Note: Descriptions are shown in the official language in which they were submitted.
WO94/16539 215 ~ ~ 9 8 PCT~S93/07524
CERAMIC HEATER ROLLER
AND METHODS OF MAKING SAME
Technical Field
The invention relates to heater rollers for use in a
variety of industrial machines, as well as methods of
making such rollers.
Back~round Art
Steam-heated and induction-heated rollers are used in
the paper making, printing, paper, film, and foil
converting industries. Some examples are: web heating
rollers, drying rollers and drums, laminating rollers,
embossing rollers, and cast film extrusion rollers.
Steam-heated rollers are actually pressure vessels,
especially at higher temperatures. The internal
construction of both steam-heated and induction-heated
cores can be quite complex and expensive in order to
provide the temperature uniformity needed. In addition, a
considerable amount of auxiliary equipment is needed to
power or heat the roller.
Internally heated fuser rollers are used in the copier
industry. The fuser roller melts the toner and presses it
into the paper. The typical fuser roller consists of an
aluminum or non-magnetic metal core with an internal quartz
heating lamp. The inner diameter of the core has a special
coating to absorb heat from the lamp. The roller is coated
with a non-stick elastomeric material (e.g. silicone
rubber) to provide a pressure nip with an opposing roller
and to release the toner to the paper.
The core construction is quite complex and expensive.
The quartz lamp is fragile, has a limited useful life, and
does not provide a uniform temperature distribution to the
core.
Heating rollers for xerography and other applications
are disclosed in the following U.S. Patents, Satomura,
No.4,628,183; Nagaska, et al., No. 4,743,940; Lee, et al.,
WO94/16539 215 3 5 9 8 PCT~S93/07524
--2--
No. 4,791,275; Kogure, et al., No. 4,813,372; Urban, et
al., No. 4,810,858; Urban, No. 4,820,904, Yoshikawa, et
al., No. 4,841,154; Landa, et al., No. 5,089,856.
It is typical in such rollers to apply a voltage
potential at one end of the heating layer and a ground
potential at the the other end of the heating layer to
produce a current in the heating layer.
For example, in Satomura, No. 4,628,183, one side of a
voltage supply is applied to one set of conductive fingers
in a ceramic heating layer, while the other side of the
voltage supply is applied to another set of conductive
fingers in the ceramic heatlng layer. The two sets of
fingers are interdigitated and electrical current is
produced in the heating layer between the two sets of
fingers.
The ceramic material is a baked ceramic material in
which the conductive electrodes are sandwiched between two
ceramic layers.
The present invention is directed to improved
constructions of heater rollers utilizing a ceramic heating
layer and to improved methods of making such heater
rollers.
D'sclosure of the Invention
The invention relates, in one aspect, to a thermal
conduction roller having a cylindrical roller core with a
ceramic heating layer of predetermined and controlled
resistance disposed around and over the core. A conductive
ground layer is disposed around and over the ceramic
heating layer, the conductive ground layer being
connectable to an electrical ground. A voltage is applied
to the core, or to a thin layer of metal on the outer
surface of the core. Current flows outwardly from the core
through the ceramic heating layer to the outer ground
layer, which may be covered with an outer functional layer
WO94/16539 2 i ~ ~ 5 9 ~ PCT~S93/07524
_
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of elastomeric or other material for durable performance
over the life of the roller.
Such a construction does not require internal
complexity and the ceramic layer provides a controlled
temperature profile across the roller surface. The core
can also be thermally isolated, if desired, from the heated
region to reduce power usage and wasted heat and to reduce
lag in thermal regulation response due to the thermal mass
of the core.
In a second aspect, the invention relates to the
method of making a heater roller in which the ceramic
heating layer is formed by plasma spraying, which is one
type of thermal spraying. This significantly decreases the
resistance of a semiconductive ceramic material. The
ceramic material is applied in a manner to control
electrical resistance of the ceramic heating layer.
The electrical resistance of the ceramic heating layer
can be controlled by blending the first ceramic material
with a metallic material or with a second semiconductive
ceramic material and applying the ceramic heating layer in
a thickness selected to control electrical resistance. The
ceramic heating layer is formed of a plurality of thinner
layers, which are applied one over the other to build up
the ceramic heating layer.
The electrical resistance of the ceramic heating layer
can also be controlled by varying the hydrogen secondary
plasma gas level during plasma spraying.
Other objects and advantages, besides those discussed
above, will be apparent to those of ordinary skill in the
art from the description of the preferred embodiment which
~ follows. In the description, reference is made to the
accompanying drawings, which form a part hereof, and which
illustrate examples of the invention. Such examples,
however, are not exhaustive of the various embodiments of
the invention, and, therefore, reference is made to the
WO94/16539 PCT~S93/07524
~ lS 3 ~ 9 R _4_
claims which follow the description for determining the
scope of the invention.
Brief DescriDtion of the Drawin~s
Fig. 1 is a perspective view of a roller of the
present invention with parts broken away;
Fig. 2 is a cross sectional view of a portion of the
roller of Fig. l; and
Fig. 3 is a left end fragment of a longitudinal
section of the roller of Fig. l;
Fig. 4 is a right end fragment of a longitudinal
section of the roller of Fig. l; and
Fig. 5 is an exploded view of the roller of Fig. 1
showing use of a metallic sleeve to form the metallic
layers of the roller.
Det~iled Descri~tion of the Preferred ~mhodiment
Fig. 1 shows a preferred embodiment of a heater roller
10 of a type for use in copying machines, or in other
industrial applications, such as steam-heated or induction-
heated rollers for the paper making, printing, paper, film,
and foil converting industries.
The finished roller 10 includes a hollow cylindrical
core 11 with suitable journal shafts 25 for disposition in
suitable machine bearing structures of a type known in the
art. The core material in the preferred embodiment is
glass, but stainless steel, brass, some steels, aluminum, or
an FRP composite type material can also be used. If a non-
insulating core is used, the shafts 25 or their bearings
must be insulated from the rest of the machine.
If the core 11 includes a non-conducting material such
as glass, a thin layer of metal 12 of 1 to 3 mils thickness
(1 mil = .001 inches) is formed over the full outer surface
of the core 11. This metal layer 12 can be formed by plasma
WO94/16539 21~ 3 ~ 9 ~ PCT~S93/07524
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spraying a bond coating over the full outer surface of the
core 11, or as shown in Fig. 5, this layer can be formed by
an expandable metal sleeve 13, which is placed over the non-
conducting material 11 as shown in Fig. 5. A bond coatiny
may then be sprayed on the metal sleeve 13 to assist the
formation of a bond to the next layer.
Next, a ceramic layer 14 from 1 to 100 mils in
thickness is formed over the full outer surface of the
bonding layer 12.
This is followed by a second thin layer of metal 15 of
1 to 3 mils thickness which is formed over the full outer
surface of the layer 14. This layer 15 can be formed by an
expandable metal sleeve similar to the sleeve 13, which is
shown in Fig. 5.
The outer surface of the roller 10 is provided by a
functional layer 16 of ceramic, alloy, tungsten carbide, or
elastomeric/polymeric material. If the outer functional
layer 16 is formed of a metal, such as stainless steel,
nickel, or tungsten carbide/cobalt composite, this outer
layer 16 is connected to a grounded negative (-) side of
the power supply. If the outer functional layer 16 is
formed of a ceramic, the ceramic is applied by plasma
spraylng .
The inner metal layer 12 forms a ring-shaped band 18
extending from one end of the roller 10 (Fig. 4). A brush,
represented by element 19, contacts bond 18 and is
electrically connected to the positive (+) voltage terminal
of voltage source 20. The outer metal layer 15 forms a
ring-shaped band 21 extending from an opposite end of the
roller 10 (Fig. 3). A brush, represented by element 22,
~ contacts bond 21 and is electrically connected to the
grounded negative (-) terminal of the voltage source 20.
~ This provides a ground layer 15 just underneath the outer
functional layer 16. The voltage source 20 may supply
either alternating current or direct current.
PC~IUS ?3 / C7 5 24
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With this arrangement, current flows in a radial
direction between layers 12 and 15 relative to a
longitudinal axis 23 of the roller 10 seen in Figs. 1 and
2.
Usually the surface of a metal core is roughened by
grit blasting to clean the metal surface and to provide a
surface roughness Ra Of about 200 to 300 microinches to
improve the mechanical bonding of the ceramic layer 14 to
the core. Where a core of non-metallic material 11 is
used, a metallic bonding layer 12 of nickel-aluminide such
as Metro 450 or 480, or nickel-chrome, such as Metro 43C,
is applied in a layer 3 mils to 5 mils thick or more. The
bonding layer 12 provides the surfacé roughness Ra Of 300
microinches or greater.
Where a metallic core is used, the heater layer 14 is
electrically and (optionally) thermally insulated from the
metallic core by an insulating }ayer (not shown) of plasma
sprayed ceramic such as alumina, Metco 101 or 105, or
preferably zirconia, Metco 2~1 or 204. Zirconia can be
used as an electrically insulating barrier coating a few
mils thick. In thicker }aye~s, zirconia is an effective
thermal barrier coating due to its low thermal
f conductivity. It can be plasma spraye~ in layers of 250
mils thick (1/4 inch) or greater.
The insulating layer does not need to be any thicker
than what is required to resist~the voltage applied to the
heater layer. The dielectric strength of plasma-sprayed
alumina for example can be up to 300 volts per miL of
coating thickness.
The preferred material for the ceramic heating layer
14 is titanium dioxide, such as Metco~-102 ceramic powder.
This is commercially available from Metco Corp., Westbury,
New York, USA. Tltanium dioxide (TiO2) is normally an
electrical insulating material. However, when the material
is plasma-sprayed, some of the dioxide form is chemically
reduced to a conductive sub-oxide (mono-oxide) form,
AMEND~ SH~ET
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prT?~ j-r ~
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46 ~ V '3~
rendering the deposited coating electrically semi-
conductive.
As used herein, the term "insulating" material shall
mean a material with a volume resistivity of 101~ ohm-
S centimeters or'greater. As used herein, the term"semiconductive" material shall mean a material with a
volume resistivity between 103 ohm-centimeters and 101~ ohm-
centimeters. Titanium dioxide (TiO2) and chromium oxide
(Cr2O4) are examples of semiconductive or lower resistance
ceramics. These ceramics have volume resistivities
typically of 108 ohm-centimeters or lower.
Titanium dioxide can be used as the only component of
the heater layer or it can be blended with other ceramics
to increase or decrease the volume resistivity of the final
coating. For example, insulating ceramics such as zirconia
or alumina can be blended with semiconductive ceramics such
as chromium oxide.
Plasma spraying, which is one type of thermal
spraying, is advantageous in adjusting the thickness of the
coating to a suitable range independent of the electrical
resistance of the titanium dloxide portion of the heater
layer.
For any ceramic layer containing titania (titanium
.
dioxide), the resistance of the layer is also affected by
the spraying conditions. Titania can be partially reduced
to a suboxide by the preqence of hydrogen or other reducing
agent~ in the pla~ma flame. It is the suboxide (probably
TiO rather than TiO2) that is the semiconductor in the
- ceramic layer 14. Titanium dioxide is normally a
dielectric material. The typical average chemical
composition of titanium dioxide is 1.8 oxygen per molecule
rather than 2.0 in a plasma sprayed coating. This level
(and thus the coating properties) can be adjusted to some
extent by raising or lowering the percent of hydrogen in
the plasma flame. The normal primary gaq is nitrogen or
argon while the secondary gas is hydrogen or helium. The
~ h~F-O i~ET
~C' 1~' ", 3 ! ~ 7 5 24
5 3 ~ ~ 8 4~ r~. ~ . 1~v J ~1995
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secondary gas raises the ionization potential of'the
mixture, thus increasing the power level at a given
electrode current. For a typical Metco plasma gun, the
hydrogen level is adjusted to maintain the electrode
voltage in the gun between 74 and 80 volts.
Regardless of the mixture of powders used, the plasma '
spray parameters should be suitably adjusted to insure that
the blend of materials in the finished ceramic layer 14 is
the same as intended. All of the powders mentioned do not
require the same power levels, spray distance,and other
parameters. Thus, adjustment of spray distance, for
example, may increase the deposit efficiency of one powder
over the other and change the material blend in the
finished coating.
Plasma sprayed ceramic coatings can be applied in one
pass (layer) of the plasma gun or in multiple passes. The
normal method for most types of coating applications is to
apply multiple thin coatings of ceramic and build up to the
required thickness. Although the ceramic layer described
above has a uniform ceramic composition the sublayers of
ceramic-in the resulting layer 14 do not have to ~ave the
same composition.
The hydrogen level can-be varied during the
application of each spray pass to apply a titanium dioxide
layer that has a non-uniform electrical resistance from end
to end of the roller. This would normally be done to apply
more heat to the end-l of the roller, where the heat losses
are greater, to achieve a uniform temperature across the
roller face in its functional environment.
The thickness of the heater layer 14 can~be adjusted
to provide the appropriate resi~tance for the application.
The heater layer 14 may vary in total thickness from about
1 mil to about }00 mils depending on the roller diameter
and length, operating temperature, wattage throughout and
JS '~' 3 / C 7 5 Z4
3 5 9 8 48 R~c~ l99S
power supply voltage. In the preferred embodiment, the
heater layer 14 is in a range from 5 mils to 10 mils thick.
Plasma-sprayed ceramic can be applied in very thin
layers (at least as low as 0.1 mil per spray pass). For
many heating applications, the heater layer formed by
plasma-spraying thin layers will provide a minimal
temperature variation due to thickness variation of the
resulting layer.
The temperature uniformity depends primarily on the
thickness uniformity of the heater layer. Since the heater
layer is composed of many, thin layers or spray passes,
material variation is generally not an issue.
Precise control of the heater layer thickness can be
- 15 achieved by conventional grinding of the ceramic layer.
A second bonding layer 15 of nickel aluminide, such as
Metco 450 or 480, or nickel chrome, such as Metco 43C, is
applied by thermal spraying to a thickness of at least 3
mils to 5 mils.
The outer functionai layer 16 is then applied. This
may be any material that can be applled by thermal
spraying, any elastomer, thermoplastic or thermoset resin,
suitable for the roller application.
The outer metal layer can be applied by
electroplatin~g,~if the ceramic is sealed, with the outer
functional layer, preferably silicone rubber, bonded to the
electroplate. The electroplate must not contact the core.
The outer layer 16 can be plasma sprayed metal, if the
ceramic is not sealed or ground, with the outer functional
layer plasma ~prayed and bonded to the sprayed metal layer
15. Such outer metallic layer 16 would preferably be a
nickel alloy, stainless steel, or low resistance cermet.
If the ceramic is ground, it can be sealed. This
increases the dielectric strength of the heater layer 14
and prevents moisture and humidity from changing the
effective ceramic resistance and causing short circuits.
AMEND~ ET
s ~7524
46 R~c'~ v~ 995
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While the roller is till hot from the plasma or
thermal spraying of the ceramic layer 14, a seal coat 24 is
applied to the ceramic layer 14 using a dielectric organic
S material such as Carnauba wax or Loctite 290 weld sealant.
The sealant 24 is cured, if necessary, (Loctite 290), with
heat, ultra violet light, or spray-on accelerators. The
ceramic porosity level is generally less than 5% by weight
(usually on the order of 2%). Once sealed, the porosity
level has a minimal effect on the coating properties for
this application.
The preferred types of materials are 100 percent
solids and low viscosity These include various kinds of
waxes, condensation cure silicone elastomers, and epoxies,
methacrylates, thermoset resins and polymerizing weld
sealants, such as Loctite 290.
The sealer will generally be a high re-sistance
material, although the electrical properties of the sealer
affect the overall properties of the sealed ceramic layers
14, 24. For example, sealing with Carnauba wax will result
in a higher resistance of the sealed ceramic layer 14, 24
than Loctite 290 weld sealant because it is a better
dielectric material.
A finishing step is to grind and polish the sealed
ceramic layer 14, 24 to thé proper-di~ensions' and surface
finish (diamond, -~ilicon carbide abrasives, etc.).
The outer metallic layer 15 can be a metallic sleeve
of nickel, steel, or aluminum, that is removeable and
replaceable. The outer functional layer 16 is then bonded
to the replaceable sleeve. The ceramic heater layer 14
would be ground and sealed in this case. if the outer
functional layer 16-is damaged or wears out, the roller can
be returned to service simply by installing a new sleeve.
The surface of the core 11 can be crowned positive or
negative, to provide a variable ceramic heater layer
thickness to compensate for non-uniform heat losses. This
AMEND~ StlE~T
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3 ~ 9 8 - 46 R~cid ~ 9~5
could be used to provide a certain temperature profile
across the face of the roller 10 in its application.
This has been a description of examples of how the
invention can be carried out. Those of ordinary skill in
S the art will recognize that vari~us details may be modified
in arriving at other detailed embodiments, and these
embodiments will come within the scope of the invention.
Therefore, to apprise the public of the scope of the
invention and the embodiments covered by the invention, the
following claims are made.
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