A UV-curable optical transparent adhesive with low shrinkage and a preparation method thereof

Abstract

The application discloses a UV-cured optical transparent adhesive with low shrinkage and a preparation method thereof. The optical transparent adhesive comprises 20-40 parts of liquid rubber acrylate macromonomer, 20-40 parts of silicone-modified liquid rubber acrylate macromonomer, 20-60 parts of active diluent monomer, 1-10 parts of photoinitiator and 0.1-3 parts of auxiliary agent. The silicone-modified liquid rubber acrylate macromonomer is obtained by reacting maleic anhydride grafted polybutadiene with amino-terminated vinyl silane oligomer and hydroxy acrylate. The mass ratio of the amino-terminated vinyl silane oligomer, the hydroxy acrylate and the maleic anhydride grafted polybutadiene is 5-10:1-3:50-200. The shrinkage of the optical transparent adhesive with the liquid rubber acrylate macromonomer as raw material is effectively reduced by introducing the silicone segment and the inert alkenyl group into the liquid rubber acrylate macromonomer.

Description

Technical Field

[0001] This application relates to the field of optically transparent adhesives, and in particular to a UV-curable low-shrinkage optically transparent adhesive and its preparation method. Background Technology

[0002] Optically clear adhesive (OCA) is a core material for bonding transparent components in electronic devices, widely used in the bonding of touch screen modules, displays, and cover plates in smartphones, tablets, foldable devices, and automotive displays. Its core function is to achieve high-strength bonding while maintaining >99% light transmittance and <0.5% haze, ensuring distortion-free optical imaging, and possessing properties such as resistance to high and low temperatures, resistance to yellowing, and absorption of mechanical shock. With the increasing popularity of flexible electronic devices such as foldable screen phones, OCA also needs to withstand more than 200,000 dynamic bends, placing even higher demands on the material's flexibility and durability.

[0003] Traditional UV-curable optical adhesives primarily rely on acrylate monomers (such as methyl methacrylate and 1,6-hexanediol diacrylate) as reactive diluents. Although they can achieve rapid curing in seconds through free radical polymerization, their molecular structure has significant defects: First, low molecular weight monomers have low viscosity, making them prone to sagging after coating, resulting in uneven adhesive layer thickness; second, the high proportion of rigid segments leads to a small free volume of the crosslinked network after curing, resulting in poor flexibility; third, the atomic rearrangement during curing, where C=C double bonds are converted to C=C single bonds, causes high volume shrinkage (typically 6-10%), leading to interfacial stress concentration and causing screen warping, optical path distortion, or even debonding. For example, in camera module lens bonding, high shrinkage rates can cause focus shift, and mismatched linear expansion coefficients are more likely to induce cracking during thermal cycling.

[0004] To address these shortcomings, the industry has been synthesizing acrylate macromonomers to replace smaller monomers, utilizing their long-chain structure to increase free volume, and using them as the prepolymer backbone in conjunction with reactive diluents to prepare optical adhesives. Currently, the mainstream macromonomers fall into three categories:

[0005] Epoxy acrylate resins: Shrinkage can be reduced by ring-opening polymerization of epoxy groups (up to 3-5%), but residual hydroxyl groups can easily cause yellowing and have poor resistance to damp heat.

[0006] Polyurethane acrylates: These are produced by grafting acrylates onto isocyanates and polyether / polyester polyols after chain extension. Their soft segments provide flexibility, but the urethane bonds are easily degraded by ultraviolet light, and the light transmittance decreases significantly after long-term use.

[0007] Liquid acrylate rubbers are prepared by esterification of maleic anhydride-grafted polybutadiene and other polyolefins with hydroxy acrylates (such as hydroxyethyl acrylate). Their main chain consists of saturated C-C bonds and isolated double bonds, lacking benzene rings, ether bonds, or urethane groups, which contribute to color development and aging. They also possess advantages such as low-temperature resistance and UV resistance to yellowing, making them the preferred macromonomer for high-performance optical adhesives.

[0008] Although the shrinkage rate of liquid rubber acrylate macromonomers is significantly reduced by the long-chain buffering effect compared to traditional monomer systems, its curing shrinkage rate is still generally greater than 2%, which limits its application in precision applications such as foldable screens and microlens arrays. Summary of the Invention

[0009] To further reduce the shrinkage rate of optically transparent adhesives made from liquid rubber acrylate macromonomers, this application provides a UV-curable low-shrinkage optically transparent adhesive and its preparation method, which reduces the shrinkage rate of the adhesive layer by introducing organosilicon segments and inert alkenyl groups into the liquid rubber acrylate macromonomers.

[0010] In a first aspect, this application provides a UV-curable low-shrinkage optically transparent adhesive, comprising the following raw materials in parts by weight: 20-40 parts of liquid rubber acrylate macromonomer, 20-40 parts of silicone-modified liquid rubber acrylate macromonomer, 20-60 parts of reactive diluent monomer, 1-10 parts of photoinitiator, and 0.1-3 parts of additives; wherein the silicone-modified liquid rubber acrylate macromonomer is obtained by reacting maleic anhydride-grafted polybutadiene with amino-terminated vinyl silane oligomer and hydroxy acrylate; wherein the mass ratio of amino-terminated vinyl silane oligomer, hydroxy acrylate, and maleic anhydride-grafted polybutadiene is 5-10:1-3:50-200.

[0011] Preferably, the amino-terminated vinyl silane oligomer is prepared by hydrolysis and condensation with a chain-extending vinyl silane coupling agent to obtain a linear vinyl silane oligomer, which is then capped with an amino silane coupling agent.

[0012] Preferably, the preparation method of the amino-terminated vinylsilane oligomer is as follows:

[0013] Hydrolysis and condensation: The vinyl silane coupling agent is dissolved in an alcohol solution, deionized water is added dropwise to carry out hydrolysis and condensation, and low-boiling substances are removed under vacuum to obtain linear vinyl silane oligomers;

[0014] Amino-terminated: The linear vinyl silane oligomer was dissolved in toluene, heated to 80-90°C under nitrogen protection, and an amino silane coupling agent was added dropwise. Tetraisopropyl titanate was added as a catalyst, and the reaction was followed by vacuum distillation to obtain the amino-terminated vinyl silane oligomer.

[0015] Preferably, the amount of toluene used is 40-60 wt% of the total mass.

[0016] Preferably, the amount of tetraisopropyl titanate used is 0.03 to 0.1 wt% of the total mass.

[0017] Preferably, the reaction time in the amino-terminated step is 2-4 hours.

[0018] Preferably, the vinyl silane coupling agent is methyl vinyl dimethoxysilane and / or methyl vinyl diethoxysilane.

[0019] This application achieves a significant reduction in the shrinkage rate of optically transparent adhesives (controllable to below 2%) by using organosilicon-modified liquid rubber acrylate macromonomers. On one hand, the introduction of these organosilicon segments regulates free volume. Linear oligomers obtained by hydrolysis and condensation polymerization of chain-extending vinyl silane coupling agents such as methyl vinyl dimethoxysilane, after curing, exhibit higher free volume cavities in the crosslinking network compared to carbon-carbon chains, effectively counteracting the atomic rearrangement shrinkage during the conversion of acrylate double bonds to single bonds. On the other hand, the inert alkenyl groups in the organosilicon segments dilute the density of acrylate groups. Due to the β-silicon effect and steric hindrance, the vinyl groups on the oligomer side chains have much lower reactivity than acrylate double bonds. These "pseudo-inert" alkenyl groups occupy system space but do not participate in photocuring, directly reducing the effective double bond density, thus thinning the crosslinking network and decreasing shrinkage stress.

[0020] It is worth noting that compared to directly introducing organosilicon polymers, the chemical grafting strategy in this scheme has unique advantages. The organosilicon segments are bonded to the polybutadiene skeleton through amide / ester bonds, avoiding phase separation and maintaining a transmittance >98%. It also stabilizes the overall refractive index at 1.46–1.50, which can be matched with cover glass (1.48–1.52), eliminating interfacial light scattering. Furthermore, the siloxane does not contain chromophores or easily oxidized groups, and its Si-C bond energy (318 kJ / mol) is higher than that of the C-C bond, resulting in excellent resistance to UV degradation and enhanced resistance to yellowing.

[0021] The amount of acrylate macromonomer used in silicone-modified liquid rubber should not be excessive to avoid loss of solubility with other components such as reactive diluent monomers, ensure homogeneity of each phase, and maintain good optical properties.

[0022] Preferably, the degree of polymerization of the linear vinylsilane oligomer is 5 to 12.

[0023] It should be noted that the degree of polymerization of oligomers can be obtained by measuring the number-average molecular weight (Mn). When the degree of polymerization is <5, the siloxane chain is too short, resulting in insufficient free volume increase; when the degree of polymerization is >12, the molecular rigidity increases and compatibility decreases, which may lead to increased haze. In addition, precise end-capping of aminosilane coupling agents (such as γ-aminopropyltriethoxysilane) ensures that each molecule carries only one primary amine group, avoiding the risk of brittleness caused by excessive crosslinking.

[0024] Preferably, the hydroxyacrylate is selected from any one or more of hydroxyethyl methacrylate, hydroxypropyl methacrylate, and hydroxybutyl methacrylate.

[0025] Preferably, the aminosilane coupling agent is selected from γ-aminopropyltrimethoxysilane or γ-aminopropyltriethoxysilane.

[0026] Preferably, the preparation method of the organosilicon-modified liquid rubber acrylate macromonomer is as follows:

[0027] Amide reaction: Maleic anhydride-grafted polybutadiene is dissolved in an organic solvent, a catalyst and a polymerization inhibitor are added, and then amino-terminated vinyl silane oligomers are added dropwise. The temperature is raised to 65-80℃ for reaction. After the reaction is completed, the low-boiling substances are removed to obtain an organosilicon-modified intermediate.

[0028] Esterification reaction: The organosilicon-modified intermediate is mixed with hydroxy acrylate, heated to 70-80℃, and reacted under nitrogen protection. The product is obtained after precipitation and purification.

[0029] Preferably, the catalyst is 4-dimethylaminopyridine.

[0030] Preferably, the polymerization inhibitor is hydroquinone.

[0031] Preferably, the reaction time for the amidation reaction is 4 to 6 hours.

[0032] Preferably, the esterification reaction takes 3 to 5 hours.

[0033] Preferably, the reactive diluent monomer is selected from any one or more of methyl methacrylate, ethyl methacrylate, hydroxyethyl methacrylate, tetrahydrofuran acrylate, isooctyl methacrylate, lauryl methacrylate, and isobornyl methacrylate.

[0034] This application does not impose any special restrictions on the maleic anhydride-grafted polybutadiene raw materials, and can use maleic anhydride-grafted polybutadiene materials that are well-known and commonly used by those skilled in the art, such as Evonik. MA-75, MA-120 from Clayville Corporation: Ricon 131MA5, Ricon 131MA10, Ricon 131MA20, Ricon 130MA8, Ricon 130MA13.

[0035] This application does not impose any special restrictions on the macromonomers of liquid rubber acrylates, and can use maleic anhydride-grafted polybutadienes that are well-known and commonly used by those skilled in the art, such as UC103 and UC203.

[0036] Preferably, the additive comprises 0.1 to 1 part of a light stabilizer and 1 to 2 parts of a silane coupling agent.

[0037] Preferably, the light stabilizer is a hindered amine light stabilizer.

[0038] Preferably, the silane coupling agent is any one or more of vinyl silane coupling agents, acryloyloxysilane coupling agents, and epoxy silane coupling agents.

[0039] Preferably, the photoinitiator is any one or more of benzophenone, 1-hydroxycyclohexanone, 3,3'-dimethyl-4-methoxybenzophenone, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, 2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone, ethyl 2,4,6-trimethylbenzoylphenylphosphonate, 2-hydroxy-2-methyl-1-phenyl-1-propanone, or 2-benzyl-2-dimethoxyamino-1-(4-morpholinylphenyl)-1-butanone.

[0040] Secondly, this application provides a method for preparing a UV-curable low-shrinkage optically transparent adhesive. The method involves mixing and stirring liquid rubber acrylate macromonomer, organosilicon-modified liquid rubber acrylate macromonomer, reactive diluent monomer, photoinitiator, and additives according to the formulation of any of the optically transparent adhesives described. After vacuum degassing, the adhesive is obtained.

[0041] In summary, this application has the following beneficial effects:

[0042] The liquid rubber acrylate macromonomer and reactive diluent achieve a breakthrough balance between shrinkage, optical properties, and durability. The free volume compensation of the organosilicon segments and the dilution of double bond density by the inert alkenyl groups inhibit curing shrinkage at the molecular level, resulting in a shrinkage rate of <2%, thus preventing screen warping and optical distortion. Furthermore, chemical grafting ensures phase homogeneity, with a light transmittance >98% and a refractive index (1.46–1.50) matching that of the glass substrate. Simultaneously, the siloxane segments resist UV attack, and combined with hindered amine light stabilizers, the yellowing index ΔYI of the adhesive layer is <1.0 after rigorous aging. Detailed Implementation

[0043] Preparation Example

[0044] Preparation Example 1: An organosilicon-modified liquid rubber acrylate macromonomer was prepared by the following method:

[0045] Hydrolysis and condensation: 80g of methylvinyldimethoxysilane was dissolved in 120g of isopropanol solution preheated to 50℃ and stirred at a constant speed of 300rpm for 20min; under stirring conditions, an alcohol-water mixture (15g of deionized water and 50g of ethanol) was added dropwise, and the temperature was raised to 65℃ for 1 hour; the temperature was raised to about 110℃ and polymerization was carried out for 4 hours, and low-boiling substances were removed by vacuum rotary evaporation (-0.095MPa, 75℃) to obtain linear vinylsilane oligomers (degree of polymerization 7-8).

[0046] Amino-terminated: The prepared linear vinyl silane oligomer was dissolved in 90g of toluene, heated to 85℃ under nitrogen, and 15g of γ-aminopropyltriethoxysilane was added dropwise over 30min. 0.04g of tetraisopropyl titanate catalyst was added, and the reaction was carried out at 85℃ for 3h. The solvent was removed by vacuum distillation to obtain the amino-terminated vinyl silane oligomer.

[0047] Amide reaction: Take 125g of maleic anhydride-grafted polybutadiene (Evonik). MA-75 was dissolved in 200 mL of tetrahydrofuran, and 1 g of 4-dimethylaminopyridine and 0.025 g of hydroquinone were added. The mixture was activated at 60 °C for 20 min. 7.5 g of amino-terminated vinylsilane oligomer was added dropwise, and the reaction was carried out at 75 °C for 5 h. THF was removed by rotary evaporation to obtain the organosilicon-modified intermediate.

[0048] Esterification reaction: The organosilicon-modified intermediate was heated to 70℃, 0.38g of p-toluenesulfonic acid was added, and 2g of hydroxyethyl acrylate was added dropwise. The reaction was carried out at 80℃ under nitrogen protection for 4 hours. After the acid value titration was <2mg KOH / g, the product was purified by methanol-water solution (methanol:water mass ratio 8:2) and vacuum dried to obtain the final product.

[0049] Preparation Example 2: An organosilicon-modified liquid rubber acrylate macromonomer was prepared by the following method:

[0050] Hydrolysis and condensation: 70g of methylvinyldimethoxysilane was dissolved in 120g of isopropanol solution preheated to 50℃ and stirred at a constant speed of 300rpm for 20min; under stirring conditions, an alcohol-water mixture (10g of deionized water and 30g of ethanol) was added dropwise, and the temperature was raised to 60℃ for 1 hour; the temperature was raised to about 120℃ and polymerization was carried out for 3 hours, and low-boiling substances were removed by vacuum rotary evaporation (-0.095MPa, 75℃) to obtain linear vinylsilane oligomers (degree of polymerization 5-6).

[0051] Amino-terminated: The prepared linear vinyl silane oligomer was dissolved in 80g of toluene, heated to 80℃ under nitrogen, and 10g of γ-aminopropyltriethoxysilane was added dropwise over 30min. 0.03g of tetraisopropyl titanate catalyst was added, and the reaction was carried out at 90℃ for 2h. The solvent was removed by vacuum distillation to obtain the amino-terminated vinyl silane oligomer.

[0052] Amide reaction: 60 g of maleic anhydride-grafted polybutadiene (Ricon 131MA5) was dissolved in 150 mL of tetrahydrofuran, and 0.5 g of 4-dimethylaminopyridine and 0.015 g of hydroquinone were added. The mixture was activated at 55 °C for 320 min. 5 g of amino-terminated vinylsilane oligomer was added dropwise, and the reaction was carried out at 65 °C for 6 h. THF was removed by rotary evaporation to obtain the organosilicon-modified intermediate.

[0053] Esterification reaction: The organosilicon-modified intermediate was heated to 70℃, 0.2g of p-toluenesulfonic acid was added, and 1.5g of hydroxypropyl methacrylate was added dropwise. The reaction was carried out at 70℃ under nitrogen protection for 3 hours. After the acid value titration was <2mg KOH / g, the product was purified by precipitation with methanol-water solution (methanol:water mass ratio 8:2) and vacuum dried to obtain the final product.

[0054] Preparation Example 3: An organosilicon-modified liquid rubber acrylate macromonomer was prepared by the following method:

[0055] Hydrolysis and condensation: 90g of methylvinyldiethoxysilane was dissolved in 150g of isopropanol solution preheated to 50℃ and stirred at a constant speed of 300rpm for 30min; under stirring conditions, an alcohol-water mixture (30g of deionized water and 70g of ethanol) was added dropwise, and the temperature was raised to 60℃ for 1.5 hours; the temperature was raised to about 105℃ and polymerization was carried out for 5 hours, and low-boiling substances were removed by vacuum rotary evaporation (-0.095MPa, 75℃) to obtain linear vinylsilane oligomers (degree of polymerization 11-12).

[0056] Amino-terminated: The prepared linear vinyl silane oligomer was dissolved in 100g of toluene, heated to 85℃ under nitrogen, and 20g of γ-aminopropyltrimethoxysilane was added dropwise over 30min. 0.08g of tetraisopropyl titanate catalyst was added, and the reaction was carried out at 90℃ for 4h. The solvent was removed by vacuum distillation to obtain the amino-terminated vinyl silane oligomer.

[0057] Amide reaction: 190 g of maleic anhydride-grafted polybutadiene (Ricon 131MA10) was dissolved in 330 mL of tetrahydrofuran, and 1.5 g of 4-dimethylaminopyridine and 0.03 g of hydroquinone were added. The mixture was activated at 60 °C for 20 min. 10 g of amino-terminated vinylsilane oligomer was added dropwise, and the reaction was carried out at 80 °C for 8 h. THF was removed by rotary evaporation to obtain the organosilicon-modified intermediate.

[0058] Esterification reaction: The organosilicon-modified intermediate was heated to 65℃, 0.5g of p-toluenesulfonic acid was added, and 3g of hydroxypropyl methacrylate was added dropwise. The reaction was carried out at 80℃ under nitrogen protection for 5h. After the acid value titration was <2mg KOH / g, the product was purified by precipitation with methanol-water solution (methanol:water mass ratio 8:2) and vacuum dried to obtain the final product.

[0059] Preparation Example 4: An organosilicon-modified liquid rubber acrylate macromonomer differs from Preparation Example 1 in that the hydrolysis-condensation step is different, as follows: 80g of methylvinyldimethoxysilane is dissolved in 120g of isopropanol solution preheated to 50℃, and stirred at a constant speed of 300rpm for 20min; under stirring conditions, an alcohol-water mixture (10g of deionized water and 30g of ethanol) is added dropwise, and the temperature is raised to 60℃ for 1.5 hours; the temperature is raised to about 110℃, and polymerization is carried out for 2.5 hours; low-boiling substances are removed by vacuum rotary evaporation (-0.095MPa, 75℃) to obtain linear vinylsilane oligomers (degree of polymerization 3-4).

[0060] Preparation Example 5: An organosilicon-modified liquid rubber acrylate macromonomer differs from Preparation Example 1 in that the hydrolysis-condensation step is different, as follows: 80g of methylvinyldimethoxysilane is dissolved in 120g of ethanol solution preheated to 50°C, and stirred at a constant speed of 300rpm for 20min; under stirring conditions, an alcohol-water mixture (25g of deionized water and 60g of ethanol) is added dropwise, and the temperature is raised to 70°C for 2 hours; the temperature is raised to about 105°C, and polymerization is carried out for 8 hours; low-boiling substances are removed by vacuum rotary evaporation (-0.095MPa, 75°C) to obtain linear vinylsilane oligomers (degree of polymerization 14-15).

[0061] Preparation Example 6 is a silicone-modified liquid rubber acrylate macromonomer, which differs from Preparation Example 1 in that an equal amount of vinyltrimethoxysilane is used instead of methylvinyldimethoxysilane.

[0062] Preparation Example 7: An organosilicon-modified liquid rubber acrylate macromonomer was prepared by the following method:

[0063] Take 125g of maleic anhydride-grafted polybutadiene (Evonik). Heat MA-75 to 70℃, add 0.38g of p-toluenesulfonic acid, and dropwise add 2g of hydroxyethyl acrylate. React at 80℃ under nitrogen protection for 4 hours. After the acid value titration is <2mg KOH / g, precipitate and purify with methanol-water solution (methanol:water mass ratio 8:2), and then vacuum dry to obtain the final product.

[0064] Example

[0065] Example 1: A UV-curable low-shrinkage optically transparent adhesive was prepared according to the following steps:

[0066] 300g of liquid rubber acrylate macromonomer (Kuraray UC203), 300g of the organosilicon-modified liquid rubber acrylate macromonomer from Preparation Example 1, 250g of isobornyl acrylate, and 150g of hydroxyethyl methacrylate were added to a reaction vessel and stirred at 60°C for 30 min. The mixture was then cooled to 40°C, and 45g of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (TPO) and 5g of hindered amine light stabilizer (…) were added. 770), 15g vinyltrimethoxysilane, stirred for 1 hour in the dark, then transferred to a vacuum degassing machine (-0.098MPa) and degassed at 40℃ for 20 minutes to obtain the product.

[0067] Example 2: A UV-curable low-shrinkage optically transparent adhesive was prepared according to the following steps:

[0068] 200g of liquid rubber acrylate macromonomer (Kuraray UC203), 400g of the organosilicon-modified liquid rubber acrylate macromonomer from Preparation Example 2, 400g of tetrahydrofuran acrylate, and 100g of lauryl methacrylate were added to a reaction vessel and stirred at 60°C for 30 min. The mixture was then cooled to 40°C, and 30g of 2-hydroxy-2-methyl-1-phenyl-1-propanone (1173) and 3g of hindered amine light stabilizer (…) were added. 770), 10g γ-methacryloxypropyltrimethoxysilane, stirred for 1h under light-protected conditions, transferred to a vacuum degassing machine (-0.098MPa), and degassed at 40℃ for 20min to obtain the product.

[0069] Example 3: A UV-curable low-shrinkage optically transparent adhesive was prepared according to the following steps:

[0070] 400g of liquid rubber acrylate macromonomer (Kuraray UC203), 200g of the organosilicon-modified liquid rubber acrylate macromonomer from Preparation Example 1, 150g of pentaerythritol triacrylate, and 250g of isooctyl acrylate were added to a reaction vessel and stirred at 60°C for 30 min. The mixture was then cooled to 40°C, and 65g of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (TPO) and 8g of hindered amine light stabilizer (…) were added. 770), 20g of 3-(2,3-epoxypropoxy)propyltrimethoxysilane, stirred for 1h under light-protected conditions, transferred to a vacuum degassing machine (-0.098MPa), and degassed at 40℃ for 20min to obtain the product.

[0071] Example 4, a UV-curable low-shrinkage optically transparent adhesive, differs from Example 1 in that an equal amount of the silicone-modified liquid rubber acrylate macromonomer of Example 4 is used to replace the silicone-modified liquid rubber acrylate macromonomer of Example 1.

[0072] Example 5, a UV-curable low-shrinkage optically transparent adhesive, differs from Example 1 in that an equal amount of the silicone-modified liquid rubber acrylate macromonomer of Example 5 is used to replace the silicone-modified liquid rubber acrylate macromonomer of Example 1.

[0073] Example 6, a UV-curable low-shrinkage optically transparent adhesive, differs from Example 1 in that an equal amount of the silicone-modified liquid rubber acrylate macromonomer of Example 6 is used to replace the silicone-modified liquid rubber acrylate macromonomer of Example 1.

[0074] Comparative Example

[0075] Comparative Example 1, a UV-curable low-shrinkage optically transparent adhesive, differs from Example 1 in that an equal amount of the silicone-modified liquid rubber acrylate macromonomer of Preparation Example 7 is used to replace the silicone-modified liquid rubber acrylate macromonomer of Preparation Example 1.

[0076] Comparative Example 2, a UV-curable low-shrinkage optically transparent adhesive, differs from Example 1 in that an equal amount of liquid rubber acrylate macromonomer (Kuraray UC203) is used to replace the silicone-modified liquid rubber acrylate macromonomer of Example 1.

[0077] Comparative Example 3 is a UV-curable low-shrinkage optically transparent adhesive, which differs from Example 1 in that an equal amount of the silicone-modified liquid rubber acrylate macromonomer of Example 1 is used to replace the liquid rubber acrylate macromonomer (Kuraray UC203).

[0078] Performance testing

[0079] Experiment 1: Light transmittance test

[0080] Sample preparation: Optical transparent adhesive was coated onto a 100×100×1.1mm optical glass substrate (refractive index 1.52); the adhesive layer thickness was controlled at 200±5μm (calibrated with a micrometer); cured by 365nm UV light (1000mJ / cm2), and allowed to stand for 24h after curing.

[0081] Test method: Refer to ASTM D1003-21, using a spectrophotometer (PerkinElmer Lambda 950), wavelength range 380-780 nm; Calibration baseline: air reference (100% transmittance) and black trap reference (0% transmittance). Samples were placed on the sample holder, and transmittance at 550 nm was measured. The average value of three samples was taken.

[0082] Experiment 2, Refractive Index Test

[0083] Sample preparation: Optical transparent adhesive was coated onto a 100×100×1.1mm optical glass substrate (refractive index 1.52); the adhesive layer thickness was controlled at 200±5μm (calibrated with a micrometer); and cured under 365nm UV light (1000mJ / cm²). 2 After curing, let it stand for 24 hours.

[0084] Test method: Using an Abbe refractometer (Atago NAR-1T SOLID), bromonaphthalene contact liquid was dropped onto the sample surface, the prism was pressed, and the refractive index value at 589 nm was read.

[0085] Experiment 3: Shrinkage Test (Density Method)

[0086] Sample preparation: Inject optically transparent adhesive into a Teflon cylindrical mold (20 mm in diameter and 10 mm in height), and degas under vacuum (-0.098 MPa / 30 min) to eliminate the influence of air bubbles.

[0087] Test procedure: Refer to ISO 3521:1997 for testing;

[0088] Liquid density ρ1 measurement: The density of the uncured adhesive was measured at 25°C using a densitometer (Mettler Toledo DE40) (accurate to 0.001 g / cm³). 3 ).

[0089] Solid density ρ² measurement: after UV curing (1000 mJ / cm²) 2 The cylindrical sample was obtained by demolding; its density was determined by Archimedes' method, specifically by immersing it in deionized water at 25°C and measuring the density by buoyancy conversion.

[0090] Shrinkage rate calculation: Shrinkage rate = (ρ2-ρ1) / ρ1×100%.

[0091] Experiment 4: Yellowing Index Test

[0092] Sample preparation: Optical transparent adhesive was sandwiched between two transparent PET films (125 μm thick) to form a 100 × 100 mm laminate, which was then UV cured (1000 mJ / cm²). 2 The edges are sealed to prevent moisture.

[0093] Aging test: Accelerated aging conditions (according to IEC 60068-2-14): -40℃ (30 min) → 85℃ (30 min), 100 temperature cycles. A colorimeter (Konica Minolta CM-5), D65 light source, and 10° viewing angle were used; the yellowing index ΔYI before and after aging was calculated according to ASTM E313.

[0094] Table 1. Test Results

[0095] sample Light transmittance (%) Refractive index Shrinkage rate (%) Yellowing index ΔYI Example 1 99.2 1.49 1.1 0.5 Example 2 99.0 1.47 1.3 0.7 Example 3 99.1 1.50 0.9 0.6 Example 4 99.1 1.48 1.8 0.9 Example 5 98.2 1.46 1.4 0.6 Example 6 97.3 1.47 1.5 0.8 Comparative Example 1 99.4 1.52 3.1 1.5 Comparative Example 2 99.2 1.51 2.9 1.9 Comparative Example 3 96.9 1.43 1.9 0.7

[0096] Analysis of experimental results:

[0097] Compared to Comparative Examples 1-2, Examples 1-3 showed a significant reduction in shrinkage, indicating that the use of an appropriate amount of silicone-modified liquid rubber acrylate macromonomer can suppress the shrinkage of optically transparent adhesives. This may be because the silicone-modified liquid rubber acrylate macromonomer can achieve free volume compensation; its siloxane segments, after curing, form larger free volume cavities, suppressing the shrinkage caused by acrylate crosslinking. Furthermore, it has a double bond density dilution effect, reducing the effective crosslinking density through inert vinyl groups.

[0098] The shrinkage rate of Examples 4 and 5 is higher than that of Example 1. This may be because the polymerization rate of the silane oligomer in Example 4 is too low, resulting in insufficient free volume compensation; while the polymerization rate in Example 5 is too high, which leads to decreased compatibility, microphase separation, and decreased optical performance.

[0099] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A UV-curable, low-shrinkage, optically transparent adhesive, characterized in that, The raw materials comprise the following parts by weight: 20-40 parts of liquid rubber acrylate macromonomer, 20-40 parts of organosilicon-modified liquid rubber acrylate macromonomer, 20-60 parts of reactive diluent monomer, 1-10 parts of photoinitiator, and 0.1-3 parts of additives. The liquid rubber acrylate macromonomer is obtained by esterification of maleic anhydride-grafted polybutadiene or polyisoprene with hydroxy acrylate. The organosilicon-modified liquid rubber acrylate macromonomer is obtained by reacting maleic anhydride-grafted polybutadiene with amino-terminated vinyl silane oligomers and hydroxy acrylate. The mass ratio of amino-terminated vinyl silane oligomers, hydroxy acrylate, and maleic anhydride-grafted polybutadiene is 5-10:1-3:50-200. The amino-terminated vinyl silane oligomer is obtained by hydrolysis and condensation with a chain-extending vinyl silane coupling agent to obtain a linear vinyl silane oligomer, which is then capped with an amino silane coupling agent. The preparation method of the organosilicon-modified liquid rubber acrylate macromonomer is as follows: Amide reaction: Maleic anhydride-grafted polybutadiene is dissolved in an organic solvent, a catalyst and a polymerization inhibitor are added, and then amino-terminated vinyl silane oligomers are added dropwise. The temperature is raised to 65-80℃ for reaction. After the reaction is completed, the low-boiling substances are removed to obtain an organosilicon-modified intermediate. Esterification reaction: The organosilicon-modified intermediate is mixed with hydroxy acrylate, heated to 70-80℃, and reacted under nitrogen protection. The product is obtained after precipitation and purification.

2. The UV-curable low-shrinkage optically transparent adhesive according to claim 1, characterized in that, The vinyl silane coupling agent is methyl vinyl dimethoxysilane and / or methyl vinyl diethoxysilane.

3. The UV-curable low-shrinkage optically transparent adhesive according to claim 1, characterized in that, The degree of polymerization of the linear vinyl silane oligomer is 5 to 12.

4. The UV-curable low-shrinkage optically transparent adhesive according to claim 1, characterized in that, The hydroxy acrylate is selected from any one or more of hydroxyethyl methacrylate, hydroxypropyl methacrylate, pentaerythritol triacrylate, and glycerol dimethacrylate.

5. The UV-curable low-shrinkage optically transparent adhesive according to claim 1, characterized in that, The reactive diluent monomer is selected from any one or more of methyl methacrylate, ethyl methacrylate, hydroxyethyl methacrylate, tetrahydrofuran acrylate, isooctyl methacrylate, lauryl methacrylate, and isobornyl methacrylate.

6. The UV-curable low-shrinkage optically transparent adhesive according to claim 1, characterized in that, The additives contain 0.1 to 1 part of a light stabilizer and 1 to 2 parts of a silane coupling agent.

7. The UV-curable low-shrinkage optically transparent adhesive according to claim 1, characterized in that, The photoinitiator is any one or more of benzophenone, 1-hydroxycyclohexanone, 3,3'-dimethyl-4-methoxybenzophenone, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, 2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone, ethyl 2,4,6-trimethylbenzoylphenylphosphonate, 2-hydroxy-2-methyl-1-phenyl-1-propanone, or 2-benzyl-2-dimethoxyamino-1-(4-morpholinylphenyl)-1-butanone.

8. A method for preparing a UV-curable low-shrinkage optically transparent adhesive, characterized in that, According to the formulation of the optically transparent adhesive according to any one of claims 1 to 7, the liquid rubber acrylate macromonomer, organosilicon-modified liquid rubber acrylate macromonomer, reactive diluent monomer, photoinitiator, and additives are mixed and stirred evenly, and then vacuum degassed to obtain the final product.