Charge control agent and particle dispersion containing the same

文档序号：1957926 发布日期：2021-12-10 浏览：12次中文

阅读说明：本技术 电荷控制剂和包含其的粒子分散体 (Charge control agent and particle dispersion containing the same ) 是由 E·布佐夫耶 J·L·马歇尔 S·J·特尔弗 B·麦克唐纳于 2020-05-01 设计创作，主要内容包括：公开了含有多个带电颜料粒子和一种或多种电荷控制剂的混合物。所述电荷控制剂中的至少一种具有包含诸如铵阳离子或亚胺鎓化合物的阳离子头基,和除了非环状仲酰胺基团以外的非离子极性官能团的化学结构。所述混合物用作分散体,用于形成可以掺入电泳显示器中的电泳介质。供选择地,所述分散体可以用于形成电子照相调色剂和用于其他印刷应用的分散体。(Mixtures containing a plurality of charged pigment particles and one or more charge control agents are disclosed. At least one of the charge control agents has a chemical structure comprising a cationic head group, such as an ammonium cation or an iminium compound, and a non-ionic polar functional group other than an acyclic secondary amide group. The mixture is used as a dispersion for forming an electrophoretic medium that can be incorporated into an electrophoretic display. Alternatively, the dispersions can be used to form electrophotographic toners and dispersions for other printing applications.)

1. A mixture comprising a plurality of charged particles and a first charge control agent comprising ammonium cations and having a chemical structure represented by formula I, formula II, formula III, formula IV, formula V, or formula VI;

wherein m is 0,1, 2, or 3;

wherein each R is independently selected from an alkyl group and an aryl group;

wherein Z is one of a branched alkanediyl group and a non-branched alkanediyl group;

wherein n is an integer less than or equal to 20;

wherein X is a moiety comprising a non-ionic polar functional group other than a non-cyclic secondary amide group; and

wherein HT is a hydrophobic moiety;

wherein R is an alkyl group or an aryl group;

wherein R is₁、R₂Independently selected from alkyl groups, aryl groups and groups- [ (Z)_n–X–HT]；

Wherein Z is one of a branched alkanediyl group and a non-branched alkanediyl group;

wherein formula II comprises at least one- [ (Z)_n–X–HT]A group;

wherein n is an integer less than or equal to 20;

wherein X is a moiety comprising a non-ionic polar functional group other than a non-cyclic secondary amide group; and

wherein HT is a hydrophobic moiety;

wherein R is an alkyl group or an aryl group;

wherein R is₃、R₄And R₅Independently selected from alkyl groupsAryl radicals and radicals- [ (Z)_n–X–HT]；

Wherein formula III contains at least one- [ (Z)_n–X–HT]A group;

wherein Z is one of a branched alkanediyl group and a non-branched alkanediyl group;

wherein n is an integer less than or equal to 20;

wherein X is a moiety comprising a non-ionic polar functional group other than a non-cyclic secondary amide group; and

wherein HT is a hydrophobic moiety;

wherein R is an alkyl group or an aryl group;

wherein R is₆、R₇And R₈Independently selected from alkyl groups, aryl groups and groups- [ (Z)_n–X–HT]；

Wherein formula IV comprises at least one- [ (Z)_n–X–HT]A group;

wherein Z is one of a branched alkanediyl group and a non-branched alkanediyl group;

wherein n is an integer less than or equal to 20;

wherein X is a moiety comprising a non-ionic polar functional group other than a non-cyclic secondary amide group; and

wherein HT is a hydrophobic moiety;

wherein R is₉And R₁₀Independently selected from alkyl groups, aryl groups and groups- [ (Z)_n–X–HT]；

Wherein formula V comprises at least one- [ (Z)_n–X–HT]A group;

wherein Z is one of a branched alkanediyl group and a non-branched alkanediyl group;

wherein n is an integer less than or equal to 20;

wherein X is a moiety comprising a non-ionic polar functional group other than a non-cyclic secondary amide group; and

wherein HT is a hydrophobic moiety.

2. The mixture of claim 1 wherein the nonionic polar functional group of the first charge control agent is selected from the group consisting of cyclic and acyclic ester, hydroxy ester, imide, carbamate, urea, tertiary amide, and cyclic secondary amide groups.

3. The mixture of claim 1, further comprising a second charge control agent, wherein the second charge control agent comprises a hydrophobic portion and a head group selected from an anionic functional group, a nonionic functional group, and a cationic functional group.

4. The mixture of claim 3, wherein the second charge control agent comprises an ammonium cation, an acyclic secondary amide group, and a hydrophobic moiety.

5. The mixture of claim 4, wherein the second charge control agent is represented by formula XV;

wherein each R₂₁、R₂₂、R₂₃Independently selected from alkyl groups and aryl groups;

wherein v is an integer less than or equal to 20; and

wherein HT is a hydrophobic moiety.

6. The mixture according to claim 5, wherein the hydrophobic moiety HT comprises a functional group selected from the group consisting of poly (hydroxystearic acid), poly (ricinoleic acid), poly (isobutylene), and unbranched or branched alkyl groups, wherein the unbranched or branched alkyl groups comprise from about 10 to about 35 carbon atoms.

7. The mixture of claim 4, wherein the second charge control agent is represented by formula XVI;

wherein HT is a hydrophobic moiety comprising a functional group selected from the group consisting of poly (hydroxystearic acid), poly (ricinoleic acid), poly (isobutylene), and unbranched or branched alkyl groups, wherein the unbranched or branched alkyl groups comprise from about 10 to about 35 carbon atoms.

8. The mixture of claim 4, wherein the second charge control agent is represented by formula XVII;

9. The mixture according to claim 1, wherein the hydrophobic moiety HT of formulae I to V is derived from a monomer selected from ricinoleic acid, isobutylene and combinations thereof.

10. The mixture of claim 1, wherein the first charge control agent has a chemical structure according to formula VII,

wherein HT is a hydrophobic moiety.

11. The mixture of claim 1, wherein the first charge control agent has a chemical structure according to formula XI,

wherein HT is a hydrophobic moiety.

12. The mixture of claim 1, wherein the first charge control agent has a chemical structure according to formula XII,

wherein HT is a hydrophobic moiety.

13. The mixture of claim 1, wherein the first charge control agent has a chemical structure according to formula XIII,

wherein HT is a hydrophobic moiety.

14. The mixture of claim 1, wherein the first charge control agent has a weight average molecular weight greater than or equal to 1000 g/mol.

15. An electrophotographic toner composition comprising a polymeric binder and the mixture of claim 1.

16. A dispersion comprising a fluid and the mixture of claim 1, wherein the plurality of charged particles are capable of moving through the fluid upon application of an electric field.

17. An electro-optic display comprising a light-transmissive electrically-conductive layer, a layer comprising the dispersion of claim 16, and a substrate comprising one or more electrodes, wherein the layer comprising the dispersion is disposed between the light-transmissive electrically-conductive layer and the substrate, and wherein the light-transmissive electrically-conductive layer and the substrate are configured to apply an electric field to the layer comprising the dispersion.

18. The electro-optic display of claim 17, wherein the layer comprising the dispersion comprises a binder and a plurality of capsules, wherein each capsule comprises the dispersion.

19. A front panel laminate or an inverted front panel laminate comprising the dispersion of claim 16.

20. An electronic book reader, portable computer, tablet computer, mobile phone, smart card, sign, watch, shelf label, flash drive, window, or window film comprising the dispersion of claim 16.

Background

Particle-based electrophoretic displays have been the subject of intensive research and development for many years. In such displays, a plurality of charged particles (sometimes referred to as pigment particles) move through a fluid under the influence of an electric field. The electric field is typically provided by a conductive film or transistor, such as a field effect transistor. Electrophoretic displays have good brightness and contrast, wide viewing angles, state bistability, and low power consumption compared to liquid crystal displays. However, such electrophoretic displays have slower switching speeds than LCD displays, and electrophoretic displays are typically too slow to display real-time video. In addition, electrophoretic displays can be sluggish at low temperatures because the viscosity of the fluid limits the movement of the electrophoretic particles. Despite these drawbacks, electrophoretic displays can be found in everyday items such as electronic books (e-readers), mobile phones and mobile phone covers, smart cards, signs, watches, shelf labels, and flash drives.

A number of patents and applications assigned to the Massachusetts Institute of Technology (MIT) and yingke Corporation (E Ink Corporation) or in the name of the massachusetts institute of technology and yingke Corporation describe various techniques for encapsulating electrophoretic media and other electro-optic media. Such an encapsulation medium comprises a plurality of capsules, each of which itself comprises an internal phase containing electrophoretically mobile particles in a fluid medium, and a capsule wall surrounding the internal phase. Typically, the capsule itself is held within a polymeric binder to form a tie layer between the two electrodes. The techniques described in these patents and applications include:

(a) electrophoretic particles, fluids, and fluid additives; see, e.g., U.S. Pat. nos. 7,002,728 and 7,679,814;

(b) bladders, adhesives, and encapsulation methods; see, e.g., U.S. patent nos. 6,922,276 and 7,411,719;

(c) microcell structures, wall materials, and methods of forming microcells; see, e.g., U.S. patent nos. 7,072,095 and 9,279,906;

(d) a method for filling and sealing a microcell; see, e.g., U.S. patent nos. 7,144,942 and 7,715,088;

(e) films and sub-assemblies containing electro-optic material; see, e.g., U.S. Pat. nos. 6,982,178 and 7,839,564;

(f) a backplane, adhesive layer, and other auxiliary layers and methods for a display; see, e.g., U.S. patent nos. 7,116,318 and 7,535,624;

(g) color formation and color adjustment; see, e.g., U.S. patent nos. 7,075,502 and 7,839,564;

(h) a method for driving a display; see, for example, U.S. Pat. nos. 7,012,600 and 7,453,445;

(i) an application for a display; see, e.g., U.S. patent nos. 7,312,784 and 8,009,348; and

(j) non-electrophoretic displays, as described in U.S. patent No. 6,241,921 and U.S. published patent application No. 2015/0277160; and the use of packaging and microcell technology in addition to displays; see, for example, U.S. published patent applications nos. 2015/0005720 and 2016/0012710.

Many commercial electrophoretic media display substantially only two colors, with a gradient between the black and white extremes, known as "grayscale". Such an electrophoretic medium uses a single type of electrophoretic particle having a first color in a colored fluid having a different second color, or first and second types of electrophoretic particles having different first and second colors in an uncolored fluid. In the former case, the first color is displayed when the particles are located near the viewing surface of the display, and the second color is displayed when the particles are spaced apart from the viewing surface. In the latter case, the first color is displayed when the first type of particles are located near the viewing surface of the display, and the second color is displayed when the second type of particles are located near the viewing surface. Typically, the two colors are black and white.

If a full color display is desired, a color filter array may be deposited on the viewing surface of the monochrome (black and white) display. Displays with color filter arrays rely on area sharing and color mixing to produce color stimuli. The available display area is shared between three or four primary colors, such as red/green/blue (RGB) or red/green/blue/white (RGBW), and the color filters may be arranged in a one-dimensional (stripe) or two-dimensional (2 × 2) repeating pattern. Other choices of primary color or more than three primary colors are also known in the art. The three (in the case of an RGB display) or four (in the case of an RGBW display) sub-pixels are chosen to be small enough that at the intended viewing distance they visually mix together to form a single pixel with a uniform color stimulus ("color mixing"). An inherent disadvantage of area sharing is that the colorant is always present and the color can only be modulated by switching the corresponding pixel of the underlying monochrome display to white or black (turning the corresponding primary color on or off). For example, in an ideal RGBW display, each of the red, green, blue and white primaries occupy a quarter of the display area (one of the four subpixels), the white subpixel is as bright as the underlying monochrome display white, and each of the colored subpixels is no brighter than one third of the monochrome display white. The luminance of the white shown by the display as a whole cannot exceed half the luminance of the white sub-pixel. This is caused by the fact that: the white area of the display results from displaying one white sub-pixel out of every four, plus each colored sub-pixel in its colored form, equal to one third of the white sub-pixel. Thus, the combined three colored subpixels contribute no more than one white subpixel. The brightness and saturation of the color are reduced by being shared with the color pixel region switched to black. When mixing yellow, region sharing is particularly problematic because it is brighter than any other color of the same brightness, and saturated yellow is almost as bright as white. Switching the blue pixels (one quarter of the display area) to black makes the yellow too dark.

Alternatively, a full color display may be provided by using an electrophoretic medium containing a plurality of colored pigments having different electrophoretic mobilities. For example, U.S. patent No. 9,921,451 teaches a colored electrophoretic display comprising an electrophoretic medium containing one type of light-scattering particles (usually white) and three substantially non-light-scattering types of particles providing three subtractive primary colors. The use of substantially non-light scattering type particles with subtractive primary colors enables mixing of colors and provides more color results at a single pixel than can be achieved with color filters. Electrophoretic media and electrophoretic devices exhibit complex behavior, particularly those containing groups of charged pigments having different charges and mobilities. A complex "waveform" is required to drive the particles between states. In combination with the complexity of the electric field, the mixture of particles (pigments) and fluid may exhibit unexpected behavior due to the interaction between the charged species and the surrounding environment (such as the encapsulation medium) upon application of the electric field. In addition, unexpected behavior may be caused by impurities in the fluid, paint, or encapsulation medium. For example, the charge on the electrophoretic particles is typically controlled by the addition of Charge Control Agents (CCAs) or surfactants to the electrophoretic medium; however, commercially available CCAs may have significant levels of impurities. It is therefore difficult to predict how an electrophoretic display will respond to changes in the internal phase composition.

Summary of The Invention

In one aspect, a mixture according to an embodiment of the present invention includes a plurality of charged particles and a first charge control agent including ammonium cations and having a chemical structure represented by formula I;

wherein m is 0,1, 2 or 3; each R is independently selected from alkyl groups and aryl groups; wherein Z is one of a branched alkanediyl group and a non-branched alkanediyl group; wherein n is an integer less than or equal to 20; wherein X is a moiety comprising a non-ionic polar functional group other than a non-cyclic secondary amide group; and wherein HT is a hydrophobic moiety.

In another aspect, a mixture according to an embodiment of the present invention includes a plurality of charged particles and a first charge control agent including ammonium cations and having a chemical structure represented by formula II;

On the other hand, the mixture according to the embodiment of the present invention includes a plurality of charged particles and a first charge control agent including ammonium cations and having a chemical structure represented by formula III;

wherein R is an alkaneA radical or an aryl radical; wherein R is₃、R₄And R₅Independently selected from alkyl groups, aryl groups and groups- [ (Z)_n–X–HT](ii) a Wherein formula III contains at least one- [ (Z)_n–X–HT]A group; wherein Z is one of a branched alkanediyl group and a non-branched alkanediyl group; wherein n is an integer less than or equal to 20; wherein X is a moiety comprising a non-ionic polar functional group other than a non-cyclic secondary amide group; and wherein HT is a hydrophobic moiety.

In another aspect, a mixture according to embodiments of the invention comprises a plurality of charged particles, a first charge control agent, and a second charge control agent, wherein the second charge control agent comprises an ammonium cation, an acyclic secondary amide group, and a hydrophobic moiety.

In another aspect, a mixture according to embodiments of the invention is present in a dispersion in a fluid, wherein the plurality of charged particles are capable of moving through the fluid upon application of an electric field. An electro-optic display having an electrophoretic medium may comprise the dispersion.

These and other aspects of the invention will be apparent from the following description.

Brief Description of Drawings

Fig. 1 is a graph showing 50 of particles, charge control agents containing acyclic secondary amide groups, and both, combined with varying amounts of charge control agents (containing an ester group as a secondary functionality) according to embodiments of the present invention: graph comparing the zeta potential changes of 50 blends.

Fig. 2 and 3 show color gamuts of dispersions comprising a plurality of color particles and a charge control agent comprising an acyclic secondary amide group.

Fig. 4 shows a color gamut of a dispersion comprising a plurality of color particles of fig. 2 and 3 and a blend of a charge control agent containing an ester group as a secondary functionality and a charge control agent containing an acyclic secondary amide group.

Detailed description of the invention

In the following detailed description, by way of example, numerous specific details are set forth in order to provide a thorough understanding of the relevant teachings. It will be apparent, however, to one skilled in the art that the present teachings may be practiced without these specific details.

The present invention provides mixtures comprising pigment particles and improved charge control agents. Particles that absorb, scatter, or reflect light in a broad band or at selected wavelengths are referred to herein as colored or pigment particles. Various materials other than pigments that absorb or reflect light (meaning insoluble coloring materials in the strict sense of the term), such as dyes or photonic crystals, may also be used in the mixture of the present invention.

The mixture may be incorporated into a dispersion that can be used in an electrophoretic medium and incorporated into a display, or into a front panel laminate (front plane laminate) or an inverted front panel laminate that is coupled to a backplane to form a display. Alternatively, the mixture may be used in other applications, such as compositions for use as electrophotographic toners in printing applications.

As used herein, electrophotography or xerography is a process of printing an image on a substrate. Forming a latent image comprising an electrostatic charge on a coated plate or roller, followed by (a) attaching oppositely charged particles to the charged portion of the plate or roller, (b) transferring the charged particles to a substrate and (c) melting the particles on the substrate by heating. Typical charged particles comprise a color pigment, a resin and one or more charge control agents. The particles are used in the form of powders, known as "toners" or "electrophotographic toners", wherein the powder comprises particles having a specific average particle size.

As used herein, the "head group" of a molecule comprising both hydrophilic and hydrophobic portions is a functional group of the hydrophilic portion of the molecule. The molecule may have one or more than one head group.

The term "molecular weight" or "MW" as used herein refers to weight average molecular weight, unless otherwise specified. The weight average molecular weight was measured by gel permeation chromatography.

"auxiliary functionality" or "auxiliary functional group" as used throughout the specification and claims means a nonionic polar functional group of the charge control agent. "ancillary functional groups" may include ester groups, hydroxyl ester groups, tertiary amide groups, urethane groups, acyclic urea groups, cyclic amide groups, and other nonionic polar functional groups.

Mixtures according to various embodiments of the invention may comprise a plurality of charged particles and a first charge control agent comprising a cationic head group and having a chemical structure according to formula I,

wherein m is 0,1, 2 or 3; wherein each R is independently selected from an alkyl group and an aryl group; wherein Z is one of a branched alkanediyl group and a non-branched alkanediyl group; wherein n is an integer less than or equal to 20; wherein X is a moiety comprising a non-ionic polar functional group other than a non-cyclic secondary amide group; and wherein HT is a hydrophobic moiety. The group R may be a methyl, ethyl, propyl, phenyl or benzyl group. If there is more than one alkyl group attached to the amine atom of the quaternary ammonium group of formula I, the alkyl groups may be the same or different. For example, formula I can comprise a trimethylammonium cationic group, a triethylammonium cationic group, a dimethylethylammonium cationic group, and the like. Radical (Z)_nMay be-CH₂-、-CH₂CH₂-、-CH₂CH₂CH₂-、-CH₂CH₂CH₂CH₂-and the like. Radical (Z)_nMay be an unbranched radical- (CH)₂)_q-, where q may be 1 to 20. Alternatively, the group (Z)_nMay be a branched alkanediyl group, such as-CH₂(CH₃)CH₂CH₂-. The X moiety may comprise various nonionic polar functional groups, such as ester [ -O-C (O) - -]Hydroxy ester group, thioester group [ -S-C (O) -]Tertiary amide [ -N (alkyl) -C (O) -O-]Carbamate [ -NH-C (O) -O-]Or [ -O-C (O) -NH-]-acyclic ureido [ -NH-C (O) -NH-]Cyclic ureido groups, cyclic amido groups, and combinations thereof.

Alternatively, mixtures according to various embodiments of the invention may comprise a plurality of charged particles and a first charge control agent comprising a cationic head group and having a chemical structure according to formula II,

wherein R is an alkyl group or an aryl group; r₁、R₂Independently selected from alkyl groups, aryl groups and groups- [ (Z)_n–X–HT](ii) a Wherein formula II comprises at least one- [ (Z)_n–X–HT](ii) a Wherein the radical (Z)_nIs one of a branched alkanediyl group and a non-branched alkanediyl group; wherein n is an integer less than or equal to 20; wherein X is a moiety comprising a non-ionic polar functional group other than a non-cyclic secondary amide group; and wherein HT is a hydrophobic moiety. In one example of the compound represented by formula II, R and R₂Both are methyl. Radical- (Z)_nMethylene groups which may be unbranched or branched. In one example, the group- (Z)_nis-CH₂CH₂-. In another example, the group- (Z)_nis-CH₂CH₂CH₂-. The X moiety can comprise various nonionic polar functional groups such as ester groups, hydroxyl ester groups, thioester groups, tertiary amide groups, urethane groups, acyclic urea groups, cyclic amide groups, and combinations thereof.

Alternatively, mixtures according to various embodiments of the invention may comprise a plurality of charged particles and a first charge control agent comprising two cationic head groups and having a chemical structure according to formula III,

wherein R is an alkyl group or an aryl group; wherein R is₃、R₄And R₅Independently selected from alkyl groups, aryl groups and groups- [ (Z)_n–X–HT](ii) a Wherein formula III contains at least one- [ (Z)_n–X–HT]A group; wherein Z is one of a branched alkanediyl group and a non-branched alkanediyl group; wherein n is an integer less than or equal to 20; wherein X is a group containing but notA portion of a nonionic polar functional group other than a cyclic secondary amide group; and wherein HT is a hydrophobic moiety. In one example of the compound represented by formula III, R and R₃Both are methyl. Radical- (Z)_nMethylene groups which may be unbranched or branched. In one example, the group- (Z)_nis-CH₂CH₂-. In another example, the group- (Z)_nis-CH₂CH₂CH₂-. The X moiety can comprise various nonionic polar functional groups such as ester groups, hydroxyl ester groups, thioester groups, tertiary amide groups, urethane groups, acyclic urea groups, cyclic amide groups, and combinations thereof.

wherein R is an alkyl group or an aryl group; wherein R is₆、R₇And R₈Independently selected from alkyl groups, aryl groups and groups- [ (Z)_n–X–HT](ii) a Wherein formula IV comprises at least one- [ (Z)_n–X–HT]A group; wherein Z is one of a branched alkanediyl group and a non-branched alkanediyl group; wherein n is an integer less than or equal to 20; wherein X is a moiety comprising a non-ionic polar functional group other than a non-cyclic secondary amide group; and wherein HT is a hydrophobic moiety. In one example of the compound represented by formula IV, R and R₆Both are methyl. Radical- (Z)_nMethylene groups which may be unbranched or branched. In one example, the group- (Z)_nis-CH₂CH₂-. In another example, the group- (Z)_nis-CH₂CH₂CH₂-. The X moiety may contain various nonionic polar functional groups such as ester groups, hydroxy ester groups, thioester groups, tertiary amide groups, carbamate groups, acyclic urea groups, tertiary amide groups, and tertiary amide groups, or the like,Cyclic ureido groups, cyclic amido groups, and combinations thereof.

wherein R is₉And R₁₀Independently selected from alkyl groups, aryl groups and groups- [ (Z)_n–X–HT](ii) a Wherein formula V comprises at least one- [ (Z)_n–X–HT]A group; wherein Z is one of a branched alkanediyl group and a non-branched alkanediyl group; wherein n is an integer less than or equal to 20; wherein X is a moiety comprising a non-ionic polar functional group other than a non-cyclic secondary amide group; and wherein HT is a hydrophobic moiety. In one example of a compound represented by formula V, the group R₁₀Is methyl. In another example, the group R₁₀Is ethyl. Radical- (Z)_nMethylene groups which may be unbranched or branched. In one example, the group- (Z)_nis-CH₂CH₂-. In another example, the group- (Z)_nis-CH₂CH₂CH₂-. The X moiety can comprise various nonionic polar functional groups such as ester groups, hydroxyl ester groups, thioester groups, tertiary amide groups, urethane groups, acyclic urea groups, cyclic amide groups, and combinations thereof.

Certain Charge Control Agents (CCAs) currently used in electrophoretic displays and other fields comprise a quaternary ammonium head group, a secondary amide-NH-C (O) -and one or more polymer tails. In general, the performance of electrophoretic displays is optimized by: (1) adjusting the relative mass of the charge control agent in the electrophoretic dispersion; and/or (2) adjusting the nitrogen content of the electrophoretic dispersion by blending the ionic polymer CCA and the aliphatic quaternary ammonium salt. The type of ancillary functionalities present in the chemical structure of the charge control agent have not heretofore been considered relevant.

Surprisingly, the inventors of the present invention have found that the pigment charge is influenced by the selection of the type of ancillary functionality present in the chemical structure of the charge control agent further comprising a cationic head group, and can be controlled by the selection of the type of ancillary functionality present in the chemical structure of the charge control agent further comprising a cationic head group. More specifically, the incorporation of ancillary functionalities other than the acyclic secondary amide groups in the quaternary charge control agents significantly alters and improves the performance of electrophoretic displays.

The charge control agents used in various embodiments of the present invention are not limited to quaternary ammonium materials. The material may include, for example, diquaternary ammonium salts, trisquaternary ammonium salts, and the like. As previously mentioned, the charge control agents incorporated into the dispersions prepared according to various embodiments of the present invention include ancillary functionalities in addition to or in place of the acyclic secondary amide groups. The auxiliary functionality may be acyclic functionality or cyclic functionality with varying ring sizes. The chemical structure of the charge control agent may also comprise multiple types of auxiliary functionalities or only one type of auxiliary functionality. For example, a diquaternary charge control agent (i.e., two quaternary amine headgroups per molecule) can contain one urea group associated with one headgroup as a ancillary functionality and one ester group associated with the other headgroup as an ancillary functionality. Alternatively, an ester group (or urea group) may serve as both of these ancillary functionalities. In yet another alternative, the moiety X in formulas I-V above may comprise a plurality of auxiliary functionalities; however, it is preferred that one of the ancillary functionalities closest to the head group (i.e., more closely proximate within the chemical structure) is an ancillary functionality other than the acyclic secondary amide group.

Examples of chemical structures of charge control agents comprising a cationic head group and ancillary functionalities other than an acyclic secondary amide group include, but are not limited to, the following structures:

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

more specific examples include, but are not limited to, the following structures represented by formulas VII through XIII;

(i)

(j)

(k)

(l)

(m)

(n)

(o)

the synthetic procedures used to prepare the charge control agents incorporated into the various embodiments of the present invention can be designed in a number of ways to provide the desired functionality profile. For example, two or more monomers comprising a cationic head group and a secondary functionality may be copolymerized with one or more monomers or oligomers for forming a hydrophobic oligomer or polymer tail. Alternatively, the charge control agent can be prepared by post-modification techniques, wherein the initial charge control activity is altered by the incorporation or modification of ancillary functionalities. Mixtures according to various embodiments of the invention may include blends of different charge control agents. For example, some blends can include two or more charge control agents, wherein at least one of the charge control agents has one or more cationic head groups associated with a secondary functionality other than an acyclic secondary amide group.

The chemical structure of the charge control agent may also include multiple hydrophobic moieties, including oligomeric or polymeric tails. The oligomer or polymer tail may be derived from one or more different monomers and/or oligomers for varying molecular weight and hydrophobicity, and may be linear or have different degrees of branching. The hydrophobic moiety HT in formulas I-V may be an oligomeric or polymeric tail. If the charge control agent is included in an electrophoretic medium comprising a dispersion, the hydrophobic portion is preferably compatible with the dispersion fluid. In some embodiments, the hydrophobic oligomeric or polymeric tail may be unsaturated, i.e., have at least one carbon-carbon double bond. The oligomeric or polymeric hydrophobic tail may be derived from one or more monomers including, but not limited to, ricinoleic acid and isobutylene.

The hydrophobic part HT of the CCA of the present invention may be comprised ofReaction between reagents A-B having a functional group A capable of reacting with another molecule G- (Z)_n-Y, which for convenience is referred to herein as a CCA precursor. The reaction scheme is shown in equation 1:

G-(Z)_n-Y+A-B→G-(Z)_n-HT equation 1.

Radical (Z)_nA linking group corresponding to the obtained CCA, which links the quaternary ammonium group of CCA with the nonionic polar functional group X. For convenience and simplicity, G represents the moiety of the CCA precursor that is attached to the linking group. G may contain one or more additional functional groups Y (or other reactive functional groups) that may react with the reagent A-B.

The reaction between functional groups a and Y may be a condensation reaction. It may also be an addition reaction. For example, the functional group a may be a carboxylic acid group, a carboxylic acid anhydride group, an acid halide group, or an epoxy group. These functional groups are capable of reacting with a functional group Y of the CCA precursor, where Y may be a hydroxyl, amine or thiol group. Of course, in order for the CCA to comprise a hydrophobic moiety HT, the agents A-B must also contain a hydrophobic group. The agents A-B may also be monomers, which are polymerized to provide hydrophobic polymers. For example, the agent A-B may be a hydroxy fatty acid, such as ricinoleic acid, which polymerizes into poly (ricinoleic acid). Alternatively, the functional group a may be a hydroxyl group, an amine group or a thiol group, and the functional group Y may be a carboxylic acid group, a carboxylic acid anhydride group, an acid halide group or an epoxy group.

In one embodiment, the HT hydrophobic moiety may be formed from the reaction of the Y functional group of the CCA precursor with two or more monomers. In one example, the Y functional group is a hydroxyl group. The two monomers may be monohydroxymonocarboxylic acids and dihydroxymonocarboxylic acids. Polymerization of the two monomers and reaction with the hydroxyl groups of the CCA precursor will yield a CCA having a polyester hydrophobic group with one or more branches. Specific examples of such CCAs may be represented by (a)3- (dimethylamino) -1-propanol, (b) ricinoleic acid, and (c)2, 2-dimethylolpropionic acid [ CH ]₃C(CH₂OH)₂COOH]By a condensation reaction between them.

The agent A-B may contain two or more groups A. In addition, mixtures of two or more monomeric reagents may be used in the same preparation. This may enable the preparation of different CCAs with various polymer structures in their hydrophobic HT part.

Non-limiting examples of the types of fatty acids that can be used as reagent (A-B) are straight chain saturated fatty acids, branched chain saturated fatty acids and unsaturated fatty acids. The linear saturated fatty acids may contain alkyl chains of from about 10 to about 35 carbon atoms. Non-limiting examples of branched saturated fatty acids include fatty acids comprising an isoalkyl group containing from about 10 carbon atoms to about 35 carbon atoms, fatty acids comprising an anteiso alkyl group containing from about 10 carbon atoms to about 35 carbon atoms, 3,7,11, 15-tetramethylhexadecanoic acid, 2,6,10, 14-tetramethylpentadecanoic acid, 4,8, 12-trimethyltridecanoic acid, 13-dimethyltetradecanoic acid, and 10-methyloctadecanoic acid. Isofatty acids are fatty acids with alkyl branches at the omega-2 position. Anteiso fatty acids are fatty acids with alkyl branches at the omega-2 position. The unsaturated fatty acid may contain a hydrocarbon chain having from about 10 carbon atoms to about 35 carbon atoms and one or more carbon-carbon double bonds. Non-limiting examples of unsaturated fatty acids include oleic acid, palmitoleic acid, myristoleic acid, linoleic acid, arachidonic acid, alpha-linolenic acid, cis 6-hexadecenoic acid (sapienic acid), elaidic acid, vaccenic acid, trans linoleic acid (linolaidic acid), eicosapentaenoic acid, erucic acid, 7-methyl-7-hexadecanoic acid, and docosahexaenoic acid.

Non-limiting examples of the types of hydroxy fatty acids that can serve as the monomeric agent (a-B) that can be polymerized to provide a hydrophobic polymer are saturated fatty acids having a hydrocarbon chain containing from about 6 carbon atoms to about 35 carbon atoms and one or more hydroxyl groups, and unsaturated fatty acids having a hydrocarbon chain containing from about 6 carbon atoms to about 35 carbon atoms, one or more carbon-carbon bonds, and one or more hydroxyl groups. Non-limiting examples of such hydroxy fatty acids are ricinoleic acid, w-hydroxy-6-dodecenoic acid, 9,10, 13-trihydroxy-11-octadecanoic acid, 9,12, 13-trihydroxy-1-octadecenoic acid, 9-hydroxy-10, 12-octadecadienoic acid, 13-hydroxy-9, 11-octadecadienoic acid, 8-hydroxystearic acid, 2-hydroxy-15-methylhexanoic acid, 3-hydroxy-15-methylhexanoic acid, omega-hydroxy-6-dodecenoic acid, 2-hydroxy-13-methyltetradecanoic acid, and 2-hydroxy-13-methyltetradecanoic acid.

In one embodiment, the-X-HT group may be a group comprising a hydrophobic group R₁₁The imide group of formula XIV, as shown in formula XIV.

This can be achieved by the corresponding succinic anhydride reagent A-B (with hydrophobic substituent R)₁₁) In its contact with the CCA precursor G- (Z)_n-Y is formed after the reaction, wherein the reactive functional group Y is an amine. Hydrophobic precursor G- (Z)_n-Y, wherein the reactive functional group Y is an amine. Hydrophobic substituent R₁₁And may be an alkyl group containing from about 10 to about 35 carbon atoms. The alkyl group may also contain one or more alkyl chains and/or one or more carbon-carbon double bonds. Alternatively, the hydrophobic substituent may be an oligo-or polyester group formed by the polymerisation of a hydroxy carboxylic acid, such as ricinoleic acid.

The inventive mixture comprising a plurality of charged particles and a first charge control agent, wherein the first charge control agent is represented by formulas I-V, may further comprise a second charge control agent. The second charge control agent may comprise one or more anionic head groups and a hydrophobic moiety. Non-limiting examples of anionic head groups are carboxylic acid anions, sulfonate anions, sulfate anions, phosphate anions, and phosphonate anions. The second charge control agent may comprise a nonionic head group and a hydrophobic portion. Non-limiting examples of nonionic head groups are polyethylene oxide, polyethylene glycol, polypropylene oxide, polypropylene glycol, and glycosides. The second charge control agent may comprise a cationic head group and a hydrophobic moiety. Non-limiting examples of cationic head groups are ammonium salts, such as quaternary ammonium salts. The second charge control agent may comprise an amide group in addition to an anionic, nonionic or cationic head group. The second charge control agent can comprise a cationic head group, such as a quaternary ammonium salt, an acyclic secondary amide functional group, and a hydrophobic moiety. Examples of the second charge control agent comprising (a) a quaternary ammonium salt, (b) an acyclic secondary amide functional group, and (c) a hydrophobic moiety include materials represented by the following formula XV,

wherein each R₂₁、R₂₂、R₂₃Independently selected from alkyl groups and aryl groups, wherein v is an integer less than or equal to 20, and wherein HT is a hydrophobic moiety. The hydrophobic moiety HT may comprise a polyester. The hydrophobic portion HT may comprise a functional group selected from the group consisting of poly (hydroxystearic acid), poly (ricinoleic acid), poly (isobutylene), and unbranched or branched alkyl groups comprising from about 10 to about 35 carbon atoms. In one example, R₂₁、R₂₂、R₂₃Is a methyl group, v is 3 and HT is poly (ricinoleic acid). In another example, R₂₁、R₂₂、R₂₃Is a methyl group, v is 2 and HT is poly (ricinoleic acid).

the charge control agent may be added to a dispersion of charged pigment particles, such as an electrophoretic medium, at a concentration of greater than 1g of charge control agent per 100g of charged particles. The charge control agent may have a weight average molecular weight (Mw) of greater than 1000 g/mole, such as greater than 2000 g/mole, such as greater than 3000 g/mole, such as greater than 4000 g/mole, such as greater than 5000 g/mole, such as greater than 6000 g/mole, such as greater than 7000 g/mole, such as greater than 8000 g/mole, such as greater than 9000 g/mole, such as greater than 10000 g/mole.

In many embodiments, the charge control agent included in the mixture according to various embodiments of the present invention adsorbs onto the surface of the particles in the mixture and changes the charge thereon. However, the invention is not limited to an adsorbed CCA and any mixture comprising charged particles and a CCA providing the desired properties is suitable. For example, CCAs may be complexed with, absorbed into, or they may be covalently bonded to the surface of charged particles. The particles and CCA may be present as charge complexes or loosely associated by van der waals forces.

As previously mentioned, a cationic charge control agent having a secondary functionality other than an acyclic secondary amide group can be blended with another type of cationic charge control agent having an acyclic secondary amide in various mixtures prepared according to embodiments of the present invention. Other types of cationic charge control agents can be purchased in purified form, or the charge control agents can be purchased as reaction products that have formed quaternary amine charge control agents. For example, SOLSPERSE 17000 (Lubrizol Corporation) may be purchased as a reaction product of a 12-hydroxy-octadecanoic acid homopolymer with N, N-dimethyl-1, 3-propanediamine and methyl hydrogen sulfate.

With respect to the electrophoretic medium, additional charge control agents may be used to provide good electrophoretic mobility to the electrophoretic particles contained in the mixture according to various embodiments of the present invention. If the medium is encapsulated within the capsule, a stabilizer may be used to prevent aggregation of the electrophoretic particles and irreversible deposition of the electrophoretic particles onto the capsule wall. Either component may be composed of a wide range of molecular weight materials (low molecular weight, oligomeric, or polymeric) and may be a single pure compound or a mixture. Optional charge control agents or charge directors may be used. These ingredients typically consist of low molecular weight surfactants, polymeric reagents, or blends of one or more components, and are used to stabilize or otherwise alter the sign and/or magnitude of the charge on the electrophoretic particles. Additional pigment properties that may be relevant are particle size distribution, chemical composition and lightfastness.

Charge adjuvants may also be added to the mixtures according to various embodiments of the present invention. These materials increase the effectiveness of the charge control agent or charge director. The charge adjuvant may be a polyol or aminoalcohol compound, and preferably may be dissolved in the suspending fluid in an amount of at least 2% by weight. Examples of polyols containing at least two hydroxyl groups include, but are not limited to, ethylene glycol, 2,4,7, 9-tetramethyldecyne-4, 7-diol, poly (propylene glycol), pentylene glycol, tripropylene glycol, triethylene glycol, glycerol, pentaerythritol, glycerol tris (12-hydroxystearate), propylene glycerol monohydroxystearate, and ethylene glycol monohydroxystearate. Examples of aminoalcohol compounds containing at least one alcohol functional group and one amine functional group in the same molecule include, but are not limited to, triisopropanolamine, triethanolamine, ethanolamine, 3-amino-1-propanol, ortho-aminophenol, 5-amino-1-pentanol, and tetrakis (2-hydroxyethyl) ethylenediamine. The charge adjuvant is preferably present in the suspending fluid in an amount of from about 1 to about 100 milligrams ("mg/g") and more preferably from about 50 to about 200mg/g of the mass of the particles per gram.

Mixtures containing charged particle CCA complexes according to various embodiments of the present invention may be advantageously used in all types of electrophoretic displays previously described (i.e., single particle, oppositely charged double particle, double particle of the same polarity, and dispersed polymer). The described charged particle CCA composite may be used to construct an electrophoretic medium having only one type of particle, such as an electrophoretic medium used in a variable transmission window. The described charged particle CCA composite may be used to build an electrophoretic medium to be used in a black/white display, i.e. comprising black and white particles. The described charged particle CCA composite may be used to build an electrophoretic medium to be used in a color display, i.e. comprising for example three, four, five, six, seven or eight different types of particles. For example, a display may be constructed in which the particles comprise black, white and red, or black, white and yellow. Alternatively, the display may comprise red, green and blue particles, or cyan, magenta and yellow particles, or red, green, blue and yellow particles.

For electrophoretic display applications, a mixture of particles and charge control agents according to various embodiments of the present invention may be dispersed in a suspending fluid and encapsulated to provide an encapsulated electrophoretic medium that may be incorporated into a display. Electrophoretic media prepared according to various embodiments of the present invention may employ the same components and preparation techniques as those described in the aforementioned patents and applications by the Massachusetts institute of technology and Ink Corporation (E Ink Corporation).

For example, the suspending fluid containing the particles should be selected based on properties such as density, refractive index, and solubility. Preferred suspending fluids have a low dielectric constant (about 2), a high volume resistivity (about 1015 ohm-cm), a low viscosity (less than 5 centistokes ("cst")), low toxicity and environmental impact, low water solubility (less than 10 parts per million ("ppm")), a high boiling point (greater than 90 ℃), and a low refractive index (less than 1.2).

The choice of non-polar fluid may be based on considerations of chemical inertness, matching the density of the electrophoretic particles, or chemical compatibility with both the electrophoretic particles and the boundary capsules (in the case of encapsulated electrophoretic displays). When particle movement is desired, the viscosity of the fluid should be low. The refractive index of the suspending fluid may also substantially match the refractive index of the particles. As used herein, the refractive index of the suspending fluid "substantially matches" the refractive index of the particles if the difference between the respective refractive indices of the suspending fluid and the particles is between about 0 and about 0.3, and preferably between about 0.05 and about 0.2.

Non-polar organic solvents such as halogenated organic solvents, saturated straight or branched chain hydrocarbons, silicone oils, and low molecular weight halogen-containing polymers are some useful non-polar fluids. The non-polar fluid may comprise a single fluid. However, the non-polar fluid will typically be a blend of more than one fluid in order to adjust its chemical and physical properties. In addition, the non-polar fluid may contain additional surface modifiers to alter the surface energy or charge of the electrophoretic particles or boundary capsules. Reactants or solvents (e.g., oil soluble monomers) used in the microencapsulation process can also be included in the suspending fluid. Additional charge control agents may also be added to the suspending fluid.

Useful organic solvents include, but are not limited to: epoxides such as decane epoxide and dodecane epoxide; vinyl ethers such as cyclohexyl vinyl ether and Decave (registered trademarks of International Flavors and Fragrances, new york city, new york state); and aromatic hydrocarbons such as toluene and naphthalene. Useful halogenated organic solvents include, but are not limited to, tetrafluorodibromoethylene, tetrachloroethylene, chlorotrifluoroethylene, 1,2, 4-trichlorobenzene, and carbon tetrachloride. These materials have a high density. Useful hydrocarbons include, but are not limited to, dodecane, tetradecane, Isopar (registered trademark) series (Exxon, houston, texas), Norpar (registered trademark) (a series of normal paraffin liquids), Shell-Sol (registered trademark) (Shell), houston, texas), and Sol-Trol (registered trademark) (Shell)), naphtha, and other petroleum solvents. These materials typically have a low density. Useful examples of silicone oils include, but are not limited to, octamethylcyclosiloxane and higher molecular weight cyclosiloxanes, poly (methylphenylsiloxane), hexamethyldisiloxane and polydimethylsiloxane. These materials typically have a low density. Useful low molecular weight halogen-containing polymers include, but are not limited to, poly (chlorotrifluoroethylene) polymers (halonated Hydrocarbon Inc.), River Edge, n.j., Galden (registered trademark) (perfluorinated ethers from austemont, Morristown, n.j.), or Krytox (registered trademark) from dupont (Wilmington, te.a.). In a preferred embodiment, the suspending fluid is a poly (chlorotrifluoroethylene) polymer. In a particularly preferred embodiment, the polymer has a degree of polymerization of from about 2 to about 10. Many of the above materials are available in a range of viscosities, densities and boiling points.

The non-polar fluid must be able to form small droplets prior to forming the capsules. Methods for forming small droplets include flow-through nozzles, membranes, jets or orifices, and shear-based emulsification schemes. The formation of small droplets may be aided by an electric or acoustic field. In the case of emulsion type encapsulation, surfactants and polymers may be used to aid in the stabilization and emulsification of the droplets. One surfactant for use in the displays of the present invention is sodium lauryl sulfate.

In some embodiments, the non-polar fluid will include an optically absorbing dye. The dye must be soluble in the fluid, but will generally not be soluble in the other components of the capsule. There is great flexibility in the choice of dye material. The dye may be a pure compound or a blend of dyes to achieve a particular color, including black. The dye may be fluorescent, which produces a display in which the fluorescent properties depend on the position of the particles. The dye may be optically active, becoming another color or becoming colorless upon irradiation with visible or ultraviolet light, providing another means for obtaining an optical response. The dye may also be polymerized, for example, thermally, photochemically or by chemical diffusion, to form a solid absorbent polymer within the boundary shell.

There are many dyes that can be used in encapsulated electrophoretic displays. Important properties here include lightfastness, solubility in the suspending fluid, colour and cost. These dyes are generally selected from the class of azo, anthraquinone and triphenylmethane type dyes and may be chemically modified in order to increase their solubility in the oil phase and reduce their adsorption by the particle surface.

Many dyes known to those skilled in the art of electrophoretic displays will prove useful. Useful azo dyes include, but are not limited to: oil red dyes and the sudan red and sudan black series of dyes. Useful anthraquinone dyes include, but are not limited to: oil blue dyes and Macrolex blue series dyes. Useful triphenylmethane dyes include, but are not limited to, 4 '-bis (dimethylaminophenyl) methanol (Michler's hydrogen), malachite green, crystal violet, and auramine O (auramine O).

Generally, charging is believed to occur as a result of acid-base reactions between some of the moieties present in the continuous phase and the particle surface. Thus, useful materials are those capable of participating in such reactions or any other charging reaction known in the art.

Particle dispersion stabilizers may be added to prevent the particles from flocculating or attaching to the capsule wall. For typical high resistivity liquids used as suspending fluids in electrophoretic displays, non-aqueous surfactants may be used. These include, but are not limited to, glycol ethers, alkynyl glycols, alkanolamides, sorbitol derivatives, alkylamines, quaternary amines, imidazolines, dialkyl oxides, and sulfosuccinates.

If a bistable electrophoretic medium is desired, it may be desirable to include in the suspending fluid a polymer having a number average molecular weight in excess of about 20000, the polymer being substantially non-absorbent on the electrophoretic particles; for this purpose, poly (isobutylene) is a preferred polymer. See application No. 10/063,236 filed on 2.4.2002 (publication No. 2002/0180687; the entire disclosure of this co-pending application is incorporated herein by reference), and corresponding international application No. PCT/US02/10267 (publication No. WO 02/079869).

The terms bistable and bistable are used herein in their conventional meaning in the art to refer to displays comprising display elements having first and second display states which differ in at least one optical property, and such that after any given element has been driven to assume its first or second display state by an addressing pulse of finite duration, that state will continue for at least a multiple, for example at least four times, the minimum duration of the addressing pulse required to change the state of the display element after the addressing pulse has terminated. It is shown in U.S. patent No. 7,170,670 that some particle-based, grayable electrophoretic displays are stable not only in their extreme black and white states, but also in their intermediate gray states, and the same is true for some other types of electro-optic displays. This type of display is properly referred to as multi-stable rather than bi-stable, although for convenience the term bi-stable may be used herein to encompass both bi-stable and multi-stable displays.

The term grayscale is used herein in its conventional meaning in the imaging art to refer to a state intermediate two extreme optical states of a pixel, and does not necessarily imply a black-to-white transition between the two extreme states. For example, several of the aforementioned imperial patents and published applications describe electrophoretic displays in which the extreme states are white and deep blue, so that the intermediate gray state is effectively pale blue. In fact, as already mentioned, the change in optical state may not be a color change at all. The terms black and white may be used hereinafter to refer to the two extreme optical states of the display and should be understood to generally include extreme optical states which are not strictly black and white, such as the aforementioned white and deep blue states.

The dispersion comprising the suspending fluid, particles and charge control agent(s) may then be encapsulated. Encapsulated electrophoretic displays generally do not suffer from the aggregation and settling failure modes of conventional electrophoretic devices and provide further advantages such as the ability to print or coat the display on a wide variety of flexible and rigid substrates. (the use of the word printing is intended to include all forms of printing and coating including, but not limited to, premetered coatings such as slot die coating, slot or extrusion coating, slide or cascade coating, curtain coating, roll coating such as knife-over-roll coating, forward and reverse roll coating, gravure coating, dip coating, spray coating, meniscus coating, spin coating, brush coating, air knife coating, screen printing processes, electrostatic printing processes, thermal printing processes, ink jet printing processes, electrophoretic deposition (see U.S. patent No. 7,339,715), and other similar techniques.) thus, the resulting display may be flexible. Furthermore, because the display medium can be printed (using various methods), the display itself can be manufactured inexpensively.

The encapsulation of the electrophoretic medium may be achieved in many different ways. Many suitable processes for microencapsulation are detailed in both: microencapsulation, methods and uses (Microencapsulation, Processes and Applications), (i.e. by vandigater), Plenum Press, New York, n.y. (1974), and Gutcho, Microencapsulation and Microencapsulation Techniques (Microcapsules and Microencapsulation Techniques), Noyes Data corp., Park Ridge, n.j. (1976). The methods fall into several broad categories, all of which can be applied to the present invention: interfacial polymerization, in situ polymerization, physical methods such as co-extrusion and other phase separation methods, solidification in liquids, and mono/complex coacervation.

A number of materials and methods should prove useful in formulating the displays of the present invention. Useful materials for the single coacervation process for forming the vesicles include, but are not limited to, gelatin, poly (vinyl alcohol), poly (vinyl acetate), and cellulose derivatives, such as carboxymethyl cellulose. Useful materials for complex coacervation processes include, but are not limited to, gelatin, gum arabic, carrageenan, carboxymethylcellulose, hydrolyzed styrene anhydride copolymers, agar, alginates, casein, albumin, methyl vinyl ether-maleic anhydride copolymers, and cellulose phthalate. Useful materials for the phase separation process include, but are not limited to, polystyrene, poly (methyl methacrylate) (PMMA), poly (ethyl methacrylate), poly (butyl methacrylate), ethyl cellulose, poly (vinyl pyridine), and polyacrylonitrile. Useful materials for the in situ polymerization process include, but are not limited to, polyhydroxyamides, using aldehydes, melamine, or urea and formaldehyde; water-soluble oligomers of melamine or condensates of urea and formaldehyde; and vinyl monomers such as, for example, styrene, Methyl Methacrylate (MMA) and acrylonitrile. Finally, useful materials for the interfacial polymerization process include, but are not limited to, diacyl chlorides such as sebacoyl chloride, adipoyl chloride, and diamines or polyamines or alcohols and isocyanates. Useful emulsion polymerized materials may include, but are not limited to, styrene, vinyl acetate, acrylic acid, butyl acrylate, t-butyl acrylate, methyl methacrylate, and butyl methacrylate.

The prepared capsules can be dispersed into a curable vehicle to give inks that can be printed or coated on large and arbitrarily shaped or curved surfaces using conventional printing and coating techniques.

In the context of the present invention, the person skilled in the art will select the encapsulation process and the wall material based on the desired properties of the capsule. These properties include the distribution of the capsular radii; electrical, mechanical, diffusive and optical properties of the capsule wall; and chemical compatibility with the internal phase of the capsule.

The capsule wall typically has a high electrical resistivity. While it is possible to use walls with relatively low resistivity, this may limit performance when relatively higher addressing voltages are required. The capsule wall should also be mechanically strong (but mechanical strength is not critical if the finished capsule powder is to be dispersed in a curable polymeric binder for coating). The capsule wall should not generally be porous. However, if it is desired to use an encapsulation process that produces porous capsules, these may be overcoated in a post-processing step (i.e., a second encapsulation). Furthermore, if the capsules are to be dispersed in a curable adhesive, the adhesive will serve to close the pores. The capsule wall should be optically transparent. However, the wall material may be selected to match the refractive index of the internal phase of the capsule (i.e., the suspending fluid) or the binder in which the capsule is to be dispersed. For some applications (e.g., insertion between two stationary electrodes), a monodisperse capsule radius is desirable.

The encapsulation technique suitable for the present invention involves the polymerization between urea and formaldehyde in the presence of a negatively charged, carboxy-substituted, linear hydrocarbon polyelectrolyte material in the aqueous phase of an oil/water emulsion. The resulting wall is a urea/formaldehyde copolymer that discretely encapsulates the internal phase. The capsules are transparent, mechanically strong, and have good resistivity properties.

The related art for in situ polymerization utilizes an oil/water emulsion formed by dispersing an electrophoretic fluid (i.e., a dielectric liquid containing a suspension of pigment particles) in an aqueous environment. The monomers polymerize to form a polymer with a higher affinity for the internal phase than for the aqueous phase, thereby agglomerating around the emulsified oil droplets. In one in situ polymerization process, urea and formaldehyde are condensed in the presence of poly (acrylic acid) (see, e.g., U.S. Pat. No. 4,001,140). In other methods described in U.S. patent No. 4,273,672, any of a variety of cross-linking agents carried in an aqueous solution are deposited around microscopic oil droplets. Such cross-linking agents include aldehydes, especially formaldehyde, glyoxal or glutaraldehyde; alum; a zirconium salt; and a polyisocyanate.

The coacervation process also utilizes an oil/water emulsion. The microcapsules are produced by controlling the temperature, pH and/or relative concentration such that one or more colloids are agglomerated (i.e., aggregated) out of the aqueous phase and deposited as a shell around the oil droplets. Materials suitable for coacervation include gelatin and gum arabic. See, for example, U.S. patent No. 2,800,457.

The interfacial polymerization process relies on the presence of oil-soluble monomers in the electrophoretic composition, which again is present as an emulsion in the aqueous phase. The monomer in the minute hydrophobic droplets reacts with the monomer introduced into the aqueous phase, polymerizes at the interface between the droplets and the surrounding aqueous medium and forms a shell around the droplets. Although the resulting wall is relatively thin and may be permeable, this approach does not require the high temperature characteristics of some other approaches and thus provides greater flexibility in the choice of dielectric liquid.

Additional materials may be added to the encapsulation medium to improve the construction of the electrophoretic display. For example, coating aids can be used to improve the uniformity and quality of the coated or printed electrophoretic ink material. Wetting agents may be added to adjust the interfacial tension at the coating/substrate interface as well as to adjust the liquid/air surface tension. Wetting agents include, but are not limited to, anionic and cationic surfactants and non-ionic species such as polysiloxane or fluoropolymer based materials. Dispersants may be used to modify the interfacial tension between the capsules and the binder, providing control over flocculation and particle settling.

Many of the aforementioned patents and applications recognize that the walls surrounding the discrete microcapsules in an encapsulated electrophoretic medium can be replaced by a continuous phase, resulting in a so-called polymer dispersed electrophoretic display, wherein the electrophoretic medium comprises a plurality of discrete droplets of an electrophoretic fluid and a continuous phase of a polymeric material, and that the discrete droplets of an electrophoretic fluid within such a polymer dispersed electrophoretic display can be considered as capsules or microcapsules, even if no discrete capsule film is associated with each individual droplet; see, for example, U.S. patent No. 6,866,760. Thus, for the purposes of this application, such polymer-dispersed electrophoretic media are considered to be a sub-species that encapsulates the electrophoretic media.

A related type of electrophoretic display is the so-called microcell electrophoretic display. In microcell electrophoretic displays, the charged particles and fluid are not encapsulated within microcapsules, but are retained within a plurality of cavities formed within a carrier medium, typically a polymer film. See, for example, U.S. patent nos. 6,672,921 and 6,788,449, both assigned to Sipix Imaging, inc. Once the microcell is filled with the electrophoretic medium, the microcell is sealed, an electrode (or electrode array) is attached to the microcell, and the filled microcell is driven with an electric field to create a display.

For example, as described in U.S. patent No. 6,930,818, a conductive substrate may be stamped using a positive stamp to form a transparent conductor film thereon. A layer of a thermoplastic or thermoset precursor is then applied over the conductor film. The thermoplastic or thermoset precursor layer is embossed by a male die in the form of a roll, plate or belt at a temperature above the glass transition temperature of the thermoplastic or thermoset precursor layer. Once formed, the mold is released during or after the hardening of the precursor layer to reveal the array of microcells. Hardening of the precursor layer may be achieved by cooling, by radiation, heat or moisture induced crosslinking. If curing of the thermoset precursor is achieved by UV radiation, the UV may be radiated onto the transparent conductor film from the bottom or top of the mesh, as shown in both figures. Alternatively, a UV lamp may be placed in the mold. In this case, the mold must be transparent to allow UV light to be radiated through the pre-patterned male mold onto the thermosetting precursor layer.

The thermoplastic or thermoset precursors used to prepare the microcells can be multifunctional acrylates or methacrylates, vinyl ethers, epoxides and oligomers, polymers, and the like thereof. Crosslinkable oligomers imparting flexibility, such as urethane acrylates or polyester acrylates, are also often added to improve the bending resistance of the embossed microcells. The composition may contain polymers, oligomers, monomers and additives or only oligomers, monomers and additives.

In general, the microcells may have any shape, and their size and shape may vary. In one system, the microcells may be of substantially uniform size and shape. However, in order to maximize the optical effect, microcells having mixed different shapes and sizes may be prepared. For example, the red-filled dispersion of microcells may have a different shape or size than either the green microcells or the blue microcells. Furthermore, a pixel may be composed of a different number of microcells of different colors. For example, a pixel may be composed of many small green microcells, many large red microcells, and many small blue microcells. The three colors do not have to have the same shape and number.

The openings of the microcells may be circular, square, rectangular, hexagonal, or any other shape. The separation areas between the openings are preferably kept small in order to achieve high color saturation and contrast while maintaining the desired mechanical properties. Thus, a honeycomb shaped opening is preferred over, for example, a circular opening.

For a reflective electrophoretic display, the size of each individual microcell may be about 10²To about 5X 10⁵μm²Preferably about 10³To about 5X 10⁴μm²Within the range of (1). The depth of the microcells is in the range of about 3 to about 100 microns, preferably about 10 to about 50 microns. The ratio of opening to wall is in the range of about 0.05 to about 100, preferably about 0.4 to about 20. The distance of the openings is typically in the range of about 15 to about 450 microns, preferably about 25 to about 300 microns, from edge to edge of the opening.

As mentioned above, electrophoretic media require the presence of a fluid. In most prior art electrophoretic media, the fluid is a liquid, but the electrophoretic media can be prepared using gaseous fluids; see, for example, Kitamura, T.et al, electronic Toner movement for electronic Paper-like displays, IDW Japan,2001, Paper HCS1-1, and Yamaguchi, Y.et al, Toner displays using triboelectrically charged insulating particles (Toner display charged), IDW Japan,2001, Paper AMD 4-4). See also U.S. patent nos. 7,321,459 and 7,236,291.

Because the encapsulated electrophoretic medium is easily applied to a flexible substrate, electrophoretic displays can be assembled using various lamination processes. The aforementioned U.S. patent No. 6,982,178 describes a method of assembling an electrophoretic display, including encapsulated electrophoretic displays. Basically, this patent describes a so-called Front Panel Laminate (FPL) comprising, in order, a light-transmissive electrically conductive layer; a solid electro-optic medium layer in electrical contact with the conductive layer; a bonding layer; and a release sheet. Typically, the light transmissive conductive layer will be carried on a light transmissive substrate, which is preferably flexible in the sense that the substrate can be manually wound onto a 10 inch (254mm) diameter drum (for example) without permanent deformation. The term light transmission is used in this patent and herein to mean a layer specified to transmit sufficient light to enable an observer looking through the layer to observe changes in the display state of the electro-optic medium that would normally be observed through the conductive layer and the adjacent substrate (if present); the term light transmission is of course to be understood to refer to the transmission of the relevant non-visible wavelengths in the case where the electro-optic medium shows a change in reflectivity at non-visible wavelengths. The substrate will typically be a polymeric film and will generally have a thickness in the range of about 1 to about 25 mils (25 to 634 μm), preferably about 2 to about 10 mils (51 to 254 μm). The conductive layer is conveniently a thin metal or metal oxide layer, for example of aluminium or Indium Tin Oxide (ITO), or may be a conductive polymer. Poly (ethylene terephthalate) (PET) films coated with aluminum or ITO are commercially available, for example aluminized Mylar (Mylar is a registered trademark) from e.i.du Pont DE Nemours & Company of Wilmington DE, and such commercial materials can be used in front panel laminates with good results.

Assembly of an electro-optic display using such a front panel laminate may be achieved by: the release sheet is removed from the front panel laminate and the adhesive layer is contacted with the backplane under conditions effective to adhere the adhesive layer to the backplane, thereby securing the adhesive layer, the electro-optic medium layer, and the conductive layer to the backplane. The method is well suited for mass production, as the front panel laminate can be mass produced, typically using roll-to-roll coating techniques, and then cut into sheets of any size required for a particular back panel.

U.S. patent No. 7,561,324 describes a so-called double peel sheet, which is essentially a simplified version of the front panel laminate of the aforementioned U.S. patent No. 6,982,178. One form of dual release sheet comprises a layer of solid electro-optic medium sandwiched between two adhesive layers, one or both of which is covered by a release sheet. Another form of dual release sheet comprises a layer of solid electro-optic medium sandwiched between two release sheets. Both forms of the double release film are intended for use in a method generally similar to the method of assembling an electro-optic display from a front panel laminate already described, but involving two separate laminations; typically, in a first lamination, a double release sheet is laminated to the front electrode to form a front sub-assembly, and then in a second lamination, the front sub-assembly is laminated to the backplane to form the final display, although the order of the two laminations can be reversed if desired.

U.S. patent No. 7,839,564 describes a so-called inverted front panel laminate that is a variation of the front panel laminate described in the aforementioned U.S. patent No. 6,982,178. The inverted front panel laminate comprises, in order, at least one of a light-transmissive protective layer and a light-transmissive electrically-conductive layer; a bonding layer; a solid electro-optic medium layer; and a release sheet. The inverted front plane laminate is used to form an electro-optic display having a laminate bonding layer between the electro-optic layer and a front electrode or front substrate; a second generally thin adhesive layer may or may not be present between the electro-optic layer and the backplane. Such electro-optic displays may combine good resolution with good low temperature performance.

The foregoing charge control agents according to various embodiments of the present invention may also be used to form electrophotographic toners. The charge control agent may be mixed or dispersed in a polymeric binder (e.g., co-extrusion) and then milled to form an electrophotographic toner. Polymers useful in forming the binder include, but are not limited to, polycarbonates, resin-modified maleic alkyd polymers, polyamides, phenol-formaldehyde polymers and their various derivatives, polyester condensates, modified alkyd polymers and aromatic polymers containing alternating methylene and aromatic units, polyesters (e.g., polymeric esters of acrylic and methacrylic acids, such as poly (alkyl acrylates)), and various styrene-containing polymers.

Examples

Examples are now given by way of illustration only to show details of preferred electrophoretic media of the present invention.

Example 1

Preparation of charge control agents-a mixture of hydrophobic monomers is combined separately with each of the monomers with auxiliary functionality. Each monomer providing the head group and ancillary functionality identified in table 1 below was mixed with a monomer comprising a hydrophobic moiety. Each mixture was heated to 210 ℃ under nitrogen and water was removed azeotropically using toluene. At the completion of the reaction, the reaction mixture was cooled and dimethyl sulfate (ll) was added, as determined by acid value titration<1 equivalent of amine) and allowing the methylation reaction to proceed at ambient conditions for a period of at least 12 hours. Upon completion of the reaction, excess toluene is removed by vacuum distillation and the product is mixed with the designed solvent (e.g., Isopar E) to the desired solids content. The molecular structure of the prepared CCA molecules is provided below.

TABLE 1

CCA	Monomers providing head group and ancillary functionality	Mw
			1124-89	3- (dimethylamino) -1-propanamine	4193*
106	3- (dimethylamino) -1-propanamine	6379*
			111	3- (dimethylamino) -1-propanamine	9038*
113	3-dimethylamino-1-propanol	3968
			116	1, 4-bis (3-aminopropyl) piperazine	10219*
117	3-dimethylamino-1-propanol	9558*
			118	1, 4-bis (3-aminopropyl) piperazine	10219*
119	1, 4-bis (3-aminopropyl) piperazine	2282
			120	Bis (3-aminopropyl) amine	4034*
122	3- (dimethylamino) -1-propanamine	～1100

-Mw of the tertiary amine precursor before reaction with dimethyl sulfate. The values of molecular weight reported in table 1 represent weight average molecular weight.

Zeta potential measurements of dispersions containing each of pigment particles (black, cyan, white and yellow) and CCA were performed on samples dispersed in Isopar E using a colloid kinetic sonic particle sizer (Colloidal Dynamics AcoustoSizer) II and a ZetaProbe. Based on the results provided in table 2 below, the type of ancillary functionality present in the charge control agent affects the zeta potential of the pigment particles. For each sample, the acyclic secondary amide functional group provided a more positive zeta charge than the ester functional group, which provided a more positive zeta charge than the imide group as the ancillary functionality.

TABLE 2

The molecular structure of CCA 1124-89, 106 and 111 is represented by formula XVIII. The molecular structures of CCAs 113 and 117 are represented by formula XIX. The molecular structure of CCA 116 is represented by formula XX. The molecular structure of CCA 118 is represented by formula XXI. The molecular structure of CCA 119 is represented by formula XXII. The molecular formula of CCA 120 is represented by formula XXIII. The molecular formula of CCA 122 is represented by formula XXIV.

Wherein P (RA) is poly (ricinoleic acid) formula XX,

wherein P (RA) is poly (ricinoleic acid) formula XXI,

wherein P (IB) is poly (isobutylene) of formula XXII,

example 2

Zeta potential measurements were again carried out using three different dispersions containing yellow pigment particles (YP190) dispersed in Isopar E and one or two CCAs from example 1. In the first dispersion sample, CCA (CCA 113) with ester groups as an auxiliary functionality was gradually added to the pigment dispersion and the zeta potential was measured after each addition. In a second sample, CCA with an acyclic secondary amide group (CCA 106) was gradually added to the pigment dispersion and the zeta potential was measured after each addition. In the final sample, a 50:50 blend of CCA 113 and CCA 106 was gradually added and the zeta potential was measured after each addition. The zeta potential of the dispersion was measured again using a colloid kinetic sonic particle sizer II and a ZetaProbe.

As shown in fig. 1, CCA containing an acyclic secondary amide group charges the yellow pigment to +29mV, while CCA containing an ester functionality charges the yellow pigment to-32 mV. The use of a 50:50 blend of the two CCAs resulted in a slightly positive average zeta potential, indicating that greater control over the charge imparted to the particles can be provided by simple blending.

Example 3

Three dispersion samples containing four types of pigment particles (WH93 white, CP207 cyan, YP190 yellow, MP170 magenta) and charge control agent(s) were prepared. The first dispersion contains a commercially available CCA containing a non-cyclic secondary amide group in purified form. The second dispersion contained one of the CCAs containing an acyclic secondary amide group from example 1 (CCA 106). The final dispersion contains a blend of CCA 106 with CCA from example 1 containing an ester group as an ancillary functionality (CCA 117).

The prepared dispersion is encapsulated and used in the electrophoretic medium layer of a corresponding electrophoretic display. Each display is electrically driven to produce various optical states, and reflectance spectra for the various optical states are acquired using a spectrophotometer. CIE L, a, and b values of reflected light from each electrophoretic display were measured. For each spectral sample, the minimum distance in space L a b of display color from each of the eight standard SNAP (newsprint ad production specifications) color primaries was calculated in units of Δ E. The panchromatic fields of all measurement points are also extracted. The primary colors are red, green, blue, yellow, cyan, magenta, white, and black (R, G, B, Y, C, M, W and K). The smaller the distance, the closer the performance of the electrophoretic display is to the SNAP target, indicating better color saturation of the optical states of the display. The results are summarized in fig. 2, 3 and 4. The solid lines in the figure correspond to the color gamut of the electrophoretic display being tested, while the dashed lines correspond to the SNAP standard color gamut. As is apparent from the color gamut chart, the use of a charge control agent blend having (a) a charge control agent comprising an acyclic secondary amide group and a quaternary ammonium group in its molecule and (b) a charge control agent comprising an ester group and a quaternary ammonium group in its molecule provides a wider color gamut for a system containing only a charge control agent having an acyclic secondary amide group and a quaternary ammonium group in its molecule. In particular, color improvement in the red-yellow-green space is achieved while maintaining comparable performance in other color regions.

While preferred embodiments of the present invention have been shown and described herein, it will be understood that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will occur to those skilled in the art in the foregoing description of specific embodiments of the invention without departing from the scope of the invention. Accordingly, the entire foregoing description is to be considered as illustrative and not restrictive.

All of the foregoing patents and patent applications are incorporated herein by reference in their entirety.

30页详细技术资料下载

Charge control agent and particle dispersion containing the same

相关技术

网友询问留言