Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2001-09-20
2003-05-06
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S108700
Reexamination Certificate
active
06558865
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a toner composition used, for example, as dry toner for developing an electrostatic latent image.
2. Description of Related Art
A toner using a binder resin as the major component and containing a pigment, a charge controlling agent, an external additive or the like has conventionally been used as a toner for a printer employing an electrostatic latent image developing system.
For example, in a printer employing an electrostatic latent image developing system as shown in
FIG. 5
, this type of toner T may be fed off from a tank
1
by a supply roller
2
. After a toner layer formed on a developing roller
3
is made uniform by a blade
7
, the toner T is applied to the surface of a photoconductor
4
.
The surface of the photoconductor
4
is charged so as to correspond to a certain image pattern by a laser scanner unit
5
and a corona unit
6
, while the toner T is charged to a polarity opposite to that on the surface of the photoconductor
4
. The toner T is therefore attracted onto a portion charged on the photoconductor
4
, but not to portions which are not charged. Namely, the toner T is dispersed so as to correspond to the certain image pattern (charge pattern) on the surface of the photoconductor
4
.
A medium
9
such as paper or the like is then pressed against the photoconductor
4
via an image transfer roller
8
so that the toner image may be transferred onto the medium
9
. Heat is then applied to the toner T by a fusing roller
10
so that it is melted and fused on the surface of the medium, thus accomplishing printing of the image.
To ensure printing of high image quality using the aforementioned method, it is necessary to prevent a fog (a symptom noted on the surface of a photoconductor and a recording medium in which toner sticks to a location to which it should not stick) and a blur (a symptom noted on a printed medium in which breaks of toner occur).
To prevent a fog, toner must be sufficiently charged so that an attraction force (a Coulomb force) acting between the toner and a charged portion on a surface of the photoconductor (to which toner is supposed to stick) becomes strong.
It is also necessary to make the level of charge of toner uniform, thereby minimizing a ratio of part of toner that is not sufficiently charged or that is charged to an opposite polarity.
It has therefore been conventionally practiced that a charge controlling agent and an external additive are added to the toner to increase the level of charge of toner and that a conductive titanium oxide is used as the external additive to make the level of charge of toner uniform.
To prevent a blur, on the other hand, an adequate amount of toner must be supplied smoothly to different components of the printer (e.g., the supply roller, the developing roller, and the photoconductor).
To accomplish it, it is necessary to increase fluidity of toner so as not to allow toner particles to be coagulated easily. To do that, it has been conventionally practiced that a hydrophobic silica is externally added to the toner.
Increasing the level of charge of toner by adding a charge controlling agent or an external additive and making the level of charge uniform by adding a conductive titanium oxide have not been sufficient to ensure high print image quality.
That is, even with these measures taken, there are left toner particles that are not sufficiently charged or toner particles that are charged to an opposite polarity (faultily charged toner particles) among the toner particles charged. The faultily charged toner particles are attracted by a Coulomb force and accumulated onto the surface of the developing roller. From the surface of the developing roller, the faultily charged toner particles are transferred to the surface of the photoconductor, thus sticking to a portion on the surface of the photoconductor, to which they are not supposed to stick, resulting at times in a fog.
Especially when running a continuous durability print cycle to print large numbers of pages, the level of charge of toner as a whole gradually drops to increase the number of faultily charged toner particles as the printer turns out more printed pages. This significantly increases the amount of faultily charged toner particles piled up on the surface of the developing roller, thus aggravating the fog problem.
Another problem that has conventionally been common is that a hydrophobic silica or other substance that is externally added to enhance fluidity of toner is separated from the toner and sticks to the photoconductor and a recording medium and the external additive prevents toner from sticking to the photoconductor and the recording medium, resulting in a blur on the printed image.
SUMMARY OF THE INVENTION
In view of the foregoing, it is therefore an object of the invention to provide a toner composition that ensures printing of clear-cut images of high quality without producing a fog or a blur.
To achieve the foregoing object, a toner composition according to one aspect of the invention has a shape of a particle containing a binder resin, and a surface of the toner composition is coated with an external additive comprising a hydrophobic silica and a conductive titanium oxide and, at the same time, the particle making up the toner composition has an average particle diameter by volume of 7 &mgr;m or less and an external additive coating ratio of 70% or less and a coagulation level indicating the degree with which each of toner particles making up the toner composition is coagulated each other is 10% or less.
<1> Effect of Preventing a Fog
i) A particle making up the toner composition according to the invention (hereinafter referred to as the toner particle) has a small average particle diameter by volume of 7 &mgr;m or less, which results in a high ratio of a surface area of the toner particle to a weight thereof. This makes it possible to inject a larger amount of the charge controlling agent to the surface of the toner particle with respect to the weight thereof, allowing the level of the charge per unit weight of the toner particle to be made high.
Since the surface of the toner composition according to the invention is covered with the conductive titanium oxide, a charge can be transferred by way of the conductive titanium oxide between toner particles, contributing to smaller variations in the level of charge among different toner particles.
In, for example, a printer that employs a system of charging toner particles by letting a blade and toner particles on a surface of a developing roller rub together as shown in
FIG. 5
, it is difficult to allow all toner particles to be in uniform contact with the blade, which tends to cause variations in the level of charge to become greater among different toner particles, which is particularly true when the toner particles become small. Thanks to the effect of the conductive titanium oxide, the toner composition according to the invention allows toner particles to be uniformly charged.
Namely, in the toner composition according to the invention, the average particle diameter by volume of the toner particle is made small and, at the same time, the surface of the toner composition is covered with the conductive titanium oxide. This allows the level of charge per unit weight of the toner composition to be higher and, at the same time, the distribution of the level of charge to be narrower.
When the toner composition according to the invention is charged, there are contained very little toner particles that are not sufficiently charged or toner particles that are charged to an opposite polarity, and there is no chance of faultily charged toner particles being accumulated on, for example, the developing roller. A fog is not, therefore, likely to result from the toner composition according to the intention.
Particularly when printing a large number of pages continuously (in a continuous durability print cycle), the charge controlling agent and the external additive made of hydrophobic silica may
Endo Akira
Ohira Hideo
Ohta Mitsuru
Brother Kogyo Kabushiki Kaisha
Goodrow John
Oliff & Berridg,e PLC
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