Illumination – Light fiber – rod – or pipe – Diffuser or diffusing of incident light
Reexamination Certificate
2002-02-22
2004-03-23
Cariaso, Alan (Department: 2875)
Illumination
Light fiber, rod, or pipe
Diffuser or diffusing of incident light
C362S330000, C362S333000, C362S355000, C359S599000
Reexamination Certificate
active
06709143
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a light diffusion sheet for use in a backlight unit incorporated in a liquid crystal display (LCD) and to a backlight unit using a light diffusion sheet.
BACKGROUND OF THE INVENTION
In the field of LCDs, backlight systems have been widely utilized for illuminating a liquid crystal layer from its back for light emission. A known LCD has a backlight unit placed on the underside of a liquid crystal layer. Such a backlight unit
20
is generally comprised of, as shown in
FIG. 8
, a bar-like lamp
21
(light source); a light guide plate
22
, in the form of a square plate, placed with one end extending along the lamp
21
; a light diffusion sheet
23
placed on the surface of the plate
22
; and a prism sheet
24
placed on the surface of the sheet
23
.
In the backlight unit
20
, light beams (ray) emitted from the lamp
21
and incident on the plate
22
are reflected off the side faces of the plate
22
and reflective dots or a reflective sheet (not shown) on the rear face of the plate
22
and then go out of the surface of the plate
22
. The light beams (ray) transmitted from the plate
22
are incident on the sheet
23
, diffused, and then, go out of the surface of the sheet
23
. Thereafter, the light beams from the sheet
23
are transmitted to the prism sheet
24
and then allowed by a prism section
24
a
formed on the surface of the sheet
24
to go out as light beams that form a distribution with a peak at an upward direction substantially normal to the sheet
24
. The light beams from the lamp
21
are diffused by the sheet
23
and, then, refracted by the sheet
24
so as to form a distribution peak at an upward direction substantially normal to the sheet
24
to illuminate the entire surface of the liquid crystal layer (not shown) disposed in an upper position.
With reference to
FIG. 9
, there is provided another type of backlight unit
20
which is designed, in view of the light collecting properties of the prism sheet
24
, such that another light diffusion sheet
23
or prism sheet is disposed on the surface of the sheet
24
.
The known light diffusion sheet
23
commonly employed in the backlight unit
20
comprises, as shown in
FIG. 10
, a light diffusion layer
26
containing beads
29
dispersed within a binder
28
; a transparent base material sheet
25
; and a sticking-inhibiting layer
27
containing beads
31
dispersed within a binder
30
, light diffusion layer
26
, base material sheet
25
and sticking-inhibiting layer
27
are laminated in this order.
The binder
30
used for the sticking-inhibiting layer
27
is poor in wear resistance and liable to scratch defects. In addition, since the beads
31
are dispersed in the binder
30
, there is a risk that the rear face of the light diffusion sheet
23
is easily damaged or deformed, resulting in depreciation of its commercial value, if a plurality of light diffusion sheets
23
are stacked together on top of one another during manufacture, delivery, storage, and the like, of the light diffusion sheets or if the light diffusion sheet
23
is laid over the irregular surface of the prism sheet, when incorporated into the backlight unit
20
.
SUMMARY OF INVENTION
The present inventors have made the present invention in consideration of the problems realized in the prior art by intensively investigating the materials to be employed in the light diffusion layer and sticking-inhibiting layer of the light diffusion sheet. Specifically, an object of the invention is to provide a light diffusion sheet comprising a transparent base material sheet; a light diffusion layer laminated on a surface of the base material sheet and containing beads dispersed within a binder; and a sticking-inhibiting layer laminated on a rear face of the base material sheet, wherein the binder of the light diffusion layer contains a thermosetting resin and the sticking-inhibiting layer is a resin layer containing an ionizing radiation curable resin In the light diffusion sheet of the invention, which employs an ionizing radiation curable resin for the binder of the sticking-inhibiting layer, the cross-linking density of the binder can be increased, whereby the wear resistance of the sticking-inhibiting layer as well as the wear resistance of the rear face of the light diffusion sheet can be increased. Further, possible occurrence of scratches in the sticking-inhibiting layer, which is attributable to the contact between the sticking-inhibiting layer and the beads of the light diffusion layer, can be effectively avoided. According to the invention, even if a plurality of light diffusion sheets, which have the light diffusion layer containing beads dispersed within the binder or projecting from the surface of the binder, are stacked together on top of one another during delivery or other occasions, scratch defects can be effectively prevented in the sticking-inhibiting layer located on the rear face of the light diffusion sheet, with the result that degradation of optical properties such as decreases in light beam transmissivity caused by scratches in the sticking-inhibiting layer can be avoided and therefore desired optical properties can be ensured.
In addition, beads may be dispersed within the sticking-inhibiting layer in order to enhance light diffusibility.
According to a preferred embodiment of the invention, the light diffusion sheet may further contain a wax whose particles are dispersed within the light diffusion layer and/or the sticking-inhibiting layer. Specifically, in the light diffusion sheet of this embodiment, light beams (ray) passing through the interfaces of the particles of the wax dispersed within the binder of the light diffusion layer are refracted in various directions, so that not only improved light diffusibility can be achieved but also scratch defects caused by the contact between the sheet surfaces when the light diffusion sheets are used in a stacked condition can be prevented. The particles of the wax dispersed within the binder are melted by a pressure or friction heat that acts upon the surface of the light diffusion sheet, so that they are present on the surface of the light diffusion sheet as a lubricant oil or crystallized extending in various directions according to the force acting on the surface of the light diffusion sheet. As a result, slippage, blocking resistance, and wear resistance are imparted to the light diffusion sheet, increasing the scratch prevention capability of the sheet.
According to another preferred embodiment of the invention, the light diffusion sheet may further include a micro inorganic filler whose particles are dispersed within the light diffusion layer and/or the sticking-inhibiting layer. More specifically, the light diffusion sheet of this embodiment contains not only beads but also a micro inorganic filler within the light diffusion layer and/or the sticking-inhibiting layer, so that the apparent crystallinity and therefore heat resistance of the light diffusion sheet can be improved. Consequently, the deflection of the light diffusion sheet when the lamp is lit can be restricted.
According to the invention, there is provided a backlight unit for use in a liquid crystal display, the unit comprising a lamp; a light guide plate disposed beside the lamp for guiding light beams to the front side of the light guide plate, the light beams having been emitted from the lamp; and a light diffusion sheet disposed on the front side of the light guide plate. The use of the light diffusion sheet of the invention enables it to assure improved wear resistance, heat resistance and the like, to prevent scratch defects and to remarkably facilitate handling of not only the light diffusion sheet but also the backlight unit during manufacture, delivery, storage and other occasions.
REFERENCES:
patent: 3832315 (1974-08-01), Bueche
patent: 4053208 (1977-10-01), Kato et al.
patent: 5706134 (1998-01-01), Konno et al.
patent: 5903391 (1999-05-01), Toshima et al.
patent: 5995288 (1999-11-01), Kashima et al.
patent: 6111699 (2000-08-01),
Harada Kenichi
Masaki Hitoshi
Cariaso Alan
Keiwa Kabushiki Kaisha
Marshall & Gerstein & Borun LLP
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