TWI838501B - Reflective display device using anisotropic optical film - Google Patents

Abstract

An objective of this invention is providing a reflective display device capable of showing white color like high-quality paper when displaying white without glare or blurring feeling, and excellent in white coloration (having a sufficient paper white feeling).

This invention provides a reflective display device includes a reflector and an anisotropic optical film whose linear transmittance changes depending on an incident light angle, wherein the anisotropic optical film is arranged closer to the viewing side than the reflector, the anisotropic optical film includes at least an anisotropic light diffusion layer, the anisotropic light diffusing layer has a matrix region and a plurality of columnar regions having different refractive indexes from the matrix region, the plurality of columnar regions are formed by orienting from one surface over to the other surface of the anisotropic light diffusion layer, the aspect ratio, which is the average major axis / average minor axis of theplurality of columnar regions on one surface of the anisotropic light diffusion layer, is 20 or less.

Description

Reflective display device using anisotropic optical film

The present invention relates to a reflective display device using an anisotropic optical film.

In the past, when a liquid crystal display device is a twisted nematic (TN) type liquid crystal display, the two polarizing plates on the two surfaces of the liquid crystal unit are arranged in a manner that their polarization planes are orthogonal. Therefore, for example, in the case of NB (Normally black) mode, when the liquid crystal unit is in a driven state, the light passing through one polarizing plate will be polarized by the liquid crystal and pass through the other polarizing plate, resulting in a white screen. In a non-driven state, the light does not pass through the other polarizing plate, resulting in a black screen. Because the light passes through the polarizing plate in the aforementioned manner, the light in the opposite direction to the polarization plane of the polarizing plate cannot pass through the polarizing plate, and the liquid crystal uses less light, which tends to become a darker display device.

In recent years, with the popularity of portable terminals or wearable devices, the opportunities for using display devices outdoors have increased. Correspondingly, reflective liquid crystal display devices that obtain light sources by allowing outdoor light to enter and reflect are also increasing.

On the other hand, reflective LCD devices cannot adjust the spectrum of the light source like transmissive LCD devices, so the wavelength characteristics of the polarizer directly become the display color, so improving the wavelength characteristics of the polarizer is an important issue. In reflective LCD devices so far, white displays tend to be slightly yellowish, and black displays tend to be bluish. Therefore, compared with other reflective display devices (electronic paper displays, etc.), the display quality is poor.

Here, Patent Document 1 discloses the following invention: When a reflective liquid crystal display device has a reflector, a liquid crystal unit, a phase difference plate, and a substrate (A) with a polarizing function in order from the back side, an anisotropic light diffusion plate with a polarizing function is arranged between the reflector and the liquid crystal unit, between the liquid crystal unit and the phase difference plate, or between the phase difference plate and the substrate (A) with a polarizing function, thereby improving the hue caused by the problem that the polarizing plate is yellow when displaying white and blue when displaying black. The polarizing plate has no wavelength dependence in either the parallel position or the orthogonal position, and displays white like high-quality paper when displaying white and displays pitch black when displaying black, which can further improve the quality of the reflective liquid crystal display device.

[Prior Art Literature]

[Patent Literature]

Patent document 1: International Publication No. 2015/111472.

The anisotropic light diffusing plate used in Patent Document 1 states that "the anisotropic light diffusing plate described in Japanese Patent Publication No. 2012-37611 also has the function of polarizing light by anisotropic light diffusion, so it can be used as a reflective polarizing plate." In the anisotropic light diffusing layer in Japanese Patent Publication No. 2012-37611, multiple layers with different refractive indices are formed into a spiral shape arranged in one direction in a plane parallel to the film surface. Hereinafter, in the present invention, a layer with such a roughly plate-like structure is referred to as a louver structure.

The optical property of the louver structure is good light transmittance, but there is a problem called glare. Patent document 1 does not record this problem when it is used in a reflective liquid crystal display device.

On the other hand, the sharpness of image display, that is, suppressing the bokeh, is also one of the important display characteristics, requiring a reflective display device that suppresses both glare and bokeh.

Therefore, the purpose of the present invention is to provide a reflective display device with excellent white color rendering (having a sufficient paper white feeling), which has no glare or bokeh as mentioned above, and can display white like high-quality paper when displaying white.

In order to solve the above problems, the reflective display device of the present invention has a reflector and an anisotropic optical film whose linear transmittance changes with the angle of incident light. The anisotropic optical film at least contains an anisotropic light diffusion layer. The anisotropic light diffusion layer has a matrix region and a plurality of columnar regions with a refractive index different from that of the matrix region. The plurality of columnar regions are arranged from one surface of the anisotropic light diffusion layer toward the other surface. The aspect ratio of the average major diameter/average minor diameter of the plurality of columnar regions on one surface of the anisotropic light diffusion layer is less than 20.

According to the present invention, a reflective display device can be provided, wherein the aspect ratio of a plurality of columnar regions in one surface of an anisotropic light diffusion layer of an anisotropic optical film becomes a specific value, whereby when the anisotropic optical film is arranged on the visual recognition side of the reflective plate of the reflective display device, the glare or bokeh is less and the display has a sufficient paper-white feeling.

1: Light source

2: Detector

100: Internal reflection type display device (reflective liquid crystal display device)

101: External reflective display device (reflective liquid crystal display device)

110: Liquid crystal layer

120: Back glass

121:Front glass

130: Reflector (metal electrode)

140: Back polarizer

141:Front polarizer

150: Anisotropic optical film

160: Back phase difference film

161: Front phase difference film

170: Adhesive layer

171: Adhesive layer

180: Reflector (back reflector)

200: Anisotropic light diffusion layer

201: Matrix area

202: Columnar area

211: Matrix area

212: Columnar area

250: Anisotropic light diffusion layer

300: Light source

301: Directional diffusion element

302: Directional diffusion element

303: Unhardened resin composition layer

FIG1 is a schematic diagram illustrating an example of the configuration of a reflective plate and an anisotropic optical film in the reflective display device of the present invention.

FIG2 is an explanatory diagram showing the incident angle dependence of the anisotropic optical film of the present invention.

Figure 3 is a surface diagram of the anisotropic light diffusion layer of the present invention in the plane direction.

Figure 4 is a schematic diagram of the anisotropic light diffusion layer of the present invention and an example of a transmitted light diagram.

Figure 5 is used to illustrate the 3D polar coordinate representation of the scattering center axis P in the anisotropic light diffusion layer.

Figure 6 is an example of the optical profile of the diffusion region and the non-diffusion region in the anisotropic light diffusing layer.

Figure 7 is a schematic diagram showing a method for measuring the incident light angle dependence of an anisotropic light diffusing layer.

FIG8 is a schematic diagram showing the manufacturing method of the anisotropic light diffusion layer of the present invention at any step 1-3.

Figure 9 is a photo of the reflective display device of Example 1 and Comparative Example 2.

1. Definition of main terms

Here we define the main terms related to anisotropic optical films (anisotropic light diffusing layers).

"Anisotropic optical film" includes the case where the anisotropic light diffusion layer is a single layer (only one layer) and the case where two or more anisotropic light diffusion layers are stacked (in this case, the anisotropic light diffusion layers can be stacked through adhesive layers, etc.). Therefore, for example, in the case where the anisotropic light diffusion layer is a single layer, the single layer anisotropic light diffusion layer is an anisotropic optical film.

"Anisotropic optical film" is anisotropic and directional, and its light diffusion, transmission and diffusion distribution have incident light angle dependence (details as described below) that changes with the incident light angle. Therefore, it is different from directional diffusion film, isotropic diffusion film and diffusion film oriented in a specific direction that have no incident light angle dependence.

"Low refractive index region" and "high refractive index region" are regions formed by the local refractive index difference of the material constituting the anisotropic optical film of the present invention, and are relative terms indicating a lower or higher refractive index relative to the other. These regions are formed when the material forming the anisotropic optical film is hardened.

"Scattering center axis" refers to the direction in which the linear transmittance is consistent with the incident light angle of light that is roughly symmetrical with respect to the incident light angle when the incident light angle to the anisotropic optical film or anisotropic light diffusion layer is changed. The reason for setting it as "slightly symmetrical" is that when the scattering center axis is tilted relative to the film normal direction, the optical characteristics ("optical profile" described later) do not have a strictly defined symmetry. The scattering center axis can be confirmed by observing the tilt of the columnar region of the anisotropic optical film cross section with an optical microscope, or by changing the incident light angle and observing the projection shape of light passing through the anisotropic optical film.

"Scattering center axis angle" refers to the angle at which the scattering center axis is tilted relative to the normal direction of the principal plane surface of the anisotropic optical film or the anisotropic light diffusion layer, and the normal direction of the anisotropic optical film or the anisotropic light diffusion layer is 0°.

In addition, "linear transmittance" is generally the linear transmittance of light incident on an anisotropic optical film or anisotropic light diffusion layer, which is the ratio of the "linear transmitted light amount" of the light amount transmitted in the same linear direction as the incident direction to the "incident light amount" of the incident light amount when the incident light is incident from an incident angle, as shown in the following formula.

Linear transmittance (%) = (linear transmittance/incident light) × 100

In addition, in the present invention, "scattering" and "diffusion" are used without distinction and are synonymous. In addition, "photopolymerization" and "photocuring" are the polymerization reactions of photopolymerizable compounds by light, and are used as synonyms.

The preferred implementation of the present invention is described in detail below with reference to the drawings. In addition, in this specification and drawings, the components with the same symbols have substantially the same structure or function.

2. Reflective display device

The reflective display device of the present invention has a reflective plate and an anisotropic optical film whose linear transmittance changes with the angle of incident light.

FIG1 is a schematic diagram illustrating an example of the configuration of a reflective plate and an anisotropic optical film in a reflective display device of the present invention, which is an example of an internal reflection type and an external reflection type of a reflective liquid crystal display device.

The reflective liquid crystal display device 100 (101) includes an "inner reflection type" in which a metal electrode 130 of a scattering reflector is arranged on the back glass 120 side of the liquid crystal layer 110, and an "outer reflection type" in which a back reflector 180 is arranged on the outer side of the back phase difference film 160 and the back polarizing plate 140.

The above description describes the placement of the reflector and the anisotropic optical film in the reflective display device of the present invention, but the anisotropic optical film can be placed at any position as long as it is closer to the external light incident surface of the reflective display device (the visual recognition side of the visual recognizer, the visual recognition reflected light side) than the reflector. As an example, in FIG1 , the anisotropic optical film 150 is placed between the front glass 121 and the front phase difference film 161 on the inner side of the front polarizing plate 141 through the adhesive layers 170 and 171.

The adhesive used in the adhesive layers 170 and 171 is not particularly limited as long as it is transparent, and preferably a room temperature pressure-sensitive adhesive is used. Such adhesives include, for example, polyester resins, epoxy resins, polyurethane resins, silicone resins, acrylic resins, and the like. In particular, acrylic resins are preferred because they have higher optical transparency and are cheaper.

The reflector of the present invention is a light-reflecting component such as a reflective film, a reflective plate, or a metal electrode, and can be installed in a reflective display device as used in the past.

2-1. Anisotropic optical film

The anisotropic optical film of the present invention changes the linear transmittance depending on the incident light angle. That is, incident light within a certain angle range will maintain linearity and transmit, while incident light within other angle ranges will show diffusion.

Figure 2 is an explanatory diagram showing the incident angle dependence of the anisotropic optical film of the present invention.

The anisotropic optical film in Figure 2 exhibits diffusion when the incident light angle is between 20° and 50°, and exhibits linear transmission instead of diffusion at other angles. That is, as shown in the figure, it exhibits linear transmission instead of diffusion at 0° (less than 20°) and 65° (greater than 50°).

The anisotropic optical film of the present invention contains at least a single layer or multiple layers of anisotropic light diffusing layer. The anisotropic light diffusing layer contained in the anisotropic optical film may contain multiple anisotropic light diffusing layers with different optical properties such as linear transmittance, haze value, and scattering center axis.

Here, the multiple layers of anisotropic light diffusion layers are multiple layers of single anisotropic light diffusion layers directly or through an adhesive layer. The adhesive used in the adhesive layer can be the adhesive described in the above FIG. 1.

On the other hand, in the case of directly laminating the anisotropic light diffusing layer, after the composition layer containing the photopolymerizable compound is cured to form a single-layer anisotropic light diffusing layer, a coating containing the photopolymerizable compound is directly applied in a sheet form on the single-layer anisotropic light diffusing layer to form a composition layer, and then the composition layer is cured to produce the film.

Furthermore, the anisotropic optical film can also be laminated with multiple layers in addition to the anisotropic light diffusion layer.

The anisotropic optical film having multiple layers can be laminated, for example, by laminating layers having other functions on the anisotropic optical film. In addition, the anisotropic optical film of the present invention can also be laminated on a transparent substrate such as a glass substrate for use.

From the perspective of manufacturing ease or cost, the anisotropic optical film of the present invention is preferably a single-layer anisotropic light diffusion layer.

Considering the application or productivity, the thickness of the anisotropic optical film is preferably 10μm to 500μm, more preferably 50μm to 150μm.

The anisotropic light diffusion layer of the present invention has a matrix region and a plurality of columnar regions with a refractive index different from that of the matrix region, and has anisotropy and directivity that are incident light angle dependent.

In addition, the anisotropic light diffusion layer is usually composed of a cured product containing a composition of a photopolymerizable compound. Therefore, the matrix region and the plurality of columnar regions are composed of the same composition and are formed by phase separation.

Here, the difference in refractive index means that at least a portion of the light incident on the anisotropic light diffusion layer will produce a difference in the degree of reflection at the interface between the matrix region and the columnar region. There is no special limitation. For example, the difference in refractive index between the matrix region and the columnar region can be greater than 0.001.

The thickness of the anisotropic light diffusion layer of the present invention (the length in the same direction as the thickness of the anisotropic optical film relative to the perpendicular direction of the main plane of the anisotropic light diffusion layer) is not particularly limited, for example, preferably 1μm to 200μm, more preferably 10μm to 100μm. When the aforementioned thickness exceeds 200μm, not only the material cost will be increased, but also the UV irradiation cost will be increased, so the manufacturing cost will be increased. In addition, the increase in the diffusion of the anisotropic light diffusion layer in the thickness direction will easily cause image blur or contrast reduction. In addition, when the thickness is less than 1μm, the light diffusion and light collection properties are likely to be insufficient.

The multiple columnar regions contained in the anisotropic light diffusion layer of the present invention are usually aligned and extended from one surface of the anisotropic light diffusion layer toward the other surface.

In the anisotropic light diffusing layer surface (the main plane surface of the anisotropic light diffusing layer) of the present invention, the surface shape of the aforementioned plurality of columnar regions can be formed into a shape having a short diameter and a long diameter.

The aforementioned surface shape is not particularly limited, and can be, for example, circular, elliptical, or polygonal. In the case of a circle, the short diameter is equal to the long diameter. In the case of an ellipse, the short diameter is the length of the minor axis, and the long diameter is the length of the major axis. In the case of a polygon, the shortest possible length when drawing a straight line inside the polygon is the short diameter, and the longest length is the long diameter.

FIG3 is a surface diagram of the anisotropic light diffusion layer of the present invention in the plane direction, showing a plurality of columnar regions (202 and 212) and matrix regions (201 and 211) viewed from the surface of the anisotropic light diffusion layer 200, 250. In the figure, LA represents the major diameter and SA represents the minor diameter.

The short and long diameters of the present invention are measured by observing the surface of the anisotropic light diffusion layer with an optical microscope, and measuring the short and long diameters of 20 randomly selected columnar regions, and the average value is obtained.

The average value of the short diameter of the multiple columnar regions (average short diameter) is preferably 0.5 μm or more, more preferably 1.0 μm or more, and even more preferably 1.5 μm or more. On the other hand, the average short diameter of the multiple columnar regions is preferably 5.0 μm or less, more preferably 4.0 μm or less, and even more preferably 3.0 μm or less. The lower limit and upper limit of the short diameter of the multiple columnar regions can be appropriately combined.

Furthermore, the average value (average length) of the length of the multiple columnar regions is preferably greater than 0.5 μm, more preferably greater than 1.0 μm, and even more preferably greater than 1.5 μm. On the other hand, the average length of the length of the multiple columnar regions is preferably less than 100 μm, more preferably less than 50 μm, and even more preferably less than 30 μm. The lower limit and upper limit of the short diameter of the multiple columnar regions can be appropriately combined.

In addition, the ratio of the average long diameter to the average short diameter of the multiple columnar regions of the present invention (average long diameter/average short diameter), that is, the aspect ratio is less than 20. Figure 3 (a) shows an anisotropic light diffusing layer with an aspect ratio of less than 2, and Figure 3 (b) shows an anisotropic light diffusing layer with an aspect ratio of 2 to 20.

The upper limit of the aspect ratio is preferably 20, and more preferably less than 5. When the aspect ratio is within this range, the effect of suppressing glare can be obtained.

Figure 4 is a schematic diagram of the anisotropic light diffusion layer of the present invention and an example of a transmitted light diagram.

When the aspect ratio of the anisotropic light diffusion layer of the present invention is greater than 1 and less than 2, when irradiated with light parallel to the axis direction of the multiple columnar regions, the penetrating light will diffuse isotropically (see Figure 4 (a)). On the other hand, when the aspect ratio is 2 to 20, when irradiated with light parallel to the axis direction, it will diffuse anisotropically according to the aspect ratio (see Figure 4 (b)).

Furthermore, the anisotropic light diffusion layer of the present invention may contain a plurality of columnar regions with a certain aspect ratio, or may contain a plurality of columnar regions with different aspect ratios.

The anisotropic light diffusion layer of the present invention may have at least one scattering central axis.

The alignment direction (extending direction) from one surface of the columnar region to the other surface can be formed in a manner parallel to the scattering center axis, and can be appropriately determined in a manner such that the anisotropic light diffusion layer has the desired linear transmittance and diffusivity. In addition, the scattering center axis and the alignment direction of the columnar region can be parallel as long as they satisfy the law of refraction (Snell’s law), and do not need to be strictly parallel.

Snell's law states that when light enters the interface of a medium with a refractive index of n ₁ and a medium with a refractive index of n ₂ , the relationship between the incident light angle θ ₁ and the refraction angle θ ₂ is n ₁ sinθ ₁ =n ₂ sinθ _2. For example, when n ₁ =1 (air), n ₂ =1.51 (anisotropic light diffusion layer) and the incident light angle is 30°, the alignment direction (refraction angle) of the columnar region is about 19°. However, even if the incident light angle and the refraction angle are different as described above, as long as Snell's law is satisfied, the concept of parallelism is included in the present invention.

As mentioned above, the scattering center axis is the direction in which the light diffusivity is consistent with the incident light angle of the light that is roughly symmetrical with respect to the incident light angle when the incident light angle of the anisotropic light diffusing layer changes. In addition, the incident light angle at this time is the roughly central part (the central part of the area called the diffusion area) of the minimum value of the minimum straight line transmittance in the optical profile (e.g., Figure 6) obtained by measuring the incident light angle straight line transmission light of the anisotropic light diffusing layer.

Next, the scattering center axis P in the anisotropic light diffusion layer is explained with reference to FIG5. FIG5 is a 3D polar coordinate representation used to explain the scattering center axis P in the anisotropic light diffusion layer.

According to the 3D polar coordinate representation in Figure 5, the scattering center axis P can be expressed as a polar angle θ and an azimuth angle φ when the principal plane of the anisotropic light diffusion layer is the xy plane and the normal relative to the principal plane is the z axis. That is, Pxy in Figure 5 can be the length direction of the scattering center axis projected on the surface of the principal plane of the anisotropic light diffusion layer.

Here, the polar angle θ (-90°<θ<90°) formed by the normal line of the anisotropic light diffusion layer (z axis shown in FIG. 5) and the orientation direction of the columnar region (scattering center axis direction) is defined as the scattering center axis angle of the present invention. The axial direction angle of the columnar region can be adjusted to the desired angle by changing the direction of light irradiated on the thin sheet-like composition containing a photopolymerizable compound during the manufacture of the same.

The scattering center axis angle is not particularly limited, for example, preferably -30° to +30°, more preferably -20° to +20°. When it exceeds the range of -30° to +30°, visual recognition will be reduced, and there is a risk that the reflective display device will not be able to obtain a sufficient paper-white feeling.

Furthermore, when multiple anisotropic light diffusion layers have the same scattering central axis, they have one scattering central axis as a whole.

Furthermore, when the anisotropic light diffusion layer of the present invention contains multiple scattering central axes, it becomes composed of multiple columnar regions parallel to the orientation directions of the multiple scattering central axes.

In addition, the length of the alignment direction of the columnar region of the present invention is not particularly limited, and can be the length from one surface of the anisotropic light diffusion layer to the other surface, or the length from one surface to the other surface. Because the linear light transmittance of the anisotropic light diffusion layer can be improved, the length of the alignment direction of the columnar region is preferably longer than the aforementioned average length.

Figure 6 is an example of the optical profiles of the diffusion region and the non-diffusion region in the anisotropic light diffusing layer.

As mentioned above, the anisotropic light diffusing layer has the incident light angle dependency of the light diffusing property that changes the linear transmittance depending on the incident light angle. Here, the curve representing the incident light angle dependency of the light diffusing property as shown in FIG6 is hereinafter referred to as the "optical profile".

FIG7 is a schematic diagram showing a method for measuring the incident light angle dependence of an anisotropic light diffusing layer. As shown in FIG7, the optical profile is to arrange the anisotropic light diffusing layer of the sample (or an anisotropic optical film composed of only a single layer of anisotropic light diffusing layer) 200 or 250 between the light source 1 and the detector 2. In this form, the incident light angle when the irradiation light I of the light source 1 is incident from the normal direction of the principal plane of the sample is set to 0°. In addition, the sample is arranged in a manner that can be arbitrarily rotated around a straight line V that can penetrate the sample, and the light source 1 and the detector 2 are fixed. That is, according to this method, a sample is placed between the light source 1 and the detector 2, and the angle is changed with the straight line V as the center axis while measuring the amount of straight line light that passes through the sample and enters the detector 2, thereby calculating the straight line transmittance.

Optical profiles do not directly reflect light diffusion, but a decrease in linear transmittance will increase diffusion, so this explanation can roughly represent light diffusion.

Generally, isotropic light-diffusing films will show a mountain-shaped optical profile with a peak at an incident light angle of around 0°.

In an anisotropic light diffusion layer, for example, the case of an anisotropic light diffusion layer with a scattering center axis angle of 0° (Figure 6) shows that the linear transmittance is relatively small at an incident light angle near 0° (-20° to +20°), and the linear transmittance increases as the incident light angle (absolute value) increases, showing a valley-shaped optical profile.

As mentioned above, the anisotropic light diffusion layer has the following properties: the incident light will be strongly diffused in the incident light angle range close to the scattering center axis, but the diffusion will be weaker in the incident light angle range above it and the linear transmittance will be increased.

As shown in Figure 6, the middle value between the maximum straight line transmittance at the incident light angle where the straight line transmittance is the largest and the minimum straight line transmittance at the incident light angle where the straight line transmittance is the smallest is taken, and the angle range of the two incident light angles relative to the straight line transmittance of the middle value is called the diffusion area (the width of the diffusion area is called the "diffusion width"), and the other incident light angle range is called the non-diffusion area (transmission area).

The maximum linear transmittance of light incident from the normal direction of the anisotropic light diffusing layer of the present invention is not particularly limited. For example, when the anisotropic light diffusing layer contained in the anisotropic optical film is one layer, it is preferably 10% to 60%, and more preferably 10% to 50%. By setting it within this range, a reflective display device with less bokeh and sufficient paper whiteness can be obtained.

The haze value of the anisotropic light diffusing layer of the present invention is an indicator of the diffusivity of the anisotropic light diffusing layer. If the haze value becomes larger, the diffusivity of the anisotropic light diffusing layer is improved. The haze value of the anisotropic light diffusing layer is not particularly limited, for example, preferably 50% to 90%, more preferably 60% to 80%. By setting it within this range, a reflective display device with less bokeh and sufficient paper whiteness can be obtained.

When the anisotropic optical film contains multiple anisotropic light diffusing layers, the haze value of the entire anisotropic light diffusing layer becomes the haze value of the anisotropic light diffusing layer of the anisotropic optical film.

The method for measuring the haze value of the anisotropic light diffusing layer is not particularly limited and can be measured by a known method. For example, it can be measured according to JIS K7136-1:2000 "Plastics - Method for determining the haze of transparent materials".

The anisotropic light diffusing layer of the present invention may have concavities and convexities on at least one surface of the anisotropic light diffusing layer. In this case, the arithmetic mean roughness Ra of the surface of the anisotropic light diffusing layer is preferably less than 0.10 μm. In addition, the arithmetic mean roughness Ra is obtained according to JIS B 0601-2001.

The arithmetic mean roughness Ra of the surface of the anisotropic light diffusion layer can be measured by a known method without any particular limitation. For example, a non-contact method using a confocal laser microscope or a contact method using a probe surface roughness measuring device can be used.

2-2. Method for manufacturing anisotropic light diffusion layer in anisotropic optical film

The manufacturing method of the anisotropic light diffusion layer in the anisotropic optical film of the present invention can be manufactured by irradiating an uncured resin composition layer with UV (ultraviolet light) or other light. The following first describes the raw materials of the anisotropic light diffusion layer, and then describes the manufacturing process. The following mainly describes the manufacturing of an anisotropic optical film containing one anisotropic light diffusion layer as an example, and other aspects are described as needed.

2-2-1. Raw materials of anisotropic light diffusion layer

The raw materials of the anisotropic light diffusion layer are described in order: (1) photopolymerizable compound, (2) photoinitiator, and (3) other optional components.

2-2-1-1. Photopolymerizable compounds

The photopolymerizable compound of the material forming the anisotropic light diffusion layer of the present invention is composed of: a polymer monomer, a polymer, an oligomer, a monomer having a free radical polymerizable or cationic polymerizable functional group, a photopolymerizable compound and a photoinitiator, and is a material that polymerizes and cures by irradiating ultraviolet rays and/or visible rays. Here, even if the material forming the anisotropic light diffusion layer contained in the anisotropic optical film is of one type, there will be no difference in refractive index due to the difference in density. The reason is that the part with stronger UV irradiation intensity cures faster, so the polymerized and cured material around the cured area will move, resulting in the formation of a higher refractive index area and a lower refractive index area. In addition, (meth)acrylate means either acrylate or methacrylate.

Free radical polymerizable compounds are mainly those containing one or more unsaturated double bonds in the molecule. Specifically, there are acrylic oligomers called epoxy acrylates, urethane acrylates, polyester acrylates, polyether acrylates, polybutadiene acrylates, polysilicone acrylates, 2-ethylhexyl acrylate, isoamyl acrylate, butoxyethyl acrylate, ethoxydiethylene glycol acrylate, phenoxyethyl acrylate, tetrahydrofuran methyl acrylate, isobornyl acrylate, 2-ethylhexyl acrylate, -Hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-acryloyloxyphthalic acid, dicyclopentenyl acrylate, triethylene glycol diacrylate, neopentyl glycol diacrylate, 1,6-hexanediol diacrylate, EO adduct diacrylate of bisphenol A, trihydroxymethylpropane triacrylate, EO-modified trihydroxymethylpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, ditrihydroxymethylpropane tetraacrylate, dipentaerythritol hexaacrylate and other acrylate monomers. In addition, these compounds can be used individually or in combination. In addition, methacrylate can also be used in the same manner, but generally speaking, acrylate has a faster photopolymerization speed than methacrylate, so it is better.

The cationically polymerizable compound may be a compound having one or more epoxy groups, vinyl ether groups, or cyclobutylene groups in the molecule. Examples of the compound having an epoxy group include 2-ethylhexyl diglycol epoxypropyl ether, epoxypropyl ether of biphenyl, bisphenol A, hydrogenated bisphenol A, bisphenol F, bisphenol AD, bisphenol S, tetramethyl bisphenol A, tetramethyl bisphenol F, tetrachlorobisphenol A, tetrabromobisphenol A, and other bisphenols, dicyclohexyl ethers, phenol novolac, cresol novolac, brominated phenol novolac, o-cresol novolac, etc. Polyglycidyl ethers of novolac resins, ethylene glycol, polyethylene glycol, polypropylene glycol, butanediol, 1,6-hexanediol, neopentyl glycol, trihydroxymethylpropane, 1,4-cyclohexanedimethanol, EO adducts of bisphenol A, PO adducts of bisphenol A, etc., diglycidyl ethers of alkylene glycols, glycidyl esters of hexahydrophthalic acid or diglycidyl esters of dimer acid, etc.

Compounds having an epoxy group include 3,4-epoxyepoxyhexylmethyl-3',4'-epoxyepoxyhexanecarboxylate, 2-(3,4-epoxyepoxyhexyl-5,5-spiro-3,4-epoxy)cyclohexane-m-dioxane, di(3,4-epoxyepoxyhexylmethyl)adipate, di(3,4-epoxy-6-methylcyclohexylmethyl)adipate, 3,4-epoxy-6-methylcyclohexyl-3',4'-epoxy-6'-methylcyclohexanecarboxylate, methylenebis(3,4-epoxyepoxyhexylmethyl)adipate, (3,4-epoxycyclohexane), dicyclopentadiene diepoxide, ethylene glycol bis(3,4-epoxycyclohexylmethyl) ether, ethylene bis(3,4-epoxycyclohexanecarboxylate), lactone-modified 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate, tetra(3,4-epoxycyclohexylmethyl)butanetetracarboxylate, di(3,4-epoxycyclohexylmethyl)-4,5-epoxytetrahydrophthalate and other aliphatic epoxy compounds, but not limited to these.

Compounds having a vinyl ether group include, but are not limited to, diethylene glycol divinyl ether, triethylene glycol divinyl ether, butanediol divinyl ether, hexanediol divinyl ether, cyclohexanedimethanol divinyl ether, hydroxybutyl vinyl ether, ethyl vinyl ether, dodecyl vinyl ether, trihydroxymethylpropane trivinyl ether, and propylene carbonate. In addition, vinyl ether compounds are generally cationic polymerizable, but can be free radical polymerized by combining with acrylates.

In addition, compounds having an oxobutyl group may include 1,4-bis[(3-ethyl-3-oxobutylmethoxy)methyl]benzene, 3-ethyl-3-(hydroxymethyl)-oxobutylene, etc.

Furthermore, the above-mentioned cationically polymerizable compounds can be used as individual monomers or as a mixture of multiple monomers. The above-mentioned photopolymerizable compounds are not limited to the above-mentioned ones. Furthermore, in order to produce a sufficient refractive index difference, fluorine atoms (F) may be introduced into the above-mentioned photopolymerizable compounds in order to lower the refractive index, and sulfur atoms (S), bromine atoms (Br), and various metal atoms may be introduced in order to increase the refractive index. Furthermore, as disclosed in Japanese Patent Publication No. 2005-514487, functional ultrafine particles having photopolymerizable functional groups such as acryl or methacryl, epoxy, etc. introduced into the surface of ultrafine particles composed of metal oxides with high refractive index such as _titanium oxide ( _TiO2 ), zirconium oxide (ZrO2), and tin oxide ( _SnOx ) may be added to the above-mentioned photopolymerizable compounds, which is also effective.

The photopolymerizable compound of the present invention preferably uses a photopolymerizable compound with a polysilicone skeleton. The photopolymerizable compound with a polysilicone skeleton will be aligned and polymerized and hardened along with its structure (mainly ether bonds) to form a low refractive index region, a high refractive index region, or a low refractive index region and a high refractive index region. By using a photopolymerizable compound with a polysilicone skeleton, it is easy to tilt the columnar region, which will improve the light collection in the front direction. In addition, the low refractive index region is equivalent to either the columnar region or the matrix region, and the other is equivalent to the high refractive index region.

In the low refractive index region, it is preferred that the cured product of the photopolymerizable compound with a polysilicone skeleton has a relatively large amount of polysilicone resin. This makes it easier to further tilt the scattering center axis, thereby improving the light collection property in the front direction. Compared with compounds without a polysilicone skeleton, polysilicone resin contains more silicon (Si), so the silicon can be used as an indicator to use EDS (energy dispersive X-ray spectrometer) to confirm the relative amount of polysilicone resin.

The photopolymerizable compound having a polysiloxane skeleton is a monomer, oligomer, prepolymer or polymer monomer having a free radical polymerizable or cationic polymerizable functional group. Examples of free radical polymerizable functional groups include acryloyl, methacryloyl, allyl, etc., and examples of cationic polymerizable functional groups include epoxide, cyclohexane, etc. There is no particular restriction on the type and amount of such functional groups. The more functional groups there are, the higher the crosslinking density is, and the easier it is to produce a refractive index difference, so it is better. Therefore, it is better to have a polyfunctional acryloyl or methacryloyl. In addition, the compound having a polysiloxane skeleton is not sufficiently compatible with other compounds due to its structure, but in this case, it can be urethanized to improve the compatibility. In this form, polysilicone, urethane, or (meth)acrylate having an acryl or methacryl group at the end is suitable.

The weight average molecular weight (Mw) of the photopolymerizable compound having a polysilicone skeleton is preferably in the range of 500 to 50,000. More preferably, it is in the range of 2,000 to 20,000. By making the weight average molecular weight in the above range, the photocuring reaction can be fully produced, and the polysilicone resin in each anisotropic light diffusion layer of the anisotropic optical film 100 is easily aligned. With the alignment of the polysilicone resin, the scattering center axis becomes easy to tilt.

The polysiloxane skeleton is, for example, represented by the following general formula (1). In general formula (1), _R1 , _R2 , _R3 , _R4 , _R5 , and _R6 independently have functional groups such as methyl, alkyl, fluoroalkyl, phenyl, epoxy, amino, carboxyl, polyether, acryl, and methacryl. In general formula (1), n is preferably an integer of 1 to 500.

If a photopolymerizable compound having a polysilicone skeleton is mixed with a compound without a polysilicone skeleton to form an anisotropic light diffusion layer, it is easy to separate and form a low refractive index region and a high refractive index region, and the degree of anisotropy is stronger, so it is better. In addition to photopolymerizable compounds, thermoplastic resins and thermosetting resins can be used as compounds without a polysilicone skeleton, and they can also be used in combination. Photopolymerizable compounds can use polymers, oligomers, and monomers (but those without a polysilicone skeleton) with free radical polymerizable or cationic polymerizable functional groups. Examples of thermoplastic resins include polyesters, polyethers, polyurethanes, polyamides, polystyrenes, polycarbonates, polyacetals, polyvinyl acetates, acrylic resins, and copolymers or modified products thereof. When using a thermoplastic resin, a solvent for dissolving the thermoplastic resin is used to dissolve, apply, and dry, and then a photopolymerizable compound having a polysilicone skeleton is hardened by ultraviolet light to form an anisotropic light diffusion layer. Thermosetting resins include epoxy resins, phenol resins, melamine resins, urea resins, unsaturated polyesters, and copolymers or modified products thereof. When using a thermosetting resin, a photopolymerizable compound having a polysilicone skeleton is hardened by ultraviolet light, and then the thermosetting resin is hardened by appropriately heating to form an anisotropic light diffusion layer. The best compound without a polysilicone skeleton is a photopolymerizable compound, because the low refractive index area and the high refractive index area are easy to separate, no solvent is required when using thermoplastic resin, and no thermal curing process is required like thermosetting resin, so the productivity is excellent.

The ratio of the photopolymerizable compound having a polysilicone skeleton to the compound without a polysilicone skeleton is preferably in the range of 15:85 to 85:15 by mass. It is more preferably in the range of 30:70 to 70:30. By being in this range, the phase separation of the low refractive index region and the high refractive index region can be easily performed, and the columnar region can be easily tilted. If the ratio of the photopolymerizable compound having a polysilicone skeleton does not reach the lower limit or exceeds the upper limit, the phase separation is difficult to perform and the columnar region is difficult to tilt. If polysilicone/urethane/(meth)acrylate is used as the photopolymerizable compound having a polysilicone skeleton, the compatibility with the compound without a polysilicone skeleton can be improved. Thereby, the columnar region can be tilted even if the material mixing ratio is widened.

2-2-1-2. Photoinitiator

Examples of the photoinitiator capable of polymerizing the radical polymerizable compound include diphenyl ketone, benzyl, michler's ketone, 2-chlorothiazolone, 2,4-diethylthiazolone, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2,2-diethoxyacetophenone, benzyl dimethyl ketal, 2,2-dimethoxy-1,2-diphenylethane-1-one, 2-hydroxy-2-methyl-1-phenylpropane-1-one, 1-hydroxycyclohexylphenyl ketone, 2 -methyl-1-[4-(methylthio)phenyl]-2-morpholinoacetone-1, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one, bis(cyclopentadienyl)-bis[2,6-difluoro-3-(pyran-1-yl)phenyl]titanium, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1,2,4,6-trimethylbenzyldiphenylphosphine oxide, etc. In addition, these compounds can be used individually or in combination.

In addition, the photoinitiator of the cationic polymerizable compound is a compound that can generate an acid by irradiation with light, and the generated acid polymerizes the above cationic polymerizable compound. Generally, onium salts and metallocene complexes are suitable. Onium salts include diazonium salts, coronium salts, iodonium salts, phosphonium salts, selenium salts, etc., and their counter ions include anions such as _BF4- ^, _PF6- ^, _AsF6- ^, _SbF6- ^, etc. Specific examples include 4-chlorobenzenediazonium hexafluorophosphate, triphenylcopperium hexafluoroacidate, triphenylcopperium hexafluorophosphate, (4-phenylthiophenyl)diphenylcopperium hexafluoroacidate, (4-phenylthiophenyl)diphenylcopperium hexafluorophosphate, bis[4-(diphenyldihydrothio)phenyl]sulfide-bis-hexafluoroacidate, bis[4-(diphenyldihydrothio)phenyl]sulfide- Bis-hexafluorophosphate, (4-methoxyphenyl) diphenylphosphonium hexafluoroantiphonate, (4-methoxyphenyl) phenyliodonium hexafluoroantiphonate, bis(4-tert-butylphenyl)iodonium hexafluorophosphate, benzyltriphenylphosphonium hexafluoroantiphonate, triphenylselenium hexafluorophosphate, (η5-isopropylbenzene)(η5-cyclopentadienyl) iron (II) hexafluorophosphate, etc., but not limited to these. In addition, these compounds can be used individually or in combination.

The photoinitiator of the present invention is blended in an amount of 0.01 to 10 parts by mass, preferably 0.1 to 7 parts by mass, and more preferably 0.1 to 5 parts by mass relative to 100 parts by mass of the photopolymerizable compound. The reason is that if the amount is less than 0.01 parts by mass, the photocurability will be reduced, and if the amount is more than 10 parts by mass, it will result in poor surface hardening, which will reduce the internal hardening, coloring, and hinder the formation of columnar regions. The photoinitiator is usually used by directly dissolving the powder in the photopolymerizable compound, but when the solubility is poor, the photoinitiator can be used by pre-dissolving it in a very small amount of solvent at a high concentration. Such a solvent is preferably photopolymerizable, and more preferably propyl carbonate, γ-butyrolactone, etc. can be mentioned. In addition, various known dyes or sensitizers may be added to improve photopolymerization. In addition, a heat-curing initiator and a photoinitiator may be used together, and the heat-curing initiator can cure the photopolymerizable compound by heating. In this case, it can be expected that the polymerization and curing of the photopolymerizable compound can be further promoted by heating after photocuring, and become more complete.

2-2-1-3. Other optional ingredients

An anisotropic light diffusion layer can be formed by curing a photopolymerizable compound alone or by curing a mixed composition of multiple compounds. In addition, the anisotropic light diffusion layer of the present invention can be formed by curing a mixture of a photopolymerizable compound and a polymer resin that is not photocurable. Examples of polymer resins that can be used include acrylic resins, styrene resins, styrene/acrylic acid copolymers, polyurethane resins, polyester resins, epoxy resins, cellulose resins, vinyl acetate resins, vinyl chloride/vinyl acetate copolymers, and polyvinyl butyral resins. These polymer resins and photopolymerizable compounds need to be sufficiently compatible before photocuring, but various organic solvents or plasticizers may be used to ensure such compatibility. Furthermore, when using acrylate as a photopolymerizable compound, it is preferably selected from the polymer resin acrylic resin from the viewpoint of compatibility.

When preparing a composition containing a photopolymerizable compound, the solvent that can be used may include ethyl acetate, butyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, toluene, xylene, etc.

2-2-2. Manufacturing steps (process) of anisotropic light diffusion layer

Next, the manufacturing steps (process) of the anisotropic light diffusion layer of this form are described. First, the coating containing the photopolymerizable compound is applied to a suitable substrate such as a transparent PET film to form a thin film, and an uncured resin component layer is provided. The uncured resin component layer is irradiated with ultraviolet light and/or visible light, thereby producing an anisotropic light diffusion layer.

The steps for forming the anisotropic light diffusion layer of this form mainly include the following steps.

(1) Step 1-1: a step of providing an uncured resin composition layer on a substrate.

(2) Step 1-2: The step of obtaining parallel light from the light source.

(3) Any step 1-3: making parallel light incident on a directional diffusion element to obtain directional light.

(4) Step 1-4: Expose light to the uncured resin composition layer to harden the uncured resin composition layer.

‧Step 1-1: The step of providing an uncured resin composition layer on the substrate

The photopolymerizable compound is applied to the substrate and molded into a sheet shape. The uncured resin composition layer can be provided by general coating methods or printing methods. Specifically, pneumatic doctor blade coating, rod coating, doctor blade coating, knife coating, reverse roll coating, transfer roll coating, gravure roll coating, matching coating, casting coating, spray coating, slot orifice coating, calender coating, weir coating, dip coating, mold coating, etc., or printing such as gravure printing such as gravure printing, stencil printing such as screen printing, etc. can be used. When the composition has low viscosity, a weir of fixed height can be set around the substrate, and the composition can be cast in the area surrounded by the weir.

Furthermore, in the above step 1-1, in order to prevent the oxygen barrier of the uncured resin component layer and efficiently form the characteristic columnar region of the anisotropic light diffusion layer of this form, a mask can be closely layered on the light irradiation side of the uncured resin component layer, and the mask can locally change the light irradiation intensity. The material of the mask is to disperse light-absorbing fillers such as carbon in the matrix, preferably so that a part of the incident light is absorbed by the carbon, but the opening of the mask can fully penetrate the light. Such a matrix can use transparent plastic films such as PET, TAC, PVAc, PVA, acrylic, polyethylene, or inorganic materials such as glass and quartz.

In addition, the mask sheet may include a pattern for controlling the amount of UV light transmitted, or a pigment that absorbs UV light.

When the above-mentioned mask is not used, oxygen barrier of the uncured resin composition layer can also be prevented by light irradiation in a nitrogen environment. In addition, when only a general transparent film is layered on the uncured resin composition layer, it is also effective to prevent oxygen barrier and promote the formation of columnar regions. During light irradiation through the above-mentioned mask or transparent film, since a photopolymerization reaction occurs in the composition containing a photopolymerizable compound in response to the light irradiation intensity, a refractive index distribution is easily generated, which is effective for the preparation of anisotropic light diffusion layers of this form.

‧Step 1-2: Steps to obtain parallel light from the light source

The light source usually uses a light source that generates short-arc ultraviolet light, specifically, a high-pressure mercury lamp, a low-pressure mercury lamp, a metal halide lamp, a xenon lamp, etc. At this time, it is necessary to obtain light parallel to the desired scattering center axis, and such parallel light can be obtained, for example, in the following manner: a point light source is arranged, and an optical lens such as a Fresnel lens for irradiating parallel light is arranged between the point light source and the uncured resin composition layer, and a reflector is arranged behind the light source to emit light in a specific direction, etc.

‧Step 1-4: Expose light to the uncured resin component layer to harden the uncured resin component layer (when any of steps 1-3 are not performed)

The light irradiated on the uncured resin composition layer and curing the uncured resin composition layer needs to contain a wavelength that can cure the photopolymerizable compound, and usually uses light with a wavelength centered at 365nm of a mercury lamp. When using this wavelength band to make an anisotropic light diffusion layer, the illumination is preferably in the range of 0.01mW/ ^cm2 to 100mW/ ^cm2 , and more preferably 0.1mW/ ^cm2 to 20mW/ ^cm2 . If the illumination is less than 0.01mW/ ^cm2 , curing takes a long time, so the production efficiency is poor. If it exceeds 100mW/ ^cm2 , the photopolymerizable compound cures too quickly and no structure is formed, and the intended optical properties cannot be exhibited. The light irradiation time is not particularly limited, but is preferably 10 to 180 seconds, more preferably 30 to 120 seconds. By irradiating the light, an anisotropic light diffusion layer of this form can be obtained.

As mentioned above, the anisotropic light diffusion layer of this form is obtained by irradiating low-intensity light for a long time, thereby forming a specific internal structure in the uncured resin composition layer. Therefore, when only the above light irradiation is performed, unreacted monomer components may remain, resulting in a sticky feeling or problems with handling or durability. In this case, high-intensity light of more than 1000mW/ ^cm2 can be additionally irradiated to polymerize the residual monomers. At this time, the light irradiation can be performed from the opposite side of the layer with the mask.

‧Any step 1-3: Make parallel light incident on the directional diffusion element to obtain directional light.

Next, the manufacturing method including any step 1-3 is described. In the manufacturing method including any step 1-3, steps 1-1 and 1-2 are as described above, so the steps after any step 1-3 are described below.

FIG8 is a schematic diagram showing the manufacturing method of the anisotropic light diffusion layer of the present invention at any step 1-3.

The directional diffusion elements 301 and 302 used in any of steps 1-3 can be any ones that can impart directivity to the parallel light D incident from the light source 300. In FIG8 , the directional light E is incident on the uncured resin composition layer 303 in a state where it diffuses more in the X direction and hardly diffuses in the Y direction. In order to obtain the above-mentioned directional light, for example, the following method can be adopted: a method in which a needle-shaped filler with a high aspect ratio is contained in the directional diffusion elements 301 and 302, and the needle-shaped filler is oriented in the Y direction in a manner that extends in the long axis direction. In addition to the method of using needle-shaped fillers, various methods can also be used for the directional diffusion elements 301 and 302.

Here, the aspect ratio of the directional light E is less than 20, preferably less than 5. A columnar region having an aspect ratio almost corresponding to the aspect ratio is formed.

In any step 1-3, the surface shape of the main plane of the columnar region (aspect ratio, short path SA, long path LA, etc.) can be appropriately determined by adjusting the expansion of the directional light E. For example, the anisotropic light diffusion layer of this form can be obtained in either Figure 8 (a) or (b). The difference between Figure 8 (a) and (b) is that the expansion of the directional light E is larger in (a), and smaller in (b). Depending on the expansion of the directional light E, the surface shape of the main plane of the columnar region will be different.

The spread of the directional light E mainly depends on the type of directional diffusion elements 301 and 302 and the distance from the uncured resin composition layer 303. As the distance becomes shorter, the size of the columnar region becomes smaller, and as the distance becomes longer, the size of the columnar region becomes larger. Therefore, the size of the columnar region can be adjusted by adjusting the distance.

‧Step 1-4: Expose light to the uncured resin component layer to harden the uncured resin component layer (when performing any of steps 1-3)

The light irradiated to the uncured resin composition layer through the directional diffusion element and curing the uncured resin composition layer needs to contain a wavelength that can cure the photopolymerizable compound, and usually uses light with a wavelength centered at 365nm of a mercury lamp. When using this wavelength band to make an anisotropic light diffusion layer, the illumination is preferably in the range of 0.01mW/ ^cm2 to 100mW/ ^cm2 , and more preferably 0.1mW/ ^cm2 to 20mW/ ^cm2 . If the illumination is less than 0.01mW/ ^cm2 , curing takes a long time, so the production efficiency is poor. If it exceeds 100mW/ ^cm2 , the photopolymerizable compound cures too quickly and no structure is formed, and the intended optical properties cannot be exhibited. The light irradiation time is not particularly limited, but is preferably 10 to 180 seconds, more preferably 30 to 120 seconds. By irradiating the light, an anisotropic light diffusion layer of the present form can be obtained.

As described above, the anisotropic light diffusion layer of this form is obtained by irradiating low-intensity light for a long time even in the case of any step 1-3, thereby forming a specific internal structure in the uncured resin composition layer. Therefore, when only the above light irradiation is performed, unreacted monomer components may remain, resulting in a sticky feeling or problems with handling or durability. In this case, high-intensity light of more than 1000mW/ ^cm2 can be additionally irradiated to polymerize the residual monomers. The light irradiation at this time can be performed from the opposite side of the laminate mask side.

3. Application of the reflective display device of the present invention

The reflective display device of the present invention can be used as a display device for outdoor use such as a tablet computer or a wearable device.

[Example]

Next, the present invention is further described in detail through embodiments and comparative examples, but the present invention is not limited to these examples.

<Preparation of anisotropic optical films 1 to 6 in the embodiment>

A 50μm high partition wall is formed using a dispenser on the entire periphery of the edge of a 100μm thick PET film (product name: A4300 manufactured by Toyobo Co., Ltd.). The following UV-curable resin coating is dripped into it, and the surface of the dripped liquid film is covered with another PET film to produce a 50μm thick uncured resin composition layer liquid film.

(UV curing resin coating)

‧Polysilicone/urethane/acrylate (refractive index: 1.460, weight average molecular weight: 5,890), 20 parts by weight

(Product name: 00-225/TM18 manufactured by RAHN).

‧Neopentyl glycol diacrylate (refractive index: 1.450), 30 parts by weight

(Trade name: Ebecryl145 manufactured by Daicel Cytec).

‧Bisphenol A EO adduct diacrylate (refractive index: 1.536), 15 parts by weight

(Trade name: Ebecyl150 manufactured by Daicel Cytec).

‧Phenoxyethyl acrylate (refractive index: 1.518), 40 parts by weight

(Trade name of Gongrong Chemical Co., Ltd.: Lightacrylate PO-A).

‧2,2-Dimethoxy-1,2-diphenylethane-1-one, 4 parts by weight

(Trade name: Irgacure 651 manufactured by BASF).

A liquid film of an uncured resin composition layer with a thickness of 50 μm sandwiched by PET films on both sides was irradiated with parallel ultraviolet light with an irradiation intensity of 5 mW/ ^cm2 directly or through a directional diffusion element from a UV point light source (trade name: L2859-01, manufactured by Hamamatsu Photonics) for 1 minute and cured, as shown in FIG. 4 , to obtain 6 types of anisotropic light diffusion layers with PET films on both sides of a single-layer anisotropic light diffusion layer with a plurality of columnar regions (anisotropic optical films for examples 1 to 6).

Specifically, no directional diffusion element is used in the production of anisotropic optical films 1, 4 to 6, and a directional diffusion element that can change the aspect ratio of parallel light is used in the production of anisotropic optical films 2 and 3.

In addition, in the production of the anisotropic optical film 6, parallel light is irradiated at an angle of 25° relative to the normal direction of the main plane of the liquid film of the uncured resin composition layer (surface normal direction).

In addition, the optical properties of each anisotropic light diffusion layer, the scattering center axis angle (relative to the normal direction of the anisotropic light diffusion layer) is adjusted by adjusting the light direction of the irradiated ultraviolet light, the maximum straight line transmittance is adjusted by adjusting the heating temperature of the liquid film formed by the ultraviolet light curing resin composition, and the aspect ratio of the columnar area is adjusted by using a directional diffusion element that can change the aspect ratio of parallel light.

The properties of the 6 types of anisotropic optical films 1 to 6 produced in the examples are shown in Table 1 below.

<Preparation of anisotropic optical film 7 in the implementation example>

The anisotropic optical film 1 was prepared in the same manner as the anisotropic optical film 1 except that a partition wall with a height of 120 μm and a liquid film of an uncured resin composition layer with a thickness of 120 μm were formed, thereby obtaining an anisotropic light diffusion layer for example with PET film on both sides of a single-layer anisotropic light diffusion layer with multiple columnar regions (anisotropic optical film for example 7). The characteristics are shown in Table 1.

<Comparative example of the preparation of anisotropic optical film 1>

A directional diffusion element capable of changing the aspect ratio of parallel light to 50 is used, and the anisotropic optical film 1 is manufactured in the same manner as the anisotropic optical film 1, thereby obtaining a comparative anisotropic light diffusion layer with PET films on both sides of a single-layer anisotropic light diffusion layer having multiple columnar regions (comparative anisotropic optical film 1).

The properties of the anisotropic optical film 1 prepared as a comparative example are shown in the following Table 1.

<Measurement of anisotropic optical films>

The properties of the anisotropic optical films 1 to 7 used in the examples and the anisotropic optical film 1 used in the comparative example in Table 1 were measured in the following manner.

(Determination of fog value)

The haze value was measured using a haze meter NDH-2000 manufactured by Nippon Denshoku Industries Co., Ltd. and in accordance with JIS K 7136.

(Determination of the scattering center axis angle and maximum linear transmittance of anisotropic light diffusion layer)

As shown in FIG7 , a variable angle photometer (manufactured by Genesia) that can arbitrarily change the light projection angle of the light source and the light receiving angle of the detector is used to measure the linear transmittance of each anisotropic optical film (anisotropic light diffusion layer) used in the embodiment and the comparative example. The detector is fixed at a position to receive the direct light from the fixed light source, and the sample holder therebetween is provided with each anisotropic optical film used in the embodiment and the comparative example of the sample. As shown in FIG7 , the sample is rotated with the straight line V passing through the sample as the rotation center axis, and the amount of linear transmitted light corresponding to the individual incident light angle is measured. This evaluation method can be used to evaluate whether the incident light will diffuse within which angle range. As shown in FIG3 , the straight line V is the same axis as the C-C axis in the sample structure. The measurement of the amount of straight-line light transmission is to use a visual sensitivity filter to measure the wavelength of the visible light region. Based on the above measurement results, the maximum straight-line transmittance (maximum straight-line transmittance) in the incident light angle and the scattering center axis angle of the incident light angle with the optical profile being roughly symmetrical are obtained based on the obtained optical profile.

(Determination of the aspect ratio of multiple columnar regions (surface observation of anisotropic light diffusion layer))

An optical microscope was used to observe one surface (light irradiation side during ultraviolet irradiation) of each anisotropic optical film (anisotropic light diffusion layer) used in the embodiment and the comparative example, and the major and minor diameters of multiple columnar regions were measured. The average major and minor diameters were calculated as the average values of any 20 structures. In addition, for the obtained average major and minor diameters, the average major diameter/average minor diameter was calculated as the aspect ratio.

<Production of reflective display device>

The polarizing plate and phase difference plate on the visual recognition side surface of the liquid crystal panel of a commercially available TN type reflective liquid crystal display are peeled off, and the anisotropic optical films 1 to 7 for the embodiments and the anisotropic optical film 1 for the comparative example are respectively laminated and bonded on the front glass surface through a transparent adhesive layer with a thickness of 10 μm. Then, the polarizing plate and phase difference plate surfaces of the phase difference plate peeled off are laminated and bonded through a transparent adhesive layer with a thickness of 10 μm relative to the exposed surfaces of each anisotropic optical film, thereby forming the reflective display device of embodiments 1 to 7 and comparative example 1.

In addition, the reflective display device of Comparative Example 2 does not use an anisotropic optical film but is directly a reflective display device.

The characteristics of the reflective display devices of Examples 1 to 7 and Comparative Examples 1 to 2 are shown in Table 2 below.

In addition, the image photographs of the reflective display devices of Example 1 and Comparative Example 2 are shown in Figure 9 (the left side is Example 1, and the right side is Comparative Example 2).

<Sensory test>

The reflective display devices of Examples 1 to 7 and Comparative Examples 1 to 2 were subjected to functional tests. The evaluation results based on the following evaluation criteria are shown in Table 2.

(Paper whiteness evaluation criteria)

○: The background color (white display) observation is white.

△: The background color (white display) is observed to be slightly white.

×: The background color (white display) is observed to be slightly yellow.

(Glare evaluation criteria)

○: No glare caused by interference.

△: There is a little glare but it is within the allowable range.

×: Glare was clearly observed.

(Bokeh evaluation criteria)

○: The image shows that the observation is clear.

△: The image appears slightly blurred.

×: The image appears blurry.

From the results in Table 2, the reflective display devices of Examples 1 to 7 are all rated above △ in all evaluations of paper whiteness, glare, and bokeh. However, the reflective display device of Example 7 performs worse than the reflective display device of Example 5 in the bokeh evaluation.

Therefore, the reflective display device using anisotropic optical film of the present invention can make the background color white, which can give a paper-white feeling. In addition, there is no significant deterioration of glare and bokeh that causes a decrease in visual recognition.

In particular, the reflective display devices of Examples 1, 2, and 6 were rated ○ in all evaluation items of paper whiteness, glare, and bokeh, and have high-level characteristics in a balanced manner.

On the other hand, the reflective display devices of Comparative Examples 1 and 2 were rated × in any of the evaluation items.

The reason why the glare of the reflective display device in Comparative Example 1 was rated × is that the multiple columnar regions of the anisotropic optical film 1 used in Comparative Example 1 have a large aspect ratio of 100-page structure, which will form a spiral arranged in one direction in a plane parallel to the film surface, thereby generating light interference.

Therefore, compared with the reflective display device using an anisotropic optical film in the embodiment of the present invention, the reflective display device in Example 1 has stronger glare and poor visual recognition.

The reflective display device in Comparative Example 2 does not use an anisotropic optical film, so the paper whiteness evaluation is ×.

From the above, it can be seen that by setting the anisotropic optical film with a specific aspect ratio of the present invention on the visual recognition side of the reflective plate of the reflective display device, a reflective display device with less glare or bokeh and a sufficient paper-white feeling can be provided.

100: Internal reflection type display device (reflective liquid crystal display device)

110: Liquid crystal layer

120: Back glass

130: Reflector (metal electrode)

140: Back polarizer

150: Anisotropic optical film

160: Back phase difference film

161: Front phase difference film

170, 171: Adhesive layer

Claims (5)

A reflective display device comprises a reflector and an anisotropic optical film whose linear transmittance varies with the angle of incident light. The anisotropic optical film is arranged closer to the visual recognition side than the reflector. The anisotropic optical film contains at least an anisotropic light diffusion layer. The anisotropic light diffusion layer has a matrix region and a refractive index that is different from that of the front light. The plurality of columnar regions are different from the matrix region, the plurality of columnar regions are aligned from one surface of the anisotropic light diffusing layer toward the other surface, the aspect ratio of the average major diameter/average minor diameter of the plurality of columnar regions in one surface of the anisotropic light diffusing layer is less than 20, and the haze value of the anisotropic light diffusing layer is 50% to 90%. A reflective display device as described in claim 1, wherein the aforementioned anisotropic light diffusion layer has at least one scattering center axis, and the angle between a surface normal direction of the aforementioned anisotropic light diffusion layer and the aforementioned at least one scattering center axis, i.e., the scattering center axis angle, is -30° to +30°. A reflective display device as described in claim 1 or 2, wherein the maximum linear transmittance of the aforementioned anisotropic light diffusion layer is 10% to 60%. A reflective display device as described in claim 1 or 2, wherein the thickness of the anisotropic light diffusion layer is 10 μm to 100 μm. A reflective display device as described in claim 1 or 2, wherein the aspect ratio is less than 5.

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