Note: Descriptions are shown in the official language in which they were submitted.
1(~6~7~
This invention relates to ~he development
of electrostatic latent images. More particularly, this
invention relates to the development of electrostatic
latent images by the use of liquid toners or developers.
Specifically, this invention relates to methods and
apparatus for dispensing liquid toner or developer to a
receiving surface.
In the process of electrostatographic imaging
as disclosed, for example, in United States Patent No.
2,297,691, a plate comprising a layer of photoconductive
insulating material on a conductive backing, is given a
uniform electric charge over its surface and is then
exposed to the subject matter or copy to be reproduced,
usually by conventional projection techniques. This exposure
discharges the plate in areas according to the radiation
intensity thereby creating an electrostatic latent image
on or in the photoconductive layer. Development of the
latent image is accomplished with an electrostatically
charged, finely-divided, developing material or toner which
is brought into surface contact with the photoconductive
layer and is held thereon electrostatically in a pattern
corresponding to the electrostatic latent image. Thereafter,
the developed powder image is usually transferred to a
support surface, such as paper, to which it may be fixed
by any suitable means.
Development of an electrostatic latent image
may also be achieved with liquid rather than dry developer
materials. In this technique, electrostatic latent images
are developed generally using the liquid development
formulations, processes and apparatus generally disclosed
.'' - 1 -
~L~6~7~
in United States Patents 3,084,043 and 3,806,354 which
are herein incorporated by reference. In these methods,
an electrostatic latent image formed as mentioned above
is developed or made visible by presenting to the imaging
surface a liquid toner or developer on the surface
of an applicator roll or developer dispensing member having
a plurality of raised portions or "lands" defining a
substantially regular patterned surface and a plurality
of portions depressed below the raised portions or "valleys".
The depressed portions of the applicator roll member
contain a layer of liquid toner which is maintained out
of contact with the electrostatographic imaging surface.
Development is achieved by moving the developer dispensing
j member loaded with liquid developer in the depressed
portions into developing configuration with the imaging
surface. The liquid developer is attracted from the
depressed portions of the applicator surface to develop
the image bearing surface. The developer liquid may be
pigmented or dyed. The development system disclosed in
2~ United States Patent 3,084,043 which is sometimes called
"out of contact" de~elopment differs from electrophoretic
development systems where substantial contact between the
liquid developer and both the charged and uncharged areas
of an electrostatic latent imaging surface occurs during
deveIopment.
The applicator rolls employed in out of contact
liquid development processes are carefully produced and
are of substantially uniform characteristics. The
working surface of such rolls for application of a liquid
developer to an electrically charged photoreceptive surface
7~3~
is composed, for example, of a multihelicoid thread pattern
having up to about 300 threads per inch at about 45 right
or left hand lead. Other angles from about 20 to about
80 from axis may be used. The thread configuration is
typically about 0.0005 inch pitch, about 0.001 inch top
land, and with about 35 to 65 micron depth. The overall
roll size may be typically about 1.5 inch in diameter and
approximately 9 inches in length, exclusive of journals.
The applicator rolls generally run either in
touching contact or in very close proximity to the latent
image bearing surface. This surface may be of any dielectric
material or it may be a photoreceptor. The photoreceptor may
comprise a suitable sensitive material coated on any suitable
base. Any suitable photoconductive material and substrate
may be employed. Preferred photoconductors are selenium,
selenium alloys, and hallogen-doped selenium, but organic
photoconduc~ors may be used. Typical substrates are nickel,
brass and aluminum. If desired, there may be an interfacial
layer between the photoconductive matarial and the substrate
to provide selected adhesive or electrical properties and
there may be an insulating coating over thé photoreceptor.
As an additional alternative, a web may be interposed over
the photoreceptor between the photoreceptor and the applicator.
In such an arrangement, liquid toner or developer is developed
onto the web and later is transferred from the web to a
receiving substrate.
It should be quite evident that the two structures,
the photoreceptor and the applicator roll, must operate in
close conformance and tolerances with one another in order
to form a high quality image.
G4~80
In compact electrostatic copying devices, the
photoreceptor and applicator roll are typically small diameter
cylinders to facilitate operation in confined space. However,
belt-like surfaces are also employed. Such operation typically
occurs at speeds of about four to ten inches per second,
although moving contact resulting in the transfer of liquid
developer from an applicator to a photoreceptor can occur at
speeds ranging generally from about 2 to about 70 inches per
second. Liquid development of images at such speeds makes
cooperation of the photoreceptor and applicator roll necessary.
Once the developer is properly applied to the
applicator roll and its patterned or gravure-like surface,
the developer must be cleaned from the lands or raised
portions prior to to contact with the latent image bearing
~` 15 surface. This requires close conformance and tolerances
between the applicator surface and a doctoring mechanism
such as a blade or web. Effective doctoring or cleaning of
excess developer from the applicator roll land surfaces will
also result in removal of at least some of the developer
from the applicator roll valleys due to surface tension
characteristics of the developer.
The quality of the applicator roll is a critical
issue in the out of contact liquid development process.
;~ Materials which are useful in manufacturing the applicator
roll are limited~ The surface conformance between a hard
metal applicator roll and a hard photoreceptor surface
is very critical since very poor development occurs if there
is any non-uniform separation, yet photoreceptor damage
results if a hard applicator roll is too close, not in perfect
alignment, and not straight with the photoreceptor.
~69~
Producing a high quality finished metal roll under
commercial conditions having little tolerance deviation is
technically difficult. Mechanical engraving requires a
num~er of steps. A master layout of the pattern, opposite
hand, many times size, is made on a polyethylene terephthalate
resin material; the master layout is photographically reduced
to the proper size, again on a clear polyethylene terephthalate
resin material; and then the master pattern is transferred to a
hardened and ground tool steel master engraving cylinder by
a photoetching process. Only the pattern outline is transferred,
not the pattern depth; the photoetched master engraving
cylinder is mechanically etched by a master engraving to the
desired depth and contour. This step is critical and requires
great skill. The tools and equipment used are relatively
simple and very similar to a jeweler's etching equipment.
Subsequent engraving success deplends almost entirely on the
skill of the master engraver; the master cylinder is then
used to make master mills for the engraving of rolls; a
~-~ roll blank is machined to tolerance by conventional means.
An extension is left on one end and this is used to drive
the roll during the mechanical engraving process After
engraving, the extension is machined off. The roll material
is usually AlSl, 1015 or 1020 steel; the roll is now ready
for engraving. During the engraving process, the roll is
placed in a special lathe designed for this purpose. The
roll is placed in the machine with the roll journals supported
by bronze "U" shaped bearings. The extension that is left on
the roll is engaged in a floating chuck that drives the roll
during the engraving process. The mastPr engraving mill is
mounted in a tool holder directly above the roll. The tool
)6~7~3~
holder rests on the lathe bed and is driven back and
forth by a lead screw. Th~ master mill freely floats in
the "U" shaped bronze bushings in the tool holder. By
means of an adjusting wheel, it is brought in contact with
the rotating blank roll, picks up the speed of the blank
roll and is driven by frictional contact. The advance along
the blank roll is controlled by the lead screw driving the
tool holder. The blank roll rotates very slowly, usually no
more than 15 rpm. The advance of the master mill along the
length of the blank roll is also very slow, approximately 1
inch over 3 minutes for small rolls and considerably slower
for larger rolls. On larger rolls it is nearly impossible
to see the mill advance down the roll as it is moving so
slowly. The master mill is rarely bottomed in a single
pass. Usually at least two passes are required on every
roll and sometimes considerably more. The amount of infeed
per pass is at the discretion of the operator. During
engraving, the roll is continuously flooded with lubricant.
After engraving, the journal extension is machined off, and
the roll is degreased and given a flash coating of copper;
the final step consists of plating with a thin coat of hard
chromium. Both plating operations require considerable
skill and the usual plating setup normally would not plate
completely and uniformly into such intricate configurations.
Other roll manufacturing processes which are
simpler in nature have one or more deficiencies. For example,
multi-die thread cutting has some feasibility for producing
a multihelicoid pattern, however, it is very difficult to
obtain about a 45 lead angle with this process, the maximum
lead angle obtainable usually being about 25 from the
:
-- 6 --
71 3~
normal to the axisO In producing a multihelicoid pattern on
an applicator roll, usually a minimum of 150 threads per inch
are desirable and about 180 threads per inch are preferred.
With multi-die thread cutting, it is difficult to produce
a die of about 180 threads per inch. Further, a special
chucking machine that can feed small rolls at about 0.5 inch
per revolution is required for a small roll such as one about one inch
in diameter and about 9 inches in length. However, even
this rate of feed is quite slow and compounded with the
considerable amount of set up time required, this process
provides low rates of productivity. Photo engraving/chemical
etching also has some feasibility for producing patterned rolls
except for one major drawback. That is, it is very difficult
to line up and join the ends of the overlay to produce
a continuous pattern. A further limitation is that the
ma~imum etched depth obtainable is usually about 25 microns~
Cylindrical panographic engraving equipment can produce a
multihelicoid pattern, but again the alignment of the thread
pattern is a problem the same as occurs in the photo-
engraving process. An electronic automatic cylinder engraving
machine may produce about a 180 TPI at about a 45 lead
angle multihelidoid pattern, or other patterns, on a con-
tinuous cylindrical surface. However, since it is a true
engraving process, it is slow and thus costly. Electro-
chemical grinding is also unsatisfactory for fabricating a
roll having about 180 TPI because the finest grinding wheel
has an individual particle size nearly as large as the
largest thread feature.
~64 ~'~3C)
With these and other problems associated with
metal applic~tor rolls, attempts have been made to use
polymers and other elastomeric materials. Thermal expansion,
swelling, elastic recovery, and pattern distortion are all
problems which have made the use of such materials difficult.
Casting techniques using such materials appear to be
impractical. Open casting attempts have generally failed
because of poor concentricity control and unreliable mold
filling. Spin casting is generally associated with shell-
mounting difficulties.
Since nearly all presently known processes for
~ manufacturing applicator rolls in sufficient quantities
; are dificient in one or more vital areas, there is a con-
tinuing need for an improved roll and method of fabricating
the rolls.
In accordance with an aspect of this invention
there is provided a method for making an applicator roll
having a hard, dimensionally stable, thin, thermosetting
surface carrying the desired applicator surface pattern coated
over a resiIient layer which is supported by a hard metal shaft.
In accordance wlth another aspect of this invention
there is provided a method of forming a patterned applicator
roll for developing electros~atographic images compxising:
forming a resilient surface on a hard shaft, coating said
resiLient surface with a thin uncured thermosetting polymeric
material, imprinting a pattern onto the surface of said uncured
thermosetting polymeric material, and curing said thermosetting
polymeric material.
In accordance with another aspect of this invention
there is provided a method of making the desired fine-textured
applicator roll comprising embossing a resilient-sleeve
.
-- 8 --
7~3~
covered steel shaft which is coated with a thin, uncured
thermosetting material. After receiving the imprint of the
desired pattern, the embossed blank is separated from the
master and heat cured
Embossing is usually performed by passing a
flat sheet of material termed the blank through an interface
zone created by a master, the patterned roll, and a back-up
roll. The embossing roll pulls the blank through the nip,
impressing an exact replica of its inverse pattern into the
relatively soft surface. Since the flat shaet is generally
continuous, there is no need to match first and last teeth
of the embossed pattern. This technique can also be used
to emboss a continuous pattern on circumferential or endless
surfaces, providing the pattern pitch is sufficiently fine
~ and the material structurally weak enough to allow
formation of integral numbers of "teeth" or lands.
Non-integral teeth, such as formed during the
fir~ revolution of a blank whose circumference is mismatched
; with the master's, can be integrally formed by movement of
material around the circumference during embossing. The
quality of the tooth profile depends upon the pitch diameter
established within the blank's surface. The process of
averaging out non-integral tooth errors is quite complicated
and involves continual redistribution of material and
reformation of pitch diameters throughout the process. During
embossing, last-tooth error averaging is a function of the
physical properties of the coating material and its sub-
strate. The floating support of the blank allows the
continual formation of pitch circumferences, depending upon
the variation of nip pressure and coating viscosity. This
~647131)
tooth averaging phenomenon continues to occur until a
stable pitch circumference is established. Failure to
stabilize the pitch circumference will result in pattern
distortions.
Any hard shaft material may be employed in this
-~ invention. Steel, stainless steels, nickel, brass or any
other like material may be used. It is preferred to use
conductive materials.
An elastomer or elastomeric-like, resilient
material is used to cover the shaft. Materials such as
nitril-butadiene rubber, resilient polyurethane rubber ;
silicone rubber, isoprene rubber, chloroprene rubber,
styrene-butadiene rubber, butadiene rubber, and the like may
be employed. These materials should have a Shore A hardness
of from about 50 to 90 but values of about 70 are preferred.
Wall thicknesses of this resilie1lt material should be from
about 0.05 to about one inch; thicknesses of from about 0.09
; to about 0.20 inch are preferred.
Particularly preferred resilient substrate
materials include nitrile rubber tubing, Compound 3431
modified, and molded conductive neoprene (105 ohm-cm),
70 Shore A, both ~rom American Roller Co., Union Grove,
Wisconsin, and molded conductive polyurethane (105 ohm-cm)
70 Shore A, from Garlock, Inc., Rochester, New York.
The resilient substrate material may be in the form
of tubing which is placed around the hard metal shaft or
material molded around the shaft. Injection molding of the
resilient, elastomeric-like material is preferred.
-- 10 --
.
~L~i647~
Preparation of the blank is an important step
in the manufacture of an applicator. While minor surface
errors of the blank may be averaged out during final coating,
existence of these can affect the efficiency of the process.
A finish grind operation for sizing and straightening may
be desirable if necessary in order to have a uniform quality
final product.
One important characteristic of this invention
lies in the surface coat. It has been found that a thin
layer of thermosetting material applied to the resilient
covered shaft, gives the applicator roll of this invention
dimensional stability coupled with the resiliency necessary
to provide for good photoreceptorjapplicator roll system
conformance without the high potential of damage to the
relatively fragile photoreceptor surface.
Many materials are useEul in providing a surface in this
invention. It has been found that polyurethanes are particularly
useful in this invention. A fine applicator pattern is
faithfully formed in the elastomer, and if uncured, this
pattern must be retained until the coating is fully cured.
The quality of the rolls are normally controlled in large
~measure by the viscoelastic properties of the elastomeric
coating and by its curing behavior. Embossing is the preferred
way to create the desired pattern.
Early in embossing, the stress level is very high
because contact is restricted to the lands of the master. As
the material deforms, the contact area increases until
total contact is reached and the stress level is lower.
After total contact there is no longer gross deformation,
but internal viscous flow continues to redistribute stress in
.. -- 11 --
7~0
the elastically deformed material and this stress relaxation
serves to reduce the magnitude of the elastic recovery.
For preferred embossing, the coating should have a
low viscosity and a high elastic modulus (low elastic
compliance). However, the need for tracking of the master
lands in the formed grooves places a lower limit on this
viscosity. Also, the cohesive (viscoelastic) strength must be
greater than the adhesive attraction to the master roll to
prevent "hot offsetting".
In using many materials, when the formed roll is
removed from the embossing fixture, residual elastic recovery
tends to decrease the depth of the grooves; this is called
; "slump". Surface tension will also promote leveling. Thus,the viscosity of the material must be high to counteract
these forces, but unfortunately, viscosity normally decreases
- with increases in temperature which are usually associated with curing.
Thixotropy of the coating material resists the
leveling forces, chiefly elastic recovery and surface tension,
until the material is cured. Thixotropy describes a charge in
viscosity with time at constant shear rate. Viscosity decreases
after an increased shear rate is imposed upon a material and
eventually reach an equilibrium value. If the shear rate is
reduced or removed, the viscosity will increase with time
until a higher equilibrium value is reached. Initial viscosity
is a function of shear history. Thixotropy is believed due
to a change in intermolecular forces, molecular ordering, or
in filled systems, the interparticle attachments. The
energy input from a shear field breaks down the order or
- 12 -
7Z~0
attachments, and when the shear field is removed, thermal
motion permits reordering or rebonding.
It has been found that uncured polyurethane
material which has carbon black pigment dipsersed therein so
that the volume resistivity is about 105 ohm-cm has the pxoper
properties to be embossed in such systems.
The excellent properties of the pigmented urethane
elastomer are believed directly due to the controlled thixo-
tropy which is controlled by the carbon black structure~
Improved materials are obtained by the addition of less
than about 20 percent by weight fumed silica which improves
the thixotropy. Well dispersed amounts of about 2 to about 8
percent are preferred.
Any blocked urethane which has an un~locking
temperature of greater than about 100C and preferably between
120 and 175C may be employed. Preferably such materials are
diluted with solvents such as xy:Lene and/or toluene to a
viscosity of about 100 centipoise for application.
The urethane is sprayed, dipped, or applied in any
; ~ 20 other conventional way to provide a uniform coating of
between 4 and 12 mils. A thickness of 5 to 7 mils is preferred.
,~ One technique for accomplishing uniform
coating is spraying. This is within the average skill of
the artO It has been found useful to apply about two mils
per pass using a pot pressure of 20 psi and an airline
pressure of 45 psi. Three passes will generally coat the
resilient covered shaft.
The coated roll should be allowed to dry thus
releasing the solvents prior to embossing. A period of
from a few minutes to 24 hours is required depending upon
- 13 -
4~80
the solvents employed. After this time the viscosity is
stabilized which allows for optimum embossing.
An engraved metal master prepared in accordance
with techniques previously described or any other high
quality technique-is prepared employing the negative of the
pattern to be produced. The embossing master and the blank
are brought together and rotated for a period of time under
pressure to impact the desired pattern in the surface of the
blank.
Embossing may be accomplished at any temperature
but it has been found that rolls of improved quality are
achieved where the operation is conducted at room temperature,
that is temperatures of from about 18 to about 35C. The
viscosity of the thixotopic polyurethane is sufficiently high
at room temperatures that offsetting does not occur.
Under these conditions a mold re:Lease agent is not necessary,
but such an agent may be optiona:Lly used.
The master is brou~ht :into contact with the
urethane coated resilient covered shaft and rotated while
contact pressure is increased. Any effective contact force
; may be employed but it is preferred to use pressures of
about 20 to about 30 pounds per lineal inch when embossing
at room temperature. Contact is maintained for from 2 to
about 20 minutes but can be extended in the case of poorly
coated blanks. After a few revolutions, a rippling or
"flowing" of the pattern may be observed which is a re-
orientation of material to eliminate last-tooth errors.
This pattern flow is really the phenomenon of cross threading
appearing and disappearing. Separation may be accomplished
by sudden release.
- 14 -
~L~G~78~)
Upon release, the uncured urethane surfaced,
patterned applicator roll is cured. Any curing technique
mav be employed. The roll may be placed in a hot air
oven at between about 100C and about 225C and cured for
from one to fifteen minutes or so. Typically, baking at
120C for from 10 to 12 minutes will unblock the urethane
and initiate curing. Materials having higher thixotropic
characteristics can be cured more rapidly thereby avoiding
material deformation if such a tendency is found. Following
the heating step, the roll should be allowed to stand at
room temperature for from about 18 to about 72 hours to
develop full properties.
Curing may be accomplished simultaneously with
embossing. In this step, the coated roll is heated for
from about 4 to about 10 minutes at temperatures of from
about 150 to 90C prior to embossing. The embossing step
is then caxried out as described above except that a radient
heat source is employed to maintain the surface temperature.
~ Upon release, the cured embossed roll should be allowed to
stand for from 18 to to about 72 hours for full property
development.
There are many effective modifications to the
embossing technique of this invention. The following non-
limiting examples further define and demonstrate the
invention. A11 parts and percentages are by weigth unless
otherwise stated.
- 15 -
~L~6~7~
EXAMPLE I
A steel shaft having a length of 12 inches and a
diameter of about 0.75 inch was covered with about 0.20 inch
wall thickness of a molded, conductive Neoprene rubber.
The Neoprene rubber, available from American Roller Company,
Union Grove, Wisconsin, was blended with carbon black in a
roll mill to achieve a resistivity of 105 ohm-cm and a
hardness of 70 Shore A prior to ~eing injection molded about
the steel shaft and simultaneously cured. The coated shaft
was ground to a constant diameter.
The surface of the ground covered shaft was
; spray coated with a five mil dry thickness of a solvent based,
end blocked, thermosetting polyurethane elastomer containing
dispersed carbon black to achieve a volume resistivity of
105 ohm-cm and fumed silica to enhance its thixotopic
properties. This material is available from Hughson Chemical
Company, a division of Lord Corporation, Erie, Pennsylvania
under the trade designation Chemglaze TS-1960-71. This
material is strongly shear thinning; at 40C, the viscosity
~` 20 decreased from 107 poise to 106 poise when the shear stress
is increased from 4.0 x 104 to 1.25 x 105 dynes per'square
centimeter. The thixotropic yield stresses were 5 x 104
and 9 x 104 dynes per square centimeter at 65C and 56C,
respectively. The urethane cures at 150C.
The uncured urethane coated, neoprene covered
steel shaft was mounted on centers. A cleaned engraved steel
master was employed having a uniform pattern of helical
; grooves, 65 ~m in depth, inclined at 67 1/2 to the roll
axis, and spaced at 180 threads per inch. This patterned
16 -
~9~713~)
master was engaged with the rotating urethane coated blank
and driven through frictional contact with it. The embossing
process was achieved by the intimate contact between the
surfaces of the urethane coated blank and the engraved steel
master. The pressure between the two surfaces is
increased to a maximum of 25 pounds per lineal inch of roll
while the two rolling surfaces increase in speed to 60
revolutions per minute. Embossing is continued for about
10 minutes and at the end of the process separation is
achieved by a spring mounted quick release mechanism in
order to avoid destruction of the freshly embossed pattern.
The embossed roll is placed in a hot air oven
having a temperature of 120C for about ten minutes which
fixes the surface of the pattern by curing. Full depth curing
is accomplished by letting the roll stand at room temperatuxe
for about 48 hours.
` ~ EXAMPLE II
The process of Example I was repeated in every
detail except that prior to embossing the coated roll was
heated in a hot air oven for about eight minutes at a
temperature of 125C to partially precure the polyurethane.
The roll was then mounted and engaged for embossing. The
engraved master and the precured blank undergoing embossing
were placed under radient heat such that the surface
~;; 25 temperature of the urethane was about 120C. The embossing
, and curing were accomplished simultaneously and after about
10 minutes the roll was comple-ted.
EXAMPLE III
, The process of Example I was substantially repeated
producing different rolls to demonstrate that the process
- 17 -
~4'7~0
had wide latitude in its variables. The results from a
representative number of these tests made after substantial
development was complete is shown below.
RDLL S~E~F SLE~ CQATING C~æD L~ND HGr. SURFACE LAND
NO. DURDMEIER IHIC~ESS THIC~ESS DEPTH DEVIATION ~V~S RADIUS
` (SHORE A) (inches) (inches) (microns) (microns) (microns) (microns)
AM~53 73 0.095 0.004 46 4.8 40 24
AM~54 73 0.095 0.004 44 2.5 42 34
G-66 75 0.119- 0.006 43 6.2 32 ?
10R-45 83 0.183 0.005 51 ? ? ?
G-33 ? 0.09 0.004 55 3.8 25 ?
#3 75 0.0g 0.004 53 3.8 21 29
G-50 76 0.09 0.009 42 6.2 15 40
G-46 75 0.09 0.006 ~3 3.8 15 36
R-42 83 0.205 0.006 45 6.2 38 40
Although specific materials and conditions are set
; forth in the foregoing examples, these are merely intended
as illustrations of the present invention. Various other
suitable roll materials such as those listed above may be
20 substituted for those in the examples with similar results.
Other materials may also be added to the roll matèrials to
sensitize, synergize or otherwise improve the fabricating
properties or desirable properties of the process.
Other modifications of the present invention will
occur to those skilled in the art upon a reading of the
present disclosure. These are intended to be included
within the scope of this invention.
