Note: Descriptions are shown in the official language in which they were submitted.
; In general~ press felts are used in papermaking machines
to suppor~ the moist~ ~reshly formed paper web as it encounters a
variety of rolls which serve to extract water from the moist paper
web. In addition to serving as a support for the paper web, the
press felt serves as a receptacle for the wa~er removed from the
paper sheetO The press felt normally has a conveyor belt-like
shape and during the various operations previously mentioned, a
large amount of water is built up in the press felt which is removed
by suction or various other drainage devices, usually after the
paper wab and press felt are no longer in direct contactO During
the break-in or start~up period of most prior art felt~ it is
usually nacessary to run the papermaking machine at a reduced speed
and/or to increase the heat energy flowing into the dryer section.
Since the amount of paper produced by a papermaking machine i9 `. ;
largely dependent upon the speed of the machine, any slowing down
cau~ed by, for example, the required break-in period in papermakers'
felts,~ results in the machine ~unctioning at less than optimum ~co-
nomic efficiency.
Paper sheet dewatering, sheet surface smoothness~ sheet
pick-up and shee~ carrying, as well as a variety of other perfor-
mance characteristics, are sensitive to felt design. It has been
observed that the physical characteristic~ of felts change during
their useful operating life9 the greates change occurring during
the first several hours of felt operation. Most pre-~s felts re-
quire an initial start-up period before peak water xemoval ef~icien- `-
cy is achieved. This start-up period usually la~ts for several
hours and~ in ~ome cases, as much a3 several days. During the
start-up period, press ~elt performance may be un~atisfactory in
terms of optimum water removal from the paper web and pick-up and -~
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~ lOG~6Z~l
carrying of the paper web from the adjacent forming section or from
an adjacent felt, thereby resulting in lost paper production and/or
higher paper production costs due to lower operating speedsO
The subject of the present invention is a felt structure de-
signed to substantially reduce or elLminate the problem of relatively
poor paper machine performance during the early part of felt life.
The new structure is based on the observation that the originally
round or irregularly shaped felt surface fibers tend to flatten out
during operation. A~ surface fibers flatten, the area of interface
lQ between felt and paper increases leading to greater adhesion between
felt and sheet and therefore to improved shee~ pick-up and sheet
carrying performance. In addition~ the increased sheet/felt inter-
face area provides a more effective sheet support in the press lead-
ing to more efficient sheet dewateringO However, since fiber flatten-
ing under papermaking conditions requires time, during the early
part of felt life ~he papermaker must do without the resultant
benefits.
The present invention teaches the construction of felts
with flat fiber~ already present in the sheet-contacting sur~ace o~
the new felt~ rather than await the natural process of fiber de~
formation, in order to substantially9 or in sGme cases totally~
eliminate the early period of relatively poor performance~
In utilizing a sheet-contacting layer comprising flat fibers
as opposed to round or irregularly haped f~bers as has been used in
the prior art, it is possible to increaæe the actual area available
on the surface of the felt for contact with the paper web~ Without
intending to present any particular theory of operation of the pre-
sent invention, it is believed that felts having a surface contacting
layer comprising flat fibers allow a more efficient transfer of water
.. . . . . .
.
ètween the paper web and press felt~ when the mechanical forces of
the presses present in the pxess ~ection of the paper machine act on
the paper web to transfer the water contained in the paper web to
the press felt.
The use of flat fibers in the sheet-contacting layer allows
for a relatively smooth surface to be presented to the paper web which
come~ in contact with the felt structure. The result of this is that
marking of the paper web is minimi2ed. Further, by utilizing flat
~ibers in the sheet-contacting layer as described herein, it is al~o
possible to reduce the tendency of the felt to fill up. By filling
up, it is meant the action of wood fibers and small particles of other
materials in the pulp to accumulate below the surface layer of a
papermakers' feit so as to interfere with proper water removal, there-
by reducing the efficiency of the papermaking process in the press
section. The reduced filling up tendency is believed to occur because
of the high fiber density present in the sheet-contacting layer of
felts constructed in accordance with the invention. The highcidensity
flat fibers on the surface of the felt tend to retard the ability of
the particles on the surface of the felt to work their way below the
sheet-contacting layer so as to prevent their being easily removed by
conventional felt-cleaning equipment which usually takes the form of ^~
a high pressure shower directed at the surface of the felt subsequent
to its contact with the paper web.
In addition, felts constructed with a sheet-contacting layer
comprised of flat fibers posses desirable proper~ies with regard;to
paper web pick-up. By paper web pick-up, it is meant the ability of
a press felt to transport the moist paper web as it leave~ the orming
fabric or wire which is the first step in the paper-forming process.
It is sometimes the case that the sheetJ instead of attaching itself
to the felt as it leaves the forming fabric, will instead.....
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move off the paper machine, thus causing a loss in the paper pro-
duction process. Since the sheet-contacting layer o~ the present
invention has a greater available surface area for contact with the
paper web than prior art felts~ it is believed that it will exhibit
substantially better sheet pick-up properties than have heretofore
been possible~
Accordingly, it is an object of the present invention to
provide a papermaker~' felt having a sheet-contacting layer comprised
o~ flat fibers.
Another object of the present i~vention is to provide a
papermakers' felt having increased surface ~iber area available
~or pressing the paper web.
It is another object of this invention to provide a paper-
makers' felt which eliminates the extensive break-in or start-up
period required with most prior art papermakers' felts.
Another object of the present invention is to provide a
papermaker3' felt having a smooth paper contacting surfac~ ;~
It is still another object of this invention to provide a
papermakers' felt having a paper web contacting surface allowing
' 20 improved paper web pick-up.
; It i~ another object of this invention to provide a paper-
makers' felt having excellent water removal properties~
A further object o~ the present invention is to provide a
papermaker3' felt having de~irable resistance to fill-up~
In the Dr~wing:
Figure 1 is a schematic cross-sectional view showing on an
enlarged scale the ~tructure of the sheet-contacting layer applied
to a woven base layer.
Figure 2 is a schamatic cros -sectional view similar to
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~OG16~ ~
Figure 1 showing another embodiment of the present invention
Referring first to Figure 1 of the drawing~ a nonwoven sheet
contacting layer 1 containing flat fibexs as well as conventional
fibers 3 is deposited on and directly joined to a base layer 4~ :
which in the embodiment illustrated, comprises a woven ~abricO The
sheet-contacting layer 1 may be joined to the base lay~r ~ in any
conventional ~ashion, preferably by needling. In ano~her embodLment
of the invention, illustrated in Figure 2, the sheet-contacting
layer 1 is joined to the base layer 4 through an intermadiate batt
of nonwoven fiber6 which may comprise either natural or synthetic
fibers~ such batt layer adding additional bulk and water reception
properties to the structure. As in the case of the sheet-contacting
layer 1, the batt layer 5 may be joined to the fabric in any con- ;
ventional manner9 and both the sheet-contacting layer and the batt
layer may be joined to the base layer 4 by one or more joint needl-
ing operations. ..
In accordance with the invention~ the sheet-contacting layer
1 in either of the ~oregoing embodLments may be composed entirely
of flat f~bers, although preferably it will comprise a blend of
flat and conventional fibers, as has been illustratedO The term
~lat ~ibers as used herein is meant to refer to fibers whose per-
pendicular diameters have a ratio o~ 3:1 or greater, i.eO fibers
with cross-sectional dimensions which are at least three times as
long as they are wide~ and are to ~e contrasted with the normal
circular fibers which are known to be used in con~tructing .he
batt or surface layer of prior art papermakers~ felts O In this ;~
connection, reference is made to Fekete, UOS~ Patent ~o. 3,392,079,
Mizell, U.S. Patent ~o~ 3,030,690; and Walsh, U.S. Patent No. ~ -
215,772. Preferably the flat fibars will constitute at least 50~ :
~ 5 - ~
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~.~6~
of the fibers of the sheet~contacting layer~ However~ depending
upon the particular press configuration and paper machine design~
as little as 10% flat fibers may be usedO The cross-sectional
dimensions of the flat fibers also will have a bearins on the
composition o~ the sheet-contacting layer. For example~ ~lat
~ibers haviny a 3:1 cross-sectional ratio would tend to permit
fewer conventional fibers than a 4:1 or 7:1 ratio.
The ~lat fibers can be for~ed from any of the well known
natural or synthetic fibers which are usually u~ed in constructing
papermakers' felts9 including such animal fibers as wool9 as well
~ Tr~e ~ k J
B as such synthetic fibers as polyacrylics~ such as Orlon~ polyeæters~
(~r2C~e ~llq2rk)
such as Dacron~ and polyamides~ such as Nylon. Likewise9 the re-
maining portion of the sheet-contacting layer may be made from
any of the synthetic fibers which have been previously mentioned.
Similarlyl the batt layer 5 can be composed of any of the afore-
mentioned types of fibers~ The sheet-contacting layer 1 and the
intenmediate batt layer 5 can be formed by carding~ air-laying
or other well-known procedures which are effective to orient the
fibers in a uniform manner as to thickness and density. Alter-
natively, the intermediate batt layer may be of a wovencons~ruction.
Although not shown~ it is contemplated that the use of flat
fibers in the sheet-contacting layer 1 may be incorporated in a
number of prior art felt structures~ such as described in Fekate,
U.SO Patent No. 3~928~699 and Wicker e~ al~ U~S. Patent NoO3~214~327
both of which teach dual layer felt construction to which the
sheet-contacting layer of the present invention can be appliedO
In addition~ one or more layers may be inserted in multiple planes
between the base layer 4 and the sheet-contacting layer 1~ and
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it is to be understood that the term sheet-contacting layer means
the layer of the felt which comes into contact with the paper web.
It also will be understood that the base layer 4 will be formed
from either natural or synthetic materials of the types previously
mentioned in connection with the sheet-contac~ing and batt layers.
The sheet-contacting and the batt and base layers can be joined
to one another by mechanical methodsD such as needling in a needle
loom, or by the use of adhesives. The base layer may be a woven
structure having a plain wea~e, or any other suitable weave con-
figuration may be used, such as twill or 4-harness satin~ Alter-
nately~ the ba~e layer may comprise a nonwoven fabricO
The following example illustrabes a felt constructed accord-
ing to the teachings of the present invention:
A base layer was woven endless with a reverse broken twill
weave containing approximately 4~2 warp yarns per centimeter and
7 1 weft yarns per centimeterO The weft and warp yarns ~e~
Nylon and the weight of the ba~e layer was approximately 560 g/m20
The intermediate nonwoven batt layer was made of Nylon
fibers~ approximately 706 centimeters in length and 43 microns i~
diameter. It wa~ ne~dled on top of the wov0n base layer in two
layers whose combined weight was 435 g/m2.
~ he sheet-contacting layer was made of a blend o ~ylon
fibers having a diameter o~ about 43 microns and modacrylic fiber~ ;
having approximately a height o 804 microns, a width of 59 microns
and a length of 11.4 centimeters, The weight of Nylon fibers was
about 92 g/m2 and that o~ the modacrylic wa~ the same~ The sheet-
contacting layer was needled on top o~ the intermediate batt layer
in a ~ingle layer weighing about 184 g/m2. ~he total weight of the
fini4hed felt was approxLmately 1180 g/m2.
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While the present invention makes frequent reference tothe term papermakers' felt, it should be understood that the inven- :
tion i5 also applicable to dryer ~elts which are used to convey a
paper web through the drying section of the paper machineO The ;
various embodiments~ terms and references to a particular material
which have been employed herein are used only by way of description
and not of limitation, and there is no intention for any of the
above to exclude any equivalents thereof. ~ence, it is recognized ~:
that various modi~ications are possible within the scope of the
present invention as claimedO
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