Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – To produce color reproduction
Reexamination Certificate
2000-08-11
2002-03-12
Goodrow, John (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
To produce color reproduction
C430S126200
Reexamination Certificate
active
06355389
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a full color image forming method for use in electrophotographic image forming apparatus such as copiers, printers and facsimiles, and a color toner and intermediate transfer material useful for the method. More particularly, the present invention relates to an electrophotographic full color image forming method using an intermediate transfer material which receives a full color toner image from one or more image bearing members and transfers the full color toner image to a receiving material to form the full color toner image thereon. In addition, the present invention relates to a method for manufacturing the color toner.
2. Discussion of the Background
Image forming methods and apparatus are well known in which a plurality of color images formed on one or more image bearing members such as photoreceptors are transferred onto an endless image transfer material one by one (i.e., a first transfer process) and all the first transferred color toner images are second transferred onto a receiving material at a time (i.e., a second transfer process). In particular, such an image forming method using an intermediate transfer material is used for a full color image forming apparatus in which an original image, which is separated into a plurality of color images, is reproduced by overlaying color toner images such as a black, cyan, magenta, and yellow toner image.
In such an image forming method and apparatus, a problem which occurs is that image omissions, which look as if an image is eaten by worms, are observed in resultant toner images formed on a receiving material. This is because omissions are formed on toner images formed in the first and second transfer process. In order to avoid such a problem, i.e., in order to improve transferability of toner images, the following techniques have been proposed:
(1) Techniques concerning surface roughness of intermediate transfer material
In attempting to avoid image omissions, Japanese Laid-Open Patent Publication No. 3-242667 discloses a technique which uses an intermediate transfer material which is made of an elastomer and which has a specific surface roughness to improve adhesion of the intermediate material with a receiving material.
In addition, Japanese Laid-Open Patent Publications Nos. 63-194272, 4-303869, 4-303872 and 5-193020 have disclosed techniques which use an intermediate transfer material which has a specific surface roughness to improve adhesion of the intermediate material with a receiving material.
When toner images are transferred in the first and second transfer process, a transfer bias voltage is typically applied. Therefore, discharging tends to occur between an image bearing member and an intermediate transfer material and between the intermediate transfer material and a receiving material. If the intermediate transfer material has sharp projections on the surface thereof, the electric field applied to toner images on the projected portions of the intermediate transfer material are greater than that applied to toner images on the recessed portions of the intermediate transfer material.
This reason will be explained in detail referring to FIG.
1
. Numeral
1
denotes an electrode having a smooth surface. Numeral
2
denotes an electrode having a serrated surface. The electrode
1
and electrode
2
face each other with a gap (Gp) therebetween. Numeral
3
denotes a projected portion of the electrode
2
, and numeral
4
denotes a recessed portion of the electrode
2
. When a transfer bias voltage is applied to the electrodes
1
and
2
, discharging mainly occurs at gaps Gp
1
, Gp
1
′ a and Gp
1
″ formed between the electrode
1
and the projected portions
3
because the electric field at the gaps Gp
1
, Gp
1
′ and Gp
1
″ is relatively high compared to any other gaps formed between the electrodes
1
and
2
including gaps Gp
2
and Gp
2
′. This is because the distance at the gaps Gp
1
, Gp
1
′ and Gp
1
″ is the shortest. This is true for the case in which the electrode
2
is replaced with an intermediate transfer material and the electrode
1
is replaced with a receiving material or an image bearing member.
When toner images on the intermediate transfer material having a rough surface are transferred, toner particles positioned on the projected portions are present in a relatively large electric field compared to toner particles positioned on the recessed portions. In addition, the toner particles on the recessed portions have a relatively large adhesion compared to the toner particles positioned on the projected portions. Therefore, the toner particles on the projected portions are transferred relatively easily compared to the toner particles on the recessed portions.
FIGS. 2A
to
2
D are schematic views illustrating several different cases in which a toner particle (T) adheres to an intermediate material having a serrated surface. In
FIG. 2A
, a toner particle T contacts the flat surface of the intermediate transfer material. In
FIG. 2B
, a toner particle T contacts a projected portion of the intermediate transfer material. In
FIGS. 2C and 2D
, a toner particle T contacts a recessed portion of the intermediate transfer material. As can be understood from
FIGS. 2A
to
2
d
, the toner particles as shown in
FIGS. 2C and 2D
have a relatively large contact area with the intermediate transfer material compared to the toner particles as shown in
FIGS. 2A and 2B
. In these cases, if the projected portions and the recessed portions are made of the same material, there is relatively large van der Waals force between the toner particles and the recessed portions (i.e., in the cases as shown in
FIGS. 2C and 2D
) compared to the cases as shown in
FIGS. 2A and 2B
. Therefore, the adhesion between the toner particle and the recessed portion is greater than that between the toner particle and the plat or projected portion. The toner on the recessed portions tends not to be easily transferred, resulting in occurrence of omissions in the resultant toner images.
Therefore, it is preferable that the intermediate transfer material has a relatively smooth surface such that the intermediate transfer material does not cause omissions in the transferred toner images. This is also true for the image bearing member. Namely, it is preferable that the image bearing member such as a photoreceptor has a relatively smooth surface such that the photoreceptor does not cause omissions in the transferred toner images. It is well known to prepare photoreceptor drums including Se as a photosensitive material having a relatively smooth surface to impart good toner transferability to the photoreceptor drum.
However, it is hard to prepare an intermediate transfer material having such a smooth surface. Therefore, it is hard to avoid the omission problem.
(2) Techniques concerning difference in feeding speed between intermediate transfer material and image bearing member and between intermediate transfer material and receiving material
Japanese Laid-Open Patent Publication No. 2-213882 discloses a technique such that the feeding speeds of an intermediate transfer material and an image bearing member are specified to improve toner transferability and to avoid image omissions.
This technique will be explained referring to the first image transfer process (i.e., a toner image transfer process from an image bearing member to an intermediate transfer material).
When the intermediate transfer material has the same feeding speed as the image bearing member, it is needed to apply an electric force (i.e., a transfer electric field) to the toner image such that the toner image on the image bearing member, which adheres on the image bearing member due to the adhesion therebetween, is transferred to the intermediate transfer material only by the transfer electric field.
On the contrary, when the intermediate transfer material has a feeding speed different from that of the image bearing member, a mechanical force caused by th
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