JP2016532895A - Electrophoretic fluid - Google Patents

Abstract

The present invention is directed to a display fluid comprising charged composite pigment particles dispersed in a solvent. The composite pigment particle includes at least a core pigment particle, a shell coated on the core pigment particle, and a steric stabilizer molecule on the surface of the composite pigment particle, wherein the shell is formed from a monomer and a co-monomer. Display fluids containing composite pigment particles provide improved display performance.

Description

  The present invention relates to the production of composite pigment particles that can be used to form an electrophoretic fluid and the resulting display fluid.

  An electrophoretic display (EPD) is a non-radioactive device based on an electrophoretic phenomenon that affects charged pigment particles dispersed in a dielectric solvent. EPD typically includes a plate electrode with a set of spacings. At least one of the electrode plates is typically on the display side and is transparent. An electrophoretic fluid composed of a dielectric solvent and charged pigment particles dispersed therein is enclosed between two electrode plates.

  The electrophoretic fluid may have one type of charged pigment particles dispersed in a solvent or in a contrasting solvent mixture. In this case, when a voltage difference is applied between the two electrode plates, the pigment particles are moved by an attractive force to a plate having a polarity opposite to that of the pigment particles. Therefore, the color shown on the transparent plate can be either the color of the solvent or the color of the pigment particles. The reversal of plate polarity moves the particles to the original opposite plate, thereby reversing the color.

  Alternatively, the electrophoretic fluid may have two types of pigment particles of contrasting color and mobile opposite charge, but the two types of pigment particles are dispersed in a clear solvent or solvent mixture. In this case, when applying a voltage difference between the two electrode plates, the two types of pigment particles will move to the opposite end (top or bottom) in the display cell. Thus, one of the colors of the two types of pigment particles will be seen on the display side of the display cell.

  In another alternative, additional colored pigment particles are added to the electrophoretic fluid for the formation of highlight or multicolor display devices.

  For all types of electrophoretic displays, the fluid contained within an individual display cell is clearly one of the most critical parts of the device. The composition of the fluid determines, to a large extent, device lifetime, brightness ratio, switching speed and bistability.

  In an ideal fluid, the charged pigment particles remain separated and do not agglomerate or adhere to each other or to the electrode under all operating conditions. In addition, all components in the fluid must be chemically stable and compatible with other materials present in the electrophoretic display.

  Currently, pigment particles in electrophoretic fluids often have a density much higher than the density of the solvent in which the particles are dispersed, causing performance problems such as poor gray level bistability and vertical precipitation problems.

  The present invention relates to a display fluid comprising composite pigment particles dispersed in a solvent, each of the composite pigment particles having at least a core pigment particle, a shell coated on the core pigment particle, and a solid on the surface of the composite pigment particle. Contains stabilizer molecules.

1a and 1b show the composite pigment particles of the present invention. FIG. 2 shows the reaction steps of a method suitable for producing the composite pigment particles of the present invention. 3 and 4 show the possibility of tuning charge polarity and charge level with comonomers in the method of synthesis of composite pigment particles. 3 and 4 show the possibility of tuning charge polarity and charge level with comonomers in the method of synthesis of composite pigment particles.

  In certain embodiments, the density of the composite pigment particles is substantially matched to the density of the solvent.

In some embodiments, the difference between the density of the composite pigment particles and the density of the solvent is less than 2 g / cm ³ .

  In certain embodiments, the core pigment particles are inorganic pigment particles, and the core pigment particles may be a treated or untreated surface. The shell may be formed from an organic material, in which case the organic content of the composite pigment particles is at least 20% by weight, preferably 20% by weight to 70% by weight, more preferably 20% by weight to 40% by weight or 30% by weight. % To 50% by weight.

  In certain embodiments, the core pigment particles can be organic pigment particles. In this embodiment, the core pigment particles may be a treated surface or an untreated surface. The polymer content of the composite pigment particles in the organic core particles may be at least 20 wt%, preferably 30 wt% to 70 wt%, more preferably 40 wt% to 60 wt% or 30 wt% to 50 wt%. .

  In certain embodiments, the shell may be completely immiscible with the solvent or relatively immiscible.

  In some embodiments, the surface of the shell may include functional groups that allow charge generation or interaction with the charge control agent.

  In certain embodiments, the steric stabilizer molecule may be formed from polyacrylate, polyethylene, polypropylene, polyester, polysiloxane, or mixtures thereof.

  In certain embodiments, the fluid may further comprise a second type of charged pigment particles. In some embodiments, the second type of charged pigment particles comprises at least core pigment particles, a shell coated on the core pigment particles, and steric stabilizer molecules on the surface of the composite pigment particles. The two types of composite pigment particles in the fluid are contrasting colors. In some embodiments, the fluid may include more than two types of pigment particles, but each type has a color that is different from the colors of the other types.

  In an embodiment, the solvent in which the composite pigment particles are dispersed may be a hydrocarbon solvent or a mixture of a hydrocarbon solvent and another solvent such as a halogenated solvent or a silicone oil type solvent.

  In certain embodiments, composite pigment particles can be prepared by dispersion polymerization or living radical polymerization.

  Another aspect of the invention relates to composite pigment particles for electrophoretic displays comprising at least a core pigment particle, a shell coated on the core pigment particle, and a steric stabilizer molecule on the surface of the composite pigment particle, Formed from monomers and comonomers.

  A further aspect of the invention relates to a method for matching the charge levels of composite pigment particles, the method comprising adding a comonomer to a composition comprising a monomer for forming a shell of composite pigment particles. .

  The first aspect of the present invention relates to composite pigment particles as shown in FIGS. 1a and 1b. The composite pigment particles (10) can have one or more core pigment particles (11). The core particle (11) is coated with a shell (12). Steric stabilizer molecules (13) are present on the surface of the composite pigment particles.

  The core pigment particles may be any color (eg, black, white, red, green, blue, cyan, magenta, yellow, etc.).

  The composite pigment particles can be of a density that closely matches the solvent to be dispersed, especially the hydrocarbon solvent.

In some embodiments, the core particles may be inorganic materials (eg, TiO _2, BaSO _4, ZnO, metal oxides, manganese ferrite black spinel, copper chromite black spinel, carbon black or zinc sulfide pigment particles).

The inorganic core particles can optionally be a treated surface. The surface treatment improves the compatibility of the core pigment particles to the monomer in the reaction medium and chemical bonding with the monomer in forming the composite pigment particle shell. As an example, surface treatment, functional groups such as acrylate, _vinyl, -NH 2, -NCO, be carried out in an organic silane having an -OH and the like. These functional groups can be chemically reacted with the monomer.

  The core particles may also be treated with inorganic raw materials, such as silica, aluminum oxide, zinc oxide, etc., or combinations thereof. Sodium silicate or tetraethoxysilane may be used for the silica coating as a common precursor.

  In the case of inorganic treatment, the structure of the coating can be porous to reduce density.

  Organic shells can be formed from organic polymers such as polyacrylates, polyurethanes, polyureas, polyethylenes, polyesters, polysiloxanes, and the like. For example, polyacrylate shells are monomers such as styrene, methyl acrylate, methyl methacrylate, n-butyl acrylate, n-butyl methacrylate, t-butyl acrylate, t-butyl methacrylate, vinyl pyridine, n-vinyl pyrrolidone, 2-hydroxyethyl acrylate. , 2-hydroxyethyl methacrylate, dimethylaminoethyl methacrylate and the like. A polyurethane shell can be formed from monomers or oligomers such as polyfunctional isocyanates or thioisocyanates, primary alcohols, and the like. Polyurea shells can be formed from monomers containing reactive groups such as amine / isocyanate, amine / thioisocyanate, and the like. One skilled in the art can select appropriate monomers or oligomers and variations thereof based on the concepts of the present invention.

  In the case of an organic shell, the “organic content” of the composite pigment particles obtained from the inorganic core particles is at least 20 wt%, preferably 20 wt% to 70 wt%, more preferably 20 wt% to 40 wt%. In this embodiment, the term “organic content” refers to the shell (12) and steric stabilizer (13) divided by the total weight of the core pigment particles (11), shell (12) and steric stabilizer (13). Determined by total weight.

The density of the shell is preferably low, lower than 2 g / cm ³ , more preferably lower than 1 g / cm ³ . The shell thickness can be controlled based on the density of the shell material and the desired final particle density.

  The shell material is completely immiscible or relatively immiscible with the display fluid in which the composite pigment particles are dispersed. As used herein, relatively “immiscible” means that 5% or less, preferably 1% or less of the shell material is miscible with the display fluid.

In order to obtain this complete or relatively immiscible polymer shell material can have polar functional groups on its main chain or side chain. Examples of such polar functional groups include —COOH, —OH, —NH ₂ , —O—R, —NH—R, and the like (wherein R is an alkyl group or an aryl group). In this case, each of the side chains preferably has less than 6 carbon atoms. In one embodiment, the main chain or side chain may contain an aromatic moiety.

  Furthermore, the core pigment particles and shell will act as a single unit. This can be achieved by cross-linking or encapsulation techniques as described below.

  The steric stabilizer (13) in FIG. 1 is typically formed from a high molecular weight polymer such as polyethylene, polypropylene, polyester, polysiloxane or mixtures thereof. The steric stabilizer becomes miscible with the solvent in which the composite pigment particles are dispersed in order to promote the dispersion of the composite pigment particles in the solvent.

  In addition to the steric stabilizer, the surface of the shell can optionally have functional groups that allow charge generation or interaction with the charge control agent.

  In another embodiment of the invention, the core particles may be formed from organic materials such as CI pigments PR 254, PR122, PR149, PG36, PG58, PG7, PY138, PY150, PY20, PY83, PB15, etc. Color index handbook “New Pigment Application Technology” (CMC Publishing Co, Ltd., 1986) and “Printing Ink Technology” (used in CMC Publishing Co, Ltd., 1984). As specific examples, Clariant Hostred Red D3G 70-EDS, Hostaper Pink E-EDS, PV fast red D3G, Hostaperred D3G 70, BASF Irginine red L 3630, CHD HR-70-EDS, Blue B2G, Green GNX, etc. are mentioned. The composite pigment particles formed from the organic core particles are usually colored such as red, green, blue, cyan, magenta, and yellow.

  The surface of the organic core particles may be treated or untreated. The surface treatment improves the miscibility of the core pigment particles to the monomer in the reaction medium or chemical bonding with the monomer in forming the shell of the composite color particle. The pre-treated functional molecule may be chemically bonded on the pigment particle surface or may be physically adsorbed. The functional molecule can be a dispersant, a surfactant, and the like.

  The shell for the organic core particles is typically formed from an organic shell material as described above.

  Composite pigment particle stabilizers prepared from organic core particles can also be prepared as described below.

  The “polymer content” of the composite pigment particles prepared from the organic core particles is at least 20 wt%, preferably 30 wt% to 70 wt%, more preferably 40 wt% to 60 wt% or 30 wt% to 50 wt%. It may be. The term “polymer content” is determined by the total weight of shell (12) and steric stabilizer (13) divided by the total weight of core pigment particles (11), shell (12) and steric stabilizer (13). The

  The second aspect of the present invention relates to the production of composite pigment particles of the present invention, which can include various techniques.

1. Dispersion polymerization It can be formed, for example, by dispersion polymerization. During dispersion polymerization, the monomer polymerizes around the core pigment particles in the presence of a steric stabilizer polymer that is soluble in the reaction medium. The solvent selected as the reaction medium must be a good solvent for both the monomer and steric stabilizer polymer, but must be a non-solvent for the polymer shell. For example, the monomer “methyl methacrylate” is soluble in Isopar GR's aliphatic hydrocarbon solvent; however, after polymerization, the resulting polymethyl methacrylate is not soluble.

  The polymer shell formed from the monomer must be completely or relatively miscible with the solvent in which the composite pigment particles are dispersed. Suitable monomers for forming the shell are those mentioned above, for example styrene, methyl acrylate, methyl methacrylate, n-butyl acrylate, n-butyl methacrylate, t-butyl acrylate, t-butyl methacrylate, vinyl pyridine, n-vinyl. It may be pyrrolidone, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, dimethylaminoethyl methacrylate, or the like.

  The steric stabilizer polymer can be a reactive and polymerizable macromonomer that adsorbs, becomes incorporated or chemically bound onto the surface of the formed polymer shell. Macromonomers as steric stabilizers determine system particle size and colloidal stability.

  Macromonomers can be acrylate-terminated or vinyl-terminated macromolecules, which are suitable because acrylate or vinyl groups can be copolymerized with monomers in the reaction medium.

  The macromonomer preferably has a long back "R" that can stabilize the composite pigment particles in a hydrocarbon solvent.

One type of macromonomer is an acrylate-terminated polysiloxane (Gelest, MCR-M11, MCR-M17, MCR-M22) shown below:

Another type of macromonomer suitable for the process of the present invention is the PE-PEO macromonomer shown below:
_{R m O - [- CH 2} CH 2 O-] n -CH 2 - phenyl -CH = CH ₂
Or _{R m O - [- CH 2} CH 2 O-] n -C (= O) -C (CH 3) = CH 2

  Substituent R may be a polyethylene chain, n is 1-60, and m is 1-500. The synthesis of these compounds is described in Dongri Chao et al., Polymer Journal (Vol. 23), no. 9, 1045 (1991) and Koichi Ito et al., Macromolecules, 1991, 24, 2348.

  A further type of suitable macromonomer is the PE macromonomer shown below:

_{CH 3 - [- CH 2 -} ] n -CH 2 O-C (= O) -C (CH 3) = CH 2

  In this case, n is 30-100. The synthesis of this type of macromonomer can be found in Seigou Kawaguchi et al., Designed Monomers and Polymers, 2000, 3,263.

2. Living Radical Dispersion Polymerization Alternatively, composite pigment particles can be prepared by living radical dispersion polymerization as shown in FIG.

  The living radical dispersion polymerization technique is similar to the dispersion polymerization described above by initiating a process with pigment particles (21) and monomers dispersed in the reaction medium.

  As monomers used in the method for forming the shell (22), styrene, methyl acrylate, methyl methacrylate, n-butyl acrylate, n-butyl methacrylate, t-butyl acrylate, t-butyl methacrylate, vinyl pyridine, n-vinyl pyrrolidone, Examples include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, dimethylaminoethyl methacrylate and the like.

  However, in this alternative method, multiple living ends (24) are formed on the surface of the shell (22). The living end should be added with an agent such as TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy), RAFT (reversible addition-cleavage chain transfer) reagent, etc. in the reaction medium. Can be generated.

  In a further step, a second monomer is added to the reaction medium to produce a living end (24) and reacted with the second monomer to form a steric stabilizer (23). The second monomer is lauryl acrylate, lauryl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, hexyl acrylate, hexyl methacrylate, n-octyl acrylate, n-octyl methacrylate, n-octadecyl acrylate, n-octadecyl methacrylate, etc. Good.

3. Non-aqueous emulsion polycondensation Further, alternatively, composite pigment particles can be formed by coating the core pigment particles by non-aqueous emulsion polycondensation.

  In this alternative method, the shell of the composite pigment particles can be a polyurethane or polyurea material. The steric stabilizer can be a nonpolar long chain hydrocarbon molecule. Polyurethanes and polyureas are not normally miscible in nonpolar hydrocarbon solvents, and their hardness and elastic properties can be adjusted from the monomer composition.

  This synthesis method is similar to emulsion or dispersion polymerization except that polycondensation with the polyurethane monomer and inorganic core pigment particles occurs inside the micelle.

  A polyurethane or polyurea coating system may be considered as an oil-in-oil emulsion containing two immiscible solvents, one of which is a nonpolar organic solvent and the other is a polar organic solvent. The system can also be a non-aqueous emulsion polycondensation where the nonpolar solvent is the continuous phase and the polar solvent is the discontinuous phase. Monomers and inorganic pigment particles are discontinuous phases. Suitable nonpolar solvents include those in the Isopar® series, cyclohexane, tetradecane, hexane, and the like. Examples of the polar solvent include acetonitrile and DMF.

  Emulsifiers or dispersants are important for this two-phase organic system. The molecular structure of the emulsifier or dispersant may contain one part that is soluble in the nonpolar solvent and another part that adheres to the polar phase. It contains monomer and inorganic pigment particles and stabilizes micelles / droplets that act as microreactors for particle formation by polycondensation.

  Suitable emulsifiers or dispersants may include diblock copolymers such as poly (isoprene) -b-poly (methyl methacrylate), polystyrene-b-poly (ethene-alt-propene) (Kraton), and the like.

Also, co-emulsifiers can be added to form chemical bonds with the particles. For example, amine-terminated hydrocarbon molecules can react with particles during polycondensation and bind to the surface as a robust steric stabilizer. Suitable auxiliary emulsifiers include the sulfonamines (B-60, B-100 or B-200) shown below:
_{CH 3 - [- OCH 2 CH} 2 -] x - [- OCH 2 CH (CH 3) -] y -NH 2
[Wherein x is 5 to 40 and y is 1 to 40. ]

  In one approach, the method of the present invention may continue to grow the polyacrylate steric stabilizer after the polycondensation reaction in the microreactor is complete. In this case, the steric stabilizer can be a polyacrylate chain while forming a shell from the polyurethane. After washing away the emulsifier or dispersant used in the method of the present invention from the particle surface, the composite pigment particles are stable in a non-polar solvent (ie, display fluid) with a polyacrylate stabilizer. Some materials that can initiate acrylate polymerization include isocyanatoethyl acrylate, isocyanatostyrene, and the like.

  Monomers for steric stabilizers are nonpolar solvents such as lauryl acrylate, lauryl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, hexyl acrylate, hexyl methacrylate, n-octyl acrylate, n-octyl methacrylate, n-octadecyl acrylate, n It can be a mixture of hydroxyethyl methacrylate and other acrylates that are miscible with octadecyl methacrylate and the like.

  In any of the above methods, a comonomer can be added to the reaction medium to incorporate a functional group for charge generation. The comonomer may directly charge the composite pigment particles or may interact with the charge control agent in the display fluid to provide the desired charge polarity and charge density to the composite pigment particles. Suitable comonomers include vinylbenzyl-aminoethylamino-propyl-trimethoxysilane, methacryloxypropyltrimethoxysilane, acrylic acid, methacrylic acid, vinyl phosphoric acid, 2-acrylamino-2-methylpropanesulfonic acid, 2- ( And dimethylamino) ethyl methacrylate and N- [3- (dimethylamino) propyl] methacrylamide.

  In the present invention, the comonomer is a monomer that is already different from the monomer in the composition for forming the shell of the composite pigment particle. When both the monomer and comonomer are present in the reaction medium for forming the shell, the charge polarity or charge intensity of the composite pigment particles can be adjusted to a desired level.

  For example, a yellow pigment (Clariant Hostaperm H4G-EDS) prepared from standard synthetic methods (methyl methacrylate used as the monomer to form the shell and PDMS (polydimethylsiloxane) acrylate used as the stabilizer polymer) is a positive zeta Indicates potential. However, when a fluorinated comonomer, such as 2-perfluorobutylethyl acrylate, is added to the reaction medium for forming the shell, the zeta potential of the yellow pigment may be in the negative range (see FIG. 3).

  In a further example, a blue pigment (Clariant Hosterperm B2G-EDS) prepared from standard synthetic methods (methyl methacrylate used as monomer to form the shell and PDMS (polydimethylsiloxane) acrylate used as the stabilizer polymer) is: It exhibits a very low positive charge level. However, when the comonomer, (2- (dimethylamino) ethyl methacrylate) is added in the shell synthesis, the amount of added comonomer increases as the charge level of the blue pigment increases (see FIG. 4).

  As shown, the charge polarity of the pigment material can change from positive to negative or vice versa by the addition of comonomer in the reaction medium to form the shell. The charge level of the pigment material can also be adjusted by this method.

  The comonomer capable of introducing a negative charge may be, but is not limited to, fluorinated acrylate or fluorinated methacrylate. Specific examples include 2-perfluorobutylethyl acrylate, 2,2,2 trifluoroethyl methacrylate, 2,2,3,3 tetrafluoropropyl methacrylate, 1,1,1,3,3,3-hexafluoroisopropyl. Acrylate, 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, 2,2,3,3,3-pentafluoropropyl acrylate, 2,2,3,3-tetrafluoropropyl acrylate, 2,2 3, 4, 4, 4-hexafluorobutyl methacrylate, 2,2,3,3,4,4,4-heptafluorobutyl methacrylate and the like.

Comonomers that can introduce a positive charge include, but are not limited to, 2- (dimethylamino) ethyl methacrylate, N- [3- (dimethylamino) propyl] -methacrylamide. Functional groups on these positive charge generating positive comonomers include —NHR, —NR ₂ , —NH—, —NH _{2 and the} like, where R is up to 4 carbon atoms, It is not limited to.

  The main monomers for forming the shell are those described herein above. Examples include styrene, methyl acrylate, methyl methacrylate, n-butyl acrylate, n-butyl methacrylate, t-butyl acrylate, t-butyl methacrylate, vinyl pyridine, n-vinyl pyrrolidone, 2-hydroxyethyl acrylate, 2-hydroxy Examples include ethyl methacrylate and dimethylaminoethyl methacrylate. In some cases, the main monomer can be an acrylate, methacrylate or styrene having a hydrocarbon side chain.

  Some examples of suitable monomer-comonomer pairs are methyl methacrylate and 2- (dimethylamino) ethyl methacrylate, methyl methacrylate and 2-perfluorobutylethyl acrylate, methyl methacrylate and 2,2,2 trifluoroethyl methacrylate, etc. is there.

  The molar ratio of charge-controlling comonomer to total monomers (main monomer plus comonomer) may be between 0.1% and 50%, preferably between 1% and 10%, based on the desired charge intensity of the particles. .

  Obtaining the desired organic content in the composite pigment particles obtained by adjusting and controlling the amount of reagents used in any of the above methods (eg, inorganic core pigment particles, shell materials and materials to form steric stabilizers) It's okay.

  A third aspect of the present invention relates to a display fluid comprising the composite pigment particles of the present invention, wherein the composite pigment particles are dispersed in a solvent. Suitable solvents have a low dielectric constant (preferably about 2-3), high volume resistance (preferably about 1015 ohm-cm or more) and low water solubility (preferably less than 10 parts per million). Suitable hydrocarbon solvents include, but are not limited to, dodecane, tetradecane, and aliphatic hydrocarbon solvents (Exxon, Houston, Tex) in the Isopar® series. The solvent may also be a mixture of hydrocarbon and halogenated carbon or silicone oil based material.

  The present invention is applicable to single particle, two particle or composite particle electrophoretic display fluid systems. In composite particle systems, there may be more than two types of pigment particles, each type having a different color from the other types.

  In other words, the present invention may be directed to a display fluid comprising only composite pigment particles prepared according to the present invention dispersed in a hydrocarbon solvent. The composite pigment particles and the solvent have a contrasting color.

  Alternatively, the present invention may include two types of pigment particles dispersed in an organic solvent, and at least one of the two types of pigment particles may be directed to a display fluid prepared according to the present invention. The two types of pigment particles have opposite charge polarities and contrast colors. For example, the two types of pigment particles can be black and white, respectively. In this case, black particles may be prepared according to the present invention, white particles may be prepared according to the present invention, or both black particles and white particles may be prepared according to the present invention.

The composite pigment particles prepared according to the present invention have many advantages when dispersed in an organic solvent. The density of the composite pigment particles may substantially match the organic solvent, thus improving the performance of the display device. In other words, the difference between the density of the composite pigment particles and the density of the solvent is less than 2 g / cm ³ , more preferably 1.5 g / cm ³ , and most preferably less than 1 g / cm ³ .

  If only one type of pigment particle is prepared according to the invention in a two particle system, another type of pigment particle may be prepared by other methods. For example, the particles can be polymer encapsulated pigment particles. The microencapsulation of the pigment particles can be performed chemically or physically. Typical microencapsulation methods include interfacial polymerization / crosslinking, in situ polymerization / crosslinking, phase separation, simple or complex coacervation, electrostatic coating, spray drying, fluidized bed coating and solvent evaporation.

  Composite pigment particles prepared by previously known techniques may further exhibit a natural charge, or may be specifically charged with a charge control agent, or charged when suspended in an organic solvent. You may get Suitable charge control agents are well known in the art; they may be polymeric or non-polymeric in nature and may be ionic or non-ionic, such as ionic surfactants such as dodecyl Sodium benzenesulfonate, metal soap, polybutenesuccinimide, maleic anhydride copolymer, vinylpyridine copolymer, vinylpyrrolidone copolymer, (meth) acrylic acid copolymer or N, N-dimethylaminoethyl (meth) acrylate copolymer), Alcorec LV30 (soy lecithin) ), Petrostep B100 (petroleum sulfonate) or B70 (barium sulfonate), Solsperse 17000 (active polymer dispersant), Solsperse 9000 (active polymer dispersant), OL A 11000 (succinimide ash-free dispersant), OLOA 1200 (polyisobutylene succinimide), Unitox 750 (ethoxylate), Petronate L (sodium sulfonate), Disper BYK 101, 2095, 185, 116, 9077 & 220 and ANTI-TERRA series Is mentioned.

Example 1
Step A: Deposition of vinylbenzylaminoethylaminopropyl-trimethoxysilane on black pigment particles A 1 L reactor was charged with Black 444 (Shepherd, 40 g), isopropanol (320 g), DI water (12 g), ammonium hydroxide (28 %, 0.4 g) and Z-6032 (Dow Corning, 16 g, 40% in methanol) were added. The reactor was heated to 65 ° C. with mechanical stirring in a sonication bath. After 5 hours, the mixture was centrifuged at 6000 rpm for 10 minutes. The solid was redispersed in isopropanol (300 g), centrifuged and dried overnight at 50 ° C. under vacuum to produce 38 g of the desired pigment particles.

Step B: Preparation of polymer coating on pigment particles by dispersion polymerization 2 g of polyvinylpyrrolidone (PVP K30) was dissolved in a mixture of 94.5 g water and 5.5 g ethanol. The solution was purged with nitrogen for 20 minutes and heated to 65 ° C. Uniform suspension of pigment particles (4 g) prepared from step A dispersed in a mixture of 3.0 g lauryl acrylate, 0.2 g divinylbenzene and 0.03 g AIBN (azobisisobutyronitrile) Formed. The suspension was added into the PVP solution at 65 ° C. While stirring, the polymerization reaction continued for about 12 hours.

  Thereafter, a mixture of 3.0 g of octadecyl acrylate and 0.03 g of AIBN was added to the reaction flask, and the reaction was continued for 12 hours.

  The produced solid was separated from the liquid by centrifugation and then washed with isopropanol and methyl ethyl ketone to remove PVP K30 and other chemicals not bound on the pigment particles. The solid was dried at 50 ° C. under vacuum to produce the final composite black particles. The organic content of the produced particles was about 34% by weight as tested by TGA (thermogravimetric analysis).

Example 2
Synthesis of colored composite pigment particles HostapermRedD3G 70-EDS (Clariant, 2.5 g), methyl methacrylate (8 g) and toluene (2 g) were added to a 20 ml vial and sonicated for 2 hours. To a 250 mL reactor was added the above mixture, MCR-M22 (Gelest, 5.7 g) and DMS-T01 (Gelest, 30 g). The reactor was heated to 70 ° C. with magnetic stirring, purged with nitrogen for 20 minutes, and then lauroyl peroxide (0.07 g) was added. After 19 hours, the mixture was centrifuged at 5000 rpm for 15 minutes. The produced solid was again dispersed in hexane and centrifuged. This cycle was repeated twice, and the solid was dried under vacuum at room temperature to produce the final particles. The polymer content of the particles produced was about 49% by weight as tested by TGA (thermogravimetric analysis).

  Although the invention has been described with reference to specific embodiments thereof, those skilled in the art will recognize that various modifications may be made and equivalent substitutions may be made without departing from the scope of the invention.

Claims (15)

A method of adjusting the charge level of composite pigment particles,
(I) supplying a composition containing a monomer;
(Ii) selecting a comonomer to add to the composition, wherein the comonomer can introduce a positive or negative charge into the composite pigment particle or alter the charge level of the composite pigment particle;
(Iii) forming a shell of composite pigment particles using the composition.   Monomers are styrene, methyl acrylate, methyl methacrylate, n-butyl acrylate, n-butyl methacrylate, t-butyl acrylate, t-butyl methacrylate, vinyl pyridine, n-vinyl pyrrolidone, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate. Or the method of Claim 1 which is dimethylaminoethyl methacrylate.   The method of claim 1, wherein the monomer is an acrylate, methacrylate or styrene having a hydrocarbon side chain.   Comonomers are vinylbenzyl-aminoethylamino-propyl-trimethoxysilane, methacryloxypropyltrimethoxysilane, acrylic acid, methacrylic acid, vinyl phosphoric acid, 2-acrylamino-2-methylpropanesulfonic acid, 2- (dimethylamino) The method of claim 1, selected from the group consisting of ethyl methacrylate and N- [3- (dimethylamino) propyl] methacrylamide.   The method of claim 1, wherein the comonomer is a fluorinated acrylate or fluorinated methacrylate that introduces a negative charge.   Comonomers include 2-perfluorobutyl ethyl acrylate, 2,2,2 trifluoroethyl methacrylate, 2,2,3,3 tetrafluoropropyl methacrylate, 1,1,1,3,3,3- Hexafluoroisopropyl acrylate, 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, 2,2,3,3,3-pentafluoropropyl acrylate, 2,2,3,3-tetrafluoropropyl acrylate, The method according to claim 1, which is 2,2,3,4,4,4-hexafluorobutyl methacrylate or 2,2,3,3,4,4,4-heptafluorobutyl methacrylate.   The process according to claim 1, wherein the comonomer is 2- (dimethylamino) ethyl methacrylate or N- [3- (dimethylamino) propyl] -methacrylamide that introduces a positive charge. The comonomer includes a functional group selected from the group consisting of —NHR, —NR ₂ , —NH—, and —NH ₂ , wherein R is an alkyl of up to 4 carbon atoms that introduces a positive charge. The method of claim 1.   The monomer and comonomer pair is methyl methacrylate and 2- (dimethylamino) ethyl methacrylate, methyl methacrylate and 2-perfluorobutylethyl acrylate, or methyl methacrylate and 2,2,2 trifluoroethyl methacrylate. The method described.   The process according to claim 1, wherein the molar ratio of comonomer to the sum of monomer and comonomer is between 0.1 and 50%.   The process according to claim 1, wherein the molar ratio of comonomer to the sum of monomer and comonomer is between 1 and 10%.   Composite pigment particles for electrophoretic display comprising at least a core pigment particle, a shell coated on the core pigment particle, and a steric stabilizer molecule on the surface of the composite pigment particle, wherein the shell is a monomer and a comonomer The monomers are styrene, methyl acrylate, methyl methacrylate, n-butyl acrylate, n-butyl methacrylate, t-butyl acrylate, t-butyl methacrylate, vinyl pyridine, n-vinyl pyrrolidone, 2-hydroxyethyl acrylate, 2 -Composite pigment particles which are hydroxyethyl methacrylate and dimethylaminoethyl methacrylate.   Comonomers are 2-perfluorobutyl ethyl acrylate, 2,2,2 trifluoroethyl methacrylate, 2,2,3,3 tetrafluoropropyl methacrylate, 1,1,1,3,3,3-hexafluoroisopropyl acrylate, 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, 2,2,3,3,3-pentafluoropropyl acrylate, 2,2,3,3-tetrafluoropropyl acrylate, 2,2,3 , 4, 4, 4-hexafluorobutyl methacrylate, or 2, 2, 3, 3, 4, 4, 4-heptafluorobutyl methacrylate.   13. Particles according to claim 12, wherein the comonomer is 2- (dimethylamino) ethyl methacrylate or N- [3- (dimethylamino) propyl] -methacrylamide.   13. Particles according to claim 12, wherein the molar ratio of comonomer to the sum of monomer and comonomer is between 0.1 and 50%.

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