Optical transparent adhesive for foldable display device and preparation method thereof

Abstract

The invention relates to a foldable optical adhesive with low Poisson ratio, which is prepared by the following steps: polymerizing a first mixture containing alkyl acrylate monomer, branched structure monomer and initiator to prepare a semi-finished product, adding a cross-linking agent for curing to obtain an adhesive, and coating a release film with the adhesive to obtain the optical adhesive. The optical adhesive has a relatively low Poisson ratio, so that the transverse stress shrinkage is reduced in the folding process, the stress concentration generated in the folding process is effectively dispersed, and the effect of inhibiting the generation of creases is achieved.

Description

Technical Field

[0001] This invention relates to optically transparent adhesives and their preparation methods, and more particularly to an optically transparent adhesive for foldable display devices and its preparation method. Background Technology

[0002] Pressure-sensitive optically transparent adhesives are widely used in the display and optics fields due to their excellent optical and adhesive properties, especially in consumer electronics such as smartphones, smartwatches, smart tablets, laptops, and touch displays. Foldable displays, with their flexibility, portability, and large-screen experience, are gradually entering everyday life and are expected to occupy a significant share of the future consumer electronics market.

[0003] With the increasing popularity of foldable displays, the market will have new demands for optically clear adhesives (OCA). OCA is mainly used for filling and bonding gaps between various components of the display (CG, PET, PC, PMMA, PI, etc.), and in foldable screens, it also plays a role in absorbing stress and protecting the components from damage when folded.

[0004] In foldable display devices, the OCA layer is subjected to extremely complex stresses and strains, such as tension, compression, and shear, during folding. Therefore, due to the special functions of foldable screens, new requirements are placed on the OCA's properties, such as bend resistance, repairability, and crease suppression.

[0005] CN202410421285.X discloses an acrylic pressure-sensitive adhesive for foldable displays and an adhesive sheet thereof. The acrylic pressure-sensitive adhesive comprises an acrylate copolymer A and an acrylate copolymer B with a weight average molecular weight of 20,000 to 35,000. The content of the acrylate copolymer B is 5 to 10 parts by weight relative to 100 parts by weight of the acrylate copolymer A.

[0006] CN202510541626.1 discloses an adhesive composition, characterized in that the adhesive composition comprises a polymeric monomer raw material and a photoinitiator; wherein the light absorption peak wavelength of the photoinitiator is 200nm-460nm; the photoinitiator accounts for 0.23%-0.52% of the polymeric monomer raw material by mass; the polymeric monomer raw material comprises the following components in parts by weight: 50-180 parts by weight of an acrylic matrix resin, 20-50 parts by weight of an acrylic resin containing flexible long chains, and 5-30 parts by weight of an acrylate having hydroxyl groups; the acrylic matrix resin is selected from at least one of 2-ethylhexyl acrylate, n-hexyl acrylate, and butyl acrylate.

[0007] The OCA adhesive used in existing foldable display devices has the following main problems: creases or white edges appear at the folding point of the screen that gradually deepen with use, which seriously affects the visual experience and product acceptance, and is one of the main technical obstacles in the industry; and there are problems such as bending cracks or interface failure when used at -40℃ to -10℃.

[0008] In mechanics of materials, Poisson's ratio (ν) describes the ratio of transverse strain to axial strain perpendicular to the direction of force when strain occurs in a material under stress. The formula is as follows:

[0009] ν=-ε t / ε l

[0010] in:

[0011] ν is Poisson's ratio.

[0012] ε t It is lateral strain.

[0013] ε l It is longitudinal strain.

[0014] The formula for calculating strain is: ε=ΔL / L0

[0015] ΔL is the change in length (elongation or shortening).

[0016] L0 is the original length.

[0017] Traditional foldable optical adhesives are typically based on incompressible elastomers with a Poisson's ratio close to 0.5. When applied to foldable display devices, the outer side of the OCA layer experiences tensile stress during repeated folding. Because materials with high Poisson's ratios undergo elongation in the tensile direction, they also experience significant shrinkage in the thickness direction. This drastic thickness shrinkage leads to stress concentration at the interface between the OCA and the upper and lower substrates (such as flexible cover plates and polarizers), resulting in defects such as microcracks and optical distortion. Ultimately, this can lead to irreversible permanent creases and may cause interface delamination, severely impacting the display's lifespan and visual performance. Summary of the Invention

[0018] This invention aims to solve the aforementioned technical problems by providing a low Poisson's ratio foldable optical adhesive and its preparation method. Through precisely controlled chemical structure, this optical adhesive exhibits a low Poisson's ratio, thereby reducing lateral stress shrinkage during folding, effectively dispersing stress concentration generated during folding, and suppressing crease formation. Furthermore, this adhesive also possesses excellent flexibility, resilience, and optical properties.

[0019] To achieve the above performance, the present invention adopts the following technical solution:

[0020] The present invention first provides an optical adhesive for flexible displays, which is prepared by polymerization of a first mixture comprising alkyl acrylate monomers, branched monomers and an initiator to obtain a semi-finished product, adding a crosslinking agent to cure, obtaining an adhesive, coating it onto a release film to obtain an optical adhesive, wherein the Poisson's ratio is controlled between 0.45 and 0.48, preferably between 0.455 and 0.475.

[0021] Furthermore, the alkyl acrylate monomers include methyl methacrylate (MMA), 2-ethylhexyl methacrylate (EHMA), ethylene glycol methacrylate (EGMA), methyl acrylate (MA), ethyl methacrylate (EMA), ethyl acrylate (EA), n-butyl methacrylate (BMA), n-butyl acrylate (BA), 2-ethylhexyl methacrylate (2-EHMA), 2-ethylhexyl acrylate (2-EHA / EHA), n-octyl acrylate (OA), lauryl acrylate (LA), lauryl methacrylate (LMA), etc., in parts by weight of 30-50, or 35, 40, or 45.

[0022] Furthermore, the branched monomers include trimethylolpropane triacrylate (TMPTA), glycerol propoxytriacrylate (GPTA), trimethylolpropane triacrylate ethoxylate (3EO-TMPTA), glycerol propoxytriacrylate ethoxylate (G3POTA), pentaerythritol penta / hexaacrylate, pentaerythritol tetraacrylate, pentaerythritol triacrylate, etc., in parts by weight of 0.1-3 parts, or 0.5 parts, 1 part, or 2 parts.

[0023] Furthermore, the initiator is a free radical initiator, including benzoyl peroxide (BPO), tert-butyl peroxide-2-ethylhexanoate (TBPEH), tert-butyl peroxide-3,5,5-trimethylhexanoate (TBPIN), 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane (TMPC), azobisisobutyronitrile (AIBN), azobisisoheptanenitrile (ABVN), etc., in parts by weight of 0.01-0.2 parts, or 0.05 parts, 0.1 parts, or 0.15 parts.

[0024] Furthermore, the crosslinking agent is selected from isocyanate curing agents, epoxy curing agents, or aziridine curing agents.

[0025] The self-isocyanate curing agents include hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), etc., in parts by weight of 0.01-2 parts, or 0.05 parts, 0.2 parts, 0.5 parts, 1 part, or 1.5 parts.

[0026] The epoxy curing agent or aziridine curing agent includes diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), isophorone diamine (IPDA), menthol diamine (MDA), diaminodiphenylmethane (DDM), diaminodiphenyl sulfone (DDS), hexahydrophthalic anhydride (HHPA), trimethylolpropane-tris(3-aziridine)propionate (CX-100), etc., in parts by weight of 0.01-2 parts, or 0.05 parts, 0.2 parts, 0.5 parts, 1 part, 1.5 parts.

[0027] Furthermore, the curing is thermosetting and / or photosetting.

[0028] Furthermore, a polar functional monomer is added to the first mixture, including hydroxyethyl acrylate (HEA), hydroxyethyl methacrylate (HEMA), hydroxypropyl acrylate (HPA), hydroxypropyl methacrylate (HPMA), acrylic acid (AA), methacrylic acid (MAA), glycidyl methacrylate (GMA), etc., in parts by weight of 1-15, or 3, 5, 8, or 10.

[0029] Furthermore, a chain transfer agent is added to the first mixture, including n-dodecyl mercaptan, tert-dodecyl mercaptan, isooctyl 3-mercaptopropionate, etc., in a mass fraction of 0.01-2 parts, or 0.02 parts, 0.05 parts, or 1 part.

[0030] Furthermore, UV initiators and silane coupling agents are added during the curing process of the semi-finished product.

[0031] The UV initiators include 1-hydroxycyclohexylbenzophenone (184), 2-hydroxy-2-methyl-1-phenyl-1-propanone (1173), 2,2-dimethoxy-1,2-diphenylethyl ketone (651), 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO), benzophenone (BP), 2-chlorothionanone (CTX), triarylthionium hexafluorophosphate (6992), etc., in parts by weight of 0.01-2 parts, or 0.02 parts, 0.05 parts, 0.4 parts, 1 part, or 1.5 parts.

[0032] The silane coupling agents include 3-aminopropyltriethoxysilane (KH-550), 3-glycidyl etheroxypropyltrimethoxysilane (KH-560), 3-methacryloyloxypropyltrimethoxysilane (KH-570), vinyltrimethoxysilane (KH-151), 3-mercaptopropyltrimethoxysilane (KH-590), etc., in parts by weight of 0.01-2 parts, or 0.02 parts, 0.05 parts, 1 part, or 1.5 parts.

[0033] Furthermore, an active diluent is introduced into the reaction system, including ethyl acetate (EA), n-butyl acetate (BAC), isobutyl acetate (IBAC), acetone (AC), butanone (MEK), methyl isobutyl ketone (MIBK), cyclohexanone (CYC), toluene (TOL), xylene (XYL), etc., in parts by mass of 30-50, or 35, 40, or 45.

[0034] The present invention also relates to a method for preparing optical adhesives for flexible displays, comprising:

[0035] Step (1): A semi-finished product is prepared by polymerization of a mixture containing alkyl (meth)acrylate monomers, polar functional monomers, branched monomers and at least one free radical initiator.

[0036] Step (2): Add the semi-finished product from step (1) to a curing agent for curing to obtain an adhesive;

[0037] Step (3): Apply the adhesive from step (2) to the release film to obtain optical adhesive.

[0038] Furthermore, a chain transfer agent is added in step (1).

[0039] Furthermore, a UV initiator and a silane coupling agent are added in step (2).

[0040] Furthermore, an active diluent is added in both steps (1) and (2).

[0041] Further, in step (1), the mixture is reacted at 50-80°C for 10-20 hours.

[0042] Further, in step (2), after adding each component, mix them evenly and degas at 0.06MPa to 0.09MPa for 30 min to 120 min.

[0043] Further, in step (2), the reactive diluent is added in batches.

[0044] Further, in step (3), the adhesive is applied to the release film and then thermally or UV crosslinked to form a solid adhesive film.

[0045] Further, in step (3), the adhesive is applied to the heavy release film, and after cross-linking and curing, the light release film is bonded together to form a sandwich structure of release film / OCA adhesive film / release film.

[0046] This invention also provides the application of OCA optical adhesive in foldable electronic devices.

[0047] Through in-depth research, the inventors have realized that if the Poisson's ratio of OCA is precisely controlled within the range of 0.45 to 0.48, OCA is less prone to creases after folding. The mechanism is as follows:

[0048] 1. A Poisson's ratio of less than 0.5 means that the material has a slight increase in volume when deformed. This micro-expansion effect can generate a small positive pressure at the interface during the folding process, which helps to counteract the peeling stress caused by deformation, thereby improving the interfacial adhesion between OCA and the upper and lower substrates and avoiding the "peeling" phenomenon in high and low temperature cycling tests.

[0049] 2. When an OCA is folded, the inner side of the neutral layer experiences compression, while the outer side experiences tension. For materials with a Poisson's ratio close to 0.5, significant shrinkage (large lateral strain) occurs in the thickness direction when stretched. This shrinkage exacerbates stress concentration at the interface, especially at the junction of a rigid cover plate (such as UTG) and a flexible OCA, easily leading to microcrack initiation and optical distortion, ultimately forming visible creases. Reducing the Poisson's ratio to 0.45–0.48 means that the material experiences less shrinkage during stretching, more effectively distributing in-plane stress across a larger volume rather than concentrating it at the interface, thus greatly suppressing crease formation.

[0050] 3. The low modulus of this invention ensures sufficient material flexibility, and the high recovery rate ensures that deformation can be recovered. An appropriate Poisson's ratio is the key indicator for achieving this flexibility and recovery. Only when all three data indicators are met simultaneously can OCA withstand 200,000 folds without failure and without noticeable creases.

[0051] This invention achieves precise control of the Poisson's ratio in the OCA through the synergistic combination of one or more of the following methods:

[0052] 1. A branched structure is constructed in the main chain of a polymer formed by photocuring or thermocuring components containing branched structures. The branching points within the polymer disrupt the regularity and compactness of the molecular chains, creating numerous small gaps between them. These gaps allow the molecular chains more space to adapt to deformation through segment rotation and rearrangement when stretched, rather than immediately responding with drastic lateral contraction (i.e., high Poisson's ratio behavior). Therefore, controlling the degree of branching is an important means of regulating the Poisson's ratio: within a reasonable range, the higher the degree of branching, the lower the Poisson's ratio tends to be.

[0053] 2. By controlling the density of UV crosslinking and thermal crosslinking networks, excessively high crosslinking density can restrict the movement of molecular chain segments, causing the material to harden (increase loss modulus). At the same time, excessively high crosslinking density can also limit the lateral deformation capacity of OCA, potentially leading to an increase in Poisson's ratio. However, by controlling the types and amounts of the two crosslinking agents, a moderately soft and hard interpenetrating network can be formed, providing sufficient recovery force while maintaining a certain degree of chain segment mobility, thereby keeping the Poisson's ratio within the target range.

[0054] This invention achieves precise control of Poisson's ratio through the synergistic effect of the branched structure and the double crosslinking network: 1. Branched structure: Branching points are introduced into the polymer backbone, disrupting the regularity and compactness of the molecular chains and increasing the small gaps between the molecular chains. This allows the molecular chain segments more space to adapt to deformation through rotation and rearrangement when the material is subjected to longitudinal stretching, thereby reducing the lateral shrinkage that occurs to maintain a constant volume and effectively lowering the Poisson's ratio. 2. Double crosslinking network: The thermosetting component includes end-capped isocyanates. During the thermosetting stage, after the end-capped isocyanates are uncapped, their isocyanate groups react with the active groups (such as hydroxyl groups) on the branched structure to form a double crosslinking network. The first network formed by photocuring and the second network formed by thermocuring together constitute a complex, entangled network structure. By controlling the type and addition ratio of the two crosslinking agents (such as 0.01 to 0.05 parts of CX100 and 0.05 to 0.1 parts of N3390), the stability of the low Poisson's ratio caused by the branched structure can be maintained while ensuring that the material is sufficiently flexible (low loss modulus) and has high resilience, thus preventing creep failure and plastic deformation under long-term or large stress.

[0055] The OCA optical adhesive described above has the following characteristics: 1. The Poisson's ratio, tested by the DIC system in a standard laboratory environment, is between 0.45 and 0.48; 2. The shear loss modulus at -30℃ does not exceed 300 kPa, and the shear loss modulus at 25℃ does not exceed 40 kPa; 3. Shear creep is tested at -20℃, 25℃, and 60℃ respectively. After 600 seconds of stress at 20 kPa, the creep is in the range of 200% to 600%, and the recovery rate after 600 seconds of recovery at 0 kPa is ≥90%; 4. After 200,000 cycles of dynamic folding equipment testing (bending radius less than 2 mm, folding angle from 180° to 0°), there is no delamination or obvious creases.

[0056] The OCA adhesive prepared by this invention exhibits excellent flexibility, folding resistance and shape recovery ability, and is particularly suitable for foldable electronic devices.

[0057] The optically transparent adhesive of this invention has the following excellent properties:

[0058] 1. Improved interface reliability: Reduced periodic stress changes in the thickness direction caused by the Poisson effect, enhanced the stability of the interface adhesion between OCA and the upper and lower substrates, passed rigorous thermal shock and high temperature and humidity tests, and showed no delamination, bubbles or other defects.

[0059] 2. By controlling the Poisson's ratio of the adhesive, the adhesive's resistance to flexural debonding is improved; compared with traditional adhesives, it has a lower Poisson's ratio, thus greatly suppressing the formation of creases; 2. By precisely controlling the Poisson's ratio within the specific range of 0.45 to 0.48, the OCA described in this invention exhibits less thickness shrinkage during folding and stretching, effectively dispersing stress from the interface to the interior of the colloid, greatly alleviating stress concentration, and thus fundamentally suppressing the formation of microcracks and visible creases.

[0060] 3. Within the operating temperature range, it exhibits a low loss modulus and a high creep recovery rate, ensuring that the adhesive has sufficient flexibility and deformation recovery properties;

[0061] 4. The adhesive showed no delamination or obvious creases after 200,000 cycles in a dynamic folding test. This adhesive is mainly used for bonding CPIs (Content Injection Points), CPIs and POLs (Polymer Injection Points), and POLs and UTGs in foldable OLED display modules.

[0062] 5. Excellent optical performance: The chemical structure design and curing process ensure that the cured adhesive layer has high light transmittance (>90%) and low haze (<1 part), meeting the optical requirements of high-end displays. Attached Figure Description

[0063] Figure 1 This is a schematic diagram of the structure of the blind hole fully bonded OCA tape.

[0064] Figure 2 This is a product photo of Example 1. Detailed Implementation

[0065] To better understand the structure, functional features, and advantages of the present invention, preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings:

[0066] Test Method 1: Dynamic Mechanical Analysis

[0067] The adhesive properties were tested using a rheometer (model HR-10) from TA Instruments, Inc., USA. The specific procedures are as follows:

[0068] The adhesive was stacked into a colloidal sample with a diameter of 1000μm±50μm, frozen in a -20℃ freezer for 30 minutes, and then a circular sample of about 8mm was taken out using an 8.5mm punch.

[0069] Peel off one layer of the release film from the sample and place it in the center of the DHR plate. Peel off the release film on the other side and press down with an 8mm rotor until it just contacts the colloid (the axial force reading is obvious).

[0070] A temperature scan was performed at a rate of 5℃ / min, increasing the temperature from -50℃ to 100℃. During this process, the strain was controlled to be 1 unit, the frequency to be 1Hz, and the axial force to be controlled to be 1.0N±0.1N.

[0071] Read the necessary information from the data recorded by the instrument: Tg and loss modulus.

[0072] Test Method 2: Creep-Recovery Test

[0073] The adhesive properties were tested using a rheometer (model HR-10) from TA Instruments, Inc., USA. The specific procedures are as follows:

[0074] The adhesive was stacked into a colloidal sample with a diameter of 1000μm±50μm, frozen in a -20℃ freezer for 30 minutes, and then a circular sample of about 8mm was taken out using an 8.5mm punch.

[0075] Peel off one layer of the release film from the sample and place it in the center of the DHR plate. Peel off the release film on the other side and press down with an 8mm rotor until it just contacts the colloid (the axial force reading is obvious).

[0076] The temperature was kept constant, and the samples were subjected to creep for 600s under a stress of 20kPa at -20℃, 25℃, and 60℃ respectively. Then, the samples were subjected to a stress of 0Pa and allowed to slowly recover under their own internal stress for 600s. During this period, the axial force was controlled at 0.8N±0.1N.

[0077] Read the necessary information from the data recorded by the instrument: strain percentage and recovery percentage.

[0078] Test Method 3: Peel Force Test

[0079] In a standard laboratory environment, a 50 μm thick sample is cut into 12 cm × 2.5 cm pieces, a release film is peeled off, one end of the sample is aligned with the edge of the glass, and a pressure roller is used to attach the sample to the clean glass surface.

[0080] Take a 50μm PET sheet and cut it into 18cm×3cm size. Remove the release film of the sample obtained in step (1). Align the PET with the sample and use a pressure roller to stick the PET to the sample surface. Immediately use a 2kg pressure roller to press back and forth on the sample surface twice and start timing.

[0081] Thirty minutes later, the sample was tested using an INSTRON instrumentation universal testing machine. The end of the sample with the glass not attached was clamped in the lower clamp, and the longer end of the PET was clamped in the upper clamp. The sample was folded 180° in the opposite direction and in the same direction as the tensile testing machine.

[0082] At a speed of 300 mm / min on the upper clamp, the test was conducted for 30 seconds to obtain the 180° peel force between the adhesive layer and the glass surface, and the average value was calculated from the uniform data generated in the last 20 seconds.

[0083] Test Method 4: Molecular Weight and Molecular Weight Distribution

[0084] The molecular weight and molecular weight distribution of the adhesive were tested using a GPC instrument from Waters Instruments, Inc., USA. A small amount of sample (about 0.5 g) from step (1) was soaked in sufficient tetrahydrofuran for 24 hours. A small amount of clear liquid was injected into a GPC-specific feed bottle using a sampler. The sample was taken and tested according to the pre-set program. After the test, the molecular weight and dispersion coefficient were read.

[0085] Test Method 5: Dynamic Folding Test

[0086] In a standard laboratory environment, ultra-thin flexible glass (UTG), bendable polyethylene terephthalate film (PET), bendable polarizing film, and OCA samples were bonded together from top to bottom using a pressure roller bonding and degassing process, forming the following structure: bendable PET / OCA / bendable PET / OCA / UTG / OCA / bendable polarizing film. The bonded samples were cut into 15cm × 7cm pieces and evenly bonded to the folding side of a folding test platform using rubber rollers. The platform was folded from 180° to 0°, i.e., from a flat position to a folded position. The folding test platform was cycled approximately 10 times / min for 200,000 cycles. The 2mm bending radius was determined by the gap after folding (0°). After the test, the samples were removed and examined visually and under a 2.5D microscope to determine: 1. whether there were obvious creases; 2. whether there were obvious white edges at the bend; 3. whether there were other abnormalities at the bend. If all results after evaluation are negative, the folding test is considered passed.

[0087] Test Method 6: Thickness and Optical Properties

[0088] Haze was measured using a NDH8000 haze meter from Japan Denshoku. The ISO standard was selected and the instrument calibrated. OCA was cut into approximately 5cm x 5cm pieces, and its thickness was measured using a thickness gauge. The sample, after the release film was removed, was adhered to a 1mm thick transparent glass plate. Then, the heavy release film was removed, and the prepared sample was placed in the test window to test transmittance and haze.

[0089] Prepare another sample in the same way, and then test the b* color value of the sample after calibration by the transmission method using a Konica Minolta (China) CM-3600A spectrophotometer.

[0090] Test Method 7: Poisson's Ratio Test

[0091] OCA samples were stacked to a thickness of 1 mm, and 1 cm × 12 cm samples were cut for testing. Poisson's ratio was measured using a universal testing machine manufactured by INSTRON Corporation, based on the principles described in ASTM E132, at room temperature (23 ± 2 °C). Considering the flexible polymer nature of the tested material, the test parameters were adjusted as follows: a digital image correlation (DIC) non-contact strain gauge was used instead of a contact extensometer. The cut sample was fixed to the testing platform of the machine using clamps with a clamp gap of 8 cm and a tensile rate of 1 mm / min. Data from the initial linear segment of the stress-strain curve (strain range 0.5 to 1.5 parts) were collected, and the Poisson's ratio was calculated from the slope of the transverse strain-longitudinal strain curve.

[0092] Example 1

[0093] An optical film adhesive for foldable screens or other flexible display devices is prepared by the following steps.

[0094] Step (1): Mix the following components in parts by weight: 45 parts 2-ethylhexyl acrylate (2-EHA), 5 parts hydroxyethyl acrylate (HEA), 4 parts acrylic acid (AA), 1 part pentaerythritol triacrylate, 0.01 parts n-dodecyl mercaptan, 0.07 parts azobisisoheptanenitrile (ABVN), and 45 parts ethyl acetate. Place the mixture in a polymerization apparatus, purge with nitrogen for 1 hour, then heat the mixture to 60°C and react for 14 hours. Use GPC to test the sample, and determine that the sample has a Mw of 1200 kDa and a polydispersity index of 3.64.

[0095] Step (2): Mix the sample obtained in step (1) according to the following parts by weight: 60 parts of sample, 0.05 parts of epoxy crosslinking agent (epoxy curing agent 810), 0.05 parts of silane coupling agent (KH560), and 40 parts of reactive diluent (ethyl acetate). After thoroughly mixing, degas at 0.06MPa to 0.09MPa for 30 min to 120 min to obtain the adhesive.

[0096] The specific mixing method for step (2) is as follows: Add the sample to the mixing vessel by weight and add a small amount of reactive diluent, stirring until homogeneous. Mix, dilute, or dissolve the other raw materials with the reactive diluent by weight, stirring until homogeneous, and reserve a portion of the reactive diluent for later use. Add the diluted materials to the mixing vessel sequentially, stirring until homogeneous. Finally, rinse the inner wall of the mixing vessel and the stirring paddle with the reserved reactive diluent. After thorough stirring, degas under vacuum for 1 hour to obtain the adhesive.

[0097] Step (3): Apply the adhesive evenly to the heavy release film, bake at a stepped temperature (not exceeding 110℃) for 10 minutes, then attach the light release film to form a three-layer structure of tape A consisting of light release film, OCA layer, and heavy release film. After curing at room temperature, it is ready for use. Tape A is an optical film adhesive that can be used in foldable screens or other flexible display devices.

[0098] Example 2

[0099] An optical film adhesive for foldable screens or other flexible display devices is prepared by the following steps.

[0100] Step (1): Mix the following components in parts by weight: 40 parts 2-ethylhexyl acrylate (2-EHA), 10 parts hydroxyethyl acrylate (HEA), 4 parts acrylic acid (AA), 1 part pentaerythritol triacrylate, 0.01 parts n-dodecyl mercaptan, 0.07 parts azobisisoheptanenitrile (ABVN), and 45 parts ethyl acetate. Place the mixture in a polymerization apparatus, purge with nitrogen for 1 hour, then heat the mixture to 60°C and react for 14 hours. Use GPC to test the sample, and determine that the sample has a Mw of 1200 kDa and a polydispersity index of 3.64.

[0101] Step (2): Mix the sample obtained in step (1) according to the following parts by weight: 60 parts of sample, 0.05 parts of aziridine crosslinking agent, 0.05 parts of silane coupling agent, and 40 parts of reactive diluent. After thorough mixing, degas at 0.06MPa to 0.09MPa for 30 min to 120 min to obtain the adhesive. The specific mixing method for step (2) is as described in Example 1.

[0102] Step (3): Apply the adhesive evenly to the heavy release film, bake at a stepped temperature (not exceeding 110℃) for 10 minutes, then attach the light release film to form a three-layer structure of tape B consisting of light release film, OCA layer, and heavy release film. After curing at room temperature, it is ready for use. Tape B is an optical film adhesive that can be used in foldable screens or other flexible display devices.

[0103] Example 3

[0104] An optical film adhesive for foldable screens or other flexible display devices is prepared by the following steps.

[0105] Step (1): Mix the following components in parts by weight: 40 parts 2-ethylhexyl acrylate (2-EHA), 10 parts hydroxyethyl acrylate (HEA), 4 parts acrylic acid (AA), 1 part pentaerythritol triacrylate, 0.01 parts n-dodecyl mercaptan, 0.07 parts azobisisoheptanenitrile (ABVN), and 45 parts ethyl acetate. Place the mixture in a polymerization apparatus, purge with nitrogen for 1 hour, then heat the mixture to 60°C and react for 14 hours. Use GPC to test the sample, and determine that the sample has a Mw of 1200 kDa and a polydispersity index of 3.64.

[0106] Step (2): Mix the sample obtained in step (1) according to the following parts by weight: 60 parts of sample, 0.01 parts of epoxy crosslinking agent, 0.03 parts of aziridine crosslinking agent, 0.05 parts of silane coupling agent, and 40 parts of reactive diluent. After thorough mixing, degas at 0.06MPa to 0.09MPa for 30 min to 120 min to obtain the adhesive. The specific mixing method for step (2) is as described in Example 1.

[0107] Step (3): Apply the adhesive evenly to the heavy release film, bake at a stepped temperature (not exceeding 110℃) for 10 minutes, then attach the light release film to form a three-layer structure of tape C consisting of light release film-OCA layer-heavy release film. After curing at room temperature, it is ready for use. Tape C is an optical film adhesive that can be used in foldable screens or other flexible display devices.

[0108] Example 4

[0109] An optical film adhesive for foldable screens or other flexible display devices is prepared by the following steps.

[0110] Step (1): Mix the following components in parts by weight: 40 parts 2-ethylhexyl acrylate (2-EHA), 10 parts hydroxyethyl acrylate (HEA), 4 parts acrylic acid (AA), 1 part pentaerythritol triacrylate, 0.01 parts n-dodecyl mercaptan, 0.07 parts azobisisoheptanenitrile (ABVN), and 45 parts ethyl acetate. Place the mixture in a polymerization apparatus, purge with nitrogen for 1 hour, then heat the mixture to 60°C and react for 14 hours. Use GPC to test the sample, and determine that the sample has a Mw of 1200 kDa and a polydispersity index of 3.64.

[0111] Step (2): Mix the sample obtained in step (1) according to the following parts by weight: 60 parts of sample, 0.05 parts of isocyanate crosslinking agent, 0.02 parts of aziridine crosslinking agent, 0.05 parts of silane coupling agent, and 40 parts of reactive diluent. After thorough mixing, degas at 0.06MPa to 0.09MPa for 30 min to 120 min to obtain the adhesive. The specific mixing method for step (2) is as described in Example 1.

[0112] Step (3): Apply the adhesive evenly to the heavy release film, bake at a stepped temperature (not exceeding 110℃) for 10 minutes, then attach the light release film to form a three-layer structure of tape D consisting of light release film, OCA layer, and heavy release film. After curing at room temperature, it is ready for use. Tape D is an optical film adhesive that can be used in foldable screens or other flexible display devices.

[0113] Example 5

[0114] An optical film adhesive for foldable screens or other flexible display devices is prepared by the following steps.

[0115] Step (1): Mix the following components in parts by weight: 40 parts 2-ethylhexyl acrylate (2-EHA), 10 parts hydroxyethyl acrylate (HEA), 3 parts acrylic acid (AA), 2 parts pentaerythritol triacrylate, 0.01 parts n-dodecyl mercaptan, 0.07 parts azobisisoheptanenitrile (ABVN), and 45 parts ethyl acetate. Place the mixture in a polymerization apparatus, purge with nitrogen for 1 hour, then heat the mixture to 60°C and react for 14 hours. Use GPC to test the sample, and determine that the sample has a Mw of 1200 kDa and a polydispersity index of 3.64.

[0116] Step (2): Mix the sample obtained in step (1) according to the following parts by weight: 60 parts of sample, 0.05 parts of isocyanate crosslinking agent, 0.02 parts of aziridine crosslinking agent, 0.05 parts of silane coupling agent, and 40 parts of reactive diluent. After thorough mixing, degas at 0.06MPa to 0.09MPa for 30 min to 120 min to obtain the adhesive. The specific mixing method for step (2) is as described in Example 1.

[0117] Step (3): Apply the adhesive evenly to the heavy release film, bake at a stepped temperature (not exceeding 110℃) for 10 minutes, then attach the light release film to form a three-layer structure of tape E consisting of light release film, OCA layer, and heavy release film. After curing at room temperature, it is ready for use. Tape E is an optical film adhesive that can be used in foldable screens or other flexible display devices.

[0118] Example 6

[0119] An optical film adhesive for foldable screens or other flexible display devices is prepared by the following steps.

[0120] Step (1): Mix the following components in parts by weight: 40 parts 2-ethylhexyl acrylate (2-EHA), 10 parts hydroxyethyl acrylate (HEA), 4 parts acrylic acid (AA), 1 part pentaerythritol triacrylate, 0.01 parts n-dodecyl mercaptan, 0.07 parts azobisisoheptanenitrile (ABVN), and 45 parts ethyl acetate. Place the mixture in a polymerization apparatus, purge with nitrogen for 1 hour, then heat the mixture to 60°C and react for 14 hours. Use GPC to test the sample, and determine that the sample has a Mw of 1200 kDa and a polydispersity index of 3.64.

[0121] Step (2): Mix the sample obtained in step (1) according to the following parts by weight: 60 parts of sample, 0.02 parts of UV initiator, 0.05 parts of isocyanate crosslinking agent, 0.05 parts of silane coupling agent, and 40 parts of reactive diluent. After thorough mixing, degas at 0.06MPa to 0.09MPa for 30 min to 120 min to obtain the adhesive. The specific mixing method for step (2) is as described in Example 1.

[0122] Step (3): Apply the adhesive evenly to the heavy release film, bake at a stepped temperature (not exceeding 110℃) for 10 minutes, then attach the light release film to form a three-layer structure of tape F consisting of light release film, OCA layer, and heavy release film. After curing with an LED lamp (365nm) and at room temperature, it is ready for use. Tape F is an optical film adhesive that can be used in foldable screens or other flexible display devices.

[0123] Comparative Example 1:

[0124] An optical film adhesive for foldable screens or other flexible display devices is prepared by the following steps.

[0125] Step (1): Mix the following components in parts by weight: 49 parts 2-ethylhexyl acrylate (2-EHA), 1 part hydroxyethyl acrylate (HEA), 4 parts acrylic acid (AA), 1 part pentaerythritol triacrylate, 0.01 parts n-dodecyl mercaptan, 0.07 parts azobisisoheptanenitrile (ABVN), and 45 parts ethyl acetate. Place the mixture in a polymerization apparatus, purge with nitrogen for 1 hour, then heat the mixture to 60°C and react for 14 hours. Use GPC to test the sample, and determine that the sample has a Mw of 1200 kDa and a polydispersity index of 3.64.

[0126] Step (2): Mix the sample obtained in step (1) according to the following parts by weight: 60 parts of sample, 0.05 parts of isocyanate crosslinking agent, 0.02 parts of aziridine crosslinking agent, 0.05 parts of silane coupling agent, and 40 parts of reactive diluent. After thorough mixing, degas at 0.06MPa to 0.09MPa for 30 min to 120 min to obtain the adhesive. The specific mixing method for step (2) is as described in Example 1.

[0127] Step (3): Apply the adhesive evenly to the heavy release film, bake at a stepped temperature (not exceeding 110℃) for 10 minutes, then attach the light release film to form a three-layer structure of tape A consisting of light release film, OCA layer, and heavy release film. After curing at room temperature, it is ready for use. Tape A is an optical film adhesive that can be used in foldable screens or other flexible display devices.

[0128] By adjusting the ratio of 2-ethylhexyl acrylate to hydroxyethyl acrylate in the formulation, the Tg and loss modulus of the resin were reduced, resulting in a resin with low loss modulus. Compared with Example 4, it was found that the adhesive layer was too soft and could not be effectively restored. The Poisson ratio was high, and obvious creases were produced after the folding test, which could not produce a significant effect on crease suppression.

[0129] Comparative Example 2

[0130] An optical film adhesive for foldable screens or other flexible display devices is prepared by the following steps.

[0131] Step (1): Mix the following components in parts by weight: 35 parts 2-ethylhexyl acrylate (2-EHA), 15 parts hydroxyethyl acrylate (HEA), 4 parts acrylic acid (AA), 1 part pentaerythritol triacrylate, 0.01 parts n-dodecyl mercaptan, 0.07 parts azobisisoheptanenitrile (ABVN), and 45 parts ethyl acetate. Place the mixture in a polymerization apparatus, purge with nitrogen for 1 hour, then heat the mixture to 60°C and react for 14 hours. Use GPC to test the sample, and determine that the sample has a Mw of 1200 kDa and a polydispersity index of 3.64.

[0132] Step (2): Mix the sample obtained in step (1) according to the following parts by weight: 60 parts of sample, 0.05 parts of isocyanate crosslinking agent, 0.02 parts of aziridine crosslinking agent, 0.05 parts of silane coupling agent, and 40 parts of reactive diluent. After thorough mixing, degas at 0.06MPa to 0.09MPa for 30 min to 120 min to obtain the adhesive. The specific mixing method for step (2) is as described in Example 1.

[0133] Step (3): Apply the adhesive evenly to the heavy release film, bake at a stepped temperature (not exceeding 110℃) for 10 minutes, then attach the light release film to form a three-layer structure of tape A consisting of light release film, OCA layer, and heavy release film. After curing at room temperature, it is ready for use. Tape A is an optical film adhesive that can be used in foldable screens or other flexible display devices.

[0134] By adjusting the ratio of 2-ethylhexyl acrylate to hydroxyethyl acrylate in the formulation, the Tg and loss modulus of the resin were increased, resulting in a resin with high loss modulus. Compared with Example 4, it was found that the adhesive layer was too hard. Although the Poisson ratio was low, obvious white edges and adhesive layer peeling occurred after the folding test.

[0135] Comparative Example 3

[0136] An optical film adhesive for foldable screens or other flexible display devices is prepared by the following steps.

[0137] Step (1): Mix the following components in parts by weight: 40 parts 2-ethylhexyl acrylate (2-EHA), 10 parts hydroxyethyl acrylate (HEA), 5 parts acrylic acid (AA), 0.01 parts n-dodecyl mercaptan, 0.07 parts azobisisoheptanenitrile (ABVN), and 45 parts ethyl acetate. Place the mixture in a polymerization apparatus, purge with nitrogen for 1 hour, then heat the mixture to 60°C and react for 14 hours. Use GPC to test the sample, and determine that the sample has a Mw of 1200 kDa and a polydispersity index of 3.64.

[0138] Step (2): Mix the sample obtained in step (1) according to the following parts by weight: 60 parts of sample, 0.05 parts of isocyanate crosslinking agent, 0.02 parts of aziridine crosslinking agent, 0.05 parts of silane coupling agent, and 40 parts of reactive diluent. After thorough mixing, degas at 0.06MPa to 0.09MPa for 30 min to 120 min to obtain the adhesive. The specific mixing method for step (2) is as described in Example 1.

[0139] Step (3): Apply the adhesive evenly to the heavy release film, bake at a stepped temperature (not exceeding 110℃) for 10 minutes, then attach the light release film to form a three-layer structure of tape A consisting of light release film, OCA layer, and heavy release film. After curing at room temperature, it is ready for use. Tape A is an optical film adhesive that can be used in foldable screens or other flexible display devices.

[0140] By removing pentaerythritol triacrylate, a structurally branching monomer, from the formulation, the degree of resin branching was reduced, resulting in an OCA material with a Poisson's ratio close to 5. Compared with Example 4, the degree of resin layer branching was lower, the Poisson's ratio was higher, and obvious creases were produced after folding tests, failing to have a significant effect on crease suppression.

[0141] Comparative Example 4

[0142] An optical film adhesive for foldable screens or other flexible display devices is prepared by the following steps.

[0143] Step (1): Mix the following components in parts by weight: 40 parts 2-ethylhexyl acrylate (2-EHA), 8 parts hydroxyethyl acrylate (HEA), 3 parts acrylic acid (AA), 4 parts pentaerythritol triacrylate, 0.01 parts n-dodecyl mercaptan, 0.07 parts azobisisoheptanenitrile (ABVN), and 45 parts ethyl acetate. Place the mixture in a polymerization apparatus, purge with nitrogen for 1 hour, then heat the mixture to 60°C and react for 14 hours. Use GPC to test the sample, and determine that the sample has a Mw of 1200 kDa and a polydispersity index of 3.64.

[0144] Step (2): Mix the sample obtained in step (1) according to the following parts by weight: 60 parts of sample, 0.05 parts of isocyanate crosslinking agent, 0.02 parts of aziridine crosslinking agent, 0.05 parts of silane coupling agent, and 40 parts of reactive diluent. After thorough mixing, degas at 0.06MPa to 0.09MPa for 30 min to 120 min to obtain the adhesive. The specific mixing method in step (2) is as described in Example 1. Step (3): Apply the adhesive evenly to the heavy release film, bake at a stepped temperature (not exceeding 110℃) for 10 min, and then attach the light release film to form a three-layer structure of light release film-OCA layer-heavy release film tape A. After curing at room temperature, it can be used. Tape A is an optical film adhesive that can be used in foldable screens or other flexible display devices.

[0145] Increasing the amount of pentaerythritol triacrylate, a structurally branching monomer, in the formulation improves the degree of resin branching, resulting in a significant decrease in the Poisson's ratio of the obtained OCA material. Compared with Example 4, the degree of resin layer branching is higher and the Poisson's ratio is lower, but the creases are obvious after the folding test, indicating that the Poisson's ratio needs to be controlled within a certain range to significantly reduce the occurrence of creases.

[0146] Comparative Example 5

[0147] An optical film adhesive for foldable screens or other flexible display devices is prepared by the following steps.

[0148] Step (1): Mix the following components in parts by weight: 40 parts 2-ethylhexyl acrylate (2-EHA), 10 parts hydroxyethyl acrylate (HEA), 4 parts acrylic acid (AA), 1 part pentaerythritol triacrylate, 0.01 parts n-dodecyl mercaptan, 0.07 parts azobisisoheptanenitrile (ABVN), and 45 parts ethyl acetate. Place the mixture in a polymerization apparatus, purge with nitrogen for 1 hour, then heat the mixture to 60°C and react for 14 hours. Use GPC to test the sample, and determine that the sample has a Mw of 1200 kDa and a polydispersity index of 3.64.

[0149] Step (2): Mix the sample obtained in step (1) according to the following parts by weight: 60 parts of sample, 0.05 parts of epoxy crosslinking agent, 0.05 parts of silane coupling agent, and 40 parts of reactive diluent. After thorough mixing, degas at 0.06MPa to 0.09MPa for 30 min to 120 min to obtain the adhesive. The specific mixing method for step (2) is as described in Example 1.

[0150] Step (3): Apply the adhesive evenly to the heavy release film, bake at a stepped temperature (not exceeding 110℃) for 10 minutes, then attach the light release film to form a three-layer structure of tape A consisting of light release film, OCA layer, and heavy release film. After curing at room temperature, it is ready for use. Tape A is an optical film adhesive that can be used in foldable screens or other flexible display devices.

[0151] Comparative Example 6

[0152] An optical film adhesive for foldable screens or other flexible display devices is prepared by the following steps.

[0153] Step (1): Mix the following components in parts by weight: 40 parts 2-ethylhexyl acrylate (2-EHA), 10 parts hydroxyethyl acrylate (HEA), 4 parts acrylic acid (AA), 1 part pentaerythritol triacrylate, 0.01 parts n-dodecyl mercaptan, 0.07 parts azobisisoheptanenitrile (ABVN), and 45 parts ethyl acetate. Place the mixture in a polymerization apparatus, purge with nitrogen for 1 hour, then heat the mixture to 60°C and react for 14 hours. Use GPC to test the sample, and determine that the sample has a Mw of 1200 kDa and a polydispersity index of 3.64.

[0154] Step (2): Mix the sample obtained in step (1) according to the following parts by weight: 60 parts of sample, 0.2 parts of aziridine crosslinking agent, 0.05 parts of silane coupling agent, and 40 parts of reactive diluent. After thorough mixing, degas at 0.06MPa to 0.09MPa for 30 min to 120 min to obtain the adhesive. The specific mixing method for step (2) is as described in Example 1.

[0155] Step (3): Apply the adhesive evenly to the heavy release film, bake at a stepped temperature (not exceeding 110℃) for 10 minutes, then attach the light release film to form a three-layer structure of tape A consisting of light release film, OCA layer, and heavy release film. After curing at room temperature, it is ready for use. Tape A is an optical film adhesive that can be used in foldable screens or other flexible display devices.

[0156] Comparative Example 7

[0157] An optical film adhesive for foldable screens or other flexible display devices is prepared by the following steps.

[0158] Step (1): Mix the following components in parts by weight: 40 parts 2-ethylhexyl acrylate (2-EHA), 10 parts hydroxyethyl acrylate (HEA), 4 parts acrylic acid (AA), 1 part pentaerythritol triacrylate, 0.01 parts n-dodecyl mercaptan, 0.07 parts azobisisoheptanenitrile (ABVN), and 45 parts ethyl acetate. Place the mixture in a polymerization apparatus, purge with nitrogen for 1 hour, then heat the mixture to 60°C and react for 14 hours. Use GPC to test the sample, and determine that the sample has a Mw of 1200 kDa and a polydispersity index of 3.64.

[0159] Step (2): Mix the sample obtained in step (1) according to the following parts by weight: 60 parts of sample, 0.05 parts of isocyanate crosslinking agent, 0.05 parts of silane coupling agent, and 40 parts of reactive diluent. After thorough mixing, degas at 0.06MPa to 0.09MPa for 30 min to 120 min to obtain the adhesive. The specific mixing method for step (2) is as described in Example 1.

[0160] Step (3): Apply the adhesive evenly to the heavy release film, bake at a stepped temperature (not exceeding 110℃) for 10 minutes, then attach the light release film to form a three-layer structure of tape A consisting of light release film, OCA layer, and heavy release film. After curing at room temperature, it is ready for use. Tape A is an optical film adhesive that can be used in foldable screens or other flexible display devices.

[0161] Comparative Example 8

[0162] An optical film adhesive for foldable screens or other flexible display devices is prepared by the following steps.

[0163] Step (1): Mix the following components in parts by weight: 40 parts 2-ethylhexyl acrylate (2-EHA), 10 parts hydroxyethyl acrylate (HEA), 4 parts acrylic acid (AA), 1 part pentaerythritol triacrylate, 0.01 parts n-dodecyl mercaptan, 0.07 parts azobisisoheptanenitrile (ABVN), and 45 parts ethyl acetate. Place the mixture in a polymerization apparatus, purge with nitrogen for 1 hour, then heat the mixture to 60°C and react for 14 hours. Use GPC to test the sample, and determine that the sample has a Mw of 1200 kDa and a polydispersity index of 3.64.

[0164] Step (2): Mix the sample obtained in step (1) according to the following parts by weight: 60 parts sample, 0.4 parts initiator, 0.05 parts silane coupling agent, and 40 parts reactive diluent. After thorough mixing, degas at 0.06MPa to 0.09MPa for 30 min to 120 min to obtain the adhesive. The specific mixing method for step (2) is as described in Example 1.

[0165] Step (3): Apply the adhesive evenly to the heavy release film, bake at a stepped temperature (not exceeding 110℃) for 10 minutes, then attach the light release film to form a three-layer structure of tape A consisting of light release film, OCA layer, and heavy release film. After curing at room temperature, it is ready for use. Tape A is an optical film adhesive that can be used in foldable screens or other flexible display devices.

[0166] Comparative Examples 5-8 used a traditional single curing method (5, 6, 7 single thermo-curing / 8 single photo-curing), which only formed a single cured network in the material. The material obtained by this method had a high Poisson ratio and produced obvious creases after folding test, and could not produce a significant effect on crease suppression.

[0167] Table 1. Raw material components of Examples 1-6 and Comparative Examples 1-8

[0168]

[0169]

[0170] Table 2 Performance parameters of Examples 1-6 and Comparative Examples 1-8

[0171] project Tg -30℃ loss modulus Loss modulus at 25℃ Loss modulus at 60℃ Loss modulus at 80℃ molecular weight Dispersion coefficient unit ℃ kPa kPa kPa kPa kDa / Example 1 -40.0 208 25.4 16.8 14.0 1200 3.64 Example 2 -36.9 276 28.8 18.4 15.1 1200 3.64 Example 3 -36.9 263 30.1 19.2 15.7 1200 3.64 Example 4 -36.9 244 31.4 20.5 16.3 1200 3.64 Example 5 -38.5 228 29.8 19.3 14.8 1200 3.64 Example 6 -36.9 251 33.6 21.8 17.4 1200 3.64 Comparative Example 1 -42.4 146 18.9 9.6 8.2 1200 3.64 Comparative Example 2 -33.7 302 32.2 20.7 18.5 1200 3.64 Comparative Example 3 -35.2 255 32.4 22.2 17.6 1200 3.64 Comparative Example 4 -39.4 206 24.6 15.5 13.9 1200 3.64 Comparative Example 5 -36.9 264 29.7 20.1 16.5 1200 3.64 Comparative Example 6 -36.9 293 32.4 21.7 17.5 1200 3.64 Comparative Example 7 -36.9 240 27.5 16.2 13.3 1200 3.64 Comparative Example 8 -36.9 238 25.4 15.9 12.7 1200 3.64

[0172] Table 3 Performance parameters of Examples 1-6 and Comparative Examples 1-8

[0173]

[0174]

[0175] Table 4 Performance parameters of Examples 1-6 and Comparative Examples 1-8

[0176] project thickness Transmittance (TT) Haze b* unit μm ％ ％ / Example 1 25 91.48 0.18 0.18 Example 2 25 90.7 0.16 0.17 Example 3 25 90.59 0.19 0.16 Example 4 25 90.26 0.19 0.15 Example 5 25 91.49 0.19 0.15 Example 6 25 90.25 0.18 0.19 Comparative Example 1 25 90.27 0.15 0.15 Comparative Example 2 25 90.19 0.19 0.18 Comparative Example 3 25 90.93 0.17 0.16 Comparative Example 4 25 91.84 0.19 0.19 Comparative Example 5 25 90.46 0.16 0.18 Comparative Example 6 25 90.33 0.20 0.17 Comparative Example 7 25 91.17 0.20 0.19 Comparative Example 8 25 90.72 0.15 0.15

[0177] Based on the test results of the above embodiments and comparative examples, it can be concluded that the OCA optical adhesive tape provided by the present invention, which can be used in foldable screens or other flexible display devices, has superior low-temperature and room-temperature loss modulus compared with the comparative product. When a stress of 20 kPa is applied at -20℃, 25℃, and 60℃, its strain is between 200% and 600%, and it has a recovery of ≥90%, ensuring that OCA has good deformation recovery performance at different temperatures during use. The lower Poisson's ratio means that the material has less thickness shrinkage when stretched, which can more effectively disperse in-plane stress to a larger volume rather than concentrate it at the interface, thereby greatly suppressing the formation of creases.

[0178] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. All equivalent variations and modifications made based on the content of the present invention are covered within the patent scope of the present invention.

Claims

1. An optical adhesive for flexible displays, comprising a first mixture containing alkyl acrylate monomers, branched monomers and an initiator, polymerized to obtain a semi-finished product, a crosslinking agent added for curing to obtain an adhesive, which is then coated onto a release film to obtain an optical adhesive, wherein the Poisson's ratio is controlled between 0.45 and 0.

48.

2. The optical adhesive according to claim 1, characterized in that, The alkyl acrylate monomers include methyl methacrylate (MMA), 2-ethylhexyl methacrylate (EHMA), ethylene glycol methacrylate (EGMA), methyl acrylate (MA), ethyl methacrylate (EMA), ethyl acrylate (EA), n-butyl methacrylate (BMA), n-butyl acrylate (BA), 2-ethylhexyl methacrylate (2-EHMA), 2-ethylhexyl acrylate (2-EHA / EHA), n-octyl acrylate (OA), lauryl acrylate (LA), and lauryl methacrylate (LMA).

3. The optical adhesive according to claim 1, characterized in that, The branched monomers include trimethylolpropane triacrylate (TMPTA), glycerol propoxy triacrylate (GPTA), trimethylolpropane triacrylate ethoxylate (3EO-TMPTA), glycerol propoxy triacrylate (G3POTA), pentaerythritol penta / hexaacrylate, pentaerythritol tetraacrylate, and pentaerythritol triacrylate.

4. The optical adhesive according to claim 1, characterized in that, The initiator is a free radical initiator, including benzoyl peroxide (BPO), tert-butyl peroxide-2-ethylhexanoate (TBPEH), tert-butyl peroxide-3,5,5-trimethylhexanoate (TBPIN), 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane (TMPC), azobisisobutyronitrile (AIBN), and azobisisoheptanenitrile (ABVN).

5. The optical adhesive according to claim 1, characterized in that, The crosslinking agent is selected from isocyanate curing agents, epoxy curing agents, or aziridine curing agents.

6. The optical adhesive according to claim 1, characterized in that, The first mixture contains polar functional monomers, including hydroxyethyl acrylate (HEA), hydroxyethyl methacrylate (HEMA), hydroxypropyl acrylate (HPA), hydroxypropyl methacrylate (HPMA), acrylic acid (AA), methacrylic acid (MAA), and glycidyl methacrylate (GMA).

7. The optical adhesive according to claim 1, characterized in that, A chain transfer agent is added to the first mixture, the chain transfer agent including n-dodecyl mercaptan, tert-dodecyl mercaptan, and isooctyl 3-mercaptopropionate.

8. The optical adhesive according to claim 1, characterized in that, UV initiators and silane coupling agents are added during the curing process of the semi-finished product.

9. The optical adhesive according to claim 1, characterized in that, An active diluent is introduced into the reaction system, including ethyl acetate (EA), n-butyl acetate (BAC), isobutyl acetate (IBAC), acetone (AC), butanone (MEK), methyl isobutyl ketone (MIBK), cyclohexanone (CYC), toluene (TOL), and xylene (XYL).

10. A method for preparing an optical adhesive according to any one of claims 1 to 9, comprising: Step (1): A semi-finished product is prepared by polymerization of a mixture containing alkyl (meth)acrylate monomers, polar functional monomers, branched monomers and at least one free radical initiator. Step (2): Add the semi-finished product from step (1) to a curing agent for curing to obtain an adhesive; Step (3): Apply the adhesive from step (2) to the release film to obtain optical adhesive.

11. The method for preparing the optical adhesive according to claim 10, characterized in that, Step (3): The adhesive is applied to the heavy release film, and after cross-linking and curing, the light release film is bonded together to form a sandwich structure of release film / OCA adhesive film / release film.

12. The use of the optical adhesive according to any one of claims 1 to 9 in foldable electronic devices.

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