With technical improvement in recent years, liquid crystal displays (LCDs), plasma display panels (PDPs), electroluminescence displays (ELDs), etc. have been developed in addition to conventional cathode ray tubes (CRTs) as image displays and have been used practically. As LCDs have been technically improved to provide wide viewing angles, high resolution, high response, good color reproduction, and the like, applications of LCDs are spreading from laptop personal computers and monitors to television sets. In a basic LCD structure, a pair of flat glass substrates each provided with a transparent electrode are opposed via a spacer to form a constant gap, between which a liquid crystal material is placed and sealed to form a liquid crystal cell, and a polarizing plate is formed on the outside surface of each of the pair of glass substrates. Conventionally, in order to provide LCDs with antiglare properties, the surface of a polarizing plate interposed between two transparent film substrates is treated to be roughened using sandblast, an embossing roll, chemical etching, etc., and thereby a fine uneven structure is formed at the surface. Furthermore, there is a technique of providing LCDs with antiglare properties using a hard-coated antiglare film.
A hard-coated antiglare film is used in which a thin hard-coating antiglare layer with a thickness of 2 to 10 μm has been formed on one or both surface of a transparent plastic film substrate. The hard-coating antiglare layer is formed using resins for forming a hard-coating antiglare layer such as thermosetting resins or ultraviolet (UV)-curable resins and fine particles. The surface of the hard-coating antiglare layer is provided with unevenness by the fine particles so as to provide antiglare properties.
With application of flat displays such as LCDs to home televisions, the following improvements are demanded: improvements in display quality such as improvements in viewing angle, rapid response, definition, etc.; improvements in antiglare properties for preventing indoor fluorescent light, sunlight incident from a window, an image of a viewer, etc. from being reflected onto a display surface; and a further improvement in display contrast in bright light, i.e. an improvement in depth of black in black display. Low display contrast in bright light causes a phenomenon that an image display surface with a hard-coated antiglare film attached thereto looks white and blurred, i.e. a phenomenon of so-called “white blur”.
However, in a hard-coated antiglare film, there is a conflicting relationship (a trade-off relationship) between the improvement in antiglare properties and the improvement in display contrast in bright light to be achieved when it is used for an image display. Accordingly, when the display contrast is considered to be important, the hard-coating antiglare layer surface is allowed to have less unevenness to have higher smoothness and thereby the antiglare properties are sacrificed slightly. On the other hand, when the antiglare properties are considered to be important, the hard-coating antiglare layer surface is allowed to have a sufficiently uneven structure and thereby the display contrast in bright light is sacrificed. These are general techniques. Hence, in order to improve the display contrast in bright light while maintaining the antiglare properties, a hard-coated antiglare film has been developed that is provided with an antireflection layer (low-refractive-index layer) on a hard-coating antiglare layer, and it is being used in practical application. However, even in the case of a hard-coated antiglare film provided with an antireflection layer, when it is used for a high-definition LCD, there are problems in that a glare (high and low brightness portions) phenomenon occurs at the LCD surface, and the display contrast in bright light is not sufficiently high and thereby white blur cannot be prevented sufficiently from occurring.
In order to prevent the glare phenomenon from occurring, for instance, there is a method in which a hard-coating antiglare layer is formed using a large number of fine particles and thereby a number of fine uneven structures are formed continuously at the hard-coating antiglare layer surface. In this method, however, the antiglare properties are improved and the glare phenomenon also is improved, but irregular reflection of outside light occurs at the surface, which results in occurrence of white blur. Particularly, in the case of black display, white blur occurs conspicuously, and as a result, a problem of deterioration in display contrast in bright light occurs, for example.
Accordingly, in designing a hard-coated antiglare film to be used for high-definition LCDs, there are proposed techniques of controlling light diffusion inside the hard-coating antiglare layer to prevent the glare phenomenon from occurring, and light diffusion properties of the hard-coating antiglare layer surface to prevent white blur from occurring. For instance, a hard-coated antiglare film has been proposed in which the surface haze value is set in the range of 7 to 30% while the inner haze value is set in the range of 1 to 15% in the hard-coating antiglare layer (JP3507719). This hard-coated antiglare film, however, does not satisfactorily prevent the glare phenomenon from occurring. In addition, an antiglare antireflection film having at least one low-refractive-index layer on a transparent support and an antiglare layer between the transparent support and the low-refractive-index layer has been proposed in which the haze value obtained due to light scattering inside the antiglare layer is set in the range of 1 to 60% while the haze value obtained due to light scattering at the antiglare layer surface is set in the range of 1 to 20% (JP-A No. 2002-202402). Furthermore, a light scattering film has been proposed in which in a hard-coating antiglare layer, the surface haze value hs is set in the range of 0.5 to 30% while the inner haze value hi is set in the range of 15 to 80%, and the sum of the surface haze value hs and the inner haze value his 30 to 90% (JP-A No. 2003-156605). Moreover an antireflection film has been proposed in which in a light diffusion layer, the inner haze value is set in the range of 30 to 60% while the surface haze value is set at 1% or lower (JP-A No. 2005-77860). However, in the aforementioned antiglare antireflection film, light scattering film, and antireflection film, it is difficult to achieve both prevention of the glare phenomenon and improvement in the display contrast in bright light (prevention of white blur) simultaneously.