研
究
方
中英文專利的搜尋
第 六 組
指導教授:林正峰老師
學生: M94L0201
黃俊智
M94L0212
廖宏彬
M94L0213
蔡建昇
法
檢索主題：背光模組(Backlight)
一.中華民國專利檢索
1.進入經濟部智慧財產局首頁
2.再進入中華民國專利資料查詢->採用進階查詢
->輸入”背光模組”
->在公告日期欄位上輸入”2001~2005”
3.總共找到了 724 筆的資料
{這 724 筆的資料的專利申請日期都在 2001 年到
2005 年間}
4.以下則簡略的列出 7 項有關背光模組的專利
(1) 專利類型： 發明
專利名稱：直下式
背光模組 之光擴散板及其製作方法
專利號碼：公告/公開號：200538810
申請案號：093114492
國際分類號：G02F-001/1111
以下是”專利影像”
(2)
專利類型： 發明
專利名稱：背光模組 之擴散板檢測方法
專利號碼：公告/公開號：200538700
申請案號：093114443
國際分類號：G01B-005/555555555555
以下是”專利影像”
(3) 專利類型： 發明
專利名稱：導光板及 背光模組
專利號碼：公告/公開號：200535514
申請案號：093112188
國際分類號：G02F-001/1111
以下是”專利影像”
(4)
專利類型： 發明
專利名稱：直下式 背光模組 及液晶顯示裝置
專利號碼：公告/公開號：200534005
申請案號：093110475
國際分類號：G02F-001/1111
以下是”專利影像”
(5)
專利類型： 發明
專利名稱：直下式點光源 背光模組 及應用其
之液晶顯示器
專利號碼：公告/公開號：200532316
申請案號：093108762
國際分類號：G02F-001/1111
以下是”專利影像”
(6)
專利類型： 發明
專利名稱：背光模組 之導光板
專利號碼：公告/公開號：200530692
申請案號：093106195
國際分類號：G02F-001/1111
以下是”專利影像”
(7)
專利類型： 發明
專利名稱：背光模組 及其擴散板
專利號碼：公告/公開號：200530633
申請案號：093105377
國際分類號：G02B-005/5555555555555555
以下是”專利影像”
二.美國專利檢索
1.進入”Quick Search”搜尋
->網址”http://patft.uspto.gov/netahtml/search-bool.html”
->在 Term 1.輸入”backlight”
->在 Term 2.輸入”Polarization”
->在 Select years 欄位選擇”1976 to
present”
2.按 search->可搜尋到 1412 篇相關專利發明
3.以下則簡略的列出 2 項有關背光模組的專利
(1) Title: Polarizing film, optical film and liquid
crystal display using polarizing film
APPL. NO.: 117843
以下是專利發明詳細資料
1. A polarizing film comprising a polarizer (A) and a protection film (B) prepared on
at least one face of the polarizer (A), wherein the protection film (B) is adhered to the
polarizer (A) without using adhesives, wherein the protection film (B) is formed by at
least two layers of the same materials but having different softening points, the layer
having the lower softening point being located on a side of the protection film (B)
facing the polarizer (A), and wherein the polarizer (A) is a dyed and stretched
hydrophilic polymer film.
2. The polarizing film according to claim 1, wherein an adhesive strength between the
polarizer (A) and the protection film (B) is not less than 10N/25 mm.
3. The polarizing film according to claim 1, wherein a retardation within a plane of
the protection film (B) is not more than 10 nm.
4. The polarizing film according to claim 1, wherein a thickness of the protection film
(B) is not more than 50 micrometers.
5. The polarizing film according to claim 1, wherein a moisture permeability of the
protection film (B) is not more than 60 g/m2-24 hours-atm.
6. The polarizing film according to claim 1, wherein an elastic modulus of the
protection film (B) is not less than 2000 N/mm2.
7. The polarizing film according to claim 1, wherein a surface free energy on a side of
the protection film (B) to which the polarizer (A) is not adhered is not less than 40
mN/m.
8. The polarizing film according to claim 1, wherein a light transmittance of a
protection film (B) is not less than 86%.
9. The polarizing film according to claim 1, wherein light transmittance is not less
than 42%, and polarization degree is not less than 95%.
10. An optical film, wherein at least one sheet of the polarizing film according to
claim 1 is laminated.
11. A visual display comprising the polarizing film according to claim 1.
12. The polarizing film according to claim 6, wherein the elastic modulus of the
protection film (B) is not less than 2500 N/mm2.
13. The polarizing film according to claim 2, wherein the adhesive strength between
the polarizer (A) and the protection film (B) is not less than 12N/25 mm.
14. The polarizing film according to claim 2, wherein the adhesive strength between
the polarizer (A) and the protection film (B) is not less than 14N/25 mm.
15. The polarizing film according to claim 7, wherein the surface free energy on a side
of the protection film (B) to which the polarizer (A) is not adhered is not less than 50
mN/m.
16. The polarizing film according to claim 7, wherein the surface free energy on a side
of the protection film (B) to which the polarizer (A) is not adhered is not less than 56
mN/m.
17. The polarizing film according to claim 8, wherein a light transmittance of a
protection film (B) is not less than 88%.
18. The polarizing film according to claim 8, wherein a light transmittance of a
protection film (B) is not less than 92.4%.
19. The polarizing film according to claim 9, wherein the light transmittance is not
less than 42.5%, and the polarization degree is not less than 98%.
20. The polarizing film according to claim 9, wherein the light transmittance is not
less than 43.6%, and the polarization degree is not less than 99.9%.
21. The polarizing film according to claim 1, wherein a difference between the
softening points is not less than 5° C.
22. The polarizing film according to claim 21, wherein a difference between the
softening points is not less than 10° C.
23. The polarizing film according to claim 1, wherein the layer with a lower softening
point on a side to which a polarizer (A) is adhered has a thickness of about 1 to about
100 micrometers.
24. The polarizing film according to any one of claims 1 and 2, wherein the protection
film (B) has a thickness of not more than 500 micrometers.
25. The polarizing film according to any one of claims 1 and 2, wherein the protection
film (B) has a thickness of 1 to 300 micrometers.
26. The polarizing film according to any one of claims 1 and 2, wherein the protection
film (B) has a thickness of 5 to 200 micrometers.
27. The polarizing film according to any one of claims 1 and 2, wherein the protection
film (B) has a thickness of from 1 to 300 micrometers.
28. The polarizing film according to any one of claims 1 and 2, wherein the protection
film (B) has a thickness of from 5 to 200 micrometers.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polarizing film. A polarizing film of the present
invention independently or a laminating optical film may form a visual display, such
as a liquid crystal display, an organic EL display, a PDP (plasma display panel) a
liquid crystal display.
2. Description of the Prior Art
In a liquid crystal display, it is indispensable that polarizers should be arranged at both
sides of a glass substrate that forms a top surface of a liquid crystal panel according to
a picture formation method. Generally, polarizing film is used a polarizer, comprising
a polyvinyl alcohol derived film, and dichroism substances, such as iodine, on which
a protection film is adhered.
Conventionally, the above described polarizing film is manufactured by adhering a
polarizer and a protection film by adhesives. Adhesives are compounds or composites
that have combining components, and are used also as solution dissolved in water or
organic solvents. Furthermore, they are hardened with heat, light irradiation or by a
chemical reaction, etc. Such adhesives are poured in between these layers,
immediately before the polarizer and the protection film are adhered, or they are
beforehand applied to either of the polarizer or the protection film.
However, when adhesives are used, many processes are needed in manufacturing
process and then a large amount of expense is required in production facilities in
which an application process, a laminating process and a drying process of adhesives
are required. Further a saponification processing, a corona treatment, a plasma
treatment, a low-pressure UV processing or an undercoat processing etc. should be
given to a protection film, in order to raise an adhesive property with a polarizer.
Consequently, production cost of the polarizing film obtained also becomes expensive.
Moreover,if the manufacturing process requires many steps, a factor of giving defects
in each of the process will also be increased.
Moreover, as the above-mentioned adhesives, many water-soluble adhesives, such as
polyvinyl alcohol aqueous solution, are used, and then a produced polarizing film
does not have sufficient durability under a heated or humidified condition. Therefore,
the portion of adhesives is easy to be influenced with moisture, and this is one of the
causes of degradation of a polarizing film in early stage of use.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a polarizing film in which problems
induced by use of adhesives are solved. Furthermore, an object of the present
invention is to provide an optical film in which the above described polarizing film is
laminated and to provide a visual display.
As a result of repeated examinations carried out wholeheartedly by the present
inventors to solve the above-mentioned problems, it was found out, as is shown below,
that the above described object is attained using a polarizing film shown below and
the present invention was completed.
Accordingly, the present invention relates to a polarizing film comprising a polarizer
(A) and a protection film (B) prepared on at least one face of the polarizer (A),
wherein the protection film (B) is adhered to the polarizer (A) without using
adhesives.
In a polarizing film of the present invention, since a polarizer (A) and a protection
film (B) are adhered together without using adhesives, neither a problem on
manufacturing process induced by using adhesives nor a problem in durability of a
polarizing film concerning adhesives is given.
In the above described polarizing film, it is preferable that a light transmittance of a
protection film (B) is not less than 86%. A protection film (B) with the above
described light transmittance has a high transparency as an optical property. The
above described light transmittance is more preferably is not less than 88%.
Moreover, preferably a polarizing film has not less than 42% of light transmittance,
and not less than 95% of polarization degree. A polarizing film with the above
described light transmittance and polarization degree has an optical property fully
satisfying panel characteristics of a liquid crystal display. More preferably a light
transmittance of a polarizing film is not less than 42.5%, and a polarization degree
not less than 98%.
Moreover, the present invention relates to an optical film, wherein at least one sheet
of the above described polarizing film is laminated, and to a visual display, wherein
the above described polarizing film or the above described optical film is used.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a polarizing film of the present invention; and
FIG. 2 is a conceptual figure where thermocompression bonding a protection film and
a polarizer.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In a polarizing film of the present invention, as is shown in FIG. 1, a protection film
(B) is directly prepared on at least one face of a polarizer (A). In FIG. 1, the protection
films (B) are prepared on both sides of a polarizer (A). The protection film (B) may
be prepared only on one side of a polarizer (A).
A polarizer(A) is not limited especially but various kinds of polarizer may be used. As
a polarizer (A), for example, a film that is uniaxially stretched after having
dichromatic substances, such as iodine and dichromatic dye, absorbed to hydrophilic
high molecular weight polymer films, such as polyvinyl alcohol type film, partially
formalized polyvinyl alcohol type film, and ethylene-vinyl acetate copolymer type
partially saponified film; poly-ene type alignment films, such as dehydrated polyvinyl
alcohol and dehydrochlorinated polyvinyl chloride, etc. may be mentioned. In these, a
polyvinyl alcohol type film on which dichromatic materials (iodine, dyes) is absorbed
and aligned after stretched is suitably used. Although thickness of polarizer is not
especially limited, the thickness of about 5 to 80 μm is commonly adopted.
A polarizer that is uniaxially stretched after a polyvinyl alcohol type film dyed with
iodine is obtained by stretching a polyvinyl alcohol film by 3 to 7 times the original
length, after dipped and dyed in aqueous solution of iodine. If needed the film may
also be dipped in aqueous solutions, such as boric acid and potassium iodide, which
may include zinc sulfate, zinc chloride. Furthermore, before dyeing, the polyvinyl
alcohol type film may be dipped in water and rinsed if needed. By rinsing polyvinyl
alcohol type film with water, effect of preventing un-uniformity, such as unevenness
of dyeing, is expected by making polyvinyl alcohol type film swelled in addition that
also soils and blocking inhibitors on the polyvinyl alcohol type film surface may be
washed off. Stretching may be applied after dyed with iodine or may be applied
concurrently, or conversely dyeing with iodine may be applied after stretching.
Stretching is applicable in aqueous solutions, such as boric acid and potassium iodide,
and in water bath.
As a materials forming the protective film (B) prepared in one side or both sides of
the above-mentioned polarizer (A), with outstanding transparency, mechanical
strength, heat stability, moisture cover property, isotropy, etc. may be preferable. As
materials of the above-mentioned protective film, for example, polyester type
polymers, such as polyethylene terephthalate and polyethylenenaphthalate; cellulose
type polymers, such as diacetyl cellulose and triacetyl cellulose; acrylics type polymer,
such as poly methylmethacrylate; styrene type polymers, such as polystyrene and
acrylonitrile-styrene copolymer (AS resin); polycarbonate type polymer may be
mentioned. Besides, as examples of the polymer forming a protective film, polyolefin
type polymers,such as polyethylene, polypropylene, polyolefin that has cyclo- type or
norbornene structure, ethylene-propylene copolymer; vinyl chloride type polymer;
amide type polymers, such as nylon and aromatic polyamide; imide type polymers;
sulfone type polymers; polyether sulfone type polymers; polyether-ether ketone type
polymers; poly phenylene sulfide type polymers; vinyl alcohol type polymer;
vinylidene chloride type polymers; vinyl butyral type polymers; allylate type
polymers; polyoxymethylene type polymers; epoxy type polymers; or blend polymers
of the above-mentioned polymers may be mentioned.
In order to adhering protection film (B) to a polarizer (A) without using adhesives, a
film formed two or more layers having each different softening point, which is
suitably selected from the above described material, is used as the protection film (B).
As shown in FIG. 2, a film layer in a side of layer with a lower softening point of a
protection film (B) is laminating onto at least one face of a polarizer (A), and
thermocompression bonding. A protection film (B) and a polarizer (A) may be
adhered without using adhesives. In FIG. 2, a protection film (B) is prepared only in
one side of a polarizer (A).
Although the each material that forms above described two or more layer s film may
be of the same material and may be of materials of different kinds, it is preferable to
be of the same material. However, a thermoplastic resin melted by
thermocompression bonding is used as a resin that forms the layer with a lower
softening point in a side adhered to a polarizer (A). A softening point of the resin that
forms the layer with a lower softening point in a side adhered to a polarizer (A) is
preferably not less than 80 degrees C. and more preferably not less than 90 more
degrees C. A difference of the softening points between the resins that form two or
more film layers is preferably not less than 5 degrees C. and more preferably not less
than 10 degrees C. In addition, a softening point is a value measured by Vicat
softening-temperature examination method of JIS K7206.
Generally, a thickness of a protection film (B) is not more than 500 micrometers,
preferably 1 to 300 micrometers, and more preferably 5 to 200 micrometers.
Especially as mentioned above a thickness of a protection film (B) is preferably not
more than 50 micrometers. In addition, when the protection films (B) having two or
more layers are used, the layer with a lower softening point on a side to which a
polarizer (A) is adhered has suitably a thickness of about 1 to 100 micrometers.
In the above described protection film (B), a hard coating layer, reflective prevention
processing, and processing aiming at sticking prevention, diffusion, or anti glare
function may be provided to the face that is not adhered to a polarizer (A). In addition,
the above described reflection prevention layer, sticking prevention layer, diffusion
layer, anti glare layer, etc. may be prepared to the protection film (B) itself, and
moreover these layers may also be prepared separately as an independent optical layer
of a protection film (B).
A polarizing film of the present invention is manufactured in a way that, for example,
the lower softening point layer of the above described protection film (B) that has two
or more layers is laminating on at least one face of the above described polarizer (A),
and thermocompression bonding at a temperature at which a higher softening point
layer is not melted but a lower softening point layer is melted, that is, at a temperature
in a range between the softening points of each resin forming the two or more layers.
A method of thermocompression bonding a polarizer (A) and a protection film (B) is
not especially limited, and a method may be adopted in which heating treatment is
performed simultaneously or sequentially with pressurization. As heating methods, for
example, non-contact heating methods using IR heater, heated air, high frequency,
ultrasonic wave, etc., and contact heating methods by heat conduction using hot plate
or hot roll etc. may be mentioned. As pressurization method, a pressurizing method by
pinch roll etc. may be mentioned. Pressurization may also be performed in a vacuum.
When pressurizing is given simultaneously with heating treatment, a method may be
adopted in which films are passed between heated pinch rolls and pressurized with
heating. After thermocompression bonding, the films are cooled, and therefore a
melted film layer (a lower softening point layer) of a protection film (B) is hardened
to give an adhesion between the polarizer (A) and the protection film (B).
The polarizing film of the present invention may be used in practical use as an optical
film laminated with other optical layers. Although there is especially no limitation
about the optical layers, one layer or two layers or more of optical layers, which may
be used for formation of a liquid crystal display etc., such as a reflective plate, a
transflective plate, a retardation plate (a half wavelength plate and a quarter
wavelength plate included), and a viewing angle compensation film, may be used.
Especially preferable polarizing films are; a reflection type polarizing film or a
transflective type polarizing film in which a reflective plate or a transflective
reflective plate is further laminated onto a polarizing film of the present invention; an
elliptically polarizing film or a circular polarizing film in which a retardation plate is
further laminated onto the polarizing film; a wide viewing angle polarizing film in
which a viewing angle compensation film is further laminated onto the polarizing film;
or a polarizing film in which a brightness enhancement film is further laminated onto
the polarizing film.
A reflective layer is prepared on a polarizing film to give a reflection type polarizing
film, and this type of plate is used for a liquid crystal display in which an incident
light from a view side (display side) is reflected to give a display. This type of plate
does not require built-in light sources, such as a backlight, but has an advantage that a
liquid crystal display may easily be made thinner. A reflection type polarizing film
may be formed using suitable methods, such as a method in which a reflective layer of
metal etc. is, if required, attached to one side of a polarizing film through a
transparent protective layer etc.
As an example of a reflection type polarizing film, a plate may be mentioned on
which, if required, a reflective layer is formed using a method of attaching a foil and
vapor deposition film of reflective metals, such as aluminum, to one side of a matte
treated protective film. Moreover, a different type of plate with a fine concavo-convex
structure on the surface obtained by mixing fine particle into the above-mentioned
protective film, on which a reflective layer of concavo-convex structure is prepared,
may be mentioned. The reflective layer that has the above-mentioned fine
concavo-convex structure diffuses incident light by random reflection to prevent
directivity and glaring appearance, and has an advantage of controlling unevenness of
light and darkness etc. Moreover, the protective film containing the fine particle has
an advantage that unevenness of light and darkness may be controlled more
effectively, as a result that an incident light and its reflected light that is transmitted
through the film are diffused. A reflective layer with fine concavo-convex structure on
the surface effected by a surface fine concavo-convex structure of a protective film
may be formed by a method of attaching a metal to the surface of a transparent
protective layer directly using, for example, suitable methods of a vacuum
evaporation method, such as a vacuum deposition method, an ion plating method, and
a sputtering method, and a plating method etc.
Instead of a method in which a reflection plate is directly given to the protective film
of the above-mentioned polarizing film, a reflection plate may also be used as a
reflective sheet constituted by preparing a reflective layer on the suitable film for the
transparent film. In addition, since a reflective layer is usually made of metal, it is
desirable that the reflective side is covered with a protective film or a polarizing film
etc. when used, from a viewpoint of preventing deterioration in reflectance by
oxidation, of maintaining an initial reflectance for a long period of time and of
avoiding preparation of a protective layer separately etc.
In addition, a transflective type polarizing film may be obtained by preparing the
above-mentioned reflective layer as a transflective type reflective layer, such as a
half-mirror etc. that reflects and transmits light. A transflective type polarizing film is
usually prepared in the backside of a liquid crystal cell and it may form a liquid
crystal display unit of a type in which a picture is displayed by an incident light
reflected from a view side (display side) when used in a comparatively well-lighted
atmosphere. And this unit displays a picture, in a comparatively dark atmosphere,
using embedded type light sources, such as a back light built in backside of a
transflective type polarizing film. That is, the transflective type polarizing film is
useful to obtain of a liquid crystal display of the type that saves energy of light
sources, such as a back light, in a well-lighted atmosphere, and can be used with a
built-in light source if needed in a comparatively dark atmosphere etc.
The above-mentioned polarizing film may be used as elliptically polarizing film or
circularly polarizing film on which the retardation plate is laminated. A description of
the above-mentioned elliptically polarizing film or circularly polarizing film will be
made in the following paragraph. These polarizing films change linearly polarized
light into elliptically polarized light or circularly polarized light, elliptically polarized
light or circularly polarized light into linearly polarized light or change the
polarization direction of linearly polarization by a function of the retardation plate.
As a retardation plate that changes circularly polarized light into linearly polarized
light or linearly polarized light in to circularly polarized light, what is called a quarter
wavelength plate (also called λ/4 plate) is used. Usually, half-wavelength plate (also
called λ/2 plate) is used, when changing the polarization direction of linearly
polarized light.
Elliptically polarizing film is effectively used to give a monochrome display without
above-mentioned coloring by compensating (preventing) coloring (blue or yellow
color) produced by birefringence of a liquid crystal layer of a super twisted nematic
(STN) type liquid crystal display. Furthermore, a polarizing film in which
three-dimensional refractive index is controlled may also preferably compensate
(prevent) coloring produced when a screen of a liquid crystal display is viewed from
an oblique direction. Circularly polarizing film is effectively used, for example, when
adjusting a color tone of a picture of a reflection type liquid crystal display that
provides a colored picture, and it also has function of antireflection. For example, a
retardation plate may be used that compensates coloring and viewing angle, etc.
caused by birefringence of various wavelength plates or liquid crystal layers etc.
Besides, optical characteristics, such as retardation, may be controlled using
laminated layer with two or more sorts of retardation plates having suitable
retardation value according to each purpose. As retardation plates, birefringence films
formed by stretching films comprising suitable polymers, such as polycarbonates,
norbornene type resins, polyvinyl alcohols, polystyrenes, poly methyl methacrylates,
polypropylene; polyallylates and polyamides; oriented films comprising liquid crystal
materials, such as liquid crystal polymer; and films on which an alignment layer of a
liquid crystal material is supported may be mentioned. A retardation plate may be a
retardation plate that has a proper phase difference according to the purposes of use,
such as various kinds of wavelength plates and plates aiming at compensation of
coloring by birefringence of a liquid crystal layer and of visual angle, etc., and maybe
a retardation plate in which two or more sorts of retardation plates is laminated so that
optical properties, such as retardation, may be controlled.
The above-mentioned elliptically polarizing film and an above-mentioned reflected
type elliptically polarizing film are laminated plate combining suitably a polarizing
film or a reflection type polarizing film with a retardation plate. This type of
elliptically polarizing film etc. may be manufactured by combining a polarizing film
(reflected type) and a retardation plate, and by laminating them one by one separately
in the manufacture process of a liquid crystal display. On the other hand, the
polarizing film in which lamination was beforehand carried out and was obtained as
an optical film, such as an elliptically polarizing film, is excellent in a stable quality, a
workability in lamination etc., and has an advantage in improved manufacturing
efficiency of a liquid crystal display.
A viewing angle compensation film is a film for extending viewing angle so that a
picture may look comparatively clearly, even when it is viewed from an oblique
direction not from vertical direction to a screen. As such a viewing angle
compensation retardation plate, in addition, a film having birefringence property that
is processed by uniaxial stretching or orthogonal bidirectional stretching and a
bidriectionally stretched film as inclined orientation film etc. may be used. As inclined
orientation film, for example, a film obtained using a method in which a heat
shrinking film is adhered to a polymer film, and then the combined film is heated and
stretched or shrinked under a condition of being influenced by a shrinking force, or a
film that is oriented in oblique direction may be mentioned. The viewing angle
compensation film is suitably combined for the purpose of prevention of coloring
caused by change of visible angle based on retardation by liquid crystal cell etc. and
of expansion of viewing angle with good visibility.
Besides, a compensation plate in which an optical anisotropy layer consisting of an
alignment layer of liquid crystal polymer, especially consisting of an inclined
alignment layer of discotic liquid crystal polymer is supported with triacetyl cellulose
film may preferably be used from a viewpoint of attaining a wide viewing angle with
good visibility.
The polarizing film with which a polarizing film and a brightness enhancement film
are adhered together is usually used being prepared in a backside of a liquid crystal
cell. A brightness enhancement film shows a characteristic that reflects linearly
polarization light with a predetermined polarization axis, or circularly polarization
light with a predetermined direction, and that transmits other light, when natural light
by back lights of a liquid crystal display or by reflection from a back-side etc., comes
in. The polarizing film, which is obtained by laminating a brightness enhancement
film to a polarizing film, thus does not transmit light without the predetermined
polarization state and reflects it, while obtaining transmitted light with the
predetermined polarization state by accepting a light from light sources, such as a
backlight. This polarizing film makes the light reflected by the brightness
enhancement film further reversed through the reflective layer prepared in the
backside and forces the light re-enter into the brightness enhancement film, and
increases the quantity of the transmitted light through the brightness enhancement
film by transmitting a part or all of the light as light with the predetermined
polarization state. The polarizing film simultaneously supplies polarized light that is
difficult to be absorbed in a polarizer, and increases the quantity of the light usable for
a liquid crystal picture display etc., and as a result luminosity maybe improved. That
is, in the case where the light enters through a polarizer from backside of a liquid
crystal cell by the back light etc. without using a brightness enhancement film, most
of the light, with a polarization direction different from the polarization axis of a
polarizer, is absorbed by the polarizer, and does not transmit through the polarizer.
This means that although influenced with the characteristics of the polarizer used,
about 50 percent of light is absorbed by the polarizer, the quantity of the light usable
for a liquid crystal picture display etc. decreases so much, and a resulting picture
displayed becomes dark. A brightness enhancement film does not enter the light with
the polarizing direction absorbed by the polarizer into the polarizer but reflects the
light once by the brightness enhancement film, and further makes the light reversed
through the reflective layer etc. prepared in the backside to re-enter the light into the
brightness enhancement film. By this above-mentioned repeated operation, only when
the polarization direction of the light reflected and reversed between the both
becomes to have the polarization direction which may pass a polarizer, the brightness
enhancement film transmits the light to supply it to the polarizer. As a result, the light
from a backlight may be efficiently used for the display of the picture of a liquid
crystal display to obtain a bright screen.
The suitable films are used as the above-mentioned brightness enhancement film.
Namely, multilayer thin film of a dielectric substance; a laminated film that has the
characteristics of transmitting a linearly polarized light with a predetermined
polarizing axis, and of reflecting other light, such as the multilayer laminated film of
the thin film having a different refractive-index anisotropy (D-BEF and others
manufactured by 3M Co., Ltd.); an aligned film of cholesteric liquid-crystal polymer;
a film that has the characteristics of reflecting a circularly polarized light with either
left-handed or right-handed rotation and transmitting other light, such as a film on
which the aligned cholesteric liquid crystal layer is supported (PCF350 manufactured
by NITTO DENKO CORPORATION, Transmax manufactured by Merck Co., Ltd.,
and others); etc. may be mentioned.
Therefore, in the brightness enhancement film of a type that transmits a linearly
polarized light having the above-mentioned predetermined polarization axis, by
arranging the polarization axis of the transmitted light and entering the light into a
polarizing film as it is, the absorption loss by the polarizing film is controlled and the
polarized light can be transmitted efficiently. On the other hand, in the brightness
enhancement film of a type that transmits a circularly polarized light as a cholesteric
liquid-crystal layer, the light may be entered into a polarizer as it is, but it is desirable
to enter the light into a polarizer after changing the circularly polarized light to a
linearly polarized light through a retardation plate, taking control an absorption loss
into consideration. In addition, a circularly polarized light is convertible into a linearly
polarized light using a quarter wavelength plate as the retardation plate.
A retardation plate that works as a quarter wavelength plate in a wide wavelength
ranges, such as a visible-light region, is obtained by a method in which a retardation
layer working as a quarter wavelength plate to a pale color light with a wavelength of
550 nm is laminated with a retardation layer having other retardation characteristics,
such as a retardation layer working as a half-wavelength plate. Therefore, the
retardation plate located between a polarizing film and a brightness enhancement film
may consist of one or more retardation layers.
In addition, also in a cholesteric liquid-crystal layer, a layer reflecting a circularly
polarized light in a wide wavelength ranges, such as a visible-light region, may be
obtained by adopting a configuration structure in which two or more layers with
different reflective wavelength are laminated together. Thus a transmitted circularly
polarized light in a wide wavelength range may be obtained using this type of
cholesteric liquid-crystal layer.
Moreover, the polarizing film may consist of multi-layered film of laminated layers of
a polarizing film and two of more of optical layers as the above-mentioned separated
type polarizing film. Therefore, a polarizing film may be a reflection type elliptically
polarizing film or a semi-transmission type elliptically polarizing film, etc. in which
the above-mentioned reflection type polarizing film or a transflective type polarizing
film is combined with above described retardation plate respectively.
Although an optical film with the above described optical layer laminated to the
polarizing film may be formed by a method in which laminating is separately carried
out sequentially in manufacturing process of a liquid crystal display etc., an optical
film in a form of being laminated beforehand has an outstanding advantage that it has
excellent stability in quality and assembly workability, etc., and thus manufacturing
processes ability of a liquid crystal display etc. may be raised. Proper adhesion means,
such as an adhesive layer, may be used for laminating. On the occasion of adhesion of
the above described polarizing film and other optical films, the optical axis may be set
as a suitable configuration angle according to the target retardation characteristics etc.
In the polarizing film mentioned above and the optical film in which at least one layer
of the polarizing film is laminated, an adhesive layer may also be prepared for
adhesion with other members, such as a liquid crystal cell etc. As pressure sensitive
adhesive that forms adhesive layer is not especially limited, and, for example, acrylic
type polymers; silicone type polymers; polyesters, polyurethanes, polyamides,
polyethers; fluorine type and rubber type polymers may be suitably selected as a base
polymer. Especially, a pressure sensitive adhesive such as acrylics type pressure
sensitive adhesives maybe preferably used, which is excellent in optical transparency,
showing adhesion characteristics with moderate wettability, cohesiveness and
adhesive property and has outstanding weather resistance, heat resistance, etc.
Moreover, an adhesive layer with low moisture absorption and excellent heat
resistance is desirable. This is because those characteristics are required in order to
prevent foaming and peeling-off phenomena by moisture absorption, in order to
prevent decrease in optical characteristics and curvature of a liquid crystal cell caused
by thermal expansion difference etc. and in order to manufacture a liquid crystal
display excellent in durability with high quality.
The adhesive layer may contain additives, for example, such as natural or synthetic
resins, adhesive resins, glass fibers, glass beads, metal powder, fillers comprising
other inorganic powder etc., pigments, colorants and antioxidants. Moreover, it may
be an adhesive layer that contains fine particle and shows optical diffusion nature.
Proper method may be carried out to attach an adhesive layer to one side or both sides
of the optical film. As an example, about 10 to 40 weight % of the pressure sensitive
adhesive solution in which a base polymer or its composition is dissolved or dispersed,
for example, toluene or ethylacetate or a mixed solvent of these two solvents is
prepared. A method in which this solution is directly applied on a polarizing film top
or a optical film top using suitable developing methods, such as flow method and
coating method, or a method in which an adhesive layer is once formed on a separator,
as mentioned above, and is then transferred on a polarizing film or an optical film
may be mentioned.
An adhesive layer may also be prepared on one side or both sides of a polarizing film
or an optical film as a layer in which pressure sensitive adhesives with different
composition or different kind etc. are laminated together. Moreover, when adhesive
layers are prepared on both sides, adhesive layers that have different compositions,
different kinds or thickness, etc. may also be used on front side and backside of a
polarizing film or an optical film. Thickness of an adhesive layer may be suitably
determined depending on a purpose of usage or adhesive strength, etc., and generally
is 1 to 500 μm, preferably 5 to 200 μm, and more preferably 10 to 100 μm.
A temporary separator is attached to an exposed side of an adhesive layer to prevent
contamination etc., until it is practically used. Thereby, it can be prevented that
foreign matter contacts adhesive layer in usual handling. As a separator, without
taking the above-mentioned thickness conditions into consideration, for example,
suitable conventional sheet materials that is coated, if necessary, with release agents,
such as silicone type, long chain alkyl type, fluorine type release agents, and
molybdenum sulfide may be used. As a suitable sheet material, plastics films, rubber
sheets, papers, cloths, no woven fabrics, nets, foamed sheets and metallic foils or
laminated sheets thereof may be used.
In addition, in the present invention, ultraviolet absorbing property may be given to
the above-mentioned each layer, such as a polarizer for a polarizing film, a transparent
protective film and an optical film etc. and an adhesive layer, using a method of
adding UV absorbents, such as salicylic acid ester type compounds, benzophenol type
compounds, benzotriazol type compounds, cyano acrylate type compounds, and
nickel complex salt type compounds.
An optical film of the present invention may be preferably used for manufacturing
various equipment, such as liquid crystal display, etc. Assembling of a liquid crystal
display may be carried out according to conventional methods. That is, a liquid crystal
display is generally manufactured by suitably assembling several parts such as a
liquid crystal cell, optical films and, if necessity, lighting system, and by incorporating
driving circuit. In the present invention, except that an optical film by the present
invention is used, there is especially no limitation to use any conventional methods.
Also any liquid crystal cell of arbitrary type, such as TN type, and STN type, π type
may be used.
Suitable liquid crystal displays, such as liquid crystal display with which the
above-mentioned optical film has been located at one side or both sides of the liquid
crystal cell, and with which a backlight or a reflective plate is used for a lighting
system may be manufactured. In this case, the optical film by the present invention
may be installed in one side or both sides of the liquid crystal cell. When installing the
optical films in both sides, they may be of the same type or of different type.
Furthermore, in assembling a liquid crystal display, suitable parts, such as diffusion
plate, anti-glare layer, antireflection film, protective plate, prism array, lens array
sheet, optical diffusion plate, and backlight, may be installed in suitable position in
one Layer or two or more layers.
Subsequently, organic electro luminescence equipment (organic EL display) will be
explained. Generally, inorganic EL display, a transparent electrode, an organic
luminescence layer and a metal electrode are laminated on a transparent substrate in
an order configuring an illuminant (organic electro luminescence illuminant). Here, an
organic luminescence layer is a laminated material of various organic thin films, and
much compositions with various combination are known, for example, a laminated
material of hole injection layer comprising triphenylamine derivatives etc., a
luminescence layer comprising fluorescent organic solids, such as anthracene; a
laminated material of electronic injection layer comprising such a luminescence layer
and perylene derivatives, etc.; laminated material of these hole injection layers,
luminescence layer, and electronic injection layer etc.
An organic EL display emits light based on a principle that positive hole and electron
are injected into an organic luminescence layer by impressing voltage between a
transparent electrode and a metal electrode, the energy produced by recombination of
these positive holes and electrons excites fluorescent substance, and subsequently
light is emitted when excited fluorescent substance returns to ground state. A
mechanism called recombination which takes place in a intermediate process is the
same as a mechanism in common diodes, and, as is expected, there is a strong
non-linear relationship between electric current and luminescence strength
accompanied by rectification nature to applied voltage.
In an organic EL display, in order to take out luminescence in an organic
luminescence layer, at least one electrode must be transparent. The transparent
electrode usually formed with transparent electric conductor, such as indium tin oxide
(ITO), is used as an anode. On the other hand, in order to make electronic injection
easier and to increase luminescence efficiency, it is important that a substance with
small work function is used for cathode, and metal electrodes, such as Mg—Ag and
Al—Li, are usually used.
In organic EL display of such a configuration, an organic luminescence layer is
formed by a very thin film about 10 nm in thickness. For this reason, light is
transmitted nearly completely through organic luminescence layer as through
transparent electrode. Consequently, since the light that enters, when light is not
emitted, as incident light from a surface of a transparent substrate and is transmitted
through a transparent electrode and an organic luminescence layer and then is
reflected by a metal electrode, appears in front surface side of the transparent
substrate again, a display side of the organic EL display looks like mirror if viewed
from outside.
In an organic EL display containing an organic electro luminescence illuminant
equipped with a transparent electrode on a surface side of an organic luminescence
layer that emits light by impression of voltage, and at the same time equipped with a
metal electrode on a back side of organic luminescence layer, a retardation plate may
be installed between these transparent electrodes and a polarizing film, while
preparing the polarizing film on the surface side of the transparent electrode.
Since the retardation plate and the polarizing film have function polarizing the light
that has entered as incident light from outside and has been reflected by the metal
electrode, they have an effect of making the mirror surface of metal electrode not
visible from outside by the polarization action. If a retardation plate is configured
with a quarter wavelength plate and the angle between the two polarization directions
of the polarizing film and the retardation plate is adjusted to π/4, the mirror surface of
the metal electrode may be completely covered.
This means that only linearly polarized light component of the external light that
enters as incident light into this organic EL display is transmitted with the work of
polarizing film. This linearly polarized light generally gives an elliptically polarized
light by the retardation plate, and especially the retardation plate is a quarter
wavelength plate, and moreover when the angle between the two polarization
directions of the polarizing film and the retardation plate is adjusted to π/4, it gives a
circularly polarized light.
This circularly polarized light is transmitted through the transparent substrate, the
transparent electrode and the organic thin film, and is reflected by the metal electrode,
and then is transmitted through the organic thin film, the transparent electrode and the
transparent substrate again, and is turned into a linearly polarized light again with the
retardation plate. And since this linearly polarized light lies at right angles to the
polarization direction of the polarizing film, it cannot be transmitted through the
polarizing film. As the result, mirror surface of the metal electrode may be completely
covered.
EXAMPLE
Examples showing constitution and effects of the present invention will be concretely
described hereinafter. Measured value is obtained by the following methods.
(Adhesive Strength)
A polarizing film was pulled using a tensile testing machine at a peeling angle of 90
degrees, and a peeling speed of 300 mm/minute, and tensile strength (N/25 mm) was
measured.
(Retardation Within a Plane)
Measurement was performed with an automatic birefringence measuring equipment
manufactured by Oji Scientific Instruments KOBRA21ADH.
(Moisture Permeability)
Measurement was performed according to the moisture-permeability examination
(cup method) of JIS Z0208. A weight (g) of water vapor that passes a sample having
0.1 mm in thickness and area of 1 m2 in 24 hours under a condition of 90% of relative
humidity difference.
(Elastic Modulus)
An elastic modulus (N/mm2) was measured according to the tensile testing examining
method of JIS K7127.
(Surface Free Energy)
Measurement was performed by contact-angle measurement method using the
extended Forks' expression (water, methylene iodide, and alpha-bromonaphthalene
were used as medium).
(Light Transmittance)
A transmittance of one sheet of a polarizing film or a protection film was measured
using the spectrophotometer (made Murakami Color Research Laboratory, CMS-500).
In addition, the transmittance of a polarizing film or a protection film is Y value in
which visibility compensation was twice carried out by the visual field (luminous
source C) of JIS Z8701.
(Polarization Degree)
A transmittance (H0) when two sheets of the same polarizing films were piled up so
that polarization axis may be parallel, and a transmittance (H90) when two sheets of
the same polarizing films were piled up so that polarization axis may be orthogonal
were measured using the above described spectrophotometer to obtain a polarization
degree from the following formula.
In addition, the transmittance (H0) in the case of being parallel and the transmittance
in the case of being orthogonal (H90) are Y values in which visibility compensation
was twice carried out by the visual field (luminous source C).
Example 1
(Polarizer)
After a polyvinyl alcohol film with a degree of polymerization 2400 and a thickness
of 80 micrometers was swelled in warm water at 30 degree C., it was dyed while
being stretched in 3 times in an iodine/potassium iodide aqueous solution at 30 degree
C. Then, after being stretched in 40 to 60-degree C. warm water, the film was
stretched again while being cross-linked in boric acid aqueous solution. In this case
stretching was carried out so that a total stretching ratio might be 6 times. Finally,
adjustment of a hue was performed in 30 to 40-degree C. potassium iodide aqueous
solution, and a polarizing film was dried so that a moisture regain might be 5 to 12%
of range was obtained.
(Protection Film)
(2) Title: Liquid crystal display viewable under all
lighting conditions
APPL. NO.: 892867
以下是專利發明詳細資料
1. A method of making an LCD viewable under all lighting condition from an LCD
having a liquid crystal cell positioned between a first dichroic polarizer and a
second dichroic polarizer, and a backlight assembly positioned behind the
second dichroic polarizer, the method comprising the steps of:
(a) positioning an anti-reflection layer with a surface of haze value less than
15% in front of the first dichroic polarizer; and
(b) positioning a diffusing transflector between the backlight assembly and the
second dichroic polarizer, the diffusing transflector comprising a diffusing
element and a reflective polarizer, the diffusing element being a transparent
substrate layer or a corrugated surface having a haze value of 10% to 85%, and
the reflective polarizer being positioned with its transmission direction forming
an angle of 0 degree, between 0 and 60 degrees, or between -60 and 0 degrees to
the transmission direction of the second dichroic polarizer.
2. A method of making an LCD viewable under all lighting condition from an LCD
having a liquid crystal cell positioned between a first dichroic polarizer and a
second dichroic polarizer, a backlight assembly positioned behind the second
dichroic polarizer, and a reflective polarizer positioned between the backlight
assembly and the second dichroic polarizer with its transmission direction
forming an angle of 0 degree, between 0 and 60 degrees, or between -60 and 0
degrees to the transmission direction of the second dichroic polarizer, the
method comprising the steps of:
(a) positioning an anti-reflection layer with a surface of haze value less than
15% in front of the first dichroic polarizer; and
(b) positioning a diffusing element between the second dichroic polarizer and
the reflective polarizer, the diffusing element being a transparent substrate layer
or a corrugated surface having a haze value of 10% to 85%.
3.
A method of making an LCD viewable under all lighting condition from an
LCD having a liquid crystal cell positioned between a first dichroic polarizer
and a second dichroic polarizer, a backlight assembly positioned behind the
second dichroic polarizer, and a diffusing transflector positioned between the
backlight assembly and the second dichroic polarizer, the diffusing transflector
comprising a diffusing element and a reflective polarizer, the diffusing element
being a transparent substrate layer or a corrugated surface having a haze value of
10% to 85%, and the reflective polarizer having its transmission direction
forming an angle of 0 degree, between 0 and 60 degrees, or between -60 and 0
degrees to the transmission direction of the second dichroic polarizer, the
method comprising the step of positioning an anti-reflection layer with a surface
of haze value less than 15% in front of the first dichroic polarizer.
4. A method of making an LCD viewable under all lighting condition from an LCD
having a liquid crystal cell positioned between a first dichroic polarizer with
anti-reflection treatment and surface haze less than 15% and a second dichroic
polarizer, a backlight assembly positioned behind the second dichroic polarizer,
the method comprising the step of: positioning a diffusing transflector between
the backlight assembly and the second dichroic polarizer, the diffusing
transflector comprising a diffusing element and a reflective polarizer, the
diffusing element being a transparent substrate layer or a corrugated surface
having a haze value of 10% to 85%, and the reflective polarizer being positioned
with its transmission direction forming an angle of 0 degree, between 0 and 60
degrees, or between -60 and 0 degrees to the transmission direction of the
second dichroic polarizer.
5.
A method of making an LCD viewable under all lighting condition from an
LCD having a liquid crystal cell positioned between a first dichroic polarizer
and a second dichroic polarizer, a backlight assembly positioned behind the
second dichroic, polarizer, and a diffusing element being a transparent substrate
layer or a corrugated surface having a haze value of 10% to 85% in front of the
backlight assembly, the method comprising the steps of:
(a) positioning an anti-reflection layer with a surface of haze value less than
15% in front of the first dichroic polarizer; and
(b) positioning a transflector between the backlight assembly and the diffusing
element, the transflector being a reflective polarizer positioned such that its
transmission direction forms an angle of 0 degree, between 0 and 60 degrees, or
between -60 and 0 degrees to the transmission direction of the second dichroic
polarizer.
6.
A method of making an LCD viewable under all lighting condition from an
LCD having a liquid crystal cell positioned between a first dichroic polarizer
with anti-reflection treatment and surface haze less than 15% and a second
dichroic polarizer, a backlight assembly positioned behind the second dichroic
polarizer, and a reflective polarizer positioned between the second dichroic
polarizer and the backlight assembly with its transmission direction forming an
angle of 0 degree, between 0 and 60 degrees, or between -60 and 0 degrees to
the transmission direction of the second dichroic polarizer, the method
comprising the step of: positioning a diffusing element between the second
dichroic polarizer and the reflective polarizer, the diffusing element being a
transparent substrate layer or a corrugated surface having a haze value of 10% to
85%.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a liquid crystal display device, and more particularly, to an
improved transflective liquid crystal display viewable under all lighting conditions,
such as total dark, indoor lighting, in shade, medium sunlight, strong sunlight, and
direct sunlight, without excessive power consumption.
2. Description of the Related Art
Many features of liquid crystal displays (LCDs), such as light weight and size, low
power consumption and high resolution, make LCDs a popular choice in various
electronic applications. These applications include digital cameras, palm PCs,
notebook computers, tablet PCs, workstations, and navigation systems in
automobiles, marine vessels, and airplanes. Most of these applications are portable
and can be transited between indoor and outdoor. Thus, there is a need to develop a
display to accommodate both indoor and outdoor environments and perform
regardless of different lighting conditions. Various types of LCDs have evolved
around this need.
With reference to FIG. 1, a conventional transmissive liquid crystal display (LCD) is
shown. The LCD includes a liquid crystal cell 100 comprising a front transparent
electrode with color filters 101, a rear transparent electrode (pixel portions) 102, and
a layer of liquid crystals 103 between the front and rear transparent electrodes. The
liquid crystal cell 100 is usually sandwiched by a front glass substrate 104 and a rear
glass substrate 105. A first dichroic polarizer 106 adheres to the front surface of the
front glass 104. Likewise, a rear dichroic polarizer 107 adheres to the rear surface of
the rear glass 105. The transmissive display further includes a backlight cell
assembly 108. A regular LCD contains 1 to 4 lamps that provide between 100 and
300 nits of illumination 110 at the surface of LCD. This level of brightness enables
this type of LCD to perform beautifully indoors. In an outdoor setting, the anti-glare
surface of the first polarizer 106 reflects and diffuses about 3% to 5% of the ambient
sunlight A to a viewer's eyes. The amount of background reflection 109 is strong,
overwhelming the illumination 110 from the backlight 108 and obscuring the image
generated by the LCD.
One approach used to improve the performance of this type of LCD under sunlight
is to apply an anti-reflection coating on the front surface. Although providing some
improvement, the anti-reflection coating alone is not sufficient to provide an LCD
viewable under direct sunlight. Further improvement is necessary.
Another solution commonly adopted is to increase the illumination of transmissive
LCDs for outdoor application by adding more lamps to the backlight cell. The term
"high-bright LCD" describes this modified transmissive LCD. In general, an LCD
requires at least 1000 nits of illumination to be viewable under sunlight. To reach
this level of brightness, an LCD requires 10 to 12 lamps. The additional lamps
consume more power, generate excessive heat, experience contrast washout and
require dimension and circuit alterations. Alterations of the LCD's dimensions and
circuits are costly. Thus, high bright LCDs generally create more problems than they
solve.
Referring now to FIG. 2, a common construction of a reflective LCD is shown. A
reflective LCD does not have problems with power consumption since ambient light
A is used for illumination. A reflector 201 is positioned behind a liquid crystal
display assembly 204. Generally, the reflector 201 is an opaque surface of highly
reflective material (such as aluminum or silver) with 90% to 98% reflection. The
LCD display assembly 204 may also contain a second dichroic polarizer (not
shown). A portion of ambient light 202 passes the liquid crystal display assembly
and reaches the reflective surface of reflector 201. The reflector 201 reflects
ambient light portion 202 and uses it as the display's illumination 203. Because the
display's illumination is tied to the amount of ambient light provided, the visibility
of reflective LCD is highly surrounding-sensitive. Under strong ambient light, the
LCD has good illumination. However, LCD brightness diminishes as ambient light
decreases. This disadvantage of the reflective LCD strongly limits its applications.
With reference to FIGS. 3A and 3B, a "transflective LCD" is shown. The
transflective LCD was developed to overcome the shortcomings of the reflective
LCD. A major element of the transflective LCD is the "transflector", which is
partially transmissive and partially reflective. The transflector uses ambient light
and/or a backlight to illuminate the LCD. One type of transflective LCD
implements the transflector as a series of electrodes 301, where the electrodes 301
are imbedded within the compartment of pixel portions 102 of the liquid crystal cell
100. FIG. 3A shows the structure of a transflective LCD with transflective
electrodes 301. In FIG. 3B, the cropped partial area of the pixel portions 102 with
transflective electrodes 301 is shown. The transflective electrodes 301 have highly
reflective regions 301r and transmissive portions 301t contacting the transparent
electrodes of pixel portions 102. When ambient light A is not strong, the
transmissive portions 301t allow the transmission of light B from backlight cell 108
as the illumination 302 of LCD. When ambient light A is strong, the reflective
portions 301r reflect ambient light 303 entering the liquid crystal panel 100, and
send it back out as illumination 304 of LCD.
Still referring to FIGS. 3A and 3B, the visibility of the LCD is excellent when the
ambient light A is strong. However, the combination of reflective portions 301r and
transmissive portions 301t within the same domain (pixel portions 102) imposes
undesirable features on the LCD. The problems are more noticeable when the LCD
is used indoors, and include low brightness, loss of color, low contrast and a narrow
viewing angle. In addition, pixel size of the LCD is limited by the need to
accommodate both transmissive and reflective electrodes. The limited pixel size
results in increased manufacturing difficulties and costs for higher resolutions.
Another type of transflective LCD comprises a transflective plastic film as the
transflector, positioned in the rear of liquid crystal panel (not shown). Although easy
to construct, this type of transflective LCD has inefficient illumination. The
commonly used transflective films normally have 20% to 40% transmission
efficiency and 50% to 70% reflection efficiency. Thus, this type of transflective
LCD is not as bright as either purely reflective or purely transmissive LCD types.
In summary, a regular liquid crystal display can have satisfactory performance
either indoors or outdoors. A high bright LCD, though acceptable for both indoor
and outdoor applications, consumes high power and demands various
complimentary re-designs of the device system to accommodate the excessive heat.
Reflective LCDs do not perform well indoors. Transflective LCDs are limited by
pixel size and do not perform optimally under certain ambient light. Thus, there is a
great need to develop a liquid crystal display assembly that consumes low power
without excessive heat generation, and has good color, adequate brightness and
sufficient contrast under all lighting conditions.
SUMMARY OF THE INVENTION
Accordingly, one object of the invention is to provide a liquid crystal display with
good color, adequate brightness and sufficient contrast for outdoor applications.
A second object of the invention is to provide a liquid crystal display with good
color, adequate brightness and sufficient contrast for indoor applications.
A third object of the invention is to provide a liquid crystal display that is viewable
in direct sunlight with no alteration of the viewing angle.
A fourth object of the invention is to provide a liquid crystal display that is viewable
under direct sunlight and does not consume high power to cause excessive heat
generation.
To achieve these and other advantages and in accordance with the purpose of the
invention, as embodied and broadly described herein, the invention provides a liquid
crystal display viewable under all lighting conditions without excessive power
consumption. The LCD comprises a first dichroic polarizer, a second dichroic
polarizer, an anti-reflection layer positioned in front of the first dichroic polarizer
and a liquid crystal panel positioned between the first dichroic polarizer and the
second dichroic polarizer. In addition, the LCD comprises a backlight assembly
positioned behind the second dichroic polarizer. Finally, the LCD comprises a
diffusing transflector positioned between the backlight assembly and the second
dichroic polarizer. The diffusing transflector comprises a selective diffusing element
and a selective transflective element.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG.1 is a diagram of the structure of a conventional transmissive liquid crystal
display (related art).
FIG. 2 is a diagram of a common structure of a reflective LCD (related art).
FIG. 3a is a diagram of the structure of a transflective LCD with transflective
electrodes (related art).
FIG. 3b is a diagram of an enlarged cropped section of the pixel portions containing
the transflective electrodes of FIG. 3a (related art).
FIG. 4 is a diagram of one embodiment of the present invention.
FIG. 5 is a diagram of the spectrum measurements of a selective reflective polarizer
in the visible region.
FIG. 6 is a diagram of the propagations of the reflective lights through the diffusing
transflector.
FIG. 7 is a diagram of an alternative embodiment of the present invention.
FIG. 8 is a diagram of the structure of a 15" desktop monitor TFT LCD (related art).
FIG. 9 is a diagram of an embodiment of the present invention modifying a 15"
desktop monitor TFT LCD.
FIG. 10 is a diagram of a comparison of temperature measurements between the
monitor of FIG. 8 and the monitor of FIG. 9.
FIG. 11 is a diagram of the structure of a 14.2" notebook computer TFT LCD
(related art).
FIG. 12 is a diagram of an embodiment of the present invention modifying a 14.2"
notebook computer TFT LCD.
FIG. 13 is a diagram of the structure of a 10.4" Tablet TFT LCD (related art).
FIG. 14 is a diagram of an embodiment of the present invention modifying a 10.4"
Tablet TFT LCD.
FIG. 15 is a diagram of the structure of a 12.1" open frame high bright TFT LCD
(related art).
FIG. 16 is a diagram of an embodiment of the present invention modifying a 12.1"
open frame high bright TFT LCD.
FIG. 17 is a diagram of the structure of a 1.5" TFT LCD (related art).
FIG. 18 is a diagram of an embodiment of the present invention modifying a 1.5"
TFT LCD.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 4, an illustration of one embodiment of the present invention
is shown. Transflective LCD 400 includes a conventional liquid crystal display
panel 409. The transflective LCD 400 also includes a low reflection first polarizer
410. The rear side of low reflection first polarizer 410 is bonded to the front side of
LCD panel 409 using optical bonding material. The low reflection first polarizer
410 is composed of an anti-reflection (AR) layer 401 and a dichroic polarizer 402.
The anti-reflection layer 401 can be a high efficiency multi-layer anti-reflection
coating applied directly on the front surface of the dichroic polarizer 402. The
anti-reflection layer 401 can also be a separate transmissive substrate, glass or
plastic, with an AR coating on the front side. The rear side of the transmissive
substrate is bonded to the front side of dichroic polarizer 402 with an index-matched
optical bonding material to lower the reflection. The low reflection front surface 401
preferably is a low haze surface (less than 15% haze, haze being the surface
scattering luminescence over the luminescence of an object) with high efficient
multi-layer AR coating, which provides an anti-reflection surface with reflection
less than 1%. The low reflection front surface 401 produces less background
reflection 415 than the regular LCD front surface 106 described in FIG. 1 (by 5 to 8
folds). In addition, the low reflection surface 401 allows more efficient transmission
of ambient light A and provides a stronger light beam 406 to be used as the
reflective illumination 408. The transflective LCD 400 also includes a second
dichroic polarizer 403 optically bonded to the rear of liquid crystal panel 409. In this
embodiment, the transmission directions of the two dichroic polarizers 402 and 403
are preferably in parallel. Such an arrangement of 402 and 403 provides a
transflective LCD that is direct sunlight readable without backlight. However, the
transmission directions of 402 and 403 can also vary from 0 to 90 degrees. It is also
preferred that AR coating is applied to the rear surface of the second dichroic
polarizer 403 (not shown). The AR coating maximizes entry of light beam 406 for
reflective illumination.
Still referring to FIG. 4, the transflective LCD 400 further comprises a diffusing
transflector 411 positioned to the rear side of second dichroic polarizer 403. The
diffusing transflector 411 comprises a diffusing element 404 and a selected
reflective polarizer 405. The reflective polarizer 405 preferably has absorption of
incident energy less than 10%. The reflective polarizer also has an extinction
coefficient, defined as the transmission of p state polarization over the transmission
of s state polarization, ranging from 1.5 to 9. In addition, the transmission axis of
the reflective polarizer 405 is parallel to or within (+/-) 60 degrees of the
transmission direction of the second dichroic polarizer 403. Reflective polarizer 405
can be formed with multiple sheets of a selective reflective polarizer with optimized
transmission directions. Reflective polarizer 405 can also be a diffuser laminated
selective reflective polarizer, which has improved mechanical and thermal
properties.
With reference to FIG. 4, the diffusing element 404 also has a corrugated diffusing
surface with haze in the range of 10% to 85%. The corrugated surface can be a
roughened surface on a transmissive polymeric substrate, such as PEN
(polyethylene naphthalate), PC (polycarbonate), or PET (polyethylene erephthalate).
The corrugated surface also can be a dielectric material, such as TiO2 (Titanium
dioxide), Ta2O5(Tantalum oxide), SiO2 (Silicon dioxide), SiN (Silicon nitride), ITO
(Indium tin oxide), ZnS (Zinc sulphide), Al2O3 (Aluminum oxide), LaF3
(Lanthanum fluoride), MgF2 (Magnesium fluoride), Ge (Germanium) or Si (Silicon)
deposited on a transmissive substrate. The corrugated surface can further be small
metal particles, ranging in size from 10 nm to 10000 nm, deposited directly on the
rear side of the second polarizer or on a separate transmissive substrate. Choices of
metal include silver, gold, aluminum, copper, titanium, tantalum, chromium, nickel
or an alloy thereof. One or more sheets of lose-packed or optically bonded
transmissive substrate with the corrugated surface can make up the diffusing
element 404. In addition, diffusing element 404 can be optically bonded to the rear
surface of the second dichroic polarizer 403 and to the front surface of the reflective
polarizer 405.
Still referring to FIG. 4, the transflective LCD 400 further includes a high efficiency
backlight cell assembly 420. Backlight assembly 420 preferably contains one or
two orthogonal sheets of brightness enhancement films and other multiple
polymeric films for enhancing transmission and optical performances. However,
any conventional backlight cell or high bright backlight cell with edge lamps or
backside lamps can be used.
With reference to FIG. 4, the transflective LCD 400 has a maximized transmission
407 with backlight transmitted by a recovery effect from the reflective polarizer 405
and the backlight cell 420. This transmission illumination coupled with the
incorporation of the low reflection front surface 401 creates good optical
performance for all indoor and some outdoor conditions, such as outdoor in shade.
In addition, diffusing transflector 411 optimizes the total reflective illumination 408.
A diffusing element with a corrugated surface to randomize light input further
optimizes the reflection efficiency of the transflector, thus providing sufficient
reflective illumination.
Referring now to FIG. 5, a diagram of the spectrum measurements of a selective
reflective polarizer in the visible region is shown. The diagram displays the
extinction coefficients (the transmission of p state polarization over the
transmission of s state polarization) for different wavelength values. The average
extinction coefficient is 3, or 75% over 25%.
With reference to FIG. 6, a diagram of the propagations of the reflective lights
through the diffusing transflector is shown. The light 406 entering the LCD consists
mainly of transmissive p polarization 601 and also has s polarization 602. The p
polarization and s polarization components are slightly randomized when they pass
the diffusing element 404. The p polarization 601 yields mainly p polarization 601t
and also has s polarization 603. When 601t reaches the reflective surface 405 (with
extinction coefficient 3.0), approximately 25% reflects as reflective illumination
601tR. When s polarization 603 reaches the reflective surface of 405,
approximately 75% reflects as reflective illumination 603R. By the similar
propagation mechanisms, reflective illuminations 602tR and 602R are produced by
s polarization 602. The transmissions of the reflected beams 604, 605, 606, and 607,
additively generate the total reflective illumination 408. Under a very strong
ambient light, the reflective illumination 408 is sufficient to overcome the front
surface background reflection 415 (FIG. 4), and to facilitate the viewing of the
images under the most challenging conditions.
Referring now to FIG. 7, an illustration of an alternative embodiment of the present
invention is shown. The transflective LCD 700 comprises a conventional liquid
crystal display panel 409. The transflective LCD 700 further comprises a low
reflection first polarizer 410. The rear side of low reflection first polarizer 410 is
bonded to the front side of LCD panel 409 using optical bonding material. The low
reflection first polarizer 410 is composed of an anti-reflection (AR) layer 401 and a
dichroic polarizer 402. The anti-reflection layer 401 can be a high efficiency
multi-layer anti-reflection coating applied directly on the front surface of the
dichroic polarizer 402. The anti-reflection layer 401 can also be a separate
transmissive substrate, glass or plastic, with an AR coating on the front side. The
rear side of the transmissive substrate is bonded to the front side of dichroic
polarizer 402 with an index-matched optical bonding material to lower the reflection.
The low reflection front surface 401 preferably is a low haze surface (less than 15%
haze) with high efficient multi-layer AR coating, which provides an anti-reflection
efficiency of less than 1%. The low reflection front surface 401 produces less
background reflection 415 than the regular LCD front surface 106 described in FIG.
1 (by 5 to 8 folds). In addition, the low reflection surface 401 allows more efficient
transmission of ambient light A and provides a stronger light beam 406 to be used as
the reflective illumination 408. The transflective LCD 700 also includes a second
dichroic polarizer 403 optically bonded to the rear of liquid crystal panel 409. In this
embodiment, the transmission directions of the two dichroic polarizers 402 and 403
are preferably in parallel. Such an arrangement of 402 and 403 provides a
transflective LCD that is direct sunlight readable without backlight. However, the
transmission directions of 402 and 403 can also vary from 0 to 90 degrees. It is also
preferred that AR coating is applied to the rear surface of the rear dichroic polarizer
403 (not shown). The AR coating maximizes entry of light beam 406 for reflective
illumination.
Still referring to FIG. 7, the transflective LCD 700 further comprises a diffusing
transflector 711 positioned to the rear side of second dichroic polarizer 403. The
diffusing transflector 711 is composed of a diffusing element 404 and a selective
beam splitter 705. The transmission of the beam splitter 705 ranges from 30% to
85%. It is preferred the beam splitter 705 is a multi-layer coating of dielectric
material directly deposited to the rear surface of the diffusing element 404. However,
the beam splitter 705 can also be a multi-layer dielectric coating deposited on the
front surface of a transmissive substrate. The coated transmissive separate substrate
is positioned on the rear side of diffusing element 404.
With reference to FIG. 7, the diffusing element 404 preferably has a corrugated
surface with haze in the range of 10% to 85%. The corrugated surface can be a
roughened surface on a transmissive polymeric substrate, such as PEN
(polyethylene naphthalate), PC (polycarbonate), or PET (polyethylene erephthalate).
The corrugated surface also can be a dielectric material, such as TiO2 (Titanium
dioxide), Ta2O5 (Tantalum oxide), SiO2 (Silicon dioxide), SiN (Silicon nitride),
ITO (Indium tin oxide), ZnS (Zinc sulphide), Al2O3 (Aluminum oxide), LaF3
(Lanthanum fluoride), MgF2 (Magnesium fluoride), Ge (Germanium) or Si (Silicon)
deposited on a transmissive substrate. The corrugated surface can further be small
metal particles, ranging in size from 10 nm to 10000 nm, deposited directly on the
rear side of the second polarizer or on a separate transmissive substrate. Choices of
metal include silver, gold, aluminum, copper, titanium, tantalum, chromium, nickel
or an alloy thereof. One or more sheets of lose-packed or optically bonded
transmissive substrate with the corrugated surface can make up the diffusing
element 404. Diffusing element 404 can be optically bonded to the front surface of
the beam splitter 705, provided the beam splitter 705 is a separate substrate, as
described above, to form the diffusing transflector 711, which can be optically
bonded to the rear side of the second dichroic polarizer 403, as shown, or the front
side of the second dichroic polarizer 403, not shown.
Still referring to FIG. 7, the transflective LCD 700 further includes a high efficiency
backlight cell assembly 420. Backlight assembly 420 preferably contains one or
two orthogonal sheets of brightness enhancement films and other multiple
polymeric films for enhancing transmission and optical performances. However,
any conventional backlight cell or high bright backlight cell, with edge lamps or
backside lamps, can be used.
Commercial TFT LCDs of various sizes and structures can easily be modified in
accordance with the teachings of the present invention to generate LCDs viewable
under direct sunlight. Optimal viewing performances are obtained by adjusting
proper orientations of the diffusing element and the reflective polarizer according to
the polarization transmission characteristics of the existing liquid crystal display
panel. The following examples illustrate how different commercial TFT LCDs can
be modified in accordance with the teachings of the present invention to generate
transflective LCDs.
EXAMPLE 1
A Direct Sunlight Readable 15" TFT LCD
Referring now to FIG. 8, a diagram of the structure of a 15" desktop monitor Thin
Film Transistor Liquid Crystal Display (TFT LCD) is shown (related art). The LCD
800 comprises a display unit 801 with a liquid crystal panel sandwiched between a
pair of dichroic polarizers. The dichroic polarizers have off-axis transmission
directions. The backlight cell 810 includes a diffusive reflector 805, a wave guide
plate with four lamps 804, a rear diffuser 803 positioned in front of wave guide
plate 804, a sheet of brightness enhancement film 802 positioned in the front side of
rear diffuser 803 and a front diffuser 806 positioned in front of the brightness
enhancement film 802. The TFT LCD illuminates about 250 to 275 nits. The display
performs nicely indoors but visibility diminishes when the display moves outdoors.
The image is totally invisible when the display is positioned towards direct sunlight.
With reference to FIG. 9, a diagram of an embodiment of the present invention
modifying the 15" desktop monitor TFT LCD 800 is shown. The transflective TFT
LCD 900 constructed in accordance to the present invention includes the major
components of the low reflection liquid crystal display unit 920, the diffusing
transflector 930, and the high efficient backlight cell 910. Applying an
anti-reflection coating 901 on the front surface of 801 generates the low reflection
display unit 920, preferably with less than 15% haze and an anti-reflection
efficiency less than 1%. The anti-reflection coating 1801 is a plastic film bound to
the front surface 1701. The diffusing transflector 930 comprises a sheet of diffuser,
902, and a diffuser laminated selective reflective polarizer 903. This diffusing
transflector 930 is positioned on the rear side of the display unit 920 in accordance
to the teaching of the present invention. The transflective LCD 900 has an enhanced
transmissive illumination between 350 and 400 nits. Indoor and outdoor
performance is greatly enhanced without altering the viewing angle or resolution.
Under direct sunlight, the transflective illumination effectively dominates the
lighting of the display and renders the display images viewable.
Referring now to FIG. 10, a diagram of a comparison of temperature measurements
between the regular LCD 800 and the modified LCD 900 is shown. Thermal
couples are adhered to the center of the rear side of the display units in 800 and 900,
as shown by 850 and 950 in FIG. 8 and FIG. 9, respectively. The displays were
provided with the same operating conditions and voltage supplies. Curve 1003
shows the outdoor air temperatures ranging from 30° C. to 40° C. Curve 1001
shows the temperature measurements of the transflective LCD 900, and curve 1002
shows the temperature measurements of the regular LCD 800. Both regular LCD
800 and transflective LCD 900 reach an equilibrium operating temperature between
76° C. and 78° C. The transflective LCD 900 does not generate any excessive heat
in the system when compared to the regular LCD 800.
EXAMPLE 2
A Direct Sunlight Readable 14.2" Notebook Computer TFT LCD
With reference to FIG. 11, a diagram of the structure of a 14.2" notebook computer
TFT LCD is shown (related art). The LCD 1100 comprises a display unit 1101 with
a liquid crystal panel sandwiched between a pair of dichroic polarizers with parallel
transmission directions. The backlight cell 1110 is composed of a diffusely reflector
1105, a wave guide plate coupled with one lamp 1104, a sheet of diffuser 1103
positioned on the front side of wave guide plate 1104, two sheets of brightness
enhancement film 1102 positioned in the front side of diffuser 1103, and another
diffuser 1106 in front of enhancement film 1102. The above described unit
illuminates between 120 and 140 nits. The display performs well indoors but is very
difficult to view under any outdoors conditions.
Referring now to FIG. 12, a diagram of an embodiment of the present invention
modifying the 14.2" notebook computer TFT LCD 1100 is shown. The transflective
TFT LCD 1200 comprises the major components of the low reflection liquid crystal
display unit 1220, the diffusing transflector 1230, and the high efficient backlight
cell 1210. Applying an anti-reflection coating 1201 on the front surface of 1101
generates the low reflection liquid crystal display unit 1220, preferably with less
than 15% haze and an anti-reflection efficiency less than 1%. The anti-reflection
coating 1801 is a plastic film bound to the front surface 1701. The diffusing
transflector 1230 is composed of one sheet of diffuser 1202 and a reflective
polarizer 1203. This diffusing transflector 1230 is positioned on the rear side of the
display unit 1220 in accordance to the teaching of the present invention. The
transflective LCD 1200 has an enhanced transmissive illumination of between 175
and 185 nits, yielding better indoor performances. In addition, the display is visible
under all outdoor lighting conditions including direct sunlight regardless of its
transmissive illumination.
EXAMPLE 3
A Direct Sunlight Readable 10.4" Tablet TFT LCD
With reference to FIG. 13, a diagram of the structure of a 10.4" Tablet TFT LCD is
shown (related art). The LCD 1300 comprises a display unit 1301 with a liquid
crystal panel sandwiched between a pair of dichroic polarizers with parallel
transmission directions. The backlight cell 1310 is composed of a diffusive reflector
1305, a wave guide plate coupled with one edge lamp 1304, a sheet of diffuser 1303
positioned in the front side of wave guide plate 1304, a sheet of brightness
enhancement film 1302 positioned in front of diffuser 1303, and a reflective
polarizer 1306 in front of enhancement film 1302. The above described unit
illuminates approximately 200 nits. The display gives good optical performances
indoors, yet is very difficult to view under any outdoor conditions.
With reference to FIG. 14, a diagram of an embodiment of the present invention
modifying the 10.4" Tablet TFT LCD 1300 is shown. The transflective TFT LCD
1400 includes the major components of the low reflection liquid crystal display unit
1420, the diffusing transflector 1430, and the high efficient backlight cell 1410.
Applying an anti-reflection coating 1401 on the front surface of 1301 generates the
low reflection liquid crystal display unit 1420, preferably with less than 15% haze
and an anti-reflection efficiency less than 1%. The anti-reflection coating 1401 is a
plastic film bound to the front surface 1301. The diffusing transflector 1430 is
composed of one sheet of diffuser 1402 and a reflective polarizer 1306. The
diffusing transflector 1430 is positioned on the rear side of the display unit 1420 in
accordance to the teaching in the present invention. The transflective LCD 1400 has
about the same transmissive illumination as LCD 1300 and is visible under all
outdoor lighting conditions, including direct sunlight.
EXAMPLE 4
A Direct Sunlight Readable Open Frame 12.1" TFT LCD
With reference to FIG. 15, a diagram of the structure of a 12.1" open frame high
bright TFT LCD is shown (related art). The LCD 1500 comprises a display unit
1501 with a liquid crystal panel sandwiched between a pair of dichroic polarizers
with off-axis transmission directions. The backlight cell 1510 comprises a diffusive
reflector 1505, a wave guide plate with ten back side lamps 1504, a sheet of diffuser
1503 positioned in the front side of wave guide plate 1504, a sheet of brightness
enhancement film 1502 positioned in front of diffuser 1503, and another diffuser
1506 in front of enhancement film 1502. The above-described unit illuminates
approximately 700 to 800 nits. The display gives very good optical performances
indoor with partial transmission illumination. With full transmission illumination
(i.e. 800 nits), the display provides good visibilities under moderate ambient light.
However, the display generates excessive heat and therefore reaches its clearing
temperature in approximately 30 minutes, a short amount of time. Upon reaching its
clearing temperature, the display turns black. Under very strong ambient light or
direct sunlight, the display is difficult to view even when provided with full
transmission illumination provided by its backlight.
With reference to FIG. 16, a diagram of an embodiment of the present invention
modifying the 12.1" open frame high bright TFT LCD 1500 is shown. The
transflective TFT LCD 1600 comprises the major components of the low reflection
liquid crystal display unit 1620, the diffusing transflector 1630, and the high
efficient backlight cell 1610. Applying an anti-reflection coating 1601 on the front
surface of 1501 generates the low reflection liquid crystal display unit 1620,
preferably with less than 15% haze and an anti-reflection efficiency less than 1%.
The anti-reflection coating 1601 is a plastic film bound to the front surface 1501.
The diffusing transflector 1630 is composed of one sheet of diffuser 1602 and a
reflective polarizer 1603. This diffusing transflector 1630 is positioned on the rear
side of the display unit 1620 in accordance to the teaching of the present invention.
The transflective LCD 1600 has approximately the same transmissive illumination
as 1500, yielding the same satisfactory indoor performances. Unlike TFT LCD 1500,
however, transflective TFT LCD 1600 is visible under all outdoor lighting
conditions, including direct sunlight, regardless of the amount of transmissive
illumination.
EXAMPLE 5
A Direct Sunlight Readable 1.5" TFT LCD
With reference to FIG. 17, a diagram of the structure of a 1.5" TFT LCD is shown
(related art). A 1.5" TFT LCD is commonly used as a monitor on a digital camera.
The LCD 1700 comprises a display unit 1701 with a liquid crystal cell, a first
dichroic polarizer, and a circular polarization-generating element (not shown). The
backlight cell 1710 comprises a diffusely reflector 1705, a wave guide plate with
four edge LED 1704, a sheet of diffuser 1703 positioned in the front side of wave
guide plate 1705, two sheets of brightness enhancement film 1702 and 1707
positioned in front of diffuser 1703, and another diffuser 1706 in front of the
brightness enhancement film sheets 1702 and 1707. The above-described unit
illuminates approximately 150 to 200 nits in the camera system. The display gives
moderate optical performances indoor, and is very difficult to view under any
outdoor conditions.
With reference to FIG. 18, a diagram of an embodiment of the present invention
modifying the 1.5" TFT LCD 1700 is shown. The transflective TFT LCD 1800
comprises the major components of the low reflection liquid crystal display unit
1820, the diffusing transflector 1830, and the high efficient backlight cell 1810.
Applying an anti-reflection coating 1801 on the front surface of 1701 generates the
low reflection liquid crystal display unit 1820, preferably with less than 15% haze
and an anti-reflection efficiency less than 1%. The anti-reflection coating 1801 is a
plastic film bound to the front surface 1701. A quarter wave plate 1804 is positioned
on the rear of the display unit 1820 to generate a linear polarization from the
circular polarization output of the display unit 1820. The second dichroic polarizer
1805 is then placed at the rear side of the quarter wave plate 1804. The transmission
direction for the second dichroic polarizer 1805 is parallel to the direction of the
linear polarization output of the quarter wave plate 1804. The diffusing transflector
1830 is composed of one sheet of diffuser 1802 and a reflective polarizer 1803. This
diffusing transflector 1830 is positioned on the rear side of the dichroic polarizer
1805 in accordance to the teaching in the present invention. The transflective LCD
1800 has less transmission illumination than TFT LCD 1700, with values between
100 nits and 150 nits. However, the display 1800 is more visible under all lighting
conditions, including direct sunlight, due to its transflective property and enhanced
contrast.
In summary, the present invention resolves and considers the reflection and
transmission properties of the transflector to provide a transflective LCD with
optical properties tailored for indoor and outdoor applications. A high efficiency
multi-layer anti-reflection coating (AR coating) not only reduces the background
reflection of the LCD front surface, but also allows the liquid crystal display unit to
transmit more energy of incident light, thus providing more reflective illumination.
Before, incident light was partially reflected on the surface of the substrate. With the
present invention, the low reflection and high transmission properties of the AR
coating and the diffusing transflector cooperatively provide the display with optimal
illuminations.
Other embodiments of the invention will appear to those skilled in the art from
consideration of the specification and practice of the invention disclosed herein. It is
intended that the specification and examples to be considered as exemplary only,
with a true scope and spirit of the invention being indicated by the following claims.