JP7488671B2 - Anti-reflection film and image display device - Google Patents

Description

The present invention relates to an anti-reflection film and an image display device.

Anti-reflection films are sometimes provided on the surfaces of image display devices such as liquid crystal displays and organic EL displays in order to improve the visibility of the displayed images. Anti-reflection films have an anti-reflection layer made of multiple thin films with different refractive indices on a film substrate.

The light reflection characteristics of an anti-reflective 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-reflective films are also required to have a neutral hue of reflected light.

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 specularly reflected light for incident light from all angles between 5 and 45 degrees is within a specified 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 in the range of incident angles between 20 and 30 degrees.

JP 2004-138662 A JP 2016-177183 A

Conventional anti-reflective films can reduce 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.

An anti-reflective film has an anti-reflective layer made of multiple thin films on a film substrate. The anti-reflective layer is a multi-layer thin film that includes at least one low refractive index layer and at least one high refractive index layer. In the anti-reflective film of the present invention, the specularly reflected light of a D65 light source irradiated from the anti-reflective layer side satisfies predetermined characteristics.

It is preferable that the luminous reflectance Y _θ of specularly reflected light of θ° incident light satisfies Y _θ /Y ₂ ≦6.0 at any angle θ in the range of 5 to 50°. Y ₂ is the luminous reflectance of specularly reflected light of 2° incident light. It is preferable that the chromaticity indices a ^* _θ and b ^* _θ of specularly reflected light of θ° incident light satisfies Δa ^{*b* ≦6.0, expressed by Δa* b *} = {(a ^* ₂ - a ^* _θ ) ² + (b ^* ₂ - b ^* _θ ^{) 2} } ^1/2 , ^at any angle θ in the range of 5 to 50 ^° .

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.

FIG. 2 is a cross-sectional view showing a lamination form of an anti-reflection film. 11 is a diagram for explaining saturation C ^* and chromaticity difference Δa ^* b ^* . FIG.

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

<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.

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 that are 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.

It is preferable that a hard coat layer 11 is provided on the surface of the film 10 on which the anti-reflection 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 anti-reflection film can be improved. It is preferable that the hard coat layer 11 has a high surface hardness and excellent scratch resistance.

Examples of curable resins include thermosetting resins, ultraviolet curing resins, and electron beam curing resins. Types of curable resins include polyester, acrylic, urethane, acrylic urethane, amide, silicone, silicate, epoxy, melamine, oxetane, and acrylic urethane resins. One or more of these curable resins can be appropriately selected and used.

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 anti-glare properties. The fine particles used to impart anti-glare 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, adhesion to the anti-reflection 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 anti-reflection 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.

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 anti-glare 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.

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. Considering 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.

<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; oxides, fluorides, sulfides, or nitrides of these metals; and the like. Among these, the material for the primer layer is preferably an inorganic oxide layer, and may be an oxide having a smaller amount of oxygen than the stoichiometric composition.

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, it is possible to achieve both improved adhesion and light transparency.

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

By stacking multiple thin films with different refractive indices, it is possible to reduce the reflectance over a wide wavelength range of visible light. The thin films constituting the anti-reflection layer 5 are preferably made of ceramic materials such as metal or semi-metal oxides, nitrides, and fluorides. The thin films constituting the anti-reflection layer 5 may have their refractive index adjusted by incorporating fine particles with a high or low refractive index into a resin binder.

The low refractive index layers 52, 54, and 56 have a refractive index of, for example, 1.6 or less, and 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.

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.

The anti-reflection 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 of the anti-reflection layer 5 (the layer farthest from the film substrate 1) is preferably a low refractive index layer. In addition to the low and high refractive index layers, the anti-reflection 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.

The thickness 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 can be designed to reduce the reflectance of visible light depending on the refractive index and layered structure, etc.

The method for forming the thin film constituting the anti-reflection 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 film thickness.

<Additional Layer on Antireflection 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.

When an anti-smudge layer is provided on the surface of the anti-reflection film, it is preferable that the difference in refractive index between the low refractive index layer 56 on the outermost surface of the anti-reflection layer 5 and the anti-smudge layer is small from the viewpoint of reducing reflection at the interface. The refractive index of the anti-smudge layer is preferably 1.6 or less, more preferably 1.55 or less. As the material for the anti-smudge layer, a fluorine group-containing silane-based compound or a fluorine group-containing organic compound is preferable. The anti-smudge 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 anti-smudge layer is usually about 1 to 100 nm, preferably 2 to 50 nm, and more preferably 3 to 30 nm.

[Characteristics of reflected light]
It is preferable that the anti-reflection film has a small change in the characteristics of reflected light depending on the viewing angle. The characteristics of light can be evaluated by three indices: hue, saturation, and brightness. The characteristics of reflected light depend on the spectrum of the irradiated light. In the following, the characteristics of reflected light when the CIE standard illuminant D65 is irradiated on the surface of the anti-reflection film on the anti-reflection layer 5 side (opposite the film substrate 1) will be mentioned.

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. To eliminate the influence of backside reflection, a sample with a black film or black plate attached to the back side of the film substrate 1 (the side opposite to the surface on which the anti-reflection layer 5 is formed) is used to evaluate the characteristics of reflected light.

<Luminous reflectance>
The luminous reflectance Y is an index representing the brightness of reflected light, and is the Y value in the XYZ color system (or the Yxy color system). The luminous reflectance Y is normalized so that the Y value of a perfect reflector is 100%.

In general, anti-reflection films are designed to have a small reflectance when irradiated with light from the front, and the reflectance of regular reflection light tends to increase as the incident angle θ increases. From the viewpoint of reducing the difference in the amount of reflected light accompanying the change in the incident angle (viewing direction) of light, the ratio Y _θ /Y 2 between the luminous reflectance Y ₂ of regular reflection light of 2° incident light and the luminous reflectance Y _θ of regular reflection light of θ° incident light is preferably 6.0 or less at any incident angle θ of θ=5 to 50°. In the range of θ=5 to 50°, Y _θ /Y ₂ is more preferably 5.5 or less, even more preferably 5.0 or less, _and particularly preferably 4.5 or less.

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 when the incident angle θ changes may be large. Therefore, _Y2 may be 0.1% or more, 0.2% or more, or 0.3% or more.

From the viewpoint of reducing reflection of environmental light and enhancing visibility regardless of the viewing direction, the luminous reflectance _Yθ of specularly reflected light of θ° incident light is preferably 3.0% or less, and more preferably 2.5% or less, at any angle θ in the range of 5 to 50°.

<Chromaticness Index>
In the CIELAB color space (L ^* a ^* b ^* color space), lightness is expressed by L ^* , and hue and saturation are expressed by chromaticity indices a ^* and b ^* . When a ^* and b ^* are 0, the color is achromatic, +a ^* indicates the red direction, -a ^* indicates the green direction, +b ^* indicates the yellow direction, and -b ^* indicates the blue direction. In the a ^* b ^* plane shown in Figure 2, the radial direction corresponds to saturation, and the circumferential direction corresponds to hue.

Saturation, defined as C ^* = {(a ^* ) ² + (b ^* ) ² } ^1/2, represents the degree of coloring, where C ^* is 0 for an achromatic color, and the larger C ^* is, the more colored the color is. The greater the distance between two points when the color space is projected onto the a ^* b ^* plane, the greater the difference in color between the two lights.

From the viewpoint of reducing the difference in color of reflected light accompanying a change in the incident angle (viewing direction) of light, it is preferable that the chromaticity indices a ^* ₂ and b ^* ₂ of the specular reflected light of 2° incident light and the chromaticity indices a ^* _θ and b ^* _θ of the specular reflected light of θ° incident light satisfy Δa ^* b ^* ≦6.0 at any angle θ in the range of θ=5 to 50°. As shown in FIG. 2, Δa ^* b ^* is the distance in the a*b ^* plane between the specular reflected light (A) of 2° incident light and the specular reflected light of θ° incident light, and is expressed as Δa ^* b ^* ={(a ^* ₂ -a ^* _θ ) ²⁺ (b ^* ₂ - ^{b *} _θ ) ² } ^1/2 . Hereinafter, Δa ^* b ^* may be referred to as "chromaticity difference". In the range of θ=5 to 50°, the chromaticity difference Δa ^* b ^* is more preferably 5.5 or less, even more preferably 5.0 or less, and particularly preferably 4.5 or less. Δa ^* b ^* may be 4.0 or less, 3.5 or less, or 3.0 or less.

The chroma C ^* of the specularly reflected light of the 2° incident light is preferably 5.0 or less, more preferably 4.0 or less, and even more preferably 3.0 or less. The chroma C ^* of the specularly reflected light of the 2° incident light may be 2.5 or less, or 2.0 or less.

From the viewpoint of suppressing coloring by making the reflected light a neutral color regardless of the viewing direction, the chroma C ^* of the specularly 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°.

<Optical design of anti-reflection layer>
By appropriately designing the thickness of the thin film constituting 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 of repeatedly applying the thin film interference formula to each interface of the thin film and adding up all the multiple reflected waves; and a method of calculating the reflection spectrum by a transfer matrix taking into account the boundary conditions of Maxwell's equations.

The reflection spectrum of the specularly reflected light when a D65 light source is incident is calculated for multiple incidence angles θ, and the luminous reflectance Y and the chromaticness indices a ^* and b ^* are calculated from the reflection spectrum for each θ. By repeatedly performing these optical calculations while changing the film thickness of the thin film constituting 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.

When the number of thin films constituting the antireflection layer is small, it is difficult to design the film thickness so that both Y _θ /Y ₂ and Δa ^* b ^* are small in any range of θ = 5 to 50 °. As shown in the following examples, when the number of stacked layers of the antireflection layer (total number of thin films) is large, it is possible to design the film thickness of the thin film so that both Y _θ /Y ₂ and Δa ^* b ^* are small regardless of the material constituting the antireflection layer. The antireflection layer preferably includes a total of 5 or more low refractive index layers and high refractive index layers, and preferably includes 3 or more low refractive index layers. It is more preferable that the antireflection layer includes a total of 6 or more low refractive index layers and high refractive index layers.

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.

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.

Reducing the reflectance near a wavelength of 550 nm tends to reduce the luminous reflectance Y. On the other hand, when an optical design is performed so that the reflectance near a wavelength of 550 nm is minimized, the reflectance at other wavelengths increases, the chromaticness indices a ^* and/or b ^* of the reflected light increase, and the reflected light tends to be colored.

In order to reduce the coloring of reflected light, it is preferable that the reflectance is uniform over a wide wavelength range of visible light. When the wavelength dependence of the refractive index of the thin film constituting the anti-reflection 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 slight differences in the film thickness of the thin film may cause coloring of the reflected light. From the viewpoint of increasing the degree of freedom in optical design and ensuring the allowable range (process margin) of the film thickness, it is preferable that the thin film constituting the anti-reflection layer has a small wavelength dispersion of the refractive index (change in the refractive index with change in wavelength).

The Abbe number ν _D of the high refractive index layer is preferably 20 or more, more preferably 23 or more, and even more preferably 25 or more. The Abbe number ν _D is expressed by ν _D = (n _D -1) / (n _{F - n C ) using the refractive index at a wavelength of 589 nm, the refractive index at a wavelength of 486 nm, and the refractive index at a wavelength of 656 nm, n D . The larger the Abbe number ν D , the smaller the} wavelength dispersion of the refractive index. There is no particular limit to the upper limit of the Abbe number ν _D of the high refractive index layer, but in general ceramic materials, the larger the Abbe number ν _D (the smaller the wavelength dispersion of the refractive index), the smaller the refractive index tends to be. From the viewpoint of sufficiently increasing the refractive index of the high refractive index layer and reducing the reflectance, the Abbe number ν _D of the high refractive index layer is preferably 40 or less, more preferably 30 or less, and even more preferably 28 or less.

The thickness of each thin film in the anti-reflection layer can 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 mentioned above, it is possible to optimize the thickness of the anti-reflection layer by calculating the reflection spectrum of the anti-reflection film using an optical model.

[Usage of anti-reflection film]
The anti-reflection film is used by being disposed on the surface of an image display device such as a liquid crystal display or an organic EL display. For example, by disposing the 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 EL 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 another film. 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.

The anti-reflection film of the present invention has a small difference in the characteristics of reflected light depending on the viewing direction, so even if the viewing direction is changed, the change in the characteristics of reflected light is small, making it possible to uniformize the image display device.

Below is an example of calculating the various characteristics of reflected light from an anti-reflection film using an optical model.

[Method for 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).

The obtained regular reflectance spectrum R(λ) was multiplied by the spectrum of CIE standard illuminant D65 to obtain a reflected light spectrum. From the obtained reflected light spectrum, the luminous reflectance Y and the chromaticness indices a ^* and b ^* of the CIELAB color system were calculated, and the chroma C ^* ={(a ^* ) ²⁺ (b ^* ) ² } ^1/2 was calculated from the values of a ^* and b ^* .

The above evaluation was performed at an incident angle of 2° and at incident angles θ in increments of 5° in the range of 5 to 50°, and the ratio Y _θ /Y ₂ of the luminous reflectance Y ₂ of specularly reflected light of 2° incident light to the luminous reflectance Y _θ of specularly reflected light of θ° incident light, and the distance Δa ^* b ^* = {(a ^* ₂ - a ^* _θ ) ² + (b ^* ₂ - b ^* _θ ) ² } ^1/2 on the a ^* b ^* plane between the specularly reflected light of 2° incident light and the specularly reflected light of θ° incident light were calculated.

<Refractive index of thin film>
In each of the examples and comparative examples, silicon oxide (SiO ₂ ) was used as the low refractive index layer, and niobium oxide (Nb ₂ O ₅ ), titanium oxide (TiO ₂ ), silicon nitride (Si ₃ N ₄ ), and silicon oxynitride (SiON) were used as the high refractive index layer. The amount of oxygen introduced during sputtering film formation 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. The refractive indexes of the other thin films were values from the database. Table 1 shows the refractive indexes n ₄₀₀ , n ₅₅₀ , and n 700 of each thin film at wavelengths of 400 nm, 500 nm, and ₇₀₀ nm, as well as the Abbe number ν _D.

Example 1
The above optical simulation was carried out for an antireflection film having an 8-layer structure of an antireflection 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 order on the acrylic hard coat layer of the hard coat film, and an antifouling layer made of a fluorine-based resin having a thickness of 5 nm thereon. The refractive indexes of the hard coat film (acrylic hard coat layer) and the antifouling layer made of a fluorine-based resin were measured by spectroscopic ellipsometry (refractive index at a wavelength of 550 nm of the hard coat layer: 1.54, refractive index at a wavelength of 550 nm of the antifouling layer: 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.

<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.

[Evaluation results]
The configurations of the antireflection films of Examples 1 to 7 and Comparative Examples 1 and 2 and the results of the optical simulation are shown in Table 2. In Table 2, the unit of the numerical values for the thickness of each layer is nm, and they are listed as the first layer, the second layer, the 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°.

In Example 1 and Example 2, in which the antireflection layer is composed of a total of eight layers, including four high-refractive index layers and four low-refractive index layers, the maximum value of Y _θ /Y ₂ is small, and the maximum value of Δa ^* b ^* is also small. In Examples 3 to 6, in which the antireflection layer is composed of a total of six layers, including three high-refractive index layers and three low-refractive index layers, the maximum value of Y _θ /Y ₂ is small, and the maximum value of Δa ^* b ^* is also small. In Example 6, in which SiON (2) with a large Abbe number ν _D (small wavelength dispersion of refractive index) is used as the high-refractive index layer, there was a tendency for Δa ^* b ^* to become small, but on the other hand, the reflectance when viewed from the front was high. This is thought to be related to the fact that the reflectance could not be sufficiently reduced due to the small refractive index difference between the high-refractive index layer and the low-refractive index layer.

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 the maximum value of _Yθ / _Y2 exceeded 6. In Comparative Example 1, the maximum value of Δa ^* b ^* also exceeded 6, whereas in Comparative Example 2, the maximum value of _Yθ / _Y2 was 6 or less, but the change in a ^* of the reflected light depending on the viewing direction was large, with the maximum value of Δa ^* b ^* being approximately 11.

[Change in thickness of 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 to carry out a similar simulation. The thickness of the antireflection layer in each antireflection film, the characteristics of 2° regular reflection light, and the maximum values of Y _θ /Y ₂ and Δa ^* b ^* in the range of θ = 5 to 45° are shown in Table 3. In Table 3, the antireflection film No. 1 is the same as that of Example 1. Nos. 2 to 5 have a changed thickness of the first layer (high refractive index layer), Nos. 6 to 9 have a changed thickness of the second layer (low and high refractive index layer), Nos. 10 to 13 have a changed thickness of the third layer (high refractive index layer), Nos. 14 to 17 have a changed thickness of the fourth layer (low and high refractive index layer), Nos. 18 to 21 have a changed thickness of the fifth layer (high refractive index layer), Nos. 22 to 25 have a changed thickness of the sixth layer (low and high refractive index layer), and Nos. Nos. 26 to 29 have a different thickness for the seventh layer (high refractive index layer), and Nos. 30 to 33 have a different thickness for the eighth layer (low/high refractive index layer).

From the results shown in Table 3, it can be seen that an antireflection film having Y θ / _{Y 2} of 6% or less in the range of θ = 5 to 45° and Δa * b * of 6 or less can be obtained if the thickness of the first layer (Nb ₂ O ₅ ) is 8 to 10 nm, the thickness of the second layer (SiO ₂ ) is 41 to 45 nm, the thickness of the third layer (Nb ₂ O ₅ ) is 21 to ₂₅ nm, the thickness of the fourth layer (SiO ₂ ) is 18 to 20 nm, the thickness of the fifth layer (Nb ₂ O ₅ ) is 77 to 95 nm, the thickness of the sixth layer (SiO ₂ ) is 10.5 to 15 nm, the thickness of the seventh layer ( _Nb 2 O 5 ) is 25 to 30 nm, and the thickness of the ^eighth layer (SiO ₂ ⁾ is about 60 to 89 nm.

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.

From the results shown in Table 4, it can be seen that an antireflection film having Y θ / _{Y2 of} 6% or less in the range of θ = 5 to 45° and Δa _*b * of 6 or less can be obtained if the thickness of the first layer (Si ₃ N ₄ ) is 5 to 10 nm, the thickness of the second layer (SiO ₂ ) is 48 to 60 nm, the thickness of the third layer (Si ₃ N ₄ ) is 23 to 27 nm, the thickness of the fourth layer (SiO ₂ ) is 23 to 32 nm, the thickness of the fifth layer (Si ₃ N ₄ ) is 85 to 105 nm, the thickness of the sixth layer (SiO ₂ ) is 4 to 7 nm, the thickness of the seventh layer (Si ³ N 4 ) is 40 to 50 nm, and the thickness of the eighth layer ( _{SiO 2} ⁾ is approximately 70 to 95 nm.

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.

From the results shown in Table ₅ , it can be seen that an antireflection film having Y θ _{/Y2 of 6% or less in the range of θ = 5 to 45° and Δa*b* of 6 or less can be obtained if the thickness of the first layer (Nb 2 O 5 ) is in} the range of 9 to 10.5 nm, the thickness of the second layer (SiO ₂ ) is in the range of 41 to 47 nm, the thickness of the third layer (Nb ₂ O ₅ ) is in the range of 25 to 28 nm, the thickness of the fourth layer (SiO ₂ ) is in the range of 39 to 42 nm, the thickness of the fifth layer ( _Nb ² O 5 ) is in the range of 17 to 23 nm, and the thickness of the sixth layer (SiO ₂ ⁾ is in the range of approximately 90 to 106 nm.

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.

The results shown in Table 6 show that _{an antireflection film having a Y θ /Y2 of 6% or less in the range of θ = 5 to 45° and a Δa*b* of 6 or less can be obtained if the thickness of the first layer (Si 3 N 4 ) is in the} range of 13 to 16.5 nm, the thickness of the second layer (SiO ₂ ) is in the range of 32 to 40 nm, the thickness of the third layer (Si ₃ N ₄ ) is in the range of 47 to 55 nm, the thickness of the fourth layer (SiO ₂ ) is in the range of 20.5 to 24 nm, the thickness of the fifth layer (Si ³ N 4 ) is in the range of 34 to 44.5 nm, and the thickness of the sixth layer ( _{SiO 2} ⁾ is in the range of 82 to 98 nm.

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.

From the results shown in Table 7, it can be seen that an antireflection film having Y θ / _Y2 of 6% or less in the range of θ = 5 to 45° and Δa*b* of 6 or less can be obtained if the thickness of the first layer (SiON) is in the range of 13 to 19.5 nm, the thickness of the second layer (SiO ₂ ) 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 (SiO ₂ ) 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 ⁽ _{SiO 2} ⁾ is in the range of approximately 65 to 95 nm.

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.

<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.

As shown in Tables 8 and 9, when the number of thin films constituting the antireflection layer was four, even if the thickness of the thin films was changed, no antireflection film was obtained in which Y _θ /Y ₂ was 6% or less and Δa ^* b ^* was 6 or less for any θ in the range of θ = 5 to 45°.

The above results show that by making the anti-reflection film consist of five or more thin layers, preferably six or more thin layers, more precise optical design becomes possible, and an anti-reflection film can be obtained that exhibits minimal change in the characteristics of reflected light when the viewing direction is changed.

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 therefore it is difficult to define it in general. On the other hand, as shown in Tables 3 to 7, it is possible to find conditions for smaller Y _θ /Y ₂ and Δa ^* b ^* by repeating optical simulations while changing the thickness of the thin film constituting the antireflection film. Therefore, even when using a thin film made of a material other than those shown in the above examples, it is possible to design an antireflection film in which the change in the characteristics of reflected light when the viewing direction is changed is small.

[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 Nb 2} O ₅ layer), and a similar simulation was carried out. The results of the optical simulation of Example 1B are shown in Table 10 together with the results of Example 1.

In Example 1B, the chromaticness indices a ^* ₂ and b ^* ₂ of the regular reflected light were slightly different from those in Example 1, but the values of _Yθ / _Y2 and Δa ^* b ^* , which are indexes of the change in the reflected light characteristics when the angle θ is changed, were not significantly different from those in Example 1. From this result, it can be seen that even when a primer layer is provided between the film substrate and the antireflection layer, an antireflection film with small changes in the characteristics of the reflected light when the viewing direction is changed can be obtained by adjusting the lamination structure and film thickness of the antireflection layer as in the above-mentioned respective examples.

REFERENCE SIGNS LIST 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-reflection film

Claims (10)

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 a total of eight thin layers including, from the film substrate side, a Nb ₂ O _5- layer having a thickness of 8 to 10 nm, a SiO _2- layer having a thickness of 41 to 45 nm, a Nb ₂ O _5- layer having a thickness of 21 to 25 nm, a SiO ₂ -layer having a thickness of 18 to 20 nm, a Nb ₂ O _5- layer having a thickness of 77 to 95 nm, a SiO _2- layer having a thickness of 10.5 to 15 nm, a Nb ₂ O _5- layer having a thickness of 25 to 30 nm, and a SiO _2- layer having a thickness of 60 to 89 nm;
An antireflection film in which specular reflection light of a D65 light source irradiated from the antireflection layer side satisfies the following characteristics (A) and (B):
(A) The luminous reflectance _Y2 of the specularly reflected light of 2° incident light and the luminous reflectance _Yθ of the specularly reflected light of θ° incident light satisfy _Yθ / _Y2 ≦6.0 at any angle θ in the range of 5 to 50°.
(B) The chromaticity indices a ^* ₂ and b ^* ₂ of the specularly reflected light of 2° incident light and the chromaticity indices a ^* _θ and b ^* _θ of the specularly reflected light of θ° incident light satisfy {(a ^* ₂ - a ^* _θ ) ² + (b ^* ₂ - b ^* _θ ) ² } ^1/2 ≦6.0 at any angle θ in the range of 5 to 50°. 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 a total of eight thin layers including, from the film substrate side, a 5-10 nm thick Si ₃ N _4- layer, a 48-60 nm thick SiO _2- layer, a 23-27 nm thick Si ₃ N _4- layer, a 23-32 nm thick SiO _2- layer, a 85-105 nm thick Si ₃ N _4- layer, a 4-7 nm thick SiO _2- layer, a 40-50 nm thick Si ₃ N _4- layer, and a 70-95 nm thick SiO _2- layer,
An antireflection film in which specular reflection light of a D65 light source irradiated from the antireflection layer side satisfies the following characteristics (A) and (B):
(A) The luminous reflectance _Y2 of the specularly reflected light of 2° incident light and the luminous reflectance _Yθ of the specularly reflected light of θ° incident light satisfy _Yθ / _Y2 ≦6.0 at any angle θ in the range of 5 to 50°.
(B) The chromaticity indices a ^* ₂ and b ^* ₂ of the specularly reflected light of 2° incident light and the chromaticity indices a ^* _θ and b ^* _θ of the specularly reflected light of θ° incident light satisfy {(a ^* ₂ - a ^* _θ ) ² + (b ^* ₂ - b ^* _θ ) ² } ^1/2 ≦6.0 at any angle θ in the range of 5 to 50°. 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 a total of six thin layers including, from the film substrate side, _five Nb ₂ O layers having a thickness of 9 to 10.5 nm, _two SiO layers having a thickness of 41 to 47 nm, _five Nb ₂ O layers having a thickness of 25 to 28 nm, _two SiO layers having a thickness of 39 to 42 nm, _five Nb ₂ O layers having a thickness of 17 to 23 nm, and _two SiO layers having a thickness of 90 to 106 nm;
An antireflection film in which specular reflection light of a D65 light source irradiated from the antireflection layer side satisfies the following characteristics (A) and (B):
(A) The luminous reflectance _Y2 of the specularly reflected light of 2° incident light and the luminous reflectance _Yθ of the specularly reflected light of θ° incident light satisfy _Yθ / _Y2 ≦6.0 at any angle θ in the range of 5 to 50°.
(B) The chromaticity indices a ^* ₂ and b ^* ₂ of the specularly reflected light of 2° incident light and the chromaticity indices a ^* _θ and b ^* _θ of the specularly reflected light of θ° incident light satisfy {(a ^* ₂ - a ^* _θ ) ² + (b ^* ₂ - b ^* _θ ) ² } ^1/2 ≦6.0 at any angle θ in the range of 5 to 50°. 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 a total of six thin layers including, from the film substrate side, a 4-layer Si ₃ N _2- layer having a thickness of 13 to 16.5 nm, a 2-layer SiO _2- layer having a thickness of 32 to 40 nm, a 4-layer Si ₃ N _2- layer having a thickness of 47 to 55 nm, a 2-layer SiO _2- layer having a thickness of 20.5 to 24 nm, a 4-layer Si ₃ N _2- layer having a thickness of 34 to 44.5 nm, and a 2-layer SiO _2- layer having a thickness of 82 to 98 nm;
An antireflection film in which specular reflection light of a D65 light source irradiated from the antireflection layer side satisfies the following characteristics (A) and (B):
(A) The luminous reflectance _Y2 of the specularly reflected light of 2° incident light and the luminous reflectance _Yθ of the specularly reflected light of θ° incident light satisfy _Yθ / _Y2 ≦6.0 at any angle θ in the range of 5 to 50°.
(B) The chromaticity indices a ^* ₂ and b ^* ₂ of the specularly reflected light of 2° incident light and the chromaticity indices a ^* _θ and b ^* _θ of the specularly reflected light of θ° incident light satisfy {(a ^* ₂ - a ^* _θ ) ² + (b ^* ₂ - b ^* _θ ) ² } ^1/2 ≦6.0 at any angle θ in the range of 5 to 50°. 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 a total of six thin layers including, from the film substrate side, a SiON layer having a thickness of 13 to 19.5 nm, a _SiO2 layer having a thickness of 22 to 37 nm, a SiON layer having a thickness of 58 to 80 nm, a _SiO2 layer having a thickness of 2 to 10 nm, a SiON layer having a thickness of 59 to 85 nm, and a _SiO2 layer having a thickness of 65 to 95 nm;
An antireflection film in which specular reflection light of a D65 light source irradiated from the antireflection layer side satisfies the following characteristics (A) and (B):
(A) The luminous reflectance _Y2 of the specularly reflected light of 2° incident light and the luminous reflectance _Yθ of the specularly reflected light of θ° incident light satisfy _Yθ / _Y2 ≦6.0 at any angle θ in the range of 5 to 50°.
(B) The chromaticity indices a ^* ₂ and b ^* ₂ of the specularly reflected light of 2° incident light and the chromaticity indices a ^* _θ and b ^* _θ of the specularly reflected light of θ° incident light satisfy {(a ^* ₂ - a ^* _θ ) ² + (b ^* ₂ - b ^* _θ ) ² } ^1/2 ≦6.0 at any angle θ in the range of 5 to 50°. The antireflection film according to any one of claims 1 to 5, wherein the luminous reflectance _Y2 of specularly reflected light of 2° incident light is 1.0% or less. 7. The anti-reflection film according to claim 1, wherein the luminous reflectance Y _θ of specularly reflected light of θ° incident light is 3.0% or less at any angle θ in the range of 5 to 50°. 8. The antireflection film according to claim 1, wherein the chromaticness indices a ^* ₂ and b ^* ₂ of specularly reflected light of 2° incident light satisfy {(a ^* ₂ ) ² +(b ^* ₂ ) ² } ^1/2 ≦5.0. 9. The antireflection film according to claim 1, wherein the chromaticity indices a ^* _θ and b ^* _θ of specularly reflected light of θ° incident light satisfy {(a ^* _θ ) ² + (b ^* _θ ) ² } ^1/2 ≦9.0 at any angle θ in the range of 5 to 50°. An image display device in which the anti-reflection film according to any one of claims 1 to 9 is disposed on the viewing side surface of an image display medium.

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