Electromagnetic shielding glue and preparation method thereof

Abstract

The invention relates to the technical field of conductive shielding materials, in particular to electromagnetic shielding glue and a preparation method thereof. The conductive adhesive comprises the following components in percentage by weight: 20-40% of silica gel, 0.2-0.5% of a catalyst, 0.1-1% of an inhibitor, 0.2-2% of an anti-aging agent, 0.2-2% of a coupling agent, 5-30% of an organic solvent and the balance of conductive powder, by adding the specific anti-aging agent, the filling amount and the compression deformation performance of the conductive powder in the material can be balanced; by adding the conductive powder with a specific structure, the shielding effectiveness of the material can be improved; through pretreatment of the conductive powder, the content of the conductive powder in the electromagnetic shielding glue can reach 50-70wt%, and meanwhile, the permanent compression deformation (high temperature of 150 DEG C for 22 hours) of the material is less than or equal to 35%.

Description

Technical Field

[0001] This invention relates to the field of conductive shielding materials technology, specifically to an electromagnetic shielding adhesive and its preparation method. Background Technology

[0002] As electronic devices become increasingly miniaturized, higher frequency, and more integrated, electromagnetic interference (EMI) problems are becoming more prominent. Electromagnetic shielding adhesives, as core materials that combine conductive shielding and structural bonding functions, are seeing a continuous increase in demand in fields such as 5G communications, automotive electronics, and precision instruments. Currently, electromagnetic shielding materials that focus on coating functions or high-shielding-efficiency composite systems all suffer from problems such as difficulty in balancing the amount of conductive powder filling with the material's mechanical properties and aging resistance, and insufficient formulation design suitable for FIP processes. Therefore, there is an urgent need to develop an electromagnetic shielding adhesive that combines high conductive powder filling, low compression deformation, excellent aging resistance, and good process compatibility.

[0003] Chinese invention patent CN102276988B discloses a single-component Ni-C filled FIP heat-cured high-conductivity silicone rubber, which achieves conductivity through a composite filler of nickel-coated graphite powder and nickel-coated carbon fiber. While suitable for applications with small and complex shells, the balance between mechanical properties and flowability is limited at high filler levels, and the vulcanization process is not adaptable enough. Chinese invention patent CN102516929B proposes a low-hardness dispensing conductive shielding adhesive, using metal-based conductive fillers and crosslinking agents containing silicon-hydrogen bonds. Although it has lower hardness and better adhesion, the viscosity of the system tends to rise sharply at high filler levels, making processing difficult, and aging resistance is not adequately considered. Chinese invention patent application CN111718672A introduces a high-performance organosilicon conductive shielding adhesive that incorporates single-walled carbon nanotubes to improve conductivity, achieving a shielding effectiveness of over 120dB, but the amount of conductive filler is as high as 300-500g. The high mass of conductive powder increases the difficulty of controlling compression deformation and leads to poor long-term stability under complex operating conditions. While the two-component conductive silicone in Chinese invention patent application CN112898945A achieves a shielding effectiveness of up to 138dB, its complex formulation relies on the synergy of nickel-coated graphite / carbon fiber and composite fillers, and its shielding effectiveness significantly degrades after high humidity and high / low temperature cycling. In summary, existing shielding adhesives generally suffer from the difficulty of balancing conductive powder filling volume with mechanical properties and aging resistance. Some formulations are not well-suited to the flowability and molding precision of the FIP process, resulting in poor shielding effectiveness stability under complex aging environments. Therefore, there is an urgent need to develop an electromagnetic shielding adhesive that combines high conductive powder filling volume, low compression deformation, excellent aging resistance, and good process adaptability to meet the needs of high-end electronic equipment. Summary of the Invention

[0004] The first aspect of this invention provides an electromagnetic shielding adhesive, comprising, by weight percentage: 20-40% silicone, 0.2-0.5% catalyst, 0.1-1% inhibitor, 0.2-2% anti-aging agent, 0.2-2% coupling agent, 5-30% organic solvent, and conductive powder to make up the balance; wherein the anti-aging agent comprises one or more of cerium oxide, iron oxide, titanium oxide, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate.

[0005] The conductive powder content in the electromagnetic shielding adhesive is 50-70 wt%.

[0006] The conductive powder is a three-layer coated conductive composite powder, which includes: a core, a conductive and corrosion-resistant layer (middle plating) coated on the core, and an outermost highly conductive layer.

[0007] The core is composed of a material with low density and suitable as a coating carrier. Specific examples of materials suitable for the core in this disclosure include, but are not limited to, at least one of the following: a density of 2.5 g / cm³. 3 Glass with a density of less than 2.5 g / cm³ 3 The hollow glass microspheres have a density of 2.3 g / cm³. 3 The graphite has a density of 2.1 g / cm³. 3 Expanded graphite.

[0008] The intermediate coating material includes, but is not limited to, at least one of the following: nickel, nickel-based superalloys, nickel-chromium alloys, nickel-molybdenum alloys, nickel-iron alloys, aluminum, and aluminum alloys.

[0009] The coating method for the intermediate coating includes, but is not limited to, at least one of the following: electroplating, chemical deposition (CVD), and electroless plating.

[0010] The material of the outermost highly conductive layer includes, but is not limited to, gold, silver, copper and their alloys, and the coating method of the outermost highly conductive layer includes, but is not limited to, electroplating, chemical deposition (CVD) and electroless plating.

[0011] This invention reveals that the three-layer coated conductive composite powder significantly improves the aging performance of electromagnetic shielding adhesive through the synergistic effect of each layer. The core provides stable skeletal support for the powder, inhibiting structural collapse under aging environments such as high temperature and humidity, and high and low temperature cycling, thus preventing the breakage of conductive pathways due to powder deformation. The middle conductive and corrosion-resistant layer possesses excellent corrosion and oxidation resistance, isolating the core from aging factors such as humidity and oxygen, preventing damage to the conductive network by core oxidation decomposition products, and buffering thermal stress generated by high and low temperature cycling, reducing the risk of interface cracking between the powder and the silicone matrix. The outermost highly conductive layer not only ensures the high conductivity of the powder, but its dense metal coating further blocks the penetration of aging media, reducing aging reactions such as oxidation and sulfidation on the surface of the conductive powder, and maintaining the integrity of the conductive pathways. Meanwhile, the three-layer coating structure optimizes the powder interface characteristics and, together with the interface bonding layer formed by the pretreatment of conductive powder, enhances the bonding force between the powder and the silicone matrix, preventing powder agglomeration or peeling during aging. This structure also complements the anti-aging agent in the formulation. The anti-aging agent captures free radicals generated by the oxidation of the silicone matrix and terminates the degradation chain reaction, while the three-layer coated powder resists the erosion of aging factors from the conductive phase level. Together, they reduce the decay of shielding effectiveness during aging, ultimately improving the aging performance of the material.

[0012] The conductive powder may also be selected from one or more of the following: silver-coated aluminum powder, silver-coated copper powder, silver-coated glass powder, nickel-coated graphite powder, and nickel-coated aluminum powder.

[0013] The conductive powder undergoes the following pretreatment steps: the conductive powder is mixed evenly with surface modifier and water, a pH adjuster is added to adjust the pH to 4-6, and then it is dried.

[0014] The surface modifier includes one or more of γ-glycidoxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, and propyl 3-trimethoxysilane acrylate.

[0015] This invention balances the filling amount and compression deformation performance of conductive powder by adding specific anti-aging agents and pre-treating conductive powder. On the one hand, during the pretreatment of conductive powder, surface modifiers can chemically bond with the hydroxyl groups on the surface of the conductive powder through the functional groups at both ends of their molecules, and bind with the silicon-oxygen bonds of the silicone matrix at the other end. This creates a stable interfacial bonding layer between the powder and the matrix, effectively improving the problem of powder agglomeration during high-powder filling. Traditional untreated powders have poor interfacial compatibility, and agglomerates easily form stress concentration points inside the compound. During compression, they are prone to interfacial peeling or local structural damage, leading to increased compression deformation. However, after pretreatment, the powder can be uniformly dispersed in the matrix, allowing stress to be transmitted along the continuous matrix-powder interface, reducing irreversible deformation. On the other hand, specific anti-aging agents can capture free radicals generated in the silicone matrix during processing and long-term use, terminating the oxidative degradation chain reaction and preventing the matrix elastic network from breaking or becoming over-crosslinked due to oxidation. This provides sufficient elastic support for the high-powder filling system, thus forming a synergy with powder pretreatment. This ensures electromagnetic shielding effectiveness through high-powder filling and suppresses compression deformation through interface optimization and matrix protection, ultimately achieving a performance balance between the two.

[0016] The weight ratio of the conductive powder to the silicone is (1.5-2.5):1.

[0017] Optionally, the weight ratio of the conductive powder to the silicone is (1.7-2.2):1.

[0018] The anti-aging agent is present in the electromagnetic shielding adhesive at a content of 0.2-1 wt%.

[0019] Optionally, the anti-aging agent is present in the electromagnetic shielding adhesive at a content of 0.2-0.8 wt%.

[0020] The silicone rubber includes one or more of liquid silicone rubber, hydrogen-containing silicone oil, vinyl MQ resin, low-phenyl silicone oil, and methyl vinyl silicone rubber.

[0021] Optionally, the silicone may be composed of polydimethylsiloxane and silica.

[0022] The coupling agent includes one or more of γ-glycidoxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, and propyl 3-trimethoxysilane acrylate.

[0023] The organic solvent includes one or more of isohexane, cyclohexane, octane, dodecane, tridecane, tetradecane, petroleum ether, halogenated hydrocarbons, and dimethyl silicone oil with a viscosity of 20-80 cp at 25°C.

[0024] The catalyst includes a perkin complex catalyst.

[0025] The inhibitors include one or more of 2-methyl-3-butyn-2-ol, 1-ethynyl-1-cyclohexanol, 3,5-dimethyl-1-hexyn-3-ol, 2-phenyl-3-butyn-2-ol, and 1-hydroxy-1-cyclohexylacetylene.

[0026] The second aspect of the present invention provides a method for preparing an electromagnetic shielding adhesive, comprising the following steps: adding silicone, inhibitor, catalyst, coupling agent and anti-aging agent to an organic solvent and stirring evenly to obtain a mixture; adding conductive powder to the mixture and stirring evenly; and performing vacuum treatment after stirring to obtain the electromagnetic shielding adhesive.

[0027] Beneficial effects 1. This invention balances the amount of conductive powder filling and the compressive deformation performance of the material by adding specific anti-aging agents and pretreating the conductive powder.

[0028] 2. The three-layer coated conductive composite powder of the present invention significantly improves the aging performance of electromagnetic shielding adhesive through the synergistic effect of each layer structure.

[0029] 3. Through the pretreatment of conductive powder, the present invention can make the content of conductive powder in electromagnetic shielding adhesive reach 50-70wt%, while the permanent compression deformation (high temperature 150℃ 22h) of the material is ≤35%.

[0030] 4. By using a three-layer coated conductive composite powder, the material can maintain excellent shielding performance in high-temperature environments.

[0031] 5. By optimizing the silicone matrix formulation, this invention enables the adhesive to meet the requirements of field-applied in-situ (FIP) molding processes. Detailed Implementation

[0032] Examples 1-7 and Comparative Examples 1-9 An electromagnetic shielding adhesive, with components listed in Tables 1 and 2 by weight percentage, where blank areas indicate no additives. Table 1

[0033] Table 2

[0034] The conductive powder is prepared as follows: 100μm pure carbon powder is ultrasonically cleaned alternately with ethanol and deionized water to remove surface oil and impurities, and then thoroughly dried in a 70℃ oven for 120 min. The purified carbon powder is placed in a strong oxidizing solution (a mixture of concentrated nitric acid and concentrated sulfuric acid at a volume ratio of 1:6) for roughening treatment. After mechanical stirring for 30 minutes in a 40℃ water bath, the carbon powder is repeatedly washed with deionized water until neutral, and then thoroughly dried in an 80℃ oven for 90 min. The roughened carbon powder is then immersed in a 20 g / L stannous chloride hydrochloric acid solution (hydrochloric acid concentration 2.5 mol / L) for sensitization treatment. After mechanical stirring for 30 minutes at room temperature, the carbon powder is repeatedly washed with deionized water until neutral, and then thoroughly dried in an 80℃ oven for 90 min. The sensitized carbon powder was then immersed in a 1.0 g / L palladium chloride dilute hydrochloric acid solution (hydrochloric acid concentration 0.8 mol / L) for activation treatment. The activated carbon powder was then immersed in a pre-prepared electroless nickel plating solution (40 g / L nickel sulfate, 30 g / L sodium hypophosphite, 30 g / L sodium citrate, 20 g / L boric acid, 5 mg / L potassium iodate, solvent: water). The pH of the plating solution was adjusted to 10.0 with ammonia. The system was stirred and reacted in a water bath at 80℃ for 60 min, and then dried at 80℃ for 120 min to obtain C@Ni composite powder. The C@Ni composite powder was then immersed in a pre-prepared chemical silver plating solution (40 g / L silver nitrate, 7 g / L ammonia, 50 g / L glucose solution, 5 g / L dimethylamine borane, with water as the solvent). The system was stirred and reacted in a water bath at 40°C for 60 min, and then dried at 70°C for 100 min to finally obtain a conductive powder with carbon as the core, nickel as the inner layer, and silver as the outermost layer.

[0035] The conductive powder described in Examples 1-5 underwent the following pretreatment steps: 120g of conductive powder and 3g of coupling agent (γ-glycidyl etheroxypropyltrimethoxysilane) and 150g of purified water were added to a three-necked flask. The pH was adjusted to 5 by adding glacial acetic acid. The mixture was mechanically stirred at 50°C for 30 minutes to ensure that the coupling agent was fully adsorbed and bonded to the surface of the conductive powder. After the solid and liquid separated into layers, the supernatant was discarded, and the mixture was washed twice with anhydrous ethanol. After discarding the supernatant, the mixture was filtered. The solid obtained by filtration was dried in an oven at 90°C for 1.5 hours to obtain the pretreated conductive powder.

[0036] The pretreatment steps for the conductive powder in Comparative Example 8 were as follows: 120g of conductive powder and 3g of coupling agent (γ-glycidyl etheroxypropyltrimethoxysilane) and 150g of purified water were added to a three-necked flask. The mixture was mechanically stirred at 50°C for 30 minutes to ensure that the coupling agent was fully adsorbed and bonded to the surface of the conductive powder. After the solid and liquid separated into layers, the supernatant was discarded and the mixture was washed twice with anhydrous ethanol. After discarding the upper layer of liquid after washing, the mixture was filtered. The solid obtained by filtration was dried in an oven at 90°C for 1.5 hours to obtain the pretreated conductive powder.

[0037] A method for preparing an electromagnetic shielding adhesive includes the following steps: mixing silicone, inhibitor, catalyst, coupling agent, anti-aging agent, and organic solvent, stirring at 15 rpm for 10-20 min, adding conductive powder and stirring at 15 rpm for 30-60 min, vacuuming after stirring, and then bottling.

[0038] Performance testing methods and data The adhesives prepared in the examples and comparative examples were used for sample preparation (100g of adhesive was taken, stirred using a homogenizer, poured into a mold, molded at 150°C for 15 minutes, and then baked in an oven at 200°C for 3.5 hours after demolding to obtain a sample) and performance testing was performed. The test methods are shown in Table 3, and the test data are listed in Tables 4 and 5. Blank spaces indicate that no test was performed.

[0039] Table 3

[0040] Table 4

[0041] Table 5

[0042] As shown in Table 4, compared with Comparative Examples 1 and 2, Examples 6 and 7, through the conductive powder with a specific structure, have low resistance, low density, and high shielding performance and aging resistance (high temperature and humidity, high and low temperature, etc.). As shown in Table 5, the adhesive of the present invention, when applied to conductive shielding FIP products, can be compatible with high powder filling and low compression deformation performance. As shown in Tables 4 and 5, Examples 1-5 exhibit significant advantages in overall performance compared to Comparative Examples 1-9. By employing pretreated three-layer coated conductive composite powder and combining it with a specific anti-aging agent, the examples effectively balanced permanent compression deformation and anti-aging performance while ensuring high conductivity (volume resistivity stably maintained at 0.003 Ω·cm, on par with the excellent conductivity group such as Comparative Example 6, and superior to the 0.015-0.019 Ω·cm of Comparative Examples 2, 3, and 9) and low density characteristics. Their permanent compression deformation at 150℃ for 22 hours was ≤35% (as in Examples 3 and 5, it was only 33%), significantly better than Comparative Example 8 (41%). The tensile strength was also better, mostly in the range of 1.48-1.61 MPa, higher than the 1.30 MPa of Comparative Example 6. Furthermore, comparing the comparative examples, it is evident that the comparative examples (such as Comparative Examples 1, 2, and 3) that did not employ the three-layer coating pretreatment powder or did not add specific anti-aging agents showed a significant decrease in shielding effectiveness (from 121-122 dB to 70-88 dB) after aging at 85℃ & 85% humidity and high / low temperatures of -40 to 125℃ for 1500 hours. In contrast, the examples, due to the synergistic effect of the three-layer coating powder and the anti-aging agent, avoided this significant decrease, and maintained a hardness of 56-61 Shore A, thus ensuring mechanical stability. Conversely, the comparative examples, due to factors such as lack of conductive powder pretreatment (e.g., Comparative Example 8), absence of specific anti-aging agents (e.g., Comparative Example 9), or incompatible conductive powder types (e.g., nickel-coated graphite powder in Comparative Example 2 and nickel-coated aluminum powder in Comparative Example 3), resulted in excessive permanent compression deformation, a sharp drop in shielding effectiveness after aging, or high volume resistivity. All of these failed to achieve a synergistic balance between high powder filling, low compression deformation, and excellent aging resistance.

Claims

1. An electromagnetic shielding adhesive, characterized in that, By weight percentage, it comprises: 20-40% silica gel, 0.2-0.5% catalyst, 0.1-1% inhibitor, 0.2-2% anti-aging agent, 0.2-2% coupling agent, 5-30% organic solvent, and conductive powder to make up the balance; the anti-aging agent includes one or more of cerium oxide, iron oxide, titanium oxide, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate.

2. The electromagnetic shielding adhesive according to claim 1, characterized in that, The conductive powder undergoes the following pretreatment steps: the conductive powder is mixed evenly with a surface modifier and water, a pH adjuster is added to adjust the pH to 4-6, and then the powder is dried.

3. The electromagnetic shielding adhesive according to claim 2, characterized in that, The weight ratio of the conductive powder to the silicone is (1.5-2.5):

1.

4. The electromagnetic shielding adhesive according to claim 3, characterized in that, The anti-aging agent is present in the electromagnetic shielding adhesive at a content of 0.2-1 wt%.

5. The electromagnetic shielding adhesive according to claim 2 or 4, characterized in that, The conductive powder content in the electromagnetic shielding adhesive is 50-70 wt%.

6. The electromagnetic shielding adhesive according to claim 5, characterized in that, The coupling agent includes one or more of γ-glycidoxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, and propyl 3-trimethoxysilane acrylate.

7. The electromagnetic shielding adhesive according to claim 5, characterized in that, The organic solvent includes one or more of isohexane, cyclohexane, octane, dodecane, tridecane, tetradecane, petroleum ether, halogenated hydrocarbons, and dimethyl silicone oil with a viscosity of 20-80 cp at 25°C.

8. The electromagnetic shielding adhesive according to claim 5, characterized in that, The catalyst includes a perkin complex catalyst.

9. The electromagnetic shielding adhesive according to claim 5, characterized in that, The inhibitors include one or more of 2-methyl-3-butyn-2-ol, 1-ethynyl-1-cyclohexanol, 3,5-dimethyl-1-hexyn-3-ol, 2-phenyl-3-butyn-2-ol, and 1-hydroxy-1-cyclohexylacetylene.

10. A method for preparing the electromagnetic shielding adhesive according to any one of claims 6-9, characterized in that, The process includes the following steps: adding silicone, inhibitor, catalyst, coupling agent, and anti-aging agent to an organic solvent and stirring until homogeneous to obtain a mixture; adding conductive powder to the mixture and stirring until homogeneous; and performing vacuum treatment after stirring to obtain electromagnetic shielding adhesive.

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