A flexible low-tg moisture-resistant one-component epoxy resin adhesive as well as a preparation method and application thereof

Abstract

The application discloses a kind of flexible low Tg moisture-resistant single-component epoxy resin adhesives and its preparation method and application.The present application is combined by flexible chain segment-rigid network collaborative design, nano-hybrid moisture-resistant reinforcing technology and multiple interface strengthening technology, to build an epoxy resin crosslinking network with high bonding strength, flexibility, low halogen environmental protection characteristics and moisture resistance.Overcome the defects in the prior art that epoxy adhesive is difficult to consider low glass transition temperature, high flexibility, high bonding strength, low halogen environmental protection requirements, excellent moisture resistance and fast curing characteristics.

Description

Technical Field

[0001] This invention relates to the field of epoxy resin adhesive technology, specifically to a flexible, low-Tg, moisture-resistant single-component epoxy resin adhesive, its preparation method, and its application. Background Technology

[0002] As electronic devices become thinner and more flexible, the encapsulation and protection of flexible printed circuit boards (FPCs) and their connectors (such as through-hole connectors and surface mount connectors) has become a key technical challenge in the industry. For potting protection of FPC connectors, adhesive materials need to meet stringent process and performance requirements: on the one hand, to adapt to fixture-free potting processes, the adhesive must possess excellent thixotropy, maintaining its original shape without dripping after dispensing; on the other hand, to alleviate the stress generated during bending or thermal cycling of the flexible circuit board, the cured adhesive must have low modulus and high elongation at break, typically requiring a glass transition temperature (Tg) controlled at 45±5℃ to form a flexible elastomer network.

[0003] Furthermore, FPCs are widely used in consumer electronics, automotive electronics, and other fields. These products may face harsh environments such as high temperature and humidity (e.g., double 85 aging), salt spray corrosion, and thermal shock. This requires adhesives to possess excellent bonding strength (shear strength ≥ 10 MPa), moisture resistance, and electrical insulation properties (volume resistivity ≥ 1 × 10¹) in addition to low Tg flexibility. 5 Ω·cm, surface resistivity ≥1×10¹ 4 (Ω·cm). Meanwhile, to meet the high-efficiency curing requirements of automated production lines, the adhesive must be able to cure rapidly at 150℃ for 15 minutes.

[0004] However, in existing technologies, epoxy resin adhesives often struggle to achieve a balance between low Tg flexibility modification, high bond strength, and resistance to damp heat. Traditional toughening methods, such as adding reactive liquid rubber (e.g., CTBN), can improve toughness but typically significantly reduce bond strength and heat resistance. While modifying with flexible segments such as polyether polyols can greatly increase elongation at break, it reduces interfacial adhesion, increases water absorption, and makes it difficult to achieve shear strength requirements above 10 MPa. Research shows that surface modification with nanofillers can achieve a significant increase in elongation at break of 46.05%, providing a new approach for the design of high-performance epoxy adhesives. Furthermore, the electronics industry has increasingly stringent environmental requirements, demanding that adhesives have a total halogen content ≤900 ppm, comply with RoHS environmental standards, and be free of heavy metal impurities.

[0005] Therefore, developing a one-component epoxy adhesive that combines low Tg flexibility, high bonding strength (≥10MPa), low halogen environmental protection properties, and excellent moisture resistance, and is suitable for fixture-free potting processes for FPC connectors, has significant industrial value. Summary of the Invention

[0006] In order to overcome the above-mentioned defects of the prior art, the purpose of this invention is to provide a flexible, low-Tg, moisture-resistant single-component epoxy resin adhesive, its preparation method, and its application.

[0007] By organically combining flexible segment-rigid network synergistic design, nano-hybrid moisture-resistant enhancement technology, and multiple interface strengthening technology, an epoxy resin crosslinking network with high bonding strength, flexibility, low halogen environmental protection properties, and moisture resistance is constructed.

[0008] This overcomes the shortcomings of existing epoxy adhesives in achieving a balance between low glass transition temperature, high flexibility, high bond strength, low halogen environmental requirements, excellent moisture resistance, and rapid curing characteristics.

[0009] A flexible, low-Tg, moisture-resistant one-component epoxy resin adhesive, comprising the following components by weight: 40-60 parts of low-halogen bisphenol A epoxy resin; 15-25 parts of epoxy-terminated polyether; 10-20 parts of flexible segment modified epoxy resin; 5-15 parts of multifunctional epoxy resin; 8-12 parts of carboxyl-terminated butadiene-acrylonitrile rubber; 5-10 parts of silicon dendritic polymer; 8-15 parts of latent curing agent; Curing accelerator 0.5-3 parts; 1-3 parts of silane coupling agent compound; 1.2-3.2 parts of hydrophobic fumed silica; 0.1-0.3 parts of non-silicone defoamer.

[0010] In a preferred embodiment of the present invention, the one-component epoxy resin adhesive comprises, by weight, the following components: 45-55 parts of low-halogen bisphenol A epoxy resin; 18-22 parts of epoxy-terminated polyether; 12-18 parts of flexible segment modified epoxy resin; 8-12 parts of multifunctional epoxy resin; 9-11 parts of carboxyl-terminated butadiene-acrylonitrile rubber; 6-8 parts of silicon dendritic polymer; 10-13 parts of latent curing agent; 1-2 parts of curing accelerator; 1.5-2.5 parts of silane coupling agent compound; 2.5-3.2 parts of hydrophobic fumed silica; 0.15-0.25 parts of non-silicone defoamer.

[0011] In a preferred embodiment of the present invention, the one-component epoxy resin adhesive comprises, by weight, the following components: 45-55 parts of low-halogen bisphenol A epoxy resin; 18-22 parts of epoxy-terminated polyether; 12-18 parts of flexible segment modified epoxy resin; 8-12 parts of multifunctional epoxy resin; 9-11 parts of carboxyl-terminated butadiene-acrylonitrile rubber; 6-8 parts of silicon dendritic polymer; 10-13 parts of latent curing agent; 1-2 parts of curing accelerator; 1.5-2.5 parts of silane coupling agent compound; 2.5-3.2 parts of hydrophobic fumed silica; 0.15-0.25 parts of non-silicone defoamer.

[0012] In a preferred embodiment of the present invention, the low-halogen bisphenol A epoxy resin is E51, which has a halogen content of ≤900ppm, an epoxy value of 0.51±0.02 eq / 100g, and a hydroxyl value of ≤0.05 eq / 100g.

[0013] The low-halogen bisphenol A epoxy resin of this invention is free of harmful halogen impurities such as chlorine and bromine, which can effectively avoid the decline in electrical insulation performance caused by halogen ion migration, while meeting environmental protection standards such as RoHS and REACH in the electronics industry.

[0014] In a preferred embodiment of the present invention, the epoxy-terminated polyether is a DGE-PPG epoxy-terminated polyether with an epoxy equivalent of 280-320 g / eq and a viscosity (25°C) of 500-800 mPa·s.

[0015] The preferred epoxy equivalent is 300 g / eq, and the epoxy end-capping rate is ≥98%.

[0016] DGE-PPG epoxy-terminated polyether is a colorless and transparent liquid that does not contain halogen impurities.

[0017] The role of DGE-PPG epoxy end-capped polyether in this invention is to introduce flexible segments into the epoxy adhesive system, reduce the crosslinking density of the cured system, and at the same time reduce the curing shrinkage rate of the epoxy adhesive (curing shrinkage rate ≤0.8%), thereby reducing the internal stress caused by shrinkage during potting.

[0018] In a preferred embodiment of the present invention, the flexible segment modified epoxy resin is a product obtained by side-linking modification of low halogen bisphenol A epoxy resin with polypropylene glycol (PPG) with a number average molecular weight of 2000-4000, wherein the side chain content in the flexible segment modified epoxy resin is 10%-15% of the total mass of the flexible segment modified epoxy resin.

[0019] In a preferred embodiment of the present invention, the flexible segment modified epoxy resin is prepared by the following method: Low-halogen bisphenol A epoxy resin was mixed with polypropylene glycol (PPG) with a number average molecular weight of 2000-4000 at a mass ratio of 100:10-15. Then, 0.1%-0.3% triphenylphosphine catalyst was added, and the mixture was reacted at 120-140℃ under nitrogen protection for 2-4 hours to obtain a side-linked modified flexible epoxy resin with an epoxy value controlled in the range of 0.25-0.35 mol / 100g.

[0020] Through extensive research, the inventors of this invention discovered that the side chain content within a reasonable range can significantly improve the elongation at break without significantly sacrificing strength, while effectively reducing the modulus and glass transition temperature.

[0021] In a preferred embodiment of the present invention, the carboxyl-terminated nitrile butadiene rubber is a CTBN carboxyl-terminated nitrile butadiene rubber with a number average molecular weight of 1300-1500, an acrylonitrile content of 26-30%, and a carboxyl content of 0.05-0.08 eq / 100g.

[0022] The preferred number average molecular weight is 1300-1400.

[0023] The carboxyl-terminated butadiene-acrylonitrile rubber of this invention is a pale yellow, transparent, viscous liquid at room temperature. Its function is to introduce flexible segments into the epoxy resin system, significantly improving the flexibility and impact resistance of the epoxy resin, and preventing the potting layer from cracking and detaching during bending and alternating high and low temperatures in FPC connectors.

[0024] Through extensive research, the inventors of this invention discovered that the synergistic effect of CTBN and nanofillers can significantly improve the mechanical properties of epoxy resins.

[0025] In a preferred embodiment of the present invention, the multifunctional epoxy resin is one or more of phenolic epoxy resin (F-51, F-44), p-aminophenol epoxy resin (AFG-90), or 4,5-epoxycyclohexane-1,2-dicarboxylic acid diglycidyl ester (TDE-85).

[0026] The introduction of multifunctional epoxy resin in this invention can increase crosslinking density, enhance cohesive strength and heat resistance, and form a network structure that combines rigidity and flexibility with flexible segments, thereby improving bonding strength while maintaining flexibility.

[0027] In a preferred embodiment of the present invention, the silicon dendritic polymer is a hyperbranched polysiloxane with a regular branching structure, the hyperbranched polysiloxane having a molecular weight of 5000-10000, and each molecule containing 8-16 epoxy functional groups.

[0028] The three-dimensional rigid structure of the silicon dendritic polymer of this invention forms an interpenetrating or hybrid structure with the flexible segment-modified epoxy resin. On the one hand, the uniform dispersion at the nanoscale enhances the density of the cross-linked network; on the other hand, its abundant epoxy groups participate in the curing reaction, forming chemical bonds. This significantly improves moisture resistance, salt spray resistance, and electrical insulation properties without increasing the Tg. Studies have shown that uniform dispersion of nano-SiO2 in the resin matrix after modification with a coupling agent can increase the elongation at break by 46.05%.

[0029] In a preferred embodiment of the present invention, the latent curing agent is a compound system of microencapsulated 2-phenyl-4-methylimidazole and liquid methyltetrahydrophthalic anhydride, with a mass ratio of 1:2 to 1:3.

[0030] This latent curing agent compound system utilizes the high-temperature unsealing and release of active centers from microencapsulated imidazole, combined with the ring-opening catalytic effect of acid anhydrides, to achieve rapid curing at 150℃ / 15min, while ensuring room temperature storage stability of ≥6 months (<25℃). Studies have shown that the microencapsulated curing agent can enable single-component epoxy resins to cure within 100℃ / 30min, with a room temperature storage period of over 50 days and a tensile shear strength of 15.36MPa.

[0031] In a preferred embodiment of the present invention, the curing accelerator is 3,4-dichlorophenyldimethylurea (DCMU). The preferred dosage is 0.5-1.5.

[0032] 3,4-Dichlorophenyldimethylurea (DCMU) works synergistically with the latent curing agent to precisely control the curing rate, avoiding difficulties in dispensing and air bubbles due to excessively fast curing, or affecting production efficiency due to excessively slow curing.

[0033] In a preferred embodiment of the present invention, the silane coupling agent complex is a complex of γ-glycidoxypropyltrimethoxysilane (KH-560) and γ-aminopropyltriethoxysilane (KH-550) in a mass ratio of 2:1 to 3:1.

[0034] The dual coupling agent system of the silane coupling agent complex can simultaneously form chemical bonds with epoxy resin and substrate surfaces (PI, PBT, nylon), significantly improving interfacial adhesion strength. Studies have shown that KH550 modified nano-SiO2 can significantly improve the mechanical properties of the resin while maintaining its original heat resistance and rheological properties.

[0035] In a preferred embodiment of the present invention, the hydrophobic fumed silica is hydrophobic fumed silica R972 with a specific surface area of ​​200-300 m² / g.

[0036] Depending on the application scenario, the amount added can be finely adjusted. In the low viscosity and high thixotropic scenario of fixture-free thixotropic type, the amount added is 1.2-1.8 parts. Under the conditions of 25℃, 34# rotor, and 12r / min, the viscosity is 3800±200 mPa·s, and the thixotropic index (6rpm / 60rpm) is ≥4.2. After dispensing, it can maintain the original dispensing shape without the aid of a mold. The setting speed is fast, which is suitable for fixture-free potting of precision and small FPC connectors and chip components.

[0037] In high-viscosity applications with fixtures, the addition amount is 2.5-3.2 parts. Under conditions of 25℃, 34# rotor, and 12r / min, the viscosity is 22000±500 mPa·s, and the thixotropic index is ≥6.8. It has high viscosity and strong anti-sagging properties, making it suitable for large FPC plug-in connectors and thick-layer potting applications. It can perfectly fit the mold without overflow or bubbles.

[0038] The two scenario versions of this invention can be achieved simply by adjusting the gradient of the amount of hydrophobic fumed silica, without changing the proportion of other components, while maintaining consistent core performance, thereby reducing production costs and improving production efficiency.

[0039] A method for preparing a flexible, low-Tg, moisture-resistant one-component epoxy resin adhesive includes the following steps: Step 1: The low-halogen bisphenol A epoxy resin, the epoxy-terminated polyether, the flexible segment modified epoxy resin, the carboxyl-terminated nitrile rubber, the multifunctional epoxy resin, and the silicon dendritic polymer are sequentially added to a high-speed stirred tank. The temperature of the stirred tank is set to 55-65℃, and the stirring speed is set to 800-1000 r / min. The mixture is stirred at high speed for 30-40 minutes until all components are completely and evenly mixed.

[0040] Step 2: Cool the material in the mixing tank to <40℃, then slowly add the latent curing agent, the curing accelerator, the silane coupling agent compound, and the non-silicone defoamer in sequence, and adjust the stirring speed to 300-400 r / min, and stir at low speed for 15-20 min. Step 3: Add the hydrophobic fumed silica to the mixing tank and adjust the stirring speed to 1200-1500 r / min. Disperse at high speed for 25-35 min until the material fineness is <10 μm and the viscosity meets the standard. Then, degas under vacuum to obtain the flexible, low-Tg, moisture-resistant single-component epoxy resin adhesive.

[0041] An application of a flexible, low-Tg, moisture-resistant, one-component epoxy resin adhesive, said application being for potting flexible printed circuit board (FPC) connectors, encapsulating chip components, bonding flexible screens to FPCs, or potting protection for automotive electronic modules.

[0042] The beneficial effects of this invention are as follows: By organically combining flexible segment-rigid network synergistic design, nano-hybrid moisture-resistant enhancement technology, and multiple interface strengthening technology, an epoxy resin crosslinking network with high bonding strength, flexibility, low halogen environmental protection properties, and moisture resistance is constructed. This overcomes the shortcomings of existing epoxy adhesives in achieving low glass transition temperature, high flexibility, high bonding strength, low halogen environmental protection requirements, excellent moisture resistance, and rapid curing characteristics. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below through embodiments. However, it should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention. Furthermore, in the following descriptions, well-known structures and technologies are omitted to avoid unnecessarily obscuring the concept of the invention.

[0044] The preparation methods of each embodiment of the present invention are as follows: S1. Material preparation: Weigh each component precisely according to weight. The low-halogen bisphenol A epoxy resin E51 needs to be dried in an 80℃ constant temperature oven for 2 hours in advance to remove surface moisture and avoid moisture affecting the moisture resistance and curing effect of the epoxy adhesive. All other components need to be placed at room temperature of 25℃ for 30 minutes to ensure that the temperature of each component is consistent and to avoid bubbles caused by temperature differences during mixing.

[0045] S2. Pre-preparation of flexible segment modified epoxy resin: Low-halogen bisphenol A epoxy resin is mixed with polypropylene glycol with a number average molecular weight of 2000-4000 at a mass ratio of 100:10-15. 0.1%-0.3% triphenylphosphine catalyst is added, and the mixture is reacted at 120-140℃ under nitrogen protection for 2-4 hours to obtain a flexible epoxy resin with side-chain branched modification. The epoxy value is controlled at 0.25-0.35 mol / 100g, and the side chain content is 10%-15%.

[0046] In this embodiment of the invention, a flexible segment modified epoxy resin with polypropylene glycol (PPG) grafting and a side chain content of 12% is used.

[0047] S3, Premixed: The dried low-halogen bisphenol A epoxy resin E51, epoxy-terminated polyether DGE-PPG, the flexible segment modified epoxy resin prepared in step S2, carboxyl-terminated nitrile butadiene rubber (CTBN), multifunctional epoxy resin, and silicon dendritic polymer were sequentially added to a high-speed stirred tank. The temperature of the stirred tank was set to 55-65℃ (60℃ in the example), the stirring speed was 800-1000 r / min, and the high-speed stirring was carried out for 30-40 min (35 min in the example) until all components were completely mixed and homogeneous, forming a uniform viscous liquid without stratification, precipitation, or obvious particles.

[0048] S4, Cooling and Dispersion: The material in the mixing vessel is cooled to <40℃ (35-38℃ in the example) to avoid premature activation of the latent curing agent due to high temperature. Then, the latent curing agent, 3,4-dichlorophenyldimethylurea (DCMU), silane coupling agent compound, and non-silicone defoamer are added slowly in sequence. The stirring speed is adjusted to 300-400 r / min, and the mixture is stirred at low speed for 15-20 min (18 min in the example) to ensure that the additives are evenly dispersed in the system without agglomeration. At the same time, low-speed stirring is used to reduce the generation of bubbles.

[0049] S5, Thickening and Refining: Add hydrophobic fumed silica R972 to the mixing vessel, adjust the stirring speed to 1200-1500 r / min, and disperse at high speed for 25-35 min (30 min in the example). During this period, stop the machine every 10 min to observe the material state until the material fineness is <10 μm (8-10 μm in the example) and the viscosity meets the requirements of the corresponding version (the viscosity requirement for the fixture-free type is 3800±200 mPa·s, and the viscosity requirement for the fixture type is 22000±500 mPa·s).

[0050] S6. Vacuum degassing and packaging: Place the well-stirred and refined material into a vacuum degassing machine, set the vacuum degree to ≤-0.095 MPa, and degas for 10-15 minutes (12 minutes in the example). Stir slowly during the process to completely remove any residual air bubbles from the material. After degassing, quickly pour the material into a sealed packaging container, seal it, and store it in a dry environment at 25°C.

[0051] The epoxy adhesive of this invention is cured at 150℃ for no more than 15 minutes. The performance requirements after curing are shown in Table 1. Table 1 Performance Category Performance indicators Test conditions / standards Basic physical properties Density: 1.25 g / cm³; Shore D hardness: 80±5 GB / T 13354; GB / T 2411 thermal properties Glass transition temperature (Tg) is 45±5℃; 5% thermal decomposition temperature is >320℃; coefficient of linear expansion is 60-70 ppm / ℃. DMA; TGA; TMA Mechanical properties Elongation at break ≥70%; Elastic modulus ≤0.9 GPa GB / T 2567 Electrical insulation performance <![CDATA[Volume resistivity ≥ 1×10¹ 5 Ω·cm; Surface resistivity ≥ 1×10¹ 4 Ω·cm; Dielectric strength > 20 kV / mm]]> GB / T 1410; GB / T 1408.1 Adhesion performance PI interfacial shear strength ≥12.0 MPa; PBT interfacial shear strength ≥11.0 MPa; Nylon interfacial shear strength ≥10.0 MPa; PI interfacial peel strength ≥4.5 N / mm GB / T 7124; GB / T 2791 Moisture resistance Water absorption rate (boiling water at 100℃ for 2 hours) < 0.8% GB / T 1034 Environmental performance Total halogen content ≤900ppm, compliant with RoHS standards - Curing properties Completely cured within 150℃ for 15 minutes, with a cure rate ≥98%. DSC Storage stability Storage period at 25℃: ≥3 months; Frozen storage at -20℃: ≥12 months - Examples 1-4 and Comparative Examples 1-2 Following the formulations (parts by weight) shown in Table 2, and using the above preparation method, one-component epoxy resin adhesives were prepared in both fixture-free potting versions (Examples 1-3) and fixture-potting versions (Example 4). Comparative Example 1 (without silicone dendritic polymer and multifunctional epoxy resin) and Comparative Example 2 (using ordinary bisphenol A epoxy resin with halogen content >1500 ppm) were also set up for comparison.

[0052] Table 2. Composition of the formulations (parts by weight) for the examples and comparative examples Components Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Low-halogen bisphenol A epoxy resin E51 (halogen ≤900ppm) 45 40 50 45 60 - Ordinary bisphenol A epoxy resin E51 (halogen > 1500 ppm) - - - - - 45 Epoxy-terminated polyether DGE-PPG 20 18 22 20 15 20 Flexible segment modified epoxy resin (PPG grafted, side chain content 12%) 15 18 12 15 - 15 Multifunctional epoxy resin (F-51 phenolic epoxy) 8 6 10 8 - 8 Carboxyl-terminated nitrile butadiene rubber (CTBN) 10 9 11 10 10 10 Silicon dendritic polymers 6 5 8 6 - 6 Latent curing agent (microencapsulated imidazole: acid anhydride = 1:2.5) 12 10 13 12 12 12 3,4-Dichlorophenyldimethylurea (DCMU) 1 0.8 1.2 1 1 1 Silane coupling agent complex (KH-560:KH-550=2.5:1) 2 1.5 2.5 2 1 1 Hydrophobic fumed silica R972 1.5 1.8 1.2 2.8 1.5 1.5 Non-silicone defoamer 0.2 0.15 0.25 0.2 0.2 0.2 Performance testing methods The adhesives prepared in Examples 1-4 and Comparative Examples 1-2 were subjected to performance tests according to the following standards and methods. Material-grade test samples were prepared under curing conditions of 150°C / 15 min.

[0053] The main testing standards and methods are shown in Table 3 below: Table 3 Test Project Test methods / standards Test conditions color Visual inspection - odor Sensory test - Viscosity GB / T 2794 Borelfeld viscometer, 34# rotor, 25℃, 12 r / min Thixotropic index Viscosity at 6 rpm / Viscosity at 60 rpm - hardness GB / T 2411 Shore D hardness tester density GB / T 13354 25℃ Water absorption rate GB / T 1034 Soak in boiling water at 100℃ for 2 hours Volume resistivity GB / T 1410 25℃, 500V Surface resistivity GB / T 1410 25℃, 500V Curing temperature and time DSC Isothermal or dynamic scanning Thermal decomposition temperature TGA <![CDATA[5% Thermal weight loss temperature, N2 atmosphere]]> Dielectric strength GB / T 1408.1 25℃, continuous pressurization coefficient of linear expansion TMA 30-100℃, heating rate 5℃ / min Glass transition temperature (Tg) DMA Loss factor tanδ peak temperature Shear strength GB / T 7124 Overlap area 25×12.5mm², stretching speed 5mm / min Peel strength (PI interface) GB / T 2791 180° peeling, T-shaped peeling Salt spray resistance test GB / T 1771 Shear strength was measured after 48 hours in 5% NaCl at 35℃. Double 85 aging - Shear strength was measured after 500h, 700h, and 1008h at 85℃ / 85%RH. High and low temperature cycling - -40℃ to 85℃, 30 min each, 500 / 700 / 1000 cycles, then measure shear strength. Halogen content - Oxygen bomb combustion-ion chromatography The material-level test results are shown in Table 4 below: Table 4. Basic performance test results of the examples and comparative examples Test Project Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 color Light gray Light gray Light gray Light gray Light gray gray-black odor slight slight slight slight slight slight Viscosity (mPa·s, 25℃, 12r / min) 3820 3750 3950 22150 3880 3910 Thixotropic index (6rpm / 60rpm) 4.3 4.5 4.2 6.8 4.0 4.2 Density (g / cm³) 1.25 1.25 1.26 1.25 1.25 1.25 Shore D hardness 82 81 83 82 78 80 Glass transition temperature Tg (°C) 45.2 44.5 46.8 45.5 42.5 46.2 Water absorption rate (%, after boiling at 100℃ for 2 hours) 0.25 0.23 0.28 0.24 0.58 0.48 <![CDATA[Volume resistivity (×10¹ 5 Ω·cm)]]> 3.5 4.0 3.2 3.8 0.4 0.9 <![CDATA[Surface resistivity (×10¹ 4 Ω·cm)]]> 3.0 3.5 2.8 3.3 0.3 0.7 Total halogen content (ppm) ≤850 ≤820 ≤880 ≤840 ≤820 ＞1600 Thermal decomposition temperature (°C, 5%) 358 352 365 360 338 348 Dielectric strength (kV / mm) 28.5 29.2 27.8 28.9 21.5 24.2 Coefficient of linear expansion (30-80℃, ppm / K) 65 62 68 64 85 72 Elongation at break (%) 78 82 72 80 38 52 Elastic modulus (GPa) 0.85 0.82 0.88 0.84 1.8 1.2 As can be seen from Table 4: The Tg values ​​of Examples 1-4 were all between 44.5-46.8℃, meeting the target requirement of 45±5℃; the Shore hardness was 81-83, which is within the range of 80±5. The total halogen content of Examples 1-4 was ≤880ppm, which met the environmental protection requirements for low halogens, while the halogen content of Comparative Example 2 was >1600ppm, which did not meet the environmental protection standards.

[0054] Compared with Comparative Example 1, the examples with added silicon dendritic polymer and multifunctional epoxy resin had significantly lower water absorption (approximately 0.23-0.28% vs 0.58%) and increased volume resistivity by more than 8 times, indicating that silicon dendritic polymer has a significant effect on improving moisture resistance and electrical insulation properties.

[0055] The example showed a breaking elongation of 72-82%, which was much higher than the 38% of Comparative Example 1 and the 52% of Comparative Example 2. The elastic modulus was 0.82-0.88 GPa, which was much lower than the 1.8 GPa of Comparative Example 1, demonstrating a significant advantage in flexibility.

[0056] Example 4 (with fixture): viscosity 22150 mPa·s, thixotropic index 6.8, meeting the requirements of high viscosity potting process.

[0057] Table 5 shows the test results for shear strength and peel strength (unit: MPa, peel strength is N / mm). Table 5 Test Project Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 25℃ shear strength PBT interface 12.8 13.2 12.5 13.0 8.2 10.5 Nylon interface 11.6 12.0 11.3 11.8 6.8 9.2 PI Interface 13.5 13.8 13.2 13.6 8.5 11.2 Peel strength at 25℃ (PI interface, N / mm) 4.6 4.9 4.4 4.7 2.2 3.5 -30℃ shear strength PBT interface 10.8 11.2 10.5 11.0 5.2 8.5 Nylon interface 9.5 9.9 9.2 9.7 4.0 7.2 PI Interface 11.5 11.9 11.2 11.7 5.8 9.5 -30℃ retention rate (PI, %) 85.2 86.2 84.8 86.0 68.2 84.8 60℃ shear strength PBT interface 11.8 12.2 11.5 12.0 6.5 9.2 Nylon interface 10.5 10.9 10.2 10.7 5.2 8.0 PI Interface 12.6 13.0 12.3 12.8 7.0 10.2 Retention rate at 60℃ (PI, %) 93.3 94.2 93.2 94.1 82.4 91.1 The following key conclusions can be drawn from Table 5: Examples 1-4 exhibited excellent adhesive strength on all three substrates, with all shear strength data exceeding 10 MPa, far exceeding the target requirements of this invention. In particular, the shear strength at the PI interface reached 13.2-13.8 MPa, at the PBT interface 12.5-13.2 MPa, and at the nylon interface 11.3-12.0 MPa, indicating that the adhesive of this invention has excellent affinity and adhesion to commonly used FPC substrates.

[0058] Compared with Comparative Example 1 (without multifunctional epoxy and silicon dendritic polymer), the shear strength of the examples was increased by about 50%-60%, which is attributed to: ① the multifunctional epoxy enhances the crosslinking density and cohesive strength; ② the dual coupling agent system (KH-560 / KH-550) forms chemical bonds at the resin-substrate interface, significantly improving the interfacial bonding force; ③ the synergistic toughening effect of epoxy-terminated polyether and CTBN; ④ the nanofiller enhances the cohesive force.

[0059] Compared with Comparative Example 2: Although the initial strength of Comparative Example 2 (ordinary epoxy, high halogen) reached 9-11 MPa, it was still lower than that of the Example and did not meet the environmental protection requirements.

[0060] At a low temperature of -30°C, the shear strength retention rate of the embodiment (relative to 25°C) is about 85-86%, which is higher than that of Comparative Example 1 (68%); at a high temperature of 60°C, the strength retention rate is about 93-94%, showing excellent thermal stability.

[0061] The PI interface peel strength of the embodiment reached 4.4-4.9 N / mm, which is much higher than 2.2 N / mm of Comparative Example 1 and 3.5 N / mm of Comparative Example 2, indicating that the adhesive of the present invention has excellent anti-peel performance on flexible substrates.

[0062] Table 6 shows the aging performance test results (PI interface shear strength, MPa). Table 6 Aging conditions Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 initial value 13.5 13.8 13.2 13.6 8.5 11.2 Salt spray test results (48 hours) 12.9 13.2 12.6 13.0 5.5 9.2 Retention rate (%) 95.6 95.7 95.5 95.6 64.7 82.1 Double 85 aging 500h 12.8 13.1 12.5 12.9 5.8 9.5 700h 12.2 12.5 11.9 12.3 4.8 8.6 1008h 11.6 11.9 11.3 11.8 3.8 7.5 1008h retention rate (%) 85.9 86.2 85.6 86.8 44.7 67.0 High and low temperature cycling 500 cycles 12.6 12.9 12.3 12.7 6.5 9.8 700 cycles 12.0 12.3 11.7 12.1 5.5 8.8 1000 cycles 11.4 11.7 11.1 11.5 4.5 7.8 1000-cycle retention rate (%) 84.4 84.8 84.1 84.6 52.9 69.6 The following key conclusions can be drawn from Table 6: Examples 1-4 showed that after aging at double 85 for 1008 hours, the shear strength remained at 11.3-11.9 MPa, with a retention rate of over 85%; after 1000 high and low temperature cycles, the strength retention rate was approximately 84%. The absolute value of the shear strength after all aging processes exceeded 10 MPa, meeting the long-term reliability requirements.

[0063] Comparative Example 1 (silicone-free dendritic polymer and multifunctional epoxy) showed a shear strength of only 3.8 MPa and a retention rate of less than 45% after aging at 85°C for 1008 hours, while the retention rate of the Example was as high as 85% or more. This indicates that the nano-dense structure formed by the silicon dendritic polymer effectively prevents water molecules from hydrolyzing and damaging the epoxy network.

[0064] Comparative Example 2 (high halogen) retained only 67% of its performance after 1008 hours of aging with dual 85, which is about 18 percentage points lower than that of Example 2, indicating that the presence of halogen impurities accelerates the performance degradation during the wet heat aging process.

[0065] Product-level test results The adhesive from Example 1 was applied to actual FPC connector potting products, and product-level reliability testing was conducted. The results are shown in Table 7. Table 7 Product-level reliability test results Test Project Test conditions Judgment criteria Test Results in conclusion warming -40℃↔125℃, air to air, 1000 cycles No cracks, no peeling The exterior is intact and there are no cracks. qualified Electricity immersion Insulation resistance was tested after soaking in deionized water for 48 hours. <![CDATA[≥1×10 9 Oh]]> <![CDATA[3.8×10¹ 0 Oh]]> qualified High temperature storage 125℃，1000h Shear strength ≥ 10 MPa 11.5 MPa (85% retention rate) qualified Double 85 Functionality tested after 1008 hours at 85℃ / 85%RH. Normal function Functionally normal, insulation is good qualified Salt spray 5% NaCl, 35℃, 48h No corrosion, no failure In good condition qualified Low temperature storage -40℃，1000h No cracks, no peeling In good condition qualified Withstand voltage AC 1000V, 1min No breakdown, no flashover pass qualified Product-level test results show that the adhesive of this invention can meet the various reliability requirements of FPC connector potting in actual application scenarios, and still maintains an adhesive strength of more than 10MPa after aging.

[0066] Storage stability test The adhesive from Example 1 was sealed and stored at 25°C and -20°C, respectively, and its viscosity change and curing activity were tested periodically. The results are shown in Table 8 below: Table 8 Storage stability test results Storage conditions Storage time Viscosity change rate (%) Curing activity (gel time at 150℃, s) Shear strength retention rate after curing (%) 25℃ initial - 285 - 1 month +5.2 292 98.5 3 months +13.5 308 95.2 6 months +24.2 338 89.5 -20℃ 3 months +2.2 288 99.2 6 months +4.6 295 98.5 12 months +8.8 308 96.2 The results in Table 8 show that the adhesive of the present invention can be stably stored for more than 3 months at 25°C and for more than 12 months under frozen storage conditions at -20°C, meeting the needs of commercial production and logistics.

[0067] In summary, compared with the prior art, the present invention has the following significant advantages: 1. Excellent combination of adhesive strength and flexibility Through a multi-flexible design incorporating low-halogen bisphenol A epoxy resin, epoxy-terminated polyether, CTBN, and flexible segment modified epoxy resin, combined with multifunctional epoxy resin to enhance cohesive strength, this invention's adhesive achieves a balance between high strength and high flexibility. It exhibits a shear strength exceeding 13.5 MPa for PI substrates, exceeding 12.8 MPa for PBT substrates, and exceeding 11.6 MPa for nylon substrates, while maintaining an elongation at break ≥70% and an elastic modulus ≤0.9 GPa. This effectively solves the technical challenge of balancing flexibility and adhesive strength in FPC connector potting.

[0068] 2. Precise regulation of low Tg By leveraging the synergistic effect of epoxy-terminated polyether and flexible segment-modified epoxy resin, long-chain flexible segments are introduced into the crosslinking network, effectively reducing the crosslinking density and stabilizing the glass transition temperature of the cured product at 45±5℃ and the Shore hardness at 80±5. Studies have shown that reducing network density by introducing flexible segments can significantly improve fracture toughness and anti-delamination properties.

[0069] 3. Excellent resistance to moisture and aging. The introduction of silicon dendritic polymers is a key innovation. Their hyperbranched structure forms dense nanoscale regions within the epoxy network, effectively blocking water molecule penetration. Simultaneously, abundant epoxy groups participate in the cross-linking reaction, forming an interpenetrating network with flexible segments, significantly improving resistance to humid heat aging. After 1008 hours of aging at double 85°C, the PI interfacial shear strength retention rate is ≥85%, and after 1000 high and low temperature cycles, the retention rate is ≥86%, far superior to the comparative example. Research indicates that the synergistic effect of nanofillers and toughening agents can significantly improve the overall performance of epoxy resins.

[0070] 4. Excellent electrical insulation By carefully selecting low-halogen bisphenol A epoxy resin (halogen content ≤900ppm) and high-purity raw materials, the volume resistivity of the adhesive of this invention can reach 3.2×10¹. 5 Ω·cm or higher, surface resistivity ≥2.8×10¹ 4 With a dielectric strength of ≥28 kV / mm and Ω·cm, it fully meets the high insulation requirements of FPCs and connectors. The low-halogen design effectively avoids the degradation of electrical insulation performance caused by halide ion migration.

[0071] 5. Thixotropy and process adaptability By precisely controlling the amount of hydrophobic fumed silica R972, both fixture-free and fixture-based potting processes can be simultaneously met. The fixture-free version (3800 mPa·s, thixotropic index ≥4.2) maintains excellent morphology after dispensing and achieves precise potting without molds; the fixture-based version (22000 mPa·s, thixotropic index ≥6.8) can meet the needs of applications with special requirements for flowability and filling properties. Both versions can be achieved simply by adjusting the amount of fumed silica, while maintaining consistent core performance.

[0072] 6. Rapid curing and good storage stability A latent curing system employing microencapsulated imidazole and anhydride compounds, combined with DCMU accelerator, enables complete curing within 150℃ / 15min, meeting the high-efficiency requirements of automated production lines. The protective microencapsulation wall material allows for storage at room temperature for over 3 months and at -20℃ for up to 12 months. Research indicates that microencapsulated curing agents are an effective method for achieving ultra-long room temperature storage and rapid low-temperature curing of single-component epoxy resins.

[0073] 7. Excellent adhesion over a wide temperature range The adhesive exhibits a PI interfacial shear strength retention rate of ≥83% at -30℃ and ≥93% at 60℃, demonstrating excellent temperature adaptability and reliability over a wide temperature range. Research indicates that the synergistic effect of hydroxyl-terminated polyethersulfone and nano-SiO2 significantly improves the ultra-low temperature mechanical properties of epoxy resin.

[0074] 8. Outstanding environmental protection characteristics The total halogen content of the entire system is ≤900ppm, which meets the RoHS environmental protection standard of the electronics industry. It is free of heavy metal impurities and can be directly used for precision potting of high-end electronic components.

[0075] The foregoing has shown and described the basic principles and main features of the invention and the advantages of the invention.

[0076] Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the present invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope. All such changes and modifications fall within the scope of the present invention as claimed, which is defined by the appended claims and their equivalents.

Claims

1. A flexible, low-Tg, moisture-resistant, one-component epoxy resin adhesive, characterized in that, Based on parts by weight, it includes the following components: 40-60 parts of low-halogen bisphenol A epoxy resin; 15-25 parts of epoxy-terminated polyether; 10-20 parts of flexible segment modified epoxy resin; 5-15 parts of multifunctional epoxy resin; 8-12 parts of carboxyl-terminated butadiene-acrylonitrile rubber; 5-10 parts of silicon dendritic polymer; 8-15 parts of latent curing agent; Curing accelerator 0.5-3 parts; 1-3 parts of silane coupling agent compound; 1.2-3.2 parts of hydrophobic fumed silica; 0.1-0.3 parts of non-silicone defoamer.

2. The flexible, low-Tg, moisture-resistant single-component epoxy resin adhesive as described in claim 1, characterized in that, The single-component epoxy resin adhesive, by weight, comprises the following components: 45-55 parts of low-halogen bisphenol A epoxy resin; 18-22 parts of epoxy-terminated polyether; 12-18 parts of flexible segment modified epoxy resin; 8-12 parts of multifunctional epoxy resin; 9-11 parts of carboxyl-terminated butadiene-acrylonitrile rubber; 6-8 parts of silicon dendritic polymer; 10-13 parts of latent curing agent; 1-2 parts of curing accelerator; 1.5-2.5 parts of silane coupling agent compound; 2.5-3.2 parts of hydrophobic fumed silica; 0.15-0.25 parts of non-silicone defoamer.

3. The flexible, low-Tg, moisture-resistant single-component epoxy resin adhesive as described in claim 1, characterized in that, The single-component epoxy resin adhesive, by weight, comprises the following components: 45-55 parts of low-halogen bisphenol A epoxy resin; 18-22 parts of epoxy-terminated polyether; 12-18 parts of flexible segment modified epoxy resin; 8-12 parts of multifunctional epoxy resin; 9-11 parts of carboxyl-terminated butadiene-acrylonitrile rubber; 6-8 parts of silicon dendritic polymer; 10-13 parts of latent curing agent; 1-2 parts of curing accelerator; 1.5-2.5 parts of silane coupling agent compound; 2.5-3.2 parts of hydrophobic fumed silica; 0.15-0.25 parts of non-silicone defoamer.

4. The flexible, low-Tg, moisture-resistant single-component epoxy resin adhesive as described in claim 1, characterized in that, The low-halogen bisphenol A epoxy resin is E51, which has a halogen content of ≤900ppm, an epoxy value of 0.51±0.02 eq / 100g, and a hydroxyl value of ≤0.05eq / 100g.

5. The flexible, low-Tg, moisture-resistant single-component epoxy resin adhesive as described in claim 1, characterized in that, The epoxy-terminated polyether is a DGE-PPG epoxy-terminated polyether with an epoxy equivalent of 280–320 g / eq and a viscosity of 500–800 mPa·s at 25°C.

6. The flexible, low-Tg, moisture-resistant single-component epoxy resin adhesive as described in claim 1, characterized in that, The flexible segment modified epoxy resin is a product obtained by side-linking and modifying low-halogen bisphenol A epoxy resin with polypropylene glycol of number average molecular weight of 2000-4000. The side chain content in the flexible segment modified epoxy resin is 10%-15% of the total mass of the flexible segment modified epoxy resin.

7. The flexible, low-Tg, moisture-resistant single-component epoxy resin adhesive as described in claim 6, characterized in that, The flexible segment modified epoxy resin is prepared by the following method: Low-halogen bisphenol A epoxy resin was mixed with polypropylene glycol (PPG) with a number average molecular weight of 2000-4000 at a mass ratio of 100:10-15. Then, 0.1%-0.3% triphenylphosphine catalyst was added, and the mixture was reacted at 120-140℃ under nitrogen protection for 2-4 hours to obtain a side-linked modified flexible epoxy resin with an epoxy value controlled in the range of 0.25-0.35 mol / 100g.

8. The flexible, low-Tg, moisture-resistant single-component epoxy resin adhesive as described in claim 6, characterized in that... The carboxyl-terminated nitrile butadiene rubber is a CTBN carboxyl-terminated nitrile butadiene rubber with a number average molecular weight of 1300-1500, an acrylonitrile content of 26-30%, and a carboxyl content of 0.05-0.08 eq / 100g. The multifunctional epoxy resin is one or more of phenolic epoxy resin, p-aminophenol epoxy resin, or 4,5-epoxycyclohexane-1,2-dicarboxylic acid diglycidyl ester; The silicon dendritic polymer is a hyperbranched polysiloxane with a regular branched structure. The hyperbranched polysiloxane has a molecular weight of 5000-10000, and each molecule contains 8-16 epoxy functional groups. The latent curing agent is a mixture of microencapsulated 2-phenyl-4-methylimidazolium and liquid methyltetrahydrophthalic anhydride, with a mass ratio of 1:2 to 1:3; The curing accelerator is 3,4-dichlorophenyldimethylurea; The silane coupling agent complex is a complex of γ-glycidoxypropyltrimethoxysilane and γ-aminopropyltriethoxysilane, with a mass ratio of 2:1 to 3:1; The hydrophobic fumed silica is hydrophobic fumed silica R972 with a specific surface area of ​​200-300 m² / g.

9. A method for preparing a flexible, low-Tg, moisture-resistant single-component epoxy resin adhesive as described in any one of claims 1-8, characterized in that, Includes the following steps: Step 1: The low-halogen bisphenol A epoxy resin, the epoxy-terminated polyether, the flexible segment modified epoxy resin, the carboxyl-terminated nitrile rubber, the multifunctional epoxy resin, and the silicon dendritic polymer are sequentially added to a high-speed stirred tank. The temperature of the stirred tank is set to 55-65°C, and the stirring speed is set to 800-1000 r / min. The mixture is stirred at high speed for 30-40 min until all components are completely and evenly mixed and ready for use. Step 2: Cool the material in the mixing tank to <40℃, then slowly add the latent curing agent, the curing accelerator, the silane coupling agent compound, and the non-silicone defoamer in sequence, and adjust the stirring speed to 300-400 r / min, and stir at low speed for 15-20 min. Step 3: Add the hydrophobic fumed silica to the mixing tank and adjust the stirring speed to 1200-1500 r / min. Disperse at high speed for 25-35 min until the material fineness is <10 μm and the viscosity meets the standard. Then, degas under vacuum to obtain the flexible, low-Tg, moisture-resistant single-component epoxy resin adhesive.

10. The application of a flexible, low-Tg, moisture-resistant single-component epoxy resin adhesive as described in any one of claims 1-8, characterized in that, The applications are for potting flexible circuit board connectors, encapsulating chip components, bonding flexible screens to FPCs, or potting protection for automotive electronic modules.