Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
1999-05-07
2001-06-05
Pendegrass, Joan (Department: 2852)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
C399S237000
Reexamination Certificate
active
06243118
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an electrostatic recording apparatus for forming an electrostatic latent image on a recording media and then developing it using a liquid toner, and an image density control method thereof.
BACKGROUND ART
An electrostatic recording apparatus obtains an image by forming an electrostatic latent image on a recording medium at an electrostatic recording head and then developing the electrostatic latent image by use of a liquid toner at a development processing unit. The recording medium is a special paper having functions of creating discharge in cooperation with the electrostatic recording head to accumulate the generated static electricity, and is an opaque paper, a tracing paper, a clear film, a synthetic paper and so forth. The recording medium may typically be manufactured by applying the conductive processing to a substrate paper used as the base and then coating it with a nonconductive dielectric layer. The mechanism of one typical electrostatic recording apparatus will be explained with reference to
FIG. 1
below.
FIG. 1
is a diagram showing an electrostatic recording head and development processing unit of an electrostatic recording apparatus. A recording medium
1
wound into a roll-like shape is transported in a direction of arrow “A” in the drawing, so that it is transported to an electrostatic recording head
2
and a development processing unit
3
. The electrostatic recording head
2
consists essentially of needle-like main electrodes (to be referred to as “nibs” hereinafter) laid out at the density equivalent to the resolution, and auxiliary electrodes provided in close proximity with the nibs (the nibs and the auxiliary electrodes are not shown in the drawing). At the electrostatic recording head
2
, a voltage of several hundreds of volt is applied to the nibs in units of pixels of image data to cause discharge between the nibs and the recording medium
1
, so that the recording medium
1
is charged. Whereby, an electrostatic latent image corresponding to the image data is formed on the recording medium
1
. The recording medium
1
passing through the electrostatic recording head
2
is coated with a liquid toner
32
by a toner roller
31
of the development processing unit
3
. The liquid toner
32
contains toner particles which are dissolved in a solvent called the “Isopar”. The toner particles include the pigment for color generation and the adhesive for fixation on the surface of the recording medium
1
. The toner particles are charged to have the opposite polarity to that of the electrostatic latent image formed on the recording medium
1
. Accordingly, the toner particles coated on the recording medium
1
by the toner roller
31
are attracted by the electrostatic force toward the electrostatic latent image to be fixed on the surface layer of the recording medium
1
. Whereby, the electrostatic latent image is developed.
The development-completed recording medium
1
is transported to a toner aspiration unit
34
of the development processing unit
3
, and any extra liquid toner
32
residing on the surface of the recording medium
1
is removed through suction by the toner aspiration unit
34
. The sucked liquid toner
32
is collected, and then is reused at later development process steps. Thereafter, the recording medium
1
is transported to a drier device
4
where any solvent residing on the surface of the recording medium
1
is dried to be removed.
As shown in
FIG. 2
, the toner aspiration unit
34
includes a vacuum channel
51
, a vacuum hose
52
and a vacuum pump
53
. The aspiration or suction of the liquid toner
32
is performed by giving a negative pressure to a groove portion
54
of the vacuum channel
51
via the vacuum hose
52
using the vacuum pump
53
. The groove portion
54
of the vacuum channel
51
is formed so that its width is narrower than the recording width of the recording medium
1
. Whereby, the groove portion
54
is sealed by the recording medium
1
to obtain the negative pressure. Additionally, one end of the vacuum hose
52
is coupled to a through hole in the bottom of the vacuum channel
51
.
Next, a color electrostatic recording apparatus of the single-path scheme will be explained with reference to FIG.
4
. While in the electrostatic recording apparatus shown in
FIG. 1
only one pair of electrostatic recording head
2
and development processing unit
3
is provided, in the color electrostatic recording apparatus of the single-path scheme, four pairs of electrostatic recording heads and development processing units are provided in order to form a color image by overlapping four different colors of black, cyan, magenta and yellow, typically. Note here that an electrostatic recording head
2
a
, toner roller
31
a
and toner aspiration unit
34
a
for black; an electrostatic recording head
2
b
, toner roller
31
b
and toner aspiration unit
34
b
for cyan; an electrostatic recording head
2
c
, toner roller
31
c
and toner aspiration unit
34
c
for magenta; and an electrostatic recording head
2
d
, toner roller
31
d
and toner aspiration unit
34
d
for yellow are shown in FIG.
4
. In the color electrostatic recording apparatus of the single-path scheme, the color image is obtained by overlapping of such four colors during one-time transportation of the recording medium
1
.
(First Problem)
In the electrostatic recording apparatus shown in
FIG. 1
, the specific phenomenon called “drop out” can take place. More specifically, in spite of the fact that the image data of the pixels to be recorded is input to the electrostatic recording head
2
, any accurate electrostatic latent image is not formed on the recording medium
1
resulting in lack of part of an image corresponding to such pixels. One possible cause of the creation of the “drop out” is the contamination of the electrostatic recording head
2
. More precisely, silica particles of about several micrometers in diameter, called “spacers”, are dispersed at the appropriate density on the surface of the recording medium
1
. These spacers are for defining a space gap corresponding in thickness to the size of such particles between the recording medium
1
and the electrostatic recording head
2
to thereby maintain a discharge gap required. When some spacers are peeled off from the recording medium
1
to attach to the electrostatic recording head
2
, an excessively widened discharge gap is generated. In addition, if the spacers drop down from the recording medium
1
onto the associative electrodes (the nibs and the auxiliary electrodes), then the resultant discharge is disturbed to decrease in effect. The “drop out” can also be different in the generation frequency depending upon the different in-use environments. Typically, the “drop out” generation frequency is less when the humidity is at low level rather than when at high level. It has been considered by those skilled in the art that this is because the higher the humidity, the more the creatability of discharge between the recording medium
1
and the electrostatic recording head
2
. Similar “drop-out” problems can occur in the color electrostatic recording apparatus shown in
FIG. 3
also.
As discussed above, while the conventional electrostatic recording apparatus is faced with a problem as to unavailability of any desired images due to the “drop out”, one approach to avoiding the problem is merely to make the electrostatic recording head clean. However, the cleanup of the electrostatic recording head should require that the electrostatic recording apparatus is interrupted in operation to permit a user to manually open its cover. In the case of continuously performing a great number of printout tasks by use of an elongate recording medium wound into a roll-like shape, a user or worker is required to clean the electrostatic recording head by rendering the electrostatic recording apparatus inoperative from time to time, which would result in an increase in workload. In addition, as the “drop out” generation frequency per se can vary wit
Akichika Yoshinori
Ohira Toshiaki
Nippon Steel Corporation
Pendegrass Joan
Pollock, Vande Sande & Amernick RLLP
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