Field of the Invention
[0001] The present invention relates generally to papermaking, and more particularly to
fabrics used in papermaking.
Background of the Invention
[0002] In the conventional fourdrinier papermaking process, a water slurry, or suspension,
of cellulosic fibers (known as the paper "stock") is fed onto the top of the upper
run of an endless belt of woven wire and/or synthetic material that travels between
two or more rollers. The belt, often referred to as a "forming fabric," provides a
papermaking surface on the upper surface of its upper run which operates as a filter
to separate the cellulosic fibers of the paper stock from the aqueous medium, thereby
forming a wet paper web. The aqueous medium drains through mesh openings of the forming
fabric, known as drainage holes, by gravity alone or with assistance from one or more
suction boxes located on the lower surface (
i.e., the "machine side") of the upper run of the fabric.
[0003] After leaving the forming section, the paper web is transferred to a press section
of the paper machine, in which it is passed through the nips of one or more pairs
of pressure rollers covered with another fabric, typically referred to as a "press
felt." Pressure from the rollers removes additional moisture from the web; the moisture
removal is often enhanced by the presence of a "batt" layer on the press felt. The
paper is then conveyed to a drier section for further moisture removal. After drying,
the paper is ready for secondary processing and packaging.
[0004] Press felts typically include one or more base fabric layers; these can be "flat-woven"
and formed after weaving into an endless belt, or can be woven in endless form. Generally,
the flat-woven process is preferred, as it is typically less expensive and more versatile
than the endless weaving process. Also, in many instances the felt is cut widthwise
and reattached to simplify installation on a paper machine, in which case some of
the advantages of endless weaving (such as the absence of a seam in the fabric) are
lost.
[0005] Of course, flat weaving a fabric of a base layer requires that provision be made
for joining it into endless belts. Such joints should be constructed in such a manner
that they are sufficiently strong to withstand the extreme load, temperature, and
wear conditions the press felt experiences, yet do not cause the surface of the press
felt above the seam to unduly mark the paper. One popular method of joining the base
fabric of a press felt is to form loops with machine direction yarns on each end of
the base fabric. To form the flat-woven base fabric into an endless belt, the ends
of the fabric are placed adjacent to each other, with each of the loops on one end
positioned between two loops on the other end in interdigitating fashion. A "pin"
(usually formed of mutilfilament polymeric fiber strands) is then inserted into all
of the loops to join the ends. After the batt layer(s) are needled or otherwise attached
to the base layer, the batt layer(s) are cut at the seam location, the pin is removed,
and the finished press felt is shipped to a paper mill. Once at the paper mill, the
press felt can be installed by placing it onto a paper machine, then inserting another
(usually more flexible) multifilament pin into the loops. Examples of this type of
seam are described in U.S. Patent Nos. 4, 764,417 and 4,737,241 to Gulya, 4,601,785
to Lilja et al., and 5,476,123 to Rydin the disclosures of which are hereby incorporated
herein by reference in their entireties.
[0006] In some press felts, the base fabric layer itself contains multiple fabric layers
(
i.e., is a "laminated" base layer). For example, a felt may contain a "duplex" fabric
(
i.e., a fabric having upper and lower sets of machine direction yarns interwoven with
at least one set of cross machine direction yarns - also known as a "double layer"
fabric) as well as a finer mesh single layer fabric (
i.e., a fabric having only one set each of machine direction yarns and cross machine direction
yarns). This combination provides a good balance of strength and durability to the
felt with relatively little marking. Typically, the felt is constructed by flat weaving
the duplex fabric, endless weaving the single layer fabric, joining the duplex fabric
with a pin as described above, overlaying the single layer fabric over the duplex
fabric, needling both fabric layers with batt to form machine side and paper side
batt layers, removing the pin from the double layer fabric and cutting the batt layers
and the single layer fabric at the seam to form a flat structure. Once at the paper mill,
the felt is installed on the papermaking machine by inserting a new, typically thinner
and more flexible pin into the duplex fabric layer.
[0007] This press felt construction has at least one significant shortcoming. When the single
layer fabric is cut, its yarns tend to fray somewhat at the cut. Thus, when the felt
is installed and operated on the paper machine, the frayed ends of the finer mesh
single layer fabric can interfere with the manner in which the cut portion of the
batt layer (which is often a flap of batt layer material) overlays the base fabric.
As such, paper formed with such a felt can have an inconsistent appearance and be
more susceptible to breaking on the paper machine due to the presence of the seam
of the felt. One approach to this problem is offered in International Application
No. PCT/US98/19850, which discusses a press felt in which a band of cross machine
direction yarns formed of a "low melt" material is included at the seam of the single
layer fabric. The low melt material can soften somewhat during heat-setting of the
fabric, which can induce the cross machine direction yarns to agglomerate somewhat
and reduce fraying.
Summary of the Invention
[0008] In view of the foregoing, it is an object of the present invention to provide a press
felt having a laminated base fabric with a reduced tendency for the fraying of yarns
at the base fabric seam.
[0009] It is also an object of the present invention to provide such a press felt at a relatively
low cost.
[0010] It is a further object of the present invention to provide a method for constructing
such a press felt.
[0011] These and other objects are satisfied by the present invention, which is directed
to a press felt that can have a reduced tendency to fray at the seam cut. The press
felt comprises: a paper side batt layer; a machine side batt layer; and a base fabric
layer sandwiched between the paper side batt layer and the machine side batt layer.
The base fabric layer comprises a first fabric and a second fabric. The first fabric
includes machine direction yarns and cross machine direction yarns interwoven with
the machine direction yarns. The first fabric has first and second ends with loops,
wherein the loops of the first end are interdigitated with the loops of the second
end, and the loops of said first and second ends receive a pin to form the first fabric
into an endless belt having a seam. The second fabric is formed into an endless belt
overlying the first fabric and includes machine direction yarns and cross machine
direction yarns interwoven with the machine direction yarns, wherein the machine direction
yarns are formed of a low melt material. In this configuration, the low melt machine
direction yarns of the second fabric may have a reduced tendency to fray at the seam
cut during prolonged operation.
[0012] Another aspect of the present invention is a papermaker's press felt comprising the
paper side batt layer, machine side batt layer, and base fabric layer described above,
wherein the second fabric includes a band overlying the pin seam that has no CMD yarns.
This configuration can also assist in reducing fraying at the seam cut.
Brief Description of the Drawings
[0013]
Figure 1 is a schematic illustration of the press section of a paper machine employing a press
felt of the present invention.
Figure 2 is an enlarged partial cutaway perspective view of the press felt of Figure 1.
Figure 3 is a greatly enlarged side section view of the press felt of Figure 1.
Figure 4A is a greatly enlarged partial perspective view of the pin seam of the press felt
of Figure 1 in a joined condition.
Figure 4B is an enlarged partial perspective view of the pin seam of Figure 4A in an unjoined position.
Figure 5 is a schematic representation of a process for constructing the press felt of Figure 1.
Detailed Description of the Invention
[0014] The present invention now will be described more fully hereinafter with reference
to the accompanying drawings, in which preferred embodiments of the invention are
shown and described. This invention may, however, be embodied in many different forms
and should not be construed as limited to the embodiments set forth herein; rather,
these embodiments are provided so that this disclosure will be thorough and complete,
and will fully convey the scope of the invention to those skilled in the art. Like
numbers refer to like components throughout. Components and layers may be exaggerated
for clarity.
[0015] As used herein, the terms "machine direction" (MD) and "cross machine direction"
(CMD) refer, respectively, to a direction aligned with the direction of travel of
the papermakers' fabric on a papermaking machine, and a direction parallel to the
fabric surface and transverse to the direction of travel. Also, both the flat weaving
and endless weaving methods described hereinabove are well known in the art, and the
term "endless belt" as used herein refers to belts made by either method.
[0016] Referring now to the drawings, a papermaking machine press section, designated broadly
at
10, is illustrated in
Figure 1. The press section
10 includes a press felt
14 that is installed upon and conveyed by a set of rollers
12. In its travel, the felt
14 travels over a press roll
15. An opposed press roll
17 is positioned to, in conjunction with the felt
14 and press roll
15, form a nip
N between the press rolls
15.
[0017] In operation, a paper web
P is conveyed from a forming section
16 through the nip
N formed by the press rollers
15, 17, wherein pressure is applied to the paper web
P by the press rolls
15, 17. The pressure forces moisture from the paper web
P that is absorbed by the felt
14. As the felt
14 is conveyed around its roller set
12, moisture is removed therefrom, and the felt
14 is conditioned by one or more suction boxes
20.
[0018] Figures 2 and
3 illustrate an enlarged section of the felt
14. As can be seen in Figure
2, the felt
14 includes a laminated base fabric layer
22 which comprises two separate fabrics: namely, a lower fabric layer comprising a duplex
fabric
24 and an upper fabric layer comprising a single layer fabric
36. The duplex fabric
24 includes two sets of machine direction yarns
26 and one set of cross machine direction yarns
28 interwoven with the machine direction yarns
26. The duplex fabric
24 is woven in a flat weave process; thus, in a flat condition, the duplex fabric
24 has two free ends
29a,
29b, one of which (
29a) includes loops
30 (formed by machine direction yarns
26), and the other of which (
29b) includes loops
32 formed by machine direction yarns
26. When the duplex fabric
24 is in an endless condition such as that illustrated in
Figures 2 and
3, the loops
30, 32 are positioned in interdigitated fashion, and a pin
34 is inserted through the loops
30,
32 to join the ends
29a, 29b of the duplex fabric
24 (see
Figures 4A and
4B). This fabric can be flat woven in a process such as that disclosed in U.S. Patent
No. 5,476,123 to Rydin.
[0019] Those skilled in this art will recognize that other types of fabrics can be employed
as the lower fabric layer of the base fabric layer
22 in the manner of the duplex fabric
24, including single layer fabrics, other duplex fabrics, and triplex fabrics (
i.e., those having two sets of machine direction yarns and two sets of cross machine direction
yarns). Virtually any weave pattern known to those skilled in this art, such as the
illustrated plain weave, twills, satins, and the like, can be used for this fabric
layer. The lower fabric layer will typically, but not always, have a mesh that is
somewhat more coarse than that of the upper fabric layer; it is preferred that the
mesh of the lower fabric layer be between about 30 to 50 machine direction yarns and
50 to 100 cross machine direction yarns per inch. The lower fabric layer should have
the aforementioned loops
30, 32 at its ends
29a, 29b to enable it to be joined into an endless belt with the pin
34. The construction of the loops
30,
32 and pin
34 are known to those skilled in this art and need not be described in detail herein;
exemplary loop and pin constructions are described in U.S. Patent Nos. 4,737,241 and
4,764,417 to Gulya.
[0020] Referring again to
Figures 2 and
3, the single layer fabric
36 comprises machine direction yarns
38 interwoven with cross machine direction yarns
40 in a plain weave pattern. The machine direction yams
38 are formed of a low melt material that differs in composition from the material employed
with the cross machine direction yarns
40 and the yarns of the duplex fabric
24. As used herein, the term "low melt" means that the yarns have a lower melting point
than at least the cross machine direction yarns
40 of the upper fabric
36, and in many instances than the other yarns of both the upper and lower fabric layers.
The melting point of the low melt yarns is preferably at least 25°C lower than that
of the machine direction yarns
26 of the lower fabric layer
24. Exemplary low melt materials to be employed as machine direction yarns
38 include nylons (including nylon 6, nylon 6-6, nylon 6-10, nylon 6-12 and nylon 12,
and blends and copolymers thereof), polyesters and copolymers thereof and polypropylene
and copolymers thereof. It is preferred that the low melt material have a melting
point of between about 130 and 200°C.
[0021] Those skilled in this art will recognize that other types of fabrics can be employed
as the upper fabric layer of the base fabric layer
22 in the manner of the single layer fabric
36, including other single layer fabrics, duplex fabrics, and triplex fabrics. Virtually
any weave pattern known to those skilled in this art, such as the illustrated plain
weave, twills, satins, and the like, can be used for this fabric layer. The mesh of
the upper fabric layer may vary from between about 16 to 100 machine direction yarns
and 16 to 100 cross machine direction yarns per inch, but typically the mesh will
be somewhat finer than that of the lower fabric layer. Those skilled in this art will
also recognize that, although it may be preferred for cost reasons to employ low melt
yarns as machine direction yarns
38 only, low melt yarns can also be used as the cross machine direction yarns
40 of for some or all of the single layer fabric
36, or even as the machine direction yarns
26 or cross machine direction yarns of the duplex fabric
24.
[0022] Illustratively and preferably, the single layer fabric 36 includes a band
42 that includes no cross machine direction yarns
40. The band
42 should overlie the pin
34 of the duplex fabric
24. The band
42 is approximately 2 to 12 inches with 8 inches being preferred in length (
i.e., the band
42 extends approximately 4 inches on either side of the pin
34). The presence of the band
42 eliminates CMD yarns that might otherwise fray in the seam area.
[0023] Preferably, the single layer fabric
36 is woven in a flat weaving process that produces a fabric with two free ends. The
single layer fabric
36 is formed into an endless belt through a joining process such as heat welding, which
forms a weld line
46, although other methods of joining known in the art may also be employed. Alternatively,
the single layer fabric
36 can be woven in an endless process so that the band
42 is formed during weaving.
[0024] The form of the yarns employed in the lower and upper fabric layers of the base fabric
layer
24 can vary, depending upon the desired properties of the final press felt. For example,
the yarns may be multifilament yarns, monofilament yarns, twisted or cabled multifilament
or monofilament yarns, spun yarns, or any combination thereof. Also, the materials
from which the "non-low melt" yarns employed in the fabric layers are formed may be
those commonly used in press felts, such as nylon, cotton, wool, polypropylene, polyester,
aramid, polyamide, or the like, and blends and combinations thereof.
[0025] Referring again to
Figures 2 and
3, the felt
14 also includes scrim sheets
44a,
44b,
44c. The scrim sheet
44a is positioned between the double layer fabric
24 and the single layer fabric
36. The scrim sheet
44b is positioned directly beneath the double layer fabric
24. The scrim layer
44c is positioned directly above the single layer fabric
36. The scrim sheets
44a,
44b,
44c overlie the seam area of the felt
14, typically extending between about 4 to 10 inches on either side of the seam formed
by the pin
34. Typically, the scrim sheets
44a, 44b, 44c comprise a non-woven, porous low melt nylon fabric.
[0026] Still referring to
Figures 2 and
3, the felt
14 also includes two batt layers: a machine side batt layer
50 and a paper side batt layer
52. Illustratively and preferably, these batt layers
50, 52 are attached to the base fabric layer
22 through a needling process, although other attachment techniques, such as heat bonding
and adhesives, can also be used with the present invention. An exemplary needling
process is illustrated and described in co-assigned and co-pending U.S. Patent Application
No. 09/359,213, the disclosure of which is hereby incorporated herein by reference
in its entirety.
[0027] The machine side and paper side batt layers
50, 52 should be formed of material, such as a synthetic fiber like acrylic, aramid, polyester,
or nylon, or a natural fiber such as wool, that assists in wicking water away from
the base fabric layer
22. Preferred materials for the batt layers
50, 52 include polyamide, polyester and blends thereof. The weight and thickness of the
batt layers
50,
52 can vary, although it is preferably that the ratio of batt weight to fabric weight
is about between about 0.5 and 2.0, with 1.0 being more preferred. Also, in some embodiments,
it may be desirable to have additional batt layers or to omit either or both of the
batt layers
50,
52. Notably, the machine side belt layer
50 has an open area
50 below the pin
34 in which batt has been removed (
Figure 3).
[0028] The felt
14 also includes a seam cut
48. The seam cut
48 extends through the paper side batt layer
52, the single layer fabric
36, and the machine side batt layer
50. Illustratively and preferably, the seam cut
48 is made at an angle of between about
30 and
80 degrees to the plane of the base fabric layer
22, and a flap
52a is formed by loosening the portion of the paper side batt layer
52 adjacent the seam cut
48. This process is described in detail in the aforementioned U.S. Patents to Gulya and
Lilja. Of course, no cut is necessary for the duplex fabric
24, as the pin
34 can simply be removed to enable the ends
29a, 29b of the duplex fabric
24 to be separated.
[0029] Figure 5 illustrates an exemplary manufacturing process for the felt
14. Initially, the duplex fabric
24 is flat woven such that machine direction loops
30, 32 are created on the ends
29a, 29b. A pin
60 (which is typically larger and less flexible than the pin
34 described above) is inserted through the loops
30, 32 (as they are interdigitated) to join them and thereby form the duplex fabric
24 into an endless belt. Separately, the single layer fabric
36 is woven in a flat weaving or endless weaving process. If flat woven, the single
layer fabric
36 is formed into an endless belt with a heat welding process, such as one that employs
heat or ultrasonic radiation. The single layer fabric
36 is then positioned to overlie the duplex fabric
24 such that the band
42 that lacks cross machine direction yarns overlies the pin
34, the scrim sheets
44a,
44b,
44c are positioned over the seam area, and the machine side and paper side batt layers
50, 52 are needled to the base fabric layer
22 (the open area
50a is typically created by removing fiber with a brush and tweezers).
[0030] Once the batt layers
50, 52 have been added, the entire felt
14 is then heat treated at a temperature sufficient to cause softening of the machine
direction yams
38 formed of low melt material without unduly softening the other yarns of the base
fabric
22. Typically, the heat treatment is carried out at a temperature of between about 130°
to 200° C. The pin
60 is then removed, and the seam cut
48 is formed with blades or other cutting devices through the paper side batt layer
52 and the single layer fabric
36. The felt
14 can then be shipped in its flat form to a paper mill, where the pin
34 can be inserted into the machine direction loops
30, 32 as the felt
14 is installed on the upper rolls
12.
[0031] Importantly, when the seam cut
48 is made, the yarns of the single layer fabric
36, and in particular the machine direction yarns
38, can have a far lower tendency to fray than the fabrics of prior art felts. This reduced
fraying is the result of the inclusion of the low melt machine direction yarns
38. As described, during the heat treatment of the felt
14, the softening of the low melt machine direction yarns
38 causes the agglomeration of the machine direction yarns
38 and the fibers of the paper side batt layer
52. As a result, the flap
52a adjacent to the seam cut
48 can lay uniformly, even during operation, which has not always been the case for
prior art fabrics.
[0032] The invention will now be more particularly described in the following non-limiting
example.
EXAMPLE
[0033] A press felt was constructed according to the following parameters
| |
MD yarns |
CMD yarns |
Mesh Count |
| Base Fabric Layer |
Size (inches) |
Material |
Size (inches) |
Materials |
|
| Duplex Layer |
0.015 |
Nylon |
0.015 |
Nylon |
40x48 |
| Single Layer* |
0.014 |
Nylon |
0.008 |
Nylon |
40x24 |
| * The single layer fabric was woven without CMD yarns in a 8 inch wide band that was
positioned directly over the pin seam of the duplex fabric. |
| Batt Layers |
Material |
Weight (g/m2) |
| Machine Side |
Nylon staple |
150 |
| Paper Side |
Nylon staple |
780 |
Heat Treatment: 3 minutes at 175°C.
[0034] The resulting press felt successfully produced linerboard paper.
[0035] The foregoing is illustrative of the present invention and is not to be construed
as limiting thereof. Although exemplary embodiments of this invention have been described,
those skilled in the art will readily appreciate that many modifications are possible
in the exemplary embodiments without materially departing from the novel teachings
and advantages of this invention. Accordingly, all such modifications are intended
to be included within the scope of this invention as defined in the claims. The invention
is defined by the following claims, with equivalents of the claims to be included
therein. In the claims, means-plus-function clauses are intended to cover the structures
described herein as performing the recited function and not only structural equivalents
but also equivalent structures.
1. A papermaker's press felt, comprising:
a paper side batt layer;
a machine side batt layer; and
a base fabric layer sandwiched between said paper side batt layer and said machine
side batt layer, said base fabric layer comprising a first fabric and a second fabric;
said first fabric including machine direction yarns and cross machine direction yarns
interwoven with said machine direction yarns, said first fabric having first and second
ends with loops, said loops of said first end being interdigitated with said loops
of said second end, said loops of said first and second ends receiving a pin to form
said first fabric into an endless belt having a seam;
said second fabric formed into an endless belt overlying said first fabric and including
machine direction yarns and cross machine direction yarns interwoven with said machine
direction yarns, wherein said machine direction yarns are formed of a low melt material.
2. The papermaker's press felt defined in Claim 1, wherein said second fabric includes
a band overlying said seam of said first fabric that has no cross machine direction
yarns.
3. The papermaker's press felt defined in Claim 1, said paper side batt layer and said
machine side batt layer are needled to said base fabric layer.
4. The papermaker's press felt defined in Claim 1, wherein said first fabric comprises
a duplex fabric.
5. The papermaker's press felt defined in Claim 1, wherein said second fabric comprises
a single layer fabric.
6. The papermaker's press felt defined in Claim 1, wherein said low melt material is
selected from the group consisting of: nylon and nylon copolymer.
7. The papermaker's press felt defined in Claim 1, wherein said first fabric layer forms
a coarser mesh than said second fabric.
8. The papermaker's press felt defined in Claim 1, wherein each of said paper side batt
layer, said machine side batt layer, and said second fabric includes a cut corresponding
to said first fabric seam to enable said press felt to take a flat condition upon
removal of said pin.
9. The papermaker's press felt defined in Claim 8, wherein said cut is oriented at an
angle of between about 30 and 80 degrees relative to the plane of the base fabric
layer.
10. A papermaker's press felt, comprising:
a paper side batt layer;
a machine side batt layer; and
a base fabric layer sandwiched between said paper side batt layer and said machine
side batt layer, said base fabric layer comprising a first fabric and a second fabric;
said first fabric including machine direction yarns and cross machine direction yarns
interwoven with said machine direction yarns, said first fabric having first and second
ends with loops, said loops of said first end being interdigitated with said loops
of said second end, said loops of said first and second ends receiving a pin to form
said first fabric into an endless belt having a seam;
said second fabric formed into an endless belt overlying said first fabric and including
machine direction yarns and cross machine direction yarns interwoven with said machine
direction yams, said second fabric including a band overlying said seam that has no
CMD yarns.
11. The papermaker's press felt defined in Claim 10, said paper side batt layer and said
machine side batt layer are needled to said base fabric layer.
12. The papermaker's press felt defined in Claim 10, wherein said first fabric comprises
a duplex fabric.
13. The papermaker's press felt defined in Claim 10, wherein said second fabric comprises
a single layer fabric.
14. The papermaker's press felt defined in Claim 10, wherein said low melt material is
selected from the group consisting of: nylon and nylon copolymer.
15. The papermaker's press felt defined in Claim 10, wherein said first fabric layer forms
a coarser mesh than said second fabric.
16. The papermaker's press felt defined in Claim 10, wherein each of said paper side batt
layer, said machine side batt layer, and said second fabric includes a cut corresponding
to said first fabric seam to enable said press felt to take a flat condition upon
removal of said pin.
17. The papermaker's press felt defined in Claim 16, wherein said cut is oriented at an
angle of between about 30 and 80 degrees relative to the plane of the base fabric
layer.
18. A method of constructing a papermaker's press felt having a laminated base fabric
layer, said method comprising the steps of:
interweaving machine direction yarns and cross machine direction yarns to form a first
fabric, said first fabric having first and second ends with loops;
positioning the loops of said first and second ends of said first fabric in interdigitated
relationship;
inserting a pin into said loops to form a seam that joins the first and second ends
of said first fabric, thereby forming said first fabric into an endless belt;
interweaving machine direction yarns and cross machine direction yarns to form a second
fabric, wherein said machine direction yarns are formed of a low melt material;
attaching said second fabric to said first fabric;
heating said low melt band to cause said low melt material to soften; and
cutting a seam through said low melt band that corresponds to said seam of said first
fabric.
19. The method defined in Claim 18, further comprising the step of attaching a first batt
layer to overlie said second fabric layer.
20. The method defined in Claim 19, wherein said cutting step further comprises cutting
said first batt layer to form a seam therein.
21. The method defined in Claim 19, further comprising the step of attaching a second
batt layer to underlie said first fabric layer.
22. The method defined in Claim 21, wherein said cutting step further comprises cutting
said second batt layer to form a seam therein.
23. The method defined in Claim 18, further comprising the step of removing the pin from
said first fabric after said heating step and prior to said cutting step.
24. The method defined in Claim 18, wherein said heating step comprises heating the low
melt material at a temperature of between about 130°C and 200°.
25. The method defined in Claim 18, wherein said step of interweaving said second fabric
comprises flat-weaving said second fabric.
26. The method defined in Claim 18, further comprising the step of heat welding said second
fabric to join ends thereof and thereby form said second fabric into an endless belt.