CA2038860A1 - Process for preparing high gloss electrostatic liquid developers - Google Patents

Abstract

TITLE
PROCESS FOR PREPARING HIGH GLOSS
ELECTROSTATIC LIQUID DEVELOPERS
ABSTRACT OF THE INVENTION

Process for the preparation of toner particles for electrostatic liquid developers, which upon fusing to paper have a gloss ? 10 units over the paper gloss comprising:
(A) dispersing at least one thermoplastic resin, at least one pigment, and a hydrocarbon liquid having a Kauri-butanol value of greater than 120 such that the dispersion contains 10% or more by weight solids by means of particulate media whereby the moving particulate media creates shear and/or impact while maintaining the temperature for 5 to 180 minutes in the vessel at a temperature of at least 15°C above the point at which the resin is plasticized or liquified by the hydrocarbon liquid and below that at which the hydrocarbon liquid boils and the resin and/or pigment decomposes, (B) continuing dispersion of the resin, pigment and hydrocarbon liquid as in Step (A) while maintaining the temperature for 5 to 180 minutes in the vessel at least 5°C below the point to at least 10°C above the point at which the resin is no longer plasticized or liquified by the hydrocarbon liquid, (C) cooling the dispersion containing 10% or more by weight solids in said vessel to permit precipitation of the resin out of the dispersant, the particulate media being maintained in continuous movement during and subsequent to cooling whereby toner particles having an average particle size of 10 µm or less are formed, and (D) separating the dispersion of toner particles from the particulate media.

Electrostatic developers are prepared by the addition of a charge director compound. The liquid developers are useful for preparation of copies and proofs of various colors and result in images having a higher gloss.

Description

;~03~ ,0 ~E
PROCESS FOR PREPARING HIGH GLOSS
ELECTROSTATIC LIQUID DEVELOPERS
DESCRIPIION
. . ~L~
Thi~ lnvention relates to an process for the preparation of toner particles. More particularly this invention relates to a process for the preparation of toner particles for electrostatic liquid developers which upon fusing to a substrate results in high gloss images.
BAC~GROUND OF THE INVENTION
It is known to develop a latent electrostatic image with toner particles dispersed in an insulating nonpolar liquid. Such dispersed materials are known as liquid toners or liquid developers. A latent electrostatic image may be produced by providing a photoconductive layer with a uniform electrostatlc charge and subsequently discharging the electrostatic charge by exposing it to a modulated beam of radiant energy.
Other methods are known for forming latent electrostatic images. For example, one method is providing a carrier with a dielectrlc surface and transferring a preformed electrostatic charge to the surface. Useful liquid developers comprise a thermoplastic resin and nonpolar liquid. Generally a suitable colorant is present such as a dye or pigment. The colored toner particles are dispersed in the nonpolar liquid which generally has a high-volume resistivity in excess of 109 ohm centimeters, a low dielectric constant below 3.0 and a high vapor pressure. ~he average particle size of the toner particles is.<30 ~m determined for example by a Malvern3600E Particle Sizer described below. After the latent electrostatic image has been formed, the image is X038~0 developed by the colored toner particles dispersed in said nonpolar llquid and the lmage may subsequently be transferred to a carrier sheet.
There are many methods of making liquid developers.
In one such method of preparation toner particles are prepared by dissolving at an elevated temperature one or more polymers in a nonpolar dispersant, together with particles of a pigment, e.g., carbon black. The solution is cooled slowly, while stirring, whereby precipitation of particles occurs. It has been found that by repeating the above process some material was observed that was greater than 1 mm in size. By increasing the ratio of solids to nonpolar liquid the toner particles can be controlled within the desired size range, but it has been found that the density of images produced may be relatively low and when transfer of an image is made to a carrier sheet, for example, the amount of lmage transferred thereto may be relatively low. The particles in this process are formed by a precipitatlon mechanism and not grinding in the presence of particulate media and this contrlbutes to the formation of an inferior liquid developer.
In another method of preparation of toner particles, the plasticizing of the thermoplastic polymer and pigment with a nonpolar liquid forms a gel or solid mass which is shredded into pieces, more nonpolar liquid is added, the pieces are wet-ground into particles, and grinding is continued which is believed to pull the particles apart to form fibers extending therefrom.
While this process is useful in preparing improved toners, it requires long cycle times and excessive material handling, i.e., several pieces of equipment are used.
Electrostatic liquid developers have been prepared in a single apparatus by a method as described in Larson ~03~8~0 U.S. Pa~ent 4,760,009. This method can provide toner particles with a particle size of 10 ~m or less as determined by Malvern 3600E Particle Sizer but requires relatively long grlnding times to achleve thi~ desired particle size.
Yet another method known for the preparation of toner particles for electrostatic liquid developers comprises:
A. dispersing at an elevated temperature in a vessel a thermoplastic resin, optionally a colorant, and a hydrocarb~n liquid having a Kauri-butanol value of less than 120, such that the dispersion contains a total % solids of at least 22% by weight by means of moving particulate media whereby the moving particulate media creates shear and/or impact, while maintaining the temperature in the vessel at a temperature sufficient to plasticize and liquify the resin and below that at which the hydrocarbon liquid boils and the resin and colorant, if present decomposes, B. cooling the dispersion containing a total %
solids of at least 22% by weight in said vessel to permit precipitation of the resin out of the dispersant, the particulate media being maintained in continuous movement during and subsequent to cooling whereby toner particles having an average by area particle size of 10 ~m or less, and C. separating the dispersion of toner particles from the particulate media. Using this process results in the preparation of liquid developers more quickly than by previously known methods using similar equipment but it has been found that in using such electrostatic liquid developers some pigments result in toner particles having low gloss on fusing to a substrate such as paper.

4 203~3~360 It has been found that the above disadvantages can be overcome and toner particles prepared by a process that does not require excessive handling of toner ingredients at elevated temperatures whereby toner particles having an average particle size of 10 ~m or less determ~ned by Malvern 3600E Particle Sizer are dispersed and formed in the same vessel with reduced grindinq times. Transfer of an image of the so prepared toner particles to a carrier sheet results in transfer of a substantial amount of the ~mage providing a suitably dense copy or reproduction. The fused images are also found to have improved gloss, better color strength, increased process latitude, i.e., no color shifts because pigment is ~ell dispersed and stable;
reduced background stain, improved dot resolution and transfer latitude, and require a lower developed mass to reach a given density.
SUMMARY OF THE INVE~TION
In accordance with this invention there is provided a process for the preparation of toner particles for electrostatic liquid developers, which upon fusing to paper have a gloss > 10 units over the paper gloss comprising:
~A) dispersing at least one thermoplastic resin, at least one pigment, and~a hydrocarbon liquid having a Kauri-butanol value of less than 120, such that the dispersion contains a total percent solids of at least 10~ by weight by means of particulate media whereby the moving particulate media creates shear and/or impact while maintaining the temperature for 5 to 180 minutes in the vessel at a temperature of at least 15C above the point at which the resin is plasticized or liquified by the hydrocarbon liquid and below that at which the hydrocarbon liquid boils and the resin and/or pigment decomposes, ..
.

;~038E~60 (B) continuing dispersion of the resin, pigment and hydrocarbon liquid as in Step (A) while maintaining the temperature for 5 to 180 minutes ln the vessel in the range of at least 5C below the point to at least 10C
S above the point at which the resin is no longer plasticized or l~quified by the hydrocarbon liquid, (C) cooling the dispersion containing a ~otal %
solids of at least 10% by weight in said vessel to permit precipitation of the resin out of the dispersant, the particulate media being maintained in continuous movement during and subsequent to cooling whereby toner particles having an average particle size of 10 ~m or less are formed, and (D) separating the dispersion of toner particles from the particulate media.
DEIalLE~ DE~RIPTION OF THE INVE~TION
The process of this invention results in toner particles adapted for electrophoretlc movement through a hydrocarbon liquid, generally a nonpolar liquid.
The toner particles are prepared from at least one thermoplastic polymer or resin, suitable pigments, and hydrocarbon dispersant liquids as described in more detail below. Additional components can be added, e.g., charge director, ad~uvants, polyethylene, fine particle size oxides such as silica, etc.
The dispersant hydrocarbon liquids are, preferably, nonpolar branched-chain aliphatic hydrocarbons and more particularly, Isopar~-G, Isopar~-H, Isopar~-X, Isopar~-L, Isopar~-M and Isopar~-V. These hydrocarbon liquids are narrow cuts of isoparaffinic hydrocarbon fractions with extremely high levels of purity. For example, the boiling range of Isopar~-G is between 157C
and 176C, Isopar~-H between I76C and 191C, Isopar~-K
between 177C and 197C, Isopar~-L between 186C and 206C and Isopar~-~ between 207C and 254C and 6 2038~i0 Isopar~-V between 254.4C and 329.4C. Isopar~-L has a mid-boiling point of approximately 194C. Isopar~-M has a flash point of 80C and an auto-ignition temperature of 338C. Stringent manufacturing specifications, such as sulphur, acids, carboxyl, and chlorides are llmited to a few parts per million. They are substantially odorless, possessing only a very mild paraffinic odor.
They have excellent odor stability and are all manufactured by the Exxon Corporation. High-purity normal paraffinic liquids, Norpar~12, Norpar~13 and Norpar~15, Exxon Corporation, may be used. These hydrocarbon liquids have the following flash points and auto-ignition temperatures:
Auto-Ignition ~i~uidFlash Point (~L Tem~ (~L
Norpar~1269 204 Norpar~1393 210 Norpar~15118 210 Additional useful hydrocarbon liquids are Aromatic~ 100, Aromatic~ 150 and Aromatic~ 200, manufactured by Exxon Corp., Houston, TX. These liquid hydrocarbons have the following Kauri-butanol values (ASTM D1133), flash point, TTC, C (~STM D56), and vapor 25 pressure, kPa at 38C (ASTM D2879).

Kauri- Flash Vapor Ti~uid Butanol ~Qi~ Pressure Aromatic~ 100 91 43C 1.7 30 Aromatic~ 150 95 66C 0.5 Aromatic~ 200 95 103C 0.17 All of the dispersant hydrocarbon liqulds have an electrical volume resistivity in excess of 10 ohm centimeters and a dielectric constant below 3Ø The 20388~iO

vapor pressures at 25C are less than 10 Torr.
Isopar~-G has a flash point, determined by the tag closed cup method, of 40C, Isopar~-H has a flash point of 53C determined by AS~M D~. Isopar~-L and Isopar~-M
, . . .
have flash points of 61C, and 80C, respectively, determined by the same method. While these are the preferred dispersant nonpo~ar liquids, the essential characteristics of all suitable dispersant hydrocarbon liquids are the electrical volume resistivity and the dielectric constant. In addition, a feature of the dispersant nonpolar liquids is a low Kauri-butanol value less than 30, preferably in the vicinity of 27 or 28, determined by ASTM D1133. The ratio of resin to dispersant hydrocarbon liquid is such that the combination of ingredients becomes plasticized or liquified at the working temperature. The plasticiza-tion or liqui~ication temperature of the resin by the hydrocarbon is easily determined by one having ordinary skill in the art. In the process described above and prior to any dilution, the hydrocarbon liquid is present in an amount of 5 to 90~ by weight, preferably 30 to 80%
by weight, based on the total weight of liquid developer. The total weight of solids in the liquid developer is 10 to 95%, preferably 20 to 70% by weight.
The total weight of solids in the liquld developer is solely based on the resin, including components dispersed therein, e.g., pigment component, ad~uvant, etc.
Useful thermoplastic resins or polymers include:
ethylene vinyl acetate ~EVA) copolymers ~Elvax~ resins, E. I. du Pont de Nemours and Company, Wilmington, DE), copolymers of ethylene and an a, ~-ethylenically unsaturated acid selected from the group consisting of acrylic acid and methacrylic acid, copolymers of ethylene ~80 to 99.9%)/acrylic or methacrylic acid (20 8 2038~3~0 to 0~)/alkyl ~C1 to C5) ester of methacrylic or acrylic acid tO to 20~), the percentages being by weight;
polyethylene, polystyrene, isotactic polypropylene ~crystalline), ethylene ethyl acrylate series sold under the trademark Bakelite~ DPD 6169, DPDA 6182 Natural and DTDA 9169 Natural by Union Carbide Corp., Stamford, CN;
ethylene vinyl acetate resins, e.g., DQDA 6479 Natural and DQDA 6832 Natural 7 also sold by Vnion Carbide Corp.; Surlyn~ ionomer resin by E. I. du Pont de Nemours and Company, Wilmington, ~E, etc., or blends thereof.
Preferred copolymers are the copolymer of ethylene and an a, B-ethylenically unsaturated acid of either acrylic acid or methacrylic acid. The synthesis of copolymers of this type are descrlbed in Ree-~ V.S. Patent 3,264,272, the disclosure of which is incorporated herein by reference. For the purposes of preparing the preferred copolymers, the reaction of the acid containing copolymer with the ionizable metal compound, as described in the Rees patent, is omitted. The ethylene constituent is present in about 80 to 99.9~ by weight of the copolymer and the acid component in about 20 to 0.1% by weight of the copolymer. The acid numbers of the copolymers range from l to 120, preferably 5~ to 90. Acid No. is milligrams potassium hydroxide required to neutralize l gram of polymer. The melt index (g/10 min) of 10 to 500 is determined by ASTM D 1238, Procedure A. Particularly preferred copolymers of this type have an acid number of 66 and 54 and a melt index of lO0 and 500 determined at 190C, respectively.
In addition, the resins have the following preferred characteristics:
l. Be able to disperse the ad~uvant, e.g., metallic soap, pigment, etc.

Z038~ 0 2. Be substantially lnsoluble in the dispersant liquid at temperatures below 40C, so that the resin will not dissolve or solvate ln storage, 3. Be able to solvate at temperatures above 50C, 4. Be able to be ground to form particles between O.1 ~m and 3.6 ~m, in diameter preferred size), e.g., determined by Horiba CAPA-500 centrifugal automatic particle analyzer, manufactured by Horiba Instruments, Inc., Irvine, CA; and between 1 ~m and 10 ~m, in diameter, e.g., determined by Malvern 3600E Particle Sizer, manufactured by Malvern, Southborough, MA, 5. Be able to form a particle (average by area) of 3.6 ~m or less, e.g., determined by Horiba CAPA-500 centrifugal automatic part~cle analyzer, manufactured by Horiba Instruments, Inc., Irvine, CA: solvent viscosity of 1.24 cps, solvent density of 0.76 g/cc, sample density of 1.32 using a centrifugal rotation of l,000 rpm, a particle cize range of 0.01 ~m to less than 3.6 ~m, and a particle size cut of 1.0 ~m, and 10 ~m average particle size determined by Malvern 3600E Particle Sizer, as described above, 6. Be able to fuse at temperatures in excess of By solvation in 3. above, the resins forming the toner particles ~ill become swollen or gelatinous.
One or more charge directors as known to those skilled in the art can be added to impart a charge, as desired. Suitable hydrocarbon liquid soluble ionic or zwitterionic charge director compounds, which are generally used in an amount of 0.25 to 1,500 mg~g, preferably 2.5 to 400 mg/g developer solids, include:
lecithin, Basic Calcium Petronate~, Basic Barium Petronate~, Neutral Barium Pet~onate, oll-soluble petro~eum sulfonate, manufactured by Sonneborn Division of Witco Corp., New York, NY; alkyl succinimlde lo 2038æ60 tmanu~actured by Chevron Chemical Company of California), etc.; sod~um dioctylsulfo succinate (manufactured by American Cyanamid Co.), ionlc charge directors such as zirconium octoate, copper oleate, iron S naphthenate, etc.; nonionic char~e directors, e.g., polyethylene glycol sorbitan stearate, nigrosine, triphenyl methane type dye~ and Emphos~ D70-30C and Emphos~ F-27-8S, sold by Witco Corp., New York, NY, sodium salts of phosphated mono- and diglycerides with unsaturated and saturated acid substituents, respectively.
As indicated above, the pigment is dispersed in the resin and renders the latent image visible. The pigment may be present in the amount of up to about 60 percent lS by weight based on the total weight of developer solids, preferably 0.01 to 30% by weight based on the total weight of developer solids. The amount of pigment may vary depending on the use of the developer. E~amples of pigments include: ~

Pi~m~n~List Colour Index p~ment Brand Name Manufacturer Piqment Permanent Yellow DHG Hoechst Yellow 12 25 Permanent Yellow GR Hoechst Yellow 13 Permanent Yellow G Hoechst Yellow 14 Permanent Yellow NCG-71 Hoechst Yellow 16 Permanent Yellow GG Hoechst Yellow 17 Hansa Yellow RA Hoechst Yellow 73 30 Hansa Brilliant Yellow 5GX-02 Hoechst Yellow 74 Dalamar~ Yellow YT-858-D Heubach Yellow 74 Hansa Yellow X Hoechst Yellow 75 e Novoperm~ Yellow HR Hoechst Yellow 83 Chromophtal~ Yellow 3G Clba-Geigy Yellow 93 35 C~lomopb~al~ Yellow GR Ciba-Geigy Yellow 95 Z038l360 Novoperm~ Yellow FGL Hoechst Yellow 97 Hansa Brilliant Yellow 10GX Hoechst Yellow 98 Lumogen~ Lig~t Yellow BASF Yellow 110 Permanent Yellow G3R-01 Hoechst Yellow 114 5 Chromophtal~ Yellow 8G Ciba-Geigy Yellow 128 Irgazin~ Yellow 5GT Ciba-Geigy Yellow 129 Hostaperm~ Yellow H4G Hsechst Yellow 151 Hostaperm~ Yellow H3G Hoechst Yellow 154 Sico Fast0 Yellow D 1155 BASF Yellow 185 10 L74-1357 Yellow Sun Chem. Yellow 14 L75-1331 Yellow Sun Chem. Yellow 17 L75-2337 Yellow Sun Chem. Yellow 83 Hostaperm~ Orange GR Hoechst Orange 43 Paliogen~ Orange BASF Orange 51 15 Irgalite~ Red C2B Ciba-Geigy Red 48:2 Irgalite~ Rubine 4BL Ciba-Geigy Red 57:1 Quindo~ Magenta Mobay Red 122 Indofast~ Brilliant Scarlet Mobay Red 123 Hostaperm~ Scarlet GO Hoechst Red 168 20 Permanent Rubine F6B Hoechst Red 184 Monastral~ Magenta Clba-Geigy Red 202 Monastral~ Scarlet Ciba-Geigy Red 207 Heliogen~ Blue L 6901F BASF Blue 15:2 Heliogen~ Blue NBD 7010 BASF Blue:3 25 Heliogen~ Blue K 7090 BASF Blue 15:3 Heliogen~ Blue L 7101F BASF Blue 15:4 Paliogen~ Blue L 6470 BASF Blue 60 Heliogen~ Green X 8683 BASF Green 7 Heliogen~ Green L 9140 BASF Green 36 30 Monastral~ Violet R C$ba-Geigy Violet 19 Monastral~ Red B Ciba-Geigy Violet 19 Quindo~ Red R6700 Mobay Violet 19 Quindo~ Red R6713 Mobay Indofast~ Violet Mobay Violet 23 Monastral~ Violet Maroon B Ciba-Geigy Violet 42 12 2 0 3 8 ~0 Sterling~ NS Black Cabot Black 7 Sterling~ NSX 76 Ca~ot Tipure~ R-101 Du Pont White 6 While practically any pigment can be used in preparing ~he electrostatic liquid developers according to the invention, it has been found that not all pigments may show a substantial increase in gloss. By gloss is meant the ratio of specular reflected incident light measured at a 759 angle as per The Technical Association of the Pulp and Paper Industry Standard Procedure 7480. Preferred pigments which show improved gloss include: Quindo~ Red R 6700, Quindo~ Red R 6713, L74-1357 Yellow, Sico Fast~ Yellow D 1155, and Irgalite~ Red C2B, set out in the Pigment List above.
Other ingredients may be added to the electrostatic liquid developer, such as fine particle size oxides, e.g., silica, alumina, titania, etc.; preferably in the order of 0.5 ~m or less can be dispersed into the liquefied resin. These optional oxides can be used as the pigment or in combination with the pigment. Metal particles can also be added.
Another additional component of the electrostatic liquid developer is an ad~uvant which can be selected from the group of polyhydroxy compound which contains at least 2 hydroxy groups, aminoalcohol, polybutylene succinimide, metallic soap, and aromatic hydrocarbon having a Kauri-butanol value of greater than 30. The ad~uvants are generally used in an amount of 1 to 1,000 mg/g, preferably 1 to 200 mg/g developer solids.
Examples of the various above-described ad~uvants include:
pQlyhvdroxv cQm~ound~: ethylene glycol, 2,4,7,9-tetramethyl-5-decyn-4,7-diol, poly(propylene glycol), pentaethylene glycol, tripropylene glycol, triethylene 13 Z038~io glycol, glycerol, pentaerythritol, glycerol-tri-12 hydroxystearate, ethylene glycol monohydroxystearate, propylene glycerol monohydroxy-stearate, etc., described in Mitchell U.S. Patent 4,734,352;
aminoalcohol comDounds: triisopropanolamine, triethanolamine, ethanolamine, 3-amino-1-propanol, o-aminophenol, 5-amino-1-pentanol, tetra~2-hydroxyethyl)ethylenediamine, etc., described in Larson U.S. Patent 4,702,985;
polybutylene succinimide: OLOA~-1200 sold by Chevron Corp., analysis information appears in Kosel U.S. Patent 3,900,412, column 20, lines 5 to 13, incorporated herein by reference; Amoco 575 having a number average molecular weight of about 600 ~vapor pressure osmometry) made by reacting maleic anhydride with polybutene to give an alkenylsuccinic anhydride which in turn is reacted with a polyamine. Amoco 575 is 40 to 45% surfactant, 36% aromatic hydrocarbon, and the remainder oil, etc., descrlbed in El-Sayed and Taggi 0 V.S. Patent 4,702,984;
meta1l1c SOaD: aluminum tristearate; aluminum distearate; barium, calcium, lead and zinc stearates;
cobalt, manganese, lead and zinc linoleates; aluminum, calcium and cobalt octoates; calcium and cobalt oleates; 5 zinc palmitate; calcium cobalt, manganese, lead and zinc naphthenates; calcium, cobalt, manganese, lead and zinc resinates; etc. The metallic soap is dispersed in the thermoplastic resin as described in Trout U.S. Patent 4,707,429; and aromatic hvdrocarbon: benzene, toluene, naphthalene, substituted benzene and naphthalene compounds, e.g., trimethylbenzene, xylene, dimethylethylbenzene, ethylmethylbenzene, propylbenzene, Aromatic~ 100 which is a mixture of Cg and Clo alkyl-14 Z~)38~3~i0 substituted benzenes manufactured by Exxon Corp., described in Mitchell U.S. Patent 4,663,264, etc.
The disclosures of the aforementioned United States patents are lncorporated herein by reference.
The particles in the electrostatic liquid developer preferably have an average particle size 10 ~m or less.
The average particle size determined by the Malvern ~600E Particle Sizer can vary depending on the use of the liquid developer. The resin particles of the developer may or may not be formed having a plurality of fibers integrally extending therefrom although the formation of fibers extending from the toner particles is preferred. The term "fibers" as used herein means pigmented toner particles formed with fibers, tendrils, tentacles, threadlets, fibrils, ligaments, hairs, bristles, or the like.
In carrying out the prOCeS-Q of the invention, a suitable mixing or blending vessel, e.g., attritor, heated ball mill, heated vibratory mill such as a Sweco Mill manufactured by Sweco Co., Los Angeles, CA, equipped with particulate media, for dispersing and grinding, etc., is u~ed. Generally the resin, pigment, and dispersant hydrocarbon liquid are placed in the vessel prior to starting the dispersing step at a percent solids of 10 to 95%, preferably 20 to 70~ by weight. Optionally the pigment can be added after homogenizing the resin and the dispersant hydrocarbon liquid. Polar additive similar to that described in Mitchell, V.S. Patent 4,6~1,244 can also be present in the vessel, e.g., up to 100~ based on the weight of polar additive and dispersant hydrocarbon liquid. The dispersing is generàlly accomplished in two ste~s at two different elevated temperature levels, the first being a temperature of at least 15C above the point at which the resin is plasticized or liquified by the hydrocarbon " :
.

liquid but b~low that at which the hydrocarbon liquid or polar additive, if present, boils and the resin decomposes and the second step ~eing at a temperature of at least 5C below the point at which the resin is no longer plasticized or liquified by the hydrocarbon liquid to a temperature of ~t least 10C above the point at which the resin is no longer plasticized or liquified by the hydrocarbon liquid. The first dispersing step may be accomplished in 5 to 180 minutes, preferably, 15 to 30 minutes, while the second step may be accomplished in 5 to 180 minutes, preferably 15 to 45 minutes.
Preferred temperature ranges are 90 to 105C and 65 to 80C for Steps A and B, respectively. Other temperatures outside this range may be suitable, however, depending on the particular ingredients used and providing they meet the above enumerated requirements. The presence of the irregularly moving particulate media in the vessel is needed to prepare the dispersion of toner particles. It has been found that stirring the ingredients, even at a high rate, is not sufficient to prepare dispersed toner partlcles of proper size, configuration and morphology. Useful particulate media are particulate materials, e.g., spherical, cylindrical, etc., selected from the group consisting of stainless steel, carbon steel, alumina, ceramic, zirconia, silica, and sillimanite. Carbon steel particulate media is partlcularly useful when colorants other than black are uaed. A typical diameter range for the particulate media is in the range of 0.04 to 0.5 inch ~1.0 to approx. 13 mm).
After dispersing the ingredients in the vessel, with or without a polar additive present, until the desired dispersion is achieved, typlcally 0.5 to 1.5 hours for both dispersing steps, with the mixture being fluid, the dispersion is cooled to permit preCipitatiOn 16 2C)38~360 of the resin out of the dispersant. Cooling is accomplished in the same vessel, such as the attritor, while simultaneously grinding with particulate media to prevent the formation of a gel or solid mass. Cooling is accomplished by means known to those skilled in the art and is not limited to cooling by circulating cold water or a cooling material through an external cooling jacket adjacent to the dispersing apparatus or permitting the dispersion to cool to ambient temperature. The resin precipitates out of the dispersant during the cooling. Typical cooling temperatures may range from 15C to 50C. Toner particles of average particle size of 10 ~m or less, as determined by a Malvern 3600E Particle Sizer, 3.6 ~m or less as determined using the Horiba centrifugal particle analyzer described above, or other comparable apparatus, are formed by grinding for a relatively short period of time when compared with former methods. It is preferred that the desired particle size be achieved within a normal work period, e.g., 8 hours or le~s, preferably 4 hours or less.
The Malvern 3600E Particle Sizer manufactured by Malvern, Southborough, MA uses laser diffraction light scattering of stirred samples to determine average particle sizes. Since the Horiba and Malvern instruments use different techniques to measure average particle size the readinqs differ. The following correlation of the average size of toner particles in micrometers ~m) for the two instruments is:

17 2038~il60 Value Determined By Expected Range For Malvern 3600E_Particle ~i~L ~oriba CAPA-500 9.9 + 3.4 6.4 + 1.9 515 4.6 + 1.3 2.8 + 0.8 1.0 + 0.5 3 0.2 + 0.6 10 This correlation is obtained by statistical analysis of average particle sizes for 67 liquid electrostatic developer samples (not of this invention) obtained on both instruments. The expected ranqe of Horiba values was determined using a linear regression lS at a confidence level of 9S~. In the claims appended to this specification the particle size values are as measured using the Malvern instrument.
After cooling ~nd separating the dispersion of toner particles from the particulate media by means known to those sk~lled in the art, lt is possible to redùce the concentration of the toner particles in the dispersion, lmpart an electrostatic charge of predetermined polarity to the toner particles, or a combination of these variations. The concentration of the toner particles in the dlspersion is reduced by the addition of additional dispersant hydrocarbon liquid as described previously above. The dllution is normally conducted to reduce the concentration of toner particles to between 0.1 to 10 percent by weight, preferably 0.3 to 4.0, and more preferably 0.5 to 2 weight percent with respect to the dispersant hydrocarbon liquid. One or more hydrocar~on liquid soluble ionic or zwitterionic charge director compounds of the type set out above, can be added to impart a positive or negative charge, as desired. The addition may occur at any time during the .

, '. , .: , ~ ' ~ : ~

X0381~iO

process; preferably at the end of the process, e.g., after the particulate media are removed and the dilution of toner particles is accomplished. If a diluting dispersant hydrocarbon li~uld is also added, the lonic or zwitterionic compound can be added prior to, concurrently with, or subsequent thereto. If an adjuvant compound of a type descr~bed above has not been previously added in the preparation of the developer, it can be added prior to or subsequent to the developer being charged. Preferably the ad~uvant compound is added after the dispersing step.
INDUSTRIAL APpLICABILITY
The improved process of this invention produces a liquid electrostatic developer which may have a plurality of fibers extending from the toner particles.
The liquid developer contains toner particles having a controlled particle size range which can be prepared more quickly than by prev~ously known processes using similar equipment for making liquid electrostatic developers and which upon fusing result in lmages having high gloss. The developer is of the liquid type and is particularly useful in copying, e.g., making office copies of black and white as well as various colors; or color proofing, e.g., a reproductlon of an image using the standard colors: yellow, cyan and magenta together with black as desired. In copying and proofing the toner particles are applied to a latent electrostatic image. Other uses are envisioned for the improved toner particles, e.g., the formation of copieg or images using toner particles containing finely divided ferromagnetic materials or metal powders; conductive lines using toners containing conductive materials, resistors, capacitors and other electronic components; llthographic printing plates, etc.

.

19 ;~038~3~i() ~AM~LE~
The following examples wherein the parts and percentages are by weight illustrate but do not llmit the invention. In the examples the melt indices were determ~ned by ASTM D 1238, Procedure A, the average particle sizes by area were determined by a Malvern 3600E Particle Sizer, manufactured by Malvern, Southborough, MA, as described above, the conductivity was measured in picomhos/cm ~pmhos) at 5 hertz and low voltage, 5 volts, and the density was measured using a Macbeth densitometer model RD918. Specular gloss was measured at a 75 degree angle using a Glossgard II~
glossmeter, Pacific Scientific, Silver Spring, MD
calibrated to a white tile with a gloss value of 49.1 and a black glass with a gloss value of 100.

Toner samples were prepared using the following procedures:
A yellow toner (Sample l-Control) was prepared by adding 370 g of a copolymer of ethylene ~91%) and methacrylic acid (9%), melt index at 190C is 500, acid No. is 60, 51 g of a yellow pigment, Sico Fast~ Yellow D 1155, BASF, Holland, MI, 4.3 grams of aluminum tristearate, and 1020 g of Isopar~-L to a Union Process lS attritor, Union Process Co., Akron, OH, charged with 0.1857 inch (4.76 mm) diameter carbon steel balls. The mixture was milled at 90C for 1 hour, cooled to 20C, an additional 600 g of Isopar~-L was added, and milled for another 2 hours. The average measured particle size was 10.4 ~m.
A second yellow toner (Sample 2 - Control) was prepared by the procedure described for Sample l with the following exceptions: the milling step of 1 hour at 90C
was replaced by milling at 75C for 1 hour. The mixture :

Z038~3~,0 was cooled to approximately 20C and an additional 600 grams of Isopar~-L were added. After grinding for two more hours the average measured part~cle size was 8.9 ~m.
A third yellow toner (Sample 3 - Control) was prepared by the procedure described for Sample 1 with the following exceptions: the milling step of 1 hour at 90C was replaced by milling at 75C for 3 hours. The mixture was cooled to approximately 20C and an additional 600 grams of Isopar~-L were added. After grinding for two more hours the average measured particle size was 10.1 ~m.
A fourth yellow toner ~Sample 4) was prepared by the procedure described for Sample 1 with the following exceptions: the milling step of 1 hour at 90C was replaced by milling at 90C for 30 minutes followed by milling an additional 30 minutes at 75C. The mixture was cooled to approximately 20C and an additional 530 grams of Isopar~-L were added. After grinding for two more hours the average measured particle size was 6.6 ~m.
Samples 1-4 were evaluated uslng the following procedure: toner concentration was ad~usted to approximately 10%, and drawdowns on Text Web paper, Champion Papers, lnc., Stamford CT, were done using a Laboratory Drawdown Machine, Paul N. Gardner Co. Inc., Pompano Beach, FL. Image density was varied from 1.0 to 1.6 by using a series of metering rods, t5 to ~25, Consler Scientific Design, Tampa, FL or by diluting the toner with additional Isopar~-L to either 5% or 7%
solids. The images were fused at 120C for 1 minute in a Fisher Isotemp Oven, Model 281. Denslty and gloss were measured. A l~inear regression of glos~ vs. density data was used to calculate the gloss at absolute density 1.4. The two step hot grind process at 90C and 75C
for a yellow toner made wlth an acidic polyethylene , 2~)3~3~3fi() resin exhibited higher gloss than a single step hot grind at either 75C or 90C for the same time, or an extended grind at 75C. Results are shown in Table 1 below.

~oner ~1Q~
Sample 1 ~Control) 51 Sample 2 (Control) 56 Sample 3 (Control) 58 10 Sample 4 64 ~XAMPLE 2 A yellow toner (Sample 5 - Control) was prepared by the procedure described for Sample l with the following exceptions: the milling step of l hour at 90C was replaced hy milling at 60C for 1 hour. The mixture was cooled to approximately 20C and an additional 600 grams of Isopar~-L were added. After grlnding for two more hours the average particle size was not measured. Large amounts of unmelted resin beads approximately 0.5 cm across were present.
Another yellow toner (Sample 6 - Control) was prepared by the procedure described for Sample 1 with the following exceptions: the milling step of l hour at 25 90C was replaced by milling at 100C for 1 hour. The mixture was cooled to approximately 20C and an additional 530 grams of Isopar~-~ were added. After grinding for two more hours the average measured particle size was 6.5 ~m.
Another yellow toner (Sample 7 - Control) was prepared by the procedure described for Sample 1 with the following exceptions: the milling step of 1 hour at 90C was replaced by milling at 100C for 3 hours. The mixture was cooled to approximately 20C and an additional 600 grams of Isopar~-L were added. After .

:

~03~ ,0 grinding for two more hours the average measured particle size was 6.5 ~m.
Another yellow toner (Sample 8) was prepared by the procedure described for Sample 1 wlth the following exceptions: the milling step of 1 hour at 90C was replaced by milling at 100C for 15 minutes followed by milling an additional 45 minutes at 60C. The mixture was cooled to approximately 20C and an additional 600 grams of Isopar~-L were added. After grinding for two more hours the average measured particle size was 6.4 ~m.
Samples 5-8 were evaluated as described in Example l with the following exceptions: drawdowns were done on Phoenogrand2 paper, Scheufelen, W. Germany. The images were fused at 140C for two minutes in a Fisher Isotemp Oven, Model 281. The two step hot grind process at 100 and 60C for a yellow toner made with an acidic polyethylene resin exhibited higher gloss than the single step hot grind at elther 100C for the same time or an extended grind at 100C. At 60C it was not possible to make a toner. Results are shown in Table 2 below.

Toner ~1Q~
Sample 5 ~Control) --Sample 6 (Control) 49 Sample 7 (Control) 56 Sample 8 59 EXAMPLE ~
A magenta toner ~Sample 9 - Control) was prepared by the procedure described for Sample 1 with the following exceptions: Quindo~ Red R6700, Mobay Corporation, Dyes and Pigments Organics Division, Pittsburgh, PA, was used in place of the yellow pigment.

~.

23 2038~60 In addition the milling step of 1 hour at 90C was replaced by milling at 100C for 1 hour. The average measured particle size was 8.9 ~m.
An~ther magenta toner (Sample 10 - Control) was prepared by the procedure described for Sample 9 with the following exception: the milling step of 1 hour at 100C was replaced by milling at 75C for one hour. The average measured particle size was 7.4 ~m.
Another magenta toner (Sample 11) was prepared by the procedure described for Sample g with the following exception: the milling step of 1 hour at 100C was replaced by milling at 100C for 15 minutes followed by milling an additional 45 minutes at 75C. The average measured particle size was 8.3 ~m.
Samples 9 - 11 were evaluated as described in Example 1 with the exception that the fusing temperature was 130C. Gloss was measured at an absolute density of 1.35. The two step hot grind process at 100C and 75C
for a magenta toner made with an acidic polyethylene resin exhibited higher gloss than a single step hot grind at either 100C or 75C for the same time.
Results are shown in Table 3 below.

lçnQL
Sample 9 (Control) 70 Sample 10 ~Control) 72 Sample 11 75 _X~MpLE 4 A yellow toner ~Sample 12 - Control) was prepared by the procedure dçscribed for Sample 1 with the following exceptions: a copolymer of vinyl acetate (18~) and ethylene ~82%), melt index 150, was used for ... . .

.

20;~ 0 the resin and 524 grams of Isopar~-L were added at 20~C.
The average measured particle size was 7.9 ~m~
Another yellow toner ~Sample 13 - Control) was prepared by the procedure described for Sample 2 with .. ..
the following exceptions: a copolymer of vinyl acetate ~18~) and ethylene (82%), melt lndex 150, was used for the resin and 524 grams of Isopar~-L were added at 20C.
The average measured particle size was 8.6 ~m.
Another yellow toner (Sample 14) was prepared by the procedure described for Sample 4 with the following exceptions: a copolymer of vinyl acetate (18%) and ethylene (82~), melt index 150, was used for the resin and 524 grams of Isopar~-L were added at 20C. The averaqe measured particle size was 7.6 ~m.
Samples 12 - 14 were evaluated as described in Example 1. Gloss was measured at an absolute density of 1.35. The two step hot grind process at 100C and 75C
for a yellow toner made with a vinyl acetate/ethylene copolymer resin exhibited higher gloss than a single step hot grind at either 100C or 75C for the same time. Results are shown in Table 4 below.

~QnQL Gloss 25 Sample 12 ~Control) 46 Sample 13 (Control) 46 Sample 14 75 A yellow toner (Sample 15) was prepared by the procedure descr~bed for Sample 1 with the following exceptions: the milling step of 1 hour at 90C was replaced by milling at 90C for 30 minutes followed by ~illin~ an additional 30 minutes at 75 C and 182 grams of Isopar~-L were used in this step. The mixture was 20388~0 cooled to approximately 20C and an additional 1561 grams of Isopar~-L were added. After grind~ng for two more hours the average measured particle size was 6.6 Samples 4 and 15 were evaluated as descrlbed ln Example 1 with the exceptions that the developers were at 12% solids and the fusing temperature was 140C.
Gloss was measured at an absolute density of 1.23. The two step hot grind process at 70% solids exhibited higher gloss than the two step hot grlnd process at 29.4% solids. Results are shown in Table 5 below.

Isner ~1Q~
Sample 4 51 Sample 15 56 :

Claims (32)

1. A process for the preparation of toner particles for electrostatic liquid developers, which upon fusing to paper have a gloss ? 10 units over the paper gloss comprising:
(A) dispersing at least one thermoplastic resin, at least one pigment, and a hydrocarbon liquid having a Kauri-butanol value of less than 120, such that the dispersion contains a total percent solids of at least 10% by weight by means of particulate media whereby the moving particulate media creates shear and/or impact while maintaining the temperature for 5 to 180 minutes in the vessel at a temperature of at least 15°C above the point at which the resin is plasticized or liquified by the hydrocarbon liquid and below that at which the hydrocarbon liquid boils and the resin and/or pigment decomposes, (B) continuing dispersion of the resin, pigment and hydrocarbon liquid as in Step (A) while maintaining the temperature for 5 to 180 minutes in the vessel in the range of at least 5°C below the point to at least 10°C above the point at which the resin is no longer plasticized or liquified by the hydrocarbon liquid, (C) cooling the dispersion containing a total % solids of at least 10% by weight in said vessel to permit precipitation of the resin out of the dispersant, the particulate media being maintained in continuous movement during and subsequent to cooling whereby toner particles having an average particle size of 10 µm or less are formed, and (D) separating the dispersion of toner particles from the particulate media.

2. A process according to claim 1 wherein the temperature for Step (A) is in the range of 90 to 105°C

and the temperature for Step (B) is in the range of 65 to 80°C.

3. A process according to claim 1 wherein Step (A) is accomplished in 15 to 30 minutes.

4. A process according to claim 1 wherein Step (B) is accomplished in 15 to 45 minutes.

5. A process according to claim 1 wherein dispersion in Step (A) has a percent solids of 10 to 95%.

6. A process according to claim 1 wherein dispersion in Step (A) has a percent solids of 20 to 70%.

7. A process according to claim 1 wherein the particulate media are selected from the group consisting of stainless steel, carbon steel, ceramic, alumina, zirconia, silica, and sillimanite.

8. A process according to claim 7 wherein the particulate media are spherical having an average diameter of 0.04 to 0.5 inch.

9. A process according to claim 1 wherein the thermoplastic resin is a copolymer of ethylene (80 to 99.9%)/acrylic or methacrylic acid (0 to 20%)/alkyl C1 to C5 ester of methacrylic or acrylic acid (0 to 20%), the percentages being by weight.

10. A process according to claim 9 wherein the thermoplastic resin is a copolymer of ethylene (89%) and methacrylic acid (11%) having a melt index at 190°C of 100.

11. A process according to claim 1 wherein the pigment is carbon black.

12. A process according to claim 1 wherein the pigment is a colored pigment.

13. A process according to claim 1 wherein a fine particle size oxide is present.

14. A process according to claim 13 wherein the oxide is silica.

15. A process according to claim 1 wherein a combination of pigments is present.

16. A process according to claim 1 wherein after Step (C) a charge director is added to the dispersion to impart an electrostatic charge of predetermined polarity to the toner particles.

17. A process according to claim 16 wherein the thermoplastic resin is a copolymer of ethylene (89%) and methacrylic acid (11%) having a melt index at 190°C of 100.

18. A process according to claim 1 wherein a plurality of thermoplastic resins are employed in the plasticizing Step (A).

19. A process according to claim 1 wherein subsequent to Step (C) the dispersion is diluted with additional hydrocarbon liquid.

20. A process according to claim 19 wherein the thermoplastic resin is a copolymer of ethylene (89%) and methacrylic acid (11%) having a melt index at 190°C of 100.

21. A process according to claim 19 wherein the dilution is conducted to reduce the concentration of toner particles to between 0.1 to 4.0 percent by weight with respect to the hydrocarbon liquid.

22. A process according to claim 1 wherein the particles have an average particle size of 5 µm or less.

23. A process according to claim 1 wherein toner particles having a plurality of fibers extending therefrom are formed in Step (B).

24. A process according to claim 16 wherein an adjuvant selected from the group consisting of polyhydroxy compound, aminoalcohol, polybutylene succinimide, metallic soap, and aromatic hydrocarbon having a Kauri-butanol value of greater than 30, with the proviso that the metallic soap is dispersed in the thermoplastic resin.

25. A process according to claim 24 wherein the adjuvant compound is added after the dispersing Step (A).

26. A process according to claim 1 wherein the hydrocarbon liquid has a Kauri-butanol value of less than 30.

27. A process according to claim 26 wherein the thermoplastic resin is a copolymer of ethylene and methacrylic acid.

28. A process according to claim 26 wherein at least one pigment is present.

29. A process according to claim 28 wherein after Step (C) a charge director is added to the dispersion.

30. A process according to claim 29 wherein the thermoplastic resin is a copolymer of ethylene and methacrylic acid.

31. A process according to claim 30 wherein subsequent to Step (C) diluting the dispersion with additional hydrocarbon liquid.

32. A process according to claim 31 wherein the toner particles having a plurality of fibers extending therefrom are formed in Step (B).