Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-09-25
2002-07-09
Rodee, Christopher (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S108600, C430S108700, C430S109400, C430S111400
Reexamination Certificate
active
06416916
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to toners, developers containing the toners, and a method of forming images with the developers utilizing a magnetic brush development system. More in particular, the invention relates to toners and developers having carefully controlled properties to provide superior print quality, while substantially avoiding/eliminating depletion defects, when used in developing electrostatic images with a magnetic brush development system.
2. Description of Related Art
U.S. Pat. No. 5,545,501 describes an electrostatographic developer composition comprising carrier particles and toner particles with a toner particle size distribution having a volume average particle size (T) such that 4 &mgr;m≦T≦12 &mgr;m and an average charge (absolute value) pro diameter in femtocoulomb/10 &mgr;m (C
T
) after triboelectric contact with said carrier particles such that 1 fC/10 &mgr;m≦C
T
≦10 fC/10 &mgr;m characterized in that (i) said carrier particles have a saturation magnetization value, M
sat
, expressed in Tesla (T) such that M
sat
≧0.30 T, (ii) said carrier particles have a volume average particle size (C
avg
) such that 30 &mgr;m≦C
avg
≦60 &mgr;m, (iii) said volume based particle size distribution of said carrier particles has at least 90% of the particles having a particle diameter C such that 0.5 C
avg
≦C≦2 C
avg
, (iv) said volume based particles size distribution of said carrier particles comprises less than b % particles smaller than 25 &mgr;m wherein b=0.35×(M
sat
)
2
×P with M
sat
: saturation magnetization value, M
sat
, expressed in T and P: the maximal field strength of the magnetic developing pole expressed in kA/m, and (v) said carrier particles comprise a core particle coated with a resin coating in an amount (RC) such that 0.2% w/w≦RC≦2% w/w. See the Abstract. This patent describes that such developer achieves images of offset-quality in systems in which a latent image is developed with a fine hair magnetic brush.
Xeikon NV currently supplies the market with developers for magnetic brush development systems. These developers are comprised of toner and carrier particles. The toner is believed to be comprised of pigments and two polyesters, a propoxylated bisphenol-A, hexanedioic acid, isophthalic acid polyester and an ethoxylated bisphenol-A ethylene glycol, isophthalic acid, terephthalic acid polyester, while the carrier is believed to be comprised of an iron-zinc-copper oxide core coated with a crosslinked siloxane. However, such developers suffer from lower triboelectric stability and image quality stability, and insufficient color gamut.
Co-pending U.S. patent application Ser. No. 09/520,360, filed Mar. 7, 2000 now U.S. Pat. No. 6,319,647 and incorporated by reference herein in its entirety, describes a toner that performs better than the Xeikon NV toners. The toner contains at least one binder, at least one colorant, and preferably one or more external additives of one or more of silicon dioxide powder, untreated titanium dioxide powder and zinc stearate (in amounts of at least 0.1 percent by weight of the toner). The toner particles, following triboelectric contact with carrier particles, exhibit a charge per particle diameter (Q/D) of from 0.6 to 0.9 fC/&mgr;m and a triboelectric charge of from 20 to 25 &mgr;C/g. The toner particles preferably have an average particle diameter of from 7.8 to 8.3 microns. The toner is combined with carrier particles to achieve a developer, the carrier particles preferably having an average diameter of from 45 to 55 microns and including a core of ferrite substantially free of copper and zinc coated with a coating comprising a polyvinylidenefluoride polymer or copolymer and a polymethyl methacrylate polymer or copolymer. The carrier particles may be comprised of ferrite particles, which are preferably substantially free of both zinc and copper as described in co-pending U.S. patent application Ser. No. 09/444,701, filed Nov. 24, 1990 now U.S. Pat. No. 6,143,456, incorporated herein by reference in its entirety.
However, the toners designed to date for use in imaging devices employing a magnetic brush development system exhibit some degree of image depletion defect (characterized by insufficient toner being deposited on an image forming medium in an area of the image being reproduced) during operation of the device. Specifically, under conditions of high area coverage of toner in an imaged area (typically greater than 50% of a page covered by a single separation image), an area of decreased toner mass in an image can occur, running parallel to the process direction of the paper in the print engine. Generally this decreased toner mass, or image density depletion, will become more pronounced as more prints are made, increasing in both the spatial extent of the defect and in the difference in developed toner mass (with respect to the target developed mass) within the defect area degree of depletion. In extreme cases, the image may be completely absent in a band in the xerographic process direction which encompasses one third to one half of the intended image. What is still desired is a set of developers comprised of toners and carriers that possess not only high stable triboelectric performance, but also do not exhibit image depletion defects when used to develop a latent image on the surface of a photoreceptor with a magnetic brush.
SUMMARY OF THE INVENTION
It is one object of the present invention to provide a set of color toners and developers that substantially avoid/eliminate the occurrence of image depletion defects while maintaining high and stable triboelectric performance, particularly when used in developing images with a magnetic brush.
It is a further object of the invention to obtain toners and developers having superior triboelectric and image quality stability.
It is a still further object of the invention to form images utilizing a magnetic brush with the developers of the invention, which images have superior quality compared to conventional magnetic brush developers and which images are substantially free of image depletion defects.
These and other objects are achieved in the present invention, in which it has been determined that the presence of higher amounts of zinc stearate as an external additive to a toner results in the developer having poor developer flow, which in turn results in the occurrence of image depletion defects.
In one aspect of the invention, the invention pertains to toner particles containing at least one binder, at least one colorant, and an external additive package comprised of zinc stearate and at least one of silicon dioxide or titanium dioxide, wherein the amount of zinc stearate is limited to no more than about 0.10 percent by weight of the toner. It has been surprisingly found that when the amount of zinc stearate is so limited, a developer formed from the toner exhibits excellent triboelectric charging and stability and excellent developer flow. When the developer is used in a magnetic brush development system, consistent, high quality copy images are formed substantially without any depletion defects over time.
In a further aspect of the invention, the invention relates to a particular toner design comprised of toner particles comprised of at least one binder resin comprising a propoxylated bisphenol A fumarate resin, at least one colorant comprising pigment selected from the group consisting of cyan, yellow, magenta and black, wherein if the pigment is cyan, magenta or black, the binder resin has a gel content of from about 5 to about 18 percent by weight of the binder resin and if the pigment is yellow, the binder resin contains no gel, and an external additive package comprised of zinc stearate and at least one of silicon dioxide or titanium dioxide, wherein the zinc stearate is present in an amount of no more than about 0.10 percent by weight of the toner.
In a still further aspect of the invention, the toner is combined with carrier particles to form a developer possessing
Chung Joo T.
DeBarr Jeffrey L.
DeYoung, Jr. Morris M.
Giannetto Brian S.
Gutman Edward J.
Palazzo Eugene O.
Rodee Christopher
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