Adhesive sheet

Abstract

This invention provides an adhesive sheet that offers excellent reliability when used in OLED display devices that do not use polarizing plates, and which can contribute to reducing environmental impact. [Solution] The adhesive sheet 1 is used in an OLED display device in which only optical elements with a polarization degree of 95% or less are laminated on the viewing side of the OLED element. The adhesive sheet 1 comprises an ultraviolet-curable adhesive layer. The ultraviolet-curable adhesive layer contains a dye compound whose maximum absorption wavelength in the absorption spectrum is in the wavelength region of 380 to 430 nm. The maximum absorbance of the adhesive sheet 1 in the wavelength region of 380 to 430 nm is 0.5 or more, the maximum absorbance in the wavelength region of 440 to 780 nm is 0.1 or less, and the maximum absorbance in the wavelength region of 300 to 800 nm is in the wavelength region of 380 to 410 nm. * The range is 2 to 10.

Description

[Technical Field]

[0001] The present invention relates to an adhesive sheet. More specifically, the present invention relates to an adhesive sheet used in conjunction with an organic electroluminescent (OLED) display device. [Background technology]

[0002] In recent years, organic light-emitting diode (OLED) displays, which are equipped with organic EL panels, have become widely used in various applications such as mobile phones, car navigation systems, PC monitors, and televisions. In OLED displays, a circular polarizer (such as a laminate of a polarizer and a quarter-wave plate) is usually placed on the viewing surface of the OLED panel to prevent ambient light from being reflected by the metal electrode (cathode) and appearing like a mirror. In addition, decorative panels may be further laminated on the circular polarizer laminated on the viewing surface of the OLED panel. The components of the OLED display, such as the circular polarizer and decorative panels, are usually laminated with bonding materials such as adhesive layers.

[0003] However, using circular polarizers results in poor light utilization efficiency (i.e., light collection rate) due to absorption by the polarizer, leading to lower brightness. Increasing the light emission intensity of the OLED element to achieve the desired brightness increases power consumption and shortens the lifespan of the OLED element. Furthermore, including the adhesive layer used to attach the polarizer, it becomes about 0.15 mm thick, which is disadvantageous for making OLED display devices thinner. In addition, circular polarizers are expensive, which increases manufacturing costs.

[0004] As an alternative to circular polarizers, a method has been proposed to improve the luminescence of an OLED element while preventing external light reflection by placing a color filter on the viewing side of the OLED element and aligning it so that the color filter is the same color as the OLED layer's emission color and faces it (for example, Patent Document 1).

[0005] Furthermore, in image display devices such as OLED displays, the components within the image display device may deteriorate due to incident ultraviolet light, and it is known that a layer containing an ultraviolet absorber is provided to suppress such deterioration due to ultraviolet light. Specifically, for example, a transparent double-sided adhesive sheet for image display devices is known (see, for example, Patent Document 2) which has at least one ultraviolet absorbing layer, a light transmittance of 30% or less at a wavelength of 380 nm, and a visible light transmittance of 80% or more at wavelengths longer than 430 nm. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2018-112715 [Patent Document 2] Japanese Patent Publication No. 2012-211305 [Overview of the project] [Problems that the invention aims to solve]

[0007] Because polarizing plates have the function of absorbing ultraviolet light, OLED display devices that do not use polarizing plates have the problem that the components constituting the OLED display device (especially the OLED elements) are prone to degradation due to ultraviolet light. Furthermore, in recent years, from the perspective of contributing to the reduction of environmental impact, there has been a demand for the use of ultraviolet-curing adhesive layers with extremely low solvent content or no solvent content in adhesive sheets, instead of solvent-type adhesive layers formed from adhesive compositions containing solvents. However, since ultraviolet-curing adhesive layers form a base polymer by the polymerization of monomer components in the adhesive composition due to ultraviolet light, it is not possible to use ultraviolet absorbers that absorb ultraviolet light and inhibit the polymerization of monomer components. As a result, OLED display devices that do not use polarizing plates have the problem of being unreliable, such as the transparency of the adhesive sheet decreasing or yellowing and discoloration occurring after prolonged use.

[0008] The present invention has been made in view of the above problems, and an object thereof is to provide an adhesive sheet that is excellent in reliability when used in an OLED display device that does not use a polarizing plate and can contribute to reducing environmental load.

Means for Solving the Problems

[0009] As a result of intensive studies to achieve the above object, the present inventors have found that a specific adhesive sheet is excellent in reliability when used in an OLED display device that does not use a polarizing plate and can contribute to reducing environmental load.

[0010] That is, the present invention is an adhesive sheet used for an OLED display device in which only an optical element having a polarization degree of 95% or less is laminated on the viewing side of an OLED element, the above adhesive sheet includes an ultraviolet curable adhesive layer, the above ultraviolet curable adhesive layer contains a dye compound whose maximum absorption wavelength of the absorption spectrum exists in the wavelength region of 380 to 430 nm, the maximum value of the absorbance in the wavelength region of 380 to 430 nm of the above adhesive sheet is 0.5 or more, the maximum value of the absorbance in the wavelength region of 440 to 780 nm is 0.1 or less, the maximum value of the absorbance in the range of the wavelength region of 300 to 800 nm is in the wavelength region of 380 to 410 nm, b * is 2 to 10, and provides an adhesive sheet.

[0011] The adhesive sheet of the present invention includes an ultraviolet curable adhesive layer. Such an adhesive sheet can form a base polymer constituting the adhesive layer by polymerizing monomer components by ultraviolet rays, so that it is possible not to use a solvent or to use an extremely small amount of a solvent, and it can contribute to reducing environmental load.

[0012] The above ultraviolet-curable adhesive layer contains a dye compound whose maximum absorption wavelength in the absorption spectrum exists in the wavelength range of 380 to 430 nm, and the maximum value of the absorbance of the adhesive sheet in the wavelength range of 380 to 430 nm is 0.5 or more. By having such a configuration, the adhesive sheet can sufficiently absorb ultraviolet light and suppress the deterioration of the OLED element due to ultraviolet light.

[0013] The maximum value of the absorbance of the adhesive sheet in the wavelength range of 440 to 780 nm is 0.1 or less, and the maximum value of the absorbance in the range of the wavelength range of 300 to 800 nm is in the wavelength range of 380 to 410 nm, and b * is 2.5 to 10. By having such a configuration, the adhesive sheet has a high visible light transmittance, excellent transparency, and suppressed yellowing, and is excellent in the reliability of the adhesive sheet.

[0014] It is preferable that the transmittance of the adhesive sheet in the wavelength range of 300 to 380 nm is 30% or more. By having such a configuration, the ultraviolet curability can be effectively exerted, and it can be effectively cured by ultraviolet light in a wavelength range lower than 380 nm and can be sufficiently cured. In addition, bleed-out can be suppressed.

[0015] It is preferable that the change rate of b * of the adhesive sheet after the following weather resistance test is 0.2 or more. By having such a configuration, the yellowing of the adhesive sheet is suppressed, and the adhesive sheet is excellent in reliability. <Weather Resistance Test> The adhesive sheet is irradiated with ultraviolet light for 48 hours by a UV lamp having a peak wavelength in the range of 360 to 430 nm in an environment of 40 °C, and this ultraviolet irradiation is repeated twice.

[0016] The above ultraviolet-curable adhesive layer is a single layer having two opposing main surfaces. When it is equally divided into two in the thickness direction, the concentration of the dye compound in the region belonging to one of the two main surfaces, the first main surface, and the concentration of the dye compound in the region belonging to the other second main surface may be different.

Effect of the Invention

[0017] The adhesive sheet of the present invention offers excellent reliability when used in OLED display devices that do not use polarizing plates, and can contribute to reducing environmental impact. [Brief explanation of the drawing]

[0018] [Figure 1] This is a cross-sectional view showing one embodiment of the adhesive sheet of the present invention. [Figure 2] This is a cross-sectional view showing one embodiment of an OLED display panel in an OLED display device of the present invention. [Figure 3] This is a cross-sectional view showing one embodiment of the OLED display device of the present invention. [Modes for carrying out the invention]

[0019] [Adhesive sheet] The adhesive sheet of the present invention comprises an ultraviolet-curable adhesive layer. The ultraviolet-curable adhesive layer contains a dye compound whose maximum absorption wavelength in the absorption spectrum is in the wavelength region of 380 to 430 nm. In this specification, the ultraviolet-curable adhesive layer may be referred to as "the adhesive layer of the present invention."

[0020] The adhesive sheet of the present invention may be a so-called "substrate-less type" adhesive sheet that does not have a base material (substrate layer), or it may be an adhesive sheet that has a base material. In this specification, a "substrate-less type" adhesive sheet may be referred to as a "substrate-less adhesive sheet," and an adhesive sheet that has a base material may be referred to as a "substrate-attached adhesive sheet." Examples of the above-mentioned substrate-less adhesive sheet include a double-sided adhesive sheet consisting only of the adhesive layer of the present invention, and a double-sided adhesive sheet consisting of the adhesive layer of the present invention and other adhesive layers (adhesive layers other than the adhesive layer of the present invention). Examples of the above-mentioned substrate-attached adhesive sheet include a single-sided adhesive sheet having the adhesive layer of the present invention on one side of the base material, a double-sided adhesive sheet having the adhesive layer of the present invention on both sides of the base material, and a double-sided adhesive sheet having the adhesive layer of the present invention on one side of the base material and other adhesive layers on the other side. The above-mentioned "substrate (substrate layer)" refers to the support, and is the part that is attached to the adherend together with the adhesive layer when the adhesive sheet of the present invention is used (attached) to an adherend. The release liner that is peeled off when the adhesive sheet is used (applied) is not included in the above-mentioned substrate.

[0021] The adhesive sheet of the present invention has a maximum absorbance of 0.5 or higher in the wavelength range of 380 to 430 nm, which may be 0.6 or higher, 0.7 or higher, 0.8 or higher, or 0.9 or higher, and preferably 1 or higher. When the maximum absorbance in the above wavelength range is 0.5 or higher, the adhesive sheet can sufficiently absorb ultraviolet light, and the degradation of OLED elements due to ultraviolet light can be suppressed.

[0022] The adhesive sheet of the present invention has a maximum absorbance of 0.1 or less in the wavelength range of 440 to 780 nm, preferably 0.08 or less, and more preferably 0.06 or less. When the maximum absorbance in the above wavelength range is 0.1 or less, the adhesive sheet has high visible light transmittance and excellent transparency, allowing the light emitted by the OLED element to be clearly visible, and the adhesive sheet has excellent reliability.

[0023] The adhesive sheet of the present invention has a maximum absorbance in the wavelength range of 300 to 800 nm in the wavelength region of 380 to 410 nm, preferably in the wavelength region of 390 to 410 nm, and more preferably in the wavelength region of 400 to 410 nm. When the maximum absorbance is within the above wavelength region, the adhesive sheet has a low transmittance of ultraviolet rays, suppresses the deterioration of the OLED element by ultraviolet rays, suppresses the yellowing of the adhesive layer, and has excellent reliability of the adhesive sheet.

[0024] The adhesive sheet of the present invention has a b * of 2 to 10, preferably 2 to 8, and more preferably 2 to 5. When b * is within the above range, the yellowing of the adhesive layer is suppressed, and the adhesive sheet has excellent reliability. The above b * value is the b * a * b * value (chromaticity) in the color system of L * and can be measured using, for example, a spectrophotometer (product name: U4100, manufactured by Hitachi High-Tech Corporation).

[0025] The adhesive sheet of the present invention preferably has an absorbance at a wavelength of 340 nm of less than 2, more preferably 1 or less, and even more preferably 0.5 or less. When the absorbance is less than 2, the ultraviolet curability can be effectively exhibited and cured.

[0026] The adhesive sheet of the present invention preferably has an absorbance at a wavelength of 405 nm (absorbance (405 nm)) of 0.5 or more, more preferably 0.7 or more, and even more preferably 1.0 or more. When the absorbance is 0.5 or more, the ultraviolet absorption can be effectively exhibited.

[0027] The adhesive sheet of the present invention preferably has an absorbance at a wavelength of 440 nm (absorbance (440 nm)) of 0.1 or less, more preferably 0.08 or less, and even more preferably 0.06 or less. When the absorbance is 0.1 or less, the absorbance in the visible light region is low, leading to a reduction in power consumption.

[0028] The adhesive sheet of the present invention preferably has a ratio of absorbance at a wavelength of 405 nm to absorbance at a wavelength of 440 nm [absorbance (405 nm) / absorbance (440 nm)] of 30 or more, more preferably 32 or more, and even more preferably 33 or more. When the above ratio is 30 or more, the brightness of the OLED display device becomes higher.

[0029] The adhesive sheet of the present invention preferably has a transmittance of 30% or more in the wavelength range of 300 to 380 nm, more preferably 35% or more, and even more preferably 40% or more. When the transmittance in the above wavelength range is 30% or more, it effectively exhibits UV curability and can be effectively cured with UV light in the wavelength range lower than 380 nm, and can be sufficiently cured. In addition, bleed-out can be suppressed. The above transmittance may be, for example, 90% or less, 80% or less, or 60% or less. The above transmittance is the average value of the transmittance measured at 1 nm intervals in the wavelength range of 300 to 380 nm. The above transmittance of 30% or more means that the transmittance is 30% or more at at least one point in the wavelength range of 300 to 380 nm. In particular, it is preferable that the transmittance is 30% or more throughout the entire wavelength range of 300 to 380 nm, that is, that the minimum transmittance in the wavelength range of 300 to 380 nm is 30% or more.

[0030] The adhesive sheet of the present invention is b after the following weather resistance test. * The rate of change is preferably 0.2 or more, more preferably 0.3 or more, and even more preferably 0.4 or more. When the rate of change is 0.2 or more, yellowing of the adhesive sheet is suppressed, and the reliability of the adhesive sheet is excellent. The rate of change is, for example, 5 or less. The rate of change is a value calculated by formula (B) described in the examples. <Weather resistance test> The adhesive sheet is subjected to 48 hours of UV irradiation using a UV lamp with a peak wavelength of 360-430 nm at a temperature of 40°C, and this UV irradiation is repeated twice.

[0031] The adhesive sheet of the present invention preferably has a transmittance of 10% or less at a wavelength of 405 nm after the heat resistance test described above, more preferably 8% or less, and even more preferably 5% or less. A transmittance of 10% or less further improves reliability.

[0032] The adhesive sheet of the present invention preferably has a change rate of transmittance at a wavelength of 405 nm after the above weather resistance test of -0.2 or more, more preferably 0 or more, and even more preferably 0.1 or more. When the above change rate is -0.2 or more, the decrease in transparency of the adhesive sheet is suppressed, and the reliability of the adhesive sheet is excellent. The above change rate is, for example, 5 or less. The above change rate is a value calculated by formula (A) described in the examples.

[0033] The thickness (total thickness) of the adhesive sheet described above is not particularly limited, but is preferably 5 to 300 μm, more preferably 8 to 200 μm, even more preferably 10 to 100 μm, and most preferably 15 to 80 μm. A thickness above a certain level is preferable for exhibiting drop impact resistance. Furthermore, a thickness below a certain level is preferable because it makes it easier to maintain an excellent appearance during manufacturing and roll storage, and prevents adhesive staining during cutting. Note that the thickness of the adhesive sheet does not include the thickness of the release liner.

[0034] The adhesive sheet of the present invention may comprise only one or more adhesive layers of the present invention. When comprising two or more adhesive layers of the present invention, the multiple adhesive layers of the present invention may be the same adhesive layer, or they may be adhesive layers with different compositions, thicknesses, physical properties, etc.

[0035] The thickness of the adhesive layer of the present invention is preferably 5 to 300 μm, more preferably 8 to 200 μm, even more preferably 10 to 100 μm, and particularly preferably 15 to 80 μm. A thickness of 5 μm or more provides the necessary adhesion as an adhesive. A thickness of 300 μm or less contributes to reducing the overall thickness of the device.

[0036] The adhesive layer of the present invention can be a known or conventional adhesive layer. Preferably, the adhesive layer is a solvent-free adhesive layer containing a photopolymerized polymer as the base polymer. Such an adhesive layer can be manufactured from a solvent-free adhesive composition. When manufacturing the adhesive layer from a solvent-free adhesive composition, there is no need to remove the solvent by volatilizing it from the coating film of the composition. Therefore, an adhesive sheet equipped with the above adhesive layer is suitable for reducing environmental impact.

[0037] The adhesive layer of the present invention is preferably a sheet-like pressure-sensitive adhesive (solvent-free adhesive sheet) formed from a solvent-free adhesive composition. Therefore, the adhesive layer (solvent-free adhesive layer) preferably contains at least a photopolymerizable polymer as a base polymer. A photopolymerizable polymer is a polymer formed by a polymerization method in which the polymerization reaction of polymerizable components is advanced by irradiation with ultraviolet light.

[0038] The base polymer is an adhesive component that exhibits tackiness in the adhesive layer of the present invention. The base polymer is not particularly limited, but examples include acrylic polymers, rubber polymers (such as natural rubber polymers and synthetic rubber polymers), silicone polymers, polyester polymers, urethane polymers, polyamide polymers, epoxy polymers, vinyl alkyl ether polymers, and fluorine polymers. One or more of the base polymers may be used.

[0039] The content of the base polymer in the adhesive layer of the present invention is not particularly limited, but is preferably 75% by mass or more (for example, 75 to 99.9% by mass) and more preferably 85% by mass or more (for example, 85 to 99.9% by mass) based on the total amount (100% by mass) of the adhesive layer.

[0040] The method for producing the adhesive layer of the present invention is not particularly limited. For example, the method may involve preparing the adhesive composition described below, applying it to a substrate or release liner, performing heating and drying as necessary, and then irradiating it with ultraviolet light.

[0041] Furthermore, known coating methods may be used for applying (coating) the above adhesive composition. For example, coaters such as gravure roll coaters, reverse roll coaters, kiss roll coaters, dip roll coaters, bar coaters, knife coaters, spray coaters, comma coaters, and direct coaters may be used.

[0042] Furthermore, it is preferable that the above adhesive composition does not contain or substantially contains organic solvents. The above organic solvent is not particularly limited as long as it is an organic compound used as a solvent, but examples include hydrocarbon solvents such as cyclohexane, hexane, and heptane; aromatic solvents such as toluene and xylene; ester solvents such as ethyl acetate and methyl acetate; ketone solvents such as acetone and methyl ethyl ketone; and alcohol solvents such as methanol, ethanol, butanol, and isopropyl alcohol. The above organic solvent may be a mixed solvent containing two or more organic solvents.

[0043] In the above-mentioned adhesive composition, "substantially free of organic solvents" means that organic solvents are not actively incorporated except in cases where they are inevitably mixed in. Specifically, an adhesive composition in which the content of organic solvents is 1.0% by mass or less (preferably 0.5% by mass or less, and more preferably 0.2% by mass or less) relative to the total amount of the adhesive composition (100% by mass) can be said to be substantially free of organic solvents.

[0044] The adhesive composition for forming the adhesive layer of the present invention is preferably an adhesive composition containing an acrylic polymer as the base polymer. That is, the adhesive layer of the present invention is preferably an acrylic adhesive layer with an acrylic polymer as the base polymer. It may also contain hydrogenated polyolefin resins, polyfunctional (meth)acrylates, silane coupling agents, and other additives as described later. Note that only one type of acrylic polymer may be used, or two or more types may be used.

[0045] The content of the acrylic polymer is not particularly limited, but it is preferably 75% by mass or more (for example, 75 to 99.9% by mass) relative to the total amount (100% by mass) of the adhesive layer of the present invention, and more preferably 85% by mass or more (for example, 85 to 99.9% by mass).

[0046] The adhesive composition that forms an adhesive layer containing an acrylic polymer as the main component is not particularly limited, but examples include compositions that contain a mixture of monomer components constituting the acrylic polymer (sometimes referred to as a "monomer mixture") or a partially polymer thereof as essential components.

[0047] In this specification, the above-mentioned "mixture of monomer components" includes cases where it is composed of a single monomer component and cases where it is composed of two or more monomer components. Furthermore, the above-mentioned "partially polymerized mixture of monomer components" means a composition in which one or more of the constituent monomer components of the above-mentioned "mixture of monomer components" are partially polymerized.

[0048] Acrylic polymers are polymers (polymers) that contain acrylic monomers (acrylic monomers) as essential monomer units (monomer units, monomer constituent units). In other words, acrylic polymers are polymers that contain constituent units derived from acrylic monomers as constituent units. That is, acrylic polymers are polymers that are composed (formed) with acrylic monomers as essential monomer components. In this specification, "(meth)acrylic" refers to either or both of "acrylic" and "methacrylic," and the same applies to other terms. The weight-average molecular weight of the acrylic polymer in the adhesive layer is not particularly limited, but is preferably between 100,000 and 5,000,000.

[0049] The above acrylic polymer is preferably a polymer that contains an alkyl (meth)acrylate (hereinafter sometimes simply referred to as "alkyl (meth)acrylate") having a linear or branched alkyl group as a monomer unit.

[0050] Examples of the above alkyl (meth)acrylate esters include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate (n-butyl (meth)acrylate), isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate (n-octyl (meth)acrylate), 2-ethylhexyl (meth)acrylate, and methyl (meth)acrylate. Examples include alkyl esters of (meth)acrylates having 1 to 24 carbon atoms in the alkyl group, such as isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isostearyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. Note that one alkyl ester of (meth)acrylate may be used alone, or two or more may be used.

[0051] As for alkyl (meth)acrylate esters, alkyl acrylates are preferred over alkyl methacrylates because they can shorten the polymerization time of the acrylic polymer and improve productivity. In particular, alkyl acrylates are preferred when the acrylic polymer is cured by active energy ray polymerization.

[0052] Among these, alkyl (meth)acrylate esters with 1 to 18 carbon atoms in the alkyl group are preferred, and more preferably methyl methacrylate (MMA), butyl acrylate (BA), and octyl acrylate (NOAA), as they exhibit low dielectric constant and drop impact resistance.

[0053] The content (percentage) of the alkyl (meth)acrylate in the total monomer units (total amount of monomer components constituting the acrylic polymer) of the above acrylic polymer is not particularly limited, but in order to exhibit a low dielectric constant and drop impact resistance, it is preferably 30 to 99% by mass, more preferably 35 to 95% by mass, and even more preferably 40 to 90% by mass, relative to the total amount of monomer components constituting the acrylic polymer (100% by mass).

[0054] In this specification, when referring to "the total amount of monomer components constituting the acrylic polymer," it also includes monomer components that are separately added to the adhesive composition containing the acrylic polymer for purposes such as adjusting the dielectric constant of the adhesive layer.

[0055] The above monomer component preferably contains an alkyl (meth)acrylate having an alkyl group with 8 or more carbon atoms (sometimes referred to as "alkyl (meth)acrylate (A)"). Alkyl (meth)acrylate (A) has a medium-chain to long-chain alkyl group, making it easy to achieve a low dielectric constant while exhibiting high tackiness.

[0056] Examples of the above-mentioned alkyl (meth)acrylate (A) include alkyl (meth)acrylates with 8 to 24 carbon atoms in the alkyl group, such as octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isostearyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate.

[0057] Of the above alkyl (meth)acrylate (A), alkyl acrylate is preferred over alkyl methacrylate because it can shorten the polymerization time of the acrylic polymer and improve productivity. In particular, alkyl acrylate is preferred from the viewpoint of superior UV curability.

[0058] Among the above alkyl (meth)acrylate (A), it is preferable to include an alkyl (meth)acrylate having a linear or branched alkyl group having 8 or more carbon atoms, more preferably an alkyl (meth)acrylate having a linear or branched alkyl group having 8 or 9 carbon atoms, even more preferably octyl (meth)acrylate, and particularly preferably octyl acrylate (NOAA). The number of carbon atoms in the side chain alkyl group of the above branched alkyl group is not particularly limited, but alkyl groups having 1 to 3 carbon atoms (e.g., methyl group, ethyl group, n-propyl group, isopropyl group) are preferred. The "side chain alkyl group" is an alkyl group that is substituted on the side chain of the carbon chain with the longest number of carbon atoms.

[0059] The content of the alkyl (meth)acrylate (A) in the above acrylic adhesive composition is not particularly limited, but from the viewpoint of easily achieving a low dielectric constant while exhibiting high adhesiveness, it is preferably 30 to 99% by mass, more preferably 35 to 95% by mass, and even more preferably 40 to 90% by mass, based on the total amount (100% by mass) of monomer components in the above acrylic adhesive composition.

[0060] If the above alkyl (meth)acrylate (A) includes an alkyl (meth)acrylate having a linear or branched alkyl group having 8 or 9 carbon atoms (hereinafter referred to as alkyl (meth)acrylate (A1) in this specification), it is preferable that it further includes an alkyl (meth)acrylate having a branched alkyl group having 10 to 24 carbon atoms (hereinafter referred to as alkyl (meth)acrylate (A2) in this specification).

[0061] When the above alkyl (meth)acrylate (A) contains alkyl (meth)acrylate (A2) in addition to alkyl (meth)acrylate (A1), the dielectric constant of the adhesive layer can be reduced due to the action of the long-chain branched alkyl group. Therefore, even when it is attached to an optical component (touch sensor film) on which a metal wiring layer such as metal mesh wiring or silver nanowire is formed, malfunctions can be prevented because the adhesive layer has a low dielectric constant.

[0062] The Tg of the (meth)acrylate (A2) homopolymer is preferably -80 to 0°C, and more preferably -70 to -10°C. If the Tg of the homopolymer is -70°C or higher, the elastic modulus of the adhesive layer at room temperature is not too low, and if it is -10°C or lower, the initial tackiness is superior. The Tg of the homopolymer is a value measured by differential scanning calorimetry (DSC). Furthermore, while branched alkyl groups with 10 to 24 carbon atoms are preferred because they satisfy a moderately low dielectric constant and elastic modulus, alkyl (meth)acrylates having appropriately preferred alkyl groups can be selected depending on the method for producing the (meth)acrylic polymer. For example, the alkyl group has more preferably 12 to 18 carbon atoms, and even more preferably 14 to 18 carbon atoms.

[0063] Examples of alkyl esters (A2) (meth)acrylates include isodecyl acrylate (10 carbon atoms, Tg of homopolymer = -60°C, hereinafter simply abbreviated as Tg), isodecyl methacrylate (10 carbon atoms, Tg = -41°C), isomistyryl acrylate (14 carbon atoms, Tg = -56°C), isostearyl acrylate (18 carbon atoms, Tg = -18°C), 2-propylheptyl acrylate, isoundecyl acrylate, isododecyl acrylate, isotridecyl acrylate, isopentadecyl acrylate, isohexadecyl acrylate, and isoheptadecyl acrylate.

[0064] Among the branched alkyl groups having 10 to 24 carbon atoms, those having a branched alkyl group such as a t-butyl group at the end of the ester group are particularly preferred because they are thought to increase the molar volume and decrease the dipole moment, resulting in an adhesive layer with a balance between the two. Preferred branched alkyl groups at the end of the ester group include branched alkyl groups having 4 to 6 carbon atoms, such as a t-butyl group, a neopentyl group, and a t-pentyl group, with the t-butyl group being particularly preferred. A preferred example of an alkyl (meth)acrylate ester (A2) having a t-butyl group at the end of the ester group is isostearyl acrylate, represented by the following formula. [ka]

[0065] The content of the alkyl (meth)acrylate (A1) in the above acrylic adhesive composition is not particularly limited, but from the viewpoint of easily achieving a low dielectric constant while exhibiting high adhesiveness, it is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and may be 30% by mass or more, based on the total amount of monomer components (100% by mass) in the above acrylic adhesive composition. Furthermore, from the viewpoint of lowering the dielectric constant of the adhesive layer and preventing malfunctions, the above content is preferably 80% by mass or less, more preferably 75% by mass or less, even more preferably 70% by mass or less, and even more preferably 65% ​​by mass or less.

[0066] The content of the alkyl (meth)acrylate (A2) in the above acrylic adhesive composition is not particularly limited, but from the viewpoint of reducing the dielectric constant of the adhesive layer and preventing malfunctions, it is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and may be 30% by mass or more, based on the total amount of monomer components (100% by mass) in the above acrylic adhesive composition. Furthermore, from the viewpoint of easily achieving a low dielectric constant while exhibiting high adhesiveness, the above content is preferably 70% by mass or less, more preferably 65% ​​by mass or less, even more preferably 60% by mass or less, even more preferably 50% by mass or less, and particularly preferably 40% by mass or less.

[0067] The mass ratio of the above alkyl methacrylate (A1) to alkyl methacrylate (A2) [(alkyl methacrylate (A2) / (alkyl methacrylate (A1)] is not particularly limited, but from the viewpoint of easily achieving a low dielectric constant while exhibiting high tackiness, it is preferably 2 or less, more preferably 1.5 or less, and even more preferably 1.2 or less. Also, from the viewpoint of reducing the dielectric constant of the adhesive layer to prevent malfunctions, the above mass ratio is preferably 0.2 or more, more preferably 0.4 or more, even more preferably 0.6 or more, and may also be 0.8 or more.

[0068] The above monomer component may also contain alkyl (meth)acrylates other than alkyl (meth)acrylate (A) (hereinafter sometimes referred to as "alkyl (meth)acrylate (B)"). Examples of alkyl (meth)acrylate (B) include alkyl (meth)acrylates having a linear or branched alkyl group with 1 to 7 carbon atoms, such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate (n-butyl (meth)acrylate), isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, and heptyl (meth)acrylate.

[0069] The content of the alkyl (meth)acrylate (B) in the above acrylic adhesive composition is not particularly limited, but from the viewpoint of easily achieving a low dielectric constant while exhibiting high adhesiveness, it is preferably 40% by mass or less, and more preferably 30% by mass or less, based on the total amount of monomer components (100% by mass) in the above acrylic adhesive composition. The above content may be 1% by mass or more, 3% by mass or more, 8% by mass or more, 13% by mass or more, or 20% by mass or more.

[0070] In the above adhesive composition, the acrylic polymer may contain copolymerizable functional group-containing monomers (copolymerizable functional group-containing monomers) in addition to the above (meth)acrylate alkyl ester as monomer units. In other words, the acrylic polymer may contain functional group-containing monomers as constituent monomer components. Note that only one type of functional group-containing monomer may be used, or two or more types may be used.

[0071] As the above-mentioned functional group-containing monomers, hydroxyl group-containing monomers are preferred. When an acrylic polymer contains a hydroxyl group-containing monomer as a monomer unit, polymerization of the constituent monomer components becomes easier, and the cohesive force can be increased. Furthermore, the interaction with the adherend interface can be enhanced. As a result, strong adhesion can be easily obtained.

[0072] The above-mentioned hydroxyl group-containing monomers refer to monomers that have at least one hydroxyl group in their molecule. Furthermore, monomers that have at least one hydroxyl group and at least one carboxyl group in their molecule are carboxyl group-containing monomers and not hydroxyl group-containing monomers. The above-mentioned hydroxyl group-containing monomers are not particularly limited, but specifically include, for example, hydroxyl group-containing (meth)acrylic acid esters such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, hydroxyoctyl (meth)acrylate, hydroxydecyl (meth)acrylate, hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl) (meth)acrylate; vinyl alcohol, allyl alcohol, etc. In particular, as the above-mentioned hydroxyl group-containing monomer, hydroxyl group-containing (meth)acrylic acid esters are preferred from the viewpoint of easily obtaining good cohesive force and improving adhesive reliability at high temperatures, and more preferably 2-hydroxyethyl acrylate (HEA), 2-hydroxypropyl (meth)acrylate (HPA), and 4-hydroxybutyl acrylate (4HBA). Note that one type of hydroxyl group-containing monomer may be used, or two or more types may be used.

[0073] Furthermore, nitrogen atom-containing monomers are preferred as the functional group-containing monomers. When an acrylic polymer contains nitrogen atom-containing monomers as monomer units, it becomes easier to obtain appropriate cohesive force, which in turn makes it easier to obtain strong adhesion and excellent foaming resistance.

[0074] A nitrogen atom-containing monomer refers to a monomer that has at least one nitrogen atom within its molecule (one molecule). However, the above-mentioned hydroxyl group-containing monomer does not include nitrogen atom-containing monomers. In other words, in this specification, monomers having both a hydroxyl group and a nitrogen atom in their molecule are included in nitrogen atom-containing monomers. Furthermore, a monomer having at least one nitrogen atom and at least one carboxyl group in its molecule is a carboxyl group-containing monomer and not a nitrogen atom-containing monomer.

[0075] From the viewpoint of exhibiting strong adhesive properties, N-vinylcyclic amides, (meth)acrylamides, etc., are preferred as the nitrogen atom-containing monomers mentioned above. Note that only one type of nitrogen atom-containing monomer may be used, or two or more types may be used.

[0076] As the above N-vinyl cyclic amide, an N-vinyl cyclic amide represented by the following formula (1) is preferred from the viewpoint of easily obtaining good cohesive force and easily obtaining adhesive reliability at high temperatures. [ka] (In formula (1), R 1 (This indicates a divalent organic group.)

[0077] R in equation (1) above 1 is a divalent organic group, preferably a divalent saturated hydrocarbon group or an unsaturated hydrocarbon group, and more preferably a divalent saturated hydrocarbon group (for example, an alkylene group having 3 to 5 carbon atoms).

[0078] From the viewpoint of exhibiting even stronger adhesiveness, the N-vinyl cyclic amide represented by formula (1) above is preferably N-vinyl-2-pyrrolidone (NVP), N-vinyl-2-piperidone, N-vinyl-2-caprolactam, N-vinyl-3-morpholinone, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholindione, more preferably N-vinyl-2-pyrrolidone and N-vinyl-2-caprolactam, and even more preferably N-vinyl-2-pyrrolidone.

[0079] Examples of the above (meth)acrylamides include (meth)acrylamide, N-alkyl(meth)acrylamide, and N,N-dialkyl(meth)acrylamide. Examples of the above N-alkyl(meth)acrylamide include N-ethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, Nn-butyl(meth)acrylamide, and N-octylacrylamide. Furthermore, the above N-alkyl(meth)acrylamide also includes (meth)acrylamides having an amino group, such as dimethylaminoethyl(meth)acrylamide, diethylaminoethyl(meth)acrylamide, and dimethylaminopropyl(meth)acrylamide. Examples of the above N,N-dialkyl(meth)acrylamide include N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, N,N-di(n-butyl)(meth)acrylamide, and N,N-di(t-butyl)(meth)acrylamide.

[0080] Furthermore, the above-mentioned (meth)acrylamides also include, for example, various N-hydroxyalkyl (meth)acrylamides. Examples of the above-mentioned N-hydroxyalkyl (meth)acrylamides include N-methylol(meth)acrylamide, N-(2-hydroxyethyl)(meth)acrylamide, N-(2-hydroxypropyl)(meth)acrylamide, N-(1-hydroxypropyl)(meth)acrylamide, N-(3-hydroxypropyl)(meth)acrylamide, N-(2-hydroxybutyl)(meth)acrylamide, N-(3-hydroxybutyl)(meth)acrylamide, N-(4-hydroxybutyl)(meth)acrylamide, and N-methyl-N-2-hydroxyethyl(meth)acrylamide.

[0081] Furthermore, the above-mentioned (meth)acrylamides also include, for example, various N-alkoxyalkyl(meth)acrylamides. Examples of the above-mentioned N-alkoxyalkyl(meth)acrylamides include N-methoxymethyl(meth)acrylamide and N-butoxymethyl(meth)acrylamide.

[0082] Furthermore, nitrogen atom-containing monomers other than the above N-vinyl cyclic amides and (meth)acrylamides include, for example, amino group-containing monomers such as (meth)aminoethyl acrylate, (meth)dimethylaminoethyl acrylate, (meth)dimethylaminopropyl acrylate, and (meth)butylaminoethyl acrylate; cyano group-containing monomers such as acrylonitrile and methacrylonitrile; (meth)acryloylmorpholine, N-vinylpiperazine, N-vinylpyrrole, N-vinylimidazole, N-vinylpyrazine, N-vinylmorpholine, N-vinylpyrazole, vinylpyridine, vinylpyrimidine, vinyloxazole, vinylisoxazole, vinylthiazole, vinylisothiazole, vinylpyridazine, (meth)acryloylpyrrolidone, (meth)acryloylpyrrolidine, (meth)acryloylpiperidine, N- Examples include heterocyclic monomers such as methylvinylpyrrolidone; maleimide monomers such as N-cyclohexylmaleimide, N-isopropylmaleimide, N-laurylmaleimide, and N-phenylmaleimide; itaconimide monomers such as N-methylitaconimide, N-ethylitaconimide, N-butylitaconimide, N-octylitaconimide, N-2-ethylhexylitaconimide, N-laurylitaconimide, and N-cyclohexylitaconimide; imide group-containing monomers such as N-(meth)acryloyloxymethylenesuccinimide, N-(meth)acryloyl-6-oxyhexamethylenesuccinimide, and N-(meth)acryloyl-8-oxyoctamethylenesuccinimide; and isocyanate group-containing monomers such as 2-(meth)acryloyloxyethyl isocyanate.

[0083] In addition to the nitrogen atom-containing monomers and hydroxyl group-containing monomers mentioned above, copolymerizable monomers in acrylic polymers include alicyclic structure-containing monomers [e.g., cyclopropyl (meth)acrylate, cyclobutyl (meth)acrylate, cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, 3,3,5-trimethylcyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, cyclooctyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate]; and alkoxyalkyl esters of (meth)acrylates [e.g., 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, methoxytriethylene glycol (meth)acrylate, 3-methoxypropyl (meth)acrylate, 3-ethoxyethyl (meth)acrylate]; Examples include propyl, 4-methoxybutyl (meth)acrylate, 4-ethoxybutyl (meth)acrylate, etc.; epoxy group-containing monomers [e.g., glycidyl (meth)acrylate, methylglycidyl (meth)acrylate, etc.]; sulfonic acid group-containing monomers [e.g., sodium vinylsulfonate, etc.]; phosphate group-containing monomers; (meth)acrylate esters having aromatic hydrocarbon groups [e.g., phenyl (meth)acrylate, phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, etc.]; vinyl esters [e.g., vinyl acetate, vinyl propionate, etc.]; aromatic vinyl compounds [e.g., styrene, vinyltoluene, etc.]; olefins or dienes [e.g., ethylene, propylene, butadiene, isoprene, isobutylene, etc.]; vinyl ethers [e.g., vinyl alkyl ether, etc.]; vinyl chloride, etc.

[0084] The above adhesive composition preferably does not contain or substantially contains carboxyl group-containing monomers as monomer components constituting the acrylic polymer. By not containing or substantially containing carboxyl group-containing monomers, a corrosion prevention effect on metal wiring can be obtained in touch panels to which optical components (touch sensor films) having metal wiring such as metal mesh films or silver nanowire films are bonded. The content of carboxyl group-containing monomers is 1 ng / cm³ of the total amount of the above adhesive composition. 2 (For example, 0-1 ng / cm²) 2 ) is preferred, and more preferably 0.8 ng / cm³ 2 (For example, 0-0.8 ng / cm²) 2 ), more preferably 0.5 ng / cm 2 (For example, 0-0.5 ng / cm²) 2 Those that are substantially free of carboxyl group-containing monomers can be said to be substantially free of carboxyl group-containing monomers. Examples of carboxyl group-containing monomers include (meth)acrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid, etc. Furthermore, the carboxyl group-containing monomers also include acid anhydride group-containing monomers such as maleic anhydride and itaconic anhydride.

[0085] The content (percentage) of the functional group-containing monomer relative to the total amount (100% by mass) of monomer components constituting the acrylic polymer is not particularly limited, but in terms of exhibiting appropriate tackiness, it is preferably 5 to 40% by mass, more preferably 7 to 35% by mass, and even more preferably 10 to 30% by mass. Furthermore, it is preferable that the total content of hydroxyl group-containing monomers and nitrogen atom-containing monomers is within the above range.

[0086] When the above-mentioned acrylic polymer contains hydroxyl group-containing monomers and nitrogen atom-containing monomers as functional group-containing monomer components constituting the polymer, the proportion of the functional group-containing monomer that is most abundant among the hydroxyl group-containing monomers and nitrogen atom-containing monomers is preferably 60% by mass or more, more preferably 65% ​​by mass or more, and even more preferably 70% by mass or more, based on the total amount (100% by mass) of the hydroxyl group-containing monomers and nitrogen atom-containing monomers.

[0087] Furthermore, when polymerizing the above-mentioned acrylic polymer, polymerization initiators such as thermal polymerization initiators and photopolymerization initiators (photoinitiators) may be used depending on the type of polymerization reaction. Note that only one polymerization initiator may be used, or two or more may be used.

[0088] The above-mentioned photopolymerization initiators are not particularly limited, but examples include benzoin ether-based photopolymerization initiators, acetophenone-based photopolymerization initiators, α-ketol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, and the like. Note that one or more photopolymerization initiators may be used.

[0089] Examples of the above-mentioned benzoin ether-based photopolymerization initiators include benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2,2-dimethoxy-1,2-diphenylethane-1-one, and anisole methyl ether. Examples of the above-mentioned acetophenone-based photopolymerization initiators include 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexylphenyl ketone, 4-phenoxydichloroacetophenone, and 4-(t-butyl)dichloroacetophenone. Examples of the above-mentioned α-ketol-based photopolymerization initiators include 2-methyl-2-hydroxypropiophenone and 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropan-1-one. Examples of the above-mentioned aromatic sulfonyl chloride-based photopolymerization initiators include 2-naphthalenesulfonyl chloride. Examples of the above-mentioned photoactive oxime-based photopolymerization initiators include 1-phenyl-1,1-propanedione-2-(o-ethoxycarbonyl)-oxime. Examples of the above-mentioned benzoin-based photopolymerization initiators include benzoin. Examples of the above-mentioned benzyl-based photopolymerization initiators include benzyl. Examples of the above-mentioned benzophenone-based photopolymerization initiators include benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, polyvinylbenzophenone, α-hydroxycyclohexylphenyl ketone. Examples of the above-mentioned ketal-based photopolymerization initiators include benzyldimethylketal. Examples of the above-mentioned thioxanthone-based photopolymerization initiators include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, dodecylthioxanthone, etc.

[0090] The amount of the above-mentioned photopolymerization initiator used is not particularly limited, but for example, it is preferably 0.001 to 1 part by mass, and more preferably 0.01 to 0.50 parts by mass, per 100 parts by mass of the total monomer units (total amount of monomer components constituting the acrylic polymer) of the acrylic polymer.

[0091] Furthermore, the above-mentioned thermal polymerization initiator is not particularly limited, but examples include azo polymerization initiators, peroxide polymerization initiators (e.g., dibenzoyl peroxide, tert-butyl permaleate, etc.), and redox polymerization initiators. Among these, the azo polymerization initiator disclosed in Japanese Patent Application Publication No. 2002-69411 is preferred. Examples of the above-mentioned azo polymerization initiators include 2,2'-azobisisobutyronitrile (hereinafter sometimes referred to as "AIBN"), 2,2'-azobis-2-methylbutyronitrile (hereinafter sometimes referred to as "AMBN"), 2,2'-azobis(2-methylpropionic acid)dimethyl, and 4,4'-azobis-4-cyanovaleric acid.

[0092] The amount of the above-mentioned thermal polymerization initiator used is not particularly limited, but for example, in the case of the above-mentioned azo polymerization initiator, it is preferably 0.05 to 0.5 parts by mass, and more preferably 0.1 to 0.3 parts by mass, per 100 parts by mass of the total monomer units of the acrylic polymer (total amount of monomer components constituting the acrylic polymer).

[0093] The above adhesive composition mainly comprises the above base polymer, and it is preferable to further add a monomer component other than the above base polymer (hereinafter sometimes referred to as "separately added monomer"). Note that only one type of separately added monomer may be used, or two or more types may be used.

[0094] As monomers to be added separately as described above, from the viewpoint of achieving low dielectric constant and drop impact resistance, the compounds presented as the above-mentioned alkyl (meth)acrylates and / or functional group-containing monomers are preferred, and more preferably the above-mentioned alkyl (meth)acrylates and / or hydroxyl group-containing monomers are preferred. Specifically, examples of alkyl (meth)acrylates include methyl methacrylate (MMA), butyl acrylate (BA), 2-ethylhexyl acrylate (2EHA), isostearyl acrylate (ISTA), etc. Furthermore, examples of hydroxyl group monomers include hydroxyl group-containing (meth)acrylic acid esters such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, hydroxyoctyl (meth)acrylate, hydroxydecyl (meth)acrylate, hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl) (meth)acrylic acid; vinyl alcohol, allyl alcohol, etc.

[0095] The amount of monomer added separately as described above is not particularly limited, but from the viewpoint of exhibiting low dielectric constant and drop impact resistance, the lower limit is preferably 25% by mass or more, more preferably 30% by mass or more, even more preferably 35% by mass or more, and particularly preferably 40% by mass or more, based on 100% by mass of the total monomer units of the acrylic polymer (total amount of monomer components constituting the acrylic polymer). Furthermore, the upper limit is preferably 75% by mass or less, more preferably 70% by mass or less, even more preferably 65% ​​by mass or less, and particularly preferably 60% by mass or less.

[0096] The adhesive layer of the present invention may contain a hydrogenated polyolefin resin. That is, the above adhesive composition may be an adhesive composition mainly composed of an acrylic polymer with a hydrogenated polyolefin resin added. The hydrogenated polyolefin resin is a material with a low dielectric constant, and by blending it with the above acrylic polymer, the dielectric constant can be reduced, thereby suppressing malfunctions of touch operations in touch panels to which optical components (touch sensor films) having metal wiring such as metal mesh films or silver nanowire films are bonded. Furthermore, it is preferable that a highly flexible adhesive layer can be realized without requiring the molecular weight of the acrylic polymer to be reduced, and that even when optical components (touch sensor films) having metal wiring such as metal mesh films or silver nanowire films are bonded, the stress with the metal wiring can be sufficiently relieved, preventing uneven display. In addition, since the hydrogenated polyolefin resin has excellent compatibility with acrylic polymers, it is preferable that the transparency of the adhesive layer of the present invention can be maintained at a higher level. Only one type of hydrogenated polyolefin resin may be used, or two or more types may be used.

[0097] Hydrogenated polyolefin resins are preferable because they can create a highly flexible adhesive layer, and when bonded to optical components (touch sensor films) having metal wiring such as metal mesh films or silver nanowire films, they can sufficiently relieve stress with the metal wiring and prevent display unevenness. Therefore, it is preferable that they exhibit liquid fluidity at 25°C. A hydrogenated polyolefin resin exhibiting liquid fluidity at 25°C means that its viscosity measured by a B-type viscometer at 25°C is 10,000 mPa·s or less.

[0098] Hydrogenated polyolefin resins are obtained by reducing the carbon-carbon double bonds contained in polyolefin resins through a hydrogenation reaction. Because hydrogenated polyolefin resins have a reduced number of carbon-carbon double bonds in their molecules, for example, when curing the adhesive composition by ultraviolet irradiation, polymerization inhibition is less likely to occur, and a decrease in polymerization rate and molecular weight reduction is less likely to occur. Therefore, the adhesive reliability of the adhesive composition at high temperatures can be maintained at a high level.

[0099] The hydrogenation rate of hydrogenated polyolefin resins is preferably 90% or higher, more preferably 95% or higher, and even more preferably 97% or higher, from the viewpoint of minimizing polymerization inhibition and ensuring adhesive reliability at high temperatures. The upper limit of the hydrogenation rate is not particularly limited, but theoretically it is 100%, and practically it may be 99.9% or lower, or even 99.8% or lower. The hydrogenation rate of hydrogenated polyolefin resins is... 1 This can be determined by quantitatively determining the amount of remaining double bonds in hydrogenated polyolefin resins using 1H-NMR measurement, among other methods.

[0100] The iodine value (Ig / 100g) of hydrogenated polyolefin resins is preferably 30 or less, more preferably 25 or less, and even more preferably 20 or less, from the viewpoint of minimizing polymerization inhibition and ensuring adhesive reliability at high temperatures. The lower limit of the iodine value is not particularly limited, but may be 0.1 or higher, or 0.2 or higher. The iodine value is measured in accordance with JIS K 0070-1992.

[0101] The number average molecular weight (Mn) of the hydrogenated polyolefin resin is preferably 1000 to 5000 in terms of imparting appropriate stress relaxation properties and fluidity to the adhesive layer and improving compatibility with acrylic polymers. The number average molecular weight (Mn) is preferably 1000 or more, more preferably 1500 or more, and even more preferably 1800 or more, in terms of being able to impart appropriate stress relaxation properties and fluidity to the adhesive composition. The number average molecular weight (Mn) is preferably 5000 or less, more preferably 4800 or less, and even more preferably 4600 or less, in terms of improving compatibility with acrylic polymers and being able to maintain a higher level of transparency of the adhesive layer of the present invention.

[0102] The polydispersity (Mw / Mn) of the hydrogenated polyolefin resin is preferably 2.0 or less, and more preferably 1.8 or less, in order to impart appropriate stress relaxation and fluidity to the adhesive layer, improve compatibility with acrylic polymers, maintain high transparency, and suppress haze. The lower limit of polydispersity is not particularly limited, but in practice it may be 1.0 or 1.1 or higher. The number-average molecular weight (Mn) and polydispersity (Mw / Mn) of the hydrogenated polyolefin resin are measured by gel permeation chromatography (GPC) and are values ​​determined on a polystyrene basis.

[0103] The above-mentioned hydrogenated polyolefin resin contains hydrogenated polyolefin. The adhesive layer of the present invention is preferable in that it contains hydrogenated polyolefin as the hydrogenated polyolefin resin, thereby lowering the dielectric constant and suppressing malfunctions of touch operations on a touch panel.

[0104] The above-mentioned hydrogenated polyolefin is a hydrogenated polymer (polyolefin) having constituent units derived from olefins. Hydrogenated polyolefins include hydrogenated homopolymers and copolymers of α-olefins such as ethylene, propylene, 1-butene, isobutene, and 1-hexene; diene compounds such as butadiene and isoprene; and aromatic vinyl compounds such as styrene. Hydrogenated polyolefins are preferably hydrogenated homopolymers or copolymers of diene compounds, such as hydrogenated polybutadiene and hydrogenated polyisoprene. One type of hydrogenated polyolefin may be used, or two or more types may be used.

[0105] From the viewpoint of reducing the dielectric constant and suppressing malfunctions in touch operations on touch panels, it is preferable that the hydrogenated polyolefin resin further contains a hydrogenated polyolefin polyol in addition to the hydrogenated polyolefin.

[0106] The above-mentioned hydrogenated polyolefin polyol is a compound in which the terminal ends of the above-mentioned hydrogenated polyolefin are modified with hydroxyl groups. Preferred hydrogenated polyolefin polyols are hydroxyl-modified products of hydrogenated homopolymers or copolymers of diene compounds, such as hydrogenated polybutadiene polyol and hydrogenated polyisoprene polyol. Only one type of hydrogenated polyolefin polyol may be used, or two or more types may be used.

[0107] Of the above-mentioned hydrogenated polyolefins and hydrogenated polyolefin polyols, hydrogenated polybutadiene polyols and hydrogenated polybutadiene polyols are preferred because they can realize a highly flexible adhesive layer, and even when bonding with optical components (touch sensor films) having metal wiring such as metal mesh films or silver nanowire films, they can sufficiently relieve stress with the metal wiring and prevent uneven display.

[0108] As the hydrogenated polybutadiene, the one represented by the following formula (2) is preferred, and as the hydrogenated polybutadiene polyol, the one represented by the following formula (3) is preferred. [ka] In the above formula, m represents the degree of polymerization of hydrogenated polybutadiene.

[0109] Commercially available hydrogenated polyolefins and hydrogenated polyolefin polyols can be used. Examples of commercially available hydrogenated polyolefins include the product names "BI-2000" and "BI-3000" (both manufactured by Nippon Soda Co., Ltd.). Examples of commercially available hydrogenated polyolefin polyols include the product names "GI-1000," "GI-2000," and "GI-3000" (all manufactured by Nippon Soda Co., Ltd.), and "EPOL" (manufactured by Idemitsu Kosan Co., Ltd.).

[0110] The content of hydrogenated polyolefin resin is not particularly limited, but from the viewpoint of reducing the dielectric constant and suppressing malfunctions of touch operations on touch panels, it is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and even more preferably 3 parts by mass or more, per 100 parts by mass of acrylic polymer. On the other hand, from the viewpoint of suppressing the rise of haze and ensuring higher transparency, and from the viewpoint of being able to maintain high adhesive strength and adhesive reliability at high temperatures, the content of hydrogenated polyolefin resin is preferably 40 parts by mass or less, more preferably 35 parts by mass or less, and even more preferably 30 parts by mass or less.

[0111] The content of hydrogenated polyolefin polyol is not particularly limited, but from the viewpoint of reducing the dielectric constant and suppressing malfunctions of touch operations on touch panels, it is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of acrylic polymer. On the other hand, from the viewpoint of suppressing the rise of haze and ensuring higher transparency, and from the viewpoint of being able to maintain high adhesion strength and adhesive reliability at high temperatures, the content of hydrogenated polyolefin polyol is preferably 40 parts by mass or less, more preferably 35 parts by mass or less, even more preferably 30 parts by mass or less, and particularly preferably 25 parts by mass or less.

[0112] The weight ratio of hydrogenated polyolefin content to hydrogenated polyolefin polyol content (hydrogenated polyolefin / hydrogenated polyolefin polyol) in the above adhesive composition is not particularly limited, but from the viewpoint of reducing the dielectric constant and suppressing malfunctions of touch operations on touch panels, it is preferably 1 / 99 or more, more preferably 2 / 98 or more, and may be 3 / 98 or more, or 4 / 96 or more. Furthermore, from the viewpoint of suppressing the rise of haze and ensuring higher transparency, the above ratio is preferably 90 / 10 or less, more preferably 80 / 20 or less, even more preferably 70 / 30 or less, and may be 55 / 45 or less, 45 / 55 or less, or 30 / 70 or less.

[0113] The above adhesive composition preferably further contains a polyfunctional (meth)acrylate. That is, the adhesive layer of the present invention preferably contains a structural component derived from a polyfunctional (meth)acrylate. The polyfunctional (meth)acrylate acts as a crosslinking component, making it easier for the adhesive composition to have appropriate cohesive force.

[0114] Examples of the above-mentioned polyfunctional (meth)acrylates include hexanediol di(meth)acrylate, butanediol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, allyl(meth)acrylate, vinyl(meth)acrylate, divinylbenzene, epoxy acrylate, polyester acrylate, urethane acrylate, etc. Note that one type of polyfunctional (meth)acrylate may be used, or two or more types may be used.

[0115] The content (percentage) of polyfunctional (meth)acrylate is not particularly limited, but from the viewpoint of the adhesive layer having appropriate cohesive force, it is preferably 0.001 parts by mass or more, more preferably 0.002 parts by mass or more, even more preferably 0.005 parts by mass or more, and may be 0.01 parts by mass or more, per 100 parts by mass of acrylic polymer. Furthermore, the content (percentage) of polyfunctional (meth)acrylate is preferably 0.5 parts by mass or less, more preferably 0.35 parts by mass or less, even more preferably 0.2 parts by mass or less, and may be 0.1 parts by mass or less, per 100 parts by mass of acrylic polymer, in order to realize a highly flexible adhesive layer and sufficiently relieve stress with metal wiring to prevent uneven display.

[0116] The content of the ultraviolet absorber in the adhesive layer of the present invention is preferably less than 0.1% by mass, more preferably 0.05% by mass or less, even more preferably 0.02% by mass or less, and particularly preferably less than 0.01% by mass, based on the total amount (100% by mass) of the adhesive layer, and preferably substantially absent. The above "substantially absent" means that the ultraviolet absorber is not actively incorporated except when it is inevitably mixed in.

[0117] The above-mentioned UV absorbers are not particularly limited, but examples include triazine-based UV absorbers, benzotriazole-based UV absorbers, benzophenone-based UV absorbers, oxybenzophenone-based UV absorbers, salicylate-based UV absorbers, cyanoacrylate-based UV absorbers, and the like.

[0118] Triazine-based UV absorbers include, specifically, 2,4-bis-[{4-(4-ethylhexyloxy)-4-hydroxy}phenyl]-6-(4-methoxyphenyl)-1,3,5-triazine (trade name "TinosorbS", manufactured by BASF) and 2,4-bis[2-hydroxy-4-butoxyphenyl]-6-(2,4-dibutoxyphenyl)-1,3,5-triazine (trade name "TINUVIN460", manufactured by BASF). Reaction product of 2-(4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine-2-yl)-5-hydroxyphenyl and [(C10-C16 (mainly C12-C13) alkyloxy)methyl]oxirane (trade name "TINUVIN400", manufactured by BASF), 2-[4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine-2-yl]-5-[3-(dodecyloxy)-2-hydroxy] [Propoxyphenol], reaction product of 2-(2,4-dihydroxyphenyl)-4,6-bis-(2,4-dimethylphenyl)-1,3,5-triazine and (2-ethylhexyl)-glycidic acid ester (trade name "TINUVIN 405", manufactured by BASF), 2-(4,6-diphenyl-1,3,5-triazine-2-yl)-5-[(hexyl)oxy]-phenol (trade name "TINUVIN 1577", manufactured by BASF) Examples include ), 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[2-(2-ethylhexanoyloxy)ethoxy]phenol (trade name "ADKSTABLA46", manufactured by ADEKA Corporation), 2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenyl)-1,3,5-triazine (trade name "TINUVIN479", manufactured by BASF), etc.

[0119] Benzotriazole-based UV absorbers include 2-(2H-benzotriazole-2-yl)-6-(1-methyl-1-phenylethyl)-4-(1,1,3,3-tetramethylbutyl)phenol (trade name "TINUVIN928", manufactured by BASF), 2-(2-hydroxy-5-tert-butylphenyl)-2H-benzotriazole (trade name "TINUVINPS", manufactured by BASF), benzenepropanoic acid, and 3-(2H-benzotriazole-2-yl)-5-( Ester compounds of 1,1-dimethylethyl)-4-hydroxy(C7-9 side chain and linear alkyl) (trade name "TINUVIN384-2", manufactured by BASF), 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol (trade name "TINUVIN900", manufactured by BASF), 2-(2H-benzotriazol-2-yl)-6-(1-methyl-1-phenylethyl)-4-(1,1,3,3-tetramethylbutyl)phenol (Trade name "TINUVIN928", manufactured by BASF), reaction product of methyl-3-(3-(2H-benzotriazol-2-yl)-5-t-butyl-4-hydroxyphenyl)propionate / polyethylene glycol 300 (Trade name "TINUVIN1130", manufactured by BASF), 2-(2H-benzotriazol-2-yl)-p-cresol (Trade name "TINUVINP", manufactured by BASF), 2(2H-benzotriazol-2-yl)-4-6-bis(1-methyl- 1-Phenylethyl)phenol (trade name "TINUVIN234", manufactured by BASF), 2-[5-chloro(2H)-benzotriazol-2-yl]-4-methyl-6-(tert-butyl)phenol (trade name "TINUVIN326", manufactured by BASF), 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol (trade name "TINUVIN328", manufactured by BASF), 2-(2H-benzotriazol-2-yl)-4-(1,1,3,Examples include 3-tetramethylbutyl)phenol (trade name "TINUVIN329", manufactured by BASF), the reaction product of methyl 3-(3-(2H-benzotriazol-2-yl)-5-tert-butyl-4-hydroxyphenyl)propionate and polyethylene glycol 300 (trade name "TINUVIN213", manufactured by BASF), 2-(2H-benzotriazol-2-yl)-6-dodecyl-4-methylphenol (trade name "TINUVIN571", manufactured by BASF), and 2-[2-hydroxy-3-(3,4,5,6-tetrahydrophthalimidomethyl)-5-methylphenyl]benzotriazole (trade name "Sumisorb250", manufactured by Sumitomo Chemical Co., Ltd.).

[0120] Examples of benzophenone-based ultraviolet absorbers (benzophenone compounds) and oxybenzophenone-based ultraviolet absorbers (oxybenzophenone compounds) include 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid (anhydrous and trihydrate), 2-hydroxy-4-octyloxybenzophenone, 4-dodecyloxy-2-hydroxybenzophenone, 4-benzyloxy-2-hydroxybenzophenone, 2,2',4,4'-tetrahydroxybenzophenone, and 2,2'-dihydroxy-4,4-dimethoxybenzophenone.

[0121] Examples of salicylic acid ester-based UV absorbers (salicylic acid ester compounds) include phenyl-2-acryloyloxybenzoate, phenyl-2-acryloyloxy-3-methylbenzoate, phenyl-2-acryloyloxy-4-methylbenzoate, phenyl-2-acryloyloxy-5-methylbenzoate, phenyl-2-acryloyloxy-3-methoxybenzoate, phenyl-2-hydroxybenzoate, phenyl-2-hydroxy-3-methylbenzoate, phenyl-2-hydroxy-4-methylbenzoate, phenyl-2-hydroxy-5-methylbenzoate, phenyl-2-hydroxy-3-methoxybenzoate, and 2,4-di-tert-butylphenyl-3,5-di-tert-butyl-4-hydroxybenzoate (TINUVIN120, manufactured by BASF).

[0122] Examples of cyanoacrylate-based ultraviolet absorbers (cyanoacrylate compounds) include alkyl-2-cyanoacrylate, cycloalkyl-2-cyanoacrylate, alkoxyalkyl-2-cyanoacrylate, alkenyl-2-cyanoacrylate, and alkynyl-2-cyanoacrylate.

[0123] Furthermore, the adhesive layer of the present invention may also contain a photopolymerization initiator in addition to those contained in the acrylic polymer described above. As the photopolymerization initiator other than those contained in the acrylic polymer, the photopolymerization initiators exemplified for use with the acrylic polymer described above can be used. Note that only one type of photopolymerization initiator other than those contained in the acrylic polymer may be used, or two or more types may be used.

[0124] The content (percentage) of photopolymerization initiators other than those contained in the above-mentioned acrylic polymer is not particularly limited, but is preferably 0.01 parts by mass or more, more preferably 0.02 parts by mass or more, even more preferably 0.05 parts by mass or more, and may be 0.1 parts by mass or more, per 100 parts by mass of the acrylic polymer. Furthermore, the content (percentage) of photopolymerization initiators is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, even more preferably 1 part by mass or less, and may be 0.5 parts by mass or less, per 100 parts by mass of the acrylic polymer.

[0125] (Pigment compounds) Dye compounds (hereinafter sometimes simply referred to as "dye compounds") whose maximum absorption wavelength in the above absorption spectrum is in the wavelength range of 380 to 430 nm are preferably compounds that have few (for example, 0 to 3) or no hydrogen-donating groups such as hydroxyl groups or phenyl groups in their molecular structure, in order to prevent crosslinking inhibition of radical generators. Note that the phenyl group that is said to be absent in the molecular structure refers to unsubstituted phenyl (-C6H5), and does not exclude substituted phenyl groups or divalent phenylene groups, etc.

[0126] The maximum absorption wavelength mentioned above is the wavelength of the absorption maximum in the spectral absorption spectrum in the wavelength range of 380 to 430 nm. If multiple absorption maxima exist in the above wavelength range, it is the wavelength of the absorption maximum that shows the highest absorbance among them; if no absorption maxima exist in the above wavelength range, it is the wavelength at which the absorbance is maximum.

[0127] The above-mentioned dye compounds are preferably materials that do not have fluorescence or phosphorescence (photoluminescence) properties so as not to interfere with the display performance of the OLED element.

[0128] The full width at half maximum (FWHM) of the above dye compound is preferably 80 nm or less, more preferably 70 nm or less (e.g., 5 to 70 nm), and even more preferably 60 nm or less (e.g., 10 to 60 nm). When the FWHM of the above dye compound is 80 nm or less, it becomes possible to control the light emission of the OLED element while sufficiently absorbing light in the region that does not affect the light emission of the OLED element, while sufficiently transmitting light on the wavelength side longer than 430 nm. The FWHM is measured by the following measurement method. <Method for measuring half-width> Using a UV-Vis spectrophotometer (product name "U-4100", manufactured by Hitachi High-Tech Corporation), the transmitted absorbance spectrum of the dye compound solution is measured under the following measurement conditions. The concentration of the solution is adjusted so that the absorbance at the maximum absorption wavelength is 1.0. From the measured spectral spectrum, the wavelength interval between two points where the peak value is 50% (full width at half maximum) is defined as the full width at half maximum of the dye compound. (Measurement conditions) Solvent: Toluene or chloroform Cell: Quartz cell Optical path length: 10mm

[0129] The above-mentioned dye compounds can be organic or inorganic. Among these, organic dye compounds are preferred from the viewpoint of dispersibility in resin components such as base polymers and maintaining transparency.

[0130] Examples of the above-mentioned organic dye compounds include azomethine compounds, indole compounds, cinnamic acid compounds, pyrimidine compounds, porphyrin compounds, and cyanine compounds.

[0131] As the above organic dye compound, commercially available products can be used. Specifically, as the above indole compound, the trade name "BONASORB" is used. Examples of cinnamic acid compounds include "UA3911" (maximum absorption wavelength in the absorption spectrum: 398 nm, full width at half maximum: 48 nm, manufactured by Orient Chemical Industry Co., Ltd.), "SOM-5-0106" (maximum absorption wavelength in the absorption spectrum: 416 nm, full width at half maximum: 50 nm, manufactured by Orient Chemical Industry Co., Ltd.), "FDB-001" (maximum absorption wavelength in the absorption spectrum: 420 nm, full width at half maximum: 14 nm, manufactured by Yamada Chemical Industry Co., Ltd.), "FDB-009" (merocyanine compound, maximum absorption wavelength in the absorption spectrum: 394 nm, full width at half maximum: 43 nm, manufactured by Yamada Chemical Industry Co., Ltd.), "DAA-247" (polymethine compound, maximum absorption wavelength in the absorption spectrum: 389 nm, full width at half maximum: 49.5 nm, manufactured by Yamada Chemical Industry Co., Ltd.), and "FDU-010" (merocyanine compound, manufactured by Yamada Chemical Industry Co., Ltd.). In particular, from the viewpoint of suppressing crosslinking inhibition and optical reliability, the above-mentioned cyanine compounds are preferred, more preferably the above-mentioned polymethine compounds, the above-mentioned merocyanine compounds, and especially preferably the merocyanine compounds.

[0132] The content of the above-mentioned dye compound is not particularly limited, but is preferably 0.05 to 2.0 parts by mass, more preferably 0.07 to 1.0 parts by mass, and even more preferably 0.1 to 0.5 parts by mass, per 100 parts by mass of the total amount of the base polymer. When the content is 0.05 parts by mass or more, it becomes easy to adjust the adhesive layer of the present invention to have the desired absorbance. When the content is 2.0 parts by mass or less, the bleed-out of the above-mentioned dye compound can be suppressed.

[0133] The adhesive layer of the present invention may optionally contain known additives such as crosslinking agents, crosslinking accelerators, tackifying resins (rosin derivatives, polyterpene resins, oil-soluble phenols, etc.), anti-aging agents, fillers, colorants (pigments, dyes, etc.), chain transfer agents, plasticizers, softeners, surfactants, antistatic agents, rust inhibitors, and antioxidants, to the extent that they do not impair the properties of the present invention. One or more of these additives may be used.

[0134] The glass transition temperature (Tg) calculated from the base polymer and the separately added monomer in the adhesive layer of the present invention is preferably -5°C or higher, more preferably -4°C or higher, and particularly preferably -3°C or higher. A glass transition temperature (Tg) of -5°C or higher makes it easier to achieve a low dielectric constant in the adhesive layer and to exhibit reworkability in the high-speed (low-temperature) range. While there is no particular upper limit, from the viewpoint of exhibiting minimum adhesive strength, it is preferably 20°C or lower, more preferably 15°C or lower, and even more preferably 10°C or lower.

[0135] The glass transition temperature (Tg) mentioned above is a calculated glass transition temperature derived from Fox's formula, which is used to determine the temperature. This calculated glass transition temperature is determined based on the type and amount of each monomer component constituting the adhesive composition, and therefore can be adjusted by selecting the type and amount of each monomer component.

[0136] The calculated glass transition temperature (calculated Tg) can be calculated from the following Fox equation [1]. 1 / Calculation Tg=W1 / Tg(1)+W2 / Tg(2)+···+Wn / Tg(n) [1] Here, W1, W2, ...Wn represent the weight fraction (weight %) of monomer component (1), monomer component (2), ...monomer component (n) that constitute the adhesive composition, relative to the total monomer components, and Tg(1), Tg(2), ...Tg(n) represent the glass transition temperatures (unit: absolute temperature: K) of the homopolymers of monomer component (1), monomer component (2), ...monomer component (n). In this specification, "glass transition temperature (Tg) of homopolymer" (sometimes simply referred to as "Tg of homopolymer") means "glass transition temperature (Tg) of the homopolymer of the monomer," and specifically, the numerical value is given in the "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1987). For monomer homopolymers not listed in the above literature, the Tg refers to the value obtained by, for example, the following measurement method (see Japanese Patent Publication No. 2007-51271), except for monomers having a polyorganosiloxane skeleton. That is, 100 parts by mass of monomer, 0.2 parts by mass of 2,2'-azobisisobutyronitrile, and 200 parts by mass of ethyl acetate as a polymerization solvent are added to a reactor equipped with a thermometer, stirrer, nitrogen inlet tube, and reflux condenser, and the mixture is stirred for 1 hour while introducing nitrogen gas. After removing oxygen from the polymerization system in this way, the temperature is raised to 63°C and the reaction is carried out for 10 hours. Next, the mixture is cooled to room temperature to obtain a homopolymer solution with a solid content of 33% by mass. Then, this homopolymer solution is cast onto a release liner and dried to prepare a test sample (sheet-like homopolymer) with a thickness of approximately 2 mm. This test sample is then punched out into a disc shape with a diameter of 7.9 mm, sandwiched between parallel plates, and the viscoelasticity is measured using a viscoelasticity tester (product name "ARES", manufactured by Rheometrics) in shear mode while applying a shear strain of 1 Hz at a frequency of 1 Hz, in a temperature range of -70 to 150°C, with a heating rate of 5°C / min. The peak top temperature of tanδ is taken as the Tg of the homopolymer.

[0137] The adhesive layer of the present invention is an ultraviolet-curable adhesive layer. That is, the adhesive layer of the present invention is an adhesive layer cured by ultraviolet irradiation. The adhesive layer of the present invention may be completely cured or partially cured. That is, the ultraviolet-curable adhesive layer may further have ultraviolet curability. Examples of ultraviolet-curable adhesive layers include an adhesive layer comprising a base polymer having a reactive functional group and a crosslinking agent reactive with the reactive functional group, an adhesive layer comprising a base polymer having two or more polymerizable functional groups, an adhesive layer comprising a polymer in which some monomer components have been polymerized and unreacted monomer components (an adhesive layer comprising a partially polymerized product (syrup)), and an adhesive layer comprising a base polymer and monomer components.

[0138] The adhesive layer of the present invention is a single layer having two opposing main surfaces, and when divided equally into two parts in the thickness direction, it is preferable that the concentration of the dye compound in the region to which one of the two main surfaces (the first main surface) belongs is different from the concentration of the dye compound in the region to which the other main surface (the second main surface) belongs. Such an adhesive layer can be produced, for example, by curing an ultraviolet-curable adhesive layer, applying a solution in which the dye compound is dissolved in a solvent to one surface of the adhesive layer, allowing the dye compound contained in the solution to penetrate the adhesive layer from the one surface in the thickness direction, and then drying the adhesive layer.

[0139] Figure 1 is a cross-sectional view showing one embodiment of the adhesive sheet of the present invention. The adhesive sheet shown in Figure 1 is a substrate-less double-sided adhesive sheet consisting of a single layer of adhesive layer 1, which is the adhesive layer of the present invention, and a release liner 2 and a release liner 3 are provided on both adhesive surfaces, respectively.

[0140] The above-mentioned adhesive sheet is not particularly limited, but is preferably manufactured according to known or conventional manufacturing methods. For example, if the adhesive sheet is a substrate-less adhesive sheet, it can be obtained by forming the adhesive layer on a release liner by the method described above. If the adhesive sheet is a substrate-attached adhesive sheet, it can be obtained by directly forming the adhesive layer on the surface of the substrate (direct transfer method), or by first forming the adhesive layer on a release liner and then transferring (bonding) it to the substrate to provide the adhesive layer on the substrate (transfer method).

[0141] The adhesive layer described above is formed by applying the adhesive composition to the release surface of the release liner or the substrate to form an adhesive composition layer, then, if necessary, volatilizing and removing the solvent by heating, and finally solidifying the adhesive composition layer by polymerization under ultraviolet irradiation. After that, an additive may be impregnated into the adhesive layer. This impregnation can be done by coating. The additive to be impregnated may be the additive itself, or it may be a solution or dispersion in which it is dissolved and dispersed in a solvent. Examples of the additive include various components that may be included in the adhesive composition, such as the dye compound, monomer component, and polymerization initiator. Even if the adhesive layer has been cured by irradiation with active energy rays, etc., the adhesive layer of the present invention that has ultraviolet curability can be obtained again by impregnating it with monomer components.

[0142] The above-mentioned adhesive sheet may have other layers in addition to the adhesive layer of the present invention. Examples of other layers include other adhesive layers (adhesive layers other than the adhesive layer of the present invention), intermediate layers, undercoat layers, etc. The above-mentioned adhesive sheet may have two or more other layers.

[0143] When the above adhesive sheet is an adhesive sheet with a base material, the base material is not particularly limited, but examples include various optical films such as plastic films, anti-reflective (AR) films, polarizing plates, and phase difference plates. Examples of materials for the above plastic films include polyester resins such as polyethylene terephthalate (PET), acrylic resins such as polymethyl methacrylate (PMMA), polycarbonate, triacetylcellulose (TAC), polysulfone, polyarylate, polyimide, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, ethylene-propylene copolymer, and cyclic olefin polymers such as the trade name "Arton" (cyclic olefin polymer, manufactured by JSR Corporation) and the trade name "Zeonor" (cyclic olefin polymer, manufactured by Nippon Zeon Co., Ltd.). Note that one or more of these plastic materials may be used. Furthermore, the above "base material" refers to the part that is attached to the adherend together with the adhesive layer when the adhesive sheet is attached to the adherend. The release liner that is peeled off when the adhesive sheet is used (attached) is not included in the "base material".

[0144] The thickness of the above-mentioned substrate is not particularly limited, but is preferably, for example, 12 to 500 μm. The substrate may be in the form of a single layer or multiple layers. Furthermore, the surface of the substrate may be appropriately subjected to known and conventional surface treatments, such as physical treatments like corona discharge treatment or plasma treatment, or chemical treatments like primer treatment.

[0145] The above-mentioned adhesive sheet may have a release liner on the adhesive surface until use. If the above-mentioned adhesive sheet is a double-sided adhesive sheet, each adhesive surface may be protected by two release liners, or it may be protected by a single release liner with both sides being release surfaces, in a roll-like manner. The release liner is used as a protective material for the adhesive layer and is peeled off when it is applied to the substrate. Furthermore, if the above-mentioned adhesive sheet is a substrate-less adhesive sheet, the release liner also serves as a support for the adhesive layer. Note that the release liner is not necessarily required.

[0146] The above-mentioned peel-off liners are not particularly limited, but examples include peel-off liners having a release layer (release treatment layer) on at least one surface of the peel-off liner substrate, low-adhesion peel-off liners made of fluorine-based polymers, and low-adhesion peel-off liners made of non-polar polymers. The release treatment agents constituting the above-mentioned release layer are not particularly limited, but examples include silicone-based release treatment agents, fluorine-based release treatment agents, long-chain alkyl-based release treatment agents, and molybdenum sulfide. The above-mentioned fluorine-based polymers are not particularly limited, but examples include polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, and chlorofluoroethylene-vinylidene fluoride copolymer. The above-mentioned non-polar polymers are not particularly limited, but examples include olefin resins such as polyethylene (PE) and polypropylene (PP). Among these, it is preferable to use a peel-off liner having a release layer on at least one surface of the peel-off liner substrate.

[0147] The above-mentioned peel-off liner substrate is not particularly limited, but examples include plastic films. Examples of such plastic films include polyester resins such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polybutylene terephthalate (PBT); olefin resins with α-olefins as monomer components such as polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), ethylene-propylene copolymer, and ethylene-vinyl acetate copolymer (EVA); polyvinyl chloride (PVC); vinyl acetate resin; polycarbonate (PC); polyphenylene sulfide (PPS); amide resins such as polyamide (nylon) and fully aromatic polyamide (aramid); polyimide resin; and polyetheretherketone (PEEK). Among these, plastic films formed from polyester resins are preferred from the viewpoint of processability, availability, workability, dustproofness, and cost, and PET films are more preferred.

[0148] The above-mentioned peel liner can be manufactured by known and conventional methods. In addition, layers such as carrier material and conductive treatment layer may be laminated on the peel layer and / or back surface of the peel liner by known methods, and the above-mentioned peel liner may have other layers (e.g., intermediate layer, undercoat layer, etc.) to the extent that it does not impair the effects of the present invention.

[0149] The thickness of the release liner is not particularly limited, but from viewpoints such as cost and handling of the adhesive sheet during bonding, it is preferably 12 to 200 μm, more preferably 25 to 150 μm, and even more preferably 38 to 125 μm.

[0150] The adhesive sheet of the present invention is used in OLED display devices in which only optical elements with a polarization degree of 95% or less are laminated on the viewing side of the OLED element (specifically, without using polarizing plates). In this case, degradation of the OLED due to ultraviolet light is suppressed, the transparency of the adhesive sheet is maintained, discoloration is suppressed, and reliability is excellent. Furthermore, it can contribute to reducing the environmental burden. For this reason, it is preferable to use the adhesive sheet of the present invention on the viewing side of the OLED element.

[0151] [OLED display device] An OLED display device equipped with the adhesive sheet of the present invention may be referred to as "the OLED display device of the present invention." The OLED display device of the present invention has a configuration in which an OLED display panel includes an OLED element in which an anode, an OLED layer including a light-emitting layer, and a cathode are stacked in that order, and the adhesive sheet of the present invention is stacked on the viewing side of the OLED element.

[0152] The OLED display device of the present invention has an OLED display panel in which only optical elements with a polarization degree of 95% or less are laminated on the viewing side of the OLED elements. "Only optical elements with a polarization degree of 95% or less are laminated on the viewing side of the OLED elements" means that the optical elements on the viewing side of the OLED elements do not include optical elements with a polarization degree exceeding 95%. Examples of "optical elements with a polarization degree exceeding 95%" are polarizers, although they are not particularly limited, such as linear polarizers, quarter phase difference plates, half phase difference plates, circular polarizers, and reflective polarizers. In other words, the OLED display device of the present invention is an OLED display device that does not have polarizers on the viewing side of the OLED elements. The above polarization degree may be 80% or less. In other words, the OLED display device of the present invention may have an OLED display panel in which only optical elements with a polarization degree of 80% or less are laminated on the viewing side of the OLED elements.

[0153] The degree of polarization is determined by the following formula, based on the parallel transmittance Tp and orthogonal transmittance Tc, which are measured using a UV-Vis spectrophotometer and corrected for luminous sensitivity. Polarization degree (%)={(Tp-Tc) / (Tp+Tc)}1 / 2×100

[0154] By eliminating the polarizing plate on the viewing side of the OLED element in this OLED display device, the absorption of light emitted from the OLED element by the polarizing plate is suppressed, improving light collection efficiency, saving power consumption, and extending the lifespan of the OLED element. Furthermore, the absence of a polarizing plate allows for a thinner design and reduces manufacturing costs.

[0155] Figure 2 shows one embodiment of the OLED panel described above. The OLED panel 100 shown in Figure 2 comprises a red OLED element 12R formed by stacking a transparent electrode 11a, a red OLED layer 10R that emits red light, and a back electrode 11b in that order; a green OLED element 12G formed by stacking a transparent electrode 11a, a green OLED layer 10G that emits green light, and a back electrode 11b in that order; and a blue OLED element 12B formed by stacking a transparent electrode 11a, a blue OLED layer 10B that emits blue light, and a back electrode 11b in that order. Each of the OLED elements 12R, 12G, and 12B of each multiple color are arranged sequentially on a substrate 13. A TFT (Thin Film Transistor) layer 14 is formed on the surface of the substrate 13 where each OLED element is arranged, and is connected to the back electrode 11b of each of the OLED elements 12R, 12G, and 12B of each multiple color.

[0156] In the OLED display panel 100, a color filter 15 is positioned on the viewing side (upper side in Figure 2) of each of the multiple-color OLED elements 12R, 12G, and 12B. The color filter 15 includes a red coloring layer 15R, a green coloring layer 15G, and a blue coloring layer 15B, with a black matrix layer 16 provided between each coloring layer. The color filter 15 is positioned so that the red coloring layer 15R, the green coloring layer 15G, and the blue coloring layer 15B face the red OLED element 12R, the green OLED element 12G, and the blue OLED element 12B, respectively. The transparent electrode 11a is either a cathode or an anode, but is generally provided as a cathode. The back electrode 11b functions as the counter electrode to the transparent electrode 11a. The back electrode 11b is either an anode or a cathode, but is generally provided as an anode on the substrate 13. A junction layer 17 is provided between the substrate 13 and the color filter 15. The bonding layer 17 is light-transmitting. In addition to the configuration shown in Figure 2, the OLED display panel 100 may also have other configurations of an OLED display panel, such as a hole injection layer, a hole transport layer, an electron transport layer, a sealing layer, a touch sensor panel, etc. (not shown).

[0157] A key feature of the OLED display panel shown in Figure 2 is that a color filter 15 is arranged on each of the multi-color OLED elements 12R, 12G, and 12B, with the same colored colored layers 15R, 15G, and 15B facing each other. As shown in Figure 2, white ambient light W passes, for example, through the red colored layer 15R, then through the transparent electrode 11a and the red OLED layer 10R that emits red light, is reflected by the back electrode 11b, and then passes through the red OLED layer 10R, the transparent electrode 11a, and the red colored layer 15R again, before the reflected light G enters the observer's eye.

[0158] When ambient light W is incident on the red colored layer 15R, the green and blue light is absorbed, reducing the light intensity to 1 / 3. Furthermore, the reflected light G passes through the red colored layer 15R and the red OLED layer 10R again, causing attenuation. Also, since the reflected light G is red, it can enhance the red light emitted from the red OLED layer 10R. Similarly, when ambient light W is incident on the green colored layer 15G and the blue colored layer 15B, the green and blue light can be enhanced, respectively. Therefore, by using a color filter in conjunction with the OLED display panel, the reflection of ambient light can be significantly reduced and the luminous intensity of the OLED element can be improved without using a circular polarizer for anti-reflection.

[0159] Furthermore, the OLED display panel 100 has a microcavity structure. Light generated from the OLED layers 10R, 10G, and 10B passes through the transparent electrode 11a and is emitted to the outside. Here, the emitted light includes both "direct light" which is emitted directly from the OLED layers 10R, 10G, and 10B toward the transparent electrode 11a, and "reflected light" which is emitted from the OLED layers 10R, 10G, and 10B toward the back electrode 11b, reflected by the back electrode 11b, and then toward the transparent electrode 11a. Specifically, a first optical path C1 is formed in which a portion of the light emitted from the OLED layers 10R, 10G, and 10B proceeds to the transparent electrode 11a side without proceeding to the back electrode 11b side and is emitted to the outside through the transparent electrode 11a, and a second optical path C2 is formed in which the remaining portion of the light emitted from the OLED layers 10R, 10G, and 10B proceeds to the back electrode 11b side, is reflected by the back electrode 11b, and is then emitted to the outside through the OLED layers 10R, 10G, 10B and the transparent electrode 11a. The thicknesses of the OLED layers 10R, 10G, and 10B are different so that the light components corresponding to each color reinforce each other through the interference of this direct light and reflected light. Specifically, the thicknesses of the OLED layers 10R, 10G, and 10B are different so that the optical path length between the back electrode (positive electrode) 11b and the transparent electrode (negative electrode) 11a is matched to the respective EL spectral peak wavelengths of red, green, and blue, and the thicknesses of the OLED layers 10R, 10G, and 10B are different so that the strongest light is extracted from each color.

[0160] In the OLED display device of the present invention, elements other than the OLED display panel (optical elements) are optical elements stacked on the viewing side of the OLED display device. Other than the adhesive sheet of the present invention include adhesive layers, adhesive layers, resin layers, glass layers, hard coat layers, anti-reflective layers, anti-glare layers, intermediate layers (compatible layers), shock-absorbing layers, anti-static layers, etc. However, the above optical elements do not include polarizers or other elements with a polarization degree exceeding 95%.

[0161] In the OLED display device of the present invention, the laminate of optical elements other than the OLED display panel may be referred to as the "optical laminate of the present invention." The optical laminate of the present invention comprises at least the adhesive sheet of the present invention. The OLED display device of the present invention can be manufactured by laminating the optical laminate of the present invention on the viewing side of the OLED display panel.

[0162] Figure 3 shows one embodiment of the OLED display device of the present invention. In the OLED display device 200 shown in Figure 3, layers (optical elements) constituting the optical laminate 20, which is the optical laminate of the present invention, are laminated on the viewing side (upper side in Figure 3) of the OLED display panel 100. The OLED display panel 100 may employ the same configuration as the OLED display panel 100 shown in Figure 2.

[0163] In the OLED display device 200, 21 to 29 are layers constituting the optical laminate 20, where 21 is an adhesive layer or bonding layer, 22 is a resin layer, glass layer, or shock-absorbing layer, 23 is a hard coat layer or anti-glare layer, 24 is an adhesive layer or bonding layer, 25 is a resin layer, glass layer, or shock-absorbing layer, 26 is an adhesive layer or bonding layer, 27 is a resin layer, glass layer, or shock-absorbing layer, 28 is a hard coat layer or anti-glare layer, and 29 is an anti-reflective layer. The laminated structure of the optical laminate 20 is not limited to this embodiment, and other layers constituting other optical elements not shown may be inserted between any layers of the laminated structure of the optical laminate 20. Furthermore, any layer of the laminated structure of the optical laminate 20 may not be present.

[0164] In the OLED display device shown in Figure 3, at least one of 21, 24, and 26 is the adhesive sheet of the present invention. In particular, from the viewpoint of suppressing degradation of the OLED display panel due to near-ultraviolet light and facilitating color correction, it is preferable that 26, which is located on the viewing side in the optical laminate 20, is the adhesive sheet of the present invention.

[0165] The optical laminate of the present invention is not particularly limited and can be manufactured by sequentially laminating the adhesive layer, adhesive layer, resin layer, glass layer, hard coat layer, anti-reflective layer, anti-glare layer, intermediate layer (compatible layer), shock-absorbing layer, etc. that constitute the optical elements on the viewing side of an OLED display panel. Alternatively, the optical laminate of the present invention can be manufactured by pre-fabricating the laminates that constitute the optical laminate of the present invention and laminating them on the viewing side of an OLED display panel. When pre-fabricating the laminates that constitute the optical laminate of the present invention, they may be laminates that constitute the entire optical laminate of the present invention, or laminates that constitute a part of the optical laminate of the present invention may be divided and laminated on the viewing side of an OLED display panel. The layers that constitute the optical elements or the laminates may be protected with a release liner or a surface protective film until use.

[0166] The embodiments described above are provided to facilitate understanding of the present invention and are not intended to limit it. [Examples]

[0167] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples.

[0168] [Manufacturing Example 1: Preparation of Polymer A] A monomer mixture consisting of 70 parts by mass of n-octyl acrylate (NOAA), 20 parts by mass of butyl acrylate (BA), 8 parts by mass of 4-hydroxybutyl acrylate (4HBA), and 2 parts by mass of N-vinyl-2-pyrrolidone (NVP) was mixed with 0.05 parts by mass of a photopolymerization initiator (trade name "Omnirad184", manufactured by IGM Resins BV) and 0.05 parts by mass of another photopolymerization initiator (trade name "Omnirad819", manufactured by IGM Resins BV). The mixture was then irradiated with ultraviolet light until the viscosity (BH viscometer No. 5 rotor, 10 rpm, measurement temperature 30°C) reached approximately 20 Pa·s, thereby obtaining polymer A in which a portion of the above monomer components had polymerized.

[0169] [Manufacturing Example 2: Preparation of Polymer B] 40 parts by mass of dicyclopentanyl methacrylate (DCPMA, dicyclopentanyl methacrylate) (trade name "FA-513M", manufactured by Resona Corporation) and 60 parts by mass of methyl methacrylate were placed in a four-necked flask as monomer components, 3 parts by mass of thioglycolic acid as a chain transfer agent, and 100 parts by mass of ethyl acetate as a polymerization solvent. The mixture was then stirred at 70°C for 1 hour under a nitrogen atmosphere, and then 0.2 parts by mass of 2,2'-azobisisobutyronitrile was added as a polymerization initiator. The mixture was reacted at 70°C for 2 hours, followed by a reaction at 80°C for 2 hours. The reaction mixture was then placed under a temperature atmosphere of 130°C to dry and remove the ethyl acetate, chain transfer agent, and unreacted monomers, yielding solid polymer B. The weight-average molecular weight of polymer B was 2500.

[0170] [Example 1] To 100 parts by mass of polymer A obtained in Production Example 1, 0.11 parts by mass of dipentaerythritol hexaacrylate (DPHA), 1.5 parts by mass of polymer B obtained in Production Example 2, 0.5 parts by mass of silane coupling agent (trade name "KBM-403", manufactured by Shin-Etsu Chemical Co., Ltd.), and 0.02 parts by mass of photopolymerization initiator (trade name "Omnirad819", manufactured by IGM Resins BV) were added and mixed to obtain an adhesive composition (pre-curing composition).

[0171] The above adhesive composition was applied to a polyethylene terephthalate (PET) release liner (first release liner, trade name "MRF75", manufactured by Mitsubishi Chemical Corporation) to a final thickness (thickness of the adhesive layer) of 100 μm, forming a coated layer (adhesive composition layer). Next, a PET release liner (second release liner, trade name "MRE75", manufactured by Mitsubishi Chemical Corporation) was placed on the coated layer to cover the coated layer and block oxygen. A laminate of [MRF75 / coated layer (adhesive composition layer) / MRE75] was then obtained. Next, a black light (manufactured by Toshiba Corporation) was used on the top surface of the laminate (MRF75 side) to measure an illuminance of 5 mW / cm². 2 The sample was irradiated with ultraviolet light for 300 seconds. It was then dried in a 90°C dryer for 2 minutes.

[0172] The second release liner was peeled off from the laminate, and 2.4 parts by mass of a 10% by weight ethyl acetate solution of the dye compound (product name "FDU-010", manufactured by Yamada Chemical Industry Co., Ltd.) (0.24 parts by mass as the dye compound) was applied to the exposed coated layer surface using a Wire Wound Rod type, No. 7 bar coater manufactured by RD Specialties (target wet coating thickness of 15 μm). After application, the coated layer was heated and dried in an oven at 110°C for 2 minutes to volatilize and remove the solvent, thereby creating an adhesive layer in which the dye compound was dissolved. In this way, a substrate-less double-sided adhesive sheet was obtained, consisting only of an adhesive layer, with both sides of the adhesive layer protected by a release liner.

[0173] [Example 2, Comparative Examples 1-2] A substrate-less double-sided adhesive sheet was obtained in the same manner as in Example 1, except that the composition of the adhesive layer was as shown in Table 1. Unless otherwise specified, the units of the numerical values ​​in Table 1 represent parts by mass. Furthermore, the amounts of dye compounds shown in Table 1 represent the amounts of dye compounds themselves, not the amounts of dye compound solutions.

[0174] [Example 3] To 100 parts by mass of polymer A obtained in Production Example 1, 0.11 parts by mass of dipentaerythritol hexaacrylate (DPHA), 1.5 parts by mass of polymer B obtained in Production Example 2, 0.5 parts by mass of silane coupling agent (trade name "KBM-403", manufactured by Shin-Etsu Chemical Co., Ltd.), 0.02 parts by mass of photopolymerization initiator (trade name "Omnirad819", manufactured by IGM Resins BV), and 0.24 parts by mass of dye compound (trade name "FDU-010", manufactured by Yamada Chemical Industry Co., Ltd.) were added and mixed to obtain an adhesive composition (pre-curing composition).

[0175] The above adhesive composition was applied to a polyethylene terephthalate (PET) release liner (first release liner, trade name "MRF75", manufactured by Mitsubishi Chemical Corporation) to a final thickness (thickness of the adhesive layer) of 100 μm, forming a coated layer (adhesive composition layer). Next, a PET release liner (second release liner, trade name "MRE75", manufactured by Mitsubishi Chemical Corporation) was placed on the coated layer to cover the coated layer and block oxygen. A laminate of [MRF75 / coated layer (adhesive composition layer) / MRE75] was then obtained. Next, a black light (manufactured by Toshiba Corporation) was used on the top surface of the laminate (MRF75 side) to measure an illuminance of 5 mW / cm². 2 The sheet was irradiated with ultraviolet light for 300 seconds. Further drying was performed in a 90°C dryer for 2 minutes to create an adhesive layer. In this way, a substrate-less double-sided adhesive sheet was obtained, consisting solely of an adhesive layer, with both sides of the adhesive layer protected by a release liner.

[0176] [Comparative Example 3] A substrate-less double-sided adhesive sheet was obtained in the same manner as in Example 3, except that the composition of the adhesive layer was as shown in Table 1.

[0177] The details of the components shown in Table 1 are as follows: DPHA: Dipentaerythritol hexaacrylate Silane coupling agent: Product name "KBM-403", manufactured by Shin-Etsu Chemical Co., Ltd. Omnirad819: Photopolymerization initiator, trade name "Omnirad819", manufactured by IGM Resins BV. FDU-010: Product name "FDU-010", manufactured by Yamada Chemical Industry Co., Ltd. DAA-247: Product name "DAA-247", manufactured by Yamada Chemical Industry Co., Ltd.

[0178] [evaluation] The following evaluations were performed on the substrate-less double-sided adhesive sheets obtained in the examples and comparative examples, and the results are shown in Table 1.

[0179] (1) Absorbance The release liner was peeled off the substrate-less adhesive sheets obtained in the examples and comparative examples, the adhesive sheet was attached to a measuring jig, and measured using a spectrophotometer (product name: U4100, manufactured by Hitachi High-Tech Corporation). Absorbance was measured in the wavelength range of 300 to 800 nm, and absorbance in the wavelength range of 340 to 780 nm was obtained.

[0180] (2) Transmittance The release liner was peeled off the substrate-less adhesive sheets obtained in the examples and comparative examples, the adhesive sheet was attached to a measuring jig, and measured using a spectrophotometer (product name: U4100, manufactured by Hitachi High-Tech Corporation). The transmittance was measured in the wavelength range of 300 to 800 nm, and the transmittance at wavelengths of 300 to 380 nm and at 405 nm was obtained. The transmittance at 405 nm after the weather resistance test described below was also measured in the same manner. The rate of change of transmittance at 405 nm was then calculated using the following formula (I). Change in transmittance at a wavelength of 405 nm = (Transmittance at a wavelength of 405 nm after weathering test) - (Transmittance at a wavelength of 405 nm (before weathering test)) (I) <Weather resistance test> The release liner was peeled off the substrate-less adhesive sheet obtained in the examples and comparative examples, the adhesive sheet was bonded to a glass plate, and ultraviolet irradiation was performed for 48 hours using a UV lamp with a peak wavelength of 360-430 nm at a temperature of 40°C using a fade meter (product name: UV fade meter U48, Suga Test Instruments Co., Ltd.), and this ultraviolet irradiation was repeated twice.

[0181] (3)b * The release liner was peeled off from the substrate-less adhesive sheets obtained in the examples and comparative examples, the adhesive sheet was attached to a measuring jig, and the b was measured using a spectrophotometer (product name: U4100, manufactured by Hitachi High-Tech Corporation). * The above weather resistance test was performed on b. * The same measurement was performed. Then, using the following formula (II), b * The rate of change was calculated. b * The rate of change of b after the weathering test = (b * )―(b * (Before weather resistance test) (II)

[0182] (4) Curability Approximately 0.5 g of the adhesive layer was taken from the substrate-less adhesive sheets obtained in the examples and comparative examples, and its weight was measured. The taken adhesive layer was dried in a hot air oven at 105°C for 2 hours, and its weight was measured thereafter. When the weight of the taken adhesive layer before drying was W1 [g] and the weight after drying was W2 [g], the non-volatile content calculated by the following formula (III) was evaluated as no curing defect if it was 90% or more, and as curing defect if it was less than 90%. Non-volatile content (weight %) = (W2 / W1) × 100 (III)

[0183] (5) Bleedout Test specimens were prepared by peeling off one release liner from the substrate-less adhesive sheets obtained in the examples and comparative examples, attaching the exposed surface to alkali glass (50 mm × 60 mm × 1.3 mm), and peeling off the other release liner, attaching the exposed surface to alkali glass (50 mm × 60 mm × 1.3 mm), resulting in alkali glass layers on both the top and bottom of the adhesive sheet. The above test specimens were stored in an oven adjusted to a temperature of 20°C and a humidity of 98% for 500 hours, then removed and left in an environment of 23°C and 55% humidity for 24 hours or more. After that, the appearance was visually inspected, and specimens in which solid matter such as dye compounds was observed between the adhesive sheet and the alkali glass layer were judged to have bleed-out.

[0184] [Table 1]

[0185] The substrate-less double-sided adhesive sheet of the example showed transmittance at a wavelength of 405 nm and b before and after the weather resistance test. * The fluctuations were small, the transparency of the adhesive sheet was maintained, discoloration was suppressed, and it was evaluated as having excellent reliability. In addition, a UV-curable adhesive layer is used, which contributes to reducing the environmental impact. In particular, when the transmittance was high in the wavelength range of 300-380 nm (Example 3), even if the dye compound was added in advance, UV light was sufficiently irradiated onto the adhesive layer, and no curing failure or bleed-out was observed. This also contributes to reducing the environmental impact by reducing the number of processes. On the other hand, b * When the value is less than 2 (Comparative Example 1), the transmittance at 405 nm after the weathering test decreased, and it was evaluated as having poor reliability. When the specific dye compound is not included and the maximum absorbance in the wavelength range of 380-430 nm is less than 0.5 (Comparative Example 2), there is no absorption at wavelengths of 380-430 nm, so when used in conjunction with an OLED display device, the OLED element deteriorates, resulting in poor durability of the OLED panel and poor reliability. * When the value was greater than 5 (Comparative Example 3), the transmittance at 405 nm decreased after the weathering test, and the reliability was evaluated as poor.

[0186] The following describes variations of the invention relating to this disclosure. [Note 1] This adhesive sheet is used in an OLED display device in which only optical elements with a polarization degree of 95% or less are laminated on the viewing side of the OLED element. The aforementioned adhesive sheet comprises an ultraviolet-curable adhesive layer, The UV-curable adhesive layer contains a dye compound whose maximum absorption wavelength in the absorption spectrum is in the wavelength range of 380 to 430 nm. The maximum absorbance of the adhesive sheet in the wavelength range of 380-430 nm is 0.5 or higher. The maximum absorbance in the wavelength range of 440-780 nm is 0.1 or less. The maximum absorbance in the wavelength range of 300-800 nm is in the wavelength range of 380-410 nm. b * The adhesive sheet is 2-10. [Note 2] The adhesive sheet described in Note 1 has a transmittance of 30% or more in the wavelength range of 300-380 nm. [Note 3] after the weather resistance test described below, b * The adhesive sheet described in Appendix 1 or 2, wherein the rate of change is 0.2 or greater. <Weather resistance test> The adhesive sheet is subjected to 48 hours of UV irradiation using a UV lamp with a peak wavelength of 360-430 nm at a temperature of 40°C, and this UV irradiation is repeated twice. [Note 4] The adhesive sheet according to any one of Notes 1 to 3, wherein the ultraviolet-curable adhesive layer is a single layer having two opposing main surfaces, and when divided equally into two parts in the thickness direction, the concentration of the dye compound in the region to which one of the two main surfaces belongs is different from the concentration of the dye compound in the region to which the other second main surface belongs. [Explanation of symbols]

[0187] 1 Adhesive sheet 2. Peel-off liner 3. Peel-off liner 100 OLED display panels 10R Red OLED Layer 10G Green OLED Layer 10B blue OLED layer 11a Transparent electrode (cathode) 11b Back electrode (anode) 12R Red OLED Element 12G Green OLED Element 12B Blue OLED Element 13 circuit boards 14 TFT layers 15 Color Filters 15R red colored layer 15G green colored layer 15B Blue colored layer 16 Black Matrix Layers W (Outdoor light) G Reflected light C1 1st optical path (direct light) C2 2nd optical path (reflected light) 17 Bonding layer 200 OLED display device 20 Optical laminate 21. Adhesive layer or adhesive layer 22. Resin layer, glass layer, or shock-absorbing layer 23. Hard coat layer or anti-glare layer 24. Adhesive layer or adhesive layer 25. Resin layer, glass layer, or shock-absorbing layer 26. Adhesive layer or adhesive layer 27. Resin layer, glass layer, or shock-absorbing layer 28. Hard coat layer or anti-glare layer 29 Anti-reflection layer

Claims

1. This is an adhesive sheet used in an OLED display device in which only optical elements with a polarization degree of 95% or less are laminated on the viewing side of the OLED element. The aforementioned adhesive sheet comprises an ultraviolet-curable adhesive layer, The UV-curable adhesive layer contains a dye compound whose maximum absorption wavelength in the absorption spectrum is in the wavelength range of 380 to 430 nm. The maximum absorbance of the adhesive sheet in the wavelength range of 380 to 430 nm is 0.5 or higher. The maximum absorbance in the wavelength range of 440-780 nm is 0.1 or less. The maximum absorbance in the wavelength range of 300-800 nm is in the wavelength range of 380-410 nm. b ＊ The adhesive sheet is 2 to 10.

2. The adhesive sheet according to claim 1, wherein the transmittance in the wavelength range of 300 to 380 nm is 30% or more.

3. b after the weather resistance test below ＊ The adhesive sheet according to claim 1 or 2, wherein the rate of change is 0.2 or more. <Weather resistance test> The adhesive sheet is subjected to 48 hours of UV irradiation using a UV lamp with a peak wavelength of 360-430 nm at a temperature of 40°C, and this UV irradiation is repeated twice.

4. The adhesive sheet according to claim 1 or 2, wherein the ultraviolet-curable adhesive layer is a single layer having two opposing main surfaces, and when divided equally into two parts in the thickness direction, the concentration of the dye compound in the region to which one of the two main surfaces belongs is different from the concentration of the dye compound in the region to which the other second main surface belongs.

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