Ultraviolet-cured electromagnetic shielding coating, preparation method thereof, coating and application thereof

Abstract

The invention discloses an ultraviolet-cured electromagnetic shielding coating, a preparation method thereof, a coating and application thereof, and relates to the technical field of electromagnetic shielding materials. Comprising modified epoxy acrylate resin, a conductive filler, a diluent and a photoinitiator. By constructing modified epoxy acrylate resin with a polyurethane side chain structure and a composite system of a free radical photoinitiator and a cationic photoinitiator, the three components supplement each other, and the modified epoxy acrylate resin optimizes the physical rheological property of the coating so as to facilitate thin layer forming; the composite photoinitiator system guarantees efficient and thorough curing in a thin layer or even a complex structure, and jointly supports comprehensive improvement of the UV curing electromagnetic shielding coating in the aspects of environmental protection (solvent-free), high efficiency (rapid curing), functionality (good shielding effectiveness), process suitability (adaptation to the fast pace of an electronic production line) and the like.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic shielding materials technology, and more specifically, to an ultraviolet-cured electromagnetic shielding coating, its preparation method, coating, and its application. Background Technology

[0002] With the rapid development of electronic information technology, computer networks and electronic communication equipment have become indispensable infrastructure in modern society. These devices inevitably generate electromagnetic radiation during operation and are also susceptible to external electromagnetic interference, leading to serious consequences such as equipment malfunctions and information leaks. Studies have shown that long-term exposure to electromagnetic pollution can also pose potential health hazards, making electromagnetic shielding technology increasingly important as an effective means of suppressing electromagnetic interference.

[0003] Electromagnetic shielding coatings have become the preferred solution for electromagnetic protection of electronic equipment components due to their ease of application and wide applicability. Traditional electromagnetic shielding coatings are typically prepared using a resin-based composite conductive filler (such as metal powder or carbon-based materials), forming a conductive network on the inner surface of the electronic device's casing to achieve electromagnetic shielding. The coating's electromagnetic shielding effectiveness primarily depends on the integrity and continuity of its internal conductive network structure. Currently, to improve electromagnetic shielding performance, the industry commonly increases the amount of conductive filler or the coating thickness, often combined with a thermosetting process to ensure overall coating quality. However, thermosetting has a long curing time, low production efficiency, and the electromagnetic shielding coating is prone to flow due to external forces during incomplete curing, ultimately affecting its performance.

[0004] Ultraviolet (UV) curing technology, due to its high efficiency and environmental friendliness, offers a new direction for the development of electromagnetic shielding coatings. This technology can complete coating curing within seconds to minutes, significantly improving production efficiency. However, when the amount of conductive filler increases, a large amount of resin material is blocked by the conductive filler, severely hindering UV penetration and resulting in poor deep curing effects. Furthermore, existing UV curing systems are susceptible to oxygen inhibition, often leading to surface stickiness and insufficient deep cross-linking when preparing thick coatings (over 1 mm) or complex structural components. These technical bottlenecks severely restrict the application of UV-cured electromagnetic shielding coatings in high-performance applications.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide an ultraviolet light-curable electromagnetic shielding coating, its preparation method, coating and its application.

[0007] This invention is implemented as follows: In a first aspect, the present invention provides an ultraviolet light-curable electromagnetic shielding coating, comprising a modified epoxy acrylate resin, a conductive filler, a diluent, and a photoinitiator.

[0008] The modified epoxy acrylate resin includes an epoxy acrylate backbone and at least one side chain unit with polyurethane structural features bonded to the epoxy acrylate backbone. The side chain unit contains at least one urethane bond with the structure –NH–COO–.

[0009] Photoinitiators include free radical photoinitiators and cationic photoinitiators.

[0010] Secondly, the present invention provides a method for preparing an electromagnetic shielding coating as described in any of the foregoing embodiments, comprising uniformly mixing a modified epoxy acrylate resin, a conductive filler, a diluent, and a photoinitiator.

[0011] Thirdly, the present invention provides an ultraviolet light-curable electromagnetic shielding coating, comprising an electromagnetic shielding coating prepared by any of the foregoing embodiments or an electromagnetic shielding coating prepared by any of the foregoing embodiments, which is then photocured.

[0012] The thickness of the electromagnetic shielding coating is 0.1~3mm; the photocuring time is 0.5~3min.

[0013] Fourthly, the present invention provides an application of the electromagnetic shielding coating as described in the foregoing embodiments in electronic devices.

[0014] The present invention has the following beneficial effects: This invention provides a UV-curable electromagnetic shielding coating, its preparation method, coating, and its application. By constructing a modified epoxy acrylate resin with a polyurethane side chain structure, the resin system achieves low viscosity and high flexibility, solving the problems of traditional epoxy acrylate coatings such as difficulty in processing under high filler loads, excessive coating thickness, and brittleness. This provides a material basis for achieving thin-layer, high-performance electromagnetic shielding coatings. Furthermore, by employing a composite system of free radical photoinitiators and cationic photoinitiators, the defects of oxygen inhibition and insufficient deep crosslinking in conventional UV curing are overcome. Especially under complex structures or thick film conditions, comprehensive and deep photocuring can still be achieved, improving the reliability and applicability of the coating. The two complement each other: the former optimizes the physical rheological properties of the coating to facilitate thin-layer forming, while the latter ensures efficient and thorough curing under thin layers and even complex structures. Together, they support a comprehensive improvement in the environmental friendliness (solvent-free), efficiency (rapid curing), functionality (good shielding effectiveness), and process adaptability (suitable for the fast pace of electronic production lines) of UV-curable electromagnetic shielding coatings. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0016] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0017] In a first aspect, the present invention provides an ultraviolet light-curable electromagnetic shielding coating, comprising a modified epoxy acrylate resin, a conductive filler, a diluent, and a photoinitiator.

[0018] The modified epoxy acrylate resin includes an epoxy acrylate backbone and at least one side chain unit with polyurethane structural features bonded to the epoxy acrylate backbone. The side chain unit contains at least one urethane bond with the structure –NH–COO–.

[0019] Side chain units with polyurethane structural characteristics were introduced into the epoxy acrylate backbone. Due to the inherent high flexibility of the polyurethane segments, this structural design significantly improves the overall flexibility of the resin. This increased flexibility helps alleviate the internal stress concentration problem that may be caused by volume shrinkage during UV curing, thereby improving the adhesion and crack resistance of the electromagnetic shielding coating to non-metallic substrates.

[0020] Furthermore, the introduction of side-chain units reduces the number of free –OH groups in the epoxy acrylate molecules, thereby weakening intermolecular forces and directly leading to a decrease in the viscosity of the modified epoxy acrylate resin. Lower viscosity facilitates subsequent mixing processes, making the coating easier to disperse uniformly. It maintains good flowability, especially in the presence of a high proportion of conductive filler, which is beneficial for forming a uniform and thin film. The thin-layer structure allows ultraviolet light to penetrate to the bottom of the coating, effectively mitigating the problem of decreased ultraviolet transmittance caused by high conductive filler content, thus improving the degree of deep crosslinking.

[0021] Therefore, by constructing a modified epoxy acrylate resin with a polyurethane side chain structure, the resin system was made more viscous and more flexible, solving the problems of traditional epoxy acrylate coatings being difficult to process under high filler loads, having excessively thick coatings, and being prone to brittleness. This provides a material basis for achieving thin-layer, high-performance electromagnetic shielding coatings.

[0022] Photoinitiators include free radical photoinitiators and cationic photoinitiators. Traditional UV-cured electromagnetic shielding coatings are prone to surface stickiness and insufficient deep crosslinking due to oxygen inhibition. This invention overcomes the defects of oxygen inhibition and insufficient deep crosslinking in conventional UV curing by using a composite system of free radical photoinitiators and cationic photoinitiators. In particular, it can achieve comprehensive and deep photocuring even under complex structures or thick film conditions, thus improving the reliability and applicability of the coating.

[0023] The free radical photoinitiator initiates the rapid free radical polymerization of acrylate monomers, providing initial strength; the cationic photoinitiator simultaneously initiates the cationic polymerization reaction, prolonging the reaction time and promoting deep and continuous crosslinking. The synergistic effect of these two mechanisms creates a dual curing mode of rapid surface setting and continuous internal deepening, significantly improving the overall crosslinking density and structural uniformity of the electromagnetic shielding coating.

[0024] By combining the two key technologies mentioned above, they complement each other. The former optimizes the physical rheological properties of the coating to facilitate thin-layer forming, while the latter ensures efficient and thorough curing in thin layers and even complex structures. Together, they support the comprehensive improvement of UV-cured electromagnetic shielding coatings in terms of environmental friendliness (solvent-free), efficiency (rapid curing), functionality (good shielding performance), and process adaptability (adapting to the fast pace of electronic production lines).

[0025] In an optional embodiment, the cationic photoinitiator includes at least one of an aromatic diazonium salt and a diaryliodomonium salt.

[0026] By employing aromatic diazonium salts and diaryliodonium salts as cationic photoinitiators, their photolysis produces protic acids, which initiate cationic polymerization reactions of monomers such as epoxy compounds or vinyl ethers. This type of cationic polymerization process does not experience oxygen inhibition and can proceed stably in an air environment, thereby ensuring that the electromagnetic shielding coating achieves complete and deep cross-linking under ultraviolet light irradiation, and improving the overall curing quality of the coating.

[0027] Furthermore, the cationic polymerization initiated by aromatic diazonium salts and diaryliodonium salts has a long active center lifetime, allowing the reaction to continue after light exposure (i.e., dark curing characteristic), which is beneficial for further cross-linking in areas where heat conduction is difficult or light penetration is limited. This characteristic effectively improves the problem of insufficient deep cross-linking caused by the reduced ultraviolet transmittance due to high conductive filler content, enabling the electromagnetic shielding coating to achieve full curing even in thicker areas or structurally complex parts.

[0028] Furthermore, using aromatic diazonium salts or diaryliodonium salts as cationic photoinitiators helps reduce volume changes during the curing process, thereby reducing internal stress accumulation and preventing coating cracking or desorption from the non-metallic casing. The low shrinkage rate also improves the mechanical properties of the electromagnetic shielding coating and its adhesion to various substrates, meeting the application requirements of electronic devices for coating stability.

[0029] Furthermore, aromatic diazonium salts and diaryliodonium salts exhibit excellent photoresponsiveness, enabling rapid polymerization reactions to be initiated under short-term (within minutes) UV irradiation, facilitating rapid film formation in conjunction with UV curing processes. This characteristic allows electromagnetic shielding coatings to adapt to the fast-paced production requirements of modern electronic assembly lines, avoiding the high energy consumption and low efficiency issues associated with the prolonged high-temperature treatment required by traditional thermosetting processes.

[0030] And / or, free radical photoinitiators include 1-hydroxycyclohexylphenyl ketone, 2,4,6 ... At least one of trimethylbenzoyl diphenoxyphosphine.

[0031] By selecting the above-mentioned free radical initiators, rapid free radical polymerization can be initiated, improving curing efficiency. At the same time, it is compatible with low-viscosity modified epoxy acrylate resin systems, ensuring uniform curing. Furthermore, the free radical initiator, in conjunction with the cationic photoinitiator, constructs a dual curing system to ensure the deep crosslinking strength of the coating.

[0032] And / or, the mass ratio of free radical photoinitiator to modified epoxy acrylate resin is 2:(15~30); the mass ratio of cationic photoinitiator to modified epoxy acrylate resin is 3:(15~30). By controlling the mass ratio of free radical photoinitiator to cationic photoinitiator within the above range, the crosslinking rate of the coating can be improved, and the crosslinking strength at various points in the coating can be guaranteed.

[0033] In an optional embodiment, the diluent includes an acrylate compound, which includes at least one of a monofunctional acrylate compound and a difunctional acrylate compound.

[0034] Monofunctional acrylate compounds include at least one of methyl methacrylate, isooctyl acrylate, butyl acrylate, and lauryl acrylate.

[0035] Bifunctional acrylate compounds include at least one of 1,6-hexanediol diacrylate and tripropylene glycol diacrylate. Bifunctional acrylate compounds can be synthesized using ethylene glycol and polyethylene glycol as reactants, or they can be purchased directly from commercial sources.

[0036] Currently, in the method of preparing electromagnetic shielding coatings using thermosetting, it is unavoidable to add organic solvents to the electromagnetic shielding coating to assist in the dispersion of various raw materials. Then, through heating and curing, the organic solvents evaporate, which leads to the release of a large amount of volatile organic compounds (VOCs) during the curing process. This not only pollutes the environment but also endangers the health of construction workers. In addition, the curing cycle is as long as several hours, resulting in low production efficiency.

[0037] This invention uses the aforementioned acrylate compounds as diluents, which can effectively reduce the viscosity of the modified epoxy acrylate resin and conductive filler mixture system without introducing volatile organic solvents, improve the material flowability and dispersion uniformity, and facilitate the implementation of subsequent coating processes, thereby realizing the preparation of electromagnetic shielding thin coatings.

[0038] Furthermore, acrylate compounds can participate in the photopolymerization process. The free radical photoinitiators 1-hydroxycyclohexylphenyl ketone and 2,4,6-trimethylbenzoyldiphenoxyphosphorus can effectively initiate the free radical polymerization of the acrylate double bonds in the diluent, allowing the diluent to be completely integrated into the three-dimensional cross-linked network and preventing the release of organic matter. This achieves zero VOC emissions, meets environmental protection requirements, and solves the environmental pollution and health hazards caused by the use of organic solvents in existing technologies.

[0039] Monofunctional acrylate compounds primarily provide a diluting effect, reducing the system viscosity while moderately participating in crosslinking; while difunctional acrylate compounds, containing two polymerizable double bonds, can significantly increase the crosslinking density, enhancing the mechanical strength and heat resistance of the coating. In some preferred embodiments, combining the two types of acrylate compounds allows for flexible adjustment of the coating's rheological properties, reaction rate, and final coating performance according to actual application requirements, meeting the comprehensive performance requirements of electronic devices.

[0040] In an optional embodiment, the conductive filler includes at least one of silver, silver-coated copper, silver-coated aluminum, nickel-coated graphite, nickel, graphite, and carbon nanotubes.

[0041] In an optional embodiment, the product comprises, by weight, 15-30 parts modified epoxy acrylate resin, 45-55 parts conductive filler, 15-25 parts diluent and 2-8 parts photoinitiator.

[0042] This invention modifies epoxy acrylate resin and, through the selection and compounding of diluents and photoinitiators, reduces the viscosity of the system, which improves the system's capacity to support conductive fillers. This allows the invention to maintain good coating performance even with the addition of 45-55 parts of conductive filler, achieving excellent electromagnetic shielding effects. Furthermore, the electromagnetic shielding coating provided by this invention can be thin-coated to prepare electromagnetic shielding films, thus facilitating rapid photocuring and improving deep cross-linking strength, avoiding surface stickiness and other problems.

[0043] It's important to note that increasing the amount of conductive filler does not simply mean adding more. Increasing the amount of conductive filler leads to a sharp increase in the viscosity of the resin system, making it difficult to stir and disperse, resulting in poor flowability and uneven coating, excessively thick coatings, and filler agglomeration. This leads to inconsistent shielding performance throughout the coating. Furthermore, increased conductive filler content hinders UV light penetration, resulting in insufficient deep curing capability. Therefore, traditional UV-cured electromagnetic shielding coatings struggle to achieve a balance between high conductive filler content, high performance, and manufacturability.

[0044] This invention does not blindly increase the amount of conductive filler, but solves the key technical obstacles caused by high filler through systematic formulation and structural design. As a result, the electromagnetic shielding coating provided by this invention can still stably produce high-quality coatings with a relatively high proportion of conductive filler, such as 45 to 55 parts.

[0045] Secondly, the present invention provides a method for preparing an electromagnetic shielding coating as described in any of the foregoing embodiments, comprising uniformly mixing a modified epoxy acrylate resin, a conductive filler, a diluent, and a photoinitiator.

[0046] In an optional embodiment, the method for preparing the electromagnetic shielding coating includes: stirring and mixing a diluent and a photoinitiator to obtain a mixed additive; adding conductive filler to the mixed additive and stirring and mixing to obtain a mixed conductive slurry; adding modified epoxy acrylate resin to the mixed conductive slurry and stirring and mixing evenly, followed by degassing treatment.

[0047] First, the diluent and photoinitiator are mixed to form a mixed additive, ensuring the photoinitiator is fully dissolved and dispersed in the low-viscosity diluent system. Since the diluent is an acrylate compound, it has good compatibility with the photoinitiator. This premixing process prevents uneven dispersion or localized precipitation of the photoinitiator in the later high-viscosity system, thus ensuring its consistent distribution throughout the coating system and improving the uniformity of initiation and reaction efficiency during curing.

[0048] Therefore, in an optional embodiment, the mixing parameters of the diluent and the photoinitiator include: a stirring speed of 800~1200 r / min and a stirring time of 1~2 h, to ensure that they are mixed evenly.

[0049] Based on the obtained mixed additives, conductive fillers are added and stirred to form a mixed conductive slurry. At this point, the system uses a diluent as the main medium, resulting in low viscosity, which is beneficial for the efficient shear dispersion of conductive fillers (such as silver, nickel-coated graphite, carbon nanotubes, etc.). This sequential design ensures that the conductive fillers are preferentially wetted and coated by the liquid diluent containing photoinitiators, reducing direct contact between particles, inhibiting agglomeration, and improving the dispersion stability and uniformity of the conductive fillers in the system. This provides the material basis for the formation of a continuous conductive network in the final electromagnetic shielding coating.

[0050] Therefore, in an optional embodiment, the mixing parameters for the mixing additives and conductive fillers include: a stirring speed of 1000~1500 r / min and a stirring time of 1~2 h, to ensure uniform mixing.

[0051] Modified epoxy acrylate resins contain polyurethane structural side chain units formed by isocyanate modification. To avoid prolonged high shear or localized high temperatures affecting the structure of the modified epoxy acrylate resin, it is added last during the raw material mixing process. Adding it earlier and stirring it at high speed with conductive fillers may cause molecular chain damage or pre-reaction risks due to frictional heat or mechanical stress, thus helping to maintain its chemical structural stability and functional properties.

[0052] Therefore, in an optional embodiment, the mixing parameters for the conductive paste and the modified epoxy acrylate resin include: a stirring speed of 800~1200 r / min and a stirring time of 0.5~1 h, to ensure uniform mixing.

[0053] In an optional embodiment, to ensure system stability, the system temperature is maintained at 20~30°C throughout the mixing process of the modified epoxy acrylate resin, conductive filler, diluent and photoinitiator.

[0054] Preferably, the degassing method can be at least one of vacuum degassing, centrifugal degassing, and ultrasonic degassing; the degassing time is 2 to 10 minutes.

[0055] In an optional embodiment, the method for preparing the modified epoxy acrylate resin provided by the present invention includes: modifying the epoxy acrylate resin with isocyanate compounds, and generating a polyurethane modified structure by in-situ reaction on the epoxy acrylate resin.

[0056] The reaction of isocyanate compounds with the hydroxyl groups (–OH) in epoxy acrylates to form urethane bonds (–NH–COO–) reduces the number of free –OH groups in the epoxy acrylate molecule, thereby weakening intermolecular forces and directly leading to a decrease in the viscosity of the modified epoxy acrylate resin. Lower viscosity facilitates subsequent mixing processes, making the coating easier to disperse uniformly, and maintaining good flowability, especially in the presence of a high proportion of conductive fillers.

[0057] Preferably, the amount of isocyanate compound added is 10 to 50 wt% of the epoxy acrylate resin.

[0058] By controlling the amount of isocyanate compounds added within the aforementioned range, sufficient –NCO groups can be provided to react chemically with the hydroxyl groups (-OH) in the epoxy acrylate molecules, thus effectively modifying the resin. The –OH groups in the epoxy acrylate molecules are appropriately capped, ensuring sufficient reaction while avoiding the risk of gelation due to excessive cross-linking. The resulting modified epoxy acrylate resin exhibits lower viscosity, which is beneficial for subsequent mixing with conductive fillers, diluents, and other components, improving the overall flowability and dispersion uniformity of the coating, and meeting the application performance requirements of the scraping process.

[0059] The flexible segments introduced by 10–50 wt% isocyanate compounds are sufficient to significantly toughen the resin backbone without causing phase separation or a decrease in mechanical properties due to excessive introduction. This increased flexibility helps alleviate internal stress caused by volume shrinkage during UV curing, improves the adhesion of the electromagnetic shielding coating to non-metallic substrates, and reduces the tendency to crack.

[0060] In optional embodiments, the isocyanate compounds include diisocyanate compounds; the diisocyanate compounds include at least one selected from 4,4'-diphenylmethane diisocyanate, toluene diisocyanate, trimethylhexane diisocyanate, and isophorone diisocyanate. The inventors have found that isocyanate compounds with bis-NCO groups can produce better modification effects on epoxy acrylate resins, resulting in modified epoxy acrylate resins with higher flexibility; epoxy acrylate resins modified with poly-NCO group isocyanate compounds have poor toughening effects, requiring a reduction in the amount of conductive filler added to ensure the shielding performance of the coating.

[0061] In an optional embodiment, the epoxy acrylate resin includes at least one of bisphenol A epoxy acrylate, phenolic epoxy acrylate, and epoxidized oil acrylate.

[0062] In an optional embodiment, the reaction temperature of the isocyanate compound with the epoxy acrylate resin is 60~80°C, and the reaction time is 2~4h.

[0063] By setting appropriate thermal reaction conditions, the sufficiency, controllability, and safety of the modification reaction were ensured, and a modified epoxy acrylate resin with low viscosity, high flexibility, and good reaction stability was successfully obtained, providing a key material guarantee for the preparation of high-performance UV-curable electromagnetic shielding coatings.

[0064] Thirdly, the present invention provides an ultraviolet light-curable electromagnetic shielding coating, comprising an electromagnetic shielding coating prepared by any of the foregoing embodiments or an electromagnetic shielding coating prepared by any of the foregoing embodiments, which is then photocured.

[0065] The thickness of the electromagnetic shielding coating is 0.1~3mm; the photocuring time of the electromagnetic shielding coating under ultraviolet light is 0.5~3min.

[0066] The electromagnetic shielding coating provided by this invention can quickly prepare electromagnetic shielding coatings with a relatively low thickness, realizing rapid, energy-saving, and environmentally friendly curing of electromagnetic shielding coatings. At the same time, it solves the technical problems commonly encountered in high-conductivity filler systems, such as insufficient deep cross-linking, poor process adaptability, and high cost.

[0067] Fourthly, the present invention provides an application of the electromagnetic shielding coating as described in the foregoing embodiments in electronic devices.

[0068] Example 1 This embodiment provides an ultraviolet-curable electromagnetic shielding coating, which, by weight, comprises 25 parts modified epoxy acrylate resin, 50 parts silver-coated copper, 20 parts isooctyl acrylate, 2 parts 1173 photoinitiator (free radical type) and 3 parts TPO-L photoinitiator (cationic type).

[0069] The preparation method of the modified epoxy acrylate resin includes: mixing 20 parts by weight of bisphenol A epoxy acrylate resin with 5 parts by weight of toluene diisocyanate, and reacting at 60~80℃ for 2~4h to obtain the modified epoxy acrylate resin.

[0070] This embodiment also provides a method for preparing an ultraviolet-cured electromagnetic shielding coating, comprising the following steps: Maintaining the system temperature at 30℃, the diluent and photoinitiator were stirred at 1200 r / min for 2 h to obtain a mixed additive. Conductive filler was added to the mixed additive, and the mixture was stirred at 1500 r / min for 2 h to obtain a mixed conductive slurry. Modified epoxy acrylate resin was added to the mixed conductive slurry, and the mixture was stirred at 1200 r / min for 1 h. The resulting mixture was then vacuum degassed for 10 min. The electromagnetic shielding coating provided in this embodiment has a strength of 80 mW / cm². 2 An electromagnetic shielding coating with a thickness of 0.15 mm can be obtained by curing it under ultraviolet light with a wavelength of 365 nm for 2 minutes.

[0071] Example 2 This embodiment provides an ultraviolet-curable electromagnetic shielding coating, which, by weight, comprises 20 parts modified epoxy acrylate resin, 55 parts silver-coated copper, 20 parts isooctyl acrylate, 2 parts 184 photoinitiator (free radical type) and 3 parts TPO-L photoinitiator (cationic type).

[0072] The preparation method of the modified epoxy acrylate resin includes: mixing 12 parts by weight of bisphenol A epoxy acrylate resin with 3 parts by weight of toluene diisocyanate, and reacting at 60~80℃ for 2~4h to obtain the modified epoxy acrylate resin.

[0073] The preparation method of the electromagnetic shielding coating provided in this embodiment is the same as that in Example 1. The obtained electromagnetic shielding coating has a strength of 100 mW / cm. 2 An electromagnetic shielding coating with a thickness of 0.12 mm can be obtained by curing it under ultraviolet light with a wavelength of 395 nm for 1.5 min.

[0074] Example 3 This embodiment provides an ultraviolet-curable electromagnetic shielding coating, which, by weight, comprises 30 parts modified epoxy acrylate resin, 45 parts silver-coated copper, 20 parts isooctyl acrylate, 2 parts 1173 photoinitiator (free radical type) and 3 parts TPO-L photoinitiator (cationic type).

[0075] The preparation method of the modified epoxy acrylate resin includes: mixing 25 parts by weight of bisphenol A epoxy acrylate resin with 5 parts by weight of toluene diisocyanate, and reacting at 60~80℃ for 2~4h to obtain the modified epoxy acrylate resin.

[0076] The preparation method of the electromagnetic shielding coating provided in this embodiment is the same as that in Example 1. The obtained electromagnetic shielding coating has a strength of 60 mW / cm. 2 An electromagnetic shielding coating with a thickness of 0.18 mm can be obtained by curing it under ultraviolet light with a wavelength of 365 nm for 3 minutes.

[0077] Comparative Example 1 This comparative example provides an electromagnetic shielding coating, which, by weight, comprises 20 parts of bisphenol A epoxy acrylate resin, 50 parts of silver-coated copper and 30 parts of ethyl acetate; the preparation method of the electromagnetic shielding coating is as described in Example 1.

[0078] Since ethyl acetate is an organic solvent in the electromagnetic shielding coating provided in this comparative example, the coating is suitable for thermosetting processes and needs to be cured at 120°C for 30 minutes. During the thermosetting process, the organic solvent will evaporate, which is not environmentally friendly.

[0079] Comparative Example 2 This comparative example provides an electromagnetic shielding coating, which, by weight, comprises 45 parts of bisphenol A epoxy acrylate resin, 50 parts of silver-coated copper, 2 parts of 1173 photoinitiator (free radical type) and 3 parts of TPO-L photoinitiator (cationic type); the preparation method of the electromagnetic shielding coating is as described in Example 1.

[0080] The electromagnetic shielding coating provided in this comparative example did not modify the epoxy acrylate resin, nor did it contain any diluent. The electromagnetic shielding coating system has a high viscosity, the prepared coating thickness is greater than 1 mm, and there is a problem of insufficient deep curing.

[0081] Comparative Example 3 This comparative example provides an electromagnetic shielding coating, which differs from Example 1 only in that unmodified bisphenol A epoxy acrylate resin is used instead of modified epoxy acrylate resin; the preparation method of the electromagnetic shielding coating is the same as in Example 1.

[0082] The electromagnetic shielding coating provided in this comparative example has the following problems: the system viscosity of the electromagnetic shielding coating is high, the prepared coating thickness is greater than 1 mm, and there are problems with insufficient deep curing, poor coating adhesion, and low shielding effectiveness.

[0083] Comparative Example 4 This comparative example provides an electromagnetic shielding coating, which differs from Example 1 only in that ethyl acetate is used instead of isooctyl acrylate; the preparation method of the electromagnetic shielding coating is the same as in Example 1.

[0084] The electromagnetic shielding coating provided in this comparative example has the problem that solvent evaporation leads to increased coating porosity and large fluctuations in shielding effectiveness.

[0085] Comparative Example 5 This comparative example provides an electromagnetic shielding coating, which differs from Example 1 only in that triphenyl thiophosphate triisocyanate is used instead of toluene diisocyanate; the preparation method of the electromagnetic shielding coating is the same as in Example 1.

[0086] The triisocyanate triphenyl thiophosphate used in this comparative example is a polymethylene polyphenyl polyisocyanate. The resulting electromagnetic shielding coating lacks sufficient flexible chain segment regulation, which leads to increased coating brittleness. After curing, the coating may develop microcracks due to excessive crosslinking density, affecting the stability of electromagnetic shielding.

[0087] Comparative Example 6 This comparative example provides an electromagnetic shielding coating, which differs from Example 1 only in that only 2 parts of free radical initiator (1173) are added, and no cationic initiator is added; the preparation method of the electromagnetic shielding coating is the same as in Example 1.

[0088] The electromagnetic shielding coating provided in this comparative example has a significantly reduced deep curing rate. A 3mm thick coating requires 8 minutes to cure (compared to only 2 minutes in Example 1), and uncured areas appear at the bottom of the coating, resulting in a problem with the gradient distribution of shielding effectiveness.

[0089] Comparative Example 7 This comparative example provides an electromagnetic shielding coating, which differs from Example 1 only in that: 20 parts by weight of bisphenol A epoxy acrylate resin are mixed with 1 part by weight of toluene diisocyanate and reacted at 60~80°C for 2~4 hours to obtain modified epoxy acrylate resin; the preparation method of the electromagnetic shielding coating is the same as in Example 1.

[0090] The electromagnetic shielding coating provided in this comparative example still has a relatively high system viscosity (1600 mPa·s), which limits the amount of conductive filler (only 45 parts), and the shielding effectiveness of the coating drops to 38 dB (55 dB in Example 1). In the flexibility test, the coating cracked after being bent 5 times.

[0091] Experimental Example 1 The performance of the UV-cured electromagnetic shielding coatings and the prepared coatings provided in Examples 1-3 and Comparative Examples 1-7 were tested, and the results are shown in Table 1.

[0092] In Table 1, viscosity was measured using a rotational viscometer (Brookfield DV-II+) at 25°C.

[0093] Shielding effectiveness: Tested in the 1-18 GHz frequency band according to AST D4935-18 standard, measured using a vector network analyzer (VNA).

[0094] Adhesion: The adhesion between the coating and the substrate was tested using the cross-cut test according to AST D3359-17 standard.

[0095] Table 1 Performance of Electromagnetic Shielding Coatings / Coatings

[0096] As shown in Table 1, the modified epoxy acrylate resin in the UV-curable electromagnetic shielding coating provided in this embodiment of the invention has a low viscosity, thus allowing for an increase in the amount of conductive filler. This results in a high shielding efficiency and excellent electromagnetic shielding performance. Furthermore, the electromagnetic shielding coating provided in this embodiment of the invention has a fast curing speed and no organic solvent evaporation, making its production process greener, more efficient, and safer. In addition, the energy used for UV curing is electricity, eliminating the need for fuel oil or gas, which helps reduce carbon emissions.

[0097] Comparative Example 1 uses a thermosetting process, which has a long curing time, low curing efficiency, and the evaporation of organic solvents during curing, which is detrimental to environmental protection. Comparative Example 2 did not add a diluent, and the epoxy acrylate resin was unmodified, resulting in a thicker coating and poor deep curing. Comparative Example 3, due to the unmodified epoxy acrylate resin, suffers from a rigid resin structure that increases the coating viscosity, resulting in a coating thickness of 1.1 mm and insufficient deep curing. In Comparative Example 4, the evaporation of organic solvents easily forms micropores, affecting coating uniformity and causing fluctuations in shielding effectiveness. In Comparative Example 5, the excessively high crosslinking density of the polyisocyanate increases the brittleness of the coating. Comparative Example 6 uses only a free radical initiator (1173), and the lack of a cationic initiator reduces the deep curing rate, leading to a gradient distribution of shielding effectiveness in the uncured area at the bottom of the coating. In Comparative Example 7, with an isocyanate addition of 4%, the viscosity is still too high, limiting the amount of conductive filler.

[0098] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A UV-curable electromagnetic shielding coating, characterized in that, It includes modified epoxy acrylate resin, conductive filler, diluent and photoinitiator; The modified epoxy acrylate resin comprises an epoxy acrylate backbone and at least one side chain unit having polyurethane structural features bonded to the epoxy acrylate backbone, wherein the side chain unit contains at least one urethane bond with the structure –NH–COO–. The photoinitiator includes free radical photoinitiators and cationic photoinitiators.

2. The electromagnetic shielding coating according to claim 1, characterized in that, By weight, it comprises 15-30 parts of the modified epoxy acrylate resin, 45-55 parts of the conductive filler, 15-25 parts of the diluent, and 2-8 parts of the photoinitiator.

3. The electromagnetic shielding coating according to claim 1, characterized in that, The cationic photoinitiator includes at least one of aromatic diazonium salt and diaryliodonium salt; And / or, the free radical photoinitiator includes at least one of 1-hydroxycyclohexylphenyl ketone and 2,4,6-trimethylbenzoyldiphenoxyphosphine; And / or, the mass ratio of the free radical photoinitiator to the modified epoxy acrylate resin is 2:(15~30); the mass ratio of the cationic photoinitiator to the modified epoxy acrylate resin is 3:(15~30).

4. The electromagnetic shielding coating according to claim 1, characterized in that, The diluent includes acrylate compounds, which include at least one of monofunctional acrylate compounds and difunctional acrylate compounds; The monofunctional acrylate compounds include at least one of methyl methacrylate, isooctyl acrylate, butyl acrylate, and lauryl acrylate; The bifunctional acrylate compounds include at least one of 1,6-hexanediol diacrylate and tripropylene glycol diacrylate.

5. The electromagnetic shielding coating according to claim 1, characterized in that, The conductive filler includes at least one of silver, silver-coated copper, silver-coated aluminum, nickel-coated graphite, nickel, graphite, and carbon nanotubes.

6. A method for preparing an electromagnetic shielding coating as described in any one of claims 1 to 5, characterized in that, This includes mixing the modified epoxy acrylate resin, the conductive filler, the diluent, and the photoinitiator evenly.

7. The preparation method according to claim 6, characterized in that, The method for preparing the modified epoxy acrylate resin includes: modifying the epoxy acrylate resin with isocyanate compounds, and generating a polyurethane modified structure by in-situ reaction on the epoxy acrylate resin. The preparation process of the modified epoxy acrylate resin satisfies at least one of the following characteristics: Feature 1: The amount of the isocyanate compound added is 10-50 wt% of the mass of the epoxy acrylate resin; Feature 2: The isocyanate compound includes diisocyanate compounds; the diisocyanate compound includes at least one of 4,4'-diphenylmethane diisocyanate, toluene diisocyanate, trimethylhexane diisocyanate and isophorone diisocyanate; Feature 3: The epoxy acrylate resin includes at least one of bisphenol A epoxy acrylate, phenolic epoxy acrylate, and epoxidized oil acrylate; Feature 4: The reaction temperature of the isocyanate compound with the epoxy acrylate resin is 60~80℃, and the reaction time is 2~4h.

8. The preparation method according to claim 6, characterized in that, include: The diluent and the photoinitiator are stirred and mixed to obtain a mixed additive; The conductive filler is added to the mixing agent and stirred to obtain a mixed conductive slurry; The modified epoxy acrylate resin is added to the mixed conductive slurry and stirred until uniformly mixed, followed by degassing treatment. And the preparation process satisfies at least one of the following characteristics: Feature 5: The mixing parameters of the diluent and the photoinitiator include: stirring speed of 800~1200 r / min and stirring time of 1~2 h; Feature 6: The mixing parameters of the mixing additive and the conductive filler include: stirring speed of 1000~1500 r / min and stirring time of 1~2 h; Feature 7: The mixing parameters of the mixed conductive paste and the modified epoxy acrylate resin include: stirring speed of 800~1200 r / min and stirring time of 0.5~1 h; Feature 8: The temperature during the mixing process of the modified epoxy acrylate resin, the conductive filler, the diluent and the photoinitiator is 20~30℃; Feature 9: The degassing method includes at least one of vacuum degassing, centrifugal degassing and ultrasonic degassing; the degassing time is 2~10 min.

9. An ultraviolet-cured electromagnetic shielding coating, characterized in that, The electromagnetic shielding coating is formed by photocuring the electromagnetic shielding coating prepared by any one of claims 1 to 5 or by any one of claims 6 to 8. The thickness of the electromagnetic shielding coating is 0.1~3mm; the photocuring time is 0.5~3min.

10. The application of the electromagnetic shielding coating as described in claim 9 in electronic devices.

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