Low shrinkage OCA optical adhesive and preparation method thereof

Abstract

This application relates to the field of optical adhesive technology, and discloses a low-shrinkage OCA optical adhesive and its preparation method. The low-shrinkage OCA optical adhesive is made from the following raw materials in the indicated mass percentages: 30.0%–40.0% polycarbonate-type aliphatic polyurethane acrylate prepolymer; 42.0%–50.0% 2-ethylhexyl acrylate; 13.0%–15.0% 4-hydroxybutyl acrylate; 2.0%–4.5% pentaerythritol tetra(3-mercaptopropionate); 0.5%–1.5% trimethylolpropane diallyl ether; and 0.5%–1.0% 2,4,6-trimethylbenzoyl-diphenylphosphine oxide. This invention employs a polyurethane acrylate formulation system containing multifunctional thiols and allyl ethers, achieving the technical effect of delayed photocuring gel point and dissipation of shrinkage deformation.

Description

Technical Field

[0001] This invention relates to the field of optical adhesives, specifically to a low-shrinkage OCA optical adhesive and its preparation method. Background Technology

[0002] Smartphones, in-vehicle infotainment screens, and various wearable electronic devices are now ubiquitous in daily life. These devices require seamless bonding between their touch layers, display panels, and cover glass. High-quality bonding is fundamental to ensuring screen clarity and touch accuracy. OCA optical adhesive, a special adhesive material with extremely high light transmittance, is the core medium for achieving physical connections between the various structural layers within the display module.

[0003] Currently, UV-curable pure acrylate OCA optical adhesives are widely used on electronic manufacturing production lines. A key advantage of this technology is its extremely high processing efficiency. After the liquid adhesive is applied, it only needs to pass through the irradiation area of ​​a high-power UV lamp to solidify. The monomers and resins in the formulation complete free radical cross-linking within seconds, rapidly establishing the initial peel force required for subsequent assembly. This production process completely eliminates traditional volatile solvents, avoids the time-consuming baking stage, and significantly reduces the floor space required for the production line.

[0004] While enjoying the advantage of rapid crosslinking, pure acrylate systems face unavoidable physical morphological abrupt changes. After initiation, the carbon-carbon double bonds in the monomers open and transform into covalent bonds, forcibly shortening the original van der Waals force distance between molecules to the chemical bond distance. This microscopic spatial reduction directly manifests as volume shrinkage of the adhesive layer on a macroscopic scale. High-intensity ultraviolet irradiation drives the polymerization rate to extremely high levels, causing the system to cross the gel point in a very short time. The molecular chain segments within the adhesive layer have no time to compensate for the free volume loss through conformational rearrangement; the rigid three-dimensional network is completely frozen. The deformation caused by shrinkage is forcibly locked within the crosslinked network and transformed into internal stress. These residual stresses continue to pull on the substrate after panel bonding, easily causing warping, peeling, or localized light leakage in flexible screens. Existing single-stage high-intensity instant curing processes physically deprive the polymer network of the time window for stress relaxation. If attempts are made to reduce shrinkage by simply increasing the molecular weight of conventional base resins to dilute the double bond concentration, the viscosity of the adhesive will increase exponentially. The material is difficult to disperse during mixing and coating. Under high viscosity, it is very easy to trap microbubbles that are difficult to remove, which ultimately seriously damages the light transmission uniformity of the optical adhesive. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a low-shrinkage OCA optical adhesive and its preparation method. This addresses the problem that existing OCA optical adhesives form crosslinked networks too quickly during rapid photocuring, leading to significant volume shrinkage and difficulty in releasing internal residual stress. Consequently, when applied to display panel bonding, this can easily cause screen warping, delamination, and light leakage.

[0006] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a low-shrinkage OCA optical adhesive, employing the following technical solution: A low-shrinkage OCA optical adhesive is made from the following raw materials in weight percentages: 30.0%–40.0% polycarbonate-type aliphatic polyurethane acrylate prepolymer; 42.0%–50.0% 2-ethylhexyl acrylate; 13.0%–15.0% 4-hydroxybutyl acrylate; 2.0%–4.5% pentaerythritol tetra(3-mercaptopropionate); 0.5%–1.5% trimethylolpropane diallyl ether; and 0.5%–1.0% 2,4,6-trimethylbenzoyl-diphenylphosphine oxide.

[0007] By adopting the above technical solution, and by using a specific ratio of polycarbonate-type aliphatic polyurethane acrylate prepolymer combined with acrylate monomers, multifunctional thiols, and allyl ethers to form a photocuring system, the effects of reducing the curing volume shrinkage of the optical adhesive and relieving internal stress in the adhesive layer are achieved. The specific reaction and mechanism of action are as follows: Under ultraviolet light irradiation, the photoinitiator absorbs light energy and decomposes to generate primary free radicals, which then initiate chain growth reactions in the free monomers and prepolymers within the system. At this time, the coexisting acrylate double bonds, thiol mercapto groups, and allyl double bonds in the system all participate in the polymerization process. Because trimethylolpropane diallyl ether readily undergoes degenerative chain transfer during free radical reactions, the proliferating free radicals abstract α-hydrogen atoms from the allyl groups, generating resonantly stable allyl free radicals. These low-activity allyl free radicals slow down the overall polymerization rate and block the rapid formation of localized high-density cross-linked networks. Simultaneously, pentaerythritol tetrakis (3-mercaptopropionate) undergoes a thiol-ene click reaction with the acrylates in the system, exhibiting stepwise polymerization kinetics. Furthermore, the multifunctional thiol can donate hydrogen atoms to the aforementioned stable allyl free radicals, undergoing a hydrogen transfer reaction and converting them back into active mercapto free radicals to resume chain growth.

[0008] Based on the aforementioned synergistic chemical interaction between thiols and allyl ethers, a chemical time window is effectively constructed in the polymerization system to delay the formation of the crosslinked network. Before reaching the gel point, the prepolymer and monomer molecular chains, still in a liquid or highly elastic state, can compensate for the free volume loss caused by chemical bond formation through physical slippage and conformational adjustment. Macroscopically, this dissipates the deformation caused by polymerization shrinkage into the flowing state, avoiding the continuous accumulation of internal stress after the structure freezes. Furthermore, the flexible thioether bonds introduced by the multifunctional thiols also improve the flexibility of the crosslinked network, which is beneficial for absorbing residual stress.

[0009] Preferably, the raw materials are expressed in the following mass percentages: 35.0% polycarbonate-type aliphatic polyurethane acrylate prepolymer, 45.0% 2-ethylhexyl acrylate, 14.0% 4-hydroxybutyl acrylate, 4.0% pentaerythritol tetra(3-mercaptopropionate), 1.0% trimethylolpropane diallyl ether, and 1.0% 2,4,6-trimethylbenzoyl-diphenylphosphine oxide.

[0010] By adopting the above technical solution, the reaction rate and network crosslinking density among the raw materials reach a balanced state. The multifunctional thiols and allyl ethers in this ratio provide good delayed gel performance, avoiding shrinkage stress caused by excessively rapid crosslinking network establishment, and also preventing the decrease in adhesive modulus caused by excessive monomer residue, so that the cured optical adhesive has both suitable peel strength and cohesive strength.

[0011] Preferably, the weight-average molecular weight of the polycarbonate-type aliphatic polyurethane acrylate prepolymer is 20,500 to 29,600.

[0012] By adopting the above technical solution and setting the weight-average molecular weight range of the prepolymer, the concentration of reactive double bonds per unit volume is reduced. During the polymerization reaction, since the long chain of the prepolymer itself occupies a fixed space volume, this reduces the volume shrinkage space caused by the polymerization of free small molecule monomers into a large molecular network from the source of the formulation, thereby reducing the theoretical volume shrinkage limit from a physical space perspective.

[0013] Preferably, the polycarbonate-type aliphatic polyurethane acrylate prepolymer is prepared by a method comprising the following steps: reacting a hydroxyl-terminated polycarbonate diol with isophorone diisocyanate at 75–80°C for 2.5–3.5 hours under the catalysis of dibutyltin dilaurate; using di-n-butylamine titration to detect the reaction system, when the isocyanate mass fraction in the reaction system drops to 0.22%–0.66%, cooling the reaction system to 60–65°C and adding 2,6-di-tert-butyl-p-cresol, followed by the dropwise addition of hydroxyethyl acrylate; after the dropwise addition is complete, maintaining the reaction at 65–70°C until the infrared spectrum reaches 2270 cm⁻¹. -1The isocyanate characteristic absorption peak at the point completely disappeared, thus obtaining the polycarbonate-type aliphatic polyurethane acrylate prepolymer.

[0014] By employing the above-mentioned technical solution, a polyurethane prepolymer with a well-defined structure was prepared using a two-step synthesis method. In the first step, the residual mass fraction of isocyanate is controlled during polymerization, limiting the degree of polymerization and molecular weight distribution of the prepolymer backbone. In the second step, hydroxyethyl acrylate is used for end-capping, grafting acrylate double bonds that can participate in photocuring crosslinking onto the backbone ends. Polycarbonate diol is used as the soft segment to provide light transmittance and UV aging resistance to the backbone, while the hard segment composed of isophorone diisocyanate enhances the cohesive energy of the system, ensuring that the final optical adhesive meets the optical requirements for long-term use of display devices.

[0015] Secondly, the present invention provides a method for preparing low-shrinkage OCA optical adhesive, which adopts the following technical solution: A method for preparing a low-shrinkage OCA optical adhesive includes the following steps: S1. Weigh the raw materials according to the mass percentage corresponding to the low shrinkage rate OCA optical adhesive; add 2-ethylhexyl acrylate and 4-hydroxybutyl acrylate to a mixing tank in sequence, add 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and stir until completely dissolved; then add polycarbonate-type aliphatic polyurethane acrylate prepolymer and continue mixing; then add pentaerythritol tetra(3-mercaptopropionate) and trimethylolpropane diallyl ether and mix to obtain a mixture; pump the mixture into a vacuum degassing tank for treatment to obtain the original adhesive solution; S2. Under tension control, the original adhesive liquid is coated onto the heavy release PET substrate. Immediately after coating, a light release PET film is laminated onto the surface of the liquid adhesive layer to form a closed sandwich structure. S3. Introduce the sandwich structure into the first curing zone, and place the sandwich structure tightly against and around the heated drum with constant surface temperature. During the synchronous rotation of the sandwich structure with the heated drum, pre-curing irradiation is performed by a cold light source through the side of the light release PET film. S4. The sandwich structure after leaving the first curing zone is introduced into the second curing zone. The sandwich structure is placed close to and around the cooling drum with constant surface temperature. The sandwich structure first passes through a physically shielded, radiation-free dark zone at the starting position of contact with the cooling drum. After passing through the radiation-free dark zone, the sandwich structure immediately enters the full-band irradiation zone for main curing irradiation. S5. After being removed from the cooling drum, the sandwich structure is treated by an electrostatic elimination device and then wound up under constant tension to obtain low-shrinkage OCA optical adhesive.

[0016] By employing the above technical solution and a curing process combining photothermal synergy and multi-segment spatial isolation, the chemical cross-linking shrinkage and physical thermal expansion and contraction of the optical adhesive are decoupled over time, eliminating internal stress during curing. The specific mechanism is as follows: When the sandwich structure enters the first curing zone and comes into close contact with the heated drum, the system is in a high-temperature environment. As the temperature rises, the movement of molecular chain segments within the system intensifies and the free volume increases, resulting in physical thermal expansion. This macroscopic thermal expansion offsets the chemical shrinkage caused by the initial free radical polymerization. The high-temperature environment also provides the thermodynamic energy required to overcome the activation energy of the hydrogen abstraction reaction, prompting the multifunctional thiols and allyl ethers in the prepolymer system to undergo sufficient chain transfer reactions to delay the gel point. Meanwhile, the low-intensity initiation conditions provided by the cold light source suppress the polymerization reaction to a low-conversion linear polymerization or branching growth stage, maintaining the rheological properties and high ductility of the system.

[0017] Next, the membrane strip detaches from the heating zone and enters the radiation-free dark zone of the second curing zone. In this stage of physical shading and constant surface cooling, the cessation of ultraviolet radiation forcibly interrupts the chain initiation process, and the previously accumulated physical thermal expansion rapidly transforms into thermophysical contraction due to the sudden temperature drop. Since the polymer network is still in an incompletely cross-linked state at this time, the prepolymer and monomer molecular chains retain sufficient degrees of freedom. The molecular chain segments can directly absorb and release the contraction deformation caused by the temperature gradient through the physical collapse and orientation rearrangement of their spatial conformation, avoiding the internal stress generated by the forced contraction after the rigid network is formed. After this crucial stress relaxation, the membrane strip passes through the dark zone and enters the high-intensity full-band irradiation zone. The instantaneously excited large number of free radicals rapidly increase the conversion rate of the remaining carbon-carbon double bonds, thereby quickly locking the three-dimensional cross-linked network structure after the residual stress has been eliminated, completing the final shaping.

[0018] Preferably, in step S1, the mixing speed after adding the polycarbonate-type aliphatic polyurethane acrylate prepolymer is set to 300-400 rpm, and the continuous mixing time is set to 40-60 minutes; the vacuum degree of the vacuum degassing tank is controlled at -0.09 to -0.095 MPa, and the processing time is controlled at 45-60 minutes.

[0019] By employing the above technical solution, the limited rotation speed and time ensure uniform dispersion of the high-viscosity resin prepolymer and the low-viscosity diluted monomer within the system. Controlling the set vacuum level and negative pressure treatment time effectively removes microbubbles entrained in the high-viscosity mixture during stirring, preventing thermal expansion of these microbubbles during subsequent heating and curing stages. This physically eliminates structural defects that cause light scattering in the optical adhesive layer and localized stress concentration.

[0020] Preferably, in step S2, the tension during the application of the original adhesive solution is controlled to be 50-100 N / m, and the wet film thickness is controlled to be 50-250 μm.

[0021] By employing the above technical solution, specific tension parameters maintain the flatness of the flexible PET substrate during coating processing, preventing excessive stretching and deformation of the substrate that could transmit additional mechanical tensile stress to the adhesive layer. The set wet film thickness boundary, combined with the transmitted light intensity of the curing process, maintains a consistent ultraviolet absorbance gradient in the thickness direction of the adhesive layer, helping to maintain synchronized curing rates on the upper and lower surfaces.

[0022] Preferably, in step S3, the surface temperature of the heated drum is controlled at 65–75°C, and the drum wrap angle is set to 185–200 degrees; the cold light source is an LED cold light source with a wavelength of 395 nm, and the irradiance is set to 30–50 mW / cm². 2 The cumulative ultraviolet energy is controlled at 200–300 mJ / cm. 2 .

[0023] By adopting the above technical solution, the temperature boundary of 65 to 75°C satisfies the activation energy conditions required to initiate the degradation chain transfer reaction, while the wrap angle of 185 to 200 degrees is adapted to the drum running speed, limiting the heating and reaction time of the first stage of pre-curing. Under this condition, the 395nm wavelength monochromatic LED cold light source has strong penetrating power. Combined with low irradiance and the set cumulative energy, it promotes photons to penetrate evenly into the depths of the liquid adhesive layer, inducing low-rate primary chain growth of deep monomers, and avoiding the rapid film formation on the surface from blocking the photochemical reaction of the underlying layer.

[0024] Preferably, in step S4, the surface temperature of the cooling drum is controlled at 15–20°C; the time the sandwich structure remains in the non-irradiated dark area is controlled to be 0.5–1.0 seconds; the full-band irradiation area is irradiated with a full-band high-pressure mercury lamp, and the irradiance is set to 500–600 mW / cm². 2 The cumulative energy is controlled at 1200–1500 mJ / cm². 2 .

[0025] By employing the above technical solution, the cooling temperature limit of 15 to 20°C forces the colloid volume to rapidly shrink physically. A dark zone residence time of 0.5 to 1.0 seconds constitutes a structural relaxation time window; too short a residence time prevents the polymer chain segments from completing their physical arrangement, while too long a time may cause bimolecular termination of free radicals, reducing the final degree of curing. The subsequent use of a full-band high-pressure mercury lamp provides high-intensity, broad-spectrum radiation. Its short-wavelength ultraviolet light promotes rapid densification of the adhesive surface to improve apparent peel strength, while its long-wavelength ultraviolet light promotes the completion of internal cross-linking reactions. The high irradiance and high energy settings ensure that the optical adhesive reaches a stable state and no longer undergoes subsequent deformation.

[0026] This invention provides a low-shrinkage OCA optical adhesive and its preparation method. It has the following beneficial effects: 1. This invention employs a polyurethane acrylate formulation system containing multifunctional thiols and allyl ethers, achieving the technical effect of delayed photocuring gel point and dissipation of shrinkage deformation. Compared to the traditional approach in existing technologies that relies solely on the rapid free radical polymerization of acrylate monomers, this invention solves the shortcomings of excessively rapid rigid molding of the crosslinked network leading to severe volume shrinkage of the adhesive layer and difficulty in releasing internal residual stress.

[0027] 2. This invention designs a primary-secondary segmented curing process that combines heating pre-curing with cooling in a radiation-free dark zone, effectively decoupling the chemical cross-linking shrinkage and physical thermal deformation of the colloid over time. Existing technologies typically employ a single, continuous high-intensity ultraviolet light irradiation scheme. In contrast, this invention overcomes the defect of conventional photocuring processes that permanently lock stress within the adhesive layer during instantaneous freezing of the structure.

[0028] 3. This invention synthesizes aliphatic polycarbonate prepolymers with a specific weight-average molecular weight range as the core, achieving the technical effects of reducing the concentration of reactive double bonds per unit volume and improving weather resistance. Compared with existing technologies that use a large number of low molecular weight reactive monomers or conventional polyether resins, this invention solves the shortcomings of the shrinkage rate being unable to break through the physical lower limit due to the excessively high density of double bonds in the bottom layer, and the tendency for the panel to yellow and age after long-term use. Attached Figure Description

[0029] Figure 1 The following are test graphs showing the photorheological dynamics and gel point evolution at different temperatures in the test examples of the present invention. Among them, (a) is the evolution curve of storage modulus and loss modulus of Example 1 with light exposure time, and (b) is the change of double bond conversion rate of Example 1 with light exposure time. Figure 2 The thermomechanical stress response test curve under a step temperature field is a test example of the present invention. Figure 3 This is a distribution diagram showing the relationship between the film volume shrinkage rate and macroscopic residual internal stress in the test examples of this invention; Figure 4 The following are test diagrams of the reliability and optical distribution of the fully laminated display module under the test example of the present invention. Among them, (a) is a line comparison of the appearance bubble and peeling defect rate under two extreme aging conditions of high temperature and high humidity and cold and heat shock, and (b) is a bar chart comparison of the brightness uniformity distribution of multiple points on the screen after aging. Figure 5The test distribution diagrams of the optical and mechanical properties of the tape and the thermomechanical dimensional stability of the auxiliary materials in the test examples of the present invention are shown. Among them, (a) is the evolution curve of the light transmittance of the defoamed adhesive film and the 180° peel force multidimensional data, and (b) is the discrete distribution diagram of the absolute dimensional change rate of the PET substrate film in the longitudinal direction of mechanical processing. Detailed Implementation

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher products. The isophorone diisocyanate, dibutyltin dilaurate, hydroxyethyl acrylate, 2,6-di-tert-butyl-p-cresol, and the photoinitiator 2,4,6-trimethylbenzoyl-diphenylphosphine oxide involved in the synthesis and formulation of the prepolymer in this invention are all common commercially available chemical substances in the art, and their chemical structures and properties are well-defined and will not be described further here.

[0032] Polycarbonate diol is a homopolymer obtained by polycondensation reaction of 1,6-hexanediol and dimethyl carbonate. It has hydroxyl groups at the end, a number average molecular weight of 2000, a molecular weight distribution index of 1.5 to 1.8, and a hydroxyl value of 54 to 58 mg KOH / g.

[0033] 2-Ethylhexyl acrylate, a commercially available common monomer, CAS number 103-11-7.

[0034] 4-Hydroxybutylacrylate, a commercially available common monomer, CAS number 2478-10-6.

[0035] Pentaerythritol tetra(3-mercaptopropionate), a commercially available polyfunctional thiol, CAS number 7575-23-7.

[0036] Trimethylolpropane diallyl ether, a commercially available common allyl ether, has a double bond equivalent of 107 g / mol and CAS number 682-09-7.

[0037] Heavy-release PET substrate, commercially available polyethylene terephthalate film with a surface coated with fluorosilicate release agent, with a thickness of 75μm and a surface peel strength ranging from 20g / 25mm to 30g / 25mm.

[0038] Light release PET film, commercially available conventional polyethylene terephthalate film with silicone oil release agent coated on the surface, with a thickness of 50μm, light transmittance greater than 92%, and surface peel strength ranging from 3g / 25mm to 5g / 25mm.

[0039] Preparation Example 1: This preparation example provides a method for preparing an aliphatic polyurethane acrylate prepolymer with a weight-average molecular weight of 24,800, including the following steps: 400.0 g of polycarbonate diol and 49.8 g of isophorone diisocyanate were added to a four-necked flask equipped with a mechanical stirrer, thermometer, and condenser. 0.23 g of dibutyltin dilaurate was added as a catalyst. Under nitrogen protection, the mixture was heated to 75 °C and reacted for 3 hours. The isocyanate mass fraction in the system was determined by di-n-butylamine titration to be 0.44%. The system temperature was then lowered to 60 °C, and 0.23 g of 2,6-di-tert-butyl-p-cresol was added as a polymerization inhibitor, followed by the slow dropwise addition of 5.85 g of hydroxyethyl acrylate. After the addition was complete, the reaction was maintained at 65 °C for 2 hours until the infrared spectrum reached 2270 cm⁻¹. -1 The isocyanate characteristic absorption peak completely disappeared, and the material was discharged and cooled to obtain a polycarbonate-type aliphatic polyurethane acrylate prepolymer with a weight average molecular weight of 24,800.

[0040] Preparation Example 2: This preparation example provides a method for preparing an aliphatic polyurethane acrylate prepolymer with a weight-average molecular weight of 20,500, including the following steps: 400.0 g of polycarbonate diol and 52.5 g of isophorone diisocyanate were added to a four-necked flask equipped with a mechanical stirrer, thermometer, and condenser. 0.23 g of dibutyltin dilaurate was added as a catalyst. Under nitrogen protection, the mixture was heated to 75 °C and reacted for 2.5 hours. The isocyanate mass fraction in the system was determined by di-n-butylamine titration to be 0.66%. The system temperature was then lowered to 60 °C, and 0.23 g of 2,6-di-tert-butyl-p-cresol was added as a polymerization inhibitor, followed by the slow dropwise addition of 8.80 g of hydroxyethyl acrylate. After the addition was complete, the reaction was maintained at 65 °C for 2 hours until the infrared spectrum reached 2270 cm⁻¹. -1 The isocyanate characteristic absorption peak completely disappeared, and the material was discharged and cooled to obtain a polycarbonate-type aliphatic polyurethane acrylate prepolymer with a weight average molecular weight of 20,500.

[0041] Preparation Example 3: This preparation example provides a method for preparing an aliphatic polyurethane acrylate prepolymer with a weight-average molecular weight of 29,600, including the following steps: 400.0 g of polycarbonate diol and 47.1 g of isophorone diisocyanate were added to a four-necked flask equipped with a mechanical stirrer, thermometer, and condenser. 0.23 g of dibutyltin dilaurate was added as a catalyst. Under nitrogen protection, the mixture was heated to 80 °C and reacted for 3.5 hours. The isocyanate mass fraction in the system was determined by di-n-butylamine titration to be 0.22%. The system temperature was then lowered to 65 °C, and 0.23 g of 2,6-di-tert-butyl-p-cresol was added as a polymerization inhibitor, followed by the slow dropwise addition of 2.90 g of hydroxyethyl acrylate. After the addition was complete, the reaction was maintained at 70 °C for 2.5 hours until the infrared spectrum reached 2270 cm⁻¹. -1 The isocyanate characteristic absorption peak completely disappeared, and the material was discharged and cooled to obtain a polycarbonate-type aliphatic polyurethane acrylate prepolymer with a weight average molecular weight of 29,600.

[0042] Example 1: This embodiment provides a low-shrinkage OCA optical adhesive and its preparation method, including the following steps: S1. Weigh out 35.0% by mass of the polycarbonate-type aliphatic polyurethane acrylate prepolymer obtained in Preparation Example 1, 45.0% of 2-ethylhexyl acrylate, 14.0% of 4-hydroxybutyl acrylate, 4.0% of pentaerythritol tetra(3-mercaptopropionate), 1.0% of trimethylolpropane diallyl ether, and 1.0% of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide. In a jacketed stainless steel stirred tank at 25°C, add 2-ethylhexyl acrylate and 4-hydroxybutyl acrylate sequentially, and start stirring to 150 rpm. Add 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and stir until completely dissolved. Increase the stirring speed to 350 rpm, add the above-mentioned polycarbonate-type aliphatic polyurethane acrylate prepolymer, and continue mixing for 50 minutes. Reduce the stirring speed to 100 rpm, add pentaerythritol tetra(3-mercaptopropionate) and trimethylolpropane diallyl ether, and mix for 20 minutes. The mixture is pumped into a vacuum degassing tank and treated at a vacuum of -0.095 MPa for 45 minutes to obtain the raw adhesive solution.

[0043] S2. The degassed raw adhesive solution is pumped to a slot coating die head via a precision gear pump. Under a tension of 75 N / m, the raw adhesive solution is coated onto a heavy release PET substrate with a thickness of 75 μm, and the wet film thickness is controlled at 150 μm. Immediately after coating, a light release PET film with a thickness of 50 μm is laminated onto the surface of the liquid adhesive layer without air bubbles using a rubber bonding roller to form a closed sandwich structure.

[0044] S3. Introduce the sandwich-structured film strip into the first curing zone, ensuring it adheres tightly to and wraps around a heated rotating drum with a surface temperature maintained at 70°C. The drum's wrap angle is set to 190 degrees. During the synchronous rotation of the film strip with the drum, a 395nm wavelength LED cold light source is used to irradiate the lightly released PET side, with an irradiance set to 40mW / cm². 2 The cumulative ultraviolet energy was controlled at 250 mJ / cm. 2 .

[0045] S4: After detaching from the heating drum, the membrane tape moves horizontally to the second curing zone, closely adhering to and wrapping around the cooling drum, whose surface temperature is maintained at 18°C. A physically shielded, radiation-free dark zone is set at the initial position where the membrane tape contacts the cooling drum, and the time the membrane tape spends in this dark zone is controlled to be 0.8 seconds. Immediately after passing through the dark zone, the membrane tape enters the full-band high-pressure mercury lamp irradiation zone, receiving an irradiance of 550 mW / cm². 2 High-intensity irradiation, with cumulative energy controlled at 1350 mJ / cm². 2 .

[0046] S5: After the sandwich-structured double-sided tape is removed from the cooling drum, it is passed through an electrostatic elimination device and then wound up with a constant tension of 65 N / m to obtain low-shrinkage OCA optical adhesive.

[0047] Example 2: This embodiment provides a low-shrinkage OCA optical adhesive and its preparation method, including the following steps: S1. Weigh out 30.0% by mass of the polycarbonate-type aliphatic polyurethane acrylate prepolymer obtained in Preparation Example 2, 50.0% of 2-ethylhexyl acrylate, 13.0% of 4-hydroxybutyl acrylate, 4.5% of pentaerythritol tetra(3-mercaptopropionate), 1.5% of trimethylolpropane diallyl ether, and 1.0% of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide. In a jacketed stainless steel stirred tank at 20°C, add 2-ethylhexyl acrylate and 4-hydroxybutyl acrylate sequentially, and start stirring to 150 rpm. Add 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and stir until completely dissolved. Increase the stirring speed to 300 rpm, add the above-mentioned polycarbonate-type aliphatic polyurethane acrylate prepolymer, and continue mixing for 60 minutes. Reduce the stirring speed to 100 rpm, add pentaerythritol tetra(3-mercaptopropionate) and trimethylolpropane diallyl ether, and mix for 20 minutes. The mixture is pumped into a vacuum degassing tank and treated at a vacuum of -0.09 MPa for 60 minutes to obtain the raw adhesive solution.

[0048] S2. The degassed raw adhesive solution is pumped to a slot coating die head via a precision gear pump. Under a tension of 50 N / m, the raw adhesive solution is coated onto a heavy release PET substrate with a thickness of 75 μm, and the wet film thickness is controlled at 50 μm. Immediately after coating, a light release PET film with a thickness of 50 μm is laminated onto the surface of the liquid adhesive layer without air bubbles using a rubber bonding roller to form a closed sandwich structure.

[0049] S3. Introduce the sandwich-structured film strip into the first curing zone, ensuring it adheres tightly to and wraps around a heated rotating drum with a surface constant temperature of 65°C. The drum's wrap angle is set to 185 degrees. During the synchronous rotation of the film strip with the drum, a 395nm wavelength LED cold light source is used to irradiate the light release PET side, with an irradiance set to 30mW / cm². 2 The cumulative ultraviolet energy is controlled at 200 mJ / cm. 2 .

[0050] S4. After the membrane tape detaches from the heating drum, it is moved horizontally to the second curing zone, closely adhering to and winding around the cooling drum, whose surface temperature is maintained at 15°C. A physically shielded, radiation-free dark zone is set at the initial position where the membrane tape contacts the cooling drum, and the time the membrane tape stays in the radiation-free dark zone is controlled to be 0.5 seconds. After passing through the radiation-free dark zone, the membrane tape immediately enters the full-band high-pressure mercury lamp irradiation zone, where it receives an irradiance of 500 mW / cm². 2 High-intensity irradiation, with cumulative energy controlled at 1200 mJ / cm². 2 .

[0051] S5. After the sandwich-structured double-sided adhesive tape is removed from the cooling drum, it is passed through an electrostatic elimination device and then wound up with a constant tension of 50 N / m to obtain low-shrinkage OCA optical adhesive.

[0052] Example 3: This embodiment provides a low-shrinkage OCA optical adhesive and its preparation method, including the following steps: S1. Weigh out 40.0% by mass of the polycarbonate-type aliphatic polyurethane acrylate prepolymer obtained in Preparation Example 3, 42.0% of 2-ethylhexyl acrylate, 15.0% of 4-hydroxybutyl acrylate, 2.0% of pentaerythritol tetra(3-mercaptopropionate), 0.5% of trimethylolpropane diallyl ether, and 0.5% of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide. In a jacketed stainless steel stirred tank at 25°C, add 2-ethylhexyl acrylate and 4-hydroxybutyl acrylate sequentially, and start stirring to 200 rpm. Add 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and stir until completely dissolved. Increase the stirring speed to 400 rpm, add the above-mentioned polycarbonate-type aliphatic polyurethane acrylate prepolymer, and continue mixing for 40 minutes. Reduce the stirring speed to 100 rpm, add pentaerythritol tetra(3-mercaptopropionate) and trimethylolpropane diallyl ether, and mix for 20 minutes. The mixture was pumped into a vacuum degassing tank and treated at a vacuum of -0.092 MPa for 55 minutes to obtain the raw adhesive solution.

[0053] S2. The degassed raw adhesive solution is pumped to a slot coating die head via a precision gear pump. Under a tension of 100 N / m, the raw adhesive solution is coated onto a heavy release PET substrate with a thickness of 75 μm, and the wet film thickness is controlled at 250 μm. Immediately after coating, a light release PET film with a thickness of 50 μm is laminated onto the surface of the liquid adhesive layer without air bubbles using a rubber bonding roller to form a closed sandwich structure.

[0054] S3. Introduce the sandwich-structured film strip into the first curing zone, ensuring it adheres tightly to and wraps around a heated rotating drum with a surface constant temperature of 75°C. The drum's wrap angle is set to 200 degrees. During the synchronous rotation of the film strip with the drum, a 395nm wavelength LED cold light source is used to irradiate the light release PET side, with an irradiance set to 50mW / cm². 2 The cumulative ultraviolet energy is controlled at 300 mJ / cm. 2 .

[0055] S4. After the membrane tape detaches from the heating drum, it is moved horizontally to the second curing zone, closely adhering to and winding around the cooling drum, whose surface temperature is maintained at 20°C. A physically shielded, radiation-free dark zone is set at the initial position where the membrane tape contacts the cooling drum, and the time the membrane tape stays in the radiation-free dark zone is controlled to be 1.0 second. After passing through the radiation-free dark zone, the membrane tape immediately enters the full-band high-pressure mercury lamp irradiation zone, receiving an irradiance of 600 mW / cm². 2 High-intensity irradiation, with cumulative energy controlled at 1500 mJ / cm². 2 .

[0056] S5. After the sandwich-structured double-sided adhesive tape is removed from the cooling drum, it is passed through an electrostatic elimination device and then wound up with a constant tension of 80 N / m to obtain low-shrinkage OCA optical adhesive.

[0057] Example 4: This embodiment provides a low-shrinkage OCA optical adhesive and its preparation method, including the following steps: S1. Weigh out the following components by mass percentage: 38.0% of the polycarbonate-type aliphatic polyurethane acrylate prepolymer obtained in Preparation Example 1, 45.0% of 2-ethylhexyl acrylate, 13.0% of 4-hydroxybutyl acrylate, 2.5% of pentaerythritol tetra(3-mercaptopropionate), 0.8% of trimethylolpropane diallyl ether, and 0.7% of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide. In a jacketed stainless steel stirred tank at 22°C, add 2-ethylhexyl acrylate and 4-hydroxybutyl acrylate sequentially, and start stirring to 180 rpm. Add 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and stir until completely dissolved. Increase the stirring speed to 380 rpm, add the above-mentioned polycarbonate-type aliphatic polyurethane acrylate prepolymer, and continue mixing for 45 minutes. Reduce the stirring speed to 100 rpm, add pentaerythritol tetra(3-mercaptopropionate) and trimethylolpropane diallyl ether, and mix for 20 minutes. The mixture is pumped into a vacuum degassing tank and treated under a vacuum of -0.095 MPa for 50 minutes to obtain the raw adhesive solution.

[0058] S2. The degassed raw adhesive solution is pumped to a slot coating die head via a precision gear pump. Under a tension of 80 N / m, the raw adhesive solution is coated onto a heavy release PET substrate with a thickness of 75 μm, and the wet film thickness is controlled to be 100 μm. Immediately after coating, a light release PET film with a thickness of 50 μm is laminated onto the surface of the liquid adhesive layer without air bubbles using a rubber bonding roller to form a closed sandwich structure.

[0059] S3. Introduce the sandwich-structured film strip into the first curing zone, ensuring it adheres tightly to and wraps around a heated rotating drum with a surface constant temperature of 65°C. The drum's wrap angle is set to 190 degrees. During the synchronous rotation of the film strip with the drum, a 395nm wavelength LED cold light source is used to irradiate the lightly released PET side, with an irradiance set to 45mW / cm². 2 The cumulative ultraviolet energy was controlled at 280 mJ / cm. 2 .

[0060] S4. After the membrane tape detaches from the heating drum, it is moved horizontally to the second curing zone, closely adhering to and winding around the cooling drum, whose surface temperature is maintained at 18°C. A physically shielded, radiation-free dark zone is set at the initial position where the membrane tape contacts the cooling drum, and the time the membrane tape spends in the radiation-free dark zone is controlled to be 0.5 seconds. After passing through the radiation-free dark zone, the membrane tape immediately enters the full-band high-pressure mercury lamp irradiation zone, where it receives an irradiance of 550 mW / cm². 2 High-intensity irradiation, with cumulative energy controlled at 1300 mJ / cm². 2 .

[0061] S5. After the sandwich-structured double-sided tape is removed from the cooling drum, it is passed through an electrostatic elimination device and then wound up with a constant tension of 60 N / m to obtain low-shrinkage OCA optical adhesive.

[0062] Example 5: This embodiment provides a low-shrinkage OCA optical adhesive and its preparation method, including the following steps: S1. Weigh out the following components by mass percentage: 33.0% of the polycarbonate-type aliphatic polyurethane acrylate prepolymer obtained in Preparation Example 3, 48.0% of 2-ethylhexyl acrylate, 14.5% of 4-hydroxybutyl acrylate, 3.0% of pentaerythritol tetra(3-mercaptopropionate), 0.7% of trimethylolpropane diallyl ether, and 0.8% of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide. In a jacketed stainless steel stirred tank at 25°C, add 2-ethylhexyl acrylate and 4-hydroxybutyl acrylate sequentially, and start stirring at 160 rpm. Add 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and stir until completely dissolved. Increase the stirring speed to 320 rpm, add the above-mentioned polycarbonate-type aliphatic polyurethane acrylate prepolymer, and continue mixing for 55 minutes. Reduce the stirring speed to 100 rpm, add pentaerythritol tetra(3-mercaptopropionate) and trimethylolpropane diallyl ether, and mix for 20 minutes. The mixture is pumped into a vacuum degassing tank and treated at a vacuum of -0.094 MPa for 45 minutes to obtain the raw adhesive solution.

[0063] S2. The degassed raw adhesive solution is pumped to a slot coating die head via a precision gear pump. Under a tension of 60 N / m, the raw adhesive solution is coated onto a heavy release PET substrate with a thickness of 75 μm, and the wet film thickness is controlled at 200 μm. Immediately after coating, a light release PET film with a thickness of 50 μm is laminated onto the surface of the liquid adhesive layer without air bubbles using a rubber bonding roller to form a closed sandwich structure.

[0064] S3. Introduce the sandwich-structured film strip into the first curing zone, ensuring it adheres tightly to and wraps around a heated rotating drum with a surface constant temperature of 75°C. The drum's wrap angle is set to 195 degrees. During the synchronous rotation of the film strip with the drum, a 395nm wavelength LED cold light source is used to irradiate the light release PET side, with an irradiance set to 35mW / cm². 2 The cumulative ultraviolet energy was controlled at 220 mJ / cm. 2 .

[0065] S4. After the membrane tape detaches from the heating drum, it is moved horizontally to the second curing zone, closely adhering to and wrapping around the cooling drum, whose surface temperature is maintained at 16°C. A physically shielded, radiation-free dark zone is set at the initial position where the membrane tape contacts the cooling drum, and the time the membrane tape stays in the radiation-free dark zone is controlled to be 1.0 second. After passing through the radiation-free dark zone, the membrane tape immediately enters the full-band high-pressure mercury lamp irradiation zone, where it receives an irradiance of 580 mW / cm². 2 High-intensity irradiation, with cumulative energy controlled at 1450 mJ / cm². 2 .

[0066] S5. After the sandwich-structured double-sided adhesive tape is removed from the cooling drum, it is passed through an electrostatic elimination device and then wound up with a constant tension of 70 N / m to obtain low-shrinkage OCA optical adhesive.

[0067] Comparative Example 1: Compared to Example 1, the differences are as follows: Pentaerythritol tetra(3-mercaptopropionate) and trimethylolpropane diallyl ether are not added to the formulation; the missing mass percentages are added to 2-ethylhexyl acrylate. Furthermore, the dual-drum and temperature control sequence settings for the first and second curing zones are omitted; UV curing is performed directly at 25°C using a high-pressure mercury lamp in a single pass, with a cumulative energy of 1600 mJ / cm². 2 The rest are the same.

[0068] Comparative Example 2: Compared with Example 1, the difference is that the dual-drum setup for the first and second curing zones and the temperature control sequence are eliminated. Instead, full-spectrum ultraviolet curing is performed directly at room temperature (25°C) using a high-pressure mercury lamp in a single operation, with the cumulative energy controlled at 1600 mJ / cm². 2 The rest are the same.

[0069] Comparative Example 3: Compared with Example 1, the difference is that pentaerythritol tetra(3-mercaptopropionate) and trimethylolpropane diallyl ether are not added to the formulation, and the missing mass percentages are added to 2-ethylhexyl acrylate, while the rest are the same.

[0070] Comparative Example 4: The difference from Example 1 is that trimethylolpropane diallyl ether is not added to the formulation, and the missing mass percentage is added to 2-ethylhexyl acrylate, while the rest are the same.

[0071] Comparative Example 5: The difference from Example 1 is that pentaerythritol tetra(3-mercaptopropionate) is not added to the formulation, and the missing mass percentage is added to 2-ethylhexyl acrylate, while the rest are the same.

[0072] Comparative Example 6: Compared with Example 1, the difference is that in the second curing zone, the 0.8-second no-irradiation dark zone set at the starting position of the film belt contacting the cooling drum is cancelled, that is, the high-intensity high-pressure mercury lamp ultraviolet irradiation is carried out simultaneously at the moment the film belt moves to contact the cooling drum. All other aspects are the same.

[0073] Comparative Example 7: Compared with Example 1, the difference is that the heating drum of the first curing zone and the cooling drum of the second curing zone are cancelled, and a conventional suspended roller drying tunnel is used for transmission and temperature control. That is, the tension of the film belt cannot be physically isolated by the wrap angle friction of the drum. Everything else is the same.

[0074] Test Example 1: Test objective: To verify the effectiveness of delaying the gel point of the system under the synergistic effect of a specific temperature field and multifunctional thiols and allyl ethers.

[0075] Test steps: 1. The defoaming virgin solutions prepared in Example 1, Comparative Example 3 and Comparative Example 4 were selected as the experimental test objects.

[0076] 2. A rotational rheometer equipped with a UV curing accessory is used, and the system is coupled with an in-situ Fourier transform infrared spectrometer to simultaneously monitor the changes in double bond conversion rate and rheological modulus during the photocuring process.

[0077] 3. Place each original adhesive solution into the parallel plate testing system of the rheometer, set the plate gap to 0.2 mm, keep the testing frequency constant at 1 Hz, and strictly control the test strain within the 0.5% linear viscoelastic range.

[0078] 4. Set two discrete test ambient temperatures, 25℃ and 75℃ respectively. After the system has reached constant temperature equilibrium for 120 seconds, turn on the 395nm wavelength LED cold light source to provide constant irradiation through the quartz lower plate. The irradiation intensity is calibrated to 40mW / cm². 2 .

[0079] 5. Simultaneously record the storage modulus (G') and loss modulus (G'') data output by the rheometer over time, and extract the coordinate time corresponding to the intersection point (G'=G'') as the time when the macroscopic gel point of the system occurs.

[0080] 6. Continuous spectral acquisition was performed using an infrared spectrometer to track 810 cm⁻¹. -1 The area integral attenuation of the characteristic absorption peak is used to calculate and derive the absolute value of the double bond conversion rate at the time when each system reaches its respective gel point.

[0081] The test data is shown in Table 1.

[0082] Table 1: Photorheological dynamics and gel point conversion rate test data under different adhesive formulations and temperature conditions ; Conclusion: Based on Table 1 and Figure 1 The data shows that the synergistic effect of ambient temperature and formulation composition fundamentally alters the evolution nodes of the crosslinking network in the system. In Example 1, the gel point at room temperature (25°C) occurred at 4.12 seconds, corresponding to a low double bond conversion rate of 14.8%, reflecting the rapid loss of macroscopic fluidity and elastic network freezing of the solution at the initial stage. When a specific thermal field of 75°C was applied, the time to reach the gel point in Example 1 was significantly extended to 11.87 seconds, with the more significant characteristic being an increase in double bond conversion rate to 47.3%. This highly nonlinear response mode confirms that the polymerization system overcomes the high activation energy barrier of the hydrogen abstraction reaction of trimethylolpropane diallyl ether at high temperatures, activating the generated allyl radical pathway and creating a profound hindrance effect on the rapid chain growth initiated by thiols.

[0083] Parallel testing of the comparative groups, through reverse logic, ruled out the possibility that a single thermal field induced this phenomenon. Maintaining the same 75°C environment, the gel time of the adhesive in Comparative Example 3, lacking the key chemical barrier, was shortened to 3.25 seconds, similar to its room-temperature curing behavior. In Comparative Example 4, which contained thiols but excluded allyl ethers, the gel point was even earlier at 2.89 seconds. This result reveals that multifunctional thiols inherently possess the accelerating property of inducing rapid chain transfer. Based on the above data discrepancies, a specific high-temperature environment must rely on a polymerization-inhibiting antagonistic cycle constructed by the dual components in the formulation to suppress the conventional acrylate polymerization process and forcibly push back the three-dimensional closed nodes of the crosslinking network.

[0084] This microscopic kinetic intervention constructs a buffer channel for shrinkage stress at the practical physical level. Since nearly half of the double bond ring-opening reactions are completed within the window during which the material maintains its liquid-phase characteristics, the proportion of the system constrained by high elastic modulus is significantly reduced. Molecular chain segments in a pseudoplastic fluid state spontaneously fill the volume deficit caused by double bond polymerization through macroscopic physical collapse along the Z-axis, dissolving the shrinkage deformation accumulation before the material completely transforms into a cross-linked solid, thereby cutting off the source of residual stress within the module.

[0085] Test Example 2: Test objective: To verify the decoupling effect of the step cooling dark region in the separation process of thermophysical contraction and chemical cross-linking contraction.

[0086] Test steps: 1. The partially cross-linked semi-solid film strips obtained after the first stage of pre-curing in Example 1, immediately after being removed from the 70°C heating drum, were used as the test objects for the experimental group, and the film strips at the same position in Comparative Example 6 were used as the test objects for the control group.

[0087] 2. Using a dynamic thermomechanical analyzer equipped with a UV light source and liquid nitrogen cooling accessories, the film strip sample is fixed with a thin film stretching clamp, and a constant initial pretension of 0.05N is applied to maintain the flatness of the sample in the test chamber.

[0088] 3. Set the temperature of the analyzer sample chamber to 75°C and allow it to equilibrate for 3 minutes to establish baseline data for the high-temperature thermal expansion state, and simultaneously record the initial internal tensile stress of the probe axial direction.

[0089] 4. Execute a step control sequence for the experimental group, activating the liquid nitrogen rapid cooling module to rapidly drop the chamber temperature to 18°C. Maintain this temperature for 0.8 seconds while keeping the UV light source off. Then, activate the UV light source at 550mW / cm². 2 High-intensity radiation.

[0090] 5. For the control group, a synchronous coupling sequence was executed. At the instant the liquid nitrogen rapid cooling module was activated to cause the temperature to drop sharply to 18°C, a UV light source at 550mW / cm² was simultaneously activated. 2 High-intensity radiation.

[0091] 6. Throughout the experiment, the minute changes in the axial tensile stress of the sample were captured and recorded in real time at a sampling rate of 50Hz. Stress data at key nodes such as the initial baseline, the end of the dark area, the exposure peak, and the final cooling steady state were extracted.

[0092] The test data is shown in Table 2.

[0093] Table 2: Evolution data of internal residual stress under different control sequences in a step temperature field ; Conclusion: Based on Table 2 and Figure 2 The data shows that the temporal differences in the experimental control sequence led to drastically different evolutionary paths in the residual stress accumulation within the system. In Example 1, after a 0.8-second no-irradiation cooling dark zone, the axial tensile stress dropped from an initial 0.051 MPa to 0.018 MPa, indicating that the polymer network possesses local segment mobility to respond to external temperature gradients before complete crosslinking. In the subsequent UV exposure stage, the tensile stress in Example 1 only showed a mild increase and a low peak of 0.142 MPa; conversely, in Comparative Example 6, when high-intensity UV radiation was applied instantaneously from 75°C to 18°C, the system stress rapidly increased to a peak of 0.493 MPa, verifying that when volumetric thermophysical contraction and photo-induced chemical crosslinking contraction interfere in the same temporal dimension, the instantaneous three-dimensional formation of the crosslinked network directly locks the molecular skeleton in a conformationally confined state.

[0094] The volume shrinkage of the polymer matrix does not necessarily translate into residual internal stress on the macroscopic surface of the material. The cooling dark zone process boundary blocks the overlapping time window of the photoinitiator free radical burst and the thermal expansion and contraction effect of the material, allowing the partially pre-cured semi-solid film to dissipate the physical deformation potential energy accumulated due to the sudden temperature change through spontaneous rearrangement of the molecular chain before completely losing its macroscopic rheological capabilities. The delayed intervention of high-pressure mercury lamp radiation allows the subsequent chemical crosslinking shrinkage to unfold in a physical ground state where the volume has already reached low-temperature thermodynamic equilibrium, avoiding the destructive superposition process of the two microscopic shrinkage mechanisms on the spatiotemporal scale.

[0095] The micro-time difference design combined with staggered curing sequences using temperature gradients fundamentally eliminates the physical and chemical coupling factors that generate internal stress. The steady-state residual internal stress remaining in the adhesive layer during the final demolding process stabilizes at 0.057 MPa, a value only about one-sixth that of the synchronous curing coupling mode, demonstrating a fundamental intervention effect on the freezing of unsteady stress. The establishment of millisecond-level process intervals allows the polymer network to capture the space margin for morphological buffering, cutting off the conversion node from microscopic deformation of the microstructure to macroscopic peeling tension, thus laying the foundation for the long-term physical dimensional stability of the optical adhesive layer after the process.

[0096] Test Example 3: Test objective: To quantitatively verify the technical effect of deep coupling of specific chemical formulations and spatiotemporal temperature control processes on eliminating double bond polymerization volume shrinkage and residual internal stress.

[0097] Test steps: 1. The original adhesive solution and the prepared adhesive tape of Examples 1 to 5 and Comparative Examples 1 to 6 were selected as test objects.

[0098] 2. Under a constant temperature of 25℃, use a calibrated 50mL standard liquid specific gravity bottle to measure the initial mass of each group of defoaming original adhesive liquid, and accurately calculate the reference value of liquid density before curing based on the known volume.

[0099] 3. Prepare individual solid adhesive films with a uniform thickness of 100 micrometers according to the corresponding process steps. The density of the solid adhesive film is determined in accordance with the national standard GB / T 1033.1-2008 "Determination of density of non-foamed plastics – Part 1: Immersion method, liquid pyrometer method and titration method". Specifically, the cured solid adhesive film is cut into regular circular pieces. Using a high-precision analytical balance with a density component, the immersion method is employed, with deionized water as the immersion medium. The dry weight of the film sample in air and its buoyancy in the liquid medium are measured. The solid density value after curing is calculated, and the percentage of volume shrinkage before and after curing is calculated accordingly.

[0100] 4. Cut a standard borosilicate glass strip with dimensions of 100mm×20mm and a thickness of 0.2mm as the coating substrate, and uniformly coat the surface of each group of original adhesive liquids. Strictly control the thickness of the single-sided adhesive layer to be 50 micrometers, and perform the photothermal sequential curing process determined in each embodiment and comparative example.

[0101] 5. A high-resolution non-contact laser interferometric curvature tester is used to scan the surface profile of the glass substrate after it has been cured and cooled to room temperature. The amount of central deflection deformation caused by biaxial tension is read, and the characteristic curvature radius of the substrate warping is obtained by fitting.

[0102] 6. Substitute the measured radius of curvature, Young's modulus and Poisson's ratio of the glass substrate, and the thickness of the adhesive layer into the Stoney stress equation to calculate the absolute value of the macroscopic residual internal stress accumulated in each sample.

[0103] The test data is shown in Table 3.

[0104] Table 3: Measurement data of film volume shrinkage rate and macroscopic residual internal stress for each group of test subjects ; Conclusion: Based on Table 3 and Figure 3 The data shows that the example group exhibits a clear low-value clustering characteristic in both volume shrinkage rate and macroscopic residual internal stress. The average shrinkage rate of the test system is constrained to fluctuate at the 0.6% level, and the accompanying underlying warpage driving stress converges to within 0.12 MPa. The comparative examples, stripped of spatiotemporal temperature control or formulation synergy factors, show a dramatic shift in the scatter distribution towards the high shrinkage and high stress quadrants. Comparative Example 1, which uses a single room-temperature light curing process, exhibits a volume shrinkage of 4.11%, accompanied by an internal stress value as high as 0.88 MPa. This order-of-magnitude deviation reflects a common defect in traditional acrylate polymerization processes: the micro-crosslinked network, lacking kinetic intervention and rheological compensation channels during densification, inevitably exerts irreversible tensile deformation on the macroscopic physical interface.

[0105] Cross-validation data from Comparative Examples 2 and 3 confirm that the triggering of the rheological self-compensation effect faces strict boundary condition constraints. Being isolated from the high-temperature physical field environment or lacking any link in the gel point-delayed chemical antagonistic mechanism will induce premature closure of the liquid-phase elastic state window. In Comparative Examples 4 and 5, where the formulation structure is incomplete, the uninhibited double-bond ring-opening reaction induces premature formation of the local cross-linked network. The rigidification of the polymer chain segments completely blocks the physical space for the liquid matrix to complete macroscopic deformation and collapse along the thickness direction. The 0.41 MPa stress baseline recorded in Comparative Example 6 exposes the indispensability of time-dimension decoupling operations. When the high-energy radiation-driven chemical network anchoring and the volumetric thermal physical contraction behavior overlap on the same transient cross-section, the molecular chain segments are forcibly frozen in a non-equilibrium tensile conformation.

[0106] The asymmetric response mechanism of polymerization rate, combined with temperature gradient separation intervention, breaks the inherent closed loop of material polymerization shrinkage constrained by the evolution of rigid networks. Relying on the artificially widened process gaps through formulation inhibition, redundant channels for absorbing volume shrinkage are established within the curing system. Physical thickness collapse, preceding the three-dimensional shaping of the network, absorbs the free volume deficit caused by the ring-opening reaction, allowing the subsequent thorough cross-linking process to steadily advance in a near-neutral physical ground state. The residual tension transmission chain between the coating and substrate interface is thus severed, preventing interlayer creep or optical interference defects in the full-lamination final process under long-term environmental stress impact, and establishing a deterministic material process architecture for addressing stress accumulation within the UV tape manufacturing process.

[0107] Test Example 4: Test objective: To verify the ability of optical adhesive layers in a low residual internal stress state to suppress appearance defects and maintain optical uniformity under extreme environmental loads in fully laminated display modules.

[0108] Test steps: 1. Peel off the light release PET film layer of the optical tapes prepared in Examples 1 to 5 and Comparative Examples 1 to 6, and accurately attach the exposed adhesive layer to a 6.0-inch flexible OLED analog screen panel substrate using a vacuum pressing device. Examples 1 to 5 are designated as E1 to E5, and Comparative Examples 1 to 6 are designated as C1 to C6.

[0109] 2. Remove the heavy release PET substrate from the back of each group of samples, and perform a second vacuum bonding with Corning glass cover plates with black edge silkscreen printing. Then, push them into a high-pressure degassing machine and treat them at 0.5MPa and 50℃ for 20 minutes. Prepare 100 complete test modules for each group.

[0110] 3. Divide the modules into two groups and put them into different environmental test chambers. The first batch is subjected to a double 85% aging test at 85℃ and 85% relative humidity in a constant temperature and humidity chamber, with a continuous running time of 500 hours.

[0111] 4. The second batch was pushed into the thermal shock test chamber and repeatedly switched between temperatures ranging from -40℃ to 85℃. The high and low temperatures were maintained for 30 minutes each, and the temperature transition time was less than 5 minutes. The test was repeated 100 times.

[0112] 5. After removing the module and allowing it to stand and return to room temperature, use a strong light backplate and a magnifying glass to screen for microbubbles, white edges, and delamination / lifting phenomena in the edge of the module and the effective display area. Record and calculate the percentage of samples with any defect in a single group.

[0113] 6. Randomly select 5 intact samples from the complete double 85 aging process, turn them on and input a full white screen signal. Use a CA-410 high-precision color luminance meter to extract the absolute brightness data of 9 areas evenly distributed on the working surface of the screen. Calculate the ratio of the lowest brightness value to the highest brightness value among the 9 points and quantify it as a percentage as the final brightness uniformity index of the module.

[0114] The test data is shown in Table 4.

[0115] Table 4: Apparent reliability and optical uniformity distribution data of tapes with different manufacturing processes in the aging test of fully laminated modules ; Conclusion: Based on Table 4 and Figure 4 The data shows a direct correlation between the microscopic residual stress and the physical reliability of the fully laminated display module in the later stages. In the test groups of Examples 1 to 5, after undergoing severe temperature and humidity shock cycles, the defect rate was strictly controlled within an extremely low limit of 2%. The brightness uniformity of the screen after illumination collectively jumped to an excellent range of over 92%, indicating that the local birefringence interference induced by the photoelastic effect was completely eliminated. The functional layers stacked within the flexible OLED panel did not experience additional shear deformation or external force during the 500-hour load process, thus preserving the original display physical optical path and avoiding the defect of local pixel light transmittance attenuation caused by material strain.

[0116] Comparative examples using conventional unidirectional photocuring or formulation systems with defects exhibited extremely fragile interfacial resistance. Comparative Examples 1 and 3 showed a dramatic increase in appearance defects, reaching approximately 30%, when subjected to high heat and moisture infiltration. The accumulated elastic contraction potential energy in the inner layer, aided by the chain segment movement capabilities provided by the external temperature field, initiated irreversible creep release towards the weak interface at the module edge, tearing the cohesive boundaries between the silicon-oxygen bonds and the acrylate matrix, inducing air intrusion and forming visible delayed-release bubble patches. The large-area drop in brightness uniformity of the comparative examples to around 70% confirms that the residual stress network exerted non-uniform microscopic tensile forces on the flexible substrate the moment the bonding assembly was completed. This implicit mechanical tension damaged the flatness of the substrate liquid crystal and light-emitting array, transforming into visually dull and whitish Mura spots when backlight penetrated.

[0117] The protective effect of polymer internal asymmetric dynamics control on the yield of terminal modules was macroscopically confirmed across scales. The intrinsic volume reduction caused by covalent bond closure was pre-digested through physical rheological collapse in the thickness direction, allowing the cross-linked tape to fill the gap between the screen and the cover plate in an ideal state close to zero stress. This approach, which places the internal mechanical countermeasure mechanism within the production process, eliminates the potential mechanical threat posed by the optical adhesive layer to the display substrate. This ensures that the assembly interface of precision electronic components not only meets the initial optical bonding standards but also establishes a long-term mechanical stability barrier against multidimensional aging corrosion.

[0118] Test Example 5: Test objective: To verify the compatibility of the process combination with the conventional photoelectric and mechanical properties of optical adhesives, and the protective effect of the large drum bonding isolation mechanism on the dimensional stability of the substrate material.

[0119] Test steps: 1. The double-sided tape products of Examples 1 to 5 and Comparative Example 7 that have completed the curing process were selected as test objects for optical and mechanical properties. Examples 1 to 5 were numbered E1 to E5, and Comparative Example 7 was numbered C7.

[0120] 2. Peel off the release film substrate from both sides of the adhesive tape and attach a 100-micron-thick pure adhesive film to the surface of a standard quartz glass slide. In this test example, the determination of transmittance and haze is performed according to ASTM D1003, "Standard Test Method for Haze and Transmittance of Transparent Plastics," issued by the American Society for Testing and Materials. Specifically, the quartz glass slide with the adhesive film attached is placed in a UV-Vis spectrophotometer to measure the average transmittance in the visible light band, and an integrating sphere haze meter is used to determine the percentage of haze caused by light scattering within the adhesive film.

[0121] 3. Roll-fit the tape with the light release PET film removed from one side to a standard stainless steel test plate. In this test example, the peel strength was determined according to the national standard GB / T 2792-2014 "Test Method for Peel Strength of Adhesive Tapes". Specifically, the bonded test piece was left to stand for 20 minutes in a standard laboratory environment, then loaded onto a computer-controlled electronic universal testing machine. A peel test was performed at a constant tensile rate of 300 mm / min at room temperature and 180 degrees Celsius. The average peel force value during the tensile stabilization phase was recorded.

[0122] 4. In a constant temperature and humidity workbench, peel off the re-release PET film substrates of the examples and comparative examples that have undergone the complete process, lay them flat and adsorb them onto the stage of the high-precision two-dimensional image measuring instrument.

[0123] 5. Multi-point coordinate picking is performed on the distance between the initial physical marker point and the final marker point of the PET substrate in the mechanical propulsion direction of the equipment. The absolute length difference in the mechanical longitudinal direction before and after the curing process is calculated, and the percentage of dimensional change rate of the film substrate after undergoing thermomechanical cycle is derived.

[0124] The test data is shown in Table 5: Table 5: Measurement data of optical and mechanical properties and thermomechanical dimensional changes of substrates in the examples and comparative examples ; Conclusion: Based on Table 5 and Figure 5 The data showed that the introduction of multifunctional thiols and allyl ethers into the crosslinked network did not induce optical phase separation or mechanical attenuation of the polymer backbone. After asymmetric kinetic high-temperature intervention and cooling dark-zone treatment in Examples 1 to 5, the transmittance of the films in the visible light band remained consistently above 99%, and the haze was suppressed to an extremely low threshold, demonstrating that the polymerization reaction constructed a highly uniform amorphous network. The peel force of the adhesive layer against the stainless steel plate remained in the range of 15 to 19 Newtons, and the free polymer segments on the surface did not experience crosslinking density distortion due to the rheological self-compensation process. The polymer bulk retained excellent interfacial wettability and cohesive strength.

[0125] The high-temperature physical field environment imposes stringent thermomechanical constraints on the substrate materials. Comparative Example 7 uses a suspended roller drying tunnel lacking physical support for high-temperature heating. The mechanical traction tension applied to the film belt by the equipment's transmission system is deeply coupled with the 75°C thermal field, resulting in a high plastic tensile creep of up to 3.15% in the PET film, which was originally intended as a rigid supporting substrate. The excessive tensile deformation of the film substrate under heat softening directly transmits the high-energy residual stress to the inner optical adhesive layer. Once freed from the equipment's tension constraints, the material's underlying recovery tendency inevitably leads to irreversible curling or interfacial shear failure of the adhesive tape.

[0126] The large-drum bonding and isolation mechanism completely cuts off the strain path of the equipment tension to the auxiliary material by reconstructing the physical force boundary. A wide wrap-around contact surface is built between the cylindrical surface of the large-diameter temperature-controlled drum and the PET film. The static friction array derived at the interface completely takes over and cancels the longitudinal belt tension at both ends of unwinding and rewinding. The film substrate, located in the heating and curing window, adheres to the outer surface of the drum and enters a zero-tension follow-up state. The longitudinal dimensional change rate of the PET material, freed from external pulling interference, falls back and locks at around 0.11%. The physical support structure maintains the intrinsic thermodynamic dimensional rigidity of the auxiliary material in the high-temperature range, eliminating the risk of coating thickness runaway caused by substrate deformation in continuous roll-to-roll processes.

[0127] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A low-shrinkage OCA optical adhesive, characterized in that, Made from the following raw materials by weight percentage: Polycarbonate-type aliphatic polyurethane acrylate prepolymer 30.0%–40.0%; 2-Ethylhexyl acrylate 42.0%~50.0%; 4-Hydroxybutyl acrylate 13.0%~15.0%; Pentaerythritol tetra(3-mercaptopropionate) 2.0%–4.5%; Trimethylolpropane diallyl ether 0.5%–1.5%; 2,4,6-Trimethylbenzoyl-diphenylphosphine oxide 0.5%–1.0%.

2. The low-shrinkage OCA optical adhesive according to claim 1, characterized in that, The raw materials are expressed in the following percentages by mass: 35.0% polycarbonate-type aliphatic polyurethane acrylate prepolymer, 45.0% 2-ethylhexyl acrylate, 14.0% 4-hydroxybutyl acrylate, 4.0% pentaerythritol tetra(3-mercaptopropionate), 1.0% trimethylolpropane diallyl ether, and 1.0% 2,4,6-trimethylbenzoyl-diphenylphosphine oxide.

3. The low-shrinkage OCA optical adhesive according to claim 1, characterized in that, The weight-average molecular weight of the polycarbonate-type aliphatic polyurethane acrylate prepolymer is 20,500 to 29,600.

4. The low-shrinkage OCA optical adhesive according to claim 1, characterized in that, The polycarbonate-type aliphatic polyurethane acrylate prepolymer is prepared by a method comprising the following steps: The hydroxyl-terminated polycarbonate diol and isophorone diisocyanate were reacted at 75–80 °C for 2.5–3.5 hours under the catalysis of dibutyltin dilaurate. The reaction system was analyzed by di-n-butylamine titration. When the mass fraction of isocyanate in the reaction system dropped to 0.22%–0.66%, the reaction system was cooled to 60–65°C and 2,6-di-tert-butyl-p-cresol was added, followed by the dropwise addition of hydroxyethyl acrylate. After the addition is complete, the reaction is maintained at a temperature of 65 to 70°C until the isocyanate characteristic absorption peak at 2270 cm -1 in the infrared spectrum disappears completely, and the polycarbonate-based aliphatic polyurethane acrylate prepolymer is obtained.

5. A method for preparing a low-shrinkage OCA optical adhesive as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Weigh the raw materials according to the mass percentage corresponding to the low shrinkage OCA optical adhesive; add 2-ethylhexyl acrylate and 4-hydroxybutyl acrylate to a mixing tank in sequence, add 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and stir until completely dissolved; then add polycarbonate-type aliphatic polyurethane acrylate prepolymer and continue mixing; then add pentaerythritol tetra(3-mercaptopropionate) and trimethylolpropane diallyl ether and mix to obtain a mixture; pump the mixture into a vacuum degassing tank for treatment to obtain the original adhesive solution; S2. Under tension control, the original adhesive liquid is coated onto a heavy release PET substrate. Immediately after coating, a light release PET film is laminated onto the surface of the liquid adhesive layer to form a closed sandwich structure. S3. The sandwich structure is introduced into the first curing zone. The sandwich structure is placed tightly against and around a heating drum with a constant surface temperature. During the synchronous operation of the sandwich structure with the heating drum, a cold light source is used to pre-cur it by passing through the side of the light release PET film. S4. The sandwich structure after leaving the first curing zone is introduced into the second curing zone. The sandwich structure is placed close to and around the cooling drum with constant surface temperature. The sandwich structure first passes through a physically shielded, radiation-free dark zone at the starting position of contacting the cooling drum. After passing through the radiation-free dark zone, the sandwich structure immediately enters the full-band irradiation zone for main curing irradiation. S5. After being removed from the cooling drum, the sandwich structure is treated by an electrostatic elimination device and then wound up under constant tension to obtain the low-shrinkage OCA optical adhesive.

6. The method for preparing low-shrinkage OCA optical adhesive according to claim 5, characterized in that, In step S1, the mixing speed after adding the polycarbonate-type aliphatic polyurethane acrylate prepolymer is set to 300-400 rpm, and the continuous mixing time is set to 40-60 minutes; the vacuum degree of the vacuum degassing tank is controlled at -0.09 to -0.095 MPa, and the processing time is controlled at 45-60 minutes.

7. The method for preparing low-shrinkage OCA optical adhesive according to claim 5, characterized in that, In step S2, the tension during the application of the original adhesive solution is controlled to be 50-100 N / m, and the wet film thickness is controlled to be 50-250 μm.

8. The method for preparing low-shrinkage OCA optical adhesive according to claim 5, characterized in that, In step S3, the surface of the heating drum is controlled at a constant temperature of 65-75℃, and the drum wrap angle is set to 185-200 degrees; the cold light source is a LED cold light source with a wavelength of 395nm, and the irradiance is set to 30-50mW / cm 2 . The cumulative ultraviolet energy is controlled to 200-300mJ / cm 2 .

9. The method for preparing low-shrinkage OCA optical adhesive according to claim 5, characterized in that, In step S4, the surface temperature of the cooling drum is controlled at 15-20°C; the time the sandwich structure stays in the radiation-free dark zone is controlled to be 0.5-1.0 seconds.

10. The method for preparing low-shrinkage OCA optical adhesive according to claim 5, characterized in that, In step S4, the full-band irradiation zone is irradiated using a full-band high-pressure mercury lamp, with the irradiance set to 500–600 mW / cm². 2 The cumulative energy is controlled at 1200–1500 mJ / cm². 2 .

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