Anti-reflection film and image display device

Abstract

To achieve image display with less variation of reflected light characteristics depending on a viewing direction.SOLUTION: An anti-reflection film (100) includes an antireflection layer (5) on a film base material (1). The antireflection layer is a multilayer film consisting of thin films of a total of six or eight layers of alternating high refractive index layers and low refractive index layers. Each of the low refractive index layers is a SiO2 layer and each of the high refractive index layers is a Nb2O5 layer, a Si3 N4 layer or a SiON layer. By having a film thickness of each thin film within a specified range, a ratio of visual reflectance Yθ / Y2 and a chromaticity difference Δa*b* between positive reflected light of light incident at 2° and positive reflected light of light incident at θ° become small.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an antireflection film and an image display device. [Background technology]

[0002] An anti-reflection film may be provided on the surface of an image display device such as a liquid crystal display or an organic EL display in order to improve the visibility of a displayed image. An anti-reflection film has an anti-reflection layer made of multiple thin films with different refractive indices on a film substrate.

[0003] The light reflection characteristics of an anti-reflection layer are generally evaluated by the luminous reflectance (Y value). The luminous reflectance can be reduced by reducing the reflectance at a wavelength of around 550 nm, where the relative luminous sensitivity is high. In addition to having a low luminous reflectance, anti-reflection films are also required to have a neutral hue of reflected light.

[0004] Anti-reflection films have been proposed that control not only the reflection characteristics when viewed from the front, but also the characteristics of reflected light in oblique directions. For example, Patent Document 1 discloses an anti-reflection film in which the hue of the specular reflected light for incident light from all angles between 5 and 45 degrees is within a predetermined range. Patent Document 2 proposes reducing the color difference of reflected light within the range of 5 to 45 degrees by performing optical design so that the chromaticity is minimized within the range of incident angles of 20 to 30 degrees. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2004-138662 A [Patent Document 2] JP 2016-177183 A Summary of the Invention [Problem to be solved by the invention]

[0006] Conventional anti-reflection films are capable of reducing the reflectance in a specific viewing direction, but it is difficult to reduce the change in reflectance over a wide range of viewing directions and to reduce the change in color of the reflected light. [Means for solving the problem]

[0007] The anti-reflection film has an anti-reflection layer made of a plurality of thin films on a film substrate. The anti-reflection layer is a multi-layer thin film including at least one low refractive index layer and at least one high refractive index layer. In the anti-reflection film of the present invention, the anti-reflection layer is a multi-layer film made of a total of six or eight thin layers in which high refractive index layers and low refractive index layers are alternately laminated. The low refractive index layer is a SiO2 layer, and the high refractive index layer is a Nb2O5 layer, a Si3N4 layer, or a SiON layer. By having the thickness of each thin film within a predetermined range, the regular reflection light of a D65 light source irradiated from the anti-reflection layer side can satisfy predetermined characteristics.

[0008] θ° Luminous reflectance of specularly reflected light of incident light Y θ is Y at any angle θ in the range of 5 to 50°. θ It is preferable that the chromaticity index a of the specular reflection light of the θ° incident light is satisfied. Y2 is the luminous reflectance of the specular reflection light of the θ° incident light. * θ and b * θ is Δa at any angle θ in the range of 5 to 50°. * b * ={(a * 2-a * θ ) 2 +(b * 2-b * θ ) 2} 1 / 2 The chromaticity difference Δa * b * But Δa * b * It is preferable that the ratio satisfies ≦6.0. Effect of the Invention

[0009] By using the anti-reflection film of the present invention, it is possible to realize an image display in which the characteristics of reflected light change little depending on the viewing direction. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a cross-sectional view showing a lamination form of an anti-reflection film. [Diagram 2] 11 is a diagram for explaining saturation C* and chromaticity difference Δa*b*. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] [Composition of anti-reflective film] Fig. 1 is a cross-sectional view showing a schematic configuration of an antireflection film according to one embodiment. The antireflection film 100 includes an antireflection layer 5 on a film substrate 1. The antireflection layer 5 is a laminate of a plurality of thin films. The antireflection layer 5 shown in Fig. 1 is a multilayer film consisting of six thin films in which, from the film substrate 1 side, high refractive index layers 51, 53, and 55 and low refractive index layers 52, 54, and 56 are alternately laminated.

[0012] <Film substrate> The film substrate 1 includes a flexible film 10. The thickness of the film substrate 1 is not particularly limited, but from the viewpoints of workability such as strength and handleability, thin layer property, etc., it is preferably about 5 to 300 μm, more preferably 10 to 250 μm, and even more preferably 20 to 200 μm.

[0013] A transparent film is generally used as the film 10. The visible light transmittance of the transparent film is preferably 80% or more, more preferably 90% or more. Examples of the resin material constituting the film 10 include thermoplastic resins excellent in transparency, mechanical strength, and thermal stability. Specific examples of such thermoplastic resins include cellulose-based resins such as triacetyl cellulose, polyester-based resins, polyethersulfone-based resins, polysulfone-based resins, polycarbonate-based resins, polyamide-based resins, polyimide-based resins, polyolefin-based resins, (meth)acrylic-based resins, cyclic polyolefin-based resins (norbornene-based resins), polyarylate-based resins, polystyrene-based resins, polyvinyl alcohol-based resins, and mixtures thereof.

[0014] A hard coat layer 11 is preferably provided on the surface of the film 10 on which the antireflection layer 5 is formed. By providing the hard coat layer 11 on the surface of the film 10, the mechanical properties such as hardness and elastic modulus of the antireflection film can be improved. The hard coat layer 11 preferably has high surface hardness and excellent scratch resistance.

[0015] Examples of the curable resin include thermosetting resin, ultraviolet curing resin, electron beam curing resin, etc. Examples of the type of curable resin include various resins such as polyester, acrylic, urethane, acryl urethane, amide, silicone, silicate, epoxy, melamine, oxetane, acryl urethane, etc. These curable resins can be used alone or in combination as appropriate.

[0016] The hard coat layer may contain fine particles. For example, the hard coat layer may contain fine particles to form irregularities on the surface of the hard coat layer 11, thereby imparting antiglare properties. The fine particles used to impart antiglare properties are preferably microparticles having a particle diameter on the order of μm. The average particle diameter of the microparticles is preferably 0.5 to 10 μm, more preferably 1 to 5 μm. By forming fine irregularities on the surface of the hard coat layer 11, the adhesion to the antireflection layer 5 (or primer layer 3) provided thereon tends to be improved. The fine particles used to form irregularities on the surface of the hard coat layer 11 that have excellent adhesion to thin films such as the primer layer 3 and the antireflection layer 5 are preferably nanoparticles having a particle diameter on the order of nm. The average particle diameter of the nanoparticles is preferably 10 to 150 nm, more preferably 20 to 100 nm, and even more preferably 25 to 80 nm.

[0017] The hard coat layer 11 can be formed, for example, by applying a solution containing a curable resin onto the film 10. The solution for forming the hard coat layer preferably contains a polymerization initiator. To form an antiglare hard coat layer containing fine particles, it is preferable to apply a solution containing the above-mentioned fine particles in addition to the curable resin onto the transparent film. The solution may contain additives such as a leveling agent, a thixotropic agent, and an antistatic agent.

[0018] The thickness of the hard coat layer 11 is not particularly limited, but in order to achieve high hardness, it is preferably 0.5 μm or more, and more preferably 1 μm or more. In consideration of the ease of formation by coating, the thickness of the hard coat layer is preferably 15 μm or less, and more preferably 10 μm or less.

[0019] <Primer layer> A primer layer 3 may be provided on the film substrate 1 for the purpose of improving the adhesion of the antireflection layer 5. Examples of materials constituting the primer layer 3 include metals such as silicon, nickel, chromium, indium, tin, gold, silver, platinum, zinc, titanium, tungsten, aluminum, zirconium, and palladium; alloys of these metals; and oxides, fluorides, sulfides, and nitrides of these metals. Among these, the material for the primer layer is preferably an inorganic oxide layer, and may be an oxide having a lower oxygen content than the stoichiometric composition.

[0020] The thickness of the primer layer 3 is, for example, about 1 to 20 nm, preferably 2 to 15 nm, and more preferably 3 to 15 nm. If the thickness of the primer layer is within the above range, both improved adhesion and light transmittance can be achieved.

[0021] <Anti-reflection layer> The antireflection layer 5 is a laminate of a plurality of thin films having different refractive indices. In this specification, the "refractive index" refers to the refractive index at a wavelength of 550 nm unless otherwise specified.

[0022] By laminating multiple thin films with different refractive indices, the reflectance can be reduced in a wide wavelength range of visible light. The thin films constituting the antireflection layer 5 are preferably made of ceramic materials such as metal or semimetal oxides, nitrides, and fluorides. The thin films constituting the antireflection layer 5 may have their refractive index adjusted by incorporating fine particles with a high or low refractive index in a resin binder.

[0023] The low refractive index layers 52, 54, 56 have a refractive index of, for example, 1.6 or less, preferably 1.5 or less. Examples of low refractive index materials include silicon oxide, titanium nitride, magnesium fluoride, barium fluoride, calcium fluoride, hafnium fluoride, and lanthanum fluoride.

[0024] The high refractive index layers 51, 53, and 53 have a refractive index of, for example, 1.8 or more, and preferably 1.9 or more. Examples of high refractive index materials include titanium oxide, niobium oxide, zirconium oxide, tantalum oxide, zinc oxide, indium oxide, indium tin oxide (ITO), antimony-doped tin oxide (ATO), silicon nitride, and silicon oxynitride.

[0025] The antireflection layer 5 is preferably an alternating laminate of high and low refractive index layers. In order to reduce reflection at the air interface, the thin film 56 provided as the outermost layer (the layer farthest from the film substrate 1) of the antireflection layer 5 is preferably a low refractive index layer. In addition to the low and high refractive index layers, the antireflection layer may also include a medium refractive index layer having a refractive index intermediate between the high and low refractive index layers. The refractive index of the medium refractive index layer is, for example, about 1.6 to 1.9.

[0026] The thickness of each of the high refractive index layer and the low refractive index layer is about 5 to 200 nm, and preferably about 10 to 150 nm. The thickness of each layer may be designed according to the refractive index, the layer structure, etc., so that the reflectance of visible light is small.

[0027] The method for forming the thin film constituting the antireflection layer 5 is not particularly limited, and may be either a wet coating method or a dry coating method. Dry coating methods such as vacuum deposition, CVD, sputtering, and electron beam vapor deposition are preferred because they can form a thin film with a uniform thickness. Among these, sputtering is preferred because it has excellent uniformity in thickness.

[0028] <Additional layer on anti-reflection layer> The antireflection film may have an additional functional layer on the antireflection layer 5. For example, an antifouling layer (not shown) may be provided on the antireflection layer 5 for the purpose of preventing contamination from the external environment and facilitating the removal of attached contaminants.

[0029] When an antifouling layer is provided on the surface of the antireflection film, it is preferable that the difference in refractive index between the low refractive index layer 56 on the outermost surface of the antireflection layer 5 and the antifouling layer is small from the viewpoint of reducing reflection at the interface. The refractive index of the antifouling layer is preferably 1.6 or less, more preferably 1.55 or less. The material of the antifouling layer is preferably a fluorine group-containing silane-based compound or a fluorine group-containing organic compound. The antifouling layer can be formed by a wet coating method such as a reverse coating method, a die coating method, or a gravure coating method, or a dry coating method such as a vacuum deposition method or a CVD method. The thickness of the antifouling layer is usually about 1 to 100 nm, preferably 2 to 50 nm, and more preferably 3 to 30 nm.

[0030] [Characteristics of reflected light] It is preferable that the anti-reflection film has little change in the reflected light characteristics depending on the viewing angle. The light characteristics can be evaluated using three indices: hue, saturation, and brightness. The reflected light characteristics depend on the spectrum of the irradiated light. Below, we will refer to the reflected light characteristics when the CIE standard illuminant D65 is irradiated onto the anti-reflection layer 5 side (opposite side to the film substrate 1) of the anti-reflection film.

[0031] When measuring reflected light by irradiating light from the anti-reflection layer 5 side, the reflectance of visible light on the back side (the interface between the film substrate 1 and air) is about 4%, and most of the light is reflected from the back side. In order to eliminate the influence of back side reflection, a sample in which a black film or black plate is attached to the back side of the film substrate 1 (the side opposite to the side on which the anti-reflection layer 5 is formed) is used for evaluating the characteristics of reflected light.

[0032] <Luminous reflectance> Luminous reflectance Y is an index that represents the brightness of reflected light, and is the Y value in the XYZ color system (or Yxy color system). Luminous reflectance Y is standardized so that the Y value of a perfect reflector is 100%.

[0033] In general, anti-reflection films are designed to have a small reflectance when irradiated with light from the front, and the reflectance of specularly reflected light tends to increase as the incident angle θ increases. From the viewpoint of reducing the difference in the amount of reflected light caused by changes in the incident angle (viewing direction) of light, the luminous reflectance Y2 of specularly reflected light at 2° incident angle and the luminous reflectance Y of specularly reflected light at θ° incident angle are calculated. θ Ratio to Y θ It is preferable that Y / Y2 is 6.0 or less at any incident angle θ between 5° and 50°. θ In the range of θ=5 to 50°, / Y2 is more preferably 5.5 or less, further preferably 5.0 or less, and particularly preferably 4.5 or less.

[0034] The luminous reflectance Y2 of the specularly reflected light of 2° incident light is preferably 1.0% or less, more preferably 0.9% or less, and even more preferably 0.8% or less. It is preferable that Y2 is as small as possible, but if optical design is performed so that the reflectance for incident light in a specific direction is small, the change in reflectance may be large when the incident angle θ is changed. Therefore, Y2 may be 0.1% or more, 0.2% or more, or 0.3% or more.

[0035] From the viewpoint of reducing the reflection of the environmental light and increasing the visibility regardless of the viewing direction, the luminous reflectance Y of the specular reflection of the θ° incident light is set to θ is preferably 3.0% or less, and more preferably 2.5% or less, at any angle θ in the range of 5 to 50°.

[0036] <Chromaticness Index> CIELAB color space (L * a * b * In the color space, lightness is L * and the hue and saturation are expressed by the chromaticity index a * and b * It is expressed as a * and b * If is 0, it is achromatic, and if is +a * is red direction, -a is red direction * is green direction, +b * is yellow direction, -b is *indicates the blue direction. * b * On the plane, the radial direction corresponds to saturation and the circumferential direction corresponds to hue.

[0037] C * ={(a * ) 2 +(b * ) 2} 1 / 2 Saturation, defined as the degree of color, is C * If is 0, it is achromatic, and C * The larger the value, the greater the coloring. * b * The greater the distance between the two points when projected onto a flat sky, the greater the difference in color between the two lights.

[0038] In order to reduce the difference in color of reflected light caused by changes in the angle of incidence (viewing direction) of light, the chromaticity index a of the specular reflection of 2° incident light is set. * 2 and b * 2, and the chromaticity index a of the specular reflection of the θ° incident light * θ and b * θ is Δa at any angle θ in the range of θ=5 to 50°. * b * It is preferable that Δa * b * is the ratio of the specular reflection of 2° incident light (A) to the specular reflection of θ° incident light (a) * b * is the distance in the plane, Δa * b * ={(a * 2-a * θ ) 2 +(b * 2-b * θ ) 2} 1 / 2 In the following, Δa * b * is sometimes called the "chromaticity difference." * b *is more preferably 5.5 or less, further preferably 5.0 or less, and particularly preferably 4.5 or less, in the range of θ=5 to 50°. * b * may be 4.0 or less, 3.5 or less, or 3.0 or less.

[0039] 2° Chroma of specular reflection of incident light C * is preferably 5.0 or less, more preferably 4.0 or less, and even more preferably 3.0 or less. * may be less than or equal to 2.5 or less than or equal to 2.0.

[0040] In order to suppress coloring by making the reflected light a neutral color regardless of the viewing direction, the saturation C of the specular reflected light of the θ° incident light * is preferably 9.0 or less, more preferably 7.0 or less, and particularly preferably 5.0 or less, at any angle θ in the range of 5 to 50°.

[0041] <Optical design of anti-reflection layer> By appropriately designing the thickness of the thin film that constitutes the antireflection layer, an antireflection film having the above characteristics can be obtained. The characteristics (spectrum) of reflected light can be accurately evaluated by optical model calculation. Known methods for calculating the reflection spectrum of a multilayer optical thin film by optical calculation include a method in which the thin film interference formula is repeatedly applied to each interface of the thin film and all the multiple reflected waves are added together; and a method in which the reflection spectrum is calculated by a transfer matrix taking into account the boundary conditions of Maxwell's equations.

[0042] The reflectance spectrum of the specular light when the D65 light source is incident is calculated for multiple incident angles θ, and for each θ, the luminous reflectance Y and the chromaticity index a are calculated from the reflectance spectrum. * and b * By repeatedly performing these optical calculations while changing the film thickness of the thin film that constitutes the antireflection layer, it is possible to optimize the set film thickness of the thin film, and an antireflection film whose reflected light satisfies the above-mentioned characteristics can be obtained.

[0043] When the number of thin films constituting the antireflection layer is small, Y θ / Y2 and Δa * b * As shown in the following examples, when the number of layers in the antireflection layer (total number of thin films) is large, Y θ / Y2 and Δa * b * It is possible to design the thickness of the thin film so that both of the above are small. The antireflection layer preferably includes a total of five or more low refractive index layers and high refractive index layers, and more preferably includes three or more low refractive index layers. It is more preferable that the antireflection layer includes a total of six or more low refractive index layers and high refractive index layers.

[0044] From the viewpoint of reducing the luminous reflectance Y, it is preferable that the antireflection layer has a large refractive index difference between the low refractive index layer and the high refractive index layer. The refractive index difference between the low refractive index layer and the high refractive index layer is preferably 0.30 or more, more preferably 0.35 or more, and even more preferably 0.40 or more.

[0045] The refractive index of the low refractive index layer is preferably 1.50 or less, more preferably 1.48 or less, and even more preferably 1.47 or less. The refractive index of the low refractive index layer is generally 1.00 or more, and may be 1.20 or more, 1.30 or more, or 1.35 or more. The refractive index of the high refractive index layer is preferably 1.80 or more, more preferably 1.84 or more, and even more preferably 1.87 or more. The refractive index of the high refractive index layer is generally 3.00 or less, and may be 2.50 or less, 2.40 or less, or 2.30 or less. The refractive index of the high refractive index layer at a wavelength of 400 nm is preferably 1.84 to 2.55, and more preferably 1.88 to 2.50. The refractive index of the high refractive index layer at a wavelength of 700 nm is preferably 1.78 to 2.35, and more preferably 1.80 to 2.30.

[0046] If the reflectance at a wavelength of 550 nm is reduced, the luminous reflectance Y tends to decrease. On the other hand, if the optical design is performed so that the reflectance at a wavelength of 550 nm is minimized, the reflectance at other wavelengths increases, and the chromaticity index a of the reflected light increases. * and / or b. * becomes larger, and reflected light tends to become colored.

[0047] In order to reduce the coloring of the reflected light, it is preferable that the reflectance is uniform over a wide wavelength range of visible light. When the wavelength dependency of the refractive index of the thin film constituting the antireflection layer is small, the change in reflectance due to wavelength becomes small, and the saturation of the reflected light tends to become small (neutralized). Even when a material with a large wavelength dispersion of the refractive index is used, it is possible to carry out optical design so that the coloring of the reflected light is small, but if the film thickness of the thin film is slightly different, the reflected light may be colored. From the viewpoint of increasing the degree of freedom of optical design and securing the allowable range (process margin) of the film thickness, it is preferable that the thin film constituting the antireflection layer has a small wavelength dispersion of the refractive index (change in the refractive index with change in wavelength).

[0048] The Abbe number ν of the high refractive index layer D is preferably 20 or more, more preferably 23 or more, and even more preferably 25 or more. D is the refractive index n at a wavelength of 589 nm D , the refractive index at a wavelength of 486 nm, n F , and the refractive index at a wavelength of 656 nm, n C Using ν D =(n D -1) / (n F -n C ) is expressed as the Abbe number ν D The larger the Abbe number ν of the high refractive index layer, the smaller the wavelength dispersion of the refractive index. D There is no particular upper limit to the Abbe number ν D The larger the Abbe number ν of the high refractive index layer, the smaller the refractive index dispersion. Dis preferably 40 or less, more preferably 30 or less, and even more preferably 28 or less.

[0049] The thickness of each thin film in the antireflection layer may be set so that the reflected light satisfies the above characteristics, taking into consideration the refractive index of each thin film, the number of layers, etc. As described above, the thickness of the antireflection layer can be optimized by calculating the reflection spectrum of the antireflection film using an optical model.

[0050] [Usage of anti-reflective film] Anti-reflection films are used by being disposed on the surface of image display devices such as liquid crystal displays and organic electroluminescence displays. For example, by disposing an anti-reflection film on the viewing side surface of a panel including an image display medium such as a liquid crystal cell or an organic electroluminescence cell, the reflection of external light can be reduced and the visibility of the image display device can be improved. The anti-reflection film may be laminated with other films. For example, a polarizing plate with an anti-reflection layer can be formed by bonding a polarizer to the side of the film substrate 1 opposite to the side on which the anti-reflection layer is formed.

[0051] The antireflection film of the present invention has a small difference in the characteristics of reflected light depending on the viewing direction, so that even when the viewing direction is changed, the change in the characteristics of reflected light is small, making it possible to uniformize the image display device. EXAMPLES

[0052] In the following, an example will be shown in which various characteristics of reflected light of an anti-reflection film are calculated by optical model calculation.

[0053] [Method of evaluating reflected light characteristics] The regular reflectance when light with a wavelength λ was incident on the antireflection film at an incident angle θ° was calculated by optical model calculation in 1 nm increments in the wavelength range of 380 to 780 nm to obtain the reflectance spectrum R(λ).

[0054] The obtained regular reflectance spectrum R(λ) was multiplied by the spectrum of CIE standard illuminant D65 to obtain the reflected light spectrum. From the obtained reflected light spectrum, the luminous reflectance Y and the chromaticness index a of the CIELAB color system were calculated. * and b * Calculate a * and b * From the value of saturation C * ={(a * ) 2 +(b * ) 2} 1 / 2 was calculated.

[0055] The above evaluation was performed at an incidence angle of 2° and at incidence angles θ in the range of 5° to 50° in increments of 5°, and the luminous reflectance Y2 of the specular reflection of the 2° incidence light and the luminous reflectance Y of the specular reflection of the θ° incidence light were measured. θ Ratio to Y θ / Y2, and the a of the specular reflection of 2° incident light and the specular reflection of θ° incident light * b * Distance on a plane Δa * b * ={(a * 2-a * θ ) 2 +(b * 2-b * θ ) 2} 1 / 2 was calculated.

[0056] <Refractive index of thin film> In each of the examples and comparative examples, silicon oxide (SiO2) was used as the low refractive index layer, and niobium oxide (Nb2O5), titanium oxide (TiO2), silicon nitride (Si3N4), and silicon oxynitride (SiON) were used as the high refractive index layer. For silicon oxynitride, the amount of oxygen introduced during sputtering deposition was changed to form two types of thin films, SiON (1) with a relatively low oxygen content and SiON (2) with a relatively high oxygen content, and the refractive index measured by spectroscopic ellipsometry was used. For the refractive indexes of the other thin films, values ​​from the database were used. The refractive indices n 400 , n 550, n 700 , and the Abbe number ν D is shown in Table 1.

[0057] [Table 1]

[0058] <Example 1> The above optical simulation was carried out for an anti-reflection film having an 8-layer anti-reflection layer in which an 8.2 nm niobium oxide layer, a 42.2 nm silicon oxide layer, a 24.6 nm niobium oxide layer, an 18.6 nm silicon oxide layer, an 80.8 nm niobium oxide layer, a 10.8 nm silicon oxide layer, a 25.6 nm niobium oxide layer, and a 25.6 nm silicon oxide layer are laminated in this order on the acrylic hard coat layer of the hard coat film, and an anti-fouling layer made of a fluorine-based resin with a thickness of 5 nm is provided thereon. The refractive indexes of the hard coat film (acrylic hard coat layer) and the anti-fouling layer made of a fluorine-based resin were measured by spectroscopic ellipsometry (refractive index of the hard coat layer at a wavelength of 550 nm: 1.54, refractive index of the anti-fouling layer at a wavelength of 550 nm: 1.32). In the optical simulation, the thickness of the film substrate of the hard coat film was set to ∞ in order to eliminate the influence of back reflection.

[0059] <Examples 2 to 7, Comparative Examples 1 and 2> An optical simulation similar to that of Example 1 was performed on an antireflection film in which the material of the high refractive index layer, the stacking configuration (the total number of thin films constituting the antireflection (AR) layer), and the film thickness of each layer were changed as shown in Table 2.

[0060] [Evaluation Results] The configurations of the antireflection films of Examples 1 to 7 and Comparative Examples 1 and 2 and the results of optical simulations are shown in Table 2. In Table 2, the unit of numerical values ​​for the thickness of each layer is nm, and they are listed as the first layer, second layer, third layer, etc. from the side closest to the film substrate. The reflected light characteristics are shown for θ=2° (front), and θ=20°, 40°, and 50°.

[0061] [Table 2]

[0062] In Examples 1 and 2, the antireflection layer is made up of a total of eight layers, including four high-refractive index layers and four low-refractive index layers. θ The maximum value of / Y2 is small and Δa * b * It can be seen that the maximum value of Y is also small. θ The maximum value of / Y2 is small and Δa * b * As a high refractive index layer, the maximum value of Abbe number v D In Example 6, which uses SiON(2) having a large refractive index (small wavelength dispersion of the refractive index), Δa * b * While there was a tendency for the reflectance to decrease, the reflectance when viewed from the front was high. This is thought to be related to the fact that the difference in refractive index between the high refractive index layer and the low refractive index layer was small, making it impossible to sufficiently reduce the reflectance.

[0063] In Comparative Example 1, in which the antireflection layer was made up of a total of four layers including two high refractive index layers and two low refractive index layers, the reflectance at the front (2°) was reduced, but θ The maximum value of / Y2 exceeded 6. In Comparative Example 1, Δa * b * In Comparative Example 2, the maximum value of Y exceeded 6. θ The maximum value of / Y2 was 6 or less, but the a * The change in Δa * b * The maximum value was about 11.

[0064] [Changing the thickness of the anti-reflection layer] Example 1A In the antireflection film of Example 1, the thickness of the eight thin films constituting the antireflection layer was changed one by one, and a similar simulation was performed. The thickness of the antireflection layer in each antireflection film, the characteristics of 2° regular reflection light, and the Y θ / Y2 and Δa * b * The maximum value of is shown in Table 3. In Table 3, the antireflection film No. 1 is the same as that in Example 1. Nos. 2 to 5 have a different thickness of the first layer (high refractive index layer), Nos. 6 to 9 have a different thickness of the second layer (low-high refractive index layer), Nos. 10 to 13 have a different thickness of the third layer (high refractive index layer), Nos. 14 to 17 have a different thickness of the fourth layer (low-high refractive index layer), Nos. 18 to 21 have a different thickness of the fifth layer (high refractive index layer), Nos. 22 to 25 have a different thickness of the sixth layer (low-high refractive index layer), Nos. 26 to 29 have a different thickness of the seventh layer (high refractive index layer), and Nos. 30 to 33 have a different thickness of the eighth layer (low-high refractive index layer).

[0065] [Table 3]

[0066] From the results shown in Table 3, if the thickness of the first layer (Nb2O5) is in the range of 8 to 10 nm, the thickness of the second layer (SiO2) is in the range of 41 to 45 nm, the thickness of the third layer (Nb2O5) is in the range of 21 to 25 nm, the thickness of the fourth layer (SiO2) is in the range of 18 to 20 nm, the thickness of the fifth layer (Nb2O5) is in the range of 77 to 95 nm, the thickness of the sixth layer (SiO2) is in the range of 10.5 to 15 nm, the thickness of the seventh layer (Nb2O5) is in the range of 25 to 30 nm, and the thickness of the eighth layer (SiO2) is in the range of about 60 to 89 nm, then Y in the range of θ = 5 to 45° will be θ / Y2 is 6% or less and Δa * b * It can be seen that an anti-reflection film having a reflectance of 6 or less can be obtained.

[0067] Example 2A A similar simulation was performed by changing the thickness of each of the eight thin films constituting the antireflection layer in the antireflection film of Example 2. The thickness and evaluation results of each layer are shown in Table 4.

[0068] [Table 4]

[0069] From the results shown in Table 4, if the thickness of the first layer (Si3N4) is 5 to 10 nm, the thickness of the second layer (SiO2) is 48 to 60 nm, the thickness of the third layer (Si3N4) is 23 to 27 nm, the thickness of the fourth layer (SiO2) is 23 to 32 nm, the thickness of the fifth layer (Si3N4) is 85 to 105 nm, the thickness of the sixth layer (SiO2) is 4 to 7 nm, the thickness of the seventh layer (Si3N4) is 40 to 50 nm, and the thickness of the eighth layer (SiO2) is about 70 to 95 nm, then Y in the range of θ = 5 to 45° will be θ / Y2 is 6% or less and Δa * b * It can be seen that an anti-reflection film having a reflectance of 6 or less can be obtained.

[0070] Example 3A A similar simulation was performed by changing the thickness of each of the six thin films constituting the antireflection layer in the antireflection film of Example 3. The thickness and evaluation results of each layer are shown in Table 5.

[0071] [Table 5]

[0072] From the results shown in Table 5, if the thickness of the first layer (Nb2O5) is in the range of 9 to 10.5 nm, the thickness of the second layer (SiO2) is in the range of 41 to 47 nm, the thickness of the third layer (Nb2O5) is in the range of 25 to 28 nm, the thickness of the fourth layer (SiO2) is in the range of 39 to 42 nm, the thickness of the fifth layer (Nb2O5) is in the range of 17 to 23 nm, and the thickness of the sixth layer (SiO2) is in the range of about 90 to 106 nm, then Y in the range of θ = 5 to 45° will be θ / Y2 is 6% or less and Δa * b *It can be seen that an anti-reflection film having a reflectance of 6 or less can be obtained.

[0073] Example 4A A similar simulation was performed by changing the thickness of each of the six thin films constituting the antireflection layer in the antireflection film of Example 4. The thickness and evaluation results of each layer are shown in Table 6.

[0074] [Table 6]

[0075] From the results shown in Table 6, if the thickness of the first layer (Si3N4) is in the range of 13 to 16.5 nm, the thickness of the second layer (SiO2) is in the range of 32 to 40 nm, the thickness of the third layer (Si3N4) is in the range of 47 to 55 nm, the thickness of the fourth layer (SiO2) is in the range of 20.5 to 24 nm, the thickness of the fifth layer (Si3N4) is in the range of 34 to 44.5 nm, and the thickness of the sixth layer (SiO2) is in the range of 82 to 98 nm, then Y in the range of θ = 5 to 45° will be θ / Y2 is 6% or less and Δa * b * It can be seen that an anti-reflection film having a reflectance of 6 or less can be obtained.

[0076] Example 5A A similar simulation was performed by changing the thickness of each of the six thin films constituting the antireflection layer in the antireflection film of Example 5. The thickness and evaluation results of each layer are shown in Table 7.

[0077] [Table 7]

[0078] From the results shown in Table 7, if the thickness of the first layer (SiON) is in the range of 13 to 19.5 nm, the thickness of the second layer (SiO2) is in the range of 22 to 37 nm, the thickness of the third layer (SiON) is in the range of 58 to 80 nm, the thickness of the fourth layer (SiO2) is in the range of 2 to 10 nm, the thickness of the fifth layer (SiON) is in the range of 59 to 85 nm, and the thickness of the sixth layer (SiO2) is in the range of about 65 to 95 nm, then Y in the range of θ = 5 to 45° will be θ / Y2 is 6% or less and Δa * b * It can be seen that an anti-reflection film having a reflectance of 6 or less can be obtained.

[0079] <Comparative Example 1A> A similar simulation was performed by changing the thickness of each of the four thin films constituting the antireflection layer in the antireflection film of Comparative Example 1. The thickness and evaluation results of each layer are shown in Table 8.

[0080] [Table 8]

[0081] <Comparative example 2A> A similar simulation was performed by changing the thickness of each of the four thin films constituting the antireflection layer in the antireflection film of Comparative Example 2. The thickness and evaluation results of each layer are shown in Table 9.

[0082] [Table 9]

[0083] As shown in Tables 8 and 9, when the number of thin films constituting the anti-reflection layer is four, even if the thickness of the thin films is changed, Y θ / Y2 is 6% or less and Δa * b * No antireflection film having a value of 6 or less could be obtained.

[0084] From the above results, it can be seen that by making the number of thin films constituting the antireflection film 5 or more, preferably 6 or more, more precise optical design is possible, and an antireflection film can be obtained in which the changes in the characteristics of reflected light are minimal when the viewing direction is changed.

[0085] The optimum value of the film thickness of the thin film varies depending on the refractive index of the material constituting the thin film, and it is difficult to stipulate it in general. On the other hand, as shown in Tables 3 to 7, by repeating optical simulations while changing the thickness of the thin film constituting the anti-reflection film, it is possible to obtain the optimum value of Y θ / Y2 and Δa * b * Therefore, even when a thin film made of a material other than those shown in the above examples is used, it is possible to design an anti-reflection film in which the change in the characteristics of reflected light when the viewing direction is changed is small.

[0086] [Insertion of primer layer] Example 1B In the anti-reflection film of Example 1, a SiOx primer layer (x=0.65, refractive index at wavelength 550 nm: 1.72) having a thickness of 3 nm was added between the acrylic hard coat layer of the hard coat film and the anti-reflection layer (first Nb2O5 layer), and a similar simulation was performed. The results of the optical simulation of Example 1B are shown in Table 10 together with the results of Example 1.

[0087] [Table 10]

[0088] In Example 1B, the chromaticity index a of the specular reflection light * 2 and b * 2 was slightly different from Example 1, but Y θ / Y2 and Δa * b * There was no significant difference between the values ​​for Example 1 and Example 2. From these results, it can be seen that even when a primer layer is provided between the film substrate and the antireflection layer, by adjusting the lamination structure and film thickness of the antireflection layer in the same manner as in each of the above examples, an antireflection film with small changes in the characteristics of reflected light when the viewing direction is changed can be obtained. [Explanation of symbols]

[0089] 1 Film substrate 3 Primer layer 5 Anti-reflection layer 51, 53, 55 Low refractive index layer 52, 54, 56 High refractive index layer 100 Anti-reflective film

Claims

1. An anti-reflection film comprising an anti-reflection layer made of a plurality of thin films on a film substrate, The antireflection layer is made of Nb having a thickness of 8 to 10 nm from the film substrate side. ２ O ５ layer, SiO ２ layer, Nb ２ O ５ layer, SiO ２ layer, Nb ２ O ５ layer, SiO ２ layer, 25-30 nm thick Nb ２ O ５ layer, and SiO ２ A total of eight thin films having layers, Anti-reflective film.

2. An anti-reflection film comprising an anti-reflection layer made of a plurality of thin films on a film substrate, The antireflection layer is a Si layer having a thickness of 5 to 10 nm from the film substrate side. ３ N ４ layer, SiO ２ layer, 23-27 nm thick Si ３ N ４ layer, SiO ２ layer, 85-105 nm thick Si ３ N ４ layer, SiO ２ layer, 40-50 nm thick Si ３ N ４ layer, and SiO ２ A total of eight thin films having layers, Anti-reflective film.

3. An anti-reflection film comprising an anti-reflection layer made of a plurality of thin films on a film substrate, The antireflection layer is made of Nb having a thickness of 9 to 10.5 nm from the film substrate side. ２ O ５ layer, SiO ２ layer, 25-28 nm thick Nb ２ O ５ layer, SiO ２ layer, 17-23 nm thick Nb ２ O ５ layer, and SiO ２ A total of six thin films having layers, Anti-reflective film.

4. An anti-reflection film comprising an anti-reflection layer made of a plurality of thin films on a film substrate, The antireflection layer is a Si layer having a thickness of 13 to 16.5 nm from the film substrate side. ３ N ４ layer, SiO ２ layer, 47-55 nm thick Si ３ N ４ layer, SiO ２ layer, 34 to 44.5 nm thick Si ３ N ４ layer, and 82-98 nm of SiO ２ A total of six thin films having layers, Anti-reflective film.

5. An anti-reflection film comprising an anti-reflection layer made of a plurality of thin films on a film substrate, The antireflection layer is made up of a SiON layer having a thickness of 13 to 19.5 nm, a SiO layer having a thickness of 22 to 37 nm, and ２ layer, a SiON layer having a thickness of 58 to 80 nm, and a SiO ２ layer, a SiON layer having a thickness of 59 to 85 nm, and a SiO ２ A total of six thin films having layers, Anti-reflective film.

6. An image display device, comprising an anti-reflection film according to any one of claims 1 to 5 disposed on a viewing side surface of an image display medium.

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