Laminated films

Details Laminated films Laminated films

2001-06-22

2003-06-24

Huff, Mark F. (Department: 1756)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

C428S001200, C428S001600

Reexamination Certificate

active

06582783

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an anisotropic diffusing film which is useful for assuring a uniform light emission on a display device (a flat-type or surface display device), a method of producing the same, and a display device utilizing the film. More particularly, the invention relates to an anisotropic diffusing film which is useful for transmission type (mode) or reflection type (mode) liquid crystal display or projection television.
BACKGROUND OF THE INVENTION
Among surface display devices (illumination devices) such as a liquid crystal display device, there is known a backlight type (transmission type) display device comprising a fluorescent tube disposed behind of a liquid crystal display module. Also is known a reflection type display device comprising a light reflecting layer formed on the back of a liquid crystal display module so that the light incident on the front surface is reflected by the light reflecting layer. In such display devices, a diffuser or diffusing film is frequently used to diffuse the light from the fluorescent tube or the reflected light from the light reflecting layer to assure a uniform luminance. As the diffusing film, a diffusing film comprising a polycarbonate or polyester base film which is transparent and highly heat-resistant, and containing refractive microfine particles (resin beads) or light-transmitting inorganic microfine particles incorporated therein by coating or containing is generally employed.
Recent years have seen an increasing demand for such diffusing films as the diffusing film for the backlight component of the backlight type liquid crystal display device. The diffusing film for backlight use is usually interposed between the backlight (cold cathode tube) and the liquid crystal layer to homogenize the light emitted from the cold cathode tube. However, when the diffusing of light is too large, no sufficient emission luminance can be obtained. Therefore, an optical element such as a prismatic lens is interposed between the diffusing film (diffuser) and the liquid crystal layer to thereby refract the diffused light so that the light will be incident perpendicularly on the liquid crystal display surface, thus upholding the luminance.
As the surface display device [i.e., a display device the image display area of which is a flat surface (a flat type display device)], the device illustrated in
FIG. 4
is known. This device comprises a surface display module
45
(particularly a transmission type liquid crystal display module) and at least one fluorescent discharge tube (cold cathode tube)
41
which is adapted to illuminate the module from its back side. Disposed on the back side of the fluorescent discharged tube
41
is a reflector
42
for reflecting the light advancing toward the back side. Moreover a diffuser
43
for diffusing light to uniformly illuminate the module
45
is interposed between the fluorescent discharged tube
41
and the module
45
and a prism sheet
44
is disposed on the module side of the diffuser
43
. This surface display module
45
, in the case of a liquid crystal display module, comprises a first polarizing film
46
a,
a first glass substrate
47
a,
a first electrode
48
a
on the glass substrate, a first alignment layer
49
a
on the electrode, a liquid crystal layer
50
, a second alignment layer
49
b,
a second electrode
48
b,
a color filter
51
, a second glass substrate
47
b,
and a second polarizing film
46
b
as successively built up (laminated) in the order mentioned. In such a display device, the display module can be directly illuminated from the back side by the built-in fluorescent tube (cold cathode tube)
41
. However, an uneven emission (luminance) distribution in the direction normal to the longitudinal axis of the fluorescent tube is inevitable, causing a streak pattern to appear, although the emission distribution in the longitudinal direction of the fluorescent tube is uniform.
Further, there is known the device constructed by using the backlight unit including a light guide illustrated in
FIG. 5
as the backlight system of the surface display device of FIG.
4
. This backlight unit has a fluorescent tube (cold cathode tube)
51
and a reflector member
55
disposed in parallel with the fluorescent tube, with a light guide
54
having a diffuser
53
at top and a reflector
52
at bottom being disposed in the direction of light emission from the fluorescent tube. The lower part of the light guide
54
is inclined so that the light from the fluorescent tube can be reflected in an upward direction. The light emerging in the direction of the top of the light guide
54
is diffused by the diffuser
53
and incident on the surface display module (not shown) constructed (laminated) on the diffuser
53
.
When such a backlight unit is used, in contrast to the backlight unit or component of
FIG. 4
, the emission distribution may appear uniform over the surface but a detailed observation of the emission distribution reveals that the distribution is still not as uniform as desired. Thus, as shown in
FIGS. 6 and 7
, the emission distribution (luminance distribution) in the longitudinal (axial) direction (x-direction) of the fluorescent tube (cold cathode tube)
51
is small as it is the case in the device of
FIG. 4
but the emission from the fluorescent tube (cold cathode tube) in the y-direction which is normal to the x-direction is repeatedly reflected by the reflector
52
and advances in the z-direction (the direction in which the liquid crystal display module is disposed) which is perpendicular to the xy plane so that the emission distribution (luminance distribution) in the y-direction is distorted (in a zigzag pattern), thus failing to assure sufficient uniformity.
Thus, in the usual backlight type display device, the emission distribution (luminance distribution) in the direction normal to the longitudinal direction (X-direction) of the fluorescent tube is not uniform and a streak-like directionality (linear dark areas) is produced in the emission distribution. Moreover, even when a diffusing film containing microfine particles is used, it is inevitable from its isotropy of light diffusing that the luminance in a certain direction (the direction of disposition of the fluorescent tube, the streaking direction, X-direction) is unduly lowered.
Japanese Patent Application Laid-Open No. 142843/1999 (JP-A-11-142843) describes a technology such that a dot pattern for scattering light is formed in rows perpendicular to the light source on the surface of the light guide. However, even with this contrivance, linear dark areas (a streak pattern) are observed in the direction of disposition of the fluorescent tube.
Japanese Patent Application Laid-Open No. 261171/1995 (JP-A-7-261171) describes a reflection type liquid crystal display device comprising a pair of glass substrates, an electrode formed on each of the opposed surfaces of the glass substrates, a liquid crystal sealed interposed between the electrodes, and a polarizing film formed on (laminated) the outer surface of the external one of the pair of glass electrodes, with a light-scattering layer composed of two or more kinds of resins differing from each other in the index of refraction and forming mutually segregated (separated) phases being disposed on the surface of the polarizing film. In this literature, it is mentioned that the polarizing film is coated or printed with a mixture of two or more kinds of resins in a solvent to form the light-scattering layer.
Furthermore, as a reflection type liquid crystal display device (or a reflection type liquid crystal module), the device (or module) illustrated in
FIG. 8
is also known. This reflection type display module comprises a pair of glass substrates
81
a,
81
b,
a pair of electrodes
82
a,
82
b
formed on the opposed surfaces of the glass substrates, and a liquid crystal
87
interposed between the electrodes forming the pair, the electrode
82
a
formed on the glass substrate
81
a
on the back side constituting light-reflective

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