Method for modifying ionomer

Abstract

The invention provides a modification treatment method of an ionomer, which can control the number of physical crosslinking points and obtain a modified ionomer with required performance and stable physical properties. A method for modifying an ionomer, comprising a preparation step for obtaining an ionomer dispersion in which molecules are dispersed by stirring an ionomer, which is a raw material, and a solvent at a predetermined temperature and a predetermined pressure, and obtaining a modified ionomer having predetermined physical properties by performing the following steps: a first step for obtaining an ionomer dispersion in which the molecules are dispersed; transferring the ionomer dispersion liquid to a subcritical region of the solvent to form physical cross-linking points of macromolecules so as to prepare gel particles; a second step in which, after the first step, an impact force is applied to the gel particles, thereby performing intermolecular phase formation; and a third step in which, after the second step, the ionomer dispersion liquid is cooled in a predetermined pattern, and the gel particles are expanded by the reaction force of the ionizing groups, thereby adjusting the swelling range.

Description

Technical Field

[0001] The present invention relates to a method for modifying an ionomer, and in particular to a method for modifying an ionomer, wherein the method can obtain a modified ionomer having the required performance suitable for a fuel cell and stable physical properties. Background Art

[0002] In recent years, fuel cells have been developed as a new power source for vehicles and other applications. These generate electricity through an electrochemical reaction between hydrogen and oxygen. Fuel cells offer the following advantages: high power generation efficiency, as they generate electricity directly through an electrochemical reaction. Furthermore, since the only product during power generation is water, their environmental impact is minimal.

[0003] Patent Document 1 discloses a method for producing a catalyst ink for producing a catalyst layer to be laminated on an electrolyte membrane constituting a fuel cell using an ionomer, which is a synthetic resin in which polymers are aggregated by utilizing the cohesive force of metal ions.

[0004] [Prior Art Literature]

[0005] (Patent Document)

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2016-66510 Summary of the Invention

[0007] [Problems to be solved by the invention]

[0008] Ionomers, resins formed by metal-crosslinking polymers composed of polyethylene units and acrylic acid units, are known to affect fuel cell performance, particularly the number of physical crosslinking points that contribute to water swelling. However, conventional treatment methods have made it difficult to control the number of physical crosslinking points. Therefore, a new modification method for obtaining modified ionomers with desired performance and stable physical properties is desired.

[0009] The object of the present invention is to solve the above-mentioned problems of the prior art and provide a method for modifying ionomers, which can control the number of physical crosslinking points and obtain modified ionomers with desired performance and stable physical properties.

[0010] [Technical means to solve the problem]

[0011] To achieve the aforementioned object, the present invention is characterized in that a method for modifying an ionomer comprises a preparatory step of stirring an ionomer as a raw material and a solvent at a predetermined temperature and a predetermined pressure to obtain an ionomer dispersion in which the molecules are dispersed. The method for modifying an ionomer obtains a modified ionomer having predetermined physical properties by performing the following steps: a first step of transferring the ionomer dispersion to a subcritical region of the solvent to form physical crosslinks between polymers to form gel particles; a second step of applying an impact force to the gel particles after the first step to induce phase formation between the molecules; and a third step of cooling the ionomer dispersion in a predetermined pattern after the second step to adjust the swelling range by causing the gel particles to expand due to the reaction force of ionized radicals.

[0012] Furthermore, a second feature is that the first step is a process of transferring the solvent to a subcritical region by pressurization by a pressure pump and heating by a heating pipe.

[0013] Furthermore, the third feature is that the second step is a process of reducing the flow rate by expanding the diameter of the pipe for transferring the ionomer dispersion.

[0014] Furthermore, a fourth feature is that the third step is a process for cooling the ionomer dispersion by a cooling pipe using a predetermined cooling pattern centered on a permeation temperature range, wherein the permeation temperature range is between a temperature range in which the viscosity of the ionomer dispersion does not change with temperature changes and a temperature range in which the viscosity of the ionomer dispersion as a whole changes with temperature changes.

[0015] Furthermore, the fifth feature is that the subcritical region in the first step is a region with a temperature of 180° C. to 350° C. and a pressure of 10 MPa to 30 MPa.

[0016] Furthermore, the sixth feature is that the infiltration temperature in the third step is 55°C to 60°C.

[0017] Furthermore, a seventh feature is that the ionomer concentration of the ionomer dispersion is 1% by weight or more and less than 30% by weight.

[0018] Furthermore, an eighth feature is that the ionomer is a powder and the solvent is water.

[0019] (Effects of the Invention)

[0020] According to a first feature, the ionomer modification method includes a preparatory step of stirring the ionomer as a raw material and a solvent at a predetermined temperature and a predetermined pressure to obtain an ionomer dispersion in which the molecules are dispersed. Furthermore, the ionomer modification method obtains a modified ionomer having predetermined physical properties by performing the following steps: a first step of transferring the ionomer dispersion to a subcritical region of the solvent to form physical crosslinks between polymers to form gel particles; a second step of applying an impact force to the gel particles after the first step to induce phase formation between the molecules; and a third step of cooling the ionomer dispersion in a predetermined pattern after the second step to expand the gel particles by the reaction force of ionized radicals to adjust the swelling range. Thus, a modified ionomer having a desired osmotic pressure and swelling limit suitable for use in fuel cells can be obtained. Furthermore, the swelling rate, swelling acceleration, and swelling limit of the gel particles can be independently controlled by the first, second, and third steps.

[0021] According to the second feature, the first step is a process of transferring the solvent to the subcritical region by pressurization by the pressure pump and heating by the heating pipe. Therefore, the first step can be performed using existing equipment.

[0022] According to the third feature, the second step is a process of reducing the flow rate by expanding the diameter of the pipe for transferring the ionomer dispersion liquid. Therefore, the second step can be performed using existing equipment.

[0023] According to the fourth feature, the third step involves cooling the ionomer dispersion using a cooling pipe using a predetermined cooling pattern centered around a permeation temperature range, which lies between a temperature range where the ionomer dispersion does not experience a viscosity change with temperature changes and a temperature range where the entire ionomer dispersion experiences a viscosity change with temperature changes. Therefore, the third step can be performed using existing equipment. Furthermore, morphology control utilizing changes in the solvent state can be performed based on the characteristics of the ionomer.

[0024] According to the fifth feature, the subcritical region in the aforementioned first step is a region with a temperature of 180°C to 350°C and a pressure of 10 MPa to 30 MPa. Therefore, by causing the dielectric constant and ion product of water to change state in the subcritical region, the reaction force between particles is reduced, and intermolecular complexation, i.e., physical cross-linking points, is generated to granulate the gel particles.

[0025] According to the sixth feature, the permeation temperature in the third step is 55° C. to 60° C., so that morphology control utilizing the state change of the solvent can be performed according to the characteristics of the ionomer.

[0026] According to the seventh feature, the ionomer concentration of the ionomer dispersion is 1% by weight or more and less than 30% by weight. Therefore, even when heated and pressurized, if the ionomer concentration is below 1% by weight, no crosslinking will occur, while if it is above 30% by weight, local gelation will occur. However, these ionomer concentrations can be avoided to obtain a modified ionomer having the desired physical crosslinking points.

[0027] According to the eighth feature, the ionomer is in the form of powder and the solvent is water. Therefore, a modified ionomer having desired physical properties can be obtained using easily available ionomer powder and water. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of an ionomer modification treatment apparatus according to one embodiment of the present invention.

[0029] Figure 2 Flowchart showing the steps of a method for modifying an ionomer according to an embodiment.

[0030] Figure 3 It is a time sequence diagram showing the process of the ionomer modification treatment method.

[0031] Figure 4 It is a graph that plots the relationship between the pressure and velocity of a solvent and the subcritical region.

[0032] Figure 5 This is a schematic diagram showing the difference in the gaps between gel particles caused by the size of the swelling limit.

[0033] Figure 6 This is a graph showing the relationship between the swelling rate and elongation of gel particles.

[0034] Figure 7 This is a graph showing the relationship between the swelling acceleration and Young's modulus of gel particles. DETAILED DESCRIPTION

[0035] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Figure 1 This is a schematic diagram of an ionomer modification apparatus 1 according to one embodiment of the present invention. Ionomers, synthetic resins that aggregate polymers by utilizing the cohesive force of metal ions, are known for their use in fuel cell catalyst layers and other applications. Heating relaxes the crosslinking in the polymer's main chain, rendering them fluid, allowing them to be molded using the same methods as thermoplastic resins. However, existing treatment methods cannot control the number of crosslinks, making it difficult to consistently obtain ionomers with properties suitable for fuel cell applications.

[0036] When ionomer powder (the raw material) is mixed with a solvent and molecularly dispersed, gel particles form, which absorb liquid and increase in volume. The rate of this swelling particularly affects the physical properties of the ionomer. To control the swelling rate to a desired value, it is necessary to control the deformation range caused by the expansion of the gel particles, i.e., the swelling limit.

[0037] The ionomer modification method of this embodiment is characterized in that, after the preparatory step of mixing ionomer powder and solvent, a morphology control process is performed, which includes a first step S2 of heating and pressurizing, a second step S2 of changing the flow rate, and a third step S3 of cooling.

[0038] The modification apparatus 1 includes a melting tank 10 with a stirrer 11, a liquid delivery pump 12, a heat-insulating and pressure-stabilizing tank 13, a pressure pump 14, a heating pipe 16, an impact-applying pipe 21 as a pipeline, cooling pipes 18 and 19, and a resin tank 20. Each of these apparatuses is connected to each other by a pipeline for transferring the ionomer dispersion A.

[0039] In the modification method of this embodiment, a preparatory step is first performed in which ionomer powder 2, which serves as a raw material, and water 3, which serves as a solvent, are stirred at a predetermined temperature and predetermined pressure to obtain a molecularly dispersed ionomer dispersion A. According to the modification method of this embodiment, a modified ionomer B having desired physical properties can be obtained using readily available ionomer powder and water.

[0040] Next, in the first step S1, a morphology control process, the dielectric constant and ion product of water undergo a state change in the subcritical region, reducing the interparticle repulsive forces and generating intermolecular complexes, or physical crosslinking points, thereby granulating the gel particles. Specifically, the ionomer dispersion A stored in the heat-insulating and pressure-stabilizing tank 13 is pressurized to a predetermined pressure by a pressure pump 14 and heated to a predetermined temperature by a heating pipe 16. A check valve 15 is provided at the upstream end of the heating pipe 16, and a pressure regulating valve 17 is provided at the downstream end of the heating pipe 16.

[0041] In the second step S2, the gel particles are formed into a phase with weak bonding, that is, low viscosity. Specifically, the impact imparting tube 21 with a mid-flow area increases the flow path area to reduce the flow rate of the ionomer dispersion A, thereby imparting an impact force to the gel particles.

[0042] Next, in the third step S3 , a predetermined cooling pattern is applied when cooling the ionomer dispersion A in the subcritical region, thereby expanding the gel particles by the reaction force of ionized radicals such as carboxyl and hydroxyl groups, thereby adjusting the swelling limit.

[0043] In this manner, the ionomer dispersion A having undergone the third step S3 becomes the modified ionomer B with fixed physical properties, and is stored in the resin tank 20 at room temperature and pressure.

[0044] Figure 2 This is a flowchart illustrating the steps of the ionomer modification method according to this embodiment. The ionomer modification method according to this embodiment includes a preparatory step S0 in which ionomer powder 2 and water 3 are stirred at a predetermined temperature and pressure to obtain a molecularly dispersed ionomer dispersion A; a first step S1 in which the ionomer dispersion A is transferred to the subcritical region of water 3 to form physical crosslinks between polymers, thereby producing gel particles; a second step S2 in which an impact force is applied to the gel particles to promote phase formation between the molecules; and a third step S3 in which the ionomer dispersion A is cooled in a predetermined pattern to expand the gel particles using the reaction force of ionized radicals to adjust the swelling range.

[0045] The first step S1, the second step S2, and the third step S3 constituting the morphology control process are performed in the order of first step S1 → second step S2 → third step S3. According to the morphology control process of this embodiment, the swelling rate, swelling acceleration, and swelling limit of the gel particles can be individually controlled.

[0046] Figure 3 This is a timing diagram illustrating the process flow of the ionomer modification method. When preparatory step S0 begins at time t1, the temperature and pressure begin to rise linearly. From time t2 to t3, the temperature and pressure are maintained at a constant level to achieve molecular dispersion. Subsequently, from time t3 to t4, further heating and heating are performed to achieve mixing.

[0047] Even after heating and treatment, the perfluoro ionomer of this embodiment will not form complexes if its concentration in the dispersion is less than 1 wt %, and will partially gel if it is greater than 30 wt %. Therefore, the ionomer concentration is preferably set to 1 wt % to 30 wt %, and in this embodiment, it is set to 2 wt %. Furthermore, the treatment temperature can be set to a temperature higher than the melting temperature of 250°C (e.g., 300°C), the pressure can be set to 10 MPa to 30 MPa, and the treatment time can be set to 2 seconds to 10 minutes.

[0048] From time t4 to t7, the morphology control process is performed, consisting of a first step S1 for forming physical crosslinks, a second step S2 for forming the phase of the gel particles, and a third step S3 for expanding the gel particles. In the first step S1 from time t4 to t5, the physical crosslinks are formed while maintaining a constant heating and pressurizing state.

[0049] Here, gel is a three-dimensional mesh structure formed by multiple polymers connected by bonds at specific chain locations. The bonds connecting the polymers are called crosslinks. Physical crosslinking points are points where these crosslinks are formed. In order to obtain physical crosslinking points of the main chain of a high-strength polymer, it is necessary to reduce the dielectric constant and ion product in a subcritical state that will reduce the interparticle reaction force generated by ionized radicals. When water molecules decompose in the subcritical region, the ion product increases and the dielectric constant decreases. As a result, the interparticle reaction force decreases, and complexation occurs in polymer particles that would not complex at room temperature and pressure to form gel particles.

[0050] Furthermore, the hydrogen bonds and electric dipoles between side chains can dissociate due to gel deformation caused by external forces, but this dissociation can be prevented by adjusting the temperature and pressure of the modification treatment. Furthermore, the number and type of physical crosslinking points can be selected by adjusting the treatment time.

[0051] Next, in the second step S2 at time t5 to t6, while maintaining a fixed heated and pressurized state, the flow rate of the ionomer dispersion A is reduced by applying an impact to the pipe 21 whose flow path area is expanded midway. In this way, an impact force is applied to the gel particles, and the phase formation of the gel particles is performed. As a method of applying an impact force to the gel particles, in addition to changing the flow rate of the ionomer dispersion A in stages, the pipe can also be reduced in diameter midway or unevenness can be provided on the inner wall of the pipe. The shear force of the gel particles can also be adjusted by the second step S2. As for the offset as the shear force, it is large when the pipe is expanded or reduced in diameter "yes", and small when it is "no".

[0052] Then, in the third step S3 from time t6 to t7, cooling is performed in a prescribed pattern, thereby adjusting the swelling limit (swelling range) caused by the expansion of the gel particles. The expansion of the gel particles is caused by the reaction force of the ion product of the ionized radicals inside the gel particles and the solvent and the dielectric constant. According to the third step S3, by cooling the ionomer dispersion A from the subcritical state in a prescribed cooling pattern, the desired swelling limit can be obtained without destroying the phase formed in the second step S2. The swelling limit affects the fracture stress of the modified ionomer. By controlling the swelling limit, the swelling rate related to the elongation of the modified ionomer can be controlled.

[0053] Ionomer gel particles have a permeation temperature range between the temperature range where viscosity does not change with temperature and the temperature range where overall viscosity changes with temperature. A cooling pattern centered around the permeation temperature is suitable for morphology control utilizing solvent state changes. In this embodiment, the permeation temperature range is 55°C to 60°C.

[0054] As the predetermined cooling pattern, for example, the first pattern: 300°C → 50°C → 100°C → 50°C → 100°C → 50°C ..., the second pattern: 300°C → 100°C × predetermined time → room temperature, the third pattern: 300°C → 50°C (sudden cooling or slow cooling), etc. can be applied.

[0055] Figure 4 This graph shows the relationship between solvent pressure and velocity and the subcritical region. In the modification method of this embodiment, the critical region of water exists in the region with a temperature of T2 or higher and a pressure of P2 or higher, while the subcritical region of water exists in the region with a temperature of T1 or higher and a pressure of P1 or higher. The first step S1 of this embodiment is performed within the subcritical region of water, at a temperature of 180°C to 350°C and a pressure of 10 MPa to 30 MPa.

[0056] Figure 5 This is a schematic diagram illustrating the difference in gaps between gel particles due to the size of the swelling limit. When using ionomers to manufacture fuel cells, the swelling limit of the ionomer coating the catalyst particles causes the gaps in the electrode layer to become narrow. When the swelling limit is small, gaps exist between gel particles 30, and even if oxygen molecules 31 enter, they can easily escape as water molecules 32. However, if the swelling limit becomes too large, the gaps become smaller, making it difficult for water molecules 32 to escape. Therefore, it is desirable to set the swelling limit so that there are appropriate gaps. According to the third step S3 of this embodiment, the swelling limit of the gel particles can be set to a desired value.

[0057] Figure 6 This graph shows the relationship between the swelling rate and elongation of gel particles. The swelling rate of gel particles is related to their elongation. By using the third step S3 to expand the gel particles through cooling in a prescribed pattern, the elongation of the gel particles can be controlled. This indicates that the swelling rate and elongation of modified samples A1, A2, A3, A4, and A5 can be arbitrarily reduced compared to unmodified sample A6 and a mixture of gel particles of various types. To adjust the cooling rate to achieve a prescribed cooling pattern, a combination of air cooling, air cooling, and water cooling can be used.

[0058] Figure 7 This graph shows the relationship between the swelling acceleration and Young's modulus of gel particles. Gel particles that have undergone the third step S3 have a uniform and strong bond strength. This bond strength is related to the swelling acceleration that contributes to osmotic pressure, making it possible to control the Young's modulus, which is related to the swelling acceleration. Compared to the unmodified sample A6, the swelling acceleration of modified samples A1, A4, and A5 was significantly suppressed, and the Young's modulus was significantly increased. Sample A5 had a Young's modulus approximately twice that of sample A6.

[0059] As described above, the ionomer modification method of this embodiment includes a preparatory step S0 of stirring the ionomer 2 and water 3 as raw materials at a predetermined temperature and a predetermined pressure to obtain an ionomer dispersion A in which the molecules are dispersed. Furthermore, the ionomer modification method obtains a modified ionomer B having predetermined physical properties by performing the following steps: a first step S1 of transferring the ionomer dispersion A to the subcritical region of water 3 to form physical crosslinks between polymers to form gel particles; a second step S2 of applying an impact force to the gel particles after the first step S1 to promote phase formation between the molecules; and a third step S3 of cooling the ionomer dispersion A in a predetermined pattern after the second step S2 to expand the gel particles by the reaction force of ionized radicals to adjust the swelling range. Consequently, a modified ionomer B having a desired osmotic pressure and swelling limit, suitable for use in fuel cells, can be obtained. Furthermore, the swelling rate, swelling acceleration, and swelling limit of the gel particles can be individually controlled by the first step S1 , the second step S2 , and the third step S3 .

[0060] Furthermore, the first step S1 is a process of shifting the water 3 to the subcritical region by pressurization by the pressure pump 14 and heating by the heating pipe 16 . Therefore, the first step can be performed using existing equipment.

[0061] Furthermore, the second step S2 is a process of enlarging the diameter of the pipe 21 for transferring the ionomer dispersion A midway to thereby reduce the flow rate. Therefore, the second step can be performed using existing equipment.

[0062] Furthermore, the third step S3 involves cooling the ionomer dispersion A via the cooling pipes 18 and 19 using a predetermined cooling pattern centered around a permeation temperature range, which lies between a temperature range where the viscosity of the ionomer dispersion A does not change with temperature changes and a temperature range where the viscosity of the entire ionomer dispersion A changes with temperature changes. Therefore, the third step can be performed using existing equipment. Furthermore, morphology control utilizing changes in the solvent state can be performed according to the characteristics of the ionomer.

[0063] The structure of the reforming apparatus, ionomer concentration, temperature, pressure, and treatment time in the preparation step, temperature, pressure, and treatment time in the first step, pipe shape and flow rate in the second step, and cooling pattern in the third step are not limited to those in the above-described embodiment and may be modified in various ways. According to the reforming apparatus 1 of this embodiment, by setting conditions such as temperature, pressure, and treatment time, the desired modified ionomer B can be obtained using existing equipment. Furthermore, the modified ionomer B modified using the ionomer reforming method of this embodiment can improve fuel cell performance by having stable and desired physical properties. The reforming method of the present invention allows the production of gel particles based not only on the same molecule but also on heterogeneous molecules with different molecular weights.

[0064] Reference numerals

[0065] 1: Modification treatment device

[0066] 2: Ionomer powder (ionomer)

[0067] 3: Water (solvent)

[0068] 13: Insulation and pressure stabilizing tank

[0069] 14: Pressure pump

[0070] 16: Heating tube

[0071] 17: Pressure regulating valve

[0072] 18,19: Cooling pipe

[0073] 21: Impact imparting pipe (pipeline)

[0074] A: Ionomer dispersion

[0075] B: Modified ionomer

[0076] S0: Preparation process

[0077] S1: First process

[0078] S2: Second process

[0079] S3: The third process

Claims

1. A method for modifying an ionomer, characterized in that: The method comprises a preparation step of stirring an ionomer as a raw material and a solvent at a predetermined temperature and a predetermined pressure to obtain an ionomer dispersion in which the molecules are dispersed. The method further comprises the following steps to obtain a modified ionomer having predetermined physical properties: In the first step, the ionomer dispersion is transferred to the subcritical region of the solvent to form physical crosslinks between polymers to produce gel particles. A second step, after the first step, applying an impact force to the gel particles to form a phase between molecules; and In the third step, after the second step, the ionomer dispersion is cooled in a predetermined pattern to expand the gel particles by the reaction force of the ionized radicals to adjust the swelling range.

2. The ionomer modification method according to claim 1, wherein: The first step is a process of transferring the solvent to a subcritical region by pressurizing with a pressure pump and heating with a heating pipe.

3. The method for modifying the ionomer according to claim 1, wherein: The second step is a process of reducing the flow rate by expanding the diameter of the pipe for transferring the ionomer dispersion.

4. The method for modifying the ionomer according to claim 1, wherein: The third step is a process of cooling the ionomer dispersion by a cooling pipe using a predetermined cooling pattern centered on a permeation temperature range, wherein the permeation temperature range is between a temperature range in which the viscosity of the ionomer dispersion does not change with temperature changes and a temperature range in which the viscosity of the ionomer dispersion as a whole changes with temperature changes.

5. The method for modifying the ionomer according to claim 1, wherein: The subcritical region in the first step is a region with a temperature of 180° C. to 350° C. and a pressure of 10 MPa to 30 MPa.

6. The method for modifying the ionomer according to claim 4, wherein: The infiltration temperature in the third step is 55°C to 60°C.

7. The method for modifying an ionomer according to claim 1 or 2, wherein: The ionomer concentration of the ionomer dispersion is 1% by weight or more and less than 30% by weight.

8. The method for modifying an ionomer according to claim 1 or 2, wherein: The ionomer is in powder form, and the solvent is water.

Images