A CLEANING ELEMENT
The present invention relates to a cleaning element, particularly although
not exclusively for use in electrostatographic reproduction or printing
apparatus.
In conventional electrostatographic apparatus, for example a
photocopier, toner is deposited onto one side of a sheet of paper, to form an
image. The paper is then fed into the fuser section of the machine where it is
heated, typically by passage between two rollers, one of which is heated to
approximately 180°C. The heated roller makes contact with the side of the
sheet of paper onto which toner has been deposited, causing the individual
toner particles to fuse together and adhere to the paper.
A problem associated with the use of heated rollers is that some toner
particles adhere to the roller, rather than to the paper. Paper dust and other
contaminants may also adhere- to the roller. A build up of toner particles and/or
paper dust on the heated roller leads to reduced image quality. In order to
minimise the build up of toner, the heated rollers in photocopier machine fuser
sections are usually coated with polytetrafluoroethylene (PTFE) which provides
a non-stick surface to which toner particles are less likely to adhere. In
addition there is also usually provided a cleaning element placed adjacent to the
heated roller which is arranged to remove toner particles from the surface of
the heated roller.
The cleaning element typically comprises a roller, the surface of which
is arranged to accumulate the excess toner particles.
In one existing system where a cleaning roller is employed, the roller
comprises a perforated aluminium cylinder, the surface of which is coated with
a fabric, the exposed side of which has fibres projecting therefrom. These
fibres comprise polyphenylene sulphide (PPS) fibres of 15 denier and are of
approximately circular cross-section. In addition, the core of the cleaning
cylinder forms a reservoir containing a silicone oil, which can pass through the
perforations in the aluminium cylinder and is distributed through the fabric
coating.
Such a cleaning roller is designed to remove and retain excess toner
particles from the rollers, and particularly the heated roller, of the fuser section.
The use of a silicone oil assists the removal of toner from the roller and also
aids the retention of toner by the fabric coating of the cleaning roller.
A problem arises with known cleaning elements in so far as when a
cleaning roller has become saturated with toner particles it becomes ineffective
and therefore requires replacement. This is inconvenient and costly as the
entire element is usually replaced.
Another problem with existing cleaning elements is that, where
polyphenylene sulphide (PPS) fibres are used there is a tendency for these
fibres to burn when in contact with the heated roller or other heated parts of
electrostatographic reproduction equipment. When the fibres burn this reduces
the cleaning performance of the roller. Also, these 15 denier fibres are
sufficiently rigid to scratch the surface of the heated roller, this is undesirable
as this exacerbates the problem of toner or other particles adhering to the
roller. If the fibres become burned this may cause them to become more rigid
making the problem worse. Wear of the heated roller can exacerbate the
problem of excess toner adhering to the roller.
It is an object of the present invention to overcome or at least minimise
the above mentioned problems associated with known cleaning elements and
thereby to increase the effective cleaning effect of these elements, particularly
the cleaning of photocopier fuser section rollers, along with a significant
increase in useful working life of the element.
According to the present invention, there is provided a cleaning element
having projections projecting from an outer surface thereof forming a pile, the
cross-section of each projection having a peripheral dimension and an area,
wherein the ratio of said peripheral dimension and cross-sectional area is
greater than said ratio for a projection of circular or substantially circular and
equal area of cross-section.
Preferably the pile comprises a cut pile of depth in the range 1 -20mm,
although a looped or partially looped pile may be used. Preferably each said
projection is of multi-lobal cross-section. Preferably the projections forming the
surface of the cleaning roller comprises a synthetic fibre which is preferably
resistant to thermal breakdown at temperatures up to 250 °C or more preferably
260°C, suitable fibres comprising polyimide or PTFE. PPS could also be used.
Also a mixture of suitable fibres could be used, intermixed or provided in zones
across the surface of the element. The fibres preferably have a denier in the
range 0.5-20 denier, more preferably 0.5-15 denier, more preferably 0.5-5
denier, still more preferably 1 -5 denier and particularly 5 denier.
It will be understood that there are many possible embodiments of the
cleaning element in which the element takes different forms to enable its
installation in different types of equipment and for different applications.
Examples of possible embodiments include cleaning rollers, cleaning pads and
cleaning belts.
In one embodiment the element comprises a roller. The roller preferably
comprises an aluminium cylinder or rod, to the surface of which is bonded a
fabric, a surface of the fabric forming the outer surface of the roller and
including the projections. The roller may incorporate a reservoir for storing and
dispensing silicone oil into the fabric that forms the surface of the roller, the oil
being utilised to enhance the performance of the cleaning roller.
In another embodiment the element comprises a pad. The pad preferably
comprises a felt pad, an example of a suitable material being that sold under
the Nomex trade mark by Dupont, to the surface of which is bonded a fabric,
a surface of the fabric forming the outer surface of the pad and including the
projections. The pad may act as, or incorporate, a reservoir for storing and
dispensing silicone oil onto the fabric that forms the surface of the pad, to
enhance the cleaning performance of the pad. Alternatively the pad may
comprise a silicone foam pad.
Other embodiments are possible, where the cleaning element is formed
by any part of a machine or other to which there is affixed a fabric, a surface
of the fabric forming the outer surface of the element and including the
projections.
A cleaning element of the present invention exhibits a far greater surface
area on which to accommodate excess toner particles than prior art elements
of similar size. This greater area is achieved in that the shaft of each individual
projection forming the pile on the surface of the element presents a larger
surface area than projections of circular cross-section as used on existing
elements. The provision of a larger surface area to accommodate toner
particles, without increasing the size of the roller itself, enables rollers of the
present invention to have an extended useful life over existing, similarly sized
elements.
The use of projections having a cross-section as described tends to
increase the rigidity of those projections over projections with a substantially
circular and equal area of cross-section. This enables projections of a lower
cross-sectional area, or lower denier in the case of fibres, to be employed
without loss of the rigidity required for efficient removal of toner particles. By
reducing the thickness of the individual projections or denier of the fibres that
form those projections this allows for a greater density of projections to be
accommodated on the surface of the element. Typically, the use of 2 denier
fibres in comparison to the 15 denier fibres employed on existing elements
enables the density of the fibres per unit surface are to be increased by a factor
of at least 4. The use of a greater density of projections each having a greater
surface area per length per unit cross-section leads to a still further increase in
the available surface area for the accumulation of excess toner particles. This
increases the useful life of the cleaning roller, typically to between 1.5 and 2.5
times that of existing rollers, and also leads to more efficient cleaning of the
heated roller.
In an experiment the performance of a cleaning roller, according to the
present invention was compared with a conventional roller in use in a
photocopier. It was found that where the conventional roller as employed the
quality of copies available from the machine deteriorated after 200,000 copies
had been made, whereas with the roller according to the present invention the
quality of copy did not deteriorate until in excess of 300,000 copies had been
made.
The use of a lower projection size, or in the case of fibres a lower denier,
and of a projection of greater resistance to thermal breakdown results in less
abrasion of the heated roller or similar, prolonging fuser section life. A further
advantage associated with the use of a lower projection size is that a greater
pile depth than with existing elements can be employed able to accommodate
still further toner particles without risk of damage to the heated roller.
The use of an element having both a greater cleaning surface area and
finer projections also reduces the requirement for silicone oil due to increased
mechanical action of the element leading to still further cost savings. Silicone
oil is conventionally used to increase adherence of toner particles to the
cleaning element and to reduce any damage caused by the element as a result
of abrasion. As cleaning elements according to the present invention use fibres
of lower denier than employed in prior art cleaning rollers it is possible for the
element to be installed with a greater degree of interference fit. This increases
the mechanical action of the element. Also, the greater degree of interference
means that the surface area on the sides of the projections is employed in
cleaning and may also accumulate toner and other particles. Increasing the
degree of interference fit with existing cleaning rollers tends to increase
scratching of the heating roller by the cleaning roller. The degree of
interference fit may be increased by increasing the diameter of the cleaning
roller compared to an equivalent prior art roller.
Using less silicone oil is advantageous where duplex printing is
concerned where it is desirable that only a minimum of silicone oil is transferred
onto the paper during its first pass through the fuser section. Excess silicone
oil can cause difficulties in getting toner to adhere to the paper.
Elements according to the present invention also have a better ability to
wick silicone oil, due in part to their increased surface area. This leads to more
efficient and even distribution of silicone oil.
In order that the invention may be more clearly understood there is now
described embodiments thereof, with reference to the accompanying drawings
in which:-
Fig.1 shows a cut away perspective view of an incomplete cleaning roller
of the present invention;
Fig.2 shows a cross-section through the fabric that is bonded to the
surface of the roller illustrated in Fig. 1 ;
Fig.3 shows a cross-section along the line Ill-Ill through the pile of the
fabric illustrated in Fig.2;
Fig. shows an end view of a cleaning roller as mounted in a photocopier
machine; and
Fig.5 shows a cross-section through a part of a cleaning pad according
to the present invention.
Referring to Fig.1 , there is illustrated, for reasons of clarity, an
incomplete cleaning roller comprising a perforated aluminium cylinder 1 having
a spindle 2 attached to the end thereof. It will be appreciated that a complete
roller is fitted with a respective spindle 2 at each end thereof. Wrapped around
the aluminium cylinder 1 there is a layer of non-woven textile 3 of
predetermined permeability. The non-woven textile 3 is secured to the cylinder
1 by a length of adhesive tape 4. Bonded to the surface of the non-woven
textile 3 is a fabric layer 5, which comprises a length of fabric, which is spirally
wound around the cylinder, and affixed by means of adhesive 6, applied to the
surface of the non-woven textile layer 3. Disposed in the centre of the
aluminum cylinder is a quantity of silicone oil 7.
In use the roller is mounted adjacent to the heated roller of the fuser
section of a photocopier, the fabric surface making contact with the heated
roller. The silicone oil 7 passes through the perforations in the aluminium
cylinder 1 and diffuses through the non-woven textile layer 3 at a
predetermined rate to the fabric 6, from which it is transferred to the heated
roller.
Referring to Fig.2 the fabric illustrated comprises a woven substrate 8
having a cut pile 9 projecting therefrom. The fibres forming the pile are
polyimide fibres of 2 denier, the pile depth is approximately 3mm.
Alternatively the pile could comprise a mixture of fibres. In one
embodiment the fabric may be so arranged that the roller has alternating bands
of different fibres along its length, for example alternating regions of 2 denier
polyimide fibres and 16 denier PTFE fibres. The arrangement is particularly
advantageous where a cleaning roller is used in conjunction with a beater or
scraper bar. The polyimide fibres will act to clean the fuser section and the
beater or scraper bar will push excess toner particles onto the PTFE section of
the brush and, optionally, into a hopper.
Referring to Fig.3 there is shown the cross-section of the polyimide fibres
forming the pile of the fabric illustrated in Fig.2. The fibres are of tri-lobal
cross-section, the ratio of the distance around the perimeter of the cross-
section of these fibres to their cross-sectional area is greater than that for fibres
of substantially circular cross-section having the same cross-sectional area.
Referring to Fig.4, there is illustrated a cleaning roller 10, shown in
relation to the fuser section of a photocopier. The fuser section comprises two
rollers 1 1 and 12, roller 12 is heated to approximately 180°C, the surface of
the roller 12 is coated with PTFE. Paper 13, onto one side of which toner 14
has been deposited is fed between rollers 1 1 and 12.
The cleaning roller 10 is disposed to rotate adjacent to the heated roller
12, in order to remove any toner particles which adhere to this roller.
Referring to Fig.5 there is illustrated a cross-section through a part of a
cleaning pad which comprises a felt pad 15, approximately 4mm thick, to
which there is bonded a fabric layer which comprises a woven substrate 16,
having a cut pile 17, projecting therefrom. The fibres forming the pile are
polyimide fibres of 2 denier and are of tri-lobal cross-section, the pile depth is
approximately 3mm.
The fabric layer is the same as the fabric illustrated by Figs. 2 and 3.
The above described embodiments afford advantages over the prior art.
By the provision of 2 denier fibres of tri-lobal cross-section there is a
substantially increased surface area on which excess toner particles can collect
when compared to known cleaning rollers or pads of similar dimensions. The
use of fibres with a tri-lobal cross-section allows a lower denier of fibre to be
used than would be required to maintain sufficient rigidity for effective cleaning
with fibres of circular cross-section. The use of a fibre of lower denier enables
more fibres to be accommodated per unit area on the surface of the roller or
pad, increasing the available surface area for the accumulation of toner
particles. The 2 denier polyimide fibres form a softer and more heat resistant
pile than that of known rollers or pads, less likely to damage photocopier fuser
section rollers or similar and reducing the requirement for silicone oil, the
diffusion of which is controlled by the intermediate non-woven layer or, in the
case of the pad is stored in the felt pad. The result is an enhanced useful life
over existing rollers or pads of similar dimension, typically between 1 .5 and 2.5
times that of existing rollers, as well as improved cleaning efficiency.
The above embodiment is described by way of example only, many
variations are possible without departing from the invention. For example the
cleaning elements could be employed in apparatus other than photocopiers, for
example laser printers. Also elements according to the present invention could
be used without silicone oil.