JP2012068273A - Light diffusion element, polarizer with light diffusion element, liquid crystal display device using the same, and light diffusion element manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light diffusion element in which angle dependence of a color tone is suppressed.SOLUTION: A light diffusion element 100 comprises a matrix 10 including a resin component 11 and light diffusion fine particles 20 scattered in the matrix. In the light diffusion element, a maximum absorption wavelength in a visible light region of 380 nm to 780 nm is within a range of 380 nm to 520 nm, and light transmittance at 460 nm is 50% to 80%. In the light diffusion element 100, light diffusion half-value angle is 20° or more; the matrix includes ultra fine particle components 12; the resin component, an ultra fine particle component, and a light diffusion fine particle satisfy a formula (1) below; a concentration modulation region 31 is formed in vicinity of an interface between the matrix and the light diffusion fine particle; and a concentration modulation region 31 having weight concentration of the ultra fine particle component increasing in locations farther away from the light diffusion fine particle is included: |n-n|<|n-n|...(1). In the formula (1), nrepresents a refractive index of the resin component of the matrix, nrepresents a refractive index of the ultra fine particle component of the matrix, and nrepresents a refractive index of the light diffusion fine particle.

Description

  The present invention relates to a light diffusing element, a polarizing plate with a light diffusing element, and a liquid crystal display device using these.

  Light diffusing elements are widely used in lighting covers, projection television screens, surface light emitting devices (for example, liquid crystal display devices), and the like. In recent years, light diffusing elements have been increasingly used for improving the display quality of liquid crystal display devices and improving viewing angle characteristics. As the light diffusing element, an element in which fine particles are dispersed in a matrix such as a resin sheet has been proposed (for example, see Patent Document 1). However, since the light diffusion intensity by the light diffusing element differs depending on the wavelength, there is a problem that the angle dependency of the hue occurs.

Japanese Patent No. 3071538

  The present invention has been made to solve the above conventional problems, and an object of the present invention is to provide a light diffusing element in which the angle dependency of hue is suppressed.

The light diffusing element of the present invention has a matrix containing a resin component and light diffusing fine particles dispersed in the matrix, and the maximum absorption wavelength in the visible light region of 380 nm to 780 nm is within the range of 380 nm to 520 nm. Yes, the light transmittance at 460 nm is 50% to 80%.
In a preferred embodiment, the light diffusion half-value angle is 20 ° or more.
In a preferred embodiment, the haze is 90% to 99.9%.
In a preferred embodiment, the matrix contains a dye component having a maximum absorption wavelength in the range of 380 nm to 520 nm in the visible light range of 380 nm to 780 nm.
In a preferred embodiment, the light diffusing fine particles have an average particle diameter of 1 μm to 5 μm.
In a preferred embodiment, the thickness is at least twice the average particle size of the light diffusing fine particles.
In a preferred embodiment, the matrix contains an ultrafine particle component, and the resin component, the ultrafine particle component, and the light diffusing fine particles have a refractive index satisfying the following formula (1), and the light diffusing fine particles are: A concentration modulation region is formed outside the vicinity of the surface, and the weight concentration of the ultrafine particle component increases as the distance from the light diffusing fine particles increases:
| N _P −n _A | <| n _P −n _B | (1)
In formula (1), n _A represents the refractive index of the resin component of the matrix, n _B represents the refractive index of the ultrafine particle component of the matrix, and n _P represents the refractive index of the light diffusing fine particles.
According to another aspect of the present invention, a polarizing plate with a light diffusing element is provided. This polarizing plate with a light diffusing element has the above light diffusing element and a polarizer.
According to still another aspect of the present invention, a liquid crystal display device is provided. The liquid crystal display device includes: a liquid crystal cell; a parallel light source device that emits collimated light toward the liquid crystal cell; and the light diffusing element that transmits and diffuses the collimated light that has passed through the liquid crystal cell. .
In a preferred embodiment, the parallel light source device has a half-value angle of 35 ° or less.

  According to the light diffusing element of the present invention, the angle dependency of hue can be effectively suppressed by absorbing a specific wavelength. Specifically, light tends to diffuse more strongly at shorter wavelengths than at longer wavelengths, and diffused light exhibits a hue of blue at a large diffusion angle and a hue of red at a small diffusion angle. Tend to show. Therefore, by setting the maximum absorption wavelength in the visible light range of 380 nm to 780 nm within the range of 380 nm to 520 nm, the oblique emission light that can have a longer optical path length is absorbed by the short wavelength component, and is reflected in the front emission light. Get closer. In addition, due to multiple diffusion and light diffusion to a wide angle (strong diffusion), the optical path length of obliquely emitted light is further increased, short wavelength components are absorbed more, and hue change can be further reduced. As a result, the angle dependency of the hue of the emitted light can be effectively suppressed.

It is a schematic diagram for demonstrating the dispersion state of the resin component and ultrafine particle component of a matrix in the light diffusing element by preferable embodiment of this invention, and a light diffusable fine particle. It is a schematic diagram for demonstrating the dispersion state of the resin component and ultrafine particle component of a matrix, and light diffusing fine particles in the light diffusing element according to another embodiment of the present invention. (A) is a conceptual diagram for demonstrating the refractive index change from the center part of light diffusible microparticles | fine-particles in the light diffusing element of FIG. 1A to a matrix, (b) is the light diffusibility in the light diffusing element of FIG. 1B. It is a conceptual diagram for demonstrating the refractive index change from fine particle center part to a matrix, (c) is a conceptual diagram for demonstrating the refractive index change from fine particle center part to a matrix in the conventional light-diffusion element. . It is a schematic diagram which shows the relationship between r1 and r2 in the light diffusible fine particle used for this invention. It is a graph which shows the relationship between drying temperature and the light-diffusion half-value angle obtained about the coating liquid from which stationary time differs. It is a schematic sectional drawing of the polarizing plate with a light-diffusion element by preferable embodiment of this invention. 1 is a schematic cross-sectional view of a liquid crystal display device according to a preferred embodiment of the present invention. It is a schematic diagram for demonstrating the method of calculating the half value angle of a light source device. It is a schematic diagram for demonstrating the method of calculating a light-diffusion half-value angle. It is a result of the transmission spectrum measurement of the light diffusing element of Example 1 and Comparative Example 1.

  Hereinafter, although preferable embodiment of this invention is described, this invention is not limited to these embodiment.

A. Light Diffusing Element The light diffusing element of the present invention has a matrix containing a resin component and light diffusing fine particles dispersed in the matrix, and has a maximum absorption wavelength in the visible light range of 380 nm to 780 nm of 380 nm to 520 nm. Within range.

  The resin component is composed of any appropriate material. Preferably it is comprised with an organic compound, More preferably, it is comprised with ionizing-ray curable resin. This is because the ionizing ray curable resin can be excellent in the hardness of the coating film. Specifically, even when a component having low mechanical strength such as an ultrafine particle component described later is used, the weak point can be compensated well. Examples of the ionizing rays include ultraviolet rays, visible light, infrared rays, and electron beams. Preferably it is an ultraviolet-ray. Therefore, the resin component is particularly preferably composed of an ultraviolet curable resin. Examples of the ultraviolet curable resins include radical polymerization monomers and / or oligomer polymers such as acrylate resins (epoxy acrylate, polyester acrylate, acrylic acrylate, ether acrylate). The molecular weight of the monomer component (precursor) constituting the acrylate resin is preferably 200 to 700. Specific examples of the monomer component (precursor) constituting the acrylate resin include pentaerythritol triacrylate (PETA: molecular weight 298), neopentyl glycol diacrylate (NPGDA: molecular weight 212), dipentaerythritol hexaacrylate (DPHA: molecular weight 632). ), Dipentaerythritol pentaacrylate (DPPA: molecular weight 578), and trimethylolpropane triacrylate (TMPTA: molecular weight 296). In one embodiment, such a monomer component (precursor) is preferable because it has a molecular weight and a three-dimensional structure suitable for penetrating the crosslinked structure (three-dimensional network structure) of the light diffusing fine particles. An initiator may be added as necessary. Examples of the initiator include a UV radical generator (Irgacure 907, 127, 192, etc., manufactured by Ciba Specialty Chemicals) and benzoyl peroxide. The resin component may contain another resin component in addition to the ionizing radiation curable resin. Another resin component may be an ionizing radiation curable resin, a thermosetting resin, or a thermoplastic resin. Representative examples of other resin components include aliphatic (for example, polyolefin) resins and urethane resins.

  The refractive index of the resin component is preferably 1.40 to 1.60.

  The compounding amount of the resin component is preferably 20 parts by weight or more, more preferably 20 parts by weight to 80 parts by weight, and further preferably 45 parts by weight to 65 parts by weight with respect to 100 parts by weight of the matrix.

  As described above, any appropriate configuration is adopted for the light diffusing element of the present invention as long as the maximum absorption wavelength in the visible light range of 380 nm to 780 nm is in the range of 380 nm to 520 nm. Preferably, the maximum absorption wavelength in the visible light region of 380 nm to 780 nm of the matrix is in the range of 380 nm to 520 nm. By adopting such a configuration, the light diffusing element can be easily manufactured. In a preferred embodiment, the matrix comprises a dye component having a maximum absorption wavelength in the range of 380 nm to 520 nm in the visible light range of 380 nm to 780 nm. The dye component is composed of any appropriate material, and may be an organic compound, an inorganic compound, or a composite compound thereof. Examples of organic compounds include dye-based pigments and pigment-based pigments. Examples of inorganic compounds include cerium oxide. Among these, organic dye-based pigments are preferably used. The dye-based pigment is very small (nanoparticles) and can realize high haze. Moreover, by using a dye-type pigment | dye, it can suppress that malfunctions, such as sedimentation and aggregation, interact with the below-mentioned ultrafine particle component in a matrix.

  When the matrix contains a pigment component, the amount of the pigment component is preferably 0.05 parts by weight to 0.30 parts by weight with respect to 100 parts by weight of the matrix. For example, by including the pigment component in such a blending amount, a light transmittance in a preferable range described later can be obtained favorably, and a light diffusing element excellent in visibility can be obtained.

  The light diffusing fine particles are made of any appropriate material. In one embodiment, the light diffusing fine particles are preferably composed of a compound similar to the resin component of the matrix. For example, when the ionizing radiation curable resin constituting the resin component of the matrix is an acrylate resin, the light diffusing fine particles are also preferably composed of an acrylate resin. More specifically, when the monomer component of the acrylate resin constituting the resin component of the matrix is, for example, PETA, NPGDA, DPHA, DPPA and / or TMPTA as described above, the acrylate constituting the light diffusing fine particles The base resin is preferably polymethyl methacrylate (PMMA), polymethyl acrylate (PMA), and a copolymer thereof, and a cross-linked product thereof. Examples of the copolymer component with PMMA and PMA include polyurethane, polystyrene (PSt), and melamine resin. Particularly preferably, the light diffusing fine particles are composed of PMMA. This is because the relationship between the refractive index and thermodynamic characteristics of the resin component of the matrix and the ultrafine particle component described later is appropriate. Further preferably, the light diffusing fine particles have a cross-linked structure (three-dimensional network structure). The light diffusing fine particles having a crosslinked structure can swell. Therefore, unlike the fine or solid inorganic particles, such light diffusing fine particles can allow a precursor of a resin component having appropriate compatibility to penetrate into the inside of the fine particles. The density modulation region can be formed satisfactorily. The crosslink density of the light diffusing fine particles is preferably small (coarse) so that a desired penetration range (described later) is obtained. For example, the degree of swelling of the light diffusing fine particles with respect to the resin component precursor (which may contain a solvent) when applying the coating liquid described below is preferably 110% to 200%. Here, the “swelling degree” refers to the ratio of the average particle size of the swollen particles to the average particle size of the particles before swelling.

  The light diffusing fine particles have an average particle size of preferably 1.0 μm to 5.0 μm, more preferably 1.0 μm to 4.0 μm, and further preferably 1.5 μm to 3.0 μm.

  The standard deviation of the weight average particle size distribution of the light diffusing fine particles is preferably 1.0 μm or less, more preferably 0.5 μm or less. If a large number of light diffusing fine particles having a small particle size with respect to the weight average particle size are mixed, the diffusibility may be excessively increased and the backscattering may not be suppressed well. If a large number of light diffusing fine particles having a large particle diameter with respect to the weight average particle diameter are mixed, a plurality of light diffusing elements cannot be arranged in the thickness direction of the light diffusing element, and multiple diffusion may not be obtained. , The light diffusibility may be insufficient.

  Any appropriate shape can be adopted as the shape of the light diffusing fine particles depending on the purpose. Specific examples include a true sphere shape, a flake shape, a plate shape, an elliptic sphere shape, and an indefinite shape. In many cases, spherical fine particles can be used as the light diffusing fine particles.

  The refractive index of the light diffusing fine particles is preferably 1.30 to 1.70, more preferably 1.40 to 1.60.

  The compounding amount of the light diffusing fine particles is preferably 10 to 100 parts by weight, more preferably 15 to 40 parts by weight with respect to 100 parts by weight of the matrix. For example, a light diffusing element having a very excellent light diffusibility can be obtained by incorporating light diffusing fine particles having an average particle diameter in the above preferred range with such a blending amount.

  The thickness of the light diffusing element can be appropriately set according to the purpose and desired diffusion characteristics. Preferably, it is at least twice the average particle size of the light diffusing fine particles, more preferably at least 2 times and no more than 50 times. By setting the thickness to be twice or more, a plurality of light diffusing fine particles can be arranged in the thickness direction of the light diffusing element, so that the light is distributed a plurality of times (multiple) while the incident light passes through the light diffusing element. It can be diffused and sufficient light diffusivity can be obtained. Further, the diffused light emitted in the oblique direction (oblique light diffused light) can have a longer optical path length than the light emitted from the front (front emitted light). As a result, the oblique light diffused light can absorb the short wavelength component more, and can further reduce the hue change. Specifically, the thickness of the light diffusing element is preferably 4 μm to 200 μm, more preferably 4 μm to 100 μm.

  The light transmittance at 460 nm of the light diffusing element is preferably 50% or more, more preferably 50% to 80%.

  The diffusion characteristic of the light diffusing element is preferably 20 ° (10 ° on one side) or more, more preferably 30 ° to 100 °, if expressed by a light diffusion half-value angle. In such a light diffusing element having a light diffusibility to a wide angle, the oblique light diffused light is diffused a plurality of times (multiple), and the optical path length can be very long. As a result, the viewing angle characteristics of the hue are improved very effectively.

Preferably, the matrix further includes an ultrafine particle component. By including an ultrafine particle component, the light diffusibility to the wide angle can be achieved satisfactorily and backscattering can be suppressed. 1A and 1B are schematic diagrams for explaining the dispersion state of the resin component and ultrafine particle component of the matrix and the light diffusing fine particles in the light diffusing element according to the preferred embodiment, respectively (the dye component is not shown). ). The light diffusing element 100 has a matrix 10 including a resin component 11 and an ultrafine particle component 12 and light diffusing fine particles 20 dispersed in the matrix 10. Preferably, the resin component and ultrafine particle component of the matrix and the light diffusing fine particles have a refractive index satisfying the following formula (1).
| N _P −n _A | <| n _P −n _B | (1)
In formula (1), n _A represents the refractive index of the resin component of the matrix, n _B represents the refractive index of the ultrafine particle component of the matrix, and n _P represents the refractive index of the light diffusing fine particles. Further, the refractive index of the resin component, the ultrafine particle component, and the light diffusing fine particles can also satisfy the following formula (2).
| N _P −n _A | <| n _A −n _B | (2)

  In one embodiment, as shown in FIG. 1A, a concentration modulation region 31 is formed outside the vicinity of the surface of the light diffusing fine particles 20. In another embodiment, as shown in FIG. 1B, it further has a second concentration modulation region 32 formed by the resin component 11 penetrating into the inside of the vicinity of the surface of the light diffusing fine particles 20. In the present specification, for convenience, the concentration modulation region 31 outside the surface of the light diffusing fine particles 20 may be referred to as a first concentration modulation region.

When only the first concentration modulation region 31 is formed as shown in FIG. 1A, | n _P −n _A | in the above formula (1) is preferably 0.0 to 0.1, and more preferably It is 0.0-0.06, Most preferably, it exceeds 0 and is 0.06 or less. If | n _P −n _A | exceeds 0.1, backscattering may increase. In the case where the first concentration modulation region 31 and the second concentration modulation region 32 are formed as shown in FIG. 1B, | n _P −n _A | in the above formula (1) is preferably 0.01-0. It is 10, More preferably, it is 0.01-0.06, Most preferably, it is 0.02-0.06. If | n _P −n _A | is less than 0.01, the second concentration modulation region may not be formed. When | n _P −n _A | exceeds 0.10, backscattering may increase. Regardless of whether or not the second concentration modulation region 32 is formed, | n _P −n _B | is preferably 0.10 to 1.50, more preferably 0.20 to 0.80. is there. If | n _P −n _B | is less than 0.10, the haze is often 90% or less. As a result, when incorporated in a liquid crystal display device, the light from the light source cannot be sufficiently diffused, The corner may be narrowed. When | n _P −n _B | exceeds 1.50, backscattering may increase. Further, regardless of whether or not the second concentration modulation region 32 is formed, | n _A −n _B | is preferably 0.10 to 1.50, and more preferably 0.20 to 0.00. 80. If | n _A −n _B | is less than 0.10, sufficient light diffusibility may not be obtained. When | n _A −n _B | exceeds 1.50, the wavelength dispersion of n _A and n _B increases, and the color tone of the scattered light may not be neutral. As described above, the resin component and the light diffusing fine particles of the matrix having a refractive index close to each other, and the ultrafine particle component having a refractive index greatly different from that of the resin component and the light diffusing fine particles are used in combination, so Backscattering can be suppressed while maintaining high haze in combination with the effects caused by the concentration modulation region and the second concentration modulation region.

  In the first concentration modulation region 31, the weight concentration of the resin component 11 decreases and the weight concentration of the ultrafine particle component 12 increases as the distance from the light diffusing fine particles 20 increases. In other words, the ultrafine particle component 12 is dispersed at a relatively low concentration in the closest region of the light diffusing fine particle 20 in the first concentration modulation region 31, and the ultrafine particle component is increased as the distance from the light diffusing fine particle 20 increases. The concentration of 12 increases. For example, in the closest region of the light diffusing fine particles 20 in the first concentration modulation region 31, the weight concentration of the resin component is higher than the average weight concentration of the resin component in the entire matrix, and the weight concentration of the ultrafine particle component is Lower than the average weight concentration of the ultrafine particle component in the whole. On the other hand, in the farthest region from the light diffusing fine particles 20 in the first concentration modulation region 31, the weight concentration of the resin component is equal to or lower than the average weight concentration of the resin component in the entire matrix. The weight concentration of the fine particle component is equal to or higher in some cases than the average weight concentration of the ultra fine particle component in the entire matrix. By forming such a first concentration modulation region, the refractive index is steep in the vicinity of the interface between the matrix 10 and the light diffusing fine particles 20 (periphery of the light diffusing fine particles 20, that is, outside the vicinity of the surface). It can be changed substantially continuously (see FIG. 2A). On the other hand, in the conventional light diffusing element, such a first concentration modulation region is not formed, and the interface between the fine particles and the matrix is clear, so that the refractive index is changed from the refractive index of the fine particles to the refractive index of the matrix. It changes discontinuously (see FIG. 2C). As shown in FIG. 2A, the first concentration modulation region 31 is formed and the refractive index is steep near the interface between the matrix 10 and the light diffusing fine particles 20 (outside the surface of the light diffusing fine particles 20). By changing substantially continuously, even when the refractive index difference between the matrix 10 and the light diffusing fine particles 20 is increased, reflection at the interface between the matrix 10 and the light diffusing fine particles 20 can be suppressed, and the rear Scattering can be suppressed. Further, outside the first concentration modulation region 31, the weight concentration of the ultrafine particle component 12 having a refractive index significantly different from that of the light diffusing fine particles 20 is relatively high. The difference in refractive index can be increased. As a result, high haze (strong diffusivity) can be achieved even with a thin film. Therefore, according to the light diffusing element of the present invention, by forming such a first concentration modulation region, it is possible to significantly suppress backscattering while realizing a high haze by increasing the refractive index difference. it can. Such a feature is particularly suitable for applications that require strong diffusibility (haze of 90% or more), such as a light diffusing element used in a collimated backlight front diffusion system. On the other hand, as shown in FIG. 2 (c), according to the conventional light diffusing element, when an attempt is made to impart strong diffusivity (high haze value) by increasing the difference in refractive index, the gap of the refractive index at the interface. Can not be resolved. As a result, backscattering due to interface reflection becomes large, and black display may not be sufficiently black (so-called black is floated).

  The dye used in the present invention can be uniformly dispersed in the light diffusing element without hindering the formation of the first concentration modulation region, achieves high haze and low backscattering, and emits light. Effectively suppresses the angle dependency of the hue of incident light.

  The thickness of the first concentration modulation region 31 (distance from the surface of the light diffusing fine particle to the end of the first concentration modulation region) may be constant (that is, the first concentration modulation region is a light diffusing fine particle. And the thickness may be different depending on the position of the surface of the light diffusing fine particles (for example, it may be an outline shape of confetti). Preferably, the thickness of the first concentration modulation region 31 varies depending on the position of the surface of the light diffusing fine particles. With such a configuration, the refractive index can be changed substantially more continuously in the vicinity of the interface between the matrix 10 and the light diffusing fine particles 20. If the first concentration modulation region 31 is formed with a sufficient thickness, the refractive index can be changed more smoothly and continuously at the periphery of the light diffusing fine particles, and the backscattering can be suppressed very effectively. can do. On the other hand, if the thickness is too large, the first concentration modulation region occupies the region where the light diffusing fine particles should originally exist, and sufficient light diffusibility (for example, haze value) may not be obtained. Therefore, the thickness of the first concentration modulation region 31 is preferably 10 nm to 500 nm, more preferably 20 nm to 400 nm, and still more preferably 30 nm to 300 nm. The thickness of the first concentration modulation region 31 is preferably 10% to 50%, more preferably 20% to 40% with respect to the average particle diameter of the light diffusing fine particles.

  The second concentration modulation region 32 is formed by the resin component 11 penetrating into the light diffusing fine particles 20. Substantially, the precursor (typically, monomer) of the resin component 11 penetrates into the light diffusing fine particles 20 and then polymerizes, whereby the second concentration modulation region 32 is formed. In one embodiment, the weight concentration of the resin component 11 is substantially constant in the second concentration modulation region 32. In another embodiment, in the second concentration modulation region 32, the weight concentration of the resin component 11 decreases as the distance from the surface of the light diffusing fine particles 20 increases (that is, toward the center of the light diffusing fine particles 20). If the second concentration modulation region 32 is formed inside the light diffusing fine particles 20, the effect is exhibited. For example, the second concentration modulation region 32 is formed from the surface of the light diffusing fine particles 20 to a range of preferably 10% to 95% of the average particle diameter of the light diffusing fine particles. The thickness of the second concentration modulation region 32 (the distance from the surface of the light diffusing fine particle to the innermost part of the second concentration modulation region) may be constant or may vary depending on the position of the surface of the light diffusing fine particle. . The thickness of the second concentration modulation region 32 is preferably 100 nm to 4 μm, more preferably 100 nm to 2 μm. When the resin component 11 permeates to form the second concentration modulation region 32, the following effects can be obtained: (1) formation of the first concentration modulation region 31 can be promoted; (2) light By forming the concentration modulation region inside the diffusing fine particles, the region where the refractive index changes stepwise or substantially continuously can be enlarged (that is, the second region inside the light diffusing fine particles). The refractive index can be changed stepwise or substantially continuously from the concentration modulation region to the first concentration modulation region outside the light diffusing fine particles (see FIG. 2B). As a result, backscattering can be further suppressed as compared with the case where only the first concentration modulation region is formed outside the light diffusing fine particles; (3) the resin component 11 penetrates into the light diffusing fine particles 20. By doing, the resin component density | concentration in the matrix 10 becomes low compared with the case where it does not permeate. As a result, the contribution of the refractive index of the ultrafine particle component 12 to the refractive index of the entire matrix 10 increases, so that the refractive index of the entire matrix increases when the refractive index of the ultrafine particle component is large (in contrast, the ultrafine particle component). When the refractive index of the matrix is small, the refractive index of the entire matrix is small), and the refractive index difference between the matrix and the light diffusing fine particles is further increased. Therefore, even higher diffusivity (haze value) can be realized as compared with the case where the resin component does not penetrate. In addition, sufficient diffusivity can be achieved even with a thinner thickness than when the resin component does not penetrate.

  The first concentration modulation region and the second concentration modulation region are selected by appropriately selecting the resin component and ultrafine particle component of the matrix, the constituent material of the light diffusing fine particles, and the chemical and thermodynamic characteristics, respectively. Can be formed. For example, by configuring the resin component and the light diffusing fine particles with the same material (for example, organic compounds), and configuring the ultra fine particle component with a system material (for example, an inorganic compound) different from the matrix and the light diffusing fine particles, The first density modulation region can be formed satisfactorily. Furthermore, for example, the second concentration modulation region can be satisfactorily formed by configuring the resin component and the light diffusing fine particles with materials having high compatibility among similar materials. The thickness and concentration gradient of the first concentration modulation region and the second concentration modulation region can be controlled by adjusting the chemical and thermodynamic properties of the resin component and ultrafine particle component of the matrix and the light diffusing fine particles. it can. In the present specification, “same system” means that chemical structures and properties are equivalent or similar, and “different system” means something other than the same system. Whether or not they are related may differ depending on how the reference is selected. For example, when organic or inorganic is used as a reference, the organic compounds are the same type of compounds, and the organic compound and the inorganic compound are different types of compounds. When the polymer repeat unit is used as a reference, for example, an acrylic polymer and an epoxy polymer are different compounds despite being organic compounds, and when a periodic table is used as a reference, alkali metals and transition metals are used. Is an element of a different system despite being inorganic elements.

  The first concentration modulation region 31 and the second concentration modulation region 32 have a radius of the light diffusing fine particles r1, and are parallel to the maximum cross section of the light diffusing fine particles (a plane including the radius of the light diffusing fine particles). When the radius of the cross section is r2, the ratio of r2 to r1 is preferably 20% to 80%, more preferably 40% to 60%, and even more preferably about 50%. Yes. By appropriately forming the first concentration modulation region 31 and, if necessary, the second concentration modulation region 32 at such a position, incident light having a large incident angle with respect to the radial direction of the light diffusing fine particles (hereinafter referred to as the “light density diffusion region”). ) (Referred to as side incident light) can be satisfactorily suppressed. The relationship between r1 and r2 is schematically shown in FIG. More specifically, backscattering due to interface reflection between the matrix and the light diffusing fine particles is roughly classified into three types as shown in FIG. That is, front-facing interface reflected light (arrow A in FIG. 3), side incident light interface reflected light (arrow B in FIG. 3), and side incident light interface reflected light forward. Is scattered from the light diffusing element due to total reflection but scattered backward (arrow C in FIG. 3). Based on Snell's law, the side incident light has a higher reflectance than the front incident light. Therefore, by suppressing the interface reflection of the side incident light, the backscattering can be reduced more efficiently. Therefore, it is preferable that the density modulation region is formed at a position where the backscattering of the side incident light can be effectively reduced. If r2 is too small, the light reflected at such a position does not reach the critical angle and passes forward, so that it often does not significantly affect the effect of reducing backscattering.

  As long as the resin component 11 is well formed with the first concentration modulation region and, if necessary, the second concentration modulation region, and the refractive index satisfies the relationship of the above formula (1), any appropriate component can be used. It is composed of various materials. Preferably, as described above, the resin component 11 is composed of a compound similar to the light diffusing fine particles and different from the ultrafine particle component. Thereby, the first concentration modulation region can be satisfactorily formed near the interface between the matrix and the light diffusing fine particles (outside the vicinity of the surface of the light diffusing fine particles). More preferably, the resin component 11 is composed of a highly compatible compound in the same system as the light diffusing fine particles. Thereby, the 2nd density | concentration modulation area | region 32 can be favorably formed in the surface vicinity inside of the light diffusable microparticle 20 as needed. More specifically, because the resin component is a material similar to the light diffusing fine particles, a precursor (typically a monomer) can penetrate into the light diffusing fine particles. As a result of the polymerization of the precursor, a second concentration modulation region by the resin component can be formed inside the light diffusing fine particles. Further, in the vicinity of the light diffusing fine particles, the resin component locally surrounds the light diffusing fine particles only with the resin component, rather than being in a state of being uniformly dissolved or dispersed with the ultra fine particle component. The energy of the whole system is stabilized. As a result, the weight concentration of the resin component is higher than the average weight concentration of the resin component in the entire matrix in the closest region of the light diffusing fine particles, and decreases as the distance from the light diffusing fine particles increases. Therefore, the first concentration modulation region 31 can be formed on the outside (peripheral portion) near the surface of the light diffusing fine particles.

  As described above, the ultrafine particle component 12 is preferably composed of a compound of a system different from the resin component and the light diffusing fine particles described later, and more preferably composed of an inorganic compound. Examples of preferable inorganic compounds include metal oxides and metal fluorides. Specific examples of the metal oxide include zirconium oxide (zirconia) (refractive index: 2.19), aluminum oxide (refractive index: 1.56 to 2.62), and titanium oxide (refractive index: 2.49 to 2.19). 74) and silicon oxide (refractive index: 1.25 to 1.46). Specific examples of the metal fluoride include magnesium fluoride (refractive index: 1.37) and calcium fluoride (refractive index: 1.40 to 1.43). These metal oxides and metal fluorides have a refractive index that is difficult to be expressed by organic compounds such as ionizing radiation curable resins and thermoplastic resins in addition to low light absorption. Since the weight concentration of the ultrafine particle component becomes relatively higher as the distance from the interface increases, the refractive index can be greatly modulated. By increasing the difference in refractive index between the light diffusing fine particles and the matrix, high haze can be realized even with a thin film, and the first concentration modulation region is formed, so that the effect of preventing backscattering is great. A particularly preferred inorganic compound is zirconium oxide. This is because the difference in refractive index with the light diffusing fine particles is large and the dispersibility with the resin component is appropriate, so that the desired first concentration modulation region 31 can be formed.

  The refractive index of the ultrafine particle component is preferably 1.40 or less or 1.60 or more, more preferably 1.40 or less or 1.70 to 2.80, and particularly preferably 1.40 or less or 2 .00 to 2.80. If the refractive index exceeds 1.40 or less than 1.60, the difference in refractive index between the light diffusing fine particles and the matrix becomes insufficient, and the light diffusing element is applied to a liquid crystal display device employing a collimated backlight front diffusion system. When used, the light from the collimated backlight cannot be sufficiently diffused and the viewing angle may be narrowed.

  The ultrafine particle component may be made porous to lower the refractive index.

  The average particle size of the ultrafine particle component is preferably 1 nm to 100 nm, more preferably 10 nm to 80 nm, and still more preferably 20 nm to 70 nm. In this way, by using an ultrafine particle component having an average particle diameter smaller than the wavelength of light, no geometrical optical reflection, refraction, or scattering occurs between the ultrafine particle component and the resin component, and an optically uniform matrix. Can be obtained. As a result, an optically uniform light diffusing element can be obtained.

  The ultrafine particle component preferably has good dispersibility with the resin component. In the present specification, “good dispersibility” means that a coating liquid obtained by mixing the resin component, the ultrafine particle component, and a volatile solvent (if necessary, a small amount of UV initiator) is applied, It means that the coating film obtained by drying and removing the solvent is transparent.

  Preferably, the ultrafine particle component is surface-modified. By performing the surface modification, the ultrafine particle component can be favorably dispersed in the resin component, and the first concentration modulation region can be favorably formed. Any appropriate means can be adopted as the surface modifying means as long as the effects of the present invention can be obtained. Typically, the surface modification is performed by applying a surface modifier to the surface of the ultrafine particle component to form a surface modifier layer. Specific examples of preferable surface modifiers include coupling agents such as silane coupling agents and titanate coupling agents, and surfactants such as fatty acid surfactants. By using such a surface modifier, the wettability between the resin component and the ultrafine particle component is improved, the interface between the resin component and the ultrafine particle component is stabilized, and the ultrafine particle component is improved in the resin component. The first concentration modulation region can be favorably formed while being dispersed.

  The blending amount of the ultrafine particle component is preferably 10 parts by weight to 70 parts by weight, and more preferably 35 parts by weight to 55 parts by weight with respect to 100 parts by weight of the matrix.

  The light diffusing element preferably has a higher haze, specifically, preferably 90% to 99.9%, more preferably 92% to 99%, and still more preferably 95% to 99%. And particularly preferably 97% to 99%. The haze is determined according to JIS 7136. According to this embodiment, even if it is the thin thickness of the said suitable range, the light-diffusion element which has such a very high haze can be obtained. Moreover, when the haze is 90% or more, it can be suitably used as a front light diffusing element in a collimated backlight front diffusing system. The collimated backlight front diffusion system is a liquid crystal display device that uses collimated backlight light (backlight light with a narrow luminance half-value width condensed in a certain direction) and the front light on the viewing side of the upper polarizing plate. A system provided with a diffusing element.

  The light diffusing element is suitably used for a liquid crystal display device, and particularly suitably for a collimated backlight front diffusing system. The light diffusing element may be provided alone as a film-like or plate-like member, or may be provided as a composite member by being attached to any appropriate base material or polarizing plate. An antireflection layer may be laminated on the light diffusing element.

[Production Method of Light Diffusing Element]
Arbitrary appropriate methods can be employ | adopted for the manufacturing method of the light-diffusion element of this invention. Hereinafter, one embodiment will be specifically described.

  In one embodiment, a step of applying to a substrate a coating liquid in which a resin component of a matrix or a precursor thereof, a pigment component, an ultrafine particle component, and a light diffusing fine particle are dissolved or dispersed in a volatile solvent. (Referred to as step A) and a step (referred to as step B) for drying the coating liquid applied to the substrate.

(Process A)
Typically, the coating liquid is a dispersion in which ultrafine particle components and light diffusing fine particles are dispersed in a precursor and a volatile solvent. Moreover, the pigment | dye component is melt | dissolved or disperse | distributed to a precursor and a volatile solvent according to the kind. Any appropriate means (for example, sonication) can be adopted as the means for dispersing.

  Any appropriate solvent can be adopted as the volatile solvent as long as the above-described components can be dissolved or uniformly dispersed. Specific examples of the volatile solvent include ethyl acetate, butyl acetate, isopropyl acetate, 2-butanone (methyl ethyl ketone), methyl isobutyl ketone, cyclopentanone, toluene, isopropyl alcohol, n-butanol, cyclopentane, and water.

  The coating liquid may further contain any appropriate additive depending on the purpose. For example, in order to disperse the ultrafine particle component satisfactorily, a dispersant can be suitably used. Other specific examples of the additive include an antioxidant, a modifier, a surfactant, a discoloration inhibitor, an ultraviolet absorber, a leveling agent, and an antifoaming agent.

  The compounding quantity of each said component in a coating liquid is as having mentioned above. The solid content concentration of the coating liquid can be adjusted to be preferably about 10% by weight to 70% by weight. If it is such solid content concentration, the coating liquid which has a viscosity with easy coating can be obtained.

  Any appropriate film can be adopted as the substrate as long as the effects of the present invention can be obtained. Specific examples include a triacetyl cellulose (TAC) film, a polyethylene terephthalate (PET) film, a polypropylene (PP) film, a nylon film, an acrylic film, and a lactone-modified acrylic film. If necessary, the base material may be subjected to surface modification such as easy adhesion treatment, and may contain additives such as a lubricant, an antistatic agent, and an ultraviolet absorber. The base material may function as a protective layer in the polarizing plate with a light diffusing element described later.

  As a method for applying the coating liquid to the substrate, a method using any appropriate coater may be employed. Specific examples of the coater include a bar coater, a reverse coater, a kiss coater, a gravure coater, a die coater, and a comma coater.

(Process B)
Any appropriate method can be adopted as a method for drying the coating solution. Specific examples include natural drying, heat drying, and vacuum drying. Heat drying is preferable. The heating temperature is, for example, 60 ° C. to 150 ° C., and the heating time is, for example, 30 seconds to 5 minutes.

  As described above, the light diffusing element as shown in FIG. 1A is formed on the substrate.

  As shown in FIG. 1B, in the case where the second concentration modulation region is formed inside the light diffusing fine particles, the production method of the present invention uses the precursor of the resin component and the light in the coating liquid of the step A. A step of contacting the diffusible fine particles (referred to as step A-1) and a step of allowing at least a part of the precursor to penetrate into the inside of the light diffusible fine particles (referred to as step A-2). .

(Process A-1)
When the precursor of the resin component is contained in the coating liquid, the contact between the precursor and the light diffusing fine particles can be realized without any special treatment or operation.

(Process A-2)
As a means for allowing at least a part of the precursor to penetrate into the light diffusing fine particles in the step A-2, typically, the coating liquid is allowed to stand. The resin component and the light diffusing fine particles are preferably composed of the same material, and more preferably composed of a highly compatible material, so that the coating liquid is allowed to stand to perform a special treatment or operation. Even if not, the precursor (monomer) of the resin component penetrates into the light diffusing fine particles. That is, by bringing the precursor of the resin component and the light diffusing fine particles into contact with each other for a predetermined time, the precursor of the resin component penetrates into the light diffusing fine particles. The standing time is preferably longer than the time until the particle size of the light diffusing fine particles is substantially maximized. Here, “the time until the particle size of the light diffusing fine particles is substantially maximized” means that the light diffusing fine particles swell to the maximum extent and do not swell any more (that is, reach an equilibrium state). (Hereinafter also referred to as the maximum swelling time). By bringing the resin component precursor into contact with the light diffusing fine particles for a time longer than the maximum swelling time, the penetration of the resin component precursor into the light diffusing fine particles becomes saturated. It becomes unincorporated into the structure. As a result, the second concentration modulation region can be satisfactorily and stably formed by the polymerization step described later. The maximum swelling time can vary depending on the compatibility between the resin component and the light diffusing fine particles. Therefore, the standing time can vary depending on the constituent material of the resin component and the light diffusing fine particles. For example, the standing time is preferably 1 hour to 48 hours, more preferably 2 hours to 40 hours, still more preferably 3 hours to 35 hours, and particularly preferably 4 hours to 30 hours. When the standing time is less than 1 hour, the precursor may not sufficiently penetrate into the light diffusing fine particles, and as a result, the second concentration modulation region may not be formed well. If the standing time exceeds 48 hours, the light diffusing fine particles aggregate due to the physical interaction between the light diffusing fine particles, and the viscosity of the coating liquid may increase, resulting in insufficient coating properties. There is. The standing may be performed at room temperature, or may be performed under a predetermined temperature condition set according to the purpose and the material used.

  In step A-2, the precursor only needs to penetrate from the surface of the light diffusing fine particles into a part of the light diffusing fine particles, and for example, the average particle diameter is preferably in the range of 10% to 95%. To penetrate. When the permeation range is less than 10%, the second concentration modulation region is not formed well, and backscattering may not be sufficiently reduced. Even if the permeation range exceeds 95%, the second concentration modulation region may not be formed well as in the case where the permeation range is small, and the backscattering may not be sufficiently reduced. The permeation range can be controlled by adjusting the resin component and the material of the light diffusing fine particles, the crosslinking density of the light diffusing fine particles, the standing time, the standing temperature, and the like.

  In this embodiment, it is important to control the penetration of the precursor into the light diffusing fine particles. For example, as shown in FIG. 4, when a light diffusing element is formed by applying it to a substrate immediately after preparing the coating solution, the light diffusing half-value angle varies greatly depending on the drying temperature. On the other hand, when the light-diffusing element is formed by applying the coating solution to the substrate after standing for 24 hours, for example, the light diffusion half-value angle is substantially constant regardless of the drying temperature. This is considered to be because the precursor penetrates into the light diffusing fine particles to a saturated state by standing, so that the formation of the concentration modulation region is not affected by the drying temperature. Therefore, as described above, the standing time is preferably longer than the maximum swelling time. By setting the standing time in this way, it is possible to obtain a light diffusion half-value angle that is almost constant regardless of the drying time, so that it is possible to stably manufacture a light diffusing element having high diffusibility without variation. it can. Furthermore, since it can manufacture by 60 degreeC low temperature drying, it is preferable also from the surface of safety | security or cost. On the other hand, if the time until the permeation reaches a saturated state can be determined according to the type of the precursor and the light diffusing fine particles, the standing time can be shortened by appropriately selecting the drying temperature. However, a light diffusing element having high diffusibility can be stably manufactured without variation. For example, even when a light diffusing element is formed by applying it to a substrate immediately after preparing the coating liquid, by setting the drying temperature to 100 ° C., a highly diffusive light diffusing element can be uniformly distributed. It can be manufactured stably. More specifically, if the light diffusing fine particles, the precursor of the resin component, and the drying conditions are appropriately selected, the second concentration modulation region can be formed without taking the standing time.

  As described above, since both the process A-1 and the process A-2 do not require special processing or operation, it is not necessary to set the timing for applying the coating liquid strictly.

(Process C)
Preferably, the manufacturing method further includes a step of polymerizing the precursor (step C) after the coating step. As the polymerization method, any appropriate method can be adopted depending on the type of the resin component (and hence its precursor). For example, when the resin component is an ionizing radiation curable resin, the precursor is polymerized by irradiating the ionizing radiation. When ultraviolet ray is used as ionizing radiation, the integrated light quantity is preferably ^{50mJ / cm 2 ~1000mJ / cm 2} . The transmittance of the ionizing rays to the light diffusing fine particles is preferably 70% or more, more preferably 80% or more. For example, when the resin component is a thermosetting resin, the precursor is polymerized by heating. The heating temperature and the heating time can be appropriately set according to the type of the resin component. Preferably, the polymerization is performed by irradiating with ionizing radiation. With ionizing ray irradiation, the coating film can be cured while maintaining a favorable refractive index distribution structure (concentration modulation region), so that a light diffusing element having good diffusion characteristics can be produced. By polymerizing the precursor, the second concentration modulation region 32 is formed in the vicinity of the surface of the light diffusing fine particles 20, and the matrix 10 and the first concentration modulation region 31 are formed. More specifically, the second concentration modulation region 32 is formed by polymerization of a precursor that has penetrated into the light diffusing fine particles 20; the matrix 10 has a precursor that has not penetrated the light diffusing fine particles 20. The first concentration modulation region 31 may be formed mainly due to the compatibility of the resin component, the ultrafine particle component, and the light diffusing fine particles. That is, according to the manufacturing method of the present embodiment, the precursor that has penetrated into the light diffusing fine particles and the precursor that has not penetrated into the light diffusing fine particles are polymerized at the same time. The matrix 10 and the first concentration modulation region 31 can be formed simultaneously with the formation of the second concentration modulation region 32 therein.

  The polymerization step (Step C) may be performed before the drying step (Step B) or after the step B.

  It goes without saying that the manufacturing method of the light diffusing element of the present invention may include any appropriate process, treatment and / or operation at any appropriate time in addition to the above-mentioned steps A to C. The type of such a process and the time when such a process is performed can be appropriately set according to the purpose.

  As described above, the light diffusing element is formed on the substrate. The obtained light diffusing element may be peeled off from the substrate and used as a single member, or may be used as a light diffusing element with a substrate, transferred from the substrate to a polarizing plate, etc. It may be used as a polarizing plate with a light diffusing element) or may be used as a composite member (for example, a polarizing plate with a light diffusing element) by being attached to a polarizing plate or the like together with the substrate. When the base material is attached to a polarizing plate or the like and used as a composite member (for example, a polarizing plate with a light diffusing element), the base material can function as a protective layer for the polarizing plate. The light diffusing element of the present invention is not limited to the viewing side diffusing element of the liquid crystal display device adopting the collimated backlight front diffusing system described above. , LED) can be used as a diffusion member.

B. Polarizing plate with light diffusing element B-1. Overall Configuration of Polarizing Plate with Light Diffusing Element The polarizing plate with a light diffusing element of the present invention includes the light diffusing element and a polarizer. The polarizing plate with a light diffusing element of the present invention is typically disposed on the viewing side of the liquid crystal display device. FIG. 5 is a schematic cross-sectional view of a polarizing plate with a light diffusing element according to a preferred embodiment of the present invention. The polarizing plate with a light diffusing element 200 includes a light diffusing element 100 and a polarizer 110. When the polarizing plate with a light diffusing element is disposed on the viewing side of the liquid crystal display device, the light diffusing element is preferably disposed on the most viewing side. In one embodiment, a low reflection layer or an antireflection treatment layer (antireflection treatment layer) is disposed on the viewing side of the light diffusing element 100 (not shown). In the illustrated example, the polarizing plate with a light diffusing element 200 has protective layers 120 and 130 on both sides of the polarizer. The light diffusing element, the polarizer and the protective layer are attached via any appropriate adhesive layer or pressure-sensitive adhesive layer. At least one of the protective layers 120 and 130 may be omitted depending on the purpose, the configuration of the polarizing plate, and the configuration of the liquid crystal display device. For example, when the base material used when forming the light diffusing element can function as a protective layer, the protective layer 120 can be omitted. The polarizing plate with a light diffusing element of the present invention can be particularly suitably used as a viewing side polarizing plate in a liquid crystal display device employing a collimated backlight front diffusion system.

B-2. Polarizer Any appropriate polarizer may be adopted as the polarizer 110 depending on the purpose. For example, dichroic substances such as iodine and dichroic dyes are adsorbed on hydrophilic polymer films such as polyvinyl alcohol films, partially formalized polyvinyl alcohol films, and ethylene / vinyl acetate copolymer partially saponified films. And polyene-based oriented films such as a uniaxially stretched product, a polyvinyl alcohol dehydrated product and a polyvinyl chloride dehydrochlorinated product. Among these, a polarizer obtained by adsorbing a dichroic substance such as iodine on a polyvinyl alcohol film and uniaxially stretching is particularly preferable because of its high polarization dichroic ratio. The thickness of these polarizers is not particularly limited, but is generally about 1 to 80 μm.

  A polarizer uniaxially stretched by adsorbing iodine to a polyvinyl alcohol film can be produced by, for example, dyeing polyvinyl alcohol in an aqueous solution of iodine and stretching it 3 to 7 times the original length. . If necessary, it may contain boric acid, zinc sulfate, zinc chloride or the like, or may be immersed in an aqueous solution such as potassium iodide. Further, if necessary, the polyvinyl alcohol film may be immersed in water and washed before dyeing.

  By washing the polyvinyl alcohol film with water, not only can the surface of the polyvinyl alcohol film be cleaned and the anti-blocking agent can be washed, but also the effect of preventing unevenness such as uneven dyeing can be obtained by swelling the polyvinyl alcohol film. is there. Stretching may be performed after dyeing with iodine, may be performed while dyeing, or may be dyed with iodine after stretching. The film can be stretched in an aqueous solution of boric acid or potassium iodide or in a water bath.

B-3. Protective layer The protective layers 120 and 130 are formed of any appropriate film that can be used as a protective layer of a polarizing plate. Specific examples of the material as the main component of the film include cellulose resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, and polysulfone-based materials. And transparent resins such as polystyrene, polynorbornene, polyolefin, (meth) acryl, and acetate. Further, thermosetting resins such as (meth) acrylic, urethane-based, (meth) acrylurethane-based, epoxy-based, and silicone-based or ultraviolet curable resins are also included. In addition to this, for example, a glassy polymer such as a siloxane polymer is also included. Moreover, the polymer film as described in Unexamined-Japanese-Patent No. 2001-343529 (WO01 / 37007) can also be used. As a material for this film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and nitrile group in the side chain For example, a resin composition having an alternating copolymer composed of isobutene and N-methylmaleimide and an acrylonitrile / styrene copolymer can be mentioned. The polymer film can be, for example, an extruded product of the resin composition.

  The protective layer (inner protective layer) 130 is preferably optically isotropic. Specifically, the thickness direction retardation Rth (550) of the inner protective layer is preferably −20 nm to +20 nm, more preferably −10 nm to +10 nm, particularly preferably −6 nm to +6 nm, and most preferably −3 nm to +3 nm. It is. The in-plane retardation Re (550) of the inner protective layer is preferably 0 nm or more and 10 nm or less, more preferably 0 nm or more and 6 nm or less, and particularly preferably 0 nm or more and 3 nm or less. Details of the film that can form such an optically isotropic protective layer are described in Japanese Patent Application Laid-Open No. 2008-180961, and the description thereof is incorporated herein by reference.

C. Liquid Crystal Display Device FIG. 6 is a schematic cross-sectional view of a liquid crystal display device according to a preferred embodiment of the present invention. The liquid crystal display device 500 includes a liquid crystal cell 510, polarizing plates 520 and 530 disposed on both sides of the liquid crystal cell, a backlight unit 540 provided outside the polarizing plate 530, and the outside (viewing side) of the polarizing plate 520. The light diffusing element 100 is provided. Any appropriate optical compensation plate (retardation plate) may be disposed between the liquid crystal cell 510 and the polarizing plates 520 and / or 530 depending on the purpose. The liquid crystal cell 510 includes a pair of substrates (typically, glass substrates) 511 and 512 and a liquid crystal layer 513 that includes liquid crystal serving as a display medium and is disposed between the substrates 511 and 512.

  The light diffusing element 100 is the light diffusing element of the present invention described in the above section A. Alternatively, instead of the light diffusing element 100 and the viewing side polarizing plate 520, the polarizing plate with a light diffusing element of the present invention described in the above section B may be disposed. The light diffusing element transmits and diffuses light that has passed through the liquid crystal cell (typically, collimated light as described below).

  The backlight unit 540 is preferably a parallel light source device that emits collimated light toward the liquid crystal cell 510. In this case, the backlight unit may have any suitable configuration that can emit collimated light. For example, the backlight unit includes a light source and a condensing element that collimates light emitted from the light source (none of which is shown). In this case, any appropriate condensing element capable of collimating light emitted from the light source can be employed as the condensing element. If the light source itself can emit collimated light, the condensing element can be omitted. Specific configurations of the backlight unit (parallel light source device) include, for example, the following: (1) A light shielding layer on a portion other than the focal point of the lens on the flat surface side of the lenticular lens or the bullet-type lens. Or the structure which arrange | positioned the condensing element which provided the reflection layer in the liquid crystal cell side of a light source (for example, cold cathode fluorescent lamp) (for example, Unexamined-Japanese-Patent No. 2008-262012); (2) Side light type LED light source, The light guide plate and a structure having a convex surface formed on the light guide plate side and a variable angle prism disposed on the liquid crystal cell side of the light guide plate (in this configuration, an anisotropic diffusion element is further used as necessary. For example, Japanese Patent No. 3442247); (3) A louver layer in which a light-absorbing resin and a transparent resin are alternately formed in a stripe shape is provided between a backlight and a backlight-side polarizing plate. (4) Configuration using a bullet-type LED as a light source (for example, JP-A-6-130255); (5) Fresnel lens and as necessary A configuration using a diffusion plate (for example, JP-A-1-126627). The above publication describing these detailed configurations is incorporated herein by reference.

  The half-value angle of light emitted from the backlight unit (parallel light source device) is preferably 35 ° or less, more preferably 3 ° to 35 °. As shown in FIG. 7, the half-value angle of the light source device refers to the full width at half maximum of the angle at which the luminance is halved when the angle is changed from the direction in which the luminance is maximum.

As a driving mode of the liquid crystal cell of the liquid crystal display device to which the light diffusing element of the present invention is applied, for example, MVA (multi-domain vertical alignment) mode, PVA (pattern VA) mode, TN (twisted nematic) mode, ECB (electric field) Controlled birefringence) mode, OCB (bend nematic) mode, IPS (transverse electric field) mode, FFS mode, BP (blue phase) mode, and strong induction liquid crystal (SmC ^* ).

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited by these Examples. Unless otherwise specified, “parts” and “%” in the examples are based on weight.

The measurement method and evaluation method of each characteristic are as follows.
(1) Thickness of the light diffusing element The total thickness of the base material and the light diffusing element is measured with a microgauge thickness meter (manufactured by Mitutoyo Corporation), and the thickness of the light diffusing element is subtracted from the total thickness. Was calculated.
(2) Light diffusing half-value angle Laser light is irradiated from the front of the light diffusing element, and the diffusion luminance with respect to the diffusion angle of the diffused light is measured every 1 ° with a goniophotometer. As shown in FIG. Measure the diffusion angle at half the brightness from the maximum value of the light diffusion brightness excluding straight transmitted light, and add the angles on both sides (angle A + angle A ′ in FIG. 8) to the light diffusion half value It was a corner.

[Example 1]
In 100 parts of resin for hard coat containing 62% of zirconia nanoparticles (average particle size 60 nm, refractive index 2.19) as an ultrafine particle component (manufactured by JSR, trade name “OPSTAR KZ6661” (including MEK / MIBK)) , 11 parts of pentaerythritol triacrylate (manufactured by Osaka Organic Chemical Co., Ltd., trade name “Biscoat # 300”, refractive index 1.52) as a precursor of the resin component, photopolymerization initiator (manufactured by Ciba Specialty Chemicals) , Trade name “Irgacure 907”), and polymethyl methacrylate (PMMA) fine particles (trade name “XX131AA” manufactured by Sekisui Plastics Co., Ltd.) as light diffusing fine particles, average particle size 2.5 μm, 20 parts of a refractive index of 1.495) was added, and MIBK was added as a diluent solvent so that the solid content was 55%. This mixture was sonicated for 5 minutes to uniformly disperse each of the above components, and then allowed to stand for 4 hours. Thereafter, 0.13 part of a dye pigment (trade name “GPX-201”, maximum absorption wavelength 500 nm, manufactured by Adeka Corporation) was further added and stirred to prepare a coating solution.
The coating liquid is applied on a TAC film (trade name “KC4UY”, thickness 40 μm, manufactured by Konica Minolta Co., Ltd.) using a bar coater, dried in an oven at 80 ° C. for 1 minute, and integrated light quantity with a high-pressure mercury lamp. A 300 mJ / cm ² ultraviolet ray was irradiated to form a 10 μm thick light diffusing element on the TAC film.

[Comparative Example 1]
A coating solution was prepared in the same manner as in Example 1 except that no dye-based pigment was added. This coating solution is applied on a TAC film (trade name “KC4UY”, thickness 40 μm, manufactured by Konica Minolta Co., Ltd.) using a bar coater, dried in an oven at 80 ° C. for 1 minute, and integrated light quantity with a high-pressure mercury lamp. A 300 mJ / cm ² ultraviolet ray was irradiated to form a 10 μm thick light diffusing element on the TAC film.

[Comparative Example 2]
(Preparation of pigment dispersion)
100 parts of pentaerythritol triacrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., trade name “Biscoat # 300”, refractive index 1.52) and organic dye (trade name “GPX-201” produced by Adeka Co., Ltd.), maximum absorption wavelength 500 nm ) Was added and diluted by adding 50 parts of MEK and 50 parts of ethyl acetate to prepare a dye dispersion.
(Preparation of light diffusing element with dye dispersion layer)
After forming a dye dispersion layer on the TAC film using the dye dispersion, a light diffusing element was formed on the dye dispersion layer in the same manner as in Comparative Example 1. The dye dispersion layer is formed by applying the dye dispersion onto a TAC film using a bar coater, drying in an oven at 80 ° C. for 1 minute, and then irradiating with a high-pressure mercury lamp with ultraviolet light with an integrated light quantity of 300 mJ / cm ^2. did. The thickness of the obtained pigment dispersion layer was 10 μm, and the appearance was yellow and transparent.

[Comparative Example 3]
After the light diffusing element was formed on the TAC film in the same manner as in Comparative Example 1, a dye dispersion layer was formed on the light diffusing element in the same manner as in Comparative Example 2 to produce a light diffusing element with a dye dispersion layer.

<Backlight unit>
The light guide plate was taken out from the backlight unit of a commercially available laptop personal computer (trade name “Dynabook RX-1” manufactured by Toshiba Corporation). A rectangular transparent acrylic plate having a thickness of 10 mm and a smooth surface was attached to one side (smooth surface side) of the light guide plate via an acrylic adhesive. A bullet-type LED (manufactured by Nichia Corporation, trade name “NSPW500CS-b1”, φ5 mm, half-value angle of 15 °) was arranged along the side surface of the acrylic plate.
On the other hand, the uppermost protective diffusion sheet was removed from the backlight unit of the laptop personal computer, and only the lower prism sheet was placed on the upper side of the light guide plate on which the LEDs were arranged to produce a condensing backlight unit.
The half value angle of the obtained backlight unit was 20 °.

<Evaluation>
The backlight unit irradiates light from the substrate (TAC film) side of the light diffusing element with substrate obtained in Example 1 and Comparative Examples 1 to 3, and emitted light (front direction 0 ° and oblique direction 60 °). ) Was measured with a conoscope (manufactured by Autronic-Melchers, Conoscope). Further, the transmission spectrum of the emitted light in the front direction was measured with a spectrophotometer (manufactured by Hitachi Instruments, U4100). The measurement results are shown in Table 1. The transmission spectra of Example 1 and Comparative Example 1 are shown in FIG.

<Evaluation>
As is apparent from Table 1, according to the light diffusing element of Example 1 of the present invention, the difference in chromaticity between the front direction (0 °) and the oblique direction (60 °) is extremely small, and the angle dependency of hue. Was well controlled. On the other hand, in Comparative Example 2 and Comparative Example 3 in which the pigment dispersion layer was provided, the hue angle dependency was not effectively suppressed.

While the laminate of the light diffusing element and the substrate obtained in Example 1 and Comparative Example 1 was cooled with liquid nitrogen, it was sliced to a thickness of 0.1 μm with a microtome to obtain a measurement sample. Using a transmission electron microscope (TEM), the state of the fine particles in the light diffusing element portion of the measurement sample and the state of the interface between the fine particles and the matrix were observed. As a result, the interface between the fine particles and the matrix was unclear, and the first concentration modulation region was confirmed.
Further, the average thickness L of the first density modulation region was calculated from the TEM image using image analysis software, and as a result, it was 60 nm.

  The light diffusing element and the polarizing plate with a light diffusing element of the present invention are suitably used for a viewing side member of a liquid crystal display device, a backlight member of a liquid crystal display device, and a diffusing member for a lighting device (for example, organic EL, LED). In particular, it can be suitably used as a front diffusion element of a liquid crystal display device of a collimated backlight front diffusion system.

DESCRIPTION OF SYMBOLS 10 Matrix 11 Resin component 12 Ultrafine particle component 20 Light diffusible fine particle 31 Density modulation area | region (1st density modulation area)
32 Second concentration modulation region 100 Light diffusing element 110 Polarizer 120 Protective layer 130 Protective layer 200 Polarizing plate with light diffusing element 500 Liquid crystal display device

Claims (10)

Having a matrix containing a resin component, and light diffusing fine particles dispersed in the matrix,
The maximum absorption wavelength in the visible light region of 380 nm to 780 nm is in the range of 380 nm to 520 nm,
A light diffusing element having a light transmittance at 460 nm of 50% to 80%.   The light-diffusion element of Claim 1 whose light-diffusion half-value angle is 20 degrees or more.   The light diffusing element according to claim 1, wherein the haze is 90% to 99.9%.   4. The light diffusing element according to claim 1, wherein the matrix includes a dye component having a maximum absorption wavelength in a range of 380 nm to 520 nm in a visible light range of 380 nm to 780 nm.   The light diffusing element according to claim 1, wherein the light diffusing fine particles have an average particle diameter of 1 μm to 5 μm.   The light diffusing element according to any one of claims 1 to 5, wherein the thickness is at least twice the average particle diameter of the light diffusing fine particles. The matrix includes an ultrafine particle component;
The resin component, the ultrafine particle component, and the light diffusing fine particles have a refractive index satisfying the following formula (1),
7. The light diffusion according to claim 1, further comprising a concentration modulation region that is formed outside the surface of the light diffusing fine particles and in which the weight concentration of the ultrafine particle component increases as the distance from the light diffusing fine particles increases. element:
| N _P −n _A | <| n _P −n _B | (1)
In formula (1), n _A represents the refractive index of the resin component of the matrix, n _B represents the refractive index of the ultrafine particle component of the matrix, and n _P represents the refractive index of the light diffusing fine particles.   A polarizing plate with a light diffusing element, comprising the light diffusing element according to claim 1 and a polarizer. A liquid crystal cell;
A parallel light source device that emits collimated light toward the liquid crystal cell;
A light diffusing element according to claim 1, which transmits and diffuses collimated light that has passed through the liquid crystal cell.   The liquid crystal display device according to claim 9, wherein a half-value angle of the parallel light source device is 35 ° or less.

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