Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Process of making developer composition
Reexamination Certificate
2001-03-22
2002-07-09
Rodee, Christopher (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Process of making developer composition
C523S339000
Reexamination Certificate
active
06416921
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to polymeric powders suitable for use as electrostatographic toners and, more particularly, to a method for forming electrostatographic toner particles comprising a quaternary ammonium tetraphenylborate salt and a polymeric phosphonium salt that operate to control the morphology of the toner particles.
BACKGROUND OF THE INVENTION
Electrostatic toner polymer particles are commonly prepared by a process referred to as “limited coalescence”. In this process, polymer particles having a narrow size distribution are obtained by forming a solution of a polymer in a solvent that is immiscible with water, dispersing the solution so formed in an aqueous medium containing a solid colloidal stabilizer and removing the solvent by evaporation. The resultant particles are then isolated, washed and dried.
In the practice of this technique, toner particles are prepared from any type of polymer that is soluble in a water-immiscible solvent. Thus, the size and size distribution of the resulting particles can be predetermined and controlled by the relative quantities of the particular polymer employed, the solvent, the quantity and size of the water insoluble solid particulate suspension stabilizer, typically silica or latex, and the size to which the solvent-polymer droplets are reduced by agitation.
Limited coalescence techniques of this type have been described in numerous patents pertaining to the preparation of electrostatic toner particles because such techniques typically result in the formation of toner particles having a substantially uniform size distribution. Representative limited coalescence processes employed in toner preparation are described in U.S. Pat. Nos. 4,833,060 and 4,965,131, the disclosures of which are incorporated herein by reference.
The shape of the toner particles has a bearing on electrostatic toner transfer and cleaning properties. Thus, for example, the transfer and cleaning efficiency of toner particles have been found to improve as the sphericity of the particles are reduced. Thus far, workers in the art have long sought to modify the shape of the evaporative limited coalescence type toners independently of pigment, binder, or charge agent choice in order to enhance the cleaning and transfer properties of the toner.
U.S. Pat. No. 5,283,151 is representative of the prior art in this field and described the use of carnauba wax to modify toner morphology. The method comprises the steps of dissolving carnauba wax in ethyl acetate heated to a temperature of at least 75° C. and cooling the solution, resulting in the precipitation of the wax in the form of very fine needles a few microns in length; recovering the wax needles and mixing them with a polymer material, a solvent, a charge control agent, and, optionally, a pigment to form an organic phase; dispersing the organic phase in an aqueous phase comprising a particulate stabilizer and homogenizing the mixture; and evaporating the solvent and washing and drying the resultant product.
This technique, however, requires the use of elevated temperature to dissolve the wax in the solvent, followed by cooling the solution to precipitate the wax. The wax does not stay in solution in ethyl acetate at ambient temperature, which makes scale-up of this method very difficult.
Tetraphenylborate quaternary salts have been employed as charge control agents for electrophotographic toners. For example, U.S. Pat. Nos. 5,194,472 and 5,516,616 disclose quaternary ammonium salt charge control agents, including tetraphenylborates, that contain ester moieties. U.S. Pat. Nos. 5,075,190 and 5,041,625 disclose mono- and bis-pyridinium tetraphenylborate charge control agents, and U.S. Pat. No.5,482,741 describes a process for absorbing a charge control agent such as potassium tetraphenylborate onto flow aid particles. Also, JP 91-41021 discloses an image-forming method using a toner containing various kinds of tetraarylborates as charge control-agents.
Polymeric phosphonium salts are known as components of xerographic or electrostatic toner particles. For example, both U.S. Pat. Nos. 4,837,394 and 4,855,396 both disclose toner particles in which quaternary phosphonium salt moieties are covalently bound to polyesters.
Thus, although both tetraphenylborate quaternary ammonium salts and polymeric phosphonium salts have been individually employed in toner particles, their use in combination as shape control agents in the limited coalescence process for making toner particles is not known.
SUMMARY OF THE INVENTION
The present invention is directed to a process for forming non-spherical toner particles by limited coalescence comprises: forming an organic phase comprising a polymeric material, a pigment, a quaternary ammonium tetraphenylborate salt, a phosphonium salt polymer formed by condensation of at least one dicarboxylic acid or dicarboxylic ester monomer with at least one diol monomer, at least one of the acid or ester monomers including a triarylphosphonium salt group, and a water-immiscible liquid; dispersing the organic phase in an aqueous phase containing a solid colloidal stabilizer; forming a suspension of small droplets of the organic phase in the aqueous phase by high shear agitation; removing the water-immiscible liquid from the small droplets, thereby forming a suspension of small solid particles in the aqueous phase; and separating and drying the solid particles, which are toner particles having a non-spherical shape.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a method for the preparation of polymeric powders suitable for use as electrostatographic toner, and more particularly, to a method for preparation of toner particles of controlled shape and charge in which certain quaternary ammonium tetraphenylborate salts, in combination with a phosphonium salt polymer formed by condensation of at least one dicarboxylic acid or dicarboxylic ester monomer with at least one diol monomer, wherein at least one of the acid or ester monomers includes a triarylphosphonium salt group, are introduced into the organic phase of a limited coalescence process to control the morphology of the particles and to function as charge control agents.
In accordance with the present invention, the pigment can be provided as a dispersion, prepared by conventional techniques as, for example, media milling, melt dispersion and the like. The pigment dispersion, polymeric material, quaternary ammonium tetraborate salt, water-immiscible solvent, and, optionally, an additional charge control agent are combined to form an organic phase in which the pigment concentration ranges from about 1 to about 40 weight percent, preferably, about 4 to about 20 weight percent, based upon the total weight of solids. The optional charge control agent is employed in an amount up to about 10 weight percent, preferably about 0.2 to about 5 weight percent, based on the total weight of solids. Suitable charge control agents are disclosed, for example, in U.S. Pat. Nos. 3,893,935, 4,323,634, and 4,079,014, and British Patent No. 1,420,839.
The solvents chosen for use in the organic phase steps may be selected from among any of the well-known solvents capable of dissolving polymers of the type employed herein. Typical of the solvents chosen for this purpose are dichloromethane, ethyl acetate, methyl ethyl ketone, and the like.
The organic phase is permitted to stir, typically overnight, and then dispersed in an aqueous phase comprising a particulate stabilizer and, optionally, a promoter. The aqueous phase may have a pH of about 2 to about 7 but preferably is buffered to a pH of about 4.
The particulate stabilizer may be selected from silicon dioxide or from highly cross-linked polymeric latex materials of the type described in the previously mentioned U.S. Pat. No. 4,965,131. Silicon dioxide is preferred and is generally used in an amount ranging from about 1 to about 15 weight percent, based on the total solids employed. The size and concentration of the stabilizer particles determine the size of the final to
Ezenyilimba Matthew C.
McGrath Gretchen S.
Wilson John C.
Heidelberg Digital L.L.C.
Jaeckle Fleischmann & Mugel LLP
Rodee Christopher
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