Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-02-20
2001-05-15
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06233031
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for producing reflectors used in reflective liquid crystal display devices and the like, and liquid crystal display devices equipped with such reflectors.
2. Description of the Prior Art
Liquid crystal display devices have been widely used, since they can be produced as small, light-weight, and thin display devices. In particular, reflective liquid crystal display devices equipped with a reflective plate have taken attention because of their reduced electric-power consumption.
FIG. 12
shows the structure of a reflective liquid crystal display device of the prior art. This reflective liquid crystal display device A is composed of: a pair of transparent substrates
1
and
2
opposing each other; a liquid crystal layer
4
encapsulated between the pair of transparent substrates
1
and
2
by a sealing member
3
; a polarizing plate
6
, phase-contrast plates
7
and
8
formed on the top side of the transparent substrate
1
in that order from the top; and a reflector
10
formed on the bottom side of the transparent substrate
2
. The reflector
10
is composed of: a glass substrate
51
having an uneven pattern
51
a
formed on the top side thereof; an Al reflective film
52
provided on the glass substrate
51
, and a sticky layer
53
formed on the Al reflective film
52
. An electrode layer
15
made of ITO, a top-coat layer
16
, and an alignment film
17
are formed on the bottom side of the transparent substrate
1
in that order from the top. A color filter layer
18
required for color displaying, an over-coat layer
19
, an electrode layer
20
, and an alignment film
54
are formed on the top side of the lower transparent substrate
2
in that order from the bottom.
According to the reflective liquid crystal display device A having the above-mentioned structure, the incident light coming from the upper side of the transparent substrate
1
is transmitted through the liquid crystal layer
4
, reflected by the reflective film
52
, re-transmitted through the liquid crystal layer
4
, and passes through the transparent substrate
1
. The polarization direction of the light is controlled according to the alignment of the liquid crystal layer
4
, and a bright state and a dark state of the display device can be switched by allowing or not allowing the reflected light to pass through the polarizing plate
6
. The uneven pattern
51
a
is formed on the glass substrate
51
for rendering the reflective film
52
uneven such that light coming from the required direction is reflected and undesired light reflection is reduced.
However, in the reflective liquid crystal display device having the above structure, the reflector
10
is provided outside the thick glass substrate
2
, and thus, the incident light must be transmitted through the substrate
2
after passing through the liquid crystal layer
4
. A parallal thereby occurs and disadvantageously results in a reduced contrast and a double image.
For forming the uneven pattern
11
a
on the glass substrate
51
of the reflector
10
, the glass surface is treated with hydrofluoric acid to form an uneven pattern on the surface. However, according to such a technique, the shape of the fine uneven pattern cannot be satisfactorily controlled.
It is technically important to control the shape of the uneven pattern of the reflector because light in the required direction is thereby efficiently reflected and undesired light reflection is reduced.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a method for producing a reflector, by which method the shape of a fine uneven pattern provided for the reflector can be controlled so that the resulting reflector has an excellent reflection efficacy. Another object of the present invention is to provide a liquid crystal display device having such a reflector.
To achieve the above object, according to the present invention, a method for producing a reflector has: a step for applying a photosensitive resin onto a base member to form a photosensitive-resin layer; a step for pressing a mold, having a fine uneven pattern on the surface thereof, to the photosensitive-resin layer so as to transfer the shape of the fine uneven pattern to the photosensitive-resin layer; a step for curing the photosensitive-resin layer by radiating a light beam to the photosensitive-resin layer while pressing the mold to the photosensitive-resin layer; a step for removing the mold from the cured photosensitive-resin layer; and a step for forming a metallic reflective film on the fine uneven pattern transferred to the surface of the cured photosensitive-resin layer. Since the fine uneven pattern is formed on the photosensitive-resin layer by pressing the mold thereto and is covered with the metallic reflective film, a reflection face of the resulting reflector can obtain the shape of the fine uneven pattern transferred from the mold.
Preferably, pre-baking is carried out in a temperature range of from 40 to 150° C. after forming the photosensitive-resin layer on the base member. During pressing the mold to the photosensitive-resin layer, bubbles entering therebetween are prevented from being generated because unnecessary volatile constituents contained in the photosensitive-resin layer can be removed by pre-baking. Therefore, the transferring of the uneven pattern of the mold to the photosensitive-resin layer is reliably carried out with accuracy, resulting in a desired uneven pattern.
When the pre-baking temperature is less than 40° C., an excessive amount of solvent remains in the resulting photosensitive-resin layer because of insufficient pre-baking. The residual solvent may volatilize and form bubbles by heat generated during ultraviolet radiation so that while pressing a mold to the photosensitive-resin layer, the resulting bubbles undesirably enter therebetween. When the pre-baking temperature exceeds 150° C., the flow of the photosensitive resin deteriorates. Thus, it becomes difficult to sufficiently transfer the uneven pattern to the photosensitive-resin layer.
According to the present invention, the photosensitive resin may contain at least one resist selected from the group consisting of acrylic resists, polystyrene resists, azide rubber resists, and imide resists, and the metallic reflective film may be composed of Al, an Al alloy, Ag, or an Ag alloy. By using such resists or metals, the resulting reflector achieves a high reflectance with an accurately transferred uneven pattern.
Preferably, pre-baking is carried out for 30 sec. to 10 min., both inclusive. When the pre-baking time-period is 30 sec. or less, an excessive amount of solvent remains in the resulting photosensitive-resin layer because of insufficient pre-baking. The residual solvent may volatilize and form bubbles by heat generated during ultraviolet radiation so that while pressing a mold to the photosensitive-resin layer, the resulting bubbles undesirably enter therebetween. When the pre-baking time-period exceeds 10 min., the flow of the photosensitive resin deteriorates. Thus, it becomes difficult to sufficiently transfer the uneven pattern to the photosensitive-resin layer.
In the present invention, the base member is transparent. Thus, the photosensitive-resin layer can be cured by radiating a light beam from the back-face side of the transparent base member while pressing the mold to the photosensitive-resin layer. As a result, the shape of the uneven pattern transferred to the surface of the photosensitive-resin layer can be kept as it is.
In addition, according to the present invention, the uneven pattern of the base member may be composed of: a plurality of ridges each having an almost constant height in one direction of the base member, with the heights and widths being set to random values for the ridges; and grooves each provided between the ridges and in the direction of the base member. When a reflector has such an uneven pattern, it can efficiently reflect light entering in a certain direction
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Nguyen Dung
Sikes William L.
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