Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02649264 2008-10-10
SEAMED FELT FOR PAPERMAKING
TECHNICAL FIELD
The present invention relates to a seamed felt for
papermaking (hereinafter referred to as a "seamed felt").
BACKGROUND ART
Recently, high-speed and high-pressure loading papermaking
machines are prevailing, and papermaking felts are required to
have high water permeability. Accordingly, a mainstream type of
papermaking felts is the one in which a base part has a fabric
structure made of monofilaments so as to improve water
permeability.
Conventional on-machine-seamable seamed felts (for example,
see W02002/035000) include a fabric for a papermaking machine in
which a batt fiber layer and a strip made of flow-resistant
material are provided above or adjacent to a seam part, so that
the seam part of a seamed felt has substantially the same air and
water permeability as in the other parts of the felt.
Figure 2 shows a machine direction sectional view of a
conventional seamed felt 10'.
The seamed felt 10' has a base fabric 14' woven with a
monofilament, and is made into an endless form on-machine by
joining of seam areas 12'.
The base fabric 14' is a woven fabric comprising machine
direction yarns 16' and cross machine direction yarns 22'.
The machine direction yarns 16' form seaming loops 18'.
The seaming loops 18' provide a passage for a pintle 201,
and the base fabrics 14' are joined by the combination of the
seaming loops 18' and the pintles 20'.
A strip 24' is disposed in the seam area 12', extending
0.5-2.0 inches (1.27-5.08cm) long on its top side. The strip 24'
is a ribbon made of either a woven fabric, an unwoven fabric, or
1
CA 02649264 2008-10-10
a polymeric film, punched into the base fabric 14' by needling.
A batt fiber layer 26' , made of staple fibers, is provided on at
least one side of the base fabric 14' by means of needle punching
etc.
Further, the batt fiber layer 26' is removed from the seaming
loop 18' on the bottom side of the base fabric 14' to provide a
gap 28'.
A slit 30' is cut obliquely through the batt fiber layer
26' and the strip 24'; however, the strip 24' is supposed to
contribute to provide a seamed felt 10' wherein air and water
permeability in the seam area 12' can be maintained.
On the other hand, endless papermaking felts have often been
used, which does not require on-machine seaming. In order to
maintain a capability to dewater a wet paper web (dewatering
capability), it is deemed important for both the endless felts
and seamed felts to have a capability to rebound from a compressed
state without flattening when depressurized, a capability to
improve smoothness of the wet paper web with smoothness of the
felt itself, and resistance to shedding and abrasion.
Unexamined Japanese Patent Publication No.30258411996,for
example, discloses a press felt with such capabilities which
includes fibers with a core-in-sheath structure made from a
two-component material. In this press felt, the two-component
material used for a fiber to form a batt layer is composed of a
sheath member with a low melting point and a core member with a
high melting point. With heat hardening processing of the press
felt, the sheath member with a low melting point gets softened
to form a matrix within the batt layer, which supposedly enhances
dewatering capability and compression resistance of the press
felt.
DISCLOSURE OF INVENTION
In the above-mentioned seamed felt with a slit, it was
2
CA 02649264 2008-10-10
necessary to dispose a strip or apply resin in the seam area to
maintain or strengthen integration of the batt fiber layer in the
seam area so as to prevent shedding of the batt fiber layer thereof .
Inevitably, therefore, it has been difficult to make the seamed
felt to have the same air and water permeability and felt
properties (compressibility, water permeability, clogging
elements accumulation) throughout the seam areas and the non-seam
areas.
When using a seamed felt in which the seam areas and the
non-seam areas have different air and water permeability and felt
properties, the texture of the wet paper web on the seam area is
affected in a papermaking process, leading to risks that the
quality of the wet paper web can be degraded or the wet paper web
can get torn. In addition, there has been a problem that durability
and quality of the seamed felt are impaired.
Further, the papermaking felt disclosed in Unexamined
Japanese Patent Publication No. 302584/1996 tends to be vulnerable
to repetitive compression by a press machine. More specifically,
the above-mentioned papermaking felt with the batt layer made from
the two-component material tends to require short-term
replacement due to cutoffs of fibers during use, shedding or
abrasion, because hot pressing in the manufacturing process of
the felt causes deterioration of mechanical strength or chemical
degradation of the core material.
Thus, it is the object of this invention to provide a seamed
felt wherein resistance to compression fatigue of a batt fiber
layer in seam areas can be improved and which has superior
smoothness, resistance to shedding and abrasion, and a dewatering
capability, while providing the felt with the same properties
throughout seam areas and non-seam areas.
The present invention resolved the above problems by a
seamed felt for papermaking comprising a base layer having a seam
part, a wet paper web side batt fiber layer formed on the wet paper
3
CA 02649264 2008-10-10
web side surface of said base layer, and a press side batt fiber
layer formed on the press side surface thereof;
said wet paper web side batt fiber layer having a
core-in-sheath fiber comprising a core member made of
high-molecular-weight nylon with an absolute viscosity of 80mPa=
s or more and a sheath member made of nylon with a lower melting
point than the core member, wherein a net-shaped fiber layer is
formed with melted sheath members of said core-in-sheath fiber.
"An absolute viscosity of 80mPa=s or more" was measured at
the temperature of 25 degrees C after solving nylon in 100m1 of
0. 5g/95% sulfuric acid, which can be measured using an oscillating
viscometer.
The content rate of said core-in-sheath fibers within said
wet paper web side batt fiber layer is preferably in the range
of 20-80%.
Said wet paper web side batt f iber layer can be multi-layered,
in which the content rate of said core-in-sheath fibers increases
incrementally from the press side toward the wet paper web side
thereof. It is specifically preferable to provide a fiber layer
without said core-in-sheath fibers on the wet paper web side
surface of said base layer.
The present invention can effectively prevent shedding of
batt fibers in the seam area, while achieving uniform properties
throughout the seam areas and the non-seam areas. Therefore, this
invention can provide a seamed felt which is capable of improving
the quality of a wet paper web, less likely to tear a wet paper
web, and demonstrates improved durability, in papermaking
processes.
Moreover, in this invention, a net-shaped fiber layer is
formed with melted sheath members of the core-in-sheath fiber,
which makes the wet paper web side batt fiber layer dense.
Resultantly, wet paper web side batt fiber layer works as a barrier
to block water within the press side layer from moving to the wet
4
CA 02649264 2008-10-10
paper web side, thereby preventing rewetting.
Further, the invention successfully enhances resistance to
shedding, abrasion, and compression fatigue of the felt by
providing the core member of the core-in-sheath fiber with high
viscosity, i.e. by using high-molecular-weight nylon. As a result,
the felt is made more durable, reducing the need for replacement,
contributes to improve the quality of the finished paper with less
fibers attached thereon due to shedding and abrasion, and is
capable of maintaining smoothness of the wet paper web contact
surface.
BRIEF DESCRIPTION OF DRAWINGS
Figure 1 is a machine direction sectional view of an
embodiment of a seamed felt of the present invention.
Figure 2 is a machine direction sectional view of a
conventional seamed felt.
PREFERRED EMBODIMENT OF THE INVENTION
A seamed felt of the present invention is to be detailed.
Figure 1 illustrates a machine direction (NID) sectional view
of a seamed felt 10 of this invention.
"Machine direction (MD)" refers to a longitudinal direction
in which a papermaking machine drives a seamed felt, whereas "cross
machine direction (CMD)" refers to a lateral direction which
crosses the direction in which a papermaking machine drives a
seamed felt.
As shown in Figure 1, the seamed felt 10 comprises a base
layer 30 having a seam part, a wet paper web side batt fiber layer
20 formed on the wet paper web side surface of said base layer,
and a press side batt fiber layer 21 formed on the press side
surface thereof.
The wet paper web side batt fiber layer 20 formed on the
wet paper web side surface of the base layer and a press side batt
CA 02649264 2008-10-10
fiber layer 21 formed on the press side surface thereof are made
of staple fibers, intertwiningly integrated with the wet paper
web side and the press side of the base layer 30 respectively by
needle punching.
The base layer 30 is produced by weaving a strip of an
open-ended fabric on a loom with a warp (MD yarn) 31 and a weft
(CMD yarn) 32.
The seam part of the base layer 30 is to be described. The
warps 31, 31 form so-called seaming loops 33, 33 on the end of
the base layer 30, which are aligned in the cross machine direction.
Stick core wires (pintle wires) 36 are set into the seaming loops
33, 33 to make the base layer 30 endless. Thus, a seam part refers
to a part where a seaming loop is formed on the end of the base
layer 30, into which a core wire is inserted to make the base layer
endless.
A slot 11 is formed by obliquely cutting the wet paper web
side batt fiber layer 20 above the core wire 36 down to the base
layer 30 along the cross machine direction of the seamed felt 10.
The wet paper web side batt fiber layer 20 is cut obliquely to
form a slot 11 sloping in the machine direction, because a mark
of a seam area 12 is less likely to be transferred onto a wet paper
web compared to the wet paper web side batt fiber layer 20 cut
vertically in the cross machine direction. Accordingly, a cut 11'
on the press side batt fiber layer can be vertical.
As shown in Figure 1, a triangular section is a flap f having
the slot 11 as a hypotenuse against the base layer 30. In this
case, the seamed felt 10 drives from the right to the left in Figure
1 on a papermaking machine.
In the seamed felt 10 of this invention, the wet paper web
side batt fiber layer 20 includes a core-in-sheath fiber 41, sheath
members of said core-in-sheath fiber being melted by heat and/or
hot pressing to form a net-shaped fiber layer, which makes the
wet paper web side batt fiber layer dense, and hence durability
6
CA 02649264 2008-10-10
of the seam area 12 is enhanced. In other words, while a seamed
felt is being used on a papermaking machine, shedding and abrasion
of the flap f in the seam area 12 and slots 11, 11', which are
vulnerable to damage, can be dramatically diminished.
Other features of the seamed felt of the present invention
are to be explained below.
A net-shaped fiber layer is formed with melted
core-in-sheath fibers 41 of the seamed felt 10, which makes the
wet paper web side batt fiber layer 20 dense and improves surface
smoothness of the seamed felt 10.
As the wet paper web side batt fiber layer 20 is made dense,
it works as a barrier to block shifting of water within the base
layer and the press side batt fiber layer 21 formed on the press
side thereof when the seamed felt 10 is released from nip pressure,
thereby preventing rewetting effectively and improving the
dewatering capability.
In the seamed felt 10 of this invention, the wet paper web
side batt fiber layer 20 comprises a core-in-sheath fiber 41, a
staple fiber, which has a core member made of
high-molecular-weight nylon with an absolute viscosity of 80mPa=
s or more and a sheath member made of nylon with a lower melting
point than the core member, whereas the press side batt fiber layer
21 formed on the press side surface of the base layer 30 is made
of a staple fiber of a conventional nylon fiber 42 which does not
include the core-in-sheath fiber 41.
"An absolute viscosity of 80mPa=s or more" was measured at
the temperature of 25 degrees C after solving nylon in 100m1 of
0.5g/95% sulfuric acid, which can be measured using an oscillating
viscometer.
In Figure 1, the core-in-sheath fiber 41 is enlarged for
the purpose of illustration.
Conventionally, no attention has been paid to viscosity of
a core member, or its molecular weight, when a fiber with a
7
CA 02649264 2008-10-10
core-in-sheath structure made from a two-component material is
used for a batt fiber layer of a papermaking felt. The present
invention achieved balanced improvements of smoothness and
resistance to shedding, abrasion, and compression fatigue by
providing the core member with higher viscosity compared to
conventional practices, i.e. by using high-molecular-weight
nylon, and by disposing a layer made of such core-in-sheath fibers
on the wet paper web side surface of the base layer of the seamed
felt so that a net-shaped fiber layer is formed with melted
core-in-sheath fibers.
Nylon used for the core member of the core-in-sheath fiber
41 should be high-molecular-weight nylon with an absolute
viscosity of 80mPa-s or more at 25 degrees C and with a higher
melting point than the sheath member. When nylon with a high
viscosity ( 80mPa= s or more) is used for the core member, shedding,
abrasion, and compression resistance of the felt can be enhanced.
It is probably because high-molecular-weight nylon has a longer
molecular chain, which improves mechanical strength (intensity
or durability such as abrasion and attrition resistance) as a
result of entanglement of such molecular chains. Nylon with an
absolute viscosity of less than 80mPa=s (moderate viscosity) can
not be sufficiently advantageousin enhancing shedding, abrasion,
and compression resistance.
Preferable nylon used for the core member includes
high-molecular-weight nylon 6, high-molecular-weight nylon 66,
high-molecular-weight nylon 46, high-molecular-weight nylon 610,
and high-molecular-weight nylon 612 and others.Morespecifically,
nylon obtained by way of polycondensation of nylon salt is
preferable, such as polymerization of f caprolactam (nylon 6),
polycondensation of hexamethylenediamine adipate (nylon 66),
polycondensation of 1,4-diaminobutane adipate (nylon 46),
polycondensation of hexamethylenediamine sebacate (nylon 610),
polycondensation of hexamethylenediamine dodecanedioic diacid
8
CA 02649264 2008-10-10
(nylon 612), and aliphatic nylon can also be included which has
a melting point of 200 degrees C or more measured by DSC
(Differential Scanning Calorimetry). Preferably, an absolute
viscosity of the high-molecular-weight nylon above in 100m1 of
0.5g/95% sulfuric acid is 8UmPa=s or more. These
high-molecular-weight nylon is produced with a well-known
polymerization procedure or a solid phase polymerization
procedure in which polimerized nylon flake is placed in an inert
gas atmosphere of 120-200 degrees C without oxygen (for example,
Unexamined Japanese Patent Publication No. 529604/2002).
Nylon used for the sheath member of the core-in-sheath fiber
41 should have a lower melting point than the core member.
Preferred nylon includes binary copolymerized nylon such as nylon
6/12, nylon 6/610, nylon 66/6, nylon 66/12, and nylon 66/610,
ternary copolymerized nylon such as nylon 6/66/12 and nylon
6/66/610. As is known in the art, a melting point of these
copolymerized nylon f luctuates depending on their composition (or
weight percentages of copolymerized elements),and only those with
a melting point of 180 degrees C or less is usable for this
invention.
The wet paper web side batt fiber layer 20 is preferably
made of a blend with a predetermined rate of the core-in-sheath
fiber 41 and the normal nylon fiber 42 to achieve a better balance
of smoothness, abrasion and compression fatigue resistance.
Preferably, the blend consists of 80-20% of the core-in-sheath
fiber 41 and 20-80% of the nylon fiber 42.
When the content rate of the core-in-sheath fiber 41 is less
than 20%, the wet paper web side batt fiber layer 20 is made less
dense. Therefore, the felt lacks resistance to shedding, abrasion
and compression fatigue, and smoothness, and is incapable of
preventing rewetting effectively.
On the other hand, when the content rate of the
core-in-sheath fiber 41 exceeds 80%, the felt tends to be flattened
9
CA 02649264 2008-10-10
with the wet paper web side batt fiber layer 20 susceptible to
compres s i on f at igue, whileithassmoothness, abrasion resistance
and is effective in prevention of rewetting.
The wet paper web side batt fiber layer 20 can be
multi-layered, in which the content rate of the core-in-sheath
fiber 41 increases incrementally from the press side toward the
wet paper web side thereof to provide more improvements in
smoothness and resistance to shedding and abrasion.
It is especially preferred to provide a batt fiber layer
without the core-in-sheath fiber 41 on the wet paper web side
surface of the base layer. More specifically, when the seam part
of the base layer 30 is intertwiningly integrated with the wet
paper web side batt fiber layer 20 by needle punching, melted and
netted fibers obstruct the seaming loops 33, 33, blocking
insertion of the core wire (pintle wire) 36. However, when a batt
fiber layer without the core-in-sheath fiber 41, preferably a batt
fiber layer with a basis weight of 50g/m2 or more, is provided
on the wet paper web side surface of the base layer, the seam part
is prevented from being intertwined with the core-in-sheath fiber
41.
Although the ratio of the volume of the core and the sheath
members of the core-in-sheath fiber 41 should not be limited, it
can range from 5:1 to 1:5, with a preferable rate of 1:1.
The nylon fiber 42 used for the wet paper web side batt fiber
layer 20, the press side batt fiber layer 21, and for the blend
with the core-in-sheath fiber 41 is preferably nylon 6, nylon 66,
nylon 46, nylon 610, and nylon 612 etc.
Preferable fineness of the core-in-sheath fiber 41 is
15-25dtex for a picking-up seamed felt used in a first stage in
a press section of a papermaking machine, 10-20dtex for a seamed
felt for a second and third press used in a middle stage of the
press section, and 5-20dtex for a seamed felt for a fourth press
and a shoe press used in the last stage of the press section.
CA 02649264 2008-10-10
Preferred fineness of the nylon fiber 42 is 10-25dtex for
the wet paper web side batt fiber layer 20 and 15-25dtex for the
press side batt fiber layer 21 respectively of a picking-up seamed
felt used in a first stage of a press section of a papermaking
machine.
In the seamed felt for a second and third press used in a
middle stage of a press section of a papermaking machine, preferred
fineness is 10-15dtex for the wet paper web side batt fiber layer
20 and 10-20dtex for the press side batt fiber layer 21
respectively.
In the seamed felt for a fourth press and a shoe press used
in a last stage of a press section of a papermaking machine,
preferred fineness is 5-15dtex for the wet paper web side batt
fiber layer 20 and 5-20dtex for the press side batt fiber layer
21 respectively.
INDUSTRIAL APPLICABILITY
The present invention can effectively prevent shedding of
batt fibers in the seam area, while achieving uniform properties
throughout the seam areas and the non-seam areas. Therefore, this
invention can provide a seamed felt which is capable of improving
the quality of a wet paper web, less likely to tear a wet paper
web, and demonstrates improved durability, in papermaking
processes.
Moreover, a net-shaped fiber layer is formed with melted
sheath members of the core-in-sheath fiber, which makes the wet
paper web side batt fiber layer dense. Resultantly, wet paper web
side batt fiber layer works as a barrier to block water within
the press side layer from moving to the wet paper web side, thereby
preventing rewetting.
Further, the invention successfully enhances resistance to
shedding, abrasion, and compression fatigue of the felt by
providing the core member of the core-in-sheath fiber with high
11
CA 02649264 2008-10-10
viscosity, i.e.by using high-molecular-weight nylon. As a result,
the felt is made more durable, reducing the need for replacement,
contributes to improve the quality of the finished paper with less
fibers attached thereon due to shedding and abrasion, and is
capable of maintaining smoothness of the wet paper web contact
surface.
12
