Optical adhesive sheet for foldable equipment

Abstract

The invention discloses an optical adhesive sheet for foldable equipment. The invention discloses a high-temperature-resistant optical adhesive sheet suitable for foldable equipment. A pressure-sensitive adhesive layer of the high-temperature-resistant optical adhesive sheet is composed of a photocuring composition containing a polyurethane type and alkyl type bi-component photocuring agent, an acrylic polymer and a photoinitiator. The acrylic polymer is formed by copolymerizing a C6-9 short-chain ester monomer, a C10-20 long-chain ester monomer, a hydroxyl-containing monomer and an N-atom-containing monomer according to a specific ratio, and the molecular weight of the acrylic polymer exceeds 1000000 g / mol. A light curing system adopts a synergistic effect of a bifunctional polyurethane curing agent and a multifunctional alkyl curing agent, and is matched with an acrylate oligomer, so that the prepared bonding sheet not only has good bonding performance, low modulus and excellent creep recovery performance and dynamic bending capacity, but also has good cohesion performance.

Description

Technical Field

[0001] The present invention relates to the technical field of adhesive sheets, and particularly to an optical adhesive sheet for foldable devices. Background Art

[0002] In recent years, due to their excellent portability, foldable devices have become increasingly popular among people and are more and more widely used in fields such as foldable screen mobile phones, smart wearables, vehicles, and electronic devices. With the popularization of foldable devices, adhesives suitable for the usage characteristics of foldable devices are also in demand in the market. Generally, the OCA adhesives used in foldable devices need to have durability in use against environmental changes, and should also have effective bonding performance, excellent high and low temperature modulus stability, good creep performance, and cohesive performance, so as to improve the service life of foldable devices.

[0003] However, generally speaking, it is difficult for a colloid to have good bonding performance under the condition of having a low storage modulus. If we want the colloid to simultaneously meet the characteristics of having a low modulus and good bonding performance, generally the method of reducing the molecular weight of the colloid is adopted. Under this condition, the cohesive performance of the prepared colloid is often poor. Therefore, it is difficult for the optical adhesives on the current market to have good cohesive performance while having a low storage modulus, excellent creep performance, and excellent bonding performance. If the cohesive force of the optical adhesive is insufficient, it will cause the separation between the adhesive layer and the display panel, cover plate, or polarizer after the screen is folded multiple times, forming bubbles or local delamination, which has an adverse impact on the service life of foldable devices.

[0004] Therefore, developing an optical adhesive with a low storage modulus, excellent creep performance, excellent bonding performance, and good cohesive performance is of great significance for the development of foldable devices. Summary of the Invention

[0005] In order to improve the above situation, the present invention provides an optical adhesive sheet for foldable devices. The optical adhesive sheet has a pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer is composed of a photocurable composition. The photocurable composition includes two or more kinds of photocuring agents, an acrylic polymer, and a photoinitiator. The photocuring agent simultaneously includes a polyurethane-type photocuring agent and an alkyl-type photocuring agent. The acrylic polymer uses an alkyl (meth)acrylate A having 6-9 carbon atoms, an alkyl (meth)acrylate B having 10-20 carbon atoms, a hydroxyl-containing monomer C, and an N-containing monomer D as monomer components.

[0006] Furthermore, the content of the polyurethane-type photocuring agent in the photocuring agent is 1-5 parts, and the content of the alkyl-type photocuring agent is 0.01-0.2 parts.

[0007] Furthermore, the molecular weight of the acrylic polymer is greater than 1000000 g / mol.

[0008] Furthermore, the molecular weight of the polyurethane-based photoinitiator in the photoinitiator is 10000 g / mol - 60000 g / mol, and the molecular weight of the alkyl-based photoinitiator is not higher than 500 g / mol.

[0009] Furthermore, the polyurethane-based photoinitiator has bifunctional groups, and the number of functional groups of the alkyl-based photoinitiator is not less than 2.

[0010] Furthermore, the (meth)acrylic acid alkyl ester A having 6 - 9 carbon atoms can be one or more of n-hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, and isononyl (meth)acrylate.

[0011] Furthermore, the (meth)acrylic acid alkyl ester B having 10 - 20 carbon atoms can be one or more of decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate (i.e., lauryl (meth)acrylate), isotridecyl (meth)acrylate, tetradecyl (meth)acrylate, tetra-decyl (meth)acrylate, pentadecyl (meth)acrylate, cetyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, and nonadecyl (meth)acrylate.

[0012] Furthermore, the hydroxyl-containing monomer C can be one or more of 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate.

[0013] Further, the N-atom-containing monomer D may be one or more of N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N,N-dimethylacrylamide, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-(methyl)acryloyl-2-pyrrolidone, N-(methyl)acryloylpiperidine, N-(methyl)acryloylpyrrolidine, N-vinylmorpholine, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-3,5-morpholinedione, and N-vinylpyrazole.

[0014] Further, the photocurable composition further includes an acrylate oligomer, and the weight average molecular weight of the acrylate oligomer is not less than 2000 g / mol and not higher than 9000 g / mol. By using an acrylate oligomer with a molecular weight in the range of 2000 - 9000, preferably 3000 - 8000, and a molecular weight distribution below 2.7, the adhesion of the optical adhesive sheet can be improved while also enabling it to have good optical properties.

[0015] Compared with the prior art, the present invention makes up for the deficiency that it is difficult for the optical adhesives on the current market to meet the requirements of low storage modulus, excellent creep properties, excellent adhesion properties, and good cohesion properties simultaneously. If the cohesion of the optical adhesive is insufficient, it will cause the separation between the adhesive layer and the display panel, cover plate, or polarizer after multiple folds of the screen, forming bubbles or local delamination, which has an adverse impact on the use of foldable devices. Using the above technical solution, the prepared optical adhesive has low storage modulus, good adhesion properties and creep properties, and good cohesion properties at the same time. Specific Embodiments

[0016] In order to make the technical problems, technical solutions, and beneficial effects solved by the present invention clearer, the following further details the present invention with reference to 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.

[0017] Table 1 Composition List of Adhesives

[0018]

[0019] Table 2 - Formulation Compositions of Examples 1 - 3 and Comparative Examples 1 - 3

[0020]

[0021] Examples 1 - 3 and Comparative Examples 1 - 3

[0022] Manufacture of Acrylic Oligomer (Oligomer A)

[0023] Mix 40 parts by weight of isobornyl acrylate as a monomer component, 55 parts by weight of methyl methacrylate, 5 parts by weight of 2-hydroxyethyl acrylate, 4 parts by weight of α-thioglycerol as a chain transfer agent, 0.2 parts by weight of AIBN, and 100 parts by weight of toluene as a polymerization solvent for 1 h under a nitrogen atmosphere, and then carry out the reaction while stirring at 80 °C. The reaction time is 6 h, and then the solvent is removed by high-temperature drying to obtain an acrylic oligomer (Oligomer A). The weight-average molecular weight Mw of the acrylic oligomer (A) is 4700, and the molecular weight distribution is 2.32.

[0024] As shown in Table 2, accurately weigh the corresponding amounts of n-octyl acrylate, dodecyl acrylate, hydroxybutyl acrylate, N,N-dimethylacrylamide, and benzoin dimethyl ether and place them in a four-necked flask equipped with a stirrer, a thermometer, and a nitrogen pipe. While stirring, introduce nitrogen, and after stirring for at least 30 minutes, prepare a prepolymer by photoinitiated polymerization. The weight-average molecular weight of the finally prepared prepolymer is about 2.3 million. Accurately weigh 100 parts of the corresponding prepolymer, and add the corresponding amounts of Oligomer A, CN9021NS, 1,6-hexanediol diacrylate, and Silquest A-187 to the prepolymer as described in Table 2. After stirring evenly, let it stand for defoaming to obtain the glue. Use the light release film R701T-C and the heavy release film R703T-C produced by Guangdong Crown New Materials Technology Co., Ltd., place them one above the other with their release surfaces facing each other, pour the above glue between the two films, control its thickness by roller extrusion, and cure it by irradiating with the UVA band under a UV lamp to prepare a 50-μm-thick optical adhesive sheet.

[0025] Performance Test

[0026] Respectively, make the optical adhesives prepared in Examples 1-3 and Comparative Examples 1-3 into OCA tapes and measure their relevant properties. The test methods are as follows, and the results are shown in Table 3.

[0027] 180-degree peel strength test: GB / T 2792-2014;

[0028] Retention force test: GB / T4851—1998. Here, hanging a weight of 1 kg at 80 °C for 168 h without falling is defined as "OK", otherwise it is defined as "NG".

[0029] Storage modulus: TA hybrid rheometer DHR-2, ASTM D4440-15;

[0030] Creep recovery test: Apply a shear stress of 10 kPa with a TA rheometer, and the recovery time is 600 s.

[0031] Dynamic bending test: radius 3 mm, 40 times / min, 50,000 times.

[0032] Table 3 - Performance of the optically adhesive sheet for foldable devices prepared in the examples and comparative examples

[0033]

[0034] The cohesive property of the optically adhesive sheet can be determined by the high-temperature holding force. If the determination result of the high-temperature holding force is "OK", it indicates that the corresponding optically adhesive sheet has good cohesive property. From the above test results, it can be seen that by using the solution disclosed in the examples of the present invention to prepare the optically adhesive sheet, the prepared optically adhesive sheet not only has good adhesion performance, low modulus, excellent creep recovery performance and dynamic bending ability, but also has good cohesive property.

[0035] The above examples are only for illustrating the technical concept and characteristics of the present invention, and the purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. It should not be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. An optical adhesive sheet for a foldable device, comprising a pressure-sensitive adhesive layer, characterized in that: The pressure-sensitive adhesive layer is composed of a photocurable composition, which includes two or more photocuring agents, an acrylic polymer and a photopolymerization initiator. The photocuring agent includes a polyurethane-type photocuring agent and an alkyl-type photocuring agent. The acrylic polymer has (meth)acrylic acid alkyl ester A having 6 to 9 carbon atoms, (meth)acrylic acid alkyl ester B having 10 to 20 carbon atoms, a hydroxyl-containing monomer C and a N-atom-containing monomer D as monomer components.

2. The optical adhesive sheet for a foldable device according to claim 1, wherein: The content of the polyurethane type photocuring agent in the photocuring agent is 1-5 parts, and the content of the alkyl type photocuring agent is 0.01-0.2 parts.

3. The optical adhesive sheet for a foldable device according to claim 1, wherein: The acrylic polymer has a molecular weight greater than 1,000,000 g / mol.

4. The optical adhesive sheet for a foldable device according to any one of claim 2, characterized in that: The molecular weight of the polyurethane type photocuring agent in the photocuring agent is 10000 g / mol-60000 g / mol, and the molecular weight of the alkyl type photocuring agent is not higher than 500 g / mol.

5. The optical adhesive sheet for a foldable device according to any one of claim 2, characterized in that: The polyurethane type photocuring agent has a bifunctional group, and the number of functional groups of the alkyl type photocuring agent is not less than 2.

6. The optical adhesive sheet for a foldable device according to claim 1, wherein: The (meth)acrylic acid alkyl ester A having 6 to 9 carbon atoms may be one or more of n-hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, and isononyl (meth)acrylate; The (meth)acrylic acid alkyl ester B having 10 to 20 carbon atoms may be one or more of decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate (i.e., lauryl (meth)acrylate), isotridecyl (meth)acrylate, tetradecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, cetyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, and nonadecyl (meth)acrylate; The hydroxyl-containing monomer C may be one or more of 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate; The N-atom-containing monomer D may be one or more of N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N,N-dimethylacrylamide, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-(methyl)acryloyl-2-pyrrolidone, N-(methyl)acryloylpiperidine, N-(methyl)acryloylpyrrolidine, N-vinylmorpholine, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-3,5-morpholinedione, and N-vinylpyrazole.

7. The optical adhesive sheet for a foldable device according to claim 1, wherein: The photocurable composition further comprises an acrylate oligomer, and the weight average molecular weight of the acrylate oligomer is not less than 2000 g / mol and not more than 9000 g / mol.

Images