KR20160037990A - Electrophoretic fluid - Google Patents

Abstract

The present invention relates to a display fluid comprising charged complex pigment particles dispersed in a solvent. The composite pigment particles include at least core pigment particles, shells coated on the core pigment particles, and steric stabilizer molecules on the surface of the composite pigment particles, wherein the shell is formed from monomers and comonomers. Display fluids comprising composite pigment particles provide improved display performance.

Description

ELECTROPHORETIC FLUID -

The present invention relates to the preparation of composite pigment particles which can be used to form electrophoretic fluids, and to the resulting display fluids.

An electrophoretic display (EPD) is a non-emissive device based on electrophoresis that affects charged pigment particles dispersed in a dielectric solvent. The EPD typically comprises a pair of spaced-apart plate-like electrodes. One or more electrode plates, generally on the viewing side, are transparent. An electrophoretic fluid consisting of a dielectric solvent and charged pigment particles dispersed in it surrounds the space between the two electrode plates.

The electrophoretic fluid may have one type of charged pigment particle dispersed in a solvent or solvent mixture of the reference color. In this case, when a voltage difference is applied between the two electrode plates, the pigment particles move to the opposite polarity plate of the pigment particle by attraction. Thus, the color seen on the transparent plate may be the color of the solvent or the color of the pigment particles. The inversion of the polarity of the plate causes the particles to return to the opposite plate, thereby reversing the color.

Alternatively, the electrophoretic fluid may have two kinds of pigment particles having a contrast color and an opposite charge, and the two kinds of pigment particles are dispersed in a transparent solvent or a mixture of solvents. In this case, when a voltage difference is applied between the two electrode plates, the two kinds of pigment particles will move toward the opposite end of the display cell (upper or lower). Thus, one of the two pigment particles will be visible on the viewer side of the display cell.

As yet another alternative, pigment particles with different colors are added to the electrophoretic fluid to form a highlight or multicolor display device.

In electrophoretic displays of all species, the fluid contained within the individual display cells of the display is clearly one of the most important parts of the device. The composition of the fluid largely determines the lifetime, contrast ratio, conversion speed and bistability of the device.

In an ideal fluid, the charged pigment particles remain separated under all operating conditions, without agglomeration or sticking to one another or to the electrodes. In addition, all elements in the fluid must be chemically stable and compatible with other materials present in the electrophoretic display.

At present, pigment particles in electrophoretic fluids often have performance problems such as poor gray level bistability and vertical fixation problems, since they have a much higher density than the density of the solvent in which the particles are dispersed.

Brief Description of Drawings

Figures 1A and 1B show the composite pigment particles of the present invention.

Figure 2 shows the reaction steps of a process suitable for the preparation of the inventive composite pigment particles.

Figures 3 and 4 demonstrate the possibility of adjusting the charge polarity and charge level using comonomers in the process of synthesizing the composite pigment particles.

SUMMARY OF THE INVENTION

The present invention relates to a display fluid comprising charged particulate pigment particles dispersed in a solvent, wherein each of the composite pigment particles has at least a core pigment particle, a shell coated on the core pigment particle, and a steric stability on the surface of the composite pigment particle And a steric stabilizer molecule.

In one embodiment, the density of the composite pigment particles is substantially consistent with the density of the solvent.

In one embodiment, the density difference between the composite pigment particles and the solvent is less than 2 g / cm < ^{3 &} gt ;.

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

In one embodiment, the core pigment particles may be organic pigment particles. In such embodiments, the core pigment particles may also be surface treated or surface untreated. The polymer content of the composite pigment particles having organic core particles may be 20% by weight or more, preferably 30 to 70% by weight, more preferably 40 to 60% by weight or 30 to 50% by weight .

In one embodiment, the shell may be totally incompatible with the solvent or relatively incompatible with the solvent.

In one embodiment, the surface of the shell may comprise a functional group to enable charge generation or to interact with the charge control agent.

In one embodiment, the steric stabilizer molecules may be formed from polyacrylates, polyethylene, polypropylene, polyesters, polysiloxanes, or mixtures thereof.

In one embodiment, the fluid may further comprise a second type of charged pigment particles. In one embodiment, the second type of charged pigment particles is a composite pigment particle comprising at least core pigment particles, a shell coated on the core pigment particles, and a steric stabilizer molecule on the surface of the composite pigment particle. Two of the composite pigment particles in the fluid have a contrasting color. In one embodiment, the fluid may comprise more than two pigment particles, and each pigment particle has a different color than the color of the other pigment particle.

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

In one embodiment, the composite pigment particles may be prepared by dispersion polymerization or living radical polymerization.

Another aspect of the present invention is directed to a composite pigment particle for electrophoretic display comprising at least core pigment particles, a shell coated on the core pigment particles and a steric stabilizer molecule on the surface of the composite pigment particle, Lt; / RTI >

A further aspect of the invention relates to a method of adjusting the charge level of a composite pigment particle, the method comprising adding a comonomer to a composition comprising a monomer for shell formation of the composite pigment particle.

A first aspect of the present invention relates to composite pigment particles, as shown in Figures 1A and 1B. The composite pigment particles 10 may have one or more core pigment particles 11. The core particle (s) (11) are coated with a shell (12). On the surface of the composite pigment particle is a steric stabilizer molecule (13).

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

The composite pigment particles may have a density substantially equal to that of the solvent in which they are dispersed, especially the hydrocarbon solvent.

In one embodiment, the core particles are TiO _2, BaSO ₄ , ZnO, metal oxide, manganese ferrite black spinel, copper chromate black spinel, carbon black or zinc sulfide pigment particles.

The inorganic core particles may optionally be surface treated. When the surface treatment forms the shell of the composite pigment particle, compatibility between the core pigment particle and the monomer in the reaction medium Or improve chemical bonding. As an example, the surface treatment may be carried out using organosilanes having functional groups such as acrylate, vinyl, -NH ₂ , -NCO, -OH, and the like. These functional groups can cause chemical reactions with monomers.

The core particles may also be surface treated with inorganic materials, such as silica, aluminum oxide, zinc oxide, or the like, or combinations thereof. The sodium silicate or tetraethoxysilane can be used as a conventional precursor in silica coating.

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

The organic shell may be formed from organic polymers such as polyacrylates, polyurethanes, polyureas, polyethylenes, polyesters, polysiloxanes, and the like. For example, polyacrylate shells can be prepared by reacting monomers such as styrene, methyl acrylate, methyl methacrylate, n-butyl acrylate, n-butyl methacrylate, t-butyl acrylate, Vinyl pyridine, n-vinyl pyrrolidone, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, dimethylaminoethyl methacrylate and the like. The polyurethane shells can be formed from monomers or oligomers, such as polyfunctional isocyanates or thiocyanates, primary alcohols, and the like. The polyurea shell may be formed from monomers containing reactive groups, such as amine / isocyanate, amine / thioisocyanate, and the like. One skilled in the art will be able to select appropriate monomers or oligomers and their modifications, in accordance with the concept of the present invention.

In the case of an organic shell, the "organic content" of the composite pigment particles prepared from the inorganic core particles can be at least 20 wt%, preferably from 20 to 70 wt%, more preferably from 20 to 40 wt% have. In this embodiment, the term "organic content" refers to 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 density of the shell is preferably low, less than 2 g / cm ³ , more preferably less than 1 g / cm ³ . The thickness of the shell can be adjusted based on the density of the material of the shell and the density of the desired final particles.

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

To be totally or relatively incompatible, the material of the polymer shell may have polar functional groups in the backbone or side chain of the material. Examples of such polar functional groups may be such as _{-COOH, -OH, -NH 2, -OR} , -NH-R ( where R is alkyl or aryl group). In this case, each side chain preferably has fewer than 6 carbon atoms. In one embodiment, the backbone or side chain may contain aromatic moieties.

In addition, the core pigment particle (s) and shell must behave as a single unit. This can be accomplished by cross-linking or encapsulation techniques, as described below.

The steric stabilizer 13 in Fig. 1 is usually composed of high molecular weight polymers such as polyethylene, polypropylene, polyester, polysiloxane or mixtures thereof. The steric stabilizer is compatible with the solvent in which the composite pigment particles are dispersed to enable dispersion of the composite pigment particles in the solvent It should be possible.

In addition to the steric stabilizers, the surface of the shell may optionally contain functional groups that enable interaction with charge generation or charge control agents.

In another embodiment of the present invention, the core particles can be used in a conventional manner as described in the Color Index Handbook "New Pigment Application Technology" (CMC Publishing Co., Ltd., 1986) and in "Printing Ink Technology" (CMC Publishing Co., Such as CI pigments PR254, PR122, PR149, PG36, PG58, PG7, PY138, PY150, PY20, PY83, Specific examples include Clariant Hostaperm Red D3G 70-EDS, Hostaperm Pink E-EDS, PV fast red D3G, Hostaperm red D3G 70, BASF Irgazine red L 3630, Cinquasia Red L 4100 HD, Irgazine Red L 3660 HD, Clariant Novoperm yellow HR- 70-EDS, Blue B2G, Green GNX, and the like. Composite pigment particles formed from organic core particles typically have a red, green, blue, cyan, magenta, yellow, or other color.

The surface of the organic core particles can be surface treated or surface untreated. The surface treatment can improve the compatibility or chemical bonding between the core pigment particles and the monomers in the reaction medium in forming the shell of the composite colored particles. The pretreated functional molecules may be chemically bonded or physically absorbed onto the pigment particle surface. The functional molecule may be a dispersant, a surfactant, or the like.

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

Stabilizers of composite pigment particles made 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 can be 20 wt% or more, preferably 30 to 70 wt%, more preferably 40 to 60 wt% or 30 to 50 wt% . The term "polymer content" is measured by the total weight of the shell 12 and the steric stabilizer 13, divided by the total weight of the core pigment particles 11, the shell 12 and the steric stabilizer 13.

A second aspect of the invention relates to the preparation of the inventive composite pigment particles, which may involve a variety of techniques.

One. Dispersion polymerization

For example, the composite pigment particles may be formed by dispersion polymerization. During the dispersion polymerization, the monomers are polymerized around the core pigment particles in the presence of a steric stabilizer polymer that is soluble in the reaction medium. The solvent chosen as the reaction medium should be a good solvent for both the monomer and the steric stabilizer polymer, but it must be a non-solvent for polymer shell formation. For example, in the aliphatic hydrocarbon solvent of Isopar G, the monomer methyl methacrylate is soluble; After polymerization, the prepared polymethylmethacrylate is not soluble.

The polymer shell formed from the monomer must be incompatible or relatively incompatible with the solvent in which the composite pigment particles are dispersed. Suitable monomers for forming the shell are the monomers described above, such as styrene, methyl acrylate, methyl methacrylate, n-butyl acrylate, n-butyl methacrylate, t-butyl acrylate, , Vinyl pyridine, n-vinyl pyrrolidone, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, dimethylaminoethyl methacrylate, and the like.

The steric stabilizer polymer may be a reactive, polymerizable macromonomer that is absorbed, incorporated, or chemically bonded onto the surface on which the polymer shell is formed. The macromonomer as the steric stabilizer determines the size of the particles and the colloidal stability of the system.

The macromonomers can be acrylate-terminated or vinyl-terminated macromolecules, which is suitable because acrylate or vinyl groups can copolymerize with the monomers in the reaction medium.

The macromonomer preferably has a long tail of R groups, which can stabilize the composite pigment particles in a hydrocarbon solvent.

One class of macromonomers are acrylate-terminated polysiloxanes (Gelest, MCR-M11, MCR-M17, MCR-M22), as shown below.

Another class of macromonomers suitable for this process is the PE-PEO macromonomer, as shown below.

or

Substituent R can 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 class of suitable macromonomers are PE macromonomers, such as those set forth below.

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

2. Living radical dispersion polymerization

Alternatively, as shown in Figure 2, the composite pigment particles can also be prepared by living radical dispersion polymerization.

 The living radical dispersion polymerization technique is similar to the dispersion polymerization described above in that the reaction is initiated using the pigment particles 21 and the monomers dispersed in the reaction medium.

The monomers used in the method for forming the shell 22 are selected from the group consisting of styrene, methyl acrylate, methyl methacrylate, n-butyl acrylate, n-butyl methacrylate, t-butyl acrylate, , Vinyl pyridine, n-vinyl pyrrolidone, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, dimethylaminoethyl methacrylate, and the like.

However, in this alternative method, a plurality of living ends 24 are formed on the surface of the shell 22. The living end can be prepared by the addition of a preparation such as TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy), RAFT (reversible addition-fragmentation chain transfer) Lt; / RTI >

In a later step, a second monomer is added to the reaction medium, and the living end (24) is reacted with the second monomer to form the steric stabilizer (23). The second monomer is selected from the group consisting of lauryl acrylate, lauryl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, hexyl acrylate, hexyl methacrylate, n-octyl acrylate, N-octadecyl acrylate, n-octadecyl methacrylate, and the like.

3. Non-aqueous emulsion polycondensation

Alternatively, the composite pigment particles may be formed by coating the core pigment particles by non-aqueous emulsion polycondensation.

In these other reactions, the shell of the composite pigment particle may be a polyurethane or polyurea material. The steric stabilizer may be a non-polar long chain hydrocarbon molecule. Polyurethanes and polyureas are generally incompatible with non-polar hydrocarbon solvents and their hardness and elasticity can be controlled through the monomer composition.

This synthetic method is similar to emulsion or dispersion polymerization except that polycondensation of the polyurethane monomer and the inorganic core pigment particles occurs in the micelle.

A polyurethane or polyurea coating system can be regarded as a oil-in-water emulsion containing two incompatible solvents of a nonpolar organic solvent and a polar organic solvent. Such a system may also be referred to as non-aqueous emulsion polycondensation, wherein the non-polar solvent is a continuous phase and the polar solvent is a discontinuous phase. The monomer and inorganic pigment particles are in a non-inverse phase. Suitable non-polar solvents may include solvents from the Isopar series, such as cyclohexane, tetradecane, hexane, and the like. The polar solvent may include acetonitrile, DMF, and the like.

Emulsifiers or dispersants are important in these two-phase organic systems. The molecular structure of the emulsifying or dispersing agent may contain one portion that is soluble in the nonpolar solvent and the remainder that is fixed on the polar phase. They can stabilize the micelles / droplets considered as microreactors containing monomers and inorganic pigment particles and forming particles through polycondensation.

Suitable emulsifiers or dispersants may include 2-block copolymers such as poly (isoprene) -b-poly (methyl methacrylate), polystyrene-b-poly (ethene-alt-propene) .

In addition, co-emulsifiers may 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 strong steric stabilizer. Suitable secondary emulsifiers may include sulfonamines (B-60, B-100 or B-200), such as those set forth below.

Where x is 5-40 and y is 1-40.

In one approach, the process can continue to grow the polyacrylate steric stabilizer after the polycondensation reaction is complete in the microreactor. In this case, the steric stabilizer may be a polyacrylate chain, but the shell is formed from polyurethane. After the emulsifier or dispersant used in the reaction has been washed on the particle surface, the composite pigment particles are stabilized in a non-polar solvent (i.e., display fluid) with the polyacrylate stabilizer. Some materials that can initiate acrylate polymerization include isocyanatoethyl acrylate, isocyanatostyrene, and the like.

Monomers for steric stabilizers include hydroxyethyl methacrylate and other acrylates compatible with 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-octadecyl methacrylate and the like.

In any of the methods described above, comonomers may be added to the reaction medium such that a functional group for charge generation is incorporated. The comonomer can directly charge the composite pigment particles or interact with the charge control agent in the display fluid to impart the desired charge polarity and charge density to the composite pigment particles. Suitable comonomers include vinylbenzyl-aminoethylamino-propyl-trimethoxysilane, methacryloxypropyltrimethoxysilane, acrylic acid, methacrylic acid, vinylphosphoric acid, 2- Dimethylamino) ethyl methacrylate, N- [3- (dimethylamino) propyl] methacrylamide, and the like.

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

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

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

As indicated, the charge polarity of the pigment material can be varied from negative to positive or reversed by adding comonomers to the reaction medium for shell formation. The charge level of the pigment material can also be adjusted in this way.

The comonomers capable of introducing a negative charge may include, but are not limited to, fluorinated acrylates or fluorinated methacrylates. Specific examples include 2-perfluorobutyl ethyl acrylate, 2,2,2-trifluoroethyl methacrylate, 2,2,3,3-tetrafluoropropyl methacrylate, 1,1,1,3 , 3,3-hexafluoroisopropylacrylate, 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 capable of introducing a positive charge may include, but are not limited to, 2- (dimethylamino) ethyl methacrylate, N- [3- (dimethylamino) propyl] -methacrylamide. The functional groups of the comonomer producing positive charge include, but are not limited to, -NHR, -NR ₂ , -NH-, -NH _2, etc. where R has 4 or fewer carbon atoms.

The main monomers in shell formation are listed above in the present application. For example, there may be mentioned styrene, methyl acrylate, methyl methacrylate, n-butyl acrylate, n-butyl methacrylate, t-butyl acrylate, t-butyl methacrylate, vinylpyridine, , 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, dimethylaminoethyl methacrylate, and the like. In some cases, the main monomer may be styrene, acrylate or methacrylate having a hydrocarbon side chain.

Some examples of suitable monomer-comonomer pairs are methyl methacrylate, 2- (dimethylamino) ethyl methacrylate, methyl methacrylate and 2-perfluorobutyl ethyl acrylate, methyl methacrylate and 2,2, 2-trifluoroethyl methacrylate and the like.

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

The amount of reactants used in any of the above described methods (e.g., inorganic core pigment particles, shell materials, and materials for forming steric stabilizers) may be adjusted to achieve the desired organic content of the resulting composite pigment particles And can be adjusted.

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

The present invention is applicable to single particle, two particle or multi-particle electrophoretic display fluid systems. In a multicomponent system, there can be more than two pigment particles and each particle has a different color from the particles of the other species.

That is, the present invention may relate to a display fluid comprising only complex pigment particles dispersed in a hydrocarbon solvent produced according to the present invention. The composite pigment particles and the solvent have a contrasting color.

Alternatively, the present invention may relate to a display fluid comprising two pigment particles dispersed in an organic solvent, and at least one of the two pigment particles is prepared according to the present invention. Two kinds of pigment particles have opposite charge polarity and contrast color. For example, the two pigment particles may be black and white, respectively. In this case, black particles may be prepared according to the invention, or white particles may be prepared according to the invention, or both black and white particles may be prepared according to the invention.

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

In a two-particle system, when only one pigment particle is produced according to the present invention, the pigment particles of the other species may be prepared by any other method. For example, the particles may be polymer encapsulated pigment particles. Microencapsulation of 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.

The composite pigment particles prepared according to the prior art techniques may also have an intrinsic charge, or may be positively charged using a charge control agent, or may obtain charge when suspended in an organic solvent. Suitable charge control agents are well known in the art; They may be polymeric or non-polymeric in nature, and may also be ionic or non-ionic and include ionic surfactants such as sodium dodecylbenzenesulfonate, metal soap, polybutene succinimide, maleic anhydride, (Meth) acrylic acid copolymer or N, N-dimethylaminoethyl (meth) acrylate copolymer, Alcolec LV30 (soy lecithin), Petrostep B100 (petroleum sulfonate), vinyl pyridine copolymer, vinyl pyrrolidone copolymer, Or OLOA 1200 (polyisobutylene succinimide), or B70 (barium sulfonate), Solsperse 17000 (active polymeric dispersant), Solsperse 9000 (active polymeric dispersant), OLOA 11000 (succinimide ashless dispersant) , Unithox 750 (ethoxylate), Petronate L (sodium sulfonate), Disper BYK 101, 2095, 185, 116, 9077 & 220 and ANTI-TERRA series.

Example

Example 1

Step A: Deposition of vinylbenzyl aminoethylaminopropyl-trimethoxysilane onto black pigment particles

Ammonium hydroxide (28%, 0.4 g) and Z-6032 (Dow Corning, 16 g, 40% in methanol) were added to a 1 L reactor (40 g), Black 444 (Shepherd, 40 g), isopropanol Lt; / RTI > The reactor was heated to 65 DEG C in an ultrasonic bath with mechanical agitation. After 5 hours, the mixture was centrifuged at 6000 rpm for 10 minutes. The solids were redispersed in isopropanol (300 g), centrifuged and dried overnight at 50 < 0 > 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 of water and 5.5 g of ethanol. The solution was purged with nitrogen for 20 minutes and heated to 65 < 0 > C. The pigment particles (4 g) prepared in Step A were dispersed in a mixture of 3.0 g of lauryl acrylate, 0.2 g of divinylbenzene and 0.03 g of AIBN (azobisisobutyronitrile) to form a uniform suspension. The suspension was added to the PVP solution at 65 占 폚. The polymerization reaction was continued for about 12 hours with stirring.

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

The prepared solids were separated from the liquid by centrifugation and washed with isopropanol and methyl ethyl ketone to remove PVP K30 and other chemicals that were not bound to the pigment particles. The solids were dried under vacuum at 50 < 0 > C to yield final composite black particles. As a result of the thermal gravimetric analysis (TGA), the organic content of the produced particles was about 34% by weight.

Example 2

Synthesis of colored pigment particles

Hostaperm Red D3G 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. The mixture, MCR-M22 (Gelest, 5.7 g) and DMS-T01 (Gelest, 30 g) were added to a 250 mL reactor. The reactor was heated to 70 DEG C with magnetic stirring and purged with nitrogen for 20 minutes before adding lauryl peroxide (0.07 g). After 19 hours, the mixture was centrifuged at 5000 rpm for 15 minutes. The resulting solid was redispersed in hexane and centrifuged. This cycle was repeated twice and the solids were dried under vacuum at room temperature to produce the final particles. As a result of the thermal gravimetric analysis (TGA), the resulting polymer had a polymer content of about 49% by weight.

Although the present invention has been described with reference to particular embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention.

Claims (15)

A method of adjusting the charge level of a composite pigment particle, comprising:
(i) providing a composition comprising a monomer,
(ii) selecting a comonomer to be added to the composition, wherein the comonomer is selected so that it can introduce positive or negative charge into the composite pigment particle or change the charge level of the composite pigment particle,
(iii) using the composition to form a shell of composite pigment particles.  The positive photosensitive composition as claimed in claim 1, wherein the monomer is selected from the group consisting of styrene, methyl acrylate, methyl methacrylate, n-butyl acrylate, n-butyl methacrylate, t-butyl acrylate, Vinyl pyrrolidone, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate or dimethylaminoethyl methacrylate.  The process according to claim 1, wherein the monomer is styrene, acrylate or methacrylate having a hydrocarbon side chain.  The composition of claim 1, wherein the comonomer is selected from the group consisting of vinylbenzyl-aminoethylamino-propyl-trimethoxysilane, methacryloxypropyltrimethoxysilane, acrylic acid, methacrylic acid, vinylphosphoric acid, 2- Sulfonic acid, 2- (dimethylamino) ethyl methacrylate, and N- [3- (dimethylamino) propyl] methacrylamide.  The method of claim 1, wherein the comonomer is a fluorinated acrylate or fluorinated methacrylate for introducing a negative charge.  The positive resist composition of claim 1, wherein the comonomer is selected from the group consisting of 2-perfluorobutyl ethyl acrylate, 2,2,2-trifluoroethyl methacrylate, 2,2,3,3-tetrafluoro Propyl methacrylate, 1,1,1,3,3,3-hexafluoroisopropylacrylate, 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.  The method of claim 1 wherein the comonomer is 2- (dimethylamino) ethyl methacrylate or N- [3- (dimethylamino) propyl] -methacrylamide for introducing a positive charge. The process of claim 1, wherein the comonomer comprises a functional group selected from the group consisting of -NHR, -NR ₂ , -NH-, and -NH ₂ for introducing a positive charge, wherein R comprises up to 4 carbon atoms Alkyl. The method of claim 1, wherein the pair of monomer and comonomer is selected from the group consisting of methyl methacrylate, 2- (dimethylamino) ethyl methacrylate, methyl methacrylate and 2-perfluorobutyl ethyl acrylate, or methyl methacrylate and 2 , 2,2-trifluoroethyl methacrylate. The process according to claim 1, wherein the molar ratio of the comonomer to the total of the monomer and the comonomer is 0.1 to 50%. 11. The process of claim 10, wherein the molar ratio of comonomer to total sum of monomer and comonomer is 1 to 10%. Composite pigment particles for electrophoretic displays comprising at least core pigment particles, shells coated on the core pigment particles, and steric stabilizer molecules on the surface of the composite pigment particles, wherein the shell is formed from monomers and comonomers , Wherein the monomer is selected from the group consisting of styrene, methyl acrylate, methyl methacrylate, n-butyl acrylate, n-butyl methacrylate, t-butyl acrylate, t-butyl methacrylate, vinylpyridine, , 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, dimethylaminoethyl methacrylate. 13. The composition of claim 12, wherein the comonomer is selected from the group consisting of 2-perfluorobutyl ethyl acrylate, 2,2,2-trifluoroethyl methacrylate, 2,2,3,3-tetrafluoropropyl methacrylate, , 1,1,3,3,3-hexafluoroisopropylacrylate, 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 2,2,3,3,3-tetrafluoropropyl acrylate, 4,4,4-heptafluorobutyl methacrylate.  13. The particles of claim 12, wherein the comonomer is 2- (dimethylamino) ethyl methacrylate or N- [3- (dimethylamino) propyl] -methacrylamide. The particles according to claim 12, wherein the molar ratio of the comonomer to the total of the monomer and the comonomer is 0.1 to 50%.

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