AB Diblock Copolymers as Charge Directors for Negative Electrostatic Liquid Developer

This invention relates to electrostatic liquid developers. More particularly this invention relates to negative-working electrostatic liquid developers containing AB diblock copolymers as charge directors.

It is known that a latent electrostatic image can be developed with toner particles dispersed in a carrier liquid, generally an insulating nonpolar liquid. Such dispersed materials are known as liquid toners or liquid developers. A latent electrostatic image may be produced by providing a photoconductive layer with a uniform electrostatic charge and subsequently discharging the electrostatic charge by exposing it to a modulated beam of radiant energy. Other methods are known for forming latent electrostatic images. For example, one method is providing a carrier with a dielectric surface and transferring a preformed electrostatic charge to the surface. Useful liquid toners comprise a thermoplastic resin and dispersant nonpolar liquid. Generally a suitable colorant is present such as a dye or pigment. The colored toner particles are dispersed in the nonpolar liquid which generally has a high-volume resistivity in excess of 10.sup.9 ohm centimeters, a low dielectric constant below 3.0, and a high vapor pressure. The toner particles are less than 10 .mu.m average by area size. After the latent electrostatic image has been formed, the image is developed by the colored toner particles dispersed in said dispersant nonpolar liquid and the image may subsequently be transferred to a carrier sheet.

Since the formation of proper images depends on the differences of the charge between the liquid developer and the latent electrostatic image to be developed, it has been found desirable to add a charge director compound and preferably adjuvants, e.g., polyhydroxy compounds, aminoalcohols, polybutylene succinimide, metallic soaps, an aromatic hydrocarbon, etc. to the liquid toner comprising the thermoplastic resin, dispersant nonpolar liquid and preferably a colorant. Such liquid developers provide images of good resolution, but it has been found that charging and image quality are particularly pigment dependent. Some formulations, suffer from poor image quality manifested by low resolution, poor solid area coverage, and/or image squash. Commercially available charge directors for toners often are by-products of the oil industry or decomposition residues of natural substances. These compounds are impure and the product composition is unreliable. In order to overcome such problems much research effort has been expended to develop new type charge directors and/or charging adjuvant for electrostatic liquid toners.

It has been found that the above disadvantages can be overcome and improved developers prepared containing a dispersant nonpolar liquid, a thermoplastic resin, a charge director compound of the invention, and preferably a colorant and an adjuvant. The improved electrostatic liquid developer charged with the charge director compound of the invention when used to develop an electrostatic image results in image quality, squash, and solid area coverage comparable to other known charge directors with the additional advantage that for a given liquid developer the charge director structure can be controlled to optimize liquid developer performance.

In accordance with this invention there is provided an improved negative-working electrostatic liquid developer consisting essentially of

(A) a nonpolar liquid having a Kauri-butanol value of less than 30, present in a major amount,

(B) thermoplastic resin particles having an average by area particle size of less than 10 .mu.m, and

(C) an AB diblock copolymer charge director substantially soluble in component (A), wherein the B block is a polymer substantially soluble in component (A) having a number average molecular weight range of 2,000 to 50,000, and the A block is quaternized trialkyl amino polymer having a number average molecular weight range of 200 to 10,000, the number average degree of polymerization (DP) ratio of the B block to the A block being in the range of 10 to 2 to 100 to 20.

In accordance with an embodiment of this invention there is provided a process for preparing a negative-working electrostatic liquid developer for electrostatic imaging comprising

(A) dispersing at an elevated temperature in a vessel a thermoplastic resin, and a dispersant nonpolar liquid having a Kauri-butanol value of less than 30, while maintaining the temperature in the vessel at a temperature sufficient to plasticize and liquify the resin and below that at which the dispersant nonpolar liquid degrades and the resin decomposes,

(B) cooling the dispersion, either

(1) without stirring to form a gel or solid mass, followed by shredding the gel or solid mass and grinding by means of particulate media;

(2) with stirring to form a viscous mixture and grinding by means of particulate media; or

(3) while grinding by means of particulate media to prevent the formation of a gel or solid mass;

(C) separating the dispersion of toner particles having an average by area particle size of less than 10 .mu.m from the particulate media, and

(D) adding to the dispersion during or subsequent to Step (A) an AB diblock copolymer charge director substantially soluble in component (A), wherein the B block is a polymer substantially soluble in component (A) having a number average molecular weight range of 2,000 to 50,000, and the A block is a quaternized trialkyl amino polymer having a number average molecular weight range of 200 to 10,000, the number average degree of polymerization (DP) ratio of the B block to the A block being in the range of 10 to 2 to 100 to 20.

Throughout the specification the below-listed terms have the following meanings:

In the claims appended hereto "consisting essentially of" means the composition of the electrostatic liquid developer does not exclude unspecified components which do not prevent the advantages of the developer from being realized. For example, in addition to the primary components, there can be present additional components, such as a colorant, fine particle size oxides, adjuvant, e.g., polyhydroxy compound, aminoalcohol, polybutylene succinimide, aromatic hydrocarbon, metallic soap, etc.

Aminoalcohol means that there is both an amino functionality and hydroxyl functionality in one compound.

Conductivity is the conductivity of the developer measured in picomhos (pmho)/cm at 5 hertz and 5 volts.

Number average degree of polymerization (DP) means the average number of monomeric units per polymer chain. It is related to the number average molecular weight (M.sub.n) by the formula M.sub.n =M.sub.o .times.DP, where M.sub.o is the molecular weight of the monomer.

The dispersant nonpolar liquids (A) are, preferably, branched-chain aliphatic hydrocarbons and more particularly, Isopar.RTM.-G, Isopar.RTM.-H, Isopar.RTM.-K, Isopar.RTM.-L, Isopar.RTM.-M and Isopar.RTM.-V. These hydrocarbon liquids are narrow cuts of isoparaffinic hydrocarbon fractions with extremely high levels of purity. For example, the boiling range of Isopar.RTM.-G is between 157.degree. C. and 176.degree. C., Isopar.RTM.-H between 176.degree. C. and 191.degree. C., Isopar.RTM.-K between 177.degree. C. and 197.degree. C., Isopar.RTM.-L between 188.degree. C. and 206.degree. C. and Isopar.RTM.-M between 207.degree. C. and 254.degree. C. and Isopar.RTM.-V between 254.4.degree. C. and 329.4.degree. C. Isopar.RTM.-L has a mid-boiling point of approximately 194.degree. C. Isopar.RTM.-M has a flash point of 80.degree. C. and an auto-ignition temperature of 338.degree. C. Stringent manufacturing specifications, such as sulphur, acids, carboxyl, and chlorides are limited to a few parts per million. They are substantially odorless, possessing only a very mild paraffinic odor. They have excellent odor stability and are all manufactured by the Exxon Corporation. High-purity normal paraffinic liquids, Norpar.RTM.12, Norpar.RTM.13 and Norpar.RTM.15, Exxon Corporation, may be used. These hydrocarbon liquids have the following flash points and auto-ignition temperatures:

All of the dispersant nonpolar liquids have an electrical volume resistivity in excess of 10.sup.9 ohm centimeters and a dielectric constant below 3.0. The vapor pressures at 25.degree. C. are less than 10 Torr. Isopar.RTM.-G has a flash point, determined by the tag closed cup method, of 40.degree. C., Isopar.RTM.-H has a flash point of 53.degree. C. determined by ASTM D 56. Isopar.RTM.-L and Isopar.RTM.-M have flash points of 61.degree. C., and 80.degree. C., respectively, determined by the same method. While these are the preferred dispersant nonpolar liquids, the essential characteristics of all suitable dispersant nonpolar liquids are the electrical volume resistivity and the dielectric constant. In addition, a feature of the dispersant nonpolar liquids is a low Kauri-butanol value less than 30, preferably in the vicinity of 27 or 28, determined by ASTM D 1133. The ratio of thermoplastic resin to dispersant nonpolar liquid is such that the combination of ingredients becomes fluid at the working temperature. The nonpolar liquid is present in an amount of 85 to 99.9% by weight, preferably 97 to 99.5% by weight, based on the total weight of liquid developer. The total weight of solids in the liquid developer is 0.1 to 15%, preferably 0.5 to 3.0% by weight. The total weight of solids in the liquid developer is solely based on the resin, including components dispersed therein, and any pigment component present.

Useful thermoplastic resins or polymers include: ethylene vinyl acetate (EVA) copolymers (Elvax.RTM. resins, E. I. du Pont de Nemours and Company, Wilmington, Del.), copolymers of ethylene and an .alpha.,.beta.-ethylenically unsaturated acid selected from the class consisting of acrylic acid and methacrylic acid, copolymers of ethylene (80 to 99.9%)/acrylic or methacrylic acid (20 to 0%)/alkyl (C.sub.1 to C.sub.5) ester of methacrylic or acrylic acid (0 to 20%), polyethylene, polystyrene, isotactic polypropylene (crystalline), ethylene ethyl acrylate series sold under the trademark Bakelite.RTM. DPD 6169, DPDA 6182 Natural and DTDA 9169 Natural by Union Carbide Corp., Stamford, Conn.; ethylene vinyl acetate resins, e.g., DQDA 6479 Natural and DQDA 6832 Natural 7 also sold by Union Carbide Corp.; Surlyn.RTM. ionomer resin by E. I. du Pont de Nemours and Company, Wilmington, Del., etc., or blends thereof, polyesters, polyvinyl toluene, polyamides, styrene/butadiene copolymers, epoxy resins acrylic resins, such as a copolymer of acrylic or methacrylic acid (optional but preferred) and at least one alkyl ester of acrylic or methacrylic acid wherein alkyl is 1 to 20 carbon atoms, e.g., methyl methacrylate(50 to 90%)/methacrylic acid(0 to 20%)/ethylhexyl acrylate(10 to 50%); and other acrylic resins including Elvacite.RTM. Acrylic Resins, E. I. du Pont de Nemours and Company, Wilmington, Del., or blends of the resins. Preferred copolymers are the copolymer of ethylene and an .alpha.,.beta.-ethylenically unsaturated acid of either acrylic acid or methacrylic acid. The synthesis of copolymers of this type are described in Rees U.S. Pat. No. 3,264,272, the disclosure of which is incorporated herein by reference. For the purposes of preparing the preferred copolymers, the reaction of the acid containing copolymer with the ionizable metal compound, as described in the Rees patent, is omitted. The ethylene constituent is present in about 80 to 99.9% by weight of the copolymer and the acid component in about 20 to 0.1% by weight of the copolymer. The acid numbers of the copolymers range from 1 to 120, preferably 54 to 90. Acid No. is milligrams potassium hydroxide required to neutralize 1 gram of polymer. The melt index (g/10 min) of 10 to 500 is determined by ASTM D 1238 Procedure A. Particularly preferred copolymers of this type have an acid number of 54 and a melt index of 100 and 500 determined at 190.degree. C., respectively.

In addition, the resins have the following preferred characteristics:

1. Be able to disperse the colorant, e.g., pigment, metallic soap adjuvant, etc.

2. Be substantially insoluble in the dispersant liquid at temperatures below 40.degree. C., so that the resin will not dissolve or solvate in storage,

3. Be able to solvate at temperatures above 50.degree. C.,

4. Be able to be ground to form particles between 0.1 .mu.m and 5 .mu.m, in diameter (preferred size), e.g., determined by Horiba CAPA-500 centrifugal particle analyzer; and between 1 .mu.m and 15 .mu.m in diameter, e.g., determined by Malvern 3600E, which uses laser diffraction light scattering of stirred samples to determine average particle sizes.

5. Be able to form a particle (average by area) of less than 10 .mu.m, e.g., determined by Horiba CAPA-500 centrifugal automatic particle analyzer, manufactured by Horiba Instruments, Inc., Irvine, Calif.: solvent viscosity of 1.24 cps, solvent density of 0.76 g/cc, sample density of 1.32 using a centrifugal rotation of 1,000 rpm, a particle size range of 0.01 to less than 10 .mu.m, and a particle size cut of 1.0 .mu.m, and about 30 .mu.m average particle size, e.g., determined by Malvern 3600E Particle Sizer as described below, and

6. Be able to fuse at temperatures in excess of 70.degree. C.

By solvation in 3. above, the resins forming the toner particles will become swollen, gelatinous or softened.

The dispersant liquid, e.g., nonpolar liquid, soluble AB diblock copolymer charge directors of the invention (Component (C)) which can be used as negative charge directors comprise a B block which is polymer that is substantially soluble in the dispersant nonpolar liquid and has a number average molecular weight in the range of about 2,000 to 50,000 and an A block which is a quaternized trialkyl amino polymer having a number average molecular weight in the range of about 200 to 10,000, the number average degree of polymerization ratio of the B block to the A block is in the range of 10 to 2 to 100 to 20, preferably 20 to 3 to 40 to 10. The AB polymers can be advantageously produced by stepwise polymerization process such as anionic or group transfer polymerization as described in Webster, U.S. Pat. No. 4,508,880, the disclosure of which is incorporated herein by reference. Polymers so produced have very precisely controlled molecular weights, block sizes and very narrow molecular weight distributions, e.g., weight average molecular weight divided by number average molecular weight. The AB diblock copolymer charge directors can also be formed by free radical polymerization wherein the initiation unit is comprised of two different moieties which initiate polymerization at two distinctly different temperatures. However, this method suffers from contamination of the block copolymers with homopolymer and coupled products.

The AB diblock copolymers can also be prepared by conventional anionic polymerization techniques, in which a first block of the copolymer is formed, and, upon completion of the first block, a second monomer stream is started to form a subsequent block of the polymer. The reaction temperatures using such techniques should be maintained at a low level, for example, 0 to -40.degree. C., so that side reactions are minimized and the desired blocks, of the specified molecular weights, are obtained.

More specifically the A block is an alkyl, aryl or alkylaryl amine-containing polymer wherein the alkyl, aryl or alkylaryl moiety which can be substituted or unsubstituted. Useful A blocks are polymers prepared from at least one monomer selected from the group consisting of (1) CH.sub.2 .dbd.CCH.sub.3 CO.sub.2 R, (2) CH.sub.2 .dbd.CHCO.sub.2 R wherein R in (1) and (2) is alkyl of 1 to 20 carbon atoms where the terminal end of R is of the general formula N(R.sup.1).sub.4.sup.+ X.sup.-, where N is nitrogen, R.sup.1 is alkyl of 1 to 200 carbon atoms, aryl of 6 to 30 carbon atoms, alkylaryl of 7 to 200 carbon atoms and X is halide, e.g., Cl, Br, I; conjugate base of an organic acid, e.g., p-toluene sulfonate, trifluoro sulfonate, hexafluorophosphate, tetrafluoroboroate, etc. and (3) 2-, 3-, or 4-vinyl pyridine wherein the ring carbon atoms not substituted by the vinyl group may be substituted with R.sup.1 and the pyridine nitrogen atom is substituted with R.sup.1 X wherein R.sup.1 and X are as defined above. Examples of monomers useful in preparing A blocks include: 2-(N,N-dimethylamino)ethyl methacrylate, 2-(N,N-diethylamino)ethyl methacrylate, 4-vinyl pyridine, 2-vinyl pyridine, 3-vinyl pyridine, (t-butylamino)ethyl methacrylate, etc. Useful B blocks are polymers prepared from at least one monomer selected from the group consisting of butadiene, isoprene and compounds of the general formulas CH.sub.2 .dbd.CCH.sub.3 CO.sub.2 R.sup.2 and CH.sub.2 .dbd.CHCO.sub.2 R.sup.2 wherein R.sup.2 is alkyl of 8-30 carbon atoms. Examples of monomers useful in preparing B block include: 2-ethyl hexyl methacrylate, lauryl methacrylate, stearyl methacrylate, butadiene, isoprene, ethyl hexyl acrylate, etc. Useful AB diblock copolymer charge directors include: the block copolymer poly-2-(N,N-dimethyl-paratoluyl ammonium) ethyl methacryl sulfonate, poly-2-(N,N-diethyl-para-toluyl ammonium) ethyl methacryl sulfonate, poly-2-(N,N-dimethyl benzyl ammonium) ethyl methacryl chloride, poly-2-(N,N-diethyl benzyl ammonium) ethyl methacryl chloride, etc. The charge director is present in 0.1 to 10,000 milligrams per gram of developer solids, preferably 1 to 1000 milligrams per gram of developer solids.

The optimum AB diblock copolymer charge director structure is dependent on the electrostatic liquid developer. To optimize the charge director structure the size of the A and B polymer blocks, as well as the ratio between A and B can be changed. The solubility of the counterion in the carrier liquid, e.g., nonpolar liquid, also affects performance.

As indicated above, additional components that can be present in the electrostatic liquid developer are colorants, such as pigments or dyes and combinations thereof, which are preferably present to render the latent image visible, though this need not be done in some applications. The colorant, e.g., a pigment, may be present in the amount of up to about 60 percent by weight based on the total weight of developer solids, preferably 0.01 to 30% by weight based on the total weight of developer solids. The amount of colorant may vary depending on the use of the developer. Examples of pigments include:

Other ingredients may be added to the electrostatic liquid developer, such as fine particle size oxides, e.g., silica, alumina, titania, etc.; preferably in the order of 0.5 .mu.m or less can be dispersed into the liquefied resin. These oxides can be used alone or in combination with the colorant. Metal particles can also be added.

Another additional component of the electrostatic liquid developer is an adjuvant which can be taken from the group of polyhydroxy compound which contains at least 2 hydroxy groups, aminoalcohol, polybutylene succinimide, metallic soap and aromatic hydrocarbon having a Kauri-butanol value of greater than 30. The adjuvants are generally used in an amount of 1 to 1000 mg/g, preferably 1 to 200 mg/g developer solids. Examples of the various above-described adjuvants include:

polyhydroxy compounds: ethylene glycol, 2,4,7,9-tetramethyl-5-decyn-4,7-diol, poly(propylene glycol), pentaethylene glycol, tripropylene glycol, triethylene glycol, glycerol, pentaerythritol, glycerol-tri-12 hydroxystearate, ethylene glycol monohydroxystearate, propylene glycerol monohydroxy-stearate, etc., as described in Mitchell U.S. Pat. No. 4,734,352.

aminoalcohol compounds: triisopropanolamine, triethanolamine, ethanolamine, 3-amino-1-propanol, o-aminophenol, 5-amino-1-pentanol, tetra(2-hydroxyethyl)-ethylenediamine, etc., as described in Larson U.S. Pat. No. 4,702,985.

polybutylene/succinimide: OLOA.RTM.-1200 sold by Chevron Corp., analysis information appears in Kosel U.S. Pat. No. 3,900,412, column 20, lines 5 to 13, incorporated herein by reference; Amoco 575 having a number average molecular weight of about 600 (vapor pressure osmometry) made by reacting maleic anhydride with polybutene to give an alkenylsuccinic anhydride which in turn is reacted with a polyamine. Amoco 575 is 40 to 45% surfactant, 36% aromatic hydrocarbon, and the remainder oil, etc. These adjuvants are described in El-Sayed and Taggi U.S. Pat. No. 4,702,984.

metallic soaps: aluminum tristearate; aluminum distearate; barium, calcium, lead, and zinc stearates; cobalt, manganese, lead, and zinc linoleates; aluminum, calcium, and cobalt octoates; calcium and cobalt oleates; zinc palmitate; calcium, cobalt, manganese, lead, and zinc naphthenates; calcium, cobalt, manganese, lead, and zinc resinates; etc. The metallic soap is dispersed in the thermoplastic resin as described in Trout, U.S. Pat. Nos. 4,707,429 and 4,740,444.

aromatic hydrocarbon: benzene, toluene, naphthalene, substituted benzene and naphthalene compounds, e.g., trimethylbenzene, xylene, dimethylethylbenzene, ethylmethylbenzene, propylbenzene, Aromatic 100 which is a mixture of C.sub.9 and C.sub.10 alkylsubstituted benzenes manufactured by Exxon Corp., etc., as described in Mitchell U.S. Pat. No. 4,631,244.

The disclosures of the above-listed United States patents describing the adjuvants are incorporated herein by reference.

The particles in the electrostatic liquid developer have an average by area particle size of less than 10 .mu.m, preferably the average by area particle size is less than 5 .mu.m as measured by the Horiba instrument described above. The resin particles of the developer may or may not be formed having a plurality of fibers integrally extending therefrom although the formation of fibers extending from the toner particles is preferred. The term "fibers" as used herein means pigmented toner particles formed with fibers, tendrils, tentacles, threadlets, fibrils, ligaments, hairs, bristles, or the like.

The electrostatic liquid developer can be prepared by a variety of processes. For example, into a suitable mixing or blending vessel, e.g., attritor, heated ball mill, heated vibratory mill such as a Sweco Mill manufactured by Sweco Co., Los Angeles, Calif., equipped with particulate media, for dispersing and grinding, Ross double planetary mixer manufactured by Charles Ross and Son, Hauppauge, N.Y., etc., or a two roll heated mill (no particulate media necessary) are placed at least one of thermoplastic resin, and dispersant liquid described above. Generally the resin, dispersant nonpolar liquid and optional colorant are placed in the vessel prior to starting the dispersing step. Optionally the colorant can be added after homogenizing the resin and the dispersant nonpolar liquid. Polar liquid can also be present in the vessel, e.g., up to 100% based on the weight of total developer liquid. The dispersing step is generally accomplished at elevated temperature, i.e., the temperature of ingredients in the vessel being sufficient to plasticize and liquefy the resin but being below that at which the dispersant nonpolar liquid or polar liquid, if present, degrades and the resin and/or colorant, if present, decomposes. A preferred temperature range is 80 to 120.degree. C. Other temperatures outside this range may be suitable, however, depending on the particular ingredients used. The presence of the irregularly moving particulate media in the vessel is preferred to prepare the dispersion of toner particles. Other stirring means can be used as well, however, to prepare dispersed toner particles of proper size, configuration and morphology. Useful particulate media are particulate materials, e.g., spherical, cylindrical, etc. taken from the class consisting of stainless steel, carbon steel, alumina, ceramic, zirconia, silica, and sillimanite. Carbon steel particulate media is particularly useful when colorants other than black are used. A typical diameter range for the particulate media is in the range of 0.04 to 0.5 inch (1.0 to approx. 13 mm). After dispersing the ingredients in the vessel, with or without a polar liquid present until the desired dispersion is achieved, typically 1 hour with the mixture being fluid, the dispersion is cooled, e.g., in the range of 0.degree. C. to 50.degree. C. Cooling may be accomplished, for example, in the same vessel, such as the attritor, while simultaneously grinding with particulate media to prevent the formation of a gel or solid mass; without stirring to form a gel or solid mass, followed by shredding the gel or solid mass and grinding, e.g., by means of particulate media with or without the presence of additional liquid; or with stirring to form a viscous mixture and grinding by means of particulate media with or without the presence of additional liquid. Additional liquid may be added at any step during the preparation of the liquid electrostatic toners to facilitate grinding or to dilute the toner to the appropriate % solids needed for toning. Additional liquid means dispersant nonpolar liquid, polar liquid or combinations thereof. Cooling is accomplished by means known to those skilled in the art and is not limited to cooling by circulating cold water or a cooling material through an external cooling jacket adjacent the dispersing apparatus or permitting the dispersion to cool to ambient temperature. The resin precipitates out of the dispersant during the cooling. Toner particles of average particle size (by area) of less than 10 .mu.m, as determined by a Horiba CAPA-500 centrifugal particle analyzer described above or other comparable apparatus, are formed by grinding for a relatively short period of time. Another instrument for measuring average particles sizes is a Malvern 3600E Particle Sizer manufactured by Malvern, Southborough, Mass. which uses laser diffraction light scattering of stirred samples to determine average particle sizes. Since these two instrument use different techniques to measure average particle size the readings differ. The following correlation of the average size of toner particles in micrometers (.mu.m) for the two instruments is:

This correlation is obtained by statistical analysis of average particle sizes for 67 liquid electrostatic developer samples (not of this invention) obtained on both instruments. The expected range of Horiba values was determined using a linear regression at a confidence level of 95%. In the claims appended to this specification the particle size values are as measured using the Horiba instrument.

After cooling and separating the dispersion of toner particles from the particulate media, if present, by means known to those skilled in the art, it is possible to reduce the concentration of the toner particles in the dispersion, impart an electrostatic charge of predetermined polarity to the toner particles, or a combination of these variations. The concentration of the toner particles in the dispersion is reduced by the addition of additional dispersant nonpolar liquid as described previously above. The dilution is normally conducted to reduce the concentration of toner particles to between 0.1 to 15 percent by weight, preferably 0.3 to 3.0, and more preferably 0.5 to 2 weight percent with respect to the dispersant nonpolar liquid. One or more AB diblock copolymer charge director compounds (C), of the type set out above, can be added to impart a negative charge to the liquid electrostatic developer. The addition may occur at any time during the process; preferably at the end of the process, e.g., after the particulate media, if used, are removed and the concentration of toner particles is accomplished. If a diluting dispersant nonpolar liquid is also added, the AB diblock copolymer charge director compound can be added prior to, concurrently with, or subsequent thereto. If an adjuvant compound of a type described above has not been previously added in the preparation of the developer, it can be added prior to or subsequent to the developer being charged.

Other process embodiments for preparing the electrostatic liquid developer include:

(A) dispersing a thermoplastic resin and optionally a colorant and/or adjuvant in the absence of a dispersant nonpolar liquid having a Kauri-butanol value of less than 30 to form a solid mass.

(B) shredding the solid mass,

(C) grinding the shredded solid mass by means of particulate media in the presence of a liquid taken from the group consisting of a polar liquid having a Kauri-butanol value of at least 30, a nonpolar liquid having a Kauri-butanol value of less than 30, and combinations thereof,

(D) separating the dispersion of toner particles having an average by area particle size of less than 10 .mu.m from the particulate media, and

(E) adding additional nonpolar liquid, polar liquid or combinations thereof to reduce the concentration of toner particles to between 0.1 to 15 percent by weight with respect to the liquid; and

(F) adding to the dispersion an AB diblock copolymer charge director compound of the invention; and

(A) dispersing a thermoplastic resin and optionally a colorant and/or adjuvant in the absence of a dispersant nonpolar liquid having a Kauri-butanol value of less than 30 to form a solid mass.

(B) shredding the solid mass,

(C) redispersing the shredded solid mass at an elevated temperature in a vessel in the presence of a dispersant nonpolar liquid having a Kauri-butanol value of less than 30, while maintaining the temperature in the vessel at a temperature sufficient to plasticize and liquify the resin and below that at which the dispersant nonpolar liquid degrades and the resin and/or colorant decomposes,

(D) cooling the dispersion, either

(1) without stirring to form a gel or solid mass, followed by shredding the gel or solid mass and grinding by means of particulate media with or without the presence of additional liquid;

(2) with stirring to form a viscous mixture and grinding by means of particulate media with or without the presence of additional liquid; or

(3) while grinding by means of particulate media to prevent the formation of a gel or solid mass with or without the presence of additional liquid;

(E) separating the dispersion of toner particles having an average by area particle size of less than 10 .mu.m from the particulate media, and

(F) adding additional nonpolar liquid, polar liquid or combinations thereof to reduce the concentration of toner particles to between 0.1 to 15 percent by weight with respect to the liquid; and

(G) adding to the dispersion an AB diblock copolymer charge director compound of the invention.

A preferred mode of the invention is described in Example 5.

The AB diblock copolymer charge directors of this invention are capable of charging electrostatic liquid developers negatively. The synthetic AB diblock copolymers are advantageous because their molecular weight, the amount of quaternized amine present, and the ratio of the quaternized amine block to the carrier liquid soluble block can be reproducibly controlled, which allows for superior batch to batch reproducibility of charge directors whose structures are selected for optimum developer performance. The AB diblock copolymers are prepared with high purity and very low toxicity. The electrostatic liquid developers demonstrate good image quality, resolution, solid area coverage, and toning of fine details, evenness of toning, reduced squash independent of the pigment present. The developers of this invention are useful in copying, e.g., making office copies of black and white as well as various colors; or color proofing, e.g., a reproduction of an image using the standard colors: yellow, cyan, magenta together with black as desired. In copying and proofing the liquid developer is applied to a latent electrostatic image. Other uses envisioned for the electrostatic liquid developers include: digital color proofing, lithographic printing plates, and resists.

The following controls and examples wherein the parts and percentages are by weight illustrate but do not limit the invention. In the examples the melt indices were determined by ASTM D 1238, Procedure A, the average particle sizes by area were determined by a Horiba CAPA-500 centrifugal particle analyzer or a Malvern Particle sizer as described above, the conductivity was measured in picomhos/cm (pmhos) at 5 hertz and low voltage, 5 volts, and the density was measured using a McBeth densitometer model RD918. The resolution is expressed in the examples in line pairs/mm (lp/mm). Weight average molecular weight can be determined by gel permeation chromatography (GPC). Number average molecular weight can be determined by known osmometry techniques.

The AB diblock copolymers of the invention to be used in the Examples are prepared as follows:

A reaction vessel was charged with 1700 g toluene, 1.0 g xylene, 43.8 g (0.25 mol)1-ethoxy-1-trimethylsiloxy-2-methylpropene ("initiator"), and 6.0 mL of 0.33 M tetrabutylammonium-3-chlorobenzoate in acetonitrile/THF ("catalyst"). Two feeds were begun simultaneously; 1485 g (7.5 mol) 2-ethylhexyl methacrylate (EHMA) were added over 30 minutes, and 6.0 ml catalyst in 4 g toluene were added over 90 minutes. Reaction of EHMA was followed by high pressure liquid chromatography. After all the EHMA had reacted (twenty minutes after the addition of the EHMA), 314.0 g (2.0 mol) of 2-(N,N-dimethylamino)ethyl methacrylate (DMAEM) were added over 10 minutes. Forty minutes after the addition of DMAEM, all the DMAEM monomer had reacted, and 40 ml of methanol were added to quench.

To quaternize the amine groups, 364 g of 97% p-methyl-toluene sulfonate (MeOTs) were added to the above solution. After stirring 30 minutes, the amount of amine left in the polymer stabilized to 5%, indicating the quaternization was complete, and had occurred to 95%.

The procedure of Preparation 1 was repeated with the following exceptions: 157 g (1.0 mol) of DMAEM were used, instead of 314 g. After polymerization and quenching, 182 g of 97% MeOTs were added to quaternize, instead of 364 g.

The procedure of Preparation 1 was repeated with the following exception: 1980 g (10 mol) of EHMA were used, instead of 1485 g.

The procedure of Preparation 1 was repeated with the following exceptions: 1980 g (10 mol) of EHMA were used, instead of 1485 g, 471 g (3.0 mol) DMAEM were used, instead of 314 g. After polymerization and quenching, 546 g of 97% MeOTs were added to quaternize, instead of 364 g.

A reaction vessel was charged with 140 grams of toluene and heated to reflux. Two feeds were begun simultaneously; a mixture of 82.5 grams of EHMA and 17.5 grams of DMAEM were added over 150 minutes, and 3.5 grams of 2,2'-azobis(2-methylbutyronitrile) in 10 grams of toluene were added over 180 minutes to initiate the reaction. After an additional 30 minutes, 16.7 grams of MeOTs were added to quaternize the random copolymer. The solution was refluxed for 2 hours to complete the quaternization reaction.

In a Union Process 30S Attritor, Union Process Company, Akron, Ohio, were placed the following ingredients:

The ingredients were heated in the range of 90.degree. C. to 110.degree. C. and milled at a rotor speed of 230 rpm with 0.1875 inch (4.76 mm) diameter stainless steel balls for 1 hour. The attritor was cooled to 42.degree. C. to 50.degree. C. while milling was continued. Milling was continued at a rotor speed of 330 rpm for 20 hours to obtain toner particles with an average size 6.1 .mu.m by area as measured on the Malvern Particle Sizer. The particulate media were removed and the toner was diluted to 0.5% solids with additional Isopar.RTM.-L. To 1.5 kg of this dispersion, 2.0 grams of a 10% solution of Basic Barium Petronate.RTM. oil-soluble petroleum sulfonate, Witco Chemical Corp. (BBP) were added (20.5 mg per gram toner solids). Image quality was fair, showing substantial squash, a resolution of 6.3 lp/mm, and a transfer efficiency of 97%.

In a Union Process 1S Attritor, Union Process Company, Akron, Ohio was placed the following ingredients:

The ingredients were heated to 100.degree. C. in a Union 1S attritor and milled with 0.1875 inch (4.76 mm) diameter stainless steel balls for two hours. The attritor was cooled to room temperature while the milling was continued. Milling was continued for 16 hours to obtain toner particles with an average size of 1.25 .mu.m by area as measured on the Horiba. The particulate media were removed and the dispersion of toner particles was then diluted to 0.5 % solids with additional Isopar.RTM.-L. To 1.5 kg of the dispersion was added 5 grams of a 5.5% solution of Basic Barium Petronate.RTM. described in Control 1 (BBP) in Isopar.RTM.-L (36.5 mg per gram toner solids). Image quality was good showing no squash, a resolution of 11 lp/mm, and a transfer efficiency of 98%. Solid areas, however, showed small, untoned pinholes.

The procedure of Control 2 was repeated with the following exceptions: 35 g of a terpolymer of methyl methacrylate (67.3%), methacrylic acid (3.1%), and ethylhexyl acrylate (29.6%), weight average molecular weight is 172,000, acid no. 13 were used, instead of the copolymer of ethylene (89%) and methacrylic acid (11%). Instead of Sterling.RTM. NS pigment, 7.0 g Lithol.RTM. Scarlet K (BASF, Holland, MI) were used. At the start of the cold grind, 10 g of Amoco 9040, an alkyl hydroxy benzyl polyamine sold as 40-45% surfactant, 36% aromatic hydrocarbon, and oil having a number average molecular weight range of about 1600 to 1800 (Amoco, Napierville, Ill.) were added. The cold grind was continued for 22 hours, until the average particle size was 0.26 .mu.m determined on a Horiba CAPA-500 centrifugal automatic particle analyzer. The dispersion was diluted to 0.5% solids and 2.8 grams of a 5.5% solution of Basic Barium Petronate.RTM. as described in Control 1 (BBP) were added (20.5 mg per gram of toner solids). The resultant toner charged positive, and no images were obtained.

The procedure of Control 1 was repeated with the following exceptions: the ingredients were heated to 100.degree. C., instead of in the range of 90.degree. C. to 110.degree. C. 16.2 lbs. of the copolymer were added, instead of 11.2 lbs. Instead of 100 lbs. of Isopar.RTM.-L, 57 lbs. were added. The pigment used was Sunbright Yellow 14 (Sun Chemical, Cincinnati, Ohio). 254 g of aluminum tristearate from Nuodex were also added. The cold grind lasted 14 hours, until the average particle size was 5.2 .mu.m as determined by a Malvern 3600E Particle Sizer. The dispersion was diluted to 0.5% solids with additional Isopar.RTM.-L and 2.8 grams of a 5.5% solution of Basic Barium Petronate.RTM. as described in Control 1 (BBP) were added per gram of toner solids. Image quality was fair showing substantial squash, a resolution of 6.3 lp/mm, and a transfer efficiency of 92%.

The procedure of Control 3 was repeated except that no pigment and no Amoco 9040 were added. After a cold grind of 47 hours, an average particle size of 1.82 .mu.m was obtained as determined by the instrument described in Control 3. The dispersion was diluted to 0.5% solids and 2.8 grams of a 5.5% solution of Basic Barium Petronate.RTM. as described in Control 1 (BBP) were added (20.5 mg per gram of toner solids). Images quality was fair showing a 5.6 lp/mm resolution, a 99% transfer efficiency, and substantial squash.

The procedure of Control 1 was repeated with the following exceptions: to 1.5 kg of this dispersion, 10 grams of a 10% solution of a random AB quaternized copolymer (DP 8/30) described in Preparation 5 above were added in place of Basic Barium Petronate.RTM. described in Control 1. Image quality was poor, with uneven toning of solid areas, including pinholes and streaking, and beading of fine features. Images had 9.0 lp/mm resolution, no squash, and a transfer efficiency of 94%.

The procedure of Control 3 was repeated with the following exception: to 1.5 kg of this dispersion, 10 grams of a 10% solution of the AB diblock copolymer made as described in Preparation 1 (DP 8/30) were added in place of Basic Barium Petronate.RTM. described in Control 1 as the charge director. Image quality was good, with a 8.0 lp/mm resolution, 94% transfer efficiency, and no squash.

The procedure of Control 4 was repeated with the following exception: to 1.5 kg of this dispersion, 10 grams of a 10% solution of the AB diblock copolymer made as described in Preparation 1 (DP 8/30) were added in place of Basic Barium Petronate.RTM. described in Control 1 as the charge director. Image quality was fair, showing slight squash, a resolution of 6.3 lp/mm, and a transfer efficiency of 93%.

The procedure of Control 5 which used an acrylic terpolymer was repeated with the following exception: To 1.5 kg of this dispersion, 10 grams of a 10% solution of the AB diblock copolymer made as described in Preparation 1 (DP 8/30) were added in place of Basic Barium Petronate.RTM. described in Control 1 as the charge director. Image quality was fair, with 5.6 lp/mm resolution, a 99% transfer efficiency, and substantial squash.

The procedure of Control 6 was repeated with the following exception: to 1.5 kg of this dispersion, 10 grams of a 10% solutions of the AB diblock copolymer made as described in Preparation 1 (DP 8/30) were added in place of Basic Barium Petronate.RTM. described in Control 1 as the charge director. Image quality was very good with a 10 lp/mm resolution, 94% transfer efficiency, and no squash.

The procedure of Control 2 was repeated except that the dispersion was charged with 5 grams of the AB diblock copolymer made as described in Preparation 1 (DP 8/30). Image quality was very good showing evenly toned solid areas, no squash, a resolution of 11 lp/mm and a transfer efficiency of 98%. Image quality is similar to the developer in Control 2 except that solid area coverage has been improved.

The procedure of Control 2 was repeated except that the dispersion was charged with 5 grams of the AB diblock copolymer made as described in Preparation 2 (DP 4/30). Image quality was good showing evenly toned solid areas, slight squash, a resolution of 10 lp/mm and a transfer efficiency of 93%.

The procedure of Control 2 was repeated except that the dispersion was charged with 5 grams of the AB diblock copolymer made as described in Preparation 3 (DP 8/40). Image quality was good in the solid areas, no squash, a resolution of 11 lp/mm and a transfer efficiency of 95%.

The procedure of Control 2 was repeated except that the dispersion was charged with 5 grams of the AB diblock copolymer made as described in Preparation 4 (DP 12/40). Image quality was fair showing small untoned holes in the solid areas, substantial squash, a resolution of 9 lp/mm and a transfer efficiency of 96%.

The results of the above Examples and Control are set out in Table 1 below.