JP7513136B2 - Retardation film, polarizing plate compensation film, and external light anti-reflection film - Google Patents

Description

The present invention relates to a retardation film, a polarizing plate compensation film including the retardation film, and an external light anti-reflection film.

As an optical film applied to image display devices, etc., there is a phase difference film that imparts a desired phase difference to incident light by a phase difference layer. For example, in an organic electroluminescence (organic EL) display device, a λ/4 phase difference film is used as a circular polarizer in combination with a linear polarizer, and functions as an external light anti-reflection film. Also, in a liquid crystal display device such as an IPS mode, a phase difference film that combines a positive A plate with positive A characteristics and a positive C plate with positive C characteristics is used as part of a polarizer compensation film in order to increase the contrast in the field of view from an oblique direction (for example, Patent Document 1).

Here, the positive A characteristics are characterized in that when the refractive index in the X-axis direction along the layer surface is Nx, the refractive index in the Y-axis direction along the layer surface and perpendicular to the X-axis is Ny, and the refractive index in the layer thickness direction is Nz, the relationship Nx>Ny≈Nz is satisfied and the optical axis is in the Nx direction.
The negative A characteristic is characterized in that the relationship Nz≈Nx>Ny holds and the optical axis is in the Ny direction.
The positive C characteristic is characterized in that the relationship Nz>Nx≈Ny holds and the optical axis is in the Nz direction.
The negative C characteristic is characterized in that the relationship Nx≈Ny>Nz holds and the optical axis is in the Nz direction.

JP 2016-53709 A

However, when the A and C plates were combined as previously proposed, the color of the film often changed depending on the viewing angle, and improvements were needed.

In view of the above problems, the present invention aims to provide a retardation film in which a positive A plate and a positive C plate are laminated, and which can suppress color change depending on the viewing angle. It also provides a polarizing plate compensation film and an external light anti-reflection film that include the retardation film.

As a result of intensive research into the above-mentioned problems, the inventors have discovered that in a retardation film in which a positive A plate and a positive C plate are laminated, the positive A plate has positive wavelength dispersion characteristics, which makes it possible to suppress color change due to viewing angle, and have completed the present invention.
Here, the positive wavelength dispersion characteristic is a wavelength dispersion characteristic in which the phase difference in the transmitted light is larger on the shorter wavelength side, and more specifically, in the positive A plate, the relationship between the front retardation (Re ₄₅₀ ) at a wavelength of 450 nm and the front retardation (Re ₅₅₀ ) at a wavelength of 550 nm is Re ₄₅₀ > Re ₅₅₀ , and Re ₄₅₀ / Re ₅₅₀ > 1.0. In the positive C plate, the relationship between the thickness direction retardation (Rth ₄₅₀ ) at a wavelength of 450 nm and the thickness direction retardation (Rth ₅₅₀ ) at a wavelength of 550 nm is Rth ₄₅₀ > Rth ₅₅₀ , and Rth ₄₅₀ / Rth ₅₅₀ > 1.
On the other hand, the inverse wavelength dispersion characteristic is a wavelength dispersion characteristic in which the phase difference in the transmitted light is smaller on the shorter wavelength side, and more specifically, in the positive A plate, the relationship between the front retardation (Re ₄₅₀ ) at a wavelength of 450 nm and the front retardation (Re ₅₅₀ ) at a wavelength of 550 nm is Re ₄₅₀ < Re ₅₅₀ , and Re ₄₅₀ /Re ₅₅₀ < 1.0. In the positive C plate, the relationship between the thickness direction retardation (Rth ₄₅₀ ) at a wavelength of 450 nm and the thickness direction retardation (Rth ₅₅₀ ) at a wavelength of 550 nm is Rth ₄₅₀ < Rth ₅₅₀ , and Rth ₄₅₀ /Rth ₅₅₀ < 1.0.
The present invention will now be described.

The present application relates to a retardation film which is used together with a liquid crystal display panel or an organic EL display panel and is arranged as a part of an image display device, the retardation film having a positive A plate having positive A type characteristics and a positive C plate having positive C type characteristics, in which, when the front retardation of the positive A plate at a wavelength of 450 nm is Re _A450 and the front retardation at a wavelength of 550 nm is Re _A550 , ΔN _A obtained by Re _A450 /Re _A550 is 0.94 or more and 1.10 or less, and when the thickness direction retardation of the positive C plate at a wavelength of 450 nm is Rth _C450 and the thickness direction retardation at a wavelength of 550 nm is Rth _C550 , ΔN A obtained by Rth _C450 /Rth _C550 is 0.94 or more and 1.10 or less. The present invention discloses a retardation film in which _C is 0.82 or more and 1.00 or less, Rth _p is a thickness direction retardation at a wavelength of 450 nm in a laminated state of a positive A plate and a positive C plate, Rth _q is a thickness direction retardation at a wavelength of 550 nm in a laminated state of the positive A plate and the positive C plate, and Rth _r is a thickness direction retardation at a wavelength of 650 nm in a laminated state of the positive A plate and the positive C plate, and the difference between the maximum value and the minimum value of Rth _p , Rth _q , and Rth _r is 25 or less.

In the above retardation film, at least one of the positive A plate and the positive C plate may contain a polymerizable rod-like liquid crystal material.

In the above retardation film, the front retardation of the positive A plate at a wavelength of 550 nm may be 110 nm or more and 160 nm or less.

This application discloses a polarizing plate compensation film that includes two polarizing plates and the above-mentioned retardation film disposed between the two polarizing plates.

This application discloses an external light anti-reflection film that includes the above-mentioned retardation film that is placed on the light output side of an organic EL laminate, and a linearly polarizing polarizer that is laminated on the retardation film.

According to the present invention, even in a retardation film in which a positive A plate and a positive C plate are laminated, it is possible to suppress color change due to the viewing angle. This can also be applied to a polarizing plate compensation film or an external light anti-reflection film.

FIG. 2 is a diagram showing an example of a layer structure of a retardation film 10. 1 is a diagram illustrating a layer structure of a liquid crystal display device 20 to which a retardation film 10 is applied. 1 is a diagram illustrating a layer structure of an organic EL display device 30 to which a retardation film 10 is applied. FIG. 1 is a diagram illustrating the evaluation method in the examples. FIG. 13 is a diagram illustrating evaluation of hue in the examples.

The present invention will be described in detail below with specific examples. However, the present invention is not limited to the following examples, and various modifications are possible without departing from the gist of the present invention.

1 is a diagram for explaining the layer structure of a retardation film 10 according to one embodiment. In this embodiment, for example, for an image display device, the retardation film 10 is arranged in a liquid crystal display panel or an organic EL display panel together with various other optical films, thereby improving various optical characteristics. Examples of the optical characteristics include external light reflection, improvement of viewing angle characteristics, and optical compensation for reducing light leakage in oblique directions.
As can be seen from FIG. 1, the retardation film 10 of this embodiment is configured to include a substrate 11, an alignment film 12, a positive C plate 13, and a positive A plate 14.

Examples of the substrate 11 include glass substrates, metal foils, and resin substrates. Among these, the substrate is preferably transparent, and can be appropriately selected from conventionally known transparent substrates. Examples of the transparent substrate include glass substrates, as well as transparent resin substrates formed using resins such as acetylcellulose-based resins such as triacetylcellulose, polyester-based resins such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, and polylactic acid, olefin-based resins such as polypropylene, polyethylene, and polymethylpentene, acrylic resins, polyurethane resins, polyethersulfone, polycarbonate, polysulfone, polyether, polyether ketone, acrylonitrile, methacrylonitrile, cycloolefin polymers, and cycloolefin copolymers.

The substrate 11 preferably has a transmittance of 80% or more in the visible light region, and more preferably 90% or more. Here, the transmittance of the substrate can be measured according to JIS K7361-1 (Test method for total light transmittance of plastic transparent materials).

The thickness of the substrate 11 is not particularly limited as long as it is within a range that can provide the necessary support depending on the application of the retardation film, but is usually in the range of about 10 μm to 200 μm. Among them, the thickness of the substrate is preferably in the range of 25 μm to 125 μm, and more preferably in the range of 30 μm to 100 μm. If the thickness is thicker than the above range, for example, when a long retardation film is formed and then cut into sheets of retardation film, processing waste may increase or the cutting blade may wear out quickly.

In this embodiment, the alignment film 12 is a layer for aligning the liquid crystal component contained in the positive C plate 13 in a certain direction, and is a vertical alignment film. However, the alignment film can be any necessary one depending on the properties of the liquid crystal component of the positive C plate. For example, if the liquid crystal component of the positive C plate itself has a vertical alignment property, the alignment film does not necessarily have a vertical alignment control force.
In this embodiment, the vertical alignment film is an alignment film having a vertical alignment control force, and can be any of various vertical alignment films used in the manufacture of known C-plate retardation films and various vertical alignment films applied to VA liquid crystal display devices, for example, a polyimide alignment film, an alignment film made of LB film, etc. Specifically, as a constituent material of the alignment film, for example, lecithin, a silane-based surfactant, a titanate-based surfactant, a pyridinium salt-based polymer surfactant, a silane coupling-based composition for vertical alignment film such as n-octadecyltriethoxysilane, a soluble polyimide having a long-chain alkyl group or an alicyclic structure in its side chain, or a polyamic acid having a long-chain alkyl group or an alicyclic structure in its side chain can be used.

The method for forming the alignment film 12 is not particularly limited, but for example, an alignment film can be formed by applying a composition for forming an alignment film onto the substrate 11 and imparting an alignment control force to the composition. The means for imparting an alignment control force to the alignment film can be a conventionally known means.

The thickness of the alignment film 12 may be set appropriately as long as it can align the liquid crystal components in the positive C plate 13 in a certain direction. The thickness of the alignment film is usually in the range of 1 nm to 10 μm, and preferably in the range of 60 nm to 5 μm.

The positive C plate 13 is a layer that performs optical functions having positive C characteristics. This positive C plate 13 can be made of a polymerizable liquid crystal composition that contains a liquid crystal compound, which is a liquid crystal material used to prepare retardation layers for various optical films. In other words, in this positive C plate 13, the liquid crystal compound is vertically (homeotropically) aligned.

Here, the positive C plate 13 only needs to have positive C-type characteristics, and it does not matter whether the wavelength dispersion characteristics are positive or negative.

The thickness of the positive C plate 13 is not particularly limited, but is preferably 0.3 μm or more and 3.0 μm or less.

In this embodiment, the polymerizable liquid crystal composition preferably contains a liquid crystal compound (rod-shaped compound) that exhibits liquid crystallinity and has a polymerizable functional group in the molecule.
Therefore, the liquid crystal compound is not particularly limited and may be any conventionally known liquid crystal compound. For example, a positive C plate having a positive wavelength dispersion characteristic may be exemplified by the one described in JP-A-2016-53709, and a positive C plate having a reverse wavelength dispersion characteristic may be exemplified by the one described in JP-A-2010-522892.
As the liquid crystal compound, a material exhibiting a liquid crystal phase such as a nematic phase or a smectic phase can be mentioned, but it is more preferable to use a liquid crystal compound exhibiting a nematic phase, since it is easier to arrange the liquid crystal compound in a regular manner compared to liquid crystal compounds exhibiting other liquid crystal phases. As the liquid crystal compound exhibiting a nematic phase, it is preferable to use a material having spacers on both ends of the mesogen. A liquid crystal compound having spacers on both ends of the mesogen has excellent flexibility.

In addition, as described above, the liquid crystal compound is preferably a polymerizable liquid crystal compound having a polymerizable functional group in the molecule. By having a polymerizable functional group, it is possible to polymerize and fix the liquid crystal compound, so that the alignment stability is excellent and the retardation property is less likely to change over time. In addition, it is more preferable that the polymerizable liquid crystal compound has a polymerizable functional group capable of three-dimensional crosslinking in the molecule. By having a polymerizable functional group capable of three-dimensional crosslinking, the alignment stability can be further improved. Note that "three-dimensional crosslinking" refers to polymerizing liquid crystal molecules with each other in three dimensions to form a network structure.

Examples of polymerizable functional groups include those that polymerize due to the action of ionizing radiation such as ultraviolet light or electron beams, or heat. Examples of such polymerizable functional groups include radically polymerizable functional groups. Representative examples of radically polymerizable functional groups include functional groups that have at least one ethylenically unsaturated double bond capable of addition polymerization, and specific examples include vinyl groups with or without substituents, acrylate groups (a general term that includes acryloyl groups, methacryloyl groups, acryloyloxy groups, and methacryloyloxy groups), etc.

In addition, it is particularly preferable that the liquid crystal compound has a polymerizable functional group at the end. By using such liquid crystal compounds, for example, the compounds can be polymerized three-dimensionally to form a network structure, making it possible to form a retardation film that is stable and has excellent optical properties.

The content of the liquid crystal compound in the polymerizable liquid crystal composition is not particularly limited, but is preferably 5 parts by mass or more and 40 parts by mass or less, and more preferably 10 parts by mass or more and 30 parts by mass or less, when the entire polymerizable liquid crystal composition is taken as 100 parts by mass. If the amount of the liquid crystal compound is less than 5 parts by mass, the content is too small and the light incident on the positive C plate 13 may not be polarized appropriately. On the other hand, if the amount exceeds 40 parts by mass, the viscosity of the polymerizable liquid crystal composition becomes too high, which reduces the workability of producing the layer.

The liquid crystal compounds can be used alone or in combination of two or more.

The liquid crystal compounds described above are usually dissolved in a solvent. The solvent must be capable of uniformly dispersing the liquid crystal compounds described above, and any known solvent can be used. Examples of such solvents include hydrocarbons such as toluene and xylene, ketones such as acetone, methyl ethyl ketone, cyclohexanone, and methyl isobutyl ketone, ethers such as tetrahydrofuran, glycol ethers such as 1-methoxy-2-propanol and 1-methoxypropyl-2-acetate, and esters such as methyl acetate, ethyl acetate, and butyl acetate.

The content of the solvent in the polymerizable liquid crystal composition is preferably 66 parts by mass or more and 1900 parts by mass or less per 100 parts by mass of the liquid crystal compound. If the amount of the solvent is less than 66 parts by mass, the liquid crystal compound may not be uniformly dissolved. On the other hand, if the amount of the solvent exceeds 1900 parts by mass, some of the solvent may remain, reducing reliability and preventing uniform coating. From this viewpoint, it is more preferable that the amount is 900 parts by mass or less.

In addition, the polymerizable liquid crystal composition may contain other additives as necessary. There are no particular limitations on the other compounds as long as they do not impair the alignment order of the above-mentioned liquid crystal compounds, and examples of such compounds include plasticizers, surfactants, and silane coupling agents.

The positive A plate 14 has positive A characteristics and preferably has positive wavelength dispersion characteristics to perform optical functions. The positive A plate 14 is a liquid crystal material used to prepare retardation layers for various optical films, and is preferably composed of a polymerizable liquid crystal composition containing a liquid crystal compound with positive wavelength dispersion characteristics. In other words, the liquid crystal compound has homogeneous orientation.

Specifically, the positive A plate 14 has positive A type characteristics, and when the front retardation at a wavelength of 450 nm is Re _A450 and the front retardation at a wavelength of 550 nm is Re _A550 , it is preferable that ΔN _A obtained by Re _A450 /Re _A550 is greater than 1.0.

The thickness of the positive A plate 14 is not particularly limited, but is preferably 0.3 μm or more and 3.0 μm or less.

The polymerizable liquid crystal composition constituting the positive A plate 14 preferably contains a liquid crystal compound (rod-shaped compound) that exhibits liquid crystallinity and has a polymerizable functional group in the molecule. The liquid crystal compound is not particularly limited and refers to all liquid crystal compounds contained in the composition that forms the positive A plate, and may be composed of one liquid crystal compound or a mixture of two or more liquid crystal compounds.

As the liquid crystal compound, any conventionally known liquid crystal compound can be used without any particular limitation as long as it exhibits positive wavelength dispersion characteristics. Examples of such compounds include those represented by the following formulas (1) to (17).

Examples of polymerizable functional groups include those that polymerize due to the action of ionizing radiation such as ultraviolet light or electron beams, or heat. Examples of such polymerizable functional groups include radically polymerizable functional groups. Representative examples of radically polymerizable functional groups include functional groups that have at least one ethylenically unsaturated double bond capable of addition polymerization, and specific examples include vinyl groups with or without substituents, acrylate groups (a general term that includes acryloyl groups, methacryloyl groups, acryloyloxy groups, and methacryloyloxy groups), etc.

The content of the liquid crystal compound in the polymerizable liquid crystal composition is not particularly limited, but is preferably 5 parts by mass or more and 40 parts by mass or less, and more preferably 10 parts by mass or more and 30 parts by mass or less, when the entire polymerizable liquid crystal composition is taken as 100 parts by mass. If the amount of the liquid crystal compound is less than 5 parts by mass, the content is too small and the light incident on the positive A plate 14 may not be polarized appropriately. On the other hand, if the amount exceeds 40 parts by mass, the viscosity of the polymerizable liquid crystal composition becomes too high, which reduces the workability of producing the layer.

The liquid crystal compounds described above are usually dissolved in a solvent. The solvent must be capable of uniformly dispersing the liquid crystal compounds described above, and any known solvent can be used. Examples of such solvents include hydrocarbons such as toluene and xylene, ketones such as acetone, methyl ethyl ketone, cyclohexanone, and methyl isobutyl ketone, ethers such as tetrahydrofuran, glycol ethers such as 1-methoxy-2-propanol and 1-methoxypropyl-2-acetate, and esters such as methyl acetate, ethyl acetate, and butyl acetate.

The content of the solvent in the polymerizable liquid crystal composition is preferably 66 parts by mass or more and 1900 parts by mass or less per 100 parts by mass of the liquid crystal compound. If the amount of the solvent is less than 66 parts by mass, the liquid crystal compound may not be uniformly dissolved. On the other hand, if the amount of the solvent exceeds 1900 parts by mass, some of the solvent may remain, reducing reliability and preventing uniform coating. From this viewpoint, it is more preferable that the amount is 900 parts by mass or less.

In addition, the polymerizable liquid crystal composition may contain other additives as necessary. The other compounds are not particularly limited as long as they do not impair the alignment order of the above-mentioned liquid crystal compounds, and examples thereof include plasticizers, surfactants, and silane coupling agents.

The retardation film 10 having the above configuration has the following features: That is, the positive A plate has a positive wavelength dispersion in which ΔN _A obtained by Re _A450 /Re _A550 is greater than 1.0, where Re _A450 is the front retardation at a wavelength of 450 nm and Re _A550 is the front retardation at a wavelength of 550 nm.

Preferably, when the thickness direction retardation of the positive C plate at a wavelength of 450 nm is Rth _C450 and the thickness direction retardation at a wavelength of 550 nm is Rth _C550 , in ΔN _C obtained by Rth _C450 /Rth _C550 ,
There is a relationship of |ΔN _A -ΔN _C |≦0.2.

More preferably, in a state where the positive A plate and the positive C plate are laminated, the thickness direction retardation at a wavelength of 450 nm is Rth _p , the thickness direction retardation at a wavelength of 550 nm is Rth _q , the thickness direction retardation at a wavelength of 650 nm is Rth _r , and the difference between the maximum value and the minimum value of Rth _p , Rth _q , and Rth _r is Rth _s , Rth _s is not more than 25. It is further preferable that the front retardation Re _A550 of the positive A plate at a wavelength of 550 nm is 110 nm or more and 160 nm or less.

This allows the retardation film to fulfill its basic functions of reflecting external light and providing optical compensation, while also suppressing color changes due to viewing angle.

In addition to the above, ΔN _A ≒ 1.0 and 0.82≦ΔN _C ≦ 1.00 may be satisfied. This also allows the retardation film to exhibit its basic functions of reflecting external light and optical compensation, and suppresses color change due to the viewing angle. Here, ΔN _A ≒ 1.0 is specifically 0.94≦ΔN _A ≦ 1.10. More preferably, 0.95≦ΔN _A ≦ 1.05. Meanwhile, ΔN _C is more preferably 0.85≦ΔN _C ≦ 0.94. In this case, when using a positive A plate with reverse wavelength dispersion characteristics, a known liquid crystal material can be applied.

Next, a method for manufacturing the retardation film 10 will be described. For example, the retardation film 10 is constructed by including a base material supplying process, an alignment film forming process, a positive C plate forming process, and a positive A plate forming process.

In the substrate supply process, the substrate 11 is provided by a roll.

In the alignment film forming step, the alignment film 12 is formed on one surface of the base material 11. Specifically, the process is as follows.
The substrate 11 is pulled out from the supply reel, and the composition constituting the alignment film is laminated on the substrate 11. The method for laminating the composition on the substrate 11 is not particularly limited, and examples that can be used include die coating, gravure coating, reverse coating, knife coating, dip coating, spray coating, air knife coating, spin coating, roll coating, printing, immersion and pulling up, curtain coating, casting, bar coating, extrusion coating, E-type coating, and the like.
The laminated composition is then dried to form the alignment film 12 .

In the process of forming the positive C plate, the composition constituting the positive C plate is laminated on the alignment film 12 in the same manner as in the process of forming the alignment film, and the composition is cured by irradiating ultraviolet light to obtain the positive C plate 13. As the light source for irradiating ultraviolet light, a low pressure mercury lamp (germicidal lamp, fluorescent chemical lamp, black light), a high pressure discharge lamp (high pressure mercury lamp, metal halide lamp), a short arc discharge lamp (ultra-high pressure mercury lamp, xenon lamp, mercury xenon lamp), etc. can be used. Among them, a metal halide lamp, a xenon lamp, a high pressure mercury lamp, etc. can be preferably used. The wavelength of the ultraviolet light is appropriately set according to the material constituting the composition, etc., and specifically, it is preferable to use irradiation light having a wavelength of 210 nm or more and 380 nm or less, preferably 230 nm or more and 380 nm or less, and more preferably 250 nm or more and 380 nm or less. The amount of ultraviolet light irradiation (accumulated light amount) is not particularly limited, but is preferably within the range of 100 mJ/ ^cm2 to 1500 mJ/ ^cm2 , and more preferably within the range of 100 mJ/ ^cm2 to 800 mJ/ ^cm2 .

In the step of forming the positive A plate, for example, a composition constituting the positive A plate is laminated on the positive C plate 13 and cured. This can be performed in the same manner as in the formation of the positive C plate 13. In this case, it is preferable to provide an alignment film on the positive A plate.
However, the present invention is not limited to this, and a positive A plate may be separately prepared and then transferred and laminated onto a positive C plate.

Next, an optical function laminate to which the above-mentioned retardation film 10 is applied will be described. In this optical function laminate, the retardation film 10 can be included in one of the configurations of various optical function laminates arranged on an image display panel.

As a more specific example, we will explain the case where the present invention is applied to a liquid crystal display device equipped with a retardation film 10. Figure 2 is a diagram showing the layer structure of a liquid crystal display device 20 including a retardation film 10. In this liquid crystal display device 20, an optically functional laminate 26 is disposed on the exit surface side of a liquid crystal display panel 23. This includes a polarizer 27 for linear polarization and a retardation film 10, and is an example used for polarizing plate compensation.

The liquid crystal display device 20 is an IPS liquid crystal display device (In-plane Switching liquid crystal display; IPS-LCD), and a liquid crystal display panel 23 is disposed on the viewer's side of the backlight 22.

The liquid crystal display panel 23 is provided with a liquid crystal cell 25 made of IPS liquid crystal, and a linear polarizer 24 is provided on the backlight 22 side of the liquid crystal cell 25, for example, by a pressure-sensitive adhesive layer (not shown). The linear polarizer 24 is configured by sandwiching a polarizer that functions as a linear polarizer between two substrates made of transparent films.

In the liquid crystal display panel 23, an optical function laminate 26 is disposed on the exit surface of a liquid crystal cell 25. This optical function laminate 26 includes a retardation film 10 constituting a polarizing plate compensation film for polarizing plate compensation, a polarizer 27, and a substrate (protective film) 28 which is a surface material. A transparent film such as TAC is applied to the substrate 28, and a polarizer 27 is provided on the substrate as a linear polarizing plate.

In this way, the retardation film 10 that constitutes the optically functional laminate 26 functions as a polarizing plate compensation film from an oblique viewing angle over a wide bandwidth.

As another specific example, we will explain the case where the present invention is applied to an organic EL display device equipped with a retardation film 10. FIG. 3 is a diagram showing the layer structure of an organic EL display device 30 including a retardation film 10. In this organic EL display device 30, an optical function laminate 36 is an external light anti-reflection film arranged on the exit surface side of an organic EL display panel 33. This optical function laminate 36 includes a polarizer 37 for linearly polarizing light and a retardation film 10, and has an external light reflection function as a so-called circular polarizer.

The organic EL display device 30 is a device that provides an observer with image light that is self-emitting in the organic EL display panel 33, and an optical function laminate 36 is disposed on the emission surface of the organic EL display panel 33. This optical function laminate 36 functions as a circular polarizing plate for preventing reflection of external light, and includes a retardation film 10, a polarizer 37 as a linear polarizing plate, and a substrate (protective film) 38 that is a surface material. In this case, the positive A plate 14 of the retardation film 10 functions as a λ/4 retardation layer, and the positive C plate 13 is laminated on this.

In this way, the retardation film 10 that constitutes the optical function laminate 36 functions as an external light anti-reflection film.

In the examples, a laminate was modeled in accordance with the liquid crystal display panel 23 shown in FIG. 2 by simulation, and the ΔN _A of the positive A plate and the ΔN _C of the positive C plate of the retardation film 10 included therein were changed to evaluate the hue change at a viewing angle of 60°.

The simulation was performed using LCD-MASTER (Shintech Co., Ltd.). The model layer structure was, from the observer side, an upper polarizing plate with an absorption axis at 90 degrees to the reference, a positive C plate, a positive A plate with an optical axis parallel to the absorption axis of the upper polarizing plate, and a lower polarizing plate with an absorption axis at 0 degrees to the reference, with light being irradiated from the lower polarizing plate side.

[evaluation]
<Viewing angle hue change>
As shown in the schematic diagram of Figure 4, the color was measured at a viewing angle inclined at θ=60° with respect to the normal n extending from the center of the surface of the laminate to be evaluated. The upper diagram of Figure 4 is a plan view of the laminate, and the lower diagram of Figure 4 is a side view of the laminate. As can be seen from Figure 4, the viewing angle of θ=60° exists in a circular manner with O as the center, so the hue at each position was obtained around one circumference, starting from S and following the arrow K to draw a circle with O as the center.
As a result, as shown in Figures 5(a) and 5(b), a change in color occurs when the lens rotates around the circumference, and this change is expressed in xy coordinates of the xy color system. This makes it possible to evaluate the relationship between the orientation (circumferential position) and the color change at a 60° viewing angle.
The less the change in hue, the better, and it is preferable that the color does not cross over various colors when going around the entire circumference at a viewing angle of 60°. Therefore, it can be said that the thin shape shown by E2 in Fig. 5(b) has less change in hue and is more preferable than the nearly circular shape shown by E1 in Fig. 5(a).
Table 1 shows the results under each condition. In Table 1, shapes close to a circle, such as E1, are labeled "circular," while thin shapes, such as E2, are labeled "linear." Shapes close to a circle are rated in three levels, large, medium, and small, depending on their area. Linear shapes are also categorized into three levels, A, B, and C, in order of thinness. Thinner shapes are more preferable, as they can further minimize color change.

The results of the change in hue versus viewing angle are shown in Table 1.

As can be seen from Table 1, when ΔN _A was in the range of more than 1.0, the relationship was linear, and the change in hue could be kept small.
Furthermore, when 0.94≦ΔN _A ≦1.10 and 0.82≦ΔN _C ≦1.00, the shape may be linear or circular, but even if it is circular, its area is medium or small, and the change in hue can be said to be relatively small.

<Retardation when stacked>
With the positive A plate and the positive C plate laminated together, the thickness direction retardation Rth _p at a wavelength of 450 nm, the thickness direction retardation Rth _q at a wavelength of 550 nm, and the thickness direction retardation Rth _r at a wavelength of 650 nm were calculated, and the difference between the maximum and minimum values of Rth _p , Rth _q , and Rth _r was calculated to obtain Rth _s . The results are shown in Table 2.

When the results of _Rths were compared with the above-mentioned evaluation results of the change in hue, it was found that when _Rths was 25 or less, the change in hue was particularly small.

REFERENCE SIGNS LIST 10 Retardation film 11 Substrate 12 Alignment film 13 Positive C plate 14 Positive A plate 20 Liquid crystal display device 22 Surface light source device 23 Liquid crystal display panel 24 Linear polarizing plate 25 Liquid crystal cell 26 Optically functional laminate 27 Polarizer 28 Substrate 30 Organic EL display device 33 Organic EL display panel 36 Optically functional laminate 37 Polarizer 38 Substrate

Claims (5)

A retardation film used together with a liquid crystal display panel or an organic EL display panel and arranged as a part of an image display device,
A positive A plate having a positive A type characteristic and a positive C plate having a positive C type characteristic,
When the front retardation of the positive A plate at a wavelength of 450 nm is Re _A450 and the front retardation at a wavelength of 550 nm is Re _A550 , ΔN _A obtained by Re _A450 /Re _A550 is 0.94 or more and 1.10 or less,
When the thickness direction retardation of the positive C plate at a wavelength of 450 nm is Rth _C450 and the thickness direction retardation at a wavelength of 550 nm is Rth _C550 , ΔN _C obtained by Rth _C450 /Rth _C550 is 0.82 or more and 1.00 or less,
the absolute value of the difference between ΔN _A and ΔN _C is 0.2 or less;
a thickness direction retardation at a wavelength of 450 nm in a laminated state of the positive A plate and the positive C plate is Rth _p , a thickness direction retardation at a wavelength of 550 nm in a laminated state of the positive A plate and the positive C plate is Rth _q , and a thickness direction retardation at a wavelength of 650 nm in a laminated state of the positive A plate and the positive C plate is Rth _r , a difference between a maximum value and a minimum value of the Rth _p , the Rth _q , and the Rth _r is 25 or less;
Phase contrast film. The retardation film according to claim 1, wherein at least one of the positive A plate and the positive C plate contains a polymerizable rod-like liquid crystal material. The phase difference film according to claim 1, wherein the front retardation of the positive A plate at a wavelength of 550 nm is 110 nm or more and 160 nm or less. Two polarizing plates;
A polarizing plate compensation film comprising: the retardation film according to claim 1 disposed between the two polarizing plates. The retardation film according to claim 1 , which is disposed on a light output side of an organic EL laminate;
A polarizer that linearly polarizes light and is laminated on the retardation film;
An external light anti-reflection film comprising:

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