Developer compositions and processes

Illustrated in U.S. Pat. No. 5,627,002, the disclosure of which is totally incorporated herein by reference, is a positively charged liquid developer comprised of a nonpolar liquid, thermoplastic resin particles, pigment, a charge director, and a charge control agent comprised of a cyclodextrin or a cyclodextrin derivative containing one or more organic basic amino groups. A number of the appropriate components of this patent, especially the cyclodextrins may be selected for the invention of the present application in embodiments thereof and wherein with the present invention the cyclodextrins, especially beta-cyclodextrin function as a charge, either positive, or negative, acceptance component, agent, or additive.

In U.S. Pat. Nos. 5,366,840; 5,346,795 and 5,223,368, the disclosures of which are totally incorporated herein by reference, there are illustrated developer compositions with aluminum complex components and which components may be selected as a charge acceptance additive for the developers of the present invention.

Disclosed in U.S. Pat. No. 5,826,147, the disclosure of which is totally incorporated herein by reference, is an electrostatic latent image development process and an apparatus thereof wherein there is selected an imaging member with an imaging surface containing a layer of marking material and wherein imagewise charging can be accomplished with a wide beam ion source such that free mobile ions are introduced in the vicinity of an electrostatic image associated with the imaging member.

The appropriate components and processes of the above copending applications and patents may be selected for the present invention in embodiments thereof.

BACKGROUND OF THE INVENTION

This invention is generally directed to liquid developer compositions and processes thereof and wherein there can be generated excellent developed images thereof in, for example, bipolar ion charging processes, and reverse charge imaging and printing development (RCP) processes, wherein a first charging device generates a positive or negative toner polarity, and a second charging device generates an opposite toner charge of a negative or positive polarity, reference U.S. Pat. No. 5,826,147, the disclosure of which is totally incorporated herein by reference, and wherein the developer contains no charge director, or wherein the developer contains substantially no charge director. Preferably the liquid developer of the present invention is clear in color and is comprised of a resin, a hydrocarbon carrier, and as a charge acceptor a polyethylene oxide-polypropylene oxide, Alohas, an aluminum-di-tertiary butyl salicylate, as illustrated in U.S. Pat. No. 5,563,015, the disclosure of which is totally incorporated herein by reference, including a mixture of Alohas and EMPHOS PS-900™, a cyclodextrin charge acceptance agent, or charge acceptance additive component, and an optional colorant.

The present invention is also specifically directed to a electrostatographic imaging process wherein an electrostatic latent image bearing member containing a layer of marking material, toner particles, or liquid developer as illustrated herein and containing a charge acceptance additive, which additive may be coated on the developer, is selectively charged in an imagewise manner to create a secondary latent image corresponding to the first electrostatic latent image on the imaging member. Imagewise charging can be accomplished by a wide beam charge source which generates free mobile charges or ions in the vicinity of the electrostatic latent image coated with the layer of marking material or toner particles. The latent image causes the free mobile charges or ions to flow in an imagewise ion stream corresponding to the latent image. These charges or ions, in turn, are accepted by the marking material or toner particles, leading to imagewise charging of the marking material or toner particles with the layer of marking material or toner particles itself becoming the latent image carrier. The latent image carrying toner layer is subsequently developed by selectively separating and transferring image areas of the toner layer to substrates like paper thereby enabling an output document.

The present invention also relates to an imaging process and imaging apparatus, wherein an electrostatic latent image including image and nonimage areas are formed in a layer of marking material, and further wherein the latent image can be developed by selectively separating portions of the latent image bearing layer of the marking material comprised of a liquid developer such that the image areas reside on a first surface and the nonimage areas reside on a second surface. In an embodiment, the present invention relates to an image development apparatus, comprising a system for generating a first electrostatic latent image on an imaging member, wherein the electrostatic latent image includes image and nonimage areas having distinguishable charge potentials, and a system or device for generating a second electrostatic latent image on a layer of marking materials situated adjacent the first electrostatic latent image on the imaging member, wherein the second electrostatic latent image includes image and nonimage areas having distinguishable charge potentials of a polarity opposite to the charge potentials of the charged image and nonimage areas in the first electrostatic latent image. The apparatus and process details can in embodiments be as illustrated in U.S. Pat. No. 5,826,147, the disclosure of which is totally incorporated herein by reference.

The liquid developers and processes of the present invention possess in embodiments thereof a number of advantages including the development and generation of images with improved image quality, the avoidance of a charge director, the use of the developers in a reverse charging development process, excellent image transfer, and the avoidance of complex chemical charging of the developer. Poor transfer can, for example, result in poor solid area coverage if insufficient toner is transferred to the final substrate and can also cause image defects such as smears and hollowed fine features. Conversely, over-charging the toner particles may result in low reflective optical density images or poor color richness or chroma since only a few very highly charged particles can discharge all the charge on the dielectric receptor causing too little toner to be deposited. To overcome or minimize such problems, the liquid toners, or developers and processes of the present invention were arrived at after extensive research. Other advantages are as illustrated herein and also include minimal or no image blooming, the generation of excellent solid area images, minimal or no developed image character defects, and the like.

PRIOR ART

A latent electrostatic image can be developed with toner particles dispersed in an insulating nonpolar liquid. These dispersed materials are known as liquid toners, toner or liquid developers. The latent electrostatic image may be generated by providing a photoconductive imaging member (PC) or layer with a uniform electrostatic charge, and developing the image with a liquid developer, or colored toner particles dispersed in a nonpolar liquid which generally has a high volume resistivity in excess of about 10

9

ohm-centimeters, a low dielectric constant, for example below about 3, and a moderate vapor pressure. Generally, the toner particles of the liquid developer are less than about or equal to about 30 μm (microns) average by area size as measured with the Malvern 3600E particle sizer.

U.S. Pat. No. 5,019,477, the disclosure of which is totally incorporated herein by reference, discloses a liquid electrostatic developer comprising a nonpolar liquid, thermoplastic resin particles, and a charge director. The ionic or zwitterionic charge directors illustrated may include both negative charge directors, such as lecithin, oil-soluble petroleum sulfonates and alkyl succinimide, and positive charge directors such as cobalt and iron naphthanates. The thermoplastic resin particles can comprise a mixture of (1) a polyethylene homopolymer or a copolymer of (i) polyethylene and (ii) acrylic acid, methacrylic acid or alkyl esters thereof, wherein (ii) comprises 0.1 to 20 weight percent of the copolymer; and (2) a random copolymer (iii) of vinyl toluene and styrene and (iv) butadiene and acrylate.

U.S. Pat. No. 5,030,535, the disclosure of which is totally incorporated herein by reference, discloses a liquid developer composition comprising a liquid vehicle, a charge additive and toner pigmented particles. The toner particles may contain pigment particles and a resin selected from the group consisting of polyolefins, halogenated polyolefins and mixtures thereof. The liquid developers can be prepared by first dissolving the polymer resin in a liquid vehicle by heating at temperatures of from about 80° C. to about 120° C., adding pigment to the hot polymer solution and attriting the mixture, and then cooling the mixture whereby the polymer becomes insoluble in the liquid vehicle, thus forming an insoluble resin layer around the pigment particles.

Moreover, in U.S. Pat. No. 4,707,429, the disclosure of which is totally incorporated herein by reference, there are illustrated, for example, liquid developers with an aluminum stearate charge adjuvant. Liquid developers with charge directors are also illustrated in U.S. Pat. No. 5,045,425. Also, stain elimination in consecutive colored liquid toners is illustrated in U.S. Pat. No. 5,069,995. Further, of interest with respect to liquid developers are U.S. Pat. Nos. 5,034,299; 5,066,821 and 5,028,508, the disclosures of which are totally incorporated herein by reference.

Lithographic toners with cyclodextrins as antiprecipitants, and silver halide developers with cyclodextrins are known, reference U.S. Pat. Nos. 5,409,803, and 5,352,563, the disclosures of which are totally incorporated herein by reference.

Illustrated in U.S. Pat. No. 5,306,591, the disclosure of which is totally incorporated herein by reference, is a liquid developer comprised of a liquid component, thermoplastic resin, an ionic or zwitterionic charge director, or directors soluble in a nonpolar liquid, and a charge additive, or charge adjuvant comprised of an imine bisquinone; in U.S. Statutory Invention Registration No. H1483 there is described a liquid developer comprised of thermoplastic resin particles, and a charge director comprised of an ammonium AB diblock copolymer, and in U.S. Pat. No. 5,307,731 there is disclosed a liquid developer comprised of a liquid, thermoplastic resin particles, a nonpolar liquid soluble charge director, and a charge adjuvant comprised of a metal hydroxycarboxylic acid, the disclosures of each of these patents, and the Statutory Registration being totally incorporated herein by reference.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1

illustrates a charging current test device; and

FIG. 2

illustrates a reverse charge printing (RCP) process and apparatus.

SUMMARY OF THE INVENTION

Examples of features of the present invention include:

It is a feature of the present invention to provide a liquid developer with many of the advantages illustrated herein.

Another feature of the present invention resides in the provision of a liquid developer capable of modulated particle charging with, for example, corona ions for image quality optimization.

It is a further feature of the invention to provide positively charged, and/or negatively charged liquid developers wherein there are selected as charge acceptance agents or charge acceptance additives cyclodextrins, inclusive of organic basic nitrogenous derivatives of cyclodextrins, or aluminum complexes.

It is still a further feature of the invention to provide positively, and negatively charged liquid developers wherein developed image defects, such as smearing, loss of resolution and loss of density, and color shifts in prints with magenta images overlaid with yellow images are eliminated or minimized.

Also, in another feature of the present invention there are provided positively charged liquid developers with certain charge acceptance agents that are in embodiments superior in some characteristics to liquid developers with no charge director in that they can be selected for RCP development, reference U.S. Pat. No. 5,826,147, the disclosure of which is totally incorporated herein by reference, and wherein there can be generated high quality images.

Furthermore, in another feature of the present invention there are provided liquid toners that enable excellent image characteristics, and which toners enhance the positive charge of the resin selected, such as ELVAX® based resins.

These and other features of the present invention can be accomplished in embodiments by the provision of liquid developers.

Aspects of the present invention relate to a liquid developer comprised of a nonpolar liquid, resin, colorant, and a cyclodextrin charge acceptance component; a developer wherein said charge acceptance component or additive is comprised of unsubstituted alpha, beta or gamma cyclodextrin of the following formulas or mixtures thereof

alpha-Cyclodextrin: 6 D-glucose rings containing 18 hydroxyl groups;

beta-Cyclodextrin: 7 D-glucose rings containing 21 hydroxyl groups; or

gamma-Cyclodextrin: 8 D-glucose rings containing 24 hydroxyl groups; a developer wherein said charge acceptance component is comprised of a tertiary aliphatic amino derivative of alpha, beta or gamma cyclodextrin of the following formulas wherein n is a number of from about 2 to about 30, and each R

1

and R

2

is an alkyl group containing from about 2 to about 30 carbons, an alkylaryl group containing from about 7 to about 31 carbons, a cycloalkyl or alkylcycloalkyl group containing from about 3 to about 30 carbons, a cycloalkyl or heterocycloalkyl group containing from about 3 to about 30 carbons wherein R

1

and R

2

are joined in a ring structure with a covalent bond or by covalent bonding to a common divalent heteroatom of oxygen, sulfur or a tertiary alkyl nitrogen group, wherein the degree of substitution can vary from 1 to 18, or 21, or 24 of the hydroxyl groups of the selected cyclodextrin

Tertiary Amino Alpha Cyclodextrin;

Tertiary Amino Beta Cyclodextrin; or

Tertiary Amino Gamma Cyclodextrin; a liquid developer wherein said liquid has a viscosity of from about 0.5 to about 500 centipoise and resistivity equal to or greater than about 5×10

9

ohm/cm, and said thermoplastic resin optionally possesses a volume average particle diameter of from about 0.1 to about 30 microns; a developer wherein the resin is a copolymer of ethylene and vinyl acetate; a developer wherein the colorant is present in an amount of from about zero (0) to about 60 percent by weight based on the total weight of the developer solids of resin colorant, and cyclodextrin; a developer wherein the colorant is carbon black, cyan, magenta, yellow, blue, green, orange, red, violet and brown, or mixtures thereof; a developer wherein the charge acceptance component is present in an amount of from about 0.05 to about 10 weight percent based on the weight of the developer solids of resin, colorant, and charge acceptance component; a developer wherein the cyclodextrin is alpha cyclodextrin; a developer wherein the cyclodextrin is beta cyclodextrin; developer wherein the cyclodextrin is gamma cyclodextrin; a developer wherein the cyclodextrin is N,N-diethylamino-N-2-ethyl beta cyclodextrin; a developer wherein the liquid for said developer is an aliphatic hydrocarbon; a developer wherein the aliphatic hydrocarbon is comprised of a mixture of branched hydrocarbons of from about 8 to about 16 carbon atoms, or a mixture of normal hydrocarbons of from about 8 to about 16 carbon atoms; a developer wherein the aliphatic hydrocarbon is comprised of a mixture of branched hydrocarbons of from about 8 to about 16 carbon atoms; a developer wherein the resin is an alkylene polymer, a styrene polymer, an acrylate polymer, a polyester, or copolymers thereof, or mixtures thereof; a developer wherein the resin is poly(ethylene-co-vinylacetate), poly(ethylene-co-methacrylic acid), poly(ethylene-co-acrylic acid), or poly (propoxylated bisphenol)fumarate; a developer wherein the resin is selected from the group consisting of alpha-olefin/vinyl alkanoate copolymers, alpha-olefin/acrylic acid copolymers, alpha-olefin/methacrylic acid copolymers, alpha-olefin/acrylate ester copolymers, alpha-olefin/methacrylate ester copolymers, copolymers of styrene/n-butyl acrylate or methacrylate/acrylic or methacrylic acid, and unsaturated ethoxylated and propoxylated bisphenol A polyesters; a developer wherein the resin is an alkylene copolymer, a styrene copolymer, an acrylate copolymer or a polyester copolymer; a developer wherein said developer contains a charge adjuvant; a positively, or negatively charged substantially color clear liquid developer comprised of a nonpolar liquid, resin, and a charge acceptance agent comprised of a cyclodextrin; a developer wherein the cyclodextrin is alpha, beta, or gamma cyclodextrin; a developer wherein the cyclodextrin is beta cyclodextrin; a developer wherein the cyclodextrin is gamma; a developer containing a colorant; a developer comprised of from about 1 to about 20 percent solids of from about 0 to about 60 weight percent colorant, from about 0.05 to about 10 weight percent charge acceptance component, and from about 30 to about 99.95 weight percent resin wherein the total of said solids components is about 100 percent, and wherein the developer contains from about 80 to about 99 weight percent of a nonpolar liquid; a developer comprised of from about 5 to about 15 percent by weight of toner solids comprised of from about 15 to about 55 weight percent of colorant, from about 0.05 to about 7 percent by weight of charge acceptance component, and from about 38 to about 85 percent by weight of resin, and wherein the developer further contains from about 85 to about 95 percent by weight of a nonpolar liquid; a developer comprised of resin, colorant, and a cyclodextrin charge acceptance additive; a developer wherein said developer contains a nonpolar liquid, and said cyclodextrin is a cyclodextrin derivative containing one or more organic basic amino groups; a liquid developer comprised of a liquid, thermoplastic resin, colorant, and a cyclodextrin charge acceptance agent capable of charging toner particles in said developer; a developer wherein said developer is colored; an imaging or printing apparatus containing the developer; an imaging method wherein images are developed with the developer; a developer which developer is free of color, and contains no colorant; a developer which developer is free of color, and contains no colorant; a clear liquid developer comprised of resin, liquid, and a cyclodextrin charge acceptance component; an imaging process comprising developing images with the developer; an imaging process comprising developing images with the developer; liquid developers comprised of a nonpolar liquid, resin, preferably a thermoplastic resin, as a charge acceptor the aluminum salts of alkylated salicylic acid, like, for example, hydroxy bis[3,5-tertiary butyl salicylic]aluminate, or mixtures thereof, optionally also containing EMPHOS PS-900™, reference U.S. Pat. No. 5,563,015, the disclosure of which is totally incorporated herein by reference, or as a charge acceptor a cyclodextrin component. In embodiments thereof of the present invention the liquid developers can be charged in a device which first charges the developer to a first polarity, such as a positive polarity, followed by a second charging with a second charging device to reverse the developer charge polarity, such as to a negative polarity in an imagewise manner. Subsequently, a biased image bearer, (IB) separates the image from the background corresponding to the charged image pattern in the toner, or developer layer. Thus, the liquid developers are preferably charged by bipolar ion charging (BIC) rather than with chemical charging.

Cyclodextrins and their nitrogenous derivatives can be selected as the nonpolar medium insoluble charge acceptance agent, and which charge acceptance agent is capable of capturing either negative or positive ions to provide either negative or positively charged liquid developers and preferably wherein the cyclodextrins, or derivatives thereof capture positive ions. Although not being desired to be limited by theory, it is believed that non-bonded electron pairs on neutral nitrogen atoms (usually amine functional groups but not limited thereto) which reside at the openings of the cyclodextrin cavity capture positive ions from the corona effluent by forming covalent or coordinate covalent (dative) bonds with the positive ions. The neutral nitrogen atom in the cyclodextrin molecule then becomes a positively charged nitrogen atom and therefore the cyclodextrin charge acceptor molecule itself becomes positively charged. Since the positively charged cyclodextrin molecule resides in the immobile toner particle and not in the mobile phase or liquid carrier, the immobile toner layer itself on the dielectric surface becomes positively charged in an imagewise manner dependent upon the charge acceptor molecule concentration. As the charge acceptor concentration can be the same throughout the toner layer, it is the amount of toner at a given location in the toner layer that controls the amount of charge acceptor and charge at that location. The amount of charge at a given location then results in differential development (due to different potentials) in accordance with the imagewise pattern deposited on the dielectric surface.

In addition to the above-described nitrogen (positive) charge acceptance mechanism, two other mechanisms may coexist when using cyclodextrin charge acceptor molecules, with or without nitrogen groups present. These mechanisms involve corona ion-acceptance (both involving both ion polarities) or acceptance of ions derived from the interaction of corona ions with other components in the toner layer. One mechanism involves the hydroxyl groups, present at the cavity entrances in the cyclodextrin molecules, which can capture either positive or negative corona effluent ions or species derived therefrom. In regard to the hydroxyl charge (ion) acceptance mechanism, it is believed that nonbonded electron pairs on one or more of the oxygen atoms in adjacent hydroxyl groups can bond positive ions from the corona effluent or from species derived therefrom, from which there results a positive charge dispersed on one or more hydroxyl oxygen atoms. Although the strength of a hydroxyl oxygen-positive ion bond is not as large as that of the amine nitrogen-positive ion bond, multiple oxygen atoms can participate at any given instant in time to complex the positive ion thereby resulting in a sufficient bonding force to acquire permanent positive charging. Optionally, the positive ion from the corona effluent or from species derived therefrom can bind to only one hydroxyl oxygen atom, however, the positive ion can then migrate around all the hydroxyl oxygen atoms surrounding the cyclodextrin cavity opening thereby providing positive charge stability by a charge dispersal mechanism. Also, in the hydroxyl oxygen-positive ion bonding mechanism, the hydroxyl group hydrogen atom is further capable of hydrogen bonding to negative ions originating from the corona effluent or from species derived therefrom. Thus, the hydroxyl group itself is ambivalent in its ability to chemically bind positive and negative ions. In the hydroxyl hydrogen bonding mechanism, hydrogen bonding is an on again-off again mechanism referring, for example, to when one hydrogen bond forms and then breaks there is an adjacent hydroxyl hydrogen atom that replaces the first broken hydrogen bond so that hydrogen bonding charge dispersion occurs to again provide charge stability by a charge dispersal mechanism. In the second mechanism, corona ion fragments (either polarity) or species derived therefrom that are small enough can become physically entrapped inside the cyclodextrin cavity opening resulting in a charged cyclodextrin molecule and hence again a charged toner layer. This ion trapping mechanism is specific to the steric size of the ion or ions emanating from the corona effluent or from species derived therefrom. Ions should be able to fit into the cavity opening to be entrapped, and ions too large cannot enter the cavity opening, will not be entrapped and will not charge the toner layer by this mechanism. Ions that are too small to rapidly pass into and out of the cyclodextrin cavity opening and are not entrapped for a significant time period, will not charge the toner layer by the aforementioned entrapment mechanism. These inappropriately sized ions however could ultimately charge the toner layer as indicated herein. Also, some of the corona effluent ions may have first interacted with other toner layer components to produce secondary ions that are captured by the cyclodextrin charge acceptance molecules. However, any secondary ion formation that might occur should not be too extensive to cause a degradation of the polymeric toner resin or the colorant during the toner layer charging, and wherein the toner layer retains its integrity and the colorant its color strength.

With regard to the aluminum salts, illustrated herein and the appropriate patents mentioned herein, such as the carboxylate salts selected as charge acceptance additives, preferably at least one of the toner resins in the developer contains a functional group capable of covalently bonding to the aluminum charge acceptance agent. Typical functional groups include a carboxylic acid and a hydroxyl group. Examples of resins with functional groups are carboxylic acid containing resins such as the NUCREL resins available from E.I. DuPont. When the carboxylic acid group in the resin forms a covalent bond with the aluminum containing charge acceptance agent, it is believed that the carboxylic acid group anchors the charge acceptance agent to the toner resin in the solid phase. Thus, when the charge acceptance agent accepts an ionic charge from the corona discharge or from species derived therefrom, the ionic charge is also anchored in the solid phase of the liquid toner. Since only toner particles then become charged, the concentration of free mobile ions in the developer liquid phase is avoided or minimized. The avoidance of mobile ions in the liquid phase is desirable since they interfere with BIC-RCP development. This type of charge acceptance agent preferentially accepts negative ions, wherein the negative ions frequently contain one or more negative oxygen atoms, to provide a negatively charged liquid developer. The aluminum salts generally accept oxygen nucleophiles (preferentially as a negative oxygen anion) from the corona effluent by forming a fourth covalent bond between the oxygen nucleophile and the aluminum atom, thereby generating a negative aluminum atom which renders the aluminum-containing molecule negatively charged. Acceptance of positive ions, generated from the corona effluent or from species derived therefrom, by an aluminum carboxylate charge acceptor may occur to generate positively charged aluminum-containing molecules. Three bonding mechanisms are plausible between positive ions and the aluminum carboxylate charge acceptors and which generate positively charged aluminum-containing molecules and a positively charged toner layer. Although not being desired to be limited by theory, (1) a low steady-state concentration of free carboxylate anions, dissociated from the aluminum carboxylate complex but contained therein, could accept positive ions; (2) the aluminum carboxylate complex positive ion acceptance mechanism could also occur by positive ion-hydrogen bonding with water of hydration surrounding the aluminum carboxylate charge acceptor; and (3) the aluminum carboxylate complex positive ion acceptance mechanism could also be accomplished by positive ion-hydrogen bonding with hydroxyl groups, attached to the aluminum atom in the aluminum carboxylate complex.

While not being desired to be limited by theory, capturing charge using a charge acceptance agent versus a charge control agent is different mechanistically. A first difference resides in the origin and location of the species reacting with a charge acceptance agent versus the origin and location of the species reacting with a charge control agent. The species reacting with a charge acceptance agent originate in the corona effluent, which after impinging on the toner layer, become trapped in the solid phase thereof. The species reacting with a charge control agent, i.e. the charge director originates by purposeful formulation of the charge director into the liquid developer and remains soluble in the liquid phase of the toner layer. Both the charge acceptance agent (in BIC-RCP developers) and the charge control additive or agent (in chemically charged developers) are insoluble in the liquid developer medium and reside on and in the toner particles, however, charge directors used for chemically charged developers, dissolve in the developer medium. A second difference between a charge acceptance agent and a charge director is that charge directors in chemically charged liquid developers charge toner particles to the desired polarity, while at the same time capturing the charge of opposite polarity so that charge neutrality is maintained during this chemical equilibrium process. Charge separation occurs only later when the developer is placed in an electric field during development. In the BIC-RCP development process, the corona effluent used to charge the liquid developer is generated from any corona generating device and the dominant polarity of the effluent is fixed by the device. Corona ions first reach the surface of the toner layer, move through the liquid phase, and are adsorbed onto the toner particle and captured by the charge acceptance agent. The mobile or free corona ions in the liquid phase rapidly migrate to the ground plane. Some of these mobile ions may include counterions, if counter ions are formed in the charging process. Counter ions bear the opposite polarity charge versus the charged toner particles in the developer. The corona ions captured by the charge acceptance agent in or on the toner charge the developer to the same polarity as the dominant polarity charge in the corona effluent. The ion-charged liquid developer particles remain charged and most counter-ions, if formed in the process, exit to the ground plane so fewer counter charges remain in the developer layer. Electrical neutrality or equilibrium is not usually attained in the BIC-RCP development process and development is not usually interfered with by species containing counter charges.

The slightly soluble charge acceptance agent initially resides in the liquid phase but prior to charging the toner layer the charge acceptance agent preferably deposits on the toner particle surfaces. The concentration of charge acceptor in the nonpolar solvent is believed to be close to the charge acceptor insolubility limit at ambient temperature especially in the presence of toner particles. The adsorption affinity between soluble charge acceptor and insoluble toner particles is believed to accelerate charge acceptor adsorption such that charge acceptor insolubility occurs at a lower charge acceptor concentration versus when toner particles are not present. When the insoluble or slightly soluble charge acceptors accept (chemically bind) ions from the impinging corona effluent (BIC) or from species derived therefrom, there is obtained a net charge on the toner particles in the liquid developer. Since the toner layer contains charge acceptors capable of capturing both positive and negative ions, the net charge on the toner layer is not determined by the charge acceptor but instead is determined by the predominant ion polarity emanating from the corona. Corona effluents rich in positive ions give rise to charge acceptor capture of more positive ions, and therefore, provide a net positive charge to the toner layer. Corona effluents rich in negative ions give rise to charge acceptor capture of more negative ions, and therefore, provide a net negative charge to the toner layer.

A difference in the charging mechanism of a charge acceptance agent versus is that after charging a liquid developer via the standard charge director (chemical charging) mechanism, the developer contains an equal number of charges of both polarity. An equal number of charges of both polarities in the developer hinders reverse charge imaging, so adding a charge director to the developer before depositing the uncharged developer onto the dielectric surface is undesirable. However, if corona ions in the absence of a charge director are used to charge the toner layer, the dominant ion polarity in the effluent will be accepted by the toner particles to a greater extent resulting in a net toner charge of the desired polarity and little if any counter-charged particles. When the toner layer on the dielectric receiver has more of one kind (positive or negative) of charge on it, reverse charge imaging is facilitated.

Of importance with respect to the present invention is the presence in the liquid developer of the charge acceptor, for example, the aluminum salts illustrated herein, cyclodextrins, and the like, which agents function to for example, increase the Q/M of both positive and negatively charged developers. The captured charge can be represented by Q=fCV where C is the capacitance of the toner layer, V is the measured surface voltage, and f is a proportionality constant which is dependent upon the distribution of captured charge in the toner layer. M in Q/M is the total mass of the toner solids. It is believed that with the developers of the present invention in embodiments all charges are associated with the solid toner particles.

Examples of charge acceptance additives present in various effective amounts of, for example, from about 0.001 to about 10, and preferably from about 0.01 to about 7 weight percent or parts, include cyclodextrins, aluminum di-tertiary-butyl salicylate; hydroxy bis[3,5-tertiary butyl salicylic]aluminate; hydroxy bis[3,5-tertiary butyl salicylic]aluminate mono-, di-, tri- or tetrahydrates; hydroxy bis[salicylic]aluminate; hydroxy bis[monoalkyl salicylic]aluminate; hydroxy bis[dialkyl salicylic]aluminate; hydroxy bis[trialkyl salicylic]aluminate; hydroxy bis[tetraalkyl salicylic]aluminate; hydroxy bis[hydroxy naphthoic acid]aluminate; hydroxy bis[monoalkylated hydroxy naphthoic acid]aluminate; bis[dialkylated hydroxy naphthoic acid]aluminate wherein alkyl preferably contains 1 to about 6 carbon atoms; bis[trialkylated hydroxy naphthoic acid]aluminate wherein alkyl preferably contains 1 to about 6 carbon atoms; and bis[tetraalkylated hydroxy naphthoic acid]aluminate wherein alkyl preferably contains 1 to about 6 carbon atoms. Generally, the aluminum complex charge acceptor can be considered a nonpolar liquid insoluble or slightly soluble organic aluminum complex, or mixtures thereof of Formula II and which additives can be optionally selected in admixtures with those components of Formula I

wherein R

1

is selected from the group consisting of hydrogen and alkyl, and n represents a number, such as from about 1 to about 4, reference for example U.S. Pat. No. 5,672,456, the disclosure of which is totally incorporated herein by reference.

Cyclodextrins can be considered cyclic carbohydrate molecules comprised, for example, of 6, 7, or 8 glucose units, or segments which represent alpha, beta and gamma cyclodextrins, respectively, configured into a conical molecular structure with a hollow internal cavity. The chemistry of cyclodextrins is described in “

Cyclodextrin Chemistry

” by M. L. Bender and M. Komiyama, 1978, Springer-Verlag., the disclosure of which is totally incorporated herein by reference. The alpha and beta, the preferred cyclodextrin for the liquid developers of the present invention, and gamma cyclodextrins are also known as cyclohexaamylose and cyclomaltohexaose, cycloheptaamylose and cyclomaltoheptaose, and cyclooctaamylose and cyclomaltooctaose, respectively, can be selected as the charge acceptor additives. The hollow interiors provide these cyclic molecules with the ability to complex and contain, or trap a number of molecules or ions, such as positively charged ions like benzene ring containing hydrophobic cations, which insert themselves into the cyclodextrin cavities. In addition, modified cyclodextrins or cyclodextrin derivatives may also be used as the charge acceptance agents for the liquid developer of the present invention. In particular, cyclodextrin molecular derivatives containing basic organic functional groups, such as amines, amidines and guanidines, also trap protons via the formation of protonated nitrogen cationic species.

Specific examples of cyclodextrins, many of which are available from American Maize Products Company now Cerestar Inc., include the parent compounds, alpha cyclodextrin, beta cyclodextrin, and gamma cyclodextrin, and branched alpha, beta and gamma cyclodextrins, and substituted alpha, beta and gamma cyclodextrin derivatives having varying degrees of substitution. Alpha, beta and gamma cyclodextrin derivatives include 2-hydroxyethyl cyclodextrin, 2-hydroxypropyl cyclodextrin, acetyl cyclodextrin, methyl cyclodextrin, ethyl cyclodextrin, succinyl beta cyclodextrin, nitrate ester of cyclodextrin, N,N-diethylamino-N-2-ethyl cyclodextrin, N,N-morpholino-N-2-ethyl cyclodextrin, N,N-thiodiethylene-N-2-ethyl-cyclodextrin, and N,N-diethyleneaminomethyl-N-2-ethyl cyclodextrin wherein the degree of substitution can vary from 1 to 18 for alpha cyclodextrin derivatives, 1 to 21 for beta cyclodextrin derivatives, and 1 to 24 for gamma cyclodextrin derivatives. The degree of substitution is the extent to which cyclodextrin hydroxyl hydrogen atoms were substituted by the indicated named substituents in the derivatized cyclodextrins. Mixed cyclodextrin derivatives, containing 2 to 5 different substituents, and from 1 to 99 percent of any one substituent may also be used.

Additional alpha, beta, and gamma cyclodextrin derivatives include those prepared by reacting monochlorotriazinyl-beta-cyclodextrin, available from Wacker-Chemie GmbH as beta W7 MCT and having a degree of substitution of about 2.8, with organic basic compounds such as amines, amidines, and guanidines. Amine intermediates for reaction with the monochlorotriazinyl-beta-cyclodextrin derivative include molecules containing a primary or secondary aliphatic amine site, and a second tertiary aliphatic amine site within the same molecule so that after nucleophilic displacement of the reactive chlorine in the monochlorotriazinyl-beta-cyclodextrin derivative has occurred, the resulting cyclodextrin triazine product retains its free tertiary amine site (for proton acceptance) even though the primary or secondary amine site was consumed in covalent attachment to the triazine ring. In addition, the amine intermediates may be difunctional in primary and/or secondary aliphatic amine sites and mono or multi-functional in tertiary amine sites so that after nucleophilic displacement of the reactive chlorine in the monochlorotriazinyl-beta-cyclodextrin derivative has occurred, polymeric forms of the resulting cyclodextrin triazine product result. Preferred amine intermediates selected to react with the monochlorotriazinyl-beta-cyclodextrin derivative to prepare tertiary amine bearing cyclodextrin derivatives include 4-(2-aminoethyl)morpholine, 4-(3-aminopropyl)morpholine, 1-(2-aminoethyl)piperidine, 1-(3-aminopropyl)-2-piperidine, 1-(2-aminoethyl)pyrrolidine, 2-(2-aminoethyl)-1-methylpyrrolidine, 1-(2-aminoethyl)piperazine, 1-(3-aminopropyl)piperazine, 4-amino-1-benzylpiperidine, 1-benzylpiperazine, 4-piperidinopiperidine, 2-dimethylaminoethyl amine, 1,4-bis(3-aminopropyl)piperazine, 1-(2-aminoethyl)piperazine, 4-(aminomethyl)piperidine, 4,4′-trimethylene dipiperidine, and 4,4′-ethylenedipiperidine. Preferred amidine and guanidine intermediates selected to react with the monochlorotriazinyl-beta-cyclodextrin derivative to prepare amidine and guanidine bearing cyclodextrin triazine CCA products after neutralization include formamidine acetate, formamidine hydrochloride, acetamidine hydrochloride, benzamidine hydrochloride, guanidine hydrochloride, guanidine sulfate, 2-guanidinobenzimidazole, 1-methylguanidine hydrochloride, 1,1-dimethylguanidine sulfate, and 1,1,3,3-tetramethylguanidine. Mixed cyclodextrins derived from the monochlorotriazinyl-beta-cyclodextrin derivative may contain 2 to 5 different substituents, and from 1 to 99 percent of any one substituent in this invention.

Cyclodextrins charge acceptance components include, for example, those of the formulas

alpha-Cyclodextrin: 6 D-glucose rings containing-18 hydroxyl groups;

beta-Cyclodextrin: 7 D-glucose rings containing 21 hydroxyl groups;

gamma-Cyclodextrin: 8 D-glucose rings containing 24 hydroxyl groups;

Tertiary Amino Alpha Cyclodextrin;

Tertiary Amino Beta Cyclodextrin; and

Tertiary Amino Gamma Cyclodextrin.

In embodiments of the present invention, the charge acceptance component or agent, such as the cyclodextrin, is selected in various effective amounts, such as for example from about 0.01 to about 10, and preferably from about 1 to about 7 weight percent based primarily on the total weight percent of the solids, of resin, colorants, and cyclodextrin, or other charge acceptor, and wherein the total of all solids is preferably from about 1 to about 25 percent and the total of nonpolar liquid carrier present is about 75 to about 99 percent based on the weight of the total liquid developer. The toner solids preferably contains in embodiments about 1 to about 7 percent cyclodextrin, about 15 to about 60 percent colorant, and about 33 to about 83 percent resin.

Examples of nonpolar liquid carriers or components selected for the developers of the present invention include a liquid with an effective viscosity of, for example, from about 0.5 to about 500 centipoise, and preferably from about 1 to about 20 centipoise, and a resistivity equal to or greater than, for example, 5×10

9

ohm/cm, such as 5×10

13

. Preferably, the liquid selected is a branched chain aliphatic hydrocarbon. A nonpolar liquid of the ISOPAR® series (manufactured by the Exxon Corporation) may also be used for the developers of the present invention. These hydrocarbon liquids are considered narrow portions of isoparaffinic hydrocarbon fractions with extremely high levels of purity. For example, the boiling range of ISOPAR G® is between about 157° C. and about 176° C.; ISOPAR H® is between about 176° C. and about 191° C.; ISOPAR K® is between about 177° C. and about 197° C.; ISOPAR L® is between about 188° C. and about 206° C.; ISOPAR M® is between about 207° C. and about 254° C.; and ISOPAR V® is between about 254.4° C. and about 329.4° C. ISOPAR L® has a mid-boiling point of approximately 194° C. ISOPAR M® has an auto ignition temperature of 338° C. ISOPAR G® has a flash point of 40° C. as determined by the tag closed cup method; ISOPAR H® has a flash point of 53° C. as determined by the ASTM D-56 method; ISOPAR L® has a flash point of 61° C. as determined by the ASTM D-56 method; and ISOPAR M® has a flash point of 80° C. as determined by the ASTM D-56 method. The liquids selected are generally known and should have an electrical volume resistivity in excess of 10

9

ohm-centimeters and a dielectric constant below 3.0 in embodiments of the present invention. Moreover, the vapor pressure at 25° C. should be less than 10 Torr in embodiments.

While the ISOPAR® series liquids may be the preferred nonpolar liquids for use as dispersant in the liquid developers of the present invention, the important characteristics of viscosity and resistivity may be achievable with other suitable liquids. Specifically, the NORPAR® series available from Exxon Corporation, the SOLTROL® series available from the Phillips Petroleum Company, and the SHELLSOL® series available from the Shell Oil Company can be selected.

The amount of the liquid employed in the developer of the present invention is preferably, for example, from about 80 to about 99 percent, and most preferably from about 85 to about 95 percent by weight of the total liquid developer. The liquid developer is preferably comprised of fine toner particles, or toner solids, and nonpolar liquid. The total solids which include resin, components such as adjuvants, optional colorants, and the cyclodextrin or aluminum complex charge acceptance agent, content of the developer in embodiments is, for example, 0.1 to 20 percent by weight, preferably from about 3 to about 17 percent, and more preferably, from about 5 to about 15 percent by weight. Dispersion is used to refer to the complete process of incorporating a fine particle into a liquid medium such that the final product consists of fine toner particles distributed throughout the medium. Since liquid developers are comprised of fine particles dispersed in a nonpolar liquid, it is often referred to as dispersion.

Typical suitable thermoplastic toner resins that can be selected for the liquid developers of the present invention in effective amounts, for example, in the range of about 99.9 percent to about 40 percent, and preferably 80 percent to 50 percent of developer solids comprised of thermoplastic resin, charge acceptance component, and optional, and in embodiments other components that may comprise the toner. Generally, developer solids include the thermoplastic resin, optional charge additive, colorant, and charge acceptance agent. Examples of resins include ethylene vinyl acetate (EVA) copolymers (ELVAX® resins, E.I. DuPont de Nemours and Company, Wilmington, Del.); copolymers of ethylene and an alpha, beta-ethylenically unsaturated acid selected from the group consisting of acrylic acid and methacrylic acid; copolymers of ethylene (80 to 99.9 percent), acrylic or methacrylic acid (20 to 0.1 percent)/alkyl (C1 to C5) ester of methacrylic or acrylic acid (0.1 to 20 percent); polyethylene; polystyrene; isotactic polypropylene (crystalline); ethylene ethyl acrylate series available as BAKELITE® DPD 6169, DPDA 6182 NATURAL™ (Union Carbide Corporation, Stamford, Conn.); ethylene vinyl acetate resins like DQDA 6832 Natural 7 (Union Carbide Corporation); SURLYN® ionomer resin (E.I. DuPont de Nemours and Company); or blends thereof; polyesters; polyvinyl toluene; polyamides; styrene/butadiene copolymers; epoxy resins; acrylic resins, such as a copolymer of acrylic or methacrylic acid, and at least one alkyl ester of acrylic or methacrylic acid wherein alkyl is 1 to 20 carbon atoms, such as methyl methacrylate (50 to 90 percent)/methacrylic acid (0 to 20 percent)/ethylhexyl acrylate (10 to 50 percent); and other acrylic resins including ELVACITE® acrylic resins (E.I. DuPont de Nemours and Company); or blends thereof.

The liquid developers of the present invention preferably contain a colorant dispersed in the resin particles. Colorants, such as pigments or dyes and mixtures thereof may be present to render a latent image visible.

The colorant may be present in the developer in an effective amount of, for example, from about 0.1 to about 60 percent, and preferably from about 15 to about 60, and in embodiments about 25 to about 45 percent by weight based on the total weight of solids contained in the developer. The amount of colorant used may vary depending on the use of the developer. Examples of pigments which may be selected include carbon blacks available from, for example, Cabot Corporation, FANAL PINK™, PV FAST BLUE™, those pigments as illustrated in U.S. Pat. No. 5,223,368, the disclosure of which is totally incorporated herein by reference; other known pigments; and the like. Dyes are known and include food dyes.

To further increase the toner particle charge and, accordingly, increase the transfer latitude of the toner particles, charge adjuvants can be added to the developer. For example, adjuvants, such as metallic soaps like or magnesium stearate or octoate, fine particle size oxides, such as oxides of silica, alumina, titania, and the like paratoluene sulfonic acid, and polyphosphoric acid, may be added. These types of adjuvants can assist in enabling improved toner charging characteristics, namely, an increase in particle charge that results in improved image development and transfer to allow superior image quality with improved solid area coverage and resolution in embodiments. The adjuvants can be added to the developer in an amount of from about 0.1 percent to about 15 percent of the total developer solids, and preferably from about 3 percent to about 7 percent of the total weight percent of solids contained in the developer.

The liquid electrostatic developer of the present invention can be prepared by a variety of processes such as, for example, mixing in a nonpolar liquid the thermoplastic resin, charge acceptance component, optional charge additives, such as charge adjuvants, and colorant in a manner that the resulting mixture contains, for example, about 30 to about 60 percent by weight of solids; heating the mixture to a temperature of from about 40° C. to about 110° C. until a uniform dispersion is formed; adding an additional amount of nonpolar liquid sufficient to decrease the total solids concentration of the developer to about 10 to about 30 percent by weight solids and isolating the developer by, for example, cooling the dispersion to about 10° C. to about 30° C. In the initial mixture, the resin, charge acceptance component, and optional colorant may be added separately to an appropriate vessel, such as, for example, an attritor, heated ball mill, heated vibratory mill, such as a Sweco Mill manufactured by Sweco Company, Los Angeles, Calif., equipped with particulate media for dispersing and grinding, a Ross double planetary mixer manufactured by Charles Ross and Son, Hauppauge, N.Y., or a two roll heated mill, which usually requires no particulate media. Useful particulate media include materials like a spherical cylinder of stainless steel, carbon steel, alumina, ceramic, zirconia, silica and sillimanite. Carbon steel particulate media are 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 (approximately 1.0 to approximately 13 millimeters).

Sufficient nonpolar liquid is added to provide a dispersion of from about 30 to about 60, and more specifically, from about 35 to about 45 percent solids. This mixture is then subjected to elevated temperatures during the initial mixing procedure to plasticize and soften the resin. Thereafter, the mixture is sufficiently heated to provide a uniform dispersion of all the solid materials of, for example, colorant, cyclodextrin or aluminum complex charge acceptance component, and resin. The temperature should not be high where degradation of the nonpolar liquid or decomposition of the resin or colorant occurs. Accordingly, the mixture in embodiments is heated to a temperature of from about 50° C. to about 110° C., and preferably from about 50° C. to about 80° C. The mixture may be ground in a heated ball mill or heated attritor at this temperature for about 15 minutes to 5 hours, and preferably about 60 to about 180 minutes.

After grinding at the above temperatures, an additional amount of nonpolar liquid may be added to the resulting dispersion. The amount of nonpolar liquid added should be sufficient in embodiments preferably to decrease the total solids concentration of the dispersion to about 10 to about 30 percent by weight.

The dispersion is then cooled, for example, to about 10° C. to about 30° C., and preferably to about 15° C. to about 25° C., while mixing is continued until the resin admixture solidifies or hardens. Upon cooling, the resin admixture precipitates out of the dispersant liquid. Cooling is accomplished by methods, such as the use of a cooling fluid like water, glycols such as ethylene glycol, in a jacket surrounding the mixing vessel. More specifically, cooling can be accomplished, for example, in the same vessel, such as an 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 by means of particulate media; or with stirring to form a viscous mixture and grinding by means of particulate media. The resin precipitate is cold ground for about 1 to about 36 hours, and preferably from about 2 to about 4 hours. Additional liquid may be added during the preparation of the liquid developer to facilitate grinding or to dilute the developer to the appropriate percent solids needed for developing. Other processes of preparation are generally illustrated in U.S. Pat. Nos. 4,760,009; 5,017,451; 4,923,778; 4,783,389, the disclosures of which are totally incorporated herein by reference.

As illustrated herein, the developers or inks of the present invention can be selected for RCP imaging and printing methods wherein, for example, there can be selected an imaging apparatus, wherein an electrostatic latent image, including image and nonimage areas, is formed in a layer of marking or liquid developer material, and further wherein the latent image can be developed by selectively separating portions of the latent image bearing layer of the marking material such that the image areas reside on a first surface and the nonimage areas reside on a second surface. In embodiments, the present invention relates to an image development apparatus, comprising a system for generating a first electrostatic latent image on an imaging member, wherein the electrostatic latent image includes image and nonimage areas having distinguishable charge potentials, and a system for generating a second electrostatic latent image on a layer of marking materials situated adjacent the first electrostatic latent image on the imaging member, wherein the second electrostatic latent image includes image and nonimage areas having distinguishable charge potentials of a polarity opposite to the charge potentials of the charged image and nonimage areas in the first electrostatic latent image. Marking material refers, for example, to the solids of the liquid developer or the liquid developer itself.

Embodiments of the invention will be illustrated in the following nonlimiting Examples, it being understood that these Examples are intended to be illustrative only, and that the invention is not intended to be limited to the materials, conditions, process parameters and the like recited. The toner particles or solids in the liquid developer can range in diameter size of from about 0.1 to about 3.0 micrometers, and the preferred particle size range is about 0.5 to about 1.5 micrometers. Particle size, when measured, was determined by a Horiba CAPA-700 centrifugal automatic particle analyzer manufactured by Horiba Instruments, Inc., Irvine, Calif. Comparative Examples and data are also provided.

CHARGING CURRENT TEST

Charging Current Test For Embodiments Using Cyclodextrins as Charge Acceptance Agents

An experimental setup for accomplishing a charging current test is illustrated in

FIG. 1. A

thin (5 to 25 micrometers) liquid toner layer 5 is prepared on a flat conductive plate 6. The plate is grounded through a meter 7. The charging wire of the scorotron is represented by 1, the scorotron grid by 3, ions by 4, ground by 8, and electrostatic voltmeter by 10 with DC representing direct current. A charging device, such as a scorotron 2, is placed above the plate. With no toner layer on the plate (bare plate), the current that passes through the plate to the ground is a constant (I

b

) during charging. Assuming a toner layer is a pure insulator, the current passing from the plate to the ground is zero during charging. By monitoring the current that passes through the plate to ground, the toner charge capture or acceptance ability can be measured. The closer the steady state current is to zero, the more charge the toner layer has captured or accepted. The closer the steady state current is to the bare plate current I

b

, the less charge the toner layer has captured or accepted. The faster the current reaches its steady state, the higher is the toner charge capturing or accepting efficiency. One way to analyze the experimental data is to calculate the absolute current difference of a toner layer on the plate and a bare plate. The larger the current difference, the more charge the toner layer has captured or accepted.

CHARGING VOLTAGE TEST

Charging Voltage Test For Embodiments Using Cyclodextrins as Charge Acceptance Agents

An experimental setup for a charging voltage test is similar to the one illustrated in

FIG. 1

except that a meter 7 is not required. A thin (5 to 25 micrometers) liquid toner layer is prepared on a flat conductive plate. A scorotron is placed above the sample plate. When the scorotron is turned off, the charged toner layer on the plate is instantly moved to an immediately adjacent location underneath the electrostatic voltmeter (ESV) in order to measure the surface voltage. The ESV 10 is located about 1 to about 2 millimeters above the charged toner layer. A typical test involves first charging the toner layer with a scorotron for 0.5 second, and then monitoring the surface voltage decay as a function of time for two minutes. This is accomplished for both positively and negatively charged toner layers.

EXAMPLES

Control 1 in Tables 1 and 2=40 Percent of PV FAST BLUE®; 5 Percent Cyclodextrin; Alohas Charge Director Concentration=1 mg/g Solids

One hundred forty-eight point five (148.5) grams of ELVAX 200W® (a copolymer of ethylene and vinyl acetate with a melt index at 190° C. of 2,500, available from E.I. DuPont de Nemours & Company, Wilmington, Del.), 108.0 grams of the cyan pigment (PV FAST BLUE B2GA® obtained from Clarient), 13.5 grams of beta cyclodextrin also known as cycloheptaamylose or cyclomaltoheptaose obtained from Cerestar, Inc.) and 405 grams of ISOPAR-M® (Exxon Corporation) were added to a Union Process 1S attritor (Union Process Company, Akron, Ohio) charged with 0.1857 inch (4.76 millimeters) diameter carbon steel balls. The mixture was milled in the attritor which was heated with running steam through the attritor jacket at 56° C. to 115° C. for 2 hours. 675 Grams of ISOPAR-M® were added to the attritor, and cooled to 23° C. by running water through the attritor jacket, and the contents of the attritor were ground for 4 hours. Additional ISOPAR-M®, about 300 grams, was added and the mixture was separated from the steel balls.

To a one-hundred gram sample of the above toner discharged from attritor (11.549 percent solids) was added 0.385 gram of Alohas charge director (3 weight percent in ISOPAR-M®) to provide a charge director level of 1.0 milligram of charge director per gram of toner solids.

Alohas is hydroxy bis(3,5-di-tertiary butyl salicylic)aluminate monohydrate, reference for example U.S. Pat. Nos. 5,366,840 and 5,324,613, the disclosures of which are totally incorporated herein by reference.

The resulting chemical charged liquid developer was comprised of toner solids containing 55 percent resin, 40 percent pigment, 5 percent cyclodextrin charge control additive (percent by weight throughout based on the total toner solids), ISOPAR-M®, and Alohas charge director, 3 weight percent, which chemically charges the toner positively.

Control 2 in Tables 1 and 2=40 Percent of PV FAST BLUE®; 5 Percent Cyclodextrin: Alohas Charge Director Concentration=2 mg/g Solids

One hundred forty-eight point five (148.5) grams of ELVAX 200W® (a copolymer of ethylene and vinyl acetate with a melt index at 190° C. of 2,500, available from E.I. DuPont de Nemours & Company, Wilmington, Del.), 108.0 grams of the cyan pigment (PV FAST BLUE B2GA® obtained from Clarient), 13.5 grams of the above beta cyclodextrin (cyclodextrin obtained by Cerestar, Inc.) and 405 grams of ISOPAR-M® (Exxon Corporation) were added to a Union Process 1S attritor (Union Process Company, Akron, Ohio) charged with 0.1857 inch (4.76 millimeters) diameter carbon steel balls. The resulting mixture was milled in the attritor which was heated with running steam through the attritor jacket at 56° C. to 115° C. for 2 hours. 675 Grams of ISOPAR-M® were added to the attritor, and cooled to 23° C. by running water through the attritor jacket, and the contents of the attritor were ground for 4 hours. Additional ISOPAR-M®, about 300 grams, was added and the mixture was separated from the steel balls.

To a one hundred gram sample of the mixture (11.549 percent solids) was added 0.770 gram of Alohas charge director (3 weight percent in ISOPAR-M®) to provide a charge director level of 2.0 milligrams of charge director per gram of toner solids.

Alohas is an abbreviated name for hydroxy bis(3,5-di-tertiary butyl salicylic)aluminate monohydrate, reference for example U.S. Pat. Nos. 5,366,840 and 5,324,613, the disclosures of which are totally incorporated herein by reference.

The resulting liquid developer was comprised of toner solids containing 55 percent resin, 40 percent pigment, 5 percent cyclodextrin charge control additive (based on the total toner solids), ISOPAR-M®, and Alohas charge director which chemically charges the toner positively. This developer is a chemically charged liquid developer composition.

Example 1 in Tables 1 and 2=40 Percent of PV FAST BLUE®; 5 Percent Cyclodextrin; No Alohas Added

One hundred forty-eight point five (148.5) grams of ELVAX 200W® (a copolymer of ethylene and vinyl acetate with a melt index at 190° C. of 2,500, available from E.I. DuPont de Nemours & Company, Wilmington, Del.), 108.0 grams of the cyan pigment (PV FAST BLUE B2GA® obtained from Clarient), 13.5 grams of the above beta cyclodextrin (Cyclodextrin obtained by Cerestar, Inc.) and 405 grams of ISOPAR-M® (Exxon Corporation) were added to a Union Process 1S attritor (Union Process Company, Akron, Ohio) charged with 0.1857 inch (4.76 millimeters) diameter carbon steel balls. The resulting mixture was milled in the attritor which was heated with running steam through the attritor jacket at 56° C. to 115° C. for 2 hours. 675 Grams of ISOPAR-M® were added to the attritor, and cooled to 23° C. by running water through the attritor jacket, and the contents of the attritor were ground for 4 hours. Additional ISOPAR-M®, about 300 grams, was added and the mixture was separated from the steel balls.

The liquid developer was used as is from attritor (11.549 percent solids).

The resulting liquid developer was comprised of toner solids containing 55 percent resin, 40 percent pigment, 5 percent cyclodextrin charge acceptance additive (percent by weight throughout based on the total toner solids), and ISOPAR-M®. This developer is considered an ion-charged liquid developer composition.

CHARGING CURRENT TEST RESULTS

Tables 1 and 2 contain the charging current test results. Table 1 lists the raw data readings and Table 2 lists the after process data. The following discussion and numbers refer to Table 2. The charging current test experimental setup is illustrated in FIG.

1

. When Alohas charge director is not added to the liquid toner formulation, the charging current difference with a bare plate in Example 1 (Table 2) indicates that after first charging the toner layer positive and then reversing to negative, the positive current difference is 0.15 μA and the reverse negative current difference is 0.14 μA. This result indicates that when using cyclodextrin as the charge acceptance agent without Alohas charge director present the charging polarity can be reversed to about the same levels. In controls 1 and 2 of Table 2, in which 1 milligram and 2 milligrams of Alohas charge director per gram of toner solids were used, respectively, reversing the charging polarity from positive to negative provided small current difference values (0.04 and 0.05 μA) which indicates that the toner layer resisted being charged to a negative polarity. It is believed that the soluble Alohas charge director captures negative charge, and that the captured negative charge immediately migrates to ground in the liquid phase leaving very little negative charge remaining on the toner particles in the solid phase.

When Alohas charge director is not added to the liquid toner formulation, the charging current difference with a bare plate in Example 1 (Table 2) indicates that after first charging the toner layer negative and then reversing to positive, the negative current difference is 0.18 μA and the reverse positive current difference is 0.15 μA. This result indicates that when using cyclodextrin as the charge acceptance agent without Alohas charge director present, the charging polarity can be easily reversed to about the same levels. In controls 1 and 2 of Table 2, in which 1 milligram and 2 milligrams of Alohas charge director per gram of toner solids were used respectively, reversing the charging polarity from negative to positive again 5 provided small current difference values (0.04 and 0.05 μA) which indicates that the toner layer resisted being charged to a positive polarity.

TABLE 1

Charging Current Test Results

Positive then Negative

Negative then Positive

Ink Composition

current of

current of

current of

current of

Solid Phase

Liquid Phase

positive

negative

negative

positive

Charge

Carrier

Charge

charging at

charging at

charging at

charging at

Resin

Pigment

acceptor

fluid

director

1 second*

1 second**

1 second*

1 second**

Control 1

55%

40%

5% cyclo-

Isopar

1:1

0.35

−0.56

−0.55

0.45

(A typical

Elvax

PVFB

dextrin

M

Alohas

LID ink)

200W

Control 2

55%

40%

5% cyclo-

Isopar

2:1

0.35

−0.55

−0.56

0.45

(A typical

Elvax

PVFB

dextrin

M

Alohas

LID ink)

200W

Example 1

55%

40%

5% cyclo-

Isopar

No

0.35

−0.46

−0.42

0.35

Elvax

PVFB

dextrin

M

200W

*The positive current that passed through a bare plate was 0.5 μA

**The negative current that passed through a bare plate was −0.6 μA

TABLE 2

Charging Current Test Results

Positive then Negative

Negative then Positive

current

current

current

current

Ink Composition

difference*

difference*

difference*

difference*

Solid Phase

Liquid Phase

of positive

of negative

of negative

of positive

Charge

Carrier

Charge

charging at

charging at

charging at

charging at

Resin

Pigment

acceptor

fluid

director

1 second

1 second

1 second

1 second

Control 1

55%

40%

5% cyclo-

Isopar

1:1

0.15

0.04

0.05

0.05

(A typical

Elvax

PVFB

dextrin

M

Alohas

LID ink)

200W

Control 2

55%

40%

5% cyclo-

Isopar

2:1

0.15

0.05

0.04

0.05

(A typical

Elvax

PVFB

dextrin

M

Alohas

LID ink)

200W

Example 1

55%

40%

5% cyclo-

Isopar

No

0.15

0.14

0.18

0.15

Elvax

PVFB

dextrin

M

200W

*current difference = |I

t

-I

b

|, where I

t

is the current that passes through the plate 6 (to ground) on which a toner layer is located; I

b

is the current that passes through the bare plate to ground.

Control in Table 3=100 Percent of DuPont ELVAX 200W®; No Charge Acceptance Agent

Two hundred and seventy (270.0) grams of ELVAX 200W® (a copolymer of ethylene and vinyl acetate resin with a melt index at 190° C. of 2,500, available from E.I. DuPont de Nemours & Company, Wilmington, Del.), and 405 grams of ISOPAR-L® (Exxon Corporation) were added to a Union Process 1S attritor (Union Process Company, Akron, Ohio) charged with 0.1857 inch (4.76 millimeters) diameter carbon steel balls. The mixture was milled in the attritor which was heated with running steam through the attritor jacket at 56° C. to 115° C. for 2 hours. 675 Grams of ISOPAR-G® were added to the attritor, and cooled to 23° C. by running water through the attritor jacket, and the contents of the attritor were ground for 2 hours. Additional ISOPAR-G®, about 900 grams, was added and the mixture was separated from the steel balls.

The liquid developer, which was used as is from the attritor, was comprised of 11.779 percent toner solids (100 percent resin), and 88.221 percent ISOPAR®.

Example 1 in Table 3=99 Percent of DuPont ELVAX 200W®; 1 Percent Tertiary Amine β-Cyclodextrin

Two hundred and sixty-seven point three (267.3) grams of ELVAX 200W® (a copolymer of ethylene and vinyl acetate with a melt index at 190° C. of 2,500, available from E.I. DuPont de Nemours & Company, Wilmington, Del.), 2.7 grams of tertiary amine β-cyclodextrin (available from Cerestar, Inc., Hammond, Ind.) and 405 grams of ISOPAR-L® (Exxon Corporation) were added to a Union Process 1S attritor (Union Process Company, Akron, Ohio) charged with 0.1857 inch (4.76 millimeters) diameter carbon steel balls. The mixture was milled in the attritor which was heated with running steam through the attritor jacket at 56° C. to 115° C. for 2 hours. 675 Grams of ISOPAR-G® were added to the attritor, and cooled to 23° C. by running water through the attritor jacket, and the contents of the attritor were ground for 2 hours. Additional ISOPAR-G®, about 900 grams, was added and the mixture was separated from the steel balls.

Liquid developer which was used as is from the attritor (11.701 percent solids based on the total of the liquid developer) was comprised of toner solids, which contains 99 percent of the above ELVAX® resin and charge acceptor of 1 percent tertiary amine β-cyclodextrin (based on total toner solids), and 88.299 percent ISOPAR®.

Example 2 in Table 3=95 Percent of DuPont ELVAX 200W®; 5 Percent Tertiary Amine β-Cyclodextrin

Two hundred and fifty-six (256.0) grams of ELVAX 200W® (a copolymer of ethylene and vinyl acetate with a melt index at 190° C. of 2,500, available from E.I. DuPont de Nemours & Company, Wilmington, Del.), 13.5 grams of tertiary amine β-cyclodextrin (available from Cerestar, Inc., Hammond, Ind.) and 405 grams of ISOPAR-L® (Exxon Corporation) were added to a Union Process 1S attritor (Union Process Company, Akron, Ohio) charged with 0.1857 inch (4.76 millimeters) diameter carbon steel balls. The mixture resulting was milled in the attritor which was heated with running steam through the attritor jacket at 56° C. to 115° C. for 2 hours. 675 Grams of ISOPAR-G® were added to the attritor, and cooled to 23° C. by running water through the attritor jacket, and the contents of the attritor were ground for 2 hours. Additional ISOPAR-G®, about 900 grams, was added and the mixture was separated from the steel balls.

Liquid developer, which was used as is from the attritor, (11.463 percent solids) was comprised of 11.463 percent toner solids containing 95 percent resin and 5 percent cyclodextrin charge acceptance additive based on total toner solids, and 88.537 percent ISOPAR-M®.

CHARGING VOLTAGE TEST RESULTS

To better understand the effect of the charge acceptor on RCP ink charging, the toner layer surface-charging voltage test illustrated herein can be selected.

TABLE 3

Test Results

Positive

Negative

Ink Composition

Surface

Surface

Solid Phase

Liquid Phase

Initial

Voltage

Initial

Voltage

Charge

Carrier

Charge

surface

after 5

surface

after 5

Resin

Pigment

acceptor

fluid

director

voltage

seconds

voltage

seconds

Control

100%

No

No

Isopar M

No

10

2

−11

−10

Elvax

200W

Example 1

99% Elvax

No

1% cyclo-

Isopar M

No

12

8

−16

−15

200W

dextrin

Example 2

95% Elvax

No

5% cyclo-

Isopar M

No

22

15

−22

−18

200W

dextrin

Ink (toner) layers, with thickness of 15 μm, were generated by draw bar coating. Scorotrons were used as the charging and recharging devices.

The positive and negative toner layer charge-capturing propensity can be measured by several techniques. One of the most frequently used techniques involves first charging the toner layer with a scorotron for a fixed time, e.g. 2 seconds, and then monitoring the surface voltage decay as a function of time when charging is avoided or turned off. This is accomplished for both positively and negatively charged toner layers.

The data in the control of Table 3 indicates that the ink layer with no charge acceptor captured or accepted negative charge equivalent to a surface voltage of −11 volts and maintained −10 volts thereof for 5 seconds. However, the same ink layer, when charged positively, captured or accepted +10 volts initially, but then the voltage of this control ink layer decayed rapidly to 2 volts in 5 seconds.

The data in Example 1 of Table 3, wherein 1 percent tertiary amine cyclodextrin was used as the charge acceptance agent, indicates that the ink layer, when charged negatively, captured or accepted negative charge equivalent to a surface voltage of −16 volts and maintained −15 volts thereof for 5 seconds. However, when charged positively, the same ink layer captured or accepted +12 volts and decayed slowly to 8 volts in 5 seconds. When charged negatively, the ink layer containing the 1 percent cyclodextrin charge acceptance agent improved (versus the control without cyclodextrin) in negative charging level from −11 volts to −16 volts (145 percent improvement). Comparing the decay for the 5 second negative surface voltage in Example 1 versus the Control indicated that in Example 1 the 5 second negative surface voltage was −15 volts (50 percent improvement) whereas in the Control the 5 second negative surface voltage was only −10 volts. When charged positively, the ink layer containing the 1 percent cyclodextrin charge acceptance agent improved in positive charging level from +10 volts to +12 volts (120 percent improvement). Comparing the decay for the 5 second positive surface voltage in Example 1 versus the Control indicated that in Example 1 the 5 second positive surface voltage was +8 volts (400 percent improvement) whereas in the Control the 5 second positive surface voltage was only +2 volts.

The data in Example 2 of Table 3, wherein 5 percent tertiary amine cyclodextrin was used as the charge acceptance agent, indicates that the ink layer, when charged negatively, captured or accepted negative charge equivalent to a surface voltage of −22 volts and maintained −18 volts thereof for 5 seconds. However, when charged positively, the same ink layer captured or accepted +22 volts and decayed slowly to 15 volts in 5 seconds. When charged negatively, the ink layer containing the 5 percent cyclodextrin charge acceptance agent improved (versus the control without cyclodextrin) in negative charging level from −11 volts to −22 volts (200 percent improvement). Comparing the decay for the 5 second negative surface voltage in Example 2 versus the Control indicated that in Example 2 the 5 second negative surface voltage was −18 volts (180 percent improvement) whereas in the Control the 5 second negative surface voltage was only −10 volts. When charged positively, the ink layer containing the 5 percent cyclodextrin charge acceptance agent improved in positive charging level from +10 volts (control without cyclodextrin) to +22 volts (220 percent improvement). Comparing the decay for the 5 second positive surface voltage in Example 2 versus the Control indicated that in Example 2 the 5 second positive surface voltage was +15 volts (750 percent improvement) whereas in the Control the 5 second positive surface voltage was only +2 volts.

The following RCP print tests were used for the liquid developers containing, for example, aluminum carboxylate complexes (such as Alohas) as charge acceptance agents:

RCP BENCH PRINT TEST

Four Options for Using the Bench Print Test

Reverse Charge Printing (RCP) development is initiated with a uniform uncharged toner layer. A first charging device charges toner to a first polarity, then a second charging device reverses the toner charge to a second polarity in an imagewise fashion. A biased Image Bearer (IB) subsequently separates the image from the background corresponding to the charge pattern in the toner layer. Thus, the toner image is formed on the IB and is ready to be transferred to final substrates. Since it is preferred that the first polarity of toner charge be the same as that of the P/R (photoreceptor imaging member) polarity, if a P/R is used, the toner layer may be first charged to a positive polarity when, for example, amorphous silicon is used as the photoreceptor and first charged to a negative polarity when an organic layered photoreceptor, reference U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference, is used. The IB bias can be either the same as or opposite to that of the recharging device depending on the latent image polarity. Table 4 summarizes the four process options in RCP development. An objective of the bench print test for RCP is to identify the optimized process parameters for each ink by acquiring four development curves for all the process options. From each print test, the expemost desired outputs are minimum photoreceptor charge contrast, maximum ROD (ROD>1.3) in solid area minimum ROD (background ROD<0.15) in background area, and excellent solid area image quality. [Delta E=the square root of sum of squares of L*, a*, and b* less than 2 for both microscopic and macroscopic uniformity].

TABLE 4

RCP Print Test Options

Charge Entire

Charge Selected

Toner Layer

Area of Toner Layer

Development

to a First

to a Second

IB Bias

Options

Polarity

Polarity

Polarity

(−, +, −)

−

+

−

(−, +, +)

−

+

+

(+, −, +)

+

−

+

(+, −, −)

+

−

−

In the first print test option in Table 4 above, the entire toner layer on the dielectric surface is first charged negative, and then only the imaged area charge is reversed to positive, and finally the image bearing member (IB) biased to a negative polarity transfers the imaged area to itself. In the second print test option in Table 4, the entire toner layer on the dielectric surface is first charged negative, and then only the background area charge is reversed to positive, and finally the image bearing member (IB) biased to a positive polarity transfers the imaged area to itself. In the third print test option in Table 4, the entire toner layer on the dielectric surface is first charged positive, and then only the imaged area charge is reversed to negative, and finally the image bearing member (IB) biased to a positive polarity transfers the imaged area to itself. The first and third options are the same except that the charge polarities are reversed at each stage. In the fourth print test option in Table 4, the entire toner layer on the dielectric surface is first charged positive, and then only the background area charge is reversed to negative, and finally the image bearing member (IB) biased to a negative polarity transfers the imaged area to itself. The second and fourth options are the same except that the charge polarities are reversed at each stage.

In

FIG. 2

,

5

represents positively charged toner particles on a photoreceptor surface; or photoreceptor or imaging element dielectric surface

6

;

3

C represents ions from a corona source;

2

A is a charging scorotron;

12

is a biased conditioning roll which functions to remove some liquid from the toner layer without changing charge polarity or charge level;

2

B is a recharging scorotron;

14

is a biased image bearer roll;

3

A and

3

B represent the scorotron grid;

1

A and

1

B represent charging wires of the scorotron; V1 is equal to 300 volts; cake charging is accomplished with N-mep+300V in the dark; cake conditioning is accomplished at 0V light on; cake recharging V2 is accomplished in the dark, and cake pickup is accomplished at 0V light on. N-mep is negatively charged migration electrophotographic charged positively, reference U.S. Pat. Nos. 4,536,458 and 4,536,457, the disclosures of which are totally incorporated herein by reference; 0V represents light on that is zero volts (V) when exposed to light; V2 in dark refers to being recharged to a voltage V2, which voltage is the same as the scorotron grid voltage; with the cake charging the toner layer contains about 5 to 15 weight percent solids coated on the N-mep, and wherein both are charged by the scorotron to 300 volts (V); cake conditioning refers to increasing the solids content of the positively charged toner layer from about 5 to about 15 percent to about 20 to about 22 percent, and wherein there is selected for this conditioning a positively charged squegee roll or image conditioning roll; re-charging refers to the imagewise recharging of the toner layer, which recharging is accomplished with a second scorotron

2

B, and wherein the polarity is negative; cake and cake pickup refers to the cake comprised of nonpolar liquid or carrier fluid, toner particles or solids of resin, charge acceptance component and colorant, 20 to 22 percent solids, and wherein the cake is picked up or developed by the positively charged IB roll or image bearer roll

14

.

In the experiments, the imaging member

6

(P/R) had permanent image patterns thereupon. After the P/R was charged in the dark, the imaged area was discharged under room light exposure while the background area held charge. In this RCP bench experiment, a draw bar coating device was used to coat a thin uniform toner layer onto the N-mep photoreceptor using an ink containing 10 to 15 weight percent solids. Two scorotrons were used to charge and recharge the toner layer and a biased metal roll was wrapped with Rexham 6262 dielectric paper with the rough side contacting the toner layer to function as the cake conditioning device (CC). Another biased metal roll, wrapped with the smooth side of the Rexham 6262 paper, contacted the toner layer to function as the image bearer (IB).

FIG. 2

illustrates the experimental steps for (+,−,+) RCP development. Charging and recharging of the N-mep photoreceptor was accomplished in the dark in order to hold the same amount of charge in every experiment. The cake conditioning and cake transfer to the image bearer were operated with a light on to permit the N-mep photoreceptor to fully discharge in order to create a strong electric field in the process nip without air breakdown, and to maintain the same experimental condition for every data point. After the toner layer was charged to a positive polarity, the N-mep photoreceptor was discharged by light and the cake conditioning roll was biased to the same polarity as that of the toner charging device. The cake conditioning roll was applied to the positively charged toner layer surface to squeeze out extra carrier fluid and to compress the toner cake to a higher solids content. The recharging step was also operated in the dark. The scorotron screen bias V2 and the electrical properties of the N-mep photoreceptor, which control the amount of negative charge delivered to the toner layer, together with the toner material properties, determine the toner charge reversal efficiency. In these experiments, the development curve was defined as the ROD of the fused toner on the IB as a function of V2. The bias on the IB

14

was set at 350V.

EXAMPLES FOR ALOHAS

Control 1=40 Percent of Rhodamine Y Magenta; 0.7 Percent Alohas Bound to Toner Resin as Charge Control Agent; Alohas as Charge Director in Liquid Phase (0.5 mg Alohas CD per gram of Toner Solids)

One hundred sixty point four (160.4) grams of NUCREL RX-76® (a copolymer of ethylene and methacrylic acid with a melt index of about 800, available from E.I. DuPont de Nemours & Company, Wilmington, Del.), 2.0 grams of Alohas Powder and 405 grams of ISOPAR-M® (Exxon Corporation) were added to a Union Process 1S attritor (Union Process Company, Akron, Ohio) charged with 0.1857 inch (4.76 millimeters) diameter carbon steel balls. The mixture was milled in the attritor, which was heated with running steam through the attritor jacket to 80° C. to 15° C. for 2.0 hours. Next, 107.6 grams of the magenta pigment (Sun Rhodamine Y 18:3 obtained from Sun Chemicals) was added to the attritor. The mixture was milled in the attritor, which was maintained at 80° C. to 115° C. for 2 hours with running steam through the attritor jacket. 675 Grams of ISOPAR-M® were added to the attritor at the conclusion of 4 hours, and cooled to 23° C. by running water through the attritor jacket, and the contents of the attritor were ground for an additional 4 hours. Additional ISOPAR-M®, about (600 grams), was added and the mixture was separated from the steel balls.

To a one hundred gram sample of the mixture (11.841 percent solids) was added 0.197 gram of Alohas charge director (3 weight percent in ISOPAR-M®) to provide a charge director level of 0.5 milligram of charge director per gram of toner solids.

The liquid developer solids contain 40 percent by weight of Rhodamine Y magenta pigment; 0.7 percent Alohas as a charge control agent bound to the toner resin, and 59.3 percent NUCREL RX-76® toner resin. The solids level was 11.841 percent and the ISOPAR M® carrier liquid and soluble Alohas charge director comprised 88.159 percent of this liquid developer.

Alohas is hydroxy bis(3,5-di-tertiary butyl salicylic)aluminate monohydrate, reference for example U.S. Pat. Nos. 5,366,840 and 5,324,613, the disclosures of which are totally incorporated herein by reference.

Control 2=40 Percent of Rhodamine Y Magenta Pigment; 0.7 Percent Alohas Bound to Toner Resin as Charge Control Agent; HBr Quat 93K as Charge Director in Liquid Phase (5.0 mg HBr Quat 93K CD Per Gram of Toner Solids)

One hundred sixty point four (160.4) grams of NUCREL RX-76® (a copolymer of ethylene and methacrylic acid with a melt index of about 800, available from E.I. DuPont de Nemours & Company, Wilmington, Del.), 2.0 grams of Alohas Powder and 405 grams of ISOPAR-M® (Exxon Corporation) were added to a Union Process 1S attritor (Union Process Company, Akron, Ohio) charged with 0.1857 inch (4.76 millimeters) diameter carbon steel balls. The mixture was milled in the attritor, which was heated with running steam through the attritor jacket to 80° C. to 115° C. for 2.0 hours. Next, 107.6 grams of the magenta pigment (Sun Rhodamine Y 18:3 obtained from Sun Chemicals) was added to the attritor. The mixture was milled in the attritor, which was maintained at 80° C. to 115° C. for 2 hours with running steam through the attritor jacket. 675 Grams of ISOPAR-M® were added to the attritor at the conclusion of 4 hours, and cooled to 23° C. by running water through the attritor jacket, and the contents of the attritor were ground for an additional 4 hours. Additional ISOPAR-M®, about 600 grams, was added, and the mixture was separated from the steel balls.

To a 100 gram sample of the mixture (11.841 percent solids) were added 1.184 grams of HBr Quat 93K (93,000 M

w

) charge director (5 weight percent in ISOPAR-M®) to provide a charge director level of 5.0 milligrams of charge director per gram of toner solids.

The liquid developer solids contain 40 percent by weight of Rhodamine Y magenta pigment, 0.7 percent Alohas as charge control agent bound to the toner resin, and 59.3 percent NUCREL RX-76® toner resin. The solids level is 11.841 percent and the ISOPAR-M® carrier liquid and soluble 93K HBr quat charge director comprise 88.159 percent of this liquid developer.

Alohas is an abbreviation for hydroxy bis(3,5-di-tertiary butyl salicylic)aluminate monohydrate, reference for example U.S. Pat. Nos. 5,366,840 and 5,324,613, the disclosures of which are totally incorporated herein by reference.

HBr Quat 93K is AB diblock copolymer of poly(2-ethylhexyl methacrylate (A Block)-co-N,N-dimethylamino-N-ethyl methacrylate ammonium bromide (B Block)) with an M

w

of 93K, reference for example U.S. Pat. No. 5,441,841, the disclosure of which are totally incorporated herein by reference.

Example 1=40 Percent of Rhodamine Y Magenta Pigment; 0.7 Percent Alohas Charge Acceptance Agent Bound to Toner Resin

One hundred sixty point four (160.4) grams of NUCREL RX-76® (a copolymer of ethylene and methacrylic acid with a melt index of about 800, available from E.I. DuPont de Nemours & Company, Wilmington, Del.), 2.0 grams of Alohas powder and 405 grams of ISOPAR-M® (Exxon Corporation) were added to a Union Process 1S attritor (Union Process Company, Akron, Ohio) charged with 0.1857 inch (4.76 millimeters) diameter carbon steel balls. The mixture was milled in the attritor, which was heated with running steam through the attritor jacket to 80° C. to 115° C. for 2.0 hours. Next, 107.6 grams of the magenta pigment (Sun Rhodamine Y 18:3 obtained from Sun Chemicals) were added to the attritor. The mixture resulting was milled in the attritor, which was maintained at 80° C. to 115° C. for 2 hours with running steam through the attritor jacket. 675 Grams of ISOPAR-M® were added to the attritor at the conclusion of 4 hours, and cooled to 23° C. by running water through the attritor jacket, and the contents of the attritor were ground for an additional 4 hours. Additional ISOPAR-M®, about 600 grams, was added, and the mixture was separated from the steel balls.

The liquid developer solids contain 40 percent by weight of Rhodamine Y magenta pigment, 0.7 percent Alohas as a charge acceptance agent bound to the toner resin, and 59.3 percent NUCREL RX-76® toner resin. The solids level was 11.841 percent and the ISOPAR-M® level was 88.159 percent of this liquid developer.

Alohas is hydroxy bis(3,5-di-tertiary butyl salicylic)aluminate monohydrate, reference for example U.S. Pat. Nos. 5,366,840 and 5,324,613, the disclosures of which are totally incorporated herein by reference.

Example 2=25 Percent of Rhodamine Y Magenta Pigment; No Charge Acceptance Agent

Two hundred and two point five (202.5) grams of NUCREL RX-76® (a copolymer of ethylene and methacrylic acid with a melt index of 800, available from E.I. DuPont de Nemours & Company, Wilmington, Del.), 67.5 grams of the magenta pigment (Sun Rhodamine Y 18:3 obtained from Sun Chemicals) and 405 grams of ISOPAR-M® (Exxon Corporation) were added to a Union Process 1S attritor (Union Process Company, Akron, Ohio) charged with 0.1857 inch (4.76 millimeters) diameter carbon steel balls. The mixture was milled in the attritor which was heated with running steam through the attritor jacket at 80° C. to 115° C. for 2 hours. 675 Grams of ISOPAR-M® were added to the attritor at the conclusion of 2 hours, and cooled to 23° C. by running water through the attritor jacket, and the contents of the attritor were ground for an additional 4 hours. Additional ISOPAR-M®, about 600 grams, was added, and the mixture was separated from the steel balls.

The liquid developer solids contained 25 percent by weight of Rhodamine Y magenta pigment; and 75 percent NUCREL RX-76® toner resin. The solids level was 12.519 percent and the ISOPAR-M® level was 87.418 percent of this liquid developer.

Example 3=25 Percent of Rhodamine Y Magenta Pigment; 0.9 Percent Alohas Charge Acceptance Agent Bound to Toner Resin

Two hundred point one (200.1) grams of NUCREL RX-76® (a copolymer of ethylene and methacrylic acid with a melt index of 800, available from E.I. DuPont de Nemours & Company, Wilmington, Del.), and 2.43 grams of Alohas powder and 405 grams of ISOPAR-M® (Exxon Corporation) were added to a Union Process 1S attritor (Union Process Company, Akron, Ohio) charged with 0.1857 inch (4.76 millimeters) diameter carbon steel balls. The mixture was milled in the attritor which was heated with running steam through the attritor jacket at 80° C. to 115° C. for 2 hours. Next, 67.5 grams of the magenta pigment (Sun Rhodamine Y 18:3 obtained from Sun Chemicals) were added to the attritor. 675 Grams of ISOPAR-M® were added to the attritor at the conclusion of 2 hours, and cooled to 23° C. by running water through the attritor jacket, and the contents of the attritor were ground for an additional 4 hours. Additional ISOPAR-M®, about 600 grams, was added, and the mixture was separated from the steel balls.

The liquid developer solids contained 25 percent by weight of Rhodamine Y magenta pigment; 0.9 percent Alohas as a charge acceptance agent bound to the toner resin and 74.1 percent NUCREL RX-76® toner resin. The solids level was 12.911 percent and the ISOPAR-M® level was 87.089 percent of this liquid developer.

Alohas is hydroxy bis(3,5-di-tertiary butyl salicylic)aluminate monohydrate, reference for example U.S. Pat. Nos. 5,366,840 and 5,324,613, the disclosures of which are totally incorporated herein by reference.

RCP PRINT TEST RESULTS

The printing test results for the Controls and Examples are listed in Table 5. Control 1 is a typical liquid ink composition wherein the charge director, Alohas, in the liquid phase charges toner particles positively. When Control 1 ink was used in the RCP development process, the positive toner charge polarity could not be reversed to a negative one, so that the Control 1 ink prints out images with very high background (requirement: background ROD<0.1) and much less image/background contrast (requirement: image/background ROD contrast>1.2). Control 2 is another typical liquid ink. With a high concentration of HBr Quat 93K charge director, the toner particles in the Control 2 ink acquire a higher negative charging level. The Control 2 ink prints high-density images (requirement: image ROD>1.2) in a traditional liquid immersion development process, however, in a RCP development process, the Control 2 ink prints background extensively (ROD=0.38, which is too large versus the required ROD<0.15). The high charge director concentration (5 milligrams of charge director per gram of toner solids) renders it more difficult to reverse toner polarity. The inability to reverse toner charge polarity results in low-efficiency toner cake reclaim following the development and charge erase steps. Example 1 (with Alohas as the charge acceptance agent) of the RCP ink composition indicated significant background improvement since, for example, without a charge director in the ink, the charge on the toner particles could be reversed.

TABLE 5

Background

Background

Image Optical

density

Image Optical

density

density

Toner charged

density

Toner charged

Ink Composition

Toner charged

to negative

Toner charged

to positive then

Solid Phase

to negative

then reversed

to positive then

reversed to

additive in

Liquid Phase

then reversed

to positive

reversed to

negative

solid

Carrier

Charge

to positive

Clean

negative

Clean

Resin

Pigment

phase

fluid

director

Print @−200 V

@+200 V

Print @+200 V

@−200 V

Comment

Control 1

59.3%

40% Rd Y

0.7%

Isopar

0.5:1

1.45

0.09

1.44

0.30

Difficult to

(A typical

RX-76

Alohas

M

Alohas

reverse to

LID ink)

negative

Control 2

59.3%

40% Rd Y

0.7%

Isopar

5:1

1.36

0.36

1.34

0.08

Difficult to

(A typical

RX-76

Alohas

M

HBrQ93K

reverse to

LID ink)

positive

Example 1

59.3%

40% Rd Y

0.7%

Isopar

No

1.40

0.46

1.46

0.06

Reversible

RX-76

Alohas

M

Example 2

75%

25% Rd Y

No

Isopar

No

1.29

0.12

1.18*

0.07

Higher

RX-76

M

background

Example 3

74.1%

25% Rd Y

0.9%

Isopar

No

1.46

0.08

1.2*

0.07

High image

RX-76

Alohas

M

ROD, dean

background

*Print @+100 V

Example 2, as a RCP ink composition, indicated that without Alohas in the particle phase as charge acceptor, the image contrast was not as large as in Examples 1 and 3, and the background was not as clean. This results indicated that the Alohas Charge Acceptor (CA) enhanced the charge-accepting efficiency of the toner particles.

With further reference to Table 5 and to further understand the effect of the charge acceptor on RCP ink charging, further print tests were accomplished using the RCP process to develop toners of Example 2 (no charge acceptor) and Example 3 (0.9 percent charge acceptor). The results in Example 3 indicated that the RCP liquid developer or ink containing 0.9 percent resin-bound Alohas charge acceptor provided a much higher image density (image ROD>1.25) and cleaner background (background ROD<0.15) when the toner layer was first charged negatively and then recharged positively in an imagewise manner using the RCP process.

Other embodiments and modifications of the present invention may occur to those skilled in the art subsequent to a review of the information presented herein; these embodiments and modifications, as well as equivalents thereof, are also included within the scope of this invention.

Number	Name	Date
4536457	Tam	Aug 1985
4536458	Ng	Aug 1985
4707429	Trout	Nov 1987
5019477	Felder	May 1991
5030535	Drappel et al.	Jul 1991
5045425	Swidler	Sep 1991
5223368	Ciccarelli et al.	Jun 1993
5306591	Larson et al.	Apr 1994
5324613	Ciccarelli et al.	Jun 1994
5346795	Pickering et al.	Sep 1994
5352563	Kawasaki et al.	Oct 1994
5366840	Larson et al.	Nov 1994
5409803	Santos et al.	Apr 1995
5441841	Larson et al.	Aug 1995
5563015	Bonsignore et al.	Oct 1996
5627002	Pan et al.	May 1997
5672456	Chamberlain et al.	Sep 1997
5826147	Liu et al.	Oct 1998

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