High-cohesion OCA optical pressure-sensitive adhesive and preparation method thereof

Abstract

The invention discloses a high-cohesion OCA optical pressure-sensitive adhesive and a preparation method thereof. The high-cohesion OCA optical pressure-sensitive adhesive is obtained by dissolving a raw material containing a triblock copolymer in a dispersion medium, coating to form a film and drying, the triblock copolymer is in reversible addition fragmentation chain transfer solution polymerization, the structural general formula of the triblock copolymer is (M1-ran-M2)-b-(M3-ran-M4)-b-(M5-ran-M6), and M1 and M5 are composed of hard monomers; m3 is composed of soft monomers; m2, M4 and M6 are composed of functional monomers; the mass content of the hard monomer in the triblock copolymer is 3-20%, the mass content of the soft monomer is 70-85%, and the mass content of the functional monomer is 8-30%. According to the invention, the segmented copolymer with high functional monomer content is designed, monomers containing hydroxyl, carboxyl, amino and other functional groups are embedded into the copolymer structure, the cohesion of the polymer is obviously improved, the bonding performance, heat resistance and the like of the prepared optical adhesive are greatly improved, and the OCA optical pressure-sensitive adhesive with excellent comprehensive performance is obtained.

Description

Technical Field

[0001] This invention relates to the field of optical adhesive technology, specifically to a high-cohesive OCA optical pressure-sensitive adhesive and its preparation method. Background Technology

[0002] The preparation and customization of polymers has always been an important research direction in materials science and engineering. To meet the needs of different applications, researchers have been seeking to develop new methods to synthesize multifunctional polymers, especially triblock copolymers.

[0003] Traditional polymerization methods have limitations, such as the difficulty in precisely controlling polymer structure and molecular weight distribution. However, the introduction of reversible addition-fragmentation chain transfer polymerization has changed this situation. This method allows for the easy introduction of different monomers during the reaction process while synthesizing polymers, enabling highly customized polymer designs. Researchers can design structures to impart various specific properties to polymers based on desired characteristics. Triblock copolymers prepared by reversible addition-fragmentation chain transfer emulsion polymerization have been well applied in the field of optical adhesives; however, due to their poor emulsion stability, polymerization of large amounts of acidic functional monomers such as acrylic acid can lead to demulsification, thus affecting product quality.

[0004] CN117844411A discloses an aqueous emulsion polymer binder for secondary batteries and its preparation method. The binder is produced by aqueous emulsion polymerization, and the specific steps include the preparation of polymer seed microemulsion and the preparation of aqueous emulsion polymer binder. The preparation method is simple, low-cost, safe and environmentally friendly. The resulting aqueous emulsion polymer binder has excellent adhesion and can reduce its usage. However, in its embodiments, it can be found that the amount of acrylic monomer added accounts for less than 5% of the total amount of monomers added, which limits the further improvement of adhesion.

[0005] CN116903806A discloses a soap-free RAFT microemulsion polymerization method for preparing a polyacrylate emulsion. The polyacrylate emulsion is a core-shell structured hydrophobic and oleophobic emulsion. The emulsion is synthesized by RAFT microemulsion copolymerization with modified flower-like nano-SiO2 as the core and acrylate and silane coupling agent copolymer as the shell. This method provides a hydrophobic and oleophobic emulsion that can be used to prepare green and environmentally friendly coatings. However, it cannot add a high content of acrylic functional monomers, resulting in low adhesion.

[0006] Therefore, introducing a large number of functional monomers into triblock copolymers is a direction for improving the adhesive strength of pressure-sensitive adhesives, providing new possibilities for the continuous expansion and improvement of polymer applications. Summary of the Invention

[0007] This invention addresses the problem that the adhesive properties of block copolymers in the prior art need to be improved due to the low content of functional monomers. It provides a block copolymer with a high content of functional monomers, which can be used to prepare OCA optical pressure-sensitive adhesive with high peel strength and high cohesion.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A high-cohesive OCA optical pressure-sensitive adhesive, wherein the OCA optical pressure-sensitive adhesive is obtained by dissolving raw materials containing triblock copolymers in a dispersion medium, coating them into a film, and then drying them;

[0010] The triblock copolymer has the general formula (M1-ran-M2)-b-(M3-ran-M4)-b-(M5-ran-M6), wherein M1 and M5 are composed of hard monomers; M3 is composed of soft monomers; and M2, M4 and M6 are composed of functional monomers.

[0011] The triblock copolymer contains 3-20% by mass of hard monomers, 70-85% by mass of soft monomers, and 8-30% by mass of functional monomers.

[0012] The functional monomers include one or more of the following: methacrylic acid, β-acryloyloxypropionic acid, acrylic acid, itaconic acid, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, ethylenedimethylamine methacrylate, methacrylamide, and N-hydroxymethylacrylamide.

[0013] The triblock copolymer was prepared by reversible addition-fragmentation chain transfer solution polymerization.

[0014] This invention designs block copolymers with high functional monomer content, embedding monomers containing functional groups such as hydroxyl, carboxyl, and amino groups into the copolymer structure, significantly improving the polymer's cohesive strength. The resulting optical adhesive exhibits greatly enhanced adhesive and heat resistance properties. Since most functional monomers are polar molecules with carboxyl groups, this invention utilizes solution polymerization to prepare the block copolymers, avoiding the demulsification caused by excessive acidic functional monomers in emulsion polymerization. This allows for a significant increase in the amount of functional monomers added, resulting in an OCA optical pressure-sensitive adhesive with excellent overall performance.

[0015] Preferably, the mass percentage of M2 or M6 in the triblock copolymer is 0-15%; the mass percentage of M6 is 8-30%. With the functional monomer located in the middle segment, the resulting block copolymer exhibits better viscosity.

[0016] The hard monomer includes one or more of styrene, methyl acrylate, isobornyl acrylate, cyclohexyl acrylate, methyl methacrylate, acrylamide, acrylonitrile, and vinyl acetate, with a glass transition temperature range of 60–150°C.

[0017] 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, with a glass transition temperature range of -90 to -30°C.

[0018] Preferably, the functional monomer is one or more of acrylic acid, β-acryloyloxypropionic acid, ethylenedimethylamine methacrylate, and amine methacrylate.

[0019] More preferably, the functional monomer is one or more of acrylic acid, β-acryloyloxypropionic acid, and ethylenedimethylamine methacrylate. The main reason is that these functional groups can form strong polar interactions with the molecular surface of the adherend, such as hydrogen bonds and dipole-dipole interactions. These interactions increase the intermolecular attraction, thereby increasing the cohesive force between the optical pressure-sensitive adhesive and the adherend material, resulting in stronger product adhesion.

[0020] This invention also provides a method for preparing the aforementioned high-cohesion OCA optical pressure-sensitive adhesive, comprising the following steps:

[0021] Step 1: Dissolve the hard monomer or a mixture of hard monomer and functional monomer, initiator, and small molecule reversible addition-fragmentation chain transfer reagent in the reaction solvent and stir until homogeneous. Heat to 40-80℃ and react for 1-5 hours in an oxygen-free environment to obtain a polymer solution.

[0022] Step 2: Add the soft monomer or a mixture of soft monomer and functional monomer as an initiator to the solution in Step 1 and continue the reaction for 2-8 hours;

[0023] Step 3: Add the hard monomer or a mixture of hard monomer and functional monomer initiator to the solution in step 2 and continue the reaction for 2-8 hours. After the reaction system is cooled, add a precipitant to precipitate, wash and dry to obtain the triblock copolymer.

[0024] Step 4: Dissolve the triblock copolymer in a dispersion medium, coat it into a film under an inert gas environment, and then dry it to obtain the OCA optical pressure-sensitive adhesive.

[0025] The advantage of reversible addition-fragmentation chain transfer solution polymerization is that it uses organic reagents as solvents to polymerize a large number of functional monomers. This helps to prepare copolymers with more complex structures, thereby improving the structure and properties of polymers, such as optimizing adhesive properties, thermal properties, and improving mechanical strength.

[0026] The chemical structural formula of the small molecule reversible addition-fragmentation chain transfer reagent is: RX; wherein R is isopropionic acid group, acetate group, 2-cyanoacetic acid group or 2-aminoacetic acid group; X group is alkyl dithioester group or alkyl trithioester group; the added mass is 1 / 500-1 / 100 of the total mass of all monomers.

[0027] The initiator is any one of azobisisobutyric acid, azobisisobutyrazoline hydrochloride, azobisisobutyramidine hydrochloride, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone, sodium persulfate / potassium persulfate redox initiator, and sodium persulfate / ammonium persulfate redox initiator; the total mass of the initiator added is 1 / 50 to 1 / 10 of the mass of the small molecule reversible addition-fragmentation chain transfer reagent.

[0028] The precipitant is one or more of methanol, ethanol, acetone, butanone, nitromethane, methyl phthalate, hexane, chlorohexane, diethyl ether, ethyl acetate, dioxane, cyclohexanol, fatty alcohol, petroleum ether, cyclohexane, tetrahydrofuran, and water. The amount used is sufficient to precipitate most of the copolymer, typically 3-10 times the total monomer mass.

[0029] The dispersion medium is any one or more of diethyl ether, methyl tert-butyl ether, tetrahydrofuran, methyl ethyl ketone, ethyl acetate and methyl propionate. The amount of dispersion medium used is preferably sufficient to substantially dissolve the copolymer, and preferably the mass of the dispersion medium is 1-4 times the total mass of all monomers.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The present invention introduces a reversible addition-fragmentation chain transfer solution polymerization method, which, compared with the reversible addition-fragmentation chain transfer emulsion polymerization method, can easily introduce a large number of functional monomers during the polymerization process, thereby adjusting the polymer properties.

[0032] (2) The preparation method of reversible addition-fragmentation chain transfer solution polymerization has obvious advantages for complex triblock copolymers and for optimizing the adhesive properties, cohesive force, heat resistance and other properties of OCA optical adhesives.

[0033] (3) The reversible addition-fragmentation chain transfer solution polymerization method achieves a highly efficient reaction process, which helps to increase yield and ensure product quality. The advantage of this method lies in its controllability, which can produce polymers with high consistency and stable performance, helping to meet the requirements of commercial applications and improve the competitiveness and feasibility of products. Attached Figure Description

[0034] Figure 1 The image shows the GPC curves of the block copolymers from different steps in Example 1.

[0035] Figure 2 The dynamic mechanical properties data are for the block copolymers prepared in Example 1 and Comparative Example 1.

[0036] Figure 3 The image shows the peel strength results of the OCA optical adhesive obtained in Example 2. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should be covered within the protection scope of this invention.

[0038] All raw materials used in the following specific implementation methods were purchased from the market.

[0039] Example 1

[0040] Preparation and properties of OCA optical pressure-sensitive adhesive containing poly(styrene-b-(isooctyl acrylate-ran-acrylic acid)-b-styrene) block copolymers: This example uses the RAFT reversible addition-fragmentation chain transfer solution polymerization method for material preparation, and the specific steps are as follows:

[0041] Step 1: Dissolve 1 part by mass of a small molecule reversible addition-fragmentation chain transfer reagent, 0.02 parts by mass of azodicyanovalerate, and 30 parts by mass of styrene in 150 parts by mass of dioxane and stir until homogeneous. Heat to 60°C and react in an anaerobic environment for 2 hours to obtain a styrene homopolymer. The chemical structural formula of the small molecule reversible addition-fragmentation chain transfer reagent is as follows:

[0042]

[0043] Step 2: Add 150 parts by weight of isooctyl acrylate and different parts by weight of acrylic acid (10-50 parts) to the reaction system and continue the reaction for 4 hours.

[0044] Step 3: Add 30 parts by mass of styrene to the reaction system and continue the reaction for 4 hours;

[0045] Step 4: Cool the system naturally to 30°C, slowly pour the solution into 600 parts by mass of n-hexane for precipitation, repeatedly wash, stir and crush until fine sand-like, then put it in a mortar and air dry in a fume hood, and vacuum dry at 35°C to obtain the block copolymer.

[0046] Step 5: Dissolve the block copolymer in tetrahydrofuran, coat it into a film in an argon atmosphere, and dry it to finally obtain OCA optical adhesive.

[0047] The molecular weight characterization of the polymer prepared in the fourth step was performed on a Waters 1525-2414-717 GPC gel permeation chromatography instrument with tetrahydrofuran as the eluent and narrow-distribution polystyrene standard as the calibration.

[0048] The mechanical properties of the polymer were tested using a universal testing machine (Zwick / Roll Z020). The polymer film from step four was cut into dumbbell-shaped strips using a standard cutting tool. The test method was GB 16421-1996, with a tensile rate of 30 mm / min. Each sample was tested at least three times.

[0049] The stress relaxation recovery performance of the polymer was tested using DMA (TAQ800). The OCA optical pressure-sensitive adhesive film from step four was cut into strips with a width of 5 mm and a length of 25 mm. The OCA optical pressure-sensitive adhesive was tested under strains of 100%, 200%, 300%, 400%, and 500% for 1 hour, and then maintained under a stress of 0 MPa for 1 hour. The recovery curves were recorded.

[0050] The dynamic mechanical properties of the polymer were characterized using a rotational rheometer (HAAKE MARS 60). The polymer film was cut into circular strips with a diameter of 2 cm. The test frequency was 0.01 Hz–1 Hz, and the test temperature was 25 °C. The loss factor tanδ of the material was recorded during the measurement process.

[0051] The peel strength of the polymer was tested using an adhesive shear strength tester (KJ-1066A). The OCA optical pressure-sensitive adhesive film from step 5 was cut into strips with a width of 25 mm and a length of approximately 300 mm. The test method adopted was GB / T 2792-2014, and the test of each sample was repeated at least three times.

[0052] Figure 1 The figures show the GPC curves of the block copolymers obtained after each stage of the reaction in Example 1. Curve 1 represents polystyrene (PSt) after the first homopolymerization step; curve 2 represents poly(styrene-b-(isooctyl acrylate-ran-acrylic acid)(PSt-P(EHA-ran-AA)) added in the second step; and curve 3 represents poly(styrene-b-(isooctyl acrylate-ran-acrylic acid)-b-styrene)(PSt-P(EHA-ran-AA)-PSt). It can be seen that as the number of blocks increases, the molecular weight of the polymer shifts towards higher molecular weights, indicating that the product is a block copolymer with molecular weights of 0.5W-15W-0.5W for each block.

[0053] Comparative Example 1

[0054] Preparation and properties of OCA optical pressure-sensitive adhesive containing poly(styrene-b-isooctyl acrylate-b-styrene) block copolymer: The adhesive was prepared via reversible addition-fragmentation chain transfer emulsion polymerization, with the specific steps as follows:

[0055] Step 1: Add 1 part by mass of the amphiphilic macromolecular RAFT reagent (an amphiphilic macromolecular reversible addition-fragmentation chain transfer reagent) and 13 parts by mass of water, stirring until completely dissolved. Then add 30 parts by mass of styrene and stir to mix. The chemical structural formula of the amphiphilic macromolecular RAFT reagent is:

[0056]

[0057] Step 2: Add the above raw materials to a four-necked flask, purge with nitrogen at room temperature for 0.5 hours to remove oxygen, then heat to 70°C in a water bath. Add potassium persulfate aqueous solution (0.02 parts by mass of potassium persulfate dissolved in 12 parts by mass of water) and react for 1 hour. Then slowly add sodium hydroxide aqueous solution (1 part by mass of sodium hydroxide dissolved in 10 parts by mass of water), followed by 150 parts by mass of isooctyl acrylate and 50 parts by mass of water, then add 0.02 parts by mass of azobisisobutyrazoline hydrochloride and react for 2 hours. Finally, add 30 parts by mass of styrene and react for 1.5 hours to obtain the polymer latex.

[0058] Step 3: After the reaction is complete, the precipitated product is washed with distilled water several times until it is neutral, dried and then placed in a vacuum oven at 120°C for 12 hours to finally obtain white polymer particles.

[0059] Step 4: Dissolve the polymer in methyl ethyl ketone (MEK) and pour it into a 12 cm diameter polytetrafluoroethylene (PTFE) petri dish to form a film. First, allow most of the solvent to evaporate at room temperature, then place it in a 130 °C vacuum oven to continue drying and annealing to prepare a polymer film with a thickness of approximately 0.8–1 mm.

[0060] Step 5: Dissolve the polymer in methyl ethyl ketone (MEK) and prepare an OCA optical pressure-sensitive adhesive film with a thickness of approximately 25 μm using a wire bar coater for peel strength testing.

[0061] Table 1 shows the mechanical properties, peel strength, and strain recovery rate of optical adhesives prepared by emulsion polymerization with different mass parts of acrylic acid (0, 20, 35, and 50 parts) and Comparative Example 1. Compared with optical adhesives prepared by reversible addition-fragmentation chain transfer emulsion polymerization, optical adhesives prepared by reversible addition-fragmentation chain transfer solution polymerization allow for the addition of a large amount of acrylic acid, resulting in a significant improvement in peel strength. For example, when the mass part of acrylic acid is 50, the peel strength of the optical adhesive is 16.8 N / 25 mm, which is significantly higher than the viscosity of the polymer without functional monomers. Compared with Comparative Example 1 (4.2 N / 25 mm), it also has a better balance between low modulus, high strain recovery rate, and peel strength.

[0062] Table 1 Properties of polymers prepared with different mass parts of acrylic acid

[0063]

[0064] Example 2

[0065] Preparation and properties of poly(styrene-b-(isooctyl acrylate-ran-functional monomer)-b-styrene) block copolymers, wherein acrylic acid can be replaced by other functional monomers, such as β-acryloyloxypropionic acid and hydroxyethyl acrylate. This example uses the RAFT reversible addition-fragmentation chain transfer solution polymerization method for material preparation, and the specific steps are as follows:

[0066] Step 1: 1 part by mass of a small-molecule reversible addition-fragmentation chain transfer reagent, 0.02 parts by mass of azodicyanovalerate, and 30 parts by mass of styrene are mixed with 150 parts by mass of dioxane until homogeneous. The mixture is heated to 60°C and reacted in an anaerobic environment for 2 hours to obtain a styrene homopolymer. The chemical structural formula of the small-molecule reversible addition-fragmentation chain transfer reagent is as follows:

[0067]

[0068] Step 2: Add 150 parts by weight of isooctyl acrylate and 35 parts by weight of functional monomers (β-acryloyloxypropionic acid, hydroxyethyl acrylate and ethylenedimethylamine methacrylate) to the reaction system and continue the reaction for 5 hours.

[0069] Step 3: Add 30 parts by mass of styrene to the reaction system and continue the reaction for 4 hours;

[0070] Step 4: Cool the system naturally to 30°C, slowly pour the solution into 600 parts by mass of n-hexane for precipitation, repeatedly wash, stir and crush until fine sand-like, then put it in a mortar and air dry in a fume hood, and vacuum dry at 35°C to obtain the block copolymer.

[0071] Step 5: Dissolve the block copolymer in tetrahydrofuran, coat it into a film in an argon atmosphere, and dry it to finally obtain OCA optical adhesive.

[0072] The molecular weight characterization and mechanical property testing of the polymer in this embodiment are similar to those in Example 1. Figure 3 This refers to the optical adhesive peel strength of Example 2 with the addition of different functional monomers.

[0073] Table 2 shows the mechanical properties, peel strength, and strain recovery rate of optical adhesives with different types of functional monomers. Compared with optical adhesives prepared by reversible addition-fragmentation chain transfer emulsion polymerization, optical adhesives prepared by reversible addition-fragmentation chain transfer solution polymerization can allow the addition of a large number of functional monomers (such as acrylic acid, β-acryloyloxypropionic acid, hydroxyethyl acrylate, ethylenedimethyl methacrylate, etc.). The optical adhesives obtained by adding different monomers also have different properties.

[0074] Among the optical adhesives containing β-acryloyloxypropionic acid, the one with the highest peel strength was the one containing hydroxyethyl acrylate, while the one with relatively lower peel strength was the one containing hydroxyl acrylate. This is because the carboxyl group is more polar than the hydroxyl group, resulting in higher peel strength. Monomers containing nitrogen groups have even higher polarity, leading to even stronger peel strength.

[0075] Table 2 Performance data of pressure-sensitive adhesives prepared with different functional monomers

[0076]

[0077] Example 3

[0078] Preparation and properties of poly((styrene-ran-β-acryloyloxypropionic acid)-b-(isooctyl acrylate)-b-(styrene)) block copolymers, wherein the functional monomer β-acryloyloxypropionic acid can be located at different positions. In this embodiment, the material is prepared by RAFT reversible addition-fragmentation chain transfer solution polymerization. The specific steps are as follows:

[0079] Step 1: Dissolve 1 part by mass of a small molecule reversible addition-fragmentation chain transfer reagent, 0.02 parts by mass of azodicyanovalerate, and a mixture of 30 parts by mass of styrene and 35 parts by mass of β-acryloyloxypropionic acid in 150 parts by mass of dioxane and stir until homogeneous. Heat to 60°C and react in an anaerobic environment for 2 hours to obtain a styrene homopolymer. The chemical structural formula of the small molecule reversible addition-fragmentation chain transfer reagent is as follows:

[0080]

[0081] Step 2: Add 150 parts by weight of isooctyl acrylate to the reaction system and continue the reaction for 5 hours;

[0082] Step 3: Continue reacting 30 parts by weight of styrene for 4 hours;

[0083] Step 4: Cool the system naturally to 30°C, slowly pour the solution into 600 parts of n-hexane for precipitation, repeatedly wash, stir and crush until fine sand-like, then put it in a mortar and dry it in a fume hood, and then vacuum dry it at 35°C to obtain the block copolymer.

[0084] Step 5: Dissolve the block copolymer in tetrahydrofuran, coat it into a film in an argon atmosphere, and dry it to finally obtain OCA optical adhesive.

[0085] Example 4

[0086] Preparation and properties of poly((styrene)-b-(isooctyl acrylate)-b-(styrene-ran-β-acryloyloxypropionic acid)) block copolymers, wherein the functional monomer β-acryloyloxypropionic acid is located at different positions. In this example, the material is prepared by RAFT reversible addition-fragmentation chain transfer solution polymerization. The specific steps are as follows:

[0087] Step 1: Dissolve 1 part by mass of a small molecule reversible addition-fragmentation chain transfer reagent, 0.02 parts by mass of azodicyanovalerate, and 30 parts by mass of styrene in 150 parts by mass of dioxane and stir until homogeneous. Heat to 60°C and react in an anaerobic environment for 2 hours to obtain a styrene homopolymer. The chemical structural formula of the small molecule reversible addition-fragmentation chain transfer reagent is as follows:

[0088]

[0089] Step 2: Add 150 parts by weight of isooctyl acrylate to the reaction system and continue the reaction for 5 hours;

[0090] Step 3: Continue reacting the mixture of 30 parts by weight of styrene and 35 parts by weight of β-acryloyloxypropionic acid for 4 hours.

[0091] Step 4: Cool the system naturally to 30°C, slowly pour the solution into 600 parts by mass of n-hexane for precipitation, repeatedly wash, stir and crush until fine sand-like, then put it in a mortar and air dry in a fume hood, and vacuum dry at 35°C to obtain the block copolymer.

[0092] Step 5: Dissolve the block copolymer in tetrahydrofuran, coat it into a film in an argon atmosphere, and dry it to finally obtain OCA optical adhesive.

[0093] Example 5

[0094] Preparation and properties of poly((styrene)-b-(isooctyl acrylate-ran-β-acryloyloxypropionic acid)-b-(styrene-ran-β-acryloyloxypropionic acid)) block copolymers, wherein the functional monomer β-acryloyloxypropionic acid is located at different positions. In this example, the material is prepared by RAFT reversible addition-fragmentation chain transfer solution polymerization. The specific steps are as follows:

[0095] Step 1: Dissolve 1 part by mass of a small molecule reversible addition-fragmentation chain transfer reagent, 0.02 parts by mass of azodicyanovalerate, and 30 parts by mass of styrene in 150 parts by mass of dioxane and stir until homogeneous. Heat to 60°C and react in an anaerobic environment for 2 hours to obtain a styrene homopolymer. The chemical structural formula of the small molecule reversible addition-fragmentation chain transfer reagent is as follows:

[0096]

[0097] Step 2: Add 150 parts by weight of the mixture of isooctyl acrylate and 25 parts by weight of β-acryloyloxypropionic acid to the reaction system and continue the reaction for 5 hours.

[0098] Step 3: Continue reacting the mixture of 30 parts by weight of styrene and 10 parts by weight of β-acryloyloxypropionic acid for 4 hours.

[0099] Step 4: Cool the system naturally to 30°C, slowly pour the solution into n-hexane to precipitate, repeatedly wash, stir and crush until fine sand-like, then put it in a mortar and dry it in a fume hood, and then vacuum dry it at 35°C to obtain the block copolymer.

[0100] Step 5: Dissolve the block copolymer in tetrahydrofuran, coat it into a film in an argon atmosphere, and dry it to finally obtain OCA optical adhesive.

[0101] The molecular weight characterization and mechanical property testing of the copolymer with added β-acryloyloxypropionic acid in Example 2, and the polymers in Examples 3-5, were similar to those in Example 1. Table 3 shows the optical adhesive mechanical properties, peel strength, and strain recovery rate data for the added functional monomer β-acryloyloxypropionic acid at different positions in the structure, with better performance observed in the middle section.

[0102] Table 3. Performance data of optical pressure-sensitive adhesives with functional monomers at different block positions.

[0103]

[0104] Figure 2 The dynamic mechanical property curves for Example 1 and Comparative Example 1 show that as the acrylic acid content increases, the storage modulus increases slightly, but the increase is small and does not affect the use of the optical adhesive.

[0105] Figure 3 The peel strength data for Example 2 shows that the stronger the polarity of the functional monomer, the higher the peel strength of the optical adhesive.

[0106] The above embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A high-cohesive OCA optical pressure-sensitive adhesive, characterized in that, The OCA optical pressure-sensitive adhesive is obtained by dissolving raw materials containing triblock copolymers in a dispersion medium, coating them into a film, and then drying them. The triblock copolymer has the general formula (M1-ran-M2)-b-(M3-ran-M4)-b-(M5-ran-M6), wherein M1 and M5 are composed of hard monomers; M3 is composed of soft monomers; and M2, M4 and M6 are composed of functional monomers. The triblock copolymer contains 3-20% by mass of hard monomers, 70-85% by mass of soft monomers, and 8-30% by mass of functional monomers. The functional monomers include one or more of the following: methacrylic acid, β-acryloyloxypropionic acid, acrylic acid, itaconic acid, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, ethylenedimethylamine methacrylate, methacrylamide, and N-hydroxymethylacrylamide. The triblock copolymer was prepared by reversible addition-fragmentation chain transfer solution polymerization.

2. The high-cohesion OCA optical pressure-sensitive adhesive according to claim 1, characterized in that, The triblock copolymer contains M2 or M6 at a mass percentage of 0-15%; M6 at a mass percentage of 8-30%.

3. The high-cohesion OCA optical pressure-sensitive adhesive according to claim 1, 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, with a glass transition temperature range of 60–150°C.

4. The high-cohesion OCA optical pressure-sensitive adhesive according to claim 1, characterized in that, 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, with a glass transition temperature range of -90 to -30°C.

5. The high-cohesion OCA optical pressure-sensitive adhesive according to claim 1 or 4, characterized in that, The functional monomer is one or more of acrylic acid, β-acryloyloxypropionic acid, ethylenedimethylamine methacrylate, and amine methacrylate.

6. The method for preparing the high-cohesion OCA optical pressure-sensitive adhesive according to any one of claims 1-5, characterized in that, Including the following steps: Step 1: Dissolve the hard monomer or a mixture of hard monomer and functional monomer, initiator, and small molecule reversible addition-fragmentation chain transfer reagent in the reaction solvent and stir until homogeneous. Heat to 40-80℃ and react for 1-5 hours in an oxygen-free environment to obtain a polymer solution. Step 2: Add the soft monomer or a mixture of soft monomer and functional monomer as an initiator to the solution in Step 1 and continue the reaction for 2-8 hours; Step 3: Add the hard monomer or a mixture of hard monomer and functional monomer initiator to the solution in step 2 and continue the reaction for 2-8 hours. After the reaction system is cooled, add a precipitant to precipitate, wash and dry to obtain the triblock copolymer. Step 4: Dissolve the triblock copolymer in a dispersion medium, coat it into a film under an inert gas environment, and then dry it to obtain the OCA optical pressure-sensitive adhesive.

7. The method for preparing the high-cohesion OCA optical pressure-sensitive adhesive according to claim 6, characterized in that, The chemical structural formula of the small molecule reversible addition-fragmentation chain transfer reagent is: RX; wherein R is isopropionic acid group, acetate group, 2-cyanoacetic acid group or 2-aminoacetic acid group; X group is alkyl dithioester group or alkyl trithioester group; the added mass is 1 / 500-1 / 100 of the total mass of all monomers.

8. The method for preparing the high-cohesion OCA optical pressure-sensitive adhesive according to claim 6, characterized in that, The initiator is any one of azobisisobutyric acid, azobisisobutyrazoline hydrochloride, azobisisobutyramidine hydrochloride, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone, sodium persulfate / potassium persulfate redox initiator, and sodium persulfate / ammonium persulfate redox initiator; the total mass of the initiator added is 1 / 50 to 1 / 10 of the mass of the small molecule reversible addition-fragmentation chain transfer reagent.

9. The method for preparing the high-cohesion OCA optical pressure-sensitive adhesive according to claim 6, characterized in that, The precipitant is one or more of methanol, ethanol, acetone, butanone, nitromethane, methyl phthalate, hexane, chlorohexane, diethyl ether, ethyl acetate, dioxane, cyclohexanol, fatty alcohol, petroleum ether, cyclohexane, tetrahydrofuran, and water.

10. The method for preparing the high-cohesion OCA optical pressure-sensitive adhesive according to claim 6, characterized in that, The dispersion medium is any one or more of diethyl ether, methyl tert-butyl ether, tetrahydrofuran, methyl ethyl ketone, ethyl acetate, and methyl propionate.

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