Micro LED image display device

Abstract

A micro LED image display device in which a surface-protective film is laminated on the outermost surface of an image display portion, the in-plane retardation of the surface-protective film being 3,000-30,000 nm.

Description

Technical Field

[0001] The present invention relates to an LED image display device.

Background Art

[0002] In recent years, image display devices such as mini-LEDs and micro-LEDs (collectively referred to as micro-LEDs) using very small LEDs as RGB pixels have been launched on the market and have attracted attention for their color reproducibility, wide dynamic range, high brightness, wide viewing angle, and fast response speed (for example, Patent Document 1). This micro-LED image display device is characterized in that it can support a large screen with a screen size of 200 inches or more, and large screens are becoming mainstream.

[0003] In addition, on the outermost surface of an image display device, an anti-reflection function is provided, and a surface protection film is often laminated for protection and to prevent scattering of glass or the like. Similarly, a surface protection film is often used in a micro-LED image display device.

[0004] Generally, films used for surface protection of image display devices include films such as triacetyl cellulose (TAC), polycyclic olefin (COP), acrylic, and polyester. However, TAC has large dimensional changes due to environmental changes such as temperature and humidity and is not suitable for large screens. COP and acrylic have low impact resistance and poor workability for large films. There were problems like these. Polyester is less likely to have the above problems and has excellent characteristics as a surface protection film. However, due to its birefringence, external light reflection may cause rainbow unevenness and degrade the image quality. Generally, whether outdoors or indoors, ambient light often contains a polarized component due to reflection. This polarization is reflected by the surface protection film of a display having birefringence, resulting in stronger rainbow unevenness.

[0005] In particular, it has been found that micro-LED image display devices exhibit little decrease in brightness or color reproduction even when viewed from an oblique angle, making even slight iridescence caused by reflection of ambient light easily noticeable. Furthermore, due to their large size, they are often used in outdoor or semi-outdoor environments (spaces separated by roofs or walls but not by doors, etc.), such as airports, train stations, and large public facilities, where they are continuous with the outdoors. When viewing the screen through polarized sunglasses, iridescence caused by reflection of ambient light containing polarized components becomes more pronounced, making the degradation of image quality more noticeable. In addition, when viewing while wearing polarized sunglasses, in areas where the image is viewed from an oblique angle, light from the image is reflected at the interface of the surface protective film, sometimes causing the light from the image itself to become iridescent. Thus, micro-LED image display devices have had the problem of iridescence occurring when viewed from an oblique angle due to the surface protective film. Furthermore, because the black areas are a deeper black compared to LCD displays, rainbow-colored discoloration caused by external light reflection is more noticeable. Moreover, since the rainbow-colored discoloration caused by external light reflection does not disappear even when the power is turned off, there was a problem in that the appearance quality of the display device itself deteriorated.

[0006] Furthermore, in black display areas and when the power is off, not only are there rainbow-like unevenness in reflected light due to the polarization component of ambient light and birefringence, but interference colors due to light interference in the polyester film coating layer are also noticeable. These interference colors also cause a decrease in display image quality and a decline in the appearance quality of the display device itself. In particular, when used in shop windows, the lobbies of luxury hotels, or high-end stores, an excellent appearance is required even when the power is off in order to avoid damaging the brand value, and improving the appearance quality was also a requirement. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2021-67763 [Overview of the project] [Problems that the invention aims to solve]

[0008] The present invention aims to solve the above problems and provide a micro-LED image display device that reduces iridescence caused by the surface protective film and has excellent visibility in various installation locations. It also aims to provide a display device with an excellent appearance. [Means for solving the problem]

[0009] As a result of diligent research to achieve the above objective, the inventor has completed the inventions represented below. Item 1 A microLED image display device in which a surface protective film is laminated on the outermost surface of the image display portion, wherein the in-plane retardation of the surface protective film is 3000 nm or more and 30000 nm or less. Section 2 The micro-LED image display device according to item 1, wherein the Nz coefficient of the surface protective film is 1.78 or less. Section 3 The micro-LED image display device according to claim 1 or 2, wherein the surface protective film is a polyester film. Section 4 The micro-LED image display device according to any one of items 1 to 3, wherein the slow axis direction of the surface protective film is substantially parallel to the long side direction or the short side direction of the image display portion of the micro-LED image display device. Section 5 The micro-LED image display device according to any one of claims 1 to 4, wherein the surface protective film has a base film and a functional layer on its visible side. Section 6 The micro-LED image display device according to any one of claims 1 to 5, wherein the functional layer is at least one of an anti-reflective layer, a low-reflection layer, and an anti-glare layer. Section 7 The micro-LED image display device according to claim 5 or 6, having an easy-adhesion layer on the side of the functional layer of the base film. Section 8 The micro-LED image display device according to item 7, wherein the resin contained in the easy-adhesion layer is a resin having a naphthalene ring structure. Section 9 The micro-LED image display device according to item 7, wherein the easy-adhesion layer includes high refractive index particles. That is the case. [Effects of the Invention]

[0010] The present invention provides a micro-LED image display device that reduces iridescence originating from the surface protective film and exhibits excellent visibility in various installation locations. Furthermore, interference fringes originating from the coating layer are also reduced, resulting in a micro-LED image display device with an excellent appearance. [Modes for carrying out the invention]

[0011] (Micro LED image display device) In the micro-LED image display device of the present invention, it is preferable that light-emitting diodes are used as light-emitting elements for each of the red (R), green (G), and blue (B) colors.

[0012] I will now explain the emission spectrum of the device. The emission peak of the red light-emitting element is preferably 600-650 nm, more preferably 610-645 nm, and even more preferably 615-640 nm. The emission peak of the green light-emitting element is preferably 500-560 nm, more preferably 510-550 nm, and even more preferably 520-540 nm. The emission peak of the blue light-emitting element is preferably 410-470 nm, more preferably 420-460 nm, and even more preferably 425-450 nm. By setting the peak within this range, a wide range of color reproduction can be ensured, allowing for the display of vivid red, green, and blue colors, and further enabling power savings.

[0013] The full width at half maximum of the emission spectrum of the blue light-emitting element is preferably 30 nm or less, more preferably 25 nm or less, and still more preferably 20 nm or less. The full width at half maximum of the emission spectrum of the green light-emitting element is preferably 40 nm or less, more preferably 35 nm or less, and still more preferably 30 nm or less. The full width at half maximum of the emission spectrum of the red light-emitting element is preferably 50 nm or less, more preferably 45 nm or less, and still more preferably 40 nm or less. The lower limit of the full width at half maximum of the emission spectrum of each light-emitting element is preferably 5 nm or more, more preferably 8 nm or more, and still more preferably 10 nm or more. By setting it within the above range, a wide color reproducibility can be ensured, vivid colors can be displayed, and further power saving can be achieved.

[0014] When each color light-emitting element is used as a pixel of a display device, it is preferably used as a chip. In the present invention, the light-emitting element represents a light-emitting component such as a light-emitting diode, and the chip represents a component in which electrodes for connecting the light-emitting diode to the outside are connected by wiring and sealed with resin or the like to form one component. In the present invention, it may be an individual chip for each of R, G, and B colors, or a chip in which three-color light-emitting elements are integrated into one package.

[0015] The shape of the chip as viewed from the direction in which light is irradiated is not particularly limited, such as square, rectangular, rhombic, parallelogram, triangular, hexagonal, or a shape bent into a < shape. Among them, a rectangle is preferred. For each chip, if it is a rectangular or square chip, the long side is preferably 2 μm or more, more preferably 5 μm or more, still more preferably 7 μm or more. The long side is preferably 700 μm or less, more preferably 500 μm or less, still more preferably 300 μm or less, particularly preferably 250 μm or less. The ratio of the long side to the short side is preferably 1.2 to 5, more preferably 1.3 to 4, and 1.4 to 3. When the light-emitting element is other than rectangular, the preferred size is such that the maximum diameter (the value that is the maximum between any two points) is within the above range. Note that relatively large chips are sometimes called mini-LEDs, and small chips are sometimes called micro-LEDs, but the distinction between the two is not strict, and in the present invention, they are generically referred to as micro-LEDs (μLEDs).

[0016] In a micro-LED image display device, it is preferable to arrange and install the above chips of each color as an array aligned vertically and horizontally on a substrate. The substrate includes glass, ceramics, metals, resins such as phenolic resin, polyimide, polyamideimide, polyaramide, and fiber-reinforced resins, and may be a laminate of these. The substrate may be coated with silicon oxide, silicon nitride, etc. The chips on the substrate are connected to a drive circuit (IC) through the electrodes of the chips by wirings on the substrate. The wirings are separated by an interlayer insulating film in the thickness direction but are partially conductive and preferably have a three-dimensional structure. The lower limit of the thickness of the substrate is preferably 10 μm, more preferably 20 μm, still more preferably 30 μm. The upper limit of the thickness of the substrate is preferably 3000 μm, more preferably 2000 μm, still more preferably 1500 μm, particularly preferably 1000 μm, and most preferably 700 μm. For reinforcement, a resin plate, a metal plate, etc. may be further laminated on the substrate.

[0017] The display surface (visible side) of the circuit board on which the wiring and chips are arranged is preferably covered with a transparent resin to protect the wiring and chips from mechanical shock, humidity, corrosive gases, etc. Preferred transparent resins include UV-curable resins and thermosetting resins. Examples include UV-curable resins using acrylic resins, silicone resins, styrene resins, polycarbonate resins, polyolefin resins, etc., as base resins, and thermosetting resins such as epoxy resins, phenolic resins, unsaturated polyester resins, urea resins, melamine resins, diallyl phthalate resins, vinyl ester resins, polyimides, and polyurethanes. The thickness of the transparent resin is preferably such that the chip is completely covered, and the distance between the top surface of the chip and the top surface of the transparent resin layer is preferably 10 μm, more preferably 20 μm, and even more preferably 30 μm, with an upper limit of preferably 1000 μm, more preferably 700 μm, and even more preferably 500 μm. When the transparent resin has the above thickness, it is preferable to select one that has a transmittance of 90% or more across the entire visible light region.

[0018] Furthermore, it is preferable that the viewing side of the transparent resin is provided with a glass plate or transparent resin plate, such as a surface plate or window sheet. Additionally, a touch sensor may be placed on the viewing side of the surface plate or between the surface plate and the transparent resin layer. The surface plate may also be equipped with a touch sensor function.

[0019] (Surface protective film) In the present invention, it is preferable that a surface protection film is provided on the outermost surface of the viewing side of the micro-LED image display device. If a glass plate is used for the front panel or the like, the surface protection film is used not only as a shatterproof film in case the glass breaks, but also to provide functions such as scratch prevention and reduced reflection, making the image easier to see, by using a film with a hard coat, anti-reflective coating, or anti-glare coating. In a micro-LED image display device, a surface protective film may be placed directly on the transparent resin layer without using a front panel. Additionally, the surface protective film may be designed to be replaceable.

[0020] The surface protection film is preferably a laminated film having a base film and a functional layer, as described later, and preferably has an easy-adhesion layer between the base film and the functional layer. The surface protection film means a laminated film having a base film and a functional layer, and the base film includes the easy-adhesion layer if one is provided. When it is necessary to distinguish and explain the portion of the base film that does not include the easy-adhesion layer, it may be called a film roll.

[0021] (Optical properties) The base film used for the surface protection film preferably has an in-plane retardation (Re) of 3000 nm or more, more preferably 4500 nm or more, even more preferably 6000 nm or more, particularly preferably 6500 nm or more, and most preferably 7000 nm or more. Re is preferably 30000 nm or less, more preferably 20000 nm or less, even more preferably 15000 nm or less, particularly preferably 12000 nm or less, and most preferably 10000 nm or less. By setting the Re to the above range, it is possible to suppress iridescence when viewed from an oblique angle within a thickness range that makes the surface protection film easy to handle.

[0022] The retardation (Rth) in the thickness direction of the substrate film is preferably 3000 nm or more, more preferably 4500 nm or more, even more preferably 6000 nm or more, particularly preferably 6500 nm or more, and most preferably 7000 nm or more. Rth is preferably 30000 nm or less, more preferably 2000 nm or less, even more preferably 15000 nm or less, particularly preferably 13000 nm or less, and most preferably 11000 nm or less.

[0023] The Re / Rth of the base film is preferably 0.60 or higher, more preferably 0.70 or higher, even more preferably 0.80 or higher, particularly preferably 0.85 or higher, and most preferably 0.90 or higher. The Re / Rth is preferably 1.4 or lower, more preferably 1.3 or lower, even more preferably 1.2 or lower, particularly preferably 1.1 or lower, and most preferably 1.05 or lower. Setting it to the above values ​​or lower reduces the likelihood of problems such as breakage during film formation, processing, and lamination to image display devices, making stable production and processing easier.

[0024] The NZ coefficient of the base film is preferably 2.2 or less, more preferably 1.9 or less, even more preferably 1.70 or less, particularly preferably 1.65 or less, and most preferably 1.62 or less. Setting it to the above values ​​or less reduces the angle dependence of retardation when viewed from an oblique direction, and even if the Re is the same, iridescence can be suppressed over a wider range. The NZ coefficient is preferably 1.0 or more, more preferably 1.2 or more, and even more preferably 1.3 or more.

[0025] The upper limit of the degree of surface orientation (ΔP) of the base film is preferably 0.150, more preferably 0.0.140, even more preferably 0.135, particularly preferably 0.130, and most preferably 0.125. The lower limit of ΔP is preferably 0.100, more preferably 0.105.

[0026] By setting at least one of Re / Rth, the NZ coefficient, and ΔP within the above range, iridescence is suppressed over a wide area when viewed from an oblique direction, and problems such as breakage are less likely to occur during film formation, processing, and lamination to image display devices, making stable production and processing easier.

[0027] (Film slow phase axis direction) The slow phase axis direction of the base film is preferably 7 degrees or less with respect to the long side direction or short side direction when the base film is cut into a rectangle as a surface protective film, more preferably 5 degrees or less, even more preferably 3 degrees or less, and most preferably 2 degrees or less. To achieve this, the slow phase axis direction is preferably 7 degrees or less with respect to the MD direction (film formation flow direction) or TD direction (direction perpendicular to the MD direction) of the base film, more preferably 5 degrees or less, even more preferably 3 degrees or less, and most preferably 2 degrees or less. Furthermore, the variation in the slow phase axis direction of the base film is preferably 10 degrees or less, more preferably 8 degrees or less, even more preferably 6 degrees or less, particularly preferably 5 degrees or less, and most preferably 4 degrees or less.

[0028] The variation in the slow phase axis is measured using a molecular orientation meter at the center point in the film's width direction and at points every 100 mm in the width direction (perpendicular to the film flow direction) from the center point. The maximum and minimum values ​​of the obtained measurements are determined, and the difference between the maximum and minimum values ​​is defined as the variation. The slow phase axis direction is measured relative to the TD direction (width direction), and is evaluated by distinguishing between positive and negative values ​​for clockwise and counterclockwise rotation. Furthermore, if the surface protective film is a single sheet and the film's width direction is unknown, the above measurements should be taken along two adjacent edges of the film, and the value with the larger difference between the maximum and minimum values ​​should be adopted. This is because the variation in the slow phase axis direction is small in the MD direction of the film.

[0029] The resin used for the film base is not particularly limited as long as it exhibits birefringence due to orientation, but polyester, polycarbonate, and polystyrene are preferred, with polyester being particularly preferred, due to their ability to achieve high retardation and low moisture permeability and hygroscopicity. Preferred polyesters include polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polytetramethylene terephthalate (PBT), and polyethylene naphthalate (PEN), with PET and PEN being the most preferred. These polyesters may also contain copolymerized carboxylic acid components and glycol components other than the main components, but when the total amount of carboxylic acid components and glycol components is set at 100 mol%, the total amount of carboxylic acid components and glycol components other than the main components is preferably 10 mol% or less, more preferably 5 mol% or less, even more preferably 2 mol% or less, particularly preferably 1.5 mol% or less, and most preferably 1.2 mol% or less. Exceeding these limits may increase the thermal shrinkage rate. Note that the glycol components other than the main components include by-products such as diethylene glycol. Furthermore, since side reactions such as glycol dimerization cannot be completely avoided in the polymerization of polyester, the amount of glycol components other than the main components is preferably 0.1 mol% or more. The most preferable range for the amount of glycol components other than the main components is 0.2 to 1.0 mol%. The above-mentioned polyester is easy to handle because it is easily stretched at high magnification and has impact resistance. Furthermore, due to its low moisture permeability and low moisture absorption, it has a low rate of dimensional change due to environmental changes, and even when used as a surface protective film for large micro-LED image display devices of 200 inches or more or 300 inches or more, it can suppress warping of the display device and peeling of the surface protective film due to aging.

[0030] The thickness of the base film is preferably 25 μm or more, more preferably 40 μm or more, even more preferably 50 μm or more, and particularly preferably 60 μm or more. The thickness of the film is preferably 200 μm or less, more preferably 150 μm or less, even more preferably 120 μm or less, and particularly preferably 100 μm or less. By setting the thickness within the above range, the necessary optical properties such as Re and the strength as a surface protective film are ensured, resulting in a film that is easy to handle.

[0031] In the case of PET, the intrinsic viscosity (IV) of the resin constituting the film is preferably 0.5 to 1.50 dL / g. The lower limit of IV is more preferably 0.53 dL / g, and even more preferably 0.55 L / g. The upper limit of IV is more preferably 1.20 dL / g, even more preferably 1.00 dL / g, and particularly preferably 0.8 dL / g. In the case of PEN, the lower limit of IV is preferably 0.45 dL / g, more preferably 0.48 dL / g, even more preferably 0.50 dL / g, and particularly preferably 0.53 dL / g. The upper limit of IV is more preferably 1.00 dL / g, more preferably 0.80 dL / g, even more preferably 0.75 dL / g, and particularly preferably 0.70 dL / g. By setting the values ​​within the above ranges, a film with excellent mechanical strength, such as impact resistance, can be obtained, and it can be manufactured efficiently without placing a heavy load on the equipment.

[0032] The surface protection film should preferably have a light transmittance of 20% or less at a wavelength of 380 nm. More preferably, the light transmittance at 380 nm is 15% or less, even more preferably 10% or less, and particularly preferably 5% or less. If the light transmittance is 20% or less, deterioration due to ultraviolet light of the surface protection film, adhesive, bonding agent, transparent resin, etc. used can be suppressed. The transmittance is measured perpendicular to the plane of the film and can be measured using a spectrophotometer (for example, Hitachi U-3500).

[0033] Reducing the light transmittance of a surface protective film to 20% or less at a wavelength of 380 nm can be achieved by methods such as adding an ultraviolet absorber to the film base, applying a coating solution containing an ultraviolet absorber to the surface of the base film, adding an ultraviolet absorber to a functional layer, or appropriately adjusting the type, concentration, and thickness of the ultraviolet absorber. The ultraviolet absorber is a known substance. Examples of ultraviolet absorbers include organic ultraviolet absorbers and inorganic ultraviolet absorbers, but organic ultraviolet absorbers are preferred from the viewpoint of transparency.

[0034] Examples of organic ultraviolet absorbers include benzotriazole-based, benzophenone-based, cyclic iminoester-based, and combinations thereof.

[0035] To improve the slipperiness of the film base, it is preferable to add particles with an average particle size of 0.05 to 2 μm. Examples of particles include inorganic particles such as titanium dioxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, calcium phosphate, mica, hectorite, zirconia, tungsten oxide, lithium fluoride, and calcium fluoride, as well as organic polymer particles such as styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and silicone-based particles. The average particle size can be determined by the weight distribution value obtained by the Coulter counter method. These particles may be added to the entire film roll, or they may be added only to the skin layer in a co-extruded multilayer skin-core structure. Alternatively, it is preferable that the film roll itself does not contain particles, and the particles are added to the easy-adhesion layer described later. When adding particles to the resin of a film base, there are two methods: using a raw resin that has already been manufactured with added particles, or using a masterbatch in which particles have been added at a high concentration during film formation. In either method, if the amount of particle aggregates increases, the haze may decrease or the surface roughness may increase. It is preferable to remove these particle aggregates using filters during the manufacturing of the raw resin or masterbatch. Furthermore, it is preferable to install a filter in the molten resin line during film formation to remove particle aggregates.

[0036] The base film can be obtained according to general film manufacturing methods. We will explain using the case where the film is PET as an example. In the following description of the manufacturing method, the base film may sometimes be referred to as polyester film. For example, one method for manufacturing polyester film involves melting polyester resin, extruding it into a sheet, stretching the unoriented polyester in the longitudinal or transverse direction at a temperature above the glass transition temperature, and then subjecting it to heat treatment.

[0037] The base film may be uniaxially oriented or biaxially oriented, but uniaxial oriented is preferred because, if the biaxiality is strong, a greater thickness is required to ensure the necessary Re, and it is easier to set the Re / Rth and NZ coefficient within an appropriate range.

[0038] The main orientation axis of the base film may be the direction in which the film runs (sometimes called the longitudinal direction or MD direction) or a direction perpendicular to the longitudinal direction (sometimes called the orthogonal direction or TD direction). Roll stretching is preferred for MD stretching, and tenter stretching is preferred for TD stretching. Tenter stretching is the preferred method in terms of the low number of scratches on the film surface, productivity, and lamination with a polarizer stretched from PVA.

[0039] In stretching, the unstretched film is preheated and stretched, preferably at 80-130°C, more preferably at 90-120°C. The stretching ratio is preferably 3.6-7.0 times in the main stretching direction, more preferably 3.8-6.5 times, even more preferably 4.0 to 6.2 times, and particularly preferably 4.1 to 6 times. Furthermore, to further enhance uniaxiality, it is preferable to shrink the material in a direction perpendicular to the stretching direction during stretching. In the case of TD stretching with a tenter, shrinkage can be achieved, for example, by narrowing the tenter clip spacing. The shrinkage treatment is preferably 1-20%, and more preferably 2-15%.

[0040] When biaxial stretching is performed, in order to ensure the above optical properties are within an appropriate range, it is preferable to perform the above as the main stretch, and before the main stretch, stretch in a direction perpendicular to the main stretch by 1.2 times or less, more preferably 1.15 times or less, and particularly preferably 1.13 times or less. The lower limit of the stretching ratio in the perpendicular direction is preferably 1.01 times, more preferably 1.03 times, and particularly preferably 1.05 times.

[0041] It is preferable to perform heat setting after stretching. The heat setting temperature is preferably 150 to 230°C, and more preferably 170 to 220°C. In heat setting, it is also preferable to perform a relaxation treatment in the main stretching direction or in a direction perpendicular thereto. The relaxation treatment is preferably 0.5 to 10%, and more preferably 1 to 5%.

[0042] To reduce variations in the slow phase axis direction of the film, it is preferable to adjust the stretching speed and temperature in the stretching-to-heat setting process so that the bowing phenomenon is minimized, and to adjust the airflow so that the temperature of the film is uniform in the TD direction.

[0043] The film roll may be subjected to treatments that improve adhesion, such as corona treatment, flame treatment, or plasma treatment.

[0044] (Easy adhesion layer) The base film may have an easy-adhesion layer. The easy-adhesion layer improves adhesion to the functional layer described later and to adhesives used when bonding to the display device surface, preventing the surface protective film itself and the functional layer from peeling off during long-term use. The resin used in the easy-adhesion layer can be polyester resin, polyurethane resin, polycarbonate resin, or acrylic resin, with polyester resin, polyester polyurethane resin, polycarbonate polyurethane resin, or acrylic resin being preferred. The easy-adhesion layer is preferably crosslinked. Examples of crosslinking agents include isocyanate compounds, melamine compounds, epoxy resins, and oxazoline compounds.

[0045] The easy-adhesion layer can be formed by applying and drying a coating made of these resins and, if necessary, crosslinking agents, particles, etc., onto the surface protective film. Examples of particles include those used in the aforementioned substrates.

[0046] The thickness of the easy-adhesion layer is preferably 10 nm at the lower limit, more preferably 15 nm, and even more preferably 20 nm. The upper limit of the thickness is preferably 500 nm, more preferably 300 nm, even more preferably 200 nm, and particularly preferably 150 nm. The thickness of the easy-adhesion layer may also be controlled by the amount applied.

[0047] When a surface protective film has an easy-adhesion layer, interference occurs between reflected light at the interface between the easy-adhesion layer and the film substrate and reflected light at the interface on the opposite side of the easy-adhesion layer from the film substrate (the interface with the functional layer, adhesive layer, or tack layer). This interference color may occur in areas where the thickness of the easy-adhesion layer is uneven. This interference color is noticeable in black display areas or when the power is turned off. To suppress this interference color, it is preferable to reduce the interference.

[0048] To reduce interference, it is preferable to bring the refractive index of the easy-adhesion layer closer to the refractive index of the film base. In the present invention, the film base has birefringence, and when the refractive index of the film base in the phase-advancing axis direction is nf and the refractive index in the phase-lagging axis direction is nl, the refractive index n of the easy-adhesion layer is preferably nf-0.05≦n≦nl+0.05, more preferably nf-0.02≦n≦nl+0.02, and even more preferably nf≦n≦nl.

[0049] For example, if the film base is polyethylene terephthalate, the refractive index in the phase-advancing axis direction is about 1.6 and the refractive index in the phase-lagging axis direction is about 1.7. Therefore, the refractive index of the easy-adhesion layer has a lower limit of preferably 1.55, more preferably 1.57, more preferably 1.58, even more preferably 1.59, and particularly preferably 1.60. The refractive index of the easy-adhesion layer has an upper limit of preferably 1.75, more preferably 1.73, more preferably 1.72, even more preferably 1.71, and particularly preferably 1.70.

[0050] The refractive index of the easy-adhesion layer may exhibit birefringence when stretched after coating as an in-line coat. In that case, the refractive index of the easy-adhesion layer is the average refractive index in the phase-advancing axis direction and the phase-lagging axis direction. The refractive index of the easy-adhesion layer can be measured, for example, by applying the coating solution of the easy-adhesion layer to a glass plate or the like, drying it, and measuring it with an ellipsometer or the like.

[0051] To achieve the above refractive index range, it is preferable to adjust the refractive index of the resin used in the easy-adhesion layer or to add high refractive index particles. If a resin is used, the refractive index can be increased by aromatic components, so it is preferable to use a resin having a benzene ring or a naphthalene ring in the main chain or side chain, and especially a resin having a naphthalene ring. Specifically, polyester copolymerized with naphthalenedicarboxylic acid is preferred. Polyester copolymerized with naphthalenedicarboxylic acid may be used as a polyester resin, blended with other resins as needed. It may also be used as a polyester polyol for polyester polyurethane. The naphthalenedicarboxylic acid component in the polyester is preferably 30 to 90 mol%, and more preferably 40 to 80 mol%, when the total silica component is 100 mol%.

[0052] The lower limit of the refractive index of the high refractive index particles is preferably 1.7, more preferably 1.75. The upper limit of the refractive index of the high refractive index particles is preferably 3.0, more preferably 2.7, and even more preferably 2.5. As high refractive index particles, particles containing metal oxides with a high refractive index are preferred. Examples of such metal oxides include TiO2 (refractive index 2.7), ZnO (refractive index 2.0), Sb2O3 (refractive index 1.9), SnO2 (refractive index 2.1), ZrO2 (refractive index 2.4), Nb2O5 (refractive index 2.3), CeO2 (refractive index 2.2), Ta2O5 (refractive index 2.1), Y2O3 (refractive index 1.8), La2O3 (refractive index 1.9), In2O3 (refractive index 2.0), Cr2O3 (refractive index 2.5), and composite oxides containing these metal atoms. Among these, SnO2 particles, TiO2 particles, ZrO2 particles, and TiO2-ZrO2 composite particles are preferred.

[0053] The average particle size of the high refractive index particles is preferably 5 nm or larger, more preferably 10 nm or larger, even more preferably 15 nm or larger, and particularly preferably 20 nm or larger. An average particle size of 5 nm or larger is preferable because it makes aggregation less likely.

[0054] The average particle size of the high refractive index particles is preferably 200 nm or less, more preferably 150 nm or less, even more preferably 100 nm or less, and particularly preferably 60 nm or less. An average particle size of 200 nm or less is preferable for good transparency. The average particle size of the added particles can be measured using dynamic light scattering and determined using the cumulant method.

[0055] The content of high refractive index particles in the easy-adhesion layer is preferably 2% by mass or more, more preferably 3% by mass or more, even more preferably 4% by mass or more, and particularly preferably 5% by mass or more. A content of 2% by mass or more of high refractive index particles in the coating layer is preferable because it allows for a high refractive index in the coating layer, effectively achieving low coherence.

[0056] The content of high refractive index particles in the easy-adhesion layer is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and particularly preferably 20% by mass or less. A content of particle A in the coating layer of 50% by mass or less is preferable as it maintains film-forming properties.

[0057] The easy-adhesion layer may be applied offline to the stretched film, but it is preferable to apply it in-line during the film-making process. When applied in-line, it may be applied before longitudinal stretching or transverse stretching, but it is preferable to apply it immediately before transverse stretching and dry and crosslink it in a preheating, heating, and heat treatment process using a tenter. If in-line coating is applied immediately before longitudinal stretching by rolls, it is preferable to dry the film in a vertical dryer after coating before guiding it to the stretching rolls. The easy-adhesion layer is provided on at least one side, preferably both sides.

[0058] (Functional layer) It is also preferable for the surface protection film to have functional layers such as a hard coat layer, anti-reflective layer, low-reflection layer, anti-glare layer, and anti-static layer on the viewing side of the film. The anti-reflective layer, low-reflection layer, and anti-glare layer are collectively called the reflection reduction layer. The reflection reduction layer not only prevents external light from reflecting onto the display screen and making it difficult to see, but also suppresses reflection at the interface, reducing iridescence and making it less noticeable.

[0059] The upper limit of the 5-degree reflectance of the surface protective film at a wavelength of 550 nm, measured from the anti-reflection layer side, is preferably 5%, more preferably 4%, even more preferably 3%, particularly preferably 2%, and most preferably 1.5%. Exceeding this limit may increase the reflection of ambient light, potentially reducing the visibility of the screen. The lower limit of the reflectance is preferably not particularly defined, but from a practical standpoint, it is preferably 0.01%, and even more preferably 0.1%. There are various types of anti-reflective layers, including low-reflection layers, anti-reflective layers, and anti-glare layers.

[0060] A low-reflectance layer is a layer that reduces reflectivity by minimizing the refractive index difference with air, achieved by providing a low-refractive-index layer on the surface of the base film.

[0061] (Anti-reflection layer) The anti-reflective layer is a layer that controls reflection by controlling the thickness of the low refractive index layer and interfering the reflected light between the upper interface of the low refractive index layer (the interface between the low refractive index layer and air) and the lower interface of the low refractive index layer (for example, the interface between the substrate film and the low refractive index layer). In this case, the thickness of the low refractive index layer is preferably about the wavelength of visible light (400-700 mN) / (refractive index of the low refractive index layer × 4). It is also preferable to provide a high refractive index layer between the anti-reflective layer and the base film. Alternatively, two or more low-refractive-index and high-refractive-index layers may be provided to further enhance the anti-reflective effect through multiple interference.

[0062] In the case of an anti-reflective layer, the upper limit of the reflectance is preferably 2%, more preferably 1.5%, even more preferably 1.2%, and particularly preferably 1%.

[0063] (Low refractive index layer) The refractive index of the low refractive index layer is preferably 1.45 or less, and more preferably 1.42 or less. Furthermore, the refractive index of the low refractive index layer is preferably 1.20 or more, and more preferably 1.25 or more. Note that the refractive index of the low refractive index layer is the value measured under the condition of a wavelength of 589 nm.

[0064] The thickness of the low refractive index layer is not limited, but it can usually be set appropriately within the range of approximately 30 nm to 1 μm. Furthermore, if the purpose is to cancel out the reflection from the surface of the low refractive index layer and the interfacial reflection between the low refractive index layer and the layer inside it (substrate film, hard coat layer, etc.) to further reduce the reflectivity, the thickness of the low refractive index layer is preferably 70 to 120 nm, and more preferably 75 to 110 nm.

[0065] Examples of low refractive index layers include (1) a layer made of a resin composition containing a binder resin and low refractive index particles, (2) a layer made of a fluororesin which is a low refractive index resin, (3) a layer made of a fluororesin composition containing silica or magnesium fluoride, and (4) a thin film of a low refractive index substance such as silica or magnesium fluoride.

[0066] The binder resin contained in the resin composition of (1) can be polyester, polyurethane, polyamide, polycarbonate, acrylic, etc., without any particular limitations. Among these, acrylic is preferred, and it is preferable that it is obtained by polymerizing (crosslinking) a photopolymerizable compound by light irradiation.

[0067] Examples of photopolymerizable compounds include photopolymerizable monomers, photopolymerizable oligomers, and photopolymerizable polymers, which can be used after being appropriately adjusted. A combination of a photopolymerizable monomer and a photopolymerizable oligomer or photopolymer is preferred as the photopolymerizable compound. These photopolymerizable monomers, photopolymerizable oligomers, and photopolymerizable polymers are preferably polyfunctional.

[0068] Examples of polyfunctional monomers include pentaerythritol triacrylate (PETA), dipentaerythritol hexaacrylate (DPHA), pentaerythritol tetraacrylate (PETTA), and dipentaerythritol pentaacrylate (DPPA). Monofunctional monomers may also be used in combination to adjust coating viscosity and hardness.

[0069] Examples of polyfunctional oligomers include polyester (meth)acrylate, urethane (meth)acrylate, polyester-urethane (meth)acrylate, polyether (meth)acrylate, polyol (meth)acrylate, melamine (meth)acrylate, isocyanurate (meth)acrylate, epoxy (meth)acrylate, and the like.

[0070] Examples of polyfunctional polymers include urethane (meth)acrylate, isocyanurate (meth)acrylate, polyester-urethane (meth)acrylate, and epoxy (meth)acrylate.

[0071] In addition to the above components, the coating agent may also contain polymerization initiators, crosslinking catalysts, polymerization inhibitors, antioxidants, UV absorbers, leveling agents, surfactants, and the like.

[0072] Examples of low refractive index particles included in the resin composition of (1) include silica particles (e.g., hollow silica particles) and magnesium fluoride particles, with hollow silica particles being preferred. Such hollow silica particles can be produced, for example, by the manufacturing method described in the examples of Japanese Patent Application Publication No. 2005-099778.

[0073] The average particle size of the primary particles of the low refractive index particles is preferably 5 to 200 nm, more preferably 5 to 100 nm, and even more preferably 10 to 80 nm.

[0074] Low refractive index particles are more preferably surface-treated with a silane coupling agent, and among these, those surface-treated with a silane coupling agent having a (meth)acryloyl group are preferred.

[0075] The content of low refractive index particles in the low refractive index layer is preferably 10 to 250 parts by mass, more preferably 50 to 200 parts by mass, and even more preferably 100 to 180 parts by mass, per 100 parts by mass of binder resin.

[0076] (2) As the fluororesin, a polymerizable compound or polymer thereof containing at least a fluorine atom in its molecule can be used. The polymerizable compound is not particularly limited, but those having curing reactive groups such as photopolymerizable functional groups and thermosetting polar groups are preferred. Compounds having multiple curing reactive groups simultaneously are also acceptable. The polymer of this polymerizable compound does not have the above-mentioned curing reactive groups, etc.

[0077] As compounds having photopolymerizable functional groups, for example, fluorine-containing monomers having ethylenically unsaturated bonds can be widely used.

[0078] To improve fingerprint resistance, it is also preferable to appropriately add known polysiloxane-based or fluorine-based antifouling agents to the low refractive index layer.

[0079] The surface of the low refractive index layer may be uneven to provide anti-glare properties, but a smooth surface is also preferable. When the surface of the low refractive index layer is smooth, the arithmetic mean roughness SRa (JIS B0601:1994) of the surface of the low refractive index layer is preferably 20 nm or less, more preferably 15 nm or less, even more preferably 10 nm or less, and particularly preferably 1 to 8 nm. Furthermore, the ten-point mean roughness Rz (JIS B0601:1994) of the surface of the low refractive index layer is preferably 160 nm or less, and more preferably 50 to 155 nm.

[0080] The refractive index of the high refractive index layer is preferably 1.55 to 1.85, and more preferably 1.56 to 1.70. Note that the refractive index of the high refractive index layer is the value measured under the condition of a wavelength of 589 nm.

[0081] The thickness of the high refractive index layer is preferably 30 to 200 nm, and more preferably 50 to 180 nm. The high refractive index layer may consist of multiple layers, but two or fewer layers are preferred, and a single layer is more preferred. In the case of multiple layers, it is preferable that the sum of the thicknesses of the multiple layers is within the above range.

[0082] When there are two high refractive index layers, it is preferable to make the refractive index of the high refractive index layer on the low refractive index layer side higher. Specifically, the refractive index of the high refractive index layer on the low refractive index layer side is preferably 1.60 to 1.85, and the refractive index of the other high refractive index layer is preferably 1.55 to 1.70.

[0083] The high refractive index layer is preferably composed of a resin composition containing high refractive index particles and resin. Among these, antimony pentoxide particles, zinc oxide particles, titanium oxide particles, cerium oxide particles, tin-doped indium oxide particles, antimony-doped tin oxide particles, yttrium oxide particles, and zirconium oxide particles are preferred as high refractive index particles. Of these, titanium oxide particles and zirconium oxide particles are particularly preferred.

[0084] Two or more types of high refractive index particles may be used in combination. In particular, adding a first high refractive index particle and a second high refractive index particle with a lower surface charge is preferable to prevent aggregation. Furthermore, surface treatment of the high refractive index particles is also preferable from the viewpoint of dispersibility.

[0085] The preferred average particle size of the primary particles of high refractive index particles is similar to that of low refractive index particles.

[0086] The content of high refractive index particles is preferably 30 to 400 parts by mass, more preferably 50 to 200 parts by mass, and even more preferably 80 to 150 parts by mass, per 100 parts by mass of resin.

[0087] The resins used in the high refractive index layer are the same as those listed for the low refractive index layer, with the exception of fluororesins.

[0088] In order to make the low refractive index layer, which is provided on top of the high refractive index layer, flat, it is preferable that the surface of the high refractive index layer is also flat. The method for making the surface of the low refractive index layer flat described above is used as a method for making the surface of the high refractive index layer flat.

[0089] High refractive index layers and low refractive index layers can be formed, for example, by applying a resin composition containing a photopolymerizable compound to a substrate film, drying it, and then irradiating the resin composition in the form of a coating with light such as ultraviolet light to polymerize (crosslink) the photopolymerizable compound.

[0090] The resin compositions for the high refractive index layer and the low refractive index layer may optionally contain thermoplastic resins, thermosetting resins, solvents, and polymerization initiators. Furthermore, dispersants, surfactants, antistatic agents, silane coupling agents, thickeners, color inhibitors, colorants (pigments, dyes), defoamers, leveling agents, flame retardants, UV absorbers, adhesion promoters, polymerization inhibitors, antioxidants, surface modifiers, lubrication agents, etc., may also be added.

[0091] (Anti-glare layer) An anti-glare layer is a layer that reduces glare by creating irregularities on its surface to cause diffuse reflection, thereby preventing the reflection of the light source's shape when external light is reflected off the surface.

[0092] The arithmetic mean roughness (SRa) of the surface irregularities of the anti-glare layer is preferably 0.02 to 0.25 μm, more preferably 0.02 to 0.15 μm, and even more preferably 0.02 to 0.12 μm.

[0093] The ten-point average roughness (Rzjis) of the surface irregularities of the anti-glare layer is preferably 0.15 to 2.00 μm, more preferably 0.20 to 1.20 μm, and even more preferably 0.30 to 0.80 μm.

[0094] SRa and Rzjis are calculated from the roughness curve measured using a contact-type roughness meter in accordance with JIS B0601-1994 or JIS B0601-2001.

[0095] Examples of methods for providing an anti-glare layer to a base film include the following: • Apply a paint containing particles (fillers), etc., for anti-glare purposes. The anti-glare layer resin is cured while in contact with a mold having an uneven structure. • The anti-glare layer resin is applied to a mold having an uneven structure and then transferred to a base film. • Apply paints that undergo spinodal decomposition during drying and film formation.

[0096] The lower limit of the anti-glare layer thickness is preferably 0.1 μm, more preferably 0.5 μm. The upper limit of the anti-glare layer thickness is preferably 100 μm, more preferably 50 μm, and even more preferably 20 μm.

[0097] The refractive index of the anti-glare layer is preferably 1.20 to 1.80, and more preferably 1.40 to 1.70. When a low-reflection effect is sought by lowering the refractive index of the anti-glare layer itself, the refractive index of the anti-glare layer is preferably 1.20 to 1.45, and more preferably 1.25 to 1.40. When a low refractive index layer, as described later, is provided on top of the anti-glare layer, the refractive index of the anti-glare layer is preferably 1.50 to 1.80, and more preferably 1.55 to 1.70. Note that the refractive index of the anti-glare layer is the value measured under conditions of a wavelength of 589 nm.

[0098] A low refractive index layer can be made into an anti-glare, low-reflectance layer by providing irregularities, or a low refractive index layer can be made into an anti-glare, anti-reflective layer by providing an anti-reflective function on top of the irregularities.

[0099] (Hard coat layer) A preferred configuration is to provide a hard coat layer as a lower layer to the above-mentioned anti-reflection layer. The hard coat layer is preferably H or higher on a pencil hardness scale, and more preferably 2H or higher. The hard coat layer can be provided, for example, by applying and curing a composition solution of a thermosetting resin or a radiation-curable resin.

[0100] Examples of thermosetting resins include acrylic resins, urethane resins, phenolic resins, urea-melamine resins, epoxy resins, unsaturated polyester resins, silicone resins, and combinations thereof. A curing agent is added to these thermosetting resin compositions as needed.

[0101] Radiation-curable resins are preferably compounds having radiation-curable functional groups. Examples of radiation-curable functional groups include ethylenically unsaturated bonding groups such as (meth)acryloyl groups, vinyl groups, and allyl groups, as well as epoxy groups and oxetanyl groups. Of these, ionizing radiation-curable compounds are preferably compounds having ethylenically unsaturated bonding groups, more preferably compounds having two or more ethylenically unsaturated bonding groups, and even more preferably polyfunctional (meth)acrylate compounds having two or more ethylenically unsaturated bonding groups. Polyfunctional (meth)acrylate compounds may be monomers, oligomers, or polymers.

[0102] Specific examples of these include the binder resins mentioned above. To achieve the hardness required for a hard coat, it is preferable that the compound having radiation-curable functional groups contains 50% or more by mass of two- or more functional monomers, and more preferably 70% or more by mass. Furthermore, it is preferable that the compound having radiation-curable functional groups contains 50% or more by mass of three- or more functional monomers, and more preferably 70% or more by mass. The above-mentioned compounds having radiation-curable functional groups can be used individually or in combination of two or more.

[0103] The thickness of the hard coat layer is preferably in the range of 0.1 to 100 μm, and more preferably in the range of 0.8 to 20 μm.

[0104] The refractive index of the hard coat layer is more preferably 1.45 to 1.70, and even more preferably 1.50 to 1.60. Note that the refractive index of the hard coat layer is the value measured under conditions of a wavelength of 589 nm.

[0105] To adjust the refractive index of the hard coat layer, methods include adjusting the refractive index of the resin, or, if particles are added, adjusting the refractive index of the particles. Examples of particles include those used in the anti-glare layer. In this invention, the hard coat layer may also be referred to as the reflection reduction layer.

[0106] When a functional layer is provided on the surface protective film, it is preferable to provide the functional layer in contact with the easily adhesive layer surface of the base film, resulting in a configuration of base film / easily adhesive layer / functional layer.

[0107] The surface protection film is preferably bonded to the surface of the image display portion of the μLED image display device using an adhesive. A substrate-less optical adhesive is preferred. One release film of the optical adhesive, which has release films bonded to both sides of the adhesive layer, is peeled off and bonded to the side of the surface protection film opposite to the functional layer, and then the other release film is peeled off and it is bonded to the microLED image display device.

[0108] While the size of the micro-LED image display device is not limited, the diagonal length is preferably 50 inches or more, more preferably 80 inches or more, even more preferably 100 inches or more, and particularly preferably 120 inches or more. The diagonal length is preferably 1000 inches or less, more preferably 700 inches or less, and even more preferably 500 inches or less.

[0109] The slow phase axis direction of the surface protective film is preferably aligned approximately parallel to the long or short side direction of the micro-LED image display device, but it is more preferable to align it approximately parallel to the short side direction. Iridescence tends to appear relatively strongly in the fast phase axis direction at a 20-50 degree angle to the slow phase axis direction and at a 50-70 degree angle to the normal direction of the film. By aligning the slow phase axis direction to the short side direction of the screen, it is possible to avoid directions in which iridescence is likely to appear when viewing the installed micro-LED image display device from an oblique angle, which is often from a horizontal oblique angle. In addition, the four corners can be avoided from directions in which iridescence is likely to appear. Furthermore, when the short side of the micro-LED image display device is installed horizontally, it is also preferable to align the slow phase axis direction of the surface protective film to the long side direction of the screen. In this context, "approximately parallel" preferably means allowing an error of 7 degrees or less, more preferably 5 degrees or less, and even more preferably 3 degrees or less. [Examples]

[0110] (1) Refractive index of polyester film Using a molecular orientation meter (MOA-6004, manufactured by Oji Instruments Co., Ltd.), the slow phase axis direction of the film was determined, and a 4cm x 2cm rectangle was cut out so that the slow phase axis direction was parallel to the longer side, and this was used as a sample for measurement. For this sample, the refractive index in two orthogonal axes (refractive index in the direction of the slow phase axis: ny, and refractive index in the direction perpendicular to the slow phase axis: nx), and the refractive index in the thickness direction (nz) were determined using an Abbe refractometer (NAR-4T, manufactured by Atago, measurement wavelength 589nm).

[0111] (2) In-plane retardation (Re) In-plane retardation is a parameter defined by the product (△Nxy × d) of the anisotropy of the refractive indices of two orthogonal axes on the film (△Nxy = nx - ny) and the film thickness d (nm), and is a measure of optical isotropy and anisotropy. The anisotropy of the refractive indices of the two axes (△Nxy) was determined by the method in (1) above, and the difference in refractive indices of the two axes (|nx - ny|) was calculated as the refractive index anisotropy (△Nxy). The film thickness d (nm) was measured using an electric micrometer (Millitron 1245D, manufactured by FineLewf Co., Ltd.), and the unit was converted to nm. Retardation (Re) was determined from the product (△Nxy × d) of the refractive index anisotropy (△Nxy) and the film thickness d (nm). nx is the refractive index in the direction orthogonal to the in-plane slow axis, ny is the refractive index in the direction of the in-plane slow axis, and nz is the refractive index in the thickness direction. In the example, a sample was cut from the center of the TD direction of a film in which the TD direction is parallel to the slow phase axis direction and measured.

[0112] (3) Thickness direction retardation (Rth) Thickness retardation is a parameter that represents the average retardation obtained by multiplying the two birefringences △Nxz (=|nx-nz|) and △Nyz (=|ny-nz|) as viewed from a cross-section in the thickness direction of the film by the film thickness d. nx, ny, nz and the film thickness d (nm) were determined using the same method as for measuring retardation, and the thickness retardation (Rth) was determined by calculating the average value of (△Nxz×d) and (△Nyz×d).

[0113] (4) NZ coefficient nx, ny, and nz were determined using the same method as for retardation measurements, and the Nz coefficient was calculated by substituting nx, ny, and nz into the formula Nz coefficient = |ny-nz| / |ny-nx|.

[0114] (5)ΔP nx, ny, and nz were determined using the same method as for retardation measurements, and the Nz coefficient was calculated by substituting nx, ny, and nz into the equation ΔP = (nx + ny) / 2 - nz.

[0115] (6) Variation in the slow axis The slow phase axis direction was measured using a molecular orientation meter (MOA-6004, manufactured by Oji Instruments Co., Ltd.). Measurements were taken at the center point in the width direction of a film cut into single sheets as a surface protection film, and at 100 mm intervals in the width direction (perpendicular to the film flow direction) from the center point. The maximum and minimum values ​​of the obtained measurements were determined, and the variation of the slow phase axis was evaluated using the following formula. (Variation of the lagging axis) = (Maximum value of the measured value - Minimum value of the measured value) The slow phase axis direction was measured relative to the TD direction (width direction), and evaluation was performed by distinguishing between positive and negative values ​​for clockwise and counterclockwise rotation.

[0116] (7) Light transmittance at a wavelength of 380 nm Using a spectrophotometer (Hitachi, Ltd., U-3500 model), the light transmittance in the wavelength range of 300-500 nm was measured with the air layer as a standard, and the light transmittance at a wavelength of 380 nm was determined. (8) Intrinsic viscosity The solution was dissolved in 50 ml of a phenol / 1,1,2,2-tetrachloroethane (60 / 40 (weight ratio)) mixed solvent and measured using an Ostwald viscometer at 30°C.

[0117] Polyester X (PET(X)) Polyethylene terephthalate with an intrinsic viscosity of 0.62 dL / g Polyester Y (PET(Y)) A molten mixture of 10 parts by mass of the ultraviolet absorber (2,2'-(1,4-phenylene)bis(4H-3,1-benzoxazinon-4-one) and 90 parts by mass of PET(X).

[0118] (Polymerization of copolymerized polyester resin) In a stainless steel autoclave equipped with a stirrer, thermometer, and partial reflux condenser, 381 parts by mass of dimethyl naphthalate, 58.3 parts by mass of dimethyl terephthalate, 41.5 parts by mass of dimethyl-5-sodium sulfoisophthalate, 46.7 parts by mass of diethylene glycol, 245.8 parts by mass of ethylene glycol, and 0.5 parts by mass of tetra-n-butyl titanate were charged, and a transesterification reaction was carried out from 160°C to 220°C for 4 hours. The temperature was then raised to 255°C, the reaction system was gradually reduced in pressure, and the reaction was carried out under reduced pressure of 30 Pa for 1 hour and 30 minutes to obtain copolymer polyester resin (A-1). The obtained copolymer polyester resin was pale yellow and transparent. The composition measured by 1H-NMR was 2,6-naphthalenedicarboxylic acid / terephthalic acid / 5-sodium sulfoisophthalic acid / / ethylene glycol / diethylene glycol = 78 / 15 / 7 / / 90 / 10 (mol%).

[0119] A copolymer polyester resin (A-2) with a different composition was obtained using a similar method. The composition was terephthalic acid / isophthalic acid / 5-sodium sulfisoisophthalic acid / / ethylene glycol / neopentyl glycol = 80 / 15 / 5 / / 85 / 15 (mol%).

[0120] (Preparation of aqueous dispersion of polyester) In a reactor equipped with a stirrer, thermometer, and reflux device, 20 parts by mass of polyester resin (A-1) and 15 parts by mass of ethylene glycol t-butyl ether were added and heated at 110°C, and the resin was dissolved by stirring. After the resin was completely dissolved, 65 parts by mass of water were gradually added to the polyester solution while stirring. After the addition, the liquid was cooled to room temperature while stirring to prepare an aqueous dispersion of polyester (B-1) with a solid content of 20% by mass and a milky white color. Similarly, an aqueous dispersion was prepared using polyester resin (A-2) instead of polyester resin (A-1), and this was designated as aqueous dispersion (B-2).

[0121] (Polymerization of blocked polyisocyanate crosslinking agents) A four-necked flask equipped with a stirrer, thermometer, reflux condenser, nitrogen inlet tube, and dropping funnel was placed under a nitrogen atmosphere. 600 parts of HMDI and 30 parts of a trihydric alcohol, polycaprolactone-based polyester polyol (Daicel Chemicals, Praxel 303, molecular weight 300), were charged, and the reactor temperature was maintained at 90°C for 1 hour under stirring to carry out the urethane reaction. After that, the reactor temperature was maintained at 60°C, and the isocyanuration catalyst tetramethylammonium capriate was added. When the yield reached 48%, phosphoric acid was added to stop the reaction and obtain polyisocyanate composition (C-1).

[0122] Next, a four-necked flask equipped with a stirrer, thermometer, reflux condenser, nitrogen blowing tube, and dropping funnel was placed under a nitrogen atmosphere. 100 parts of polyisocyanate composition (C-1), 19 parts of methoxypolyethylene glycol with a molecular weight of 400 (manufactured by Nippon Oil & Fats Co., Ltd., Uniox M400) (which reacts with 10% of the total isocyanate groups of the polyisocyanate), and 37 parts of propylene glycol monomethyl ether acetate were charged into the flask, and the mixture was maintained at 80°C for 7 hours. After that, the reaction solution temperature was maintained at 50°C, and 38 parts of methyl ethyl ketoxime were added dropwise. The infrared spectrum of the reaction solution was measured, and the isocyanate groups disappeared, yielding an aqueous block polyisocyanate resin (C-2) with a solid content of 80% by mass.

[0123] Example 1 Preparation of coating solution (D-1) The following coating agents were mixed to create a coating solution. Particle A is SnO2 with a refractive index of 2.1, and particle B is silica particle with an average primary particle size of approximately 500 nm. Water 43.26% by mass Isopropanol 30.00% by mass Polyester aqueous dispersion (B-1) 20.07% by mass Aqueous block polyisocyanate resin (C-2) 0.74% by mass Particle A 5.58% by mass (Taki Chemical Co., Ltd. Ceramace S-8, solid content concentration 8% by mass) Particle B 0.30% by mass (Nippon Shokubai Seahostar KEW50, solid content concentration 15% by mass) Surfactant 0.05% by mass (Nisshin Chemical Industry Co., Ltd. Dynol 604, solid content concentration 100% by mass) Preparation of coating solution (D-2) Coating solution (D-2) was obtained in the same manner as coating solution (D-1), except that the polyester aqueous dispersion was changed to B-2 and particle A was changed to SiO2 with a refractive index of 1.46 (Snowtex ZL manufactured by Nissan Chemical Industries, solid content concentration 40% by mass). Example 1 (Base film A) As raw materials for the intermediate layer of the base film, 90 parts by mass of particle-free PET(X) resin pellets and 10 parts by mass of PET(Y) resin pellets containing an ultraviolet absorber were dried under reduced pressure (1 Torr) at 135°C for 6 hours, and then supplied to extruder 2 (for intermediate layer II). PET(X) was dried by conventional methods and supplied to extruder 1 (for outer layer I and outer layer III), respectively, and melted at 285°C. These two polymers were filtered using a stainless steel sintered filter medium (nominal filtration accuracy, 95% particle cut of 10 μm particles), laminated in a 2-layer 3-combination block, extruded into a sheet from a die, and then cooled and solidified using an electrostatic casting method on a casting drum with a surface temperature of 30°C to produce an unstretched film. At this time, the discharge rate of each extruder was adjusted so that the thickness ratio of layers I, II, and III was 10:80:10.

[0124] Next, coating solution (D-1) was applied to both sides of the unstretched PET film so that the dry coating amount was 0.08 g / m2, and then dried at 80°C for 20 seconds.

[0125] The unstretched film with this coating layer was guided to a tenter stretcher, and while holding the ends of the film with clips, it was guided to a 100°C tenter and stretched to 4.0 times its original width. Next, while maintaining the stretched width, it was treated for 10 seconds in a heat-setting zone at 190°C, and then a further 2.0% relaxation treatment was performed in the width direction to obtain a uniaxially oriented PET film with a thickness of 60 μm.

[0126] Examples 2 and 3 Base film B, C Substrate film B was obtained in the same manner as substrate film A, except that the thickness was changed.

[0127] Examples 4 and 5 Base film D, E An unstretched PET film obtained in the same manner as base film A was stretched to a 1.1x ratio at 90°C using an MD stretcher consisting of low-speed and high-speed rolls. Then, base film D was obtained in the same manner as base film A, except that coating solution D-1 was applied and the stretching ratio in the tenter was set to 4.2x. Furthermore, base film E was obtained in the same manner as base film D, except that the stretching ratio of MD was set to 1.25 times and the tenter temperature was set to 110°C.

[0128] Example 6 Base film F Substrate film F was obtained in the same manner as substrate film A, except that the thickness was changed, the tenter temperature was set to 110°C, and the stretching ratio was set to 4.8 times.

[0129] Example 7 Base film G Substrate film G was obtained in the same manner as substrate film D, except that the MD stretching ratio was 3.1 times, the tenter temperature was 120°C, and the magnification ratio was 3.5 times.

[0130] Example 8 Base film H Substrate film H was obtained in the same manner as substrate film B, except that the coating solution was D-2.

[0131] Evaluation of iridescence by external light reflection 1 A commercially available full-color serial LED strip was arranged on a 1m x 1.5m white plastic ramp. A diffuser plate, similar to those used in the backlight units of liquid crystal displays, was placed on top of the strip, and a glass plate was placed on top of that. By making the LEDs emit white light, a pseudo-μLED image display device was created. The serial LED strip consists of chips, each containing red, green, and blue light-emitting diodes, mounted in a strip-like configuration. The parts other than the chips were covered with black paper tape. The obtained base film was cut from the center in the width direction to a 1m x 1.5m section, with the slow phase axis parallel to the short side. This section was then attached to the glass plate of a simulated μLED image display device using optical adhesive to create a simulated μLED image display device with a surface protective film for evaluation. The simulated μLED image display device with a protective surface film was installed on the wall of a room that receives natural light, with the center of the device at a height of 160 cm and its longer side horizontal. The room was lit with fluorescent white LEDs, had a brown linoleum floor, and the walls were covered with slightly glossy cream-colored vinyl wallpaper. Participants stood approximately 1 meter away from a wall where a simulated μLED image display device was installed, moving horizontally while wearing polarized sunglasses. They observed the unlit simulated μLED image display device and the indoor and outdoor scenes projected onto the screen. The evaluation was as follows, with ◎ and ○ indicating a passing grade. ◎: No iridescent spots were observed on the screen, regardless of the observer's position. ○: Iridescence was observed in a very limited range of the observer's position, particularly in areas with a large angle from the front, such as the edges of the screen. △: Iridescent spots were observed in a wide area of ​​the screen due to the observer's position. ×: Iridescence was observed over a wide area of ​​the screen, regardless of the observer's position. Although there were differences in the intensity of the iridescence when the simulated μLED image display device was lit and when observed without polarized sunglasses, there was no difference in the ranking of the evaluation results. Therefore, the evaluation results obtained when the device was turned off and polarized sunglasses were worn were used as representative.

[0132] Evaluation of iridescence by external light reflection 2 The process was the same as in evaluation 1 of iridescence by ambient light reflection, except that the slow phase axis was cut from the substrate film so that it was parallel to the long side.

[0133] Iridescent effect evaluation of displayed image: 1, 2 Similar to the evaluation of iridescence due to external light reflection 1 and 2, a simulated μLED image display device with a surface protective film attached was turned on, and the screen was observed while wearing polarized sunglasses. In addition, a panel with black cloth attached was placed in the position where reflected light entered the screen to eliminate the influence of reflected light from the screen.

[0134] Interference color evaluation (Formation of the hard coat layer) A hard coat layer forming solution with the following composition was applied to one side of the prepared base film using a #10 wire bar, dried at 70°C for 1 minute, and the solvent was removed. Next, the film with the hard coat layer was irradiated with ultraviolet light at 300 mJ / cm2 using a high-pressure mercury lamp to obtain a surface protective film having a hard coat layer with a thickness of 5 μm. • Coating solution for forming a hard coat layer Methyl ethyl ketone 65.00% by mass Dipentaerythritol hexaacrylate 27.20% by mass (Shin Nakamura Chemical A-DPH) Polyethylene diacrylate 6.80% by mass (Shin Nakamura Chemical A-400) Photopolymerization initiator 1.00% by mass (Irgacure 184, manufactured by Ciba Specialty Chemicals) A hard-coated surface protection film was cut to an area of ​​10 cm (film width direction) x 15 cm (film length direction) to create a sample film. Black glossy tape (Nitto Denko Corporation, vinyl tape No. 21; black) was attached to the side of the obtained sample film opposite to the hard-coated layer. With the hard-coated layer side of this sample film facing upwards, it was observed using a three-wavelength daylight white light source (National Palook, FL 15EX-N 15W) at an oblique angle from above, at a position where the reflection was strongest when viewed visually.

[0135] The results of visual observations were ranked according to the following criteria. The observations were conducted by three individuals familiar with the evaluation process, and any disagreements were resolved through consensus. ○ and △ were considered passing grades. ○: Almost no interference colors are visible when observed from any angle. △: Slight iridescent coloration is observed. ×: Clear iridescent coloration is observed.

[0136] (Anti-reflective laminated surface protective film) In Example 2, a coating solution for forming a medium refractive index layer with the following composition was applied to one side of the base film B obtained using a bar coater. After drying at 70°C for 1 minute, ultraviolet light at 400 mJ / cm2 was irradiated using a high-pressure mercury lamp to obtain a medium refractive index layer with a dry film thickness of 5 μm. Next, a coating solution for forming a high refractive index layer with the following composition was formed on the formed medium refractive index layer using a bar coater in the same manner as for the medium refractive index layer. Furthermore, a coating solution for forming a low refractive index layer with the following composition was formed on top of that in the same manner as for the medium refractive index layer, thereby obtaining a surface protection film with a laminated anti-reflective layer. A desirable surface protection film with anti-reflective properties was obtained. The reflectance was 0.7%. The reflectance was measured using a spectrophotometer (Shimadzu Corporation, UV-3150) at a wavelength of 550 nm, with the 5-degree reflectance being measured. For the measurement, black marker was applied to the side of the film opposite to the side with the anti-reflective (or low-reflectance) layer, and then black vinyl tape (Kyowa Vinyl Tape HF-737, 50 mm wide) was applied. • Coating solution for forming a medium refractive index layer (refractive index 1.52) Dipentaerythritol hexaacrylate 70 parts by mass 1,6-Bis(3-acryloyloxy-2-hydroxypropyloxy)hexane 30 parts by mass Photopolymerization initiator: 4 parts by mass (Manufactured by Chiba Specialty Chemicals Co., Ltd., Irgacure 184) Isopropanol 100 parts by mass • Coating solution for forming a high refractive index layer (refractive index 1.64) ITO fine particles (average particle 0.07μm) 85 parts by mass 15 parts by mass of tetramethylolmethane triacrylate Photopolymerization initiator (KAYACURE BMS, manufactured by Nippon Kayaku Co., Ltd.) 5 parts by mass 900 parts by mass of butyl alcohol • Coating solution for forming a low refractive index layer (refractive index 1.42) 1,10-Diacryloyloxy-2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-Hexadecafluorodecane 70 parts by mass Dipentaerythritol hexaacrylate 10 parts by mass Silica gel microparticles (XBA-ST, manufactured by Nissan Chemical Corporation) 60 parts by mass Photopolymerization initiator (KAYACURE BMS, manufactured by Nippon Kayaku Co., Ltd.) 5 parts by mass

[0137] [Table 1] [Industrial applicability]

[0138] The present invention provides a micro-LED image display device that does not produce iridescence originating from the surface protective film and has excellent visibility in various installation locations. It also provides a display device with an excellent appearance.

Claims

1. A micro-LED image display device in which a surface protective film is laminated on the outermost surface of the image display portion, wherein the surface protective film is laminated in any of the following forms (1) to (3): (1) The surface protective film is directly bonded to the glass plate or transparent resin plate which is the front panel via an adhesive or bonding agent. (2) The surface protective film is directly attached to the touch sensor located on the viewing side of the glass plate or transparent resin plate which is the front panel, via an adhesive or bonding agent. (3) The surface protective film is directly bonded to the transparent resin covering the wiring and chips of the microLEDs via an adhesive or bonding agent. A micro-LED image display device in which the in-plane retardation of the surface protective film is 3000 nm or more and 30000 nm or less.

2. The micro-LED image display device according to claim 1, wherein the Nz coefficient of the surface protective film is 1.78 or less.

3. The micro-LED image display device according to claim 1 or 2, wherein the surface protective film is a polyester film.

4. The micro-LED image display device according to claim 1, wherein the slow axis direction of the surface protective film is substantially parallel to the long side direction or the short side direction of the image display portion of the micro-LED image display device.

5. The micro-LED image display device according to claim 1, wherein the surface protective film has a functional layer on the visible side of the base film.

6. The micro-LED image display device according to claim 5, wherein the functional layer is at least one of an anti-reflective layer, a low-reflection layer, and an anti-glare layer.

7. The micro-LED image display device according to claim 5 or 6, wherein the base film has an easy-adhesion layer on the surface side of the functional layer.

8. The micro-LED image display device according to claim 7, wherein the resin contained in the easy-adhesion layer is a resin having a naphthalene ring structure.

9. The micro-LED image display device according to claim 7, wherein the easily adhesive layer includes high refractive index particles.

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