Depolarization film and image display device

Abstract

The present invention addresses the problem of providing: a depolarization film that does not cause blacking-out of an image display device even when one is wearing polarized sunglasses that cut linearly polarized light or glasses that cut circularly polarized light; and an image display device. This problem is solved by a depolarization film comprising a first retardation film that includes a liquid crystal compound and that has a random axial distribution.

Description

Depolarizing film and image display device

[0001] The present invention relates to a depolarizing film and an image display device.

[0002] Conventionally, retardation films such as quarter-wave plates have been used to impart optical functions to image display devices. For example, when an observer wearing polarized sunglasses observes an image displayed on an image display device using a polarizing plate on the light exit side, the screen appears completely black (blackout), which is a problem. To address this issue, it is known that by placing a quarter-wave plate on the light exit side of the image display device so that the absorption axis of the polarizer of the polarizing plate and the slow axis of the quarter-wave plate form an angle of approximately 45 degrees, the exiting light is made approximately circularly polarized, thereby preventing blackout (Patent Document 1).

[0003] JP 2019-174636 A

[0004] Polarized sunglasses absorb one type of linearly polarized light and transmit the other, orthogonal, linearly polarized light. Therefore, blackouts can be suppressed by circularly polarizing the light emitted from an image display device. Meanwhile, polarized glasses for passive 3D display devices and circularly polarized AR (Augmented Reality) glasses are also known as polarized glasses that absorb specific polarized light. It has been discovered that wearing these polarized glasses can sometimes cause blackouts when viewing an image display device that emits circularly polarized light. This is thought to be because, while image display devices emit circularly polarized light, polarized glasses for passive 3D display devices and circularly polarized AR glasses may not transmit the circularly polarized light emitted by the display device.

[0005] Therefore, an object of the present invention is to provide a depolarizing film that prevents image display devices from blacking out, whether the user is wearing polarized sunglasses that cut linearly polarized light or polarized glasses that cut circularly polarized light, and to provide an image display device that uses this depolarizing film.

[0006] The present inventors have conducted extensive research into the above-mentioned problems and have found that the above-mentioned problems can be achieved by the following configuration.

[0007] [1] A depolarizing film comprising a first retardation film having a random axial distribution. [2] The depolarizing film according to [1], wherein the domain size of the first retardation film is 1.5 to 30 μm when defined as the autocorrelation length × 3. [3] The depolarizing film according to [1], wherein the domain size of the first retardation film is 100 to 2000 μm when defined as the autocorrelation length × 3. [4] The depolarizing film according to any one of [1] to [3], wherein the first retardation film contains a liquid crystal compound. [5] The depolarizing film according to any one of [1] to [4], further comprising a second retardation film having a random axial distribution. [6] The depolarizing film according to [5], wherein the retardation of the first retardation film at a wavelength of 550 nm is 100 to 180 nm, and the retardation of the second retardation film at a wavelength of 550 nm is 230 to 320 nm. [7] The depolarizing film according to [5] or [6], wherein the first retardation film has negative birefringence and the second retardation film has positive birefringence. [8] The depolarizing film according to any one of [1] to [7], further comprising a retardation layer having a retardation of 1,000 to 100,000 nm at a wavelength of 550 nm. [9] An image display device having the depolarizing film according to any one of [1] to [8].

[10] The image display device according to [9], wherein the image display device uses a light source whose spectrum during white display has two or more maxima in the visible range, and wherein the full width at half maximum of the peak corresponding to at least one of the maxima is 20 nm or less.

[0008] According to the present invention, a depolarizing film can be provided that prevents blackout of an image display device, whether the user is wearing polarized sunglasses that cut linearly polarized light or eyeglasses that cut circularly polarized light. The present invention also provides an image display device that uses this depolarizing film.

[0009] Fig. 1 is a schematic diagram showing an example of a depolarizing film of the present invention, when viewed from the normal direction to the surface of a retardation film having a random axis distribution. Fig. 2 is a schematic diagram showing an example of a depolarizing film of the present invention, when viewed from the cross section of a retardation film having a random axis distribution. Fig. 3 is a schematic diagram showing an example of a depolarizing film of the present invention. Fig. 4 is a photograph of a retardation film having a random axis distribution taken under crossed Nicols using an optical microscope.

[0010] The present invention will be described in detail below. The following description of the constituent elements may be based on representative embodiments and specific examples, but the present invention is not limited to such embodiments. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0011] In this specification, "orthogonal" does not mean an angle of exactly 90°, but means 90°±10°, preferably 90°±5°. "Parallel" does not mean an angle of exactly 0°, but means 0°±10°, preferably 0°±5°. "45°" does not mean an angle of exactly 45°, but means 45°±10°, preferably 45°±5°.

[0012] As used herein, the term "absorption axis" refers to the polarization direction in which absorbance is maximized in-plane when linearly polarized light is incident. Furthermore, the term "reflection axis" refers to the polarization direction in which reflectance is maximized in-plane when linearly polarized light is incident. Furthermore, the term "transmission axis" refers to the direction perpendicular to the absorption axis or reflection axis in-plane. Furthermore, the term "slow axis" refers to the direction in which refractive index is maximized in-plane. In this specification, unless otherwise specified, phase difference refers to in-plane retardation, and is expressed as Re(λ). Here, Re(λ) represents the in-plane retardation at a wavelength λ, and unless otherwise specified, the wavelength λ is 550 nm. Furthermore, the retardation in the thickness direction at a wavelength λ is expressed as Rth(λ). Unless otherwise specified, the wavelength λ is 550 nm. Re(λ) and Rth(λ) can be values ​​measured at a wavelength λ using an AxoScan OPMF-1 (manufactured by OptoScience). By inputting the average refractive index ((nx+ny+nz) / 3) and film thickness (d (μm)) into AxoScan, the slow axis direction (°) Re(λ) = R0(λ) Rth(λ) = ((nx+ny) / 2-nz) × d can be calculated.

[0013] The depolarizing film of the present invention will now be described.

[0014] The depolarizing film of the present invention includes a first retardation film having a random axis distribution. Specifically, as conceptually shown in FIG. 1 , the depolarizing film of the present invention includes a first retardation film in which the slow axes 13 are oriented in various directions without any regularity in the plane, i.e., having a random (slow) axis distribution. Such a depolarizing film of the present invention is suitable for applications in which images displayed on an image display device are observed while wearing polarized glasses. That is, the depolarizing film of the present invention can effectively depolarize incident light. Therefore, by observing images displayed on an image display device with polarized glasses through the depolarizing film of the present invention, an image display without blackout can be achieved, whether the image is viewed while wearing polarized glasses that cut linearly polarized light, such as polarized sunglasses, or while wearing polarized glasses that cut circularly polarized light, such as AR glasses.

[0015] As described above, retardation films are used to prevent blackout, in which the screen appears completely black when viewing an image displayed on an image display device that emits linearly polarized light while wearing polarized sunglasses that cut linearly polarized light. Conventional retardation films (λ / 4 wave plates) have a polarization axis in a fixed direction. Therefore, when an image displayed on an image display device that emits linearly polarized light is viewed through the retardation film with polarized glasses that cut linearly polarized light, the retardation film converts the linearly polarized light into circularly polarized light, thereby suppressing blackout. However, when an image displayed on an image display device that emits linearly polarized light is viewed through the retardation film with polarized glasses that cut circularly polarized light, the retardation film converts the linearly polarized light into circularly polarized light, which can cause blackout.

[0016] In contrast, the depolarizing film of the present invention includes a first retardation film having a random axial distribution. Therefore, the depolarizing film of the present invention can randomly change the polarization state of the image displayed by an image display device, i.e., the emitted light, for each location within the film plane. As a result, light emitted from a certain region, such as a single pixel of an image display device, is in a so-called depolarized state, which includes various polarization states, thereby eliminating blackout when using polarized glasses. In this case, although multiple partial blackouts occur within a single pixel, the entire pixel region is not blacked out, and the pixel functions as a whole, allowing the image to be observed.

[0017] The depolarizing film of the present invention having such properties is particularly useful in fields requiring high optical performance utilizing polarization, such as image display devices that display (emit) linearly polarized images, such as liquid crystal displays and organic EL display devices, projectors, optical sensors, and head-mounted displays.

[0018] <Structure of the first retardation film having a random axis distribution> The depolarizing film of the present invention has a first retardation film having a random axis distribution. As described above, having a random axis distribution means that the direction of the axis (slow axis) in the retardation film, i.e., the axis orientation, is oriented in various directions without regularity in the plane, that is, the axis is randomly distributed. Here, it is preferable that the axis orientation of the first retardation film is randomly distributed in the plane and the retardation is approximately uniform in the plane.

[0019] FIG. 1 is a conceptual diagram of a depolarizing film viewed from the normal direction of the film surface. FIG. 2 is a conceptual diagram of the depolarizing film 1 viewed from the side. The direction (orientation) of the slow axis 13 of the first retardation film 11 included in the depolarizing film 1 varies depending on the location in the plane. In the first retardation film 11, the distribution of the slow axes may be separated into domains or may be continuous. The dotted line 12 in FIG. 1 schematically represents the boundary when the distribution of the slow axes is separated into domains. It is preferable that the first retardation film has a substantially uniform in-plane thickness and the slow axis orientation varies in-plane. By making the thickness substantially uniform in-plane, light scattering can be suppressed, resulting in good image clarity.

[0020] Here, in the depolarizing film of the present invention, the domains in the retardation film having a random axis distribution are regions in which the axes (slow axes) in the plane of the retardation film are oriented in similar directions.

[0021] Whether a retardation film has a random axis distribution can be confirmed, for example, by using a polarizing microscope ECLIPSE LV100POL manufactured by Nikon Corporation, setting polarizers on the light source side and the detector side, and observing the retardation film at 50x magnification in a crossed Nicol arrangement, and checking whether a light-dark pattern appears in the crossed Nicol arrangement (see FIG. 4).

[0022] Although the first retardation film having a random axis distribution has been described above, as will be described later, even in an embodiment having a plurality of retardation films having a random axis distribution, the preferred embodiment of each of the retardation films having a random axis distribution is the same as that of the first retardation film described above. For example, the preferred embodiment of the second retardation film having a random axis distribution described later is also the same as that of the first retardation film described above.

[0023] Here, in the present invention, the random axis distribution refers to the state in which the axes of the retardation film, for example, the orientation direction of the liquid crystal compound, do not follow any specific rule or pattern, but are statistically uniformly distributed.That is, the random axis distribution means that the axes of the retardation film, for example, the orientation of each liquid crystal compound, are unpredictable, and orientation in any direction occurs with equal probability.Such randomness is realized by specific conditions during the manufacturing process, and has a significant impact on the properties of the film.

[0024] <Optical Properties of First Retardation Film Having Random Axis Distribution> The first retardation film having a random axis distribution is preferably designed to exhibit a desired retardation at a specific wavelength. This allows for effective depolarization of incident light. The retardation of the first retardation film can be adjusted by known methods, such as the thickness of the film and the degree of optical anisotropy (birefringence) of the optically anisotropic material. This also applies to other retardation films in a case where multiple retardation films having a random axis distribution are used. The retardation of the first retardation film having a random axis distribution is not limited and may be set appropriately depending on the application of the depolarizing film of the present invention. As an example, the first retardation film having a random axis distribution preferably has a retardation of 100 to 180 nm at a wavelength of 550 nm. By setting the retardation of the first retardation film having a random axis distribution within this range, polarized light can be effectively depolarized. The retardation at a wavelength of 550 nm of the first retardation film having a random axis distribution is more preferably 120 to 160 nm, and even more preferably 130 to 150 nm. When the first retardation film having a random axis distribution is used as a single layer, that is, when the depolarizing film of the present invention has only one layer of retardation film having a random axis distribution, the retardation of the retardation film is preferably in the above range. Such characteristics are preferable for suppressing a decrease in brightness when observing an image display device while wearing polarized glasses.

[0025] <Lamination of Multiple Retardation Films Having Random Axis Distribution> The depolarizing film of the present invention may have one or more layers of retardation films having a random axis distribution in addition to the first retardation film having a random axis distribution. The number of retardation films having a random axis distribution in the depolarizing film of the present invention is not limited, but is preferably two layers. That is, the depolarizing film of the present invention preferably further includes, for example, a second retardation film having a random axis distribution. That is, the depolarizing film of the present invention preferably has a first retardation film having a random axis distribution and a second retardation film having a random axis distribution.

[0026] FIG. 3 is a schematic diagram showing an example of a depolarizing film of the present invention having two layers of retardation films with a random axis distribution. The depolarizing film 1 shown in FIG. 3 is formed by laminating a first retardation film 31 and a second retardation film 32 via an adhesive 33. When laminating multiple retardation films with a random axis distribution, as shown in FIG. 3, each retardation film may be laminated via an adhesive or directly. There are no particular restrictions on the adhesive, and known adhesives and adhesives can be used. Alternatively, two retardation films may be laminated by forming a base layer on the first retardation film and then forming a second retardation film on top of that.

[0027] By stacking multiple retardation films having a random axis distribution, a suitable depolarization effect can be achieved over a wide band and for various states of polarized light. When multiple retardation films having a random axis distribution are stacked, the composite retardation layer obtained by stacking can have different phase differences for each retardation film in addition to the random axis distribution possessed by each retardation film. This makes it possible to more effectively improve the depolarization ability for various types of polarized light (e.g., linearly polarized, circularly polarized, elliptically polarized light). In addition, the depolarization ability can be improved over a wide wavelength range. That is, in a configuration in which multiple retardation films having a random axis distribution are stacked, as described above, each retardation film can have a different phase difference. Therefore, for example, in the case of a two-layer retardation film, even if one retardation film is insufficiently depolarized depending on the state of incident polarized light, sufficient depolarization can be achieved by depolarizing the other retardation film having a different phase difference. As a result, polarization can be suitably depolarized regardless of whether the incident polarized light is linearly polarized, circularly polarized, or elliptically polarized. Furthermore, in a configuration in which multiple retardation films having a random axis distribution are stacked, each retardation film has a random axis distribution, regardless of the retardation of each retardation film. Therefore, the overall axis distribution in the laminate becomes more random and large, and the effect of depolarizing incident light can be enhanced. Such characteristics are preferable for suppressing a decrease in brightness and a change in color when viewing an image display device while wearing polarized glasses.

[0028] As described above, when the depolarizing film of the present invention has a plurality of retardation films having a random axis distribution, there is no limitation on the number of retardation films. Here, in terms of depolarization function, a larger number of retardation films is preferable. On the other hand, in terms of the brightness and image clarity of images observed through polarized glasses, a smaller number of retardation films is advantageous. From the above viewpoints, when the depolarizing film has a plurality of retardation films having a random axis distribution, the number of layers is preferably two or three, and more preferably two.

[0029] <Optical Properties of Laminated Retardation Films Having a Random Axis Distribution> Each retardation film of a laminated retardation film having a random axis distribution is preferably designed to exhibit a desired retardation at a specific wavelength. This allows the polarization state of light to be effectively eliminated regardless of the polarization state of incident light. This retardation can be adjusted by known methods such as the thickness of the film and the degree of optical anisotropy (birefringence) of the optically anisotropic material.

[0030] For example, when the depolarizing film has two retardation layers with random axis distribution, as an example, a combination of a quarter wave plate with random axis distribution and a half wave plate with random axis distribution is preferred.In this case, the first retardation film may be a quarter wave plate with random axis distribution, and the second retardation film may be a half wave plate with random axis distribution, or the first retardation film may be a half wave plate with random axis distribution, and the second retardation film may be a quarter wave plate with random axis distribution.

[0031] The retardation of the quarter-wave plate (e.g., the first retardation film) at a wavelength of 550 nm is preferably 100 to 180 nm, more preferably 120 to 160 nm, and even more preferably 130 to 150 nm. The retardation of the half-wave plate (e.g., the second retardation film) at a wavelength of 550 nm is preferably 230 to 320 nm, more preferably 250 to 300 nm, and even more preferably 260 to 290 nm. Such characteristics are preferable for suppressing a decrease in brightness and a change in color when observing an image display device while wearing polarized glasses.

[0032] In the case of a laminate of three or more layers, the preferred embodiment of the two-layer laminate may further include a quarter-wave plate having a random axis distribution and / or a half-wave plate having a random axis distribution. Furthermore, in the case of a laminate of three or more layers having a random axis distribution, a retardation film other than a quarter-wave plate or a half-wave plate, such as a three-quarter-wave plate, may also be included. Such a configuration can be appropriately designed according to the purpose required for the depolarizing film.

[0033] <Control of Rth> When the depolarizing film of the present invention has a plurality of retardation films having a random axis distribution, it is preferable to control the Rth value of each retardation film. By controlling the Rth value of each retardation film, the retardation in the oblique direction can also be suitably controlled. As a result, in addition to when the image display device is observed from the front, i.e., when light is incident on the depolarizing film from the front, the depolarizing ability can be improved when the image display device is observed from an oblique angle, i.e., when light is incident on the depolarizing film from an oblique angle.

[0034] When the depolarizing film of the present invention has a retardation film having a plurality of random axis distributions, a suitable example of controlling Rth is a method of laminating a retardation film having a negative Rth value with a retardation film having a positive Rth value. A retardation film having a negative Rth value can be produced, for example, by using a liquid crystal compound having positive birefringence in the production of the retardation film. Examples of liquid crystal compounds having positive birefringence include rod-shaped liquid crystal compounds. On the other hand, a retardation film having a positive Rth value can be produced, for example, by using a liquid crystal compound having negative birefringence in the production of the retardation film. Examples of liquid crystal compounds having negative birefringence include discotic liquid crystal compounds.

[0035] In addition, when the depolarizing film of the present invention has a retardation film having a plurality of random axis distributions, the control of Rth is not limited to the configuration of laminating a retardation film having a negative Rth value and a retardation film having a positive Rth value, as described above, and various configurations can be used.For example, when the depolarizing film has two retardation films, that is, a first retardation film and a second retardation film, as described above, the first retardation film and the second retardation film may have positive birefringence, the first retardation film and the second retardation film may have negative birefringence, the first retardation film may have positive birefringence and the second retardation film may have negative birefringence, or the first retardation film may have negative birefringence and the second retardation film may have positive birefringence. In the case where light is incident on the depolarizing film from an oblique direction, that is, from the viewpoint of blackout and color change when the image display device is observed from an oblique direction, it is preferable that the first retardation film has negative birefringence and the second retardation film has positive birefringence, or that the first retardation film has positive birefringence and the second retardation film has negative birefringence.

[0036] Whether the birefringence is positive or negative can be confirmed by measuring Rth. When Rth is negative, the film has positive birefringence. When Rth is positive, the film has negative birefringence.

[0037] <Retardation Film Material> There are no limitations on the material for forming the retardation film (retardation layer), and various known materials used in forming retardation films can be used. Examples include birefringent particles, birefringent polymers, and liquid crystal compounds. Among these, liquid crystal compounds that can form a retardation film with a uniform thickness and a high aspect ratio (in-plane length / thickness) and that further have high optical anisotropy are preferred. In particular, liquid crystal compounds having a polymerizable group are preferably used. By using a liquid crystal compound to form a retardation film, not only excellent retardation properties but also processability and durability can be improved.

[0038] Liquid crystal compounds can be easily fixed by heating, ultraviolet irradiation, etc., and maintain stable optical properties for a long period of time. Moreover, liquid crystal compounds can precisely adjust the desired retardation properties, and because they exhibit a liquid crystal phase within a specific temperature range, the retardation properties can be optimized by temperature control during the manufacturing process.

[0039] Although there are no limitations on the wavelength dispersion characteristics of the birefringence of the liquid crystal compound, reverse wavelength dispersion is preferred. Reverse wavelength dispersion represents Re(450) / Re(550)<1.00 and Re(650) / Re(550)≧1.00. Therefore, by producing a retardation film using a liquid crystal compound with reverse wavelength dispersion, it is possible to suppress color changes when viewing an image display device that emits polarized light while wearing polarized glasses.

[0040] Furthermore, when selecting a liquid crystal compound, it is preferable to select a material that has durability appropriate for the usage environment, taking into consideration physical properties such as heat resistance, light resistance, and moisture resistance, thereby ensuring long-term reliability in image display devices such as liquid crystal displays and other optical devices.

[0041] The first retardation film having a random axis distribution preferably contains a liquid crystal compound. Even when the depolarizing film of the present invention has a plurality of retardation films having a random axis distribution, each retardation film preferably contains a liquid crystal compound. For example, as described above, when the depolarizing film has a first retardation film and a second retardation film, it is preferable that both the first retardation film and the second retardation film contain a liquid crystal compound. Note that the preferred embodiment of the liquid crystal compound in each retardation film is the same as described above.

[0042] <Domain Size> As described above, in the first retardation film having a random axis distribution, the distribution of the slow axis may be divided into domains or may be continuous. Furthermore, as described above, the domain in the first retardation film having a random axis distribution is a region in which the axis (slow axis) in the plane of the retardation film faces in a similar direction. In FIG. 1, in order to clearly show the configuration of the first retardation film having a random axis distribution, the boundary line when the domain is divided is schematically shown by a dotted line 12. However, in reality, it is difficult to clearly determine the boundary of the domain in the first retardation film having a random axis distribution.

[0043] The first retardation film having a random axis distribution preferably has liquid crystals free of defects. Here, liquid crystal defects refer to areas where the alignment of liquid crystal molecules is disturbed, resulting in discontinuities. These defects are caused by sudden changes in liquid crystal alignment, impurities, external factors, and the like. In particular, a phenomenon called discontinuity is a type of defect that occurs when molecular alignment changes suddenly, and can affect the optical properties of the liquid crystal material. The absence of such defects prevents sudden spatial changes in the alignment axis (slow axis) of the liquid crystal, reducing light scattering. This results in good image quality without the visible glare, which is a phenomenon in which pixels in a displayed image are distorted and perceived as glare. Furthermore, the discoloration of external light reflection can be minimized when the screen display is off or in black, resulting in a high-quality display surface. Defects can be observed using an optical microscope. By performing unpolarized transmission observation, light scattering occurs at the defective areas, reducing brightness, and they are visually recognized as dark spots. This allows discontinuities in the liquid crystal alignment to be visualized. Specifically, the observation is performed using an optical microscope with a magnification of 50 times, with the observation field being 283 μm × 188 μm. Under these conditions, the number of dark areas (defective areas) present within the field of view is preferably 100 or less, more preferably 50 or less, and even more preferably 10 or less.

[0044] Here, the axial distribution in the first retardation film having a random axial distribution can be adjusted by the formation conditions, forming material, characteristics of the base alignment film, etc. of the retardation film. In addition, in the first retardation film having a random axial distribution, the state of the axial distribution, the size of the domain, and the degree of distribution in the axial distribution do not vary significantly within the plane of the retardation film. Correspondingly, in the present invention, in the first retardation film having a random axial distribution, regardless of whether the distribution of the slow axes (axial distribution) is divided into domains or continuous, the autocorrelation coefficient of the luminance distribution measured with the retardation film placed between polarizers arranged in crossed Nicols is calculated, and the value obtained by multiplying this autocorrelation length by three is defined as the domain size.

[0045] Specifically, as described above, a polarizing microscope is used, polarizers are set in a crossed Nicol arrangement on the light source side and the detector side, and a retardation film is placed between the polarizers and observed at 50x magnification. In this case, if the retardation film has a random axial distribution, a light-dark pattern will appear in the observed image as described above (see FIG. 4). A luminance profile on any line in this observed image is extracted, and the autocorrelation coefficient of this luminance profile is calculated. The distance at which the autocorrelation coefficient is 0.5 is then defined as the autocorrelation length in the luminance profile of the retardation film. In the present invention, the value obtained by multiplying this autocorrelation length by three is defined as the domain size in a retardation film having a random axial distribution.

[0046] As described above, when a retardation film has a random axis distribution, a light-dark pattern appears in the observation image of the retardation film observed with a polarizing microscope under polarizers arranged in a crossed Nicol configuration. This light-dark pattern in the observation image corresponds to the direction of the slow axis at each position in the plane of the retardation film having a random axis distribution arranged between the polarizers arranged in a crossed Nicol configuration. Therefore, the light-dark pattern in the observation image changes depending on the state of the random axis distribution in the retardation film. In other words, this domain size is one of the numerical values ​​indicating the state of the axis distribution in the first retardation film of the depolarizing film of the present invention.

[0047] It is preferable to control the domain size of the first retardation film having a random axis distribution. This can improve optical uniformity. The domain size is preferably 32 μm or less, more preferably 30 μm or less, even more preferably 25 μm or less, and particularly preferably 20 μm or less. The domain size is preferably 0.5 μm or more, more preferably 1.5 μm or more, even more preferably 2.5 μm or more, and particularly preferably 4 μm or more. In particular, the domain size is preferably 0.5 to 32 μm, more preferably 1.5 to 30 μm, even more preferably 2.5 to 25 μm, and particularly preferably 4 to 20 μm.

[0048] On the other hand, the preferred range of the domain size of the first retardation film having a random axis distribution varies depending on the use of the image display device and the structure of the image display device.

[0049] A. When the depolarizing film of the present invention is disposed near a pixel, i.e., an image display device, the preferred range of domain size is estimated from the following viewpoints: A-(1) Reduction of image blur: The degree of image blur is determined from the relationship between the scattering angle θ (∝1 / domain size), the light spreading distance calculated from the distance L between the pixel and the depolarizing film, and the pixel size d. Specifically, if the light spreading distance is large enough to be the pixel size, the image will appear blurred. From the viewpoint of reducing image blur, the preferred range of domain size can be expressed by the formula: Domain size [μm]>(8π / 180) / tan -1 (d / 2L). A-(2) Suppression of pixel blocking: The degree of pixel blocking is determined from the relationship between the pixel size d and the domain size. If the domain size is larger than the sub-pixels (RGB), some pixels will be blocked, causing a color change. From the viewpoint of suppressing pixel blocking (color change), the preferable range of domain size can be expressed by the formula: Domain size [μm]<d / 3.

[0050] B. When the depolarizing film of the present invention is placed far from the pixel, i.e., the image display device, and close to the eye, the preferred range of domain size can be estimated from the following viewpoints: B-(1) Reduction of image blur: The degree of image blur is calculated from the scattering angle θ (∝1 / domain size). If the light spread angle is larger than the resolution of the eye, the image will appear blurred. From the viewpoint of reducing image blur, the preferred range of domain size can be expressed by the formula: Domain size [μm] > 100. B-(2) Sufficiently smaller than pupil size: When the depolarizing film is placed close to the eye, if the domain size is larger than the pupil size (approximately 2000 μm in diameter in a bright environment), depolarization utilizing the random orientation direction cannot be achieved, which may result in blackout. From the viewpoint of pupil size, the preferred range of domain size can be expressed by the formula: Domain size [μm] < 2000.

[0051] The domain size can be measured by the method described above, i.e., the method described in the Examples below. Furthermore, when the domain size is equal to or greater than the lower limit of each of the above-mentioned ranges, the diffraction angle of light diffraction caused by the Pancharatnam Berry Phase (PBP) phase due to the difference in axial orientation can be kept small, thereby obtaining a clear image. On the other hand, when the domain size is equal to or less than the upper limit of each of the above-mentioned ranges, the variation in light intensity between pixels can be kept low, thereby suppressing noise.

[0052] Below, examples of preferred domain sizes corresponding to the use and structure of the image display device are shown. <In the case of tablet surface> As a first example, consider the case where a depolarizing film is placed on the surface of a tablet (the front side of a touch panel). This example corresponds to the case where a depolarizing film is placed near the pixel shown in "A" above. As an example, assume that the distance L between the pixel and the depolarizing film is 1000 μm, and the pixel size d is 96 μm. In this case, the domain size is preferably 32 μm or less, more preferably 30 μm or less, even more preferably 25 μm or less, particularly preferably 24 μm or less, more particularly preferably 20 μm or less, and most preferably 16 μm or less. Furthermore, the domain size is preferably 1.5 μm or more, more preferably 2.5 μm or more, even more preferably 2.9 μm or more, particularly preferably 3.9 μm or more, more particularly preferably 4 μm or more, and most preferably 6 μm or more. In particular, the domain size is preferably 1.5 to 32 μm, more preferably 1.5 to 30 μm, even more preferably 2.5 to 30 μm, even more preferably 2.5 to 25 μm, particularly preferably 3.9 to 24 μm, more particularly preferably 4 to 20 μm, and most preferably 6 to 16 μm. Even when a plurality of retardation films having a random axis distribution are used, it is preferable to control the domain size of each retardation film, and the domain size is preferably within the above-mentioned range. For example, the domain sizes of the first retardation film and the second retardation film are preferably within the above-mentioned range.

[0053] <Directly Above the Display> As a second example, consider the case where a depolarizing film is placed directly above the display device of a smartphone (behind the touch panel). This example also corresponds to the case where a depolarizing film is placed near the pixel shown in "A" above. As an example, the distance L between the pixel and the depolarizing film is 100 μm, and the pixel size d is 55 μm. In this case, the domain size is preferably 20 μm or less, more preferably 14 μm or less, and most preferably 9 μm or less. Furthermore, the domain size is preferably 0.5 μm or more, more preferably 0.7 μm or more, and most preferably 1.0 μm or more. In particular, the domain size is preferably 0.5 to 20 μm, more preferably 0.7 to 14 μm, and most preferably 1.0 to 9 μm. The domain size can be measured by the method described in the Examples below. Furthermore, even when multiple retardation films with random axis distributions are used, it is preferable to control the domain size of each retardation film, and the domain size is preferably within the above-mentioned range. For example, the domain sizes of the first retardation film and the second retardation film are preferably within the above-mentioned ranges.

[0054] <When Placed Far From the Display> Third, as an example shown in "B" above, consider the case where the depolarizing film is placed far from the smartphone and directly in front of the eyes. In this case, the domain size is preferably 2000 μm or less, more preferably 1400 μm or less, and most preferably 800 μm or less. Furthermore, the domain size is preferably 100 μm or more, more preferably 150 μm or more, and most preferably 200 μm or more. In particular, the domain size is preferably 100 to 2000 μm, more preferably 150 to 1400 μm, and most preferably 200 to 800 μm. Even when multiple retardation films with random axial distributions are used, it is preferable to control the domain size of each retardation film, and the domain size is preferably within the above-mentioned range. For example, the domain sizes of the first retardation film and the second retardation film are preferably within the above-mentioned range.

[0055] <Method of controlling domain size> The domain size can be controlled by appropriately adjusting the conditions in the alignment process of the liquid crystal compound, such as temperature, time, and UV irradiation intensity. The domain size can also be controlled by appropriately adjusting the physical properties of the liquid crystal compound, such as the elastic constant. Furthermore, the domain size can also be controlled by the distance from the underlayer. The distance from the underlayer can also be controlled by the film thickness of the retardation layer. When the film thickness of the retardation layer is thin, the domain size becomes small, and when the film thickness is thick, the domain size becomes large.

[0056] Another method for controlling domain size is to use the following material as a base layer that serves as an alignment film and to impart a distribution of alignment directions in advance so as to obtain a target domain size. Specific examples of methods for imparting a distribution of alignment directions (methods for controlling domain size) include the following: (1) A method for imparting a distribution of alignment directions includes first using a photo-alignment film as a base layer and exposing each microscopic region of the photo-alignment film to linearly polarized light, such as laser light, while changing the polarization direction. Forming a liquid crystal layer as a retardation layer on such an alignment film makes it possible to obtain a retardation layer with a desired domain size. (2) When a liquid crystal layer formed on a base without alignment constraints is used as the base layer, the domain size can be controlled by the distance from the base without alignment constraints and the elastic modulus of the layer. The distance from the base without alignment constraints can be controlled by the film thickness of the liquid crystal layer. A thin liquid crystal layer results in a smaller domain size, while a thicker film results in a larger domain size. Furthermore, a high elastic modulus of the liquid crystal layer results in a smaller domain size, while a low elastic modulus results in a larger domain size. The elastic modulus of the liquid crystal layer can also be controlled by the type of material and the temperature of the liquid crystal layer during drying and UV curing. When the temperature of the layer during drying and UV curing is high, the elastic modulus decreases, resulting in a larger domain size. By forming a liquid crystal layer on such a liquid crystal layer as a retardation layer, a retardation layer with any desired domain size can be obtained. (3) Another method for imparting a distribution of the alignment direction is to use a cholesteric liquid crystal as an underlayer and change the director orientation of the liquid crystal compound on the outermost surface of the cholesteric liquid crystal layer in-plane. Examples of methods for changing the director orientation of the liquid crystal compound on the outermost surface of the cholesteric liquid crystal layer in-plane include changing the film thickness of the cholesteric liquid crystal layer in-plane and changing the helical pitch of the cholesteric liquid crystal layer in-plane.Methods for varying the film thickness of the cholesteric liquid crystal layer in-plane include wind unevenness due to exposure to air, step unevenness due to pump pulsation, streaks due to bar coating, Marangoni convection, and, when a photo-alignment film is used as a base for the cholesteric liquid crystal layer, a method for imparting a distribution to the height of the photo-alignment film, which can generate a fine film thickness distribution. On the other hand, an example of a method for varying the helical pitch of the cholesteric liquid crystal layer in-plane is a method for varying the HTP (helical twisting power) of a chiral agent added to the cholesteric liquid crystal layer after coating and before curing by changing the intensity of isomerization exposure. By forming a liquid crystal layer as a retardation layer on the cholesteric liquid crystal layer obtained by such a method as a base, it is possible to form a liquid crystal layer with various alignment directions.

[0057] These methods for controlling the domain size may be used in combination.

[0058] The above-mentioned description of the domain size is applicable not only to the first retardation film having a random axis distribution but also to the second retardation film having a random axis distribution. That is, the above-mentioned description of the domain size is applicable to all retardation films, whether the depolarizing film of the present invention has only one layer of retardation film or a plurality of layers of retardation film.

[0059] <Method for manufacturing retardation film> There is no limitation on the method for manufacturing the retardation film, and known methods can be used depending on the material for forming the retardation film. One example is a method for manufacturing a retardation film by uniformly applying a liquid crystalline material having a crosslinkable group onto a support, followed by heat treatment at a specific temperature and curing treatment by ultraviolet irradiation or the like. In other words, the liquid crystalline material having a crosslinkable group is a liquid crystal composition containing a liquid crystal compound having a crosslinkable group.

[0060] A typical retardation film using a liquid crystal compound is produced by using an underlayer (alignment film) that has liquid crystal alignment regulating power and a uniform alignment direction, and then applying and curing a liquid crystal composition to this underlayer to form a retardation layer. Methods for making the alignment regulating direction uniform in the plane include rubbing the underlayer and irradiating the photo-alignment film with uniform linearly polarized light. In contrast, to produce a retardation film with a random axis distribution, an underlayer that has no alignment regulating power or whose alignment regulating direction is random in the plane is used. An example of an underlayer that has no alignment regulating power is an underlayer that is coated with a composition containing crosslinkable non-liquid crystal molecules and then cured. Furthermore, a plastic film that is not rubbed can also be used as an underlayer with a random alignment regulating direction.

[0061] In addition, in order to produce retardation in a retardation film, it is preferable to align rod-shaped liquid crystal compounds horizontally or discotic liquid crystal compounds vertically. To achieve this, it is preferable to control the surface energy of the underlayer. Specifically, when preparing a retardation film made of rod-shaped liquid crystal compounds, it is preferable to make the underlayer hydrophobic. On the other hand, when preparing a retardation film made of discotic liquid crystal compounds, it is preferable to make the underlayer hydrophilic.

[0062] To suppress defects in the fabrication of the first retardation film, it is preferable to optimize the design and control of the alignment film and liquid crystal layer, etc., and ensure continuity of the liquid crystal molecular alignment. Proper material and process design are required to fabricate a high-quality retardation film with reduced defects. Specifically, methods for optimizing the properties of the underlying alignment film or adopting appropriate patterning techniques can be used. This allows for the preparation of an alignment film in which the azimuthal control direction changes continuously and gradually, effectively suppressing the occurrence of discontinuities in the liquid crystal alignment. One example is a method using a cholesteric liquid crystal layer with a wavy alignment as the underlying alignment film. This method allows the alignment direction of the liquid crystal molecules on the surface of the cholesteric liquid crystal layer to change randomly yet continuously. Achieving this "random and gradual" alignment reduces the formation of discontinuities in the liquid crystal alignment, thereby suppressing the occurrence of defects. When observing a cross-section of a cholesteric liquid crystal layer with a scanning electron microscope (SEM), alternating bright and dark lines are observed in the thickness direction due to the cholesteric alignment of the liquid crystal compound. These bright and dark lines are usually linear and parallel to the major surface. A cholesteric liquid crystal layer with wavy alignment is one in which the bright and dark lines in a cross-sectional SEM image appear as meandering waves. A cholesteric liquid crystal layer with such wavy alignment can be formed, for example, by forming a cholesteric liquid crystal layer on an underlayer that does not have alignment control power. Another effective method is to use a photo-alignment film and perform polarized light exposure with a random polarization direction. This method imparts randomness to the alignment direction of liquid crystal molecules generated during exposure while controlling the alignment distribution to maintain a gradual change so as not to become extreme. As a result, it is possible to form a liquid crystal layer with smooth and continuous overall alignment while also incorporating random characteristics. This reduces the occurrence of discontinuities and suppresses defects. These approaches are effective individually, but can also be used in combination depending on the situation. Using such a method, high-quality and stable liquid crystal alignment can be achieved in the production of a first retardation film, minimizing performance degradation due to defects.

[0063] The depolarizing film of the present invention may be composed of only a retardation film, or may have the above-mentioned support (substrate) and underlayer. Various known supports can be used as long as they are capable of supporting the retardation film and transmitting target light, such as visible light. Examples of materials for forming the transparent support include cellulose-based polymers (hereinafter referred to as cellulose acylate), such as triacetyl cellulose, thermoplastic norbornene-based resins (such as Zeonex and Zeonor manufactured by Zeon Corporation and Arton manufactured by JSR Corporation), plastic films such as acrylic resins and polyester-based resins, and glass. Various known underlayers can be used as long as they do not have the ability to regulate the alignment of liquid crystal compounds and can transmit target light, such as visible light. Examples of underlayers include a layer (hard coat layer) formed by curing crosslinkable non-liquid crystal molecules, a layer (liquid crystal layer) formed by curing crosslinkable liquid crystal compounds, a plastic film layer made of a polymer, and a photo-alignment film such as an azo-based or cinnamate-based film. In the depolarizing film of the present invention, the underlayer may also serve as the support, as in the case of the non-rubbing plastic film described above. Furthermore, in addition to these layers, the depolarizing film of the present invention may also have various other layers (films) such as an antireflection layer, a retardation layer, a depolarizing layer made of a highly birefringent material, a polarizer layer, a color absorption layer, a transparent conductive layer, and an antistatic layer, as necessary.

[0064] It is particularly preferable to further include a depolarizing layer made of a highly birefringent material, as this provides a glare suppression effect. A retardation film with a random axial distribution also has an in-plane distribution of its scattering properties, which causes pixel disorder and glare. In contrast, if the depolarization film further includes a depolarizing layer made of a highly birefringent material, the in-plane distribution of the scattering properties can be more finely varied, thereby reducing glare. The depolarizing layer made of a highly birefringent material is preferably located closer to the image display device than the first and second retardation films. It is preferable to have, in order from the image display device side, a depolarizing layer made of a highly birefringent material, a first retardation film, and a second retardation film. An example of a depolarizing layer made of a highly birefringent material is a retardation layer having a phase difference of 1,000 to 100,000 nm at a wavelength of 550 nm.

[0065] <<Depolarization layer made of a highly birefringent material>>

[0066] <In-plane retardation in the normal direction of the depolarizing layer made of a highly birefringent material> The depolarizing layer (retardation layer) made of a highly birefringent material is preferably a high retardation film having a phase difference of at least several times the wavelength of light in the visible range. The in-plane retardation (phase difference) in the normal direction of the depolarizing layer (retardation layer) made of a highly birefringent material at a wavelength of 550 nm is preferably 1,000 to 100,000 nm, more preferably 5,000 to 50,000 nm, and most preferably 7,000 to 20,000 nm. If the in-plane retardation in the normal direction of the depolarizing layer made of a highly birefringent material at a wavelength of 550 nm is greater than 1,000 nm, the change in the polarization state with respect to wavelength increases, resulting in higher depolarization ability and suppressing color unevenness and blackout. On the other hand, if the in-plane retardation in the normal direction at a wavelength of 550 nm of the depolarizing layer made of a highly birefringent material is less than 100,000 nm, it is possible to suppress a decrease in transmittance and deterioration in transmitted image clarity due to an excessively thick depolarizing layer made of a highly birefringent material. Here, the retardation of the depolarizing layer made of a highly birefringent material can be adjusted by the formation conditions, formation material, film thickness, lamination of multiple retardation films, etc.

[0067] <Lamination of Multiple Retardation Films> The depolarizing layer made of a highly birefringent material may have two or more retardation films. There is no limitation on the number of retardation films that the depolarizing layer made of a highly birefringent material has, but in order to reduce interface reflection and obtain high transmitted image clarity, the number is preferably less than 20 layers, more preferably less than 10 layers, even more preferably less than 6 layers, and most preferably less than 3 layers.

[0068] By stacking multiple retardation films, a high retardation value can be obtained while precisely controlling the retardation in the oblique direction, and therefore a suitable depolarization effect can be achieved for various states of polarization and light sources of various spectra. That is, in a configuration in which multiple retardation films are stacked, as described above, each retardation film can have a different retardation. Therefore, by adjusting the film thickness of each layer according to the retardation of the combined retardation film, the difference between the retardation in the normal direction and the retardation in the oblique direction of the composite consisting of the depolarization element and the retardation layer can be reduced, and therefore, blackout can be suppressed while suppressing color unevenness when observed through polarized sunglasses.

[0069] <Optical Properties of Laminated Retardation Films> Each retardation film of the laminated retardation film is preferably designed to exhibit a desired retardation at a specific wavelength. This allows the polarization state of light to be effectively eliminated regardless of the polarization state of incident light. This retardation can be adjusted by known methods such as the thickness of the film and the degree of optical anisotropy (birefringence) of the optically anisotropic material.

[0070] Furthermore, the film may have multiple depolarizing layers made of highly birefringent materials. There is no limit to the number of depolarizing layers made of highly birefringent materials. In terms of depolarizing function, a larger number of depolarizing layers made of highly birefringent materials is preferable because it provides higher retardation and thus better blackout suppression. On the other hand, in terms of the brightness of an image observed through a polarizing element and the clarity of a transmitted image, a smaller number of retardation films is advantageous.

[0071] <Material for depolarizing layer made of highly birefringent material> There are no particular limitations on the composition and material of the film that satisfies the optical properties of the depolarizing layer made of a highly birefringent material used in the depolarizing film of the present invention. Hereinafter, the material that constitutes the depolarizing layer made of a highly birefringent material will be described.

[0072] The material constituting the depolarizing layer made of a highly birefringent material can be, for example, a thermoplastic resin that has excellent transparency, mechanical strength, thermal stability, moisture blocking properties, isotropy, etc. as its main component. Examples of thermoplastic resins include polyester resin and polycarbonate resin. The term "main component" refers to a material that constitutes 50% or more by mass of the highly birefringent depolarizing layer.

[0073] In addition to the thermoplastic resin material described above, the depolarizing layer made of a highly birefringent material may contain one or more suitable additives. Examples of additives include ultraviolet absorbers, particles, lubricants, antiblocking agents, heat stabilizers, antioxidants, antistatic agents, lightfastness agents, impact resistance modifiers, lubricants, dyes, and pigments. The content of the thermoplastic resin in the highly birefringent material depolarizing layer is preferably 50 to 100% by mass, more preferably 50 to 99% by mass, even more preferably 60 to 98% by mass, and particularly preferably 70 to 97% by mass. When the content of the thermoplastic resin in the highly birefringent material depolarizing layer is 50% by mass or more, the inherent high transparency and other properties of the thermoplastic resin can be fully exhibited.

[0074] The depolarizing layer made of a highly birefringent material may be a single-layer film or a multilayer film. Furthermore, both or one side of these single-layer or multilayer films may be subjected to a surface treatment. This surface treatment may be surface modification by corona treatment, saponification treatment, heat treatment, ultraviolet irradiation, electron beam irradiation, or the like, or thin film formation by coating or vapor deposition of a polymer material, metal compound, or the like. Furthermore, an easy-adhesion layer, as described below, may be formed to improve adhesion to other components.

[0075] The material for forming the depolarizing layer made of a highly birefringent material is not limited, and various known materials used in forming retardation films can be used. Examples include birefringent particles, birefringent polymers, and liquid crystal compounds. Among these, birefringent polymers that can achieve high retardation values ​​through simple processes are preferred. Among these, polyester resins and polycarbonate resins, which have high birefringence, are particularly preferred.

[0076] --Polyester Resin-- The depolarizing layer made of a highly birefringent material is preferably a polyester film containing a polyester resin as a main component. Furthermore, the depolarizing layer made of a highly birefringent material is preferably a polyester film stretched at least uniaxially. Examples of polyester resins include polyethylene terephthalate, polyethylene isophthalate, polyethylene-2,6-naphthalate, polybutylene terephthalate, and 1,4-cyclohexanedimethylene terephthalate, and two or more of these may be used as needed. Among these, polyethylene terephthalate and polyethylene-2,6-naphthalate are preferred. From the viewpoint of material cost, polyethylene terephthalate is more preferred.

[0077] Polyethylene terephthalate is a polyester having structural units derived from terephthalic acid as the dicarboxylic acid component and structural units derived from ethylene glycol as the diol component. Preferably, at least 80 mol% of all repeating units are ethylene terephthalate, but structural units derived from other copolymerization components may also be included. Examples of other copolymerization components include dicarboxylic acid components such as isophthalic acid, p-β-oxyethoxybenzoic acid, 4,4'-dicarboxydiphenyl, 4,4'-dicarboxybenzophenone, bis(4-carboxyphenyl)ethane, adipic acid, sebacic acid, 5-sodium sulfoisophthalic acid, and 1,4-dicarboxycyclohexane, and diol components such as propylene glycol, butanediol, neopentyl glycol, diethylene glycol, cyclohexanediol, ethylene oxide adducts of bisphenol A, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. These dicarboxylic acid components and diol components may be used in combination of two or more types, if necessary. It is also possible to use an oxycarboxylic acid such as p-oxybenzoic acid in combination with the above-mentioned carboxylic acid component and diol component. A dicarboxylic acid component and / or a diol component containing a small amount of an amide bond, a urethane bond, an ether bond, a carbonate bond, etc. may be used as another copolymerization component. Polyethylene terephthalate can be produced by any production method, including a so-called direct polymerization method in which terephthalic acid is directly reacted with ethylene glycol, and, if necessary, other dicarboxylic acid and / or other diol, and a so-called transesterification method in which a dimethyl ester of terephthalic acid is transesterified with ethylene glycol, and, if necessary, the dimethyl ester of other dicarboxylic acid and / or other diol.

[0078] --Polycarbonate Resin-- The depolarizing layer made of a highly birefringent material preferably contains polycarbonate resin as a main component.

[0079] Known resins can be used as the polycarbonate resin. For example, polycarbonate resins having a bisphenol A skeleton can be mentioned, which are obtained by reacting a dihydroxy component with a carbonate precursor by interfacial polymerization or melt polymerization. For example, those described in JP-A-2006-277914, JP-A-2006-106386, and JP-A-2006-284703 can be preferably used. Commercially available products include "Toughlon MD1500" (manufactured by Idemitsu Kosan Co., Ltd.). Two or more of these may be used as needed.

[0080] --Ultraviolet Absorber-- It is preferable that a depolarizing layer made of a highly birefringent material contains an ultraviolet absorber to prevent ultraviolet degradation of polarizing plate protective films and the like of image display devices. The ultraviolet absorber is not particularly limited as long as it is a compound that has ultraviolet absorption ability and can withstand the heat applied in the manufacturing process of the depolarizing layer made of a highly birefringent material.

[0081] UV absorbers include organic and inorganic UV absorbers, with organic UV absorbers being preferred from the standpoint of transparency. Examples of suitable organic UV absorbers include benzotriazole-based, hydroxyphenyltriazine-based, and benzoxazine-based UV absorbers. In the present invention, 2,2'-(p-phenylene)di-3,1-benzoxazin-4-one (product name UVSORB 101, manufactured by Fujifilm Fine Chemicals Co., Ltd.) is a preferred UV absorber. Furthermore, to broaden the UV absorption bandwidth, two or more UV absorbers with different maximum absorption wavelengths may be used in combination. The amount of UV absorber added is preferably 0.01 to 2% by mass, and more preferably 0.01 to 1.5% by mass, of the resin contained in the depolarizing layer made of a highly birefringent material.

[0082] Furthermore, when the depolarizing layer made of a highly birefringent material is a multilayer film, it is preferable that it has at least a three-layer structure, and the UV absorber is preferably incorporated into an intermediate layer. By incorporating the UV absorber into the intermediate layer, it is possible to prevent the UV absorber from bleeding out onto the film surface, thereby maintaining the properties of the film, such as adhesiveness.

[0083] -Method for manufacturing a depolarizing layer made of a highly birefringent material- There are no particular limitations on the method for manufacturing a depolarizing layer made of a highly birefringent material, but in order to impart the above-mentioned properties, it is preferable to manufacture it by the following method. First, a resin (e.g., a polyester resin) used for the depolarizing layer made of a highly birefringent material is melt-extruded into a film, and cooled and solidified on a casting drum to form an unstretched film. If necessary, a coating liquid for forming an easy-adhesion layer is applied, and this unstretched film is preferably stretched 3 to 10 times, preferably 3 to 7 times, in the width direction at a temperature of Tg to (Tg + 60)°C of the polyester film. The depolarizing layer made of a highly birefringent material is preferably a polyester film stretched at least uniaxially, and more preferably a polyester film stretched uniaxially at least in the width direction from the viewpoint of exhibiting a large in-plane retardation Re.

[0084] Next, it is preferable to perform a heat treatment at 140 to 220°C for 1 to 60 seconds. Hereinafter, this heat treatment at 140 to 220°C for 1 to 60 seconds is also referred to as heat setting. The heat setting temperature is more preferably 150 to 220°C, and particularly preferably 150°C or higher but lower than 220°C.

[0085] Furthermore, it is preferable to perform a re-heat treatment (relaxation treatment) at a temperature 10 to 20°C lower than the heat setting temperature while shrinking the film by 0 to 20% in the longitudinal and / or transverse directions. This method reduces contact of the film with the roll, making it less likely to develop minute scratches on the film surface than the method described above, making it advantageous for optical applications. The glass transition temperature of the film is referred to as Tg. A heat setting temperature of 150°C or higher but lower than 220°C is preferable because it reduces deviation in the orientation direction of the resin used in the depolarizing layer made of a highly birefringent material and also reduces thermal dimensional change. In particular, when the depolarizing layer made of a highly birefringent material has a hard coat layer, peeling and cracking of the hard coat layer are less likely to occur.

[0086] <Image display device> The image display device of the present invention is an image display device having the depolarizing film of the present invention described above. In other words, the image display device of the present invention is an image display device having an image display device main body (display) and the depolarizing film of the present invention provided on the image display surface side of the image display device main body. In the image display device of the present invention, the image display device main body and the depolarizing film may be in contact with each other or may be spaced apart. In other words, the image display device of the present invention also includes the above-mentioned "B. Case where the depolarizing film is placed far from the pixels and close to the eyes."

[0087] Various known image display devices can be used as the image display device (image display device main body) of the present invention. Examples include liquid crystal display devices, OLED (organic light emitting diode) display devices, LED (light emitting diode) display devices, projectors, MEMS (micro electro mechanical systems) display devices, and LCOS (liquid crystal on silicon) display devices. Applications of image display devices include smartphones, tablets, notebook PCs, monitors, televisions, movies, and public viewing.

[0088] It is preferable that the spectral width of each color of light in an image display device is narrow. Narrowing the spectral width increases the color gamut. Examples of image display devices with narrow spectral widths include image display devices that use quantum dots, lasers, or the like as light sources. By using the depolarizing film of the present invention in such image display devices, the polarization state of the emitted light can be changed from place to place, making it possible to depolarize even light sources with narrow spectral widths and suppress blackouts.

[0089] <Spectrum During White Display> The spectrum of the image display device during white display preferably has two or more maxima in the visible range (visible light wavelength range). Here, the visible range refers to a wavelength range of 380 to 780 nm. The spectrum during white display preferably has maxima in at least two wavelength ranges: red, green, and blue. The red range (R) preferably has a maximum at a wavelength of 600 nm or more. The green range (G) preferably has a maximum between 510 and 570 nm. The blue range (B) preferably has a maximum between 430 and 470 nm. The image display device preferably uses a light source in which the full width at half maximum of the peak corresponding to each maxima is 20 nm or less. Examples of such light sources include quantum dots and lasers, as described above. By using the depolarizing film of the present invention in an image display device using such a light source, the polarization state of the emitted light can be changed from location to location, as described above. This makes it possible to depolarize even light sources with narrow spectral widths and suppress blackouts. The full width at half maximum of the peak can be determined by measuring the spectral radiance spectrum using a spectroradiometer or the like, and calculating the difference between the long-wavelength wavelength and the short-wavelength wavelength at half the peak intensity (50%) for each peak. In the examples described below, a spectroradiometer SR-UL2 manufactured by Topcon Technohouse Corporation was used as the spectroradiometer.

[0090] The present invention will be specifically described below based on examples. The materials, reagents, amounts and proportions of substances, procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the present invention is not limited to or by the following examples.

[0091] <Formation of Underlayer 1> A 100 μm thick PET film (Cosmoshine A4265, manufactured by Toyobo Co., Ltd.) was prepared as a support. This PET film had an easy-adhesion layer on one side. On the side of the PET film without the easy-adhesion layer, underlayer coating solution 1 having the following composition was applied using a #3.6 wire bar coater. Thereafter, the film was dried at 45° C. for 60 seconds, and then irradiated at 25° C. with 500 mJ / cm using an ultraviolet irradiation device using a mercury lamp as an ultraviolet light source. 2 The substrate was irradiated with ultraviolet light of 1.4 μm in thickness to prepare a support having an underlayer 1.

[0092] [Undercoat layer coating solution 1] KAYARAD PET30 (manufactured by Nippon Kayaku Co., Ltd.) 100 parts by weight IRGACURE 907 (manufactured by Ciba-Geigy Co., Ltd.) 3.0 parts by weight Kayacure DETX (manufactured by Nippon Kayaku Co., Ltd.) 1.0 part by weight Surfactant F1 (listed below) 0.01 part by weight Methyl isobutyl ketone 243 parts by weight

[0093] Surfactant F1

[0094] <Preparation of Retardation Film 1> A retardation layer coating solution 1 having the following composition was applied onto the underlayer 1 using a wire bar coater. Thereafter, the film was dried at 25°C for 30 seconds, and then heated at 80°C for 120 seconds for liquid crystal alignment. After that, the film was irradiated with 500 mJ / cm2 at 40°C using an ultraviolet irradiation device using a mercury lamp as an ultraviolet light source. 2 to form a retardation layer having a thickness of 0.85 μm, thereby producing a retardation film 1. The retardation film 1 has positive birefringence.

[0095] [Coating liquid 1 for retardation layer] Methyl ethyl ketone 144.9 parts by mass Mixture X of the following rod-like liquid crystal compound 100.0 parts by mass Photopolymerization initiator A 0.02 parts by mass Photopolymerization initiator B 1.00 parts by mass Surfactant F1 above 0.027 parts by mass Surfactant F2 below 0.067 parts by mass

[0096] Mixture X of rod-shaped liquid crystal compounds

[0097] In the above mixture, the numerical values ​​are in mass %. R is a group bonded via an oxygen atom. The average molar absorption coefficient of the above rod-shaped liquid crystal compound in the wavelength range of 300 to 400 nm was 140 / mol cm.

[0098] Photopolymerization initiator A: IRGACURE 907 (manufactured by Ciba-Geigy) Photopolymerization initiator B: Kayacure DETX (manufactured by Nippon Kayaku Co., Ltd.)

[0099] Surfactant F2

[0100] <Preparation of Retardation Film 2> Retardation film 2 was prepared in the same manner as in the preparation of retardation film 1, except that the thickness of the retardation layer was changed to 1.7 μm. Retardation film 2 has positive birefringence.

[0101] <Preparation of Retardation Film 3> The underlayer 1 was heated to a discharge rate of 150 W·min / m 2 After corona treatment, the retardation layer coating solution 2 having the following composition was applied using a wire bar coater. Thereafter, the film was dried at 25°C for 30 seconds, and then heated at 80°C for 120 seconds for liquid crystal alignment. Then, the film was irradiated with 500 mJ / cm2 at 40°C using an ultraviolet irradiation device using a mercury lamp as an ultraviolet light source. 2 to form a retardation layer having a thickness of 0.85 μm, thereby producing a retardation film 3. The retardation film 3 has negative birefringence.

[0102] [Coating liquid 2 for retardation layer] 80 parts by mass of the following discotic liquid crystal compound (A) 20 parts by mass of the following discotic liquid crystal compound (B) 10 parts by mass of the following polymerizable monomer E1 0.3 parts by mass of the following surfactant F3 3 parts by mass of photopolymerization initiator (manufactured by BASF, Irgacure 907) 290 parts by mass of methyl ethyl ketone 50 parts by mass of cyclohexanone

[0103] Discotic Liquid Crystal Compound (A)

[0104] Discotic Liquid Crystal Compound (B)

[0105] Polymerizable Monomer E1

[0106] Surfactant F3

[0107] <Preparation of Retardation Film 4> Retardation film 4 was prepared in the same manner as for retardation film 1, except that the base on which the retardation layer coating liquid was applied was changed from base layer 1 to a rubbed PET film. Retardation film 4 has positive birefringence.

[0108] <Measurements> The following measurements were carried out for each of the prepared retardation films. Each measurement was carried out by transferring each retardation film to glass. As a transfer method, the coated surface was first attached to the glass via an adhesive. Next, the PET support was peeled off. In this way, an optical object consisting of glass / retardation layer / underlayer was prepared.

[0109] Measurement of Retardation and Axial Distribution: Using a Nikon polarizing microscope, ECLIPSE LV100POL, the retardation and axial distribution (in-plane distribution of axial angles) were measured by the rotational compensator method (reference: Spectroscopic Ellipsometry, by Fujiwara Hiroyuki). The retardation was measured as the in-plane retardation Re and the retardation Rth in the thickness direction. The axial distribution was evaluated by the average value and standard deviation in an evaluation system in which the axial orientation was obtained as a value in the range of -90° to 90°. When the average value of the axial orientation was in the range of -5° to 5° and the standard deviation of the axial orientation was in the range of 45° to 55°, the axial angles were considered random, i.e., the axial distribution was random.

[0110] <<Domain Size Measurement>> Using a Nikon polarizing microscope, ECLIPSE LV100POL, polarizers were set on the light source side and the detector side, and the retardation film was observed at 50x magnification in a crossed Nicol configuration. As an example of an image obtained by this method, an image of retardation film 1 is shown in Figure 4. The appearance of a light-dark pattern in the crossed Nicol configuration indicates that the axes of the retardation layer have an in-plane distribution (random axis distribution). A luminance profile on any line in this image was extracted, and the autocorrelation coefficient of this luminance profile was calculated. The distance at which the autocorrelation coefficient was 0.5 was defined as the autocorrelation length, and the value obtained by multiplying this autocorrelation length by three was defined as the domain size.

[0111] The measurement results for each retardation film are shown in Table 1. Since a light / dark pattern was confirmed under the crossed Nicols arrangement, retardation films 1 to 3 had random axial orientations (axial orientation distribution), and the average azimuth angle was 0 degrees. Furthermore, retardation films 1 to 3 had domains. On the other hand, retardation film 4, in which a liquid crystal layer was formed on rubbed PET, had an azimuth angle of 45 degrees and no domains. Furthermore, since a light / dark pattern was not confirmed under the crossed Nicols arrangement, retardation film 4 did not have a random axial distribution.

[0112]

[0113] <Preparation of Image Display Device of Example 1> The retardation film 1 was transferred onto the surface of a commercially available image display device 1 via an adhesive. A commercially available TV, LC-46LX1, manufactured by Sharp Corporation was used as the image display device 1. It was confirmed that the light emitted from this image display device 1 was linearly polarized. Furthermore, when this image display device 1 displayed white light, the full widths at half maximum of the red (R), green (G), and blue (B) light sources were R: overlapping and indistinguishable, G: overlapping and indistinguishable, and B: 23 nm, respectively. The transfer method was to first attach the coated surface to the surface of the liquid crystal display device via the adhesive. Next, the PET support was peeled off. In this way, the image display device of Example 1, consisting of the image display device 1 / adhesive layer / retardation film 1 / underlayer, was prepared.

[0114] <Fabrication of Image Display Devices of Examples 2 and 3, and Comparative Example 1> The retardation film to be transferred to the image display device 1 was changed to the configuration shown in Table 2. Here, in Examples 2 and 3, two retardation films were transferred to form a depolarizing film with a laminated configuration on the image display device 1. The order of lamination was such that first, the retardation film shown in the first layer column of the table was transferred to the image display device 1, and then the retardation film shown in the second layer column was transferred.

[0115] <Fabrication of Image Display Devices of Examples 11 to 13 and Comparative Example 11> Image display devices of Examples 11 to 13 and Comparative Example 11 were fabricated in the same manner as in Examples 1 to 3 and Comparative Example 1, except that the image display device was changed to image display device 2. The configuration combinations are shown in Table 3. Here, a Creator 17, a commercially available notebook PC manufactured by MSI, was used as image display device 2. It was confirmed that the light emitted from this image display device 2 was linearly polarized. Furthermore, when this image display device 2 displayed white, the full widths at half maximum of the red (R), green (G), and blue (B) light sources were R: 45 nm, G: 45 nm, and B: 17 nm, respectively.

[0116] <Evaluation of Blackout> The Examples and Comparative Examples were visually evaluated for blackout according to the following criteria. The results are shown in Tables 2 and 3. The evaluation of blackout was performed by observation from the front and from an oblique angle. Observation from an oblique angle was performed by appropriately changing the azimuth angle from the front, i.e., from the direction of a polar angle of 45° with respect to the normal to the image display device. The image display devices of Comparative Examples 1 and 11, which used retardation film 4 without a random axis distribution, exhibited blackout when observed with circularly polarized glasses. On the other hand, the image display devices of Examples 1 to 3 and Examples 11 to 13, which used the depolarizing film of the present invention having retardation films 1 to 3 with random axis distributions, did not exhibit blackout. Among these, Examples 2 and 12, which were laminated with a λ / 4 wave plate (first retardation film) having a random axis distribution using a rod-like liquid crystal compound and a λ / 2 wave plate (second retardation film) having a random axis distribution using a rod-like liquid crystal compound, were preferable to Examples 1 and 11 in that they did not appear dark when viewed from the front. Furthermore, it was found that Examples 3 and 13, in which a λ / 4 wave plate (first retardation film) using a discotic liquid crystal compound and having a random axis distribution was laminated with a λ / 2 wave plate (second retardation film) using a rod-shaped liquid crystal compound and having a random axis distribution, were even more preferable because they did not appear dark even when viewed from an oblique direction.

[0117] The evaluation was carried out according to the following criteria: A: No blackout, no change in color. B: No blackout, but slight change in color. C: No blackout, but darkening and slight change in color. D: No blackout, but darkening and color change. E: Blackout occurs.

[0118]

[0119]

[0120] <Preparation of Depolarizing Layer Made of Highly Birefringent Material> A polyethylene terephthalate (PET) film having a thickness of 100 μm was prepared by the following method.

[0121] —Synthesis of Raw Material Polyesters— Raw Material Polyester 1— As shown below, raw material polyester 1 (Sb catalyst-based PET) was obtained in a continuous polymerization apparatus using a direct esterification method in which terephthalic acid and ethylene glycol were directly reacted to distill off water, followed by esterification and then polycondensation under reduced pressure.

[0122] (1) Esterification Reaction 4.7 tons of high-purity terephthalic acid and 1.8 tons of ethylene glycol were mixed in a first esterification reaction tank over 90 minutes to form a slurry, which was continuously supplied to the first esterification reaction tank at a flow rate of 3,800 kg / h. Furthermore, an ethylene glycol solution of antimony trioxide was continuously supplied, and the reaction was carried out at a reactor temperature of 250°C with stirring for an average residence time of approximately 4.3 hours. Antimony trioxide was continuously added so that the amount of Sb added was 150 ppm in terms of elemental value.

[0123] This reaction product was transferred to a second esterification reaction tank and reacted for an average residence time of 1.2 hours under stirring at a reaction tank temperature of 250° C. An ethylene glycol solution of magnesium acetate and an ethylene glycol solution of trimethyl phosphate were continuously supplied to the second esterification reaction tank so that the Mg and P addition amounts were 65 ppm and 35 ppm, respectively, in elemental equivalent values.

[0124] (2) Polycondensation Reaction The esterification reaction product obtained above was continuously supplied to a first polycondensation reactor, and the mixture was stirred at a reaction temperature of 270°C and a pressure inside the reactor of 20 torr (2.67 x 10 -3 The polycondensation was carried out at a pressure of 1.8 MPa for an average residence time of about 1.8 hours.

[0125] The mixture was then transferred to a second condensation reactor, where it was stirred at a temperature of 276°C and a pressure of 5 torr (6.67 x 10 -4 The reaction (polycondensation) was carried out under conditions of a pressure of 1.2 MPa and a residence time of about 1.2 hours.

[0126] Next, the mixture was transferred to a third polycondensation reactor, where the temperature inside the reactor was 278°C and the pressure inside the reactor was 1.5 torr (2.0 x 10 -4The mixture was reacted (polycondensed) under conditions of a pressure of 1.5 MPa and a residence time of 1.5 hours to obtain a reaction product (polyethylene terephthalate (PET)).

[0127] The resulting reaction product was then extruded into cold water in the form of strands and immediately cut into polyester pellets (cross section: major axis approximately 4 mm, minor axis approximately 2 mm, length approximately 3 mm). The resulting polymer had an intrinsic viscosity (IV) of 0.63. This polymer was designated Raw Material Polyester 1.

[0128] The intrinsic viscosity IV was determined by dissolving the raw material polyester 1 in a mixed solvent of 1,1,2,2-tetrachloroethane / phenol (=2 / 3 [mass ratio]) and measuring the solution viscosity in this mixed solvent at 25°C.

[0129] --Starting Material Polyester 2-- 10 parts by mass of dried ultraviolet absorber (2,2'-(1,4-phenylene)bis(4H-3,1-benzoxazinon-4-one) and 90 parts by mass of Starting Material Polyester 1 (IV=0.63) were mixed and processed using a kneading extruder to obtain Starting Material Polyester 2 containing an ultraviolet absorber.

[0130] -Film Forming Process- Raw material polyester 1 (90 parts by mass) and raw material polyester 2 (10 parts by mass) containing an ultraviolet absorber were dried to a moisture content of 20 ppm or less, then charged into hopper 1 of a 50 mm diameter single-screw kneading extruder 1 and melted at 300°C in extruder 1. The resulting mixture was extruded through a die via a gear pump and a filter (hole diameter 20 μm) under the following extrusion conditions. The molten resin was extruded through the die under the following extrusion conditions: a pressure fluctuation of 1% and a temperature distribution of the molten resin of 2%. Specifically, the back pressure was increased by 1% relative to the average pressure in the extruder barrel, and the extruder piping temperature was heated to a temperature 2% higher than the average temperature in the extruder barrel. The molten resin extruded through the die was extruded onto a cooling casting drum set at a temperature of 25°C and adhered to the cooling casting drum using an electrostatic application method. The resin was peeled off using a peeling roll arranged opposite the cooling casting drum to obtain unstretched polyester film 1.

[0131] —Transverse Stretching Step— —Preheating Section— The preheating temperature was set to 90° C., and the unstretched polyester film 1 coated with the polarizer-side easy-adhesion layer was heated to a temperature at which it could be stretched.

[0132] Stretching Section: The preheated unstretched polyester film 1 was introduced into a tenter (transverse stretching machine), and while holding the edges of the film with clips, it was transversely stretched in the TD direction (film width direction, transverse direction) by the following method and under the following conditions to obtain a transversely stretched polyester film 1. Conditions: Transverse stretching temperature: 90°C Transverse stretching ratio: 4.3 times

[0133] Heat Setting Section Next, a heat setting treatment was carried out while controlling the film surface temperature of the laterally stretched polyester film 1 to the following temperature: <Conditions> Heat setting temperature: 180°C Heat setting time: 15 seconds

[0134] --Heat Relaxation Section-- The laterally stretched polyester film 1 after heat setting was heated to the following temperature to relax the film: Heat relaxation temperature: 170°C Heat relaxation rate: 2% in TD direction (film width direction, lateral direction)

[0135] --Cooling Section-- Next, the laterally stretched polyester film 1 after heat relaxation was cooled at a cooling temperature of 50°C.

[0136] The in-plane retardation of the depolarizing layer 1 made of a highly birefringent material using the transversely stretched polyester film 1 after heat relaxation obtained in this manner was measured using an Axoscan, and the in-plane retardation at a wavelength of 550 nm was Re(550)=10,000 nm.

[0137] <Preparation of Image Display Device of Example 32> The prepared depolarizing layer 1 made of a highly birefringent material was attached to the surface of a commercially available image display device 1 via an adhesive. Retardation Film 1 and Retardation Film 2 were then transferred to prepare the image display device of Example 32. A blackout evaluation was performed, and it was found that no blackout occurred in the image display device of Example 32. The results are shown in Table 22. Furthermore, compared to the image display device of Example 2, which does not have a depolarizing layer 1 made of a highly birefringent material, Example 32 exhibited less visible glare and was therefore more preferable. The evaluation of glare was performed, similar to the evaluation of blackout, by observing from the front and from an oblique angle, and the degree of glare was determined visually. Observation from an oblique angle was performed from the front, i.e., from a direction at a polar angle of 45° relative to the normal to the image display device, while appropriately changing the azimuth angle.

[0138]

[0139] <Preparation of Retardation Film 13>

[0140] <Formation of Underlayer 6> The above-described underlayer 1 was prepared as a support, and underlayer coating solution 3 having the following composition was applied thereon using a wire bar coater of a suitable size selected so as to obtain a desired film thickness. After that, the film was dried at 25°C for 60 seconds, heat-treated at 90°C for 150 seconds, and then irradiated with 500 mJ / cm using an ultraviolet irradiator using a mercury lamp as an ultraviolet light source. 2 The substrate was irradiated with ultraviolet light of 1000 kJ / cm 2 at 1000 kJ / cm 2 to prepare a support having an underlayer 6. The coating thickness was adjusted so that the thickness of the underlayer 6 after curing would be 6 μm. In this process, a cholesteric liquid crystal layer was formed on the underlayer 1, which does not have any alignment control power for the liquid crystal, and therefore, an underlayer 6 consisting of a cholesteric liquid crystal layer with wavy alignment was obtained. The fact that the underlayer 6 was a cholesteric liquid crystal layer with wavy alignment was confirmed by observing the cross-sectional SEM image, where the light and dark lines were meandering.

[0141] [Undercoat Layer Coating Solution 3] The composition shown below was stirred and dissolved in a container kept at 70°C to prepare Undercoat Layer Coating Solution 3.

[0142] [Undercoat layer coating liquid 3] Methyl ethyl ketone 333.3 parts by mass Mixture X of the rod-like liquid crystal compound described above 100.0 parts by mass Chiral agent B described below 1.00 parts by mass Polymerizable monomer E1 described above 4.00 parts by mass Photopolymerization initiator (manufactured by BASF, Irgacure 907) 6.00 parts by mass Surfactant F1 described above 0.027 parts by mass Surfactant F2 described above 0.067 parts by mass

[0143] Chiral agent B

[0144] The above-described retardation layer coating solution 1 was applied onto the underlayer 6 using a wire bar coater. Thereafter, the film was dried at 25°C for 30 seconds, and then heated at 80°C for 120 seconds for liquid crystal alignment. Then, the film was irradiated with 500 mJ / cm2 at 40°C using an ultraviolet irradiation device using a mercury lamp as an ultraviolet light source. 2 The retardation film 13 was then irradiated with ultraviolet light of 1000 kJ / cm to form a retardation layer with a film thickness of 0.85 μm, thereby producing a retardation film 13. The retardation film 13 has positive birefringence. When the retardation film 13 was observed under a microscope, it was confirmed that the number of defects within a 283 μm × 188 μm field of view at a magnification of 50 times was 20.

[0145] <Preparation of Retardation Film 14> A retardation film 14 was prepared in the same manner as the retardation film 13, except that the thickness of the retardation layer was changed to 1.7 μm. The retardation film 14 has positive birefringence. When the retardation film 14 was observed under a microscope, it was confirmed that the number of defects within a 283 μm × 188 μm field of view at a magnification of 50 times was 10.

[0146] <Preparation of Image Display Devices of Examples 41 to 43> The prepared retardation films 13 and 14 were transferred to the surface of a commercially available image display device 1 via an adhesive to prepare the image display devices of Examples 41 and 42. Furthermore, the retardation films 13 and 14 were transferred in this order to the surface of the commercially available image display device 1 to prepare the image display device of Example 43. A blackout evaluation was performed, and it was found that the image display devices of Examples 41 to 43 did not exhibit blackout. The results are shown in Table 5. Furthermore, it was confirmed that the image display device of Examples 41 to 43 exhibited less visible glare than the image display device of Example 1, making them more preferable. The evaluation of glare was performed from the front and from an oblique angle, similar to the evaluation of blackout, and the degree of glare was determined visually. Observation from an oblique angle was performed from the front, i.e., from a direction at a polar angle of 45° relative to the normal to the image display device, by appropriately changing the azimuth angle.

[0147]

[0148] <Formation of Underlayer 2> A 100 μm thick PET film (Cosmoshine A4265, manufactured by Toyobo Co., Ltd.) was prepared as a support. This PET film had an easy-adhesion layer on one side. After rubbing treatment on the side of the PET film without the easy-adhesion layer, underlayer coating solution 2 having the following composition was applied to the surface using a wire bar coater of an appropriate size so as to obtain a target film thickness. Thereafter, the film was dried at 25° C. for 60 seconds, heat-treated at 90° C. for 150 seconds, and then irradiated with 500 mJ / cm using an ultraviolet irradiation device using a mercury lamp as an ultraviolet light source. 2 The substrate was irradiated with ultraviolet light of 1000 kJ / cm 2 to prepare a support having an underlayer 2. The coating thickness was adjusted so that the thickness of the underlayer 2 after curing would be 1 μm. During these processes, wind unevenness occurred during the drying process and streaks were generated due to the wire bar during the bar coating process, so an underlayer 2 consisting of a cholesteric liquid crystal layer with a film thickness distribution was obtained.

[0149] [Undercoat layer coating solution 2] The composition shown below was stirred and dissolved in a container kept at 70°C to prepare undercoat layer coating solution 2.

[0150] [Undercoat layer coating liquid 2] Methyl ethyl ketone 120.9 parts by mass Cyclohexanone 21.3 parts by mass Mixture X of the above rod-like liquid crystal compound 100.0 parts by mass Photopolymerization initiator C described below 1.00 parts by mass Chiral agent A described below 6.00 parts by mass Surfactant F4 described below 0.1 parts by mass

[0151] Chiral agent A

[0152] Surfactant F4

[0153] Photopolymerization initiator C

[0154] The chiral agent A is a chiral agent whose helical twisting power (HTP) is reduced by light. That is, this underlayer is a cholesteric liquid crystal.

[0155] <Formation of Underlayers 3 to 5> Underlayers 3 to 5 were formed in the same manner as underlayer 2, except that the underlayer thicknesses were set as shown in Table 6. By changing the underlayer thickness, it is possible to change the magnitude of the in-plane change in the orientation of the liquid crystal compound on the outermost surface of the underlayer, and to control the domain size.

[0156] <Preparation of Retardation Films 5 to 12> Retardation film 5 was prepared in the same manner as for retardation film 1, except that the base on which the retardation layer coating liquid was applied was changed from base layer 1 to base layer 2. Similarly, retardation films 6 to 12 were prepared in the same manner as for retardation film 1, except that the base layer and the retardation of the retardation layer were changed as shown in Table 6. That is, retardation films 7, 9, and 11 formed layers having the same thickness (i.e., the same retardation) as retardation film 1, and retardation films 6, 8, 10, and 12 formed layers having the same thickness as retardation film 2. The retardation and axial distribution (in-plane distribution of axial angle), as well as the domain size, of the prepared retardation films were measured in the same manner as for retardation film 1.

[0157]

[0158] <Preparation of depolarizing films of Examples 21 to 25 and Comparative Example 21> Depolarizing films (retardation films) of Examples 21 to 25 and Comparative Example 21 were prepared with the configurations shown in Table 7. Here, for the first and second layers, the respective retardation films were transferred onto transparent glass to form depolarizing films with a laminated configuration. The layering order was as follows: first, the retardation film shown in the first layer column of the table was transferred onto the glass, and then the retardation film shown in the second layer column was transferred.

[0159] <Evaluation> Visual evaluation was performed on the Examples and Comparative Examples using the following methods and criteria. A display that emits linearly polarized light (linearly polarized display) and a display that emits circularly polarized light (circularly polarized display) were prepared. A stripe pattern with a period of 1 cm and black and white widths of 0.5 cm each was displayed on the display. The depolarizing films of the Examples and Comparative Examples prepared were peeled from the glass, and a linear polarizer was attached to the surface of the first layer. The linear polarizer was placed on the eye side, and the display was observed from a distance of 1 m. Visual observation was evaluated in terms of blackout and image blur according to the following criteria.

[0160] <Evaluation of Blackout> Blackout of the observed image was evaluated according to the same evaluation criteria as in Example 1. However, the observation was carried out only from the front.

[0161] <Image blur> A: The stripe pattern is not blurred. B: The stripe pattern is slightly blurred. C: The stripe pattern is blurred, but not noticeable. D: The stripe pattern is significantly blurred. E: The stripe pattern cannot be identified.

[0162] The evaluation results are shown in Table 7. The evaluations of Examples 1 to 3, Examples 11 to 13, and Comparative Examples 1 and 11 described above correspond to a state in which the depolarizing film was placed near the image display device (pixels). In contrast, the evaluation method for the depolarizing films of Examples 21 to 25 and Comparative Example 21 correspond to a state in which the depolarizing film was placed near the eyes and observed at a distance from the image display device. In Comparative Example 21, which used retardation film 4 without a random axial distribution, blackout occurred when a circularly polarized display was observed. On the other hand, no blackout occurred when the depolarizing films of Examples 21 to 25 were used. Regarding image blur, when the depolarizing films of Examples 21 to 24 were used, image blur was noticeable but not noticeable. In Comparative Example 21, the stripe pattern was not visible when the circularly polarized display was observed, but this was due to blackout. Furthermore, when the depolarizing film of Example 25 was used, image blur occurred, but it was at a level that could be used in devices that do not require high image clarity. That is, in applications in which a depolarizing film is placed near the eyes and observed at a distance from an image display device, both blackout and image blur can be suitably suppressed by setting the domain size of the retardation film of the polarizing interference film of the present invention to 100 to 2000 μm.

[0163]

[0164] REFERENCE SIGNS LIST 1 depolarizing film 11 first retardation film 12 boundary line of first domain 13 slow axis 31 first retardation film 32 second retardation film 33 adhesive

Claims

1. A depolarizing film comprising a first retardation film having a liquid crystal compound and having a random axis distribution.

2. The depolarizing film according to claim 1, wherein the domain size of the first retardation film is defined as the autocorrelation length x 3, and the domain size is 1.5 to 30 μm.

3. The depolarizing film according to claim 1, wherein the domain size of the first retardation film is defined as the autocorrelation length x 3, and the domain size is 100 to 2000 μm.

4. The depolarizing film according to any one of claims 1 to 3, further comprising a second retardation film having a random axial distribution.

5. The depolarizing film according to claim 4, wherein the first retardation film has a retardation of 100 to 180 nm at a wavelength of 550 nm, and the second retardation film has a retardation of 230 to 320 nm at a wavelength of 550 nm.

6. The depolarizing film of claim 4, wherein the first retardation film has negative birefringence and the second retardation film has positive birefringence.

7. The depolarizing film according to any one of claims 1 to 3, further comprising a retardation layer having a retardation of 1,000 nm to 100,000 nm at a wavelength of 550 nm.

8. An image display device comprising the depolarizing film according to any one of claims 1 to 3.

9. The image display device according to claim 8, wherein the image display device uses a light source whose spectrum during white display has two or more maximum values ​​in the visible range, and the full width at half maximum of the peak corresponding to at least one of the maximum values ​​is 20 nm or less.

Images