Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Process of making developer composition
Reexamination Certificate
1999-11-30
2001-03-13
Goodrow, John (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Process of making developer composition
C430S106100, C430S110100
Reexamination Certificate
active
06200722
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to electrophotographic imaging and in particular to a formulation and method for making electrophotographic toner materials surface treated with metal oxides.
BACKGROUND OF THE INVENTION
Digital electrophotographic printing products are being developed for printing high quality text and half tone images. Thus, there is a need to formulate electrophotographic toners and developers that have improved image quality. Surface treatment of toners with fine metal oxide powders, such as fumed silica or titania, 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, for example, Schinichi Sata, et al. Study On The Surface Properties Of Polyester Color Toner, IS&T NIP13, 149-152 (1997). The improved powder fluidity of the toner or developer can, however, create unwanted print density in white image areas.
The triboelectric charging level of electrophotographic developers is known to change as prints are made. See, Nash, R. and 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, 112-120, (1997). This instability in charging level is one of the factors that require active process control systems in electrophotographic printers in order to maintain consistent image density from print to print. Toners with a low triboelectric charge level produce prints with high reflection optical density; toners with a high triboelectric charge level produce prints with a low reflection optical density. A toner with a constant triboelectric charge level would consistently produce prints with the same reflection optical density.
What is needed in the art are toners with more stable triboelectric charge levels which decrease the incidence of dusting (defined below).
SUMMARY OF THE INVENTION
The present invention describes a method of using metal oxides to surface-treat toner particles thereby making toners with more stable triboelectric charge. These toners form less low-charge toner dust and image background, and produce images with fewer image voids. The present invention describes a method to apply the metal oxide to the toner surface. Formulations for surface treated toners have been described in U.S. Pat. Nos. 5,272,040; 4,513,074; 4,623,605; and 4,933,251, but there is no teaching that a process of applying the surface treatment could cause embedment of metal oxide particles below the surface of the toner particles and affect the performance of the toner. Toners made by the process described herein have lower levels of voids in printed characters and a lower background level in the non image areas of the print. “Character voids” are image defects where a complete letter character is not formed, there are areas where toner has not been deposited resulting in white spots in the character. “Background” is a image defect where toner is deposited in the white portion of a print, causing the print to look less sharp and white print areas to look slightly gray.
The present invention also discloses that the atomic percent of elemental metal in the metal oxide on the toner particle surface:the total weight percent of metal oxide in the toner formulation (herein referred to as “bulk metal oxide”) affects the triboelectric properties and imaging characteristics of the toner. The present invention also discloses that within this preferred ratio range, toner fluidity and image quality are improved. The examples of the present invention demonstrate that there is a preferred concentration range for metal oxide on the surface of the toner particles and that toners falling within the preferred range provide the best image quality. The concentration of metal oxide on the surface of the toner particle is controlled by the process used in mixing and blending the toner particles with the fine metal oxide powder.
Hence, the present invention discloses a process for making an electrophotographic toner comprising:
(a) uniformly mixing a metal oxide selected from titanium dioxide and silicon dioxide with toner particles to form a mixture having 5 to 15 weight percent metal oxide; preferably 8 to 12 weight percent metal oxide;
(b) mixing the product of step (a) with additional toner particles at a mixing intensity ≧500,000 (cm/minute) minute;
wherein in the mixed product of (b) the metal oxide is 0.1 to 5.0 weight percent of the mixed product; and the toner particles have on their surfaces a metal oxide concentration in a ratio of 1.0-3.0:1.0 with respect to titanium dioxide on the surface of the toner particles:total titanium dioxide in the mixed product; and a ratio of 10.0-25.0:1.0 with respect to silicon dioxide on the surface of the toner particles:total silicon dioxide in the mixed product.
The present invention provides a method for making toners that produce images having a low level of character voids and reduced background levels in the white image areas. Further, replenishment toners create lower levels of airborne toner particles when mixed with developers, resulting in cleaner printer operation.
REFERENCES:
patent: 4513074 (1985-04-01), Nash et al.
patent: 4546060 (1985-10-01), Miskinis et al.
patent: 4623605 (1986-11-01), Kato et al.
patent: 4933251 (1990-06-01), Ichimura et al.
patent: 5212037 (1993-05-01), Julien et al.
patent: 5272040 (1993-12-01), Nakasawa et al.
patent: 5350657 (1994-09-01), Anno et al.
patent: 6010814 (2000-01-01), Kotsugai et al.
Schinichi Sata, et al. Study on the Surface Properties of Polyester Color Toner, IS&T NIP 13, 149-152 (1997).
Nash, R. and 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, 112-120, (1997).
Fields Robert D.
Srinivaan Satyanarayan A.
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