use as a reinforced fabric in ion exchange membrane applications, The woven mesh fabric comprises monofilament fibers for the warp and weft, each monofilament fiber being made of at least one of the polymers: polyphenylene sulfide, polyether ether ketone, perfluoroalkoxyalkane, fluorinated ethylene propylene, and liquid crystal polyester, and each monofilament fiber is made of a single polymer from the above. The monofilament fibers of the woven mesh fabric are heat-treated at 240°C to 350°C after weaving to remove surface contaminants, thereby fixing them together and stabilizing their dimensions. - A plasma pretreatment step for the woven mesh fabric, which further cleans the surface of the woven mesh fabric by removing impurities, firmly attached dust particles, and organic, inorganic, and microbial contaminants from the surface of the monofilament fibers, and / or - A plasma etching step in which the surface of the monofilament fibers of the woven mesh fabric is etched to an average roughness of 30 nm to 200 nm by exposing the woven mesh fabric to plasma, At least one pretreatment step is performed, including Subsequently, a plasma coating incorporating at least one functional group selected from the group consisting of hydroxyl groups, carboxyl groups, amino groups, and sulfonic acid groups is deposited onto the woven mesh fabric by plasma polymerization, thereby adding at least one functional group selected from the group consisting of carboxyl groups, amino groups, and sulfonic acid groups. A woven mesh fabric having a filament diameter of 10 μm to 60 μm, a mesh opening of 20 μm or more, and a fabric thickness of 10 μm to 80 μm.

18. In the woven mesh fabric according to claim 17, The water contact angle, measured according to DIN EN ISO 19403:2020-04, - The angle relative to the introduced hydroxyl group or carboxyl group is in the range of 20° to 90°, preferably 40° to 80°, more preferably 50° to 70°. A woven mesh fabric having a temperature range of 80° to 145°, preferably 110° to 135°, with respect to sulfonic acid groups and amino groups.

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