Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2000-06-21
2004-08-17
Thibodeau, Paul J. (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S423100, C428S500000, C428S522000, C525S454000, C525S455000, C526S284000, C526S301000
Reexamination Certificate
active
06777070
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an anti-reflection material and to a polarization film employing the anti-reflection material, suitable for use in displays such as liquid crystal displays (LCDs), plasma displays (PDPs), CRTs, ELs, etc., and in particular, relates to an anti-reflection material and to a polarization film employing the anti-reflection material, having superior light resistance, contamination resistance on image display surfaces, anti-reflection properties, chemical resistance, and wear resistance.
BACKGROUND ART
Displays typified by LCDs, PDPs, CRTs, and ELs are widely used in various fields such as television and computer technologies, and have been rapidly developed. Recently, it is desirable that the above displays be used in cellular phones, PHS devices, and other portable terminals.
As a display for portable terminals, it is believed that liquid crystal displays, that are light, compact, and suitable for general use, may come to monopolize the market. Portable terminals containing touch-panels, to which a plastic pen or a finger directly contacted for operation, have been widely used. Therefore, requirements for wear resistance, chemical resistance, and contamination resistance have become stricter than ever. Furthermore, requirements for anti-reflection, that is, preventing the external lights such as sunlight, fluorescent light, and the like from being reflected by a display when the display is used in lighted conditions, such as outdoors, has become stricter than ever. These requirements extend not only to portable terminals but also to various types of displays from small to large.
In order to solve this problem, a method for suppressing the reflectivity of most of the surface of a display was developed by forming a multilayer composition consisting of two or more layers in which a layer having a high refractive index and a layer having a low refractive index are alternately laminated on the surface of the display, and in which most of the surface layer is a layer having a low refractive index. As a material for the layer having a low refractive index, MgF
2
, SiO
2
, etc., can be employed. As a material for the layer having a high refractive index, TiO
2
, ZrO
2
, etc., can be employed. These materials usually are laminated by a gas phase method such as vapor deposition, sputtering, etc., a sol-gel method, or the like. However, there were problems in cost, since with respect to the gas phase method, apparatus for manufacturing is very expensive and the manufacturing is not suitable in a large area, and with respect to the sol-gel method, coating and burning are repeatedly carried out. In addition, a method for low cost production, in which a film is formed by the coating material containing these materials, using roll coating, printing, etc., has also been proposed. However, there was a problem in color nonuniformity (interference nonuniformity), since the method can not control the film thickness to a precision of 10 nm and the properties are thereby obtained.
In the case in which an anti-reflection film provided with an anti-reflection layer as described above on a transparent substrate such as polyethylene terephthalate (PET) is used by adhering on the surface of a touch panel operated by directly touching pen or finger, high wear resistance, high chemical resistance, and high contamination resistance are required. In order to satisfy these properties, generally, a hard coat layer is provided between the above transparent substrate and the above anti-reflection layer. It is necessary to also control the refractive index in the hard coat layer in order to improve anti-reflection properties of the anti-reflection film.
Optically, by increasing the refractive index of the hard coat layer and by providing a low refractive index layer consisting of conventional silica, etc., on the hard coat layer, an anti-reflection material having some range of properties can be obtained and the layer composition of the anti-reflection material can be simplified. Furthermore, in this case, severely controlled film layer thickness is limited only to a low refractive index layer, and the anti-reflection material can be thereby produced by the above roll coating or by printing.
As resins used in the hard coat layer constituting the anti-reflection material according to the conventional techniques, transparent thermosetting resins, thermoplastic resins, radiation-curing-type resins, etc., have been employed. In addition, hardeners such as crosslinking agents, polymerization initiators, etc., polymerization promotors, solvents, viscosity modifiers, etc., have been added to this resin as necessary. In order to increase the refractive index of this hard coat layer, a method for adding the ultrafine particles having a high refractive index to the above binder resin has been proposed. As a processing method, a method in which a coating material is mixed with the above resin and ultrafine particles with additives and solvents, and is coated by coater or printing, can be used. According to these methods, the refractive index of the hard coat layer can be controlled to some extent by the content of the above ultrafine particles. However, when the content is too high, problems occur in that transparency is reduced and that durability such as wear resistance, chemical resistance, etc., is deteriorated. In addition, there was also a problem in that as the content of the above ultrafine particles increased, the ultrafine particles aggregated with each other in the film forming process, coarse particles formed, and transparency was thereby substantially reduced.
Therefore, in such case, in order to suppress the content of filler, it is desirable that {circle around (1)} resin having a high refractive index be employed as binder resin, {circle around (2)} binder resin having superior dispersibility of the ultrafine particle be employed, and {circle around (3)} ultrafine particles having the highest possible refractive index be selectively employed.
As binder resin having a high refractive index, resin containing aromatic rings, halogens other than F, or components having high refractive index such as S, N, P, etc., can be employed. However, when the refractive index of the above resin increases, there is a problem in stability of the coating material, and in addition, it easily weakens, and there are problems also in excoriation resistance, light resistance, coloring, etc. Therefore, under present circumstances, suitable material has not been available as a material for forming a hard coat layer having both high refractive index and durability.
As a ultrafine particle having high refractive index, titanium oxide which is inexpensive and which has superior safety, is generally employed; however, in this case, the hard coat layer becomes white and hazy over time due to a photocatalytic effect of the titanium oxide, and there was a problem in the light resistance. Furthermore, since the photocatalytic effect of the titanium oxide is dependent on the amount of ultraviolet radiation, the hard coat layer becomes remarkably hazy and white in outdoor use, and there was a problem in practice.
Thus, according to the conventional anti-reflection material, it is very difficult to provide both high refractive index of the hard coat layer and durability of the surface of the anti-reflection material such as wear resistance, chemical resistance, light resistance, etc., and an anti-reflection material having sufficient properties did not exist until now.
DISCLOSURE OF INVENTION
Therefore, the present invention has been made in view of the above circumstances, and it is an object thereof to provide an anti-reflection material which can exhibit superior anti-reflection properties by preventing external light such as sunlight, fluorescent light, etc., from being reflected on a display, which can yield a clear image without sparkling and reducing image contrast, and which has superior durability even if it is employed in displays, touch panels, etc., for outdoor use, as well as exhibits s
Matsunaga Yasuhiro
Murata Chikara
Ohishi Kazuya
Yamamoto Tomohisa
Thibodeau Paul J.
Tomoegawa Paper Co. Ltd.
Uhlir Nikolas J.
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