U.S. patent application number 12/087300 was filed with the patent office on 2009-01-22 for press felt for papermaking.
This patent application is currently assigned to Ichikawa Co., Ltd. Invention is credited to Shin Kawashima, Hiroyuki Oda, Akira Onikubo.
Application Number | 20090020252 12/087300 |
Document ID | / |
Family ID | 38228313 |
Filed Date | 2009-01-22 |
United States Patent
Application |
20090020252 |
Kind Code |
A1 |
Onikubo; Akira ; et
al. |
January 22, 2009 |
Press Felt for Papermaking
Abstract
A press felt comprises a base body, a wet paper web side batt
layer, and a press side batt layer. The wet paper web side batt
layer includes a web contact side batt layer and a base body side
batt layer, the latter being composed of core-in-sheath fibers with
a core of high molecular weight nylon with an absolute viscosity of
80 mPas or more and a sheath of nylon with a lower melting point
than the core. The wet paper web contact side batt layer is made of
nylon fibers which are not core-in-sheath fibers.
Inventors: |
Onikubo; Akira; (Tokyo,
JP) ; Kawashima; Shin; (Tokyo, JP) ; Oda;
Hiroyuki; (Tokyo, JP) |
Correspondence
Address: |
HOWSON AND HOWSON
SUITE 210, 501 OFFICE CENTER DRIVE
FT WASHINGTON
PA
19034
US
|
Assignee: |
Ichikawa Co., Ltd
Tokyo
JP
|
Family ID: |
38228313 |
Appl. No.: |
12/087300 |
Filed: |
December 28, 2006 |
PCT Filed: |
December 28, 2006 |
PCT NO: |
PCT/JP2006/326405 |
371 Date: |
July 1, 2008 |
Current U.S.
Class: |
162/358.2 |
Current CPC
Class: |
D21F 7/083 20130101 |
Class at
Publication: |
162/358.2 |
International
Class: |
D21F 3/02 20060101
D21F003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 6, 2006 |
JP |
2006-001000 |
Claims
1. A press felt for papermaking comprising a base body and a batt
layer having a wet paper web side layer and a press side layer,
characterized in that said wet paper web side layer is composed of
a wet paper web contract side batt layer and a base body side batt
layer, said base body side batt layer having a core-in-sheath fiber
comprising a core member made of high-molecular-weight nylon with
an absolute viscosity of 80 mPas or more and a sheath member made
of nylon with a lower melting point than the core member; and said
wet paper web contact side batt layer being made of nylon without
said core-in-sheath fiber.
2. A press felt as claimed in claim 1, in which a content rate of
said core-in-sheath fiber in said base body side batt layer ranges
from 10% to 60%.
3-4. (canceled)
5. A press felt as claimed in claim 1, in which said base body side
batt layer has a plurality of layers in which the content rate of
said core-in-sheath fiber increases incrementally from the side
press side toward the paper side thereof.
6. A press felt as claimed in claim 1, in which said base body is a
fabric woven with a warp yarn and a weft yarn which are
monofilament single yarns.
7. A press felt as claimed in claim 2, in which said base body side
batt layer has a plurality of layers in which the content rate of
said core-in-sheath fiber increases incrementally from the press
side toward the paper side thereof.
8. A press felt as claimed in claim 5, in which said base body is a
fabric woven with a warp yarn and a weft yarn which are
monofilament single yarns.
9. A press felt as claimed in claim 7, in which said base body is a
fabric woven with a warp yarn and a weft yarn which are
monofilament single yarns.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a press felt for papermaking used
in a papermaking machine (hereinafter referred to as a "press
felt").
BACKGROUND ART
[0002] Press machines have been used to dewater a wet paper web in
a papermaking process. In a press machine, a wet paper web formed
with layers therein is dewatered within a press nip, sandwiched
between a pair of press felts. Press machines generally have a
plurality of press nips.
[0003] FIG. 5 is a schematic view of a press nip in a press
machine.
[0004] A pair of press rolls P', P' and a pair of press felts 11',
11' form a press nip. The press felts 11', 11' and a wet paper web
W are compressed within a pressure portion between the press rolls
P', P', where water is removed from the wet paper web W' and
absorbed by the press felts 11', 11'.
[0005] The volume of the wet paper web W' and the press felts 11',
11' rapidly expands when they travel through the middle of the
press portion (the nip) to the exit thereof, as they are rapidly
released from compression. This expansion generates negative
pressure within the press felts 11', 11' which, coupled with the
capillary phenomenon within the wet paper web W' associated with
thin fibers therein, results in rewetting, a phenomenon in which
water absorbed by the press felts 11', 11' backs to the wet paper
web.
[0006] Unexamined Japanese Patent Publication No. 143627/2004
discloses a press felt intended to prevent rewetting. This felt
comprises a base layer, a paper side batt layer, and press side
batt layer, with a hydrophilic nonwoven fabric being disposed
within the paper web side batt layer. According to this invention,
the hydrophilic nonwoven fabric absorbs and retains water contained
within the wet paper web, thereby effectively preventing
rewetting.
[0007] Moreover, it is also essential for a press felt to have a
capability of recovering to its uncompressed state after
compression without being flattened (resistance to compression
fatigue), a capability of improving smoothness of the wet paper web
by smoothness of the felt itself (smoothness), and dehairing and
abrasion resistance.
[0008] Unexamined Japanese Patent Publication No. 302584/1996, for
example, discloses a felt with such capabilities which includes
fibers with a core-in-sheath structure made from a two-component
material.
[0009] According to this invention, 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 enhances dewatering capability and
compression resistance of the press felt.
[0010] Further, press felts made of a woven fabric with improved
dewatering capability and smoothness are employed in recent
high-speed papermaking machines. The fabric is woven with a warp
yarn (CMD yarn) and a weft yarn (MD yarn), both of which are
monofilament single yarns (Unexamined Japanese Patent Publication
No. 170086/2000).
DISCLOSURE OF THE INVENTION
[0011] However, the press felts disclosed in the first two
publications tend to be vulnerable to compression.
[0012] In addition, the press felt with the batt layer made from
the two-component material, as disclosed in the second publication
No. 302584/1996, tends to require short-term replacement due to
cutoffs of fibers during use, dehairing or abrasion, because
thermal pressurization in the manufacturing process causes
deterioration of mechanical strength or chemical degradation.
[0013] On the other hand, the press felt disclosed in the third
publication No. 170086/2000 is known to be much inferior to
conventional felts using twist yarns in terms of dehairing and
abrasion resistance, because batt fibers and the woven fabric are
not firmly integrated by needlepunching.
[0014] Thus, there is a need for a press felt not only with an
anti-rewetting capability but with a balanced combination of
advantages, such as resistance to compression, smoothness, and
dehairing and abrasion resistance.
[0015] In view of the above problems, the object of the present
invention is to provide a press felt for papermaking being capable
of preventing rewetting and having superior smoothness and
resistance to abrasion and compression fatigue.
[0016] The present invention solved the above-mentioned problems
with a press felt comprising a base body and batt layers having a
wet paper web side layer and a press side layer, characterized in
that said wet paper web side layer is composed of a wet paper web
contact side batt layer and a base body side batt layer, said base
body side batt layer having a core-in-sheath fiber comprising a
core member made of high-molecular-weight nylon with an absolute
viscosity of 80 mPas or more and a sheath member made of nylon with
a lower melting point than the core member, said wet paper web
contact side batt layer being made of nylon without said
core-in-sheath fiber.
[0017] "An absolute viscosity of 80 mPas or more" was measured at
the temperature of 25 degrees C. after solving nylon in 100 ml of
0.5 g/95% sulfuric acid, which can be measured using an oscillating
viscometer.
[0018] The content rate of said core-in-sheath fibers within said
base body side batt layer is preferably in the range of 10-60%.
[0019] Said base body side batt layer can be multi-layered, in
which the content rate of said core-in-sheath fibers increases
incrementally from the press side toward the paper side
thereof.
[0020] Further, said base body is preferably a fabric woven with a
warp yarn (CMD yarn) and a weft yarn (MD yarn), both of which are
monofilament single yarns.
[0021] According to this invention, the base body side batt layer
is made dense due to melting of the sheath portion of the
core-in-sheath fiber. As a result, said base body side batt layer
works as a barrier to block water within the press side layer from
moving to the paper side, thereby preventing rewetting.
[0022] Moreover, the invention successfully enhances resistance to
dehairing, abrasion, and compression fatigue of the press 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 press felt of this invention 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 dehairing
and abrasion, and is capable of maintaining smoothness of the paper
contact surface.
[0023] Further, since the base body side batt layer is made of the
core-in-sheath fiber while the wet paper web contact side batt
layer is made of nylon without the core-in-sheath fiber, the press
felt of this invention is provided with a balanced combination of
smoothness and resistance to dehairing, abrasion, and compression
fatigue.
[0024] Furthermore, the present invention improves dewatering
capability as well as resistance to dehairing and abrasion of the
press felt by using a fabric woven with monofilament single yarns
for the base body and thus enhancing water permeability
thereof.
BRIEF DESCRIPTION OF DRAWINGS
[0025] FIG. 1 is a sectional view of an embodiment of the press
felt of the present invention.
[0026] FIG. 2 is a sectional view of another embodiment of the
press felt of the present invention.
[0027] FIG. 3 is a schematic view of an apparatus to evaluate the
effects of the press felt of the present invention.
[0028] FIG. 4 is a schematic view of an apparatus to evaluate the
effects of the press felt of the present invention.
[0029] FIG. 5 is a schematic view of a press apparatus of a
papermaking machine.
PREFERRED EMBODIMENTS OF THE INVENTION
[0030] A press felt of this invention is to be detailed
hereafter.
[0031] FIG. 1 is a CMD sectional view of a press felt 10 of the
present invention.
[0032] "Machine direction (MD)" refers to the longitudinal
direction in which a press felt is transferred in a papermaking
machine, whereas "cross machine direction (CMD)" refers to the
lateral direction which crosses the machine direction.
[0033] As shown in FIG. 1, the press felt 10 comprises a base body
30, a wet paper web side batt layer 20, and a press side batt layer
23, the wet paper web side batt layer 20 having a wet paper web
contact side batt layer 21 and a base body side batt layer 22 which
is formed on the side closer to the base body of the wet paper web
contact side batt layer 21.
[0034] The wet paper web contact side batt layer 21, the base body
side batt layer 22, and the press side batt layer 23 are made of
staple fibers, with the base body side batt layer 22 and the press
side batt layer 23 intertwiningly integrated by needlepunching with
the wet paper web side and the press side of the base body 30
respectively. The wet paper web contact side batt layer 21 is
intertwiningly integrated with the base body side batt layer 22 by
needlepunching.
[0035] In the press felt 10 of this invention, the base body side
batt layer 22 is made of 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 80 mPas or more and a sheath member of nylon
with a lower melting point than the core member, whereas the wet
paper web contact side batt layer 21 is made of a staple fiber of a
conventional nylon fiber 42 without the core-in-sheath fiber
41.
[0036] "An absolute viscosity of 80 mPas or more" was measured at
the temperature of 25 degrees C. after solving nylon in 100 ml of
0.5 g/95% sulfuric acid, which can be measured using an oscillating
viscometer.
[0037] In FIG. 1, the core-in-sheath fiber 41 is enlarged for the
purpose of illustration.
[0038] Conventionally, no attention has been paid to viscosity of a
core member, or its molecular weight, when a fiber with a
core-in-sheath structure made from two-component material is used
for a batt layer of a press felt. However, the present invention
successfully achieved a balance of such advantages as smoothness,
dehairing and abrasion resistance, and resistance to compression
fatigue by employing a fiber with a higher viscosity as compared to
conventional practices, namely high-molecular-weight nylon, for a
core member, and by disposing a layer made of this core-in-sheath
material on the base body side of the wet paper web contact side
batt layer.
[0039] Nylon used for the core member of the core-in-sheath fiber
41 should be high-molecular-weight nylon with an absolute viscosity
of 80 mPas or more at 25 degrees C. and with a higher melting point
than the sheath member. When nylon with a high viscosity (80 mPas
or more) is used for the core member, dehairing, abrasion, and
compression resistance of the felt can be enhanced. It may be
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 long molecular chains. Nylon with an absolute viscosity of
less than 80 mPas (moderate viscosity) is not advantageous in
enhancing dehairing, abrasion, and compression resistance.
[0040] 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. More specifically, nylon
obtained by way of polycondensation of nylon salt is preferable,
such as polymerization of .epsilon. 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
(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 100 ml of 0.5
g/95% sulfuric acid is 80 mPas 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).
[0041] 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 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
fluctuates 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.
[0042] Accordingly, the sheath member is melted by thermal
pressurization in the manufacturing process, which leads to
constriction of the core-in-sheath fiber 41, thereby making the
base body side batt layer 22 and the wet paper web contact side
batt layer 21 more dense and therefore adding smoothness to the
felt surface.
[0043] The base body side batt layer 22 and the wet paper web
contact side batt layer 21 with added density are also effective in
preventing rewetting, because they block water within the press
side batt layer 23 from moving therein.
[0044] In the present invention, only the base body side batt layer
22 is composed of the core-in-sheath fiber 41, with the wet paper
web contact side batt layer 21 being made of the normal nylon fiber
42 without the core-in-sheath fiber 41. This composition enabled
the press felt to have a balanced combination of smoothness,
dehairing and abrasion resistance, and resistance to compression
fatigue. When the wet paper web contact side batt layer 21 has the
core-in-sheath fiber 41, surface areas to contact with the wet
paper web is expanded due to melting of the sheath member, and
hence smoothness of the press felt is improved. However, dehairing
and abrasion resistance, and durability are degraded, because
mechanical strength of copolymerized nylon is relatively low.
[0045] The base body side batt layer 22 is preferably made of a
blend of the core-in-sheath fiber 41 and the normal nylon fiber 42
to achieve a better balance of smoothness, abrasion and compression
resistance. Preferably, the blend consists of 60-10% of the
core-in-sheath fiber 41 and 40-90% of the nylon fiber 42.
[0046] When the content rate of the core-in-sheath fiber 41 is less
than 10%, the press felt lacks smoothness and is incapable of
preventing rewetting effectively.
[0047] On the other hand, when the content rate of the
core-in-sheath fiber 41 exceeds 60%, the felt tends to be flattened
with the base body side batt layer 22 susceptible to compression
fatigue, while it has smoothness, abrasion resistance and is
effective in prevention of rewetting.
[0048] The base body side batt layer can be multi-layered, in which
the content rate of the core-in-sheath fiber 41 increases
incrementally from the press side toward the paper side thereof to
provide more improvements in smoothness and abrasion
resistance.
[0049] FIG. 2 illustrates an embodiment in which the base body side
batt layer comprises a first layer 22a and a second layer 22b, the
first layer 22a having more core-in-sheath fibers 41 than the
second layer 22b.
[0050] Such a structure increases density of the base body side
batt layer 22 and the wet paper web contact side batt layer 21.
More specifically, as compared to the embodiment in which the base
body side batt layer 22 is a single layer, the felt is provided
with enhanced anti-rewetting capability due to the doubled dense
layers as well as improved smoothness and resistance to dehairing
and abrasion.
[0051] On the contrary, when the base body side batt layer 22 is
formed with incrementally decreasing content rate of the
core-in-sheath fiber 41 from the press side toward the paper side,
smoothness, dehairing and abrasion resistance, and anti-rewetting
properties of the felt are degraded, as compared to the embodiment
in which the base body side batt layer 22 is a single layer.
[0052] Although the base body side batt layer 22 is double-layered
in FIG. 2, it may comprise three or more layers.
[0053] The ratio of the volume of the core and the sheath members
of the core-in-sheath fiber 41 can range from 5:1 to 1:5, but
preferably 1:1.
[0054] The nylon fiber 42 used for the wet paper web contact side
batt layer 21, the press side batt layer 23, 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.
[0055] Preferably, the base body 30 is a fabric woven with a warp
yarn 31 (CMD yarn) and a weft yarn 32 (MD yarn) which are
monofilament single yarns. It can be a double cloth such as [2/1,
1/2], [3/1, 1/3], and [5/1, 1/5], a triple cloth, or multilayered
texture such as [a single cloth+a double cloth], [a double cloth+a
double cloth]. The monofilament single yarn may be the one with a
diameter of 0.1 mm-0.6 mm and a yarn density of the texture can be
10-100 yarns/25 mm.
[0056] However, the base body 30 need not be a woven fabric, and
other structures and methods can be employed as appropriate, such
as simply overlapping an MD yarn and a CMD yarn, a film, a knitted
fabric, or winding a narrow belt-shaped body to make a belt-shaped
body of relatively large width. Further, appropriate materials for
the base body 30 include natural fibers such as wool, and synthetic
fibers such as polyester, nylon 6, and nylon 66 which have superior
abrasion and fatigue resistance, distensibility, and antifouling
properties.
[0057] Preferable fineness of the core-in-sheath fiber 41 is
15-25dtex for a pick-up felt used in a first press in a press
section of a papermaking machine, 10-20dtex for a felt in a second
and third press, and 5-20dtex for a felt in a fourth press and a
shoe press.
[0058] Preferred fineness of the nylon fiber 42 is 10-25dtex and
15-25dtex for the paper side batt layer 20 and the press side batt
layer 23 of the pick-up felt used in the first press respectively,
whereas it is 10-15dtex and 10-20dtex for the corresponding layers
of the felt used in the second and third press, and 5-15dtex and
5-20dtex for the corresponding layers of the felt used in the
fourth press and the shoe press.
EXAMPLES
[0059] A first embodiment of the press felt of this invention is to
be described using following examples. However, it should be noted
that the present invention is not limited to these examples.
Production of the Core-in-Sheath Fiber;
[0060] Refined nylon 6 (caprolactam, melting point: 220 degrees C.)
and copolymerized nylon 6/12 (caprolactam/laurolactam, melting
point: 140 degrees C.) are individually put into an extruder with
an opening to ablate volatiles. Melted nylon 6 of the core member
and copolymerized nylon 6/12 of the sheath member are quantified by
a metering gear pump and sent to respective spinning nozzles.
Core-in-sheath fibers spun out of the spinning nozzles are reeled
at a natural draw ratio after cooling and oiling, stretched,
crimped, and then cut with a fixed length.
[0061] In the procedure above, a spinning machine of MODEL-EMF made
by Toyo Seimitsu Kogyo Co., Ltd. can be employed, which can be used
with an extruder, a multistage stretching machine of a Nelson
roller system, and winder.
[0062] In the examples, high-molecular-weight nylon 6 (absolute
viscosity: 85 mPas at 25 degrees C., melting point: 220 degrees C.)
and middle-molecular-weight nylon 6 (absolute viscosity: 70 mPas at
25 degrees C., melting point: 220 degrees C.) are used for the core
member and copolymerized nylon 6/12 (melting point: 140 degrees C.)
is used for the sheath member to produce two kinds of
core-in-sheath staple fibers in which a volume ratio of the core
and sheath member is 1:1. A fiber with the core member made of
high-molecular-weight nylon 6 is hereinafter referred to as a
composite fiber A, while the one with the core member made of
middle-molecular-weight nylon 6 is referred to as a composite fiber
B.
[0063] The absolute viscosity of 85 mPas and 70 mPas are 4.5 and
3.0 .eta.r respectively in relative viscosity measured by
generally-used Ubbelohde viscosimeter. For reference, absolute
viscosity of 80 mPas equals 4.0 .eta.r.
Production of the Press Felt for Papermaking;
[0064] For comparison, examples and comparative examples are all
provided with a common basic structure as follows, so that they can
be compared under the same conditions; [0065] Base body: Woven
fabric A [a double cloth of (3/1, 1/3) using plied yarns made by
twisting two yarns made of two nylon monofilaments of 240dtex for
an MD yarn and a CMD yarn], basis weight: 300 g/m.sup.2 [0066] :
Woven fabric B [a double cloth of (3/1, 1/3) using single yarns of
1100dtex nylon monofilament for an MD yarn and a CMD yarn], basis
weight: 300 g/m.sup.2 [0067] Batt layer: staple fibers of 17 dtex
nylon 6 and 17 dtex composite fibers A or B for the wet paper web
contact side batt layer, total basis weight: 120 g/m.sup.2 [0068]
:staple fibers of 17 dtex nylon 6 and 17 dtex composite fibers A or
B for the base body side batt layer (the first layer), total basis
weight: 120 g/m.sup.2 [0069] :staple fibers of 17 dtex nylon 6 and
17 dtex composite fibers A for the base body side batt layer (the
second layer), total basis weight: 120 g/m.sup.2 [0070] : staple
fibers of 17 dtex nylon 6 for the press side batt layer, total
basis weight: 100 g/m.sup.2 [0071] Needling frequency: 700
times/cm.sup.2 [0072] Thermal pressurization: a needled felt was
subjected to compression 5 times between a pair of calendar rolls
(heated at 160 degrees C., with a pressure of 50 kg/cm) at a speed
of 2 m/min to have a density of 0.5 g/cm.sup.3
[0073] The compositions of Examples 1-7 and Comparative Examples
1-7 are shown in Table 1 and 2 respectively.
TABLE-US-00001 TABLE 1 Examples 1 2 3 4 5 6 7 8 Wet Paper Web
Contact Nylon Nylon Nylon Nylon Nylon Nylon Nylon Nylon Side Batt
Layer Base Body Side Batt Composite Composite Composite Composite
Composite Composite Composite Composite Layer (First Layer) Fiber A
60% Fiber A 40% Fiber A 10% Fiber A 60% Fiber A 40% Fiber A 70%
Fiber A 70% Fiber A 60% Base Body Side Batt Nylon Nylon Nylon
Composite Composite Nylon Composite Nylon Layer (Second Layer)
Fiber A 40% Fiber A 10% Fiber A 40% Base Body Woven Woven Woven
Woven Woven Woven Woven Woven Fabric A Fabric A Fabric A Fabric A
Fabric A Fabric A Fabric A Fabric B Press Side Batt Layer Nylon
Nylon Nylon Nylon Nylon Nylon Nylon Nylon
TABLE-US-00002 TABLE 2 Comparative Examples 1 2 3 4 5 6 7 8 Wet
Paper Web Contact Composite Composite Nylon Nylon Nylon Nylon Nylon
Nylon Side Batt Layer Fiber A 60% Fiber B 40% Base Body Side Batt
Nylon Nylon Composite Nylon Composite Composite Composite Nylon
Layer (First Layer) Fiber A 5% Fiber A 5% Fiber A 10% Fiber A 40%
Base Body Side Batt Nylon Nylon Nylon Nylon Composite Composite
Nylon Nylon Layer (Second Layer) Fiber A 5% Fiber A 40% Base Body
Woven Woven Woven Woven Woven Woven Woven Woven Fabric A Fabric A
Fabric A Fabric A Fabric A Fabric A Fabric A Fabric B Press Side
Batt Layer Nylon Nylon Nylon Nylon Nylon Nylon Nylon Nylon
[0074] Tests are conducted with following conditions and methods to
evaluate anti-rewetting properties, resistance to compression
fatigue, dehairing and abrasion resistance, and smoothness, using
Examples and Comparative Examples listed above.
Evaluation of Anti-Rewetting Properties;
[0075] Tests to evaluate anti-rewetting properties are conducted by
using the apparatus shown in FIGS. 3 and 4.
[0076] In FIGS. 3 and 4, P is a press roll, 110 is an upper side
felt, 10 is a downside felt, SC is a suction tube, and SN is a
shower nozzle.
[0077] Examples and Comparative Examples of the above are all used
as the downside felt 10, whereas Comparative Example 4 is used for
the upper side felt.
[0078] The apparatuses shown in FIGS. 3 and 4 drive the felt at a
speed of 500 m/min with a pressure of 100 kg/cm.
[0079] In the apparatus of FIG. 3, a wet paper web released from
compression within a nip is placed onto and transferred by the
downside felt 10. Accordingly, water content data of a rewetted
paper web can be gathered by measuring humidity of the paper web
when it passes through the nip and is placed onto and transferred
by the downside felt 10 (at a press exit 1).
[0080] On the other hand, in the apparatus of FIG. 4, the downside
felt 10 contacts with the press roll over a larger area, which
means the wet paper web released from the nip pressure is in
contact with the press felts 10 and 110 only briefly. Therefore,
water content data of a slightly rewetted paper web can be gathered
by measuring humidity of the paper web immediately after it
traveled out of the nip (at a press exit 2).
[0081] Anti-rewetting properties can be evaluated based on the
differences between the water content data gathered using the
apparatuses of FIGS. 3 and 4. A felt with the difference less than
0.5% is regarded to be not rewetted (evaluated as "good"), whereas
with the difference of 0.5%-less than 1.0% is regarded to be
slightly rewetted (evaluated as "fair"), and with the difference of
more than 1.0% is regarded to be rewetted (evaluated as
"failure").
Compression Fatigue Resistance Test;
[0082] Felts are subjected to 200,000 times of 10 Hz pulse load at
150 kg/cm.sup.2. Resistance to compression fatigue is evaluated
based on a ratio of density after tests to that of a finished felt,
where the ratio of less than 1.4 is evaluated as "excellent",
1.40-1.49 as "good", and over 1.50 as "failure".
Dehairing and Abrasion Resistance Test;
[0083] dehairing and abrasion resistance of the felts was
determined by means of a Taber abrasion tester based on
JIS1023-1992. The amount of fibers dropped was measured by placing
a discoidal sample piece on a rotating turntable and applying a
rotating roll with intense resistance on the sample piece (load: 1
kg, wheel: CS-17, rotation: 5000 times, unit of measurement:
mg).
[0084] The amount of less than 50 mg is evaluated as "excellent",
with 50 mg-99 mg evaluated as "good" and over 100 g evaluated as
"failure".
Surface Roughness Test;
[0085] Smoothness of felt surfaces are determined by measuring
average roughness Rz (.mu.m) of 10 points of finished felts
(JIS-B0601) before the dehairing and abrasion test. The average
roughness of less than 30 .mu.m is evaluated as "excellent", with
30 .mu.m-70 .mu.m evaluated as "good" and over 71 .mu.m evaluated
as "failure".
[0086] Results of measurement and evaluation are shown in Table
3.
TABLE-US-00003 TABLE 3 Deharing Dewatering & Anti-rewetting
Tests and Water Content Water Content Compression Abrasion Surface
at at Evaluation Density Fatigue Resistance Roughness Press Exit 1
Press Exit 2 of (g/cm.sup.3) Resistance (mg) (.mu.m) (%) (%)
Rewetting Example 1 0.505 1.46 (Good) 55 (Good) 25 (Excellent) 48.3
48.6 Good Example 2 0.505 1.43 (Good) 60 (Good) 50 (Good) 48 48.5
Good Example 3 0.500 1.40 (Good) 75 (Good) 70 (Good) 47.5 48.4 Fair
Example 4 0.510 1.49 (Good) 40 (Good) 20 (Excellent) 48.4 48.6 Good
Example 5 0.510 1.46 (Good) 45 (Good) 35 (Good) 48.3 48.4 Good
Example 6 0.505 1.49 (Good) 75 (Good) 25 (Excellent) 48.5 48.6 Good
Example 7 0.510 1.51 (Failure) 40 (Good) 20 (Excellent) 48.4 48.6
Good Example 8 0.510 1.48 (Good) 60 (Good) 25 (Excellent) 47.1 47.3
Good Comparative Example 1 0.530 1.48 (Good) 105 (Failure) 15
(Excellent) 49.5 49.7 Good Comparative Example 2 0.550 1.51
(Failure) 130 (Failure) 20 (Excellent) 49.5 49.7 Good Comparative
Example 3 0.500 1.35 (Excellent) 75 (Good) 80 (Failure) 47.3 49
Failure Comparative Example 4 0.500 1.30 (Excellent) 80 (Good) 100
(Failure) 47 49 Failure Comparative Example 5 0.500 1.36
(Excellent) 75 (Good) 75 (Failure) 47.3 48.4 Failure Comparative
Example 6 0.505 1.47 (Good) 70 (Good) 70 (Good) 48 49 Failure
Comparative Example 7 0.510 1.50 (Failure) 75 (Good) 60 (Good) 48.1
48.6 Fair Comparative Example 8 0.500 1.30 (Excellent) 100
(Failure) 100 (Failure) 46 48.6 Failure
[0087] As indicated by the test results of Examples 1-5 in Table 3,
it is determined that the press felt of this invention not only
prevents rewetting but achieves a balanced combination of
resistance to compression fatigue, dehairing and abrasion
resistance, and smoothness.
[0088] Although Comparative Examples 1 and 2, in which the wet
paper web contact side batt layer is made of the core-in-sheath
fiber, are superior in terms of smoothness, they lack dehairing and
abrasion resistance, and hence are not durable. In addition, they
have anti-rewetting properties but not dewatering capability, as
indicated by the water content data at both the exit 1 and 2.
[0089] Comparative Examples 3 and 5 with less than 10% of the
core-in-sheath fiber in the base body side batt layer and
Comparative Example 4 without such fibers, on the other hand, have
resistance to compression fatigue but not anti-rewetting
properties.
[0090] Further, Comparative Example 6, in which the content rate of
the core-in-sheath fiber decreases incrementally from the press
side toward the paper side of the base body side batt layer, does
not have anti-rewetting capability, while it has all the other
effects, i.e. resistance to compression fatigue, dehairing and
abrasion resistance, and smoothness. The explanation may be that
the density of the base body side batt layer and the wet paper web
contact side batt layer is made relatively low due to the distance
between the base body side batt layer (the second layer) and the
wet paper web contact side batt layer, letting water within the
base body side batt layer (the first layer) pass through the wet
paper web contact side batt layer to rewet the wet paper web when
the press felt is released from nip pressure.
[0091] Furthermore, Comparative Example 7, in which
middle-molecular-weight nylon is used for the core member of the
core-in-sheath fiber, is inferior to examples with
high-molecular-weight nylon in terms of resistance to compression
fatigue.
[0092] And finally, Example B, in which the base body is the fabric
B woven with monofilament single yarns, is superior to Example 1,
in which the base body is the fabric A woven with monofilament
twist yarns, in terms of dewatering capability as indicated by the
water content rate at both the press exits 1 and 2.
INDUSTRIAL APPLICABILITY
[0093] As stated above, according to the present invention,
rewetting of the wet paper web can be avoided, because water within
the press side layer is blocked from moving to the wet paper web
side due to increased density of the base body side batt layer
resulted from melting of the sheath member of the core-in-sheath
fiber.
[0094] Moreover, the invention successfully enhances resistance to
dehairing, abrasion, and compression fatigue of the press felt by
enhancing viscosity of the core member of the core-in-sheath fiber,
i.e. by using high-molecular-weight nylon. As a result, the press
felt of this invention 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 dehairing and
abrasion, and is capable of maintaining smoothness of the paper
contact surface.
[0095] Further, since the base body side batt layer is made of the
core-in-sheath fiber while the wet paper web contact side batt
layer is made of nylon without the core-in-sheath fiber, the press
felt of this invention is provided with a balanced combination of
smoothness and resistance to dehairing, abrasion, and compression
fatigue.
[0096] Furthermore, the present invention improves dewatering
capability as well as resistance to dehairing and abrasion of the
press felt by using a fabric woven with monofilament single yarns
for the base body and thus enhancing water permeability
thereof.
* * * * *