Image display devices such as cathode ray tubes (CRTs), liquid crystal display devices (LCDs), plasma display devices (PDPs), electroluminescence display devices (ELDs), and electronic paper are generally provided with optical laminated bodies for antireflection on the outermost surface thereof. Such optical laminated bodies for antireflection suppress reflection of images and decrease the reflectivity by light diffusion or interference of light.
As one of such antireflection optical laminated bodies, an anti-glare film including an anti-glare layer that has a surface roughness and is provided on a surface of a transparent substrate is known. Such a surface roughness of an anti-glare film diffuses ambient light, whereby a decrease in visibility can be prevented.
Conventional anti-glare films are known in which anti-glare layers formed by applying resins containing filler such as silicon dioxide (silica) on surfaces of transparent base films (see, for example, Patent Literatures 1 and 2).
For example, in such anti-glare films, a surface roughness is formed by adding cohesive particles, an inorganic filler and/or an organic filler in a resin; laminating a film with unevenness on an anti-glare layer; and phase separation using compatibility among compounds such as two or more different polymers, which constitute a binder.
In all such conventional anti-glare films, a light diffusion function and an anti-glare function are obtained by the effect of a surface shape of the anti-glare layer. In order to increase such an anti-glare function, the size of the surface roughness needs to be increased. However, the large-sized projection and depression increases a haze of a coating, whereby white muddiness is generated.
Further, the twinkling brightness which is called scintillation is generated on the surfaces of conventional anti-glare films, which results in a decrease in visibility of display screens.
In recent years, high definition liquid crystal displays have been developed. However, scintillation is generated in such high definition liquid crystal displays when conventional anti-glare films are used therein. Such scintillation is a serious problem.
Furthermore, in the conventional anti-glare films, cracks are generated during a process for adhering the films to polarizing elements or a fabrication process of liquid crystal cells, at, for example, an interface between light-transmitting fine particles and a light-transmitting resin that are included in an anti-glare layer. Furthermore, in the conventional anti-glare films, anti-glare performance and a scintillation state are changed over time due to the haze variation in response to temperature and moisture changes. Therefore, the conventional anti-glare films are less resistant to moisture and heat.
Patent Literature 3 discloses an anti-glare material obtainable by mixing a binder resin with resin beads in which 70% or more thereof is swollen with a solvent.
In an anti-glare film provided with an anti-glare layer including such resin beads that are previously swollen with a solvent, the adhesion at the interface between the resin beads and the binder resin is expected to be improved. Such an anti-glare film is expected to be used in high definition displays.
In such an anti-glare film provided with an anti-glare layer including resin beads that are previously swollen with a solvent, the adhesion at the interface between the swollen resin beads and the binder resin in the anti-glare layer is improved only by an anchor effect created at the interface. Therefore, the adhesion and the like can be further improved.
Patent Literature 4 discloses a method for producing a light diffusion film in which the density of light-transmitting fine particles, a coating composition, and the average particle size of light-transmitting fine particles are in a specific relation to one another. Patent Literature 5 discloses an optical film including light-transmitting particles having a certain average particle size that depends on the thickness of a light diffusion layer. Patent Literature 6 discloses an optical film including an anti-glare layer formed from a coating composition in which a binder and two types of resin fine particles different in particle sizes and swelling rates that satisfy a certain relation with each other are dispersed in a dispersion. Patent Literature 7 discloses a method for producing a light diffusion film, including a coating composition for a light diffusion layer. The coating composition includes light-transmitting fine particles, a light-transmitting resin containing a certain amount of a light-transmitting polymer with a molecular weight of 1000 or more, and a solvent.
However, Patent Literatures 4 to 7 do not disclose at all that light-transmitting fine particles are impregnated with a binder, and do not disclose at all, either the effect exerted by the impregnation of light-transmitting fine particles with a binder. Therefore, the anti-glare films disclosed in the patent literatures do not sufficiently achieve an anti-glare property, prevention of white muddiness, and prevention of scintillation.
Therefore, in conventional anti-glare films, generation of cracks at the interface between resin beads and a binder resin is required to be prevented at a high level in a process for attaching the films to polarizing elements and a fabrication process of liquid crystal cells. Furthermore, white muddiness is required to be reduced by reducing reflection at the interface between a binder and resin beads and scintillation is also required to be prevented by appropriately dispersing resin beads.