Optical: systems and elements – Diffusing of incident light
Reexamination Certificate
2002-08-13
2004-01-27
Sikder, Mohammad (Department: 2872)
Optical: systems and elements
Diffusing of incident light
C359S883000, C359S884000, C359S707000
Reexamination Certificate
active
06683720
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a reflector having high reflectivity and brightness, which is yet reduced in uneven brightness, to a sidelight type backlighting apparatus using the same, applied to a liquid crystal display apparatus, and to a reflector substrate.
BACKGROUND ART
Liquid crystal displays are thinner and are more compact as compared with CRT (Cathode Ray Tube) displays known heretofore, and because they operate at lower voltage, consume less power, and hence are energy saving, they are used not only as displays of small to medium size apparatuses, but also in a wider field.
The liquid crystal displays widely used at present are transmission type liquid crystal displays using backlighting for the light source. The display clarity of the liquid crystal display owes not only on the performance of the liquid crystal itself, but also on the performance of the backlighting. Due to the recent indispensable requirements on further lightweight and thinner liquid crystal displays, uniformity in brightness, and for reasons that the heat from the light source is hardly transmitted to the liquid crystal panel, the reflector is no longer placed on the front of the light source as in the direct transflective type, but backlighting of a sidelight type using a light guiding plate to provide a planar light source, which is produced by allowing the light from the light source set on one end to undergo multipath reflection, is employed as the method of backlighting.
An uneven reflection member made of white-colored PET (polyethylene terephthalate) film and the like is often provided on one main surface of the light guiding plate, and uniform brightness is there by achieved by diffusing light with the uneven reflection member. However, since such an uneven reflection member yields almost no regular reflection component, the brightness obtained as a result is uniform, but there is a problem that the luminance as a whole is still insufficient. Further, although the luminance can be improved in the case a sheet comprising aluminum vapor-deposited on a transparent or light transmitting PET film is used, the diffuse reflection component is lost, and a slight strain of the sheet causes irregular luminance and makes it impossible to obtain an image of high quality. In order to overcome these problems, a sheet comprising a metal vapor-deposited on a surface-roughened film was developed; however, in the case aluminum is used for the metal, a sheet having excellent durability could be obtained, but the brightness remained yet to be improved. In the case of using silver, which has the highest reflectance in the visible wavelength region, there was found a problem that, even though sufficiently high brightness is obtained, the brightness decreases with the passage of time due to rapid degradation ascribed to the poor durability of silver.
DISCLOSURE OF INVENTION
The invention provides a reflector having high brightness and long durability, capable of preventing uneven brightness caused by strain which may occur on the reflector; a sidelight type backlighting apparatus having the reflector incorporated therein; and a reflector substrate.
The present inventors have extensively conducted studies in order to solve the problems mentioned above, and, as a result, they have found that a sidelight type backlighting apparatus can be achieved in which uneven brightness is eliminated or considerably reduced and high brightness is obtained, by providing a reflector having adequate diffuse reflectance on one main surface of a light guiding plate so as to make space between the light guiding plate and a reflection layer of the reflector. More specifically, uneven brightness could be reduced by forming on the reflector specific protrusions which also serve as spacers for making the space between the light guiding plate and the reflection layer.
The invention provides a reflector comprising a substrate and a reflection layer formed on one main surface of the substrate, wherein diffusivity of the reflector exists within a range of 1 to 50%, the diffusivity being defined as ratio of diffuse reflectance to total reflectance.
According to the invention, since an adequate reflectance can be obtained, when the reflector is incorporated in a backlighting apparatus for liquid crystal display apparatuses, uneven brightness can be eliminated or considerably reduced while high brightness being simultaneously obtained.
Further, in the invention it is preferable that the substrate is made of a polymer film.
According to the invention, it is possible to realize a reflector which has a high degree of flexibility in configuration and high productivity.
Further, in the invention it is preferable that the reflector has a total reflectance of 90% or higher and a diffuse reflectance of 15% or lower at a wavelength of 550 nm.
According to the invention, it is possible to achieve a reflectance which is adequate for human sensitivity to light.
Furthermore, in the invention it is preferable that the reflector comprises protrusions on the reflection layer side of the substrate, number of the protrusions per square millimeter area of the substrate being two or more but not more than 100, the protrusions each having a maximum width of 0.1-50 &mgr;m and a height of 0.1-45 &mgr;m.
According to the invention, it is possible to achieve an optimal reflectance.
In the invention it is preferable that the protrusions have a maximum width of 10-50 &mgr;m and a height of 5-45 &mgr;m.
According to the invention, it is possible to achieve an optimal reflectance.
Furthermore, it is preferable that the protrusions are formed by applying to the substrate a coating solution which contains particles having a mean particle size of 0.1 &mgr;m or greater but not greater than 50 &mgr;m, and a binder resin.
According to the invention, it is possible to achieve high productivity and cost reduction.
Furthermore, in the invention it is preferable that the protrusions are formed by applying to the reflection layer a coating solution which contains particles having a mean particle size of 0.1 &mgr;m or greater but not greater than 50 &mgr;m, and a binder resin.
According to the invention, it is possible to form suitable protrusions in accordance with the conditions of the coating solution and substrate.
Furthermore, in the invention it is preferable that the polymer film has protrusions which are formed by fine particles contained therein.
According to the invention, it is possible to achieve high productivity and cost reduction.
Furthermore, in the invention it is preferable that the reflection layer comprises a base layer (a), a metallic layer mainly containing silver (b), and a protective layer (c), the layers being laminated in the order of (a), (b), (c) on the substrate.
According to the invention, it is possible to form a reflector which has high reflectivity and excellent durability.
Furthermore, in the invention it is preferable that the base layer (a) comprises a metallic layer made of one metal selected from the group consisting of gold, copper, nickel, iron, cobalt, tungsten, molybdenum, tantalum, chromium, indium, manganese, titanium, and palladium, and/or of an alloy of two or more selected from the group, the metallic layer having a thickness of 5 nm or more but not more than 50 nm; and/or a light transmitting oxide layer made of a light transmitting oxide, having a thickness of 1 nm or more but not more than 20 nm.
According to the invention, it is possible to achieve a desired barrier effect, to prevent agglomeration from occurring on the metallic layer mainly containing silver, and to obtain excellent adhesiveness between the substrate and the reflection layer.
Furthermore, in the invention it is preferable that the metallic layer mainly containing silver (b) has a thickness of 70 nm or more but not more than 400 nm, and comprises simply silver, or comprises at least one selected from the group consisting of gold, copper, nickel, iron, cobalt, tungsten, molybdenum, tantalum, chromium, indium, manganese, titanium, and palladium, or
Fukuda Shin
Ishikawa Hiroshi
Tanabe Masaru
Yoshida Hirotaka
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