Low-temperature-resistant and low-shrinkage UV-cured adhesive and preparation method thereof

Abstract

The application discloses a low-temperature-resistant and low-shrinkage UV curing adhesive and a preparation method thereof. The adhesive is composed of the following components: base epoxy resin, special modifier, photoinitiator, filler and toughening agent. The low-temperature fast curing, low volume shrinkage and high low-temperature toughness are integrated by the formula synergistic design. The ring-opening polymerization volume expansion of the spirocyclic orthocarbonate low-shrinkage agent during curing effectively offsets the polymerization shrinkage of the epoxy resin. The chain segment activity at low temperature is provided by the polyurethane acrylate oligomer, the curing reaction activity is ensured, the interface combination and stress dispersion capacity are further enhanced by the introduction of the temperature responsive nanoparticles and the core-shell toughening particles, the performance combination of the fast surface drying, the extremely low volume shrinkage and the excellent flexibility in the low-temperature environment is realized, and a solution with excellent comprehensive performance is provided for the low-temperature and high-reliability bonding.

Description

Technical Field

[0001] This invention relates to the field of chemical materials technology, specifically to a low-temperature resistant, low-shrinkage UV-curable adhesive and its preparation method. Background Technology

[0002] UV-curable adhesives, also known as ultraviolet curing adhesives, are a type of special adhesive that can only cure rapidly under ultraviolet light. They are widely used in modern industry, electronics, medicine, and daily life.

[0003] Currently, common UV-curable adhesives on the market generally suffer from problems such as poor curing, high shrinkage, and decreased mechanical properties under low-temperature conditions. Most of these products are based on epoxy resin and contain photoinitiators, toughening agents, and other components. They are rapidly cured by ultraviolet irradiation. However, in low-temperature environments, the curing speed of the adhesive slows down significantly, and the shrinkage rate after curing is high, resulting in reduced bonding strength and affecting the reliability and service life of electronic components.

[0004] Secondly, increasing the speed of low-temperature curing usually requires increasing the reactivity, but this may exacerbate polymerization shrinkage, leading to increased internal stress, decreased bond strength, or substrate deformation. Excessive pursuit of low-temperature curing may reduce the toughness, heat resistance, or aging resistance of the cured material.

[0005] Therefore, it is necessary to design and create UV-curable adhesives that are resistant to low temperatures and low shrinkage, as well as their preparation methods. Summary of the Invention

[0006] To address the problems mentioned in the background art, the present invention aims to provide a low-temperature resistant, low-shrinkage UV-curable adhesive and its preparation method, which has the advantages of improving low-temperature resistance while reducing shrinkage.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a low-temperature resistant and low-shrinkage UV-curable adhesive, comprising the following components: a base epoxy resin, a special modifier, a photoinitiator, a filler, and a toughening agent. The special modifier includes: a low-shrinkage agent, a low-temperature flexible component, an adhesion promoter, a UV absorber, a hindered amine light stabilizer, and an antioxidant. The filler is composed of quartz powder and temperature-responsive nanoparticles, wherein the particle size of the quartz powder ranges from 1 μm to 10 μm.

[0008] Based on the total amount of the UV-curable adhesive being 100%, the UV-curable adhesive is composed of the following components by mass percentage: 50-60% base epoxy resin, 10-20% special modifier, 3-5% photoinitiator, 10-20% filler, and 5-10% toughening agent;

[0009] Based on the total amount of the special modifier being 100%, the content of each component is as follows: low shrinkage agent 20-40%, low temperature flexibility component 30-50%, adhesion promoter 5-15%, ultraviolet absorber 3-8%, hindered amine light stabilizer 5-10%, and antioxidant 2-5%.

[0010] As a preferred embodiment of the present invention, the low-shrinkage agent is a spirocyclic monomer, the low-temperature flexible component is a polyurethane acrylate, the adhesion promoter is a silane coupling agent, the toughening agent is a core-shell structured acrylate rubber particle, the ultraviolet absorber is Tinuvin 1130, the hindered amine light stabilizer is Tinuvin 123, and the antioxidant is Irganox 1010.

[0011] As a preferred embodiment of the present invention, based on the total amount of the filler being 100%, the content of each component is: 70-90% quartz powder and 10-30% temperature-responsive nanoparticles.

[0012] As a preferred embodiment of the present invention, a method for preparing a low-temperature resistant, low-shrinkage UV-curable adhesive includes step a) ingredient preparation and premixing; step b) stepwise mixing and dispersion; and step c) vacuum degassing.

[0013] Step a) Ingredients and premixing: Weigh 50-60% of the base epoxy resin and 5-10% of the toughening agent by weight percentage, place them in a mixing container and mix them to obtain the premixed material;

[0014] Step b) Stepwise mixing and dispersion: Transfer the premixed material obtained in step a) to a temperature-controlled stirrer, add 10-20% of special modifier and 3-5% of photoinitiator in sequence, and stir continuously at 300-500 rpm for 20-30 minutes until the system is uniform and transparent. Then, add 10-20% of filler until the filler is uniformly dispersed to obtain a homogeneous colloid.

[0015] Step c) Vacuum degassing: Transfer the homogeneous adhesive obtained in step b) to a vacuum degassing device for degassing treatment until no visible bubbles are precipitated in the adhesive, thus obtaining the low-temperature resistant and low-shrinkage UV curing adhesive.

[0016] As a preferred embodiment of the present invention, step b) involves stepwise mixing and dispersion. First, the base epoxy resin and toughening agent are stirred at 45℃-50℃ and 400-500 rpm for 15-25 minutes. Then, a special modifier and photoinitiator are added, and the mixture is stirred at the same temperature at 300-400 rpm for 25-35 minutes. Finally, all the fillers are added, and the speed is increased to 1000-1200 rpm for high-speed dispersion for 40-50 minutes. The temperature of high-speed dispersion is controlled at 45℃±2℃.

[0017] As a preferred embodiment of the present invention, the process conditions for step c) of vacuum degassing are: a vacuum degree of -0.095MPa to -0.098MPa and a temperature of 30℃ to 40℃, and the degassing treatment is carried out for 30 to 60 minutes.

[0018] As a preferred embodiment of the present invention, step a) ingredient preparation and premixing: stirring at a speed of 200-400 rpm for 10-20 minutes at a temperature of 25-30℃.

[0019] As a preferred embodiment of the present invention, step b) stepwise mixing and dispersion: the temperature-controlled stirrer needs to be heated to 40℃-50℃ during the mixing of the premixed materials.

[0020] As a preferred embodiment of the present invention, step b) stepwise mixing and dispersion: after the filler is added, the stirring speed is increased to 800-1200 rpm, and high-speed dispersion is carried out for 30-60 minutes.

[0021] As a preferred embodiment of the present invention, in step b), when high-speed dispersion is carried out after adding all the fillers, the linear velocity of the stirring paddle is controlled at 8-12 m / s; the vacuum degassing treatment time in step c) is 30-60 minutes.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1. This invention integrates low-temperature rapid curing, low volume shrinkage, and high and low temperature toughness through synergistic formulation design. The spirocyclic carbonate low-shrinkage agent undergoes ring-opening polymerization and volume expansion during curing, effectively offsetting the polymerization shrinkage of epoxy resin. The polyurethane acrylate oligomer provides segmental mobility at low temperatures, ensuring the activity of the curing reaction. The introduction of temperature-responsive nanoparticles and core-shell toughening particles further enhances the interfacial bonding and stress dispersion capabilities. This results in a combination of performance characteristics that allows for rapid surface drying (≤15s) at low temperatures (0°C), extremely low volume shrinkage (≤2.1%), and excellent flexibility (no cracking when bent 180° at -20°C). This provides a comprehensive and high-performance solution for low-temperature, high-reliability bonding.

[0024] 2. This invention employs a three-step preparation process: premixing of ingredients, stepwise mixing and high-speed dispersion, and vacuum degassing. Premixing allows the base resin and toughening agent to initially fuse, providing a foundation for toughness. Stepwise mixing first fully homogenizes the resin with a special modifier containing multiple functional monomers, then adds a photoinitiator to prevent premature consumption, and finally high-speed dispersion of the filler ensures uniform distribution. Vacuum degassing completely eliminates air bubbles inside the adhesive, preventing them from becoming performance defects. The entire process is carried out under temperature-controlled and light-protected conditions, ensuring the effective functioning of each component and the homogeneity and stability of the final adhesive, achieving a highly efficient and reliable conversion from the performance of the formulation design to the performance of the finished product.

[0025] 3. This invention achieves performance breakthroughs through the synergistic mechanism of functional components. During the curing process, the photoinitiator absorbs ultraviolet light to generate active species, which simultaneously initiates the cationic polymerization of epoxy resin, the ring-opening expansion polymerization of spirocyclic orthocarbonate, and the free radical polymerization of polyurethane acrylate. The expansion polymerization effectively compensates for volume shrinkage, and the flexible chain segments embedded in the network enhance low-temperature toughness. Temperature-responsive nanoparticles increase the reaction interface and may assist low-temperature initiation through photothermal effects. Meanwhile, the core-shell toughening particles and silane coupling agents enhance interfacial bonding and stress transfer through physical dispersion and chemical bonding, respectively, ultimately forming a composition with low internal stress, high toughness, and stability.

[0026] 4. This invention maintains the system's reactivity and conversion efficiency by utilizing the low-temperature flexibility of polyurethane acrylate and the interfacial reinforcement effect of nanofillers. Addressing the large curing shrinkage of epoxy resin, the invention directly offsets this shrinkage using the ring-opening expansion characteristics of spirocyclic orthocarbonate. Addressing the high brittleness of the material at low temperatures, the invention utilizes flexible long chains and core-shell particles for synergistic toughening, stress absorption, and dispersion. For long-term reliability, the invention ensures the material's performance stability during thermal aging and storage through light stabilizers, antioxidants, and vacuum degassing processes. Ultimately, this invention achieves an excellent balance between low-temperature curability, dimensional stability, mechanical properties, and durability. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only 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 are within the scope of protection of the present invention.

[0028] Base epoxy resin: Bisphenol A type epoxy resin, epoxy equivalent (EEW) approximately 190 g / eq, viscosity (25°C) 12000±1500 mPa.s, industrial grade;

[0029] Special modifiers:

[0030] Low shrinkage agent: spirocyclic orthocarbonate monomer, CAS number: registered product, industrial grade;

[0031] Low-temperature flexible component: polyurethane acrylate oligomer, functionality 2, viscosity (25°C) 4500±500mPa·s, industrial grade registered product;

[0032] Adhesion promoter: γ-methacryloyloxypropyltrimethoxysilane (KH-570), CAS No.: 2530-85-0, industrial grade;

[0033] UV absorber: Tinuvin 1130 (benzotriazole), CAS No.: 104810-48-2, industrial grade;

[0034] Hindered amine light stabilizer: Tinuvin 123, CAS No.: 129757-67-1, industrial grade;

[0035] Antioxidant: Irganox 1010, CAS No.: 6683-19-8, industrial grade;

[0036] Photoinitiator: 2-hydroxy-2-methyl-1-phenyl-1-propanone (HMPP), CAS No.: 7473-98-5, industrial grade;

[0037] filler:

[0038] Quartz powder: treated with silane, particle size D50=5μm, CAS No.: 14808-60-7, industrial grade;

[0039] Temperature-responsive nanoparticles: These are surface-modified nano-silica particles with photothermal conversion function. For example, polydopamine-coated nano-silica (PDA@SiO2) with a particle size of 20-30 nm can be used. The polydopamine coating layer can generate a thermal effect under 365nm ultraviolet light irradiation, which can be used to help improve local reaction activity during low-temperature curing. At the same time, the active groups on its surface can enhance the interfacial bonding with the resin matrix. The preparation method can refer to the example, that is, disperse nano-silica in alkaline Tris buffer, add dopamine hydrochloride, stir and react at room temperature for 24 hours, and then obtain the product after centrifugation, washing and drying. Alternatively, commercially modified nanoparticles with similar photothermal conversion functions can be used, such as silica composite materials loaded with specific absorbents, such as Cytodiagnostics brand gold nanorods with absorption peaks around 808 nm (example catalog number: GNR-10-800) or surface-aminated silica-coated gold nanorods provided by Sigma-Aldrich (example catalog number: 747246). Those skilled in the art can select appropriate products according to their photothermal conversion efficiency, excitation wavelength, surface functional groups and compatibility requirements with the resin matrix.

[0040] Toughening agent: Core-shell structured acrylate rubber particles, average particle size 200nm, industrial grade registered product.

[0041] Preparation Example 1: Preparation of Low-Temperature Resistant, Low-Shrinkage UV-Curing Adhesive:

[0042] Step a) Ingredients and premixing: Under light-protected conditions, weigh 55% of the base epoxy resin and 7.5% of the toughening agent, place them in a mixing container, and stir for 15 minutes at 28°C and 300 rpm to obtain the premixed material.

[0043] Step b) Stepwise mixing and dispersion: Transfer the premixed material to a temperature-controlled stirrer and heat to 45°C. Add 15% of the special modifier (premixed according to Preparation Example 2) and 4% of the photoinitiator HMPP sequentially, and stir continuously at 45°C and 400 rpm for 30 minutes until the system is homogeneous and transparent. Then, add 15% of the filler (premixed according to Preparation Example 3), increase the stirring speed to 1100 rpm, and disperse at high speed at 45°C for 45 minutes until the filler is uniformly dispersed, obtaining a homogeneous solution.

[0044] Step c) Vacuum degassing: Transfer the obtained homogeneous adhesive to a vacuum degassing device and degas for 45 minutes at -0.097MPa and 35°C until no visible bubbles are precipitated in the adhesive. The low-temperature resistant, low-shrinkage UV-curable adhesive is then obtained and stored in a light-proof, sealed container.

[0045] Preparation Example 2: Premixing of Special Modifiers:

[0046] Weigh the following by mass percentage, based on a total special modifier amount of 100%: 30% low-shrinkage agent (spirocyclic carbonate), 40% low-temperature flexible component (polyurethane acrylate), 10% adhesion promoter (KH-570), 5% UV absorber (Tinuvin 1130), 8% hindered amine light stabilizer (Tinuvin 123), and 3% antioxidant (Irganox 1010). Mix at room temperature and 400 rpm for 20 minutes to obtain a homogeneous and transparent special modifier premix for later use.

[0047] Preparation Example 3: Premixing of fillers:

[0048] Weigh out the following by mass percentage, based on a total filler content of 100%: 80% quartz powder and 20% temperature-responsive nanoparticles. Dry mix them in a high-speed mixer at 800 rpm for 15 minutes to achieve initial homogeneity, and set aside for later use.

[0049] Example 1:

[0050] This embodiment provides a low-temperature resistant, low-shrinkage UV-curable adhesive, using process parameters that are the midpoints of various ranges. The specific steps are as follows:

[0051] Step a) Ingredients and premixing: Weigh 55% of the base epoxy resin and 7.5% of the toughening agent, and stir at 28°C and 300 rpm for 15 minutes.

[0052] Step b) Stepwise mixing and dispersion: Heat to 45°C, add 15% special modifier (prepared according to Preparation Example 2) and 4% photoinitiator sequentially, and stir at 400 rpm for 30 minutes. Then add 15% filler (prepared according to Preparation Example 3), increase the rotation speed to 1100 rpm, and disperse at high speed at 45°C for 45 minutes.

[0053] Step c) Vacuum degassing: Vacuum degassing at -0.097MPa and 35°C for 45 minutes to obtain the finished product.

[0054] Example 2:

[0055] This embodiment provides a low-temperature resistant, low-shrinkage UV-curable adhesive, which uses process parameters that are combinations of the lower limits of various ranges. The specific steps are as follows:

[0056] Step a) Ingredients and premixing: Weigh 50% of the base epoxy resin and 5% of the toughening agent, and stir at 25°C and 200 rpm for 20 minutes.

[0057] Step b) Stepwise mixing and dispersion: Heat to 40°C, add 10% special modifier and 3% photoinitiator sequentially, and stir at 300 rpm for 35 minutes. Then add 10% filler, increase the speed to 800 rpm, and disperse at high speed at 43°C for 60 minutes.

[0058] Step c) Vacuum degassing: Vacuum degassing at -0.095MPa and 30°C for 60 minutes to obtain the finished product.

[0059] Example 3:

[0060] This embodiment provides a low-temperature resistant, low-shrinkage UV-curable adhesive, which uses process parameters that are combinations of the upper limits of various ranges. The specific steps are as follows:

[0061] Step a) Ingredients and premixing: Weigh 60% of the base epoxy resin and 10% of the toughening agent, and stir at 30°C and 400 rpm for 10 minutes.

[0062] Step b) Stepwise mixing and dispersion: Heat to 50°C, add 20% special modifier and 5% photoinitiator sequentially, and stir at 500 rpm for 25 minutes. Then add 20% filler, increase the speed to 1200 rpm, and disperse at high speed at 47°C for 30 minutes.

[0063] Step c) Vacuum degassing: Vacuum degassing at -0.098MPa and 40°C for 30 minutes to obtain the finished product.

[0064] Comparative Example 1:

[0065] Compared with Example 1, the difference is that in step b), the low-shrinkage agent (spirocyclic carbonate) and the low-temperature flexible component (polyurethane acrylate) in the special modifier are omitted and replaced with an equal amount of basic epoxy resin. The remaining steps and parameters are exactly the same as in Example 1.

[0066] Comparative Example 2:

[0067] Compared with Example 1, the difference is that in step b), only quartz powder is used as the filler, and no temperature-responsive nanoparticles are added. The remaining steps and parameters are exactly the same as in Example 1.

[0068] Comparative Example 3:

[0069] Compared with Example 1, the difference lies in the order of adding materials in step b). First, the photoinitiator is added and mixed with the base epoxy resin, and finally the special modifier is added. The remaining steps and parameters are exactly the same as in Example 1.

[0070] Comparative Example 4:

[0071] Compared with Example 1, the difference is that the vacuum degassing treatment in step c) is omitted, and the mixture is discharged directly after dispersion. The remaining steps and parameters are exactly the same as in Example 1.

[0072] Test Example 1: Low-Temperature Curing Performance and Shrinkage Test

[0073] The UV curing speed and curing shrinkage rate of the UV curing adhesive samples obtained in Examples 1-3 and Comparative Examples 1-4 were tested respectively.

[0074] Low-temperature curing speed: The adhesive was applied to a glass slide to form a 100μm thick film, and then placed in a constant temperature environment at 0°C for 10 minutes to equilibrate. Subsequently, it was irradiated with a 365nm UVLED point light source (10mm away from the adhesive surface) with an intensity of 80mW / cm². The surface was touched lightly with a cotton swab every 1 second, and the time was recorded as the standard for surface dryness when no cotton fibers adhered.

[0075] Volume shrinkage rate: Referring to GB / T13354-1992 "Determination of density of liquid adhesives - weight cup method", the density of the adhesive before curing and after complete curing (365nm, 1000mJ / cm²) was measured respectively. The volume shrinkage rate was calculated according to the formula: Shrinkage rate = ,in This refers to the density after curing. This represents the density before curing.

[0076] Test Results and Analysis:

[0077] Table 1. Test results of low-temperature curing performance and volume shrinkage of UV-curable adhesives in each embodiment and comparative example;

[0078] Group Surface drying time (s) at 0°C Volume shrinkage rate (%) in conclusion Example 1 8-10 1.8 It cures rapidly at low temperatures with extremely low shrinkage. The spirocyclic orthocarbonate expands in volume during cationic ring-opening polymerization, effectively offsetting the curing shrinkage of the epoxy resin; the polyurethane acrylate enhances the chain segment mobility, and the synergistic effect with the photoinitiator ensures the reactivity and conversion rate at low temperatures. Example 2 12-15 2.1 It exhibits good low-temperature curing and low shrinkage. While using the lower limit of the formulation range, the content of functional components is relatively low, but the core mechanism still functions, and the performance meets the requirements. Example 3 6-8 1.5 It achieves the fastest curing at low temperatures and the lowest shrinkage rate. Utilizing the upper limit of the formulation range, it boasts the highest content of functional components, the strongest effects of low-temperature flexible components and low-shrinkage agents, and the high specific surface area of ​​nanofillers also contributes to improving photothermal conversion and curing efficiency at low temperatures. Comparative Example 1 >60 (Incomplete curing) 5.2 The low-temperature curing is extremely poor, with a large shrinkage rate. The lack of a core low-shrinkage agent and a low-temperature flexible component results in high viscosity and low activity of the system at low temperatures, and the inherent high polymerization shrinkage of epoxy resin cannot be offset. Comparative Example 2 20-25 3.0 Low-temperature curing is slow and the shrinkage rate is high. Only quartz powder is used, lacking temperature-responsive nanoparticles. Nanoparticles can provide more reaction interfaces and potential photothermal effects; their absence leads to reduced low-temperature initiation efficiency and weakened inhibition of shrinkage and stress dispersion. Comparative Example 3 15-20 2.5 The curing speed and shrinkage rate were both inferior to those of Example 1. The change in the order of addition and the premature addition of the photoinitiator may have caused pre-reaction or adsorption with the resin, affecting its dispersion and efficiency when special modifiers are added subsequently, resulting in the failure of the curing network formation and shrinkage compensation mechanism to reach their optimal levels. Comparative Example 4 10-12 (Uneven curing) 2.0 (with bubbles) Uneven curing leads to interference from air bubbles in shrinkage rate measurements. Failure to degas results in the presence of tiny air bubbles within the adhesive layer. During curing, these bubbles expand or migrate due to heat, affecting not only the uniformity of curing but also distorting the shrinkage rate data measured by the density method. The actual shrinkage within the adhesive may be greater.

[0079] Test Example 2: Low-Temperature Bond Strength and Toughness Test

[0080] Low-temperature shear strength: Referring to GB / T7124-2008 "Determination of tensile shear strength of adhesives (rigid material to rigid material)", LY12 aluminum alloy specimens (single lap joint, lap area 12.5mm×25mm) were sanded, cleaned with acetone, coated with adhesive, and cured under 365nm UV light (cumulative light intensity 1000mJ / cm²). After curing, the specimens were placed in a -20°C low-temperature chamber for 2 hours, and then the shear strength was tested on a universal testing machine at -20°C with a loading speed of 10mm / min.

[0081] Low-temperature toughness: The adhesive is coated onto a polyester film and cured to form an adhesive film approximately 1 mm thick. Strip samples are cut and placed in a -20°C environment for 1 hour. After being folded 180°, the surface of the adhesive film is observed to see if cracks or whitening appear.

[0082] Test Results and Analysis:

[0083] Table 2. Low-temperature bond strength and toughness test results of UV-cured adhesives in each example and comparative example:

[0084] Group Shear strength at 20°C (MPa) Bending performance at -20°C in conclusion Example 1 15.2 No cracks or whitening after bending 180°. It exhibits high strength at low temperatures and excellent flexibility. The flexible long chains of polyurethane acrylate and the core-shell toughening particles can effectively absorb and disperse stress at low temperatures, while the low shrinkage of the spirocyclic monomer reduces interfacial stress, together ensuring a strong and tough bond at low temperatures. Example 2 13.5 No cracks after bending 180° It exhibits good low-temperature performance. The proportion of functional components is appropriate, meeting the basic mechanical performance requirements at low temperatures. Example 3 16.8 No cracks after bending 180° Optimal low-temperature performance. The high content of flexible components, toughening agents and nanofillers produces the best synergistic toughening and reinforcement effect, with the most outstanding strength and crack resistance at low temperatures. Comparative Example 1 4.1 (Cohesion Destruction) Brittle cracking occurs when bent at 90°. It exhibits high brittleness and low strength at low temperatures. Lacking flexible components and low-shrinkage agents, the cured adhesive layer is hard and brittle, with internal stress concentration at low temperatures, making it highly susceptible to brittle fracture. Comparative Example 2 9.8 Microcracks appear when bent 180° Insufficient low-temperature toughness. Due to the lack of interfacial reinforcement and stress dispersion effects from nanoparticles, the solidified network's resistance to crack propagation at low temperatures decreases. Comparative Example 3 11.5 It turns white when bent 180°. The adhesion and toughness decreased slightly. The suboptimal feeding sequence may have affected the uniformity of the network structure and the interfacial bonding, resulting in an increase in stress concentration points at low temperatures and the appearance of streaks (whitening). Comparative Example 4 12.0 (Data fluctuates greatly) Stress lines caused by bubble defects are visible at the bend. The strength is unstable and defects exist. Bubbles, as physical defect points, become stress concentration sources and crack initiation sites, severely reducing the effective load-bearing area of ​​the adhesive layer and its reliability at low temperatures.

[0085] Test Example 3: Thermal Performance and Storage Stability Test

[0086] Test method:

[0087] Glass transition temperature (Tg): Differential scanning calorimetry (DSC) was used. Approximately 10 mg of fully cured gel sample was taken and heated from -60°C to 150°C at a rate of 10°C / min under a nitrogen atmosphere. The DSC curve was recorded and the midpoint method Tg was taken.

[0088] Performance retention rate after thermal aging: The prepared shear strength test specimens (same as in Test Example 2) were placed in a 125°C forced-air drying oven for 1000 hours. After being removed and cooled to room temperature, their shear strength was tested, and the retention rate of strength relative to the initial room temperature was calculated.

[0089] Storage stability: The uncured adhesive was sealed in an opaque sample bottle and stored at 5°C. The sample was removed at 0, 7, 14, and 30 days, and after being restored to 25°C, its viscosity was measured. The appearance was also observed for any layering, precipitation, or crystallization.

[0090] Test Results and Analysis:

[0091] Table 3. Test results of thermal properties and storage stability of UV-curable adhesives in each example and comparative example:

[0092] Group Tg (°C) Strength retention rate after 125°C / 1000h Viscosity change rate after 30 days of storage at 5°C in conclusion Example 1 -25 90% +8% (Clear and uniform appearance) Low Tg ensures low-temperature toughness, good resistance to heat aging, and stable storage. Flexible components and toughening agents reduce Tg; antioxidants and light stabilizers effectively delay thermal oxidation; special modifier premixing and optimized processes ensure component compatibility, and it is not prone to crystallization or separation during low-temperature storage. Example 2 -22 88% +10% (Clear appearance) Stable and reliable performance. Example 3 -28 92% +5% (Clear appearance) It exhibits outstanding low-temperature performance, excellent aging resistance, and stable storage. The higher content of flexible components further reduces the thermal aging temperature (Tg), but the optimized stabilizer system still ensures good resistance to thermal aging. Comparative Example 1 15 60% +40% (There is sediment at the bottom) Excessive temperature glyc (Tg) leads to low-temperature brittleness, easy thermal aging, and unstable storage. Pure epoxy systems have high Tg; the lack of anti-aging components results in severe thermal oxidation; poor compatibility between components makes them prone to stratification during long-term storage. Comparative Example 2 -18 85% +15% (Slight thickening) The temperature glycemic index (Tg) is relatively high, resulting in slightly poorer low-temperature fluidity, but the stability is acceptable. The lack of nanoparticles makes the system viscosity more sensitive to temperature, and thickening is slightly more noticeable during low-temperature storage. Comparative Example 3 -20 82% +20% (slightly cloudy) The stability is slightly poor. Improper feeding sequence may lead to unsatisfactory dispersion of photoinitiators or some additives, resulting in slight phase separation or degradation after long-term storage or thermal aging. Comparative Example 4 -24 89% +9% (Stable microbubbles are visible in the adhesive solution) The thermal properties are similar, but it contains air bubble defects. Air bubbles do not significantly affect Tg and chemical stability after thermal aging, but they exist in the adhesive as physical defects, affecting the product's appearance and long-term uniformity.

[0093] Test results show that Examples 1-3 achieved performance breakthroughs by introducing spirocyclic carbonate low-shrinkage agent, polyurethane acrylate low-temperature flexible component, and temperature-responsive nanoparticles, and scientifically compounding them with basic epoxy resin, toughening agent, and other components.

[0094] Low-temperature rapid curing: Polyurethane acrylate enhances the low-temperature reactivity and chain segment mobility of the system, while nanoparticles increase the reaction interface, together ensuring full curing at low temperatures (surface drying time ≤15s at 0°C).

[0095] Extremely low volume shrinkage: The spirocyclic monomer undergoes ring-opening polymerization under cationic initiation, resulting in volume expansion, which effectively offsets the polymerization shrinkage of epoxy resin and reduces the volume shrinkage rate to below 2.1%.

[0096] Excellent low-temperature mechanical properties: The flexible segments and core-shell toughening particles can still effectively absorb and disperse stress at low temperatures. Combined with the low internal stress caused by low shrinkage, the adhesive layer still maintains high shear strength (≥13.5MPa) and excellent bending flexibility (no cracks when bending 180°) at -20°C.

[0097] Balanced overall performance: While achieving the above-mentioned performance, the cured adhesive maintains a low glass transition temperature (Tg≤-22°C), good thermal aging stability (strength retention rate ≥88% after 125°C / 1000h) and storage stability.

[0098] The necessity of process optimization has been confirmed:

[0099] Comparative Example 3 (change in the order of adding materials) resulted in a decrease in performance, indicating that the order of first fully integrating the resin with the toughening agent and special modifier, then adding the photoinitiator, and finally dispersing the filler at high speed is beneficial for forming a uniform and stable prepolymer system and avoiding premature consumption or adsorption of the initiator. Although the basic performance of Comparative Example 4 (without degassing) was acceptable, the bubble defects caused fluctuations in performance data and posed potential risks, proving the indispensability of vacuum degassing for obtaining a homogeneous and defect-free adhesive.

[0100] Comparative Example 1 (lacking the core modifier) ​​showed a comprehensive deterioration in performance, especially with almost complete failure in low-temperature curing, a shrinkage rate as high as 5.2%, and significant low-temperature brittleness. This conversely proves that the special modifier (low-shrinkage agent, low-temperature flexible component) is a necessary and core component for solving this technical problem. Comparative Example 2 (lacking temperature-responsive nanoparticles) was inferior to the example in terms of low-temperature curing speed, shrinkage rate, and low-temperature toughness, indicating that nanofillers play a key auxiliary reinforcing role in improving the overall low-temperature performance.

[0101] In summary, the low-temperature resistant, low-shrinkage UV-curable adhesive and its preparation method provided by this invention, through unique formulation design (compounding of special modifiers and reinforcement with nanofillers) and process control (optimized feeding sequence and degassing), successfully prepared a UV-curable adhesive product that achieves an excellent balance in terms of low-temperature curing speed, low polymerization shrinkage, low-temperature mechanical properties (strength and toughness), and long-term thermal reliability. This provides an effective solution for high-reliability bonding applications such as electronic components in low-temperature environments.

[0102] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0103] 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 UV-curable adhesive with low temperature resistance and low shrinkage, characterized in that: It is composed of the following components: base epoxy resin, special modifier, photoinitiator, filler and toughening agent. The special modifier includes: low shrinkage agent, low temperature flexibility component, adhesion promoter, ultraviolet absorber, hindered amine light stabilizer and antioxidant. The filler is composed of quartz powder and temperature-responsive nanoparticles. The particle size of the quartz powder ranges from 1μm to 10μm. Based on the total amount of the UV-curable adhesive being 100%, the UV-curable adhesive is composed of the following components by mass percentage: 50-60% base epoxy resin, 10-20% special modifier, 3-5% photoinitiator, 10-20% filler, and 5-10% toughening agent; Based on the total amount of the special modifier being 100%, the content of each component is as follows: low shrinkage agent 20-40%, low temperature flexibility component 30-50%, adhesion promoter 5-15%, ultraviolet absorber 3-8%, hindered amine light stabilizer 5-10%, and antioxidant 2-5%.

2. The low-temperature resistant, low-shrinkage UV-curable adhesive according to claim 1, characterized in that: The low-shrinkage agent is made of spirocyclic monomer, the low-temperature flexible component is made of polyurethane acrylate, the adhesion promoter is made of silane coupling agent, the toughening agent is made of core-shell structured acrylate rubber particles, the ultraviolet absorber is Tinuvin 1130, the hindered amine light stabilizer is Tinuvin 123, and the antioxidant is Irganox 1010.

3. The low-temperature resistant, low-shrinkage UV-curable adhesive according to claim 1, characterized in that: Based on the total amount of the filler being 100%, the content of each component is as follows: quartz powder 70-90%, temperature-responsive nanoparticles 10-30%.

4. A method for preparing a low-temperature resistant, low-shrinkage UV-curable adhesive according to any one of claims 1-3, characterized in that: This includes steps a) ingredient preparation and premixing; step b) stepwise mixing and dispersion; and step c) vacuum degassing. Step a) Ingredients and premixing: Weigh 50-60% of the base epoxy resin and 5-10% of the toughening agent by weight percentage, place them in a mixing container and mix them to obtain the premixed material; Step b) Stepwise mixing and dispersion: Transfer the premixed material obtained in step a) to a temperature-controlled stirrer, add 10-20% of special modifier and 3-5% of photoinitiator in sequence, and stir continuously at 300-500 rpm for 20-30 minutes until the system is uniform and transparent. Then, add 10-20% of filler until the filler is uniformly dispersed to obtain a homogeneous colloid. Step c) Vacuum degassing: Transfer the homogeneous adhesive obtained in step b) to a vacuum degassing device for degassing treatment until no visible bubbles are precipitated in the adhesive, thus obtaining the low-temperature resistant and low-shrinkage UV curing adhesive.

5. The method for preparing a low-temperature resistant, low-shrinkage UV-curable adhesive according to claim 4, characterized in that: Step b) Stepwise mixing and dispersion: First, stir the base epoxy resin and toughening agent at 45℃-50℃ and 400-500rpm for 15-25 minutes. Then, add the special modifier and photoinitiator, and continue stirring at 300-400rpm for 25-35 minutes at the same temperature. Finally, add all the fillers, increase the speed to 1000-1200rpm, and disperse at high speed for 40-50 minutes. The temperature of high-speed dispersion is controlled at 45℃±2℃.

6. The method for preparing a low-temperature resistant, low-shrinkage UV-curable adhesive according to claim 4, characterized in that: Step c), the vacuum degassing process conditions are: a vacuum degree of -0.095MPa to -0.098MPa, a temperature of 30℃ to 40℃, and a degassing treatment time of 30-60 minutes.

7. The method for preparing a low-temperature resistant, low-shrinkage UV-curable adhesive according to claim 4, characterized in that: Step a) Ingredients and premixing: Stir at 200-400 rpm for 10-20 minutes at a temperature of 25-30℃.

8. The method for preparing a low-temperature resistant, low-shrinkage UV-curable adhesive according to claim 4, characterized in that: Temperature-controlled mixers need to be heated to 40℃-50℃ during the mixing of premixed materials.

9. The method for preparing a low-temperature resistant, low-shrinkage UV-curable adhesive according to claim 4, characterized in that: Step b) Stepwise mixing and dispersion: After adding the filler, increase the stirring speed to 800-1200 rpm and disperse at high speed for 30-60 minutes.

10. The method for preparing a low-temperature resistant, low-shrinkage UV-curable adhesive according to claim 4, characterized in that: In step b), when high-speed dispersion is carried out after adding all the fillers, the linear velocity of the agitator is controlled at 8-12 m / s; the vacuum degassing treatment time in step c) is 30-60 minutes.