Bonding sheet and optical display device including the same

Abstract

The present invention relates to an adhesive sheet and an optical display device including the same. The present invention provides an adhesive sheet having a HU hardness of 10 to 13 N / mm 2 at a temperature condition of -30℃, a HU hardness of 9 to 10 N / mm 2 at a temperature condition of 25℃, and a bending property suitable for a foldable optical display device. The present invention relates to an adhesive sheet and an optical display device including the same. The present invention provides an adhesive sheet having a HU hardness of 10 to 13 N / mm 2 at a temperature condition of -30℃, a HU hardness of 9 to 10 N / mm 2 at a temperature condition of 25℃, and a bending property suitable for a foldable optical display device.

Description

Technical Field

[0001] This invention relates to an adhesive sheet for optical display devices. Background Technology

[0002] In recent years, with the rapid development of information and communication technology and the expansion of the market, the demand for optical display devices, such as display devices, has been increasing. Representative examples of such optical display devices include liquid crystal displays (LCDs), plasma display panels (Plasma Display Panels), and organic light-emitting diodes (OLEDs).

[0003] On the other hand, there is an adhesive sheet at the bottom of the display device, which is used to protect the display device from external forces and prevent static electricity. In recent years, as the application range of display devices has gradually expanded, reliability in high and low temperature operating environments has also been considered a necessary characteristic. With the emergence of flexible and foldable displays, the flexibility or flexibility of the sheet also needs to be improved to ensure the durability of the product.

[0004] Therefore, there is a need to develop an adhesive sheet that can exhibit reliability under different temperature conditions and applied external forces.

[0005] As mentioned above, flexible optical display devices are currently being developed, especially those using adhesive sheets that require excellent bending properties. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a novel adhesive sheet with hardness characteristics to achieve a low energy storage modulus at low temperatures, while minimizing creep strain and enhancing resistance to compression during folding.

[0007] To address the aforementioned problems, the adhesive sheet of the present invention achieves a HU hardness of 10–13 N / mm² at a temperature of -30°C. 2 The hardness of HU at 25℃ is 9-10 N / mm. 2 .

[0008] Preferably, the creep strain of the adhesive sheet of the present invention can be measured by using a ball indenter with a diameter of 2 mm at a temperature of 25°C to lift the load to 200 mN at a specified speed and apply pressure for 10 seconds, holding the load at 200 mN for 5 seconds, and then reducing the load from 200 mN to 0 mN at a specified speed within 10 seconds.

[0009] In addition, the creep strain of the adhesive sheet of the present invention can be measured by using a ball indenter with a diameter of 2 mm at a temperature of -30°C to lift the load to 200 mN at a specified speed and apply pressure for 10 seconds, holding the load at 200 mN for 5 seconds, and then reducing the load from 200 mN to 0 mN at a specified speed within 10 seconds.

[0010] The adhesive composition forming the adhesive sheet of the present invention may include an acrylic monomer having 8 to 12 carbon atoms and an isocyanate adduct type curing agent. Preferably, the curing agent may include a first curing agent represented by the following chemical formula 1 and a second curing agent represented by the following chemical formula 2.

[0011] Chemical Formula 1

[0012]

[0013] Chemical formula 2

[0014]

[0015] Typically, adhesive sheets with low energy storage modulus exhibit weak restoring force. However, the adhesive sheet of the present invention possesses the characteristic of achieving low energy storage modulus without weakening its restoring force. Furthermore, the adhesive sheet of the present invention possesses the characteristic of achieving low energy storage modulus while enhancing compressive strength. Thus, the adhesive sheet of the present invention has bending characteristics suitable for foldable optical display devices. Attached Figure Description

[0016] Figure 1 This is a cross-sectional view showing the display component of the present invention. Detailed Implementation

[0017] The above-mentioned objectives, features, and advantages will be described in detail below, thereby enabling those skilled in the art to readily implement the technical concept of this invention. In the process of describing this invention, if it is determined that a detailed description of specific known technologies related to this invention might unnecessarily obscure the spirit of the invention, such detailed description will be omitted. Preferred embodiments of the invention will be described in detail below.

[0018] This invention is not limited to the embodiments disclosed below, but can be implemented in various different forms. This embodiment is only intended to make the disclosure of this invention more complete and to enable those skilled in the art to fully understand the scope of this invention.

[0019] The adhesive sheet and the optical display element comprising the present invention will be described in detail below.

[0020] Adhesive sheet

[0021] In this invention, an adhesive sheet refers to a structure comprising a sheet-like or film-like adhesive layer formed from an adhesive composition.

[0022] The adhesive sheet of the present invention satisfies a HU hardness of 10 to 13 N / mm at a temperature of -30°C. 2 The hardness of HU at 25℃ is 9-10 N / mm. 2 .

[0023] The HU hardness mentioned above, used to indicate the degree of compressive strength, refers to the general hardness (surface hardness) of the aforementioned adhesive sheet. As an example, the HU hardness can be measured using a commercially available microhardness tester (PICODENTORHM500) from Helmut Fischer. This is done by applying pressure to the surface of the adhesive sheet using a 2mm diameter ball indenter, increasing the load to 200mN at a specified speed, holding the 200mN load for 5 seconds, and then decreasing the load from 200mN to 0mN at a specified speed within 10 seconds. The physical properties at low temperatures can be measured by cooling the sample using a separate cooling device (DHTCD-01).

[0024] The adhesive sheet of the present invention has the HU hardness as defined above under both low-temperature and normal-temperature conditions. If the HU hardness of the adhesive sheet of the present invention is less than 10 N / mm² at a temperature of -30°C... 2 Or, the HU hardness is less than 9 N / mm at a temperature of 25°C. 2 If the adhesive sheet is too soft, it may result in reduced processability and resilience. Conversely, if the HU hardness of the adhesive sheet of the present invention exceeds 13 N / mm at a temperature of -30°C... 2 Or, the HU hardness exceeds 10 N / mm at a temperature of 25°C. 2 If the hardness of the adhesive sheet is too high, it will result in insufficient flexibility, which may lead to problems such as cracks in the display components.

[0025] Therefore, the adhesive sheet of the present invention satisfies the requirement of a HU hardness of 10 to 13 N / mm at a temperature of -30°C. 2 The hardness of HU at 25℃ is 9-10 N / mm. 2 This allows for the bending characteristics required for foldable displays.

[0026] Furthermore, the creep strain measured by the method of using a ball indenter with a diameter of 2 mm to lift the load to 200 mN at a specified speed and apply pressure for 10 seconds under a temperature of 25°C, holding the load at 200 mN for 5 seconds, and then reducing the load from 200 mN to 0 mN at a specified speed within 10 seconds can be equivalent to 8-9%.

[0027] Furthermore, the creep strain measured by the method of using a ball indenter with a diameter of 2 mm to lift the load to 200 mN at a specified speed and apply pressure for 10 seconds under a temperature of -30°C, holding the load at 200 mN for 5 seconds, and then reducing the load from 200 mN to 0 mN at a specified speed within 10 seconds can be equivalent to 8-9%.

[0028] If the creep strain is less than 8%, the resistance during folding will be greater and the shock absorption capacity will be insufficient, which may lead to damage to the panel. If it exceeds 9%, the compressive strength during folding will be weak, which may lead to permanent deformation of the material and wrinkles.

[0029] Since the adhesive sheet of the present invention meets the above conditions, it can provide excellent protection for the adhered object under multiple deformations and maintain reliability at low and high temperatures.

[0030] This adhesive sheet of the present invention can be formed from an adhesive composition, which may include an acrylic resin as the main resin and a curing agent.

[0031] The aforementioned acrylic resins comprise acrylic monomers. For example, these acrylic monomers may include alkyl methacrylate monomers, which may include unsubstituted linear or branched alkyl methacrylates having 1 to 20 carbon atoms. For example, they may include at least one of methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, isobutyl methacrylate, amyl methacrylate, hexyl methacrylate, heptyl methacrylate, ethylhexyl methacrylate, octyl methacrylate, isooctyl methacrylate, nonyl methacrylate, decyl methacrylate, and lauryl methacrylate.

[0032] Furthermore, the aforementioned acrylic monomers may include hydroxyl-containing methacrylic acid monomers, which may be methacrylic acid monomers containing one or more hydroxyl groups and a hydrocarbon group having 1 to 20 carbon atoms. The hydrocarbon group having 1 to 20 carbon atoms may, for example, be a methacrylate having an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 5 to 20 carbon atoms, or an aryl group having 6 to 20 carbon atoms. Specifically, the hydroxyl-containing methacrylate monomers can be at least one of the following: 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxybutyl methacrylate, 4-hydroxybutyl methacrylate, 6-hydroxyhexyl methacrylate, 1,4-cyclohexanediol mono(meth)acrylate, 1-chloro-2-hydroxypropyl(meth)acrylate, diethylene glycol mono(meth)acrylate, 1,6-hexanediol mono(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol penta(meth)acrylate, neopentyl glycol mono(meth)acrylate, trimethylolpropane di(meth)acrylate, trimethylolethane di(meth)acrylate, 2-hydroxy-3-phenoxypropyl(meth)acrylate, 4-hydroxycyclopentyl(meth)acrylate, 4-hydroxycyclohexyl(meth)acrylate, and cyclohexanediol mono(meth)acrylate.

[0033] Preferably, the adhesive composition of the present invention may contain an acrylic monomer having 8 to 12 carbon atoms as a monomer contained in an acrylic resin. The aforementioned acrylic monomer having 8 to 12 carbon atoms may be at least one selected from 2-ethylhexyl acrylate, octyl methacrylate, isooctyl methacrylate, nonyl methacrylate, decyl methacrylate, and lauryl methacrylate, but the acrylic monomer having 8 to 12 carbon atoms in the present invention is not limited to the examples described above.

[0034] Preferably, based on 100 parts by weight of the acrylic main resin, the content of the acrylic monomer with 8 to 12 carbon atoms is 86 to 96 parts by weight, more preferably 88 to 94 parts by weight, and most preferably 90 to 92 parts by weight. If the content of the acrylic monomer with 8 to 12 carbon atoms is less than 86 parts by weight, the functional groups will increase, resulting in increased hardness and reduced adhesion. If it exceeds 96 parts by weight, the functional groups will decrease, resulting in decreased hardness and processability problems.

[0035] In addition, the above-mentioned adhesive composition may contain the above-mentioned curing agent, which may be selected from curing agents commonly used in the field of acrylic adhesives, preferably containing an isocyanate adduct type curing agent to impart the above-mentioned bending properties.

[0036] Preferably, based on 100 parts by weight of acrylic main resin, the content of the above-mentioned isocyanate adduct type curing agent is 0.002 to 0.018 parts by weight, more preferably, it contains 0.004 to 0.016 parts by weight, and most preferably, it contains 0.006 to 0.014 parts by weight.

[0037] In particular, preferably, the curing agent may comprise a first curing agent represented by the following chemical formula 1 and a second curing agent represented by the following chemical formula 2.

[0038] Chemical Formula 1

[0039]

[0040] Chemical formula 2

[0041]

[0042] Preferably, the adhesive composition of the present invention comprises both the first curing agent and the second curing agent described above.

[0043] Preferably, when the content ratio of the first curing agent and the second curing agent is 4:6 to 6:4, and more preferably 5:5, excellent bending characteristics, durability, and reliability can be achieved. If the content ratio of the first curing agent and the second curing agent exceeds the range of 4:6 to 6:4, the creep strain increases, the compressive strength during folding is weak, which may lead to permanent deformation of the material, wrinkles, and other problems.

[0044] Furthermore, the aforementioned adhesive composition may selectively include, as needed, common additives such as antistatic agents, molecular weight regulators, antioxidants, anti-aging agents, curing accelerators, ionic liquids, lithium salts, silane coupling agents, organic fillers, inorganic fillers, softeners, stabilizers, tackifying resins, modified resins (polyol resins, phenolic resins, acrylic resins, polyester resins, polyolefin resins, epoxy resins, epoxidized polybutadiene resins, etc.), wetting agents, leveling agents, defoamers, plasticizers, dyes, pigments (coloring pigments, sieved pigments, etc.), treatment agents, sunscreens, fluorescent whitening agents, dispersants, heat stabilizers, light stabilizers, ultraviolet absorbers, antistatic agents, lubricants, and solvents.

[0045] Display Components

[0046] Figure 1 The image shows a display component including the adhesive sheet of the present invention.

[0047] Reference Figure 1 The display component 100 of the present invention includes: an optical film 20; and the aforementioned adhesive sheet 10, which is attached to one or both surfaces (not shown) of the optical film 20.

[0048] Any thin film used in optical fields such as displays can be applied to the aforementioned optical films without restriction. For example, the aforementioned optical films may include touch panels, windows, polarizers, color filters, phase retardation films, elliptical polarizing films, reflective films, antireflection films, compensation films, brightness enhancement films, alignment films, light diffusion films, glass anti-scattering films, surface protective films, OLED element blocking layers, plastic liquid crystal display (LCD) substrates, transparent electrode films containing indium tin oxide (ITO), fluorinated tin oxide (FTO), aluminum-doped zinc oxide (AZO), carbon nanotube (CNT) films, Ag nanowire films, and graphene films.

[0049] The present invention will now be described in more detail through preferred embodiments. These embodiments are provided by way of example only to illustrate the invention in more detail. Therefore, the invention is not limited to these embodiments.

[0050] Example

[0051] 1. Preparation of adhesive sheet

[0052] (1) Preparation of the adhesive sheet of Example 1

[0053] An adhesive composition was prepared by mixing 100 parts by weight of an acrylic resin with polyethylhexyl acrylate as the main monomer (weight average molecular weight 1,000,000 g / mol), 0.003 parts by weight of xylene diisocyanate adduct and 0.003 parts by weight of toluene diisocyanate adduct as crosslinking agents, 0.1 parts by weight of ionic liquid (ammonium salt) as the first antistatic agent, and 7 parts by weight of ethyl acetate 1 as a solvent.

[0054] A polyethylene terephthalate (PET) substrate was used as the base material. The base material was prepared by coating the lower surface of the base material with a thin film of PEDOT / PSS (poly(3,4-ethylenedioxythiophene) polystyrene sulfonate) and performing an antistatic treatment. The adhesive sheet of Example 1 was prepared by coating the upper surface of the base material with the adhesive composition described above.

[0055] (2) Examples 2-3, Comparative Examples 1 to 8

[0056] Based on the composition shown in Table 1 below, adhesive sheets of Examples 2, 3 and Comparative Examples 1 to 8 were prepared.

[0057] Table 1

[0058]

[0059] BA: Butyl acrylate

[0060] 2-EHA: 2-Ethyl hexyl acrylate

[0061] OA: Octyl acrylate

[0062] DA: Decyl acrylate

[0063] LA: Lauryl Acrylate

[0064] 4-HBA: 4-Hydroxybutyl acrylate

[0065] AA: Acrylic acid

[0066] Toluene diisocyanate adduct (TDI-adduct):

[0067] Chemical formula 2

[0068]

[0069] Xylene diisocyanate adduct (XDI-adduct):

[0070] Chemical Formula 1

[0071]

[0072] HDI-trimer: hexamethylene diisocyanate trimer

[0073] Epoxy curing agent: Tetraglycidyl-m-xylenediamine

[0074] 2. Evaluate physical properties

[0075] The physical properties of the adhesive sheets of the above embodiments and comparative examples were evaluated. The evaluated physical properties are listed in Table 2 below.

[0076] Table 2

[0077]

[0078] HU (hardness) was measured using a commercially available microhardness tester (PICOD ENTOR HM500) from Helmut Fischer, following standard hardness measurement methods.

[0079] Creep characteristics are evaluated based on the creep strain measured under the above temperature conditions by using a ball indenter with a diameter of 2 mm to increase the load to 200 mN at a specified speed and apply pressure for 10 seconds, holding the load at 200 mN for 5 seconds, and then slowly reducing the load from 200 mN to 0 mN at a specified speed within 10 seconds.

[0080] All embodiments meet the requirement of a HU hardness of 10–13 N / mm at a temperature of -30°C. 2 The hardness of HU at 25℃ is 9-10 N / mm. 2 Furthermore, all embodiments meet the requirement of 8-9% creep strain at temperatures of 25°C and -30°C.

[0081] As can be seen, compared with the examples, the hardness of Comparative Examples 1 and 2 increased. Furthermore, the creep strain of Comparative Example 3 increased, while the hardness of Comparative Example 4 decreased at room temperature. Additionally, the creep strain of Comparative Examples 5 and 6 increased. Moreover, the hardness of Comparative Examples 7 and 8 decreased at room temperature, while the creep strain of Comparative Example 8 also increased at room temperature.

[0082] Therefore, it can be expected that the bending characteristics of Comparative Examples 1 to 8, which do not meet the hardness and creep strain characteristics, will be reduced.

[0083] 3. Evaluate bending characteristics

[0084] The bending characteristics of the embodiments and comparative examples were evaluated based on whether warping, bubbles, cracks (whitening phenomenon) were observed during bending.

[0085] Each adhesive sheet was attached to the substrate and subjected to 200,000 bending cycles to confirm the presence of any abnormalities in the bent portions. Adhesive sheets exhibiting delamination (lifting), bubbles, or cracks (whitening) were deemed defective.

[0086] In Examples 1 to 3, no abnormal phenomena such as warping, bubbles, or cracks (whitening) occurred in the adhered materials after 200,000 bending cycles. However, bubbles, warping, and cracks (whitening) were observed in the comparative examples.

[0087] The present invention has been described above, but it is not limited to the embodiments disclosed in this specification. Obviously, those skilled in the art can make various modifications within the scope of the inventive concept. Furthermore, even if the functions and effects produced by the structure of the present invention are not explicitly stated or described in the above description of the embodiments, the effects that can be predicted through this structure should be acknowledged.

Claims

1. An adhesive sheet, characterized in that, The hardness of HU at a temperature of -30℃ is 10~13N / mm. 2 The hardness of HU at 25℃ is 9-10 N / mm. 2 , The aforementioned adhesive sheet is formed from an adhesive composition. The above adhesive composition comprises acrylic resin and isocyanate adduct type curing agent. Based on 100 parts by weight of the aforementioned acrylic resin, the aforementioned adhesive composition contains 86 to 96 parts by weight of an acrylic monomer having 8 to 12 carbon atoms. The aforementioned acrylic monomers with 8 to 12 carbon atoms are composed of 2-ethylhexyl acrylate, octyl acrylate, and decyl acrylate. The aforementioned isocyanate adduct type curing agent includes a first curing agent represented by the following chemical formula 1 and a second curing agent represented by the following chemical formula 2, with a content ratio of 4:6 to 6:4: Chemical Formula 1: ， Chemical formula 2: 。 2. The adhesive sheet according to claim 1, characterized in that, The creep strain was measured to be 8-9% by using a ball indenter with a diameter of 2 mm at a specified speed to lift the load to 200 mN and apply pressure for 10 seconds at a temperature of 25°C, holding the load at 200 mN for 5 seconds, and then reducing the load from 200 mN to 0 mN at a specified speed within 10 seconds.

3. The adhesive sheet according to claim 1, characterized in that, The creep strain was measured to be 8-9% by using a ball indenter with a diameter of 2 mm at a temperature of -30°C, raising the load to 200 mN at a specified speed and applying pressure for 10 seconds, holding the load at 200 mN for 5 seconds, and then reducing the load from 200 mN to 0 mN at a specified speed within 10 seconds.

4. The adhesive sheet according to claim 1, characterized in that, Based on 100 parts by weight of the above-mentioned acrylic resin, the above-mentioned adhesive composition contains 0.002 to 0.018 parts by weight of the above-mentioned curing agent.

5. A display component, characterized in that, include: Optical film; as well as The adhesive sheet of claim 1 is attached to one or both surfaces of the optical film.

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