Optically clear adhesive for flexible folding display and method of making the same

Abstract

The present application relates to the technical field of chemical materials, in particular to an optical transparent adhesive for flexible folding display screen, which is compounded by modified acrylic copolymer, acrylic resin and the like; firstly, the nano-silicon dioxide is treated by KH570 silane coupling agent, the vinyl group is introduced into the silicon dioxide to obtain the vinyl modified silicon dioxide, then the acrylic ester monomer, the vinyl modified silicon dioxide and the vinyl POSS are mixed, and the polymerization reaction is carried out under the action of the initiator, so that the acrylic ester copolymer containing the silicon dioxide and the POSS group chain segment is obtained, and the modified acrylic copolymer with organic-inorganic hybrid network is formed; on the one hand, the silicon dioxide is treated by KH570, which can effectively improve the compatibility of the silicon dioxide in the component, avoid the agglomeration phenomenon of the silicon dioxide during the reaction, make the silicon dioxide reaction more sufficient and complete, and improve the stability and consistency of the adhesive performance.

Description

Technical Field

[0001] This invention relates to the field of chemical materials technology, and in particular to an optically transparent adhesive for flexible folding displays and its preparation method. Background Technology

[0002] With the rapid development of flexible display technology and the widespread adoption of foldable smartphones, foldable tablets, and other terminal devices, more stringent requirements have been placed on the performance of the core supporting material—optical transparent adhesive (OCA). As a key material for achieving interlayer bonding in flexible foldable displays, OCA must simultaneously meet multiple performance requirements, including high optical transparency, excellent adhesive strength, good flexibility, and resistance to repeated folding fatigue.

[0003] Traditional optically transparent adhesives are primarily designed for rigid displays. Their core system is mostly a single acrylate polymer, achieving basic adhesion and transparency requirements by simply adjusting the monomer ratio or crosslinking density. However, in flexible folding scenarios, the limitations of these traditional materials are becoming increasingly apparent, mainly in the following aspects: First, insufficient resistance to folding fatigue. When a folding screen is repeatedly opened and closed, the adhesive layer bears complex stress. Traditional materials, with their simple molecular chain structure, are prone to problems such as bubbles and delamination due to creep accumulation, affecting the lifespan of the display. Second, difficulty in balancing mechanical strength and flexibility. Increasing the crosslinking density or adding fillers to enhance strength reduces flexibility, making it prone to breakage; conversely, reducing the crosslinking density to ensure flexibility results in insufficient cohesive strength, leading to tearing or delamination, and a high risk of failure in critical areas such as hinges. Third, poor compatibility with inorganic fillers. Adding nano-inorganic fillers easily leads to agglomeration, reducing optical transparency and affecting performance stability. Fourth, insufficient adhesive strength and interfacial adaptability. Weak interfacial forces with substrates such as polyimide result in decreased peel strength with long-term use or environmental changes.

[0004] Therefore, developing adhesives that combine high transparency, resistance to folding fatigue, suitable mechanical strength, and stable bonding performance is key to solving the interlayer bonding problem of flexible foldable displays and is of great significance to the development of flexible display technology. Summary of the Invention

[0005] One object of the present invention is to provide an optically transparent adhesive for flexible folding displays, comprising the following components in parts by weight:

[0006]

[0007] The modified acrylic copolymer is obtained by polymerizing acrylate monomers, vinyl-modified silica, and vinyl POSS.

[0008] Furthermore, the acrylate monomer is selected from one or more of butyl acrylate, isooctyl acrylate, ethyl acrylate, methyl acrylate, lauryl acrylate, isobornyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, acrylic acid, and vinyl acetate.

[0009] Furthermore, the curing agent is selected from one or more of amino resin curing agents, isocyanate curing agents, and epoxy curing agents.

[0010] Furthermore, the solvent is selected from one or more of ethyl acetate, toluene, propanol, and isopropanol.

[0011] Furthermore, the additive is selected from one or more of antistatic agents and defoamers.

[0012] Furthermore, the antistatic agent is selected from one or more of sulfuric acid derivatives, phosphoric acid derivatives, amines, quaternary ammonium salts, imidazoles, and ethylene oxide derivatives.

[0013] Furthermore, the defoamer is selected from one or more of silicone defoamers, polyether defoamers, and mineral oil defoamers.

[0014] The present invention also provides a method for preparing the optically transparent adhesive for the flexible folding display screen, comprising the following steps:

[0015] S1. Nano silica and KH570 are added to a solvent and heated to react, yielding vinyl silica.

[0016] S2. Mix acrylate monomers, vinyl silica, and vinyl POSS, add an initiator, and heat to react to obtain a modified acrylic copolymer;

[0017] S3. The modified acrylic copolymer is blended with other components to obtain the optically transparent adhesive for the flexible folding display screen.

[0018] Furthermore, in step S1, the temperature of the heating reaction is 65-75°C.

[0019] Furthermore, in step S2, the temperature of the heating reaction is 75-85°C.

[0020] The present invention has the following beneficial effects:

[0021] The optically transparent adhesive for flexible folding displays of this invention is formulated with modified acrylic copolymers, acrylic resins, etc. First, nano-silica is treated with KH570 silane coupling agent to introduce vinyl groups into the silica, resulting in vinyl-modified silica. Then, acrylate monomers, vinyl-modified silica, and vinyl POSS are mixed and polymerized under the action of an initiator to obtain an acrylate copolymer containing silica and POSS group segments, forming an organic-inorganic hybrid network of modified acrylic copolymer.

[0022] On the one hand, treating silica with KH570 can effectively improve the compatibility of silica in the components, avoid the phenomenon of silica agglomeration during the reaction, make the silica reaction more complete and efficient, and improve the stability and consistency of the adhesive performance.

[0023] Because the cage-like skeleton of the POSS group has excellent dimensional and thermal stability, it can physically entangle with the main chain of the modified acrylate copolymer and the silica segments; while the nano silica segments can fill the voids in the modified acrylate copolymer. The two can work together to absorb some of the pressure during screen folding and disperse the pressure, reducing the risk of screen damage due to repeated folding and effectively improving the mechanical strength of the adhesive.

[0024] Furthermore, during subsequent curing, the modified acrylic copolymer can undergo a crosslinking reaction with the acrylic resin and curing agent to form a three-dimensional crosslinked structure. This structure not only enhances the stability of the adhesive components but also increases the hydrogen bond density due to the introduction of a large number of oxygen-containing polar groups, resulting in strong hydrogen bonding with the substrate of the display screen. This, in turn, improves the adhesion and peel strength to the substrate. Detailed Implementation

[0025] To more clearly illustrate the technical solution of the present invention, the following embodiments are provided. Unless otherwise stated, the raw materials, reactions, and post-processing methods appearing in the embodiments are all commercially available raw materials and technical methods well known to those skilled in the art.

[0026] The terms "preferred," "more preferably," and "more suitable" used in this invention refer to embodiments of the invention that provide certain beneficial effects under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of this invention.

[0027] It should be understood that, except in any operational instance or otherwise indicated, all figures representing the amounts of ingredients used, for example, in the specification and claims, should be understood to be modified in all cases by the term "about". Therefore, unless otherwise stated, the numerical parameters set forth in the following specification and appended claims are approximations varying with the desired performance to be obtained according to the invention.

[0028] Ethyl acetate, solvent.

[0029] Vinyl POSS, P815521, purchased from Shanghai McLean Biochemical Technology Co., Ltd.

[0030] Nano silica, S776198, was purchased from Shanghai McLean Biochemical Technology Co., Ltd.

[0031] Defoamer, silicone defoamer, BYK088.

[0032] Antistatic agent, antistatic agent SN, octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate, purchased from Haian Petrochemical Plant, Jiangsu Province.

[0033] Curing agent, epoxy curing agent, GA-240, purchased from Shenzhen Jiadida New Material Technology Co., Ltd.

[0034] Acrylic resin, a polymer of 2-butyl acrylate and 2-hydroxyethyl acrylate, CAS: 32409-50-0.

[0035] KH570, silane coupling agent.

[0036] In the embodiments of this invention, "parts" refers to parts by mass.

[0037] Example 1

[0038] An optically transparent adhesive for flexible folding displays comprises the following components in parts by weight:

[0039]

[0040] The preparation method of the above-mentioned optically transparent adhesive for flexible foldable displays includes the following steps:

[0041] S1. Add 10 parts of nano silica and 1 part of KH570 to 50 parts of ethanol, stir for 3 hours, react at 70°C for 3 hours, filter, wash with deionized water 3 times, and dry to obtain vinyl silica.

[0042] S2. Add 15 parts butyl acrylate, 3 parts ethyl acrylate, 1 part hydroxyethyl acrylate, 3 parts methyl acrylate, 1.5 parts vinyl acetate, 5 parts vinyl silica, and 3 parts vinyl POSS to 40 parts ethyl acetate, add 0.5 parts azobisisobutyronitrile, mix well, heat to 80°C, and react for 5 hours to obtain the product. Then add ethyl acetate to dilute the product to a solid content of 45% to obtain the modified acrylic copolymer.

[0043] S3. Blend the other components of the modified acrylic copolymer according to the above-mentioned mass proportions to obtain the optically transparent adhesive for the flexible folding display screen.

[0044] Example 2

[0045] An optically transparent adhesive for flexible folding displays comprises the following components in parts by weight:

[0046]

[0047] The preparation method of the above-mentioned optically transparent adhesive for flexible foldable displays includes the following steps:

[0048] S1. Add 10 parts of nano silica and 1 part of KH570 to 50 parts of ethanol, stir for 3 hours, react at 70°C for 3 hours, filter, wash with deionized water 3 times, and dry to obtain vinyl silica.

[0049] S2. Add 15 parts butyl acrylate, 3 parts ethyl acrylate, 1 part hydroxyethyl acrylate, 3 parts methyl acrylate, 1.5 parts vinyl acetate, 5 parts vinyl silica, and 3 parts vinyl POSS to 40 parts ethyl acetate, add 0.5 parts azobisisobutyronitrile, mix well, heat to 80°C, and react for 5 hours to obtain the product. Then add ethyl acetate to dilute the product to a solid content of 45% to obtain the modified acrylic copolymer.

[0050] S3. Blend the other components of the modified acrylic copolymer according to the above-mentioned mass proportions to obtain the optically transparent adhesive for the flexible folding display screen.

[0051] Example 3

[0052] An optically transparent adhesive for flexible folding displays comprises the following components in parts by weight:

[0053]

[0054] The preparation method of the above-mentioned optically transparent adhesive for flexible foldable displays includes the following steps:

[0055] S1. Add 10 parts of nano silica and 1 part of KH570 to 50 parts of ethanol, stir for 3 hours, react at 70°C for 3 hours, filter, wash with deionized water 3 times, and dry to obtain vinyl silica.

[0056] S2. Add 15 parts butyl acrylate, 3 parts ethyl acrylate, 1 part hydroxyethyl acrylate, 3 parts methyl acrylate, 1.5 parts vinyl acetate, 5 parts vinyl silica, and 3 parts vinyl POSS to 40 parts ethyl acetate, add 0.5 parts azobisisobutyronitrile, mix well, heat to 80°C, and react for 5 hours to obtain the product. Then add ethyl acetate to dilute the product to a solid content of 45% to obtain the modified acrylic copolymer.

[0057] S3. Blend the other components of the modified acrylic copolymer according to the above-mentioned mass proportions to obtain the optically transparent adhesive for the flexible folding display screen.

[0058] Comparative Example 1

[0059] An adhesive, the difference between this comparative example and Example 1 is that step S1 is removed, and in step S2, vinyl silica is replaced with an equal mass of vinyl POSS, while the other components and preparation methods are the same.

[0060] Comparative Example 2

[0061] An adhesive, the difference between this comparative example and Example 1 is that in step S2, vinyl POSS is replaced with an equal mass of vinyl silica, while the other components and preparation methods are the same.

[0062] Comparative Example 3

[0063] An adhesive, the difference between this comparative example and Example 1 is that the acrylic resin in the components is replaced with an equal mass of n-butyl acrylate, while the other components and preparation method are the same.

[0064] Test Example 1

[0065] The adhesives of Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests.

[0066] The adhesives of Examples 1-3 and Comparative Examples 1-3 were applied to the surface of 50µm PET release film using a slot coating process, heated to 120°C, cured for 5 minutes, and then their performance was tested.

[0067] 180° peel strength test: Cut the test sample into strips 2.5cm wide, attach them to the surface of the polyimide board, and test according to ASTM D3330 "Standard for Testing the Peel Strength of Pressure-Sensitive Adhesive Tapes";

[0068] Test method: The test sample was placed at room temperature for 20 minutes before the test was conducted. The average adhesion required to tear the sample strip from the test panel was recorded and expressed as gf / 25mm.

[0069] Shear modulus test: Multiple samples were stacked to obtain a sample with a thickness of about 1 mm, and then cut into a disc shape with a diameter of 8 mm. The shear modulus at 35 °C was measured using a rheometer (TA company, model: HR10) at a frequency of 1 Hz, and the measured shear modulus value was recorded.

[0070] Folding performance test: The sample was bonded to the surface of a polyimide board to form a structure of polyimide layer, adhesive layer, polyimide layer, adhesive layer, and polyimide layer. It was then subjected to a pressure of 0.5 MPa and 50℃ for 30 minutes to remove bubbles. Its folding performance at 35℃ was then tested using a folding device (Beijing Wohua Huitong Measurement and Control Technology Co., Ltd., device model: WH-1711-2W), with a folding radius of curvature R = 1 mm.

[0071] The test results are shown in Table 1.

[0072] Table 1. Performance test results of the adhesives in Examples 1-3 and Comparative Examples 1-3

[0073]

[0074]

[0075] Table 1 shows that the adhesives in Examples 1-3 are significantly superior to the comparative examples in terms of shear modulus, 180° peel force, and folding durability. Comparative Examples 1 and 2 show reduced shear modulus and folding life due to the lack of the synergistic mechanism of silica and POSS groups; Comparative Example 3 experiences a sharp drop in peel force due to weakened crosslinking network.

[0076] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0077] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. An optically transparent adhesive for a flexible folding display screen, characterized in that, It is made from the following components in parts by weight: 55-75 parts of modified acrylic copolymer 10-25 parts acrylic resin 1-3 parts of curing agent 30-45 parts of solvent Additives: 0.1-5 parts; The modified acrylic copolymer is obtained by polymerizing butyl acrylate, ethyl acrylate, methyl acrylate, hydroxyethyl acrylate, vinyl acetate, vinyl silica and vinyl POSS; A method for preparing an optically transparent adhesive for flexible foldable displays includes the following steps: S1. Nano silica and KH570 are added to a solvent and heated to react, yielding vinyl silica. S2. Mix butyl acrylate, ethyl acrylate, methyl acrylate, hydroxyethyl acrylate, vinyl acetate, vinyl silica, and vinyl POSS, add an initiator, and heat to react to obtain a modified acrylic copolymer. S3. Blend the modified acrylic copolymer with other components of the adhesive to obtain the optically transparent adhesive for the flexible folding display screen; Acrylic resin is a polymer of butyl acrylate and 2-hydroxyethyl acrylate.

2. The optically transparent adhesive for flexible folding displays according to claim 1, characterized in that, The curing agent is selected from one or more of amino resin curing agents, isocyanate curing agents, and epoxy curing agents.

3. The optically transparent adhesive for flexible folding displays according to claim 1, characterized in that, The solvent is selected from one or more of ethyl acetate, toluene, propanol, and isopropanol.

4. The optically transparent adhesive for flexible folding displays according to claim 1, characterized in that, The additives are selected from one or more of antistatic agents and defoamers.

5. The optically transparent adhesive for flexible folding displays according to claim 4, characterized in that, The antistatic agent is a quaternary ammonium salt.

6. The optically transparent adhesive for flexible folding displays according to claim 4, characterized in that, The defoamer is selected from one or more of silicone defoamers, polyether defoamers, and mineral oil defoamers.

7. The method for preparing the optically transparent adhesive for the flexible folding display screen according to any one of claims 1-6, characterized in that, Includes the following steps: S1. Nano silica and KH570 are added to a solvent and heated to react, yielding vinyl silica. S2. Mix butyl acrylate, ethyl acrylate, methyl acrylate, hydroxyethyl acrylate, vinyl acetate, vinyl silica, and vinyl POSS, add an initiator, and heat to react to obtain a modified acrylic copolymer. S3. The modified acrylic copolymer is blended with other components to obtain the optically transparent adhesive for the flexible folding display screen.

8. The method for preparing the optically transparent adhesive for flexible foldable displays according to claim 7, characterized in that, In step S1, the temperature of the heating reaction is 65-75℃.

9. The method for preparing the optically transparent adhesive for flexible foldable displays according to claim 7, characterized in that, In step S2, the temperature of the heating reaction is 75-85℃.

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