Flex-resistant acrylic adhesives, films and flexible devices

Abstract

The present invention relates to a bending-resistant acrylic adhesive, a film and a flexible device, wherein the bending-resistant acrylic adhesive comprises a (meth)acrylic acid copolymer, wherein the (meth)acrylic acid copolymer has a structural unit derived from a cyclopolymerizable monomer, wherein the cyclopolymerizable monomer accounts for 0.1 to 20 wt % of all monomers synthesizing the (meth)acrylic acid copolymer. The acrylic adhesive can exhibit excellent bendability and excellent recovery to bending action under a normal high temperature environment.

Description

Technical Field

[0001] The invention relates to the technical field of adhesives, and in particular to a bending-resistant acrylic adhesive, a film and a flexible device. Background Art

[0002] In recent years, with the popularity of foldable devices, adhesives suitable for the use characteristics of foldable devices have also been in demand in the market. Generally speaking, the adhesive film with optical properties used in foldable devices needs to have durability against environmental changes and good bending resistance at the use temperature of foldable devices, so as to increase the service life of foldable devices.

[0003] At present, most adhesive films on the market will increase their deformation under the same stress conditions as the temperature rises. When the deformation is too large, it is difficult to return to its original shape even when the stress is removed, which is not conducive to the use of folding devices at high temperatures. Therefore, adhesives and adhesive films with good bending resistance under various operating temperatures of foldable devices are currently required. Summary of the invention

[0004] In view of the shortcomings of the prior art, the first object of the present invention is to provide a bending-resistant acrylic adhesive that can exhibit both excellent bendability and excellent recovery to bending action in a normal high temperature environment.

[0005] A second object of the present invention is to provide an adhesive film having the above acrylic adhesive, the adhesive film having good bending resistance at room temperature and high temperature.

[0006] A third object of the present invention is to provide a flexible device having the above adhesive film, which can be used at high temperatures.

[0007] To achieve the first object of the present invention, the present invention provides a bending-resistant acrylic adhesive, which comprises a (meth)acrylic acid copolymer, wherein the (meth)acrylic acid copolymer has structural units derived from the following cyclopolymerizable monomers:

[0008]

[0009] Wherein R is a hydrocarbon group or a substituted hydrocarbon group;

[0010] The mass proportion of the cyclopolymerizable monomer in all monomers for synthesizing the (meth)acrylic acid copolymer is 0.1 to 20 wt %.

[0011] It can be seen that in order to solve the problems of poor high-temperature bending resistance of adhesives in the prior art, the present invention provides an adhesive with good room temperature and high temperature bending and recovery performance, which can meet the use environment of flexible devices such as foldable devices and rollable devices that are being developed in recent years. It involves many aspects and requires that even in a high temperature environment, it can take into account the excellent performance of bending action while still maintaining excellent recovery. The present invention uses a cyclopolymerizable monomer to prepare a (meth) propylene copolymer, so that the prepared optical adhesive film has good creep recovery performance at 25°C and 65°C. The mass proportion of the cyclopolymerizable monomer in all monomers of the synthetic (meth) acrylic copolymer can be, for example, 0.1wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, etc.

[0012] In some embodiments of the present invention, R is an alkyl group or a cyclohexyl group, so that the (meth)acrylic acid copolymer has good chemical resistance and weather resistance.

[0013] In some embodiments of the present invention, the mass proportion of the cyclopolymerizable monomer in all monomers for synthesizing the (meth)acrylic acid copolymer is 0.5-6 wt %. A small amount of the cyclopolymerizable monomer can significantly improve the bending resistance of the adhesive.

[0014] In some embodiments of the present invention, the (meth)acrylic acid copolymer has structural units derived from alkyl acrylate and hydroxyalkyl acrylate. The number of alkyl carbon atoms of the alkyl acrylate is greater than or equal to 4. Alkyl acrylate is a soft monomer that can adjust the flexibility of the adhesive. The alkyl acrylate can be, for example, at least one of 2-ethylhexyl acrylate and isostearyl acrylate. In some examples, the alkyl acrylate is a mixture of 2-ethylhexyl acrylate and isostearyl acrylate, and the mass ratio of 2-ethylhexyl acrylate to isostearyl acrylate is (81-85):13. The mass proportion of alkyl acrylate in all monomers for synthesizing the (meth)acrylic acid copolymer is 80-98wt%, for example, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, etc. Hydroxyalkyl acrylate is a functional monomer that can adjust the viscosity and adhesion of the adhesive. The hydroxyalkyl acrylate may be, for example, at least one of hydroxyethyl acrylate, hydroxypropyl acrylate, and hydroxybutyl acrylate. The mass proportion of the hydroxyalkyl acrylate in all monomers for synthesizing the (meth)acrylic acid copolymer is 1 to 10%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc.

[0015] In some embodiments of the present invention, the acrylic adhesive further comprises acrylic oligomers, crosslinking agents and silane coupling agents. Additives such as acrylic oligomers, crosslinking agents and silane coupling agents are added to the (meth)acrylic copolymer to further improve the adhesion and mechanical strength of the adhesive. Relative to 100 parts by mass of the (meth)acrylic acid copolymer, the amount of acrylic oligomer is 1 to 5 parts by mass, for example, 1 part, 2 parts, 3 parts, 4 parts, 5 parts, etc.; the amount of cross-linking agent is 0.05 to 1 part by mass, for example, 0.05 part, 0.1 part, 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1 part, etc.; the amount of silane coupling agent is 0.05 to 1 part by mass, for example, 0.05 parts, 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1 part, etc.

[0016] In some embodiments of the present invention, the weight average molecular weight of the acrylic oligomer is 2000-9000 g / mol, preferably 3000-8000 g / mol; the molecular weight distribution of the oligomer is below 2.7. The addition of the acrylic oligomer improves the adhesion of the optical adhesive sheet and also makes it have good optical properties.

[0017] In some embodiments of the present invention, the acrylic adhesive has a creep value of 95% or more at 25°C, a recovery value of 85% or more at 25°C, a creep value of 80% or more at 65°C, and a recovery value of 85% or more at 65°C. The acrylic adhesive of the present invention has good creep recovery performance at both 25°C and 65°C.

[0018] In some embodiments of the present invention, the storage modulus of the acrylic adhesive at -20°C is 100 kPa or less, and the storage modulus at 65°C is 15 kPa or more. The acrylic adhesive provided by the present invention has a low modulus.

[0019] In some embodiments of the present invention, the acrylic adhesive has a bonding strength of 900 gf / 25 mm or higher relative to glass, polyethylene terephthalate, and polyimide in a peel test at 25°C, a peel angle of 180°, and a tensile speed of 300 mm / min. The acrylic adhesive of the present invention has good adhesion performance to materials such as glass, polyethylene terephthalate, and polyimide at room temperature.

[0020] To achieve the second object of the present invention, the present invention provides an adhesive film having an adhesive layer formed by any of the above-mentioned acrylic adhesives. The adhesive film can be excellent in bending performance and still maintain excellent recovery under normal temperature or high temperature environment. In addition to the adhesive layer, the adhesive film can also have release films arranged on both sides of the adhesive layer. The thickness of the adhesive layer can be 30 to 100 μm, for example, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, etc. The adhesive film can be obtained by curing the acrylic adhesive with ultraviolet light.

[0021] To achieve the third object of the present invention, the present invention provides a flexible device, which has the above-mentioned adhesive film. The flexible device can be an image display device, such as a bendable image display, such as a foldable or rollable display screen of a television, a mobile terminal, etc. When the flexible device is used at room temperature or the device heats up after being used for a long time, the adhesive film can be bent and deformed and return to its original appearance. DETAILED DESCRIPTION

[0022] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0023] The names of the raw materials represented by the abbreviations in the formulations of Examples 1-3 and Comparative Example 1 are shown in Table 1 below.

[0024] Table 1 Abbreviations of raw material names

[0025] abbreviation name factory 2-EHA 2-Ethylhexyl acrylate BASF ISTA Isostearyl acrylate Osaka Organic 4-HBA Hydroxybutyl acrylate BASF AOMA Cyclic polymer monomer Nippon Shokubai ikB Benzoin dimethyl ether BASF Oligomer A Oligomer Guangdong Crown HDDA 1,6-Hexanediol diacrylate BASF Silquest A-187 Silane coupling agent MOMENTIVE

[0026] Preparation of (meth)acrylic acid copolymer:

[0027] Example 1-3: As shown in Table 2, accurately weigh corresponding proportions of 2-ethylhexyl acrylate, isostearyl acrylate, hydroxybutyl acrylate, cyclized polymer monomer, and dimethyl benzoate, and place them in a four-necked flask equipped with a stirrer, a thermometer, and a nitrogen tube. Stir and introduce nitrogen. After stirring for at least 30 minutes, prepare the prepolymer by photoinitiated polymerization.

[0028] Comparative Example 1: As shown in Table 2, corresponding proportions of 2-ethylhexyl acrylate, isostearyl acrylate, hydroxybutyl acrylate, and dimethyl benzoate were accurately weighed and placed in a four-necked flask equipped with a stirrer, a thermometer, and a nitrogen tube. Nitrogen was introduced while stirring. After stirring for at least 30 minutes, a prepolymer was prepared by photoinitiated polymerization.

[0029] Preparation of adhesive:

[0030] Examples 1-3 and Comparative Example 1: Accurately weigh 100 parts of the corresponding prepolymer, add corresponding proportions of Oligomer A (weight average molecular weight of about 5000 g / mol, molecular weight distribution of about 2.0), 1,6-hexanediol diacrylate, and Silquest A-187 to the prepolymer as shown in Table 2, stir it evenly and let it stand for degassing to obtain glue.

[0031] Table 2 Formulation

[0032]

[0033] Preparation of adhesive film:

[0034] Use the light release film R701T-C and the heavy release film R703T-C, place them up and down with their release surfaces facing each other, pour the above glue between the two films, control the thickness by roller extrusion and use UVA band irradiation curing under UV lamp to prepare a 50μm thick optical adhesive sheet.

[0035] Performance Testing:

[0036] The optical adhesives prepared in the above Examples 1-3 and Comparative Example 1 were respectively made into OCA tapes and the relevant properties were measured. The test method is as follows and the results are shown in Table 3.

[0037] 180 degree peel force test: GB / T 2792-2014;

[0038] Storage modulus: TA hybrid rheometer DHR-2, ASTM D4440-15;

[0039] Creep recovery test: TA rheometer applies a shear stress of 10 kPa, and the recovery time is 600 s;

[0040] Dynamic bending test: radius 3mm, 40 times / min, 50,000 times.

[0041] Table 3 Test results

[0042]

[0043] The above test results show that the optical adhesive film prepared by the scheme of the embodiment of the present invention can make the prepared optical adhesive film have good creep recovery performance at 25°C and 65°C, and the ratio of the loss tangent value tanδ(65°C) at 65°C to the loss tangent value tanδ(25°C) at 25°C is tanδ(65°C) / tanδ(25°C) < 1. Moreover, the optical adhesive film prepared by the method provided by this patent has good adhesive performance while having low modulus.

[0044] Finally, it should be emphasized that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A bending-resistant acrylic adhesive, characterized in that The invention comprises a (meth)acrylic acid copolymer, wherein the (meth)acrylic acid copolymer has a structural unit derived from the following cyclopolymerizable monomer: Wherein R is a hydrocarbon group or a substituted hydrocarbon group; The mass proportion of the cyclopolymerizable monomer in all monomers for synthesizing the (meth)acrylic acid copolymer is 0.1 to 20 wt %.

2. The flex-resistant acrylic adhesive according to claim 1, characterized in that R is an alkyl group or a cyclohexyl group; The mass proportion of the cyclopolymerizable monomer in all monomers for synthesizing the (meth)acrylic acid copolymer is 0.5 to 6 wt %.

3. The flex-resistant acrylic adhesive according to claim 1, characterized in that The (meth)acrylic acid copolymer has structural units derived from alkyl acrylate and hydroxyalkyl acrylate; the alkyl acrylate has an alkyl carbon number greater than or equal to 4; The mass percentage of the alkyl acrylate in all monomers for synthesizing the (meth)acrylic acid copolymer is 80-98 wt %.

4. The flex-resistant acrylic adhesive according to claim 1, characterized in that The acrylic adhesive further comprises an acrylic oligomer, a crosslinking agent and a silane coupling agent. Relative to 100 parts by mass of the (meth)acrylic copolymer, the acrylic oligomer is 1 to 5 parts by mass, the crosslinking agent is 0.05 to 1 part by mass, and the silane coupling agent is used in an amount of 0.05 to 1 part by mass.

5. The flex-resistant acrylic adhesive according to claim 5, characterized in that The weight average molecular weight of the acrylic oligomer is 2000-9000 g / mol, preferably 3000-8000 g / mol; the molecular weight distribution of the acrylic oligomer is below 2.

7.

6. The flex-resistant acrylic adhesive according to any one of claims 1 to 5, characterized in that The acrylic adhesive has a creep value of more than 95% at 25°C and a recovery value of more than 85% at 25°C; a creep value of more than 80% at 65°C and a recovery value of more than 85% at 65°C.

7. The flex-resistant acrylic adhesive according to any one of claims 1 to 5, characterized in that The acrylic adhesive has a storage modulus of 100 kPa or less at -20°C and a storage modulus of 15 kPa or more at 65°C.

8. The flex-resistant acrylic adhesive according to any one of claims 1 to 5, characterized in that The acrylic adhesive can achieve an adhesive strength of 900 gf / 25 mm or higher with respect to glass, polyethylene terephthalate and polyimide in a peeling test at 25° C., a peeling angle of 180° and a tensile speed of 300 mm / min.

9. An adhesive film, characterized in that A plastic film having an adhesive layer formed of the flex-resistant acrylic adhesive according to any one of claims 1 to 8.

10. A flexible device, characterized in that An adhesive film according to claim 9.

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