Casting polymerization for producing light guide of LCD

Details Casting polymerization for producing light guide of LCD Casting polymerization for producing light guide of LCD

1998-08-07

2001-06-05

Vargot, Mathieu D. (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

Optical article shaping or treating

Optical fiber, waveguide, or preform

C264S001100

Reexamination Certificate

active

06241919

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to light guides (photo conductive plates) of a liquid crystal display (LCD), and particularly to the method of manufacturing light guides of relatively big size for LCDs.
BACKGROUND OF THE INVENTION
The backlight device of a LCD is classified into two types: direct light and edge light (side light) as respectively shown in FIG.
1
and FIG.
2
. In
FIG. 1
where FIG.
1
(
a
) is the cross sectional view of Fig.
1
(
b
), a backlight device of direct light type comprises an array of light source
10
, a reflective plate
12
and a dispersion plate
14
respectively installed in the front and back sides of light source
10
. The backlight device of edge light type shown in
FIG. 2
comprises a light source
20
seated beside light guide
22
and surrounded by a light reflector
24
, a dispersion plate
26
and a reflective plate
28
respectively seated in the front and back sides of light guide
22
. FIG.
2
(
a
) is the cross sectional view of FIG.
2
(
b
). In terms of brightness, weight, and power consumption, the backlight device of edge light type is classified into three types: single edge, double edge, and tri-edge. Shown in
FIG. 2
is the single edge type, while FIGS.
3
(
a
) and
3
(
b
) where light guides
32
and
36
are respectively accompanied by double edge light source
30
and tri-edge light source
34
, are respectively the double edge and tri-edge types.
For a backlight device of edge light type, the light guide is a plate made of Acrylic material (PMMA), to guide light from edge, so that the light is dispersed to form an even surface light source. The light guide is usually made of Acrylic particles processed by injection molding, or is an Acrylic plate.
To achieve an even brightness for light guide, material with refractive index different from that of light guide (acrylic plate in the example) is usually printed on the surface of the light guide, or refractive faces of different angles are usually directly formed on the surface of the light guide.
FIGS. 4-6
show three popular types of embodiments wherein FIGS.
4
(
a
),
5
(
a
), and
6
(
a
) are respectively the cross sectional views of FIGS.
4
(
b
),
5
(
b
), and
6
(
b
). Shown in
FIG. 4
is a light guide
22
with printed organic layer
38
comprising light dispersion particles (for dispersing light) formed on one surface thereof. Shown in
FIG. 5
is a light guide
22
with coarse structure
40
made on one surface thereof to form a face comprising concavities and convexities. Shown in
FIG. 6
is a light guide
22
with concavities dug on one surface thereon to form a face in the shape of sawteeth.
For a LCD of relatively large size such as those bigger than 12 inches in diagonal, an Acrylic plate is too heavy to be used as a light guide. Although the problem may be solved by changing the shape of the light guide, it is hardly achievable by injection molding to manufacture the light guide because of the limitation on the size and the thickness difference control in injection molding, thereby acrylic plate is currently still used as the light guide for mass production of LCD of bigger size.
SUMMARY OF THE INVENTION
The primary object of the present invention is to provide a new manufacturing process for manufacturing light guides of LCDs.
Another objects of the present invention are:
Based on casting polymerization, the method according to the present invention for manufacturing the light guide of an LCD comprises the steps of:
preparing a casting mold in the shape of double wedge for processing casting polymerization;
mixing up methyl methacrylicate (MMA) with polymerization initiator to form a mix;
proceeding prepolymerization of the mix to form a prepolymerized mix;
processing the prepolymerized mix to form a slurry mix;
casting the slurry mix into the casting mold;
enabling polymerization of the slurry mix in the casting mold by heat treatment; and stripping the casting mold to obtain a light guide composed of transparent acrylic resin and in the shape of a double wedge.
One of the features of the present invention is that the bottom plate of the casting mold has surface which is not smooth, thereby a light guide with better light dispersion efficacy can be produced. The surface of the double wedge shaped light guide for different embodiments can be either a face with concavities and convexities or a face with sawteeth as long as the light guide can provide an even brightness throughout its surface.
Glass such as that produced by die-casting melted glass is preferred for manufacturing the casting mold.
With the casting polymerization method provided by the present invention for manufacturing light guides of LCDs, a light guide with thickness varying in a relatively large range from one part thereof to another part thereof can be realized, and the weight of a light guide can be significantly reduced, thereby the mass production of light guides of LCDs of relatively large size can be achieved.
The present invention may best be understood through the following description with reference to the accompanying drawings, in which:


REFERENCES:
patent: 4931521 (1990-06-01), Matsuda et al.
patent: 5101325 (1992-03-01), Davenport et al.
patent: 5283563 (1994-02-01), Allen et al.
patent: 5449703 (1995-09-01), Mitra et al.
patent: 5866047 (1999-02-01), Nagino et al.
patent: 5883684 (1999-03-01), Millikan et al.

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