Epoxy resin and preparation method thereof, glue composition and packaging glue film

Abstract

In order to improve the high light transmittance, long-acting ultraviolet aging resistance and permanent high reliability of the flame-retardant epoxy resin packaging material, the invention provides epoxy resin, the chemical formula of the epoxy resin is as shown in the formula 1, in the formula 1, any two of R1-R6 are selected from glycidyl ether, and the rest are selected from H.

Description

Technical Field

[0001] This invention relates to the field of optical adhesive technology, and more particularly to an epoxy resin and its preparation method, adhesive composition, and encapsulating film. Background Technology

[0002] Epoxy resin is widely used in LED encapsulation due to its excellent properties. However, with the development of Mini / Micro LED display technology, encapsulation materials need to meet high optical transparency requirements. For example, the transmittance at a wavelength of 550 nanometers usually needs to be greater than 90%, and the haze needs to be less than 2% to ensure the clarity and brightness of the display. They also need to have excellent resistance to ultraviolet aging to ensure a service life of more than 50,000 hours and avoid yellowing and performance degradation. At the same time, they also need to have a permanent and reliable high flame retardant rating, such as meeting the UL-94 V-0 standard, and the flame retardant properties do not decrease or migrate during long-term use.

[0003] Current mainstream flame retardant modification schemes have significant drawbacks. High levels of flame retardants can severely impair the light transmittance and mechanical strength of materials. For example, adding 20% ​​aluminum hydroxide can reduce light transmittance from 90% to below 70%. Furthermore, small-molecule flame retardants are prone to migration and precipitation, leading to increased haze and decreased flame retardant durability. While reactive flame retardant schemes based on DOPO improve the migration problem, their flame retardant efficiency is low, typically requiring 2% to 4% phosphorus content and lacking synergistic effects. Additionally, their molecular structure makes it difficult for light transmittance to exceed 91%, and they yellow under ultraviolet light, failing to meet long-term aging resistance requirements.

[0004] Therefore, there is an urgent need for an epoxy resin encapsulation material that can simultaneously achieve high light transmittance, long-lasting UV aging resistance, and permanent high reliability flame retardancy. Summary of the Invention

[0005] The purpose of this invention is to provide an epoxy resin and its preparation method, an adhesive composition, and an encapsulating film, so as to solve the problem that the existing technology cannot balance the flame retardancy, transparency, reliability and processability of the encapsulating film.

[0006] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: In a first aspect, the present invention provides an epoxy resin, the chemical formula of which is shown in Formula 1: Formula 1, In Formula 1, any two of R1-R6 are selected from glycidyl ether, and the rest are selected from H.

[0007] Optionally, R1 and R4 are each independently selected from glycidyl ether.

[0008] Secondly, the present invention provides a method for preparing the above-mentioned epoxy resin, comprising the following steps: Hexachlorocyclotriphosphazene and phenol are dissolved in a first solvent, an acid-binding agent is added, and the reaction is carried out to generate dichloro-tetra(phenoxy)cyclotriphosphazene. Dichloro-tetra(phenoxy)cyclotriphosphazene is dissolved in a second solvent, and hydroquinone and an acid-binding agent are added to react and generate bis(4-hydroxyphenoxy)-tetra(phenoxy)cyclotriphosphazene. Bis(4-hydroxyphenoxy)-tetra(phenoxy)cyclotriphosphazene, epichlorohydrin, and catalyst were dissolved in a third solvent and reacted to carry out ring-opening etherification, yielding a solution containing the intermediate. An alkaline solution is added to a solution containing the intermediate, and a reaction is carried out to obtain the epoxy resin shown in Formula 1.

[0009] Optionally, the molar ratio of hexachlorocyclotriphosphazene to phenol is 1:4 to 1:4.2; and / or, The molar ratio of dichloro-tetra(phenoxy)cyclotriphosphazene to hydroquinone is 1:2 to 1:2.2; and / or, The molar ratio of bis(4-hydroxyphenoxy)-tetra(phenoxy)cyclotriphosphazene to epichlorohydrin is 1:2 to 1:8.

[0010] Optionally, the step of generating dichloro-tetra(phenoxy)cyclotriphosphazene further includes: Hexachlorocyclotriphosphazene and phenol are dissolved in a first solvent, an acid-binding agent is added, and the mixture is reacted at -10 to 0°C for 3 to 4 hours. Then, the temperature is raised to 30 to 40°C and the mixture is reacted for 16 to 20 hours.

[0011] Optionally, the acid-binding agent includes triethylamine; The catalyst comprises one or more of tetrabutylammonium bromide, tetraoctylammonium bromide, and benzyltriethylammonium chloride; and / or The alkaline solution includes one or both of sodium hydroxide solution and potassium hydroxide solution, and the mass concentration of the alkaline solution is 20%-30%.

[0012] Thirdly, the present invention provides an adhesive composition comprising bisphenol A epoxy resin, a curing agent, and a functional epoxy resin, wherein the functional epoxy resin is the aforementioned epoxy resin.

[0013] Optionally, it includes the following components by weight: 55-70 parts bisphenol A epoxy resin, 20-30 parts functional epoxy resin and 20-40 parts curing agent.

[0014] Optionally, the adhesive composition further includes 5-15 parts epoxy diluent, 0.2-2 parts coupling agent, 0.2-2 parts antioxidant, and 0.2-2 parts ultraviolet absorber.

[0015] Fourthly, the present invention provides an encapsulating film comprising the above-described adhesive composition.

[0016] This invention intrinsically integrates the cyclotriphosphazene (containing a triazine nitrogen source) structure into the epoxy resin molecular chain via chemical bonds, forming a molecular-level PN synergistic system. The cyclotriphosphazene skeleton provides phosphorus and nitrogen elements, realizing an intrinsic phosphorus-nitrogen (PN) synergistic flame-retardant mechanism at the molecular level. When the material is heated or burned, the phosphorus element generates acidic catalysts such as phosphoric acid and polyphosphoric acid, promoting the carbonization of resin molecules to form a dense char layer. The nitrogen component releases inert gases, diluting oxygen in the combustion zone and inhibiting flame propagation. Simultaneously, it reacts with phosphorus compounds to generate intumescent ammonium phosphate, further thickening the char layer. Firstly, this synergistic effect significantly improves flame retardant efficiency, enabling the resin to achieve a high flame retardant rating with relatively low phosphorus content. Secondly, this molecular structure avoids strongly light-absorbing conjugated fused rings such as phenanthrene rings found in DOPO, with phenoxy groups as the main side chains. This greatly reduces the absorption of visible light, providing a molecular basis for the material to achieve high light transmittance and low haze. Thirdly, by firmly anchoring flame retardant elements to the resin backbone through chemical bonds, the migration and precipitation of small molecule flame retardants can be prevented, thus ensuring the permanence of flame retardant performance and the long-term stability of the material interface. Meanwhile, the epoxy resin shown in Formula 1 has cyclotriphosphazene as its core, with phenoxy groups and two glycidyl ether groups connected to its side chains. It has no phenanthrene ring structure, is resistant to yellowing, and has uniform polarity of molecular chain segments. When mixed with the base resin, it can form a molecular-level homogeneous system without macroscopic phase separation, ensuring optical stability and meeting the high-definition image quality requirements of Mini / Micro LED displays. The six-membered heterocyclic structure of cyclotriphosphazene (bond energy > 350 kJ / mol) and the aromatic ring structure of phenoxy form a rigid molecular skeleton, which makes the resin thermal decomposition temperature (Td5%) reach 355℃. Furthermore, the flame retardant participates in the reaction and enters the crosslinking network, with little impact on heat resistance, so that the epoxy resin of the present invention has excellent heat resistance. Detailed Implementation

[0017] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0018] One embodiment of the present invention provides an epoxy resin, the chemical formula of which is shown in Formula 1: Formula 1, In Formula 1, any two of R1-R6 are selected from glycidyl ether, and the rest are selected from H.

[0019] Specifically, this invention intrinsically integrates the cyclotriphosphazene (containing a triazine nitrogen source) structure into the epoxy resin molecular chain through chemical bonds, forming a molecular-level PN synergistic system. The cyclotriphosphazene skeleton provides phosphorus and nitrogen elements, realizing an intrinsic phosphorus-nitrogen (PN) synergistic flame retardant mechanism at the molecular level. When the material is heated or burned, the phosphorus element generates acidic catalysts such as phosphoric acid and polyphosphoric acid, promoting the carbonization of resin molecules to form a dense char layer. Meanwhile, the nitrogen component releases inert gases, diluting oxygen in the combustion zone and inhibiting flame propagation. Simultaneously, it reacts with phosphorus compounds to generate intumescent ammonium phosphate, further enhancing flame retardancy. The thick char layer significantly enhances flame retardant efficiency, enabling the resin to achieve a high flame retardant rating with relatively low phosphorus content. Secondly, the molecular structure avoids strongly light-absorbing conjugated fused rings such as phenanthrene rings found in DOPO, with phenoxy groups as the main side chains. This greatly reduces the absorption of visible light, providing a molecular basis for the material to achieve high light transmittance and low haze. By firmly anchoring flame retardant elements to the resin backbone through chemical bonds, the migration and precipitation of small molecule flame retardants can be prevented, thus ensuring the permanence of flame retardant performance and the long-term stability of the material interface. Meanwhile, the epoxy resin shown in Formula 1 has cyclotriphosphazene as its core, with phenoxy groups and two glycidyl ether groups connected to its side chains. The reason for choosing two glycidyl ether groups is that only one end of a single glycidyl ether group can participate in the crosslinking reaction, which affects the growth of the molecular chain. The crosslinking network formed by three or more glycidyl ether groups is too dense, which leads to increased brittleness of the cured product. The compound shown in Formula 1 has no phenanthrene ring structure, is resistant to yellowing, and has uniform polarity of molecular chain segments. When mixed with the base resin, it can form a molecular-level homogeneous system without macroscopic phase separation, ensuring optical stability and meeting the high-definition image quality requirements of Mini / Micro LED displays. The six-membered heterocyclic structure of cyclotriphosphazene (bond energy > 350 kJ / mol) and the aromatic ring structure of phenoxy form a rigid molecular skeleton, which makes the resin thermal decomposition temperature (Td5%) reach 355℃. In addition, the flame retardant participates in the reaction and enters the crosslinking network, with little impact on heat resistance, so that the epoxy resin of the present invention has excellent heat resistance.

[0020] In some embodiments, R1 and R4 are each independently selected from glycidyl ether.

[0021] Specifically, the epoxy resin of this invention is chemically named bis(glycidyl ether)-tetra(phenoxy)cyclotriphosphazene, with the molecular formula N3P3(OC6H5)4(OC6H4-O-CH2-CH(O)CH2)2. The specific substitution sites of glycidyl ether optimize the spatial distribution and reactivity of epoxy functional groups in the molecule, resulting in a more uniform and dense cross-linked network structure after curing. This uniform network structure helps reduce internal light scattering points, thereby further reducing the haze of the cured material and improving the uniformity of light transmittance. Simultaneously, the regular molecular structure also helps improve the glass transition temperature and thermal stability of the cured material, enhancing the dimensional stability and reliability of the encapsulation material under high-temperature operating conditions.

[0022] An embodiment of the present invention also provides a method for preparing the above-mentioned epoxy resin, comprising the following steps: Hexachlorocyclotriphosphazene and phenol are dissolved in a first solvent, an acid-binding agent is added, and the reaction is carried out to generate dichloro-tetra(phenoxy)cyclotriphosphazene. Dichloro-tetra(phenoxy)cyclotriphosphazene is dissolved in a second solvent, and hydroquinone and an acid-binding agent are added to react and generate bis(4-hydroxyphenoxy)-tetra(phenoxy)cyclotriphosphazene. Bis(4-hydroxyphenoxy)-tetra(phenoxy)cyclotriphosphazene, epichlorohydrin, and catalyst were dissolved in a third solvent and reacted to carry out ring-opening etherification, yielding a solution containing the intermediate. An alkaline solution is added to a solution containing the intermediate, and a reaction is carried out to obtain the epoxy resin shown in Formula 1.

[0023] Specifically, this method aims to synthesize the target molecular structure efficiently and with high purity through multi-step reactions and precise process control. The steps first involve synthesizing a specifically substituted cyclotriphosphazene intermediate, then introducing a linker arm containing a phenolic hydroxyl group, and finally attaching an epoxy functional group through ring-opening etherification and ring-closing reactions. This controllable synthetic route ensures the accuracy and uniformity of the target product structure, avoids the generation of byproducts and unreacted small molecule impurities, and enables the encapsulation film to achieve high light transmittance and low haze. This ensures long-term stability of color reproduction and brightness uniformity in Mini / Micro LED display panels. The entire fabrication process design provides a reliable pathway to obtaining high-performance, highly consistent products.

[0024] In some embodiments, the first solvent comprises anhydrous tetrahydrofuran.

[0025] In some embodiments, the acid-binding agent includes triethylamine.

[0026] In some embodiments, the reaction of hexachlorocyclotriphosphazene with phenol is carried out under a protective gas atmosphere.

[0027] In some embodiments, the second solvent includes acetonitrile.

[0028] In some embodiments, the reaction conditions between dichloro-tetra(phenoxy)cyclotriphosphazene and hydroquinone are reflux at 70-80°C for 10-12 hours.

[0029] In some embodiments, the generated bis(4-hydroxyphenoxy)-tetra(phenoxy)cyclotriphosphazene is purified by recrystallization from toluene and n-hexane.

[0030] Specifically, the purification step of the intermediates can remove impurities that affect optical performance and avoid light scattering sites. This is a key process to ensure that the final encapsulation film achieves high light transmittance and low haze, and can ensure the long-term stability of color reproduction and brightness uniformity of the Mini / Micro LED display panel. In some embodiments, the third solvent includes one or both of butanone and cyclohexanone.

[0031] In some embodiments, the reaction conditions between bis(4-hydroxyphenoxy)-tetra(phenoxy)cyclotriphosphazene and epichlorohydrin are a temperature of 80°C to 100°C for 4 to 5 hours.

[0032] In some embodiments, the reaction conditions with the alkaline solution are a temperature of 50°C to 60°C and a holding time of 3 to 4 hours.

[0033] In some embodiments, the reaction with the alkaline solution is stopped when the epoxy value reaches 0.22~0.25 eq / 100g.

[0034] Specifically, epoxy values ​​include, but are not limited to, 0.22eq / 100g, 0.23eq / 100g, 0.24eq / 100g, and 0.25eq / 100g.

[0035] In some embodiments, the molar ratio of hexachlorocyclotriphosphazene to phenol is 1:4 to 1:4.2; and / or, The molar ratio of dichloro-tetra(phenoxy)cyclotriphosphazene to hydroquinone is 1:2 to 1:2.2; and / or, The molar ratio of bis(4-hydroxyphenoxy)-tetra(phenoxy)cyclotriphosphazene to epichlorohydrin is 1:2 to 1:8.

[0036] Specifically, controlling the ratio of hexachlorocyclotriphosphazene to phenol allows for precise control of the number of phenoxy substitutions, ensuring the formation of a product primarily composed of a tetraphenoxydichloro intermediate and avoiding over- or under-substitution. Controlling the ratio of dichloro-tetra(phenoxy)cyclotriphosphazene to hydroquinone ensures the introduction of two reaction sites on each target molecule, laying the structural foundation for the subsequent symmetrical introduction of two epoxy groups. This guarantees that the final product's molecular structure conforms to the design and that its performance is stable and reproducible.

[0037] In some embodiments, the step of generating dichloro-tetra(phenoxy)cyclotriphosphazene further includes: Hexachlorocyclotriphosphazene and phenol are dissolved in a first solvent, an acid-binding agent is added, and the mixture is reacted at -10 to 0°C for 3 to 4 hours. Then, the temperature is raised to 30 to 40°C and the mixture is reacted for 16 to 20 hours.

[0038] Specifically, a stepwise temperature control strategy, which involves reacting at a low temperature first and then raising the temperature to a medium temperature and holding it thereafter, effectively controls the reaction rate and selectivity. The low-temperature stage helps control the intensity of the initial reaction and reduces side reactions; the subsequent temperature increase promotes complete reaction and improves conversion rate. Compared to single-temperature reactions, this staged temperature control process can more accurately obtain intermediates with the desired substitution mode, reduce the formation of isomers or impurities, and ensure the purity and performance consistency of the final product.

[0039] In some embodiments, the acid-binding agent includes triethylamine; The catalyst comprises one or more of tetrabutylammonium bromide, tetraoctylammonium bromide, and benzyltriethylammonium chloride; and / or The alkaline solution includes a sodium hydroxide solution, and the mass concentration of the alkaline solution is 20%-30%.

[0040] Specifically, triethylamine, as an organic base, can effectively neutralize the HCl produced in the reaction and promote the forward reaction; tetrabutylammonium bromide, etc., as phase transfer catalysts, can significantly improve the reaction efficiency in heterogeneous reactions (such as the ring-opening etherification reaction of epichlorohydrin); using sodium hydroxide solution of a specific concentration for ring-closing reaction, the concentration range of which can balance the reaction rate and the suppression of hydrolysis side reactions of epoxy groups, ensures the stability and controllability of epoxy value.

[0041] An embodiment of the present invention also provides an adhesive composition comprising bisphenol A epoxy resin, a curing agent, and a functional epoxy resin, wherein the functional epoxy resin is the aforementioned epoxy resin. Specifically, the functional epoxy resin is compounded with a general-purpose bisphenol A type epoxy resin and a curing agent. This combination ensures excellent overall performance while also considering cost and processability. The introduction of intrinsic PN synergistic flame-retardant epoxy resin provides the entire curing system with efficient and long-lasting flame retardancy. At the same time, due to its good compatibility with the base resin and its own excellent optical properties, it will not negatively affect the overall light transmittance and haze of the composition. The curing agent can cure the functional epoxy resin and the bisphenol A type epoxy resin to form a cross-linked network.

[0042] In some embodiments, the product comprises the following components by weight: 55-70 parts of bisphenol A epoxy resin, 20-30 parts of functional epoxy resin, and 20-40 parts of curing agent.

[0043] Specifically, the functional epoxy resin uses cyclotriphosphazene as its core, with phenoxy groups and two glycidyl ether groups linked to its side chains. It lacks a phenanthrene ring structure, is resistant to yellowing, and has uniform polarity in its molecular chain segments. Its solubility parameter differs from that of bisphenol A epoxy resin by <0.8 (cal / cm³). 3 ) 1 / 2 When mixed with bisphenol A epoxy resin, it can form a molecular-level homogeneous system without macroscopic phase separation, ensuring optical stability and meeting the high-definition image quality requirements of Mini / Micro LED displays. Bisphenol A epoxy resin, as the main component, provides basic mechanical strength and adhesive properties. The amount of functional epoxy resin added must be sufficient to bring significant PN synergistic flame retardant effect to the system to achieve the UL-94 V-0 rating, while not too much to avoid affecting the viscosity, processability, or other mechanical properties of the system. The amount of curing agent must be matched with the total epoxy groups to ensure complete curing and the formation of a dense network.

[0044] The bisphenol A epoxy resin is available in parts by weight, including but not limited to 55 parts, 60 parts, 65 parts, and 70 parts.

[0045] The functional epoxy resins are available in parts by weight, including but not limited to 20 parts, 22 parts, 25 parts, 27 parts, and 30 parts.

[0046] The curing agent is available in parts by weight, including but not limited to 20 parts, 22 parts, 25 parts, 27 parts, and 30 parts.

[0047] In some embodiments, the adhesive composition further includes 5-15 parts epoxy diluent, 0.2-2 parts coupling agent, 0.2-2 parts antioxidant, and 0.2-2 parts ultraviolet absorber.

[0048] Specifically, epoxy diluents can adjust the viscosity of the adhesive solution to meet different application process requirements; coupling agents can enhance the chemical bonding force between the encapsulating adhesive and heterogeneous materials such as chips and substrates, and improve the resistance to damp heat, thereby enhancing the long-term reliability of the encapsulating film; the synergistic addition of antioxidants and UV absorbers can inhibit the oxidative degradation reaction of resin under long-term heat and UV irradiation at the molecular level. These auxiliary components can significantly delay the yellowing of materials and maintain stable light transmittance.

[0049] The epoxy diluent is available in parts by weight, including but not limited to 5 parts, 8 parts, 10 parts, 12 parts, and 15 parts.

[0050] The coupling agent is available in parts by weight, including but not limited to 0.2 parts, 0.5 parts, 1 part, 1.5 parts, and 2 parts.

[0051] The antioxidants are available in parts by weight, including but not limited to 0.2 parts, 0.5 parts, 1 part, 1.5 parts, and 2 parts.

[0052] The weight parts of the ultraviolet absorber include, but are not limited to, 0.2 parts, 0.5 parts, 1 part, 1.5 parts, and 2 parts.

[0053] An embodiment of the present invention also provides an encapsulating film comprising the above-described adhesive composition.

[0054] Specifically, the encapsulating film of the present invention can simultaneously possess high light transmittance and low haze, intrinsic and permanent UL-94V-0 flame retardant properties, and excellent resistance to ultraviolet radiation and damp heat aging. It can effectively solve the core contradiction of high optical requirements, permanent flame retardancy and long-term reliability, and meet the stringent requirements of next-generation high-end display technology for encapsulating materials.

[0055] In one specific embodiment, the specific steps for preparing the epoxy resin include: 1. Preparation of dichloro-tetra(phenoxy)cyclotriphosphazene (intermediate 1) (1) Preparation of experimental apparatus: Use a 2000mL three-necked round-bottom flask, equip it with a mechanical stirrer (stirring speed adjustable range 0-1000rpm), a constant pressure dropping funnel (500mL specification, with polytetrafluoroethylene piston), and a reflux condenser (the upper end is connected to the nitrogen inlet tube), and place the three-necked flask in a low temperature constant temperature reaction bath (temperature control range -20℃~100℃).

[0056] (2) Raw material pretreatment: Hexachlorocyclotriphosphazene (HCCP, purity 99%, purchased from Aladdin Reagent) was dried at 80℃ and vacuum degree -0.095MPa for 4h to remove moisture; Phenol (analytical grade, purity 99.5%, purchased from Sinopharm Group) was purified by vacuum distillation (boiling point 182℃ / 0.1MPa) to remove impurities; Anhydrous tetrahydrofuran (THF, analytical grade, water content <0.05%) was dried with 4A molecular sieve for 24h before use; Triethylamine (analytical grade, purity 99%) was dried with potassium hydroxide and then purified by vacuum distillation.

[0057] (3) Feeding and reaction control: Under nitrogen protection (nitrogen flow rate 50 mL / min), add 1.0 mol (347.7 g) of dried HCCP and 500 mL of anhydrous THF to a three-necked flask, turn on the mechanical stirrer, adjust the stirring speed to 300 rpm, so that the HCCP is completely dissolved and a colorless and transparent solution is formed; lower the temperature of the low temperature constant temperature reaction bath to 0℃ and maintain this temperature for 30 min to ensure the system temperature is stable.

[0058] (4) Dropping operation: Dissolve 4 mol (376.4 g) of purified phenol and 4 mol (404.8 g) of purified triethylamine in 300 mL of anhydrous THF to prepare a mixed solution, and transfer it to a constant pressure dropping funnel; under stirring, slowly add the mixed solution to the three-necked flask, strictly control the dropping rate to 1-2 drops / second (about 5 mL / min), and at the same time control the temperature of the reaction system to not exceed 5℃ through a low temperature constant temperature reaction bath (if the temperature exceeds 5℃, stop the dropping, and continue the dropping after the temperature drops below 5℃), the dropping process lasts for about 60-80 min.

[0059] (5) Heat preservation reaction: After the addition is completed, the system temperature is maintained at 0℃ and the reaction is stirred for 4h (samples are taken every 1h during this period, and the reaction progress is monitored by high performance liquid chromatography (HPLC, mobile phase: acetonitrile / water = 80 / 20, detection wavelength 254nm). When the peak area ratio of HCCP is <1%, the reaction is considered to be completed in this stage); then the temperature of the low temperature constant temperature reaction bath is raised to 40℃, and the heating rate is controlled at 20℃ / h to avoid excessive heating and violent local reaction. After the temperature is raised to 40℃, the temperature is maintained and the reaction continues for 12h. Samples are taken every 3h during this period, and the reaction progress is monitored by HPLC. When the peak area ratio of intermediate 1 is >95%, the reaction is stopped.

[0060] (6) Post-processing: After the reaction is completed, turn off the heating device and wait for the system temperature to drop to room temperature (25℃). Stop stirring and filter the reaction solution (using a Buchner funnel, the filter cake is triethylamine hydrochloride). Collect the filtrate. Transfer the filtrate to a 2000mL separatory funnel and wash it 3 times with deionized water (500mL each time) until the pH of the aqueous phase after washing is 7 (tested with pH paper) to remove excess triethylamine and triethylamine hydrochloride. Transfer the washed organic phase to a 1000mL round-bottom flask, add 10g of anhydrous magnesium sulfate (analytical grade), and dry for 12h. Then perform vacuum distillation (vacuum degree -0.090MPa, temperature 50℃) to remove the solvent THF and obtain a white solid product. Place the white solid product in a vacuum drying oven (temperature 60℃, vacuum degree -0.095MPa) and dry for 6h to obtain dichloro-tetra(phenoxy)cyclotriphosphazene (intermediate 1).

[0061] 2. Preparation of bis(4-hydroxyphenoxy)-tetra(phenoxy)cyclotriphosphazene (intermediate 2) (1) Preparation of experimental apparatus: A 1000mL three-necked round-bottom flask is used, equipped with a mechanical stirrer, a reflux condenser (with a nitrogen inlet tube connected to the upper end), and a thermometer (accuracy ±0.1℃), and placed in an oil bath heating device (temperature control range 0~200℃).

[0062] (2) Raw material feeding: Under nitrogen protection (nitrogen flow rate 30 mL / min), add 1 mol (599.5 g) of intermediate 1 and 500 mL of acetonitrile (analytical grade, dried for 24 h by 4A molecular sieve) to a three-necked flask, and start stirring (speed 400 rpm) to completely dissolve intermediate 1 and form a light yellow transparent solution; then add 2 mol (220.22 g) of hydroquinone (analytical grade, vacuum dried at 80 °C for 4 h) and 2 mol (202.4 g) of triethylamine (same purification process as before), and continue stirring for 10 min. The system is a light yellow suspension.

[0063] (3) Reflux reaction control: Turn on the oil bath heating and slowly increase the temperature to 80℃ (acetonitrile reflux temperature) at 5℃ / h, and maintain the reflux reaction for 12h; take samples every 2h and monitor them by HPLC (mobile phase: methanol / water = 75 / 25, detection wavelength 254nm). When the peak area of ​​intermediate 1 is <2%, stop heating.

[0064] (4) Post-processing and purification: After the system is cooled to room temperature, the triethylamine hydrochloride filter cake is removed by vacuum filtration, and the pale yellow filtrate is collected. The filtrate is transferred to a rotary evaporator (vacuum degree -0.095MPa, temperature 50℃) to remove acetonitrile and obtain a pale yellow viscous solid. 300mL of toluene (dried with anhydrous sodium sulfate) is added to the solid and heated to 60℃ to dissolve it, forming a pale yellow transparent solution. Hexane (analytical grade) is slowly added dropwise at a rate of 3mL / min until a stable white turbidity appears in the solution (the amount added is about 400mL). The system is placed in a 0℃ refrigerator and allowed to stand for 12h to allow the crystals to fully separate. The white crystals are collected by vacuum filtration and washed twice with cold hexane at 0℃ (50mL each time). Then, the solution is dried at 70℃ and vacuum degree -0.095MPa for 8h to obtain intermediate 2.

[0065] pass 1 HNMR (400MHz, CDCl3) characterization, chemical shift δ: 9.25 (s, 2H, -OH, hydroxyl hydrogen), 7.25-6.75 (m, 28H, Ar-H, benzene ring hydrogen), sharp peak shape without impurity peak interference, integral ratio precisely matches theoretical value (2:28), confirming that the number of hydroxyl groups and benzene ring hydrogens in bis(4-hydroxyphenoxy)-tetra(phenoxy)cyclotriphosphazene (intermediate 2) match the theoretical structure in terms of chemical environment; 3. Preparation of bis(epoxypropyl ether)-tetra(phenoxy)cyclotriphosphazene (epoxy resin) (1) Preparation of experimental apparatus: Use a 1000mL three-necked round bottom flask, equip it with a mechanical stirrer (0-800rpm), thermometer, reflux condenser, and place it in an oil bath heating device.

[0066] (2) Ring-opening etherification reaction: Under nitrogen protection (flow rate 20 mL / min), add 1.0 mol intermediate 2, 6 mol epichlorohydrin (ECH, dried for 24 h by 5 Å molecular sieve), 0.5 g tetrabutylammonium bromide (TBAB, catalyst) and 200 mL butanone (dried for anhydrous magnesium sulfate) to the flask; start stirring (500 rpm) to completely dissolve the solid; raise the temperature to 85 °C at 10 °C / h and maintain the reaction for 5 h; take a sample every 1 h and titrate the epoxy value by hydrochloric acid-acetone method. Stop heating when the epoxy value change rate is <0.01 eq / 100 g.

[0067] (3) Separation of epichlorohydrin after ring opening: Cool down to 40-45℃, remove the reflux condenser and replace it with a distillation apparatus; turn on the oil bath heating and raise the temperature to 100℃ at 5℃ / h, maintain this temperature for vacuum distillation (vacuum degree -0.085~-0.090MPa), collect the fraction (i.e. the recovered epichlorohydrin, purity >98%, which can be recycled); when the volume of the fraction in the receiving flask no longer increases, stop the distillation, at which point the residual epichlorohydrin content in the system is <2%; add 150mL of butanone to the remaining reaction solution after distillation (to maintain the solubility of the system), stir evenly (300rpm, 10min), and set aside.

[0068] (4) Closed-loop reaction: Cool the system to 55℃ and slowly add 2.2mol sodium hydroxide solution (300rpm) dropwise at a rate of 2mL / min. Control the temperature of the system by using an ice-water bath to ensure that the temperature of the system is stable at 55±2℃. After the addition is complete, maintain the reaction at 55℃ for 4h. Titrate the epoxy value every 30min. Stop the reaction when the epoxy value reaches 0.22-0.25eq / 100g (theoretical value 0.23eq / 100g).

[0069] (4) Post-treatment: Add 300 mL of deionized water to the system, stir for 30 min (400 rpm), let stand for 30 min to separate the layers, and remove the lower aqueous phase (containing sodium chloride and excess NaOH); add 200 mL of saturated brine to the organic phase, stir for 20 min to separate the layers, and remove the aqueous phase again; repeat the washing with saturated brine twice until the pH of the aqueous phase is 7; transfer the organic phase to a rotary evaporator (vacuum degree -0.098 MPa, temperature 70℃), first remove the butanone, then raise the temperature to 90℃ and continue vacuum distillation for 1 h to remove residual solvent and water; cool to room temperature to obtain a light yellow viscous target resin with an epoxy value of 0.23 eq / 100 g and a phosphorus content of 10.8% (determined by X-ray fluorescence spectrometry).

[0070] The target resin structure is shown in Formula 2: Equation 2.

[0071] pass1 Characterized by ¹H NMR (400 MHz, CDCl₃), the chemical shifts δ were: 7.28–6.80 (m, 28H, Ar-H, benzene ring hydrogen), 4.05–3.95 (d, 4H, -O-CH₂-, glycidyl ether methylene hydrogen), 3.45–3.35 (m, 2H, -CH- on the epoxy ring, methylene hydrogen), and 2.85–2.75 (d, 4H, -CH₂- on the epoxy ring, methylene hydrogen). The peaks were sharp and free of interference from other peaks, and the integral ratio strictly matched the theoretical value (28:4:2:4). This confirms that the number of various hydrogens and the chemical environment in the target molecule match the theoretical structure.

[0072] In some embodiments, the specific preparation steps of the adhesive composition include: 1. Add bisphenol A epoxy resin, functional epoxy resin, epoxy diluent, coupling agent, antioxidant, and UV absorber to a planetary mixer, close the mixing tank, turn on the vacuum (≤-0.095MPa), stir at 800-1000rpm for 30min, disperse at 1500rpm for 15min, and finally degas at 300rpm for 10min to obtain transparent encapsulating adhesive component A. 2. Add 70-100 parts of component A of the transparent encapsulating adhesive and 20-40 parts of the curing agent (D230) to a planetary mixer; close the mixing tank, turn on the vacuum (≤-0.095MPa), stir at 800-1000rpm for 20min, and finally degas at 300rpm for 10min. 3. Curing process: Keep warm at 80℃ for 2 hours.

[0073] The present invention will be further illustrated by the following examples.

[0074] Example 1 This embodiment is used to illustrate the epoxy resin, its preparation method, adhesive composition, and encapsulating film disclosed in this invention.

[0075] The functional epoxy resin has the structure shown in Formula 2.

[0076] Preparation steps of the adhesive composition: 1. According to the weight proportions shown in Table 1, add bisphenol A epoxy resin E51 (bisphenol A diglycidyl ether, epoxy value 0.51eq / 100g), functional epoxy resin (Formula 2), epoxy diluent 622 (1,4-butanediol diglycidyl ether), coupling agent KH560 (γ-glycidyl etheroxypropyltrimethoxysilane), antioxidant 1010 (pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]), and ultraviolet absorber UV327 (2-(2'-hydroxy-3',5'-di-tert-butylphenyl)-5-chlorobenzotriazole) to a planetary mixer, close the mixing tank, turn on the vacuum (≤-0.095MPa), stir at 800-1000rpm for 30min, disperse at 1500rpm for 15min, and finally degas at 300rpm for 10min to obtain transparent encapsulating adhesive component A. 2. Add 100 parts of component A of the transparent encapsulating adhesive and 30 parts of curing agent D230 (polyetheramine) to a planetary mixer; close the mixing tank, turn on the vacuum (≤-0.095MPa), stir at 800-1000rpm for 20min, and finally degas at 300rpm for 10min. 3. Curing process: Keep warm at 80℃ for 2 hours.

[0077] Examples 2-9 Examples 2-9 are mostly the same as those in Example 1, with the differences shown in Table 1.

[0078] Table 1. Parts of each component in the adhesive composition of the examples Comparative Example 1 Comparative Example 1 is similar to Example 2 in most steps, except that DOPO type epoxy resin (phosphorus content 3%, epoxy value 0.30eq / 100g) is used instead of functional epoxy resin.

[0079] Comparative Example 2 Comparative Example 2 is the same as Example 2 in most steps, except that: 63 parts of bisphenol A type epoxy resin E51 (epoxy value 0.51eq / 100g), 25 parts of dimethyl methylphosphonate (DMMP), and non-functional epoxy resin.

[0080] Comparative Example 3 Comparative Example 3 is similar to Example 2 in most steps, except that it uses 88 parts of bisphenol A type epoxy resin (EEW=186) and non-functional epoxy resin.

[0081] Comparative Example 4 Comparative Example 4 is the same as Example 2 in most steps, except that it contains 63 parts of bisphenol A type epoxy resin (E51), 15 parts of resorcinol bis(diphenyl phosphate) (RDP), 10 parts of ammonium polyphosphate (APP), 22 parts of curing agent polyetheramine (D230), and non-functional epoxy resin.

[0082] Comparative Example 5 Comparative Example 5 is similar to Example 2 in most steps, except that the functional epoxy resin has the structural formula shown in Formula 3: Formula 3.

[0083] Performance testing The samples prepared in the above examples and comparative examples were subjected to the following performance tests: (1) Light transmittance: The resin was made into a 1mm thick cured block and tested using a light transmittance haze meter according to the ASTM-D1003 standard. The instrument emits parallel light through the sample and measures and reads its haze value directly.

[0084] (2) Haze: The resin was made into a 1mm thick cured block and tested using a transmittance haze meter according to the ASTM-D1003 standard. The instrument emits parallel light through the sample and measures and reads the haze value directly.

[0085] (3) Flame retardant rating: The resin was made into a cured sample strip with a length of 130mm, a width of 12.7mm and a thickness of 3mm. The flame retardant performance of vertical burning was tested according to the UL94 standard.

[0086] (4) Glass transition temperature: Tested by differential scanning calorimetry (DSC) at a heating rate of 10℃ / min.

[0087] (5) Light transmittance after damp heat aging: The rubber block was tested in the same way as (1) after aging for 7 days with double 85.

[0088] (6) Thermal shock performance: The resin is uniformly applied to the LED display panel and placed in a thermal shock test chamber. The panel is subjected to 168 cycles of thermal shock at -20 to 80°C, with one cycle per hour. After the test, observe whether there is any cracking or delamination between the adhesive and the LED display panel. If there is no cracking, the test is pass; if there is cracking, the test is NG.

[0089] The sample test results of the examples and comparative examples are shown in Table 2.

[0090] Table 2. Sample test results of the examples and comparative examples As shown in Tables 1 and 2, the functional epoxy resin (Formula 2) provides the flame retardancy of epoxy resin. When the weight component of the functional epoxy resin is 20-30 parts, the flame retardancy of the resin reaches UL-94 V1. Reducing the content of the functional epoxy resin (Formula 2), if the weight component of the functional epoxy resin is reduced to 18 parts (Example 6), the flame retardancy decreases to V1. If the weight component of the functional epoxy resin is higher than 30 parts (Example 7), the glass transition temperature (Tg) becomes lower. If no functional epoxy resin is added (Comparative Example 3), it is not flame retardant. Furthermore, a comparison of the test results of Comparative Example 3 and Example 2 shows that the functional epoxy resin (Formula 2) has a very low effect on light transmittance. This is because the functional epoxy resin (Formula 2) is completely reacted and cross-linked into the resin network, resulting in a homogeneous and stable system.

[0091] A comparison of the test results of Comparative Example 1 and Example 2 shows that when DOPO type epoxy resin (phosphorus content 3%, epoxy value 0.30eq / 100g) is used instead of functional epoxy resin, the flame retardant rating is only HB when the same amount is added. This is because the phosphorus content of DOPO type epoxy resin is too low, and the flame retardant effect is significantly lower than that of Example 2. Furthermore, after damp heat aging, the light transmittance decreases from 91.2% to 87.2%, and yellowing occurs. The yellowing chromogenic groups selectively absorb some visible light. In contrast, the light transmittance of Example 2 decreases very little after damp heat aging, demonstrating its heat resistance and yellowing resistance.

[0092] Comparison of the test results of Comparative Example 2 and Example 2 shows that the flame retardant DMMP significantly reduces the heat resistance of the resin, and the Tg drops from 68°C to 35°C. It will crack after thermal shock. This is because DMMP does not participate in the crosslinking network, resulting in a decrease in mechanical properties and cracking after thermal shock.

[0093] A comparison of the test results of Comparative Example 4 and Example 2 shows that the light transmittance of Comparative Example 4 is significantly lower than that of Example 2. This is because the addition of the powdered flame retardant APP will reflect and absorb visible light, resulting in a decrease in light transmittance, making it unsuitable for use in the optical display industry.

[0094] A comparison of the test results of Comparative Example 5 and Example 2 shows that the LED display panel of Comparative Example 5 cracked due to thermal shock. This is because the resin (Formula 3) used in Comparative Example 5 has three active epoxy groups. The three active epoxy groups participate in the cross-linking network. The cross-linking network density is too high, which causes the resin to become brittle, resulting in thermal shock cracking.

[0095] In summary, the functional epoxy resin (Formula 2) of the present invention exhibits significant advantages over existing technical solutions in terms of light transmittance, flame retardancy, resistance to damp heat aging, and thermal shock performance when used in the optical display industry.

[0096] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. An epoxy resin, characterized in that, The chemical formula of the epoxy resin is shown in Formula 1: Formula 1, In Formula 1, any two of R1-R6 are selected from glycidyl ether, and the rest are selected from H.

2. The epoxy resin according to claim 1, characterized in that, R1 and R4 are each independently selected from glycidyl ether.

3. The method for preparing epoxy resin as described in claim 1 or 2, characterized in that, Includes the following steps: Hexachlorocyclotriphosphazene and phenol are dissolved in a first solvent, an acid-binding agent is added, and the reaction is carried out to generate dichloro-tetra(phenoxy)cyclotriphosphazene. Dichloro-tetra(phenoxy)cyclotriphosphazene is dissolved in a second solvent, and hydroquinone and an acid-binding agent are added to react and generate bis(4-hydroxyphenoxy)-tetra(phenoxy)cyclotriphosphazene. Bis(4-hydroxyphenoxy)-tetra(phenoxy)cyclotriphosphazene, epichlorohydrin, and catalyst were dissolved in a third solvent and reacted to carry out ring-opening etherification, yielding a solution containing the intermediate. An alkaline solution is added to a solution containing the intermediate, and a reaction is carried out to obtain the epoxy resin shown in Formula 1.

4. The preparation method according to claim 3, characterized in that, The molar ratio of hexachlorocyclotriphosphazene to phenol is 1:4 to 1:4.2; and / or, The molar ratio of dichloro-tetra(phenoxy)cyclotriphosphazene to hydroquinone is 1:2 to 1:2.2; and / or, The molar ratio of bis(4-hydroxyphenoxy)-tetra(phenoxy)cyclotriphosphazene to epichlorohydrin is 1:2 to 1:

8.

5. The preparation method according to claim 3, characterized in that, The step of generating dichloro-tetra(phenoxy)cyclotriphosphazene further includes: Hexachlorocyclotriphosphazene and phenol are dissolved in a first solvent, an acid-binding agent is added, and the mixture is reacted at -10 to 0°C for 3 to 4 hours. Then, the temperature is raised to 30 to 40°C and the mixture is reacted for 16 to 20 hours.

6. The preparation method according to claim 3, characterized in that, The acid-binding agent includes triethylamine; The catalyst comprises one or more of tetrabutylammonium bromide, tetraoctylammonium bromide, and benzyltriethylammonium chloride; and / or The alkaline solution includes one or both of sodium hydroxide solution and potassium hydroxide solution, and the mass concentration of the alkaline solution is 20%-30%.

7. An adhesive composition, characterized in that, It includes bisphenol A epoxy resin, a curing agent, and a functional epoxy resin, wherein the functional epoxy resin is the epoxy resin as described in claim 1 or 2.

8. The adhesive composition according to claim 7, characterized in that, It comprises the following components by weight: 55-70 parts bisphenol A epoxy resin, 20-30 parts functional epoxy resin and 20-40 parts curing agent.

9. The adhesive composition according to claim 7, characterized in that, The adhesive composition further includes 5-15 parts epoxy diluent, 0.2-2 parts coupling agent, 0.2-2 parts antioxidant, and 0.2-2 parts ultraviolet absorber.

10. An encapsulating film, characterized in that, Includes the adhesive composition described in any one of 7-9.

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