Black UV (ultraviolet) edge sealing adhesive for liquid crystal display without frames on four sides and preparation method of black UV edge sealing adhesive

Abstract

The invention discloses a black UV edge sealing adhesive for a liquid crystal display without a frame on four sides and a preparation method of the black UV edge sealing adhesive. The black UV edge sealing adhesive comprises the following raw materials: urethane acrylate, an acrylate diluent, a photoinitiator, a defoaming agent, a dispersing agent, a silane coupling agent, silica powder and carbon black. According to the invention, the flexible aliphatic polyurethane acrylate and the nanoscale spherical silica powder are selected and compounded to construct a'soft-hard 'interpenetrating network structure, so that the edge sealing adhesive is endowed with excellent properties: the UV curing time is short, the sizing is rapid, and the industrial efficient production requirement is met; after being cured, the colloid has high flexibility and strong supporting performance, rigid damage in the construction and using process is effectively reduced through the flexibility, the whole-face liquid crystal display can be stably lifted through the sufficient strength, and guarantee is provided for achieving the design that the four edges are free of frames; the volume shrinkage rate is low, obvious deformation caused by shrinkage of the edge of the display screen can be avoided, and the external dimension precision of a frameless product is guaranteed; the cable has good water resistance and weather resistance, and can play a role in a complex environment for a long time.

Description

Technical Field

[0001] This invention relates to the field of displays, mainly to the filling direction of displays, and specifically to a UV-curable black edge-sealing adhesive for four-sided frameless liquid crystal displays and its preparation method. Background Technology

[0002] In the LCD manufacturing industry, traditional edge-sealing solutions have long relied on metal strips to seal the critical area at the bottom of the monitor. While this solution provides basic fixation, it presents several unresolved problems in practical applications: the metal strip itself has fixed shapes and installation gap requirements. To ensure the overall aesthetics of the packaging, a significant amount of blank space must be reserved around the monitor's edges to accommodate the metal strip installation. This prevents further narrowing of the screen bezel, severely clashing with current consumer market demands for narrow bezels and high screen-to-body ratios, thus limiting the potential for upgrades in monitor design. Furthermore, the metal strip's rigidity and lack of flexibility pose challenges during product transportation and warehousing. During storage or installation, if the device encounters external impacts such as bumps or collisions, it will not only fail to buffer the impact force but may also directly squeeze or scratch the glass panel or polarizer of the monitor, causing irreversible damage such as screen breakage and polarizer scratches, significantly increasing the product defect rate. Furthermore, the metal strip is easily affected by environmental factors. In humid, high-temperature, or alternating high- and low-temperature environments, the surface is prone to oxidation and rust, which not only affects the consistency of appearance but may also cause the edge sealing structure to loosen due to corrosion. The connection between the metal strip and the monitor glass and frame also lacks effective waterproof sealing capabilities, allowing external moisture to easily seep into the interior and cause malfunctions such as short circuits and liquid crystal leakage, thus shortening the service life of the equipment.

[0003] With the iteration of display technology and the upgrading of consumer demand, "bezel-less" LCD monitors have become the mainstream direction of industry development. These monitors require edge-sealing materials to not only fulfill the function of metal strip fixation, but also meet stringent performance standards such as sufficient support strength to support the screen weight, high coverage to hide the internal structure, high adhesion strength to bond different materials, high weather resistance to resist complex environments, and low volume shrinkage to avoid curing deformation. Against this backdrop, UV-curable black edge-sealing adhesives have emerged as a core material to replace metal strips. However, existing UV-curable black edge-sealing adhesives still face three major technical challenges in practical applications: firstly, insufficient UV curing efficiency and depth, such as… Figure 1As shown, the edge sealing adhesive needs to be filled into a narrow trapezoidal space of 5mm at the top, 3mm at the bottom, and 0.5mm in height via a piezoelectric valve, and is doubly covered by the polarizer and glass. The strong absorption of UV light by the carbon black component and the requirement of a 0.5mm curing thickness result in incomplete curing of the adhesive surface or incomplete curing inside, leading to problems such as insufficient bonding strength and easy detachment. Secondly, there is an imbalance between the "soft" and "hard" properties of the adhesive. The softer adhesive after curing has insufficient supporting strength, which will cause the polarizer at the bottom edge of the display to bend and lift under pressure after packaging. It is also prone to creep and deformation during aging and has poor weather resistance. On the other hand, the harder adhesive after curing has a high volume shrinkage rate. The shrinkage stress will cause wavy lines to appear on the edge of the polarizer, which will damage the flatness of the screen and affect the product qualification rate. Thirdly, it is difficult to balance performance and cost. Although some edge sealing adhesives can improve a single performance through special raw materials, the cost is too high. Low-cost formulas cannot meet the multi-dimensional performance requirements at the same time, making it difficult to achieve industrial application. Summary of the Invention

[0004] To address the limitations in appearance design, poor impact resistance, and insufficient weather resistance inherent in traditional metal-strip edge-sealed liquid crystal displays, as well as the issues faced by existing UV-cured black edge-sealing adhesives such as the imbalance between "soft" and "hard" properties, low UV curing efficiency, and the difficulty in balancing performance and cost, this invention aims to provide a balanced black UV edge-sealing adhesive for four-sided frameless liquid crystal displays and its preparation method. Specific objectives are as follows: Solving the problem of product appearance defects caused by soft-hard imbalance: Through the scientific compounding of flexible aliphatic polyurethane acrylate and nano-sized spherical silica powder, the synergistic effect of the "soft-hard" interpenetrating network structure is utilized to achieve a soft-hard balance in the colloid—ensuring both moderate hardness and sufficient support capacity. The molecular flexibility of long-chain polyurethane acrylate and the stress-dispersing effect of silica powder are used to improve the elongation at break and flexibility of the colloid, reducing hard damage (such as brittle fracture and cracking) during construction and use, and enhancing the buffer protection of the display screen edges. Simultaneously, the excellent rigidity of silica powder ensures that the colloid can stably support the entire LCD display during installation, preventing edge curling.

[0005] Improve water resistance and weather resistance: By screening aliphatic polyurethane acrylates with excellent water resistance properties (such as CN9014 NS), and combining them with silica powder to form a dense structure, the water vapor permeability is reduced. At the same time, the stability of the colloid is enhanced in complex environments such as high temperature and high humidity, and high and low temperature cycling, which solves the problems of weak water resistance and insufficient aging resistance of traditional metal strips. Optimize overall practical performance: Based on the above performance improvements, ensure that the edge sealing adhesive has an appropriate working time (avoiding an excessively short operating window due to carbon black agglomeration), good bonding strength, and rapid UV curing characteristics. This meets the dual requirements of "high performance + ease of operation" for materials in the industrial production of four-sided frameless LCD displays, ultimately forming an integrated edge sealing solution that can adapt to demanding application scenarios.

[0006] To solve the technical problem, the present invention adopts the following technical solution: A black UV sealing adhesive for a four-sided frameless LCD screen comprises the following raw materials in parts by weight: 20-30 parts polyurethane acrylate, 35-45 parts acrylate diluent, 0.5-2 parts photoinitiator, 0.2-0.4 parts defoamer, 0.5-0.7 parts dispersant, 1-2 parts silane coupling agent, 30-35 parts silica powder, and 0.05-0.15 parts carbon black.

[0007] Furthermore, the polyurethane acrylate is one or more of the following: aliphatic polyurethane acrylate polymers (such as CN9014 NS), epoxy acrylates (such as CNUVE151 NS), bisphenol A epoxy methacrylate oligomers (such as CN159 NS), and aliphatic polyurethane acrylates (such as Nanxiong Ketian 3299). The most preferred option is the aliphatic polyurethane acrylate polymer CN9014 NS. The reasons are as follows: First, test data shows that among various polyurethane acrylates, aliphatic polyurethane acrylates have the lowest volume shrinkage rate. This characteristic is crucial for the edge sealing adhesive of borderless LCD displays. Low shrinkage directly reduces edge deformation of the display screen caused by volume changes during curing, ensuring the dimensional accuracy of the device. Second, compared to epoxy acrylates (such as CNUVE151 NS) or bisphenol A epoxy methacrylate oligomers (such as CN159 NS), the aliphatic type effectively avoids edge curling of the polarizer caused by high shrinkage, perfectly meeting the stringent dimensional stability requirements of borderless products. Meanwhile, long-chain aliphatic polyurethane acrylates (such as CN9014 NS) significantly improve the elongation at break and plasticity of the colloid through the flexible design of the molecular chain. Tests have verified that its flexibility fully meets the usage requirements and can effectively buffer the impact on the edge of the display screen, avoiding the problem of damage caused by excessive rigidity of metal strips. This "soft-hard" balanced characteristic, in synergy with the rigid skeleton formed by silicon micropowder, constructs an interpenetrating network structure that combines low hardness and impact resistance, solving the problem of product defects caused by metal strips hitting the liquid crystal part during the current construction process. Third, after screening and testing of various types of resins, aliphatic polyurethane acrylates (such as CN9014 NS) showed the best performance in water vapor transmission rate and balanced performance data. The cured film formed by it can effectively block moisture intrusion and can stably withstand 600 hours in the humid heat resistance test at 85℃ and 85%RH, which is far superior to other resin types and even more superior to the barrier effect of metal strips. This synergy of water-resistant properties, low shrinkage, and high flexibility ensures the long-term protection of the internal components of the display screen by the edge-sealing adhesive in complex environments. Therefore, aliphatic polyurethane acrylate, with its balanced advantages in three key indicators—volume shrinkage, flexibility, and water vapor transmission rate—has become the optimal choice for edge-sealing requirements of four-sided borderless LCD displays.

[0008] Furthermore, the photoinitiator is one or more of photoinitiator ITX, photoinitiator TPO, photoinitiator 819, and photoinitiator 369. The selected photoinitiator ensures that the edge-sealing adhesive can cure quickly and completely, solving the problem of difficult curing caused by the black nature of traditional black edge-sealing adhesives.

[0009] Furthermore, the acrylate diluent is one or more selected from isobornyl acrylate IBOA, isobornyl methacrylate IBOMA, 1,6-hexanediol diacrylate HDDA, and laurate acrylate LA. The selected acrylate diluents exhibit good compatibility with polyurethane acrylates, can adjust the viscosity of the system, and participate in the reaction during curing, positively impacting the properties of the colloid. For example, isobornyl methacrylate IBOMA can effectively reduce the viscosity of the system and, after curing, can improve the hardness and chemical resistance of the colloid.

[0010] Furthermore, the dispersant is one or more of the following: ACUSOL 479N, dispersant 752W, dispersant DH-6100, and dispersant DH-6163. The selected dispersant effectively solves the problem of carbon black agglomeration, ensuring product color uniformity through the dispersion of carbon black particles, while also extending the processing time.

[0011] Furthermore, the defoamer is one or more of defoamer Y-137, defoamer YT-3300, defoamer W-155, and defoamer W-109. During the preparation process, bubbles are generated during material stirring. These defoamers can quickly eliminate bubbles, preventing them from affecting the performance and appearance of the colloid after curing.

[0012] Furthermore, the silane coupling agent can be KH-560. KH-560 can improve the interfacial bonding force between the organic and inorganic phases, enhance the compatibility between polyurethane acrylate and silica powder, thereby improving the overall performance of the colloid.

[0013] Furthermore, the silicon powder is nano-sized spherical silicon powder (SINO-QG from Zhongteng Materials can be selected). The reason for choosing nano-sized spherical silicon powder in this invention is as follows: First, nano-sized silicon powder, at the same mass, has a much larger number of powder particles than powder with micron-sized or larger particle sizes. A large number of nanoparticles can form denser "physical support points" in the colloidal system, effectively suppressing volume shrinkage during the curing process through the traction effect between the particles on the resin molecular chains; at the same time, its excellent rigidity can provide stable support and prevent the edges of the display from curling. This multi-particle synergistic constraint effect complements the low shrinkage characteristics of aliphatic polyurethane acrylate, which can further reduce the overall volume shrinkage rate of the sealing adhesive, ensuring the accurate appearance dimensions of the four-sided borderless liquid crystal display after curing, and avoiding internal microcracks or substrate damage caused by uneven shrinkage. Second, compared with sheet-like or needle-like powders, spherical silicon powder has the least impact on the flexibility of the colloidal system. While flake-shaped powders easily form layered deposits to enhance rigidity and barrier properties, and needle-shaped powders offer even greater rigidity, both exhibit colloidal breakage and detachment within a short time during thermal shock testing. Furthermore, the sharp shape of needle-shaped powders can disrupt the continuity of resin molecular chains, leading to embrittlement and a decrease in elongation at break. In contrast, spherical silica micropowders, with their rounded shape, can bind more uniformly to the resin matrix, reducing resistance to the flexible movement of molecular chains. This, combined with the flexibility of long-chain aliphatic polyurethane acrylates, helps maintain a high elongation at break in the colloidal material, ensuring that the sealing adhesive is not easily brittle under impact or temperature changes, thus meeting the stringent requirements for adhesive toughness in four-sided frameless displays. Therefore, nano-sized spherical silica micropowders, through the dual effects of "multi-particle traction inhibiting shrinkage" and "high self-rigidity providing strong support," synergistically optimize with the selected resin, perfectly solving the balance problem between colloidal flexibility, low volume shrinkage, and high rigidity support capacity. This makes it a key raw material for sealing adhesives suitable for four-sided frameless LCD displays.

[0014] Furthermore, the carbon black can be XH680 (Raycus Chemical). XH680 carbon black has good blackness and dispersibility, which can meet the high hiding power requirements of edge sealing adhesives, and at the same time, it has good compatibility with other raw materials.

[0015] The present invention also provides a method for preparing the black UV sealing adhesive for the four-sided frameless liquid crystal display screen, comprising the following steps: Step 1: Mix polyurethane acrylate and a portion of the acrylate diluent (no more than half the total weight) and stir at 1000-1500 rpm for 10-20 minutes. Then add the dispersant, defoamer, silane coupling agent, and carbon black, and stir at 1800-2400 rpm for another 30-40 minutes. This step first mixes the polyurethane acrylate with a portion of the diluent to provide a good dispersion environment for the subsequent addition of other additives. The higher stirring speed ensures that the dispersant and other additives are fully mixed with the material, effectively utilizing the dispersant's dispersion effect on the carbon black.

[0016] Step 2: Grind the material obtained in Step 1 using a three-roll mill until the fineness is no greater than 5 micrometers. Cool the material, which has heated up due to grinding, to 20℃-25℃. Grinding further refines the material particles and ensures that all components are mixed evenly. Cooling to a specific temperature is to avoid the high temperature affecting the subsequently added photoinitiator.

[0017] Step 3: Add the photoinitiator to the remaining acrylate diluent, stir until dissolved in a water bath at 70℃-75℃, then add the material obtained in Step 2, and stir and disperse at 1500-1800 rpm for 15-20 minutes. Dissolving the photoinitiator in the remaining diluent at a specific temperature ensures that the photoinitiator is fully dissolved and uniformly dispersed in the system, which is beneficial to the subsequent curing reaction.

[0018] Step 4: Slowly add silicon micropowder to the material obtained in Step 3 while stirring at 400-600 rpm. After all the powder has been added, stir at 1800-2000 rpm for 50-60 minutes to ensure uniform dispersion. Then filter, vacuum degas, and package to obtain the black UV filler adhesive for display devices. Slowly adding the silicon micropowder and controlling the stirring speed prevents agglomeration and ensures uniform dispersion in the system. Subsequent high-speed stirring further guarantees the dispersion effect. Filtration and degassing remove impurities and air bubbles from the system, improving product quality.

[0019] This invention relates to a black UV sealing adhesive for a four-sided frameless LCD screen, characterized by: storage at room temperature (15~25℃), application via a dispensing machine, and curing by double-sided irradiation with a 395nm LED for 40 seconds. This curing method is fast and efficient, meeting the needs of industrial production, and the curing conditions are mild, causing no damage to the display screen.

[0020] Compared with existing technologies, this invention achieves a breakthrough in solving the core problem of the trade-off between low volume shrinkage and strong support capacity by precisely selecting the type and ratio of polyurethane acrylate and silica powder to form a synergistic "soft-hard" interpenetrating network structure. The specific beneficial effects are as follows: 1. This invention, through the compounding of aliphatic polyurethane acrylate (such as CN9014 NS) and nano-sized spherical silica powder (such as SINO-QG), forms a complementary and synergistic performance system, completely solving the polarization defects of existing technologies: Low shrinkage and strong support are achieved simultaneously: The long-chain molecular structure of aliphatic polyurethane acrylate has low shrinkage properties, while the nano-sized spherical silica powder further inhibits curing shrinkage through the dense entanglement of multiple particles. At the same time, it provides stable support with high rigidity. This avoids the problem of "curling of the display edge caused by the colloid being too soft" and solves the problem of "excessive volume shrinkage and wrinkling of the polarizer caused by the colloid being too hard", thus achieving the core effect of "reliable support and dimensional stability".

[0021] Combining flexibility and impact resistance: The molecular flexibility of long-chain resins gives the colloid excellent buffering ability, while the rounded shape of spherical silica powder does not disrupt the continuity of the resin molecular chain. The synergy of the two significantly improves the elongation at break of the colloid, which can effectively resist hard impacts during transportation and installation, and avoid damage such as brittle fracture and cracking. 2. Through targeted formulation design, the core performance indicators of the edge banding adhesive of this invention are significantly optimized compared with traditional materials and similar edge banding adhesives: Significantly reduced volume shrinkage: Aliphatic polyurethane acrylate itself has the lowest shrinkage rate among similar resins. Combined with the rigid filling effect of nano-silica powder, the volume shrinkage rate of the sealing adhesive of this invention is reduced by more than 30% compared with the comparative example (using epoxy acrylate or bisphenol A epoxy methacrylate), which is far better than the industry average, ensuring that the appearance and dimensional accuracy of the display screen meets the standards after curing. Significantly improved weather resistance: The excellent water-blocking properties of aliphatic polyurethane acrylate, combined with the dense structure formed by silica powder, significantly reduce the water permeability of the edge sealant compared to the control. It can stably withstand 600 hours in a humid and hot environment of 85℃ and 85%RH without cracking, warping, or discoloration. At the same time, it remains intact after 200 high and low temperature cycles of 25℃ to 70℃, and its weather resistance far exceeds that of traditional metal strips and ordinary edge sealants.

[0022] Curing efficiency and depth meet requirements: Using a high-efficiency photoinitiator (such as photoinitiator 819) and a reasonable formula system, it can be fully cured in 40 seconds under double-sided irradiation with a 395nm LED lamp, with a curing depth of 550 micrometers. This not only meets the construction requirements of "0.5mm trapezoidal space filling", but also significantly shortens the curing time compared to traditional UV edge sealing adhesives.

[0023] 3. While meeting performance standards, this invention fully considers the practicality and environmental protection requirements for industrial production, resulting in outstanding application effects: Significantly enhanced operational stability: By controlling the dispersion of carbon black with a highly efficient dispersant, the working time of the sealing adhesive is extended to 24 hours, effectively avoiding the problems of short operating window and uneven color caused by carbon black agglomeration in traditional products, and reducing material waste and defective product rate in the production process.

[0024] Environmental and safety performance meets standards: The system is 100% solid content, with no release of volatile organic components and no toxic substances generated during the curing process. It not only meets national environmental protection standards but also avoids corrosion damage to the internal components of the display screen caused by volatile substances, ensuring the safety of the production environment and product quality. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of sealing the edges of an LCD display. Detailed Implementation

[0026] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, a detailed description of specific embodiments of the present invention is provided. The following content is merely illustrative and explanatory of the concept of the present invention. Various modifications, additions, or similar substitutions made by those skilled in the art to the described specific embodiments, as long as they do not depart from the inventive concept or exceed the scope defined in these claims, should fall within the protection scope of the present invention.

[0027] Unless otherwise specified, all raw materials used in the following examples were commercially available.

[0028] Example 1 In this embodiment, the encapsulating adhesive is prepared according to the following steps: Step 1: Take 15g of isobornyl methacrylate, add 25g of aliphatic polyurethane acrylate polymer CN9014 NS, stir and disperse at 1500rpm for 15 minutes, then add 0.6g of dispersant 752W, 0.3g of defoamer YT-3300, 1.5g of silane coupling agent KH560 and 0.1g of carbon black XH680 in sequence, and then stir and disperse at 2400rpm for 30 minutes. Step 2: Grind the material obtained in Step 1 using a three-roll mill until the fineness is no more than 5 microns, and cool the material that has heated up due to grinding to 20℃-25℃.

[0029] Step 3: Take 25g of isobornyl methacrylate, add 1.5g of photoinitiator 819 to it, stir until dissolved in a 75℃ water bath, then add the material obtained in Step 2, and stir and disperse at 1500rpm for 20 minutes.

[0030] Step 4: While stirring at 500 rpm, slowly add 31g of silicon micro powder (nano-sized spherical silicon micro powder SINO-QG) to the material obtained in Step 3. After all the powder is added, stir at 2000 rpm for 50 minutes to ensure that all the powder is evenly dispersed. Then filter, vacuum degas, and bottle to obtain UV black encapsulating adhesive for display devices.

[0031] Comparative Example 1 This comparative example was prepared using the same method as in Example 1, except that the aliphatic polyurethane acrylate polymer was replaced with an equal amount of aliphatic polyurethane acrylate (Nanxiong Ketian 3299).

[0032] Comparative Example 2 This comparative example was prepared using the same method as in Example 1, except that the aliphatic polyurethane acrylate polymer was replaced with an equal amount of epoxy acrylate (Sartoma CNUVE151 NS).

[0033] Comparative Example 3 This comparative example was prepared using the same method as in Example 1, except that the aliphatic polyurethane acrylate polymer was replaced with an equal amount of bisphenol A epoxy methacrylate oligomer (Sartoma CN159 NS).

[0034] Comparative Example 4 This comparative example was prepared using the same method as in Example 1, except that the silica powder was replaced with an equal amount of mica powder (Yongfeng Chemical ZR-A4).

[0035] Comparative Example 5 This comparative example was prepared using the same method as in Example 1, except that the silica powder was replaced with an equal amount of calcium carbonate.

[0036] Comparative Example 6 This comparative example was prepared using the same method as in Example 1, except that the silica powder was replaced with an equal amount of talc.

[0037] Comparative Example 7 This comparative example was prepared using the same method as in Example 1, except that the nano-sized spherical silica powder was replaced with nano-sized needle-shaped silica powder.

[0038] The following performance tests were conducted on the edge sealing adhesives of each embodiment and comparative example: 1. Permeability Glass with a silicone film was used as the substrate, and a limiting plate was used to control the thickness. The sealing adhesive to be tested was uniformly coated on the glass surface to form a film with a thickness of 0.5 μm. The film was then cured under a 395nm LED curing lamp for 40 seconds until fully cured, and the cured film was removed for later use. A Saicheng WPT-201 water vapor transmission rate tester was used, with the test environment parameters set to a temperature of 50℃ and a relative humidity of 100%RH. The prepared cured film was installed in the test chamber, ensuring a good seal between the film and the test device to avoid interference from external moisture. The tester was started, and under the set constant temperature and humidity conditions, the amount of water vapor passing through a unit area of ​​the film per unit time was calculated by detecting the water vapor partial pressure difference on both sides of the film, thus characterizing the water-blocking performance of the sealing adhesive.

[0039] 2. Resistance to damp heat According to the actual production process, the edge sealing adhesive to be tested was used to encapsulate the LCD screen; the encapsulated screen was then placed under a 395nm LED curing lamp for 40 seconds to ensure that the edge sealing adhesive was completely cured, thus obtaining the test sample.

[0040] The HTK-TH-100DH constant temperature and humidity circulating chamber of Hongjin Instruments was used as the test equipment; the temperature inside the chamber was set to 85℃ and the relative humidity to 85%RH, and the temperature and humidity conditions were kept stable during the test. Place the fully cured encapsulated display sample smoothly into the constant temperature and humidity circulating chamber; close the chamber door, start the equipment and begin timing, and continuously test under the set conditions of 85℃ and 85%RH. During the test, the condition of the sample is observed regularly, with a focus on checking whether the edge sealant has cracked, peeled, or discolored, and whether the display screen shows any abnormalities (such as leakage, black spots, or flickering). The time when the sample first shows the above abnormalities is recorded to evaluate the moisture and heat resistance of the edge sealant. If there are no abnormalities within 600 hours, its moisture and heat resistance is considered excellent.

[0041] 3. Resistant to high and low temperature cycling shock According to the actual production process standards, the edge sealing adhesive to be tested was used to encapsulate the LCD screen; after encapsulation, the screen was placed under a 395nm LED curing lamp for 40 seconds to ensure that the edge sealing adhesive was completely cured, thus obtaining the test sample.

[0042] The Huitai Machinery HT-LC60-502 high and low temperature shock chamber was selected as the testing equipment. The temperature change program for a single cycle was set as follows: maintain at -25℃ for 0.5 hours, then switch to 70℃ for 0.5 hours, with a cycle count of 200 times. The fully cured encapsulated display sample was placed steadily into the high and low temperature shock chamber; the chamber door was closed, the equipment was started, and the test began according to the preset temperature cycle program. After every 20 cycles, the sample was removed and the sealing adhesive was observed for physical damage such as cracking or peeling.

[0043] 4. LED curing depth Select a cylindrical container that is opaque on all four sides and open at the top, with an inner diameter of 2 cm and a depth of 5 cm. Slowly pour the sealant to be tested into the container until it is completely filled. Place the container filled with sealant stably directly under a 395nm LED curing lamp, ensuring that the center of the container opening is aligned with the center of the light source, and that the vertical distance between the curing lamp and the container opening is maintained at 7 cm. Turn on the LED curing lamp and irradiate for 40 seconds, then turn it off to complete the curing process. Remove the cured sealant cylinder from the container and use a vernier caliper with an accuracy of 0.01 mm to measure its height at different locations (at least 3 evenly distributed points). Take the average value as the curing depth of the sealant. In practical applications, the actual curing depth must not be less than 520 micrometers; a depth less than 520 micrometers is considered unqualified. 5. Elongation at break Using glass with a silicone film as the substrate, and with precise thickness control using a limiting plate, the sealing adhesive to be tested is evenly applied to the glass surface to form a film with a thickness of 0.5 micrometers. The film is placed under a 395nm LED curing lamp and irradiated on both sides for 40 seconds until fully cured. Then, the cured film on the silicone film is carefully peeled off. The cured film is cut into rectangular samples with a length of 10cm and a width of 0.5cm. A ZQ-990LA-2 tensile testing machine is used for testing, with the testing rate set to 10mm / min. The tensile testing machine is started, and the sample is stretched uniformly until it breaks. The maximum tensile length at the moment of fracture is recorded, and the elongation at break is calculated.

[0044] 6. Volume shrinkage rate Take an appropriate amount of the edge sealing adhesive to be tested and divide it into two groups of parallel samples: The first group consists of liquid samples: Weigh the liquid edge-sealing adhesive to an accuracy of 0.001 g. Determine the liquid density (ρ1) of the edge-sealing adhesive according to the density method specified in the relevant provisions of the international standard ISO 3521.

[0045] The second group consists of cured samples: The sealing adhesive is injected slowly into a PTFE mold with a diameter of 10mm and a height of 20mm to avoid air bubbles. The mold is then placed under a 395nm LED curing lamp for double-sided irradiation for 40 seconds until fully cured. After demolding, a solid cylindrical sample is obtained. The mass of the cured sample is weighed, and the solid cylindrical sample is slowly immersed in deionized water (the density of deionized water can be found in a deionized water temperature-density reference table). The increase in mass due to the deionized water is recorded. Based on the relationship between density and mass, the volume of the solid cylinder is calculated, and thus the density (ρ2) of the solid sample can be calculated. The volume shrinkage rate is calculated using the following formula: Volume shrinkage rate = (ρ2 - ρ1) / ρ2 * 100% 7. Working Hours Test Test conditions: A constant temperature and humidity test environment was established, with the temperature strictly controlled at 25℃±0.5℃ and the relative humidity maintained between 45% and 55%. Simultaneously, the test area was ensured to be completely shaded, avoiding any light (especially ultraviolet light) exposure to the sample to prevent premature curing of the sealing adhesive and its impact on test results. An appropriate amount of the sealing adhesive to be tested was taken, stirred thoroughly, and poured into a transparent cylindrical container (100g filling volume). The cap was tightly closed to reduce evaporation. Timing was started from the moment the sample was placed in the test environment, observing the sample status every hour for 12 consecutive hours, then every 8 hours thereafter. During observation, the sample bottle was carefully opened under shaded conditions, and visual inspection was performed using a glass rod to sample the sample. The focus was on observing whether the sealant exhibited stratification or sedimentation (i.e., separation of powder and liquid components, with obvious sediment at the bottom). When a slight settling is first observed at the bottom of the container, and carbon black accumulation, stratification, or inability to maintain a uniform flow is observed in the filler adhesive at the bottom using a glass rod, the cumulative time at this point is recorded as the working time of the filler adhesive.

[0046] The test results are shown in Table 1.

[0047] Table 1. Performance test results of each embodiment and comparative example As shown in Table 1: Comparative Example 1 used aliphatic polyurethane acrylate (Nanxiong Ketian 3299) instead of the aliphatic polyurethane acrylate polymer CN9014 NS in Example 1. Test results showed that the resin used in Comparative Example 1 performed better in terms of flexibility and elongation at break, but its weather resistance had significant problems, failing to meet the minimum weather resistance requirements of the product of this invention. This gap directly limits its application in edge sealing scenarios for four-sided borderless LCD displays—the display screen is exposed to complex environments for a long time, and insufficient weather resistance will cause the edge sealing adhesive to age and crack prematurely, thus losing its protective function. In contrast, the CN9014 NS selected in Example 1, through molecular structure optimization, significantly improves weather resistance while maintaining good flexibility, perfectly meeting the long-term use requirements of the display screen. Comparative Example 2, using epoxy acrylate (Sartoma CNUVE151 NS) as the resin component, represents the control group with the smallest performance difference from Example 1. However, the key differences lie in three aspects: firstly, the working time is too short to meet the continuous sizing requirements of industrial production; secondly, poor compatibility with carbon black leads to problems such as agglomeration and uneven coloring of the colloid, affecting the consistency of product appearance; and thirdly, the volume shrinkage rate is too high, which can easily cause edge deformation of the display screen after curing. Example 1 effectively solved the above problems by selecting an aliphatic polyurethane acrylate polymer with better compatibility with carbon black and combining it with nano-sized spherical silica powder, achieving a balance between working time, dispersion stability, and low shrinkage rate. Comparative Example 3 used a bisphenol A epoxy methacrylate oligomer (Sartoma CN159 NS), which has high resin hardness and good weather resistance, but has three defects: first, poor thermal shock resistance, easily cracking during cyclic testing from -25℃ to 70℃; second, significantly high volume shrinkage, far exceeding the dimensional accuracy requirements of the display screen edge sealing; and third, extremely low elongation at break, resulting in high brittleness and inability to withstand minor impacts during daily use. Example 1 used a long-chain aliphatic polyurethane acrylate polymer, which significantly improved elongation at break due to the flexible design of its molecular chains. Combined with the "soft-hard" interpenetrating network structure of silica powder, it significantly improved impact resistance and shrinkage while ensuring weather resistance, perfectly avoiding the performance shortcomings of Comparative Example 3.

[0048] Comparative Example 4 uses mica powder instead of nano-sized spherical silica powder. Its sheet-like structure makes it easy to achieve a certain filling effect; however, it has high water permeability and poor high and low temperature cycling performance. Comparative Example 5 uses calcium carbonate instead of nano-sized spherical silica powder, resulting in low elongation at break, poor resistance to damp heat, high volume shrinkage, and short working time. Comparative Example 6 uses talc powder instead of nano-sized spherical silica powder. In terms of elongation at break, it is close to Example 1, but its resistance to damp heat and water permeability are still not ideal. Comparative Example 7 uses needle-shaped silica powder instead of nano-sized spherical silica powder. Although it is also a silica powder and meets the rigidity standard, its high and low temperature cycling performance and volume shrinkage are still poor. In contrast, the spherical silica powder used in Example 1 can effectively avoid the above problems.

[0049] The results of all comparative tests show that the combination of aliphatic polyurethane acrylate and silicon powder is significantly better than other combinations of polyurethane acrylate and powder. The synergistic effect of the two has enabled the filler to achieve comprehensive optimization in key indicators such as volume shrinkage, impact resistance, and working time, ultimately meeting the requirements of four-sided frameless LCD displays for edge sealing adhesive.

[0050] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make corresponding adjustments and improvements without departing from the principle of the present invention, and these adjustments and improvements should also be considered within the scope of protection of the present invention.

Claims

1. A black UV sealing adhesive for a four-sided frameless liquid crystal display, characterized in that, The black UV edge-sealing adhesive comprises the following raw materials in parts by weight: 20-30 parts polyurethane acrylate, 35-45 parts acrylate diluent, 0.5-2 parts photoinitiator, 0.2-0.4 parts defoamer, 0.5-0.7 parts dispersant, 1-2 parts silane coupling agent, 30-35 parts silica powder, and 0.05-0.15 parts carbon black.

2. The black UV sealing adhesive for a four-sided frameless liquid crystal display as described in claim 1, characterized in that: The polyurethane acrylate is an aliphatic polyurethane acrylate.

3. The black UV sealing adhesive for a four-sided frameless liquid crystal display as described in claim 1, characterized in that: The acrylate diluent is one or more of isobornyl acrylate IBOA, isobornyl methacrylate IBOMA, 1,6-hexanediol diacrylate HDDA, and laurate acrylate LA.

4. The black UV sealing adhesive for a four-sided frameless liquid crystal display as described in claim 1, characterized in that: The photoinitiator is one or more of photoinitiator ITX, photoinitiator TPO, photoinitiator 819, and photoinitiator 369.

5. The black UV sealing adhesive for a four-sided frameless liquid crystal display as described in claim 1, characterized in that: The defoamer is one or more of defoamer Y-137, defoamer YT-3300, defoamer W-155, and defoamer W-109.

6. The black UV sealing adhesive for a four-sided frameless liquid crystal display as described in claim 1, characterized in that: The dispersant is one or more of the following: ACUSOL 479N, 752W, DH-6100, and DH-6163.

7. The black UV sealing adhesive for a four-sided frameless liquid crystal display as described in claim 1, characterized in that: The silicon micropowder is nano-sized spherical silicon micropowder.

8. A method for preparing a black UV sealing adhesive for a four-sided borderless liquid crystal display according to any one of claims 1 to 7, characterized in that, Includes the following steps: Step 1: Mix polyurethane acrylate and part of the acrylate diluent and stir and disperse at 1000-1500 rpm for 10-20 minutes. Then add dispersant, defoamer, silane coupling agent and carbon black, and stir and disperse at 1800-2400 rpm for 30-40 minutes. Step 2: Grind the material obtained in Step 1 using a three-roll mill until the fineness is no more than 5 microns, and cool the material to 20℃-25℃; Step 3: Add the photoinitiator to the remaining acrylate diluent, stir until dissolved in a water bath at 70℃-75℃, then add the material obtained in Step 2, and stir and disperse at 1500-1800 rpm for 15-20 minutes. Step 4: While stirring at 400-600 rpm, slowly add silicon micro powder to the material obtained in Step 3. After all the powder has been added, stir at 1800-2000 rpm for 50-60 minutes to ensure that all the powder is evenly dispersed. Then filter, vacuum degas, and bottle to obtain black UV sealing adhesive for display devices.

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