Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
1999-12-01
2001-04-03
Martin, Roland (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S111400
Reexamination Certificate
active
06210851
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to electrostatographic imaging and in particular to electrostatographic toner materials surface-treated with silica mixtures.
BACKGROUND OF THE INVENTION
Digital electrostatographic printing products are being developed for printing high quality text and half tone images, hence there is a need to formulate electrostatographic toners and developers that produce improved image quality (See Schinichi Sata, et al., STUDY ON THE SURFACE PROPERTIES OF POLYESTER COLOR TONER, IS&T NIP13, 149-152 (1997) and Nash, R. & Muller, R. N. THE EFFECT OF TONER AND CARRIER COMPOSITION ON THE RELATIONSHIP BETWEEN TONER CHARGE TO MASS RATIO AND TONER CONCENTRATION, IS&T NIP 13, 112-10, (1997)). Surface treatment of toners with fumed silica powders, results in toner and developer formulations that have improved powder flow properties and reproduce text and half tone dots more uniformly without character voids (See, Schinichi Sata, et. al., supra). The improved powder fluidity of the toner or developer can however create unwanted print density in white background areas.
The triboelectric charge of electrostatographic developers changes as prints are made, referred to as the “life” of the developer. This instability in charging level is one of the factors that require active process control systems in electrostatographic printers to maintain consistent image-density from print to print.
There is need in the art for developers that are stable with life and that have the advantage of improved electrostatic transfer and higher density capabilities.
SUMMARY OF THE INVENTION
It has been discovered that the problems outlined above can be overcome by blending toner at 2000-3000 RPM with a mixture of either (a) a combination of ultrafine fumed silica and solvents selected from among aliphatic alcohols, diols and triols, alicyclic alcohols, aliphatic ethers, aliphatic esters, cyclic ethers or (b) a combination of ultrafine fumed silica (See, for example, Technical Bulletin Aerosil No. 27, Nippon Aerosil Co. Ltd.) and larger (0.05-30.0 &mgr;m) silica particles which contain solvents selected from among aliphatic alcohols diols or triols, alicyclic alcohols, aliphatic ethers, aliphatic esters, cyclic ethers. (See, for example, Tadahiro Yoneda, Ibaraki et. al., U.S. Pat. No. 5,236,622). Ultrafine fumed silica has a BET surface area between 40 and 400 m
2
/g. Larger silica particles are between 0.05 and 30 &mgr;m. The resulting surface-treated toner contains either (a) 0.1 to 5 weight percent and preferably 0.1 to 2 weight % ultrafine fumed silica (based on the weight of untreated toner) and 0.1-5.0 weight % solvent or (b) 0.1 to 5 weight percent and preferably 0.1 to 2 weight % ultrafine fumed silica (based on the weight of untreated toner) and 0.1 to 5 weight %, preferably 0.5 to 3 weight % larger (0.05-30 &mgr;m) silica particles which contain 0.1-5 weight % solvent. Electrostatographic developers made from this toner exhibit low dust levels and lower charge characteristics when compared to either toners that had no surface treatment at all or toners that were treated with only ultrafine fumed silica. The toners of the invention also exhibit lower charge and dust characteristics when compared to toners surface-treated with a combination of ultrafine filmed silica and ultrafine filmed titanium dioxide.
Hence, the present invention describes an electrostatographic toner comprising toner particles that have been surface treated with a solvent and silica particles having a BET surface area of 40 to 400 m
2
/g; wherein the solvent is selected from aliphatic alcohols, diols and triols, aliphatic ketones, aliphatic esters, cyclic ethers and aliphatic ethers.
Alternatively, the toner of the invention may also be treated with silica particles having a BET surface area of 0.05 to 3.0 mm. Such larger (0.05 to 3.0 mm) silica particles are commercially available already containing the solvent required for the invention. If these are used, no additional solvent is required.
Formulations for surface treated toner have been previously described, but Applicants are aware of no teaching which suggests that a combination of surface treatments, as disclosed herein, can affect the resulting toner performance. Such teaching would be useful in the art.
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Schinichi Sata et al., Study on the Surface Properties of Polyester Color Toner, IS&T NIP 13, 149-152 (1997).
Nash, R. & Muller, R.N., The Effect of Toner and Carrier Composition on the Relationship Between Toner Charge to Mass Ratio and Toner Concentration, IS&T NIP 13, 112-122 (1997).
Technical Bulletin Aerosil®, No. 27, Nippon Aerosil Co., Ltd.
Nippon Aerosil Co., Ltd., (a joint venture of Degussa-Huls AG and Mitsubishi Materials Corp.), Technical Information, 1-1222-0, pp. 2-5 & 10.
Alexandrovich Peter S.
Srinivasan Satyanarayan A.
Eastman Kodak Company
Martin Roland
Wells Doreen M.
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