Display panel

Abstract

To provide a display panel in which warpage under high-temperature environments is reduced.SOLUTION: A display panel sequentially includes: a first polarizer having a first transmission axis; a first adhesive layer; a display cell; a second adhesive layer; and a second polarizer having no retardation film and having a second transmission axis perpendicular to the first transmission axis. The storage modulus G' of the second adhesive layer at the temperature of at least 85°C and 95°C or lower is 40 KPa or less. It is preferable that the storage modulus G' of the second adhesive layer at the temperature of 85°C or higher and 95°C or lower be 5 KPa or more and 40 KPa or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The following disclosure relates to a display panel. [Background technology]

[0002] Display panels such as liquid crystal panels are widely used in a variety of devices such as televisions, mobile phones, and PC displays. Display panels generally have a configuration in which an optical film such as a polarizing plate is attached to a display cell. For example, a liquid crystal panel has a structure in which a liquid crystal cell is sandwiched between a pair of polarizing plates. Patent Documents 1 to 5 disclose technologies related to display panels. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-90251 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-18245 [Patent Document 3] Japanese Patent Application Laid-Open No. 2007-041116 [Patent Document 4] Japanese Patent Application Laid-Open No. 2006-316181 [Patent Document 5] International Publication No. 2017 / 212960 Summary of the Invention [Problem to be solved by the invention]

[0004] The above Patent Documents 1 to 5 disclose techniques for reducing warpage of display panels, but the effects are still insufficient.

[0005] The present invention has been made in view of the above-mentioned current situation, and has an object to provide a display panel that is less prone to warping in a high-temperature environment. [Means for solving the problem]

[0006] (1) One embodiment of the present invention relates to a display panel comprising, in order: a first polarizing plate having a first transmission axis; a first pressure-sensitive adhesive layer; a display cell; a second pressure-sensitive adhesive layer; and a second polarizing plate having no retardation film and a second transmission axis perpendicular to the first transmission axis, wherein the second pressure-sensitive adhesive layer has a storage modulus G' of 40 KPa or less at 85°C or higher and 95°C or lower.

[0007] (2) Furthermore, in addition to the configuration of (1), one embodiment of the present invention is a display panel, wherein the storage modulus G' of the second pressure-sensitive adhesive layer at 85°C or higher and 95°C or lower is 5 KPa or higher and 40 KPa or lower.

[0008] (3) Furthermore, in addition to the configuration of (1) or (2), one embodiment of the present invention is a display panel, wherein, when the display panel is aged with a temperature change ΔT (°C), the storage modulus G' of the second adhesive layer at 85°C or higher and 95°C or lower satisfies the following (formula 1-1):

[0009]

number

number

number

[0010] (4) In one embodiment of the present invention, in addition to the configuration of (1), (2), or (3), the first polarizing plate has a retardation film.

[0011] (5) In one embodiment of the present invention, in addition to the configuration of (1), (2), (3), or (4), the storage modulus of the first adhesive layer at 85°C or higher and 95°C or lower is 80 KPa or higher.

[0012] (6) Furthermore, in an embodiment of the present invention, in addition to the configuration of (1), (2), (3), (4), or (5), the retardation film is a film in which either one of an in-plane retardation or an absolute value of a thickness direction retardation is 10 nm or more. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a display panel that is less likely to warp in a high-temperature environment. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 2 is a cross-sectional view schematically illustrating a display panel according to an embodiment. [Figure 2] FIG. 2 is an enlarged cross-sectional view of a display panel according to an embodiment. [Figure 3] FIG. 2 is a cross-sectional view schematically illustrating a test panel corresponding to the display panel according to the embodiment. [Figure 4] FIG. 10 is an enlarged schematic cross-sectional view of a display panel according to a modified example of the embodiment. [Figure 5] FIG. 2 is a cross-sectional view showing a configuration of a bimetal; [Figure 6] 10 is a graph showing the amount of warpage of a panel versus the storage modulus G′ of a second pressure-sensitive adhesive layer. [Figure 7]10 is a graph showing measured values ​​of the amount of warpage of a rectangular panel portion versus the storage modulus G′ of the second pressure-sensitive adhesive layer. [Figure 8] 10 is a graph showing actual measured values ​​of the amount of warpage of a rectangular panel portion. [Figure 9] 10 is a graph showing the average amount of warpage of a normal-sized panel versus the storage modulus G' of the second PSA layer disposed on the back side. [Figure 10] 10 is a graph showing the difference between the measured data of the amount of warpage of a normal panel and σ(G′). DETAILED DESCRIPTION OF THE INVENTION

[0015] (Definition of terms) In this specification, the "observation surface side" means the side closer to the screen (display surface) of the image display device, and the "rear side" means the side farther from the screen (display surface) of the image display device.

[0016] The storage modulus is a value determined using a rotational rheometer in accordance with JIS K7244-10 (2005).

[0017] "Parallel" means that the angle (absolute value) between them is within the range of 0°±10°, preferably within the range of 0°±5°, more preferably within the range of 0°±3°, even more preferably within the range of 0°±1°, and particularly preferably 0° (completely parallel).

[0018] "Perpendicular" means that the angle (absolute value) between them is within the range of 90°±10°, preferably within the range of 90°±5°, more preferably within the range of 90°±3°, even more preferably within the range of 90°±1°, and particularly preferably 90° (completely perpendicular).

[0019] "(Meth)acrylic" is a general term for acrylic and methacrylic. For example, "(meth)acrylic acid ester" is a general term for acrylic acid ester and methacrylic acid ester. The same applies to other compounds that include the notation "(meth)."

[0020] The following describes a display panel according to an embodiment of the present invention. The present invention is not limited to the contents described in the following embodiment, and design changes can be made as appropriate within the scope of the configuration of the present invention.

[0021] (Embodiment) Fig. 1 is a cross-sectional schematic diagram of a display panel according to an embodiment. As shown in Fig. 1, the display panel 1 of this embodiment includes, in order, a first polarizing plate (front polarizing plate) 41 having a first transmission axis 41A, a first pressure-sensitive adhesive layer (front pressure-sensitive adhesive layer) 51, a display cell 20, a second pressure-sensitive adhesive layer (back pressure-sensitive adhesive layer) 52, and a second polarizing plate (back polarizing plate) 42 that does not include a retardation film and has a second transmission axis 42A that is perpendicular to the first transmission axis 41A. The first polarizing plate 41 is disposed on the viewing surface side of the display cell 20 via the first pressure-sensitive adhesive layer 51, and the second polarizing plate 42 is disposed on the back surface side of the display cell 20 via the second pressure-sensitive adhesive layer 52.

[0022] The storage modulus G' of the second pressure-sensitive adhesive layer 52 at temperatures of 85°C or higher and 95°C or lower is 40 KPa or lower. This configuration can reduce warpage of the display panel 1 in a high-temperature environment. Hereinafter, the amount of warpage of the panel in a high-temperature environment will be simply referred to as the amount of warpage of the panel or the amount of warpage. Hereinafter, the phrase "the storage modulus G' in a certain temperature range is within a certain range" means that the storage modulus G' is within the certain range at at least a portion of the certain temperature range, and preferably means that the storage modulus G' is within the certain range over the entire temperature range.

[0023] Here, the storage modulus of a typical front pressure-sensitive adhesive layer used when bonding a display cell to a front polarizing plate and a typical back pressure-sensitive adhesive layer used when bonding a display cell to a back polarizing plate is about 80 KPa (or more) at 85°C or more and 95°C or less. If a pressure-sensitive adhesive layer having a storage modulus of less than 80 KPa at 85°C or more and 95°C or less is used to bond a polarizing plate to a display cell, the polarizing plate may shift from its original bonding position. Therefore, to prevent misalignment between the display cell and the polarizing plate, the storage modulus of a typical front pressure-sensitive adhesive layer and back pressure-sensitive adhesive layer is set to about 80 KPa (or more).

[0024] On the other hand, the storage modulus of the second adhesive layer 52 of this embodiment is 40 KPa or less at temperatures between 85°C and 95°C, which is different from the storage modulus of a typical adhesive layer used when bonding a display cell and a polarizing plate.

[0025] The display panel 1 of this embodiment will be described in detail below.

[0026] 2 is an enlarged schematic cross-sectional view of a display panel according to an embodiment. The first polarizing plate 41 and the second polarizing plate 42 may be collectively referred to as polarizing plate 40.

[0027] The first polarizing plate 41 has a first transmission axis 41A and a first absorption axis 41B perpendicular to the first transmission axis 41A. The second polarizing plate 42 has a second transmission axis 42A and a second absorption axis 42B perpendicular to the second transmission axis 42A. The first transmission axis 41A is perpendicular to the second transmission axis 42A.

[0028] The second polarizing plate 42 does not have a retardation film. Here, "the second polarizing plate 42 does not have a retardation film" not only means that the second polarizing plate 42 does not have a retardation film as one of its components, but also means that no retardation film is attached to the second polarizing plate 42, either directly or indirectly via another member, on the side of the second pressure-sensitive adhesive layer 52 opposite the display cell 20. In other words, when all members located on the side of the second pressure-sensitive adhesive layer 52 opposite the display cell 20 are considered to be the second polarizing plate 42, the second polarizing plate 42 does not include a retardation film.

[0029] The retardation film is a film in which either the absolute value of the in-plane retardation or the absolute value of the thickness direction retardation is 10 nm or more, and preferably 20 nm or more.

[0030] The in-plane retardation (Re) refers to the in-plane retardation of a layer (film) at 23°C and at a wavelength of 550 nm unless otherwise specified. Re is calculated by Re = (nx - ny) x d, where d (nm) is the thickness of the layer (film). In this specification, unless otherwise specified, "retardation" refers to the in-plane retardation.

[0031] The thickness direction retardation (Rth) refers to the retardation in the thickness direction of a layer (film) at 23°C and at a wavelength of 550 nm unless otherwise specified. Rth is calculated by Rth = {(nx + ny) / 2 - nz} × d, where d (nm) is the thickness of the layer (film). In this specification, the thickness direction retardation is also referred to as "thickness retardation."

[0032] "nx" is the refractive index in the direction in which the in-plane refractive index is maximum (i.e., the slow axis direction), "ny" is the refractive index in the in-plane direction perpendicular to the slow axis, and "nz" is the refractive index in the thickness direction. Unless otherwise specified, the refractive index refers to the value at 23°C for light with a wavelength of 550 nm.

[0033] The first polarizing plate 41 may or may not have a retardation film. When the first polarizing plate 41 does not have a retardation film, the first pressure-sensitive adhesive layer 51 preferably has a storage modulus G'' of 40 KPa or less at 85°C or higher and 95°C or lower. Here, "the first polarizing plate 41 does not have a retardation film" not only means that the first polarizing plate 41 does not have a retardation film as one of its components, but also means that no retardation film is attached to the first polarizing plate 41, either directly or indirectly via another member, on the side of the first pressure-sensitive adhesive layer 51 opposite the display cell 20. In other words, when all members located on the side of the first pressure-sensitive adhesive layer 51 opposite the display cell 20 are defined as the first polarizing plate 41, the first polarizing plate 41 does not include a retardation film.

[0034] 2, the polarizing plate 40 preferably has a protective layer 410 on at least one of the observation side and the back side of a polarizing layer (also referred to as a polarizer) 420. In the display panel 1 of this embodiment, the polarizing plate 40 used has the protective layer 410 on both sides of the polarizing layer 420, as shown in FIG.

[0035] There are no particular limitations on the polarizing layer 420, and any conventionally known material can be used. Specific examples include a hydrophilic polymer film that has been uniaxially stretched after adsorbing an anisotropic material such as iodine or a dichroic dye, and a polyene-based oriented film such as a dehydrated product of polyvinyl alcohol or a dehydrochlorinated product of polyvinyl chloride.

[0036] Although there is no particular limitation on the protective layer 410, a preferred example is a protective film such as a triacetyl cellulose (TAC) film. The protective layer 410 is attached to the polarizing layer 420 via any appropriate adhesive layer (not shown).

[0037] The adhesive layer is a layer that bonds the surfaces of adjacent optical elements or layers together and integrates them with sufficient adhesive strength and bonding time for practical use. Examples of materials that can form the adhesive layer include adhesives and anchor coating agents. The adhesive layer may have a multilayer structure in which an anchor coating layer is formed on the surface of the adherend, and an adhesive layer is formed on top of that. It may also be a thin layer that is not visible to the naked eye.

[0038] The polarizing plate 40 is preferably a linear polarizing plate, and more preferably an absorptive polarizing plate.

[0039] The first pressure-sensitive adhesive layer 51 and the second pressure-sensitive adhesive layer 52 may be collectively referred to as pressure-sensitive adhesive layer 50. The pressure-sensitive adhesive layer 50 is formed from a pressure-sensitive adhesive composition. There are no particular limitations on the pressure-sensitive adhesive composition, but for example, a resin composition containing as a main component a resin such as a (meth)acrylic resin, a rubber resin, a urethane resin, an ester resin, a silicone resin, or a polyvinyl ether resin is preferred. Among these, from the viewpoints of transparency, weather resistance, heat resistance, and storage modulus, it is preferred to use a pressure-sensitive adhesive composition having a (meth)acrylic resin as a base polymer. The pressure-sensitive adhesive composition may be either an active energy ray-curable type or a thermosetting type.

[0040] The (meth)acrylic resin used as the base polymer is preferably a polymer or copolymer containing one or more (meth)acrylic acid esters as monomers. As the (meth)acrylic acid ester, a (meth)acrylic acid alkyl ester having 1 to 20 carbon atoms in the alkyl group is preferred. The number of carbon atoms in the alkyl group is preferably 1 to 8. Specific examples of suitable (meth)acrylic acid esters include butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0041] The base polymer may be copolymerized with a polar monomer. The polar monomer is a monomer having a polar group such as a carboxyl group, a hydroxyl group, an amide group, an amino group, and / or an epoxy group. Specific examples of suitable monomers include (meth)acrylic acid, 2-hydroxypropyl (meth)acrylate, hydroxyethyl (meth)acrylate, (meth)acrylamide, N,N-dimethylaminoethyl (meth)acrylate, and glycidyl (meth)acrylate.

[0042] The pressure-sensitive adhesive composition may contain only the base polymer, or may further contain a crosslinking agent. The crosslinking agent is not particularly limited, and examples thereof include divalent or higher metal ions capable of forming a metal carboxylate with a carboxyl group; polyamine compounds capable of forming an amide bond with a carboxyl group; polyepoxy compounds or polyols capable of forming an ester bond with a carboxyl group; and polyisocyanate compounds capable of forming an amide bond with a carboxyl group. Among these, polyisocyanate compounds are preferred.

[0043] The pressure-sensitive adhesive composition may also contain one or more additives, including, but not limited to, glass fibers, glass beads, resin beads, fillers, pigments, colorants, antioxidants, ultraviolet absorbers, antistatic agents, etc.

[0044] The thickness of the pressure-sensitive adhesive layer 50 (thickness of the dry film) is preferably, for example, 100 μm or less. More preferably, it is 60 μm or less, even more preferably, it is 50 μm or less, particularly preferably, it is 30 μm or less, and most preferably, it is 20 μm or less. The lower limit is preferably 1 μm or more. More preferably, it is 2 μm or more, even more preferably, it is 3 μm or more, particularly preferably, it is 5 μm or more, and most preferably, it is 10 μm or more.

[0045] The method for adjusting the storage modulus of the adhesive layer 50 varies depending on the type of adhesive layer 50. For example, if the adhesive layer 50 is a thermosetting resin, the storage modulus can be adjusted by changing conditions such as the heating temperature, heating time, and amount of curing agent. If the adhesive layer 50 is a UV (ultraviolet) curable resin, the storage modulus can be adjusted by changing conditions such as the UV irradiation amount and UV irradiation time. The adhesive layer 50 of this embodiment is a thermosetting resin.

[0046] The display panel 1 of this embodiment is obtained, for example, by bonding a first polarizer laminate including a first polarizer 41 and a first adhesive layer 51, and a second polarizer laminate including a second polarizer 42 and a second adhesive layer 52 to a display cell 20. The first polarizer laminate and the second polarizer laminate may be collectively referred to as a polarizer laminate.

[0047] The polarizing plate laminate can be produced, for example, by bonding each layer together. Specifically, it can be obtained by a method in which an adhesive sheet is first obtained and then bonded to the polarizing plate 40. The adhesive sheet can be obtained, for example, by applying an adhesive liquid, in which an adhesive composition is dissolved or dispersed in an organic solvent, to the release surface of a release sheet to form a sheet, and then bonding another release sheet onto the formed adhesive layer. The adhesive sheet obtained in this manner has a structure in which an adhesive layer is sandwiched between two release sheets. One release sheet is peeled from this adhesive sheet and bonded to the polarizing plate 40 to obtain a polarizing plate laminate. To obtain the display panel 1, the other release sheet is peeled from the adhesive sheet and bonded to the display cell 20. However, the manufacturing method is not limited to this.

[0048] The method for applying the pressure-sensitive adhesive liquid is not particularly limited, and can be, for example, a conventional coating method such as bar coating, knife coating, roll coating, blade coating, die coating, or gravure coating. For coating, a die coater, comma coater, reverse roll coater, gravure coater, rod coater, wire bar coater, doctor blade coater, or air doctor coater can be used as appropriate. When applying the first pressure-sensitive adhesive layer 51 and the second pressure-sensitive adhesive layer 52 using two types of pressure-sensitive adhesive compositions with different storage moduli, the layers can be applied separately by, for example, switching coaters for each coating region.

[0049] Next, we will explain in detail the storage modulus G' at 85°C or higher and 95°C or lower of the adhesive layer (in this embodiment, second adhesive layer 52) provided adjacent to a polarizing plate (in this embodiment, second polarizing plate 42) that does not have a retardation film.

[0050] The storage modulus G' of the second pressure-sensitive adhesive layer 52 at temperatures from 85° C. to 95° C. is 40 KPa or less. The storage modulus G' of the second pressure-sensitive adhesive layer 52 at temperatures from 85° C. to 95° C. is preferably 35 KPa or less, and more preferably 30 KPa or less. By adopting such an embodiment, warping of the display panel 1 in a high-temperature environment can be further suppressed.

[0051] The storage modulus G' of the second pressure-sensitive adhesive layer 52 at 85° C. or higher and 95° C. or lower is preferably 5 Kpa or higher, more preferably 10 Kpa or higher, and even more preferably 15 Kpa or higher. By adopting such an embodiment, the adhesion between the display cell 20 and the second polarizing plate 42 can be improved.

[0052] The storage modulus G' of the second pressure-sensitive adhesive layer 52 at 85° C. or higher and 95° C. or lower is preferably 5 Kpa or higher and 40 KPa or lower, more preferably 10 Kpa or higher and 35 KPa or lower, and even more preferably 15 Kpa or higher and 30 KPa or lower. By adopting such an embodiment, it is possible to improve the adhesion between the display cell 20 and the second polarizing plate 42 while suppressing warping of the display panel 1 in a high-temperature environment.

[0053] The storage modulus G' of the second adhesive layer 52, which reduces warpage of the display panel 1 in a high-temperature environment, can be determined as follows. FIG. 3 is a cross-sectional schematic diagram of a test panel corresponding to the display panel according to the embodiment. As shown in FIG. 3, the test panel 1T (hereinafter simply referred to as panel 1T) is composed of a first polarizing plate 41, a first adhesive layer 51, a glass plate 60, a second adhesive layer 52, and a second polarizing plate 42. Here, the display cell 20 has a configuration in which a layer made of a display medium is sandwiched between a pair of glass plates, and therefore the glass plate 60 can be regarded as the display cell 20. Therefore, in the following, in order to consider the amount of warpage of the display panel 1, the amount of warpage Σ(G') (mm) of panel 1T, in which the display cell 20 in the display panel 1 is replaced with the glass plate 60, will be considered.

[0054] 3, in a case where a first polarizing plate 41 is disposed on the observation side of a glass plate 60 (corresponding to a display cell 20) via a first adhesive layer 51, and a second polarizing plate 42 without a retardation film is disposed on the rear side of the glass plate 60 via a second adhesive layer 52, the actual amount of warpage Σ(G') of the panel after high-temperature aging can be calculated using the storage modulus G' of the second adhesive layer 52 according to the following formula (1). By setting the storage modulus G' of the second adhesive layer 52 using formula (1) so that the amount of warpage Σ(G') of the panel satisfies the desired value, the amount of warpage of the panel due to high-temperature aging can be suppressed within a desired range.

[0055]

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[0056]

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[0057]

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[0058] As described above, the glass plate 60 can be regarded as the display cell 20, so in (Equation 3), E2 represents the Young's modulus (GPa) of the display cell, t2 represents the thickness (mm) of the display cell, and α2 represents the linear expansion coefficient (10 -6 / °C). The Young's modulus and linear expansion coefficient of the display cell are respectively the Young's modulus and linear expansion coefficient of the glass plates of the display cell. The thickness of the display cell is the sum of the thicknesses of the two glass plates of the display cell.

[0059] The temperature change ΔT (°C) of the panel before and after aging is preferably 25°C or more and 85°C or less, more preferably 25°C or more and 75°C or less, and even more preferably 25°C or more and 65°C or less.

[0060] The panel temperature TP1 before aging is preferably 15°C or higher and 35°C or lower, more preferably 15°C or higher and 30°C or lower, and even more preferably 15°C or higher and 25°C or lower. The panel temperature TP2 after aging is preferably 60°C or higher and 100°C or lower, more preferably 60°C or higher and 90°C or lower, and even more preferably 60°C or higher and 80°C or lower. Here, the temperature change ΔT is expressed as TP2 - TP1.

[0061] The amount of warpage Σ(G') of the panel is preferably 0 mm or more and 0.30 mm or less. That is, the storage modulus G' of the second pressure-sensitive adhesive layer at 85°C or more and 95°C or less preferably satisfies the following (Formula 1-1). By adopting such an embodiment, warpage of the panel in a high-temperature environment can be effectively suppressed.

[0062]

number

[0063] The amount of warpage Σ of the panel is preferably 0 mm or more and 0.25 mm or less. That is, it is more preferable that the storage modulus G' of the second pressure-sensitive adhesive layer at 85° C. or more and 95° C. or less satisfies the following (Formula 1-2). By adopting such an embodiment, warpage of the panel in a high-temperature environment can be more effectively suppressed.

[0064]

number

[0065] For example, the length of one side of the display panel 1 is preferably 90 mm or more and 300 mm or less, more preferably 90 mm or more and 250 mm or less, and even more preferably 90 mm or more and 200 mm or less. By adopting such an embodiment, warping of the display panel 1 in a high-temperature environment can be effectively suppressed.

[0066] The display cell 20 has a structure in which a layer of a display medium such as a liquid crystal material, which displays by optical modulation, is sandwiched between a pair of substrates. Such a display cell 20 is generally manufactured by injecting the display medium into a so-called empty cell made of a pair of substrates bonded together via a sealant except for an injection port for the display medium, and then sealing the injection port with a sealant.

[0067] The display cell 20 may be any cell that has the function of displaying an image. The display cell 20 can turn on and off image display. The display cell 20 is preferably a display cell for an in-vehicle panel. By adopting such an embodiment, the amount of warping of the panel in a high-temperature environment can be effectively reduced.

[0068] The display cells 20 are preferably, for example, liquid crystal cells or self-luminous cells. When liquid crystal cells are used as the display cells 20, the display panel 1 becomes a liquid crystal display panel. In the following, an example will be described in which a liquid crystal cell 21 is used as the display cell 20.

[0069] The liquid crystal cell 21 is a display cell having a liquid crystal layer. The configuration of the liquid crystal cell 21 is not particularly limited, but an example thereof is a configuration in which a liquid crystal layer 240 is sandwiched between a pair of glass plates 230, as shown in Fig. 2. Specific examples include a display device in which a liquid crystal layer is sandwiched between a pair of substrates, one of which has a pixel electrode and a common electrode formed on it, and a voltage is applied between the pixel electrode and the common electrode to apply a horizontal electric field (including a fringe electric field) to the liquid crystal layer; a display device in which a liquid crystal layer is sandwiched between a pair of substrates, one of which has a pixel electrode formed on it and the other has a common electrode formed on it, and a voltage is applied between the pixel electrode and the common electrode to apply a vertical electric field to the liquid crystal layer; and the like.

[0070] More specifically, examples of horizontal electric field modes include FFS (Fringe Field Switching) mode and IPS (In Plane Switching) mode, in which the liquid crystal molecules in the liquid crystal layer are aligned parallel to the substrate surface when no voltage is applied, and examples of vertical electric field modes include vertical alignment (VA), in which the liquid crystal molecules in the liquid crystal layer are aligned perpendicular to the substrate surface when no voltage is applied.

[0071] The liquid crystal mode of the liquid crystal cell 21 is not particularly limited, and black display may be achieved by aligning the liquid crystal molecules in the liquid crystal layer 240 perpendicular to the substrate surface, or by aligning the liquid crystal molecules in the liquid crystal layer 240 in a direction parallel to the substrate surface or neither perpendicular nor parallel to the substrate surface. The liquid crystal panel may be driven by a TFT system (active matrix system), a simple matrix system (passive matrix system), a plasma address system, or the like.

[0072] The method for manufacturing the display panel 1 of this embodiment is not particularly limited, and it can be manufactured, for example, by bonding a polarizing plate laminate to the display cell 20. At that time, the polarizing plate laminate is disposed so that the pressure-sensitive adhesive layer 50 of the polarizing plate laminate is in contact with the display cell 20.

[0073] The display panel 1 of this embodiment may also have a light source. When a liquid crystal cell 21 is used as the display cell 20, it is preferable that the display panel 1 has a backlight.

[0074] The light source is not particularly limited as long as it can emit light, and may be a direct type, an edge type, or any other type. Specifically, it is preferable that the light source comprises a light source unit including a light guide plate and a light source, a reflective sheet, and a diffusion sheet. For example, a light emitting diode (LED) can be used as the light source.

[0075] The display panel 1 of this embodiment may have a cover glass on the side closest to the viewing surface. Conventional display panels have had problems with display unevenness due to warping of the display panel being pressed down by the cover glass or the like, but the display panel 1 of this embodiment is able to sufficiently suppress warping even in high-temperature environments, thereby preventing such display unevenness.

[0076] (Modification of the embodiment) 4 is an enlarged schematic cross-sectional view of a display panel according to a modified example of the embodiment. As shown in FIG.

[0077] When the first polarizing plate 41 has a retardation film, the first pressure-sensitive adhesive layer 51 preferably has a storage modulus G'' of 80 KPa or more, more preferably 85 KPa or more, and even more preferably 90 KPa or more at a temperature of 85°C or more and 95°C or less. By adopting such an embodiment, the adhesion between the display cell 20 and the first polarizing plate 41 can be improved.

[0078] When the first polarizing plate 41 has a retardation film, the first pressure-sensitive adhesive layer 51 has a storage modulus G'' of, for example, 150 KPa or less at 85° C. or more and 95° C. or less.

[0079] The phrase "the first polarizing plate 41 has a retardation film 71" not only means that the first polarizing plate 41 has the retardation film 71 as one of its components, but also means that the retardation film is attached to the first polarizing plate 41 directly or indirectly via another member on the side of the first adhesive layer 51 opposite the display cell 20. In other words, when all members located on the side of the first adhesive layer 51 opposite the display cell 20 are defined as the first polarizing plate 41, the first polarizing plate 41 includes the retardation film 71. For example, the phrase "the first polarizing plate 41 has a retardation film 71 between the first adhesive layer 51 and a polarizing layer 420 (described below) included in the first polarizing plate 41." The retardation film 71 includes at least one retardation layer. The retardation film 71 may be a laminate composed of multiple retardation layers. The retardation film 71 is, for example, a laminate including a first retardation layer 71A and a second retardation layer 71B in this order from the polarizing layer 420 toward the first adhesive layer 51.

[0080] The retardation film 71 is preferably a laminate including, for example, a negative B plate that is the first retardation layer 71A and a positive B plate that is the second retardation layer 71B. The negative B plate has a refractive index anisotropy of nx>ny>nz. The positive B plate has a refractive index anisotropy of nz>nx>ny.

[0081] The retardation film 71 is also preferably a laminate of a positive A plate, which is the first retardation layer 71A, and a positive C plate, which is the second retardation layer 71B. The positive A plate has a refractive index anisotropy of nx>ny=nz. The positive C plate has a refractive index anisotropy of nz>nx=ny.

[0082] The retardation film 71 may be a laminate of a biaxially aligned first retardation layer 71A and a second retardation layer 71B.

[0083] When the retardation film 71 includes a plurality of retardation layers, each retardation layer preferably has an in-plane retardation or an absolute value of thickness direction retardation of 10 nm or more.

[0084] Although the embodiments of the present invention have been described above, the individual matters described can all be applied to the present invention as a whole.

[0085] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the examples shown below, unless otherwise specified, a liquid crystal cell 21 having a rectangular planar shape and having a liquid crystal layer sandwiched between a pair of glass plates (substrates) was used as the display cell 20, and absorptive linear polarizers were used as the first polarizer 41 and the second polarizer 42.

[0086] (Example) In this example, calculations were performed according to the following procedure so that the amount of warpage of the panel in a high-temperature environment could be determined regardless of the configuration of the display panel or the aging conditions. In this specification, unless otherwise specified, the storage modulus G' refers to the storage modulus of the second pressure-sensitive adhesive layer.

[0087] <Step 1> Using a bimetal model as a reference, the amount of warpage is calculated when the second polarizing plate 42 (a polarizing plate without a retardation film) is bonded to the glass plate 60. In this example, an alkali-free glass plate with an alkali oxide content of 0.10% or less was used as the glass plate 60. <Step 2> The amount of warpage of the rectangular panel portion (composed of a glass plate, a pressure-sensitive adhesive layer, and a polarizing plate) relative to the storage modulus G' is calculated using the results of Step 1 and the measured data of the amount of warpage of the rectangular panel portion. The amount of warpage is the amount of warpage in the direction of the absorption axis (in this example, the second absorption axis 42B) of the polarizing plate that does not have a retardation film. <Step 3> The amount of warpage of a normal-sized panel (composed of a front polarizing plate + front adhesive layer + glass plate + back adhesive layer + back polarizing plate) relative to the storage modulus G' is calculated using the results of Step 2 above and the actual measured data of the amount of warpage of a normal-sized panel.

[0088] <Addition to Step 1> The basic structure of an in-vehicle panel is a glass plate with polarizing plates attached to both sides. Because the polarizing plate and the glass plate have different thermal contraction rates, the bimetal concept can be applied. Figure 5 is a cross-sectional schematic diagram showing the structure of a bimetal. The basic model of the bimetal shown in Figure 5 has a structure in which a first material 110 and a second material 120, which have different thermal contraction rates, are completely bonded together. The amount of warp δ of the basic model of the bimetal is expressed by the following (Equation M).

[0089]

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[0090] The δ on the left side of the above formula (M) is normally expressed as the amount of deflection, but here it is expressed as the amount of warpage. The parameters on the right side of the above formula (M) are the sample length (L), Young's modulus (E1, E2), thickness (t1, t2), linear expansion coefficient (α1, α2), and temperature change (ΔT).

[0091] As a result of extensive investigations, the present inventors have found that it is useful to examine the amount of warpage after high-temperature aging by dividing the panel into four rectangular panel portions (first panel portion 14A, second panel portion 14B, third panel portion 14C, and fourth panel portion 14D) shown in FIG. 3 . The first panel portion 14A is a laminate of a first polarizing plate 41, a first adhesive layer 51, and a glass plate 60. The first panel portion 14A is a rectangular laminate with a major axis along the first transmission axis 41A (the minor axis direction of panel 1T in FIG. 3 ) and a minor axis (e.g., a width of 5 mm) along the first absorption axis 41B. The second panel portion 14B is a laminate of a first polarizing plate 41, a first adhesive layer 51, and a glass plate 60. The second panel portion 14B is a rectangular laminate with a major axis along the first absorption axis 41B (the major axis direction of panel 1T in FIG. 3 ) and a minor axis (e.g., a width of 5 mm) along the first transmission axis 41A. The third panel unit 14C is a laminate of the second polarizing plate 42, the second adhesive layer 52, and the glass plate 60, and is a strip-shaped laminate with the second transmission axis 42A direction (the long axis direction of the panel 1T in FIG. 3) as its major axis and the second absorption axis 42B direction as its minor axis (for example, a width of 5 mm). The fourth panel unit 14D is a laminate of the second polarizing plate 42, the second adhesive layer 52, and the glass plate 60, and is a strip-shaped laminate with the second absorption axis 42B direction (the short axis direction of the panel 1T in FIG. 3) as its major axis and the second transmission axis 42A direction as its minor axis (for example, a width of 5 mm).

[0092] The amounts of warpage of the first panel portion 14A to the fourth panel portion 14D shown in Fig. 3 were calculated using the bimetal calculation formula shown in the above (Formula M). In an actual in-vehicle panel, as shown in Fig. 3, a first polarizing plate 41 and a second polarizing plate 42 are attached to both sides of a glass plate 60 so that the first absorption axis 41B and the second absorption axis 42B are perpendicular to each other.

[0093] In our experiments, we found that the amount of warping of the panel had the following two characteristics. Feature A: The panel warps in the direction of the absorption axis of the polarizing plate without the retardation film. Feature B: The warpage of the panel depends only on the storage modulus of the polarizing plate to which the retardation film is not attached.

[0094] A supplementary explanation of the above feature A is provided. A typical panel has a retardation film attached to either the front polarizing plate or the rear polarizing plate, and the panel is warped in the absorption axis direction of the polarizing plate that does not have a retardation film attached. In this embodiment, a polarizing plate that does not have a retardation film attached (second polarizing plate 42) is disposed on the rear side (back side) of the display cell 20 (glass plate 60), and a polarizing plate that has a retardation film attached (first polarizing plate 41) is disposed on the observation side (front side) of the display cell 20 (glass plate 60).

[0095] A further explanation of Feature B is provided. In an experiment in which the storage modulus G'' of the first pressure-sensitive adhesive layer 51 and the storage modulus G' of the second pressure-sensitive adhesive layer 52 were varied on a standard-sized panel, a change in the amount of warpage of the panel was observed when the storage modulus G'' of the first pressure-sensitive adhesive layer 51 arranged on the front side was fixed and the storage modulus G' of the second pressure-sensitive adhesive layer 52 arranged on the back side was varied. However, conversely, when the storage modulus G' of the second pressure-sensitive adhesive layer 52 arranged on the back side was fixed and the storage modulus G'' of the first pressure-sensitive adhesive layer 51 arranged on the front side was varied, almost no change in the amount of warpage of the panel was observed. The results are shown in Figure 6. Figure 6 is a graph showing the amount of warpage of the panel versus the storage modulus G' of the second pressure-sensitive adhesive layer.

[0096] In Figure 6, the amount of warpage of the panel is plotted against the storage modulus G' of the second adhesive layer 52 for three patterns: when the storage modulus G'' of the first adhesive layer 51 is 120 KPa, 74 KPa, and 15 KPa.

[0097] Focusing on the area indicated by the double arrow in Figure 6, for example, when the storage modulus G' of the second adhesive layer 52 is 120 KPa, the amount of warping of the panel when the storage modulus G'' of the first adhesive layer 51 is 15 KPa and when it is 74 KPa changes by only about 0.30 mm, and it was found that the amount of change is clearly smaller than when the storage modulus G' of the second adhesive layer 52 is changed from 15 KPa to 74 KPa.

[0098] Due to the above two characteristics, the amount of warpage of the strip-sized panel portion was calculated by only calculating the amount of warpage in the absorption axis direction of the polarizing plate (second polarizing plate 42) that does not have a retardation film attached. That is, in this example, the amount of warpage of only the fourth panel portion 14D obtained by cutting the configuration from the glass plate 60 to the second polarizing plate 42 of panel 1T into a strip in the direction of the second absorption axis 42B was calculated. Specific results will be described later.

[0099] <Step 1 Results> The second polarizing plate 42 and the glass plate 60 had the physical properties shown in Table 1 below. The shape of the glass plate 60 that was to be suppressed from warping in a high-temperature environment was 260 mm × 150 mm (thickness on the TFT side: 0.15 mm, thickness on the CF side: 0.15 mm, total thickness: 0.30 mm), and the length of the absorption axis of the polarizing plate (second polarizing plate 42) without a retardation film was 150 mm. When calculating the amount of warping of the panel, L was defined as half the length of the actual absorption axis. In other words, L was 75 mm.

[0100] [Table 1]

[0101] The linear expansion coefficient of a polarizing plate changes depending on the aging environment (temperature, heating time) as well as the characteristics of the polarizing plate, so it needs to be measured each time. The measurement method will be explained separately. In this example, the aging conditions were set to 85°C and 1 hour. The linear expansion coefficient of the sample at that time is shown in Table 1 above.

[0102] First, the amount of warpage C1 in the direction of the second absorption axis 42B of the rectangular panel portion was calculated using the above-mentioned (Equation 3), which corresponds to the above-mentioned (Equation M). Since the temperature before aging was 25°C and the temperature after aging was 85°C, ΔT in (Equation 3) was set to 60°C. As a result, C1 = 4.4772 was obtained. This value represents the amount of warpage when the second polarizing plate 42 and the glass plate 60 are completely bonded (no adhesive layer is present) and immediately after aging is completed (removed).

[0103] <Step 2 Results> In step 2, a formula was created to calculate the amount of warpage of the rectangular panel portion relative to the storage modulus G' from the amount of warpage C1 obtained in step 1 and the actual measured data of the amount of warpage of the rectangular panel portion. In this example, the rectangular panel portion had a pressure-sensitive adhesive layer, and the amount of warpage was measured after leaving it for one hour after aging (removal). Therefore, the actual measured value of the amount of warpage was lower than the calculated value of the amount of warpage obtained from the above (formula 3). Therefore, a formula was created to calculate the amount of warpage of the rectangular panel portion so as to approximate the actual measured value.

[0104] First, Fig. 7 shows the measured data for warpage of a rectangular-sized panel (composed of a glass plate, an adhesive layer, and a polarizing plate). Fig. 7 is a graph showing the measured values ​​of the warpage of the rectangular-sized panel portion versus the storage modulus G' of the second adhesive layer. The rectangular-sized panel measured had an adhesive layer, and in this example, the warpage was measured after leaving it for one hour after removal. When an adhesive layer is present, the degree to which the warpage of the polarizing plate is transmitted to the glass is reduced compared to when an adhesive layer is not present (i.e., the calculated value of C1), so the warpage of the rectangular-sized panel is smaller. Similarly, the smaller the storage modulus of the adhesive layer, the less the warpage of the polarizing plate is transmitted to the glass, so the warpage of the rectangular-sized panel is reduced. It has also been found that leaving the panel for a certain period of time after heating reduces the warpage.

[0105] As shown in FIG. 7, the measured data of warpage of the strip size changes almost linearly depending on the storage modulus of the adhesive layer. If the storage modulus is G' and the actual warpage of the strip size taking into account the adhesive layer and storage after heating is σ(G'), the following formula (Equation A) can be derived.

[0106]

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[0107] Here, if the formula for converting the calculated value of C1 into the actual warpage amount σ(G') of the strip size is f(G'), the following (Formula B) is derived.

[0108]

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[0109] The actual warpage amount σ(G′) of the strip size is expressed as shown in the following (Equation B-1) using this conversion function f(G′).

[0110]

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[0111] Note that the measured data in Figure 7 represents the amount of warpage for a strip of 150 mm long and 5 mm wide, but data was obtained showing that the amount of warpage remains almost unchanged even when the width is wider than 5 mm (Figure 8). Figure 8 is a graph showing the measured values ​​of the amount of warpage for a rectangular panel. Figure 8 shows the measured value of the amount of warpage for a rectangular panel consisting of two sets of sides, one of which is fixed at 150 mm in length, relative to the length of the other set of sides. Figure 8 shows that even when the configuration of glass plate + adhesive layer + polarizing plate is made into a standard panel size (260 mm x 150 mm), Equation A above can be applied to express the amount of warpage.

[0112] <Step 3 Results> In step 3, a formula was created to calculate the amount of warpage of a normal-sized panel relative to the storage modulus G' using the results of step 2 above and the measurement data shown in Figures 6 and 9. Figure 9 is a graph showing the average value of the amount of warpage of a normal-sized panel relative to the storage modulus G' of the second PSA layer disposed on the back side. Figure 9 shows the measurement data for the amount of warpage of a normal panel (averaging the difference due to the storage modulus of the front PSA layer).

[0113] The amount of warpage Σ(G') of a normal panel is smaller than the amount of warpage σ(G') because part of the amount of warpage σ(G') of the glass plate + backing adhesive layer + back polarizer is offset by the added front polarizer + front adhesive layer. Figure 9 shows that the amount of warpage reduction (the difference from σ(G')) varies depending on the storage modulus G' of the backing adhesive layer.

[0114] In this example, the objective is to reduce the warpage Σ(G') of a normal panel to 0.30 mm or less, so an equation expressing the warpage Σ(G') was derived using three of the four actual measurement data with the smallest storage modulus G' of the backing adhesive layer.

[0115] Fig. 10 is a graph showing the difference between the measured data of the amount of warpage of a normal panel and σ(G'). The approximate function D(G') of the difference shown in Fig. 10 is expressed as the following (Equation C).

[0116]

number

[0117] Therefore, the amount of warpage Σ(G′) of a normal panel is expressed as shown in the following formula C-1.

[0118]

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[0119] The amount of warpage can be set appropriately, and is preferably within 0.30 mm, for example. In order to satisfy the requirement of a warpage of 0.30 mm or less, it has been found that, for example, the storage modulus G' of second pressure-sensitive adhesive layer 52 may be set to 40 KPa or less from the above (Formula C-1) (i.e., the above (Formula 1)).

[0120] The linear expansion coefficient can be calculated as follows. Step 1: Cut the polarizing plate to a size of 90 mm x 5 mm and measure the initial dimensions. Step 2: Place in a thermostatic chamber under the specified aging conditions. Step 3: After adding the product, let it cool for 1 hour, then measure the dimensions after aging. Step 4: Substitute the values ​​from Steps 1 and 3 into the following (Equation N) to find the linear expansion coefficient.

[0121]

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[0122] The above-described aspects of the present invention may be combined as appropriate within the scope of the present invention. [Explanation of symbols]

[0123] 1: Display panel 1T: Panel (test panel) 14A, 14B, 14C, 14D: Panel section 20: Display cell 21: Liquid crystal cell 40, 41, 42: Polarizing plates 41A, 42A: Transmission axis 41B, 42B: Absorption shaft 50, 51, 52: adhesive layer 60, 230: Glass plate 71: Phase difference film 71A, 71B: Retardation layer 110, 120: Substance 240: Liquid crystal layer 410: Protective layer 420: Polarizing layer

Claims

1. a first polarizing plate having a first transmission axis, a first pressure-sensitive adhesive layer, a display cell, a second pressure-sensitive adhesive layer, and a second polarizing plate having no retardation film and a second transmission axis perpendicular to the first transmission axis, in that order; The display panel, wherein the second pressure-sensitive adhesive layer has a storage modulus G' of 40 KPa or less at 85° C. or higher and 95° C. or lower.

2. The display panel according to claim 1 , wherein the second pressure-sensitive adhesive layer has a storage modulus G′ of 5 KPa or more and 40 KPa or less at 85° C. or more and 95° C. or less.

3. 2. The display panel according to claim 1, wherein, when the display panel is aged with a temperature change ΔT (°C), the storage modulus G' of the second pressure-sensitive adhesive layer at 85°C or higher and 95°C or lower satisfies the following (Formula 1-1): [Equation 1] (In (Equation 1-1), σ(G′) is expressed by the following (Equation 2).) [Equation 2] (However, in (Equation 2), C1 is expressed by the following (Equation 3).) [Equation 3] ((Formula 3), L represents half the length (mm) of the absorption axis of the second polarizing plate. E １ represents the Young's modulus (GPa) of the second polarizing plate. E ２ represents the Young's modulus (GPa) of the display cell. t １ represents the thickness (mm) of the second polarizing plate. t ２ represents the thickness (mm) of the display cell. α １ is the linear expansion coefficient of the second polarizing plate (10 －６ / °C). α ２ is the linear expansion coefficient of the display cell (10 －６ / °C). ΔT represents the temperature change (°C) of the panel before and after aging.

4. The display panel of claim 1 , wherein the first polarizing plate comprises a retardation film.

5. The display panel according to claim 4 , wherein the first pressure-sensitive adhesive layer has a storage modulus of 80 KPa or more at a temperature of 85° C. or more and 95° C. or less.

6. 6. The display panel according to claim 1, wherein the retardation film is a film having an absolute value of either an in-plane retardation or a thickness direction retardation of 10 nm or more.

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