Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Process of making developer composition
Reexamination Certificate
2001-08-31
2002-11-19
Dote, Janis L. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Process of making developer composition
C430S137100
Reexamination Certificate
active
06482562
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method for the preparation of polymeric particles suitable for use as electrostatographic toner, and more particularly, to a method for the preparation of toner particles of controlled shape in which flocculating agents are employed for controlling morphology of the toner particles.
BACKGROUND OF THE INVENTION
Electrostatic toner polymer particles can be prepared by a process frequently 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 solvent that is immiscible with water. 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 to Nair et al.
U.S. Pat. No. 5,283,151 is representative of earlier work in this field and describes the use of carnauba wax to achieve similar 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, so 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 and optionally a pigment and a charge control agent to form an organic phase; dispersing the organic phase in an aqueous phase comprising a particulate stabilizer and homogenizing the mixture; evaporating the solvent and washing and drying the resultant product.
Unfortunately, this technique requires the use of elevated temperature to dissolve the wax in the solvent and cooling the solution to precipitate the wax. The wax does not stay in solution of ethyl acetate at ambient temperature and as a result it is very difficult to scale up using this methodology.
The shapes of the toner particles have a bearing on the 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 toner particles by means other than the choice of pigment, binder, or charge agent. The shape of the toner particles are modified to enhance the cleaning and transfer properties of the toner.
SUMMARY OF THE INVENTION
In accordance with the present invention, the prior art limitations are effectively obviated by a novel process in which specified flocculating agents are introduced into the aqueous phase of the limited coalescence process. The use of the flocculating agents result in the formation of non-spherical toner particles after the solvent is removed. The toner morphology is controlled independently of the toner composition (i.e. resin, binder matrix, pigment, charge control agent, etc.). The degree of non-sphericity is directly related to the concentration of flocculating agent.
Thus, viewed from one aspect, the present invention is directed to a method for the preparation of electrostatographic toner comprising the steps of:
a) dissolving a polymer material and optionally a pigment and a charge control agent in an organic solvent to form an organic phase;
b) dispersing the organic phase in an aqueous phase comprising a particulate stabilizer and optionally a promoter to form a dispersion and homogenizing the resultant dispersion wherein a flocculating agent is added to the aqueous phase either before or after homogenation;
c) evaporating the organic solvent and recovering a resultant product; and
d) washing and drying the resultant product.
Viewed from another aspect, the present invention is directed to a process for preparing electrophotographic toner by dispersing an organic phase in an aqueous phase to yield a layer of particulate suspension stabilizer on the surface of the polymer. The improvement in the process comprises adding the flocculating agent, particulate stabilizer and promoter to the aqueous phase in the aforementioned limited coalescence process.
It is an advantage of the present invention that elevated temperatures are not needed. It is also an advantage that the flocculating agents are water soluble or water dispersible and so it is relatively easy to scale up production.
These and other features and advantages of the present invention will be better understood taken in conjunction with the following detailed description and claims.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with the present invention, a pigment dispersion is prepared by conventional techniques as, for example, by media milling, melt dispersion and the like. The pigment dispersion, polymer material, a solvent and optionally a charge control agent are combined to form an organic phase. This mixture is permitted to stir overnight and then dispersed in an aqueous phase comprising a particulate stabilizer and optionally a promoter.
The resultant mixture is then subjected to mixing and homogenization. The flocculating agent is added to the aqueous phase either before or after mixing/homogenization. In this process, the particulate stabilizer forms an interface between the organic globules in the organic phase. Due to the high surface area associated with small particles, the coverage by the particulate stabilizer is not complete. Coalescence continues until the surface is completely covered by particulate stabilizer. Thereafter, no further growth of the particles occurs. Accordingly, the amount of the particulate stabilizer is inversely proportional to the size of the toner obtained. The relationship between the aqueous phase and the organic phase, by volume may range from 1:1 to approximately 9:1. This indicates that the organic phase is typically present in an amount from about 10% to 50% of the total homogenized volume.
Following the homogenization treatment, the solvent present is removed by evaporation or boiling, optionally under vacuum, and the resultant product washed and dried.
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. Typical of the solvents chosen for this purpose are chloromethane, dichloromethane, ethyl acetate, vinyl chloride, n-propyl acetate, iso-propyl acetate, trichloromethane, carbon tetrachloride, ethylene chloride, trichloroethane, toluene, xylene, cyclohexanone, 2-nitropropane and the like.
The particulate stabilizer selected for use herein may be selected from among highly cross-linked polymeric latex materials of the type described in U.S. Pat. No. 4,965,131 to Nair et al., or silicon dioxide. Silicon dioxide is preferred. It is generally used in an amount ranging from 1 to 15 parts, by weight, based on 100 parts of the total solids in the toner. The size and concentration of these stabilizers control and predetermine the size of the final toner particles. In other words, the smaller the size and/or the higher the concentration of such particles, the smaller the size of the final toner particles.
Any suitable promoter that is water solub
Ezenyilimba Matthew C.
Regan Michael T.
Smith Dennis E.
Yoon Hichang
Zion Todd C.
Dote Janis L.
Eastman Kodak Company
Konkol Chris P.
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