WO2013050431A1

WO2013050431A1 - A salt for color filter application, a process for making the same, and a colorant comprising the same

Info

Publication number: WO2013050431A1
Application number: PCT/EP2012/069553
Authority: WO
Inventors: Kisuck Jung; Sangmin Han; Iljo Choi; Eunha Jeong
Original assignee: Solvay SA
Current assignee: Solvay SA
Priority date: 2011-10-06
Filing date: 2012-10-03
Publication date: 2013-04-11
Anticipated expiration: 2014-04-06
Also published as: KR20140082764A; CN103987794A; JP2014534290A

Abstract

Disclosed are a salt comprising, as cation, at least one cationic cyanine compound, and, as anion, at least one anionic xanthene compound, as well as its use in color filters, e.g. for displays, and its preparation process. The salt of the present invention provides improved characteristics, especially in terms of a thermal stability and/or brightness.

Description

A salt for color filter application, a process for making the same, and a colorant comprising the same

This application claims priority to European patent application No.

11184165.6 filed on October 6, 2012, the whole content of this application being incorporated herein by reference for all purposes.

Technical Field

This invention is generally directed to a salt suitable for color filter application, especially to a cyanine-xanthene salt, and processes for the preparation thereof. More specifically, the present invention is directed to the preparation of a salt comprising at least one cationic cyanine compound and at least one anionic xanthene compound, which exhibits better characteristics for color filters. Further, the present invention also relates to a display device, especially a liquid crystal display in which the foregoing salt is incorporated. Background Art

Color filters, particularly those used in liquid crystal display (LCD) device and the like, are usually produced by first forming a pattern from a photoresist and subsequently dyeing the pattern. However, this method is mostly

disadvantageous in that the dyeing process is complicated and difficult to control. Thus, methods for producing color filters by patterning a photoresist containing a dyestuff such as pigment or dye as colorant, have been proposed. However, those methods are sometimes not suitable for production of color filters requiring a high resolution, because the pigment/dye itself used therein contains particles with relatively large size, e.g., of about 1 μιη size, or the stability of the resultant colored pattern is inferior.

In addition to the above, these methods are involved with another important problem. That is, usual dyestuffs exist as an extraneous matter different from the alkali-developable resist. Since the preferable thickness of resist film is 1 μιη or less in the case of producing a color filter, a large amount of dyestuffs must be added to a resist composition comprising a resin and an organic solvent. Actual dyestuffs, however, are soluble in neither of aqueous (alkali) solution and organic solvent, and therefore it is difficult to prepare a fine color pattern having a desired spectrum and a small film thickness from such dyestuffs. Another disadvantage from such insolubility is that dyestuff particles sometimes agglomerate and the performances of color filter prepared from the composition, such as brightness and contrast ratio, become deteriorated.

Recently, use of soluble dyes such as cyanine dye, xanthene dye and azo dye is proposed to improve solubility of the colorant for color filter.

US20080237553 Al discloses a colored photosensitive resin composition comprising an alkali- solution resin, a photosensitive compound, a curing agent, a solvent and a cyanine colorant, in which a cyanine molecule is used as a violet colorant.

US20040074018 Al discloses dye mixtures consisting essentially of an azo compound such as C.I. Reactive Red 23, and a xanthene compound such as C.I. Acid Red 52, and their use in ink-jet printing and yields storage-stable and water-proof ink formulations.

However, the above-described colorants and/or dyes have problems in that they still exhibit poor performances when used in color filters, particularly in terms of contrast ratio and brightness. Further, some dyes, particularly cyanine- based dyes, are not sufficiently stable and thus do not meet the requirements for the device fabrication, where processing at high temperature is frequently required. Thus, there is still a strong desire in the art to develop a method of effectively improving color filter performances along with thermal stability by modifying such soluble dyes, without the above-described drawbacks.

Disclosure of Invention

One of the purposes of the invention is to develop compositions for color filters exhibiting good performances including contrast ratio and brightness when used as the pigment of color filters for liquid crystal displays (LCDs).

The inventors of the present invention have tried to resolve the problems, and discovered that the performances of the color filter pigment can be improved when a cyanine-xanthene salt is used. Further, they also discovered that if the salt is formed using an anionic xanthene compound and a cationic cyanine compound, it shows improved thermal stability, and the resultant color filter from the salt can exhibit better performances in terms of contrast ratio and brightness.

The present invention, therefore, relates to a salt comprising, as cation, at least one cationic cyanine compound, and, as anion, at least one anionic xanthene compound.

Hereinafter, the present invention is described in detail. The term "dye" is defined herein as a colorant that is soluble in water or other solvents. Especially, the dye has an affinity to the substrate to which it is applied. The term "pigment" is defined herein as a colorant that changes the color of reflected or transmitted light as the result of wavelength- selective absorption and is not soluble in water and other solvents. Even though, both dyes and pigments appear to be colored because they absorb some wavelengths of light preferentially, in contrast with a dye, a pigment generally is insoluble, and has no affinity for the substrate. The term "salt" is defined herein as materials in solid or in solution formed from an anion(s) and a cation(s).

In a first specific embodiment of the present invention, the anionic xanthene compound is re resented by Formula (I) below

Formula (I)

wherein:

- Rl, R2, R3 and R4 are same or different at each occurrence and

independently selected from a group consisting of hydrogen, and alkyl, cycloalkyl and aralkyl having 1 to 4, preferably 1 to 2, more preferably 2 carbon atoms, and

- m is from 2 to 5.

In this first specific embodiment, Rl, R2, R3 and R4 may be the same or different at each occurrence, preferably the same. Rl, R2, R3 and R4 are advantageously independently selected from a group consisting of alkyl having 1 to 4 carbon atoms, preferably methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl and t-butyl, more preferably ethyl.

In this first specific embodiment, m is typically from 2 to 5, especially from 2 to 4, more especially 2 or 3, for instance 2.

In this first specific embodiment, the at least one SO₃ ^" group may be located in ortho, meta or para, advantageously in ortho or para, preferably in at least both ortho and para if at least two SO₃ ^" groups are present. In an especially preferred embodiment, the anionic xanthene compound is represented by Formula I-l) below.

Formula (I-l)

In the present invention, the xanthene compounds as represented by Formula (I) and more specifically by Formula (I-l) can be prepared by any methods known in the art. For instance, the xanthene compounds of

Formula (I-l) can be prepared by addition of aminophenol and formyl- sulfonic acid sodium salt in p-toluene-sulfonic acid, filtering the mixture, washing and evaporation of the resultant filtrate.

In a second specific embodiment of the present invention, the cationic cyanine compound is typically represented by Formula (II) below

Formula (II)

wherein:

- A and B are same or different at each occurrence, preferably the same, and independently selected from a group consisting of aromatic ring, heteroaromatic ring, and polyaromatic ring having 3 to 20 carbon atoms, preferably 6 to 16 carbon atoms, especially benzene or naphthalene, said group being optionally substituted by fluorinated or non-fluorinated alkyl, - R5 and R6 are same or different at each occurrence, especially the same, and independently selected from a group consisting of alkyl, alkoxy and hydroxyalkyl having 1 to 30 carbon atoms, preferably 2 to 20 carbon atoms, most preferably 4 to 15 carbon atoms, which may be optionally substituted by other atoms, preferably halogen, more preferably fluorine, - Xi, X₂, X3 and X4 may be any kind of substituents, preferably the same or different at each occurrence, in particular the same, and independently selected from a group consisting of hydrogen or alkyl which may be substituted by halogen, preferably fluorine,

- Yi, Y₂ and Y₃ are same or different at each occurrence and independently selected from a group consisting of hydrogen, halogen, cyano, nitro, alkyl, and aryl groups, which may be taken together to form a 5 or 6 membered ring and

- n is 1 to 5, preferably 1 to 3.

In some further specific embodiments, at least one of Yi, Y2 and Y₃ of Formula (II) is cyano or halogen, preferably cyano or chlorine. In preferred embodiments, at least one of Xi to X₄, R5 and R6 is an alkyl substituted by at least one fluorine atom.

In more specific embodiments, the cationic cyanine compound is represented by any one of Formulae (II- 1) to (II-6) :

rmula (II- 1),

rmula (II- 2),

Formula (II-3),

Formula (II-4),

rmula (II-5), and

Formula (II-6).

In a more preferable embodiment, the cationic cyanine compound is represented by Formula (II-6) above.

In the present invention, the cyanine compounds as represented by Formula (II) and more specifically by Formulae (II- 1) to (II-6) can typically be prepared by at least three steps. In the first step, an indolenine compound such as 2,3,3-trimethyl indolenine is prepared. In the second step, starting from the indolenine compound, a N- substituted indolium halide such as N-butyl 2,3,3-trimetyl indolium iodide is synthesized. Said N-substituted indolium halide then is subjected to the third step where a cyanine compound is produced by an anion exchange reaction with an organic or inorganic anion. The preparation of cyanine compounds is, for example, described in US Patent No. 6589706, the disclosures of which being incorporated herein by reference.

In one further embodiment, the salt of the present invention can be obtained by the following steps :

(a) at least partially dissolving at least one anionic xanthene compound in an aqueous solvent to provide a xanthene solution ;

(b) adding the xanthene solution to another solution comprising at least one cationic cyanine compound to form a precipitate,

(c) filtering the obtained precipitate, and

(d) optionally washing with water.

In more specific embodiments of this process of the invention, the anionic xanthene compound is present in the xanthene solution of step (a) in an amount of at least 1-20 %, preferably at least 1-10 %, more preferably at least 2-7 %, especially at least 5 % by weight of the solution. In some embodiments, at least a part of the anionic xanthene compound may be present in a dispersed state in the solution, the whole amount of the anionic xanthene being not in a dissolved state. In step (b) of said process, the solution comprising the anionic xanthene compound, optionally partially in a dispersed state, may be added dropwise or more rapidly to the solution comprising the cationic cyanine compound, preferably dropwise. After the addition of the solution comprising the anionic xanthene compound to the solution comprising the cationic cyanine compound is completed, a salt containing an anionic xanthene compound and a cationic cyanine compound is typically precipitated. In step (c), the precipitate may be recovered by any method known in the art, for example by filtration or centrifugation. The recovered precipitate is typically washed, usually with water.

In the process of the present invention, the weight ratio of the anionic xanthene compound to the cationic cyanine compound is typically 2:1, preferably 1.5:1, most preferably around 1:1.

In said process of the invention, the solvent used for dissolving the anionic xanthene compound and the cationic cyanine compound may be the same or different, most often the same. As the solvent used for dissolving the anionic xanthene compound and/or the cationic cyanine compound, any solvent known in the art may be used but water, water-miscible solvents such as alcohol, or mixtures thereof are generally used.

The salt of the present invention is especially suitable as a dye, in particular as a violet dye. According to another embodiment of the present invention, a millbase composition for a color filter may be prepared by mixing the salt of the present invention, used as a violet colorant, with at least one other dye or pigment ; and kneading the mixture. Such a millbase composition can be used as such but, if necessary, it can also be used together with different types of organic or inorganic pigments, preferably organic pigments. In the case of using different types of blue organic pigments together with the millbase composition described herein, it is desirable to use said millbase composition as a main component since it leads to better contrast ratio and brightness.

The millbase composition may include further additives, such as a binder, a polymer-based dispersion aid, a dispersant, a liquid medium and mixtures thereof, as described in US 7368148 which is incorporated herein by reference in its entirety.

For example, a solvent such as butanol, a dispersant and a binder

(including polymeric or resin material) are mixed. Then, the salt of the present invention may be added while stirring the mixture. Thereafter, the resultant mixture is subjected to milling for finely-dividing the particles of the components. In some embodiments of the present invention, the milling can be conducted in at least two steps utilizing milling beads having a different size. In specific embodiments, the milling is first conducted in the presence of large beads and then in the presence of small beads. After the milling step, the beads are removed by an appropriate separation means such as a glass filter, and a millbase composition is recovered.

The present invention is also directed to a colorant, preferably a violet colorant, comprising the salt according to the above-described invention. Said colorant may further comprise at least another dye or pigment, for instance a blue pigment such as ε-type copper phthalocyanine particles or a violet pigment such as PV-23. It is also related to a composition for color filter comprising the salt or the colorant of the present invention, as well as to a millbase composition for a color filter, comprising the salt or the colorant of the present invention and optionally any additive selected from a group consisting of a binder, a polymer- based dispersion aid, a dispersant and a liquid medium. The present invention therefore also relates to a color filter comprising said colorant. Such color filters may be prepared by lithographic methods, especially through the following steps: applying the millbase composition according to the present invention on a substrate, drying, exposing and developing. The color filters are applicable for preparation of a liquid crystal display device, a LED display device, or a solid- state image sensing device such as a charge coupled device (CCD) or the like.

The present invention therefore also relates to the use of the salt of the present invention as a dye, preferably as a violet dye, and to the use of the salt or of the colorant of the present invention for preparation of color filters, and in particular for forming the blue portion of color filters.

Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it might render a term unclear, the present description shall take precedence.

Examples

Example 1 (Preparation of Cyanine compound)

Synthesis oftrimethyl indolenine

80 g of phenyl hydrazine and 53 g of 3-methyl-2-butanone were added in 400 mL of acetic acid, and the mixture was stirred at 100°C for 3 hours. Then, the resultant mixture was cooled, and filtered to remove the solid by-products.

The filtrate was mixed with methylene chloride, and the mixture was then poured into water. The product was recovered, in the methylene chloride fraction, by extraction, and the methylene chloride was then evaporated. The yield in trimethyl indolenine was 90.8 % (80 g).

Synthesis of trimethyl indolium iodide

The obtained trimethyl indolenine, and 102 g of n-butyl iodide were added in 150 mL of o-chlorobezene. The mixture was stirred at 100°C for 24 hours. After the reaction, the resultant mixture was cooled, and the product was extracted with hot water from the mixture. The water was evaporated to give the product. The reaction yield in trimethyl indolium iodide was 77.1 % (133 g). Synthesis of cyanine compound

The obtained trimethyl indolium iodide and 86.1 g of trimethyl orthoformate, were added to 250 mL of pyridine. The mixture was stirred at 100°C for 3 hours, and then was subjected to cooling to the room temperature. The mixture was used in Example 3 without any further purification.

Example 2 (Preparation of Xanthene Compound)

Synthesis of Xanthene Dye Compound

22.14 g of dibutylaminophenol and 15.6 g of formyl-2,4-disulfonic acid disodium salt were added in 2 g of p-Toluene-sulfonic acid, and the mixture was stirred at 120°C for 3 hours. Then, the resultant mixture was cooled, and filtered to remove the salt by using mixed with water/ethanol (1 : 1) and was washed with water/ethanol (1 : 1) and the filtrate was evaporated. The reaction yield was 60 %. Example 3 (Preparation of the Salt of Present Invention)

The xanthene compound prepared according to Example 2 was dispersed in water so that a concentration of 5 % was reached. To the resultant mixture of Example 1 , 2640 mL of the 5 % dispersion of xanthene were added dropwise, which led to precipitation of the product. After completion of the addition of the xanthene dispersion, the precipitate was filtered and washed with water several times, and the product was obtained. The reaction yield in salt was 60 %

(64.5 g).

Example 4 (Preparation of a millbase composition)

A millbase composition was prepared by dissolving a methacrylate-based dispersant (10 parts) in 70 parts of ethanol containing 6 parts of a methacrylate- based binder with heat as necessary. 3mm diameter glass beads (100 parts) and ε-type copper phthalocyanine particles (10 parts), and the salt obtained in Example 3 (2 parts) were added and milling was carried out for 24 hours on a horizontal shaker to give a millbase composition. Comparative Example 1 (Preparation of a reference millbase composition comprising Pigment Violet 23)

A millbase composition was prepared according to an identical manner to Example 4 except that Pigment Violet 23 (PV 23) was used instead of the salt of Example 3.

Example 5 (Test of the color filters)

Color filters which were fabricated using the millbase composition according to Example 4 yielded improvements in contrast ratio and brightness by approximately 20 % and 3 %, respectively, compared to those prepared in Comparative Example 1 where Pigment Violet 23 (PV 23) was used instead of the salt of the present invention, as shown in Table 1.

As shown in the results of color properties below, the salt of the present invention used as violet colorant in the millbase represents improved performances compared to the Pigment Violet 23 typically used as violet pigment in the prior art.

Table 1

Industrial Application

The salt according to the present invention has the advantage of having improved thermal stability. The salt of the present invention also allows preparation of color filters having improved performances, specifically in terms of brightness. The salt of the present invention is further useful as a colorant for color filters, not only for liquid crystal displays (LCDs), but also for subtractive color generation, as for example in electro-optical systems such as charge coupled devices, plasma displays or electroluminescent displays, and also as a colorant for electronic inks ("e-inks") or electronic paper ("e-paper").

It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Claims

C L A I M S

1. A salt comprising, as cation, at least one cationic cyanine compound, and, as anion, at least one anionic xanthene compound.

2. The salt of Claim 1 , wherein the anionic xanthene compound is represented by Formula (I)

Formula (I) wherein:

- Rl , R2, R3 and R4 are same or different at each occurrence and

independently selected from a group consisting of hydrogen, and alkyl, cycloalkyl and aralkyl having from 1 to 4 carbon atoms ; preferably 1 to 2 more preferably 2 carbon atoms, and

- m is from 2 to 5, especially 2 to 4, more especially 2 or 3.

3. The salt of Claim 1 or 2, wherein the cationic cyanine compound is represented by Formula (II)

Formula (II) wherein:

- A and B are same or different at each occurrence and independently selected from a group consisting of aromatic ring, heteroaromatic ring, and polyaromatic ring having 3 to 20 carbon atoms, preferably from 6 to 16 carbon atoms, especially benzene or naphthalene, said group being optionally substituted by fluorinated or non-fluorinated alkyl ;

- R5 and R6 are same or different at each occurrence and independently selected from a group consisting of alkyl, alkoxy and hydroxyalkyl having 1 to 30, preferably 2 to 20, most preferably 4 to 15 carbon atoms which may be optionally substituted by other atoms, preferably alkyl or halogen, more preferably fluorine ;

- Xi, X₂, X3 and X4 may be any kind of substituents, preferably hydrogen or alkyl which may be substituted by halogen, preferably fluorine ;

- Yi, Y₂ and Y3 are same or different at each occurrence and independently selected from a group consisting of hydrogen, halogen, cyano, nitro, alkyl, and aryl groups, which may be taken together to form a 5 or 6 membered ring ; and

- n is 1 to 5.

4. The salt of any one of Claims 1 to 3 wherein - Rl, R2, R3 and R4 are same or different at each occurrence, preferably the same, and independently selected from a group consisting of alkyl having 1 to 4 carbon atoms, preferably methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl and t-butyl, more preferably ethyl, and

- m is from 2 to 3, especially 2.

5. The salt of any one of Claims 1 to 4, wherein the at least one SO₃ ^" group is located in ortho or para, preferably in at least both ortho and para if at least two SO₃ ^" groups are present.

6. The salt of any one of Claims 1 to 5, wherein the anionic xanthene compound is represented by Formula (Tl).

Formula (1-1)

7. The salt of any one of Claims 1 to 6, wherein at least one of Yi, Y2 and Y3 is cyano or halogen, preferably cyano or chlorine.

8. The salt of any one of Claims 1 to 7, wherein at least one of Xi to X₄, R5 and R6 is an alkyl substituted by at least one fluorine atom.

9. The salt of any one of Claims 1 to 8, wherein the cationic cyanine compound is represented by any one of Formulae (II- 1) to (II-6), preferably Formula (II-6).

rmula (II- 1),

rmula (II- 2),

Formula (II-3),

Formula (II-4),

10. A process for preparation of the salt of any one of Claims 1 to 9, comprising:

(a) at least partially dissolving at least one anionic xanthene compound in an aqueous solvent to provide a xanthene solution;

(c) filtering the obtained precipitate, and

(d) optionally washing with water.

11. A colorant comprising the salt of any one of Claims 1 to 9, and optionally at least another dye or pigment, preferably a violet colorant.

12. A composition for color filter comprising the salt of any one of Claims 1 to 9 or the colorant of Claim 11.

13. A millbase composition for a color filter comprising the salt of any one of Claims 1 to 9 or the colorant of Claim 11 , optionally comprising any additive selected from a group consisting of a binder, a polymer-based dispersion aid, a dispersant and a liquid medium.

14. Use of the salt of any one of Claims 1 to 9 or of the colorant of Claim 11 for preparation of color filters.

15. Use of the salt of any one of Claims 1 to 9 as a dye, especially as a violet dye.