Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating – Optical fiber – waveguide – or preform
Reexamination Certificate
2000-11-22
2003-12-16
Vargot, Mathieu D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Optical article shaping or treating
Optical fiber, waveguide, or preform
C205S070000, C249S135000, C264S002500, C425S808000
Reexamination Certificate
active
06663800
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a technique of fabricating a light guide used for a liquid crystal display, and more particularly to a light guide fabricating apparatus and a manufacturing method thereof having a simplified mold structure.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) controls light transmissivity of liquid crystal cells arranged in a matrix pattern with the aid of a video signal applied thereto to display a picture corresponding to the video signal. To this end, the LCD includes a liquid crystal display panel having liquid crystal cells arranged in an active matrix which control an amount of light transmitted from the lower portion thereof; a backlight unit for emitting light from the lower portion of the liquid crystal display panel; red, green and blue color filters corresponding to each liquid crystal cell at the lower portion of the liquid crystal display panel; and a black matrix layer for defining pixels. The backlight unit functions to evenly emit white light from the rear side of the liquid crystal display panel, and consists of a light source, a light guide, a reflector and a diffuser, etc. for uniformly transmitting light emitted from the light source into the panel.
FIG. 1
shows a sectional structure of a conventional backlight unit provided at the lower portion of a liquid crystal display panel. Referring to
FIG. 1
, the backlight unit includes a backlight lamp
22
for generating white light, a prism light guide
4
for guiding light passing through a light input
20
from the backlight lamp
22
, a lamp housing
24
for mounting the backlight lamp
22
and reflecting light into the light guide
4
, a reflector
2
for reflecting light from the lower portion of the prism light guide
4
toward the upper portion thereof where the liquid crystal display panel is positioned, first and second diffusing films
6
and
12
, and first and second prism films
8
and
10
for controlling diffusion and transmission direction of the light passing through the prism light guide
4
. The light guide
4
is formed in a prism shape with an inclined lower surface as shown in FIG.
2
and allows light inputted from the backlight lamp
22
to smoothly progress toward the upper portion thereof. Light transmission, via the lower surface of the prism light guide
4
, toward the lower portion thereof is reflected upward by the reflector
2
provided at the lower portion of the light guide
4
. Light passing through the prism light guide
4
is uniformly diffused by means of the first diffusing film
6
. Light passing through the first diffusing film
6
is controlled to make its transmission direction perpendicular to the liquid crystal display panel at the first and second prism films
8
and
10
. Light passing through the first and second prism films
8
and
10
is incident on the liquid crystal display panel by way of the second diffusing film
12
again.
For instance, the lower surface of the prism light guide
4
is inclined and provided with minute grooves
26
having a uniform distance as shown in FIG.
2
. Such grooves
26
are referred to as “prism unevenness”, which smooths a diffusion of light as well and reduces light loss on a path where light is transmitted toward the upper portion of the light guide
4
. This increases the amount of light transmitted toward the liquid crystal display panel. Typically, the prism light guide
4
is made from an acryl such as PMMA, etc., and the grooves
26
are formed in an equal distance to have a pitch width of about 0.07 to 0.08 mm by a machine working.
The prism light guide
4
having the structure as mentioned above is, for example, fabricated by an injection-molding device
30
as shown in FIG.
3
. Referring to
FIG. 3
, the conventional light guide injection-molding device
30
consists of a stamper
32
for forming groves
26
, a stationary core
34
to which the stamper
32
is attached, a vacuum tube
36
and a vacuum device (not shown) for attaching the stamper
32
to the stationary core
34
by a vacuum force, a stamper fixing segment
38
provided at the side portion of the stationary core
34
to determine an attached position of the stamper
32
, a movable core
40
defining a mold
46
along with the stationary core
34
, and a stationary molding plate
42
and a movable molding plate
44
for fixing the stationary and movable cores
34
and
40
at the exterior thereof. The stationary core
34
has a thickness of about 20 mm while the stamper
32
has a thickness of about 0.1 to 0.4 mm. In the conventional art, a brass plate (which is easy to work by a grinding process) is preferably used to make the stamper
32
. Recently, a high-hardness nickel has been used because the relatively soft brass plate wears too easily, which affects mass production operation. However, since nickel is very hard, it is difficult to form the grooves
26
at an equal distance by a grinding process. In order to solve this problem, a nickel stamper
32
has been made by using a brass plate provided with the prism unevenness grooving as a master, then electroplating nickel on the surface of the brass plate provided with the prism unevenness grooving to a desired thickness. In manufacturing the stamper
32
according to the electroplating method, the stamper
32
has a thickness of about 0.1 to 0.4 mm because it is difficult to make a large plating thickness.
Hereinafter, a conventional method of fabricating the prism light guide
4
is described. First, a position of the stamper
32
to be attached to the stationary core
34
is determined by the stamper fixing segment
38
. The stamper
32
is then attached to the attached portion of the stationary core
34
. The portion of the stamper
32
attached to the stationary core
34
has a plurality of vacuum holes connected the vacuum tube
36
. The stamper
32
is attached to the stationary core
34
by a vacuum force provided by evacuating air through the vacuum tube
36
. Thereafter, a prism light guide material is injected into a space between the stationary core
40
and the stamper
32
and then injection-molded to be made into the prism light guide
4
having the prism unevenness grooves
26
.
The conventional injection-molding device has a structure in which the stamper
32
is separate from the core
34
of the mold
46
. The stamper
32
is temporarily attached to the stationary core
34
of the mold
46
by evacuating air through the vacuum holes provided at the attached portion of the stamper
32
to the stationary core
34
. Such a stamper fixing method is mainly used for a product that must be changed frequently. In conventional compact disc injection-molding device (as an example of another application), various kinds of discs must be formed so various kinds of stampers must be changed frequently. Thus, the stamper fixing method employing a vacuum system is used in which attachment and detachment of the appropriate stamper is easy. However, the prism light guide
4
in the LCD is mass produced and therefore does not require frequent attachment and detachment of the stamper until a life of the stamper
32
expires. Therefore, the above-mentioned stamper attaching method using a vacuum system is not available. The conventional injection-molding device
30
has a drawback because it requires an additional device for evacuating air and the attached portion of the stamper
32
to the stationary core
34
must be provided with a plurality of vacuum holes, so device
30
has complex structure and facilities. Also, the conventional injection-molding device
30
unstable attachment due to a deterioration of the vacuum force applied to the stamper
32
, its manufacturing becomes unstable. Furthermore, it is inconvenient because cleaning and fine surface grinding work, etc. on the attached portion of the stationary core
34
to the stamper
32
are required to provide an easy air evacuation and strengthen the vacuum force.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides an appar
Hwang Jae Ho
Kim Wook Sung
Lee Hong Su
Birch & Stewart Kolasch & Birch, LLP
LG. Philips LCD Co. Ltd.
Vargot Mathieu D.
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