An acrylic resin liquid crystal monomer, a preparation method and application thereof

Abstract

The application discloses an acrylic resin liquid crystal monomer, and a structure is shown as formula I. The application further discloses a preparation method of the acrylic resin liquid crystal monomer, an intrinsic high-thermal-conductivity liquid crystal material prepared from the acrylic resin liquid crystal monomer and application of the intrinsic high-thermal-conductivity liquid crystal material. The intrinsic high-thermal-conductivity liquid crystal material is obtained by electric field orientation and in-situ ultraviolet light polymerization of a mixture of the acrylic resin liquid crystal monomer and a curing agent. The application makes full use of crystallization performance and response to an electric field of the liquid crystal, realizes arrangement of the liquid crystal in a longitudinal direction, and utilizes an in-situ light polymerization method to fix the orientation structure, so that the prepared intrinsic high-thermal-conductivity liquid crystal material can realize longitudinal high-thermal-conductivity performance, and retains selection of compounding with other fillers, and has wide application prospects in the field of high-thermal-conductivity composite material preparation.

Description

Technical Field

[0001] This invention belongs to the field of thermally conductive materials for electronic devices, specifically relating to an acrylic resin liquid crystal monomer, its preparation method, and its application. Background Technology

[0002] As microelectronic devices become increasingly integrated, waste heat has become a critical issue hindering industry development. Waste heat from electronic devices raises device temperature, reducing system stability, affecting device performance, and shortening device lifespan. Thermal pads, as a key material for improving the thermal conductivity between heat and cold sources, are widely used in the electronics and electrical engineering fields to solve the heat dissipation problem of electronic devices.

[0003] In applications, the thermal conductivity of materials is generally improved by adding high thermal conductivity fillers to the polymer resin matrix. With ongoing research, more and more high thermal conductivity fillers are being discovered and prepared. However, improving the thermal conductivity of the resin in composite materials remains challenging. Compared to thermally conductive fillers with conductivity ranging from 100-5000 W / m², this improvement is still difficult. -1 K -1 The thermal conductivity of commonly used resins is only 0.5 W / m. -1 K -1 The difference of two orders of magnitude limits the development of the overall thermal conductivity of composite materials. If a high thermal conductivity resin matrix can be prepared, the overall thermal conductivity of the composite material can be effectively improved.

[0004] To prepare high thermal conductivity resins, a common method is to stretch polymers into nanofibers. Within these fibers, the polymer chains are highly oriented and crystalline, achieving directional high thermal conductivity. However, while this method achieves both polymer chain orientation and high thermal conductivity, it cannot be combined with thermally conductive fillers. The stretched polymer fibers are too fine to be compatible with micron-sized thermally conductive fillers, thus losing the opportunity to further improve thermal conductivity.

[0005] Another method for preparing high thermal conductivity resins is to use liquid crystal polymers. Due to the high crystallinity of liquid crystal polymers, phonon scattering caused by the disordered structure of the polymer matrix is ​​avoided, which helps to improve thermal conductivity.

[0006] Patent document CN113234042A discloses a disc-shaped liquid crystal epoxy resin monomer and its preparation method, as well as an intrinsically high thermal conductivity liquid crystal epoxy resin material and its preparation method. The disc-shaped liquid crystal epoxy resin monomer provided by this invention uses a benzo[a]phenanthrene-based disc-shaped liquid crystal structure as a rigid central core, surrounded by six identical flexible side chains. The benzo[a]phenanthrene-based disc-shaped liquid crystal structure can self-assemble into positionally ordered columnar and layered phases through π-π stacking interactions between benzene rings, exhibiting high one-dimensional charge and energy transport performance. This high charge and energy transport performance results in excellent thermal conductivity for the disc-shaped liquid crystal epoxy resin.

[0007] Although liquid crystal polymers can achieve high crystallinity and resin-filler blending to prepare resin materials with high thermal conductivity, this method makes it difficult to orient molecules in a direction perpendicular to the material. In practical applications, this direction is precisely where the heat source and heat sink are connected, making it a critical direction. Summary of the Invention

[0008] In view of the shortcomings of the prior art, the present invention provides an acrylic resin liquid crystal monomer, which can be used to synthesize liquid crystal polymer molecules. By orienting the liquid crystal polymer molecules by means of an electric field, the thermal conductivity of the polymer can be further improved in the direction perpendicular to the surface of the thermally conductive material.

[0009] An acrylic resin liquid crystal monomer has the structure shown in Formula I:

[0010]

[0011] The present invention also provides a method for preparing the above-mentioned acrylic resin liquid crystal monomer. The preparation method is simple, the raw materials are readily available, the cost is low, and the prepared monomer can be used to synthesize highly thermally conductive liquid crystal polymer molecules.

[0012] A method for preparing an acrylic resin liquid crystal monomer includes the following steps:

[0013] (1) Dissolve p-hydroxybenzoic acid, 4,4'-dihydroxydiphenyl and p-toluenesulfonic acid monohydrate in xylene, heat and stir the resulting mixed solution to carry out the reaction, filter the reaction solution after the reaction is completed, and dry the resulting precipitate and label it as BPE.

[0014] (2) Dissolve 3-chloro-1-propanol, iodine salt, inorganic strong base and BPE obtained in step (1) in an aprotic polar solvent. Heat and stir the resulting mixed solution for at least 24 hours and then stop the reaction. Filter the reaction solution and dry the resulting precipitate and label it as BPE-C3.

[0015] (3) Inject N,N-dimethylacetamide into the reactor, add BPE-C3 obtained in step (2) under nitrogen protection, place the reactor in a cooling device to cool, remove the hydrochloric acid generated in the reaction, add acryloyl chloride into the reactor within 10 minutes, remove the cooling device after reacting for 10 to 50 minutes, place the reactor in a light-proof environment, stop the reaction after reacting for 5 to 12 hours, filter the reaction solution, dry the obtained precipitate to obtain acrylic resin liquid crystal monomer, labeled as BPE-C3-AA.

[0016] Preferably, in step (1), the mass fraction of p-hydroxybenzoic acid in the mixed solution is 5-10 wt%, the mass fraction of 4,4'-dihydroxydiphenyl is 5-8 wt%, and the mass fraction of p-toluenesulfonic acid monohydrate is <2 wt%.

[0017] Preferably, in step (1), the heating temperature is 150-185°C and the reaction time is 8 hours or more.

[0018] Preferably, in step (2), the iodized salt includes sodium iodide, potassium iodide or silver iodide.

[0019] Preferably, in step (2), the organic strong alkali includes sodium hydroxide, potassium hydroxide, aluminum oxide, calcium hydroxide, or barium hydroxide.

[0020] Preferably, in step (2), the aprotic polar solvent includes 2-butanone, acetone dimethyl sulfoxide, or N,N-dimethylformamide.

[0021] Preferably, in step (2), the mixed solution contains 3-8 wt% iodine salt, 2-6 wt% inorganic strong alkali, and 3-8 wt% BPE.

[0022] Preferably, in step (2), the volume ratio of 3-chloro-1-propanol to the aprotic polar solvent is 0.03 to 0.12:1.

[0023] Preferably, in step (2), the heating temperature is 50-70°C.

[0024] Preferably, in step (2), the heating and stirring time is 72 hours.

[0025] Preferably, in step (3), the mass ratio of BPE-C3 to the volume ratio of N,N-dimethylacetamide is 2-4 g: 25-45 mL.

[0026] Preferably, in step (3), the volume ratio of acryloyl chloride to N,N-dimethylacetamide is 0.05 to 0.2:1.

[0027] Preferably, in step (3), triethylamine is used to remove the hydrochloric acid generated in the reaction, wherein the volume ratio of triethylamine to N,N-dimethylacetamide is 1-4:25-45.

[0028] Preferably, in steps (1) to (3), the drying temperature is 60 to 90°C.

[0029] The present invention also provides an intrinsically high thermal conductivity liquid crystal material, which can achieve high thermal conductivity in the longitudinal direction and retains the option of compounding with other fillers.

[0030] An intrinsically high thermal conductivity liquid crystal material is obtained by mixing and curing the aforementioned acrylic resin liquid crystal monomer and curing agent.

[0031] Preferably, the curing agent comprises diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide.

[0032] Preferably, the mass ratio of the acrylic resin liquid crystal monomer to the curing agent is 100:5 to 30.

[0033] Preferably, the mixing method involves directly mixing acrylic resin liquid crystal monomer powder and curing agent powder, melting and stirring, or dissolving acrylic resin liquid crystal monomer and curing agent together in a solvent and then evaporating the solvent.

[0034] Preferably, the solvent includes N,N-dimethylacetamide or ethyl acetate.

[0035] Preferably, the curing method involves subjecting a mixture of acrylic resin liquid crystal monomer and curing agent to electric field orientation and in-situ polymerization under ultraviolet light.

[0036] This invention fully utilizes the crystallization properties and responsiveness of liquid crystals to electric fields to achieve the vertical alignment of liquid crystals. At the same time, it uses in-situ photopolymerization to fix the orientation structure, avoiding the destruction of the orientation structure caused by molecular relaxation after the electric field is removed.

[0037] Preferably, the step of subjecting the mixture of acrylic resin liquid crystal monomer and curing agent to electric field orientation and in-situ polymerization under ultraviolet light is as follows: the mixture of acrylic resin liquid crystal monomer and curing agent is heated and melted on a conductive metal, and ITO glass is placed at a distance of 0.5 to 5 mm from the metal plate. The conductive metal and ITO glass are respectively connected to the positive and negative terminals of a power supply, a voltage is applied, and ultraviolet light is used for irradiation.

[0038] Preferably, the melting temperature is 110–150°C.

[0039] Preferably, the voltage is 1 to 10 kV.

[0040] Preferably, the ultraviolet light wavelength is 335-400 nm and the irradiation time is 5-90 min.

[0041] This invention also provides the application of the intrinsically high thermal conductivity liquid crystal material in the field of high thermal conductivity composite material preparation. The intrinsically high thermal conductivity liquid crystal material of this invention has a longitudinal thermal conductivity as high as 1.4–1.6 W / m. -1 K -1 It also retains the option of compounding with other fillers, and has broad application prospects in the field of high thermal conductivity composite material preparation.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] (1) This invention makes full use of the crystallization properties and responsiveness of liquid crystals to electric fields to solve the problem of vertical alignment of liquid crystals. At the same time, it uses in-situ photopolymerization to fix the orientation structure, avoiding the destruction of the orientation structure caused by molecular relaxation after the electric field is removed.

[0044] (2) The intrinsic high thermal conductivity liquid crystal material of the present invention is based on liquid crystal polymer material, is an all-organic material, and does not use inorganic fillers as fillers.

[0045] (3) The intrinsic high thermal conductivity liquid crystal material of the present invention can achieve high thermal conductivity in the longitudinal direction, which is usually connected to the heat source and the heat sink, and can efficiently transport heat in the shortest path.

[0046] (4) The intrinsically high thermal conductivity liquid crystal material prepared by this invention has a longitudinal thermal conductivity as high as 1.4–1.6 W / m. -1 K -1 It also retains the option of compounding with other fillers, and has broad application prospects in the field of high thermal conductivity composite material preparation. Attached Figure Description

[0047] Figure 1 The example shows the synthesis route of the acrylic resin liquid crystal monomer.

[0048] Figure 2 The image shows a polarized image of the acrylic resin liquid crystal monomer prepared in Example 1.

[0049] Figure 3 The data are DSC test data of the acrylic resin liquid crystal monomer prepared in Example 1.

[0050] Figure 4 Wide-angle XRD data for the intrinsically high thermal conductivity liquid crystal materials prepared in Examples 1 and 2. Detailed Implementation

[0051] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0052] Unless otherwise specified, all raw materials used in the examples were purchased commercially.

[0053] The thermal conductivity test method in this embodiment is as follows: the test is performed using a laser thermal conductivity meter in accordance with the ASTM E1461 standard.

[0054] Example 1

[0055] according to Figure 1 The process shown is for synthesizing acrylic resin liquid crystal monomers. The specific steps are as follows:

[0056] 5 g of p-hydroxybenzoic acid, 6 g of 4,4'-dihydroxydiphenylene, and 0.5 g of p-toluenesulfonic acid monohydrate were dissolved in 80 mL of xylene and heated at 160 °C for 24 hours. The reaction was carried out in a flask equipped with a magnetic stirrer and a water separator. The solution was filtered through a Buchner funnel, and the resulting precipitate was dried overnight at 60 °C. The dried precipitate was labeled BPE.

[0057] 5 g BPE, 7 mL 3-chloro-1-propanol, 6 g sodium iodide (NaI), and 3 g sodium hydroxide (NaOH) were dissolved in 60 mL 2-butanone. The mixture was heated to 60 °C and stirred for 72 hours. The resulting product was poured into ice-cold deionized water to stop the reaction. The solution was filtered through a Buchner funnel, and the resulting precipitate was dried overnight at 60 °C. The dried precipitate was labeled BPE-C3.

[0058] To prevent the influence of water, a nitrogen-filled flask was used. 35 mL of dry N,N-dimethylacetamide was injected into the flask, and 5 g of BPE-C3 was added under nitrogen protection. The resulting solution was cooled in an ice-water bath. At 0 °C, 1.2 mL of triethylamine was added to remove the generated hydrochloric acid. Then, 1.5 mL of acryloyl chloride was slowly added to the flask over 10 minutes. After 30 minutes, the ice-water bath was removed, and the flask was immediately covered with aluminized paper. The reaction was allowed to proceed for 12 hours. The solution was then poured into ice water to stop the reaction, filtered, and the resulting precipitate was dried overnight at 60 °C. The dried precipitate was labeled BPE-C3-AA, i.e., an acrylic resin liquid crystal monomer.

[0059] The acrylic resin liquid crystal monomer obtained in this embodiment was observed under a polarizing microscope, and the following can be observed: Figure 2 The polarization phenomenon shown proves that this monomer has liquid crystal properties.

[0060] The acrylic resin liquid crystal monomer obtained in this embodiment was subjected to DSC detection, and the results are as follows: Figure 3 As shown, phase transition peaks were observed at 101℃ and 165℃, respectively, which correspond to the phase transition temperature and clearing point of the liquid crystal.

[0061] BPE-C3-AA and curing agent TPO were dissolved in N,N-dimethylacetamide, with BPE-C3-AA having a mass fraction of 10 wt% and TPO a mass fraction of 1 wt%. After thorough mixing, the solvent was evaporated and placed on a copper stage. The mixture was heated to 125°C, melting the sample into a liquid. ITO glass was then placed 3 mm away from the metal plate, and the mixture was cured by irradiation with 356 nm ultraviolet light for 30 min, yielding an intrinsically high thermal conductivity liquid crystal material. The thermal conductivity of the obtained sample was approximately 0.5 W / m². -1 K -1 .

[0062] Example 2

[0063] according to Figure 1 The process shown is for synthesizing acrylic resin liquid crystal monomers. The specific steps are as follows:

[0064] 5 g of p-hydroxybenzoic acid, 6 g of 4,4'-dihydroxydiphenylene, and 0.5 g of p-toluenesulfonic acid monohydrate were dissolved in 80 mL of xylene and heated at 160 °C for 24 hours. The reaction was carried out in a flask equipped with a magnetic stirrer and a water separator. The solution was filtered through a Buchner funnel, and the resulting precipitate was dried overnight at 60 °C. The dried precipitate was labeled BPE.

[0065] 5 g BPE, 7 mL 3-chloro-1-propanol, 6 g sodium iodide (NaI), and 3 g sodium hydroxide (NaOH) were dissolved in 60 mL 2-butanone. The mixture was heated to 60 °C and stirred for 72 hours. The resulting product was poured into ice-cold deionized water to stop the reaction. The solution was filtered through a Buchner funnel, and the resulting precipitate was dried overnight at 60 °C. The dried precipitate was labeled BPE-C3.

[0066] To prevent the influence of water, a nitrogen-filled flask was used. 35 mL of dry N,N-dimethylacetamide was injected into the flask, followed by the addition of 5 g of BPE-C3 under nitrogen protection. The solution was cooled in an ice-water bath. At 0 °C, 1.2 mL of triethylamine was added to remove the generated hydrochloric acid. Then, 1.5 mL of acryloyl chloride was slowly added to the flask over 10 minutes. After 30 minutes, the ice-water bath was removed, and the flask was immediately covered with aluminized paper. The reaction was allowed to proceed for 12 hours. The solution was then poured into ice water to stop the reaction, filtered, and the resulting precipitate was dried overnight at 60 °C. The dried precipitate was labeled BPE-C3-AA, representing an acrylic resin liquid crystal monomer.

[0067] BPE-C3-AA and curing agent TPO were dissolved in N,N-dimethylacetamide, with BPE-C3-AA having a mass fraction of 10 wt% and TPO a mass fraction of 1 wt%. After thorough mixing, the solvent was evaporated and placed on a copper stage. The mixture was heated to 125°C, melting the sample into a liquid. ITO glass was then placed 3 mm away from the metal plate. The ITO glass was connected to the copper stage as positive and negative electrodes, respectively, with a voltage of 2V. The mixture was then cured by irradiation with 356 nm ultraviolet light for 30 min, yielding an intrinsically high thermal conductivity liquid crystal material, labeled PBPE-C3-AA-2kV. The thermal conductivity of the obtained sample was approximately 1 W / m². -1 K -1 .

[0068] The intrinsically high thermal conductivity liquid crystal materials prepared in Examples 1 and 2 were analyzed using wide-angle XRD, as follows: Figure 4 As shown, without an electric field, the sample pattern is very close to a ring, while with a 2kV electric field applied, the pattern is deformed into two arcs, indicating the change in the orientation of the organic crystal.

[0069] Example 3

[0070] according to Figure 1 The process shown is for synthesizing acrylic resin liquid crystal monomers. The specific steps are as follows:

[0071] 5 g of p-hydroxybenzoic acid, 6 g of 4,4'-dihydroxydiphenylene, and 0.5 g of p-toluenesulfonic acid monohydrate were dissolved in 80 mL of xylene and heated at 160 °C for 24 hours. The reaction was carried out in a flask equipped with a magnetic stirrer and a water separator. The solution was filtered through a Buchner funnel, and the resulting precipitate was dried overnight at 60 °C. The dried precipitate was labeled BPE.

[0072] 5 g BPE, 7 mL 3-chloro-1-propanol, 6 g sodium iodide (NaI), and 3 g sodium hydroxide (NaOH) were dissolved in 60 mL 2-butanone. The mixture was heated to 60 °C and stirred for 72 hours. The resulting product was poured into ice-cold deionized water to stop the reaction. The solution was filtered through a Buchner funnel, and the resulting precipitate was dried overnight at 60 °C. The dried precipitate was labeled BPE-C3.

[0073] To prevent the influence of water, a nitrogen-filled flask was used. 35 mL of dry N,N-dimethylacetamide was injected into the flask, followed by the addition of 5 g of BPE-C3 under nitrogen protection. The solution was cooled in an ice-water bath. At 0 °C, 1.2 mL of triethylamine was added to remove the generated hydrochloric acid. Then, 1.5 mL of acryloyl chloride was slowly added to the flask over 10 minutes. After 30 minutes, the ice-water bath was removed, and the flask was immediately covered with aluminized paper. The reaction was allowed to proceed for 12 hours. The solution was then poured into ice water to stop the reaction, filtered, and the resulting precipitate was dried overnight at 60 °C. The dried precipitate was labeled BPE-C3-AA, representing an acrylic resin liquid crystal monomer.

[0074] BPE-C3-AA and curing agent TPO were dissolved in N,N-dimethylacetamide, with BPE-C3-AA having a mass fraction of 10 wt% and TPO a mass fraction of 1 wt%. After thorough mixing, the solvent was evaporated and placed on a copper stage. The mixture was heated to 125°C, melting the sample into a liquid. ITO glass was then placed 3 mm away from the metal plate. The ITO glass was connected to the copper stage as the positive and negative electrodes, respectively, with a voltage of 3V. The mixture was then cured by irradiation with 356 nm ultraviolet light for 30 min, yielding an intrinsically high thermal conductivity liquid crystal material, labeled PBPE-C3-AA-3kV. The thermal conductivity of the obtained sample was approximately 1.4 W / m². -1 K -1 .

[0075] By comparing the thermal conductivity of the intrinsically high thermal conductivity liquid crystal materials prepared in Examples 1-3, the influence of the electric field on the directional thermal conductivity can be confirmed.

[0076] Example 4

[0077] according to Figure 1 The process shown is for synthesizing acrylic resin liquid crystal monomers. The specific steps are as follows:

[0078] 5 g of p-hydroxybenzoic acid, 6 g of 4,4'-dihydroxydiphenylene, and 0.5 g of p-toluenesulfonic acid monohydrate were dissolved in 80 mL of xylene and heated at 160 °C for 24 hours. The reaction was carried out in a flask equipped with a magnetic stirrer and a water separator. The solution was filtered through a Buchner funnel, and the resulting precipitate was dried overnight at 60 °C. The dried precipitate was labeled BPE.

[0079] 5 g BPE, 7 mL 3-chloro-1-propanol, 6 g sodium iodide (NaI), and 3 g sodium hydroxide (NaOH) were dissolved in 60 mL 2-butanone. The mixture was heated to 60 °C and stirred for 72 hours. The resulting product was poured into ice-cold deionized water to stop the reaction. The solution was filtered through a Buchner funnel, and the resulting precipitate was dried overnight at 60 °C. The dried precipitate was labeled BPE-C3.

[0080] To prevent the influence of water, a nitrogen-filled flask was used. 35 mL of dry N,N-dimethylacetamide was injected into the flask, followed by the addition of 5 g of BPE-C3 under nitrogen protection. The solution was cooled in an ice-water bath. At 0 °C, 1.2 mL of triethylamine was added to remove the generated hydrochloric acid. Then, 1.5 mL of acryloyl chloride was slowly added to the flask over 10 minutes. After 30 minutes, the ice-water bath was removed, and the flask was immediately covered with aluminized paper. The reaction was allowed to proceed for 12 hours. The solution was then poured into ice water to stop the reaction, filtered, and the resulting precipitate was dried overnight at 60 °C. The dried precipitate was labeled BPE-C3-AA, representing an acrylic resin liquid crystal monomer.

[0081] BPE-C3-AA and curing agent TPO were dissolved in N,N-dimethylacetamide, with BPE-C3-AA having a mass fraction of 10 wt% and TPO a mass fraction of 1 wt%. After thorough mixing, the solvent was evaporated and placed on a copper stage. The mixture was heated to 125°C, melting the sample into a liquid. 30 wt% carbon fiber was mixed into the liquid. ITO glass was placed 3 mm away from the metal plate, and the ITO glass was connected to the positive and negative electrodes of the copper stage, respectively, with a voltage of 3V. The sample was then cured by irradiation with 356 nm ultraviolet light for 30 min. The resulting sample had a thermal conductivity of approximately 28 W / m². -1 K -1 This indicates that the composite material prepared in this embodiment not only has good thermal conductivity, but also has the potential to serve as a matrix for thermally conductive composite materials.

[0082] This application proposes a method for preparing intrinsically high thermal conductivity liquid crystal materials. By combining liquid crystal structures and electric field alignment methods, ideal thermal conductivity is obtained. The highest longitudinal thermal conductivity of the product approaches 1.4 W / m. -1 K -1 This provides an excellent platform for the subsequent development of high thermal conductivity composite materials.

[0083] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

Claims

1. The application of an intrinsically high thermal conductivity liquid crystal material in the preparation of high thermal conductivity composite materials, characterized in that, The intrinsically high thermal conductivity liquid crystal material is obtained by mixing and curing an acrylic resin liquid crystal monomer and a curing agent. The acrylic resin liquid crystal monomer has the structure shown in Formula I: 。 2. The application according to claim 1, characterized in that, The curing agent is diphenyl (2,4,6-trimethylbenzoyl)phosphine oxide, and the mass ratio of the acrylic resin liquid crystal monomer to the curing agent is 100:5~30.

3. The application according to claim 1 or 2, characterized in that, The curing method involves subjecting a mixture of acrylic resin liquid crystal monomers and curing agent to electric field orientation and in-situ polymerization under ultraviolet light.

4. The application according to claim 3, characterized in that, The steps of electric field orientation and in-situ polymerization of the mixture of acrylic resin liquid crystal monomer and curing agent are as follows: the mixture of acrylic resin liquid crystal monomer and curing agent is heated and melted on a conductive metal, and ITO glass is placed at a distance of 0.5~5 mm from the metal plate. The conductive metal and ITO glass are respectively connected to the positive and negative terminals of a power supply, a voltage is applied, and ultraviolet light is used for irradiation.

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