Silk-screen printing type conductive adhesive and preparation method thereof

Abstract

The invention belongs to the technical field of conductive adhesives, and particularly relates to a silk-screen printing type conductive adhesive and a preparation method thereof.The silk-screen printing type conductive adhesive is prepared from, by mass, 500 parts of vinyl silicone oil; 5 to 50 parts of MQ resin; 25 to 125 parts of fumed silica; 10 to 100 parts of hydrogen-containing silicone oil; 0.5-25 parts of a heat-resistant agent; 0.5 to 50 parts of a coupling agent; 0.05 to 25 parts of an inhibitor; 0.05 to 25 parts of a catalyst; 100 to 400 parts of a diluent; 500 to 2000 parts of a conductive filler; wherein the conductive filler is rod-shaped carbon powder, and a nickel layer is plated on the surface of the carbon powder. The surface-modified rod-shaped carbon powder is adopted as the conductive filler, and is matched with the optimized silicone oil system, MQ resin and fumed silica, so that the conductive adhesive can realize low volume resistivity and smoothly pass through a 180-mesh silk screen for printing under the condition of keeping relatively low conductive filler content, and the contradiction between high filler content and printing smoothness is solved.

Description

Technical Field

[0001] This invention relates to a screen-printable conductive adhesive and its preparation method, belonging to the field of conductive adhesive technology. Background Technology

[0002] In the field of electromagnetic interference (EMI) shielding and environmental sealing technology, form-in-place (FIP) conductive adhesives are a widely used functional material. By applying the adhesive to a substrate surface and then curing it at room temperature or high temperature, a conductive and sealing gasket structure can be formed, achieving both EMI shielding and environmental sealing. For this type of FIP conductive adhesive product, stringent process and performance requirements must be met: before dispensing, the material must possess appropriate viscosity and thixotropy to adapt to dispensing speeds and process requirements under different operating conditions; after curing, it must possess stable mechanical and electrical properties to ensure its shielding and sealing effects during service.

[0003] However, with the continuous expansion of application scenarios in related fields, some scenarios have placed stringent requirements on conductive adhesive products, demanding extremely small dimensions, extremely low heights, and complex patterns. Due to its inherent process characteristics, FIP conductive adhesives struggle to accurately meet these requirements for dimensional precision and molding complexity, and also suffer from low production efficiency. In contrast, screen printing, with its unique technical characteristics, can efficiently achieve rapid prototyping of conductive adhesive products with small dimensions and complex patterns, effectively compensating for the shortcomings of FIP conductive adhesives in relevant application scenarios.

[0004] Conductive adhesives, designed for screen printing, often increase the content of conductive fillers to ensure conductivity. However, excessively high filler content can lead to a dramatic increase in viscosity, poor thixotropy, and clogged mesh openings, affecting printing smoothness and graphic quality. Furthermore, high filler content can also impair the adhesion and flexibility of the adhesive layer. Therefore, optimizing the adhesive formulation to achieve good screen printing passability while maintaining low volume resistivity and high shielding effectiveness, while also considering overall performance such as adhesion and heat resistance, presents a significant technical challenge. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing a screen-printable conductive adhesive and its preparation method.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: One objective of this invention is to provide a screen-printable conductive adhesive, comprising the following components by weight: 500 parts of vinyl silicone oil; 5-50 parts of MQ resin; 25-125 parts of fumed silica; 10-100 parts of hydrogen-containing silicone oil; Heat resistant agent 0.5-25 parts; Coupling agent 0.5-50 parts; Coupling agent 2, 0.5-50 parts; Inhibitor 0.05-25 parts; Catalyst 0.05-25 parts; 100-400 parts of diluent; Conductive filler 100-400 parts; The conductive filler is rod-shaped carbon powder, and the surface of the carbon powder is plated with a nickel layer.

[0007] Furthermore, the viscosity of the vinyl silicone oil is 0.5-500 Pa·s.

[0008] Furthermore, the ratio of the M segment to the Q segment of the MQ resin is 0.5-3.

[0009] Furthermore, the specific surface area of ​​the fumed silica is 100-300 m². 2 / g, with a surface that is either hydrophilic or lipophilic.

[0010] Furthermore, the active hydrogen mass fraction of the hydrogen-containing silicone oil is 0.5%-1.5%.

[0011] Furthermore, the coupling agent one is selected from one or more of vinyltrimethoxysilane (A171), vinyltriethoxysilane (A151), γ-aminopropyltriethoxysilane (KH550), γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH560), and single-end reactive polysiloxane; and / or, the coupling agent two is hexamethyldisilazane.

[0012] Furthermore, the inhibitor is methylbutynol.

[0013] Furthermore, the catalyst is a platinum catalyst.

[0014] Furthermore, the diluent is one or more solvent oils of D40 to D120, which evaporate quickly and have low toxicity.

[0015] Furthermore, the heat-resistant agent is hexaphenoxycyclotriphosphazene (HPCTP).

[0016] Furthermore, the particle size of the toner is 20-50 μm.

[0017] The second objective of this invention is to provide a method for preparing the screen-printed conductive adhesive as described above, comprising the following steps: S1. Preparation of base material: Mix vinyl silicone oil, MQ resin, coupling agent II and water evenly in a kneader; add fumed silica in 3-5 batches and knead for 1-2 hours; heat to 145-155℃ and knead for another 2-3 hours; vacuum and heat to 180-210℃ and continue kneading for 2-3 hours, then cool; add hydrogen-containing silicone oil, heat resistant agent and inhibitor, and stir evenly; finally add catalyst and stir evenly to obtain the base material. In step S1 above, the batch addition of fumed silica optimizes dispersibility and improves processing performance due to the nanoscale particle size (typically 7-40 nm) and high specific surface area (typically 90-450 m²) of fumed silica. 2 (g) Fillers are prone to agglomeration, and adding them in large batches at once may lead to localized overconcentration, increasing the viscosity of the compound and structural effects (such as hydrogen bonding), thus affecting flowability. Adding them in batches, however, can gradually disperse the filler, reduce agglomeration, and improve uniformity within the silicone rubber matrix, thereby enhancing interfacial bonding and the efficiency of three-dimensional network formation. Simultaneously, batch addition can mitigate the sudden increase in processing viscosity, reduce structural effects, extend the storage stability of the compound, and optimize thixotropy, preventing sagging or collapse. Experiments show that dispersibility directly affects mechanical properties, such as tensile strength and hardness, and batch addition may reduce the need for structure control agents, simplifying the process.

[0018] S2. Processing conductive powder: Conductive filler and macromolecular polysiloxane coupling agent are dispersed and mixed at high speed to modify the surface of nickel-carbon powder and obtain modified conductive powder. S3. Preparation of conductive adhesive: The base material obtained in step S1 is mixed with diluent, coupling agent 1 and modified conductive powder obtained in step S2, stirred evenly and degassed to obtain the screen printing conductive adhesive.

[0019] Further, in step S2, the preparation method of the macromolecular polysiloxane coupling agent is as follows: dissolve single-end hydrogen-containing silicone oil in an organic solvent, and add a solution of vinyltrimethoxysilane dropwise in the presence of an inert atmosphere and a catalyst to carry out the reaction. After the reaction is completed, remove the solvent and low-boiling substances to obtain the product.

[0020] Compared with the prior art, the present invention has the following beneficial effects: I. This invention uses surface-modified rod-shaped carbon powder as a conductive filler, combined with an optimized silicone oil system, MQ resin and fumed silica, to achieve a volume resistivity of less than 0.03 Ω·cm while maintaining a low conductive filler content (100-400 parts), and can be successfully printed through an 180-mesh screen, thus resolving the contradiction between high filler content and smooth printing.

[0021] Second, this invention uses rod-shaped carbon powder as the nickel plating substrate, which has a large specific surface area, facilitating the acquisition of a more uniform and stronger nickel plating layer, resulting in a more efficient nickel-carbon powder conductive network. The final product achieves a shielding effectiveness of over 100 dB in a wide frequency range of 0.3-10 GHz.

[0022] Third, the MQ resin introduced in this invention significantly improves the adhesion of the adhesive layer to the substrate (especially inorganic and metallic materials); the addition of hexaphenoxycyclotriphosphazene (HPCTP) as a heat resistant agent, its phosphorus-nitrogen synergistic effect effectively improves the thermal stability and flame retardancy of the colloid.

[0023] Fourth, the preparation method of the present invention has clear steps. By first preparing a stable base material, then modifying the surface of the conductive powder, and finally blending, the process ensures that the components are evenly dispersed and have stable performance, which is suitable for large-scale production. Detailed Implementation

[0024] The principles and features of the present invention are described below. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0025] The raw materials used in the embodiments of this invention are described below: Vinyl silicone oil: Runhe Chemical vinyl silicone oil with a viscosity of 500 Pa·s.

[0026] MQ resin: Shenzhen Tianqi MQ resin, MQ ratio is 0.8.

[0027] Fumed silica: Evonik hydrophobic fumed silica with a specific surface area of ​​110 ± 20 m². 2 / g.

[0028] Hydrogen-containing silicone oil: Runhe Chemical's side-chain hydrogen-containing silicone oil, with an active hydrogen mass fraction of 0.5% and a viscosity of 80 mPa·s.

[0029] Heat resistant agent: hexaphenoxycyclotriphosphazene.

[0030] Coupling agent 1: Dow Corning's Z6040.

[0031] Single-ended hydrogen-containing silicone oil: Runhe Chemical's single-ended hydrogen-containing silicone oil has an active hydrogen mass fraction of 0.3% and a viscosity of 100 mPa·s.

[0032] Inhibitor: Methylbutynol.

[0033] Catalyst: Platinum catalyst from Guangzhou Silicon Friends New Materials Co., Ltd.

[0034] Diluent: 80℃ flash point solvent oil.

[0035] Nickel-carbon powder: Oerlikon nickel-carbon powder 2707, with a particle size D50 of 30 μm.

[0036] Macromolecular polysiloxane coupling agent: prepared according to the following method.

[0037] Synthesis example 1 Preparation of macromolecular polysiloxane coupling agents: 40 g of single-ended hydrogen-containing silicone oil and 50 mL of anhydrous toluene were added to a three-necked flask. The mixture was heated to 60 °C under nitrogen protection and stirred until dissolved. 30 mL of a toluene solution containing 1.5 g of vinyltrimethoxysilane (A171) was slowly added dropwise, along with 0.2 g of platinum catalyst. The reaction was carried out at 70 °C for 6 hours. After the reaction was complete, the toluene solvent and unreacted low-boiling substances were removed by vacuum distillation to obtain a macromolecular polysiloxane coupling agent with a molar mass of approximately 3956 g / mol.

[0038] Example 1 A method for preparing a screen-printable conductive adhesive includes the following steps: (1) Preparation of base material: Take 500g of vinyl silicone oil (viscosity 1000 Pa·s), add 5g of MQ resin (M / Q=0.8), 40g of hexamethyldisilazane and 40g of deionized water, and mix them evenly in a kneader. Divide the mixture into four batches and add a total of 50g of fumed silica (specific surface area 110m²). 2 / g), knead at room temperature for 1.5 hours. Then heat to 150℃ and knead for 2.5 hours. Vacuum and heat to 200℃, continue kneading for 2.5 hours. Stop heating and cool to room temperature (approximately 25℃). Add 10g of hydrogen-containing silicone oil (0.5% active hydrogen content), 2g of HPCTP, and 0.1g of inhibitor (ethynylcyclohexanol) to the kneader, and stir until homogeneous. Finally, add 0.15g of platinum catalyst, stir until homogeneous, and obtain a uniform base material.

[0039] (2) Treatment of conductive powder: 350g of nickel carbon powder and 0.5% of the self-made macromolecular polysiloxane coupling agent of the above synthesis example 1 were added to a high-speed disperser and dispersed at a speed of 1200 r / min for 10 minutes to obtain surface-modified conductive powder.

[0040] (3) Preparation of conductive adhesive: Take 100g of the base material obtained in step (1), add 10g of diluent, 2g of single-end reactive polysiloxane with a molecular weight of about 5000 (as coupling agent one) and the conductive powder (350g) obtained in step (2), stir evenly in a planetary mixer, and then transfer to a degassing tank for vacuum degassing to obtain the final screen printing conductive adhesive.

[0041] Example 2 The difference from Example 1 is that: 60g of fumed silica was added in step (1) (added in four batches); and 380g of conductive powder was added in step (3). The remaining raw materials and steps are the same as in Example 1.

[0042] Example 3 The difference from Example 1 is that: in step (1), 70g of fumed silica was added (in four batches), and 9g of hydrogen-containing silicone oil was added; in step (3), 400g of conductive powder was added. The remaining raw materials and steps are the same as in Example 1.

[0043] Comparative Example 1 The difference from Example 3 is that MQ resin was not added when preparing the base material in step (1). The remaining raw materials and steps are the same as in Example 3.

[0044] Comparative Example 2 The difference from Example 3 is that step (2) "processing conductive powder" is omitted, that is, 400g of unmodified raw nickel-carbon powder is used directly in step (3). The other raw materials and steps are the same as in Example 3.

[0045] Performance testing The conductive adhesives prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to performance tests, and the results are shown in Table 1.

[0046] Testing standards: Hardness (Shore A): Refer to ASTM D2240.

[0047] Shielding effectiveness: Tested in the 0.3-10GHz frequency band according to the MIL-DTL-83528C standard method.

[0048] Volume resistivity: Tested according to the standard method of MIL-DTL-83528C.

[0049] 180-mesh screen printing: Manual or mechanical scraping, observe the smoothness of the print through the mesh and the integrity of the printed image.

[0050] Adhesion: Refer to GB / T 9286-1998, the adhesion between the adhesive layer and the aluminum plate is tested by cross-cut test, and the unit is Newton (N).

[0051] Table 1 Performance test data of the examples and comparative examples

[0052] As shown in Table 1: The conductive adhesives prepared in Examples 1-3 all exhibited excellent overall performance: low volume resistivity (≤0.03 Ω·cm), high shielding effectiveness (100 dB), and all could pass smoothly through 180-mesh screen printing with strong adhesion (≥21 N). This indicates that the formulation and process of the present invention successfully achieved a balance between high performance and good printability.

[0053] Comparative Example 1, without the addition of MQ resin, showed a significant decrease in adhesion (only 9.6 N), demonstrating that MQ resin plays a crucial role in improving the adhesion of conductive adhesive to the substrate.

[0054] Comparative Example 2 did not undergo surface modification treatment on the nickel-carbon powder. Although its conductivity and shielding effectiveness were unaffected, its screen printing passability was extremely poor, easily clogging the mesh and preventing continuous and smooth printing operations. This demonstrates that surface modification of the nickel-carbon powder using a specific macromolecular polysiloxane coupling agent is one of the core steps in imparting excellent printability to the conductive adhesive. This can be achieved by reducing powder agglomeration and improving the compatibility and dispersibility of the powder with the organosilicon matrix.

[0055] In summary, the screen-printable conductive adhesive and its preparation method provided by this invention effectively solve the contradiction between the high conductivity requirements and the adaptability of screen printing processes in the prior art. The product exhibits excellent performance in electromagnetic shielding, conductivity, adhesion, and printing processing, and has broad application prospects.

[0056] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A screen-printable conductive adhesive, characterized in that, Based on parts by weight, it includes the following components: 500 parts of vinyl silicone oil; 5-50 parts of MQ resin; 25-125 parts of fumed silica; 10-100 parts of hydrogen-containing silicone oil; Heat resistant agent 0.5-25 parts; Coupling agent 0.5-50 parts; Coupling agent 2, 0.5-50 parts; Inhibitor 0.05-25 parts; Catalyst 0.05-25 parts; 100-400 parts of diluent; 0.5-2 parts of macromolecular polysiloxane coupling agent; Conductive filler 100-400 parts; The conductive filler is rod-shaped carbon powder, and the surface of the carbon powder is plated with a nickel layer.

2. The screen-printable conductive adhesive according to claim 1, characterized in that, The viscosity of the vinyl silicone oil is 0.5-500 Pa·s.

3. The screen-printable conductive adhesive according to claim 1, characterized in that, The molar ratio of the M segment to the Q segment of the MQ resin is 0.5-3.

4. The screen-printable conductive adhesive according to claim 1, characterized in that, The specific surface area of ​​the fumed silica is 100-300 m². 2 / g, with a surface that is either hydrophilic or lipophilic.

5. The screen-printable conductive adhesive according to claim 1, characterized in that, The active hydrogen mass fraction of the hydrogen-containing silicone oil is 0.5%-1.5%.

6. The screen-printable conductive adhesive according to claim 1, characterized in that, The coupling agent one is selected from one or more of vinyltrimethoxysilane, vinyltriethoxysilane, γ-aminopropyltriethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, and single-ended reactive polysiloxane; and / or, the coupling agent two is hexamethyldisilazane.

7. The screen-printable conductive adhesive according to claim 1, characterized in that, The catalyst is a platinum catalyst; the diluent is one or more solvent oils of D40 to D120; and the heat resistant agent is hexaphenoxycyclotriphosphazene.

8. The screen-printable conductive adhesive according to claim 1, characterized in that, The particle size of the toner is 20-50 μm.

9. A method for preparing a screen-printable conductive adhesive as described in any one of claims 1-8, characterized in that, Includes the following steps: S1. Preparation of base material: Mix vinyl silicone oil, MQ resin, coupling agent II and water evenly in a kneader; add fumed silica in 3-5 batches and knead for 1-2 hours; heat to 145-155℃ and knead for another 2-3 hours; then vacuum and heat to 180-210℃ and continue kneading for 2-3 hours, then cool; add hydrogen-containing silicone oil, heat resistant agent and inhibitor, and stir evenly; finally add catalyst and stir evenly to obtain the base material. S2. Processing conductive powder: Conductive filler and macromolecular polysiloxane coupling agent are dispersed and mixed at high speed to modify the surface of nickel-carbon powder and obtain modified conductive powder. S3. Preparation of conductive adhesive: The base material obtained in step S1 is mixed with diluent, coupling agent 1 and modified conductive powder obtained in step S2, stirred evenly and degassed to obtain the screen printing conductive adhesive.

10. The preparation method according to claim 9, characterized in that, In step S2, the preparation method of the macromolecular polysiloxane coupling agent is as follows: dissolve single-end hydrogen-containing silicone oil in an organic solvent, add a solution of vinyltrimethoxysilane dropwise in the presence of an inert atmosphere and a catalyst to carry out the reaction, and remove the solvent and low-boiling substances after the reaction is completed to obtain the product.

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