Optical laminate, method for manufacturing an optical laminate, and image display device

Abstract

To provide an optical laminate and a method for manufacturing an optical laminate that can reduce minute defects in image display devices. [Solution] An optical laminate according to an embodiment of the present invention comprises a first optical film, an adhesive layer, and a second optical film in this order. The optical laminate satisfies the following formula (1). [(n1+n3) / 2-n2] 2 ×d×1000<1···(1) (In equation (1), n1 represents the average refractive index of the first optical film, n2 represents the average refractive index of the adhesive layer, n3 represents the average refractive index of the second optical film, and d represents the thickness [μm] of the adhesive layer.)

Description

Technical Field

[0001] The present invention relates to an optical laminate, a method for manufacturing an optical laminate, and an image display device.

Background Art

[0002] Conventionally, image display devices typified by liquid crystal display devices and electroluminescence (EL) display devices (for example, organic EL display devices, inorganic EL display devices) have been rapidly spreading. In order to impart desired optical characteristics to such an image display device, it is known to apply an optical laminate including a plurality of optical films. Examples of the optical film include a polarizer and a retardation layer (film). As such an optical laminate, for example, an optical film including a quarter-wave plate and a linear polarizer has been proposed, in which the quarter-wave plate is formed by adhering a half-wave retardation layer and a quarter-wave retardation layer with an adhesive layer, and the half-wave retardation layer is attached to the linear polarizer with an adhesive layer (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in an image display device including the optical film described in Patent Document 1, minute defects such as dot-like interference unevenness (hereinafter sometimes referred to as spot unevenness) may occur. A main object of the present invention is to provide an optical laminate capable of reducing minute defects in an image display device.

Means for Solving the Problems

[0005] [1] An optical laminate according to an embodiment of the present invention comprises a first optical film, an adhesive layer, and a second optical film in this order. The optical laminate satisfies the following formula (1). [(n1+n3) / 2-n2] 2 ×d×1000<1···(1) (In equation (1), n1 represents the average refractive index of the first optical film, n2 represents the average refractive index of the adhesive layer, n3 represents the average refractive index of the second optical film, and d represents the thickness [μm] of the adhesive layer.) [2] In the optical laminate described in [1] above, the thickness d of the adhesive layer may be 0.10 μm or less. [3] In the optical laminate described in [1] above, the thickness d of the adhesive layer may be 0.07 μm or less. [4] In the optical laminate described in [1] above, the thickness d of the adhesive layer may be 0.03 μm or less. [5] In the optical laminate described in any of [1] to [4] above, the adhesive layer may be an adhesive layer. [6] In the optical laminate described in any of [1] to [5] above, the polyvinyl alcohol content in the adhesive layer may be 1% by mass or less. [7] In the optical laminate described in any of [1] to [6] above, the average refractive index n1 of the first optical film may be 1.55 or more and 1.60 or less. [8] In the optical laminate described in any of [1] to [7] above, the average value of the average refractive index n1 of the first optical film and the average refractive index n3 of the second optical film may be 1.55 or more and 1.60 or less. [9] In the optical laminate described in any of [1] to [8] above, the average refractive index n2 of the adhesive layer may be 1.50 or more and 1.65 or less.

[10] In the optical laminate described in any of [1] to [9] above, the first optical film may include an orientation solidified layer of a liquid crystal compound.

[11] In the optical laminate described in any of [1] to

[10] above, the second optical film may include an orientation solidified layer of a liquid crystal compound.

[12] An optical laminate according to another aspect of the present invention may comprise a first optical film, an adhesive layer, and a second optical film in this order. The thickness d of the adhesive layer is 0.10 μm or less. The average refractive index n1 of the first optical film is 1.55 or more and 1.60 or less.

[13] An image display device according to yet another aspect of the present invention comprises an optical laminate as described in any of [1] to

[12] above.

[14] A method for manufacturing an optical laminate according to yet another aspect of the present invention comprises, in this order, a coating step, a lamination step, and a curing step. In the coating step, a curable adhesive is applied to the surface of a first optical film and / or the surface of a second optical film to form a coating film. In the lamination step, the first optical film and the second optical film are overlapped so as to sandwich the coating film of the curable adhesive. In the curing step, the coating film of the curable adhesive located between the first optical film and the second optical film is cured. The curing process may separately include a heating step and an irradiation step. In the heating step, the coating film of the curable adhesive is heated. In the irradiation step, the coating film of the curable adhesive is irradiated with active energy rays.

[15] In the method for manufacturing an optical laminate described in

[14] above, the curable adhesive used in the coating step may contain a curing component and a solvent. In this case, the solvent is evaporated from the coating film of the curable adhesive in the heating step.

[16] In the method for manufacturing an optical laminate described in

[15] above, the curable adhesive may contain a photopolymerization initiator.

[17] In the method for producing an optical laminate described in

[15] or

[16] above, the solvent may include an organic solvent. [Effects of the Invention]

[0006] According to embodiments of the present invention, an optical laminate capable of reducing minute defects in an image display device can be realized. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic cross-sectional view of an optical laminate according to one embodiment of the present invention. [Modes for carrying out the invention]

[0008] The following describes representative embodiments of the present invention, but the present invention is not limited to these embodiments. Furthermore, in order to clarify the explanation, the drawings may schematically represent the width, thickness, shape, etc., of each part compared to the embodiments; however, these are merely examples and do not limit the interpretation of the present invention.

[0009] (Definitions of terms and symbols) The definitions of terms and symbols used in this specification are as follows: (1) Refractive index (nx, ny, nz) "nx" is the refractive index in the direction where the refractive index is maximum in the plane (i.e., the slow phase axis direction), "ny" is the refractive index in the direction perpendicular to the slow phase axis in the plane (i.e., the fast phase axis direction), and "nz" is the refractive index in the thickness direction. The "average refractive index" can be calculated using (nx+ny+nz) / 3. (2) In-plane phase difference (Re) "Re(λ)" is the in-plane phase difference measured with light of wavelength λnm at 23°C. For example, "Re(550)" is the in-plane phase difference measured with light of wavelength 550nm at 23°C. Re(λ) can be calculated using the formula: Re(λ) = (nx - ny) × d, where d (nm) is the thickness of the layer (film). (3) Phase difference in the thickness direction (Rth) "Rth(λ)" is the phase difference in the thickness direction measured with light of wavelength λnm at 23°C. For example, "Rth(550)" is the phase difference in the thickness direction measured with light of wavelength 550nm at 23°C. Rth(λ) can be calculated using the formula: Rth(λ) = (nx - nz) × d, where d (nm) is the thickness of the layer (film). (4) Nz coefficient The Nz coefficient is obtained by Nz = Rth / Re.

[0010] A. Overview of the optical laminate FIG. 1 is a schematic cross-sectional view of an optical laminate according to one embodiment of the present invention. In one embodiment, the optical laminate 100 includes a first optical film 1, an adhesive layer 4, and a second optical film 2 in this order. The adhesive layer 4 typically bonds the first optical film 1 and the second optical film 2 and is adjacent to each of the first optical film 1 and the second optical film 2. The optical laminate 100 typically satisfies the following formula (1). The left side of formula (1) may be referred to as a micro defect parameter. [(n1 + n3) / 2 - n2] 2 ×d×1000 < 1 ··· (1) (In formula (1), n1 represents the average refractive index of the first optical film, n2 represents the average refractive index of the adhesive layer, n3 represents the average refractive index of the second optical film, and d represents the thickness [μm] of the adhesive layer.) On the other hand, the lower limit of the micro defect parameter exceeds, for example, 0 (that is, 0 < [(n1 + n3) / 2 - n2] 2 ×d×1000), and is also, for example, 0.01 or more (that is, 0.01 ≦ [(n1 + n3) / 2 - n2] 2 ×d×1000). The average refractive index n1 of the first optical film, the average refractive index n2 of the adhesive layer, and the average refractive index n3 of the second optical film are each measured, for example, by a thin film waveguide method (prism coupler) using light with a wavelength of 594 nm. The inventor has found that in an image display device to which an optical laminate including a plurality of optical films is applied, the refractive index and thickness of the adhesive layer located between adjacent optical films among the plurality of optical films, and the average refractive index of the optical films located on both sides in the thickness direction of the adhesive layer affect the occurrence of minute defects such as dot-like interference unevenness. Therefore, the inventors diligently investigated the relationship between the refractive index of the optical film and the refractive index and thickness of the adhesive layer, and found that if these satisfy a specific relationship, it is possible to reduce minute defects in image display devices. More specifically, if the optical laminate satisfies equation (1) above, it is possible to suppress the reflection of light (visible light) incident on the optical laminate at the interface between the adhesive layer and the layer adjacent to the adhesive layer (typically the first optical film or the second optical film), and to suppress interference of the reflected light. Therefore, it is possible to suppress the occurrence of minute defects (typically spot unevenness) in image display devices to which the optical laminate is applied.

[0011] The average refractive index n1 of the first optical film 1 is, for example, 1.45 or higher, preferably 1.50 or higher, and more preferably 1.55 or higher. On the other hand, the average refractive index n1 of the first optical film 1 is, for example, 1.65 or less, and preferably 1.60 or less. If the average refractive index of the first optical film is within this range, the optical laminate can stably satisfy equation (1) described above.

[0012] The range of the average refractive index n3 of the second optical film 2 is, for example, the same as the range of the average refractive index n1 of the first optical film 1 described above. When the average refractive index of the second optical film is within this range, the optical laminate can more stably satisfy equation (1) described above.

[0013] The average value (=(n1+n3) / 2) of the average refractive index n1 of the first optical film 1 and the average refractive index n3 of the second optical film 2 is, for example, 1.45 or more, preferably 1.50 or more, and more preferably 1.55 or more. On the other hand, the average value of the average refractive index n1 of the first optical film 1 and the average refractive index n3 of the second optical film 2 (=(n1+n3) / 2) is, for example, 1.65 or less, and preferably 1.60 or less. When the average value of the average refractive index of the first optical film and the average refractive index of the second optical film is within this range, the optical laminate can more stably satisfy equation (1) described above.

[0014] The average refractive index n2 of the adhesive layer 4 is, for example, 1.43 or higher, preferably 1.45 or higher, more preferably 1.50 or higher, and even more preferably 1.55 or higher. On the other hand, the average refractive index n2 of the adhesive layer 4 is, for example, 1.70 or less, preferably 1.65 or less, and more preferably 1.60 or less. When the average refractive index of the adhesive layer is within this range, the reflection of light (visible light) incident on the optical laminate can be stably suppressed.

[0015] The absolute value of the difference between the average refractive index n1 of the first optical film 1 and the average refractive index n2 of the adhesive layer 4 (|n1-n2|) is, for example, 0.20 or less, preferably 0.10 or less, more preferably 0.06 or less, even more preferably 0.04 or less, and particularly preferably 0.03 or less. On the other hand, the lower limit of |n1-n2| is typically 0. When the refractive index difference between the adhesive layer and the first optical film is within this range, even if the adhesive layer and the first optical film are adjacent to each other, reflection of light (visible light) incident on the optical laminate at the interface between the adhesive layer and the first optical film can be suppressed. As a result, minute defects in image display devices to which the optical laminate is applied can be suppressed more stably.

[0016] The range of the absolute value (|n3-n2|) of the difference between the refractive index n3 of the second optical film and the average refractive index n2 of the adhesive layer 4 is similar to, for example, the range of the absolute value (|n1-n2|) of the difference between the average refractive index n1 of the first optical film 1 and the average refractive index n2 of the adhesive layer 4. When the refractive index difference between the second optical film and the adhesive layer is within this range, even if the second optical film and the adhesive layer are adjacent to each other, reflection of light (visible light) incident on the optical laminate at the interface between the second optical film and the adhesive layer can be suppressed. As a result, minute defects in image display devices to which the optical laminate is applied can be suppressed more stably.

[0017] The thickness d of the adhesive layer 4 is, for example, 2.00 μm or less, preferably 1.20 μm or less, more preferably 0.80 μm or less, even more preferably 0.40 μm or less, particularly preferably 0.10 μm or less, especially preferably 0.07 μm or less, and most preferably 0.03 μm or less. If the thickness of the adhesive layer is below this upper limit, the adhesive layer can be made sufficiently thin with respect to the wavelength of visible light. Therefore, interference of reflected light having visible light wavelengths can be stably suppressed on both sides in the thickness direction of the adhesive layer. On the other hand, the thickness d of the adhesive layer 4 is, for example, 0.001 μm or more, or for example, 0.005 μm or more, or for example, 0.010 μm or more. If the thickness of the adhesive layer is above this lower limit, the adhesive strength of the adhesive layer can be improved, and adjacent layers on both sides in the thickness direction of the adhesive layer (typically the first optical film and the second optical film) can be stably bonded together.

[0018] The adhesive layer 4 can employ any suitable configuration, as long as it can reduce the minute defect parameter to a predetermined value. The adhesive layer 4 may be an adhesive layer composed of an adhesive, or it may be an adhesive layer composed of a tack agent. The adhesive layer 4 is substantially free of polyvinyl alcohol (PVA). The PVA content in the adhesive layer 4 is, for example, 1% by mass or less. With this configuration, water absorption and moisture permeability can be suppressed, and durability in humid environments can be improved.

[0019] In one embodiment, the adhesive layer 4 is an adhesive layer 41 composed of an adhesive (more specifically, a cured product of the adhesive). In adhesive layers, curing shrinkage, uneven coating, coating repellency, and uneven drying can cause waviness and / or thickness variations in the adhesive layer. In this case, the waviness and / or thickness variations in the adhesive layer may cause variations in the optical path length in the optical laminate, potentially resulting in interference variations. Image display devices equipped with such optical laminates may have minute defects. In this regard, according to one embodiment, since the thickness d of the adhesive layer 41 is within the above-described range, the degree of curing shrinkage of the adhesive, coating unevenness, coating repellency, and drying unevenness can be sufficiently reduced, and the occurrence of waviness and / or thickness unevenness in the adhesive layer can be significantly suppressed. As a result, unevenness in the optical path length in the optical laminate can be reduced, and minute defects in the image display device to which the optical laminate is applied can be suppressed more stably.

[0020] B. Details of the optical laminate Next, with reference to Figure 1, the details of an optical laminate according to one embodiment will be described. As shown in Figure 1, in one embodiment, the optical laminate 100 comprises a first optical film 1, an adhesive layer 41, and a second optical film 2 in this order.

[0021] B-1. First optical film and second optical film B-1-1. First Optical Film The first optical film 1 is positioned on the opposite side of the second optical film 2 from the adhesive layer 4 (adhesive layer 41) in the lamination direction of the optical laminate 100. Typically, the first optical film 1 is attached to the second optical film 2 via the adhesive layer 4. In the illustrated example, the first optical film 1 is attached to the second optical film 2 via the adhesive layer 41.

[0022] The first optical film 1 has any suitable optical properties. The first optical film 1 may be optically isotropic or optically anisotropic. The thickness of the first optical film 1 is arbitrarily and appropriately adjusted to obtain the desired optical properties. The thickness of the first optical film 1 is, for example, 10 μm or less, preferably 5 μm or less, more preferably 3 μm or less, and even more preferably 2 μm or less. On the other hand, the lower limit of the thickness of the first optical film 1 is typically 1 μm.

[0023] The first optical film 1 typically has a single-layer structure. Examples of the first optical film 1 include polarizers, phase difference films, polarizer protective films, phase difference protective films, image display device protective films, ultraviolet light transmission suppression films, and infrared light transmission suppression films.

[0024] In one embodiment, the first optical film 1 is a first phase difference film 1a. When an optical laminate includes a phase difference film, unevenness in the optical path length can occur in the optical laminate due to waviness or thickness variations in the adhesive layer, which may lead to interference variations in the optical laminate. In this regard, according to one embodiment, since the optical laminate satisfies the above-described formula (1), interference variations in the optical laminate can be stably suppressed even if the first optical film is a first phase difference film.

[0025] The first phase difference film 1a may have an in-plane phase difference, or it may have a phase difference in the thickness direction. The first phase difference film 1a may function as a λ / 4 plate, or it may function as a λ / 2 plate, a λ / 5 plate, a λ / 6 plate, or a C-Plate.

[0026] In one embodiment, the first phase difference film 1a has an in-plane phase difference. In this case, the refractive index of the first phase difference film 1a satisfies, for example, the relationship nx > ny, and preferably nx > ny ≥ nz. The in-plane phase difference Re(550) of the first phase difference film 1a, where the refractive index is nx > ny, is, for example, between 80 nm and 300 nm. The Nz coefficient of the first phase difference film 1a, which exhibits the relationship nx > ny for refractive index, is, for example, between 0.9 and 1.5. The first retardation film 1a showing the relationship of refractive index nx > ny may exhibit an inverse wavelength dispersion characteristic in which the in-plane birefringence increases according to the wavelength of the measurement light, a positive wavelength dispersion characteristic in which the in-plane birefringence decreases according to the wavelength of the measurement light, or a flat wavelength dispersion characteristic in which the in-plane birefringence hardly changes according to the wavelength of the measurement light.

[0027] In another embodiment, the first retardation film 1a has a retardation in the thickness direction and substantially no in-plane retardation. In this case, the refractive index of the first retardation film 1a shows a relationship of, for example, nx = ny, preferably a relationship of nz > nx = ny. Note that in this specification, "nx = ny" includes not only the case where nx and ny are exactly equal but also the case where they are substantially equal. Therefore, within a range not impairing the effects of the present invention, nx > ny or nx < ny may occur. The in-plane retardation Re(550) of the first retardation film 1a showing the relationship of refractive index nx = ny is, for example, 0 nm or more and 3 nm or less, preferably 0 nm. The retardation Rth(550) in the thickness direction of the first retardation film 1a showing the relationship of refractive index nx = ny is, for example, -200 nm or more and 200 nm or less, preferably -200 nm or more and less than 0 nm, more preferably -140 nm or more and -100 nm or less.

[0028] The first retardation film 1a is typically a stretched film prepared by stretching a film made of a transparent resin or includes an alignment and curing layer of a liquid crystal compound. In this specification, the "alignment and curing layer of a liquid crystal compound" refers to a layer in which the liquid crystal compound is aligned in a predetermined direction within the layer and the alignment state is fixed. Note that the "alignment and curing layer" is a concept including an alignment and curing layer obtained by curing a liquid crystal monomer as described later.

[0029] In one embodiment, the first phase difference film 1a includes an orientation solidification layer of a liquid crystal compound. In the illustrated example, the first optical film 1 has a single-layer structure of the orientation solidification layer of the liquid crystal compound. Hereinafter, the orientation solidification layer of the liquid crystal compound contained in the first optical film 1 may be referred to as the first liquid crystal orientation solidification layer 11. If the first phase difference film includes a first liquid crystal alignment solidification layer, the difference between nx and ny of the first phase difference film can be made significantly larger compared to non-liquid crystal materials, thus significantly reducing the thickness of the phase difference film having the desired phase difference. As a result, the thickness of the first phase difference film (first liquid crystal alignment solidification layer) can be stably adjusted within the above range, and consequently, the optical laminate can be made thinner. On the other hand, light interference is more likely to occur in thinner layers with stronger interfacial reflection. In other words, light interference is more likely to occur on the surface of thin layers with relatively high refractive indices, such as the oriented solidified layer of a liquid crystal compound. In this regard, according to one embodiment, since the optical laminate satisfies formula (1) described above, even if the first optical film includes a first liquid crystal alignment solidification layer, interference of visible light in the optical laminate can be sufficiently suppressed.

[0030] In the first liquid crystal alignment solidification layer 11, rod-shaped liquid crystal compounds are oriented in a predetermined direction within the first liquid crystal alignment solidification layer 11 (homogeneous orientation). Examples of liquid crystal compounds include liquid crystal compounds in which the liquid crystal phase is a nematic phase (nematic liquid crystals). Examples of such liquid crystal compounds include liquid crystal polymers and liquid crystal monomers. Liquid crystal polymers and liquid crystal monomers may be used individually or in combination. The mechanism by which liquid crystalline properties are expressed in liquid crystal compounds may be lyotropic or thermotropic.

[0031] When a liquid crystal compound contains a liquid crystal monomer, the liquid crystal monomer is preferably a polymerizable monomer or a crosslinkable monomer. The orientation state of the liquid crystal monomer can be fixed by polymerizing or crosslinking (i.e., curing) the liquid crystal monomer. After oriented the liquid crystal monomer, the orientation state can be fixed by polymerizing or crosslinking the liquid crystal monomers together, for example. Here, polymerization forms a polymer and crosslinking forms a three-dimensional network structure, but these are non-liquid crystal. Therefore, the formed first liquid crystal orientation solidified layer does not undergo transitions to liquid crystal phase, glass phase, or crystalline phase due to temperature changes, which is characteristic of liquid crystal compounds. As a result, the first optical film can have extremely excellent stability that is unaffected by temperature changes.

[0032] Any suitable liquid crystal monomer can be used. Examples of liquid crystal monomers include polymerizable mesogenic compounds described in Japanese Patent Publication No. 2002-533742 (WO00 / 37585), EP358208 (US5211877), EP66137 (US4388453), WO93 / 22397, EP0261712, DE19504224, DE4408171, and GB2280445. Specific examples of such polymerizable mesogenic compounds include BASF's trade name LC242, Merck's trade name E7, and Wacker-Chem's trade name LC-Silicon-CC3767.

[0033] An orientation-solidified layer of liquid crystal compounds can be formed by applying an appropriate orientation treatment to any suitable coated substrate, then applying a coating liquid containing a liquid crystal compound to the surface to orient the liquid crystal compound in a direction corresponding to the orientation treatment, and fixing that orientation state. Orientation treatments include, for example, mechanical orientation treatments, physical orientation treatments, and chemical orientation treatments. Specific examples of liquid crystal compounds and details of the method for forming the orientation solidified layer are described in Japanese Patent Publication No. 2006-163343. The description in said publication is incorporated herein by reference.

[0034] The birefringence Δn of the first liquid crystal alignment solidification layer 11 is, for example, 0.06 or more, preferably 0.08 or more, more preferably 0.09 or more, and even more preferably 0.10 or more. On the other hand, the upper limit of the birefringence Δn of the first liquid crystal alignment solidification layer 11 is, for example, 0.13, and also, for example, 0.12. If Δn is within this range, a desired in-plane phase difference can be achieved with a very thin thickness.

[0035] B-1-2. Second Optical Film The second optical film 2 has any suitable optical properties. The second optical film 2 may be optically isotropic or optically anisotropic. The thickness of the second optical film 2 is arbitrarily and appropriately adjusted to obtain the desired optical properties. The range of the thickness of the second optical film 2 is, for example, the same as the range of the thickness of the first optical film 1 described above.

[0036] The second optical film 2 typically has a single-layer structure. Examples of the second optical film 2 include polarizers, phase difference films, polarizer protective films, phase difference protective films, image display device protective films, ultraviolet light transmission suppression films, and infrared light transmission suppression films.

[0037] In one embodiment, the second optical film 2 is a second phase difference film 2a. According to one embodiment, since the optical laminate satisfies the above-described formula (1), interference unevenness in the optical laminate can be stably suppressed even if the second optical film is a second phase difference film.

[0038] The second phase difference film 2a may have an in-plane phase difference, or it may have a phase difference in the thickness direction. The second phase difference film 2a may function as a λ / 4 plate, or it may function as a λ / 2 plate, a λ / 5 plate, a λ / 6 plate, or a C-Plate.

[0039] The second phase difference film 2a will be described in the same manner as the first phase difference film 1a described above. Therefore, a detailed explanation of the second phase difference film 2a will be omitted as appropriate. The refractive index of the second phase difference film 2a may be expressed as either nx > ny or nx = ny. In one embodiment, the refractive indices of the first phase difference film 1a and the second phase difference film 2a satisfy the relationship nx > ny. With such a configuration, it is possible to have wavelength dispersion characteristics that are better than those of the individual phase difference films. Furthermore, the viewing angle characteristics, i.e., the optical characteristics for any azimuth angle and polar angle, can also be improved. The respective ranges of phase difference and thickness in the second phase difference film 2a are, for example, the same as the respective ranges of phase difference and thickness in the first phase difference film 1a described above.

[0040] The second phase difference film 2a typically includes a stretched film or an orientation-solidified layer of a liquid crystal compound. In one embodiment, the second phase difference film 2a includes an orientation solidification layer of a liquid crystal compound. In the illustrated example, the second optical film 2 has a single-layer structure of the orientation solidification layer of the liquid crystal compound. Hereinafter, the orientation solidification layer of the liquid crystal compound contained in the second optical film 2 may be referred to as the second liquid crystal orientation solidification layer 21. The second liquid crystal orientation solidification layer 21 will be described in the same manner as the first liquid crystal orientation solidification layer 11. If the second phase difference film includes a second liquid crystal alignment solidification layer, the difference between nx and ny of the second phase difference film can be made significantly larger compared to non-liquid crystal materials, thus significantly reducing the thickness of the phase difference film having the desired phase difference. As a result, the thickness of the second phase difference film (second liquid crystal alignment solidification layer) can be stably adjusted within the above range, and the optical laminate can be made even thinner. Furthermore, according to one embodiment, since the optical laminate satisfies formula (1) described above, even if the second phase difference film includes a second liquid crystal alignment solidification layer, interference of visible light in the optical laminate can be sufficiently suppressed.

[0041] B-1-3. Combination of the first phase difference film and the second phase difference film When the first optical film 1 is the first phase difference film 1a and the second optical film 2 is the second phase difference film 2a, the first phase difference film 1a may function as a λ / 2 plate and the second phase difference film 2a may function as a λ / 4 plate. Alternatively, the first phase difference film 1a may function as a λ / 4 plate and the second phase difference film 2a may function as a λ / 2 plate. The combination of two phase difference films being a λ / 2 plate and a λ / 4 plate is sometimes referred to as the first combination. With this configuration, the wavelength dispersion characteristics of the laminate of the first phase difference film and the second phase difference film can be brought closer to ideal inverse wavelength dispersion characteristics. Therefore, excellent anti-reflective properties can be imparted to the optical laminate.

[0042] In the first combination, the in-plane phase difference Re(550) of the phase difference film functioning as a λ / 4 plate is, for example, 90 nm to 180 nm, preferably 100 nm to 160 nm, and more preferably 110 nm to 150 nm. In the first combination, the in-plane phase difference Re(550) of the phase difference film functioning as a λ / 2 plate is, for example, 200 nm to 300 nm, preferably 220 nm to 290 nm, and more preferably 230 nm to 280 nm.

[0043] Furthermore, if the first optical film 1 is the first phase difference film 1a and the second optical film 2 is the second phase difference film 2a, the first phase difference film 1a may function as a λ / 4 plate and the second phase difference film 2a may function as a C-Plate (i.e., nx=ny). Alternatively, the first phase difference film 1a may function as a C-Plate and the second phase difference film 2a may function as a λ / 4 plate. The combination of the two phase difference films being a λ / 4 plate and a C-Plate is sometimes referred to as the second combination. Even with such a configuration, excellent anti-reflective properties can be imparted to the optical laminate.

[0044] In the second combination, the in-plane phase difference Re(550) of the phase difference film functioning as a λ / 4 plate is, for example, 90 nm to 190 nm, preferably 100 nm to 170 nm, and more preferably 110 nm to 160 nm. In the second combination, the range of the phase difference Rth(550) in the thickness direction of the phase difference film functioning as a C-Plate is, for example, the same as the range of the phase difference Rth(550) in the thickness direction of the first phase difference film 1a whose refractive index exhibits the relationship nx=ny. This configuration also makes it possible to stably impart excellent anti-reflective properties to the optical laminate.

[0045] B-2.Adhesive layer The adhesive layer 41 is located between the first optical film 1 and the second optical film 2 in the stacking direction of the optical laminate 100, and bonds the first optical film 1 and the second optical film 2 together. In the illustrated example, the adhesive layer 41 is in contact with both the first optical film 1 and the second optical film 2. In one embodiment, the contact surface of the first optical film 1 with the adhesive layer 41, and / or the contact surface of the second optical film 2 with the adhesive layer 41, is an activated surface that has undergone an activation treatment. With this configuration, polar groups such as hydroxyl groups can be introduced to the surface of the optical film, and as a result, the adhesion between the optical film and the adhesive layer can be improved. Examples of activation treatments include corona treatment, plasma treatment, saponification treatment, and low-pressure UV treatment. These activation treatments can be performed individually or in combination.

[0046] The adhesive layer 41 contains a cured product of any suitable adhesive. Examples of adhesives include water-based adhesives, thermosetting adhesives, moisture-curing adhesives, and UV-curing adhesives. In typical curing adhesives, curing shrinkage can occur due to polymerization reactions, condensation reactions, and solvent drying caused by irradiation with active energy rays and / or heating. Furthermore, curing shrinkage, unevenness during coating, repulsion immediately after coating, and uneven drying can cause waviness and / or thickness variations in the adhesive layer. Adhesives can be used alone or in combination.

[0047] In one embodiment, the adhesive layer 41 contains a cured product of a curable adhesive. When the adhesive layer contains a cured product of a curable adhesive, the first optical film and the second optical film can be stably bonded together. Any suitable configuration can be employed for the curing adhesive, as long as the minute defect parameter can be kept below a predetermined value.

[0048] Curing adhesives typically contain a curing component and a photopolymerization initiator and / or a solvent. Since well-known compositions can be used for the curing component and photopolymerization initiator, detailed explanations will be omitted as appropriate. Examples of solvents include water and organic solvents.

[0049] In one embodiment, the curable adhesive further contains (meth)acrylate and / or metal oxide particles having an aromatic ring skeleton. When the curable adhesive contains (meth)acrylate and / or metal oxide particles having an aromatic ring skeleton, the average refractive index of the adhesive layer can be stably adjusted to the above range.

[0050] (Meth)acrylates having an aromatic ring skeleton can function as curing agents. Examples of (meth)acrylates having an aromatic ring skeleton include (meth)acrylates having a polycyclic aromatic ring skeleton and (meth)acrylates having two or more aromatic rings. Specific examples of (meth)acrylates having an aromatic ring skeleton include benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxydiethylene glycol acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 1-naphthalenemethyl (meth)acrylate, phenoxybenzyl (meth)acrylate, ethylene oxide-modified orthophenylphenol (meth)acrylate, and reaction products of 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene with (meth)acrylic acid. Among (meth)acrylates having an aromatic ring skeleton, phenoxybenzyl (meth)acrylate and phenoxyethyl (meth)acrylate are preferred, and phenoxybenzyl (meth)acrylate is more preferred. (Meth)acrylates having an aromatic ring skeleton can be used alone or in combination. The content of (meth)acrylate having an aromatic ring skeleton is, for example, 0% to 50% by mass, preferably 20% to 40% by mass, when the solid content of the adhesive is considered to be 100% by mass.

[0051] Examples of metal oxide particles include silicon oxide, zirconium oxide, titanium oxide, zinc oxide, antimony pentoxide, tin oxide, aluminum oxide, indium oxide, indium tin oxide, ferric oxide, cerium oxide, yttrium oxide, manganese oxide, holomium oxide, copper oxide, bismuth oxide, cobalt oxide, cobalt trioxide, iron trioxide, magnesium oxide, lanthanum oxide, praseodymium oxide, neodymium oxide, samarium oxide, eurobium oxide, gadolinium oxide, terbium oxide, dysprosium oxide, erbium oxide, thulium oxide, ytterbium oxide, lutetium oxide, scandium oxide, tantalum pentoxide, niobium pentoxide, iridium oxide, rhodium oxide, ruthenium oxide, and composite oxides formed by combining these. Among the metal oxide particles, zirconium oxide and titanium oxide are preferred, and zirconium oxide is more preferred. Metal oxide particles can be used alone or in combination. The metal oxide particles may consist solely of the metal oxides listed above, or they may contain other components, but it is preferable that metal oxides constitute the largest weight component of the particles. The shape of the metal oxide particles can be any shape, such as spherical, ellipsoidal, cuboidal, rectangular prism, or pyramidal. Furthermore, metal oxide particles that have been surface-treated by any appropriate method may be used.

[0052] The average particle size of the metal oxide particles is, for example, 1 nm to 150 nm, preferably 1 nm to 50 nm. Having an average particle size within this range can improve both the stability of the metal oxide particles in the adhesive and the refractive index of the adhesive layer. The average particle size of metal oxide particles can be derived, for example, by the following method: by observing the particles under magnification using a transmission electron microscope (TEM), field emission transmission electron microscope (FE-TEM), and field emission scanning electron microscope (FE-SEM), for example, 1000 particles are randomly selected, their maximum lengths are measured, and the arithmetic mean is calculated.

[0053] The content of metal oxide particles is, for example, 0% to 50% by mass, preferably 20% to 40% by mass, when the solid content of the adhesive is considered to be 100% by mass. When the content ratio of metal oxide particles is within this range, the stability of the metal oxide particles in the adhesive and the refractive index of the adhesive layer can be stably improved.

[0054] The curing adhesive may further contain hydroxyl group-containing (meth)acrylate. The hydroxyl group-containing (meth)acrylate can function as a curing component. Such a configuration can improve the adhesive strength of the adhesive layer. The content of hydroxyl group-containing (meth)acrylate is, for example, 0% to 30% by mass, preferably 1% to 30% by mass, and more preferably 3% to 20% by mass, when the solid content of the adhesive is considered to be 100% by mass.

[0055] Furthermore, by adjusting the number, type, combination, and amount of resin components, curing components, photopolymerization initiators, and additives in the adhesive (adhesive composition), an adhesive (adhesive composition) with a desired refractive index that reduces the minute defect parameter to a predetermined value can be obtained.

[0056] B-3.Adhesive layer In one embodiment, the optical laminate 100 further comprises an adhesive layer 6. The adhesive layer 6 is located on the side of the second optical film 2 opposite to the first optical film 1. In the illustrated example, the adhesive layer 6 is laminated on the surface of the second liquid crystal alignment solidification layer 21 opposite to the first optical film 1. With this configuration, the optical laminate can be attached to any suitable substrate (typically an image display panel) of the image display device by the adhesive layer 6.

[0057] The adhesive layer 6 is composed of any suitable adhesive. Examples of adhesives include (meth)acrylic adhesives, urethane adhesives, and silicone adhesives. The adhesives can be used alone or in combination. Among adhesives, (meth)acrylic adhesives are preferred.

[0058] The thickness of the adhesive layer 6 is, for example, 3 μm or more, preferably 5 μm or more, and preferably 10 μm or more. On the other hand, the thickness of the adhesive layer 6 is, for example, 50 μm or less, and preferably 30 μm or less.

[0059] B-4. Peel-off liner The optical laminate 100 may further include a release liner 7. The release liner 7 is attached to the surface of the adhesive layer 6 opposite to the second optical film 2. Typically, the release liner 7 is temporarily attached to the adhesive layer 6 until the optical laminate is attached to the substrate, and is peeled off from the adhesive layer 6 when the optical laminate is attached.

[0060] The release liner 7 contains any suitable resin material. Examples of resin materials include polyethylene terephthalate (PET), polyethylene, and polypropylene. Resin materials can be used alone or in combination.

[0061] In one embodiment, a release treatment layer is provided on the contact surface of the release liner 7 with the adhesive layer 6. The release layer typically contains a release agent. Examples of release agents include silicone-based release agents, fluorine-based release agents, and long-chain alkyl acrylate-based release agents, with silicone-based release agents being preferred, and vinyl group-containing addition-type silicones being even more preferred. Release agents can be used alone or in combination. The thickness of the release layer is, for example, 50 nm to 400 nm.

[0062] B-5. Other Optical Films The optical laminate 100 may include other optical films in addition to the first optical film 1 and the second optical film 2. The other optical films are attached, for example, to the surface of the first optical film 1 opposite to the second optical film 2 via any suitable adhesive layer. Other optical films include, for example, polarizers, phase difference films, polarizer protective films, phase difference protective films, image display device protective films, ultraviolet light transmission suppression films, and infrared light transmission suppression films. Other optical films may have a single-layer structure containing these films individually, or a laminated structure in which two or more of these films are laminated.

[0063] C. Method for manufacturing optical laminates Next, a method for manufacturing the optical laminate 100 according to one embodiment will be described. An optical laminate according to one embodiment is manufactured by any and appropriate method depending on its configuration. For convenience, the following describes in detail a method for manufacturing an optical laminate 100 in which the adhesive layer 4 is an adhesive layer 41 containing a cured product of a curable adhesive.

[0064] In one embodiment, the method for manufacturing the optical laminate 100 includes a coating step, a lamination step, and a curing step in that order.

[0065] C-1.Coating process In one embodiment, first, the first optical film 1 and the second optical film 2 described above are prepared. Each of the first optical film 1 and the second optical film 2 is preferably elongated. Furthermore, if the first optical film 1 and / or the second optical film 2 include a liquid crystal alignment solidification layer, the liquid crystal alignment solidification layer is prepared in a state supported on the coated substrate. Furthermore, if necessary, the activation treatment described above is performed on the surface of the first optical film 1 and / or the second optical film 2 in the thickness direction.

[0066] Next, a curable adhesive is applied to the surface of the first optical film 1 and / or the surface of the second optical film to form a coating. More specifically, the above-mentioned curable adhesive is applied to at least one surface (preferably the activated surface) of the first optical film 1 and the second optical film 2 by any suitable method.

[0067] The curable adhesive used in the coating process is diluted with a solvent beforehand. In other words, the curable adhesive used in the coating process contains a curing component and a solvent. If the curing component is a polymerizable substance such as an acrylic monomer, the curing adhesive further contains a photopolymerization initiator. If the curing component is a condensing substance such as an organosilane compound, the curing adhesive does not need to contain a photopolymerization initiator. Examples of solvents include water and organic solvents. Examples of organic solvents include halogenated hydrocarbons, aromatic hydrocarbons, aliphatic or alicyclic hydrocarbons, ketones, esters, alcohols, ethers, glycol ethers, and glycol ether acetates. Among these solvents, organic solvents are preferred, and esters are more preferred. Examples of esters include ethyl acetate and butyl acetate. When the solvent contains an organic solvent, the solvent can be smoothly evaporated when drying the coating film of the curable adhesive, and a thinning of the adhesive layer can be stably achieved. Solvents can be used alone or in combination.

[0068] The solid content concentration in the diluted curable adhesive is, for example, 50% by mass or less, preferably 30% by mass or less. On the other hand, the solid content concentration in the diluted curable adhesive is, for example, 1% by mass or more, preferably 2% by mass or more. When the solid content concentration of the curable adhesive after dilution is within this range, the curable adhesive can be applied stably, and the solvent can be evaporated more smoothly when the adhesive film is dried. Therefore, a thinner adhesive layer can be achieved more stably.

[0069] Examples of methods for applying the curing adhesive include dip coating, curtain coating, spray coating, bar coating, rod coating, roll coating, die coating, and gravure coating, with gravure coating being preferred.

[0070] C-2.Lamination process Next, the first optical film 1 and the second optical film 2 are superimposed so that a coating of hardening adhesive is sandwiched between them. In one embodiment, the first optical film 1 and the second optical film 2 are superimposed by roll-to-roll so that their longitudinal directions are substantially parallel.

[0071] C-3.Curing process Next, the coating of the curable adhesive located between the first optical film 1 and the second optical film 2 is cured. The curing method for the coating is arbitrarily and appropriately selected depending on the adhesive.

[0072] In one embodiment, the curing process includes a heating step and an irradiation step separately.

[0073] In the heating process, the coating film of the curable adhesive located between the first optical film 1 and the second optical film 2 is heated. This allows the solvent to volatilize from the coating film of the curable adhesive, thereby increasing the solid content concentration in the coating film. The heating temperature is, for example, 35°C to 120°C. The heating time is, for example, 30 seconds to 60 minutes.

[0074] In the irradiation process, an active energy ray is irradiated onto the coating film of the curable adhesive located between the first optical film 1 and the second optical film 2. This causes the curing components contained in the coating film to harden. The irradiation conditions for the active energy rays are set arbitrarily and appropriately depending on the type of curing adhesive. The irradiation process may be performed either before or after the heating process. The irradiation step is preferably performed after the heating step. This allows the coating film, whose solid content concentration has increased during the heating step, to be irradiated with active energy rays. As a result, the curing components contained in the coating film can be cured smoothly. Curing by active energy rays is typically triggered by the initiation reaction of polymerization initiators and the vaporization reaction of residual solvents contained in the coating film.

[0075] As a result, an adhesive layer 41 containing the cured product of the curing type adhesive is formed, and the first optical film 1 and the second optical film 2 are bonded together by the adhesive layer 41. Furthermore, the adhesive layer 41 is substantially free of solvent. The solvent content in the adhesive layer is, for example, 0.05% by mass or less, and preferably 0.01% by mass or less.

[0076] Furthermore, if the first optical film 1 and / or the second optical film 2 include a liquid crystal alignment solidification layer, the coated substrate is peeled off and removed from the liquid crystal alignment solidification layer as necessary. As described above, an optical laminate 100 having a laminated structure of a first optical film 1 / adhesive layer 4 / second optical film 2 is prepared. Subsequently, if necessary, the adhesive described above may be applied to the surface of the second optical film 2 opposite to the adhesive layer 4 by any suitable method to form an adhesive layer 6.

[0077] D. Another Embodiment The optical laminate 100 in the above-described embodiment satisfies formula (1) above. This suppresses the reflection of visible light incident on the optical laminate at the interface between the adhesive layer 4 and the adjacent layer (typically the first optical film 1 or the second optical film 2), and suppresses interference between these reflected lights. However, the present invention is not limited thereto. In one embodiment, the thickness d of the adhesive layer 4 is 0.10 μm or less, and the average refractive index n1 of the first optical film 1 is 1.55 or more and 1.60 or less. With such a configuration, even if the optical laminate does not satisfy the above formula (1), it is possible to stably suppress the reflection of visible light incident on the optical laminate at the interface between the adhesive layer and the adjacent layer (typically the first optical film or the second optical film), and to suppress interference between these reflected lights.

[0078] E. Image display device The optical laminates described in sections A to D above can be applied to any suitable image display device. Therefore, one embodiment of the present invention also includes an image display device using such an optical laminate. Examples of image display devices include liquid crystal displays and organic EL displays, and preferably organic EL displays. An image display device according to an embodiment of the present invention comprises an image display panel and the optical laminate 100 described above. An image display panel typically includes an image display cell. The optical laminate 100 is positioned on the viewing side of the image display panel. Typically, the optical laminate 100 is attached to the image display panel by an adhesive layer 6. In the image display device, the first optical film 1 is located on the viewing side, i.e., the side opposite to the image display panel, relative to the second optical film 2. The optical laminate 100 has any suitable shape depending on the image display device to which it is applied. The size of the optical laminate 100 can be adjusted arbitrarily and appropriately. Since such an image display device is equipped with an optical laminate that can suppress the reflection of visible light and the interference of reflected light, it can significantly suppress minute defects such as point-like interference unevenness (spot unevenness). [Examples]

[0079] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The measurement methods for each characteristic are as follows.

[0080] (1) Measurement of the average refractive index The adhesives used in the examples and comparative examples were coated onto a cycloolefin polymer film (COP film) (100 μm thick), and the same COP film was bonded to the coated surface. The film was then heated and dried at 60°C for 10 minutes, and subsequently cured by irradiation with ultraviolet light. This yielded an adhesive layer (single film) containing the cured adhesive. The refractive index in the plane and the refractive index in the thickness direction of the obtained adhesive layer were measured using a prism coupler (Sylon Technology Co., Ltd., product name "SPA-4000"). The measurement wavelength was 594 nm and the measurement temperature was 25°C. Furthermore, the refractive index of the optical film (liquid crystal alignment solidified layer) used in the examples and comparative examples was measured in the same manner as the refractive index of the cured layer described above. Both the adhesive layer and the optical film (liquid crystal alignment solidification layer) were optically isotropic. The average refractive index n1 of the first optical film, the average refractive index n2 of the adhesive layer, and the average refractive index n3 of the second optical film are shown in Tables 1 to 3.

[0081] (2) Measurement of the thickness of the adhesive layer Cross-sections of the optical laminates obtained in the examples and comparative examples were observed using a transmission electron microscope (TEM) with a Hitachi HT7820 instrument by the freeze-ultrathin sectioning method including heavy metal staining. The acceleration voltage during measurement was 100kV. This allowed us to measure the thickness of the adhesive layer. The results are shown in Tables 1-3.

[0082] (3) Measurement of minute defects Samples measuring A4 size (297 mm × 210 mm) were cut from the optical laminates obtained in the examples and comparative examples. The TAC film was then peeled off and removed from the samples. More specifically, the TAC film was peeled off from the surfaces of the first liquid crystal alignment solidification layer and the second liquid crystal alignment solidification layer, respectively. Subsequently, a (meth)acrylic adhesive was applied to the surface of the second liquid crystal alignment solidification layer opposite to the adhesive layer to form an adhesive layer. The thickness of the adhesive layer was 25 μm. Next, the sample was attached to a black acrylic plate using an adhesive layer. Next, the sample, attached to a black acrylic plate, was placed under a three-wavelength fluorescent lamp. Polarizing plates were placed between the fluorescent lamp and the sample, and between the sample and the observer, creating a crossed nicol relationship (where the absorption axes of the two polarizing plates are perpendicular to each other). In this state, the sample was observed visually, and the number of white minute defects was measured. The results are shown in Tables 1-3.

[0083] <Preparation of adhesive> <<Preparation Example 1>> Acryloyl morpholine (trade name "ACMO", manufactured by KJ Chemicals) 25 parts by mass, ε-caprolactone 1mol modified 2-hydroxyethyl acrylate (trade name "PLACCEL FA1DDM", manufactured by Daicel Chemicals) 10 parts by mass, lauryl acrylate (trade name "Light Acrylate LA", manufactured by Kyoeisha) 10 parts by mass, isostearyl acrylate (trade name "ISTA", manufactured by Osaka Organic Chemical Industry Co., Ltd.) 20 parts by mass, 1,9-nonanediol diacrylate (trade name "Light Acrylate 1.9ND-A", manufactured by Kyoeisha Chemicals) 15 parts by mass, acrylic oligomer (trade name "ARUFON UP-1190", manufactured by Toagosei Co., Ltd.) 15 parts by mass, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (trade name "Omnirad 819", manufactured by IGM Resins) One part by mass of (manufactured by BV), two parts by mass of 1-hydroxycyclohexyl phenyl ketone (trade name "Omnirad 184", manufactured by IGM Resins BV), and two parts by mass of diethylthioxanthone (trade name "KAYACURE DETX-S", manufactured by Nippon Kayaku Co., Ltd.) were stirred at 50°C for 1 hour to obtain a composition containing a curing component. Next, the composition containing the curing component was diluted with ethyl acetate as a solvent to prepare an ultraviolet-curable adhesive. The solid content concentration of the ultraviolet-curable adhesive was 5% by mass.

[0084] <<Preparation Example 2>> 10 parts by mass of hydroxyethyl acrylamide (trade name "HEAA", manufactured by KJ Chemicals), 4 parts by mass of 2-acetoacetoxyethyl methacrylate (trade name "AAEM", manufactured by Mitsubishi Chemicals), 60 parts by mass of acryloyl morpholine (trade name "ACMO", manufactured by KJ Chemicals), 11 parts by mass of tripropylene glycol diacrylate (trade name "Aronics M-220", manufactured by Toagosei Co., Ltd.), 1 part by mass of 4-vinylphenylboronic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 10 parts by mass of acrylic oligomer (trade name "ARUFON UP-1190", manufactured by Toagosei Co., Ltd.), 1 part by mass of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (trade name "Omnirad 819", manufactured by IGM Resins BV), 1 part by mass of 1-hydroxycyclohexyl phenyl ketone (trade name "Omnirad 184", manufactured by IGM Resins Two parts by mass of BV Co., Ltd. and one part by mass of diethylthioxanthone (trade name "KAYACURE DETX-S", manufactured by Nippon Kayaku Co., Ltd.) were stirred at 50°C for 1 hour to obtain a composition containing a curing component and a photopolymerization initiator. Next, a composition containing a curing component and a photopolymerization initiator was diluted with ethyl acetate to prepare an ultraviolet-curable adhesive. The solid content concentration of the ultraviolet-curable adhesive was 5% by mass.

[0085] <<Preparation Example 3>> A composition containing a curing component and a photopolymerization initiator was obtained by stirring 60 parts by mass of Ogusol EA-F5710 (manufactured by Osaka Gas Chemical Co., Ltd.), 10 parts by mass of Praxel FA1DDM (manufactured by Daicel Corporation), 20 parts by mass of acryloylmorpholine (trade name "ACMO", manufactured by KJ Chemicals Co., Ltd.), 5 parts by mass of ARFON UP-1190 (manufactured by Toagosei Co., Ltd.), 1 part by mass of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (trade name "Omnirad 819", manufactured by IGM Resins BV Co., Ltd.), 2 parts by mass of 1-hydroxycyclohexyl phenyl ketone (trade name "Omnirad 184", manufactured by IGM Resins BV Co., Ltd.), and 2 parts by mass of diethylthioxanthone (trade name "KAYACURE DETX-S", manufactured by Nippon Kayaku Co., Ltd.) at 50°C for 1 hour. Next, the composition containing the curing component was diluted with ethyl acetate to prepare an ultraviolet-curable adhesive. The solid content concentration of the ultraviolet-curable adhesive was 5% by mass.

[0086] <<Preparation Example 4>> (Preparation of dispersant) 415 g (1 mol) of tristyrenated phenol and 1 g (0.018 mol) of potassium hydroxide were charged into an autoclave and mixed uniformly. Under conditions of 130°C, 352 g (8 mol) of ethylene oxide (EO) was added dropwise to the reaction system. After the addition of ethylene oxide was complete, the system was aged for 1 hour at 130°C while maintaining a pressure of 0.1 MPa to obtain an 8-mol EO adduct of tristyrenated phenol. 767 g (1 mol) of the obtained 8-mol EO adduct of tristyrenated phenol and 152 g (1.3 mol) of sodium monochloroacetate were placed in a reactor and stirred until homogenized. Next, under conditions of 60°C, 52 g of sodium hydroxide was added, and the temperature was raised to 80°C and aged for 3 hours. After aging, the system was cooled to 50°C, and 117 g (1.2 mol) of 98% sulfuric acid was added dropwise at the same temperature to obtain a white suspension. This white suspension was washed with distilled water, and the solvent was removed under reduced pressure to obtain a dispersant. (Preparation of zirconia dispersion) To 100 parts by mass of a methanol dispersion of zirconium oxide (manufactured by Sakai Chemical Industry Co., Ltd., grade name "SZR-CM", average particle size (D50) based on dynamic light scattering method: 8 nm, zirconium oxide solid content concentration: 30%), 1.5 parts by mass of the dispersant obtained above and 28.5 parts by mass of m-phenoxybenzyl acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Light Acrylate POB-A"; hereinafter referred to as "POB-A") were added and mixed. Next, the solvent was removed under reduced pressure using a rotary evaporator to obtain a zirconia dispersion, which is a monomer dispersion of zirconium oxide. This zirconia dispersion contained zirconium oxide / dispersant / POB-A in a mass ratio of 50 / 2.5 / 47.5. (Preparation of adhesive) A composition containing a curing component, a photopolymerization initiator, and metal oxide particles was obtained by stirring 35 parts by mass of zirconia dispersion, 40 parts by mass of "POB-A", 10 parts by mass of 4-hydroxybutyl acrylate, 10 parts by mass of tripropylene glycol diacrylate (trade name "Aronics M-220", manufactured by Toagosei Co., Ltd.), 1 part by mass of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (trade name "Omnirad 819", manufactured by IGM Resins BV), 2 parts by mass of 1-hydroxycyclohexyl phenyl ketone (trade name "Omnirad 184", manufactured by IGM Resins BV), and 2 parts by mass of diethylthioxanthone (trade name "KAYACURE DETX-S", manufactured by Nippon Kayaku Co., Ltd.) at 50°C for 1 hour. Next, a composition containing a curing component, a photopolymerization initiator, and metal oxide particles was diluted with ethyl acetate to prepare an ultraviolet-curable adhesive. The solid content concentration of the ultraviolet-curable adhesive was 5% by mass.

[0087] <<Preparation Example 5>> 55 parts by mass of zirconia dispersion, 25 parts by mass of "POB-A", 10 parts by mass of 4-hydroxybutyl acrylate, 10 parts by mass of "Aronics M-220", 1 part by mass of "Omnirad 819", 2 parts by mass of "Omnirad 184", and 2 parts by mass of "KAYACURE DETX-S" were stirred at 50°C for 1 hour to obtain a composition containing a curing component, a photopolymerization initiator, and metal oxide particles. Next, a composition containing a curing component, a photopolymerization initiator, and metal oxide particles was diluted with ethyl acetate to prepare an ultraviolet-curable adhesive. The solid content concentration of the ultraviolet-curable adhesive was 5% by mass.

[0088] <Preparation of optical films> <<Preparation Example 6>> A photopolymerizable liquid crystal compound exhibiting a nematic liquid crystal phase (BASF's "Paliocolor LC242," chemical formula below) was dissolved in cyclopentanone to prepare a solution with a solid content of 30% by mass. [ka] A surfactant (BYK-360, manufactured by BY-Chemie) and a photopolymerization initiator (Omnirad907, manufactured by IGM Resins) were added to this solution to prepare a liquid crystal coating solution. The amount of surfactant added was 0.01 parts by mass per 100 parts by mass of the photopolymerizable liquid crystal compound. The amount of polymerization initiator added was 3 parts by mass per 100 parts by mass of the photopolymerizable liquid crystal compound. Next, a liquid crystal coating solution was applied to the surface of the triacetylcellulose (TAC) film using a bar coater and heated and dried at 100°C for 3 minutes. The resulting liquid crystal layer was cooled to room temperature (25°C) and then exposed to a nitrogen atmosphere with an integrated light intensity of 400 mJ / cm². 2 The liquid crystal layer was cured by irradiating it with ultraviolet light. This formed a liquid crystal alignment solidified layer (LC) as an optical film on the TAC film. The liquid crystal alignment solidification layer was elongated. The thickness of the liquid crystal alignment solidification layer was 1 μm.

[0089] [Comparative Examples 1 and 2 and Examples 1-3] Two liquid crystal alignment solidification layers obtained in Preparation Example 6 were prepared. In the following, one of the two liquid crystal alignment solidification layers was used as the first optical film (first liquid crystal alignment solidification layer), and the other of the two liquid crystal alignment solidification layers was used as the second phase difference film (second liquid crystal alignment solidification layer). The surface of the first liquid crystal alignment solidification layer is treated using a corona treatment machine at a treatment density of 50 W·min / m². 2 We dealt with the coronavirus. Next, the UV-curable adhesive obtained in Preparation Example 1 was applied to the corona-treated surface of the first liquid crystal alignment solidification layer using a bar coater to form a UV-curable adhesive coating. Furthermore, the surface of the second liquid crystal alignment solidification layer was also subjected to corona treatment in the same manner as described above. Next, the first liquid crystal alignment solidification layer and the second liquid crystal alignment solidification layer were stacked on top of each other, sandwiching the UV-curing adhesive coating. The corona-treated surface of the liquid crystal alignment solidification layer was in contact with the UV-curing adhesive coating. This resulted in the preparation of an intermediate laminate having a laminated structure of TAC film / first liquid crystal alignment solidification layer / UV-curable adhesive coating / second liquid crystal alignment solidification layer / TAC film. Subsequently, the intermediate laminate was placed in an oven and the UV-curing adhesive coating was heated and dried at 60°C for 30 minutes. During this time, the ethyl acetate (solvent) contained in the UV-curing adhesive coating was removed by evaporation. Next, the coating film of the UV-curing adhesive was irradiated with ultraviolet light to cure the curing components. This formed an adhesive layer that served as the bonding layer.

[0090] Based on the above, an optical laminate having a laminated structure of TAC film / first liquid crystal alignment solidification layer / adhesive layer / second liquid crystal alignment solidification layer / TAC film was manufactured. The minute defect parameters of the optical laminate (values ​​calculated from equation (1) above) are shown in Table 1.

[0091] [Comparative Examples 3 and 4 and Examples 4-6] The optical laminate was manufactured in the same manner as in Comparative Examples 1 and 2 and Examples 1 to 3, except that the UV-curable adhesive constituting the adhesive layer was changed to the UV-curable adhesive obtained in Preparation Example 2. The minute defect parameters of the optical laminate (values ​​calculated from equation (1) above) are shown in Table 1.

[0092] [Examples 7-11] The optical laminate was manufactured in the same manner as in Comparative Examples 1 and 2 and Examples 1 to 3, except that the UV-curable adhesive constituting the adhesive layer was changed to the UV-curable adhesive obtained in Preparation Example 3. The minute defect parameters of the optical laminate (values ​​calculated from equation (1) above) are shown in Table 2.

[0093] [Examples 12-16] The optical laminate was manufactured in the same manner as in Comparative Examples 1 and 2 and Examples 1 to 3, except that the UV-curable adhesive constituting the adhesive layer was changed to the UV-curable adhesive obtained in Preparation Example 4. The minute defect parameters of the optical laminate (values ​​calculated from equation (1) above) are shown in Table 2.

[0094] [Comparative Example 5, Examples 17-20] The optical laminate was manufactured in the same manner as in Comparative Examples 1 and 2 and Examples 1 to 3, except that the UV-curable adhesive constituting the adhesive layer was changed to the UV-curable adhesive obtained in Preparation Example 4. The minute defect parameters of the optical laminate (values ​​calculated from equation (1) above) are shown in Table 3.

[0095] [Table 1]

[0096] [Table 2]

[0097] [Table 3]

[0098] [evaluation] As is clear from Tables 1 to 3, if the optical laminate satisfies the above formula (1), the occurrence of minute defects can be significantly reduced in an image display device equipped with the optical laminate. Furthermore, it can be seen that if the thickness d of the adhesive layer is 0.1 μm or less, and the average refractive index n1 of the first optical film is 1.55 or more and 1.60 or less, the occurrence of minute defects in the image display device can be stably reduced. [Industrial applicability]

[0099] The optical laminate manufactured according to the embodiments of the present invention can be suitably used in image display devices (typically liquid crystal display devices and organic EL display devices). [Explanation of symbols]

[0100] 1. First optical film 11. First liquid crystal alignment solidification layer 2. Second optical film 21. Second liquid crystal alignment solidification layer 4 Adhesive layer 41 Adhesive layer 6. Adhesive layer 100 Optical laminate

Claims

1. An optical laminate comprising a first optical film, an adhesive layer, and a second optical film in this order, satisfying the following formula (1): ([(n1+n3) / 2-n2] ２ ×d×1000<1・・・(1) (In equation (1), n1 represents the average refractive index of the first optical film; n2 represents the average refractive index of the adhesive layer; n3 represents the average refractive index of the second optical film; and d represents the thickness [μm] of the adhesive layer.)

2. The optical laminate according to claim 1, wherein the thickness d of the adhesive layer is 0.10 μm or less.

3. The optical laminate according to claim 1, wherein the thickness d of the adhesive layer is 0.07 μm or less.

4. The optical laminate according to claim 1, wherein the thickness d of the adhesive layer is 0.03 μm or less.

5. The optical laminate according to claim 1, wherein the adhesive layer is an adhesive layer.

6. The optical laminate according to claim 1, wherein the polyvinyl alcohol content in the adhesive layer is 1% by mass or less.

7. The optical laminate according to claim 1, wherein the average refractive index n1 of the first optical film is 1.55 or more and 1.60 or less.

8. The optical laminate according to claim 1, wherein the average value of the average refractive index n1 of the first optical film and the average refractive index n3 of the second optical film is 1.55 or more and 1.60 or less.

9. The optical laminate according to claim 1, wherein the average refractive index n2 of the adhesive layer is 1.50 or more and 1.65 or less.

10. The optical laminate according to claim 1, wherein the first optical film includes an orientation solidified layer of a liquid crystal compound.

11. The optical laminate according to claim 1, wherein the second optical film includes an orientation solidification layer of a liquid crystal compound.

12. The device comprises a first optical film, an adhesive layer, and a second optical film in this order. The thickness d of the adhesive layer is 0.10 μm or less. An optical laminate in which the average refractive index n1 of the first optical film is 1.55 or more and 1.60 or less.

13. An image display device comprising an optical laminate according to any one of claims 1 to 12.

14. A coating step of applying a curing adhesive to the surface of the first optical film and / or the surface of the second optical film to form a coating film, A lamination step in which the first optical film and the second optical film are superimposed on each other so as to sandwich the coating film of the curable adhesive, The process includes, in this order, a curing step of curing the coating film of the curable adhesive located between the first optical film and the second optical film, The aforementioned curing step is A heating step for heating the coating film of the curing adhesive, A method for manufacturing an optical laminate, comprising separately an irradiation step of irradiating the coating film of the curable adhesive with active energy rays.

15. The curable adhesive used in the coating process comprises a curing component and a solvent. The method for manufacturing an optical laminate according to claim 14, wherein in the heating step, the solvent is volatilized from the coating film of the curable adhesive.

16. The method for producing an optical laminate according to claim 15, wherein the curing adhesive includes a photopolymerization initiator.

17. The method for producing an optical laminate according to claim 15, wherein the solvent includes an organic solvent.

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