Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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My invention relates to a method of producing
cast polyuret'~ne elastomeric squeegee rollers having a surface
finish of between 2 and 10 micro-inches and to the rollers
produced by that method.
Background of the Invention
In order to be able to remove excess developer
liquid from the surface of a photoconductive drum by means
of a squeegee roller, it is vital that the squeegee roller
possess an extremely smooth surface finish of between two
and ten micro-inches. If the surface finish is not sufficiently
smooth, the remarkable results obtained by a roller made by
the instant method will not be achieved. There will be streaking
and tailing of liquid which is not removed, so that the
developed image becomes distorted and blurred.
The desirability of removing excess liquid from the
surface of a photoconductive drum by means of a polyurethane
squeegee roller is taughtiby Smith et al
.
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Patent 3,955,533~ There is no disclosure in this patent
of the method of making the squeegee roller and no teaching
of the instant invention, as will be pointed out more fully
hereinafter.
It also has been suggested by Hunstiger, in Patent
3,384,051, to pass a sheet of paper coated on both sides with
a photoconductive material and bearing a latent electrostatic
image through a bath of liquid developer snd then through a
nip formed by a drum of solid polished aluminum or chromium
or Teflon (trademark) coated metal and a roller of cast solid
polyurethane elastomer. The object of the arrangement is to
maintain the non-image side of the electrophotoconductive
coated paper dry, so that the dry side can be used again to
form an electrostatic image and developed on the opposite side
of the first image. While the specification does not describe
it, Claim 1 of Hunstiger indicates that excess carrier liquid
will be removed from the developed surface of the image-bearing
member. Any slippage which occurs will occur on the polished
metal roller of the pair. There is no disclosure whatever, in
Hunstiger, of the method of making the roller nor of the critical
nature of the smoothness of the polyurethane roller.
Hill Patent 3,2~3,728 discloses a process of making an
ink-applying roller for use in the lithographic field. The
Hill process, however, makes no reference to
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the salient feature of the instant invention--namely, the sur-
face smoothness of the roller, which produces remarkable and
unexpected results.
Seanor et al Patent 3,959,574 discloses a biasable
polyurethane roller for use in transferring developed electro-
static images ~y means of a directional force field from a photo-
conductor to plain paper. The resistivity of the polyureth~ne is
a critical feature o~ Seanor et al, and there is no disclosure
whatever of the salient characteristic of the instant invention
--namely, the smoothness of the surface of the ~olyurethane roller.
Lindsay Patent 3,914,817 has for its obiect the re-
moval of dust particles from a photographic film and, for this
purpose, uses a pair of Neoprene rollers. Furthermore, the sur-
faces of the neoprene rollers are such that they are "tacky", so
that they may pull dust particles from the surface of the film
being cleaned. This patent does disclose a surface finish of
under 20 micro-inches, but does not teach the unexpected and re-
markable results obtained with the instant invention. The mater-
ial is Neoprene, and not polyurethane, and Lindsay's rollers are
non-analogous art. Removing dust from photographic negatives
by tacky rollers is one thing, but drying the liquid-developed
photoconductive surface bearing the developed image is quite
another.
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I have previously devised a method in which a roller
could be produced by supporting a shaft centrally of a highly
polished tu~ular mold made from a precision drawn tube. The
fabrication of such molds required polishing their interior
surface, which was an expensive and time-consuming task.
Furthermore, it was difficult to obtain an interior surface of
the mold to a finish of less than 8 micro-inches. A finish
of this fineness was required to produce a cast roller having
a surface image of less than 10 micro-inches. It is known
that the surface roughness of a sand casting, a saw cut, or a
rough turning is between 500 and 1000 micro-inches root-mean-
square (rms~. This can be reduced to 100 micro-inches by
further turning or milling and then to about 20 micro-inches
by grinding. Superfinishing requires an abrasive block,
contoured to match the surface to be finished, and a
combination of light pressure and a~generous supply of collant
lubricant. This will produce a surface of from 1 to 5 micro-
inches. It will be apparent to those skilled in the art that
the production of metal tubes to be used as molds for the
2~ casting of my polyurethane rollers having the required smoothness
is extremely expensive.
~ esides roughness, there is the question of waviness
to be considered. A surface may be described as peak-to-peak
heignt of roughness or waviness. Throughout this specification,
the term "micro-inches" will he used to mean root-mean-square,
as defined by:
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rmS = ~ 2
where "y" is the height of the surface above the mean, "x"
is the horizontal distance between peaks, and "L" is the
horizontal distance over which readings are taken.
Broadly speaking, therefore, the present in-
vention provides a method o~ making a squcegee roller ha~ring
a surface finish of between two and ten micro-inches including
the steps of coating the interior of a drawn vitreous tube
with a release agent comprising a solution of between 0.5
percent and 1.5 percent by weight of a wax having a melting
point below 100C. in an or~anic solvent, positioning a metal
sha~t concentric with the tube, depositing elastomeric poly-
urethane within the tube around the shaft, curing the polyure-
thane, and then removing the roller from the tube.
The above method will produce a squeegee roller
comprising a shaft and a cast elastomeric polyurethane cylinder
positioned around the shaft, the surface of the roller having
a ~inish between 2 and 10 micro-inches.
In the accompanying drawings which form part of
the instant specification and which are to be read in coniunction
therewith, and in which like reference numberals are used to in-
dicate like parts in the various views:
FIGURE 1 is a flow diagram showing the steps of my
process, with necessary steps indicated by solid lines and option-
al steps indicated by dashed lines.
FIGURE 2 is a diagramma-~ic ~riew, with parts sho~n~
in section, of a battery o~ glass tubes containing ~inislle~
ro~lers made in accordance with my inventi~n be~ore their remo~al
-- from the mol~s.
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FIGU~E 3 is a perpsective view of a roller made
in accordance with my invention.
FIGURE 4 is a sectional view taken along the
line 4-4 of FIGURE 3.
Description of the Preferred Embodiment
Referring now to the drawings, the shaft may be of
any appropriate diameter. In the preferred e~bodiment, I
finish the shaft end portions to avoid having to handle
the finished roller unnecesarily after it has been
produced. After the end portions of the shaft are finished,
the shaft may be machined between the end portions if
desired. The roughness of the shaft between the end
portions may serve to bond the polyurethane to the shaft.
Preferably, I coat the shaft between the finished ends with
a thin coating (of the order of 0.05 mm.) of a high
, dielectric epoxy resin to insulate the shaft from the
polyurethane.
In my prior method, where polished metal molds
were used, a finished roller was removed from a mold by
first heating the mold to slightly expand it and then
removing the roller from the mold. Owing to the smoothness
of the glass, I have founa that it is preferable to coat
the inside of the glass tube with a very thin coating of a
release agent. I form an extremely thin coating hy dissolving
from be~ween 0.5 percent to 1.5 percent hy weight of a wax in
a solvent. A preferred solution is 1~ ~y wei~ht of carnauba
wax in trichloroethylene solvent. Any so}uble wax in which
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the solvent does not adversely affect the polyurethane can
be used for example:
Carnauba wax, which has a melting point of
approximately 86C.
Indian wax, which has a melting point of
ap~roximately 61~C.
Reeswax, which has a melting point of
approximately 62C.
Sugar cane wax, which has a melting point of
approximately 77C.
Chinese insect wax, which has a melting point
of approximately 83C.
Castor wax, which has a melting point of
~ ap~roximately 85~C.
:~ A simple and preferred method of coating the
Pyrex (trademark) glass tube is to dip it in a solution
of the release agent After this is done, the coated glass tube
is positioned in a fixture adapted to hold the glass tube
precisely perpendicular and concentric to an axis. A shaft
: 20 is then inserted into the fixture, the lower end of the
shaft being coaxial with the glass tube. Means are provided
for adjusting the upper end of the shaft so the entire shaft
will be concentric or coaxial with the glass tube mold.
The polyurethane is prepared from polybutadiene polyol and a
diisocyanate, being a reaction product of about 80% by
weight of the polyol and about 20% by weight
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of the diiocyanate. Oel-er polyurethanes, such as the reaction
product of castor oil and 2,4-tolylene diisocyanate, may be
used. The reagents are mixed at a temperature of approximately
130F and then poured into the mold to the desired level.
The mold is then placed in a curing oven and the temperature
elevated to 265F and held at this temperature for a period
of about 4 hours. It is understood that the temperatures
and times for curing are those specified by various manufacturers
of the polyurethane forming reagents and any appropriate
temperature may be used, depending on the particular reagents
involved. After the polyurethane has been cured, the mold is
removed from the oven and allowed to cool to room temperature.
In cooling, the polyurethane roller contracts slightly so
that, when a solvent is poured into the top of the mold, it
dissolves the wax release agent and the finished roller slips
out of the glass mold like wet soap.
Referring now to Figure 2, there is shown a battery
of molds formed of glass tubes 2, of which there can be any
appropriate number, positioned on a support 4 of a fixture.
The bottom of each glass tube 2 is cut so that it forms a
right angle with the tube axis. The support 4 is leveled by
appropriate means (not shown). A templet 6 is posi~ioned on
the support 4 so that each glass tube will be concentric with
the axis of each opening ~ through which each shaft 10 extends.
An abutment 12 is provided for each shaft to position its
lower end. Each shaft may be coated intermediate its end
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portions with a thin coating 14 of insulating epoxy resin.
The center of the upper end 16 of each shaft 10 is positioned
to be aligned with the axis of each glass tube 2 by means of
a plumb bob 18. Adjusting screws 20 supported in a fixture
22 are positioned 120 apart. They can be manipulated to
position the center of the shaft so that it is vertical or
coaxial with its tube 2. After the shaft has been concentrically
positioned within the glass tube, the polyurethane 24 is poured
into the glass tube 2 and then cured and removed as described
hereinabove.
The finished roller exhibits remarkable properties.
When placed horizontally on a vertical windowpane, it adheres
to the glass pane as if magnetically held thereto and slowly
rolls downward by gravity. In the prior art, an 8-1/2" x 11"
sheet of paper coated with a photoconductor, passing through
a development bath and through squeegee rollers of the prior
art, will have a surface liquid of between 120 and 150 mg.
These conventional rollers of the prior art generally have
an upper metal type roller, sometimes coated with Teflon*, and
a lower rubber roller which presses the developed and wet paper
against the upper roller. The upper roller is usually polished
to prevent it from picking up part of the image and reprinting
it or offsetting it on the next sheet of paper to be processed.
Using two of my rollers as squeegee rollers for the developed
photoconductor-coated paper coming out of the developing bath,
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there is only between 10 and 30 mg. of developer liquid on
the paper sheet. Strangely enough, this improvement obtains
almost irrespective of the pressure between the rollers. It
will be clear to those skilled in the art that there is
between 400% and 1500Z improvement in efficiency by the use of
my rollers in the removal of surface liquid. Since most
liquid developers comprise a light hydrocarbon as a dispersant,
the evaporation of hydrocarbon vapors into the printing room
- is vastly reduced. This not only lessens the odor, but avoids
a health hazard where the hydrocarbon-containing liquid
developers are used in an office copier located in an enclosed
space.
Because of the smoothness of my squeegee rollers ~between
0 and 10 micro-inches), they appear to have a highly polished
surface. They are so efficient that a light wiper for the
roller on the image side prevents reprinting. r have found
that the image quality is improved by reducing the water
absorption of the roller. This is accomplished by using a
hydrophobic polyurethane elastomer or by using a filler material
which prevents water absorption into the polyurethane. The
insulation of the rollers from ground also helps image clarity.
Both rollers are reasonably soft, having a Shore A hardness
of between 20 and 40. A pair of my rollers act as an efficient
dynamic seal; that is, they make continuous contact with the
section of the paper which lies between the nip and act as a
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dam and prevent li~uid from passing through this dam. Owing
to the relative softness of the rollers, there is conformation
to the micro-irregularities present in the paper.
It will be seen that I have accomplished the objects of
my invention. I have provided a method of making an improved
s~ueegee roller which is inexpensive and efficient. The
squeegee roller made by my invention exhibits unexpected and
remarkable properties, in that it enables liquid-developed
electrostatic images on photoconductive paper to leave the copy
machine substantially dry, without the necessity of applying
heat, and without blurring the developed image. Squeegee rollers
made by my invention have an extremely smooth surface of
between 2 and 10 micro-inches, owing to the fact that they are
cast in glass tubes instead of the usual molds where the
desired smoothness is extremely difficult and expensive to
obtain.
It will be understood that certain features and
subcombinations are of utility and may be employed without
reference to other features and subcombinations. This is
contemplated by and is within the scope of my claims. It is
further obvious that various changes may be made in details
within the scope of my claims without departing from the
spirit of my invention. It is, therefore, to be understood
that my invention is not to be limited to the specific details
shown and described.
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