Preparation method of mobile phone low-temperature heat-cured narrow-frame sealant

Abstract

The present application relates to the technical field of adhesive, and discloses a preparation method of a mobile phone low-temperature thermal curing narrow frame sealant, which comprises the following steps: firstly, mixing epoxy resin, fillers and titanate coupling agent, and performing in-situ modification and water removal under the condition of heating and vacuum; then, adding borate ester type inhibitor to perform complex inhibition treatment after temperature reduction; finally, adding ester-free polyether type trifunctional mercaptan, latent curing agent and other additives for dispersion to obtain the sealant. The mercaptan curing agent is prepared by etherification reaction of trimethylolpropane and allyl halide and subsequent photochemical addition reaction, and does not contain ester groups in the molecular structure. The sealant prepared by the present application has excellent low-temperature fast curing capacity and room temperature storage stability, and the curing product has significantly improved resistance to humid heat aging, and is suitable for high-reliability sealing and bonding of mobile phone narrow frame.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, and in particular to a method for preparing a low-temperature thermosetting narrow-bezel sealant for mobile phones. Background Technology

[0002] As smart terminals evolve towards full-screen and high screen-to-body ratios, the bezel width of mobile phones continues to shrink, placing more stringent demands on the dispensing process and material properties of structural sealants. To protect temperature-sensitive precision components such as batteries and LCD modules, the curing window of sealants is limited, typically requiring rapid curing at lower temperatures below 80°C.

[0003] One-component epoxy resin adhesives are widely used in this field due to their excellent adhesion and mechanical strength. To achieve rapid low-temperature curing, polythiol compounds are often introduced as curing agents. The thiol groups in polythiols have high nucleophilic reactivity, rapidly undergoing ring-opening addition reactions with epoxy groups at relatively low temperatures. However, this high reactivity poses a challenge to the storage stability of the adhesive system. Thiol groups and epoxy groups readily react at room temperature, leading to increased viscosity or even gelation of the adhesive, resulting in a short pot life. While adding latent curing agents or inhibitors can alleviate this problem to some extent, in practical applications, it is often difficult to simultaneously achieve long-term storage stability at room temperature and rapid curing response at low temperatures. Furthermore, residual trace amounts of moisture in the system often act as catalysts to accelerate the reaction or form bubbles during curing, and conventional simple physical mixing processes are insufficient to completely remove moisture or effectively shield the active groups.

[0004] On the other hand, the chemical structure of the thiol curing agent itself is a key factor affecting the long-term reliability of the sealant. Most commercially available general-purpose polythiol curing agents are prepared by esterification of polyols and mercaptans, resulting in a large number of ester bonds in their molecular structure. Under high temperature and humidity conditions, these ester bonds are prone to hydrolysis, leading to the breakage of the cross-linked network in the cured product. This degradation directly causes a significant decrease in adhesive strength and sealant failure, making it difficult for sealants using ester-based thiols to pass the stringent double 85 (85°C, 85% relative humidity) damp heat aging test, thus limiting their application in high-end electronic products with extremely high reliability requirements. Therefore, developing a preparation method that can both ensure process stability and fundamentally solve the problem of damp heat aging resistance at the molecular structure level has become a pressing technical challenge in this field. Summary of the Invention

[0005] The technical problem solved by this invention is that existing mobile phone narrow bezel sealants are difficult to simultaneously achieve both low-temperature rapid curing capability and room-temperature storage stability. Furthermore, the presence of ester bonds in conventional thiol curing systems results in poor resistance to humid heat aging, making it difficult to meet the increasingly stringent reliability requirements of electronic products.

[0006] To address the above problems, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing a low-temperature thermosetting narrow-bezel sealant for mobile phones, comprising the following steps:

[0008] (1) Pre-dispersion and dehydration modification: Bisphenol F type epoxy resin, toughened modified epoxy resin, spherical silica powder, hydrophobic modified fumed silica and pyrophosphate type titanate coupling agent are mixed and stirred and dispersed under heating and vacuum conditions. The titanate coupling agent is used to modify the surface of the filler in situ and remove trace amounts of water in the system.

[0009] (2) Complexation inhibition treatment: Cool down the mixture obtained in step (1), release the vacuum and add borate ester inhibitors, stir under vacuum conditions to allow the borate ester to form a complexation equilibrium with the residual active groups and titanate in the system;

[0010] (3) Adhesive preparation and defoaming: Add ester-free polyether trifunctional thiol, latent curing agent, stabilizer, epoxy silane coupling agent and pigment to the system in step (2), and disperse evenly under vacuum conditions to obtain sealant;

[0011] Among them, the ester-free polyether trifunctional thiol is trimethylolpropane tri(3-mercaptopropyl) ether.

[0012] By adopting the above technical solution, the present invention achieves step-by-step control of the process of "modification and dehydration - complexation inhibition - low temperature compounding".

[0013] First, in step (1), the filler is subjected to in-situ surface treatment using a pyrophosphate-type titanate coupling agent under heating and vacuum conditions. The alkoxy groups of the titanate not only react with the hydroxyl groups on the surface of the inorganic filler to form a monolayer hydrophobic film, significantly reducing the interfacial tension between the filler and the resin matrix and improving dispersibility and rheology; more importantly, the titanate is highly sensitive to water and can chemically consume the trace amounts of water adsorbed in the system through a hydrolysis reaction. This process not only eliminates the potential threat of moisture to the subsequent storage stability of the epoxy groups but also avoids bubble defects caused by moisture vaporization during the curing process.

[0014] Secondly, in step (2), borate ester inhibitors are introduced to construct a latent curing system. Under specific conditions after cooling, borate esters, as Lewis acids, can form coordination complexes with titanate esters and active groups (hydroxyl groups) in the epoxy resin. This complex structure is in a stable equilibrium state at room temperature, effectively shielding the active sites and inhibiting side reactions between the resin and the curing agent during storage, thereby significantly extending the pot life of the adhesive. When the sealant is heated after dispensing, this complex equilibrium is disrupted, the active groups are released, and a rapid curing reaction is initiated.

[0015] Finally, in step (3), a special structure of ester-free polyether trifunctional thiol is selected as the curing agent. Conventional thiol curing agents are mostly prepared by esterification of carboxylic acids and alcohols, containing ester bonds, which are prone to hydrolysis and chain scission under high temperature and high humidity conditions, leading to sealing failure. The trimethylolpropane tri(3-mercaptopropyl) ether used in this invention has a molecular skeleton composed entirely of ether bonds (COC) and carbon-carbon bonds, and is completely free of ester groups. The ether bonds have high bond energy and stable chemical properties, giving the cured product excellent resistance to hydrolysis and humid heat aging. At the same time, the thiol group (-SH) has extremely high reactivity to epoxy groups at low temperatures. Combined with a latent curing agent, it achieves rapid curing at a low temperature of about 80°C, protecting the precision components of the mobile phone from high temperature damage.

[0016] Preferably, the sealant is made from raw materials comprising the following parts by weight: 25 to 35 parts of bisphenol F type epoxy resin; 10 to 20 parts of toughened modified epoxy resin; 35 to 45 parts of spherical silica powder; 0.5 to 2.5 parts of hydrophobically modified fumed silica; 0.3 to 0.8 parts of pyrophosphate type titanate coupling agent; 0.3 to 0.8 parts of borate ester inhibitor; 8 to 12 parts of ester-free polyether type trifunctional thiol; 3 to 8 parts of latent curing agent; 0.1 to 0.3 parts of stabilizer; 0.3 to 0.8 parts of epoxy silane coupling agent; and 0.1 to 0.5 parts of pigment.

[0017] By adopting the above technical solution, bisphenol F epoxy resin exhibits low viscosity, enabling it to accommodate a high proportion of spherical silica powder fillers, thereby reducing curing shrinkage and improving the mechanical strength of the colloid. The addition of toughened modified epoxy resin introduces flexible segments, improving the impact resistance of the cured product and preventing brittleness of the adhesive layer. The optimized proportions of each component ensure that the rheological properties meet the requirements of narrow-frame spray dispensing, while the crosslinking density after curing is moderate, combining sealing and adhesion.

[0018] Preferably, the heating temperature in step (1) is 60 to 70°C, the vacuum degree is -0.09 MPa to -0.1 MPa, and the stirring and dispersing time is 40 to 80 minutes.

[0019] By adopting the above technical solution, a temperature range of 60 to 70°C can ensure that the resin viscosity is reduced to facilitate filler dispersion, while also accelerating the coupling reaction between titanate and the hydroxyl groups on the filler surface and the rate of water consumption through hydrolysis. Simultaneously, it avoids excessively high temperatures that could lead to resin prepolymerization or aging. High vacuum combined with sufficient stirring time ensures that microbubbles and small-molecule alcohol byproducts generated during the reaction are completely extracted.

[0020] Preferably, in step (2), the temperature is lowered to 25 to 35°C and the stirring time is 20 to 40 minutes; in step (3), the dispersion temperature is controlled at 20 to 30°C and the dispersion time is 15 to 30 minutes.

[0021] By adopting the above technical solution, the cooling treatment in step (2) is to prevent uncontrollable reactions after the addition of borate ester. Low temperature is conducive to the complexation equilibrium shifting towards the formation of complexes, ensuring the inhibition effect. Step (3) strictly controls the dispersion at room temperature to avoid the highly active thiol curing agent reacting with the epoxy resin prematurely under shear heat, ensuring the quality of the adhesive output and the storage period.

[0022] Preferably, the stabilizer is barbituric acid and the pigment is carbon black slurry.

[0023] By employing the above technical solution, barbituric acid, as an acidic stabilizer, can neutralize alkaline impurities in the system, further inhibit the early activity of thiol groups, and synergistically improve storage stability with borate esters. Carbon black paste provides light-shielding properties, meeting the aesthetic requirements of mobile phone bezels.

[0024] Preferably, the ester-free polyether trifunctional thiol in step (3) is prepared by a method comprising the following steps:

[0025] 1) Preparation of intermediate: Trimethylolpropane was dissolved in a solvent, an alkaline catalyst was added, and allyl halides were added dropwise to carry out an etherification reaction. The intermediate trimethylolpropane triallyl ether was obtained after post-treatment.

[0026] 2) Photochemical addition: The intermediate is mixed with a photoinitiator, and hydrogen sulfide gas is introduced under ultraviolet light to carry out a thiol-alkene click reaction. After the reaction is completed, residual hydrogen sulfide and low-boiling point impurities are removed to obtain the target product.

[0027] By adopting the above technical solution, the preparation route design cleverly avoids the traditional esterification reaction route.

[0028] In the etherification reaction of step 1), the Williamson etherification synthesis principle is utilized. Under alkaline conditions, the three hydroxyl groups of trimethylolpropane are deprotonated to form an alkoxy anion, which then undergoes nucleophilic substitution of the allyl halide to generate an ether intermediate containing three terminal alkenyl groups. This step constructs a stable ether backbone for the product.

[0029] In the photochemical addition in step 2), the principle of thiol-olefin click chemistry is utilized. Under ultraviolet light excitation, the photoinitiator generates a free radical, which abstracts a hydrogen atom from hydrogen sulfide to form a sulfur free radical. The sulfur free radical attacks the carbon-carbon double bond (allyl) on the intermediate, forming a carbon free radical intermediate. Subsequently, the carbon free radical abstracts a hydrogen atom from the hydrogen sulfide molecule, completing the addition cycle and regenerating the sulfur free radical. This reaction exhibits the characteristics of anti-Markovnikov addition, enabling efficient and highly selective introduction of thiol groups to the end of the side chain. Furthermore, the reaction conditions are mild, with very few byproducts, ensuring high functionality and high purity of the product.

[0030] Preferably, in step 1), the alkaline catalyst is potassium hydroxide, and the allyl halide is allyl bromide; the etherification reaction includes the dropwise addition of allyl bromide at 55 to 70°C, followed by a reaction at 75 to 85°C. In step 1), the molar ratio of trimethylolpropane, alkaline catalyst, and allyl halide is 1:(3.0 to 3.6):(3.0 to 3.6).

[0031] By employing the above technical solution, and strictly controlling the molar ratio of catalyst and allyl bromide to trimethylolpropane in a slightly excess of hydroxyl equivalent (theoretical ratio 1:3), combined with a segmented temperature control strategy, it is possible to ensure that the three hydroxyl groups on trimethylolpropane are completely substituted, avoiding the formation of mono- or di-substituted byproducts, thereby guaranteeing that the final thiol product has strict trifunctionality. The trifunctional structure is the basis for forming a dense cross-linked network, providing excellent mechanical strength and resistance to media.

[0032] Preferably, in step 2), the photoinitiator is 2,2-dimethoxy-2-phenylacetophenone; the ultraviolet wavelength is 365 nm. In step 2), the reaction pressure is controlled at 0.2 to 0.3 MPa, the reaction temperature at 20 to 30°C, and the reaction time at 6 to 8 hours.

[0033] By employing the above technical solution, 2,2-dimethoxy-2-phenylacetophenone exhibits a high absorption coefficient and pyrolysis efficiency in the 365nm wavelength range, enabling rapid initiation of a chain reaction. Controlling the micro-positive pressure environment (0.2 to 0.3 MPa) increases the solubility of hydrogen sulfide gas in the liquid phase, thereby improving the reaction rate, while avoiding safety risks caused by excessive pressure. Maintaining the reaction temperature within the room temperature range ensures the activity of free radicals while suppressing polymerization side reactions that may result from thermal effects.

[0034] In summary, the present invention has at least one of the following beneficial technical effects:

[0035] 1. The sealant prepared in this invention uses a self-synthesized trifunctional thiol with a fully ether-bonded structure as a curing agent, completely eliminating the weakness of easily hydrolyzed ester groups at the molecular structure level. Under long-term use in high-temperature and high-humidity environments, the colloidal network does not degrade or break down, significantly improving the reliability of mobile phone frame sealing.

[0036] 2. This invention successfully constructs a temperature-sensitive latent curing system through a unique titanate dehydration and borate complexation synergistic modification process, combined with a latent curing agent. Under low-temperature storage conditions, the active groups of this sealant are effectively shielded, resulting in slow viscosity growth and a long pot life. When heated to approximately 80°C, the complex structure dissociates, and the thiol groups rapidly participate in the reaction, achieving rapid curing. This meets the dual requirements of narrow-bezel dispensing for production efficiency and protection of heat-sensitive components.

[0037] 3. The optimized epoxy resin combination and high-filling spherical silica powder of this invention, combined with in-situ surface modification technology, result in a cured adhesive layer with low shrinkage, high modulus and good toughness, exhibiting excellent bonding strength to both metal frames and glass screens, and effectively resisting drop impacts. Attached Figure Description

[0038] Figure 1 This is a comparison chart of the effects of different preparation processes and formulation systems on the residual moisture and storage stability of the sealant in Test Example 1 of the present invention; wherein, (a) is a comparison chart of the residual moisture content of each example and the comparative example before the addition of the inhibitor; (b) is a comparison chart of the viscosity growth rate of each group under storage conditions at 25°C.

[0039] Figure 2 The following is a comparison of the effects of borate ester inhibitors on the curing kinetics of the epoxy-thiol system in Test Example 2 of the present invention; wherein, (a) is a comparison of dynamic heating DSC heat flow curves (heating rate 10℃ / min); and (b) is a comparison of the degree of curing versus time curves under isothermal conditions of 80℃.

[0040] Figure 3 The following are comparative diagrams of the rheological properties and thixotropic behavior of different formulation systems in Test Example 3 of the present invention; wherein, (a) is a comparative diagram of steady-state shear flow curves; and (b) is a comparative diagram of yield stress for each group.

[0041] Figure 4 This is a comparison chart of the dispensing process adaptability and anti-collapse performance of different formulation systems in Test Example 4 of the present invention; wherein, (a) is a comparison chart of the extrusion rate test results under 0.4MPa pressure; (b) is a comparison chart of the aspect ratio of the adhesive strip after it has been left to stand.

[0042] Figure 5 This is a comparison chart of the resistance to humid heat aging of the polyether-type and ester-type thiol systems in Test Example 5 of the present invention; wherein, (a) is a comparison chart of the curves of shear strength change with aging time; and (b) is a bar chart of strength retention rate.

[0043] Figure 6 The following are performance verification comparison diagrams of the embodiments in Test Example 6 of the present invention under low temperature rapid curing conditions; wherein, (a) is a comparison diagram of chemical curing degree after being kept at 80°C for 30 minutes; and (b) is a comparison diagram of Shore D hardness of the cured products. Detailed Implementation

[0044] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0045] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0046] The bisphenol F type epoxy resin is bisphenol F diglycidyl ether, CAS number 2095-03-6, with an epoxy equivalent of 160-175 g / eq and a viscosity of 2000-4000 mPa·s at 25℃.

[0047] The toughening modified epoxy resin is a bisphenol A type epoxy resin modified with carboxyl-terminated butadiene-acrylonitrile rubber, with a rubber phase content of 10% to 15% and an epoxy equivalent of 300 to 400 g / eq.

[0048] The latent curing agent is a modified imidazole adduct microcapsule with an average particle size D50 of 3-5 μm and an initial reaction temperature of 75-85℃.

[0049] The borate ester inhibitor used is tributyl borate, CAS number 688-74-4, with a purity ≥99%. The pyrophosphate titanate coupling agent used is isopropyltris(dioctylpyrophosphate)titanate, CAS number 65345-34-8. The epoxy silane coupling agent used is 3-glycidoxypropyltrimethoxysilane, CAS number 2530-83-8. The spherical silica powder used is silica with an average particle size D50 of 0.5–2.0 μm, CAS number 7631-86-9. The hydrophobically modified fumed silica used is fumed silica surface-treated with dimethyldichlorosilane, CAS number 68611-44-9, with a specific surface area of ​​100–130 m². 2 / g.

[0050] The CAS numbers for the raw materials used in the synthesis are: trimethylolpropane (CAS number 77-99-6), allyl bromide (CAS number 106-95-6), and 2,2-dimethoxy-2-phenylacetophenone (CAS number 24650-42-8).

[0051] Preparation Example 1:

[0052] This preparation example provides a method for preparing an ester-free polyether-type trifunctional thiol (trimethylolpropane tris(3-mercaptopropyl) ether), comprising the following steps:

[0053] In a four-necked flask equipped with a mechanical stirrer, a reflux condenser, and a thermometer, 134.2 g of trimethylolpropane (1.0 mol) and 300 mL of dimethyl sulfoxide were added and stirred until dissolved. Then, 185.2 g of potassium hydroxide powder (3.3 mol) was added, and the mixture was heated to 60 °C and stirred for 1 hour. Subsequently, 399.3 g of allyl bromide (3.3 mol) was slowly added dropwise, and the dropping rate was controlled to maintain the temperature of the reaction system between 65 and 70 °C. After the addition was completed, the temperature was raised to 80 °C and the reaction was continued for 4 hours. After the reaction was completed, the reaction solution was poured into ice water and extracted with ethyl acetate. The organic phase was washed with water until neutral, dried over anhydrous sodium sulfate, and the solvent was removed by vacuum distillation to obtain the intermediate trimethylolpropane triallyl ether. 215g of the above intermediate was added to a photochemical reactor, along with 2.1g of photoinitiator 2,2-dimethoxy-2-phenylacetophenone. The reactor was sealed, and the air was purged three times with nitrogen. An ultraviolet light source (wavelength 365nm) was turned on, and hydrogen sulfide gas was continuously introduced into the reactor. The pressure inside the reactor was maintained at 0.25MPa, and the reaction temperature was controlled at 25℃ for 7 hours. After the reaction, the reaction solution was purged with nitrogen for 30 minutes to remove residual hydrogen sulfide. The product was then subjected to vacuum distillation to remove low-boiling-point impurities, yielding the colorless, transparent liquid target product, trimethylolpropane tris(3-mercaptopropyl) ether. Infrared spectroscopy revealed that the product had a wavelength of 2550 cm⁻¹. -1 It exhibits a characteristic thiol absorption peak and lacks a 1740 cm⁻¹ peak. -1 The absorption peak of the ester carbonyl group at that location.

[0054] Preparation Example 2:

[0055] This preparation example provides a method for preparing an ester-free polyether-type trifunctional thiol (trimethylolpropane tris(3-mercaptopropyl) ether), comprising the following steps:

[0056] 134.2 g of trimethylolpropane (1.0 mol) and 300 mL of dimethyl sulfoxide were added to a reaction vessel, along with 168.3 g of potassium hydroxide (3.0 mol). The mixture was pretreated at 55 °C for 1 hour. Subsequently, 363 g of allyl bromide (3.0 mol) was added dropwise, with the temperature controlled to not exceed 65 °C during the addition process. After the addition was complete, the mixture was reacted at 75 °C for 3.5 hours. The post-treatment steps were the same as in Preparation Example 1, yielding the intermediate trimethylolpropane triallyl ether. 210 g of the intermediate was mixed with 1.8 g of photoinitiator and placed in a photochemical reactor. Hydrogen sulfide was introduced under ultraviolet light irradiation, and the reaction pressure was controlled at 0.2 MPa. The reaction temperature was controlled at 20 °C, and the reaction time was 6 hours. The post-treatment steps were the same as in Preparation Example 1, yielding the target product, trimethylolpropane tris(3-mercaptopropyl) ether.

[0057] Preparation Example 3:

[0058] This preparation example provides a method for preparing an ester-free polyether-type trifunctional thiol (trimethylolpropane tris(3-mercaptopropyl) ether), comprising the following steps:

[0059] 134.2 g of trimethylolpropane (1.0 mol) and 350 mL of dimethyl sulfoxide were added to a reaction vessel, along with 202 g of potassium hydroxide (3.6 mol). The mixture was stirred at 65 °C for 1 hour. Subsequently, 435.6 g of allyl bromide (3.6 mol) was added dropwise, with the temperature controlled. After the addition was complete, the temperature was raised to 85 °C and the reaction was carried out for 5 hours to ensure complete substitution. The post-treatment steps were the same as in Preparation Example 1, yielding the intermediate trimethylolpropane triallyl ether. 220 g of the intermediate was mixed with 2.2 g of photoinitiator, and hydrogen sulfide was introduced under ultraviolet light irradiation. The reaction pressure was controlled at 0.3 MPa, the reaction temperature at 30 °C, and the reaction time at 8 hours. The post-treatment steps were the same as in Preparation Example 1, yielding the target product, trimethylolpropane tris(3-mercaptopropyl) ether.

[0060] Example 1:

[0061] This embodiment provides a method for preparing a low-temperature thermosetting narrow bezel sealant for mobile phones, including the following steps:

[0062] (1) Pre-dispersion and dehydration modification: Add 30g of bisphenol F type epoxy resin, 15g of toughened modified epoxy resin, 40g of spherical silica powder, 1.5g of hydrophobic modified fumed silica and 0.5g of pyrophosphate type titanate coupling agent to a planetary vacuum mixer; start stirring, control the speed at 600rpm, raise the temperature to 65℃, and stir and disperse for 60 minutes under a vacuum of -0.098MPa to modify the surface of the filler in situ and remove trace amounts of moisture in the system using titanate;

[0063] (2) Complexation inhibition treatment: Cool the mixture from step (1) to 30°C, remove the vacuum, and add 0.5g of borate ester inhibitor; stir for 30 minutes at 30°C and vacuum degree -0.098MPa to allow the borate ester to form a complexation equilibrium with the residual active groups and titanate in the system.

[0064] (3) Adhesive preparation and defoaming: Add 10g of the ester-free polyether trifunctional thiol prepared in Example 1, 5g of latent curing agent, 0.2g of barbituric acid, 0.5g of epoxy silane coupling agent and 0.3g of carbon black slurry to the system in step (2); disperse at 800rpm for 20 minutes at 25℃ (cooling water is used to control the material temperature) and vacuum degree -0.098MPa, and the target sealant is obtained by discharging.

[0065] Example 2:

[0066] This embodiment provides a method for preparing a low-temperature thermosetting narrow bezel sealant for mobile phones, including the following steps:

[0067] (1) Pre-dispersion and dehydration modification: Add 25g of bisphenol F type epoxy resin, 15g of toughened modified epoxy resin, 45g of spherical silica powder, 2.5g of hydrophobic modified fumed silica and 0.8g of pyrophosphate type titanate coupling agent to a planetary vacuum mixer; start stirring, control the speed at 600rpm, heat to 65℃, and stir and disperse for 60 minutes under a vacuum of -0.098MPa;

[0068] (2) Complexation inhibition treatment: Cool the mixture from step (1) to 30°C, release the vacuum, and add 0.8g of borate ester inhibitor; stir for 30 minutes at 30°C and vacuum degree -0.098MPa.

[0069] (3) Adhesive preparation and defoaming: Add 8g of the ester-free polyether trifunctional thiol prepared in Example 1, 5g of latent curing agent, 0.2g of barbituric acid, 0.5g of epoxy silane coupling agent and 0.3g of carbon black slurry to the system in step (2); disperse at 800rpm for 20 minutes at 25℃ and vacuum degree -0.098MPa, and the target sealant is obtained by discharging.

[0070] Example 3:

[0071] This embodiment provides a method for preparing a low-temperature thermosetting narrow bezel sealant for mobile phones, including the following steps:

[0072] (1) Pre-dispersion and dehydration modification: Add 35g of bisphenol F type epoxy resin, 15g of toughened modified epoxy resin, 35g of spherical silica powder, 0.5g of hydrophobic modified fumed silica and 0.3g of pyrophosphate type titanate coupling agent to a planetary vacuum mixer; start stirring, control the speed at 600rpm, raise the temperature to 65℃, and stir and disperse for 60 minutes under a vacuum of -0.098MPa;

[0073] (2) Complexation inhibition treatment: Cool the mixture from step (1) to 30°C, release the vacuum, and add 0.3g of borate ester inhibitor; stir for 30 minutes at 30°C and vacuum degree -0.098MPa.

[0074] (3) Adhesive preparation and defoaming: Add 12g of the ester-free polyether trifunctional thiol prepared in Example 1, 5g of latent curing agent, 0.2g of barbituric acid, 0.5g of epoxy silane coupling agent and 0.3g of carbon black slurry to the system in step (2); disperse at 800rpm for 20 minutes at 25℃ and vacuum degree -0.098MPa, and the target sealant is obtained by discharging.

[0075] Example 4:

[0076] This embodiment provides a method for preparing a low-temperature thermosetting narrow bezel sealant for mobile phones, including the following steps:

[0077] (1) Pre-dispersion and dehydration modification: The formulation components are the same as in Example 1; start stirring, control the speed at 600 rpm, heat to 60°C, and stir and disperse for 60 minutes under vacuum of -0.098 MPa;

[0078] (2) Complexation inhibition treatment: The process steps are the same as in Example 1;

[0079] (3) Adhesive preparation and defoaming: The process steps are the same as in Example 1, and the target sealant is obtained upon discharge.

[0080] Example 5:

[0081] This embodiment provides a method for preparing a low-temperature thermosetting narrow bezel sealant for mobile phones, including the following steps:

[0082] (1) Pre-dispersion and dehydration modification: The formulation components are the same as in Example 1; start stirring, control the speed at 600 rpm, heat to 70°C, and stir and disperse for 60 minutes under vacuum of -0.098 MPa;

[0083] (2) Complexation inhibition treatment: The process steps are the same as in Example 1;

[0084] (3) Adhesive preparation and defoaming: The process steps are the same as in Example 1, and the target sealant is obtained upon discharge.

[0085] Example 6:

[0086] This embodiment provides a method for preparing a low-temperature thermosetting narrow bezel sealant for mobile phones, including the following steps:

[0087] (1) Pre-dispersion and dehydration modification: Add 30g of bisphenol F type epoxy resin, 15g of toughened modified epoxy resin, 40g of spherical silica powder, 1.5g of hydrophobic modified fumed silica and 0.6g of pyrophosphate type titanate coupling agent to a planetary vacuum mixer; start stirring, control the speed at 600rpm, raise the temperature to 65℃, and stir and disperse for 60 minutes under a vacuum of -0.098MPa;

[0088] (2) Complexation inhibition treatment: Cool the mixture from step (1) to 30°C, release the vacuum, and add 0.4g of borate ester inhibitor (adjust the ratio of borate ester to titanate ester to 0.67:1); stir for 30 minutes at 30°C and vacuum degree -0.098MPa.

[0089] (3) Adhesive preparation and defoaming: Add 10.0g of the ester-free polyether trifunctional thiol prepared in Example 1, 5g of latent curing agent, 0.2g of barbituric acid, 0.5g of epoxy silane coupling agent and 0.3g of carbon black slurry to the system in step (2); disperse at 800rpm for 20 minutes at 25℃ and vacuum degree -0.098MPa, and the target sealant is obtained by discharging.

[0090] Comparative Example 1:

[0091] Compared with Example 1, the difference is that the ester-free polyether trifunctional thiol obtained in Preparation Example 1 in step (3) is replaced with an equimolar amount of commercially available ester-based thiol trimethylolpropane tri(3-mercaptopropionate) (TMPMP), while the other raw materials and process steps are the same.

[0092] Comparative Example 2:

[0093] Compared with Example 1, the difference is that no borate ester inhibitors were added in step (2), and the complexation equilibrium process in step (2) was omitted, and the preparation of the adhesive in step (3) was carried out directly. The other raw materials and process steps are the same.

[0094] Comparative Example 3:

[0095] Compared with Example 1, the difference is that the pyrophosphate titanate coupling agent used in step (1) is replaced with an equal mass of epoxy silane coupling agent (3-glycidyl etheroxypropyltrimethoxysilane), while the other raw materials and process steps are the same.

[0096] Comparative Example 4:

[0097] Compared with Example 1, the difference is that the process flow is changed, and the heating to 65°C and vacuum dehydration process in step (1) are not performed. Specifically, all raw materials are directly mixed at 25°C and stirred and degassed under vacuum for 60 minutes.

[0098] Comparative Example 5:

[0099] Compared with Example 1, the difference is that hydrophobic modified fumed silica was not added in step (1), but its mass was replaced with an equal amount of spherical silicon micropowder (i.e., the total amount of spherical silicon micropowder increased), and the other raw materials and process steps were the same.

[0100] Test Example 1:

[0101] The experimental steps are as follows:

[0102] 1) Sampling and moisture determination: During the preparation process of each example and comparative example, after the pre-dispersion and dehydration modification in step (1) is completed and before the addition of borate ester inhibitors, about 5g of mixed slurry is drawn using a syringe. The sample is quickly injected into the titration cell of the Karl Fischer coulometric moisture analyzer to determine the absolute water content (unit: ppm) in the system. Each group of samples is tested in parallel three times and the average value is taken.

[0103] 2) Initial viscosity determination: After the final sealant is prepared and discharged, immediately take a sample and place it in a 25℃ constant temperature water bath for 30 minutes. Use a rotational rheometer to measure the initial viscosity at a shear rate of 10s. -1 Its initial viscosity (η0) was measured.

[0104] 3) Aging and viscosity monitoring: Seal the remaining adhesive in an opaque PP tube and place it in a 25°C constant temperature and humidity chamber for standing. After standing for 24 hours and 72 hours respectively, remove it and measure the instantaneous viscosity (ηt) under the same conditions as above.

[0105] 4) Calculate the viscosity growth rate according to the formula: growth rate = instantaneous viscosity / initial viscosity, and use this to characterize the pot life and storage stability of the adhesive.

[0106] The test results are shown in Table 1, and the corresponding comparison charts are shown below. Figure 1 As shown.

[0107] Table 1. Data on residual moisture and viscosity increase under different dehydration processes and coupling agent systems:

[0108]

[0109] According to Table 1 and Figure 1 Data analysis shows that the high-temperature vacuum combined with titanate chemical dehydration process proposed in this invention has a significant impact on the stability of the system.

[0110] Data from Examples 1, 4, and 5 indicate that temperature is a key parameter affecting dehydration efficiency. In Example 1, after treatment at 65°C, the system moisture content decreased to 184.5 ppm, and the viscosity increase rate over 72 hours was only 1.12, demonstrating excellent storage stability. In Example 5, the temperature was increased to 70°C, further reducing the moisture content to 152.8 ppm, but the improvement in viscosity increase rate was limited, and the initial viscosity increased slightly, indicating that 65°C was close to the optimal process equilibrium point. In contrast, in Example 4, after treatment at 60°C, the residual moisture content was close to 300 ppm, resulting in a viscosity increase rate of 1.27 over 72 hours, indicating that the hydrolysis rate and moisture evaporation efficiency of titanate were reduced at low temperatures, but remained within a controllable range.

[0111] Comparative Example 4 data confirms the necessity of the heat treatment process. Even with the addition of titanate, the system moisture content remained as high as 1382.4 ppm when relying solely on physical mixing at 25°C. This high concentration of residual water caused severe hydrolysis of the subsequently added borate ester inhibitor, resulting in the loss of its complexing and shielding effect on the amine curing agent. Consequently, the viscosity of the adhesive doubled within 24 hours, and gelled within 72 hours, rendering it completely unusable.

[0112] Comparative Example 3 used a silane coupling agent instead of titanate. Although the same 65°C process was employed, the residual moisture content was still as high as 845.6 ppm, and the viscosity increase rate after 72 hours reached 2.86. This result verifies the mechanism of pyrophosphate titanate in this system: the silane coupling agent mainly relies on surface adsorption and slow hydrolysis condensation, and its water removal capacity is far weaker than that of titanate, which is extremely sensitive to water. Titanate achieves a dual water removal effect of chemical removal and physical volatilization by preferentially reacting with water to generate volatile isopropanol.

[0113] In summary, by using a high-temperature vacuum environment of 65–70°C combined with treatment with pyrophosphate-type titanate, the moisture content of the system can be effectively controlled below 200 ppm. This extremely dry microenvironment is a prerequisite for the long-term latency of borate ester inhibitors, thus verifying the decisive role of the "sacrificial dehydration-delayed complexation" synergistic mechanism in the preparation of single-component low-temperature thermosetting sealants.

[0114] Test Example 2:

[0115] The experimental steps are as follows:

[0116] 1) Dynamic scanning test: Approximately 5–10 mg of fresh gel samples prepared in Example 1 and Comparative Example 2 were placed in aluminum crucibles and sealed with caps. Differential scanning calorimetry (DSC) was used, with an empty aluminum crucible as a reference. Under a nitrogen atmosphere with a flow rate of 50 mL / min, the temperature program was set from 25 °C to 250 °C at a heating rate of 10 °C / min. The heat flux versus temperature curve was recorded, and the initial exothermic temperature, peak exothermic temperature, and total exothermic enthalpy of the curing reaction were obtained through software analysis.

[0117] 2) Isothermal Curing Test: Take approximately 5-10 mg of fresh adhesive sample and encapsulate it in an aluminum crucible. Preheat the DSC furnace to 80°C and stabilize it. Quickly place the sample crucible in the furnace and start timing. Record the heat flow curve over time under constant temperature of 80°C until the heat flow curve returns to the baseline, indicating the end of the reaction.

[0118] 3) Data processing: Integrate the isothermal curing curve to calculate the total enthalpy of reaction. Define the time at which the degree of reaction reaches 90% of the total enthalpy as the curing time at that temperature.

[0119] The test results are shown in Table 2, and the corresponding comparison chart is shown below. Figure 2 As shown.

[0120] Table 2 Comparison of DSC curing kinetic parameters between Example 1 and Comparative Example 2:

[0121]

[0122] According to Table 2 and Figure 2 The data show that Example 1 and Comparative Example 2 exhibit fundamental differences in curing kinetics.

[0123] The initial exothermic temperature of Example 1 was 72.4℃, and the peak exothermic temperature was 91.8℃. This result indicates that within the temperature range of room temperature to 70℃, the amine curing agent in the system is effectively complexed and shielded by the borate ester, preventing significant ring-opening addition reactions and thus imparting excellent storage stability to the adhesive at room temperature. When the temperature exceeds 70℃, the boron-amine coordination bond dissociates upon heating, and the released active amine rapidly catalyzes the reaction between the thiol and the epoxy resin, with the peak temperature controlled below 100℃, meeting the process requirements for low-temperature rapid curing. Under isothermal conditions at 80℃, Example 1 achieves 90% curing in just 18.6 minutes, meeting the production line cycle time.

[0124] Comparative Example 2, without the addition of borate ester inhibitors, had an initial exothermic temperature of only 38.2°C and a peak exothermic temperature of 65.7°C. This excessively low initial temperature means that the system begins to undergo significant chemical reactions at temperatures slightly above room temperature, resulting in a very short pot life that fails to meet the time window for dispensing. Furthermore, although its reactivity is high, the premature reaction means that some active groups are consumed or encapsulated in the early stages of mixing, leading to a lower measured total exothermic enthalpy (298.1 J / g) than in Example 1 (342.5 J / g), indicating that the final cured network crosslinking density may be insufficient.

[0125] In summary, borate ester inhibitors successfully controlled the curing reaction temperature window through a Lewis acid-base complexation mechanism, ensuring both chemical inertness at room temperature (high onset temperature) and rapid reaction capability after heating (moderate peak temperature), thus verifying the effectiveness of the thermosensitive delayed curing mechanism.

[0126] Test Example 3:

[0127] The experimental steps are as follows:

[0128] 1) Sample loading and pre-shearing: A rotational rheometer was used, with a test gap set to 0.5 mm. The adhesive samples from the examples and comparative examples were placed at the center of the test stage. After pressing the rotor down to the preset gap, excess adhesive overflowing from the edges was scraped off. To eliminate historical shear memory during the loading process, a 5-second pre-shearing time was first applied. -1 The shear rate was pre-sheared for 60 seconds, followed by resting for 120 seconds to allow the internal microstructure to be reconstructed.

[0129] 2) Thixotropic index (TI) determination: Steady-state flow scanning mode was used, with the temperature controlled at 25℃. First, a low shear rate of 0.5 s⁻¹ was applied. -1 A constant shear rate was applied for 120 seconds, and the viscosity value after equilibrium was recorded as the low-shear viscosity; then the shear rate was jumped to 5.0 s. -1 The viscosity was constant for 120 seconds, and the resulting viscosity was recorded as the high-shear viscosity. The ratio of the low-shear viscosity to the high-shear viscosity was calculated, which is the thixotropic index.

[0130] 3) Yield stress scan: After reloading the fresh sample and allowing it to stand, the shear stress control mode was used. The shear stress was set to be logarithmically scanned from 0.1 Pa to 1000 Pa, and the stress values ​​corresponding to the viscosity drop or modulus crossover point were recorded to define the minimum yield stress required for the adhesive to undergo macroscopic flow.

[0131] The test results are shown in Table 3, and the corresponding comparison charts are shown below. Figure 3 As shown.

[0132] Table 3. Test results of rheological parameters under different filler and coupling agent systems:

[0133]

[0134] According to Table 3 and Figure 3 According to the data, the "titanium ester-silica" synergistic network constructed in this invention has a decisive influence on the rheological properties of the adhesive.

[0135] Example 1 exhibits a thixotropic index of 4.4 and a yield stress of 215.6 Pa. This indicates that under static or low-shear conditions, a high-strength network structure forms within the adhesive, resisting gravity and preventing sagging; while at high shear rates, the viscosity rapidly decreases to 42.1 Pa·s, ensuring smooth dispensing. Example 2 further enhances this effect by adjusting the formulation, increasing the TI value to 5.56 and achieving a yield stress of 342.8 Pa, making it particularly suitable for ultra-narrow bezel dispensing scenarios with extremely high shape retention requirements.

[0136] Comparative Example 5, without fumed silica, had a thixotropic index of only 1.05 and a yield stress close to zero, exhibiting characteristics similar to a Newtonian fluid. This indicates that fumed silica is the basic framework for constructing a physical thixotropic network; the absence of this component will cause the adhesive to fail to maintain its shape after dispensing, making it highly susceptible to collapse and overflow.

[0137] Comparative Example 3, while retaining fumed silica, removed the titanate coupling agent (replacing it with silane), resulting in a thixotropic index of 2.83 and a yield stress of only 86.4 Pa. This significant difference confirms the crucial bridging role of titanate in the system. The long-chain structure of pyrophosphate-type titanate not only improves the dispersibility of the filler but, more importantly, forms a dual "chemical-physical" anchoring effect through its terminal polar groups with the hydroxyl groups on the surface of fumed silica and the resin matrix. This synergistic effect strengthens the interparticle interactions, constructing a more robust cardboard structure than simple physical aggregation, thereby endowing the adhesive with superior anti-sagging properties and shear sensitivity.

[0138] Test Example 4:

[0139] The experimental steps are as follows:

[0140] 1) Load the adhesive sample to be tested into a 30cc standard black light-proof dispensing syringe, and place it in a centrifugal degassing machine at 2000rpm for 3 minutes to eliminate the influence of air bubbles on the fluid continuity. Install the syringe into a high-precision pneumatic dispensing machine, connect it with a 0.3mm inner diameter stainless steel precision needle (25G), and adjust the air source pressure to a constant 0.4MPa.

[0141] 2) Place weighing paper on a precision balance, turn on the dispensing controller, and set the dispensing time to 30 seconds. Record the weight of the dispensing material during this time period. Repeat the test 5 times and take the average value. Calculate the extrusion rate per unit time (mg / s) to characterize the high shear flowability of the adhesive in a micro-tube.

[0142] 3) Fix the syringe on the triaxial automatic dispensing platform, set the moving speed to 15mm / s, and the gap between the needle and the substrate to 0.2mm. Dispense adhesive in a straight line on a clean glass slide to form an adhesive strip with a length of 50mm.

[0143] 4) After applying the adhesive, let the glass slide stand at room temperature (25℃) for 10 minutes to allow the adhesive to level naturally under the influence of gravity and surface tension. Then, use a laser profilometer (or an optical microscope with a scale) to cut a cross-section of the adhesive strip, measure the height (H) of the highest point and the width (W) of the bottom of the adhesive strip, and calculate the aspect ratio (H / W) to quantify the adhesive's resistance to collapse and its shape retention.

[0144] The test results are shown in Table 4, and the corresponding comparison charts are shown below. Figure 4 As shown.

[0145] Table 4. Micro-dispensing process parameters and shape retention test results for different formulation systems:

[0146]

[0147] According to Table 4 and Figure 4The data showed that the performance of the examples and the comparative examples in the micro-dispensing process was significantly different, which verified the precise control of rheological properties by the titanate-silicon synergistic mechanism.

[0148] Examples 1 through 5 all exhibited ideal high extrusion and high shape retention characteristics. Their extrusion rates remained stable between 21.3 and 25.8 mg / s, indicating a high shear field (shear rate > 10) inside the needle. 3 s -1 Under the action of [unclear], the titanate coupling agent effectively reduced the frictional resistance between inorganic particles and the resin matrix, achieving significant shear thinning and ensuring that the adhesive could smoothly pass through the 0.3 mm micro-needle without clogging or breakage. Simultaneously, the aspect ratio of the adhesive strips in these groups remained above 0.80, with Example 2 (high thixotropic formulation) reaching 0.95. This indicates that once the adhesive leaves the needle and deposits on the substrate (shear force removed), the hydrogen bond and coordination bond network within the system can be rapidly rebuilt within milliseconds, generating sufficient yield stress to resist flow caused by gravity and surface tension, thus maintaining a robust three-dimensional morphology on narrow borders.

[0149] In contrast, Comparative Example 5 exhibited an extrusion rate as high as 92.1 mg / s, but its aspect ratio was only 0.12. This indicates that the adhesive lacking a fumed silica framework exhibits near-Newtonian fluid properties. Although it has excellent fluidity, it completely loses its resistance to collapse, spreading rapidly after dispensing. This makes it unable to meet the limitations of narrow bezels on the width and height of the adhesive path, and it is extremely easy to contaminate the display area.

[0150] The test results of Comparative Example 3 revealed the crucial role of titanate. In the absence of titanate, despite the presence of fumed silica in the system, the extrusion rate decreased to 14.2 mg / s, and the aspect ratio was only 0.52. Notably, although this group exhibited a low high-shear viscosity (39.8 Pa·s) in the rheological tests of Example 3, indicating a weak bulk network structure easily damaged by shear, in actual passage through a micro-needle (0.3 mm inner diameter), the lack of long-chain lubrication and dispersion from titanate led to a high degree of micro-agglomeration and bridging blockage of the highly packed inorganic particles in the narrow flow channel, resulting in a sharp increase in tube wall friction resistance. This dynamic resistance caused by poor dispersion negated the advantage of low viscosity, creating a process contradiction of low viscosity but difficult extrusion. Simultaneously, the lack of a stable thixotropic network support prevented the extruded adhesive from maintaining its shape, leading to severe collapse. Therefore, only through the synergistic effect of titanate and fumed silica can the dual contradictory requirements of precision dispensing processes for flowability (internal lubrication to prevent clogging) and thixotropy (high yield strength to prevent collapse) be simultaneously met.

[0151] Test Example 5:

[0152] The experimental steps are as follows:

[0153] 1) An anodized aluminum alloy plate with dimensions of 100mm × 25mm × 2mm was selected as the substrate. The bonding area was ultrasonically cleaned with acetone for 10 minutes to remove surface oil and impurities, and then dried for later use. The adhesive samples from Example 1 and Comparative Example 1 were taken and uniformly coated on one side of the substrate, with the adhesive layer thickness controlled at 0.1mm and the overlap length set at 12.5mm. The overlap was fixed with a long-tail clip, and the plates were placed in an 80℃ oven for 30 minutes to cure. After curing, they were removed and allowed to cool naturally to room temperature for 24 hours to eliminate internal stress.

[0154] 2) Using a universal testing machine, shear failure tests were performed on 5 specimens in each group at a tensile rate of 5 mm / min at room temperature (25℃). The maximum load at which the specimen broke was recorded, and the initial shear strength (MPa) was calculated based on the overlap area. The average value was taken as the baseline data before aging.

[0155] 3) Place the remaining prepared cured samples into a programmable temperature and humidity test chamber. Set the environmental conditions to a temperature of 85℃ and a relative humidity of 85%. Take out the specified number of samples at the aging time points of 500 hours and 1000 hours respectively.

[0156] 4) The removed aging samples need to be conditioned for 24 hours in a standard laboratory environment (23±2℃, 50±5%RH) to stabilize their condition. Then, test their shear strength according to the method described in step 2. Calculate the strength retention rate, i.e., (strength after aging / initial strength) × 100%, to evaluate the chemical stability of the adhesive under high temperature and high humidity conditions.

[0157] The test results are shown in Table 5, and the corresponding comparison chart is shown below. Figure 5 As shown.

[0158] Table 5. Changes in shear strength of Example 1 and Comparative Example 1 under double 85 aging conditions:

[0159]

[0160] According to Table 5 and Figure 5 The data shows that Example 1 exhibited excellent mechanical stability under humid and hot conditions, verifying the core advantage of polyether thiols in terms of aging resistance.

[0161] The initial shear strength of Example 1 was 18.4 MPa. After aging under test conditions of 85°C and 85% RH for 1000 hours, the strength remained at 16.9 MPa, with a retention rate as high as 91.8%. Failure mode analysis showed that the aged sample still exhibited cohesive failure, indicating that the colloidal bulk structure did not degrade. This result is attributed to the use of a polythiol curing agent with a fully ether-bonded (-COC-) backbone in Example 1. Ether bonds have extremely high chemical inertness, making it difficult for water molecules to nucleophilically attack them, thus ensuring the integrity of the crosslinked network under high temperature and high humidity conditions.

[0162] Conversely, while Comparative Example 1 initially exhibited acceptable strength (16.8 MPa), its strength plummeted to 11.2 MPa after 500 hours of aging and further decreased to only 6.4 MPa after 1000 hours, resulting in a retention rate of less than 40%. Its failure mode shifted to powdering of the adhesive layer, a typical characteristic of chemical degradation. Comparative Example 1 used a conventional ester-based thiol (TMPMP), whose molecular structure contains numerous ester bonds (-COO-). Under conditions of 85°C and 85% RH, water molecules readily attack the carbonyl carbon in the ester bonds, initiating an irreversible hydrolysis reaction. This leads to the breakage of the polymer backbone, a sharp decrease in crosslinking density, and ultimately, the loss of its load-bearing capacity.

[0163] In summary, by introducing polyether segments to replace unstable ester segments, this invention completely solves the problem of poor resistance to moisture and heat in traditional thiol epoxy adhesives at the molecular structure level, ensuring the structural reliability of the adhesive throughout the entire life cycle of consumer electronics products.

[0164] Test Example 6:

[0165] The experimental steps are as follows:

[0166] 1) Take fresh adhesive solutions prepared in Examples 1 to 6 and inject them into polytetrafluoroethylene molds (cavity size 20mm×20mm×5mm). At the same time, take a small amount of sample (about 5-10mg) and seal it in an aluminum crucible for thermal analysis reference. Place the mold and crucible in a precision forced-air drying oven preheated to 80°C and heat at a constant temperature for 30 minutes. Then remove them and place them in a desiccator to cool naturally to room temperature (25°C).

[0167] 2) Use a Shore D hardness tester to test the cured block sample. Select 5 different positions at least 6 mm apart on the sample surface for measurement, read the instantaneous readings, and calculate the arithmetic mean as the cured hardness of the group.

[0168] 3) The crucible sample cured at 80℃ / 30min was scanned using differential scanning calorimetry (DSC). Under a nitrogen atmosphere, the temperature was increased from 25℃ to 200℃ at a rate of 10℃ / min, and the residual enthalpy of reaction was obtained by integrating the exothermic peak area. Combined with the total exothermic enthalpy of complete curing of the system measured in Test Example 2, the final degree of curing was calculated using the formula: Degree of curing = (1 - Residual enthalpy of reaction / Total exothermic enthalpy) × 100%.

[0169] The test results are shown in Table 6, and the corresponding comparison chart is shown below. Figure 6 As shown.

[0170] Table 6. Results of curing degree and hardness tests for Examples 1-6 at 80℃ / 30min:

[0171]

[0172] According to Table 6 and Figure 6 The data shows that the formulation system designed in this invention fully meets the requirements of the low-temperature rapid curing process at 80℃ / 30min, verifying the reactivity advantage of the thiol-epoxy click chemical reaction in the low-temperature region.

[0173] All embodiments achieved a degree of cure between 95.2% and 98.1%, with a hard, non-sticky surface. This indicates that at 80°C, the borate ester complex dissociates, and the released tertiary amine catalyst rapidly initiates a nucleophilic addition reaction between the thiol groups and the epoxy groups. Compared to traditional anhydride-epoxy systems requiring curing temperatures above 120°C, this system has a lower activation energy, enabling efficient chemical crosslinking while protecting heat-sensitive components such as mobile phone camera modules and OLED screens from thermal damage.

[0174] Data fluctuation analysis showed that Example 4 (adjusted inhibitor) had a slightly lower degree of curing (95.2%), which was due to the higher inhibitor concentration leading to a longer reaction induction period, but it still reached a usable level of over 95% within 30 minutes. Example 2 (high thixotropic) had a higher hardness (83.8HD), attributed to the physical reinforcement effect of the high content of inorganic filler (fumed silica). Example 5 (adjusted coupling agent) exhibited the highest degree of curing (98.1%), confirming that optimized interfacial bonding facilitated the diffusion and collision of reactive groups, reduced steric hindrance, and further improved the completeness of the reaction. In summary, this system balances the process requirements of cryogenic protection and rapid production.

[0175] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a low-temperature thermosetting narrow bezel sealant for mobile phones, characterized in that, Includes the following steps: (1) Pre-dispersion and dehydration modification: Bisphenol F type epoxy resin, toughened modified epoxy resin, spherical silica powder, hydrophobic modified fumed silica and pyrophosphate type titanate coupling agent are mixed and stirred and dispersed under heating and vacuum conditions. The pyrophosphate type titanate coupling agent is used to modify the surface of the filler in situ and remove trace amounts of water in the system. (2) Complexation inhibition treatment: Cool the mixture obtained in step (1) to 25-35°C, release the vacuum and add borate ester inhibitors, stir under vacuum for 20-40 minutes to allow the borate ester to form a complexation equilibrium with the residual active groups and pyrophosphate titanate coupling agents in the system. (3) Adhesive preparation and defoaming: Add ester-free polyether trifunctional thiol, latent curing agent, stabilizer, epoxy silane coupling agent and pigment to the system in step (2), and disperse evenly for 15 to 30 minutes under vacuum conditions with the temperature controlled at 20 to 30°C to obtain the sealant. The ester-free polyether trifunctional thiol is trimethylolpropane tri(3-mercaptopropyl) ether.

2. The preparation method of the low-temperature thermosetting narrow bezel sealant for mobile phones according to claim 1, characterized in that, The sealant is made from the following raw materials in parts by weight: 25-35 parts of bisphenol F type epoxy resin; 10-20 parts of toughened modified epoxy resin; 35-45 parts of spherical silica powder; 0.5–2.5 parts of hydrophobically modified fumed silica; 0.3–0.8 parts of pyrophosphate-type titanate coupling agent; Boronate inhibitors, 0.3–0.8 parts; 8-12 parts of ester-free polyether trifunctional thiol; 3-8 parts of latent curing agent; Stabilizer 0.1-0.3 parts; 0.3–0.8 parts of epoxy-based silane coupling agent; Pigment 0.1 to 0.5 parts.

3. The preparation method of the low-temperature thermosetting narrow bezel sealant for mobile phones according to claim 1, characterized in that, The heating temperature in step (1) is 60-70℃, the vacuum degree is -0.09MPa to -0.1MPa, and the stirring and dispersing time is 40-80 minutes.

4. The preparation method of the low-temperature thermosetting narrow bezel sealant for mobile phones according to claim 1, characterized in that, The stabilizer is barbituric acid, and the pigment is carbon black slurry.

5. The preparation method of the low-temperature thermosetting narrow bezel sealant for mobile phones according to claim 1, characterized in that, The ester-free polyether trifunctional thiol mentioned in step (3) is prepared by the following steps: 1) Preparation of intermediate: Trimethylolpropane was dissolved in a solvent, an alkaline catalyst was added, and allyl halides were added dropwise to carry out an etherification reaction. The intermediate trimethylolpropane triallyl ether was obtained after post-treatment. 2) Photochemical addition: The intermediate is mixed with a photoinitiator, and hydrogen sulfide gas is introduced under ultraviolet light to carry out a thiol-alkene click reaction. After the reaction is completed, residual hydrogen sulfide and low-boiling point impurities are removed to obtain the target product.

6. The preparation method of the low-temperature thermosetting narrow bezel sealant for mobile phones according to claim 5, characterized in that, The alkaline catalyst in step 1) is potassium hydroxide, and the allyl halide is allyl bromide; the etherification reaction includes the dropwise addition of allyl bromide at 55-70°C and the reaction being kept at 75-85°C.

7. The preparation method of the low-temperature thermosetting narrow bezel sealant for mobile phones according to claim 5, characterized in that, The photoinitiator mentioned in step 2) is 2,2-dimethoxy-2-phenylacetophenone; the ultraviolet light wavelength is 365nm.

8. The preparation method of the low-temperature thermosetting narrow bezel sealant for mobile phones according to claim 5, characterized in that, In step 2), the reaction pressure is controlled at 0.2–0.3 MPa, the reaction temperature at 20–30 °C, and the reaction time at 6–8 hours.

9. The preparation method of the low-temperature thermosetting narrow bezel sealant for mobile phones according to claim 5, characterized in that, In step 1), the molar ratio of trimethylolpropane, alkaline catalyst and allyl halide is 1:(3.0-3.6):(3.0-3.6).

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