[DESCRIPTION]

[invention Title]

REACTIVE DICHROIC DYES, PREPARATION METHOD OF THE SAME, POLY(VINYL ALCOHOL)-BASED FILM COMPRISING REACTIVE DICHRONIC DYES AND POLARIZING FILM

[Technical Field]

The present invention relates to a reactive dichroic dye, which is reactive to polyvinylalcohol, a method of preparing the same, a polyvinylalcohol-based film including the same, and a polarizing film.

[Background Art]

A variety of dyes have been developed for various applications, including fabric dyeing, textile printing, plastic coloring, color imaging of photographs, etc. Such dyes are designed to have molecular structures and binding strength suitable for each application so as to exhibit essential properties, including hue, solubility, affinity for a substrate, chemical resistance, and miscibility with the medium to which the dye is to be applied. Dichroism is a property in which the orientation of assembled dye molecules results in low absorption at a predetermined light wavelength in any one orientation state depending on the direction of polarization of a light

source, and high absorption at the same wavelength in another orientation state. Thus, dyes having such dichroism may also be applied to the development of polarizing films, in addition to fabric dyeing. In particular, a dichroic dye is applied to the dyeing of a polyvinylalcohol (hereinafter, referred to as "PVA") film constituting the polarizer of a polarizing film. A typical PVA film, serving as the polarizer, is obtained through the iodine immersion method. However, the iodine-doped PVA film is disadvantageous because it undergoes high sublimation, drastically decreasing polarizing properties and durability, upon long exposure under conditions of high temperature and high humidity. Accordingly, instead of iodine, dyes having very low sublimation have been used.

Meanwhile, a polarizing film, which was first studied by E. H. Land in 1928, is very limited in the use thereof for industrial purposes. However, as modern industrial society has advanced to the high information age, the demand for polarizing film is increasing. This is considered to be due to the increase in the importance of electronic displays.

Polarizing films that are presently commercially available may be classified into various types depending on the kind and performance thereof. First, there is an iodine-based polarizing film, particularly suitable as a

polarizing film for high definition LCDs having high transmittance and high polarizing properties, which is a film using iodine, having high dichroism, to impart a transparent PVA film with the ability to absorb light in the visible range. To date, the iodine-based polarizing film has been chiefly used as a polarizing film for LCDs. Second, there is a dye-based polarizing film, which has been studied to overcome the durability problems caused by the sublimation of iodine. This is a highly durable polarizing film, the optical properties of which do not change much even under conditions of high temperature and high humidity, and is useful for LCDs requiring high durability, thanks to the high durability thereof. Further, it is relatively easy to control the color of the dye-based polarizing film, thus enabling the manufacture of polarizing films having various colors and making it suitable for use in the field of sunglasses. Third, there is a polarizing film for super twisted nematic LCD (STN- LCD) , called a phase difference polarizing film. Depending on the angle at which a phase difference film having predetermined properties is applied to the polarizing film, many various products may be obtained. The phase difference film is a film for correcting a phase difference occurring in liquid crystals, and presently useful is a phase difference film made of polycarbonate. Fourth, there is a transflective polarizing film having both transmission

properties and reflection properties. The transflective polarizing film has an effect on power consumption efficiency, which is regarded as the most important factor in the display of a mobile apparatus. Because the lifespan of the product is undesirably decreased at high power consumption rates, in the LCD of the mobile apparatus, a conventional transmissive product having high power consumption has been replaced with a functional film, which is useful as a material for the lower plate of a transflective LCD imparted with a reflection function using external light. The transflective film types vary depending on the kind of material used and the properties thereof. Exemplary are products (ST type) having adjusted transmittance through the addition of an adhesive with a pigment, and products composed of hundreds of polymer thin film layers having different refractive indexes. Fifth, a transflective polarizing film having high reflectance, which is a polarizing film having increased reflectance thanks to a metal-deposited film and having an improved outer appearance thanks to a diffusion adhesive, instead of the transflective polarizing film using a conventional pigment, in order to decrease the power consumption of an STN-LCD and to more clearly exhibit the outer appearance of the display, has been used in recent years. Sixth, there is a polarizing film (AG/AR) for surface anti-reflection. Surface anti-reflection includes anti-glare (AG) and anti-

reflection (AR) . The AG process is conducted by roughening the surface of a film to thus induce the diffuse reflection of external light from the surface thereof, so as to exhibit anti-reflection effects, and the AR process manifests anti-reflection effects by forming a thin film composed of a plurality of layers having different refractive indexes on the surface of a film through deposition or coating. The reflectance of a polarizing film not subjected to AR processing is about 4%, and the AG film has reflectance of about 2%, and the AR film has reflectance less than 1%. Finally, there is a reflective polarizing film, which is a product obtained by laminating a metal-deposited reflective film on a general iodine-based polarizing film to thus make it suitable for use in reflective LCDs.

Generally commercially available polarizing films include, as the polarizer thereof, a film having polarizing properties, in which PVA is treated with iodine or dichroic dye as mentioned above. Further, with the goal of preventing the deformation of the film due to the low durability and high sublimation of iodine, a protective layer is formed. To this end, the use of triacetyl cellulose, polyesters, polycarbonates, etc., which are free from birefringence, exhibit high transmittance, are not wavelength dependent, and show high heat resistance, high moisture resistance and mechanical strength, is known.

Moreover, it is known that the film may be treated with an adhesive and then the outermost surface thereof may be covered with a protective film. The principle of the polarizing film thus formed is as follows. The polarizing film functions to convert natural light, which is incident while vibrating in various directions, into light (that is, polarized light) vibrating in only one direction. In particular, because the LCD uses the birefringence of liquid crystals, it is very important to control the direction of vibration of light incident on the liquid crystal molecules.

The function of the polarizing film is ensured by stretching the PVA film and subjecting the stretched PVA film to dyeing and immersion in a solution of iodine or dichroic dye such that iodine molecules or dye molecules are arranged in the stretching direction. Because the iodine or dye molecules are dichroic, the polarizing film may have the function of absorbing light vibrating in the stretching direction and transmitting light vibrating in the direction perpendicular thereto.

Most polarizing films that are presently available are a PVA-I ₂ based polarizing film obtained by immersing optical PVA in an aqueous solution of iodine and iodine- potassium complex to thus dye PVA, which is then uniaxially stretched about 400%. The PVA has properties such as high linearity, high film formability, high crystallinity,

superior alkali resistance even at a pH of 13.5 or more, and high adhesion, so that a PVA-I ₂ polarizing film for LCDs, which is presently commercialized, may exhibit sufficient electrical and optical performance. Although the PVA-I ₂ polarizing film has superior properties, it suffers because it has drastically deteriorated polarizing properties and durability, attributable to the high sublimation of iodine, when allowed to stand under conditions of high temperature and high humidity for a long period of time, undesirably causing problems in which a protective film must be applied on both surfaces of the film.

Therefore, these days, attempts are continuously made to overcome the problems of the PVA-I ₂ polarizing film by means of a PVA-dye polarizing film using a dichroic direct dye having very high vapor pressure.

However, in the case where the film is used after merely dyeing it with the dichroic dye, transmittance is remarkably decreased despite the high durability and polarizing properties equal to those of iodine.

[Disclosure] [Technical Problem]

Accordingly, the present invention is intended to develop, to replace iodine, a dichroic dye, which includes a trihalotriazine group, thereby exhibiting optical

properties similar to iodine and further improving durability while transmittance is not decreased.

The present invention provides a novel reactive dichroic dye, which is reactive to PVA-based resin. In addition, the present invention provides a method of preparing the novel reactive dichroic dye.

In addition, the present invention provides a PVA- based film, which includes the reactive dichroic dye, in which a dichroic dye is introduced with trihalotriazine, thus exhibiting superior transmittance, in particular, high durability, while maintaining polarizing properties.

In addition, the present invention provides a PVA- based film having superior transmittance and improved durability while maintaining polarizing properties equal to those of an iodine-based polarizing film.

In addition, the present invention provides a polarizing film having superior polarizing properties and transmittance and improved durability.

In addition, the present invention provides a method of preparing the PVA-based film, which involves dyeing with a dichroic dye not under a strong alkaline condition but in the presence of an organic solvent, thereby improving working environments.

In addition, the present invention provides a method of preparing the PVA-based film, which involves dyeing with a reactive dichroic dye having a functional group at an end

portion thereof, not under a strong alkaline condition but in the presence of an organic solvent, thereby improving working environments without deteriorating the action of the functional group contributing to the increase in transmittance .

In addition, the present invention provides a method of preparing the PVA-based film having higher transmittance than that of a product dyed under a strong alkaline condition.

[Technical Solution]

According to the present invention, a reactive dichroic dye, represented by Formula 1 below, may have an azo chromophore and at least one amine group (-NH ₂ ) at an end portion thereof, in which at least one hydrogen atom of the amine group is substituted with a halotriazine group:

Formula 1

B' -N=N-A-N=N-B

wherein A is , in which Ri and R ₂ , which are the same as or different from each other, are H, NH ₂ , OH, SO ₃ Na, CH ₃ or OCH ₃ ,

B is , in which R ₃ , R ₄ , R ₅ and

Re, which are the same as or different from each other, are H, NH ₂ , OH, SO ₃ Na, CH ₃ , OCH ₃ , COONa, COOH, SO ₂ NH ₂ , SO ₂ NHCH ₃ , SO ₃ Na, SO ₃ CH ₃ , NHCOCH ₃ , NHCONH ₂ , NHCH ₂ SO ₃ Na or NHCH ₂ COONa, at least one of R ₃ to Re being NH ₂ , and R ₇ and Rs, which are the same as or different from each other, are H, NH ₂ , OH, SO ₃ Na, CH ₃ or OCH ₃ , and

B' is , in which R ₉ , R ₁₀ and Rn, which are the same as or different from each other, are (in which X ₁ is a halogen group) , H, NH ₂ , OH, SO ₃ Na, CH ₃ , OCH ₃ , COONa, COOH, SO ₂ NH ₂ , SO ₂ NHCH ₃ , SO ₃ Na, SO ₃ CH ₃ , NHCOCH ₃ , NHCONH ₂ , NHCH ₂ SO ₃ Na or NHCH ₂ COONa, at least one of R ₉ to Rn being

In the reactive dichroic dye according to the present invention, Ri and R ₂ may be H, R ₃ may be NH ₂ , R ₄ may be OH, R ₅

and Re may be SO ₃ Na, R ₇ and R ₈ may be H, R ₉ may be

Rio may be CH ₃ , and Rn may be NH ₂ .

In the reactive dichroic dye according to the present invention, Xi may be Cl.

In addition, a method of preparing the reactive dichroic dye may comprise reacting a dichroic dye represented by Formula 2 below, having an azo chromophore and at least one amine group at an end portion thereof, with a trihalotriazine compound represented by Formula 3 below, thus preparing a reactive dichroic dye represented by Formula 1, having an azo chromophore and at least one amine group (-NH ₂ ) at an end portion thereof, in which at least one hydrogen atom of the amine group is substituted with a halotriazine group :

Formula 2 B"-N=N-A-N=N-B wherein A and B are defined as in Formula 1, and

B" is , in which R ₉ , Ri ₀ and Rn, which are the same as or different from each other, are H, NH ₂ , OH, SO ₃ Na,

CH ₃ , OCH ₃ , COONa, COOH, SO ₂ NH ₂ , SO ₂ NHCH ₃ , SO ₃ Na, SO ₃ CH ₃ , NHCOCH ₃ , NHCONH ₂ , NHCH ₂ SO ₃ Na or NHCH ₂ COONa, at least one of R ₉ ' to R _u being NH ₂ ; and

Formula 3

wherein Xi is defined as in Formula 1. In the method of preparing the reactive dichroic dye according to the present invention, reacting may be conducted at 10~30 ^° C for 20-30 hours.

In the method of preparing the reactive dichroic dye according to the present invention, reacting may be conducted using one or more solvents selected from among dimethylformamide (DMF) , dimethylacetamide (DMδc) and N- methylpyrrolidone (NMP) .

In addition, a PVA-based film may comprise a reactive dichroic dye represented by Formula 1, having an azo chromophore and at least one amine group (-NH ₂ ) at an end portion thereof, in which at least one hydrogen atom of the amine group is substituted with a halotriazine group.

In the PVA-based film according to the present invention, of the reactive dichroic dye, Ri and R ₂ may be H, R ₃ may be NH ₂ , R ₄ may be OH, R ₅ and R ₆ may be SO ₃ Na, R ₇ and R ₈

may be H, R ₉ may be , Ri ₀ may be CH ₃ , and Rn may be NH ₂ .

Further, in the PVA-based film, Xi of the reactive dichroic dye may be Cl .

The PVA-based film may be obtained through dyeing using the reactive dichroic dye represented by Formula 1, wherein the dyeing is conducted not under an alkaline condition but in the presence of an organic solvent. The organic solvent may be selected from among chloroform, dimethylformamide, ethyleneglycol, dimethylsulfoxide, and mixtures thereof.

In addition, a method of preparing the PVA-based film using a dichroic dye may comprise dyeing a PVA-based film with a dichroic dye, wherein the dyeing is conducted not under an alkaline condition but in the presence of an organic solvent .

In addition, a method of preparing the PVA-based film using a dichroic dye may comprise dyeing a PVA-based film with a reactive dichroic dye having an azo chromophore and at least one amine group (-NH ₂ ) at an end portion thereof, in which at least one hydrogen atom of the amine group is substituted with a halotriazine group, wherein the dyeing is conducted not under an alkaline condition but in the presence of an organic solvent.

In the method of preparing the PVA-based film according to the present invention, the organic solvent may be selected from among chloroform, dimethylformamide, ethyleneglycol, dimethylsulfoxide, and mixtures thereof. In the method of preparing the PVA-based film, the reactive dichroic dye may be represented by Formula 4 below:

Formula 4

C-N=N-A' -N=N-C wherein A' is or ^ , in which X is NH, N=N, CH=CH, NHCONH, NHOC or SO ₂ O, and Ri and R ₂ , which are the same as or different from each other, are H, NH ₂ , OH, SO ₃ Na, CH ₃ or OCH ₃ ,

which R ₃ , R ₄ , R ₅ and R ₆ , which are the same as or different from each other, are H, NH ₂ , OH, SO ₃ Na, CH ₃ , OCH ₃ , COONa, COOH, SO ₂ NH ₂ , SO ₂ NHCH ₃ , SO ₃ Na, SO ₃ CH ₃ , NHCOCH ₃ , NHCONH ₂ ,

NHCH ₂ SO ₃ Na or NHCH ₂ COONa, at least one of R ₃ to R ₆ being NH ₂ , R ₇ , Rs, R ₉ and Ri ₀ , which are the same as or different from each other, are H, NH ₂ , OH, SO ₃ Na, CH ₃ or OCH ₃ , and Rn and Ri ₂ , which are the same as or different from each other, are H, NH ₂ , OH, SO ₃ Na, CH ₃ , OCH ₃ , COONa, COOH, SO ₂ NH ₂ , SO ₂ NHCH ₃ ,

SO ₃ Na, SO ₃ CH ₃ , NHCOCH ₃ , NHCONH ₂ , NHCH ₂ SO ₃ Na or NHCH ₂ COONa, at least one of Ru and R _i2 being NH ₂ , and

which Ri ₃ , Ri ₄ , R _i5 and Ri ₆ , which are the same as or different

from each other, are (in which X _x is a halogen group) , H, NH ₂ , OH, SO ₃ Na, CH ₃ , OCH ₃ , COONa, COOH, SO ₂ NH ₂ ,

SO ₂ NHCH ₃ , SO ₃ Na, SO ₃ CH ₃ , NHCOCH ₃ , NHCONH ₂ , NHCH ₂ SO ₃ Na or

NHCH ₂ COONa, at least one of Ri ₃ to Ri ₆ being , R ₇ ,

Rs, R ₉ and Rio are defined as above, and Ri ₇ and Ri ₈ , which are

the same as or different from each other, are

(in which Xi is a halogen group) , H, NH ₂ , OH, SO ₃ Na, CH ₃ , OCH ₃ , COONa, COOH, SO ₂ NH ₂ , SO ₂ NHCH ₃ , SO ₃ Na, SO ₃ CH ₃ , NHCOCH ₃ , NHCONH ₂ , NHCH ₂ SO ₃ Na or NHCH ₂ COONa, at least one of R ₁₇ and R ₁₈

being

As such, of the reactive dichroic dye, A' may be

may be , in which Ri is H, R ₂ is

NaSO ₃ , X is NH, R ₇ is OH, R ₈ and R ₉ are H, Ri ₀ is NaSO ₃ , Rn and

Ri ₂ are NH ₂ , Ri ₇ is , and Ri ₈ is NH ₂ .

Further, X ₁ of the reactive dichroic dye may be Cl.

In addition, the present invention provides a PVA- based film, obtained through the method of preparing the PVA-based film as above, and also provides a polarizing film, comprising such a PVA-based film.

[Advantageous Effects] According to the present invention, in the case where the reactive dichroic dye having a halotriazine group, which is reactive to PVA, is used to manufacture a polarizing film, a polarizing film having increased transmittance, in particular, superior durability, while maintaining polarizing efficiency, can be realized. Further, in the case where the PVA-based film is dyed with a dichroic dye in the presence of an organic solvent, working environments can be improved, and also, transmittance can be further increased compared to when dyeing is conducted under a strong alkaline condition. Thereby, the PVA-based film according to the present invention can be usefully applied to the manufacture of a polarizing film requiring high transmittance.

[Description of Drawings]

FIG. 1 illustrates the IR (KBr pellet) spectrum of Direct Black 4, which is the dichroic dye;

FIG. 2 illustrates the NMR (DMSO-d ₆ ) spectrum of Direct Black 4, which is the dichroic dye;

FIG. 3 illustrates the IR (KBr pellet) spectrum of the reactive dichroic dye having a chlorotriazine group, synthesized in Example 1;

FIG. 4 illustrates the NMR (DMSOd ₆ ) spectrum of the reactive dichroic dye having a chlorotriazine group, synthesized in Example 1;

FIG. 5 is a graph illustrating the transmittance and polarizing efficiency of the iodine-adsorbed PVA film (Comparative Example 1) ; FIG. 6 is a graph illustrating the transmittance and polarizing efficiency of the Direct Black 4-dyed PVA film (Comparative Example 2);

FIG. 7 is a graph illustrating the transmittance and polarizing efficiency of the PVA film (Example 2) prepared through the reaction with the reactive dichroic dye of Example 1;

FIG. 8 is a graph illustrating the results of evaluation of the durability of the iodine-adsorbed PVA film (Comparative Example 1) ; FIG. 9 is a graph illustrating the results of evaluation of the durability of the PVA film (Example 2)

prepared through the reaction with the reactive dichroic dye of Example 1;

FIG. 10 is a graph illustrating the transmittance and polarizing efficiency of the PVA film of Reference Example 1;

FIGS. 11 to 14 are graphs illustrating the transmittance and polarizing efficiency of the PVA films of Examples 3 to 6, respectively;

FIG. 15 is a graph illustrating the transmittance and polarizing efficiency of the PVA film of Reference Example 2; and

FIGS. 16 to 20 are graphs illustrating the transmittance and polarizing efficiency of the PVA films of Examples 7 to 11, respectively.

[Best Mode]

The present invention pertains to a novel reactive dichroic dye, the novel reactive dichroic dye of the present invention having a halotriazine group, and specifically represented by Formula 1. In the reactive dichroic dye represented by Formula 1, Ri and R ₂ of A may be a hydrogen atom, R ₃ of B is NH ₂ , R ₄ is

OH, R ₅ and R ₆ are SO ₃ Na, R ₇ and R ₈ are H, B' is

Rio is CH ₃ , and Rn is NH ₂ .

In the reactive dichroic dye represented by Formula 1, Xi is a halogen atom, preferably Cl, Br or F, and more preferably Cl.

The reactive dichroic dye represented by Formula 1 may be obtained by reacting a dichroic dye represented by Formula

2 below, having an azo chromophore and at least one amine group at the end portion thereof, with a trihalotriazine compound represented by Formula 3 below.

Formula 2 B"-N=N-A-N=N-B wherein A and B are defined as in Formula 1, and B" is

.--*? ^'

¹¹ U *° , in which Rg, Ri ₀ and Rn, which are the same as or different from each other, are H, NH ₂ , OH, SO ₃ Na, CH ₃ , OCH ₃ ,

COONa, COOH, SO ₂ NH ₂ , SO ₂ NHCH ₃ , SO ₃ Na, SO ₃ CH ₃ , NHCOCH ₃ , NHCONH ₂ , NHCH ₂ SO ₃ Na or NHCH ₂ COONa, at least one of R ₉ ' to Rn being NH ₂ .

Formula 3

Preferred examples of the dichroic dye represented by Formula 2 include Direct Black 4 and so on. Specific examples of the trihalotriazine compound represented by Formula 3 include 2, 4, 6-trichloro-l, 3, 5- triazine (cyanuric chloride), 1,2,3- and 1, 2, 4-triazine or

triazine derivatives, such as melamine and benzoguanamine .

The reaction ratio of the dichroic dye to the trihalotriazine compound represented by Formula 3 may fall in the range from about 1:0.9 to about 1:1.5. The reaction may take place at 10-30 ^° C for 20-30 hours. As such, a solvent, such as dimethylformamide (DMF) , dimethylacetamide (DMAc) , or N-methylpyrrolidone (NMP) may be used.

For the reaction, an additive, such as triethylamine or pyridine, may be further added, if necessary.

After the completion of the reaction, the solid precipitate is removed through filtration, and the solvent is removed using a vacuum distillation device. The residue obtained after the removal of the solvent is washed with alcohol, filtered, and vacuum dried at 40~60 ^° C, thus obtaining the reactive dichroic dye represented by Formula 1 according to the present invention.

The structure of the reactive dichroic dye product may be confirmed using FT-IR and ¹ H-NMR spectroscopy. In the FT- IR and ¹ H-NMR spectroscopy, because the expected value of the product after the completion of the reaction is not greatly different from that of the mixture of the reaction materials, it is difficult to estimate the extent of progress of the reaction. Hence, in the present invention, after the completion of the reaction, the product is thoroughly washed using alcohol, which is a solvent for the reaction materials,

but is not a solvent for the product, until there is no change in the weight thereof, thus indicating the complete removal of unreacted materials, followed by performing spectroscopy. In the reactive dichroic dye thus obtained, the PVA- based film is immersed, yielding a PVA-based film according to the present invention. The immersion method is not particularly limited, but is exemplarily conducted in a manner such that the reactive dichroic dye is dissolved in water and then the PVA-based film is immersed in the dye solution. The reactive dichroic dye is dissolved at a concentration of 0.0001~10 wt% in water, thus preparing a salt bath. As such, the pH is preferably set within the range from 8 to 12. Alternatively, dyeing may be conducted in the presence of an organic solvent, which will be described later. In the case where dyeing is conducted in the presence of an organic solvent, the reactive dichroic dye is dissolved at a concentration of 1~2 wt% in the organic solvent, thus preparing a salt bath. This case is advantageous in terms of reaction and adsorption of the dye and an increase in transmittance .

The PVA-based film dyed with the reactive dichroic dye is washed with an aqueous solution, thus removing the remaining reactive dichroic dye. Thereafter, stretching is performed, thereby obtaining the PVA-based film in which the

dichroic dye molecules are arranged in the stretching direction. The stretching may be conducted through a wet process or a dry process, or alternatively, before the dyeing, a process of stretching the PVA-based film may be adopted. Further, post-treatment, including boric acid treatment or the like, may be conducted for the purpose of increasing beam transmittance, the degree of polarization, and light resistance of a polarizing film. Although conditions for boric acid treatment may vary depending on the type of dye used, boric acid treatment is generally conducted at 30~80 ^° C using an aqueous boric acid solution prepared at a concentration of 1-15 wt%. Also, fix treatment using an aqueous solution containing a cationic polymer compound may be performed together therewith, if necessary. In addition, the present invention pertains to a method of preparing the PVA-based film using a dichroic dye. Specifically, the preparation method according to the present invention is characterized in that dyeing of the PVA-based film using the dichroic dye is performed not under an alkaline condition but in the presence of an organic solvent.

In the case of the dichroic dye, dyeing is typically conducted in a manner such that a strong alkaline salt solution is prepared and then a PVA-based film is immersed therein. Typically, a strong alkaline condition for the dyeing of the PVA-based film using the dye (hereinafter, referred to

as "dye-PVA-based film' ) is originally intended to be used in a fiber dyeing process, which is not a film dyeing process. For example, a PVA-based film is immersed in a solution of a dichroic dye dissolved in water. As such, the dichroic dye is dissolved in a predetermined concentration to prepare a salt bath, the pH of which is adjusted to have an alkaline condition ranging from 8 to 12. In practice, the pH of the salt bath is set to 11 or higher, which is a strong alkaline condition, and accordingly, the dyeing environment becomes poor. In the case of a dichroic dye having a functional group at an end portion thereof, there is a worry about the side reaction of the functional group under a strong alkaline condition, which would thus negatively affect the action of the functional group. In particular, if a dichroic dye, which has an azo chromophore and in which an NH ₂ group is present at an end portion thereof, is used for a dyeing process under a strong alkaline condition, the action of the end group may be deteriorated, consequently lowering the light transmittance of the film.

Further, in the case of a reactive dichroic dye having a halotriazine group at an end portion thereof to induce a reaction with a PVA-based film, dyeing under a strong alkaline condition causes great concern about a negative effect on the action of the functional group of the end portion of the reactive dichroic dye.

Accordingly, in the present invention, dyeing is conducted not under a strong alkaline condition but in the presence of an organic solvent, thereby enabling the preparation of a PVA-based film having high light transmittance. That is, the PVA-based film thus obtained is considered to be applicable to fields in which greater light transmittance, rather than polarizing efficiency, is required.

Useful in the present invention, the type of solvent is selected in consideration of the degree of swelling of a

PVA film and the solubility of a dye, and specific examples of the solvent include chloroform, dimethylformamide, ethyleneglycol, and dimethylsulfoxide.

Further, in order to increase transmittance upon dyeing in the presence of such an organic solvent, a reactive dichroic dye having an azo chromophore and at least one amine group (-NH ₂ ) at an end portion thereof, in which at least one hydrogen atom of the amine group is substituted with halotriazine, is used. Examples of the reactive dichroic dye include a reactive dichroic dye represented by Formula 1 and a reactive dichroic dye represented by Formula 4 below:

Formula 4

C-N=N-A' -N=N-C

wherein A' is or

, in which X is NH, N=N, CH=CH, NHCONH, NHOC or SO ₂ O, and Ri and R ₂ , which are the same as or different from each other, are H, NH ₂ , OH, SO ₃ Na, CH ₃ or OCH ₃ ,

which R ₃ , R ₄ , R ₅ and R ₆ , which are the same as or different from each other, are H, NH ₂ , OH, SO ₃ Na, CH ₃ , OCH ₃ , COONa, COOH, SO ₂ NH ₂ , SO ₂ NHCH ₃ , SO ₃ Na, SO ₃ CH ₃ , NHCOCH ₃ , NHCONH ₂ , NHCH ₂ SO ₃ Na or NHCH ₂ COONa, at least one of R ₃ to R ₆ being NH ₂ , R ₇ , R ₈ , Rg and Ri ₀ , which are the same as or different from each other, are H, NH ₂ , OH, SO ₃ Na, CH ₃ or OCH ₃ , and Rn and Ri ₂ , which are the same as or different from each other, are H, NH ₂ , OH, SO ₃ Na, CH ₃ , OCH ₃ , COONa, COOH, SO ₂ NH ₂ , SO ₂ NHCH ₃ , SO ₃ Na, SO ₃ CH ₃ , NHCOCH ₃ , NHCONH ₂ , NHCH ₂ SO ₃ Na or NHCH ₂ COONa, at least one of Rn and R _i2 being NH ₂ , and

which R ₁₃ , R ₁₄ , R ₁₅ and R ₁₆ , which are the same as or different

from each other, are (in which Xi is a halogen group) , H, NH ₂ , OH, SO ₃ Na, CH ₃ , OCH ₃ , COONa, COOH, SO ₂ NH ₂ ,

SO ₂ NHCH ₃ , SO ₃ Na, SO ₃ CH ₃ , NHCOCH ₃ , NHCONH ₂ , NHCH ₂ SO ₃ Na or

NHCH ₂ COONa, at least one of R _i3 to Ri ₆ being , R ₇ ,

Rs, Rg and Ri ₀ are defined as above, and Ri ₇ and Ris, which are

the same as or different from each other, are (in which Xi is a halogen group) , H, NH ₂ , OH, SO ₃ Na, CH ₃ ,

OCH ₃ , COONa, COOH, SO ₂ NH ₂ , SO ₂ NHCH ₃ , SO ₃ Na, SO ₃ CH ₃ , NHCOCH ₃ , NHCONH ₂ , NHCH ₂ SO ₃ Na or NHCH ₂ COONa, at least one of R ₁₇ and Ri ₈

ing

More specifically, in the reactive dichroic dye, A' is

which R _x and R ₂ are H, R ₃ is NH ₂ , R ₄ and R ₅ are H, R ₆ is NaSO ₃ ,

Ri ₃ is , Ri ₄ and Ri ₅ are H, and R _i6 is NaSO ₃ .

Also, in the reactive dichroic dye, A' is

, in which Ri is H, R ₂ is NaSO ₃ , X is NH, R ₇ is OH, R ₈ and R ₉ are H, Ri ₀ is NaSO ₃ , Rn and Ri ₂ are NH ₂ ,

According to the present invention, in the reactive dichroic dye represented by Formula 4, Xi is a halogen atom, preferably Cl, Br or F, and more preferably Cl.

Also, in the reactive dichroic dye represented by Formula 4, when A' is naphthalene, the preferred substitution position is 2,6- or 1,4-. In order to efficiently exhibit the properties of the dichroic dye, there is a need for anisotropy depending on the molecular orientation. This is because the linear substitution position is favorable for maintaining the linearity of molecules, and the linearity of molecules may favorably affect the orientation of molecules

when a film is stretched.

The reactive dichroic dye represented by Formula 4 may be obtained by reacting a dichroic dye represented by Formula

5 below, having an azo chromophore and at least one amine group at an end portion thereof, with a trihalotriazine compound represented by Formula 3 below.

Formula 5

C-N=N-A' -N=N-C wherein A' and C are defined as in Formula 4. Formula 3

Preferred examples of the dichroic dye represented by Formula 5 include Congo red, Direct Black 17, 19 and 22, Direct Red 2 and 28, Direct Blue 1 and 15, and Direct Violet 12.

The specific example of the trihalotriazine compound represented by Formula 3 is mentioned as above.

The reaction ratio of the dichroic dye to the trihalotriazine compound represented by Formula 3 may range from about 1:0.9 to about 1:1.5.

The reaction may be carried out at 10-30 ^° C for 20-30 hours, and the solvent therefor is exemplified by dimethylformamide (DMF), dimethylacetamide (DMAc), or N- methylpyrrolidone (NMP) .

For the reaction, an additive, such as triethylamine or pyridine, may be further added, if necessary.

After the completion of the reaction, the solid precipitate is removed through filtration, and the solvent is removed using a vacuum distillation device. The residue obtained after the removal of the solvent is washed with alcohol, filtered, and then vacuum dried at 40~60 ^° C, thus obtaining the reactive dichroic dye represented by Formula 4.

Such a reactive dichroic dye is dissolved in an organic solvent, after which a PVA-based film is immersed in the dye solution. In order to improve the reaction and adsorption of the dye and the transmittance, the reactive dichroic dye is dissolved at a concentration of 1~2 wt% in an organic solvent to thus prepare a salt bath. The PVA-based film dyed with the reactive dichroic dye is washed with an organic solvent, thereby removing the remaining reactive dichroic dye. Then, stretching is conducted, resulting in a PVA-based film in which the dichroic dye molecules are arranged in the stretching direction. The stretching may be conducted through a wet process or a dry process, or alternatively, before the dyeing, a process of stretching the PVA-based film may be adopted.

Further, post-treatment, including boric acid treatment or the like, may be conducted to increase beam transmittance, the degree of polarization and light resistance of a polarizing film. Although conditions for

boric acid treatment may vary depending on the type of dye used, boric acid treatment is generally conducted at 30~80 ^° C using an aqueous boric acid solution prepared at a concentration of 1-15 wt% . Further, fix treatment using an aqueous solution containing a cationic polymer compound may be performed together therewith, if necessary.

[Mode for Invention]

A better understanding of the present invention may be obtained through the following examples, which are set forth to illustrate, but are not to be construed as the limit of the present invention. Example 1

Direct Black 4 [1] (1.88 g, 2.7 ^χ lO ^"3 mol, Aldrich) was added with dimethylformamide (25 m£) and was thus dissolved at room temperature in a nitrogen atmosphere, after which cyanuric chloride (0.5 g, 2.7 ^χ lO ^~3 mol) was added to the solution in which Direct Black 4 was dissolved. After 1 min, 0.38 mi (2.7*10 ^~3 mol) of triethylamine was added in droplets thereto. Thereafter, stirring was conducted at 20 ^° C for 24 hours. After the completion of the reaction, the solid precipitate was removed through filtration using a filter device, and the solvent was removed using a vacuum distillation device. The residue obtained after the removal of the solvent was washed with ethanol, filtered again, and vacuum dried at 60 ^° C, thus obtaining a compound [2] . The

reaction route of the compound thus obtained is schematically represented by Scheme 1 below. Scheme 1

LU

Ul

The dichroic dye used as the starting material and the product were confirmed using FT-IR and ¹ H-NMR spectroscopy.

The results of FT-IR spectroscopy of Direct Black 4, which was used as the starting material, are shown in FIG. 1. As seen in this drawing, N-H and 0-H stretching vibrations were observed over a wide range from 3099 cm ^"1 to 3667 cm ^" , aromatic C=C stretching vibration was observed at 1490 cm ^"1 and 1635 cm ^"1 , S=O stretching vibration was observed at 1176 cm ^"1 , and C-N stretching vibration was observed at 1145 cm ^"1 . The results of NMR spectroscopy of Direct Black 4 dissolved with deuterium-substituted methylenesulfoxide (DMSO-d ₆ ) are shown in FIG. 2. As seen in this drawing, the

resonance peaks for the protons of the phenyl groups were observed over 5.8-10.4 ppm, and the resonance peaks for the methyl group were observed at 2.05 ppm.

The results of FIGS. 1 and 2 are summarized as follows. IR (KBr) Y _m3x (Cm ^"1 ): 3443, 1635, 1490, 1176, 1145.

¹ H-NMR(DMSO-D ₆ , 200MHz) δ (ppm) : 10.39(d, J 0.05ppm, IH, NaSO ₃ -C=CH-C-CH=C-NaSO ₃ ), 8.15 (s, 4H, -N=N-C=CH-C=), 7.93- 7.82 (m, 4H, -N=N-C=CH-CH=C-), 7.50 (s, 2H, -N=N-C=CH-CH=CH- CH=CH), 7.42(S, IH, NH ₂ -C=C-CH=C-N=N-), 7.32 (s, 3H, -N=N- C=CH-CH=CH-CH=), 6.96(d, J 0.03ppm, IH, -N=N-C=CH-CH=NH-), 5.97(d, J 0.06ppm, IH, IH, H ₂ N-C=CH-C-NH ₂ ), 2.05(s, 3H, NH ₂ - C=CH ₃ )

The results of FT-IR of the compound [2] obtained through substitution are shown in FIG. 3. As seen in this drawing, N-H and O-H stretching vibrations were observed at 3451 cm ^"1 . Further, aromatic C=C stretching vibration were observed at 1566 cm ^"1 , S=O stretching at 1180 cm ^"1 , and C-N stretching at 1040cm ^"1 . The peaks for triazine were observed at 2776 cm ^"1 , 2674 cm ^"1 , and 1715 cm ^"1 . Further, the results of NMR spectroscopy of the compound [2], dissolved using deuterium-substituted methylenesulfoxide (DMSO-dβ) , are shown in FIG. 4. As seen in this drawing, the protons of the phenyl groups manifested the same chemical shift as in FIG. 2, so that the positions of the resonance peaks over 8.37-12.08 ppm were equal to the expected values.

The results of FIGS. 3 and 4 are summarized as follows.

IR (KBr) Y _m3x (Cm ^"1 ): 3451, 2776, 2674 1715, 1566, 1180, 1040.

¹ H-NMR(DMSO-D ₆ , 200MHz) δ (ppm) : 12.08(d, J 0.02ppm, IH, NaSO ₃ -C=CH-C-CH=C-NaSO ₃ ), 11.19(s, 4H, -N=N-C=CH-C=), 8.85- 8.73 (m, 4H, -N=N-C=CH-CH=C-), 8.49 (s, 2H, -N=N-C=CH-CH=CH- CH=CH), 8.37 (s, IH, NH ₂ -C=C-CH=C-N=N-), 8.11 (s, 3H, -N=N- C=CH-CH=CH-CH=), 7.92 (d, J 0.02ppm, IH, -N=N-C=CH-CH=NH-), 7.05 (d, J O.Oβppm, IH, IH, H ₂ N-C=CH-C-NH ₂ ), 2.09(s, 3H, NH ₂ - C=CH ₃ )

Example 2

The reactive dichroic dye of Example 1 was prepared, dissolved at a concentration of 1 wt% in 50 mi of distilled water, added with 1 wt% of Na ₂ SO ₄ to increase the adsorption of the dye, and then added with NaOH little by little to adjust the pH to 11.

In the solution thus prepared, a 4 cmx 4 cm sized PVA film, which was washed with distilled water and dried, was allowed to react for 30 min. After the completion of the reaction, the PVA was washed with distilled water, washed several more times with an aqueous solution having a pH adjusted to 11 and distilled water to remove the unreacted doped dye, and then stretched five times in a 2 wt% aqueous boric acid solution. The stretched film was vacuum dried at 40 ^° C for 24 hours.

This schematic reaction is exemplarily represented by

Scheme 2 below. Scheme 2

PVA

Comparative Example 1

A typical iodine-dyed PVA film was prepared. The preparation of the iodine-dyed PVA film was as follows.

PVA was simply washed with distilled water. 0.1 M iodine (I) and 0.2 M potassium iodide (KI) were dissolved in 100 mi of distilled water at 40 ^° C. In the solution thus obtained, the PVA film was immersed for 2 min. The iodine

(I) , which was not doped, was removed through washing using cold distilled water. The PVA-I ₂ sample film thus obtained was vacuum dried in an oven at 40 ^° C for 24 hours.

Comparative Example 2

Each PVA film was prepared using the dichroic dye. The specific preparation procedure thereof was as follows. Direct Black 4, which was used as the starting material of the reactive dichroic dye of Example 1, was prepared, dissolved at a concentration of 0.5 wt% in 50 mi of distilled water, and then added with 1 wt% of Na ₂ SO ₄ to increase the adsorption of the dye. In the solution thus obtained, a 4 cm * 4 cm sized PVA film, which was washed with distilled water and dried, was immersed for 120 sec. After the completion of the immersion, the resultant PVA was washed with distilled water, washed several more times with distilled water to remove the dye, which was not doped but remained on the surface thereof, and then stretched four times in a 2 wt% aqueous boric acid solution. The stretched film was vacuum dried at 40 ^° C for 24 hours .

Test Example 1

The optical properties and durability of the PVA films obtained in Example 2 and Comparative Examples 1 and 2 were measured.

(1) Optical Properties The optical properties of the film were determined by measuring the UV-Vis absorption spectrum using an S-1100,

available from Scinco.

The absorbance of the center portion of the film, which had the greatest stretch ratio and was uniform, was measured. First, single-film transmittance was measured. Second, parallel transmittance was measured by laminating two films parallel to the stretching direction. Third, perpendicular transmittance was measured by laminating two films perpendicular to each other.

The polarizing efficiency was calculated from Equation 1 below.

Equation 1

„ , . . „„ . .. .. I parallel transmittance - perpendicular transmittance . _nn

Polarizing Efficiency (%) = — ^£ -- ^£ - x 100

I parallel transmittance + perpendicular transmittance

As the transmittance value, transmittance at a maximum absorption wavelength was used.

In FIG. 5, showing the transmittance and polarizing efficiency of the PVA-I ₂ film (Comparative Example 1) , the single-film transmittance at a maximum absorption wavelength was determined to be 42.8%, and the polarizing efficiency was calculated to be 99.8%.

In FIG. 6, showing the optical properties of the

Direct Black 4-dyed PVA film (Comparative Example 2), the single-film transmittance at a maximum absorption wavelength was determined to be 7.5%, and the polarizing efficiency was calculated to be 88.4%.

In FIG. 7, showing the optical properties of the PVA

film (Example 1) obtained using the reactive dichroic dye of Example 1 according to the present invention, the single-film transmittance at a maximum absorption wavelength was determined to be 17.8%, and the polarizing efficiency was calculated to be 98.8%.

Consequently, the effect of the reactive dichroic dye reacted with the surface of PVA could be confirmed as follows. That is, the PVA film (Example 2) obtained using the reactive dichroic dye of Example 1 had slightly lower polarizing efficiency or transmittance than the PVA-I ₂ film (Comparative Example 1) , but was improved in both transmittance and polarizing efficiency over the PVA film (Comparative Example 2) dyed with Direct Black 4 as the dichroic dye. (2) Durability In order to evaluate the durability of the PVA film, the durability test was conducted.

The test was carried out in a desiccator under conditions of temperature of 50 ^° C and humidity of 85% or more for five days, and changes in transmittance and polarizing efficiency were measured at intervals of 24 hours.

FIG. 8 shows the results of evaluation of the durability of the PVA-I ₂ film (Comparative Example 1) , and FIG. 9 shows the results of evaluation of the durability of the PVA film (Example 2) . As is apparent from the results shown in FIGS. 8 and 9, in the case of the iodine-based polarizing film (Comparative

Example 1) , the minimum single-film transmittance was determined to be 74.7% based on the rate of change in absorption wavelength of 31.9 for 120 hours, and accordingly the polarizing efficiency was determined to be 65.1% based on the rate of change of polarizing efficiency of 34.7, from which it was concluded that the polarizing properties were drastically lowered. However, in the film (Example 2) obtained using the reactive dichroic dye of Example 1, according to the heat and humidity durability test, the initial polarizing efficiency of 98.8% was changed to 94.8%, and the rate of change was 4.0%. The transmittance was changed from 17.9% to 43.5%, and the rate of change was 25.6%. That is, the polarizing efficiency and transmittance of the inventive film were not superior to those of the iodine-based polarizing film. From this, even though the dyed film (Comparative Example 1) had excellent polarizing efficiency, the very poor transmittance thereof before the durability test was greatly worsened after the durability test, making it impossible to use the above film in practice. Consequently, compared to the iodine-based polarizing film, the polarizing efficiency and transmittance of which were greatly changed due to the high sublimation of iodine, the PVA film obtained through the reaction of the reactive dichroic dye according to the present invention could be seen to have relatively lower rates of change.

Reference Example 1

Congo Red [3] (1.88 g, 2.7 ^χ lO ^"3 mol, Aldrich) was added with dimethylformamide (25 and was thus dissolved at room temperature in a nitrogen atmosphere, after which cyanuric chloride (0.5 g, 2.7 ^χ lO ^~3 mol) was added to the solution in which Congo Red was dissolved. After 1 min, 0.38 mi (2.7 ^χ lO ^~3 mol) of triethylamine was added in droplets thereto.

Thereafter, stirring was conducted at 20 ^° C for 24 hours. After the completion of the reaction, the solid precipitate was removed through filtration using a filter device, and the solvent was removed using a vacuum distillation device. The residue obtained after the removal of the solvent was washed with ethanol, filtered again, and vacuum dried at 60 ^° C, thus obtaining a compound [4]. The reaction route of the compound thus obtained is schematically represented by Scheme 3 below. Scheme 3

DMF triethylatnine

The reactive dichroic dye thus obtained was dissolved at a concentration of 1 wt% in 100 ml of distilled water,

added with 1 wt% of Na ₂ SO ₄ to increase the adsorption of the dye, and then added with NaOH little by little to adjust the pH to 11.

In the solution thus prepared, a 4 cmx 4 cm sized PVA film, which was washed with distilled water and dried, was allowed to react for 30 min. After the completion of the reaction, the PVA was washed with distilled water, washed several more times with an aqueous solution having a pH adjusted to 11 and distilled water to remove the unreacted doped dye, and then stretched four times in a 2 wt% aqueous boric acid solution. The stretched film was vacuum dried at

40 ^° C for 24 hours.

Examples 3~6 A reactive dichroic dye obtained in the same manner as in Reference Example 1 was dissolved at a concentration of 1 wt% in 50 in.fi of each of chloroform, ethyleneglycol, dimethylsulfoxide and a solvent mixture comprising chloroform and dimethylsulfoxide (mixing weight ratio of chloroform: dimethylsulfoxide = 1:1), and then added with 1 wt% of Na ₂ SO ₄ to increase the adsorption of the dye.

In the solution thus prepared, a 4 cmx 4 cm sized PVA film, which was washed with distilled water and dried, was allowed to react for 30 min. After the completion of the reaction, the PVA was washed with distilled water, washed several more times with the corresponding organic solvent

used upon reaction to remove the unreacted doped dye, and then stretched four times in a 2 wt% aqueous boric acid solution. The stretched film was vacuum dried at 40 ^° C for 24 hours .

Reference Example 2

Direct Black 22 [5] (2.9 g, 2.7 ^χ lO ^"3 mol, CiBA specialty chemicals) was added with dimethylformamide (25 mi) and was thus dissolved at room temperature in a nitrogen atmosphere, after which cyanuric chloride (0.5 g, 2.7 ^χ lO ^"3 mol) was added to the solution in which Direct Black 22 was dissolved. After 1 min, 0.38 ml (2.7 ^χ lO ^~3 mol) of triethylamine was added in droplets thereto. Thereafter, stirring was conducted at 20 ^° C for 24 hours. After the completion of the reaction, the solid precipitate was removed through filtration using a filter device, and the solvent was removed using a vacuum distillation device. The residue obtained after the removal of the solvent was washed with ethanol, filtered again, and vacuum dried at 60 ^° C, thus obtaining a compound [6] . The reaction route of this compound is schematically represented by Scheme 4 below. Scheme 4

The reactive dichroic dye thus obtained was dissolved at a concentration of 1 wt% in 100 ml of distilled water, added with 1 wt% of Na ₂ SO ₄ to increase the adsorption of the dye, and then added with NaOH little by little to adjust the pH to 11.

In the solution thus prepared, a 4 cmx 4 cm sized PVA film, which was washed with distilled water and dried, was allowed to react for 30 min. After the completion of the reaction, the PVA was washed with distilled water, washed several more times with an aqueous solution having a pH adjusted to 11 and distilled water to remove the unreacted doped dye, and then stretched four times in a 2 wt% aqueous boric acid solution. The stretched film was vacuum dried at 40 ^° C for 24 hours.

Examples 7~11

The reactive dichroic dye obtained in Reference Example 2 was dissolved at a concentration of 1 wt% in 50 mi

of each of chloroform, DMF, ethyleneglycol, dimethylsulfoxide and a solvent mixture comprising chloroform and dimethylsulfoxide (mixing weight ratio of chloroform: dimethylsulfoxide = 1:1), and then added with 1 wt% of Na ₂ SU ₄ to increase the adsorption of the dye.

In the solution thus prepared, a 4 cmx 4 cm sized PVA film, which was washed with distilled water and dried, was allowed to react for 30 min. After the completion of the reaction, the PVA was washed with distilled water, washed several more times with the corresponding organic solvent used upon the reaction to remove the unreacted doped dye, and then stretched four times in a 2 wt% aqueous boric acid solution. The stretched film was vacuum dried at 40 ^° C for 24 hours .

Test Example 2

The optical properties and durability of the PVA films obtained in Reference Examples 1 and 2 and Examples 3 to 11 were measured. (1) Optical Properties

The optical properties of the film were determined by measuring the UV-Vis absorption spectrum using an S-1100, available from Scinco.

The absorbance of the center portion of the film, which had the greatest stretch ratio and was uniform, was measured. First, single-film transmittance was measured.

Second, parallel transmittance was measured by laminating two films parallel to the stretching direction. Third, perpendicular transmittance was measured by laminating two films perpendicular to each other. The polarizing efficiency was calculated from Equation 1 below.

Equation 1 parallel transmittance - perpendicular transmittance

Polarizing Efficiency (%) = xlOO parallel transmit tance + perpendicular transmittan ce

As the transmittance value, transmittance at a maximum absorption wavelength was used.

In FIG. 10, showing the optical properties of Reference Example 1, the single-film transmittance at a maximum absorption wavelength was determined to be 25.3%, and the polarizing efficiency was calculated to be 98.4%.

FIGS. 11 to 14 show the optical properties of the films of Examples 3 to 6, respectively, obtained through dyeing in the presence of the organic solvent using the same reactive dichroic dye as in Reference Example 1. FIG. 11 shows the case in which dyeing was conducted in the presence of chloroform using the same reactive dichroic dye as in Reference Example 1. In this case, the single-film transmittance at a maximum absorption wavelength was determined to be 51.8%, and the polarizing efficiency was calculated to be 24.5%.

In FIG. 12, showing the case in which dyeing was conducted in the presence of ethyleneglycol, the single-film transmittance at a maximum absorption wavelength was determined to be 36.0%, and the polarizing efficiency was calculated to be 57.1%.

In FIG. 13, showing the case in which dyeing was conducted in the presence of dimethylsulfoxide, the single- film transmittance at a maximum absorption wavelength was determined to be 39.9%, and the polarizing efficiency was calculated to be 41.4%.

In FIG. 14, showing the case in which dyeing was conducted in the presence of the solvent mixture comprising chloroform and dimethylsulfoxide (mixing weight ratio of 1:1), the single-film transmittance at a maximum absorption wavelength was determined to be 41%, and the polarizing efficiency was calculated to be 45.7%.

Comparing the results of FIGS. 11 to 14 with the results of FIG. 10, the case in which the dyeing was conducted in the presence of the organic solvent resulted in slightly decreased polarizing efficiency but remarkably increased transmittance. The preparation method of the present invention is considered to be useful in the manufacture of a polarizing film requiring high transmittance . In FIG. 15 showing the optical properties of Reference Example 2, the single-film transmittance at a maximum

absorption wavelength was determined to be 34.8%, and the polarizing efficiency was calculated to be 82.7%.

FIGS. 16 to 20 show the optical properties of the films of Examples 7 to 11, respectively, obtained through dyeing in the presence of the organic solvent using the same reactive dichroic dye as in Reference Example 2. FIG. 16 shows the case in which dyeing was conducted in the presence of chloroform using the same reactive dichroic dye as in

Reference Example 1. In this case, the single-film transmittance at a maximum absorption wavelength was determined to be 52.0%, and the polarizing efficiency was calculated to be 19.6%.

In FIG. 17, showing the case in which dyeing was conducted in the presence of DMF, the single-film transmittance at a maximum absorption wavelength was determined to be 39.6%, and the polarizing efficiency was calculated to be 25.3%.

In FIG. 18, showing the case in which dyeing was conducted in the presence of ethyleneglycol, the single-film transmittance at a maximum absorption wavelength was determined to be 66.9%, and the polarizing efficiency was calculated to be 13.8%.

In FIG. 19, showing the case in which dyeing was conducted in the presence of dimethylsulfoxide, the single- film transmittance at a maximum absorption wavelength was

determined to be 62.5%, and the polarizing efficiency was calculated to be 20.2%.

In FIG. 20, showing the case in which dyeing was conducted in the presence of the solvent mixture comprising chloroform and dimethylsulfoxide (mixing weight ratio of 1:1), the single-film transmittance at a maximum absorption wavelength was determined to be 78.2%, and the polarizing efficiency was calculated to be 16.7%.

Comparing the results of FIGS. 16 to 20 with the results of FIG. 15, the case in which the dyeing was conducted in the presence of the organic solvent showed slightly decreased polarizing efficiency but remarkably increased transmittance. Therefore, the preparation method of the present invention is considered to be useful in the manufacture of a polarizing film requiring high transmittance.