Illumination – Light source and modifier – Including translucent or transparent modifier
Reexamination Certificate
2000-12-26
2003-12-30
Husar, Stephen (Department: 2875)
Illumination
Light source and modifier
Including translucent or transparent modifier
C362S035000, C362S027000, C362S331000, C362S360000
Reexamination Certificate
active
06669356
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an illumination device for use in a transmissive liquid crystal display or the like.
2. Description of the Prior Art
FIG. 11
is a longitudinal sectional view showing the structure of a liquid crystal display equipped with a conventional illumination device of an edge-light type. This liquid crystal display is provided with an illumination device
1
and a liquid crystal display panel
2
illuminated by the illumination device
1
. The illumination device
1
is provided with a main body
3
including tubular light sources
8
, a frame
4
fitted to the main body
3
, and a plurality of sheets
5
,
6
, and
7
arranged between the main body
3
and the frame
4
.
The main body
3
is provided with a box-shaped lamp case
9
open at the top, a reflecting plate
10
arranged inside the lamp case
9
and shaped like a flat tube, and a light guide plate
11
arranged inside the reflecting plate
10
and having a diffusive pattern formed or printed on its bottom surface. The light sources
8
extend in the direction perpendicular to the plane of the figure, and are supported and fixed, through unillustrated supporting members, in spaces formed between each side surface of the light guide plate
11
and the side wall of the reflecting plate
10
facing it so as to be placed in the vicinity of the two side surfaces (light entrance surfaces) of the light guide plate
11
.
The reflecting plate
10
is so formed as to extend parallel to and close to the inner surfaces of the bottom and side walls of the lamp case
9
and on the bottom surface of the frame
4
, and has a part of its top wall cut out along the axial direction to form an opening. The top wall of the reflecting plate
10
covers the light sources
8
from above, and reaches both side edges of the top surface of the light guide plate
11
.
The sheets
5
to
7
have diffusive, condensing, or other optical properties, and are all so formed as to transmit light. The sheets
5
and
7
are diffusive sheets, and the sheet
6
is a condensing sheet. The sheets
5
to
7
are so arranged as to face each other, and are supported and fixed on the main body
3
by being sandwiched, at their edges, between the frame
4
and the reflecting plate
10
so as to face an opening
4
a
of the frame
4
.
The liquid crystal display panel
2
is arranged above the frame
4
so as to face the opening
4
a
of the frame
4
. The placement of the sheets
5
to
7
between the frame
4
and the reflecting plate
10
permits the liquid crystal display panel
2
to be illuminated with uniform light all over its surface.
FIG. 12
is a longitudinal sectional view showing the structure of a liquid crystal display equipped with a conventional direct backlight, which illuminates a display panel directly from beneath. Here, such components as have their counterparts in the liquid crystal display shown in
FIG. 11
are identified with the same reference numerals, and overlapping descriptions will not be repeated. In this liquid crystal display, the main body
3
is provided with a reflecting plate
12
shaped like a bottomed flat tube, and a diffusive plate
13
that is arranged on the top surface of a flange
12
a
formed around the opening of the reflecting plate
12
and that has a diffusive pattern printed on its top surface.
The light sources
8
extend in the direction perpendicular to the plane of the figure, and are supported and fixed, through unillustrated supporting members, inside the reflecting plate
12
. The sheets
5
to
7
are supported and fixed on the main body
3
by being sandwiched, at their edges, between the frame
4
and the diffusive plate
13
so as to face the opening
4
a
of the frame
4
.
In the conventional illumination devices described above, when the sheets
5
to
7
are placed between the frame
4
and the reflecting plate
10
(or the diffusive plate
13
), the sheets leave a clearance C of 0 to 0.1 mm in the direction of their thickness. The clearance C here is the value given by L−T, where L represents the length, as measured in the direction of the thickness of the sheets
5
to
7
, of the space (hereinafter called the sheet placement space) in which the sheets
5
to
7
are sandwiched between the frame
4
and the reflecting plate
10
(or the diffusive plate
13
), and T represents the sum of the thickness of the sheets
5
to
7
.
When the sheets having optical properties as described above (hereinafter called the optical sheets) exhibit a high degree of thermal expansion/contraction and their bases are made of materials prone to deformation due to thermal stress, under conditions where the ambient temperature around the liquid crystal display exceeds 85° C. as when, for example, the liquid crystal display is employed in car-mounted equipment mounted on a car under the flaming sun in summer, the optical sheets
5
to
7
curl within the space between the frame
4
and the reflecting plate
10
(or the diffusive plate
13
), as shown in
FIGS. 13 and 14
, under the influence of heat. This causes the sheets
5
to
7
to interfere with each other and develop wavelike bends, and thus leads to degradation in the display quality of the liquid crystal display. Specifically, by bringing the liquid crystal display into a display state and observing it obliquely from above, from below, from the left, or from the right, one can visually recognize the bends in the optical sheets
5
to
7
.
In tropical or desert regions of the world, it is not rare that the ambient temperature around the liquid crystal display exceeds 95° C. Even in such a harsh temperature environment, the liquid crystal display needs to maintain satisfactory display quality.
Incidentally, as shown in
FIG. 15
, an optical sheet is given its function by forming on the surface of a base
21
made of polyethylene terephthalate (hereinafter abbreviated to PET) a coating layer
22
that is a thin film of a material having a condensing, diffusive, or other optical property.
In a liquid crystal display, in addition to an optical sheet, a shielding sheet is also used as a measure against unwanted emission such as electromagnetic radiation and noise. A shielding sheet is given its function by forming on the surface of a base
21
made of PET a coating layer
23
that is a thin film of a transparent conductive material. A shielding sheet is a transparent sheet.
These sheets are formed by being punched out from a large master sheet into the desired shapes. The sheets are thin plates of resin, and are thus relatively soft. Therefore, unlike metal sheets, of which the edges are liable to injure the hands of their handlers during assembly and transportation, there is no need to treat the edges of the sheets so as not to injure their handlers' hands; that is, the sheets are used as they are punched out.
In these sheets, the base
21
has a different thermal expansion speed from the coating layer
22
or
23
, and therefore, as temperature rises, the sheets curl. The greater the rise &Dgr;T
1
in temperature, the more conspicuous the phenomenon. Likewise, the base
21
has a different thermal contraction speed from the coating layer
22
or
23
, and therefore, as temperature falls by &Dgr;T
2
from a high temperature to an ordinary temperature, the sheets develop conspicuous curl even during cooling.
For example, in a diffusive sheet having properties as described above, when thermal expansion/contraction produces a force that tends to curl the sheet, the sheet
14
develops, as shown in
FIG. 16
, wavelike bends where there is a scant margin in the direction of the thickness of the sheet
14
as between the frame
4
and the reflecting plate
10
, i.e. where there is nowhere for stress to escape.
Such bends can be reduced by, as shown in
FIGS. 17A and 17B
, bonding the sheet
14
, along all four sides thereof, to the inner surface of the frame
4
. This helps prevent bends around the bonded portion
15
of the sheet
14
, but instead causes large bends in the central
Husar Stephen
Nixon & Vanderhye P.C.
Payne Sharon
Sharp Kabushiki Kaisha
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