Note: Descriptions are shown in the official language in which they were submitted.
`V093/ ~ 12 PCT/GB92/01958
1 2121128
OIL TRANSFER CONPONENT
FIELD OF THE INVENTION
The present invention relatos to the use of a porous
polytetrafluoroethylene structure as an oil transfer
component for oilinq and/or wiping a fuser roll in a
copying machine, which term includes plain paper copying
and fax machines and laser printers
PRIOR ART
Tn a plain-paper copying machine, toner images
appliod to the surface of paper or other recording medium
are fixat-d by application of heat and pressure In
c-rtain plain paper copying machines fixation is
accomplished by pa~sing the image-bearing recording medium
b~t~o n a hot ther~al fixation roll and a pr ssure roll
When thi- type o~ ther~al fixation device is u~od ~he
toner ~aterial is dir~ctly contactod by a roll surface,
~ . .
and~a portion of the toner usually becomes adhered to the
roll~surface On subsequent rotation of the roll, the
.
dh red toner material ~ay be red~posited on thQ recording
dium re~ulting in undesirab1e ofrset images, stains, or
s~ear~; or in severe casos the recording medium may stick
to~tb~ adhered toner material on thQ roll and become
:
wrapp d around the roll
~ To counter these problems, materials ha~ing good
r lease properties such as silicone rubber or
W093/08512 21 21 1 2 ~ 2 - rcT/GBg2/ol~*-
polytetrafluoroethylene are often used for the roll
surfaces. Although improving performance of the thermal
fixation devices, use of silicone rubber or
polytetrafluoroethylene roll surfaces alone does not
eliminate the problem. Another approach i8 to include
release agents with the toner materials, which prevent the
toner materials from adhering to the roll surface. These
oil-less toners improve the performance of the
thermal-fixation devices but again, particularly in the
case of high-~peed type copying machines, do not
completely eliminate the problems associated with toner
pick-up and transfer.
Toner pick-up by the rolls can be controlled by
coating the ~urface of at least one of the rolls with a
liguid relea~e agent, such as a silicone oil. It is
important that the release liquid be applied unifor~ly and
in~prQci~e guantiti-~ to the ~urface of the roll. Too
littl- liquid or non-uniform surface coverage, will not
prevent the toner from being picked up and redeposited on
the~roll. On the other hand, excessive guantities of the
:
releas~ liquid ~ay caufie silicone rubber roll ~urfaces to
~w~ll and wr1nkle, thus~producing copies of unacceptable
quallty.
D~vice~ to uniformly ~eter and coat a relea~e liquid
onto copy machine roll surfaces are described in JapanQse
laid-open patent No. 62-178992. $hese devices consist of
an oiI permeation control layer adhered to a thick porous
,
.
'~093/08512 212 1 1 2 8 PCT/GB92/01 ~
- 3 -
material which serves as a wick or reservoir for supplying
oil to the permeation control layer. The permeation
control layer is typically a porous
polytetrafluoroethylene film which has been i~pregnated
with a mixture of silicone oil and silicone rubber
followed by a heat treatment to cross-link the silicone
rubber. The thick porous material to which the
permeation control layer is adhered is typically a porous
thermosetting resin foam or a felt of Nomex
(Trademark~ fibres, glass fibres, carbon fibres,
polytetrafluoroethylene fibres, or any other high
temperature fibre.
Conventional plain paper copiers which use silicone
oil as the liquid release agent generally comprise a means
for coatihg the silicone oil onto the fuser roll and also
a ans for wiping th roll to remove undesirable adhered
toner, paper dust and other undesirab}e material. In many
case-, the coating and wiping functions are performed by a
d ngle device. In one particular type of machine, there
i8 provided a reservoir wick which is generally formed of
a No~ x felt, vith a cover wick placed over the top of it
for~met ring the flow of oil from the reservoir wick to
the fuser roll and also for providing improved wear and
distribution characteristics. The cover wi¢k is
typically a Nomex fabric. It is found, however, that the
cover wick has only a limited lifetime, typically lasting
for around 60,000 copies before requiring replacement.
W093/08512 1 211 2 8 4 PCT/GB92/01958
It would be desirable to have a cover wick which lasts as
long as the life of the fuser rollers.
In another commonly used type of copying machine, the
oil coating and wiping function is provided by a length of
felt, typically formed of Nomex or polytetrafluoroethylene
fibres. The roll is typically 435 millimetres wide by
l.4 metres long. Whilst the machine is copying, the
roll, which is laden with silicone oil, travels past the
fuser roll at a speed of about 2cm per hour. This oiling
roll applies silicone oil. Also excess toner cleaned from
the fuser roll is picked up and carried away on the oiling
roll. Typically, the felt of the oiling roll has a weight
of 700 grammes per square metre and a thickness of 1.3
milimetres. Due to the physical restraints of the
copying machine, this limits the length of material on the
oiling roll to about l.4 metres. It is generally
speaking not possible to make satisfactory felts which are
lighter than 700 grammes per square metre for this
purpose. In practise, it is therefore necessary to
replace the oiling roll about every lO days of operation.
British published patent application 2242431
(9106768.6) discloses a porous polytetrafluoroethylene
structure for use as a filter in industrial filtration.
The porous polytetrafluoroethylene material is produced by
fusing particles of polytetrafluoroethylene such as to
form a porous integral network of interconnected
particles. The disclosure of this patent specification is
' ~93/08512 21211 2 ~ PCT/GB92/01958
- 5
incorporated herein. The specification is particularly
concerned with the f iltration of aqueous slurries.
It is an object of the pre~ent invention to provide
an oil transfer component having suitable oil retention
characteristics and enhanced mechanical properties which
allows a longer lifetime between changes.
SUMMARY OF THE INVENTION
Generally speaking, the present invention envisages
the use of a porous polytetrafluoroethylene material such
as disclosed in GB 2242431 for use as an oil transfer
component for ¢oating or wiping a fuser roll in a copying
machine. The material is able to withstand the high
temperatures (around 200C) encountered and has excellent
mechanical properties and durability in this application.
Specifically, one aspect of the invention provides an
oil transfer component for coating or wiping a fuser roll
in a copying machine which comprises a porous
polytetrafluoroethylene structure formed from particles of
granular-type polytetrafluoroethy}ene fused together such
as to form a porous integral network of interconnected
particles.
In order to act as an oil transfer component, the
porous polytetrafluoroethylene (PTFE) structure will
generally include a support means for supporting the
structure within the copying machine. In the case of a
cover wick, the support means may be in the form of a
wo93/n85l2 2121 1 2 8 - 6 - PCT/CB92/01X~ ~
frame or pair of parallel rods extending along either side
of the cover wick strip. Alternatively, the porous
polytetrafluoroethylene structure may be laminated to a
reservoir material acting as a support structure. The
porous polytetrafluoroethylene structure may also be
provided in the form of a roll or may be applied onto a
roller formed of an oil reservoir material (such as a foam
as disclosed in Japanese 62-178992 or a porous ceramic)
which is optionally covered by a felt cover. Generally,
the porous polytetrafluoroethylene structure is in the
form of a sheet material, typically of a thickness in the
range 50 microns to 750 microns, particuiarly lO0 to 400
microns, and especially 200 to Soo microns.
The porous polytetrafluoroethylene structure is
hydrophobic but has a high affinity for liquid release
agents such as ilicone oil. Where the oil transfer
co~ponent is to be ufiQd for coating the fuser roll, it
will generally be supplied pre-loaded with release oil.
~$ypically, the oil will constitute 20 to 80% by weight of
the total w:ei~ht of the oil transfer component,
particularly 40 to 6Q% by weight. In order to provide
~suoh oil retention capacities, the porous
polytetrafluoroethylene structure usually has a specific
gravity of 0.8 to 1.8, typicaliy 0.9 to 1.2. In
comparison, pure non-porous PTFE typically has a specific
gravity of 2.16.
Preferably, the porous polytetrafluoroethylene
-093/0~12 21 2 1 1 2 8 PCT/GB92/01958
- 7
structure does not include any filler materials, since
these are generally of mineral origin and tend to be of an
abrasive nature which would damage the fuser rolls.
In order to improve the wiping abilities of the oil
transfer component, it is preferred that the porous
polytetrafluoroethylene structure have a slightly uneven
surface texture. This surace texture can be obtained by
spraying onto a smooth substrate in order to produce the
porous PTFE structure. After spraying and heat treating,
the porous PTFE may be peeled from the substrate to yield
a sheet material which is smooth on the side which was
adjacent the substrate and textured on the other side as a
result of the spray technique. In use the textured
surface is placed adjacent the photocopier roll.
The surface texture could also be provided by
spraying onto a substrate carrying an embossed pattern of
ridges, valleys, indentations, protrusions etc. such that
the textured surface is provided on the side of the sheet
facing the subst~ate.
Other methods could also be used to provide a surface
texture on the porous PTFE structure, such as by pulsing
the laydown of the material, e.g. by using a ~ibrating
doctor-blade. Alternatively, the surface of the PTFE
could be ~echanically embossed e.q. by passage through the
nip of embossing rollers.
In another embodiment, the texture is provided by
applying a fabric of suitable material (e.g. a Nomex
WO93/08512 21 21 1 ~ ~ PCT/G~92/01958~
-- 8
fabric) over the PTFE surface.
The surface texture acts to scrape unused material
off the surface of the copier roll and to carry it away in
the depressions in the textured surface pattern.
The porous polytetrafluoroethylene structure of the
present invention provides excellent wear characteristics
in comparison to conventional materials and does not shed
fibres. In the case of an oiling roll, the porous
polytetrafluoroethylene structure can be provided much
thinner than conventional felts, which allows much longer
lengths to be used, whilst maintaining the same oiling and
wiping characteristics. There is also reduced frictional
drag on the rollers.
The porous polytetrafluoroethylene structure may be
produced as described in patent specification GB 2242431. -
It is particularly preferred to form the structure from a
mixture of particles of different grades of granular-type
polytetrafluoroethylene. As is well known, PTFE is
produced in two distinct types so-called "granular PTFE"
and so-called "fine powder PTFEn. These materials have
guite different properties and the present invention is
concerned with the former. A particularly useful product
for use in the present invention comprises 40 to 60% of
Teflon (Trademark) resin grade 7A: and 40 to 60% of Teflon
resin grade 9B. Teflon resin grades 7A and 9B are
available from Du Pont Speciality Polymers Division,
Wilmington, U.S.A. The porous polytetrafluoroethylene
wo93/n8sl2 2121I2 PCI`/GB92/OlgS8
structure is usually prepared by spraying onta a
substrate, such as a ceramic tile or sheet of metal.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
~. _ .
Embodiments of the present invention will now be
described by way of example only.
The attached Figures show schematically various
conventional fuser roll arrangements as used in
photocopying machines, fitted with oil transfer components
according to the present invention.
Figure 1 shows a conventional PTFE-covered fuser roll
2 and a silicone rubber covered roll 4, which are oiled
and wiped by an oil-containing oiling roll or web 6 of
porous PTFE wound on a spool 8, which passes around
pressure rollers 10, 12 onto take-up spool 14.
Figure 2 show a similar arrangement, except that oil
is applied to the porous PTFE oiling roll or web by means
of an o~l supply mechanism 16.
Figure 3 shows a conventional PTFE covered fuser roll
2 and silicone rubber covered roll 4 to which silicone oil
is applied by oil supply mechanism 16, reservoir wick 26,
and cover wick 20. The cover wick is formed of porous
PTFE and is supported on a pair of rods 22, 24.
Figure 4 shows use of a roller 30 to deliver oil onto
the conventional PTFE-covered fuser roller 2.
Alternatively, it may contact the silicone rubber covered
roller 4. The roller has a porous PTFE covering. The
WO93/08512 2121128 PCT/GB92/01958 ~-
-- 10 --
roller may be pre-oiled, or oil may be supplied into the
centre of the roller by an oil supply mechanism.
Figure 5 shows a laser printer arrangement. An
oil-containing felt 40 in channel 42 applies oil to a
conventional PTFE-covered fuser roll 2. The felt has a
porous PTFE covering laminated thereto. Specific Examples
of the invention will now be described.
ExamPle 1 (Cover Wick)
(1) An oiling assembly for the fuser rolls in a
conventional Kodak Ektoprint 850 photocopier comprises a
re ervoir formed of 1600 gms per sguare metre Nomex felt
of thickness approximately 16mm, and a cover wick
comprising a Nomex felt of 400 gms per sguare metre fitted
with ~ide bars for locating the cover wick against the
fuser roll (i.e. in the manner of Figure 3).
(a) ~he cover wick was removed and a strip of porous
polytetrafluoroethylene sheet material of thickness 380
microns,-~porosity approxi~t~ly 50% and density 1 gm per
c.c. ~dhered to the side bars across the Nomex felt, such
as to contact th~ fuser roller in use. The porous
polytetrafluoroethylene material comprise S0% Teflon grade
7A and 50% T-flon grade 9B produced according to Exampl- 1
of p~t nt specification G82242431. Tho Kodak Ektoprint
850 photocopying machine was run continuously for seven
~;~ days before the machine was stopped and the cover wick
inspected. In that period, about 120,000 copies had been
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~''D 93/08512 ' - 11 11 2 1 1 2 8
produced. When the wick was inspected, there was no
damage to the porous polytetrafluoroethylene sheet and no
fibre shed. Thereafter the machine continued to run and
produced a total of about 300,000 copies before the PTFE
cover wick failed mechanically by tearing at the side
bars. A conventional wick usually lasts for 160-220,000
copies.
(b) In a further test, the conventional cover wick
was replaced by the same porous PTFE material, but in this
case the porous PTFE sheet was adhered using a gravure
printed polyimide adhesive (Mitsubishi A310) pattern to a
woven glassfibre fabric. The polyimide adhesive is
capable of withstanding temperatures of 180-200C. The
photocopier produced 1,000,000 copi-s before the cover ;~
wick failed.
(2) A further trisl was carried out using a Xerox 5046
photocopier ln which a porous PTFE sheet as d-scribed
above was adhered to a woven Nomex Scrim to produce a
.
cover wick. The adh sive was a polyimide adhesive
~ Nitsubishi A310) in a gravure printed pattern. The cover
;~ wick was still intact when changed together with the fuser
~ roller after having made 350,000 copies. A conventional
; woven Nomex cover wick is usually capable of producing
~ 60,000 copies only.
. .
ExamPl- 2 ~Oilinq Roll)
A conventional Siemens ND2 photocopying machine
WO 93/08512 PCT/GB92/01958
- 12 -
comprises an oil-containing oiling roll which oils the
fuser roll with silicone oil and also wipes it clean (in
the manner of Figure 1). The converntional roll is formed
of 700 gms per square metre PTFE felt, of thickness 1.3
mm, 435 mm wide and 1.4 metres long. The felt is wound
on bakelit spools and the roll has an overall diameter of
approximately 63 mm., which represents the maximum allowed
according to the photocopying machine construction. The
oiling roll is advanced at a rate of 2 cm per hour of
copying operation, which delivers 1.06 grams/hour to the
fuser roll. Typically, the roll requires to be changed
three tiems a month.
According to the invetnion. the convertnianl roll was
rplaced by a rollof pourous polytetrafluorethylene
material (of composition given in Example 1) having the
same width. The pourous polytetrafluorethylene material
had a thickness of 375 microns, a weight of 375 gram/m2,
and a length of 4.2 metres for the same 63 mm diameter
roll. This is three times as long as the conventional
roll. The oiling roll was advanced at 2 cm per hour of
copying operation. The roll contained 0.8 grams/cc of
silicone oil and provided 1.6 grams/hour to the fuser
roller.
In the tests, the porous polytetrafluoroethylene
material transferred oil well and wiped well and produced
prints of consistently high quality. There was no
apparent wear no shedding of material. It is therefore
'093/08512 PCT/GBg2/01
- 13 21 ~ 1 2~
possible to obtain at least three times the lifetime from
an oil retention roll of the pre~ent invention (up to 30
days of operation) as opposed to the conventional material.
ExamDle 3 (thin oilinq web)
Certain Cannon, Xerox, Ninolta and Ronica
photocopiers use a thin web of Nomex and polyester having
a weight of 25-3S grams/m2 and a thickness of 0.060 -
0.080 mm (in the manner of Figure 1). A length of 10 - 13
m of the web is wound onto a metal core (roll diameter
31.5mm) and impregnated with an average of 31 grams/m2 of
~ilicone oil. m e web is advanced at about 2mm per minute
of copier operation, delivering 0.018 grams/min of oil to
the fuser roll.
(a) According to the invention, the standard web may
be seplaced by a shorter length of porous
tQtrafluoroethylene film of the composition of Example
1. The ~11 has a weight of 125 grams/m2 and a thickness
of 0.125 ~m. The final diameter of the roll ~31.5~m)
.
allows 7.2m of film to be wound onto the core. m e film
holds twice as much oil as the conventional web, and is
therefore`advanced at half the speed i.e. lmm/min. This
provid s an increased lifetime for the film of 120 hours,
compared to a lifetime of 96 hours for the qonventional
web. The film also has better oil retention properties,
eliminating any oil drops; and gives good toner and paper
WO 93/U8512 21 21 1 2 8 14 - PCI/GB92/01958
dust adsorption. Higher fusing temperatures may be used,
and there is reduced frictional drag.
(b) In another embodiment of the invention, the
st3ndard thin web in a Xerox photocopier was replaced by a
PTFE film of composition as in Example 1. The thickness
was 0.13mm. Its lifetime was found to be about four times
as long as that of the conventional web.
(c) ~n another embodiment, a conventional web of
layers of polyester and Nomex in a Siemens ND2
photocopying machine was replaced by a sheet of PTFE as in
Example 1 having a layer of woven Nomex fabric bonded to
the front face thereof (i.e. the face in contact with the
fuser roll). The material performed well and ha~ a
lifetime at least three times as long as the conventional
web.
Examle 4 (Laser Printers)
Conventional laser printers use as the oil supply and
wiping # chanism a square section length of Nomex felt,
typically 2 cm x 2 cm x 40 cm (see Figure 5). Such Nomex
felts conventionally suffer from fibre shed and may run
dry through lack of oil towards the end of their working
life.
An oil transfer component according to the present
invention was produced by laminating a surface sheet of
porous polytetrafluoroethylene as used in Example 1 over
the surface of the Nomex felt. The life of the component
'`'093/08512 21 21 1 2 ~ PCT/GB92/01958
-- 15 --
was 250,000 copies in comparison to 80,000 with the
conventional component.
This material may also ~e impregnated with oil for
use as a coating/wiping component on a laser printer, or
may be used dry as a wiper.
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