OCA optical pressure-sensitive adhesive with high tensile strength and high rebound resilience and preparation method of OCA optical pressure-sensitive adhesive

Abstract

The invention discloses an OCA (Optical Clear Adhesive) with high tensile strength and high rebound resilience and a preparation method thereof, and the OCA is prepared from the following raw material components in parts by mass: 50-100 parts of low molecular weight polymer, 0-60 parts of block copolymer, 5-50 parts of polyurethane and 3-20 parts of tackifying resin; the low-molecular-weight polymer is an acrylic ester-based copolymer prepared through reversible addition fragmentation chain transfer solution polymerization, and the number-average molecular weight of the low-molecular-weight polymer is 0.1-10,000 g / mol; the block copolymer is an acrylic ester-based copolymer prepared by reversible addition fragmentation chain transfer emulsion polymerization, and the number-average molecular weight of the block copolymer is 800000-800000 g / mol. The low-molecular-weight polymer, the block copolymer, the polyurethane and the tackifying resin are dissolved in a dispersion medium, coating is performed in an argon environment to form a film, and drying is performed to obtain the adhesive. According to the invention, the RAFT solution polymerized low molecular weight polymer, the emulsion polymerized segmented copolymer, the polyurethane and the tackifying resin are matched to obtain the optical pressure-sensitive adhesive with high mechanical strength, high tensile strength and high resilience.

Description

Technical Field

[0001] The present invention relates to the technical field of optical adhesives, and specifically relates to an OCA optical pressure-sensitive adhesive with high tensile strength and high resilience and a preparation method thereof. Background Art

[0002] Optical Clear Adhesive (OCA) is a key material widely used in various optical devices and components, especially in the fields of foldable displays and curved displays. With the continuous progress of technology, the development of multi-fold-axis displays such as foldable mobile phones has become increasingly popular, which makes the requirements for OCA performance more stringent.

[0003] In a multi-fold-axis display, each fold axis exerts a huge force on the OCA during the folding process, transferring its own displacement to the overall adhesive layer. Therefore, the OCA needs to have a higher elongation at break and excellent resilience to maintain the integrity and performance of the display. In this case, traditional OCAs often fail to meet the requirements because of their limited elongation at break and less-than-ideal resilience.

[0004] CN 113025243 A discloses a method for preparing an acrylate composite adhesive by soap-free emulsion polymerization. Soap-free emulsion polymerization is used to prepare the acrylate composite adhesive, and RAFT living radical polymerization is used to synthesize an acrylic block oligomer with emulsifying properties. Then, the acrylic block oligomer is used to emulsify acrylate monomers for semi-continuous emulsion polymerization, which solves the defects that traditional small-molecule emulsifiers are prone to migrate to the surface of the adhesive film to form a weak interfacial layer, resulting in a decrease in bonding strength and poor water resistance. Using n-pentanol as a chain transfer agent can not only reduce the molecular weight of the polymer, improve the fluidity and composite uniformity of the adhesive, but also reduce the surface tension of the emulsion, improve the coating wettability and leveling property of the acrylate composite adhesive emulsion. However, this colloid has a problem of poor resilience when used as an optical adhesive.

[0005] CN 116925680A discloses a preparation method of a novel acrylate OCA optical adhesive, including 10-25 parts of methyl methacrylate, 10-15 parts of methyl acrylate, 20-35 parts of ethyl acrylate, 3-6 parts of isocyanate, 7-10 parts of multi-functional polymer, 12-24 parts of propylene glycol dimethyl ether solvent, 11-18 parts of ethylene glycol methyl ether solvent, 3-4 parts of hydroxybenzoate, 3-5 parts of phenyl dihydroxybenzoate, 4-7 parts of benzotriazoles, 5-6 parts of benzodiazoles, and 8-10 parts of phenol. The use of diisocyanate can improve the optical adhesive, improve the bonding strength of the optical adhesive, react with acrylate groups to form a cross-linked structure, and increase the strength and stability of the adhesive. Styrene-butadiene rubber can increase the toughness and impact resistance of the optical adhesive, thereby improving the bonding strength, but the problem of resilience is not mentioned either. Summary of the Invention

[0006] In view of the problem that the mechanical strength, elongation at break, and resilience of optical OCA pressure-sensitive adhesives cannot be achieved simultaneously, the present invention provides an OCA optical pressure-sensitive adhesive with both high tensile strength and high resilience. This pressure-sensitive adhesive maintains the resilience of OCA while achieving a high elongation at break, and has excellent mechanical properties, enabling it to perform outstandingly in highly challenging applications such as multi-fold axis displays.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] An OCA optical pressure-sensitive adhesive with high tensile strength and high resilience, according to mass parts, comprises the following raw material components: 50 - 100 parts of low molecular weight polymer, 0 - 60 parts of block copolymer, 5 - 50 parts of polyurethane, and 3 - 20 parts of tackifying resin;

[0009] The low molecular weight polymer is an acrylate-based copolymer prepared by reversible addition-fragmentation chain transfer (RAFT) solution polymerization, with a number average molecular weight of 0.1 - 10,000 g / mol;

[0010] The block copolymer is an acrylate-based copolymer prepared by reversible addition-fragmentation chain transfer emulsion polymerization, with a number average molecular weight of 8 - 800,000 g / mol.

[0011] In the present invention, a low molecular weight polymer prepared by RAFT solution polymerization, a block copolymer prepared by emulsion polymerization, polyurethane, and a tackifying resin are combined to obtain an optical pressure-sensitive adhesive with both high mechanical strength, high tensile strength, and high resilience. Among them, the block copolymer can reach a relatively high molecular weight through emulsion polymerization, has strong cohesive force, and has excellent properties such as peel strength, but shows a limited elongation at break. The ultra-low molecular weight copolymer prepared by RAFT solution polymerization usually has good ductility, and its main function is to provide fluidity. When the two are blended, the material can exhibit an elongation at break of more than 2000%. Although the material prepared at this time has a high elongation at break, its resilience is poor. Therefore, a short-chain network of polyurethane is introduced to act as an entropy spring, mainly contributing high resilience, and finally an OCA optical pressure-sensitive adhesive with excellent mechanical properties is realized, which can meet the requirements of high-demand applications such as multi-fold axis displays, and is also expected to play a more extensive role in the future optical device field, improving the performance and reliability of products.

[0012] The structural general formula of the low molecular weight polymer is M1-b-M2……-b-M j , where the value range of j is 3 - 11; where M1, M2……M jIt is a comonomer in the low molecular weight polymer and is independently selected from a soft monomer, a hard monomer or a functional monomer; and the mass contents of the soft monomer, the hard monomer and the functional monomer in the low molecular weight polymer are 70-100%, 0-30% and 0-5% respectively;

[0013] In the present invention, the low molecular weight polymer is a multi-segment polymer with a low molecular weight and mainly composed of soft monomers, so that the low molecular weight polymer can ensure the fluid state. As the content of the soft monomer increases, the modulus of the polymer will be lower, and it will show more characteristics of a fluid. Appropriate hard monomers can provide a certain cohesive force to keep the polymer in good physical form; adding functional monomers can improve the peel strength of the polymer and increase the adhesiveness of the optical adhesive.

[0014] Preferably, when the molecular weight of the low molecular weight polymer is below 3k, the cohesive force of the polymer is too small and the fluid viscosity is too small. At this time, an appropriate amount of hard monomer is added to improve the strength of the polymer.

[0015] The structural general formula of the block copolymer is N1-b-N2-b-N3; where N1, N2 and N3 are comonomers in the block copolymer, and their number average molecular weight is 100,000-400,000 g / mol; N1 and N3 are selected from hard monomers or a mixture of hard monomers and functional monomers, and N2 is selected from soft monomers or a mixture of soft monomers and functional monomers; and the mass contents of the soft monomer, the hard monomer and the functional monomer in the block copolymer are 70-98%, 2-30% and 0-5% respectively. The hard monomer in the block copolymer provides cohesive force to make the material have high strength, and the soft monomer mainly provides flexibility. As the content of the soft monomer increases, the modulus of the polymer will be lower and the elongation at break will be higher. However, the elongation at break that can be achieved by the emulsion polymerization block copolymer is only within 1500%, so it needs to be further improved.

[0016] On the other hand, in the present invention, when the block copolymer is not used, the low molecular weight polymer can also cooperate with polyurethane and tackifying resin to obtain a pressure-sensitive adhesive with excellent comprehensive performance. Preferably, when the molecular weight of the low molecular weight polymer is 5000-10000 g / mol, the dosage of the block copolymer can be 0. Preferably, the dosage of the block copolymer is not 0. When the molecular weight of the low molecular weight polymer is relatively high, appropriately adding the block copolymer can further improve the mechanical strength of the pressure-sensitive adhesive.

[0017] The hard monomer includes one or more of styrene, methyl acrylate, isobornyl acrylate, cyclohexyl acrylate, methyl methacrylate, acrylamide, acrylonitrile and vinyl acetate, and the glass transition temperature range formed by it is 60-150 °C; the higher the glass transition temperature of the hard monomer, the higher the modulus of the formed polymer, the better the heat resistance and the better the resilience.

[0018] The soft monomers include one or more of ethyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, isooctyl acrylate, octyl acrylate, 2-propylheptyl acrylate, isononyl acrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, isooctyl methacrylate, butadiene, isoprene, ethylene-butene, and methacrylic acid. The block glass transition temperature range formed thereby is -90 to -30 °C. The lower the glass transition temperature of the polymer, the lower the modulus of the formed polymer, the better the flexibility, and the better the tensile properties.

[0019] The functional monomers include one or more of methacrylic acid, acrylic acid, itaconic acid, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, N,N-dimethylaminoethyl methacrylate, methacrylamide, N-hydroxymethylacrylamide, glycidyl methacrylate, and maleic anhydride. The present invention also introduces functional monomers, which can form a hydrogen bond network with polyurethane, further improving the high stress relaxation and high strain recovery capabilities of the optical adhesive under large strains (>1000%), and increasing the performance and reliability of the OCA.

[0020] The molecular weight of the polyurethane is 2000 - 10000 g / mol. The higher the molecular weight of the polyurethane, the better its entropy elasticity, but too high a molecular weight will cause a significant increase in the modulus. The preferred range is 5000 - 8000.

[0021] The types of the tackifying resin include one or more of TP2019, T801, and T801 / L. The light transmittance of the optical adhesive prepared by using these tackifying resins is greater than 90%, and the haze is less than 1%.

[0022] When the number average molecular weight of the low molecular weight polymer is below 3000 g / mol, the content of the block copolymer is 5 - 60 parts. At this time, if the block copolymer is not added, the optical adhesive is in a fluid state, prone to flow, and unable to maintain a stable state. The block copolymer must be added for stabilization.

[0023] The present invention also provides a method for preparing the high-tensile and high-elasticity OCA optical pressure-sensitive adhesive, which is characterized by including the steps of dissolving a low molecular weight polymer, a block copolymer, a polyurethane, and a tackifying resin in a dispersion medium, and coating and drying in an argon environment to obtain the OCA optical pressure-sensitive adhesive.

[0024] The preparation of the low molecular weight polymer includes the steps:

[0025] Step 1: Dissolve 1 / 6 - 1 / 2 of the soft monomer, 1 / 6 - 1 / 2 of the hard monomer, 1 / 6 - 1 / 2 of the functional monomer, 1 / 2 of the first initiator, and all of the small - molecule reversible addition - fragmentation chain - transfer agent in dioxane, stir until evenly mixed, heat up to 50 - 80 °C, and react for 2 - 10 h in an anaerobic or low - oxygen environment;

[0026] Step 2: Add the remaining soft monomer, hard monomer, functional monomer, and first initiator drop - by - drop. Control the dropping time within 2 - 4 h. After dropping, continue to keep warm for 6 - 10 h;

[0027] Step 3: Cool the reaction solution and pour it into a precipitating agent for precipitation, wash, dry in air, and then dry under vacuum to obtain the low - molecular polymer;

[0028] Or omit Step 2. In Step 1, add all the comonomers and initiators, and the reaction time is 5 - 20 h.

[0029] The chemical structural formula of the small - molecule reversible addition - fragmentation chain - transfer agent is: R - X; where R is isopropyl acid group, acetic acid group, 2 - cyanoacetic acid group, or 2 - aminoacetic acid group; the X group is an alkyl dithiocarbonate group or an alkyl trithiocarbonate group; the mass of the small - molecule reversible addition - fragmentation chain - transfer agent is 1 / 100 - 1 / 10 of the total mass of the comonomers.

[0030] The first initiator is any one or more of ammonium persulfate, potassium persulfate, hydrogen peroxide, and hydrogen peroxide derivatives; the molar mass of the first initiator is 1 / 50 - 1 times the molar mass of the small - molecule reversible addition - fragmentation chain - transfer agent;

[0031] The preparation of the block copolymer includes the following steps:

[0032] Step 1: Dissolve the amphiphilic macromolecular reversible addition - fragmentation chain - transfer agent in water, add the hard monomer or a mixture of the hard monomer and the functional monomer, mix evenly, add the first initiator at 70 - 90 °C, and react for 1 - 3 h to obtain a homopolymer. The homopolymer is stably dispersed in water in the form of particles to form a latex;

[0033] Step 2: Add an aqueous solution of inorganic base with a certain concentration to the latex obtained in Step 1, then add the soft monomer or a mixture of the soft monomer and the functional monomer. At 40 - 60 °C, add water and the second initiator as a supplement, react for 4 - 10 h in an anaerobic environment, then add the hard monomer or a mixture of the hard monomer and the functional monomer, and react for 5 - 10 h in an anaerobic environment to obtain a block - polymer latex;

[0034] Step 3: Pour the block - polymer latex obtained in Step 2 into dilute hydrochloric acid for precipitation, wash and dry the product to obtain the block copolymer.

[0035] The chemical structural formula of the amphiphilic macromolecular reversible addition-fragmentation chain transfer reagent is: R-(M n1 -b-N n2 )-X; wherein, R is isopropyl acid group, acetic acid group, 2-cyanoacetic acid group or 2-aminoacetic acid group; M n1 , in M, M is a methacrylic acid monomer or an acrylic acid monomer unit, n1 is the average degree of polymerization of M, and the range of n1 is 10-30; N n2 , in N, N is a styrene monomer, n-butyl acrylate monomer, methyl acrylate, isooctyl acrylate or methyl methacrylate monomer unit, n2 is the average degree of polymerization of N, and the range of n2 is 1-8; the X group is an alkyl dithiocarbonate group or an alkyl trithiocarbonate group;

[0036] The molar mass of the amphiphilic macromolecular reversible addition-fragmentation chain transfer reagent is 1 / 50-1 of the molar mass of the small-molecule reversible addition-fragmentation chain transfer reagent.

[0037] The aqueous solution of inorganic base includes aqueous solutions of inorganic bases such as sodium hydroxide, ammonium hydroxide, sodium bicarbonate, etc.

[0038] The first initiator is any one or more of ammonium persulfate, potassium persulfate, hydrogen peroxide and hydrogen peroxide derivatives; the molar mass of the first initiator is 1 / 50-1 of the molar mass of the macromolecular reversible addition-fragmentation chain transfer reagent.

[0039] The second initiator is any one or more of 2,2'-azobis(2-methylpropionamidine) dihydrochloride, 2,2'-azobis(2-methylpropionamidine) dihydrochloride, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, sodium bisulfate / potassium persulfate redox initiator and sodium persulfate / ammonium persulfate redox initiator; the molar mass of the second initiator is 1 / 50-1 of the molar mass of the macromolecular reversible addition-fragmentation chain transfer reagent.

[0040] In step 2, the addition of inorganic base adjusts the pH of the reaction solution to 6-14.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The present invention uses a low-molecular polymer to provide fluidity, so that the polymer exhibits an ultra-high elongation at break. By introducing polyurethane, the material can achieve high stress relaxation and high strain recovery under large strains. Combining the combination of low-molecular polymer, block copolymer, polyurethane and tackifying resin, the excellent mechanical properties of high elongation at break, excellent resilience under high tensile degree and high peel strength of the optical pressure-sensitive adhesive are achieved. The optical pressure-sensitive adhesive performs excellently in high-demand applications such as multi-fold axis displays, provides reliability for the application of optical devices in complex stress environments, and has broad application prospects and commercial value. Description of the Drawings

[0043] Figure 1 It is the mechanical tensile curve graph of the OCA optical adhesive obtained in Example 1.

[0044] Figure 2 It is the strain recovery rate data graph of the OCA optical adhesives obtained in Examples 1-3 and Comparative Example 2.

[0045] Figure 3 It is the peeling strength result graph of the OCA optical adhesives obtained in Examples 1-3 and Comparative Examples 1-2. Detailed implementation manners

[0046] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Those skilled in the art who make modifications or equivalent replacements on the basis of understanding the technical solutions of the present invention, without departing from the spirit and scope of the technical solutions of the present invention, shall all be covered within the protection scope of the present invention.

[0047] The raw materials used in the following detailed implementation manners are all purchased from the market.

[0048] Example 1

[0049] Example 1: The formulation is 40 parts by mass of a low-molecular-weight polymer, 30 parts by mass of a block copolymer, 5 parts by mass of polyurethane and 5 parts by mass of TP2019. The specific preparation steps are as follows:

[0050] First step: Dissolve 10 parts by mass of isooctyl acrylate, 0.02 parts by mass of ammonium persulfate and 0.01 parts by mass of a small molecule reversible addition-fragmentation chain transfer agent in dioxane, stir until evenly mixed, heat up to 75 °C, and react for 5 h in an anaerobic or low-oxygen environment; the chemical structural formula of the small molecule reversible addition-fragmentation chain transfer agent is as follows:

[0051]

[0052] Second step: Adopt a dropping method for 50 parts by mass of isooctyl acrylate and 0.02 parts by mass of ammonium persulfate, control the dropping time at 3 h, and continue to keep warm for 8 h after the dropping is completed.

[0053] Third step: Naturally cool the system to about room temperature, slowly pour the solution into cyclohexane for precipitation, wash and stir repeatedly, remove the upper clear liquid, put the lower layer copolymer into a mortar, dry it in a fume hood, and vacuum dry it at 70 °C to obtain a low molecular weight polymer.

[0054] Step 4: Dissolve 0.01 part by mass of the amphiphilic macromolecule reversible addition-fragmentation chain transfer reagent in water, then add 10 parts by mass of styrene and stir until evenly mixed. Add 0.02 part by mass of ammonium persulfate at 70 °C and react for 3 h to obtain a homopolymer. The homopolymer is stably dispersed in water in the form of particles to form a latex; wherein the chemical structural formula of the amphiphilic macromolecule RAFT reagent is:

[0055]

[0056] Step 5: Add an aqueous sodium hydroxide solution with a concentration of 10 wt% to adjust the pH between 8 and 9, then add 100 parts by mass of isooctyl acrylate, then add water, add 0.01 part by mass of 2,2'-azobis(2-methylpropionamidine) dihydrochloride at 40 °C, and continue to react for 6 h in an anaerobic environment. Then add 5 parts by mass of the hard monomer and continue to react for 5 h in an anaerobic environment to obtain a block polymer latex;

[0057] Step 6: After the reaction is completed, pour the polymer latex into dilute hydrochloric acid, wash the precipitated product with distilled water until neutral, dry it in air, and then place it in a vacuum oven at 120 °C for vacuum drying for 20 h to finally obtain a block copolymer;

[0058] Step 7: Dissolve 50 parts by mass of the low molecular weight polymer, 30 parts by mass of the block copolymer, 5 parts by mass of polyurethane and 5 parts by mass of the tackifying resin TP2019 in tetrahydrofuran, coat and dry it into a film in an argon environment to finally obtain an OCA optical adhesive.

[0059] The molecular weight of the polymer was characterized on a gel permeation chromatography Waters 1525-2414-717 GPC instrument. The eluent was tetrahydrofuran and was calibrated with a narrow distribution polystyrene standard sample.

[0060] The mechanical properties of the polymer were tested by a universal material testing machine (Zwick / Roll Z020). The polymer film in the above Step 4 was cut into dumbbell-shaped specimens with a standard sample cutter for standby. The test method was GB 16421-1996, the tensile rate was 30 mm / min, and the test of each sample was repeated at least three times.

[0061] The strain recovery rate of the polymer was characterized by a dynamic thermomechanical analyzer with environmental control (DMA, TA Q800, TA Instruments, USA). The sample was cut into a long strip of 20 mm × 5 mm. The test temperature was 25 °C, the mode was the tensile mode. At the beginning of the test, the sample was stretched to the set strain within 1 s, and the strain was recorded as ε0 at this time and maintained for 1 h; then the applied force was unloaded and maintained for 1 h, and the strain was recorded as ε 60 . The strain recovery rate b was calculated according to the following formula.

[0062]

[0063] The peel strength of the polymer was tested by an adhesive shear strength testing machine (KJ-1066A). The OCA optical pressure-sensitive adhesive film in the above fifth step was cut into strips with a width of 25 mm and a length of about 300 mm. The testing method was GB / T 2792-2014, and the test for each sample was repeated at least three times.

[0064] The folding resistance performance of the polymer was measured by a temperature and humidity bending durability testing machine (Beijing WoHuaHuiTong Measurement and Control Technology Co., Ltd.). Two layers of PET with a thickness of 50 μm were respectively attached to both sides of the adhesive film to minimize the bubbles generated during the lamination process. Then the sample was cut into a strip with a width of 5 cm and a length of 20 cm. Subsequently, the longer two sides were fixed to the testing machine with tape. The bending angle was set at 180°, the testing frequency was 60 times / min, the bending radius was set at 3 mm as required, and the test temperature was recorded as 20±5°C, and the test humidity was 50±5%.

[0065] Through GPC testing, the GPC molecular weight of the low molecular weight polymer obtained in the third step was about 3 kg / mol. Figure 1 The middle is the mechanical property curve of this optical adhesive. It can be seen that this material has a low modulus of 80.4 KPa, a low stress of 0.32 MPa, and a high elongation at break close to 2500%.

[0066] Figure 2 It is the strain recovery curve of the OCA optical pressure-sensitive adhesive. It can be seen that at a tensile strain of 1000%, the strain recovery rate is about 88%; at a tensile strain of 1500%, the strain recovery rate is about 87%; at a tensile strain of 2000%, the strain recovery rate is about 87%. Figure 3 It is the peel strength data of the OCA optical pressure-sensitive adhesive. When the thickness of the adhesive film is 25 μm, the peel strength of this OCA optical pressure-sensitive adhesive film is 12.8 N / 25 mm. In addition, the OCA optical pressure-sensitive adhesive in Example 1 was tested for folding resistance performance, and its folding resistance times exceeded 200,000 times.

[0067] Comparative Example 1:

[0068] The preparation of the block copolymer was the same as that in Example 1, and its formula was 70 parts by mass of a block copolymer, 25 parts by mass of poly urethane and 5 parts by mass of TP2019, without low-molecular-weight polymer, to obtain an OCA optical pressure-sensitive adhesive. Comparing Example 1 with Comparative Example 1, it can be found (see Table 1) that the presence of short chains of low molecular weight polymers is equivalent to a fluid. When the polymer is stretched to a greater extent, the polymers can maintain a certain connection, resulting in a greater elongation at break. For the optical adhesive in Comparative Example 1 prepared without a low molecular copolymer, it will break when the elongation rate exceeds 800%, and it cannot support the high resilience at an ultra-high tensile degree and an ultra-high tensile degree.

[0069] Table 1 Mechanical Properties of Optical Adhesives with and without Low Molecular Weight Polymers

[0070]

[0071] Example 2:

[0072] The formulation is 70 parts by mass of low-molecular-weight polymers with different molecular weights, 30 parts by mass of a block copolymer, 5 parts by mass of poly urethane and 5 parts by mass of TP2019. The specific preparation steps are as follows:

[0073] The block copolymer used in this example is the same as that in Example 1.

[0074] Step 1: Dissolve 20 parts by mass, 40 parts by mass, or 60 parts by mass of isooctyl acrylate, 0.02 of ammonium persulfate, and 0.01 part by mass of a small molecule reversible addition-fragmentation chain transfer agent in dioxane, stir until evenly mixed, heat to 80 °C, and react for 10 h under an anaerobic environment; the chemical structural formula of the small molecule reversible addition-fragmentation chain transfer agent is as follows:

[0075]

[0076] Step 2: Naturally cool the system to room temperature, slowly pour the solution into cyclohexane for precipitation, wash and stir repeatedly, remove the supernatant, put the lower-layer copolymer into a mortar, dry it in a fume hood, and vacuum dry it at 35 °C to obtain low molecular weight polymers with different molecular weights. The molecular weights are specifically shown in Table 2.

[0077] Step 3: 70 parts by mass of the above low-molecular-weight polymer, 30 parts by mass of a block copolymer, 5 parts by mass of polyurethane and 5 parts by mass of TP2019 Dissolve it in methyl ethyl ketone, coat it into a film and dry it in an argon environment to finally obtain an OCA optical adhesive.

[0078] Table 2 shows the strain resilience data of this example. It can be seen that when the molecular weight is 10 kg / mol, the elongation at break of the optical adhesive shows a significant decrease. This is because when the molecular weight is 10 kg / mol, the elasticity of the polymer is greater than its viscosity, presenting a state similar to that of a solid. At a high degree of stretching, the chains are easily pulled out from each other. While when the molecular weight is 3 kg / mol or 5 kg / mol, the polymer presents a fluid state. At a high degree of stretching, the chains are similar to a fluid and do not break. When the stress is removed, the polymer can rebound.

[0079] Table 2 Mechanical Properties of Optical Pressure-Sensitive Adhesives Prepared from Low Molecular Weight Polymers with Different Molecular Weights

[0080]

[0081] Figure 2 In this example prepared from a low-molecular-weight polymer of 3 kg / molThe strain recovery curve of the OCA optical pressure-sensitive adhesive shows that at a tensile strain of 1000%, the strain recovery rate is about 90%; at a tensile strain of 1500%, the strain recovery rate is about 90%; at a tensile strain of 2000%, the strain recovery rate is about 85%. Figure 3 In this embodiment 3 kg / mol prepared from a low-molecular-weight polymer of The peel strength data of the OCA optical pressure-sensitive adhesive shows that when the thickness of the adhesive film is 25μm, the peel strength of the OCA optical pressure-sensitive adhesive film is 10.2N / 25mm. In addition, the OCA optical pressure-sensitive adhesive in this embodiment was also tested for its folding resistance performance, and the number of folding resistance exceeded 200,000 times.

[0082] Example 3:

[0083] The formulation is 70 parts by mass of a low-molecular-weight polymer, 30 parts by mass of a block copolymer, 5 - 50 parts by mass of polyurethane (the addition amount and performance are shown in Table 3) and 3 parts by mass of TP2019. The specific preparation steps are as follows: Figure 2

[0084] Step 1: Dissolve 30 parts by mass of isooctyl acrylate, 2 parts by mass of styrene, 0.02 parts of ammonium persulfate, and 0.01 part by mass of a small molecule reversible addition-fragmentation chain transfer agent in dioxane and stir until evenly mixed, then heat to 80°C; the chemical structural formula of the small molecule reversible addition-fragmentation chain transfer agent is as follows:

[0085]

[0086] Step 2: Use a dropping method to add the remaining 30 parts by mass of isooctyl acrylate, 2 parts by mass of styrene, and 0.02 parts of ammonium persulfate. The dropping time is controlled within 2h, and after the dropping is completed, keep warm for 6h.

[0087] Step 3: Naturally cool the system to room temperature, slowly pour the solution into cyclohexane for precipitation, wash and stir repeatedly, remove the upper clear liquid, put the lower layer copolymer into a mortar and dry it in a fume hood, and then vacuum dry it at 35°C to obtain a low molecular weight polymer.

[0088] Step 4: Dissolve 0.01 part by mass of an amphiphilic macromolecular reversible addition-fragmentation chain transfer agent in water, then add 1 part by mass of styrene and stir until evenly mixed. Add 0.01 part by mass of 2,2'-azobis(2-methylpropionamidine) dihydrochloride at 70°C and react for 3h to obtain a homopolymer. The homopolymer is stably dispersed in water in the form of particles to form a latex; the chemical structural formula of the amphiphilic macromolecular RAFT reagent is:

[0089]

[0090] Step 5: Add an aqueous sodium hydroxide solution with a concentration of 10 wt% to adjust the pH to 8 - 9, then add 100 parts by mass of isooctyl acrylate, and then add water. Add 0.01 part by mass of ammonium persulfate at 40°C and react for 6 h in an anaerobic environment to obtain a block polymer latex;

[0091] Step 6: After the reaction is completed, pour the polymer latex into dilute hydrochloric acid, wash the precipitated product with distilled water until neutral, dry it in air, and then place it in a vacuum oven at 120°C for vacuum drying for 20 h to finally obtain a block copolymer;

[0092] Step 7: Dissolve 70 parts by mass of a low-molecular polymer, 30 parts by mass of the block copolymer, 10 - 50 parts by mass of polyurethane, and 3 parts by mass of a tackifying resin in a dispersion medium, coat and dry the film in an argon environment to finally obtain an OCA optical adhesive.

[0093] Table 3 shows the strain resilience data of this example. It can be seen that with the increase of polyurethane, the resilience performance of the optical adhesive can be effectively compensated. However, when too much polyurethane is added, the elongation at break will also decrease, resulting in fracture at a high fracture tensile length. Compared with Comparative Example 2, when no polyurethane is contained, its elongation at break can reach 2700%, but its strain resilience rate is lower than that with the addition of polyurethane because polyurethane can provide entropy resilience.

[0094] Table 3 Mechanical properties of optical pressure-sensitive adhesives with different amounts of polyurethane

[0095]

[0096] Figure 3 This is the strain recovery curve of the 15 parts by mass of polyurethane OCA optical pressure-sensitive adhesive in this example. It can be seen that at a tensile strain of 1000%, the strain recovery rate is about 96%; at a tensile strain of 1500%, the strain recovery rate is about 83%; at a tensile strain of 2000%, the strain recovery rate is about 75%. Among them, when the amount of polyurethane used is 0 part, it is used as Comparative Example 2, and its resilience and peel strength are respectively as This is the peel strength data of the 15 parts by mass of polyurethane OCA optical pressure-sensitive adhesive in this example. When the thickness of the adhesive film is 25 μm, the peel strength of the OCA optical pressure-sensitive adhesive film is 14.6 N / 25 mm.

[0097] Figure 2 Figure 3 and ​ As shown, it can be seen that polyurethane can improve the resilience of the optical adhesive, indicating that in the absence of polyurethane, the resilience of the optical pressure-sensitive adhesive decreases significantly and the peel strength decreases slightly. The above examples are used to explain the present invention rather than limit the present invention. Any modification and change made within the spirit and scope of the claims of the present invention fall within the protection scope of the present invention.

Claims

1. A high-tensile and high-rebound OCA optical pressure-sensitive adhesive, characterized in that, By mass parts, it includes the following raw material components: 50 - 100 parts of low molecular weight polymer, 0 - 60 parts of block copolymer, 5 - 50 parts of polyurethane and 3 - 20 parts of tackifying resin; The low molecular weight polymer is an acrylate copolymer prepared by reversible addition-fragmentation chain transfer solution polymerization, with a number average molecular weight of 0.1 - 10,000 g / mol; The block copolymer is an acrylate copolymer prepared by reversible addition-fragmentation chain transfer emulsion polymerization, with a number average molecular weight of 8 - 800,000 g / mol.

2. The OCA optical pressure-sensitive adhesive with high tensile strength and high resilience according to claim 1, characterized in that The general structural formula of the low molecular weight polymer is M1-b-M2……-b-M j , where the value range of j is 3 to 11; where M1, M2……M j are comonomers in the low molecular weight polymer, independently selected from soft monomers, hard monomers or functional monomers; and the mass contents of the soft monomer, hard monomer and functional monomer in the low molecular weight polymer are 70 to 100%, 0 to 30% and 0 to 5% respectively; The structural general formula of the block copolymer is N1-b-N2-b-N3; where N1, N2, and N3 are copolymer monomers in the block copolymer, with a number average molecular weight of 10 - 400,000 g / mol; N1 and N3 are selected from hard monomers or a mixture of hard monomers and functional monomers, N2 is selected from soft monomers or a mixture of soft monomers and functional monomers; and the mass contents of the soft monomer, hard monomer, and functional monomer in the block copolymer are 70 - 98%, 2 - 30%, and 0 - 5% respectively.

3. The OCA optical pressure-sensitive adhesive with high tensile strength and high resilience according to claim 2, characterized in that The hard monomer includes one or more of styrene, methyl acrylate, isobornyl acrylate, cyclohexyl acrylate, methyl methacrylate, acrylamide, acrylonitrile, and vinyl acetate, and the glass transition temperature range of the formed block is 60 - 150 °C; The soft monomer includes one or more of ethyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, isooctyl acrylate, octyl acrylate, 2-propylheptyl acrylate, isononyl acrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, isooctyl methacrylate, butadiene, isoprene, ethylene-butene, and methacrylic acid, and the glass transition temperature range of the formed block is -90 - -30 °C; The functional monomer includes one or more of methacrylic acid, acrylic acid, itaconic acid, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, ethyl dimethylamine methacrylate, methacrylamide, N-hydroxymethylacrylamide, glycidyl methacrylate, and maleic anhydride.

4. The OCA optical pressure-sensitive adhesive with high tensile strength and high resilience according to claim 1, characterized in that, The molecular weight of the polyurethane is 2000 - 10000 g / mol; The types of the tackifying resin include one or more of TP2019, T801, and T801 / L.

5. The OCA optical pressure-sensitive adhesive with high tensile strength and high resilience according to claim 1, characterized in that When the number average molecular weight of the low molecular weight polymer is below 3,000 g / mol, the content of the block copolymer is 5 - 60 parts.

6. The preparation method of the OCA optical pressure-sensitive adhesive with high tensile strength and high resilience according to any one of claims 1-5, characterized in that, It includes the steps: dissolving the low molecular weight polymer, block copolymer, polyurethane, and tackifying resin in a dispersion medium, coating and forming a film in an argon environment, and drying to obtain the OCA optical pressure-sensitive adhesive.

7. The preparation method of the OCA optical pressure-sensitive adhesive with high tensile strength and high resilience according to claim 6, characterized in that, The preparation of the low molecular weight polymer includes the steps: Step 1, dissolve 1 / 6 - 1 / 2 of the soft monomer, 1 / 6 - 1 / 2 of the hard monomer, 1 / 6 - 1 / 2 of the functional monomer, 1 / 2 of the first initiator, and all of the small molecule reversible addition-fragmentation chain transfer reagent in dioxane, stir until evenly mixed, heat up to 50 - 80 °C, and react for 2 - 10 h in an anaerobic or low-oxygen environment; Step 2: The remaining soft monomers, hard monomers, functional monomers, and the first initiator are added dropwise, with the dropping time controlled within 2 - 4 h. After the dropping is completed, continue to keep the temperature for 6 - 10 h. Step 3: After cooling the reaction solution, pour it into a precipitating agent for precipitation, wash, dry in air, and then dry under vacuum to obtain the low molecular weight polymer. Or omit Step 2. In Step 1, all the comonomers and the initiator are added, and the reaction time is 5 - 20 h.

8. The preparation method of the OCA optical pressure-sensitive adhesive with high tensile strength and high resilience according to claim 7, characterized in that The chemical structural formula of the small molecule reversible addition-fragmentation chain transfer reagent is: R-X; where R is isopropyl acid group, acetic acid group, 2-cyanoacetic acid group, or 2-aminoacetic acid group; the X group is an alkyl dithiocarbonate group or an alkyl trithiocarbonate group; the mass of the small molecule reversible addition-fragmentation chain transfer reagent is 1 / 100 - 1 / 10 of the total mass of the comonomers. The first initiator is any one or more of ammonium persulfate, potassium persulfate, hydrogen peroxide, and hydrogen peroxide derivatives; the molar mass of the first initiator is 1 / 50 - 1 times the molar mass of the small molecule reversible addition-fragmentation chain transfer reagent.

9. The preparation method of the OCA optical pressure-sensitive adhesive with high tensile strength and high resilience according to claim 6, characterized in that, The preparation of the block copolymer includes the steps: Step 1: Dissolve the amphiphilic macromolecular reversible addition-fragmentation chain transfer reagent in water, add the hard monomer or a mixture of the hard monomer and the functional monomer, and mix evenly. Add the first initiator at 70 - 90 °C and react for 1 - 3 h to obtain a homopolymer. The homopolymer is stably dispersed in water in the form of particles to form a latex. Step 2: Add an aqueous solution of inorganic base with a certain concentration to the latex obtained in Step 1, then add the soft monomer or a mixture of the soft monomer and the functional monomer. Add water and the second initiator at 40 - 60 °C, and react for 4 - 10 h in an anaerobic environment. Then add the hard monomer or a mixture of the hard monomer and the functional monomer, and react for 5 - 10 h in an anaerobic environment to obtain a block polymer latex. Step 3: Pour the block polymer latex obtained in Step 2 into dilute hydrochloric acid for precipitation, and after washing and drying the product, obtain the block copolymer.

10. The preparation method of the OCA optical pressure-sensitive adhesive with high tensile strength and high resilience according to claim 9, characterized in that, The chemical structural formula of the amphiphilic macromolecular reversible addition-fragmentation chain transfer reagent is: R-(M n1 -b-N n2 )-X; wherein, R is isopropyl acid group, acetic acid group, 2-cyanoacetic acid group or 2-aminoacetic acid group; M n1 In M, M is a methacrylic acid monomer or an acrylic acid monomer unit, n1 is the average degree of polymerization of M, and the range of n1 is 10 to 30; N n2 In N, N is a styrene monomer, n-butyl acrylate monomer, methyl acrylate, isooctyl acrylate or methyl methacrylate monomer unit, n2 is the average degree of polymerization of N, and the range of n2 is 1 to 8; the X group is an alkyl dithiocarbonate group or an alkyl trithiocarbonate group; The molar mass of the amphiphilic macromolecular reversible addition-fragmentation chain transfer reagent is 1 / 50 - 1 times the molar mass of the small molecule reversible addition-fragmentation chain transfer reagent. The first initiator is any one or more of ammonium persulfate, potassium persulfate, hydrogen peroxide, and hydrogen peroxide derivatives; the molar mass of the first initiator is 1 / 50 - 1 times the molar mass of the macromolecular reversible addition-fragmentation chain transfer reagent. The second initiator is any one or more of 2,2'-azobis(2-methylpropionamidine) dihydrochloride, 2,2'-azobis(2-methylpropionamidine) hydrochloride, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, sodium persulfate / potassium persulfate redox initiator, and sodium persulfate / ammonium persulfate redox initiator; the molar mass of the second initiator is 1 / 50 - 1 times the molar mass of the macromolecular reversible addition-fragmentation chain transfer reagent. In Step 2, the addition of the inorganic base adjusts the pH of the reaction solution to 6 - 14.

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