Note: Descriptions are shown in the official language in which they were submitted.
1077256
BACK~ROUND OF TEIE INVENTION
This invention relates generally to electrostato-
graphy, and more particularly it relates to improvements in
developer liquid supplying devices in electrostatographic
copying systems employing liquid development techniques.
In a known electrostatographic copying system
a charge pattern is established on an imaging surf~ce and
is developed by a liquid development process wherein the
liquid developer is presented to the charge pattern by
an applicator or liquid supplying device which has a surface
comprising raised areas or portions ~"lands"l and recessed
portions or depressions ("valleys") adapted to contact
liquid developer between or among the raised portions. The
; liquid developer is drawn to the imaging surface in lmage
configuration by the electrostatic forces of the charge
pattern.
Preferred methods and~devices for the liquid
development of electrostatic charge patterns are shown in
United States Patent 3,084,043 and United States Patent
3,806,354. In these systems a developer liquid supplying
member, generally an applicator roll, is utilized to present
liquid developer to the surface of the member carrying the
charge pattern. The applicator roll is normally prepared
for coming into developing contact with the imaging surface
by first contacting it with a doctoring or metering blade
or other resilient or absorbent meterinq device or combina-
tions thereof, in order to adjust the liquid in the valleys
to a predetermined level and to clean the lands so that they
- are substantially free from liquid developer.
" 1 " ~
1077Z56
In the foregoing system a liquid developer supply
member having on the surface thereof finely d~vided raised
portions and depressions in a regular geometric pattern,
is used to develop a latent image by the steps of supplying
a liquid developer to the depressions of the developer
8upply member and bringing the raised portions of the
developer supply member into contact with a latent image
supporting member bearing an electrostatic latent image so
as to cause the electrically conductive developer liquid
retained in the depressions to creep up along the side of
the raised portions by the attraction of the charges of the
latent image into contact with the latent image. Undesirable
amounts of liquid developer in the depressions results in
i~ the deposit of liquid developer in the background, and this
; 15 is caused by the inability of the prior art metering devices
both to meter the depth of the liquid developer at proper
levels in the applicator valley8 and to render the lands
substantially clean. The volume of liquid developer which
must be pushed aside by or absorbed by the prior art metering
devices is frequently more than the device can handle and
still clean the lands, or the absorbent type of metering
device can only meter to the extent of its absorbing
capacity without the use of additïonal means to clean
liquid developer from the absorbing device. Furthermore,
~ the absorbing type doctoring devices, even when used in
conjunction with a resilient or rigid land cleaning member,
tend to remove too much liquid developer from the depressions
or too little liquid developer from the depressions or both,
. depending upon the absorbency of the absorbent material.
- 30 Representative of tl-ese prior art devices are the disclosures
.
1077Z56
~'
in United States Patent No. 3,830,199 and U. S. Patent No.
3,667,428.
In the foregoing liquid development methods and
devices there is also a risk of the surface of the latent
image supporting member being damaged due to contact with
the developer supplying member. In order to avoid this
damage, liquid developer supplying members formed from a
resilient, compressible electrically conductive material
are used, and excess developer liquid supplied in the de-
pressions is wiped or scraped therefrom by a doctor blade
or similar member to leave a desired amount of developer
in the depressions.
As reference to the drawings now will be made,
the drawings will first be briefly described.
Figure 1 is a side view of a section of a prior
' art liquid developer supply member for explaining the con-
;, ..
struction and function of such a device.
L' Figure 2 is a side view of a section of a prior
art liquid developer supply member showing the relationship
of the member to a section of a prior art resilient doctor-
ing device.
':'
; Figure 3 is a side view of a prior art liquid
developer supply member (gravure member) having a spiral
pattern.
Figure 4 is a schematic representation of one
.
stage of development of a charged image bearing member
~, relative to a liquid developer supply member according to
~? the prior art.
Figure 5 is a schematic representation of
another'stage of development of a charged image bearing
member relative to a liquid developer supply member accord-
; ing to the prior art.
:'
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1077~5f~
Figure 6 is a schematic representation of a devel-
oped image bearing member according to the prior art.
Figure 7 is a schematic representation of an
embodiment of the developer supply device according to the
present invention.
Figure 8 is a front elevation of a preferred
developer supply member employ~d in the device of Figure 7.
Figure 9 is a perspective view in an enlarged
scale of part of the surface of a preferred developer supply
member employed in the device of Figure 7.
Figure 10 is a side view of a section of a pre-
ferred developer supply member prior to mètering or doctoring.
Figure 11 is a side view of a section of a pre-
ferred developer supply member illustrating metering or
doctoring with a rigid squeegee member.
In the aforementioned devices and methods, the
liquid developer _ remains within the depressions b of the
liquid developer supplying member a after doctoring, and liquid
developer does not adhere to the rigid raised portions d, that
is, the position in which the level of the developer is
maintained below peaks of the raised portions by a distance
as illustrated in Figure 1. The value of the distance ~ ,
together with the electrostatic attractive force of the latent
image supporting member, may affect development greatly. In
particular, a residual developer liquid remaining at the
raised portions d transfers to the imaging member and results
in dirtying the background areas of the image. For this
reason, in the aforementioned method in which the excess
developer is removed or wiped off with a doctor blade
or similar member, the wiper or scraper member e is made
of a resilient material and in such a configuration
that duxing wiping or scraping part of the wiper is deformed
to project toward the bottom of the depressions b of the
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1077Z5~;
developer liquid supply member a as shown in Figure 2.
To this end, the depressions b of the supply member a
axe formed in the form of a spiral having rigid, non-
compressible raised areas or lands as illustrated in
Figure 3.
However, the use of a liquid developer supply
member a having spiral depressions b for liquid developing
a latent image has inherently presented a disadvantage in
that, where an electrostatic latent image on the latent image
supporting member f lies across the depression b as shown
in Figure 4, the developer liquid is caused to adhere merel~
to the portions of the latent image supporting member f
adjacent the peaks of raised portions d as illustrated in
Figure 5 so that areas of the latent image placed between
the raised portions d and above the depression b remain
undeveloped, thereby resulting in image discontinuity as
shown in Figure 6. Furthermore: developer supply members
having spiral depressions as in Figure 3 are disadvantageous
in that the flow of the developer liquid is control.lable
20 only in the direction perpendicular to that of the spiral
depressions while the flow control in other directions is
impossible. Therefore, the sharpness of developed image
in the direction perpendicular to that of the depressions is
~ oi low quality.
~ 25 Although satisfactory developed images can be
obtained using the metering blades, rollers and other devices
of the prior art, an alternative and improved means for
preparing a liquid developer supplying device or applicator
surface for coming into developing contact with an imaging
surface is desirable, especially in those systems where the
~077ZS~
liquid supplying member is one having at least compressible,
resilient raised areas or lands.
SUMMARY OF THE INVENTION
It is therefore an object of an aspect of the present i~
invention to overcome the foregoing disadvantages and to
provide a novel liquid developer supply device and method
capable of affecting excellent development which is free from
image discontinuity and degradation of image sharpness.
It is an object of an aspect of this invention to
provide an improved apparatus and method for preparing a liquid
; developer supplying device or applicator for coming into
developing contact with an imaging surface in those liquid
development systems where the liquid developer supplying
member has finely divided discrete depressions for containing
; 15 liquid developer and at least compressible, resilient raised
areas.
According to one aspect of the invention there is
provided an improved apparatus for preparing a liquid developer
, applicator having lands and valleys prior to its being brought
into developing contact with an imaging surface, the improved
apparatus comprising a liquid developer supplying member
::,
having on the surface thereof finely divided discrete depres-
sions for containing liquid developer and at least compressible,
resilient raised areas; a non-absorbent, relatively rigid,
squeegee member capable of contacting the liquid supplying
member and adapted to meter the liquid developer in the supply
member depressions to a predetermined level by compressing
at least the compressible resilient raised areas; a cleaning
means for cleaning excess liquid developer from the surface of
the raised areas, said cleaning means being positioned to
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:
iO77'~5~;
contact the raised areas subsequcnt to the contact between
the squeegee member and the raised areas; and means for
providing relative movemert between the squeegee member and
cleaning means and the applicator surface.
S According to another aspect of the invention,
there is provided a method for preparing a patterned liquid
developer applicator having on the surface thereof finely
divided discrete depressions for containing liquid developer
and at least compressible, resilient raised areas, to come
into developing contact with an imaging surface, said method
comprising squeezing the liquid developer from the depressions
of the applicator by contacting the applicator with a non-
absorbent, relativel_ rigid squeegee member at a force
sufficient to remove the liquid developer to a predetermined
depth in the depressions, there being relative motion between
the applicator and the squeegee member and cleaning the
surface of the raised areas by contacting the raised areas
with a cleaning means, there being relative motion between
the applicator and the cleaning means.
As used herein, imaging member refers to any
prior art surface, such as a photoconductive surface, an
interposition surface and the like.
The term "at least compressible, resilient raised
areas" means that the lands must be compressible to the
extent that the rigid squeegee member in contact therewith
will cause a compression of at least the raised areas,
however, it does no~ preclude the compression of the base
material of which the liquid developer applicator is con-
structed and upon which the lands or raised areas are
situated. Thus, this phrase also encompasses those liquid
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1077ZSfà
developer supply members where the entire member including
the lands is compressible to the desired extent so that
sufficient force can be applied by the rigid squeegee member
consistently to remove liquid developer to a predetermined
depth in the depression and/or at a predetermined distance
from the peaks of the raised areas or lands.
These and other objects of this invention will
become apparent to those versed in the art of electrostatic
copying in view of the following detailed description of
the method and apparatus taken in conjunction with the
accompanying drawings in which preferred embodiments of the
apparatus are shown.
DESCRIPTION OF THE PREFERRED EMBODIMæNTS
Referring now to Figures 1-6, discussed supra,
there are shown schematically and in cross-section prior art
liquid developer supply members, metering apparatus, and
explanatory views showing the function of such members and
apparatus of the prior art.
Although images can be developed from liquid
developer supply members (applicators) metered as shown in
Figures 1-6, problems are sometimes encountered both in
; efficiently metering the valleys and cleaning the rigid
lands, especially when a comparatively large amount of
liquid developer has been placed on the applicator surface
prior to the metering station. The prior art devices
including absorbent rollers (not shown) frequently provide
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~077ZS6
metering of uneven depth. An alternative means for
preparing a liquid developer applicator which provides more
efficient metering of the valleys and cleaning of the lands
and which overcomes the uneven metering problems causec
by irregularities in the applicator surface is desirable.
~his can be accomplished by the present invention when
the liquid developer supply member or applicator is one
having at least compressible, resilient raised areas or
lands. Especially preferred configurations for the surface
of such applicators is shown in Figures 8 and 9.
A preferred embodiment of this invention will
now be described with reference to the attached drawings,
in which Figure 7 is a schematic cross sectional view of
the liquid developer supply device according to the present
, . . .
invention. In Figure 7 there are shown a latent image supporting
; member 1, and a developer liquid supply member 2 rotatable
in contact ~ith the latent image supporting member 1 in the
direction of the arrow. As shown in Figure 8, the supply
member 2 is formed of a metallic core roller 3 and a
surrounding compressible, resilient electrically conductive
material 4 of preferably about 5-10 mm in thickness. The
surface of the resilient material 4 is provided with a
plural number of finely divided grooves with a pitch of
about 4-10 grooves per millimeter and having a depth of about
0.04 to~about 0.1 millimeters. The grooves form an
angle of about 45-90 with respect to the axis of the supply
member. The resilient, compressible, electrically conducti~e
member 4, may include, for example, such materials as nitrile-
butadiene rubber, polyurethane, silicone rubber, isoprene
rubber, chloroprene rubber, styrene-butadiene rubber,
_ 9 _
;,
1077Z56
. . .
'.~ butadiene rubber and the like. Additives may be added to
the resilient material to adjust the electrica,l conductivity
to less than about 108 ohms per centimeter by volume
resitivity and to hardness of more than about 60 Shore A
hardness as desired.
In another preferred configuration the surface
of the developer supply member may be provided with a plural
',' number of finely divided discrete depressions or valleys 5
' as illustrated in Figure 9. The depressions 5 may be formed,
for example, into a square configuration enclosed with side
t'' walls 5a each of the depressions being arranged in axial
rows and transversal columns crossing at a right angle to
, form a desired pattern. The depressions 5 a.. e divided by
raised portions 6 which are continuous with each other.
'lS These raised portions or lands must be compressible so that
' the desired amount of liquid developer can be me'tered
~,' from the depressions in accordance with the present invention.
~,' In Figure 7, adjacent the developer supply member,
.,
; 2 having the construction above described, there is provided
'~ 20 a developer loading member or wetting roller 9, a bottom
~ portion of which is dipped into the developer liquid 8 within
; a reservoir 7. The developer liquid loaded on the wetting
'' roller 9 is then transferred to the surface of the supply
' member 2 as these two members 2 and 9 rotate in close proximity,
of each other. The developer 8 loaded on the surface of the
supply member 2 is squeezed from supply member 2 by a squeegee
roller 10 which compresses the lands on supply member 2, and
:
~" thereby leaves a desired amount of developer liquid in the
depressions or valleys. The supply memmber 2 is then wiped
by a scraper or wiper member 11 or other equivalent means to,
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1077'Z56
clean developer liquid from the lands.
In a preferred embodiment, an adjusting member 12
may be provided in contact with the squeegee member 10 for
controlling the surface of the squeegee member. It should
S ~e understood that, although it ,s preferable to provide at
least one developer loading roller 9 between the reservoir
7 and the supply member 2, it is possible to arrange the
developer supply member 2 in direct contact with the developer
8 within the reservoir.
The operations and function of the preferred
device are as follows: first, the developer 8 is applied to
the surface of the developer supply member 2 by means of
loading roller 9. At this moment, there is a layer 8a of
excess developer on the surface of the developer supply
member 2 as shown in Figure 10. As the developer supply
member 2 is rotated past the squeegee roller 10, the excess
developer 8a and part of the developer 8b retained within
the depressions 5 are squeezed due to the temporary deforma-
tion of the surface of the supply member 2 so that a pre-
determined amount of developer 8b is left in the depressions
5 as shown in Figure 1. The residual developer liquid 8c
adhering to the peaks of the raised portions 6 is then removed
by the scraper or wiper blade 11 or other suitable cleaning
device. The resulting developer liquid 8a properly retained
~S in the depressions 5 is then moved past the developing
station for development of a latent image. Since the
depressions 5 of the supply member 2 are enclosed in all the
four directions by means of the walls of compressible raised
,
portions 6 in the embodiment shown in the drawings, the number
of flow paths is increased when compared with the conventional
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107725~
sp~ral-grooved developer supply roller. This prevents
discontinuity of the developed image. Moreover, it is
possible to control a flow of the developer liquid in more
than two directions and hence, to prevent the degradati~n
~ 5 in the sharpness of the end areas of the obtained image.
,,~ According to the present invention, the resilient
~urface of the liquid developer supply member is provided
with a plural number of finely divided discrete depressions
and excess developer is removed by means of a squeegee member
' 10 which forms a nipfwith the supply member and actually com-
1~ presses the raised portions thereof to leave a proper amount
' of liquid developer in the depressions, and a scraper, wiper
' , or absorbent member is then used to clean li~uid developer
'; from the raised areas. The risk of image discontinuity as
'; 15 experienced in the conventional, non-compressible, non-
-' resilient developer supply devices employing a spirally
grooved roller is eliminated and the dirtying or smudging of
. .
the background areas due to the residual developer remaining
';' at the peaks of the raised portions is avoided. Further,
since the flow of develo~er liquid can be ccntrolled in
~, more than two directions, the development of the end portions
`' of the image can be affected advantageously without causing
', degradation of the sharpness of the image.
,It should be understood that the form of pattern,
2S or arrangement of the depressions may be altered or varied
in any suitable manner without prejudice to the function
thereof, as long as there is sufficient resiliency and com-
pressibility of the supply member or at least the lands of
said supply member so that liquid developer can be squeezed
; ~ 3n from the depressions of the supply member by contacting the
~ 12 -
,. ~ ~. . . . . . . . . . . .
1~77256
supply ~ember with a non-absorbent, relatively rigid squeegee
member, preferably a squeegee roller. The force applied by
the squeegee member against the liquid developer supply member
must be sufficient to remove the liquid developer to a pre-
determined depth in the depressions, for example, 0.02 mm from
the surface of the raised portions. The depth of the liquid
developer in the depressions depends upon various machine
and material parameters and can be easily determined by one
skilled in the art. Preferred cooperating supply and squeegee
members may be manipulated or constructed so that liquid
developer may be metered in the depressions to within about
0.01 mm from the surface of the lands to within about 0.01 mm
from the lowest portion of the depressions or valleys.
Thus, any suitable applicator surface may be used
which will be useful in accordance with the liquid development
method disclosed in United States Patent No. 3,084,043 or
United States Patent No. 3,806,354 as long as the applicator
surface has the desired resilience and compressibility as
described herein.
Gundlach in United States Patent No. 3,084,043
discloses and claims a liquid development system wherein
liquid developer from a reservoir is deposited on a gravure
roll and fills the depressions in the roller surface. The
gravure roller is doctored to remove excess developer
therefrom, and as a receiving surface charged in image configu-
ration passes against the gravure roller, the liquid developer
is attracted from the depressions in image configuration by
the charge. Amidon et al in United States Patent No. 3,806,354
discloses an electrostatographic imaging system wherein an
electrostatic latent image is developed by placing the imaging
- 13 -
1077Z56
-~ surface in developing configuration with a patterned applicator
surface having a substantially uniform distribution of raised
portions or "lands" and depressed portions or "valleys" and
containing a relatively non-conductive liquid developer in
S the depressed portions thereof while the raised portions are
substantially free of developer. Amidon et al claim a method
of cyclically developing electrostatic latent images on a
reusable electrostatographic imaging surface comprising the
steps of forming an electrostatic latent image on the reusable
imaging surface, providing an applicator having a substantially
uniform pattern of raised portions and depressed portions,
said depressed portions containing developing quantities
of an electrically non-conductive liquid developer having a
bulk resisitivity of from about 101 ohm cm to about 1014 ohm cm
while said raised portions are substantially free of liquid
developer, positioning said applicator adjacent said imaging
surface so as to induce equal and opposite charges in the
liquid developer in regions corresponding to those areas of
; the imaging surface intended to be developed, such that the
liquid developer is electrostatically pulled from the applicator
to the imaging surface in image configuration, transferring
said liquid developer from said imaging surface to a receiving
surface, preparing said reusable imaging surface for the next
imaging sequence repeating the steps of forming, providing,
positioning and transferring at least one additional time
whereby residues of said non-conductive liquid developer
remaining on the imaging surface are not damaging to cyclical
use of the imaging surface.
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1077ZS6
~ypically, the applicator is a roller having a
pattern of raised portions "lands" on its surfaces with
r~cesses "valleys" therebetween said valleys adapted to
contain liquid developer. In a preferred embodiment the
valleys are a pattern of helically wound grooves. Other
suitable applicator surface patterns are described in United
States Patent No. 3,772,012 where typical applicator surfaces
include among others, patterned webs or belts, and cylindrical
rolls having surface patterns such as single screwcuts or
trihelicoid, pyramidal or quadragravure indentations.
In an especially preferred embodiment of the present
invention the surface of the liquid developer supply member,
or at least the raised areas or lands thereof, has a hardness
of more than 60 Shore A, and the hardness of the surface of
the squeegee member is greater than the hardness of the
surface of the supply member or at least the raised areas or
lands thereof. In these modes, the cooperating squeegee
member and liquid developer supply member, may form a nip at
a force sufficient to compress the raised areas up to about
95 percent of their original elevations and prefexably from
about 0.05 percent to about 50 percent of their original
elevation. The maximum fo~ce applied to any such member must
be no greater than the force which compresses the lands to
the extent that they remain compressed, deformed or otherwise
rendered unsuitable for developing electrostatic latent images
on an imaging member.
The land cleaning means may be formed from any
; suitable material. Typically, the land cleaning means may bean absorbent roller, an absorbent blade or a resilient blade,
- 15 -
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1077256,
--~ for example, a hard plastic blade, sufficient to remove
liquid developer from the surface of the lands or raised
areas.
The instant liquid developer supply device and
method may be used in most xerographic systems where liquid
developers are applied to imaging members from a patterned
liquid developer applicator. E~emplary of such a system is
a xerographic member which may be photoconductive selenium
; coated on a conductive drum. In operation, the xerographic
member is charged in the dark to a uniform electrostatic
potential by a charging device such as a source of corona.
Alternatively, the xerographic member may be charged, for
example, by friction contact. The charged member is then
exposed to a light image at an exposure station. The charged
sUrface~ being photoconductive, when exposed to light to
which it is responsive, will become conductive in light struck
areas allo~ing the surface charge to move through to the conductive
drum leaving a pattern of charge on the surface of drum corres-
ponding to the non-light struck areas. The charge pattern
thus formed is then made visible at a developing station where
liquid developer is applied to the photoconductive surface.
The developing station is a liquid aeveloper applicator
surface having a surface pattern of lands and valleys supplied
with a liquid developer from a liquid developer reservoir.
;~ 25 According to the present invention, the resilient, compressible
applicator surface is then prepared to come into developing
contace with the imaging surface by first contacting it with
a squeegee member and a cleaning member so that the lands
of the applicator surface are substantially free from liquid
developer and the valleys contain a metered amount of developer.
,:
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107725~
The liquid developer is then brought into a developing
relationship with the xerographic member so that the
uid developer is deposited on the charged areas in
accordance with the teachings of United States Patent No.
3,084,043. The image, now visible, may be transferred to
a receiver member at a transfer station. The receiver member
may be, for example, paper entrained over a roller and pressed
into contact with the toner image. The developer is thus
transferred to the receiver member forming the final copy.
t 10 The instant invention described in Figures 7-11 is
suitable to prepare an applicator surface to come into
developing contact with an imaging surface. Prints developed
by an applicator which has been so prepared show substantially
uniform density and a desirably low amount of developer
in the background areas of the image.
While particular embodiments of the invention are
described above, it will be appreciated that various modifi-
cations may be made by one skilled in the art wichout departing
from the scope of the invention as defined in the appended
; 20 claims.
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