UV-cured low-shrinkage optical transparent adhesive and preparation method thereof

Abstract

The invention discloses a UV-cured low-shrinkage optical transparent adhesive and a preparation method thereof. The optical transparent adhesive comprises 20-40 parts of a liquid rubber acrylate macromonomer, 20-40 parts of an organosilicon modified liquid rubber acrylate macromonomer, 20-60 parts of an active diluent monomer, 1-10 parts of a photoinitiator and 0.1-3 parts of an auxiliary agent, the organic silicon modified liquid rubber acrylate macromonomer is obtained by reacting maleic anhydride grafted polybutadiene with an amino-terminated vinyl silane oligomer and hydroxyl acrylate; the mass ratio of the amino-terminated vinyl silane oligomer to the hydroxyl acrylate to the maleic anhydride grafted polybutadiene is (5-10): (1-3): (50-200). According to the present invention, the organic silicon chain segment and the inert alkenyl group are introduced into the liquid rubber acrylate macromonomer, such that the shrinkage rate of the optical transparent adhesive tape using the liquid rubber acrylate macromonomer as the raw material is effectively reduced;

Description

Technical Field

[0001] The present application relates to the field of optically transparent adhesives, and in particular to a UV-curable low-shrinkage optically transparent adhesive and a preparation method thereof. Background Art

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

[0003] Traditional UV-curing optical adhesives mainly rely on acrylate monomers (such as methyl methacrylate and 1,6-hexanediol diacrylate) as active 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 and are prone to sagging after coating, resulting in uneven thickness of the adhesive layer; second, the proportion of rigid segments is high, and the free volume of the cross-linked network after curing is small, resulting in poor flexibility; third, the atomic rearrangement of the C=C double bond to the CC single bond during the curing process causes high volume shrinkage (usually 6-10%), resulting in interfacial stress concentration, causing screen warping, optical path distortion, and even debonding. For example, in the bonding of camera module lenses, high shrinkage can lead to focus offset, while mismatched linear expansion coefficients are more likely to induce cracking during hot and cold cycles.

[0004] To improve the above defects, the industry has replaced small molecule monomers with synthetic acrylate macromonomers, using their long chain structure to increase free volume, and using them as prepolymer skeletons in combination with reactive diluents to prepare optical adhesives. Currently, the mainstream macromonomers include three categories:

[0005] Epoxy resin acrylates: Reduce shrinkage (to 3-5%) through ring-opening polymerization of epoxy groups, but residual hydroxyl groups are prone to yellowing and have poor resistance to moisture and heat.

[0006] Polyurethane acrylates: Made by chain extension of isocyanate and polyether / polyester polyol followed by grafting of acrylate. The soft segment provides flexibility, but the urethane bond is susceptible to degradation by ultraviolet rays, and the light transmittance decreases significantly after long-term use.

[0007] Liquid rubber acrylates: These are made by esterifying maleic anhydride-grafted polybutadiene and other polyolefins with hydroxy acrylates (e.g., hydroxyethyl acrylate). Their backbone consists of saturated C—C bonds and isolated double bonds, without benzene rings, ether bonds, or urethane groups that are prone to coloration or aging. They offer both low-temperature resistance and UV resistance, making them the preferred macromonomer for high-performance optical adhesives.

[0008] Although liquid rubber acrylate macromonomers significantly reduce shrinkage through long-chain buffering effects compared to traditional monomer systems, their curing shrinkage is still generally greater than 2%, limiting their application in precision scenarios such as folding screens and microlens arrays. Summary of the Invention

[0009] In order to further reduce the shrinkage rate of optically transparent adhesive using liquid rubber acrylate macromonomer as raw material, the present application provides a UV-curable low-shrinkage optically transparent adhesive and a preparation method thereof, which reduces the shrinkage rate of the adhesive layer by introducing silicone segments and inert alkenyl groups into the liquid rubber acrylate macromonomer.

[0010] In the first aspect, the present application provides a UV-curable low-shrinkage optically transparent adhesive, comprising the following raw materials in parts by mass: 20 to 40 parts of liquid rubber acrylate macromonomer, 20 to 40 parts of silicone-modified liquid rubber acrylate macromonomer, 20 to 60 parts of reactive diluent monomer, 1 to 10 parts of photoinitiator, and 0.1 to 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, hydroxy acrylate and maleic anhydride grafted polybutadiene is 5 to 10:1 to 3:50 to 200.

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

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

[0013] Hydrolysis and condensation: dissolve the vinyl silane coupling agent in an alcohol solution, add deionized water dropwise for hydrolysis and condensation, remove low-boiling substances in vacuum to obtain linear vinyl silane oligomers;

[0014] Amino-terminated: Dissolve the linear vinylsilane oligomer in toluene, heat to 80-90°C under nitrogen protection, dropwise add aminosilane coupling agent, add tetraisopropyl titanate as a catalyst, and distill under reduced pressure after the reaction to obtain amino-terminated vinylsilane oligomer.

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

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

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

[0018] Preferably, the vinylsilane coupling agent is methylvinyldimethoxysilane and / or methylvinyldiethoxysilane.

[0019] This application achieves a significant reduction in the shrinkage of optically transparent adhesives (controllable to below 2%) by using silicone-modified liquid rubber acrylate macromonomers. On the one hand, the introduction of the silicone segment has the effect of regulating the free volume. The linear oligomers prepared by hydrolysis and condensation of extended chain vinyl silane coupling agents such as methyl vinyl dimethoxysilane have higher free volume cavities in the cross-linked network after curing than the carbon-carbon chain, which effectively offsets the atomic rearrangement and shrinkage when the acrylate double bond is converted into a single bond. On the other hand, the inert alkenyl groups in the silicone segment have a diluting effect on the density of the acrylate group. The vinyl groups in the oligomer side chains have much lower reaction activity than the acrylate double bond due to the β-silicon effect and steric hindrance. These "pseudo-inert" alkenyl groups occupy the system space but do not participate in photocuring, which directly reduces the effective double bond density, makes the cross-linked network sparse, and reduces the shrinkage stress.

[0020] It is worth noting that compared to the direct introduction of silicone polymers, the chemical grafting strategy of this scheme has unique advantages. The silicone segments are bonded to the polybutadiene backbone via amide / ester bonds, avoiding phase separation and maintaining a transmittance of >98%. The overall refractive index is stabilized at 1.46-1.50, matching the cover glass (1.48-1.52), eliminating interfacial light scattering. In addition, siloxane does not contain chromophores or easily oxidized groups, and its Si-C bond energy (318kJ / mol) is higher than that of the C-C bond, providing excellent resistance to UV degradation and enhanced yellowing resistance.

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

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

[0023] It should be noted that the degree of polymerization (DP) of oligomers can be determined by measuring the number-average molecular weight (Mn). When the DP is less than 5, the siloxane chains are too short, resulting in insufficient free volume increase. When the DP is greater than 12, the molecular rigidity increases and compatibility decreases, potentially leading to increased haze. Furthermore, 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 cross-linking.

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

[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] Amidation reaction: dissolve maleic anhydride grafted polybutadiene in an organic solvent, add a catalyst and a polymerization inhibitor, then dropwise add amino-terminated vinyl silane oligomer, raise the temperature to 65-80°C for reaction, remove low-boiling substances after the reaction is completed, and obtain an organosilicon modified intermediate;

[0028] Esterification reaction: Mix the organosilicon modified intermediate with hydroxy acrylate, raise the temperature to 70-80°C, react under nitrogen protection, and obtain the product by precipitation and purification.

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

[0030] Preferably, the polymerization inhibitor is hydroquinone.

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

[0032] Preferably, the reaction time of the esterification reaction is 3 to 5 hours.

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

[0034] The present application has no special restrictions on the raw materials of maleic anhydride grafted polybutadiene, and it can be any maleic anhydride grafted polybutadiene commonly used by those skilled in the art, such as Evonik MA-75, MA-120 Crayon & Velvet's Ricon 131MA5, Ricon 131MA10, Ricon 131MA20, Ricon 130MA8, Ricon130MA13.

[0035] The present application has no particular limitation on the liquid rubber acrylate macromonomer, which may be a conventional maleic anhydride grafted polybutadiene well known to those skilled in the art, such as UC103 and UC203.

[0036] Preferably, the auxiliary agent comprises 0.1 to 1 parts 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 a vinyl silane coupling agent, an acryloxy silane coupling agent and an epoxy silane coupling agent.

[0039] Preferably, the photoinitiator is any one or more of benzophenone, 1-hydroxycyclohexylbenzophenone, 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-morpholinophenyl)-1-butanone.

[0040] In the second aspect, the present application provides a method for preparing a UV-curable low-shrinkage optically transparent adhesive. According to the ratio of any of the optically transparent adhesives, liquid rubber acrylate macromonomer, silicone-modified liquid rubber acrylate macromonomer, active diluent monomer, photoinitiator, and additives are mixed and stirred evenly, and then vacuumed and degassed to obtain the adhesive.

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

[0042] Liquid rubber acrylate macromonomers and reactive diluents achieve a breakthrough balance between shrinkage, optical properties, and durability. The free volume compensation of the silicone chain segments and the dilution of double bond density by the inert alkenyl groups inhibit cure shrinkage at the molecular level, reducing shrinkage to less than 2%, thus avoiding screen warping and optical distortion. Chemical grafting ensures the uniformity of each phase, with a transmittance of >98% and a refractive index (1.46-1.50) that matches the glass substrate. At the same time, the siloxane segments resist UV attack, and combined with hindered amine light stabilizers, the yellowing index ΔYI of the adhesive layer is less than 1.0 after rigorous aging. DETAILED DESCRIPTION

[0043] Preparation Example

[0044] Preparation Example 1: A silicone-modified liquid rubber acrylate macromonomer was prepared as follows:

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

[0046] Amino-terminated: The obtained linear vinylsilane oligomer was dissolved in 90 g of toluene, heated to 85°C under nitrogen, 15 g of γ-aminopropyltriethoxysilane was added dropwise within 30 min, 0.04 g of tetraisopropyl titanate catalyst was added, the reaction was carried out at 85°C for 3 h, and the solvent was removed by distillation under reduced pressure to obtain amino-terminated vinylsilane oligomer.

[0047] Amidation reaction: Take 125g maleic anhydride grafted polybutadiene (Evonik Dissolve MA-75 in 200 mL of tetrahydrofuran, add 1 g of 4-dimethylaminopyridine and 0.025 g of hydroquinone, and activate at 60°C for 20 min. Add 7.5 g of amino-terminated vinylsilane oligomer dropwise, and react at 75°C for 5 h. Remove the THF by rotary evaporation to obtain the organosilicon-modified intermediate.

[0048] Esterification: Heat the organosilicon-modified intermediate to 70°C, add 0.38g of p-toluenesulfonic acid, and dropwise add 2g of hydroxyethyl acrylate. React at 80°C under nitrogen for 4 hours. After the acid value is titrated to <2mg KOH / g, precipitate and purify with methanol-water solution (methanol:water mass ratio 8:2) and dry under vacuum.

[0049] Preparation Example 2: A silicone-modified liquid rubber acrylate macromonomer was prepared as follows:

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

[0051] Amino-terminated: The obtained linear vinylsilane oligomer was dissolved in 80 g of toluene, heated to 80°C under nitrogen, 10 g of γ-aminopropyltriethoxysilane was added dropwise within 30 min, 0.03 g of tetraisopropyl titanate catalyst was added, the reaction was carried out at 90°C for 2 h, and the solvent was removed by distillation under reduced pressure to obtain amino-terminated vinylsilane oligomer.

[0052] Amidation reaction: Dissolve 60g of maleic anhydride-grafted polybutadiene (Ricon 131MA5) in 150mL of tetrahydrofuran, add 0.5g of 4-dimethylaminopyridine and 0.015g of hydroquinone, and activate at 55°C for 320min. Add 5g of amino-terminated vinylsilane oligomer dropwise and react at 65°C for 6h. Remove the THF by rotary evaporation to obtain the organosilicon-modified intermediate.

[0053] Esterification: Heat the organosilicon-modified intermediate to 70°C, add 0.2g of p-toluenesulfonic acid, and dropwise add 1.5g of hydroxypropyl methacrylate. React at 70°C under nitrogen for 3 hours. After the acid value is titrated to <2mg KOH / g, precipitate and purify with methanol-water solution (methanol:water mass ratio 8:2) and dry under vacuum.

[0054] Preparation Example 3: A silicone-modified liquid rubber acrylate macromonomer was prepared as follows:

[0055] Hydrolysis and condensation: 90 g of methylvinyldiethoxysilane was dissolved in 150 g of isopropanol solution preheated to 50°C and stirred at 300 rpm for 30 min. Under stirring, a mixed alcohol-water solution (30 g of deionized water and 70 g of ethanol) was added dropwise, and the temperature was raised to 60°C for reaction for 1.5 hours. The temperature was raised to approximately 105°C and polymerization was carried out for 5 hours. Low-boiling substances were removed by vacuum rotary evaporation (-0.095 MPa, 75°C) to obtain linear vinylsilane oligomers (DP 11-12).

[0056] Amino-terminated: The obtained linear vinylsilane oligomer was dissolved in 100 g of toluene, heated to 85°C under nitrogen, 20 g of γ-aminopropyltrimethoxysilane was added dropwise within 30 min, 0.08 g of tetraisopropyl titanate catalyst was added, the reaction was carried out at 90°C for 4 h, and the solvent was removed by distillation under reduced pressure to obtain amino-terminated vinylsilane oligomer.

[0057] Amidation reaction: Dissolve 190g of maleic anhydride-grafted polybutadiene (Ricon 131MA10) in 330mL of tetrahydrofuran. Add 1.5g of 4-dimethylaminopyridine and 0.03g of hydroquinone. Activate at 60°C for 20min. Add 10g of amino-terminated vinylsilane oligomer dropwise and react at 80°C for 8h. Remove the THF by rotary evaporation to obtain the organosilicon-modified intermediate.

[0058] Esterification: Heat the organosilicon-modified intermediate to 65°C, add 0.5g of p-toluenesulfonic acid, and dropwise add 3g of hydroxypropyl methacrylate. React at 80°C under nitrogen for 5 hours. After the acid value is titrated to <2mg KOH / g, precipitate and purify with methanol-water solution (methanol:water mass ratio 8:2) and dry under vacuum.

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

[0060] Preparation Example 5, a silicone-modified liquid rubber acrylate macromonomer, differs from Preparation Example 1 in that the hydrolysis and condensation step is operated differently, specifically as follows: 80 g of methylvinyldimethoxysilane is dissolved in 120 g of ethanol solution preheated to 50°C, and stirred at a constant speed of 300 rpm for 20 min; under stirring conditions, an alcohol-water mixed solution (25 g of deionized water and 60 g of ethanol) is added dropwise, and the temperature is raised to 70°C for reaction 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 (-0.095 MPa, 75°C) to obtain a linear vinylsilane oligomer (degree of polymerization 14 to 15).

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

[0062] Preparation Example 7, a silicone-modified liquid rubber acrylate macromonomer was prepared as follows:

[0063] Take 125g maleic anhydride grafted polybutadiene (Evonik MA-75) was heated to 70°C, 0.38g of p-toluenesulfonic acid was added, and 2g of hydroxyethyl acrylate was added dropwise. The reaction was continued at 80°C under nitrogen for 4 hours. After the acid value was titrated to <2mg KOH / g, the product was purified by precipitation with methanol-water solution (methanol:water mass ratio 8:2) and dried under vacuum.

[0064] Example

[0065] Example 1, a UV-curable low shrinkage optically transparent adhesive, is prepared by the following operations:

[0066] Take 300g of liquid rubber acrylate macromonomer (Kuraray UC203), 300g of silicone modified liquid rubber acrylate macromonomer of Preparation Example 1, 250g of isobornyl acrylate, and 150g of hydroxyethyl methacrylate and add them into the reactor, stir and mix at 60℃ for 30min. Cool to 40℃, add 45g of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (TPO), 5g of hindered amine light stabilizer ( 770), 15 g of vinyltrimethoxysilane, stir for 1 h in the dark, transfer to a vacuum degassing machine (-0.098 MPa), and degas at 40 ° C for 20 min to obtain the product.

[0067] Example 2, a UV-curable low-shrinkage optically transparent adhesive, is prepared by the following operations:

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

[0069] Example 3, a UV-curable low shrinkage optically transparent adhesive, is prepared by the following operations:

[0070] Take 400g of liquid rubber acrylate macromonomer (Kuraray UC203), 200g of silicone modified liquid rubber acrylate macromonomer of Preparation Example 1, 150g of pentaerythritol triacrylate, and 250g of isooctyl acrylate and add them into the reactor, stir and mix at 60℃ for 30min. Cool to 40℃, add 65g of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (TPO), 8g of hindered amine light stabilizer ( 770), 20g 3-(2,3-epoxypropoxy)propyltrimethoxysilane, stir for 1h in the dark, transfer to a vacuum degassing machine (-0.098MPa), and degas at 40℃ for 20min to obtain the product.

[0071] Example 4 is a UV-curable low-shrinkage optically transparent adhesive. The difference from Example 1 is that the silicone-modified liquid rubber acrylate macromonomer of Preparation Example 1 is replaced with an equal amount of the silicone-modified liquid rubber acrylate macromonomer of Preparation Example 4.

[0072] Example 5 is a UV-curable low-shrinkage optically transparent adhesive. The difference from Example 1 is that the silicone-modified liquid rubber acrylate macromonomer of Preparation Example 1 is replaced with an equal amount of the silicone-modified liquid rubber acrylate macromonomer of Preparation Example 5.

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

[0074] Comparative Example

[0075] Comparative Example 1 is a UV-curable low-shrinkage optically transparent adhesive. The difference from Example 1 is that the silicone-modified liquid rubber acrylate macromonomer of Preparation Example 1 is replaced by an equal amount of the silicone-modified liquid rubber acrylate macromonomer of Preparation Example 7.

[0076] Comparative Example 2 is a UV-curable low-shrinkage optically transparent adhesive. The difference from Example 1 is that the silicone-modified liquid rubber acrylate macromonomer of Preparation Example 1 is replaced by an equal amount of liquid rubber acrylate macromonomer (Kuraray UC203).

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

[0078] Performance testing

[0079] Test 1: Light transmittance test

[0080] Sample preparation: Apply optically clear adhesive to a 100 × 100 × 1.1 mm optical glass substrate (refractive index 1.52). Maintain adhesive layer thickness at 200 ± 5 μm (calibrated with a micrometer). Curing with 365 nm UV light (1000 mJ / cm²) followed by 24 h of curing.

[0081] Test method: Refer to ASTM D1003-21, using a spectrophotometer (PerkinElmer Lambda 950) with a wavelength range of 380-780 nm. Calibrate the baseline using an air reference (100% transmittance) and a black well reference (0% transmittance). Place the sample in the sample holder and measure transmittance at 550 nm. Take the average of three samples.

[0082] Test 2: Refractive index test

[0083] Sample preparation: Optically transparent adhesive was coated on a 100×100×1.1 mm optical glass substrate (refractive index 1.52); the adhesive layer thickness was controlled to 200±5 μm (calibrated by micrometer); 365 nm UV light was used for curing (1000 mJ / cm 2 ), and let it stand for 24 hours after solidification.

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

[0085] Test 3: Shrinkage test (density method)

[0086] Sample preparation: Optically transparent adhesive was injected into a Teflon cylindrical mold (20 mm in diameter and 10 mm in height) and vacuum degassing was performed (-0.098 MPa / 30 min) to eliminate the influence of bubbles.

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

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

[0089] Solid state density ρ2 measurement: after UV curing (1000mJ / cm 2 ), demoulding to obtain a cylindrical sample; determining its density by Archimedes method, specifically by immersing it in 25°C deionized water and measuring the buoyancy converted to density;

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

[0091] Test 4: Yellowing index test

[0092] Sample preparation: Optically clear adhesive was sandwiched between two transparent PET films (thickness 125 μm) to make a 100 × 100 mm laminate. UV curing (1000 mJ / cm 2 ), the edges are sealed to prevent moisture.

[0093] Aging test: Accelerated aging conditions (according to IEC 60068-2-14): -40°C (30 min) → 85°C (30 min), 100 temperature cycles. A Konica Minolta CM-5 colorimeter was used, using a D65 illuminant and a 10° observation angle. 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 (%) 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 test results:

[0097] Examples 1-3 exhibit significantly lower shrinkage than Comparative Examples 1-2, demonstrating that using an appropriate amount of organosilicon-modified liquid rubber acrylate macromonomer can suppress the shrinkage of optically clear adhesives. This may be due to the fact that, on the one hand, the organosilicon-modified liquid rubber acrylate macromonomer can achieve free volume compensation. Upon curing, its siloxane segments form larger free volume cavities, suppressing the shrinkage caused by acrylate crosslinking. On the other hand, it has a double bond density diluting effect, reducing the effective crosslink density through the inert vinyl groups.

[0098] The shrinkage rates of Examples 4 to 5 increased compared to Example 1. This may be because the polymerization degree of the silane oligomer in Example 4 was too low, resulting in insufficient free volume compensation; while the polymerization degree in Example 5 was too high, resulting in decreased compatibility, microphase separation, and decreased optical properties.

[0099] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A UV curable low shrinkage optically transparent adhesive, characterized in that: The invention comprises the following raw materials in parts by mass: 20 to 40 parts of liquid rubber acrylate macromonomer, 20 to 40 parts of organosilicon-modified liquid rubber acrylate macromonomer, 20 to 60 parts of reactive diluent monomer, 1 to 10 parts of photoinitiator, and 0.1 to 3 parts of auxiliary agent; the organosilicon-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 amino-terminated vinyl silane oligomer, hydroxy acrylate and maleic anhydride grafted polybutadiene is 5 to 10:1 to 3:50 to 200.

2. The UV curable low shrinkage optically transparent adhesive according to claim 1, characterized in that: The amino-terminated vinyl silane oligomer is prepared by hydrolyzing and polycondensing a chain-extending vinyl silane coupling agent to obtain a linear vinyl silane oligomer, which is then terminated with an amino silane coupling agent.

3. The UV curable low shrinkage optically transparent adhesive according to claim 2, characterized in that: The vinylsilane coupling agent is methylvinyldimethoxysilane and / or methylvinyldiethoxysilane.

4. The UV curable low shrinkage optically transparent adhesive according to claim 2, characterized in that: The polymerization degree of the linear vinylsilane oligomer is 5-12.

5. The UV curable low shrinkage optically transparent adhesive according to claim 2, characterized in that: The hydroxy acrylate is selected from any one or more of hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, pentaerythritol triacrylate, and glycerol dimethacrylate.

6. The UV curable low shrinkage optically transparent adhesive according to any one of claims 1 to 5, characterized in that: The preparation method of the organosilicon-modified liquid rubber acrylate macromonomer is as follows: Amidation reaction: dissolve maleic anhydride grafted polybutadiene in an organic solvent, add a catalyst and a polymerization inhibitor, then dropwise add amino-terminated vinyl silane oligomer, raise the temperature to 65-80°C for reaction, remove low-boiling substances after the reaction is completed, and obtain an organosilicon modified intermediate; Esterification reaction: Mix the organosilicon modified intermediate with hydroxy acrylate, raise the temperature to 70-80°C, react under nitrogen protection, and obtain the product by precipitation and purification.

7. The UV curable low shrinkage optically transparent adhesive according to claim 1, characterized in that: The active diluent monomer is selected from any one or more of methyl (meth)acrylate, ethyl (meth)acrylate, hydroxyethyl (meth)acrylate, tetrahydrofuran acrylate, isooctyl (meth)acrylate, lauryl (meth)acrylate, and isobornyl (meth)acrylate.

8. The UV curable low shrinkage optically transparent adhesive according to claim 1, characterized in that: The auxiliary agent comprises 0.1 to 1 parts of a light stabilizer and 1 to 2 parts of a silane coupling agent.

9. 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-hydroxycyclohexylbenzophenone, 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.

10. A method for preparing UV-curable low-shrinkage optically transparent adhesive, characterized in that: According to the ratio of any one of claims 1 to 9, the optically transparent adhesive is prepared by uniformly mixing liquid rubber acrylate macromonomer, organosilicon-modified liquid rubber acrylate macromonomer, reactive diluent monomer, photoinitiator and additives, and then vacuuming and degassing to obtain the adhesive.