KR20240127718A - Manufacturing method of ion exchange membrane including non-conductive pattern and ion exchange membrane manufactured thereby - Google Patents

Abstract

The present invention relates to a method for manufacturing an ion exchange membrane including a non-conductive pattern, and to an ion exchange membrane manufactured thereby, the method comprising the steps of (a) irradiating a non-conductive film with laser light to form a plurality of aperture patterns at predetermined intervals, and (b) bonding the non-conductive film to one surface of an ion exchange membrane.

Description

MANUFACTURING METHOD OF ION EXCHANGE MEMBRANE INCLUDING NON-CONDUCTIVE PATTERN AND ION EXCHANGE MEMBRANE MANUFACTURED THEREOF

The present invention relates to a method for manufacturing an ion exchange membrane having a non-conductive pattern on its surface and to an ion exchange membrane manufactured thereby.

Ion exchange membranes are receiving much attention for their application in traditional separation processes such as dialysis and electrodialysis as well as in renewable energy fields such as fuel cells and flow batteries, due to their property of selectively allowing ions to pass through.

When the phenomenon of ion concentration polarization, which is a local imbalance in ion concentration due to diffusion limitation in the process of ion transfer through an ion exchange membrane in an electrolyte solution, becomes severe, bulk eddy flow due to electrostatic force is additionally generated. This phenomenon of electroconvective vortices is known to be the main cause of the second kind of electroosmotic flow occurring at high voltage to flow an overlimiting current exceeding the limiting current density.

Recently, with the expansion of research based on microfluidic systems, academic experimental results are being reported through monitoring of the electric eddy flow in internal channels. However, since the electric eddy is fundamentally an interfacial flow occurring on the surface of the ion exchange membrane, it is closely related to the electric/chemical properties and shape of the surface of the ion exchange membrane, more than other factors.

Research on the surface of ion exchange membranes can be broadly divided into surface hydrophobicity, geometric heterogeneity, and electrical heterogeneity. It can be divided into studies that changed the surface of the membrane. Such studies on the surface treatment of ion exchange membranes can be expected to be another application technology that utilizes electric eddies in ion exchange membrane systems, as they can be controlled by users, such as promoting the generation and growth of electric eddies, which are interfacial flows that occur in the high-voltage range, the limit current and the overcurrent section.

Recently, our research team attached a nonconductive masking film to the surface of an ion exchange membrane to repeatedly form conductive areas that allow ion transfer and nonconductive areas that do not, and visualized electric eddy currents at high voltage and analyzed their electrical characteristics. However, when producing regular nonconductive patterns, there was a limitation in producing more precise and dense patterns because the minimum width or gap of the pattern was large (~3.75 mm) due to the reliance on manual processing alone.

Korean Patent Publication No. 10-2016-0117449 (Publication Date: October 10, 2016)

H. Strathmann, Elsevier, (2004) J. G. Wijmans and R. W. Baker, J. Membr. Sci., 107, 1 (1995). S. Al-Amshawee, MYBM. Yunus, A.M. Azoddein, D.G. Hassell, I.H. Dakhil and H.A. Hasan, Chem. Eng. J., 380, 122231 (2020).

The technical problem to be solved by the present invention is to provide a method for manufacturing an ion exchange membrane having conductive regions and non-conductive regions alternately formed on the surface capable of ion transfer in order to visualize the electric eddy flow of the ion exchange membrane under high voltage and analyze the electrical characteristics.

To achieve the above technical task, the present invention proposes a method for manufacturing an ion exchange membrane including a non-conductive pattern, comprising the steps of (a) irradiating a non-conductive film with laser light to form a plurality of aperture patterns at predetermined intervals, and (b) bonding the non-conductive film to one surface of the ion exchange membrane.

At this time, in the step (a), the frequency, scan speed, and number of scans of laser light irradiated to an area of the non-conductive film where an aperture pattern is to be formed are adjusted to form an aperture pattern in the non-conductive film.

More specifically, the width of the heat affected zone can be precisely controlled by increasing the frequency and scan speed of the laser light, while the number of scans can be increased to obtain sufficient energy density for forming an aperture pattern.

Meanwhile, it is preferable that the laser light used to form the aperture pattern in the above step (a) is a pulsed wave having a wavelength band of ultraviolet (UV) and a pulse width of nanoseconds or femtoseconds.

As described above, a non-conductive film in which an aperture pattern is formed through laser processing can be configured to include a non-conductive substrate made of a non-conductive material such as an insulating polymer, and an adhesive layer formed on one surface of the substrate.

At this time, the material forming the non-conductive substrate is not particularly limited in type as long as it does not have ion conductivity, and may be, for example, a polyolefin resin (a resin formed of a homopolymer or copolymer of a monomer including an ethylenically unsaturated group, such as polyethylene, polypropylene, an ethylene-propylene copolymer, polybutene-1, poly-4-methylpentene-1, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-acrylic acid copolymer or ionomer), a polyester resin (a resin formed of polyethylene terephthalate or polyethylene naphthalate), a polycarbonate resin, a polyurethane resin, an engineering plastic (e.g., polymethyl methacrylate), a synthetic rubber (e.g., styrene-ethylene-butene or pentene copolymer), a thermoplastic elastomer (e.g., polyamide-polyol copolymer), etc.

In addition, the adhesive layer serves to bond a non-conductive film having an aperture pattern formed through laser processing in step (a) to one surface of the ion exchange membrane in step (b), and the adhesive constituting the adhesive layer is not particularly limited in type, but may be formed of a silicone-based adhesive, a rubber-based adhesive, an acrylic-based adhesive, a hot melt adhesive, or the like.

And, in another aspect of the present invention, an ion exchange membrane including a non-conductive pattern manufactured according to the above manufacturing method is provided.

The ion exchange membrane obtained through the above-described manufacturing method alternately has a non-conductive region formed by a non-conductive film and a conductive region formed by an ion exchange membrane surface exposed through an aperture pattern.

The ion exchange membrane according to the present invention can suppress the growth of electric eddies occurring on the surface of the ion exchange membrane or control the size thereof depending on the width, length, and spacing between the non-conductive and conductive regions of the surface, and thus can be usefully used for observation and analysis of various electric eddies occurring on the surface of the ion exchange membrane.

According to the present invention, by manufacturing an ion exchange membrane having a non-conductive region on the surface using a non-conductive film in which an aperture pattern is formed by laser processing, the width, length, and spacing between patterns can be precisely controlled as desired, and the growth of electric eddies occurring on the surface of the ion exchange membrane can be suppressed or the size can be controlled.

In addition, the characteristics of various electric eddies generated on the surface of an ion exchange membrane can be observed and analyzed using an ion exchange membrane in which conductive regions and non-conductive regions are formed alternately according to the present invention.

Figure 1(a) is a schematic diagram of an electrodialysis system, and Figure 1(b) is a schematic diagram showing the current lines (black) and electric eddies (blue), which are the direction of ion flow according to the physical screen of the ion exchange membrane surface (green arrows and red arrows represent the movement of cations (α ⁺ ) and anions (β ^- ), respectively, by the electric field).
Fig. 2(a) is a schematic diagram showing a process for manufacturing a non-conductive pattern ion exchange membrane, Fig. 2(b) is a schematic diagram showing a process for manufacturing non-conductive patterns at regular intervals using a UV laser, and Fig. 2(c) is a schematic diagram (plan view) of the manufactured non-conductive pattern ion exchange membrane.
Fig. 3(a) shows the results of measuring the laser cutting performance according to the laser frequency and scan speed (the UV laser mark formed on the worktable is classified into Typeⅰ,ⅱ,ⅲ according to each condition), and Fig. 3(b) shows the results of measuring the width of the heat affected zone (HAZ) according to the number of laser scans (b1, b2: 30 kHz, 40 mm/s; b3, b4: 30 kHz, 120 mm/s; b5, b6: 100 kHz, 40 mm/s; b7, b8: 100 kHz, 120 mm/s).
Figure 4 shows a photograph and an SEM image (left) of an ion exchange membrane having a pattern of L _P and L _S of 1500 μm and a photograph and an SEM image (right) of an ion exchange membrane having a pattern of L _P and L _S of 300 μm.
Figure 5 is a schematic diagram showing the experimental apparatus and method used to observe electric eddies.
Figure 6 Fluorescence images of electric vortices in the desalination channel when voltages of 6, 10, and 20 V are applied in the absence of shear flow (the dark region indicates the ion depletion region).
Figure 7 Fluorescence images of electric convection vortices propagating in the desalination channel (all images were captured 60 seconds after applying voltage (6, 10, 20 V).

In describing the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description will be omitted.

Since embodiments according to the concept of the present invention can have various changes and can take various forms, specific embodiments are illustrated in the drawings and described in detail in this specification or application. However, this is not intended to limit embodiments according to the concept of the present invention to specific disclosed forms, but should be understood to include all modifications, equivalents, or substitutes included in the spirit and technical scope of the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. It should be understood that, as used herein, the terms "comprises" or "has" and the like are intended to specify the presence of a described feature, number, step, operation, component, part, or combination thereof, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

Hereinafter, the present invention will be described in more detail by way of examples.

The embodiments according to this specification can be modified in many different forms, and the scope of this specification is not construed as being limited to the embodiments described below. The embodiments of this specification are provided to more completely explain this specification to a person having average knowledge in the art.

<Example>

The electrodialysis system is a structure in which cation exchange membranes (CEMs) and anion exchange membranes (AEMs) are alternately placed and an electrolyte solution is filled and flows between them. When an electric field is applied perpendicular to the direction of flow, selective permeation of ions occurs through the ion exchange membranes, and this is used to desalt or concentrate the electrolyte solution (Figure 1(a)). At this time, ion concentration polarization occurs due to the difference in the transfer rate of ions occurring in the electrolyte solution and the ion exchange membrane, which causes a problem of low energy efficiency, especially in the high current section. At high voltage, the concentration of counter-ions with the opposite polarity to the membrane is very low in the ion depletion zone that occurs on the ion-selective surface, and an extended space charge layer is formed. A horizontal electric field is applied to this space charge layer, causing ions to move. At this time, since the ions attract and move water molecules, a dynamically unstable eddy flow occurs at the ion exchange membrane interface. Such eddies are a mass transfer phenomenon that allows ions to be transported by convection from the bulk fluid to the membrane interface, thereby allowing a supercurrent to flow above the limiting current density.

Figure 1(b) shows the current line (black), which is the direction of ion flow, and the electric vortex (blue), which is a swirling flow, according to the physical screen on the surface of the ion exchange membrane. In the case of the Reference type without screen, the current lines are widely and evenly distributed because the membrane surface is fully exposed, whereas in the case of the Pattern type with screen, the funneling effect, which is a phenomenon in which the current lines are densely concentrated on the exposed ion exchange membrane surface, can be observed. On the other hand, the electric vortex, which is a swirling flow generated due to the non-uniform space charge layer on the membrane surface, undergoes an unstable growth process as it continuously merges with other nearby electric vortices as it grows. At this time, in the case of the Reference type without screen, the unstable growth and merge can be continuously repeated, but in the case of the Pattern type with regular screen, the width of the conductive region is fixed during this growth and merge process, so that the formation of different types of electric vortices can be expected.

In this embodiment, the process for fabricating a non-conductive patterned ion exchange membrane largely consists of four steps, as illustrated in Fig. 2(a). First, a thin non-conductive film (Scotch 810, 3M, USA) having a thickness of 50 ㎛ is attached to a working table. In the second step, a UV laser is used to fabricate non-conductive patterns at regular intervals (Fig. 2(b)). In the third step, a film with a micro-pattern applied is attached onto the ion exchange membrane, and unnecessary film portions are removed to fit the size of the ion exchange membrane. Finally, an optical microscope is used to confirm whether the micro-patterns are fabricated at regular intervals. The micro-patterns are fabricated at regular intervals by fixing the length ratio of the L _P (unit permeable length) that enables ion transport to the LS (unit impermeable length) that does not allow ion transport to 1:1 (Fig _. 2(c)).

The laser equipment used for film cutting is a UV nanosecond laser (INNGU LASER, Pulse 3553A) that uses a Nd:YVO ₄ laser source, operates at a pulse frequency of 30 to 100 kHz, and has a maximum output of less than 5 W. The laser process has various process variables that affect the cutting aspect of the sample, such as laser output, scan speed, scan number, and focus position. According to these various process variables, the width of the heat affected zone (HAZ) is determined, which is a very important factor that affects the quality of the fine pattern. If a non-conductive pattern is produced due to incorrect process variables, the heat affected zone is large and not uniform, so the ratio of the ion exchange area cannot be controlled, and accurate experimental results cannot be obtained. Therefore, in order to find the process variables for precise film cutting, the effects of the process variables were analyzed for the frequency of 30 to 100 kHz and the scan speed of 20 to 140 mm/s at the maximum output of the laser (Fig. 3(a)). The experimental results confirmed that the higher the frequency or the faster the scan speed, the narrower the heat-affected zone (b1, b3, b5, b7). On the other hand, when producing with a frequency of 100 kHz and a scan speed of 120 mm/s, the laser energy density used for film cutting was insufficient, which made it unsuitable for the cutting process (b7). Therefore, in order to secure laser energy conditions suitable for film cutting, the number of scans was increased and whether or not a fine pattern was cut was confirmed (Fig. 3(b)). Based on this, in this example, a non-conductive patterned ion exchange membrane was manufactured by controlling the number of scans at the maximum frequency (100 kHz) and high scan speed (140 mm/s) to minimize the heat-affected zone and cut the film.

To confirm the change in the generation and growth process of electric eddies according to the length of the micropattern, three types of ion exchange membranes (Reference, L _P , L _S = 1500 ㎛, L _P , L _S = 300 ㎛) were fabricated. Each type was observed by optical and SEM photographs (Fig. 4). Looking at the SEM photographs, a slight undulation (line undulation) due to thermal deformation of the material is observed at the edge of the film, but overall, it can be confirmed that the nonconductive micropattern film is neatly adhered to the surface of the ion exchange membrane.

<Experimental example>

In this experimental example, a microfluidic device was fabricated to visualize the flow of electric eddies generated on the surface of an ion exchange membrane. For the visualization experiment, a polydimethylsiloxane (PDMS)-based microscale electrodialysis device was fabricated by inserting a cation exchange membrane and an anion exchange membrane with nonconductive pattern films and two electrodes into PDMS slots. At this time, one main channel (the channel between the cation exchange membrane and the anion exchange membrane) and two rinsing channels (the channels between the electrodes and the ion exchange membrane) were formed, and the channel height was fixed to 0.2 mm and the width was fixed to 1.5 mm. The effective ion exchange length, where the electrolyte solution and the ion exchange membrane actually come into contact, was fixed to 12 mm for the three types. The ion exchange membrane used in the experiment was Ralex AMHPP/CMHPP from MEGA. Figure 5 shows the experimental apparatus and method used to observe the electric eddies. An electrolyte solution was injected into the main channel at a constant flow rate (0/0.5 mm/s) using a syringe pump (Fusion 200-X, Chemyx, Inc.). To visualize the internal flow, 19.1 μM fluorescent dye (Alexa 488 Triethylammonium, Thermo Fisher Scientific) was added to a 10 mM sodium chloride (NaCl) solution in the main channel, and a 5 mM sodium sulfate (Na ₂ SO ₄ ) solution was injected into the rinsing channels, respectively. A Source Measurement Unit (Keithley 2460, Keithley Instruments, Inc.) was used to apply voltage.

To observe the presence or absence of nonconductive patterns on the surface of ion exchange membranes and the generation and growth process of electric vortices, flow visualization (without shear flow) experiments were performed on three types of devices (Reference, L _P , L _S = 1500 μm, L _P , L _S = 300 μm). After applying three voltages of 6, 10, and 20 V without applying shear flux, the change in the shape of the electric vortices over time (t = 20 s, 30 s) was observed (Fig. 6). The green and orange regions represent the anion exchange membrane and cation exchange membrane, respectively, and the black hatched region represents the nonconductive region where ions cannot permeate. As the voltage is applied, the ion depletion region where ions are removed at the ion exchange membrane interface is observed as dark, and the region where ions are not removed is observed as bright. Since the Reference type has no non-conductive region where ion transfer is impossible, electric vortices are observed on all surfaces. On the other hand, in the L _P , L _S = 1500, 300 ㎛ types that have parts covered by non-conductive films, electric vortices occur only in conductive regions, which can be seen to completely block ion transfer on the surface of the ion exchange membrane to which the non-conductive film is attached. In addition, it can be observed that the size and number of electric vortices change in proportion to the change in the spacing of non-conductive patterns, and it is confirmed that the physical distance of the non-conductive patterns affects the growth of electric vortices. This can be confirmed by looking at the fact that the size of the electric vortices is the smallest in the L _P , L _S = 300 ㎛ type with the narrowest spacing of non-conductive patterns.

In electrochemical membrane processes such as electrodialysis, since shear flow actually exists, visualization of electric vortices according to non-conductive patterns was performed under the application of a shear flux (0.5 mm/s). Fig. 7 shows fluorescence images taken 60 seconds after the application of the same voltage (6, 10, 20 V) to the same device type (Reference, L _P , L _S = 1500 μm, L _P , L _S = 300 μm) as when the shear flux was not applied. Unlike the case where there was no shear flux (Fig. 6) seen above, when a shear flux was applied, it could be confirmed that electric vortices growing from a locally fixed location roll while being connected by the shear flux. Through this visualization experiment, two phenomena were observed. First, as the spacing between non-conductive patterns becomes narrow, the thickness of the ion depletion region decreases. This is because, just like in the case of no shear flux, the non-conductive pattern not only hinders the growth of electric vortices, but also the length of the unit conductive region ( L _P ) in which the electric vortices moving along the shear flow can grow decreases as the spacing between the patterns becomes narrower. This phenomenon is more clearly observed in the case of L _P , L _S = 300 ㎛, and it can be confirmed that the growth of the electric vortices is greatly suppressed as the size of the electric vortices is relatively the smallest compared to other types (Reference, L _P , L _S = 1500 ㎛) at 20 V. Second, when there is a non-conductive region on the surface of the ion exchange membrane, large electric vortices can be observed near the boundary between the conductive region through which ions penetrate and the non-conductive region. This is clearly observed in the case of L _P , L _S = 1500 ㎛, and it is presumed that the main cause is the funnel effect in which ions that cannot penetrate into the non-conductive region are concentrated into the conductive region. Therefore, it can be seen that the spacing of non-conductive patterns applied to the surface of the ion exchange membrane is a major factor affecting the growth and suppression of electric eddies.

As described above, in the examples and experimental examples of the present invention, an ion exchange membrane surface applied with a micro-scale fine pattern was fabricated, a micro electrodialysis device was created, and electric vortices were observed. To this end, instead of the conventional manual work, a UV nanosecond laser process was applied to a non-conductive film to fabricate a micro-scale (~300 ㎛) pattern, which was then transferred to the ion exchange membrane surface. In particular, the UV nanosecond laser process variables for fabricating the fine pattern were investigated, and the process conditions, such as minimizing the heat affected zone, were optimized. In addition, in order to confirm the change in the flow characteristics of the electric vortex according to the non-conductive pattern spacing, three types (Reference, L _P , L _S = 1500 ㎛, L _P , L _S = 300 ㎛) of ion exchange membranes were fabricated and experiments were performed.

Through the examples and experimental examples of the above invention, the following conclusions could be obtained. First, in order to reduce the width of the heat-affected zone when producing a nonconductive pattern film, a high frequency and a fast scan speed should be used. Second, by using a nonconductive pattern, the growth of electric eddies occurring on the surface of an ion exchange membrane can be suppressed or the size can be controlled. The experimental results performed in this example are expected to be good reference materials for research related to the physical processing of the surface of an ion exchange membrane, and are expected to be helpful for new engineering application research of electric eddies using a nonconductive patterned ion exchange membrane.

The present invention is not limited to the above embodiments, but can be manufactured in various different forms, and a person having ordinary skill in the art to which the present invention pertains will understand that the present invention can be implemented in other specific forms without changing the technical idea or essential characteristics of the present invention. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

Claims (6)

(a) a step of irradiating laser light on a non-conductive film to form a plurality of aperture patterns at predetermined intervals; and
(b) a step of bonding the non-conductive film to one surface of the ion exchange membrane;
A method for manufacturing an ion exchange membrane comprising a non-conductive pattern. In the first paragraph,
In the above step (a),
characterized in that the aperture pattern is formed by controlling the frequency, scan speed and scan number of the laser light.
A method for manufacturing an ion exchange membrane comprising a non-conductive pattern. In the first paragraph,
In the above step (a),
The above laser light is characterized in that it has a wavelength band of UV (ultraviolet) and is a pulsed wave with a pulse width of nanoseconds or femtoseconds.
A method for manufacturing an ion exchange membrane comprising a non-conductive pattern. In the first paragraph,
The above non-conductive film is characterized by including a non-conductive substrate and an adhesive layer.
A method for manufacturing an ion exchange membrane comprising a non-conductive pattern. In paragraph 4,
In the above step (b),
Characterized in that the non-conductive film is bonded to one surface of the ion exchange membrane via the adhesive layer.
A method for manufacturing an ion exchange membrane comprising a non-conductive pattern. An ion exchange membrane comprising a non-conductive pattern, manufactured by a method according to any one of claims 1 to 5.