OCA (Optical Clear Adhesive) for folding screen and preparation method of OCA

Abstract

The invention relates to the field of adhesives, and particularly discloses an OCA optical adhesive for a folding screen and a preparation method of the OCA optical adhesive. The OCA optical adhesive for the folding screen is prepared from the following raw materials in parts by weight: 60 to 80 parts of urethane acrylate, 15 to 25 parts of organic silicon grafted glycidyl ether, 20 to 30 parts of a diluent, 5 to 10 parts of a photoinitiator and 1 to 2 parts of an antioxidant, the organic silicon grafted glycidyl ether is prepared by reacting vinyl siloxane, pentaerythritol triallyl ether, allyl glycidyl ether and a catalyst. The OCA optical cement for the folding screen prepared by the invention is applied to the folding screen, and can keep relatively good elasticity, bending resistance and bonding strength in the long-term repeated folding use process, and wrinkles and bubbles are not easy to appear.

Description

Technical Field

[0001] The present application relates to the field of adhesives, and more specifically, it relates to an OCA optical adhesive for foldable screens and a preparation method thereof. Background Art

[0002] With the update and iteration of electronic products, the technology of foldable mobile phones has become increasingly mature. In response to the special requirements of foldable mobile phones, foldable OCA, as an adhesive material specifically designed for foldable screens, exhibits excellent flexibility and fold resistance. It can maintain stable adhesion, continuously provide protection for the display screen during repeated folding and unfolding, and ensure the continuity and stability of the displayed image. It is widely used in the flexible OLED display structure of foldable mobile phone screens, including the cover plate layer, polarizer layer, touch film layer, and OLED layer, etc.

[0003] When all the functional films of the foldable screen are firmly adhered by the OCA adhesive film to form an integral whole, a problem will arise: during the use of the foldable screen, the external force will be decomposed into two opposite acting forces at the bending position. The outer side of the bending part is the tensile stress layer, and the inner side is the compressive stress layer. When the adhesive force of the OCA optical adhesive is too high, the functional film in the tensile stress layer will break. If the adhesive force of the OCA optical adhesive is too low, the functional film in the compressive stress layer will have problems such as delamination.

[0004] The foldable OCA optical adhesive used in the prior art is generally an acrylic pressure-sensitive adhesive, which can endow the foldable screen with excellent optical properties, flexibility, and adhesion properties. The traditional linear polymer structure of the acrylic pressure-sensitive adhesive has a relatively low cohesive strength and has good adhesion strength, but it reduces the resilience and fold resistance of the acrylic pressure-sensitive adhesive. Although crosslinking can improve the elasticity and fold resistance of the acrylic pressure-sensitive adhesive, crosslinking will also reduce the mobility of the polymer chains, thereby affecting the adhesion strength of the acrylic pressure-sensitive adhesive. As a result, during the long-term repeated folding use of the OCA optical adhesive, problems such as screen interlayer separation and bubbles are likely to occur. Therefore, further research is still needed for the existing foldable OCA. Summary of the Invention

[0005] In order to solve the problem that the existing foldable OCA cannot well balance the fold resistance and adhesion strength during long-term repeated folding use, the present application provides an OCA optical adhesive for foldable screens and a preparation method thereof.

[0006] In the first aspect, the present application provides an OCA optical adhesive for foldable screens, adopting the following technical solution: An OCA optical adhesive for foldable screens is prepared from the following raw materials in parts by weight: Polyurethane acrylate 60 - 80 parts 15 - 25 parts of silicone - grafted glycidyl ether 20 - 30 parts of diluent 5 - 10 parts of photoinitiator 1 - 2 parts of antioxidant; The silicone - grafted glycidyl ether is prepared by reacting vinyl siloxane, pentaerythritol triallyl ether, allyl glycidyl ether and a catalyst.

[0007] By adopting the above - mentioned technical solution, the OCA optical adhesive for foldable screens in this application uses polyurethane acrylate as the matrix. By adding silicone - grafted glycidyl ether to the matrix and compounding it with a diluent, a photoinitiator and an antioxidant, under the action of the photoinitiator, the polyurethane acrylate and the diluent carry out a polymerization reaction, and the silicone - grafted glycidyl ether and the polymerization system are intertwined and dispersed to form a network - intertwined structure with good elasticity and cohesion. The prepared OCA optical adhesive has good elasticity and flexibility while also being able to endow the OCA optical adhesive with good bonding strength, solving the problem that neither a single linear polymer structure nor a single cross - linked structure can better combine the bend resistance and bonding strength of the OCA optical adhesive. When applied to foldable screens, it has good bend resistance during long - term folding use and is not prone to wrinkles and bubbles.

[0008] Preferably, the silicone - grafted glycidyl ether is prepared from the following raw materials in parts by weight: 25 - 35 parts of vinyl siloxane 10 - 20 parts of pentaerythritol triallyl ether 4 - 8 parts of allyl glycidyl ether 0.05 - 0.15 parts of catalyst.

[0009] Preferably, the silicone - grafted glycidyl ether is prepared by the following steps: Add vinyl siloxane, pentaerythritol triallyl ether, allyl glycidyl ether and a catalyst into a reaction device, and react for 60 - 90 min under the condition of a temperature of 75 - 85 °C to obtain the silicone - grafted glycidyl ether.

[0010] By adopting the above technical solutions, the silicone graft glycidyl ether of the present application is prepared by reacting vinyl siloxane, pentaerythritol triallyl ether, allyl glycidyl ether and a catalyst in a preferred ratio. The prepared silicone graft glycidyl ether group has a branched crosslinked structure, and at the same time, a soft branched ether group segment is introduced into the molecular chain segment, which can fully stretch and interweave and disperse in the polyurethane acrylate system, avoiding the problem of decreased bonding strength caused by excessive crosslinking of the system, significantly improving the cohesive strength and elasticity of the OCA optical adhesive, and at the same time enabling the OCA optical adhesive to maintain good bonding performance. When applied to a folding screen, during the process of repeated bending and use of the folding screen, the OCA optical adhesive has good elastic modulus and shear stress, so that the folding screen is not prone to problems of bubbles and wrinkles; during the reaction process, by optimizing the reaction time and temperature, each raw material can fully contact and react to form a silicone graft glycidyl ether with a stable structure.

[0011] Preferably, the vinyl siloxane is tetramethyldivinyldisiloxane and / or tetramethyltetravinylcyclotetrasiloxane.

[0012] By adopting the above technical solutions, the vinyl group and siloxane structure in the molecular chain segment of tetramethyldivinyldisiloxane and / or tetramethyltetravinylcyclotetrasiloxane contribute to the formation of a more stable chemical bonding network, improving the overall elasticity of the OCA optical adhesive while ensuring the bonding strength.

[0013] Preferably, the catalyst is benzoyl peroxide or diisopropylbenzene peroxide.

[0014] By adopting the above technical solutions, using benzoyl peroxide or diisopropylbenzene peroxide as the catalyst can effectively promote the synthesis reaction of the silicone graft glycidyl ether and improve the reaction efficiency.

[0015] Preferably, the diluent is composed of methyl methacrylate, tetraethylene glycol dimethacrylate and dicyclopentadiene acrylate in a weight ratio of 1:(3 - 4):(0.5 - 1).

[0016] By adopting the above technical solutions, using methyl methacrylate, tetraethylene glycol dimethacrylate and dicyclopentadiene acrylate in a preferred weight ratio as the diluent can effectively adjust the overall performance of the OCA optical adhesive. While improving the fluidity and coating performance of the polyurethane acrylate system, it can fully polymerize to form a macromolecular crosslinked structure, enhancing the elasticity and flexibility of the prepared OCA optical adhesive.

[0017] Preferably, the photoinitiator is 1 - hydroxycyclohexyl phenyl ketone and / or 2 - hydroxy - 2 - methyl - 1 - phenyl - 1 - propanone.

[0018] By adopting the above technical solution, the prepared OCA optical adhesive can efficiently initiate a polymerization reaction under light conditions, ensuring that the OCA optical adhesive can be cured quickly and uniformly.

[0019] Preferably, the antioxidant is antioxidant 1010 and / or antioxidant 168.

[0020] By adopting the above technical solution, the prepared OCA optical adhesive can effectively resist oxidation degradation and yellowing problems during long-term repeated folding use, improving the service life and quality.

[0021] In a second aspect, the present application provides a method for preparing an OCA optical adhesive for a folding screen, adopting the following technical solution: A method for preparing an OCA optical adhesive for a folding screen, comprising the following steps: S1. Mix polyurethane acrylate, silicone-grafted glycidyl ether, diluent, photoinitiator and antioxidant evenly, and perform vacuum degassing to obtain an adhesive; S2. Coat the adhesive on the surface of the release film, first perform ultraviolet curing, then perform thermal curing, and wind up to obtain the OCA optical adhesive for a folding screen.

[0022] By adopting the above technical solution, mixing each component evenly and performing vacuum degassing treatment can significantly reduce the generation of bubbles, ensuring the uniformity and stability of the OCA optical adhesive. Subsequently, using a dual-curing method combining ultraviolet curing and thermal curing enables the formation of a tight cross-linked network structure between the adhesive molecules, further enhancing the comprehensive performance of the OCA optical adhesive; when in use, it can be adhered by peeling off the release film.

[0023] Preferably, the thickness of the OCA optical adhesive is 15 - 25 μm.

[0024] By adopting the above technical solution, an OCA optical adhesive with a relatively optimal thickness can have good bonding strength while effectively reducing the stress concentration problem caused by uneven thickness. It avoids wrinkles caused by excessive thickness and bonding failure caused by excessive thinness, thereby improving the overall reliability and service life of the folding screen.

[0025] In summary, the present application includes at least one of the following beneficial technical effects: 1. The OCA optical adhesive for foldable screens of the present application is prepared from polyurethane acrylate, silicone grafted glycidyl ether, diluent, photoinitiator and antioxidant. Under the action of the photoinitiator, the polyurethane acrylate and the diluent carry out a polymerization reaction, and the silicone grafted glycidyl ether and the polymerization system are intertwined and dispersed to form a network intertwined structure with good elasticity and cohesion. The prepared OCA optical adhesive has good elasticity and flexibility while also being able to endow the OCA optical adhesive with good bonding strength, solving the problem that neither a single linear polymer structure nor a single crosslinked structure can better combine the bending resistance and bonding strength of the OCA optical adhesive. When applied to foldable screens, it has good bending resistance during long-term folding use and is not prone to wrinkles and bubbles.

[0026] 2. The silicone grafted glycidyl ether is prepared by reacting vinyl siloxane, pentaerythritol triallyl ether, allyl glycidyl ether and a catalyst in a preferred ratio. The prepared silicone grafted glycidyl ether group has a branched crosslinked structure, and at the same time, soft branched ether group segments are introduced into the molecular chain segments, which can fully stretch and be intertwined and dispersed in the polyurethane acrylate system, avoiding the problem of decreased bonding strength caused by excessive crosslinking of the system, significantly improving the cohesive strength and elasticity of the OCA optical adhesive, and at the same time enabling the OCA optical adhesive to maintain good bonding performance.

[0027] 3. Tetramethyldivinyldisiloxane and / or tetramethyltetravinylcyclotetrasiloxane are selected as the vinyl siloxane. The vinyl and siloxane structures in the molecular chain segments contribute to the formation of a more stable chemical bonding network, improving the overall elasticity of the OCA optical adhesive while ensuring the bonding strength.

[0028] 4. Methyl methacrylate, tetraethylene glycol dimethacrylate and dicyclopentadiene acrylate are used as diluents in a preferred weight ratio. While improving the fluidity and coating performance of the polyurethane acrylate system, they can fully polymerize to form a macromolecular crosslinked structure, enhancing the elasticity and flexibility of the prepared OCA optical adhesive. Detailed implementation mode

[0029] The following further elaborates on the present application in conjunction with examples.

[0030] The following are the sources and specifications of some raw materials of the present application. The raw materials used in the preparation examples and implementation examples of the present application can all be obtained commercially, including but not limited to the raw materials of the following models and manufacturers, and raw materials with the same performance can all be used: Polyurethane acrylate: Sartomer EBECRYL 4150; Pentaerythritol triallyl ether: CAS No. 1471-17-9, content 99%; Tetraethylene glycol dimethacrylate: CAS No. 109-17-1, content 99%; Dicyclopentadiene acrylate: Bluecol L-6101; Tetramethyldivinyldisiloxane: CAS No. 2627-95-4, content 99%; Tetramethyltetravinylcyclotetrasiloxane: CAS No. 2554-06-5, content 99%.

[0031] Preparation Example of Organosilicon Grafted Glycidyl Ether Preparation Example 1 Preparation Example 1 discloses an organosilicon grafted glycidyl ether, which is prepared by the following steps: 2.5 kg of vinyltrimethoxysilane as vinyl siloxane, 1 kg of pentaerythritol triallyl ether, 0.8 kg of allyl glycidyl ether and 0.005 kg of dibenzoyl peroxide as a catalyst were added to a reaction device, and reacted at a temperature of 75 °C for 90 min to obtain an organosilicon grafted glycidyl ether.

[0032] Preparation Examples 2-3 The differences between Preparation Examples 2-3 and Preparation Example 1 are that the raw material dosages and preparation process parameters are different. See Table 1 below for details.

[0033] Table 1 Parameter Table of Preparation Examples 1-3 Preparation Example 4 The difference between Preparation Example 4 and Preparation Example 1 is that vinyltrimethoxysilane was replaced with an equal amount of tetramethyldivinyldisiloxane, and the others were the same as Preparation Example 1.

[0034] Preparation Example 5 The difference between Preparation Example 5 and Preparation Example 1 is that vinyltrimethoxysilane was replaced with an equal amount of tetramethyltetravinylcyclotetrasiloxane, and the others were the same as Preparation Example 1.

[0035] Preparation Example 6 The difference between Preparation Example 6 and Preparation Example 1 is that vinyltrimethoxysilane was replaced with 1 kg of tetramethyldivinyldisiloxane and 1.5 kg of tetramethyltetravinylcyclotetrasiloxane, and the others were the same as Preparation Example 1.

[0036] Preparation Comparative Example 1 The difference between Preparation Comparative Example 1 and Preparation Example 4 is that pentaerythritol triallyl ether was replaced with an equal amount of allyl glycidyl ether, and the others were the same as Preparation Example 1.

[0037] Preparation Comparative Example 2 The difference between Preparation Comparative Example 2 and Preparation Example 4 is that allyl glycidyl ether was replaced with an equal amount of polyethylene glycol 800, and the others were the same as Preparation Example 1. Examples

[0038] Example 1 Example 1 discloses an OCA optical adhesive for a folding screen, which is prepared by the following steps: S1. Mix 6 kg of polyurethane acrylate, 1.5 kg of the silicone graft glycidyl ether prepared in Preparation Example 1, 3 kg of a diluent (composed of methyl methacrylate, isobornyl acrylate, and neopentyl glycol diacrylate in a weight ratio of 1:3:1), 0.5 kg of 1-hydroxycyclohexyl phenyl ketone as a photoinitiator, and 0.1 kg of an antioxidant (composed of antioxidant 1010 and antioxidant 168 in a weight ratio of 2:1) evenly, and perform vacuum degassing to obtain an adhesive; S2. Coat the adhesive on the surface of a PET release film, first perform ultraviolet curing for 10 min under the condition of an ultraviolet curing energy of 800 mj / cm 2 , and then perform thermal curing for 30 min under the condition of a temperature of 80 °C to form an adhesive layer, and wind it up to obtain the OCA optical adhesive for a folding screen; the thickness of the OCA optical adhesive prepared in this application is 15 - 25 μm, and the thickness of the OCA optical adhesive in this example is 25 μm.

[0039] Examples 2 - 3 The differences between Examples 2 - 3 and Example 1 are that the raw material dosages and preparation conditions are different. For details, see Table 2 below.

[0040] Table 2 Parameter table of Examples 1 - 3 Example 4 The difference between Example 4 and Example 1 is that the silicone graft glycidyl ether is from Preparation Example 4, and the others are the same as Example 1.

[0041] Example 5 The difference between Example 5 and Example 1 is that the silicone graft glycidyl ether is from Preparation Example 5, and the others are the same as Example 1.

[0042] Example 6 The difference between Example 6 and Example 1 is that the silicone graft glycidyl ether is from Preparation Example 6, and the others are the same as Example 1.

[0043] Example 7 The difference between Example 7 and Example 6 is that the diluent is composed of methyl methacrylate, tetraethylene glycol dimethacrylate, and dicyclopentadiene acrylate in a weight ratio of 1:3:0.5, and the others are the same as Example 6.

[0044] Example 8 Example 8 is different from Example 6 in that the diluent consists of methyl methacrylate, tetraethylene glycol dimethacrylate, and dicyclopentadiene acrylate with a weight ratio of 1:4:1, and the others are the same as in Example 6.

[0045] Comparative example Comparative example 1 Comparative example 1 is different from Example 1 in that the silicone-grafted glycidyl ether is derived from the preparation of Comparative example 1, and the others are the same as in Example 1.

[0046] Comparative example 2 Comparative example 2 is different from Example 1 in that the silicone-grafted glycidyl ether is derived from the preparation of Comparative example 2, and the others are the same as in Example 1.

[0047] Comparative example 3 Comparative example 3 is different from Example 1 in that the silicone-grafted glycidyl ether is equally replaced by polyurethane acrylate, and the others are the same as in Example 1.

[0048] Performance detection test The following is a performance test on the OCA optical adhesives prepared in Examples 1-8 and Comparative examples 1-3: 1. Flexural resistance test Apply the OCA optical adhesive to a flexible OLED display screen. After placing it at room temperature (25 °C) and at -10 °C for 7 days respectively, use a folding screen flexural life tester to conduct a flexural test. The test temperature is 25 °C, the bending radius R = 2 mm, and the bending angle is 180°. Observe whether there are wrinkles or bubbles on the flexible OLED display screen every 50,000 times, record the number of bending times (unit: 10,000 times) when wrinkles or bubbles appear, and test and record the test results; 2. Shear strength test: Refer to the test method in GB / T 7124-2008 to test the shear strength (unit: MPa) of the OCA optical adhesive, and test and record the test results; The following are the performance test data of the OCA optical adhesives in Examples 1-8 and Comparative examples 1-3. For details, see Table 3 below.

[0049] Table 3 Data table of OCA optical adhesives in Examples 1-8 and Comparative examples 1-3 Combined with Examples 1-6 and Comparative Examples 1-3 and Table 3, it can be concluded that when the silicone grafted glycidyl ether and polyurethane acrylate prepared by the present application are compounded, the OCA optical adhesive prepared is applied to the folding screen and used for a long time, it can have good bending resistance while having good bonding strength, and it is not easy to have problems of wrinkles and bubbles. Compared with Example 1, in Examples 4-6, the types and ratios of vinyl siloxanes were optimized, and the number of bending resistance times of the prepared OCA optical adhesive increased by 50,000 times, and the shear strength also increased, indicating that the preferred vinyl siloxane can improve the flexibility and bonding performance of the prepared OCA optical adhesive; compared with Example 1, in Comparative Examples 1-2, the types and ratios of pentaerythritol triallyl ether and allyl glycidyl ether were changed, and the number of bending resistance times of the prepared OCA optical adhesive decreased, and the shear strength also decreased significantly. It may be because the grafting performance of the prepared silicone grafted glycidyl ether was reduced, and then the network interweaving structure of the silicone grafted glycidyl ether and polyurethane acrylate system was changed, resulting in the reduction of the performance of the OCA optical adhesive. In Comparative Example 3, no silicone grafted glycidyl ether was added, and the bending resistance performance and shear strength of the prepared OCA optical adhesive decreased significantly. It may be that the cohesion of the OCA adhesive decreased without the synergistic effect of the network interweaving structure.

[0050] Combined with Example 6 and Examples 7-8 and Table 3, it can be concluded that by further optimizing the components and ratios of the diluent, and compounding methyl methacrylate, tetraethylene glycol dimethacrylate and dicyclopentadiene acrylate in a preferred weight ratio as the diluent, the bending resistance performance and bonding performance of the prepared OCA optical adhesive can be improved.

[0051] This specific embodiment is only an interpretation of the present application, and it is not a limitation of the present application. After reading this specification, those skilled in the art can make modifications without creative contributions to this embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. An OCA optical adhesive for a folding screen, characterized in that, Prepared from the following raw materials by weight: Polyurethane acrylate 60 - 80 parts Silicone grafted glycidyl ether 15 - 25 parts Diluent 20 - 30 parts Photoinitiator 5 - 10 parts Antioxidant 1 - 2 parts; The silicone grafted glycidyl ether is prepared by reacting vinyl siloxane, pentaerythritol triallyl ether, allyl glycidyl ether and a catalyst.

2. The OCA optical adhesive for a folding screen according to claim 1, wherein, The silicone grafted glycidyl ether is prepared from the following raw materials by weight: Vinyl siloxane 25 - 35 parts Pentaerythritol triallyl ether 10 - 20 parts Allyl glycidyl ether 4 - 8 parts Catalyst 0.05 - 0.15 parts.

3. An OCA optical adhesive for a folding screen according to claim 1 or 2, characterized in that, The silicone grafted glycidyl ether is prepared by the following steps: Add vinyl siloxane, pentaerythritol triallyl ether, allyl glycidyl ether and a catalyst into a reaction device, and react for 60 - 90 min under the condition of a temperature of 75 - 85 °C to obtain the silicone grafted glycidyl ether.

4. An OCA optical adhesive for a folding screen according to claim 2, wherein, The vinyl siloxane is tetramethyldivinyldisiloxane and / or tetramethyltetravinylcyclotetrasiloxane.

5. The OCA optical adhesive for a folding screen according to claim 2, wherein, The catalyst is benzoyl peroxide or diisopropylbenzene peroxide.

6. The OCA optical adhesive for a folding screen according to claim 1, characterized in that, The diluent is composed of methyl methacrylate, tetraethylene glycol dimethacrylate and dicyclopentadiene acrylate in a weight ratio of 1:(3 - 4):(0.5 - 1).

7. An OCA optical adhesive for a foldable screen according to claim 1, characterized in that, The photoinitiator is 1 - hydroxycyclohexyl phenyl ketone and / or 2 - hydroxy - 2 - methyl - 1 - phenyl - 1 - propanone.

8. An OCA optical adhesive for a folding screen according to claim 1, wherein, The antioxidant is antioxidant 1010 and / or antioxidant 168.

9. A preparation method of an OCA optical adhesive for a folding screen according to any one of claims 1-8, characterized in that, Including the following steps: S1. Mix polyurethane acrylate, silicone grafted glycidyl ether, diluent, photoinitiator and antioxidant evenly, and perform vacuum degassing to obtain an adhesive; S2. Coat the adhesive on the surface of a release film, first perform ultraviolet curing, then perform thermal curing, and wind it up to obtain an OCA optical adhesive for a folding screen.

10. The preparation method of an OCA optical adhesive for a folding screen according to claim 9, wherein, The thickness of the OCA optical adhesive is 15 - 25 µm.

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