Epoxy insulating adhesive for heat-conducting photovoltaic module electrode and preparation method and application thereof

Abstract

The application belongs to the field of epoxy insulating glue, and provides an epoxy insulating glue for a heat-conducting photovoltaic component electrode, a preparation method and application thereof, the insulating glue comprising component A and component B; the component A comprises 20-50 parts of organic silicon modified vinyl resin, 50-100 parts of epoxy resin, 0.2-5 parts of curing accelerator, 0.5-5 parts of initiator, 40-90 parts of heat-conducting filler and 0.2-5 parts of silane coupling agent, according to mass fraction; the component B comprises 40-60 parts of acid anhydride curing agent. The application introduces the organic silicon modified vinyl resin into the epoxy insulating glue system, and under the joint action of DCP and the acid anhydride curing agent, the insulating glue is chemically connected with the EVA packaging film at the interface through free radical polymerization grafting during the curing process. This fundamentally solves the interface delamination problem caused by the difference in thermal expansion coefficients between the epoxy resin and the EVA, significantly improves the bonding strength and temperature cycle performance; meanwhile, the moisture resistance, heat conduction and water resistance are also improved.

Description

Technical Field

[0001] This invention relates to the field of thermally conductive and insulating materials, specifically to an epoxy insulating adhesive for electrodes of thermally conductive photovoltaic modules and its preparation method. Background Technology

[0002] Solar photovoltaic (PV) technology, as an important method for utilizing renewable energy, has been widely applied and developed rapidly in recent years. Traditional PV modules mainly consist of a glass cover, encapsulation materials, solar cells, a backsheet, and an electrode system (including busbars and wires). In actual operation, PV modules are affected by environmental factors such as solar radiation, temperature changes, and humidity corrosion, with the electrode system facing particularly severe heat dissipation challenges.

[0003] Photovoltaic modules generate a significant amount of heat during operation, leading to elevated temperatures. Studies show that for every 1°C increase in module temperature, power generation efficiency decreases by approximately 0.4%-0.5%. In high-temperature summer environments, module temperatures can reach over 70°C, implying a power generation efficiency loss of around 20%. Electrodes, as crucial channels for current collection and transmission within the module, often become hotspots due to resistance losses and uneven heat dissipation, further accelerating module performance degradation and aging. To address this challenge, photovoltaic manufacturers typically employ two strategies: optimizing module structural design to enhance heat dissipation capabilities and developing new thermally conductive materials to improve thermal management efficiency. Among these, the application of thermally conductive insulating adhesive has become an effective means of solving electrode heat dissipation problems. It provides electrical insulation while rapidly transferring heat generated by the electrodes to heat dissipation components or the environment, reducing localized temperatures and improving overall module performance and reliability.

[0004] Epoxy resins, due to their excellent adhesion, good mechanical strength, and outstanding chemical resistance, have become one of the main materials in the fields of electronic packaging and insulation protection. While traditional epoxy insulating adhesives possess high insulation strength and adhesion, their thermal conductivity is poor (typically only 0.2-0.3 W / m·K), making it difficult to meet the heat dissipation requirements of high-power-density photovoltaic modules. To address this issue, researchers have developed thermally conductive epoxy insulating adhesives. By adding highly thermally conductive fillers to the epoxy resin matrix, the thermal conductivity of the material is significantly improved. Commonly used thermally conductive fillers include metal oxides (such as alumina and zinc oxide), nitrides (such as boron nitride and aluminum nitride), and carbon materials (such as graphene and carbon nanotubes). These fillers significantly improve the thermal conductivity of the epoxy insulating adhesive by forming thermally conductive pathways. However, adding thermally conductive fillers also brings a series of challenges, such as increased brittleness of the insulating adhesive, poorer interfacial bonding between the insulating adhesive and the matrix, and reduced insulation performance due to high thermal conductivity fillers (such as metal particles). Furthermore, the poor interfacial bonding between the insulating adhesive and the matrix, besides affecting bond strength, also allows air and moisture to penetrate the interface, leading to a decrease in thermal conductivity. In addition, in the special application environment of photovoltaic modules, epoxy insulating adhesives also need to possess properties such as resistance to UV aging, resistance to damp heat corrosion, and resistance to temperature cycling. For example, current advanced photovoltaic module encapsulation technology involves first screen printing insulating adhesive onto the electrodes, then laying an EVA film on the insulating adhesive for heat pressing encapsulation, and finally covering it with a protective glass layer. When epoxy resin insulating adhesive is used on an EVA matrix, the epoxy resin has a high crosslinking density and high modulus after curing, and its coefficient of thermal expansion differs significantly from that of EVA. During the temperature cycling of the module operation, the two materials are prone to microcracks at the interface due to repeated thermal stress, which gradually propagate and eventually lead to problems such as interface delamination and electrical insulation failure. Furthermore, in existing technologies, the bonding between epoxy resin insulating adhesive and EVA mainly relies on physical adsorption and limited polarity, lacking strong chemical bond connections. In humid and hot environments, water molecules can easily penetrate the interface, weakening this physical bonding force and causing rapid deterioration under the combined effects of moisture and stress.

[0005] CN 103059515 A discloses a vinyl ester resin-modified epoxy potting compound and its preparation method. The vinyl ester resin-modified epoxy potting compound consists of component A and component B. Component A consists of epoxy resin and silica powder; component B consists of acid anhydride, vinyl ester resin, initiator, and accelerator. This epoxy potting compound improves the temperature cycling resistance of epoxy resin; however, the vinyl ester resin and epoxy resin do not form effective chemical bonds, resulting in defects such as weak peel strength in the potting compound.

[0006] Therefore, there is an urgent need to develop an insulating adhesive with strong insulation ability, excellent thermal conductivity, outstanding weather resistance and water resistance, and the ability to resist long-term outdoor aging. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides an epoxy insulating adhesive for thermally conductive photovoltaic module electrodes, comprising component A and component B. By weight, component A comprises 20-50 parts of silicone-modified vinyl resin, 50-100 parts of epoxy resin, 0.2-5 parts of curing accelerator, 0.5-5 parts of initiator, 40-90 parts of thermally conductive filler, and 0.2-5 parts of silane coupling agent; component B comprises 40-60 parts of anhydride curing agent.

[0008] Furthermore, the preparation of the organosilicon-modified vinyl resin includes the following steps: (1) Vinylsiloxane, water and catalyst are mixed and subjected to hydrolysis and condensation reaction to obtain polysiloxane; (2) After mixing polysiloxane, vinyl resin and initiator, free radical polymerization reaction is carried out to obtain organosilicon modified vinyl resin.

[0009] Furthermore, component A also includes 0.1-2 parts of defoamer, 0.1-5 parts of antioxidant, and 0.05-2 parts of UV protectant.

[0010] Furthermore, the defoamer includes at least one of silicone defoamers or non-silicone polymer defoamers.

[0011] Furthermore, the antioxidant includes at least one of phenolic antioxidants, phosphite antioxidants, or ketone antioxidants.

[0012] Furthermore, the UV absorber includes at least one of ketone UV absorbers or triazole UV absorbers.

[0013] Furthermore, the initiator includes at least one of dicumyl peroxide, di-(tert-butylperoxyisopropyl)benzene, tert-butyl peroxide, or 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane.

[0014] Further, the curing accelerator includes at least one of 2,4,6-tris(dimethylaminomethyl)phenol, benzyldimethylamine, 2-ethyl-4-methylimidazolium, benzyltriethylammonium chloride, triphenylphosphine, zinc octanoate, or boron trifluoride-monoethylamine.

[0015] Furthermore, the epoxy resin includes at least one of bisphenol A type epoxy resin, phenolic epoxy resin, pentaerythritol epoxy resin, diglycidyl isophthalate, aniline epoxy resin, or dicyclopentenyl dioxide ether.

[0016] Furthermore, the anhydride curing agent includes at least one of dodecenyl succinic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methylnadic anhydride, or hexahydrophthalic anhydride.

[0017] Furthermore, the thermally conductive filler includes at least one of spherical alumina, boron nitride, nano-calcium carbonate, or silicon dioxide.

[0018] Furthermore, the silane coupling agent includes at least one of γ-glycidoxypropyltrimethoxysilane, aminopropyltriethoxysilane, or γ-methacryloyloxypropyltrimethoxysilane.

[0019] Further, the catalyst in step (1) comprises at least one of concentrated hydrochloric acid, sodium hydroxide, potassium hydroxide or tetramethylamine hydroxide.

[0020] Further, the vinylsiloxane in step (1) includes at least one of vinylmethyldimethoxysilane, vinylmethyldiethoxysilane, vinyltriethoxysilane or vinyltrimethoxysilane.

[0021] Further, the mass ratio of vinylsiloxane to water in step (1) is (3-7):1.

[0022] Further, the hydrolysis-condensation reaction conditions in step (1) are: stirring at 50-70℃ for 3-5 hours.

[0023] Further, the mass ratio of polysiloxane, vinyl resin and initiator in step (2) is 1:(3-5):(0.01-0.1).

[0024] Furthermore, the free radical polymerization reaction conditions in step (2) are: stirring at 70-85℃ for 1-2 hours.

[0025] The present invention also provides a method for preparing the above-mentioned epoxy insulating adhesive, comprising the following steps: mixing the materials of component A evenly to obtain adhesive A, component B being adhesive B, mixing adhesive A and adhesive B evenly, and vacuum degassing to obtain an epoxy insulating adhesive for thermally conductive photovoltaic module electrodes.

[0026] The epoxy insulating adhesive used for the electrodes of the aforementioned thermally conductive photovoltaic module is used for heat sealing of the photovoltaic module at a temperature of 145-155℃.

[0027] Furthermore, the encapsulation film in the photovoltaic module is an encapsulation film made of polyolefin or polyolefin derivative material.

[0028] Furthermore, the encapsulation film is an EVA encapsulation film.

[0029] The core concept of this invention lies in designing and preparing an organosilicon-modified vinyl resin containing active vinyl double bonds, and introducing it into an epoxy resin curing system. During the photovoltaic module lamination and curing (hot-press encapsulation) process, the initiator in the insulating adhesive system, such as dicumyl peroxide (DCP), decomposes upon heating, abstracting active hydrogen from the EVA molecular chain to form EVA macromolecular free radicals. These free radicals undergo a grafting reaction with the vinyl double bonds on the organosilicon-modified vinyl resin, thereby forming a strong covalent bond connection at the interface between the epoxy insulating adhesive and the EVA encapsulation film. Simultaneously, the epoxy resin and the anhydride curing agent complete cross-linking and curing. The hydroxyl groups on the organosilicon-modified vinyl resin also participate in the anhydride curing reaction, and the organosilicon segments are subsequently incorporated into the epoxy network through chemical bonds.

[0030] The beneficial effects of this invention are as follows: (1) This invention introduces silicone-modified vinyl resin into the epoxy resin system. Under the synergistic effect of the initiator and the anhydride curing agent, the insulating adhesive forms a chemical bond with the EVA encapsulation film at the interface through free radical grafting during the curing process. This fundamentally solves the problem of interfacial delamination caused by the difference in thermal expansion coefficients between epoxy resin and EVA, and significantly improves the bonding strength and temperature cycling performance. At the same time, the bridging of interfacial chemical bonds reduces phonon scattering and improves thermal conductivity; the dense chemical interface effectively blocks water molecule penetration and enhances water-blocking performance; in addition, by constructing a covalent bond interface between the insulating adhesive and the EVA film, physical interface defects are eliminated, and high-resistivity silicone segments are introduced to form a dense double cross-linked network, which synergistically improves the volume resistivity of the system from both interfacial and intrinsic levels.

[0031] (2) The ceramic thermally conductive filler added in this invention has excellent insulation properties, giving the insulating adhesive good thermal conductivity and anti-leakage properties. The addition of antioxidants and UV stabilizers further improves the material's heat resistance and UV aging resistance, extending the service life of the photovoltaic module.

[0032] (3) In the preparation process of the organosilicon modified vinyl resin of the present invention, a controlled free radical copolymerization strategy is adopted. By controlling the amount of initiator, reaction temperature and reaction time, a chemical bond is formed between the polysiloxane and the vinyl resin, while a sufficient amount of vinyl double bonds are retained for subsequent grafting. The process is highly controllable. Detailed Implementation

[0033] The embodiments of the present invention will be described in detail below with reference to the examples. The following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention.

[0034] Example 1 (1) Preparation of organosilicon-modified vinyl resin: 25g of vinyltrimethoxysilane, 5.4g of deionized water and 0.1g of concentrated hydrochloric acid (concentration of 42wt%) were mixed and stirred at 60°C for 4 hours for hydrolysis and condensation reaction at a stirring speed of 120r / min. Then, methanol and excess water were removed by vacuum distillation to obtain polysiloxane (a vinyl-containing polysiloxane intermediate).

[0035] 10g of polysiloxane and 40g of vinyl resin (model Derakane 411-350) were mixed at room temperature, followed by the addition of 0.5g of free radical initiator methyl ethyl ketone peroxide. The mixture was stirred at 80°C for 1.5 hours at a stirring speed of 120r / min, and then cooled to room temperature to obtain organosilicon-modified vinyl resin. During this process, the double bond consumption rate was approximately 40%.

[0036] (2) Preparation of epoxy insulating adhesive: 30g of silicone-modified vinyl resin, 70g of bisphenol A epoxy resin (model E-51), 1g of curing accelerator 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30), 2g of dicumyl peroxide, 0.5g of defoamer (BYK-A350), 1g of antioxidant 1010, 0.5g of UV stabilizer UV-327, and 1g of silane coupling agent KH-560 were added to a mixing tank and stirred for 30 minutes (800 rpm). After stirring evenly, 80g of boron nitride was added to the mixing tank, and stirring was continued for 1 hour (1200 rpm). Vacuum degassing was then performed to obtain adhesive A.

[0037] 50g of methyl hexahydrophthalic anhydride curing agent is adhesive B.

[0038] Mix A and B adhesives evenly and then degas under vacuum to obtain an epoxy insulating adhesive for thermally conductive photovoltaic module electrodes.

[0039] Example 2 Unlike Example 1, in step (1), 25g of vinyltrimethoxysilane was replaced with 12.5g of vinyltrimethoxysilane and 12.5g of vinyltriethoxysilane, and the rest was the same as in Example 1.

[0040] Example 3 The difference from Example 1 is that the methyl hexahydrophthalic anhydride curing agent is replaced with methyl tetrahydrophthalic anhydride, while the rest is the same as in Example 1.

[0041] Example 4 Unlike Example 1, the amount of organosilicon-modified vinyl resin used in step (2) is 40g, while the rest is the same as in Example 1.

[0042] Comparative Example 1 The difference from Example 1 is that the methyl hexahydrophthalic anhydride curing agent of adhesive B is replaced with the amine curing agent polyetheramine D230, otherwise it is the same as Example 1.

[0043] Comparative Example 2 Unlike Example 1, the polysiloxane in step (1) is replaced with double-ended vinyl silicone oil with a viscosity of 1000 mPa·s, and the rest is the same as in Example 1.

[0044] Comparative Example 3 100g of bisphenol A epoxy resin (model E-51), 1g of curing accelerator 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30), 0.5g of defoamer (BYK-A350), 1g of antioxidant 1010, 0.5g of UV stabilizer UV-327, and 1g of silane coupling agent KH-560 were added to a mixing tank and stirred for 30 minutes (800 r / min). After stirring evenly, 80g of boron nitride was added to the mixing tank, and stirring was continued for 1 hour (1200 r / min). Vacuum degassing was then performed to obtain adhesive A.

[0045] 50g of methyl hexahydrophthalic anhydride curing agent is adhesive B.

[0046] Mix A and B adhesives evenly and then degas under vacuum to obtain an epoxy insulating adhesive for thermally conductive photovoltaic module electrodes.

[0047] The epoxy insulating adhesives (mixtures of A and B) prepared in the above examples and comparative examples were uniformly coated on the surface of a photovoltaic-grade EVA film (0.5 mm thick, Hangzhou Foster). The adhesive layer thickness was controlled to be 0.2 mm. Another EVA film was then applied, and the film was placed in a vacuum laminator and laminated and cured at 150°C and 0.1 MPa for 20 minutes to obtain a three-layer composite film test sample of EVA / adhesive / EVA. Performance tests were conducted according to the following methods: (1) Thermal conductivity: The overall thermal conductivity of the composite film was measured using a thermal conductivity meter based on the ASTM D5470 standard.

[0048] (2) Water vapor transmission rate at 38℃: The water vapor transmission rate of the composite membrane was measured at 38℃ and 100% relative humidity according to ASTM F1249 standard.

[0049] (3) Peel strength (damp heat resistance): According to GB / T 2790 standard, after the sample is aged for 1000 hours under damp heat conditions of 85℃ and 85% RH, a 180° peel test is performed at a peel speed of 100 mm / min to test the peel strength between the epoxy adhesive layer and the EVA film.

[0050] (4) Volume resistivity: The volume resistivity of the cured pure adhesive layer was measured according to GB / T 1410 standard.

[0051] (5) Temperature cycling performance: The composite film sample was placed in a temperature cycling test chamber and cycled 200 times at temperatures ranging from -40℃ (holding for 30 min) to 85℃ (holding for 30 min), with a heating / cooling rate of 5℃ / min. After the cycle, the interface was observed for delamination or cracks, and the adhesive strength retention rate was tested.

[0052] The test results are shown in Table 1.

[0053] Table 1

[0054] As shown in Table 1, Examples 1-4 are significantly superior to Comparative Examples 1-3 in terms of thermal conductivity, water vapor permeability, adhesive strength, volume resistivity, and temperature cycling performance. In particular, the advantages of the Examples are extremely evident in adhesive strength and strength retention after temperature cycling, which represent interfacial bonding performance, fully demonstrating the technical effectiveness of this invention in connecting EVA and epoxy insulating adhesive through chemical bonds. In this invention, a grafting reaction (free radical polymerization) occurs at the interface between the insulating adhesive and EVA—during hot-press encapsulation, the vinyl double bonds retained on the silicone-modified vinyl resin, the molecular chains of the EVA encapsulation film, and a small amount of unreacted double bonds in EVA undergo free radical polymerization under the initiation of an initiator (such as dicumyl peroxide DCP, with a half-life temperature of approximately 135°C after 1 hour); including the following reactions: Step 1 (DCP thermal decomposition): C6H5-C(CH3)2-OOC(CH3)2-C6H5→ 2 C6H5-C(CH3)2-O•; Step 2 (hydrogen abstraction, forming EVA macromolecular free radicals): C6H5-C(CH3)2-O• + -CH2-CH(OAc)- (EVA main chain VAc unit) → C6H5-C(CH3)2-OH + -CH2- (OAc)-; Step 3 (grafting reaction): -CH2- (OAc)- + CH2=CH-Si≡→ Graft copolymer of EVA and organosilicon segments connected by C-C bonds.

[0055] The lamination curing temperature is 150℃, during which DCP rapidly decomposes, triggering the grafting reaction described above. The grafting reaction and the anhydride curing reaction proceed simultaneously and do not interfere with each other. The grafting reaction enhances the bonding strength between the insulating adhesive and the EVA matrix, while the anhydride curing reaction constructs the cross-linked network of the insulating adhesive matrix.

[0056] Comparative Example 1 used an amine-based curing agent, and Comparative Example 2 used a hydroxyl-free vinyl silicone oil. The silicone-modified resin could not effectively integrate into the epoxy network through the formation of chemical bonds using the anhydride curing agent or hydroxyl groups, resulting in a significant performance degradation. Comparative Example 3 was a pure epoxy system; there were no chemical bonds between the insulating adhesive and EVA, resulting in the weakest interfacial bonding and the worst performance.

Claims

1. An epoxy insulating adhesive for electrodes of a thermally conductive photovoltaic module, characterized in that, It includes component A and component B; by mass parts, component A includes 20-50 parts of silicone-modified vinyl resin, 50-100 parts of epoxy resin, 0.2-5 parts of curing accelerator, 0.5-5 parts of initiator, 40-90 parts of thermally conductive filler, and 0.2-5 parts of silane coupling agent, and component B includes 40-60 parts of acid anhydride curing agent.

2. The epoxy insulating adhesive for electrodes of a thermally conductive photovoltaic module according to claim 1, characterized in that, The preparation of the organosilicon-modified vinyl resin includes the following steps: S1. Vinylsiloxane, water and catalyst are mixed and then subjected to hydrolysis-condensation reaction to obtain polysiloxane; S2. Polysiloxane, vinyl resin and initiator are mixed and subjected to free radical polymerization to obtain organosilicon modified vinyl resin.

3. The epoxy insulating adhesive for electrodes of a thermally conductive photovoltaic module according to claim 1, characterized in that, Component A also includes 0.1-2 parts of defoamer, 0.1-5 parts of antioxidant, and 0.05-2 parts of UV protectant; The defoamer includes at least one of silicone defoamers or non-silicone polymer defoamers; The antioxidants include at least one of phenolic antioxidants, phosphite antioxidants, or ketone antioxidants; The UV absorber includes at least one of ketone UV absorbers or triazole UV absorbers.

4. The epoxy insulating adhesive for electrodes of a thermally conductive photovoltaic module according to claim 1, characterized in that, The initiator includes at least one of dicumyl peroxide, di-(tert-butylperoxyisopropyl)benzene, tert-butyl peroxide, or 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane.

5. The epoxy insulating adhesive for electrodes of a thermally conductive photovoltaic module according to claim 1, characterized in that, The curing accelerator includes at least one of 2,4,6-tris(dimethylaminomethyl)phenol, benzyl dimethylamine, 2-ethyl-4-methylimidazolium, benzyl triethylammonium chloride, triphenylphosphine, zinc octanoate, or boron trifluoride-monoethylamine. The epoxy resin includes at least one of bisphenol A type epoxy resin, phenolic epoxy resin, pentaerythritol epoxy resin, diglycidyl isophthalate, aniline epoxy resin, or dicyclopentenyl dioxide ether. The anhydride curing agent includes at least one of dodecenyl succinic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methylnadic anhydride, or hexahydrophthalic anhydride.

6. The epoxy insulating adhesive for electrodes of a thermally conductive photovoltaic module according to claim 1, characterized in that, The thermally conductive filler includes at least one of spherical alumina, boron nitride, nano-calcium carbonate, or silicon dioxide. The silane coupling agent includes at least one of γ-glycidoxypropyltrimethoxysilane, aminopropyltriethoxysilane, or γ-methacryloxypropyltrimethoxysilane.

7. The epoxy insulating adhesive for electrodes of a thermally conductive photovoltaic module according to claim 2, characterized in that, The catalyst described in S1 contains at least one of concentrated hydrochloric acid, sodium hydroxide, potassium hydroxide, or tetramethylamine hydroxide, and the vinylsiloxane includes at least one of vinylmethyldimethoxysilane, vinylmethyldiethoxysilane, vinyltriethoxysilane, or vinyltrimethoxysilane. The mass ratio of vinylsiloxane to water is 3-7:

1. The hydrolysis-condensation reaction conditions are: stirring at 50-70°C for 3-5 hours.

8. The epoxy insulating adhesive for electrodes of a thermally conductive photovoltaic module according to claim 2, characterized in that, The mass ratio of polysiloxane, vinyl resin and initiator in S2 is 1:3-5:0.01-0.1; the free radical polymerization reaction conditions are: stirring at 70-85℃ for 1-2 hours.

9. A method for preparing an epoxy insulating adhesive for electrodes of a thermally conductive photovoltaic module according to any one of claims 1-8, characterized in that, Includes the following steps: Mix all materials in component A evenly to obtain adhesive A, and component B is adhesive B. Mix adhesive A and adhesive B evenly and degas under vacuum to obtain epoxy insulating adhesive for thermally conductive photovoltaic module electrodes.

10. The application of the epoxy insulating adhesive for electrodes of a thermally conductive photovoltaic module according to any one of claims 1-8, characterized in that, Used for heat-sealing photovoltaic modules, with a heat-sealing temperature of 145-155℃; the encapsulation film in the photovoltaic module is an encapsulation film made of polyolefin or polyolefin derivative.

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