U.S. patent application number 11/260795 was filed with the patent office on 2006-03-02 for direct backlight module.
This patent application is currently assigned to BENQ CORPORATION. Invention is credited to Hermit Huang, Pang-Lun Yang.
Application Number | 20060044829 11/260795 |
Document ID | / |
Family ID | 32710131 |
Filed Date | 2006-03-02 |
United States Patent
Application |
20060044829 |
Kind Code |
A1 |
Yang; Pang-Lun ; et
al. |
March 2, 2006 |
Direct backlight module
Abstract
A direct backlight module has a light guide plate, a plurality
of lamp tubes, a reflecting plate and a frame. The light guide
plate has a upper surface and a lower surface, and at least one
surface of the light guide plate is coated with an ink layer. The
lamp tubes are located below the light guide plate. The reflection
plate is located below the lamp tubes. The frame covers the
reflecting plate, lamp tubes and light guide plate. The ink layer
contains a plurality of diffusing granules for diffusing lights to
produce uniform lights.
Inventors: |
Yang; Pang-Lun; (Taichung
Hsien, TW) ; Huang; Hermit; (Taoyuan, TW) |
Correspondence
Address: |
Ladas & Parry
26 West 61st Street
New York
NY
10023
US
|
Assignee: |
BENQ CORPORATION
|
Family ID: |
32710131 |
Appl. No.: |
11/260795 |
Filed: |
October 27, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10747379 |
Dec 29, 2003 |
|
|
|
11260795 |
Oct 27, 2005 |
|
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Current U.S.
Class: |
362/613 |
Current CPC
Class: |
G02B 6/0043
20130101 |
Class at
Publication: |
362/613 |
International
Class: |
F21V 7/04 20060101
F21V007/04 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 2002 |
TW |
91137716 |
Claims
1. A direct backlight module, comprising: a light guide plate
having a upper surface and a lower surface; at least one ink layer
formed on the upper surface of the light guide plate; a plurality
of lamp tubes located below the light guide plate to provide lights
into the light guide plate; a reflecting plate located below the
lamp tubes for reflecting lights to the light guide plate; and a
frame for holding the reflecting plate, the lamp tubes, and the
light guide plate; wherein the ink layer has a plurality of
diffusion granules for diffusing lights to produce uniform
lights.
2. The direct backlight module of claim 1, wherein the light guide
plate is made from transparent acrylic.
3. The direct backlight module of claim 1, wherein the ink layer is
formed on the upper surface of the light guide plate by a
screen-printing process.
4. The direct backlight module of claim 1, wherein the ink layer
comprises a white fluorescent paint.
5. The direct backlight module of claim 1, wherein the ink layer
comprise a transparent resin for absorbing and retaining lights of
the lamp tubes before emitting from the light guide plate.
6. The direct backlight module of claim 1 further including a
plurality of optical films located above the ink layer.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a backlight module for
liquid crystal displays (LCDs) and particularly to a direct
backlight module with an ink layer.
BACKGROUND OF THE INVENTION
[0002] With rapid advance of manufacturing technologies in thin
film transistor LCD (TFT-LCD), and the advantages of slim and
light, power saving and low radiation, LCDs have been widely used
in various types of electronic products such as personal digital
assistant (PDA), notebook computers, digital cameras, video
cameras, mobile phones, and the like. In addition, the industry has
invested heavily in research and development and uses mass
production facilities. As a result, quality of LCD continuously
improves and the price drops relentlessly, application scope of LCD
is expanded drastically. However LCD cannot generate light by
itself. It requires a backlight module to accomplish a display
function.
[0003] FIG. 1 is a cross-sectional view of a conventional edge type
backlight module 10. The module 10 includes a light guide plate 11,
a reflecting plate 12, a lamp tube 13, a plurality of optical films
14 and a frame 15. The light guide plate 11 is made from a
transparent acrylic plate which has a lower surface forming
circular, hexagonal or square granular patterns by a screen
printing or injection method to serve as diffusion dots 16 for
scattering light. The reflecting plate 12 is located below the
light guide plate 11 to reflect light emitted from the lamp tube 13
into the light guide plate 11 and to increase the utilization
efficiency of the backlight module 10. The lamp tube 13 is located
on one lateral side of the light guide plate 11 and is usually a
cold cathode tube for projecting light into the light guide plate
11 from one end thereof. The optical films 14 are located above the
light guide plate 11 and include a diffuser plate, prism sheet and
polarizing sheet and the like. The frame 15 is for holding the
reflecting plate 12, lamp tube 13, and light guide plate 11 and
protects the backlight module 11 and the elements contained
therein.
[0004] In the edge type backlight module depicted above, light
emitted from the lamp tube enters the light guide plate from one
end thereof and reaches the other end thereof to generate uniform
lights. However, the size of the light guide plate increases with
the dimension of LCD becomes larger. Light of the edge type
backlight module cannot fully transmit from one end of the light
guide plate to the other end due to a long path. As a result,
bright variations occur from the end close to the lamp tube to the
other end away from the lamp tube. Therefore, the LCD cannot
generate uniform brightness.
[0005] Refer to FIG. 2 for a direct type backlight module 20. The
module 20 includes a diffuser plate 21, a plurality of lamp tubes
22, a reflecting plate 23, a frame 24 and a plurality of optical
films 25. The diffuser plate 21 is a white transparent acrylic
plate. The diffuser plate 21 has a lower surface, a upper surface,
and a plurality of diffusion dots located therein (not shown in the
drawing) for diffusing lights. The lamp tubes 22 are located below
the diffuser plate 21. The reflecting plate 23 is located under the
lamp tubes 22. A portion of light emitted from the lamp tubes 22
directly enters the diffuser plate 21, while the rest portion of
the light is reflected by the reflecting plate 23 and then enters
the diffuser plate 21. The frame 24 covers the diffuser plate 21,
lamp tubes 22 and reflecting plate 23 so as to protect the elements
located in the backlight module 20. The optical films 25 are the
same as the conventional ones depicted before, thus the details are
omitted.
[0006] In the aforesaid direct backlight module 20, several lamp
tubes 22 are uniformly located below the diffuser plate 21, the
diffuser plate 21 may transmit uniform lights theoretically.
However, due to the thickness of the diffuser plate 21, usually 2
to 4 mm, the light path is very short for lights passing through
the diffuser plate 21, and lights are very difficult to be evenly
diffused. As a result, some areas of the diffuser plate 21 transmit
stronger scattering light beams while some other areas do not. This
causes uneven brightness of the backlight module 20 as shown in
FIG. 3, and a significant variation of brightness occurs on the LCD
screen as shown in FIG. 4. It serious affects visual satisfactions
of consumers. To remedy this problem, another conventional
technique was developed. Several diffuser sheets are used to
diffuse lights and obtain a more uniform light output for the
backlight module. However, the improvement is limited, and each
diffuser sheet has a high shielding ratio that result in a great
impact to the brightness of the backlight module.
[0007] Therefore to overcome the disadvantages occurred to the
conventional direct backlight modules and to develop improvement to
achieve more uniform lighting to enhance the visual appealing of
LCD is a goal hotly pursed in the industry at present.
SUMMARY OF THE INVENTION
[0008] The primary object of the invention is to provide a direct
backlight module to generate more uniform lights.
[0009] The direct backlight module according to the invention
includes a light guide plate, a plurality of lamp tubes, a
reflecting plate, a frame and a plurality of optical films. The
light guide plate is made from transparent acrylic. The light guide
plate has an upper surface and a lower surface. At least one of the
surfaces is coated with an ink layer by a screen-printing process.
The ink layer is a white fluorescent layer containing a plurality
of diffusion granules and a transparent resin. The lamp tubes are
distributed below the light guide plate. The reflecting plate is
located below the lamp tubes to reflect light. The frame covers the
reflecting plate, the lamp tubes, and the light guide plate so as
to protect the elements in the backlight module from being damaged
by external forces.
[0010] When both the upper and lower surfaces of the light guide
plate are coated with an ink layer, lights emitted from the lamp
tubes, whether directly entering the light guide plate or
reflecting by the reflecting plate, will be diffused for the first
time by the ink layer on the lower surface, then diffused for the
second time by the ink layer on the upper surface. The resin in
each ink layers can absorb the incident lights and retain the
lights in the resin temporarily before emitting. The diffusion
granules can diffuse the incident lights, thus the incident lights
are diffused twice by the two ink layers and become more uniform
lights when transmitting out of the light guide plate. Therefore,
variations of brightness of the LCD screen can be reduced to
enhance the visual appealing.
[0011] The foregoing, as well as additional objects, features and
advantages of the invention will be more readily apparent from the
following detailed description, which proceeds with reference to
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a sectional view of a conventional edge light
backlight module.
[0013] FIG. 2 is a sectional view of a conventional direct
backlight module.
[0014] FIG. 3 is a schematic view of light output of a conventional
direct backlight module.
[0015] FIG. 4 is a schematic view of brightness distribution of a
conventional direct backlight module.
[0016] FIG. 5 is a sectional view of the direct backlight module
according to the invention.
[0017] FIG. 6 is a schematic view of the ink layer according to the
invention.
[0018] FIG. 7 is a schematic view of light output according to the
invention.
[0019] FIG. 8 is a schematic view of brightness distribution
according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] The invention discloses a direct backlight module with an
ink layer on upper and lower surfaces of a light guide plate to
increase the uniformity of output lights of the backlight module
and enhance visual appealing of LCD. Preferred embodiments of the
invention are elaborated as follows.
[0021] Referring to FIG. 5, the direct backlight module 50
according to the invention includes a light guide plate 51, a
plurality of lamp tubes 52, a reflecting plate 53, a frame 54, and
a plurality of optical films 55. The light guide plate 51 is made
from transparent acrylic. The light guide plate includes an upper
surface and a lower surface. The upper and lower surfaces are
coated with an ink layer 56a and 56b by a screen-printing process.
Each ink layer 56 contains a plurality of diffusion granules 561
and a white fluorescent paint made from triacetate cellulose (TAC)
or the like that composes of a transparent resin 562 (referring to
FIG. 6). The lamp tubes 52 are distributed below the light guide
plate 51 as light sources off the backlight module 50. The
reflecting plate 53 is located below the lamp tubes 52. The frame
54 covers the reflecting plate 53, lamp tubes 52, and the lower
surface of the light guide plate 51 so as to protect the elements
in the backlight module 50 from being damaged by external forces.
The optical films 55 are located above the light guide plate 51.
Each of the optical films 55 has its specific function to treat
lights outputted from the light guide plate 51.
[0022] By means of the aforesaid structure, with the ink layer 56
formed on the upper and lower surfaces of the light guide plate 51,
the transparent resin 562 contained in the ink layer 56 can absorb
and retain incident lights temporarily before emitting. The
granules 561 can diffuse a light beam with a greater brightness to
several light beams with smaller brightness so that the diffusion
effect of the light guide plate 51 is increased and output lights
of the light guide plate 51 have higher brightness.
[0023] Referring to FIG. 7, due to the ink layers 56, each light
beam of a greater brightness will be diffused to a plurality of
light beams with a less brightness. Therefore, in the direct
backlight module 50, light emitted from the lamp tubes 52, whether
enters the light guide plate 51 directly or is reflected by the
reflecting plate 53, will be diffused for the first time by the ink
layer 56b on the lower surface, then diffused for the second time
by the ink layer 56a on the upper surface. After lights have been
diffused twice, more uniform lights can be transmitted from the
upper surface of the light guide plate 51, so significant
brightness variations will not occur to the LCD screen, and visual
appealing may be enhanced as shown in FIG. 8.
[0024] Comparing FIG. 4 to FIG. 8, the direct backlight module of
the invention can generate more uniform lights and reduce
brightness variations on the LCD screen. Moreover, one diffusing
plate is more expensive than a transparent light guide plate. In
the present invention, one transparent light guide plate with at
least one ink layer is used to replace the diffusing plate, so the
manufacturing cost is reduced. Moreover, the overall brightness of
the backlight module also increases.
[0025] While the preferred embodiments of the invention have been
set forth for the purpose of disclosure, modifications of the
disclosed embodiments of the invention as well as other embodiments
thereof may occur to those skilled in the art. Accordingly, the
appended claims are intended to cover all embodiments which do not
depart from the spirit and scope of the invention.
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