BACKGROUND 1. Field of the Invention
This invention relates to stable colorants of high extinction coefficient and high solubility or dispersibility for an electrophoretic, magnetophoretic or electromagnetophoretic display. More particularly, it relates to stable colorants for a microcup-based electrophoretic, magnetophoretic or electromagnetophoretic display the cells of which are filled with charged and/or magnetic particles dispersed in a halogenated, preferably a fluorinated, solvent. The use of the stable colorants allows the display to be of superior contrast ratio and longevity, and suitable for high-quality imagery applications. 2. Brief Description of Related Art
The electrophoretic display (EPD) is a non-emissive device based on the electrophoresis phenomenon influencing the migration of charged pigment particles in a solvent, preferably a colored dielectric solvent. This type of display was first proposed in 1969. An EPD typically comprises a pair of opposed, spaced-apart plate-like electrodes, with spacers predetermining a certain distance between the electrodes. At least one of the electrodes, typically on the viewing side, is transparent. For the passive type of EPDs, row and column electrodes on the top (the viewing side) and bottom plates respectively, are needed to drive the displays. In contrast, an array of thin film transistors (TFTs) on the bottom plate and a common, non-patterned transparent conductor plate on the top viewing substrate are required for the active type EPDs.
An electrophoretic fluid composed of a colored dielectric solvent with charged pigment particles dispersed therein is enclosed between the two electrodes. When a voltage difference is imposed between the two electrodes, the pigment particles migrate by attraction to the plate of polarity opposite that of the pigment particles. Thus, the color showing at the transparent plate, determined by selectively charging the plates, can be either the color of the solvent or the color of the pigment particles. Reversal of plate polarity will cause the particles to migrate back to the opposite plate, thereby reversing the color. Intermediate color density (or shades of gray) due to intermediate pigment density at the transparent plate may be obtained by controlling the plate charge through a range of voltages or pulsing time.
EPDs of different pixel or cell structures have been reported previously, for example, the partition-type EPD (M. A. Hopper and V. Novotny, IEEE Trans. Electr. Dev., Vol. ED 26, No. 8, pp.1148-1152 (1979)) and the microencapsulated EPD (U.S. Pat. Nos. 5,961,804 and 5,930,026).
An improved EPD technology was recently disclosed in co-pending applications, U.S. Ser. No. 09/518,488, filed on Mar. 3, 2000 (corresponding to WO 01/67170), U.S. Ser. No. 09/606,654, filed on Jun. 28, 2000 (corresponding to WO02/01281) and U.S. Ser. No. 09/784,972, filed on Feb. 15, 2001 (corresponding to WO02/65215), all of which are incorporated herein by reference. The improved EPD comprises isolated cells formed from microcups and filled with charged particles dispersed in a dielectric solvent. The filled cells are individually sealed with a polymeric sealing layer, preferably formed from a composition comprising a material selected from a group consisting of thermoplastics, thermosets and precursors thereof.
Other types of displays, namely magnetophoretic displays (MPDs) and electromagnetophoretic displays (EMPDs), are disclosed in U.S. Serial No. 60/367,325, filed on Mar. 21, 2002 and U.S. Serial No. 60/375,299, filed on Apr. 23, 2002, the contents of both are incorporated herein by reference in their entirety.
The magnetophoretic display generally comprises display cells sandwiched between two layers of substrate and filled with a magnetophoretic dispersion wherein the pigment particles are magnetic but not charged. The display is driven by a magnetic field. At least the substrate layer on the viewing side is transparent.
In the electromagnetophoretic display, the display cells sandwiched between two substrate layers are filled with an electromagnetophoretic fluid wherein the pigment particles are both charged and magnetic. One of the substrate layers, preferably on the non-viewing side, is coated with a conductive layer facing the filled display cells. The display is driven by a combination of electric and magnetic fields. The substrate layer on the viewing side is transparent.
For all types of displays, the dispersion contained within the display cells is undoubtedly one of the most crucial parts of the device. The dispersion, as stated earlier, usually is composed of pigment particles dispersed in a colored dielectric solvent or solvent mixture. The composition of the dispersion determines, to a large extent, the longevity, contrast ratio, switching rate, response waveform and bistability of the device. In an ideal dispersion, the dispersed pigment particles remain separate and do not aggregate or flocculate under all operating conditions. Furthermore, all components in the dispersion must be chemically and electrochemically stable and compatible not only with each other but also with the other materials present in a display, such as the electrodes and sealing and substrate materials.
The dispersing medium may be colored by dissolving or dispersing a dye or colorant in the dielectric solvent or solvent mixture.
Halogenated solvents of high specific gravity have been widely used in EPD applications, particularly in those involving an inorganic pigment, such as TiO2, as the charged whitening or coloring particles. The halogenated solvents of high specific gravity are very useful in reducing the rate of sedimentation of the pigment particles in the solvent. Fluorinated solvents are among the most preferred because they are chemically stable and environmentally friendly.
However, most dyes or pigments are not soluble in fluorinated solvents, particularly not in high boiling-point perfluorinated solvents. For example, phthalocyanines are highly desirable colorants due to their high extinction coefficients, narrow absorption bands and chemical stability; but they are normally insoluble in most solvents, and are particularly insoluble in fluorinated solvents. Therefore, displays based on fluorinated dielectric solvents colored by this type of dyes typically show poor shelf-life stability, contrast ratio and switching performance.
Certain soluble fluorinated copper phthalocyanine dyes are disclosed in U.S. Pat. No. 3,281,426 (1966). The process for the preparation of these dyes involves heating a mixture of an aromatic starting compound and a perfluoroalkyliodide at a temperature in the range of from 200° C. to 350° C. The reaction is performed in an autoclave or a pressure ampoule due to the pressure developed. This synthesis involves complicated reaction conditions (e.g., high pressure and temperature) and long reaction time and has a low yield. Other phthalocyanine derivatives (U.S. Pat. Nos. 6,043,355 and 5,932,721) show improved solubility in various organic solvents or even in water, but not in highly fluorinated solvents.
Thus, there is a need for stable dyes or colorants that exhibit high solubility or dispersibility in halogenated, particularly fluorinated, dielectric solvents for use in display applications. The dyes or colorants should also have a high extinction coefficient, narrow adsorption bands and chemical or electrochemical stability, and can be manufactured in high yields at low cost.
SUMMARY OF THE INVENTION
The first aspect of the present invention is directed to a group of novel fluorinated silicon phthalocyanine and naphthalocyanine dyes which comprise a fluorine content of at least 20% by weight, preferably at least 30% by weight and more preferably at least 50% by weight.
A second aspect of the invention is directed to a display composition which comprises one or more fluorinated silicon phthalocyanine or naphthalocyanine dye of the first aspect of the invention as a colorant dissolved or dispersed in a dielectric solvent or solvent mixture, particularly in a fluorinated dielectric solvent or solvent mixture in which pigment particles are suspended.
A third aspect of the invention is directed to a display composition of the second aspect of the invention further comprising a non-silicon phthalocyanine or naphthalocyanine dye, preferably a fluorinated metal phthalocyanine dye in addition to the dyes of the first aspect of the invention.
A fourth aspect of the invention is directed to an electrophoretic, magnetophoretic or electromagnetophoretic display the cells of which are filled with a display composition of the second or third aspect of the invention.
A fifth aspect of the invention is directed to a microcup-based display which comprises sealed display cells filled with a display composition of the second or third aspect of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Unless defined otherwise in this specification, all technical terms are used herein according to their conventional definitions as they are commonly used and understood by those of ordinary skill in the art.
The term “alkyl” is broader than the customary chemical definition and refers to a linear, branched or cyclic hydrocarbon radical. Unless otherwise indicated, the alkyl group may have 1 to 20, preferably 1 to 12 carbon atoms. For example, it may be methyl, ethyl, cyclohexyl, octyl, n-decyl or the like which is optionally unsaturated, such as ethenyl, 3-hexenyl or the like.
The term “heteroalkyl” refers an “alkyl” as defined above in which one or more carbon atoms are replaced by O, S or N.
The term “alkoxy” refers to the group —O—R wherein R is an alkyl as defined above. The term “heteroalkoxy” refers to the group —O—R wherein R is a heteroalkyl as defined above.
The term “aryl”, as in “aryl”, “arylalkyl” or “alkylaryl”, refers to an organic radical derived from an aromatic hydrocarbon having 6 to 18 carbon atoms including, but not limited to, phenyl, naphthyl, anthracenyl and the like.
The term “heteroaryl” refers to an organic radical derived from an aromatic hydrocarbon in which one or more of the ring carbon atoms are replaced by O, S or N, such as pyridyl, thienyl, furanyl or pyrrolyl.
The term “halogenated” or “fluorinated” refers to a moiety which is partially or completely substituted with halogen atoms or fluorine atoms, respectively.
II. Fluorinated Silicon Phthalocyanine and Naphthalocyanine Dyes
The novel fluorinated silicon phthalocyanine (I) and naphthalocyanine (11) dyes of the present invention may be expressed by the following formulas:
each n is individually 0-4 for silicon phthalocyanine (1) or 0-6 for silicon naphthalocyanine (11);
R1 is independently Rf-A- (wherein Rf is as defined below and A is a single bond, —CH2O—, H2CH2O— or —CO—), alkyl, heteroalkyl, aryl, heteroaryl, heteroalkylaryl, alkyl-heteroaryl, heteroarylalkyl aryl-heteroalkyl, R′O—, R′S—, R′R″N—, R′CO—, R′OCO—, R′COO—, R′CONR″—, R′R″NCO—, R′NHCONR″—, R′SO2NR″— or R′R″NSO— (in which R′ and R″ are independently hydrogen, Rf (as defined below), alkyl, heteroalkyl, aryl, heteroaryl, heteroarylalkyl, aryl-heteroalkyl, heteroalkyaryl or alkyl-heteroaryl) or halogenated, particularly fluorinated derivatives thereof;
Z is O or NR′ wherein R′ is defined as above;
R2 is hydrogen, Rf—B— (wherein Rf is as defined below and B is a single bond, —CH2— or —CH2CH2—), alkyl, heteroalkyl or halogenated, particularly fluorinated derivatives thereof, or —SiR3R4R5 wherein R3, R4, and R5 are independently an alkyl or fluoroalkyl group of 1 to 20 carbon atoms or alkoxy or fluoroalkoxy of 2 to 40 carbon atoms; and
Rf is a low molecular weight (100-100,000) fluorinated polymeric or oligomeric moiety prepared from one or more types of fluorinated monomers.
Useful fluorinated monomers may include, but are not limited to, epoxide, hydrofuran, cyclolactone, cyclolactam, acrylate, methacrylate, styrene, vinylether and vinylalkane.
The substituents, R1, R2, R3, R4, R5, Rf, and n are so selected that the total fluorine content of the silicon phthalocyanine dye is at least 20%, preferably at least 30% and more preferably at least 50%, by weight of the dye molecule.
It will be recognized that when the preparation of the compounds involves the reaction of a formed phthalocyanine/naphthalocyanine or silicon phthalocyanine/naphthalocyanine with a reagent that inserts R1 groups, the resulting product may be a mixture of compounds having different degrees of R1 substitution on the phthalocyanine/naphthalocyanine rings, so that n, when not 0, may be different on each of the phenyl or naphthyl moiety within a compound; and it will also be recognized that substitution may occur at different positions on the different phenyl/naphthyl rings of the phthalocyanine/naphthalocyanine; and all such compounds are within the scope of the present invention. In addition, when n is not 0, not all R1 groups need be the same, either within the compound as a whole or even on a particular phenyl or naphthyl moiety within a compound.
In the compounds of Formula (I) and (II), n is preferably 0-2, preferably 0-1. For example, n may be 0.
Each R1 is independently an alkyl or alkoxy group, preferably a halogenated alkyl or alkoxy group, more preferably a fluorinated alkyl or alkoxy group. Especially preferred R1 groups are fluorinated, especially completely fluorinated alkyl of 1 to 12 carbon atoms, more preferably 6 to 10 carbon atoms.
The substituent, Z, is preferably oxygen.
The substituent, R2, is preferably hydrogen, Rf—CH2—, alkyl and fluoroalkyl as defined above or —SiR3R4R5 wherein R3, R4 and R5 are independently an alkyl group such as methyl, a fluorinated alkyl chain of 6 to 12 carbon atoms or a fluorinated alkoxy of 6 to 18 carbon atoms. In one embodiment, R3, R4 and R5 may be independently an alkyl, a fluorinated alkyl such as —(CH2)2(CF2)5CF3 or —(CH2)2(CF2)7CF3 or a fluorinated alkoxy such as —OCH2(CF2)12CF3 or —OCH2(CF2)6CF3.
Rf is as defined above and is preferably a low molecular weight (200-20,000, more preferably 400-10,000) fluorinated polymer or oligomer. Examples of Rf may include perfluoropolyether and hydrofluoropolyether derived from the monomer, perfluoropropylene oxide, or from oligomers such as Krytox® K-fluids (trifluorohomopolymer) from Dupont and HT or ZT series from Ausimont; and poly(chlorotrifluoroethylene) derived from the monomer, chlorotrifluoroethylene, or from oligomers such as Halocarbon Oils from Halocarbon Product Corp. (River Edge, N.J.).
In one embodiment, Rf is a monovalent radical derived from a halogenated, especially a fluorinated, optionally substituted, alkylene or alkylene oxide homopolymer or copolymer having a molecular weight between 200 and 20,000.
In another embodiment, Rf
may be expressed by the following formula:
wherein the open substituent positions (not designated) on the main chain of the formula can be the same or different and may independently be selected from a group consisting of hydrogen, halogen (especially fluorine), alkyl, aryl, alkylaryl, fluorinated alkyl, fluorinated aryl, fluorinated alkylaryl, —OR6, OCOR6, —COOR6, —CONR6R7 (wherein R6 and R7 are independently hydrogen, alkyl, aryl, alkylaryl, fluorinated alkyl, especially perfluoroalkyl, fluorinated aryl, especially perfluorinated aryl) and substituted derivatives thereof; Z1, Z2, and Z3 are independently oxygen or absent; and a, b, and c are the weight fractions of the corresponding repeating units and are independently in the range of 0-1 with their sum equal to 1.
In one embodiment, the open substituent positions on the main chain of Formula (III) may be independently fluorine or fluoroalkyl, such as —CF(CF3)[OCF2CF(CF3)]nF or the like
When R1 is Rf-A-, A is preferably —CH2O—, —CH2CH2O— or —CO—. When R2 is Rf—B—, B is preferably —CH2—.
The dyes of the present invention are highly soluble or dispersible in fluorinated solvents, and exhibit high extinction coefficients and good thermal and light fastness. Therefore, they are particularly suitable for use as colorants in displays. They may also be used as colorants for color filters, coatings, adhesives and lubricants.
III. Synthesis of Fluorinated Silicon Phthalocyanine Dyes
The compounds of the present invention may be prepared according to conventional methods. Most of the compounds in the present invention may be synthesized according to the following reaction scheme:
wherein n, R1, R2 and Z are as defined above;
X is halogen or hydroxy; and Y is hydrogen or an alkali metal such as sodium, potassium or lithium.
The compounds of Formulas III and IV are commercially available (for example, from Aldrich) or may be prepared by commercially available compounds. The X substituent in Formula III and Formula IV is preferably chlorine or hydroxy. The compound of Formula (V) wherein Y is hydrogen can be converted to an alkali salt by, for example, refluxing with an alkali metal in anhydrous ether.
A compound of Formula I or II wherein Z is oxygen and R2 is —SiR3R4R5 may be prepared by reacting a compound of Formula III or IV wherein X is hydroxy with SiR3R4R5Cl or SiR3R4R5Br. The Si reagents are commercially available (for example, from Gelest) or may be prepared according to Example 3A below. In general, these reagents are prepared according to methods described in J. Org. Chem., 1997, 62, 2917-2924.
Alternatively, the preparation of a compound of Formula I or Formula II wherein Z is oxygen and R2 is —SiR3R4R5 may be carried out in steps. For example, a compound of Formula III wherein X is hydroxy may be first reacted with SiR3Cl3; the intermediate compound thus obtained is then reacted with a compound of R4OH to form a compound of Formula I wherein R2 is —SiR3R4R5 in which R3 and R4 are as defined above and R5 is the same as R4. The reaction conditions of the two step process are exemplified in Example 2 below.
The substituent, R1, on the ring structure may be added on by conventional methods as demonstrated in Example 5 below.
IV. Display Compositions Containing the Fluorinated Silicon Phthalocyanine or Naphthalocyanine Dye
The term “display composition” refers to an electrophoretic, magnetophoretic or electromagnetophoretic dispersion.
The dyes of the present invention are highly soluble in fluorinated solvents, particularly perfluorinated solvents and have high extinction coefficients in the 500-700 nm region. A solvent having low vapor pressure, low viscosity and a dielectric constant in the range of about 1.5 to about 30, more preferably about 2 to about 10, are generally needed as the dielectric solvent of the electrophoretic fluid. Examples of suitable fluorinated solvents for EPD applications include, but are not limited to, fluorinated and perfluorinated solvents such as perfluoroalkanes or perfluorocycloalkanes (e.g., perfluorodecalin), perfluoroarylalkanes (e.g., perfluorotoluene or perfluoroxylene), perfluoro-tert-amines, perfluoropolyethers such as those from Galden/Fomblin and perfluoropolyethers HT series, and hydrofluoropolyethers (ZT series) from Ausimont, FC-43 (heptacosafluorotributylamine), FC-70 (perfluorotri-n-pentylamine), PF-5060 or PF-5060DL (perfluorohexane) from 3M Company (St. Paul, Minn.), low molecular weight (preferably less than 50,000, more preferably less than 20,000) polymers or oligomers such as poly(perfluoropropylene oxide) from TCI America (Portland, Oreg.), poly(chlorotrifluoroethylene) such as Halocarbon Oils from Halocarbon Product Corp. (River Edge, N.J.), Krytox® K-fluids (trifluorohomopolymer) from Dupont, and Demnum lubricating oils from Daikin Industries. Perfluoropolyethers and hydrofluoropolyethers such as Ausimont HT-170, HT-200, HT-230, ZT-180 and Dupont trifluoro(trifluoromethyl)-oxirane homopolymers (such as K-6 and K-7 fluids) are particularly useful.
The display composition may comprise one or more fluorinated silicon phthalocyanine dye and fluorinated naphthalocyanine dye as a colorant in a dielectric solvent, especially a fluorinated dielectric solvent. The composition may further comprise a fluorinated non-silicon phthalocyanine or naphthalocyanine dye, particularly a fluorinated metal phthalocyanine or naphthalocyanine dye to enhance the color saturation. The metal may be Cu, Mg or Zn. These metal phthalocyanine dyes are available commercially or may be synthesized according to U.S. Pat. No. 3,281,426.
The use of a mixture of a dye of the present invention and a Cu phthalocyanine dye is preferable because the colorant mixture increases the low temperature (particularly subzero C) latitude of the display over that of a comparable display using only the fluorinated Cu phthalocyanine dye. Without being limited by theory, it is considered that this may be due to the higher solubility of the present dye in the electrophoretic fluid. The solubility of the present dye in a perfluorinated solvent such as HT-200 is about 3-5 wt % whereas the solubility of the Cu dye in the same solvent is only about 1-1.5 wt %. To achieve a high contrast ratio, a concentration of about 1.5 wt % of the Cu dye is needed. However, due to its low solubility, the Cu dye inevitably will precipitate out at low temperature (subzero) and as a result, the switching performance of the display deteriorates dramatically. By mixing a Si dye of the present invention with the Cu dye, a high contrast ratio can be achieved without tradeoff in the low temperature latitude. It also broadens the visible spectrum and increases the color saturation in a monochrome display. The ratio of the Si dye to the Cu dye in the mixture may range from 1/10 to 10/1, preferably 1/5 to 5/1 and more preferably 1/3 to 3/1.
The charged pigment particles visually contrast with the fluorinated solvent in which the particles are suspended. The primary pigment particles may be organic or inorganic pigments, such as TiO2, diarylide yellow, diarylide AAOT yellow, and quinacridone, azo, rhodamine, perylene pigment series from Sun Chemical, Hansa yellow G particles from Kanto Chemical and Carbon Lampblack from Fisher. The pigment particles may be prepared by any of the well-known methods including grinding, milling, attriting, microfluidizing and ultrasonic techniques. For example, pigment particles in the form of a fine powder are added to the suspending solvent and the resulting mixture is ball milled or attrited for several hours to break up the highly agglomerated dry pigment powder into primary particles. Particle size of the pigment particles is preferably in the range of 0.01-10 microns, more preferably in the range of 0.05-3 microns. These particles should have acceptable optical characteristics, should not be swollen or softened by the dielectric solvent and should be chemically stable. The resulting dispersion must also be stable against sedimentation, creaming or flocculation under normal operating conditions.
In order for the display composition to achieve high hiding power or light scattering efficiency, high dispersion stability, low rate of sedimentation or creaming and high mobility even with a high solid content and under a wide range of applied voltages, the pigment particles are preferably microencapsulated or coated with a polymer matrix of low specific gravity. Microencapsulation of the pigment particles may be accomplished chemically or physically. Typical microencapsulation processes include interfacial polymerization/crosslin king, in-situ polymerization/crosslin king, phase separation, simple or complex coacervation, electrostatic coating, spray drying, fluidized bed coating and solvent evaporation. Improved processes of making density-matched pigment microcapsules of high mobility involving the use of reactive protective colloids and charge controlling agents are disclosed in U.S. Serial No. 60/345,936, filed on Jan. 3, 2002, U.S. Serial No. 60/345,934 filed on Jan. 3, 2002, U.S. Ser. No. 10/335,210 filed on Dec. 31, 2002 and U.S. Ser. No. 10/335,051 filed on Dec. 31, 2002, all of which are incorporated herein by reference.
The resulting display composition may then be filled into the display cells and sealed.
V. Electrophoretic, Magnetophoretic or Electromagnetophoretic Display of the Present Invention
The display cells may be the conventional partition type cells (as disclosed in M. A. Hopper and V. Novotny, IEEE Trans. Electr. Dev., Vol. ED 26, No. 8, pp.1148-1152 (1979)), the microcapsule type cells (as disclosed in U.S. Pat. Nos. 5,961,804 and 5,930,026) and the display cells prepared from the microcup technology as disclosed in co-pending applications, U.S. Ser. No. 09/518,488, filed on Mar. 3, 2000 (corresponding to WO 01/67170 published on Sep. 13, 2001), U.S. Ser. No. 09/759,212, filed on Jan. 11, 2001 (corresponding to WO02/56097 published on Jul. 18, 2002), U.S. Ser. No. 09/606,654, filed on Jun. 28, 2000 (corresponding to WO 02/01281 published on Jan. 3, 2002) and U.S. Ser. No. 09/784,972, filed on Feb. 15, 2001 (corresponding to WO02/65215 published on Aug. 22, 2002), all of which are incorporated herein by reference. The improved microcup-based display comprises isolated cells formed from microcups of well-defined shape, size and aspect ratio and filled with charged particles dispersed in a dielectric solvent or solvent mixture, preferably a halogenated solvent, particularly a fluorinated solvent. The filled cells are individually sealed with a polymeric sealing layer, preferably formed from a composition comprising a material selected from a group consisting of thermoplastics, thermosets and precursors thereof.