Oca full bonding optical adhesive and preparation method thereof

Abstract

The application discloses an OCA full-adhesion optical adhesive and a preparation method thereof, and belongs to the technical field of optical adhesives, and aims to provide an optical adhesive with high optical performance, excellent flexibility and self-repairing capability. The optical adhesive is prepared from a prepolymer system composed of a soft monomer, a hard monomer, a functional monomer, a dynamic crosslinking agent, a photoinitiator, an ultraviolet absorber and a silane coupling agent, and is cured by gradient initiation of single-side ultraviolet light. The gradient network structure with continuously decreasing crosslinking density along the thickness direction is formed in-situ in a single adhesive layer through the light intensity depth attenuation effect caused by competitive light absorption of the ultraviolet absorber; and the double-sulfur bond is introduced into the polymer network through the dynamic crosslinking agent, so that the material is endowed with the functions of self-repairing and stress relaxation.

Description

Technical Field

[0001] This invention belongs to the field of optical adhesive technology, specifically relating to an OCA full-lamination optical adhesive and its preparation method. Background Technology

[0002] With the rapid development of flexible display technology, new display products such as foldable screen phones, flexible wearable devices, and automotive curved screens place extremely high demands on adhesive materials. Optically clear adhesives (OCA), as an indispensable bonding medium in display modules, not only need to provide extremely high light transmittance, low haze, and good weather resistance, but also need to maintain interlayer mechanical stability during frequent bending cycles. Traditional OCA optical adhesives are usually homogeneous polymer systems with a permanently covalently cross-linked network structure. This homogeneous structure has significant drawbacks when dealing with non-uniform bending strain: on the one hand, stress tends to accumulate at the interface between the adhesive layer and the rigid film, leading to delamination, debonding, or blistering; on the other hand, the traditional permanent network will experience mechanical fatigue under repeated deformation, and may even form microcracks. Once cracks form, because the molecular chains are permanently locked, they cannot be repaired through molecular rearrangement, leading to permanent degradation of optical performance.

[0003] Existing technology CN115404020A proposes a three-layer optical adhesive film for flexible foldable screens, which balances performance by forming a soft-hard-soft sandwich structure through multiple physical coatings. However, this physical composite method is cumbersome, and the interlayer interfaces may cause optical distortion or interlayer delamination. CN120988287A discloses an organosilicon-modified optical adhesive, which reduces stress, but the organosilicon system is expensive and has poor compatibility with existing acrylate production lines.

[0004] Therefore, there is an urgent need to develop an OCA optical adhesive that can achieve a gradient crosslinking structure with a hard surface and a soft bottom within a single adhesive layer and has dynamic damage repair capabilities, so as to solve the problems of stress dissipation, anti-denting and self-healing without the need for complex multi-layer coating. Summary of the Invention

[0005] The present invention aims to provide an OCA full-lamination optical adhesive that combines high optical performance, excellent flexibility and self-healing ability.

[0006] The specific technical solution is as follows:

[0007] An OCA (Optical Cordless Autoclave) fully bonded optical adhesive is made from the following raw materials in parts by weight: 50-80 parts soft monomer, 10-30 parts hard monomer, 1.0-6.0 parts functional monomer, 5.0-12 parts dynamic crosslinking agent, 0.5-3.0 parts photoinitiator, 0.05-0.5 parts ultraviolet absorber, and 0.1-1.0 parts silane coupling agent; the preparation method of the OCA fully bonded optical adhesive includes the following steps:

[0008] S1: Mix the soft monomer, the hard monomer, the functional monomer and the dynamic crosslinking agent, then add the photoinitiator, the ultraviolet absorber and the silane coupling agent, stir and mix and perform degassing treatment to obtain a prepolymer solution;

[0009] S2: The prepolymer adhesive obtained in step S1 is continuously extruded and coated on the release surface of the first heavy release film, and the absolute dry adhesive layer thickness is controlled to obtain a smooth adhesive film.

[0010] S3: The film obtained in step S2 is sent into the ultraviolet exposure tunnel. An ultraviolet light source with a center wavelength of 365nm is arranged above the coating side that is not covered by the film material to initiate irradiation. In-situ gradient photocuring is completed by using a low-intensity long exposure mode.

[0011] S4: Lay a second light release film onto the light-receiving surface of the cured adhesive film, roll it up, and place it in a darkroom to complete static heating and curing.

[0012] Furthermore, the dynamic crosslinking agent is an acrylate functional monomer containing a disulfide bond structure; the ultraviolet absorber is a benzotriazole ultraviolet absorber or a hydroxyphenyltriazine ultraviolet absorber.

[0013] Furthermore, the acrylate functional monomer with the disulfide bond structure is specifically bis-2-methacryloyloxyethyl disulfide or bis-2-acryloyloxyethyl disulfide; the ultraviolet absorber is specifically Tinuvin 234 or Tinuvin 400.

[0014] Furthermore, the soft monomer is any one or a combination of 2-ethylhexyl acrylate or lauryl acrylate; the hard monomer is any one or a combination of isobornyl acrylate or acrylmorpholine; the functional monomer is any one or a combination of 4-hydroxybutyl acrylate, hydroxyethyl acrylate or hydroxypropyl acrylate; and the silane coupling agent is 3-methacryloyloxypropyltriethoxysilane or 3-acryloyloxypropyltrimethoxysilane.

[0015] Furthermore, the stirring and mixing conditions described in step S1 are as follows: the rotation speed is controlled at 300-500 rpm, the system temperature is maintained at 20-30℃, and during the stirring process, the overall moisture content of the system is controlled to be below 500 ppm by purging with high-purity nitrogen.

[0016] Furthermore, the degassing treatment conditions in step S1 are: under a negative pressure of -0.09 MPa and continuous static evacuation for 30 minutes.

[0017] Furthermore, in step S2, the first layer of release film is a transparent polyethylene terephthalate film with a thickness of 75 μm and a preset release force of 20-30 gf / 25 mm on the surface; the absolute dry adhesive layer thickness is controlled at 180 μm with an error range of ±2 μm.

[0018] Furthermore, the control parameters for the low-intensity long exposure mode in step S3 are: setting the surface light intensity to 10-50 mW / cm². 2 The conveying rate is adjusted to keep the film in the exposure tunnel for 100-200 seconds, controlling the total cumulative irradiation energy to be 2000-5000 mJ / cm². 2 .

[0019] Furthermore, in step S4, the second light release film is a light release polyethylene terephthalate film with a thickness of 50 μm and a preset release force of 3-5 gf / 25 mm.

[0020] Furthermore, in step S4, the static heating and curing temperature is kept constant at 40-50°C and the curing time is 24-48 hours.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) This invention introduces an ultraviolet absorber during the single-sided ultraviolet curing process, causing the light energy to attenuate in a gradient along the thickness direction of the adhesive layer, thereby forming a dense network with high cross-linking density and high modulus on the light-receiving side and a loose network with low cross-linking density and low modulus on the back-light side. This structure combines the surface's resistance to indentation with the back side's high wettability and stress dissipation capability. The back-light side retains some degrees of freedom of movement of polymer chains, which can effectively fill the ink step difference of the cover plate and absorb the organic gases released at high temperature, solving the problem of delayed bubble formation and achieving a unity of contradictory mechanical properties.

[0023] (2) This invention introduces a dynamic crosslinking agent containing disulfide bonds to form crosslinking sites in the polymer network that can be locally rearranged. When the optical adhesive layer generates local stress during the folding or bending of the flexible screen, these crosslinking sites can allow the polymer network to undergo limited local rearrangement, alleviate stress concentration, improve the micro-stress distribution, and thus enhance the bending durability and stress dissipation capacity of the adhesive layer.

[0024] (3) Compared with the traditional technical route of achieving modulus transition through multi-layer physical composite, the present invention adopts one-step continuous coating and in-situ photocuring molding, which eliminates the complicated multi-pass coating and multiple bonding operations. While ensuring high light transmittance and low haze, it also has the advantages of high production efficiency and controllable cost. Attached Figure Description

[0025] Figure 1 This is a flowchart illustrating the preparation process of an OCA fully bonded optical adhesive according to the present invention.

[0026] Figure 2 The depth-resolved confocal Raman spectrum (left) and the curve of curing degree as a function of depth (right) of the optical adhesive prepared in Example 1 of the present invention.

[0027] Figure 3 This is a comparison chart of the transmittance and haze test results of the embodiments and comparative examples of the present invention;

[0028] Figure 4 This is a comparison chart of the gradient modulus difference and self-healing efficiency test results of the embodiments and comparative examples of the present invention. Detailed Implementation

[0029] The following embodiments further explain and illustrate the technical solutions of the present invention. It should be specifically noted that each specific embodiment is a concretization and explanation of the technical solution and should not be considered as a limitation on the scope of protection of the present invention. Those skilled in the art still have the right to modify the technical solutions of these embodiments and make equivalent substitutions for some or all of the technical features, and these modifications or substitutions do not change the essence of the corresponding technical solutions, nor do they cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions described in the present invention.

[0030] This invention provides an OCA full-lamination optical adhesive and its preparation method. By weight, the raw materials for preparing the optical adhesive include: 50-80 parts of soft monomer; 10-30 parts of hard monomer; 1.0-6.0 parts of functional monomer; 5.0-12 parts of dynamic crosslinking agent; 0.5-3.0 parts of photoinitiator; 0.05-0.5 parts of ultraviolet absorber; and 0.1-1.0 parts of silane coupling agent.

[0031] The soft monomer is one or a combination of 2-ethylhexyl acrylate (2-EHA) or lauryl acrylate (LA) to provide a low glass transition temperature and flexible segments, enabling the adhesive layer to have good compliance and stress absorption capacity when folded and bent.

[0032] The hard monomer is one or a combination of isobornyl acrylate (IBOA) or acrylamide (ACMO) to provide a rigid cyclic structure, increase the crosslinking density and surface hardness of the light-receiving surface, thereby enhancing peel strength and scratch resistance.

[0033] The functional monomer is one or a combination of 4-hydroxybutyl acrylate (4-HBA), hydroxyethyl acrylate, or hydroxypropyl acrylate. The hydroxyl groups in the functional monomer can form hydrogen bonds with hydroxyl, carboxyl, or silanol groups present on the substrate surface, thereby forming polar anchoring points at the interface between the adhesive layer and the substrate, enhancing interfacial adhesion and inhibiting interfacial slippage. Simultaneously, due to its flexible methylene segments, it does not significantly increase the glass transition temperature of the system, making it suitable for the flexible bonding requirements of foldable display modules.

[0034] The dynamic crosslinking agent is an acrylate functional monomer containing a disulfide bond structure, specifically bis(2-methacryloyloxyethyl) disulfide or bis(2-acryloyloxyethyl) disulfide. When introduced into the polymer backbone, it forms dynamic crosslinking sites, enabling local network rearrangement and self-healing, thus improving bending durability and impact energy dissipation.

[0035] The photoinitiator is 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO) or 1-hydroxycyclohexylbenzophenone, used to initiate the polymerization reaction of acrylates under UV irradiation and control the crosslinking rate and network formation.

[0036] The ultraviolet absorber is either benzotriazole ultraviolet absorber Tinuvin 234 or hydroxyphenyltriazine ultraviolet absorber Tinuvin 400, used to absorb UV light and reduce photodegradation, while forming a light intensity gradient in the thickness direction to achieve longitudinal control of the crosslinking density of the adhesive layer.

[0037] The silane coupling agent is 3-(methacryloyloxy)propyltriethoxysilane or 3-(acryloyloxy)propyltrimethoxysilane. The silane coupling agent forms covalent or hydrogen bonds by condensation reactions between its silane end groups and hydroxyl or carboxyl groups on the substrate surface, thereby providing chemical anchoring points at the interface between the adhesive layer and the substrate, improving interfacial adhesion, peel resistance, and long-term reliability. Simultaneously, its acrylate functional groups can participate in photopolymerization and crosslinking reactions, forming chemical interlocks with the internal network of the adhesive layer, making the interfacial bonding more stable without affecting the flexible stress dissipation capability.

[0038] The preparation method of the present invention includes the following steps, the flowchart of which is attached. Figure 1 As shown:

[0039] S1. Preparation of prepolymer solution

[0040] The process is carried out in a reaction vessel equipped with mechanical stirring, nitrogen protection, and temperature control devices.

[0041] (1) Add the soft monomer, hard monomer, functional monomer, and dynamic crosslinking agent in sequence according to the formulation amount, followed by the photoinitiator, ultraviolet absorber, and silane coupling agent. Start stirring, control the speed at 300-500 rpm, and maintain the system temperature at 20-30℃ to ensure that the components are fully miscible at the molecular level. Purge the system with high-purity nitrogen throughout the process and monitor the trace water in the reactor in real time. Strictly control the overall moisture content of the system to be less than 500 ppm to avoid high-temperature bubbles and interface failure caused by trace moisture in the adhesive solution during storage and curing.

[0042] (2) After the system is fully miscible, stop nitrogen purging and switch the system to vacuum mode. Perform static degassing treatment for 30 minutes under a negative pressure of -0.09 MPa to forcibly extract microbubbles and some volatile small molecules entrained during stirring. This completely removes microbubbles from a physical perspective, cutting off the path of light scattering sources and stress concentration points during subsequent coating and film formation, thereby ensuring that the OCA adhesive layer after lamination has excellent light transmittance and low haze. Seal and store for later use after vacuuming.

[0043] S2. Precision coating film formation

[0044] The prepolymer adhesive is transferred to a slot extrusion coater in a cleanroom for processing.

[0045] (1) The solvent-free prepolymer liquid prepared in S1 is continuously and smoothly pumped into the slot coating head using a high-precision screw pump, and uniformly extruded and coated on the release surface of the first layer of heavy release film. The heavy release film is made of transparent polyethylene terephthalate (PET) with a thickness of 75μm, and its surface release force is preset to 20-30gf / 25mm to provide sufficient coating tension and flatness.

[0046] (2) After coating, the film material directly enters the dust-free conveyor roller. The online laser thickness measuring device is turned on to perform real-time closed-loop scanning of the adhesive layer thickness, and the feeding pressure of the coating head is adjusted accordingly to strictly control the absolute dry adhesive thickness at 180μm, with an error range of ±2μm.

[0047] This step is the physical basis for the successful realization of the subsequent three-dimensional modulus gradient in this process. Optically, the coating process requires absolute dust protection and uniform thickness, because the thickness of the adhesive layer directly participates in the in vivo attenuation calculation of ultraviolet rays as an optical variable; if the thickness tolerance is too large, it will not only cause local stress points when the display module is bonded, but also destroy the calculation model of longitudinal photon interception by the ultraviolet absorber, resulting in the loss of consistency and control of the crosslinking gradient distribution.

[0048] S3. In-situ gradient photocuring

[0049] After the coating is smoothed, the adhesive film is passed uniformly through a specific UV exposure tunnel, and the following curing procedure is performed: A UV-LED low-heat cold light source array with a center wavelength of 365nm is arranged above the single side of the coating where the light release film is not attached. A low-intensity long exposure mode is used, and the surface light intensity is set to 10-50mW / cm². 2 By adjusting the conveyor belt speed, the adhesive layer is kept in the exposure tunnel for 100-200 seconds, controlling the total cumulative irradiation energy to be 2000-5000 mJ / cm². 2 This ensures that a dense cross-linked network forms rapidly on the surface, while the underlying layer maintains a gradient cross-linked structure.

[0050] During the photocuring process, when ultraviolet light penetrates the adhesive layer from the surface inwards, it encounters strong competitive absorption by the ultraviolet absorbers in the formulation. The light flux decreases exponentially along the thickness direction. Driven directly by the light intensity gradient, the photoinitiator on the light-receiving surface is highly excited, resulting in an extremely high concentration of primary free radicals. The polymerization and cross-linking rates of double bonds are much greater than the chain growth rate, rapidly forming a dense cross-linked network, leading to a harder surface and providing excellent resilience and indentation resistance for the cover layer. On the backlight side, due to the scarcity of photons and the scarcity of initial free radicals, the system mainly exhibits slow linear chain growth, forming only loose cross-links, resulting in a softer surface with more free chain segments. This provides excellent interfacial wettability and strong bending stress dissipation capability for the underlying flexible panel, naturally forming an integrated stress-buffered neutral layer.

[0051] S4. Composite and thermal curing

[0052] (1) After the adhesive film is cured in a gradient to form a tunnel, a second light release film is bonded to the surface of the light-receiving surface in a clean environment using a bubble-free bonding device. The light release film is made of 50μm thick PET, and its release force is preset to 3-5gf / 25mm to facilitate peeling during subsequent module assembly. Then, it is flattened and wound up.

[0053] (2) Transfer the rolled OCA roll to a darkroom constant temperature curing room and perform static heating curing for 24-48 hours at 40-50℃.

[0054] Example 1

[0055] The raw materials for preparing the optical adhesive include: 65 parts 2-EHA, 20 parts IBOA, 4 parts 4-HBA, 8 parts bis(2-methacryloyloxyethyl) disulfide, 2.0 parts TPO, 0.3 parts Tinuvin 400, and 0.6 parts 3-(methacryloyloxy)propyltriethoxysilane.

[0056] The preparation steps are as follows:

[0057] (1) Add 2-EHA, IBOA, 4-HBA, and bis(2-methacryloyloxyethyl) disulfide sequentially according to the formula amount, followed by TPO, Tinuvin 400, and 3-(methacryloyloxy)propyltriethoxysilane. Start stirring, control the speed at 300-500 rpm, maintain the system temperature at 20-30℃, and control the overall moisture content of the system to less than 500 ppm by purging with high-purity nitrogen and monitoring the trace water in the reactor in real time. After 30 minutes, the system is fully miscible. Stop nitrogen purging, switch the system to vacuum mode, and perform static degassing treatment under a negative pressure of -0.09 MPa for 30 minutes to obtain the prepolymer solution. After breaking the vacuum, seal it for later use.

[0058] (2) The prepolymer adhesive is transferred to a slot extrusion coating machine in a cleanroom. A high-precision screw pump is used to continuously and smoothly pump the prepolymer adhesive obtained in step (1) into the slot coating head, and it is uniformly extruded and coated onto a transparent PET film with a thickness of 75 μm. The surface release force of the PET film is preset to 25 gf / 25 mm. After coating, the film enters the cleanroom conveyor roller. The online laser thickness measuring device is turned on to perform real-time closed-loop scanning of the adhesive layer thickness. The feeding pressure of the coating head is adjusted according to feedback, and the absolute dry adhesive thickness is strictly controlled within a fine tolerance range of 180 μm ± 2 μm.

[0059] (3) Pass the coated film through a specific UV exposure tunnel at a uniform speed. Place a UV-LED low-heat cold light source array with a center wavelength of 365nm above the side of the coating where the release film is not adhered. Set the surface light intensity to 25mW / cm². 2 A low-intensity, long-exposure mode was employed. By adjusting the conveyor belt speed, the exposure time was set to 140 seconds, and the total cumulative irradiation energy was controlled at 3500 mJ / cm². 2 .

[0060] (4) The cured adhesive film is applied on a clean, bubble-free lamination fixture. A 50μm thick PET film is laminated onto the light-receiving surface of the adhesive film. The surface release force of the PET film is preset to 4gf / 25mm. After lamination, the OCA roll is flattened and wound up. The wound OCA roll is then transferred to a darkroom constant temperature curing chamber and statically heated and cured at 45℃ for 30 hours.

[0061] Depth-resolution confocal Raman spectroscopy characterization

[0062] (1) Parameter setting and detection process: The 180 μm thick OCA optical film prepared in Example 1 was subjected to in-situ Z-axis depth analysis using a high-resolution laser confocal Raman microscope. The film sample was placed flat on the test stage, and the laser focusing point was precisely controlled using a piezoelectric ceramic displacement stage. With the light-receiving surface of the film as the origin (0 μm), the film was scanned layer by layer along the thickness direction towards the back-lighting surface, with the stepping accuracy set to the micrometer level. Raman scattering spectral data of three key depths were collected, namely 0 μm (light-receiving surface), 90 μm (intermediate layer), and 180 μm (back-lighting surface).

[0063] (2) Characterization results: as shown in the appendix Figure 2 As shown, the left figure displays Raman spectra at different depths. The intensity of the CH saturated bond characteristic peak remains essentially constant at different depths, and is therefore used as an internal reference standard for calculations. At the 0 μm light-receiving surface, the characteristic peak of the C=C double bond exhibits low normalized intensity due to the extremely high light intensity, resulting in extensive initiator excitation and vigorous polymerization and cross-linking reactions that consume a large amount of the double bond. With increasing test depth, the relative intensity of the C=C characteristic peak gradually and significantly increases. This is because the UV absorber in the formulation exhibits strong competitive absorption of UV light, leading to an exponential decay of luminous flux along the thickness direction. The right figure shows the degree of cure as a function of depth, calculated based on the ratio of characteristic peak intensities. The curve shows a smooth, non-linear decreasing trend, with the degree of cure approaching saturation on the light-receiving surface and significantly decreasing on the backlit surface. This quantitative data strongly demonstrates that the present invention successfully constructs a continuously transitioning gradient cross-linked structure within a single adhesive layer during a single coating and curing process, achieving the expected modulus design.

[0064] Example 2

[0065] The raw materials for preparing the optical adhesive include: 80 parts LA, 30 parts ACMO, 6.0 parts hydroxyethyl acrylate, 12 parts bis(2-acryloyloxyethyl) disulfide, 3.0 parts 1-hydroxycyclohexylbenzophenone, 0.5 parts Tinuvin 234, and 1.0 part 3-(acryloyloxy)propyltrimethoxysilane. Preparation process: The release force of the 75μm thick transparent PET film is preset to 30gf / 25mm; the surface light intensity is set to 50mW / cm² during photocuring. 2 The adhesive layer remained in the exposure tunnel for 100 seconds, with a total cumulative irradiation energy of 5000 mJ / cm². 2 The preset thickness for laminating a 50μm PET film is 5gf / 25mm. The rolled-up OCA roll is then heat-cured at 50℃ for 48 hours. The remaining processes are the same as in Example 1.

[0066] Example 3

[0067] The raw materials for preparing the optical adhesive include: 50 parts 2-EHA, 10 parts IBOA, 1.0 part hydroxypropyl acrylate, 5.0 parts bis(2-methacryloyloxyethyl) disulfide, 0.5 parts TPO, 0.05 parts Tinuvin 400, and 0.1 parts 3-(methacryloyloxy)propyltriethoxysilane. Preparation process: The release force of the 75μm thick transparent PET film is preset to 20gf / 25mm; the surface light intensity is set to 10mW / cm² during photocuring. 2 The adhesive layer remained in the exposure tunnel for 200 seconds, with a total cumulative irradiation energy of 2000 mJ / cm². 2 The preset thickness for laminating a 50μm PET film is 3gf / 25mm. The rolled-up OCA roll is then heat-cured at 40℃ for 24 hours. The remaining processes are the same as in Example 1.

[0068] Example 4

[0069] The raw materials for preparing the optical adhesive include: 50 parts 2-EHA, 10 parts LA, 10 parts IBOA, 10 parts ACMO, 2 parts 4-HBA, 2 parts hydroxyethyl acrylate, 8 parts bis(2-acryloyloxyethyl) disulfide, 1.5 parts TPO, 0.3 parts Tinuvin 234, and 0.5 parts 3-(methacryloyloxy)propyltriethoxysilane. The preparation process is the same as in Example 1.

[0070] Comparative Example 1

[0071] No UV absorber was added, i.e., the amount of Tinuvin 400 was 0, and the rest was the same as in Example 1.

[0072] Comparative Example 2

[0073] The dynamic crosslinking agent bis(2-methacryloyloxyethyl) disulfide was replaced with an equimolar amount of the common crosslinking agent 1,6-hexanediol diacrylate (HDDA), and the rest was the same as in Example 1.

[0074] Performance testing

[0075] 1. Light transmittance / haze test

[0076] Refer to GB / T 2410-2008 "Determination of light transmittance and haze of transparent plastics".

[0077] Sample preparation: Cut the prepared OCA film into flat samples of 100mm×100mm, remove the surface protective film, and place them in a standard test environment for 24 hours.

[0078] Testing procedure: A transmittance and haze meter was used to conduct the test under visible light conditions, measuring the total transmittance (%) and haze (%) of the samples. Each group of samples was tested three times, and the average value was taken, retaining one decimal place.

[0079] 2. Light release force, heavy release force test, and adhesion test on glass.

[0080] Refer to GB / T 2792-2014 "Test method for 180° peel strength of pressure sensitive adhesive tape".

[0081] Sample preparation: Cut OCA into sample strips with a width of 25mm and a length of 150mm, attach them to a standard glass plate, roll them back and forth twice with a 2kg roller, and let them stand for 20 minutes.

[0082] Test Procedure: A 180° peel test was performed on a tensile testing machine at a peel rate of 300 mm / min. The average peel force (gf / 25 mm) during the stable section was recorded. Each test was repeated three times, and the average value was taken, retaining one decimal place. Light Release Force Test: The side with the light release film was tested; Heavy Release Force Test: The side with the heavy release film was tested; Glass Adhesion Test: The peel strength between OCA and glass was tested.

[0083] 3. Gradient Modulus Difference Test

[0084] Sample preparation: Remove the light release film and heavy release film from the OCA adhesive layer to expose the light-receiving side and the back-light side, and cut the sample into 20mm×20mm pieces.

[0085] Testing Procedure: At 25℃, a nanoindenter was used with indentation depth control mode, ensuring the maximum indentation depth did not exceed 10% of the adhesive layer thickness. The storage modulus (E') of the light-receiving and backlighting surfaces was tested separately. Five test points were randomly selected for each surface, and the average value was taken. The difference in modulus between the light-receiving and backlighting surfaces was calculated in MPa, and the result was rounded to two decimal places.

[0086] 4. Folding performance test

[0087] Sample preparation: OCA was laminated between two 50μm thick colorless polyimide (CPI) films to form a standard laminated sample.

[0088] Testing process

[0089] (1) Dynamic bending performance at room temperature: A 180° reciprocating dynamic bending test was conducted using a folding tester, with an inward folding mode, i.e., the adhesive layer is located on the compression side, the bending radius R=1.5mm, the frequency 60 times / minute, and 200,000 continuous dynamic bends without dwell time. The test temperature was 23±2℃. After the test, the folded area was observed under a microscope to check for creases, whitening, or bubbles.

[0090] (2) Extreme environment tolerance test

[0091] Low-temperature bending test: Place the sample in a low-temperature environment chamber at -20℃ and let it stand for 2 hours to ensure the sample reaches thermal equilibrium. Perform 50,000 dynamic 180° reciprocating bends at a constant temperature of -20℃, with a bending radius R = 1.5 mm and a frequency of 60 times / minute. After the test, restore the sample to 23±2℃ and let it stand for 2 hours, then observe for cracks, interface delamination, whitening, or bubbles.

[0092] High-temperature bending test: The sample was placed in a high-temperature environment chamber at 60℃ and left to stand for 2 hours to ensure the material reached thermal equilibrium. Under constant temperature of 60℃, 50,000 180° reciprocating dynamic bends were performed, with a bending radius R = 1.5 mm and a frequency of 60 times / minute. After the test, the sample was returned to 23±2℃ and left to stand for 2 hours before visual and interface inspections were conducted.

[0093] 5. Self-repair efficiency

[0094] Sample preparation: Use a copper brush to create scratches with a depth of about 5μm on the surface of the OCA adhesive layer.

[0095] Test procedure: After heating the sample in a 60℃ oven for 30 minutes, remove it and use a haze meter to measure the haze change in the scratched area. Self-healing efficiency (%) = (H0 - H t )×100% / (H0-H base ), where H0 is the haze after the scratch, H t To repair the haze, H base The haze is for the unscratched sample.

[0096] Table 1. Results of light transmittance, haze, light release force, heavy release force, and adhesion to glass in the examples and comparative examples.

[0097]

[0098] Table 2 shows the test results of gradient modulus difference, self-healing efficiency, and folding performance for the examples and comparative examples.

[0099]

[0100] Results analysis:

[0101] (1) As shown in Tables 1 and 2, Examples 1-4 exhibit excellent optical, mechanical, and flexible properties. They have high light transmittance and low haze, as indicated in the attached table. Figure 3This ensures clear illumination of the display module. The light and heavy release forces are well-matched, and the adhesion to the glass is strong, indicating a stable anchoring between the adhesive layer and the substrate. The gradient modulus difference shows that each embodiment successfully constructed a gradient network structure with continuously decreasing crosslinking density in the thickness direction within a single-layer adhesive film. This structure, combined with a dynamic crosslinking system, gives the adhesive layer excellent self-healing ability and anti-folding properties, with Example 1 exhibiting the best overall performance.

[0102] (2) In Comparative Example 1, the ultraviolet absorber was removed, which prevented the formation of a naturally decaying gradient light intensity along the thickness direction. The cross-linking structure of the adhesive layer tended to be uniform, resulting in a significant reduction in the gradient modulus difference, as shown in the attached figure. Figure 4 The lack of a low-modulus buffer layer in the bottom layer hinders effective stress dispersion, leading to decreased optical performance, reduced light transmittance, and increased haze. Simultaneously, the uniform high-modulus structure results in slightly higher peel resistance and increased release force on the back surface. However, due to the absence of low-modulus regions, the adhesive layer cannot fully adhere to the glass substrate, significantly reducing adhesion. In folding tests, continuous creases appeared during room-temperature bending, cracks appeared at low temperatures, and interface stability decreased significantly during high-temperature bending. These results indicate that the lack of a thickness-direction crosslinking gradient structure weakens stress dispersion capabilities and reduces the flexibility and durability of the adhesive layer.

[0103] (3) Comparative Example 2 uses an irreversible conventional crosslinking agent instead of a dynamic crosslinking agent. Due to the lack of dynamic reversible crosslinking bonds, the self-healing efficiency of the adhesive layer is extremely low, as shown in the attached figure. Figure 4 The inability of polymer chains to undergo in-situ recombination and exchange reactions resulted in limited adhesion to the backlight surface, a significant decrease in adhesive strength, and a slightly higher release force than in the previous example. In the folding test, noticeable cracks appeared after cyclic bending at room temperature, with further damage at low temperatures. Interfacial stability also decreased significantly under high-temperature conditions, further illustrating the crucial role of the dynamic crosslinking system in maintaining flexible adhesion and resistance to stress concentration.

[0104] In summary, the OCA full-lamination optical adhesive provided by this invention, through a single-sided ultraviolet gradient curing process, constructs a gradient network structure with continuously decreasing crosslinking density in situ along the adhesive layer thickness direction, and introduces active dynamic covalent bonds. This structure maintains optical transparency and substrate adhesion while achieving self-healing capabilities and excellent resistance to folding and breakage, thus ensuring the reliability of flexible display modules.

Claims

1. An OCA full-lamination optical adhesive, characterized in that, It is made from the following raw materials in parts by weight: 50-80 parts soft monomer, 10-30 parts hard monomer, 1.0-6.0 parts functional monomer, 5.0-12 parts dynamic crosslinking agent, 0.5-3.0 parts photoinitiator, 0.05-0.5 parts ultraviolet absorber, and 0.1-1.0 parts silane coupling agent; wherein the dynamic crosslinking agent is an acrylate functional monomer containing a disulfide bond structure; the acrylate functional monomer with the disulfide bond structure is bis-2-methacryloyloxyethyl disulfide or bis-2-acryloyloxyethyl disulfide; the soft monomer is any one or a combination of 2-ethylhexyl acrylate or lauryl acrylate; the hard monomer is any one or a combination of isobornyl acrylate or acryloylmorpholine; the functional monomer is any one or a combination of 4-hydroxybutyl acrylate, hydroxyethyl acrylate, or hydroxypropyl acrylate; and the silane coupling agent is 3-methacryloyloxypropyltriethoxysilane or 3-acryloyloxypropyltrimethoxysilane. The preparation method of the OCA full-lamination optical adhesive includes the following steps: S1: Mix the soft monomer, the hard monomer, the functional monomer and the dynamic crosslinking agent, then add the photoinitiator, the ultraviolet absorber and the silane coupling agent, stir and mix and perform degassing treatment to obtain a prepolymer solution; S2: The prepolymer adhesive obtained in step S1 is continuously extruded and coated on the release surface of the first heavy release film, and the absolute dry adhesive layer thickness is controlled to obtain a smooth adhesive film. S3: The film obtained in step S2 is placed into an ultraviolet exposure tunnel. An ultraviolet light source with a center wavelength of 365nm is placed above the unshielded side of the coating for initiation irradiation. In-situ gradient photocuring is completed using a low-intensity long exposure mode. The control parameters for the low-intensity long exposure mode are: the surface light intensity is set to 10-50mW / cm². 2 The conveying rate is adjusted to keep the film in the exposure tunnel for 100-200 seconds, controlling the total cumulative irradiation energy to be 2000-5000 mJ / cm². 2 ; S4: Lay a second light release film onto the light-receiving surface of the cured adhesive film, roll it up, and place it in a darkroom to complete static heating and curing.

2. The OCA full-lamination optical adhesive as described in claim 1, characterized in that, The ultraviolet absorber is a benzotriazole ultraviolet absorber or a hydroxyphenyltriazine ultraviolet absorber.

3. The OCA full-lamination optical adhesive as described in claim 1, characterized in that, The ultraviolet absorber is specifically Tinuvin 234 or Tinuvin 400.

4. The OCA full-lamination optical adhesive as described in claim 1, characterized in that, The stirring and mixing conditions described in step S1 are as follows: the rotation speed is controlled at 300-500 rpm, the system temperature is maintained at 20-30℃, and during the stirring process, the overall moisture content of the system is controlled to be below 500 ppm by purging with high-purity nitrogen.

5. The OCA full-lamination optical adhesive as described in claim 1, characterized in that, The degassing treatment conditions in step S1 are: under negative pressure of -0.09MPa and continuous static evacuation for 30 minutes.

6. The OCA full-lamination optical adhesive as described in claim 1, characterized in that, In step S2, the first release film is a transparent polyethylene terephthalate film with a thickness of 75 μm and a preset release force of 20-30 gf / 25 mm; the absolute dry adhesive layer thickness is controlled at 180 μm with an error range of ±2 μm.

7. The OCA full-lamination optical adhesive as described in claim 1, characterized in that, In step S4, the second light release film is a light release polyethylene terephthalate film with a thickness of 50 μm and a preset release force of 3-5 gf / 25 mm.

8. The OCA full-lamination optical adhesive as described in claim 1, characterized in that, In step S4, the static heating and curing temperature is kept constant at 40-50℃ and the curing time is 24-48 hours.

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