Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2001-04-26
2003-01-07
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...
C430S108600, C430S045320, C428S405000
Reexamination Certificate
active
06503676
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a toner used for a developer for developing an electrostatic latent image formed by an image forming method such as electrophotography, electrostatic recording methods and electrostatic printing methods. In addition, the present invention relates to an external additive for use in the toner, and to an image forming method using the toner.
2. Discussion of the Related Art
Developers used for developing an electrostatic latent image formed by an image forming method such as electrophotography, electrostatic recording methods and electrostatic printing methods are classified into two component developers consisting of a carrier and a toner, and one component developers which include only a toner and do not include a carrier. The one component developers are also classified into one component magnetic developers and one component non-magnetic developers. In addition, toners are also classified into positively-charged toners and negatively-charged toners.
In order to improve the fluidity and charge properties of toner, an inorganic powder such as metal oxides is typically included in a toner while the inorganic powder is mixed with the toner particles. Such an inorganic powder is called as an external additive. As the external additive, silicone dioxide (i.e., silica), titanium dioxide (titania), aluminum oxide (alumina), zinc oxide, magnesium oxide, cerium oxide, iron oxide, copper oxide, tin oxide and the like metal oxides are known.
In order to improve the hydrophobic property of the surface of such inorganic powders and the charge properties thereof, various methods have been proposed. In particular, methods in which silica powders are reacted with an organic silicon compound such as dimethyldichlorosilane, hexamethylenedisilazane and silicone oils to substitute the silanol groups on the surface of the silica powders with an organic group are popularly used.
Among these organic silicon compounds, silicone oils are preferable as the hydrophobizing agent because of having good hydrophobic property and low surface energy, thereby imparting good transferability to the resultant toner. Therefore various proposals regarding silicone oils have been made. For example, Japanese Laid-Open Patent Publications Nos. 7-271087 and 8-29598 have disclosed developers which include an additive having a specific carbon content and a specific silicone oil content to improve the charge stability of the resultant developer under high humidity conditions.
However, the developers including such additives including a silicone oil have the following drawbacks:
(1) the resultant images tend to have background fouling, and omissions in the edge parts and/or center parts of character images, line images and dot images, which omissions are caused by unsatisfactory image transfer from an image bearing member to a receiving material; and
(2) when an image is formed on a receiving material having a rough surface, the image tends to have omissions which are typically observed in the recessed portions of the surface of the rough receiving material.
In attempting to remedy the drawbacks, Japanese Laid-Open Patent Publication 11-212299 discloses an external additive in which a specific amount of a liquid silicone oil is included in a particulate inorganic material. However, the drawbacks cannot fully remedied.
On the other hand, currently, a need exists for copiers and printers which can produce images having qualities as high as those of the prints produced by offset printing methods at a recording speed as high as that of the offset printing methods. When images are formed on only one side of receiving material, fairly high speed copying or printing can be achieved. However, when images are formed on both sides of a recording paper, the copying or printing speed is much slower than that in the one-side printing. In particular, when a double-sided copy is produced by forming and fixing a toner image on one side of a receiving material and then forming and fixing another toner image on the other side of the receiving material, the recording time is about twice the recording time needed for producing a one-side copy.
Therefore, an image forming method, in which toner images are continuously transferred on both sides of a receiving material by two image bearing members which are arranged at different positions in the vertical direction as shown in FIG.
1
and the thus prepared double-sided toner images are then fixed at the same time has been proposed.
The image transfer method of the image forming method is classified into two types with respect to the method for driving the image bearing members. One of the types is to drive the image bearing members using a motor or a belt (this method is hereinafter referred to as a motor-drive method). The other is to drive the image bearing members using friction between the image bearing members and a receiving material without providing a rotation mechanism (hereinafter referred to as a paper-drive method).
In the motor-drive method, it is difficult to control the timing of transferring toner images on both sides of a receiving material. In order to accurately transfer images on both sides of a receiving material, the image forming apparatus has to have precise and complex mechanisms, resulting in increase of manufacturing costs and enlargement in size of the image forming apparatus. In particular, in multiple color image forming apparatus a problem of difference in positions between the transferred color toner images (hereinafter referred to as color image offset), in which color toner images constituting a color image do not have accurate positions in one side of a receiving material, occurs as well as a problem of variation of transfer timing of a color image (hereinafter referred to as transfer timing variation), in which an entire color image is formed on an undesired position of a receiving material. The costs of providing a mechanism for preventing these problems are much greater than those needed for monochrome image forming apparatus.
The paper-drive method will be explained referring to
FIG. 1
which illustrates a typical embodiment of a paper-drive type image transfer mechanism.
In this method, a receiving material
1
is contacted with an image bearing member
2
a
on which a toner image
5
a
is formed to drive the image bearing member
2
a
while the toner image
5
a
is transferred on one side of the receiving material
1
by a transfer member
3
a.
In addition, the receiving material
1
is contacted with another image bearing member
2
b
on which a toner image
5
b
is formed to drive the image bearing member
2
b
while the toner image
5
b
is transferred on the other side of the receiving material
1
by a transfer member
3
b.
In the paper-drive method, image bearing members are driven by friction and/or electrostatic force between the image bearing members and a receiving material. Namely, the image bearing members are driven by the receiving material, and therefore, it is relatively easy to time the development and transfer operations with the feeding operation of the receiving material compared to the former method, and thereby the problems such as the color image offset and transfer timing variation hardly occur. Therefore the image forming apparatus can be simplified.
However, since the receiving material is contacted with the image bearing member, toner images sandwiched by the receiving material and the image bearing member receives a large pressure by the receiving material. Therefore the adhesion of the toner images to the image bearing member increases, and thereby omissions tend to be produced in the resultant transferred toner images, particularly in edge parts or center parts of the transferred character images, line images and dot images.
In attempting to solve this image omission problem, toners including an additive such as particulate inorganic materials e.g., silica and titanium oxide, have been proposed. However, such toners cannot fully solve t
Kondou Tomio
Sugiura Hideki
Suguro Yoshihiro
Tosaka Hachiroh
Uchinokura Osamu
Cooper & Dunham LLP
Goodrow John
Ricoh & Company, Ltd.
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