GB2250103A - Encapsulated toner preparation - Google Patents

Abstract

Processes for the preparation of encapsulated loners which comprise the polymerization of shell monomers in a first reaction vessel, and thereafter accomplishing complete polymerization of core monomer in a second reaction vessel which is of the same size or larger than said first reaction vessel.

Description

PROCESSES FOR THE PREPARATION OF ENCAPSULATED TONER COMPOSITIONS The present invention is generally directed to processes for the preparation of encapsulated toner compositions.

Encapsulated toner compositions comprised of a core and a polymeric shell thereover preferably prepared by interfacial polymerization are known. An example of an encapsulated toner composition is comprised of a core comprised of a suitable known polymer resin, and dye or pigment particles, which core is encapsulated within a polymeric shell coating such as a polyurea, a polyurethane, a polyamide, a polyester, or mixtures thereof. These toners are usually prepared by a batch process in one reaction vessel wherein core and shell polymerizations are accomplished, thereby causing, for example, undesirable reaction fouling.

The aforementioned encapsulated toners can be prepared by a number of different processes including the interfacial/free radical polymerization process which comprises (1) mixing or blending of a core monomer or monomers, up to 25 in some embodiments, a free radical initiator or initiators, pigments, dyes or a mixture thereof, and an oil-soluble shell monomer or monomers; (2) dispersing the resulting mixture by high shear blending into stabilized microdroplets in an aqueous medium with the assistance of suitable dispersants or emulsifying agents; (3) thereafter subjecting the aforementioned stabilized microdroplets to a shell forming interfacial polycondensation by adding a water-soluble shell monomer or monomers and a suitably functionalized organosilane; and (4) subsequently forming the core resin binder by heat-induced free radical polymerization within the newly formed microcapsules. The shell forming interfacial polycondensation is generally accomplished at ambient temperature, however, elevated temperatures may also be employed depending on the nature and functionality of the shell monomer selected. The core polymer resin forming free radical polymerization is generally effected at a temperature of from ambient temperature to about 140"C, and preferably from ambient or room temperature, about 25"C temperature to about 90"C. In addition, more than one initiator may be utilized to enhance the polymerization conversion, and to generate the desired molecular weight and molecular weight distribution.With these processes, only one reaction vessel is selected as indicated herein.

Encapsulated toner compositions can thus be prepared in accordance with known processes in one reaction vessel by first dispersing the toner precursor materials into stabilized microdroplets of controlled droplet size and size distribution, followed by shell formation around the microdroplets via interfacial polymerization, and subsequently generating the core polymer resin within the newly formed microcapsule by addition polymerization, preferably free radical polymerization within the resultant microcapsules.In one process, the preparation of pressure fixable encapsulated toner compositions is accomplished by interfacial/free radical polymerization methods wherein there are selected as the core polymer resin precursors an addition-type monomer or monomers, a colorant including pigments, dyes or mixtures thereof, and shell forming monomers, wherein at least one of the shell monomers is oil-soluble, and at least one is water-soluble, which monomers are capable of undergoing condensation polymerization at the microdropletlwater interface.Further, in another process the encapsulated toners can be prepared without organic solvents as the diluting vehicle or as a reaction medium, thus eliminating explosion hazards associated therewith; and furthermore, these processes, therefore, do not require expensive and hazardous solvent separation and recovery steps.

Moreover, with the aforementioned processes there can be obtained an improved product yield per unit volume of reactor size since, for example1 the extraneous s6vent component can be replaced by liquid core and shell monomers. In the aforementioned processes, there are certain disadvantages that result because, for example, a single reaction vessel is utilized.

The following prior art, all U. S. patents, has been noted: 4,851,318, which discloses an improved process for the preparation of encapsulated toner compositions by interfacial and free radical polymerization, see for example the Abstract; also note, for example, Example I, columns 10 and 11, and in column 2, reference U. S. Patent 4,727,011, and the processes illustrated therein for the preparation of encapsulated toners; and 4,016,099; 4,097,404 and 4,725,522.

There are disclosed in U.S. Patent 4,307,169 microcapsular electrostatic marking particles containing a pressure fixable core, and an encapsulating substance comprised of a pressure rupturable shell, wherein the shell is formed by an interfacial polymerization. One shell prepared in accordance with the teachings of this patent is a polyamide obtained by interfacial polymerization. Furthermore, there are disclosed in U.S. Patent 4,407,922 pressure sensitive toner compositions comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctyldecylvinylether-co-maleic anhydride as a soft component. Interfacial polymerization processes can be selected for the preparation of the toners of this patent.Also, there are disclosed in the prior art encapsulated toner compositions containing in some instances costly pigments and dyes, reference for example the color photocapsule toners of U.S. Patents 4,399,209; 4,482,624; 4,483,912 and 4,397,483.

Moreover, illustrated in U.S. Patent 4,758,506 are single component cold pressure fixable toner compositions, wherein the shell selected can be prepared by an interfacial polymerization process. Also, illustrated in European patent application No. 0413 604 is an encapsulated toner composition comprised of a core comprised of pigments or dyes, and a polysiloxane-incorporated core binder resin, which core is encapsulated in a shell.

Known batch processes for the preparation of microencapsulated toners are believed to suffer from the problems of excessive reactor wall fouling, low product yield due to large toner agglomerates and high capital investment for industrial sca!e production facilities. It is an object of the present invention to enable those problems to be avoided.

In accordance with the present invention, there are provided semi batch processes for the preparation of encapsulated toner compositions comprised of emulsification to form particles and interfacial polycondensation to form a capsule shell in a first reaction vessel and free radical polymerization to form core polymer in a second reaction vessel.

The volume of the second reaction vessel may be one to six times the volume of the first reaction vessel.

The first reaction vessel may be equipped with a rotor-stator mixer and a scraper blade agitator.

The present invention also provides a process for the preparation of encapsulated toners, wherein pigment dispersion, emulsification and shell polymerization are effected in a first reaction vessel equipped with a high shear mixer and a scraper blade agitator, and subsequently core polymerization is accomplished in a second reaction vessel of an equal or larger volume, or size.

The present invention further provides a process for the preparation of encapsulated toners wherein pigment dispersion, emulsification and shell polymerization are effected in a first small, from about 20 to an about 800 gallon, reaction vessel, and subsequently core polymerization is accomplished in a second larger, from about 30 to an about 4,000 gallon reaction vessel.

In accordance with the present invention, there are also provided processes for the preparation of black and colored toner compositions, in which the shell is generated by interfacial polymerization, and the core is formed by free radical polymerization, and wherein the aforementioned polymerizations are accomplished in two reaction vessels which can be of equal or different volume.

The present invention also provides processes for the preparation of encapsulated toners wherein a microcapsule shell is formed around the core components in one reactor, and subsequently transferred to another reactor to effect polymerization of the core binder resin within the shell.

In a semibatch process in accordance with the invention a number, for example up to 10, of successive batches of encapsulated particles may be formed by interfacial polymerization in a first small reaction vessel, and subsequently combined in a larger second reactor wherein free radical polymerization of the core is accomplished.

In accordance with the present invention, there are further provided processes for the preparation of encapsulated toners comprised of a core comprised of a polymer, pigment, dye or mixtures thereof; and thereover a polymeric shell, which process comprises effecting shell polymerization in one reaction vessel equipped with a high shear mixer and a scraper blade agitator, and core polymeriztion in a second reaction vessel after the shell polymerization product is added thereto.

One embodiment of the present invention comprises dissolving initiator in an organic mixture comprised of core monomer and shell monomer by a rotor-stator system, such as the Ultra-Turrax, available from Janke & Kunkel, IKA-Werk, Germany, operating at a peripheral speed of about 5 to about 30 meters per second in a first stainless steel reaction vessel equipped with a scraper-blade agitator. The diameter of the stator can range in size from, for example, about 45 millimeters to about 350 millimeters with the peripheral speed of the rotor being from about 5 meters per second to about 30 meters per second. The width of the scraper blade can range in size of from about 1 inch to about 20 inches operating at speeds at from about 1 to about 100 revolutions per minute.The size of the first vessel can vary, for example, in embodiments from about 8 inches in diameter and about 10 inches in depth to about 100 inches in diameter and about 125 inches in depth. The pigment or dye can be dispersed in the organic mixture by means of a rotor-stator mixer and the scraper blade agitator in a period of from about 1 to about 10 minutes, and preferably about 3 minutes. The scraper-blade agitator can rotate in the same or counter direction with respect to the rotor-stator mixer. The aforementioned organic phase pigment dispersion can then be emulsified in an aqueous phase containing a surfactant using the same combination of rotor-stator mixer and scraper-blade agitator for about 1 to about 20 minutes, and preferably about 4 minutes. A water-soluble shell component can then be added to initiate interfacial polymerization at room temperature.The resultant particle slurry can then be transferred to a second reaction vessel which has one to ten times the volume of the first reaction vessel, preferably 4 times larger, and equipped with an impeller-type agitator. The described process in the first reaction vessel is repeated as many times as desired or needed, and the particle slurry is combined in the second reaction vessel where the slurry is stirred, for example, at about 100 to 300 revolutions per minute, and preferably 150 revolutions per minute, and is heated to between about 50 C and 140"C, and preferably 85"C for a period of from about 2 to about 10 hours, and preferably 4 hours to complete the free radical polymerization of the core.

The present invention also provides (1) processes for the preparation of encapsulated toners which comprises the polymerization of shell monomers in a first reaction vessel equipped with a rotor-stator mixer and a scraper blade agitator, and thereafter accomplishing complete polymerization of core monomer in a second reaction vessel which is of the same size or larger than the first reaction vessel; (2) processes for the preparation of encapsulated toners which comprises mixing in a first reaction vessel equipped with a rotor-stator mixer and a scraper blade agitator, core monomer1 shell monomer, polymerization initiator and pigment to form a pigmented organic mixture; emulsifying the aforementioned pigmented mixture in an aqueous phase containing surfactant whereby the resulting formed mixture is suspended in the aqueous phase; adding a second shell monomer to the aforementioned suspension to form a capsule shell by interfacial polycondensation of the shell monomers; and subsequently transferring the suspended slurry which is comprised of dispersed encapsulated particles in stabilized aqueous phase to a second reactor which is of the same size or larger than the first reaction vessel, and wherein the resulting formed suspension is suspended and heated to complete core formation by free radical polymerization; and (3) processes for the preparation of encapsulated toners which comprises mixing in a first reaction vessel core monomer(s), shell monomer and polymerization initiator, wherein the initiator is dissolved in an organic phase, comprised of the core monomer and shell monomer, by a rotor-stator mixer; dispersing pigment, such as known magnetites, like Mapico Black in the aforementioned organic phase by means of both a rotor-stator mixer and a scraper blade agitator to form a homogeneous magnetic pigment dispersion; emulsifying the aforementioned pigment dispersion in an aqueous phase comprised of a surfactant and water by means of both a rotor-stator mixer and a scraper agitator; adding a second shell monomer to the aforementioned suspension which is being stirred by the scraper blade agitator to allow interfacial polymerization of the shell monomers to enable formation of a capsule shell; and subsequently transferring the slurry comprised of dispersed encapsulated particles in a stabilized aqueous phase to a second reactor wherein the resulting formed suspension is heated to complete core formation by free radical polymerization.

The encapsulated toners obtained with the processes of the present invention can be comprised of a core comprised of the polymer product of a monomer or monomers, pigment, dyes, or mixtures thereof; and wherein the core is encapsulated in a polymeric shell preferably obtained by interfacial polymerization.

Further, in accordance with the present invention there are provided processes for black and colored pressure fixable toner compositions which are obtained without organic solvents as the diluting vehicles or as reaction media. These processes involve, for example, dispersing a mixture of organic materials and colorants to form stabilized microdroplets in an aqueous medium containing a dispersant or emulsifying agent. The resulting organic mixture is comprised of from about 20 to about 95 weight percent of core monomer or monomers, up to about 20 monomers, about 1 to about 65 weight percent of a colorant or colorants, about 2 to about 25 weight percent of an oil-soluble shell monomer component and a free radical initiator.

The shell formation around the dispersed, stabilized microdroplets via interfacial polycondensation is initiated by adding to the reaction mixture a water-soluble shell monomer component into the aqueous phase. Subsequently, the reaction mixture is subjected to heating to initiate free radical polymerization to form the desired core polymer resin within the newly formed microcapsules. The aforementioned core and shell polymerizations are accomplished in separate reaction vessels, and wherein the second reaction vessel is usually larger than, or about the same size as the first reaction vessel.

One specific embodiment of the present invention is a process which comprises mixing and dispersing a core monomer or monomers, pigment particles, dyes, or mixtures thereof, and a shell monomer component into microdroplets of specific droplet size and size distribution in an aqueous medium containing a dispersant or stabilizer wherein the volume average diameter of the microdroplet is preferably from about 5 microns to about 30 microns, and its volume average droplet size dispersity is preferably less than 1.4 as determined from Coulter Counter measurements of the microcapsule particles after encapsulation; forming a microcapsule shell around the microdroplets via interfacial polymerization in a first reaction vessel by adding a water-soluble shell monomer component; and subsequently affecting a free radical polymerization to form a core resin binder within the newly formed microcapsules in a second larger reaction vessel by, for example, heating the reaction mixture from room temperature to about 90"C for a period of from about 1 to about 10 hours.

Examples of core monomers present in effective amounts, for example of from about 20 to about 95 weight percent, selected include, but are not limited to, addition-type monomers such as styrenes, acrylates, methacrylates, and the like including propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, hexyl acrylate, pentyl acrylate, pentyl methacrylate, hexyl acrylate, hexyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate, stearyl methacrylate, benzyl acrylate, benzyl methacrylate, ethoxypropyl acrylate, ethoxypropyl methacrylate, heptyl acrylate, heptyl methacrylate, isobutyl acrylate, isobutyl methacrylate, methylbutyl acrylate, methylbutyl methacrylate, tolyl acrylate, tolyl methacrylate, styrene, dodecyl styrene, hexyl methyl styrene, nonyl styrene, tetradecyl styrene, other substantially equivalent addition monomers, and the like.

Various known colorants, such as pigments or dyes, or mixtures thereof, present in the core in an effective amount of, for example, from about 1 to about 75 percent by weight of toner, and preferably in an amount of from about 5 to about 60-weight percent that can be selected include carbon blacks, like those available from Cabot Corporation, such as Regal 330@ carbon black, magnetic pigments, such as Pfizer magnetites MO-8029, MO-8028 CB-4799, CB5600, BK-5399, Columbian magnetites, Mapico Blacks, and surface treated magnetites, Bayer magnetites, Bayferrox 8600, 8610, Northern Pigments magnetites NP-604, NP-608, Magnox magnetites TMB-100 or TMB-104, other substantially equivalent black pigments, and the like.As colored pigments there can be selected various known components, such as Heliogen Blue L6900, D6840, D7080, D7020, Pylam Oil Blue and Pylam Oil Yellow, Pigment Blue 1 available from Paul Uhlich & Company Inc., Pigment Violet 1, Pigment Red 48, Lemon Chrome Yellow DCC 1026, E.D.

Toluidine Red and Bon Red C available from Dominion Color Corporation Ltd., Toronto, Ontario, NOVAperm Yellow FGL, Hostaperm Pink E from Hoechst, Cinquasia Magenta available from E l.

DuPont de Nemours & Company, and the like. Generally, colored pigments that can be selected are red, blue, green, brown, cyan, magenta, or yellow pigments, and mixtures thereof, which mixtures can contain various amounts of each pigment, inclusive of about equal amounts of each pigment selected. Examples of magenta materials that may be selected as pigments include, for example, 2,9-dimethyl-substituted quinacridone and anthraquinone dye identified in the Color Index as Cl 60710, CI Dispersed Red 15, diazo dye identified in the Color Index as Cl 26050, C Solvent Red 19, and the like.Illustrative examples of cyan materials that may be used as pigments include copper tetra-(octadecyl sulfonamido) phthalocyanine, x-copper phthalocyanine pigment listed in the Color Index as Cl 74160, CI Pigment Blue, and Anthrathrene Blue identified in the Color Index as Cl 69810, Special Blue X-2137, and the like; while illustrative examples of yellow pigments that may be selected are diarylide yellow 3,3-dichlorobenzidene acetoacetanilides, a monoazo pigment identified in the Color Index as CI 12700, Cl Solvent Yellow 16, a nitrophenyl amine sulfonamide identified in the Color Index as Foron Yellow SEIGLN, CI Dispersed Yellow 33 2,5-dimethoxy-4-sulfonanilide phenylazo-4'-chloro-2,5-dimethoxy acetoacetanilide, and Permanent Yellow FGL.Known colored magnetites, such as mixtures of Mapico Black, and cyan components may also be used as pigments for toners prepared by processes in accordance with the present invention.

Examples of typical shell polymers include polyureas, polyamides, polyesters, polyurethanes, mixtures thereof, and other similar polycondensation products. The shell amounts are generally from about 5 to about 30 weight percent of the toner, and have a thickness generally, for example, of less than about 5 microns, and more specifically from about 0.1 micron to about 3 microns. Other shell polymers, shell amounts, and thicknesses may be selected.

The shell forming monomer components present are in an embodiment comprised of known materials, such as diisocyanates, diacyl chloride, bischloroformate, together with appropriate polyrunctional crosslinking agents such as triisocyanate, triacyl chloride, and the like.

Illustrative examples of the shell monomer components include benzene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, cyclohexane di isocyanate, hexane di isocyanate, adipoyl chloride, fumaryl chloride, suberoyl chloride, succinyl chloride, phthaloyl chloride, isophthaloyl chloride, terephthaloyl chloride, ethylene glycol bischloroformate, diethylene glycol bischloroformate, and the like. The water-soluble shell forming monomer components which are added to the aqueous phase containing water include polyamine or polyol including bisphenol, and the like.Illustrative examples of the water-soluble shell monomers that react with the aforementioned diisocyanates, and the like include diethylenediamine, ethylenediamine, triethylenediamine, diaminotoluene, diaminopyridine, bis(aminopropyl)piperazi ne, bisphenol A, bisphenol Z, and the like. When desired, a water soluble crosslinking component such as triamine or triol can also be added to improve the mechanical strength of the shell structure.

Surfactants acting as both surface active agents and suspension stabilizers in the amounts from 0.03 weight percent to 4 weight percent in water, and selected for the process of the present invention include water soluble polymers such as poly(vinyl alcohols), methyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose and the like. Illustrative examples of free radical initiators selected for the preparation of toners by processes in accordance with the present invention include known initiators such as azo compounds like 2,2' azobis-(2,4-dimethylvaleronitrile), 2,2'-azobis-(isobutyronitri le), azobiscycl ohexa nenitri le, 2methylbutyronitrile or mixtures thereof, with the quantity of initiator(s) being, for example, from about 0.5 percent to about 10 percent by weight of that of core monomer(s).Interfacial polymerization processes selected for the toner shell formation and shells thereof are as illustrated, for example, in U.S. Patents 4,000,087 and 4,307,169.

Surface additives which can be incorporated by known methods, such as mixing, subsequent to formation of the toner compositions include, for example, metal salts, metal salts of fatty acids, colloidal silicas, mixtures thereof, and the like, which additives are usually present in an amount of from about 0.1 to about 2 weight percent, reference U.S. Patents 3,590,000; 3,720,617; 3,655,374 and 3,983,045. Preferred additives include magnesium stearate, zinc stearate and Aerosil R972.

Also, the toner compositions can be rendered conductive with, for example, a volume resistivity, which can be measured in a cell test fixture at 10 volts of from about 1 x 103 ohm-cm to about 1 x 108 ohm-cm by adding with mixing in effective amounts of, for example, from about 0.2 to about 10 weight percent to the surface thereof components such as known carbon blacks, like Vulcan carbon black available from Cabot Corporation, graphite, copper iodide, other conductive metal salts, or conductive organic or organometallic materials. Preferred conductive additives include Vulcan XC-72R or Black Pearls 2000 carbon black available from Cabot Corporation in the amounts ranging from 0.2 to 3 weight percent of toner.

The following examples are being submitted to illustrate the present invention.

Parts and percentages are by weight unless otherwise indicated.

EXAMPLE I A semibatch process was used for the preparation of an encapsulated single component development cold pressure fixable toner composition by adding to a first 50 gallon reaction vessel, followed by high-shear mixing with an IKA rotor-stator mixer (Model T115/4) at room temperature for 90 seconds at 3,600 revolutions per minute (rpm) 13.68 kilograms (kg) of lauryl methacrylate (Rocryl 320, Rohm and Haas Company), 5.37 kilograms of toluene diisocyanate, 2.42 kiligrams of tris(p-isocyanato-phenyl)-thiophosphate (Desmodur RF in methylene chloride available from Mobay Chemical Company) and 242.3 grams of 2,2'-azobis (isobutyronitrile).Into the mixture were dispersed 35.5 kilograms of magnetic iron oxide (foe304, MO-8029 commercially available from Pfizer Pigments Inc.) with the IKA rotor-stator mixer at 3,600 rpm and a scraper-blade agitator at 40 rpm for 3 minutes to obtain a homogeneous magnetic pigment dispersion.

Separately, an aqueous solution comprised of 53.1 grams of polyvinylalcohol (Vinol 523 commercially available from Air Products) in 116 kilograms of deionized water at 25"C was prepared by stirring in a 40 gallon plastic container for 3 hours. The polyvinylalcohol solution was then pumped into the first reaction vessel. Thereafter, the IKA rotor-stator mixer was raised to about 2 inches above the surface of above prepared magnetic pigment dispersion. The magnetic dispersion was emulsified into the aqueous phase for 4 minutes by means of the IKA rotor-stator mixer operating in a clockwise direction at 3,600 rpm and a scraper-blade agitator operating in a counter-clockwise direction at 40 rpm.There was obtained an oil-in-water suspension containing pigmented oily spherical particles with an average particle diameter of 23 microns as determined by a Coulter Counter.

The resulting suspension was agitated by the scraper blade agitator alone under low speed stirring of about 40 rpm, and 3.75 kilograms of diethylenetriamine (99 percent grade, commercially available from Dow Chemical Company) in 10 kilograms of water was added to the reaction vessel to initiate the formation of the polyurea shell. Stirring in the first reaction vessel was continued for 5 minutes. The resulting encapsulated particle suspension was then transferred to a second 200 gallon reaction vessel.

The above procedure was repeated 3 times in the first 50 gallon reaction vessel with each batch of the suspension transferred and combined in the second reaction vessel. When the semi batch process was completed, the temperature of the second reaction vessel was raised at 1"C per minute to 85"C and maintained at that temperature for 4 hours at which time polymerization of the lauryl methacrylate was completed. By the end of the reaction, the slurry was cooled down to 25"C and filtered through a 177 micron sieve to remove large agglomerates. The amount of coarse particles retained on the sieve was about 0.5 percent by weight of toner produced. Upon close visual inspection, the second reaction vessel was free from materials fouling. Total product yield was 94 percent.

The resulting slurry was subsequently washed with deionized water in a centrifuge until the effluent was clear and neutral (7) in pH. The slurry was then mixed with 1.2 percent by weight of a conductive graphite (Aquadag E obtained from Acheson Colloids Ltd.), spray dried with a Bowen No. 1 Tower spray dryer (Bowen Engineering, Inc.) at an inlet temperature of 140"C and air exit temperature of 70"C, and at a drying rate of about 8 pounds per hour, blended with 1.5 percent of zinc stearate; and the encapsulated toner was then tested in a Delphax S-6000'" ionographic cold pressure fix printer. The known Scotch" tape test for image fix quality showed an initial fix level of about 26 percent, a final fix level of 68 percent, and an optical density of 1.5 which was measured using an optical reflection densitomer (Model RC + , Tobias Associates, Inc.).

EXAMPLE II An encapsulated toner was prepared by repeating the procedure of Example I with the exception that only one batch of particle suspension was generated in the first reaction vessel which was not equipped with a scraper blade agitator, followed by shell formation through interfacial polymerization and core formation by free radical polymerization in the first reaction vessel. When the reaction was completed, about 12 percent of coarse particles greater than 177 nlicrons was removed by wet sieving, and the wall of the first reaction vessel was fouled with a thick layer of toner agglomerates as noted by close visual observation. Total product yield was 80 percent EXAMPLE III An encapsulated toner was prepared by repeating the procedure of Example I with the exception that the scraper blade agitator was not used throughout the dispersion process.

When the resulting toner slurry was screened through the 177 micron sieve, about 4 percent by weight of coarse particles was removed as large agglomerates. Total product yield was 87 percent.

EXAMPLE IY, V, VI Four toner compositions were prepared by repeating the procedure of Example I with the exception that the weight of polyvinylalcohol was adjusted to obtain toners with different mean particle sizes (determined by a Coulter Counter) as follows:

Weight of iol Mean Particle Size Polyvinylaicohol Example IV 92.8 grams 17 microns Example V 232.0 grams 15 microns Example VI 464.0 grams 12 microns EXAMPLE VII The process of Example I was repeated with the exception that Black Pearls 2000, 0.51 percent, were selected in place of the graphite, and substantially similar results were obtained. The amount of coarse materials greater than 177 microns in diameter was about 1 percent, and the total product yield was 93 percent. When the process of Example I was repeated with the exception that instead of three times, the procedure in the 50 gallon reaction vessel was accomplished twice, substantially similar results were obtained. The total product yield was 94 percent and the amount of coarse materials of greater than 170 microns in diameter was about 0.5 percent.

The present invention provides processes for the preparation of microencapsuated toners wherein core polymerization can be accomplished subsequent to shell polymerization, and wherein the aforementioned polymerizations can be effected in different reaction vessels.

Through the present invention, for example, there is provided a semi batch process for the preparation of encapsulated toners which comprises the generation of a number of successive batches of encapsulated toner particles by interfacial polymerization of the shell monomers in one reaction vessel equipped with a high shear mixer and a scraper blade agitator, and subsequently introducing the resulting particles in a larger reaction vessel wherein free radical polymerization of the core can be accomplished. Advantages of processes embodying the present invention, especially as compared to batch processes as illustrated in United States Patents 4,727,011 and 4,725,522, include reductions in reaction fouling, higher toner product yields, flexibility in the amount of toner produced, greater process confidence, and capital cost savings.

In the preparation of encapsulated toners as disclosed in the batch process of the prior art, reference for example U.S. Patent 4,877,706, both interfacial polymerization of. the shell monomers and free-radical polymerization of the core monomer are accomplished in the same reaction vessel. Thus, build-up of sticky components comprised mainly of the core polymer on the reactor wall during the heat-up stage can result in severe reactor wall fouling and generation of coarse particles, resulting in higher material ioss and lower product yield. Major cleaning is also usually required to remove the wall fouling after each production run contributing to the overall equipment down time. A semi batch process in accordance with the present invention can eliminate, or minimize these disadvantages.By the generation of encapsulated particles through interfacial polymerization of the shell monomers in a first reaction vessel, the core monomer becomes encapsulated. When the aforementioned encapsulated material is subsequently introduced and heated in a second reaction vessel, no exposed core monomer can polymerize into a sticky polymer, and contaminate the wall of the second reaction vessel. Also, with semi batch processes in accordance with the present invention, small size rotor-stator mixing equipment can be selected to formulate large batches of encapsulated toners, thus reducing capital cost.

Moreover, it is a well known fact that process reproducibility decreases with increasing batch size.

Semi bath processes in accordance with the present invention can maintain a greater process confidence by, for example1 accomplishing the emusification step in a smaller first reaction vessel.

Processes in accordance with the invention enable formation of large particles greater than 250 microns to be eliminated; reactor wall fouling to be avoided, or minimized; toner agglomeration to be eliminated, or minimized; and toner yield to be increased Processes in accordance with the invention can be used to prepare colored1 that is other than black, encapsulated toners.

Toners prepared by processes in accordance with the invention can be selected for imaging processes, especially processes wherein cold pressure fixing is selected.

Processes in accordance with the invention can be used for producing encapsulated toner compositions which are suitable for duplex imaging applications; for producing colored and black encapsulated toner compositions which are suitable for inductive single component development; and for producing insulative encapsulated toner compositions for use in electrostatic imaging and printing apparatus.

More generally, toner compositions obtained by processes of the present invention can be selected for a variety of known reprographic imaging processes including electrophotographic and ionographic processes. In one case, the toner compositions formulated can be selected for pressure fixing processes wherein the image is fixed with pressure. Pressure fixing is common in ionographic processes in which latent images are generated on a dielectric receiver such as anodic aluminum oxide. The latent images can then be toned with a conductive encapsulated toner of the present invention by inductive single component development, and transferred and fixed simultaneously (transfix) in one single step onto paper with pressure.

Specifically, the toner compositions of the present invention can be selected for the commercial Delphax printers, such as the Delphax S9000 , 56000", 54500", 53000", and Xerox printers such as the 4060" and 4075" wherein, for example, transfixing is utilized. In another case, the toner compositions of the present invention can be utilized in xerographic imaging apparatus wherein image toning and transfer are accomplished electrostatically, and transferred images are fixed in a separate step by means of a pressure roll with or without the assistance of thermal or photochemical energy fusing. Also, the encapsulated toners can be selected, it is believed, for magnetic image character image recognition (MICR) processes, reference U.S. Patent 4,517,268 and Reissue 33,172.

Claims (49)

CLAIMS:

1. Processes for the preparation of encapsulated toners which comprise the polymerization of shell monomers in a first reaction vessel, and thereafter accomplishing complete polymerization of core monomer in a second reaction vessel which is of the same size or larger than said first reaction vessel.

2. Processes for the preparation of encapsulated toners which comprise the polymerization of shell monomers in a first reaction vessel equipped with a rotor-stator mixer and a scraper blade agitator, and thereafter accomplishing polymerization of core monomer in a second reaction vessel which is of the same size or larger than the first reaction vessel.

3. A process for the preparation of encapsulated toners which comprises the polymerization of shell monomers in a first reaction mixing container with a rotor-stator mixer and a scraper blade agitator, transferring the formed product from the first reaction mixing container to a second reaction vessel, and thereafter accomplishing polymerization of core monomer in the second reaction vessel which is larger in size than the first reaction vessel.

4. A process for the preparation of encapsulated toners which comprises mixing in a first reaction vessel equipped with a rotor-stator mixer and a scraper blade agitator, core monomer1 shell monomer, polymerization initiator, and pigment to form a pigmented organic mixture; dispersing the aforementioned pigmented mixture in an aqueous phase containing surfactant whereby the resulting formed mixture is suspended in the aqueous phase; adding a second shell monomer to the aforementioned suspension to form a capsule shell by interfacial polycondensation of the shell monomers; and subsequently transferring the suspended slurry comprised of dispersed encapsulated particles in a stabilized aqueous phase to a second reactor which is of the same size or of a larger size than the first reaction vessel, and wherein the resulting formed suspension is suspended and heated to complete core formation by free radical polymerization.

5. A process for the preparation of an encapsulated toner which comprises mixing in a first reaction vessel core monomer, shell monomer, and polymerization initiator, wherein the initiator is dissolved in an organic phase comprised of the core monomer and a shell monomer by a rotor-stator mixer; dispersing magnetite in the aforementioned organic phase by means of a rotor-stator mixer and a scraper blade agitator to form a homogeneous magnetic pigment dispersion; dispersing the aforementioned pigment dispersion in an aqueous phase comprised of a surfactant and water by means of a rotor-stator mixer and a scraper agitator; adding a second shell monomer to the aforementioned suspension which is being stirred by the scraper blade agitator to allow interfacial polymerization of the shell monomers to form a capsule shell; and subsequently transferring the resulting slurry comprised of dispersed encapsulated particles in a stabilized aqueous phase to a second reactor wherein the resulting formed suspension is heated to complete core formation by free radical polymerization.

6. A process in accordance with daim 4 wherein up to 10 batches of suspended encapsulated particle slurry are produced in a first reaction vessel, and these batches are subsequently transferred to a second larger reactor wherein the combined suspension is heated to complete core formation by free radical polymerization.

7. A process in accordance with daim 4 wherein the monomer is selected from the group consisting of acrylate esters, methacrylate esters, chloroacrylate esters, styrenes, and dienes.

8. A process in accordance with claim 4 wherein the monomer is lauryl methacrylate.

9. A process in accordance with claim 5 wherein the monomer is selected from the group consisting of acrylate esters, methacrylate esters, chloroacrylate esters, and styrene.

10. A process in accordance with claim 4 wherein the initiator is selected from a group consisting of peroxide and azo materials.

11. A process in accordance with claim 4 wherein the first shell monomer is a diisocyanate.

12. A process in accordance with claim 4 wherein the first shell monomer or oligomer is selected from a group consisting of polymethylene polyphenyl diisocyanate, di phenyl methane di isocyanates and tris(p-isocyanatophenyl)-thiophate.

13. A process in accordance with claim 4 wherein the first shell monomer is a toluene diisocyanate.

14. A process in accordance with claim 4 wherein the second shell monomer is an amine our a dialkylamine.

15. A process in accordance with claim 4 wherein the second shell monomer is selected from the group consisting of ethylenediamine, tetramethylen'ediamine, pentamethylenediamine, hexamethylenediamine, p-phenylenediamine, m-phenylenediamine, 2hydroxy trimethylenediamine, diethylenetriamine, triethylenetetraamine, tetraethylenepentaamine, xylylene diamine, piperazine, and 1 ,3-bis(aminopropyl)piperazine.

16. A process in accordance with claim 4 wherein mixing in the first reaction vessel is accomplished with a scraper blade agitator and a high-shear mixer.

17. A process in accordance with claim 3 or claim 4, wherein the initiator is dissolved in the organic mixture comprised of core monomer and oil-soluble shell monomer by a rotor-stator m;xer operating at a speed of from about 2,000 to about 16,000 revolutions per minute.

18. A process in accordance with claim 5 wherein the magnetite is dispersed in an organic mixture comprised of core monomer and oil-soluble shell monomer with a rotor-stator mixer operating at a range of from about 2,000 to about 16,000 revolutions per minute, and a scraper blade agitator operating at a speed of from about 10 to about 300 revolutions per minute.

19. A process in accordance with claim 18 wherein the agitator moves in the same, or counter direction with respect to the rotor-stator mixer.

20. A process in accordance with claim 4 wherein the surfactant is selected from a group of anionic surfactants, nonionic surfactants, and cationic surfactants.

21. A process in accordance with claim 4 wherein the surfactant is a cellulose ether, a gelatin, or a natural gum.

22. A process in accordance with claim 4 wherein the surfactant is polyvinyl alcohol.

23. A process in accordance with claim 3 wherein emulsification is completed by dispersing the pigment dispersion in the stabilized surfactant solution by a rotor-stator mixer operating at about 2,000 to about 16,000 revolutions per minute, and a scraper blade agitator operating at about 10 to about 300 revolutions per minute.

24. A process in accordance with claim 4 wherein an interfacial polymerization is initiated with the addition of the second shell monomer.

25. A process in accordance with claim 5 wherein an interfacial polymerization is initiated with the addition of the second shell monomer and water.

26. A process in accordance with claim 26 wherein the second reactor is a larger reaction vessel.

27. A process in accordance with any one of claims 3 to 5, wherein the first reaction vessel is of a size of from about 20 to about 800 gallons and the second reaction vessel is of a size of from about 100 to about 4,000 gallons.

28. A process in accordance with claim 4 wherein the suspension of encapsulated particles resulting in the first reaction vessel is transferred to the second vessel and is heated to complete formation of the core.

29. A process in accordance with claim 4 or claim 5 wherein the suspension of encapsulated particles in the second reaction vessel is heated to a temperature of from about 60 to about 140"C to complete formation of the core by free radical polymerization.

30. A process in accordance with claim 4 or claim 5 wherein the encapsuleted toner composition is comprised of a core comprised of a polymer, or polymers, pigment, dye or mixtures thereof, which core is encapsulated in a polymeric shell.

31. A process in accordance with claim 4 wherein the encapsulated toner composition is comprised of a core comprised of a polymer and pigment, which core is encapsulated in a polymeric shell.

32. A process in accordance with claim 4 or claim 31 wherein the pigment is carbon black, magnetite, or mixtures thereof.

33. A process in accordance with claim 4 claim 31 wherein the pigment is cyan, yellow, magenta, red, green, blue, brown, or mixtures thereof.

34. A process in accordance with claim 31 wherein the pigment is selected from the group consisting of Heliogen Blue, Pylam Oil Blue, Pylam Oil Yellow, Pigment Blue, Pigment Violet, Pigment Red, Lemon Chrome Yellow, Bon Red, NOVAperm Yellow FGL, Hostaperm Pink, 2,9-dimethyl-substituted qui nacridone, Dispersed Red, Solvent Red, copper tetra-(octadecyl sulfonamido) phthalocyanine, copper phthalocyanine, diarylide yellow 3,3-dichlorobenzidene acetoacetanilides, a nitrophenyl amine sulfonamide, Dispersed Yellow 2,5-dimethoxy-4 sjlfonanilide phenylazo-4'-chloro-2,5-dimethoxy acetoacetani lide, and Permanent Yellow FGL.

35. A process in accordance with claim 4 wherein the shell is present in an amount of from about 1 to about 30 weight percent of the toner, the core polymer is present in an amount of from about 20 to about 95 weight percent of the toner, and the pigment is present in an amount of from about 1 to about 65 weight percent of the toner.

36. A process in accordance with claim 4 wherein the encapsulated toner resulting has added thereto surface additives.

37. A process in accordance with claim 36 wherein the surface additives are metal salts, metal salts of fatty acids, colloidal silicas, colloidal graphite or carbon blacks.

38. A process in accordance with claim 37 wherein zinc stearate is selected.

39. A process in accordance with claim 36 wherein the additives are present in an amount of from about 0.05 to about 5 weight percent

40. A process in accordance with claim 3 wherein the core polymer is prepared by free radical polymerization.

41. A process in accordance with claim 3 wherein the polymeric shell is prepared by interfacial polymerization.

42. A process in accordance with claim 3 or claim 4 wherein the polymeric shell is a polyurea, a polyurethane, a polyamide, a polyester, a liquid crystalline thermotropic polymer, or mixtures thereof.

43. A process in accordance with claim 42 wherein the shell contains conductive components.

44. A process in accordance with claim 43 wherein the conductive components are comprised of carbon black, graphite, or mixtures thereof.

45. A process in accordance with claim 3 or claim 4 wherein the core monomer for formation of the core polymer is selected from the group consisting of n-butyl acrylate, s-butyl acrylate, isobutyl acrylate, butyl methacrylate, s-butyl methacrylate, isobutyl methacrylate, benzyl acrylate, benzyl methacrylate, propyl acrylate, isopropyl acrylate, hexyl acrylate, cyclohexyl acrylate, hexyl methacrylate, cyclohexyl methacrylate, lauryl acrylate, lauryl methacrylate, pentyl acrylate, pentyl methacrylate, stearyl acrylate, stearyl methacrylate, ethoxypropyl acrylate, ethoxypropyl methacrylate, heptyl acrylate, heptyl methacrylate, methyl butyl acrylate, methylbutyl methacrylate, m-tolyl acrylate, styrene, dodecyl styrene, hexylmethyl styrene, nonyl styrene, tetradecyl styrene, and mixtures thereof.

46. A process in accordance with claim 36 wherein the volume resistivity of the toner is from about 103 to about 108 ohm-cm.

47. A process in accordance with claim 3 or claim 4, wherein for the core there is selected from 1 to about 20 monomers.

48. A process for the preparation of encapsulated toners which comprises mixing in a first mixing vessel equipped with a rotor-stator mixer and a scraper blade agitator, core monomer, shell monomer, polymerization initiator, and pigment to form a pigmented organic mixture; emusifying the aforementioned pigmented mixture in an aqueous phase containing a surfactant, whereby the resulting formed mixture is suspended in the aqueous phase; adding a second shell monomer to the aforementioned suspension to form a capsule shell by interfacial polycondensation of said shell monomers; and subsequently transferring the suspended slurry comprised of dispersed encapsulated particles in a stabilized aqueous phase to a second reactor which is substantially the same size, or of a larger size than the first mixing vessel, and wherein the resulting formed suspension is suspended and heated to complete core formation by free radical polymerization.

49. A process in accordance with claim 1, substantially as described herein.