WO2005106542A1

WO2005106542A1 - Dye and optical film for flat panel display device

Info

Publication number: WO2005106542A1
Application number: PCT/KR2005/001252
Authority: WO
Inventors: Hee-Won Lee; Won-Keun Yoon; Sang-Kug Lee
Original assignee: Ace Digitech, Ltd.
Priority date: 2004-04-30
Filing date: 2005-04-29
Publication date: 2005-11-10

Abstract

Disclosed is an optical film, comprising a direct dye having absorption wavelength ranging from 550 to 600 nm. The optical film improves color purity by effectively blocking neon light, which is generated during driving of a flat panel display device, and enhances contrast by reducing internal reflection without an additional color compensation layer or color compensation film. This optical film can be applied in a variety of flat panel display devices, particularly as an optical filter of a plasma display.

Description

DYE AND OPTICAL FILM FOR FLAT PANEL DISPLAY DEVICE BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a dye and an optical film for a flat

panel display device, the dye being a direct dye having absorption

wavelength ranging from 550 to 600 nm and that is used for an optical film

of a flat panel display device, the optical film absorbing orange light in the

above-mentioned range, thereby improving color purity, and preventing internal reflection, thereby improving contrast and offering high-quality

images, and an optical filter comprising the same.

(b) Description of the Related Art

Currently, a variety of research is under way in order to offer

higher-quality images and improve color purity and contrast of flat panel

display devices, including liquid crystal display (LCD), organic

electroluminescence display (OLED), and plasma display panel (PDP).

In flat panel display devices, every color is generated from the

three primary colors of red, green, and blue. However, due to adding extra

light to the three primary colors in actual images, the grayscale colors

between them are emitted, thereby decreasing the color purity. For example, the PDP has a problem of generating a red color due

to emitting neon light (orange light) near 550 to 600 nm. To solve this

problem, it is suggested that a color compensation film including a specific

color compensation pigment is added to an optical filter for the PDP. Japanese Patent Laid-Open No. 2001 -192350 and Korean Patent

Publication No. 2003-0065338 teach that color purity of a flat panel display

device can be improved by using a squarylium compound as the pigment.

On the other hand, in a flat panel display such as CRT, LCD, and

PDP, it has the problem of blurred images due to decreasing contrast by

reflection of the external light entered from outside. Thus, a single-layer

anti-reflection filter is placed in front of the flat panel display device to

enhance contrast. Up to now, however, there still remains problem in

contrast of the flat panel display despite of employing anti-reflection filter,

like this. U.S. Patent No. 4,989,953 describes that an optical film or filter

comprises a ND (neutral density) filter or attenuator being capable of

transmitting specific lights regardless of wavelength. However, in spite of

enhancing contrast, such an approach leads to reduce brightness of the flat

display panel. To solve this problem, a method of combining an ND filter and an

anti-reflection layer has been proposed. Although this method was

effective in reducing reflection of external light at the luminous body and

light at the surface of the driving unit, there are therefore problems that not

only decreasing brightness but also reducing color purity.

Moreover, there has been proposed another method in LCDs

technical field to use a polarizer (neutral gray) and a color compensation

film together for enhancing contrast and improving color purity. However, another problem arises in that using the polarizer and the color

compensation film together leads to lessen brightness down to about 29%

SUMMARY OF THE INVENTION

It is an aspect of the present invention to provide a direct dye for a

flat panel display device capable of effectively absorbing light of wavelength

ranging from 550 to 600 nm, corresponding with un-illuminated pixels

generated from when the display device is driving, thereby improving color

purity of images. It is another aspect of the invention to provide an optical film

capable of improving color purity by effectively blocking neon light (orange

light) without using a color compensation dye, and of enhancing contrast by

preventing internal reflection due to improvement of polarizing efficiency.

It is still another aspect of the invention to provide an optical filter

for a plasma display device comprising the optical film. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of the optical film according to an

embodiment of the present invention.

FIG. 2 is a cross-sectional view of the optical film according to

another embodiment of the present invention. FIG. 3 is a cross-sectional view of the optical film according to still

another embodiment of the present invention.

FIG. 4 is a schematic view of a conventional plasma display device. FIG. 5 shows parallel and orthogonal transmission spectra of two sheets of optical films prepared by using SOLOPHENYL BORDEAUX 3BLE

3BLE direct dye in Example 1.

FIG. 6 shows the transmission spectrum of the single optical film

prepared in Example 1. FIG. 7 shows the transmission spectrum of the optical film prepared

by using SOLOPHENYL RED 7BE direct dye in Example 2.

FIG. 8 shows the transmission spectrum of the optical film prepared

by using SLOPHENYL VIOLET 4BLE direct dye in Example 3.

FIG. 9 shows the transmission spectrum of the optical film

prepared by using SIRIUS RED VOLET RL direct dye in Example 4.

FIG. 10 shows the transmission spectrum of the optical film

prepared by using SIRIUS RUBINE K-2BL direct dye in Example 5.

FIG. 11 shows the transmission spectrum of the optical film prepared by using iodine as a dichromatic dye and the squarylium pigment

as a color compensation dye in Comparative Example 1. ,

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS The present inventors completed this invention by determining that

when a direct dye, which is used for dyeing textiles and has an absorption

wavelength corresponding to neon light and polarizing characteristic,

thereby improving color purity and enhancing contrast of a flat panel display

device.

"Direct dye" refers to a dye which is compatible with such celluosic

fibers as cotton and rayon, so that it is directly dyed in neutral or weak alkaline water-solutions without pretreatments such as mordancy or primary immersing.

The present invention improves color purity of a flat panel display device by using an optical film or filter comprising the direct dye. There has been no attempt of employing the direct dye in an optical film of a flat panel display device as yet.

The direct dye can be used any dye which can absorb light of wavelength ranging from 550 to δOOnm, which is not limited to. Suitable direct dyes are at least one dye compound selected from the group consisting of benzadine direct dye; azo direct dye selected from the group consisting of diaryl amine derivatives tyepe azo dye, cyanur ring type azo dye, stilbene type azo dye and thiazole type azo dye; dioxazine direct dye and phthalocyanine direct dye.

Preferably, the azo direct dye may be a compound represented by Chemical Formula 1 below:

Ri is selected from the group consisting of and

, wherein each of R₂, R₃, and R₄ is an identical or different functional group selected from the group consisting of hydrogen, hydroxy ,

C-i-C alkyl , amine, and -S0₃Na; and X is selected from the group consisting of -NH- and -NHCONH-.

More preferably, the azo direct dye can be used the follwing

compounds of the Chemical Formulas 2 to 8:

Chemical Formula 2

Chemical Formula 3

Chemical Formula 4

Chemical Formula 5

Chemical Formula 6

Chemical Formula 7

Chemical Formula 8

Specifically, the compound represented by Formula 2 (product

from 490 to 630 nm; the compound represented by Formula 3 (product

from 480 to 620 nm; the compound represented by Formula 4 (product

name: C.I. DIRECT RED 149) absorbs light having wavelength ranging from of 490 to 630 nm; the compound represented by Formula 5 (product

from 550 to 600 nm; the compound represented by Formula 6 (product

580 nm; the compound represented by Formula 7 (product name: CI.

DIRECT RED 54) absorbs light having wavelength ranging from 460 to 600

nm; and the compound represented by Formula 8 (product name: CI.

DIRECT RED 98) absorbs light having wavelength ranging from 500 to 600

nm.

The above-mentioned direct dye can be employed in an optical film

for a flat panel display device. The optical film can absorb light having

wavelength raging from 550 to 660, corresponding to neon light (orange

light) which lessens to color purity of the flat panel display device. Namely,

as being dyed the direct dye on the optical film prevents from reducing luminance of un-illuminated pixels, it leads to increase the color purity of the

flat panel display device. In addition, due to stability of the direct dye in

high temperature, such effects can maintain for a prolonged time during the

flat panel display device is driving. In particular, the direct dye used in the present invention has

dichroism due to its long and linear molecular structure, like iodine dye used

for a polarizer of LCD. Therefore, the contrast of the flat panel display

device can be enhanced by reducing internal reflection by outer light, since

the optical film comprising the direct dye has dichroism as well. Therefore, the optical film comprising the direct dye of the present

invention has a compensation effect for color and polarizing for light, due to

optical properties such as absorption of specific wavelength and dichroism

of the direct dye. The optical film according to the first embodiment of the present

invention comprises a base film and a direct dye, which it molecular is

aligned in parallel along the stretched direction of the base film.

The base film offers polarizing ability to the optical film (polarizer)

through a stretching process. Any appropriate transparent polymer film

can be used for the base film. Suitable transparent polymer are one

homopolymer, copolymer or blends thereof prepared by at least one or

more polymer selected from the group consisting of polyvinyls including

polyvinyl alcohol, poly vinylformal and poly vinylacetal; polyesters including

polycarbonate, polyethyleneterephthalate and polybutyleneterephthalate; polyolefins including polyethylene and polypropylene; unsaturated

polycarboxylayes including poly acrylic acid, poly methacrylic acid and

polycrotonic acid; polyacrylamides; modified polymer by unsaturated

carboxylic monomer and acrylamide modified by alkyl ester. The optical

film of the first embodiment plays a role similar to that of the polarizer of an

LCD. Whereas the conventional polarizer just offers polarizing ability using

such a dichroic dye as iodine, the optical film of the present invention offers

a color compensation effect as well as polarizing ability by using the direct

dye. Thus, the optical film according to the first embodiment of the

present invention can be utilized in many ways, such as laminated with a

polarizing film of an LCD or a PDP filter of a PDP.

FIG. 1 shows a cross-sectional view of the optical film according to

the second embodiment of the present invention. The adhesive layer is

not shown in the figure. Referring to FIG. 1 , the optical film 1 a according to the second

embodiment of the invention comprises the first optical film 10 having a

base film comprising a direct dye, and transparent protecting films 12

laminated on both sides of the first optical film 10. The transparent protecting films 12, which are laminated on both

sides of the first optical film 10 increase durability or mechanical strength of

the optical film 1a.

The transparent protecting films 12 may be prepared or purchased. Preferably, at least one selected from the group consisting of triacetate

cellulose (TAC), cellulose acetate butylene (CAB), polycarbonate,

polyvinylchloride, polystyrene, polyacrylate, polymethacrylate,

polymethylacrylate, polymethylmethacrylate, polyethylene, polypropylene,

and polyethylene terephthalate may be used. Particularly, triacetate

cellulose is more preferred from the aspect of birefringence property,

adhesion strength, and durability.

The transparent protecting films 12 can be used without any

treatments or treated to provide properties EMI (electromagnetic

interference) shielding, anti-reflection, as long as the purposes of the

present invention are not sacrificed. For example, EMI (electromagnetic

interference) shielding treatment carries out by sputtering EMI shielding

materials on the transparent film and anti-reflection treatment is performed

by coating materials having low and high reflective index on the transparent

film.

The transparent protecting films 12 and the first optical film 10 are

adhered via appropriate adhesive film or layer. The adhesive is not

particularly limited, but at least one selected from the group consisting of

polyvinylalcohol, polyacrylate, polymethacrylate, polymethylacrylate,

polymethylmethacrylate, a silicone polymer, polyester, polyurethane,

polyamide, polyether, and fluorine or rubber polymer can be used.

Particularly, polyvinylalcohol is more preferred from the aspect of optical

transparency, wettability, adhesivness, weather resistance, and heat- resistance.

The optical film 1a of the second embodiment plays a role similar to

that of the "polarizing film" of an LCD, and characterizes having color

compensation effect as well as the polarizing ability due to comprising the

direct dye. FIG. 2 is a schematic diagram of the optical film 1 b according to the

third embodiment of the present invention. The adhesive layer is not

shown in the figure. Referring to FIG. 2, the optical film 1 b according to the third embodiment of the present invention comprises a first optical film 10 having

a base film comprising a direct dye, transparent protecting films 12

laminated on both sides of the first optical film 10, and phase contrast films

14 laminated on one side of the transparent protecting films 12. The phase contrast films 14 offer a phase difference of about 1/4 λ

to each light of wavelengths in the visible region. They are aligned at an

angle of 35 to 55° and 125 to 145° to the absorption axis of the first optical

film 10, so that they can shield light of a broad wavelength range incident

from inside. The result leads to enhance contrast with regard to B W and

to increase clearness of images. As a phase contrast film used in the present invention, any films

can be used without any specific limitations, including conventional ones.

The examples include a homopolymer, a copolymer, or a blend polymer

thereof, which the polymer is selected from the group consisting of polycarbonate, polyethylene, polypropylene, polynorbornene,

polyvinylchloride, polystyrene, polyacrylonitrile, polyester, polysulfone,

polyallylate, polyvinylalcohol, polymethacrylate ester, polyacrylate ester,

and cellulose ester uniaxially or biaxially, or one coating the polymer film

with liquid crystal to give a phase contrast effect may be used.

The phase contrast films 14 are laminated with the transparent

protecting films 12 of the optical film by an adhesive, as above-mentioned.

The optical film 1 b of the third embodiment is characterized by

improved color compensation and an enhanced contrast by using the direct

dye. In addition, the optical film 1 b is characterized by further enhancing

contrast by using phase contrast films 14 to prevent internal reflection

without additional anti-reflection film or layer.

FIG. 3 is a schematic diagram of the optical film 1 c according to the

fourth embodiment of the present invention. The adhesive layer is not

shown in the figure.

Referring to FIG. 3, the optical film 1 c according to the fourth

embodiment of the present invention comprises a first optical film 10 having

a base film comprising a direct dye, transparent protecting films 12

laminated on both sides of the first optical film 10, and functional films 16

laminated on one side of the transparent protecting films 12. On one side

of the transparent protecting films 12, phase contrast films 14 may be

further laminated.

The "functional films" cited in this description refer to films laminated on both sides of the optical film and having many functional materials

dispersed into or coated on them.

The functional film 16 may be a hard coat film, a surface anti-

reflection film, an anti-glare film, an EMI shielding film, a view angle

compensating film, a brightness improving film, a reflection film, or a semi-

transmissive reflection film. An adhesive layer or film is used to insert into

each film for adhering.

The hard coat film is formed to protect the surface of the optical film

and is made of such UV-setting resin as acryl and silicone resins having superior hardness and slide characteristics.

The surface anti-reflection film is used for anti-reflection of external

light at the surface. It may be anti-stick treated to prevent it from being

adhered to adjacent film layers. The anti-glare film is used to prevent a decrease in visibility of light

from the optical film by reflecting external light on the surface of the optical

film. The anti-refection effect can be obtained by forming irregular and

rough surfaces using by the method of sand-blasting, embossing or mixing

with transparent fine particles.

The EMI shielding film can be used a mesh type or transparent

metal film type, which is a conductive film.

The view angle compensating film is used to widen view angle, so

that the image of the flat panel display can be viewed clearly at out of the

perpendicular. It is preferably used a triacetyl cellulose film comprising discotic liquid crystal or a phase contrast film.

The brightness enhancement film is used to intensify light

illuminated from the flat panel display and offer polarized light which is

hardly absorbed by the polarizer in order to improve brightness. A film in

which cholesteric liquid crystal layers are aligned, particularly one in which

cholesteric liquid crystal polymers are aligned, or a base film supported by

such a film is used for the purpose.

In addition, a reflection film or a semi-transmissive reflection film

capable of reflecting or transmitting the incident light may be further

included. The optical film of the present invention further comprises an

adhesive layer or film between each functional film or layer. Adhesive can

be applied, for example, by using adhesives comprising at least an acryl

polymer, a silicone polymer, polyester, polyurethane, polyether, or

copolymers thereof. Particularly, acryl resin is more preferred from the

aspect of adhesive strength and transparent property.

The above-mentioned each functional film 14 laminates on one or

both sided of the transparent protecting film, which the order of lamination is

not limited to. It is preferably for a use adhesion treatment on each

functional film 14 before using.

To take an example, the optical film according to the fourth

embodiment of the present invention is laminated in the order of anti-

reflection film/hard coat film/EMI shielding film/transparent protecting film/base film comprising a direct dye/transparent protecting film/adhesive

film/phase contrast film/anti-reflection film/near IR blocking film/hard coat

film/color compensating film/EMI shielding film/transparent protecting

film/base film comprising a direct dye/transparent protecting film/adhesive

film/phase contrast film/hard coat film/anti-glare film/transparent protecting

film/base film comprising a direct dye /transparent protecting film/adhesive

film/phase contrast films/EMI shielding film/hard coat film/transparent

protecting film/base film comprising a direct dye/transparent protecting

film/EMI shielding film/adhesive film/phase contrast film or hard coat

film/anti-reflection film/EMI shielding film/transparent protecting film/base

film comprising a direct dye/transparent protecting film/adhesive film/phase

contrast film. The optical film comprising a direct dye of the present invention can

be prepared by the conventional method without any limitation. In a first step, it is performed by soaking a base film into a water

bath for a while, and swelling the base film.

Although the soaking time and temperature varies depending on a

factor such as a material or amount of the base film, the temperature is

preferably in the range of 20 to 30 °C . If the base film is not sufficiently

swollen in this step, non-uniform swelling on the inside surface of the base

film interrupts dyeing of the direct dye of the following step. Otherwise, if

the film is swollen excessively, part of the base film is dissolved by water,

thereby causing non-uniform dyeing and poor polarization. In the next step, it is performed by dyeing a direct dye in the

swollen base film prepared in the previous step. Preferably, the dyeing

process carries out in the temperature of 35 to 40 ^°C for 3 to 6 minutes to

dye the direct de on the base film uniformly, since the dyeing is dependent

on the degree of swelling of the base film. The direct dye is used an

amount of 0.9 to 1.5 part by weight per 100 parts of by weight of the base

film, considering optical characteristics of the polarizer and image balance.

The content of the direct dye depends on the temperature of sink having the

direct dye, soaking time, concentration of the direct dye, etc., and can be

adjusted depending on the processing conditions.

Subsequently, stretching process carries out by drawing the dyed

film prepared in a previous step. Preferably, the stretching process carries

out being drawing ratio in the range of from 1.5 to 20.0, considering

extension, wrinkling, or non-uniform elongation of the dyed film, The

stretching method can be applied any conventional method used in this art.

After, it is performed by drying the stretched film at the temperature

of 35 to 50 °C to obtain a polarizer of film type, and laminating transparent

films on both sides of the polarizer to prepare an optical film. The optical

film of the present invention has a thickness of 15 to 40 μm, which can be

varied the degree of stretching. Preferably, the optical film has a

transmittance of 30 to 50%, polarizing efficiency of 40.00 to 99.98%, and

absorption of 75% or higher at a wavelength of 583 nm. Accordingly, the

optical film of the present invention offers polarizing ability and color compensation effect without an additional color compensation dyes due to

use of the direct dye, while the conventional optical film employs a dichroic

dye such as iodine and a color compensation dye. According to the

testing example for the present invention, an optical film prepared by

forming triacetyl cellulose films on both sides of a base film comprising the

direct dye, and forming phase contrast films on one side of the resultant

films, had improved color purity and contrast.

Additionally, the optical film of the present invention has a superior

degree of color purity without using additional color compensation film or

layer, because as a dye it is used the direction dye having absorption

wavelength ranging from 550 to 600 nm.

The optical film may have further improved contrast by using or not using an internal anti-reflection layer or internal anti-reflection film because

of effective prevention of internal reflection. By introducing a variety of films on the optical film, a variety of

consumer needs for an optical film or an optical filter of flat panel display

devices can be satisfied.

In addition, because the direct dye is inexpensive and highly soluble

in water, an optical film with better dye-ability can be easily prepared. And,

because no additional color compensation film (color compensation layer)

or internal anti-reflection film (internal anti-reflection layer) for improving

color compensation or contrast is required, production cost is saved.

The optical film of the present invention can be preferably used for producing a flat panel display such as liquid crystal display devices (LCDs),

plasma display devices (PDPs), organic electroluminescent display devices

(OLEDs), and cathode-ray tubes (CRTs) as an optical film or optical filter,

with varied configuration designed by one skilled in the art. FIG. 4 is a schematic view of a conventional plasma display device.

Preferably, the optical film of the present invention is employed in such a

PDP as an optical filter.

Referring to FIG. 4, a plasma display device 200 generally

comprises, although this is variable depending on the driving method, a

panel part comprising a back panel 220 coated with phosphors and

equipped with an anode, and a front panel 240 equipped with a cathode, an

optical filter 260 positioned in front of the front panel 240, and a driving part

(not shown in the figure) for driving the panel part. The optical filter 260 is installed to offer high quality images. All or

part of the optical filter 260 may be the optical film in which the direct dye of

the present invention is uptaken, and may be equipped with a phase

contrast films.

The PDP employing the optical filter equipped with the optical film

of the present invention has improved color purity because the problem of

color purity reduction caused by neon emission at 550 to 600 nm (orange

light). Also, high-quality images can be attained as internal reflection is

prevented and contrast increases.

Hereinafter, the present invention is described in further detail through examples. However, the following examples are only for the

understanding of the present invention and they do not limit the present invention.

Examples

Example 1

A: Preparation of first optical film

Roll-type polyvinylalcohol having a DP of 1 ,700, a thickness of 70

μm, a width of 20 cm and a total length of 1,000 m (purchased from Kurarei,

Japan) was used as a base film. As a direct dye, SOLOPHEYL

BORDEAUX 3BLE (250%, purchased from Ciba-Geigy) was used, which

absorbs light of wavelength ranging from 530 to 590 nm.

The PVA film was passed through a water bath of 25 °C at a speed

rate of 0.1 m/min to wash off impurities, transferred to another water bath of

37 °C at the same rate, and then soaked to swell. The swollen PVA film was transferred to a dyeing bath of 47 °C at a

speed rate of 0.2 m/min, which is dispersed 8 g of SOLOPHENYL

BORDEAUX 3BLE and 20 g of Na₂S0₄ in water solution, and then soaked

to dispose the direct dye in PVA film uniformly.

After washing the dyed PVA film with pure water of 35 °C , it carried

out stretching it to have a draw ratio of 3.5 times. The stretched PVA film

was passed through a dryer of 50 °C to prepare the first optical film. The

obtained first optical film has a thickness of 2.3 μm, a width of 5.4 m, and a

length of 10 m. B: Preparation of the second optical film

On both sides of the first optical film prepared in step A, each

transparent protecting film was laminated to prepare the second optical film.

As the transpatent protecting film was used a triacetate cellulose (TAC)

films having a thickness of 80 μm.

C: Preparation of an optical filter

After coating acryl adhesive solution on one side of the second

optical film, it carried out laminating 1/4 λ-phase contrast film on the acryl

adhesive coated side to prepare an optical flter. As a 1/4 λ-phase contrast film was used a thickness of 80 μm, purchased from Teijin in Japan.

Example 2

The first and second optical films and an optical filter were prepared

in the same manner as in Example 1 , except that SOLOPHENYL RED 7BE

(purchased from Ciba-Geigy) was used as a direct dye.

Example 3

The first and second optical films and an optical filter were prepared

in the same manner as in Example 1 , except that SOLOPHENYL VIOLET

4BLE (purchased from Ciba-Geigy) was used as a direct dye.

Example 4 The first and second optical films and an optical filter were prepared

in the same manner as in Example 1 , except that SRIUS RED VIOLET RL

(purchased from DYSTAR) was used as a direct dye.

Example 5 The first and second optical films and an optical filter were prepared

in the same manner as in Example 1 , except that SIRIUS RUBINE K-2BL

(purchased from DSTAR) was used as a direct dye.

Examples 6-10 Using an acryl adhesive, it carried out laminating an anti-reflection

layer, an anti-glare layer, and an EMI shielding layer on the transparent film

of the optical film prepared in Examples 1 to 5, in sequence.

Comparative Example 1

A polarizer was prepared by laminating a base film dispersed iodine dichromic dye with transparent films sputtered squarylium pigment. The

transparent film was used polyethylene terephthalate film.

Testing Example 1

To evaluate optical properties of the second optical films prepared

in Examples 1 to 5 and Comparative Example 1 , parallel and transmittance

crossed transmittances were measured at 25 °C using a spectrophotometer,

and polarizing efficiency was calculated by Equation 1 below.

Equation 1 Polarizing efficiency —

where, A is parallel-transmittance when the axes of the two sheets of the

optical films are parallel with each other; and

B is crossed-transmittance when the two axes of the two sheets of

the optical films are crossed with each other. Table 1

As shown in Table 1 , the second optical films of the present

invention had a transmittance of at least 36% and a polarizing efficiency of

at least 43% through Examples 1 to 6. In connection with this result, it was

observed the same optical characteristic in case of the first optical films and optical filters prepared in Examples 1 to 6.

FIG. 5 and FIG. 6 show transmission spectra of the optical film

prepared in Example 1 , in which SOLOPHENYL BRDEAUX 3BLE was used

as direct dye.

In FIG. 5, the solid line shows change of transmittance measured

with the polarizing axes of two sheets of optical films parallel to each other,

and the dotted line shows change of transmittance measured with the

polarizing axes of two sheets of optical films crossed with each other.

Referring to FIG. 5, it was observed that the optical film of Example

1 absorbs light of wavelength ranging from 510 to 600 nm, particularly 75%

at 583 nm, corresponding to the absorption wavelength of the direct dye, in both parallel and crossed cases.

FIG. 6 is a transmission spectrum of a single optical film.

Referring FIG. 6, it was observed that the optical film absorbed neon light

near 583 nm, effectively. FIG. 7 is a transmission spectrum of the optical film prepared in

Example 2, in which SOLOPHENYL BORDEAUX 3BLE was used as a

direct dye.

Referring to FIG. 7, the optical film of Example 2 has an absorption

wavelength ranging from 470 to 610 nm broadly. Particularly, the optical

film has a good absorption of as high as 88.3% at 580 nm, and thus it can

effectively absorb neon light at around 580 nm.

FIG. 8 is a transmission spectrum of the optical film prepared in

Example 3, in which SOLOPHENYL VIOLET 4BLE was used as a direct

dye. Referring to FIG. 8, the optical film of Example 3 shows absorption

at 490 to 630 nm, and particularly good absorption of as high as 88.3% at

580 nm. Thus, it can effectively absorb neon light at around 580 nm.

FIG. 9 is a transmission spectrum of the optical film prepared

Example 4, in which SIRIUS RED VIOLET RL was used as a direct dye. Referring to FIG. 9, the optical film of Example 4 shows absorption ^•

at 490 to 590 nm, and particularly good absorption of as high as 36.0% at

570 nm. Thus, it can effectively absorb neon light at around 570 nm.

FIG. 10 is a transmission spectrum of the optical film prepared in Example 5, in which SIRIUS RUBINE K-2BL was used as a direct dye.

Referring to FIG. 10, the optical film of Example 5 shows absorption

at 490 to 600 nm, and particularly good absorption of as high as 54.0% at

540 nm. Thus, it can effectively absorb neon light at around 540 nm. FIG. 11 is a transmission spectrum of the optical film prepared in

Comparative Example 1 , in which iodine dye and squarylium pigment were

used as a dichroic dye and a color compensation dye, respectively.

Referring to FIG. 11 , the optical film of Comparative Example 1

shows absorption at 550 to 630 nm, and particularly good absorption of as

high as 86.0% at 590 nm. This result means that for using a direct dye as a dye the optical

film of the present invention absorbs effectively neon light (orange light)

without a color compensation layer or film in comparison with the

conventional optical film incuding a polarzer or a polarizing film.

Testing Example 2

To evaluate color properties of the optical films prepared in

Examples and Comparative Example, "L", "a", and "b" values were

measured using a chromameter (Coloreye, Macbath). The result is given

in Table 2 below. The "L" values indicate degree of brightness. In "a"

value, a positive (+) and negative (-) mean a red color and green color,

respectively. In "b" value, a positive (+) and negative (-) mean a yellow

color and blue color, respectively.

Table 2

Referring to Table 2, it can be seen that the result for the present

invention, in which a direct dye was used, is similar to that in which iodine

and squarylium dye were used in brightness and color properties.

To sum up, the polarizer and the optical film of the present invention, in which only a direct dye was used, improve color purity by effectively

absorbing neon light (orange light) even without using a color compensation

dye.

Testing Example 3

To evaluate optical properties of the optical filters prepared in the

Examples, reflectance and reflection brightness were measured using a

spectrophotometer, and contrast ratio was calculated by the following

Equation 2. One with no optical filter was used as a blank, and a

commercially available optical filter for a plasma display device was used in

Comparative Example 2.

Equation 2 „ . _ external luminance -display luminance Contrast ratio — - — - external luminance Table 3

Referring to Table 3, it can be seen that the optical filters of the

present invention (Examples 1 to 5) have reflectance smaller than 15.4 %,

and thus they can effectively control internal reflection. In case of contrast, the optical filters of the present invention were

superior to the conventional optical filter.

Since the optical filter of the present invention, in which an optical

film and a phase contrast film are laminated, has polarizing ability, it can

control internal reflection better than the conventional optical filter for a

plasma display device and effectively improve contrast by preventing

internal reflection without an additional internal anti-reflection layer or

internal anti-reflection film.

As described above, the present invention offers good color purity

with a superior color compensation effect and high-quality images with

increased contrast by employing a direct dye absorbing light in the wavelength range of 550 to 600 nm.

Claims

WHAT IS CLAIMED IS:

1. A dye for a flat panel display device comprising a direct dye having absorption wavelength ranging from 550 to 600 nm.

2. The dye for a flat panel display device of claim 1 , wherein the direct dye is at least one dye selected from the group consisting of benzadine direct dye; azo direct dye selected from the group consisting of diaryl amine derivatives tyepe azo dye, cyanur ring type azo dye, stilbene type azo dye and thiazole type azo dye; dioxazine direct dye and phthalocyanine direct dye.

3. The dye for a flat panel display device of claim 2, wherein the azo direct dye is a compound represented by Chemical Formula 1 below: Chemical Formula 1

Where Ri is selected from the group consisting of

and

wherein each of R₂, R₃, and R is, identically or differently, a functional group selected from the group consisting of hydrogen, hydroxy, Cι-C alkyl, amine, and -

S0₃Na; and X is selected from the group consisting of -NH- and

NOCONH-.

The dye for a flat panel display device of claim 3, wherein the azo direct dye is a compound selected from the group consisting of Chemical Formulas 2 to 8 below:

Chemical Formula 2

Chemical Formula 3

Chemical Formula 4

Chemical Formula 5

Chemical Formula 6

Chemical Formula 7

Chemical Formula 8

5. An optical film comprising a base film dyed by the direct dye of claim 1.

6. The optical film of claim 5, wherein the base film is selected from the group consisting of at least one homopolymer, copolymer and blends thereof, in which the polymer is selected from the group consisting of polyvinyls including polyvinyl alcohol, poly vinylformal and poly vinylacetal; polyesters including polycarbonate, polyethyleneterephthalate and polybutyleneterephthalate; polyolefins including polyethylene and polypropylene; unsaturated polycarboxylayes including poly acrylic acid, poly methacrylicacid and polycrotonic acid; polyacrylamides; modified polymer by unsaturated carboxylic monomer and acrylamide modified by alkyl ester.

7. The optical film of claim 5, wherein the base film has a drawing ratio ranging from 1.5 to 20.0.

8. The optical film of claim 5, wherein the optical film has an optical transmittance ranging from 30 to 50% and a polarizing efficiency ranging from 40.00 to 99.98%.

9. The optical film of claim 5, wherein the optical film further comprises a transparent protecting film laminated on one or both sides of the base film.

10. The optical film of claim 9, wherein the transparent protecting film is at least one selected from the group consisting of triacetate cellulose, cellulose acetate butylene, polycarbonate, polyvinyl chloride, polystyrene, polyacrylate, polymethacrylate, polymethylacrylate, polymethylmethacrylate, polyethylene, polypropylene and polyethyleneterephthalate.

1 1. The optical film of claim 5, wherein the optical film further comprises a phase plate laminated on one or both sided of the base film.

12. The optical film of claim 11 , wherein the phase plate is aligned at an angle of 35 to 55° and 125 to 145° relative to the absorption axis of the base film.

13. The optical film of claim 5, wherein the optical film further comprises at least one film selected from the group consisting of a hard coat film, a surface anti-reflection film, an anti-glare film, an EMI shielding film, a view angle compensating film, a brightness improving film, a reflection film, a semi-transmittance reflection film, and an adhesive film.

14. An optical filter for a plasma display device comprising the optical film of any one of claims 5 to 13.

15. A method of preparing the optical film of claim 5 comprising the steps of soaking a swollen base film into a dye sink containing a direct dye and stretching it.

16. A method of preparing the optical film of claim 9 comprising the steps of soaking a swollen base film into a dye sink contaning a direct dye, stretching and laminating the stretched film with a transparent protecting film.