Note: Descriptions are shown in the official language in which they were submitted.
CA 02748789 2011-08-15
EMBOSSING FABRIC INCLUDING WARP YARN SETS
Field of the Invention
This invention relates to industrial textiles for filtration or conveyance,
such as papermakers'
fabrics. In particular, the invention relates to woven embossing fabrics whose
component
yarns are interwoven according to a pattern which will impart a macroscopic
topography
onto cellulosic products which are formed or conveyed thereon, and more
particularly such
fabrics in which warp yarns are arranged in groups of at least two yarns which
are
interwoven together according to the same path and pattern in the fabric and
present an
aspect ratio for each yarn set of at least 2:1 and a ribbed surface to the
sheet.
Background of the Invention
Papermaker's fabrics woven using various arrangements of paired or similar
sets of yarns
are known, for example, as disclosed in US 2,088,447 and US 2,269,869 (both to
Specht);
US 3,143,150 (Buchanan); US 3,167,281 (Hill); and US 5,465,764 (Eschmann et
al.).
It is known to provide paired MD yams, for example to provide a fabric having
a tight
weave (i.e. low air permeability), as disclosed in US 5,799,708 (Josef); or to
minimize
drainage and crossover point topographical markings, as disclosed in US
6,953,065 (Martin
et al.).
It is also known, for example from US 4,592,396 (Borel et al.), to use paired
weft so as to
allow the PS surface to be as flat and smooth as possible; and from US
4,636,426 (Fleischer)
to arrange either, or both, the warp and weft yarns in a side-by-side paired
relationship,
preferably glued together, so as to improve sheet release and reduce wire mark
without
having to use yarns having a generally rectangular cross-sectional shape.
It is also known from US 5,429,686 (Chiu et al.) to use high, long warp floats
in a through-
air dryer (TAD) fabric to produce a quilted effect in the paper, by providing
a so-called
"sculpture layer" which contacts the web and embosses a pattern upon it.
US 7,114,529 (Johnson et al.) discloses a TAD fabric woven so that the warp
and weft yams
are stacked in the fabric having a warp fill of at least 100% and a weft fill
of at least 75%.
The yarns are interwoven so that the warp are set above the fabric plane by
0.3 to 1.5 times
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the thickness of the yarns and so that diagonal apertures are formed within
the fabric to
produce a high air permeability of at least about 7300 m3/mz/h. The fabric
design is
particularly suited for the production of a high bulk imprinted (patterned)
paper product; the
warp yarns are not arranged in sets or pairs.
It is known from US 7,121,306 (Harrison) to provide yarn assemblies of two or
more
vertically stacked warp or weft yarns interwoven as one yarn (i.e. each yarn
follows the
same weave path as its immediately adjacent neighbor so as to be in generally
continuous,
contiguous contact with each other substantially throughout the fabric).
It is also known from US 7,740,029 (Hodson et al.) to use weft yarns arranged
in pairs and
weave as one through a dryer fabric, for the purpose of providing increased
sheet contact,
decreased weaving time and reduced air permeability.
For bulk sheet products such as towel and tissue, it is known to emboss the
sheets by
providing a profiled upper surface to the conveying fabrics. Many prior art
embossing
fabrics, such as those intended for through air drying (TAD) and forming
applications, are
woven using generally flat or rectangular warp or weft yarns so as to provide
suitable
contact area between the sheet and fabric to enable sheet handling and release
characteristics.
However, as the majority of industrial textiles of this general nature, such
as other
papermaking fabrics, are woven using circular warp yarns, rethreading the loom
to include
rectangular warp yarns is disadvantageously time-consuming.
Summary of the Invention
It has now been found that weave patterns in which the warp yarns are arranged
in groups of
two or more yarns which are interwoven together according to the same path and
pattern in
the fabric, and present an aspect ratio for each yarn group of at least 2:1,
and present a
profile above the weft yarns in the paper side surface of the fabric by an
amount between 50%
and 100% of the width of the individual warp yarns, are particularly
advantageous in the
production of patterned sheets such as towel and tissue.
The grouping of two or more warp yarns, preferably but not necessarily of
circular cross-
section, so that they interweave together throughout the fabric, as a set,
allows for a
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replication of the aspect ratio and effect previously provided by using a
single rectangular
cross-section monofilament warp yarn having the same aspect ratio and
interwoven in the
same manner.
The weave patterns of the invention have the further advantages that the
contact area
between the sheet and the fabric can be increased as desired by increasing the
number of
warp yams weaving in parallel adjacent paths; and the resulting structure now
includes MD
oriented striations (i.e. the space between the yams) which provide
contamination resistance
effects similar to those known to be provided by ribbed or grooved yam
profiles, such as
those described in US 6,773,786 (Kuckart).
This also allows for the use of looms already threaded with round warp yarns.
As those
yarns and looms are of appropriate size and are suitably equipped to weave
embossing
fabrics, they may now advantageously be used to produce the fabrics of the
invention,
eliminating the previous necessity, noted above, of having to change the
existing warp
system from round to flat yams in order to weave such a fabric. This provides
for the
advantage of using a single warp platform for these and other fabrics, such as
disclosed in
WO 2011/011676 (Chaplin et al.).
The invention therefore seeks to provide a woven industrial fabric for at
least one of
filtration and conveyance, the fabric having a product conveying surface,
being woven to a
repeating weave pattern and comprising
(i) at least one set of weft yams; and
(ii) one set of warp yarns, comprising a plurality of groups of warp yarns,
each group
comprising at least two warp yarns, wherein for each group the warp yarns
(a) together follow an identical coplanar path;
(b) are retained in lateral adjacency to provide a profile to the product
conveying
surface; and
(c) are dimensioned such that a ratio of a width of the group in the product
conveying surface to a height of the group is at least 2:1.
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In the fabrics of the invention, the warp yams comprise groups of at least two
or three, or
possibly more, individual yams. The warp yams of a group are woven together,
in direct
adjacency and in the same manner. The yams in each group follow identical
coplanar paths
throughout the fabric and, as a group, provide an effective aspect ratio
(which is the ratio of
the total width of all of the yams in one group, to the height of the group)
of at least 2:1. The
aspect ratio of each set of yarns simulates a single rectangular cross-section
yarn having the
same aspect ratio. Where the warp yams have a circular cross-section, each yam
group is
effectively ribbed due to the adjacency of the yarns, and the ribs are
effective in releasing
contaminants and other undesirable foreign matter from the fabric surface
during cleaning
cycles.
In general, sets or groupings of two or more adjacent warp yams interwoven as
a pair, triplet,
quadruplet, simulate in the fabric a single rectangular yam with dimensions
(aspect ratio) of
nh x h where h is the diameter (height) of the yam and where n = the number of
warp yams
in the group.
For example, two or three circular cross-section warp yams, each having a
diameter of e.g.
0.22mm, could be used to replicate the effect provided by a single rectangular
warp yam
whose aspect ratio is 2:1 (i.e. two circular cross-section warp yams each
having diameters of
0.22mm provide a warp yam group which measures 0.44 x 0.22mm) or 3:1 (i.e.
three
circular cross-section warp yams each having a diameter of 0.22mm provide a
warp yarn
group which measures 0.66 x 0.22mm).
Preferably, the profile provided by the groups of warp yams comprises a
profile height
above the weft yams in the product conveying surface, and for each group of
warp yams the
profile height is between 50% and 100% of a width of each warp yam in the
group.
The fabrics of the invention are flat woven according to a pattern requiring
at least 10 sheds
in the loom using circular cross-section polymeric (e.g. PET, PPS)
monofilament MD warp
yarns and CD well yams (e.g. PET, PPS, nylon, others) arranged so as to
provide a warp fill
of approximately 95% to 110% in the fabric following heatsetting. The warp
yams may be
arranged on either one or two beams in the loom for weaving.
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In a first embodiment of the invention, the warp yarns are interwoven with a
single set of
weft yarns to provide a single layer fabric.
In a second embodiment, the warp yarns are interwoven with first and second
sets of weft
yams to provide a double layer fabric, in which the first set of weft yams are
located entirely
on the PS of the fabric, and the second set of weft yarns are located entirely
on the MS of the
fabric. The weft yams of the first set may be arranged so as to be vertically
stacked with
corresponding weft yarns of the second set in the fabric (i.e. the PS:MS weft
ratio is 1:1).
In an alternative double layer fabric construction, not all of the weft yarns
of the first system
are vertically stacked over corresponding weft yams of the second weft system.
Additional
weft yams may be included in the PS of the fabric; in a version of this
embodiment,
additional weft yams are provided so as to effectively double the number of
weft yarns in
the PS, to provide a fabric in which the PS:MS weft yarn ratio is 2:1. Other
ratios can be
selected to provide the desired weft yarn ratio according to the intended end
use of the fabric,
for example ratios of 1.5:1, or e.g. 3:1 or higher. Weft yarn ratios greater
than 1:1 will
provide extra support for the papermaking fibers in the sheet conveyed by the
fabric and
may be used to adjust air permeability. In double layer fabrics where the weft
yarn ratio is
greater than 1:1, some of the weft yarns of the first set will be vertically
stacked over
corresponding weft yams of the second set.
In the fabrics of the invention, the groups of warp yarns are interwoven with
the weft yams
according to patterns which provide for a weft float length of between one and
eleven warp
yam groups on the MS of the fabric.
The polymeric warp and/or weft yarn material is preferably PET which is
optionally heat or
hydrolysis stabilized; in high temperature environments such as may be found
in a through-
air dryer, it may also be beneficial to use a heat resistant material such as
PPS in either, or
both, the warp and weft positions in the fabric. However, the invention is not
so limited, and
polymers such as are commonly used in industrial textiles intended for
papermaking
applications may be utilized in either the warp or weft yams from which the
fabric is made.
When the intended end use of the fabric is in a through-air dryer type
application, it may be
preferred to use known hydrolysis or heat stabilized materials so as to
increase the service
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life of the fabric. Where the intended end use of the fabric is in the forming
section, where
heat and hydrolysis are not major concerns, it may be appropriate to use
nylons, various
polyesters, or blends of PET and thermoplastic polyurethane such as are known
in the art,
for example as disclosed in US 5,169,711 (Bhatt et al.) and US 5,502,120
(Bhatt et al.).
However, in all cases, the materials and dimensions for the yarns, and the
fabric processing
conditions, will be selected and adjusted so that the weft yams have a greater
resistance to
crimping than the warp yarns, so as to ensure that the warp yams are raised
above the plane
of the weft yams in the woven fabric to provide the required amount of profile
as discussed
above.
Brief Description of the Drawings
The invention will now be described with reference to the drawings, in which:
Figure 1 is a cross-sectional view along the weft yarns through a fabric in an
embodiment of
the invention;
Figure 2 is a cross-sectional view along the weft yarns through a fabric in a
second
embodiment of the invention;
Figure 3a is a 24-shed weave diagram for a double layer embossing fabric in a
third
embodiment of the invention;
Figure 3b is a diagram showing an approximation of the paper side surface
embossing
pattern of a fabric woven according to the pattern shown in Figure 3a.-
Figure 3c is a photograph of a tissue sheet sample formed and embossed on a
fabric woven
according to the pattern shown in Fig. 3a having a paper side surface as shown
in Figure 3b;
Figure 4a is a 24-shed weave diagram for a double layer embossing fabric in a
fourth
embodiment of the invention;
Figure 4b is a diagram showing an approximation of the paper side surface
embossing
pattern of a fabric woven according to the pattern shown in Figure 4a;
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Figure 4c is a photograph of a tissue sheet sample formed and embossed on a
fabric woven
according to the pattern shown in Fig. 4a having a paper side surface as shown
in Figure 4b;
Figure 5a is a 24-shed weave diagram for a double layer embossing fabric in a
fifth
embodiment of the invention;
Figure 5b is a diagram showing an approximation of the paper side surface
embossing
pattern of a fabric woven according to the pattern shown in Figure 5a;
Figure 5c is a depiction of an approximate 3-dimensional representation of a
fabric
constructed according to the weave diagram shown in Figure 5a;
Figure 6a is a 24-shed weave diagram for a double layer embossing fabric in a
sixth
embodiment of the invention;
Figure 6b is a diagram showing an approximation of the paper side surface
embossing
pattern of a fabric woven according to the pattern shown in Figure 6a;
Figure 6c is a depiction of a 3-dimensional representation of a fabric
constructed according
to the weave diagram shown in Figure 6a;
Figure 6d is a photograph of a tissue sheet sample formed and embossed on a
fabric woven
according to the pattern shown in Fig. 6a;
Figure 7a is a 24-shed weave diagram for a double layer embossing fabric in a
seventh
embodiment of the invention;
Figure 7b is a diagram showing an approximation of the paper side surface
embossing
pattern of a fabric woven according to the pattern shown in Figure 7a;
Figure 7c is a depiction of a 3-dimensional representation of a fabric
constructed according
to the weave diagram shown in Figure 7a; and
Figure 7d is a photograph of a tissue sheet sample formed and embossed on a
fabric woven
according to the pattern shown in Fig. 7a.
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Detailed Description of the Drawings
Figure 1 is a cross-sectional view along the weft yams through a fabric in an
embodiment of
the invention. In this embodiment, each group of warp yams consists of two
yams, and the
figure shows them as they would appear in a cross-section along the weft yams
through the
fabric.
Figure 2 is an illustration similar to Figure 1, being a cross-sectional view
along the weft
yams through a fabric in a second embodiment of the invention. In this
embodiment, each
group of warp yams consists of three yams, and the figure shows them as they
would appear
in a cross-section along the weft yams through the fabric.
Figure 3a is a 24-shed weave diagram for a double layer embossing fabric in a
third
embodiment of the invention. In this embodiment, the warp yams are arranged in
groups
consisting of two yarns. Figure 3b is a diagram showing an approximation of
the paper side
surface embossing pattern of a fabric woven according to the overall 24-shed
pattern shown
in Figure 3a; and Figure 3c is a photograph of a tissue sheet sample formed
and embossed
on a fabric woven according to the pattern shown in Fig. 3a, and having a
paper side surface
as shown in Figure 3b;
Figure 4a is a 24-shed weave diagram for a double layer embossing fabric in a
fourth
embodiment of the invention. In this embodiment, the warp yarns are arranged
in groups
consisting of two yarns, and the fabric is woven using a double beam loom.
Figure 4b is a
diagram showing an approximation of the paper side surface embossing pattern
of a fabric
woven according to the overall 24-shed pattern shown in Figure 4a; and Figure
4c is a
photograph of a tissue sheet sample formed and embossed on a fabric woven
according to
the pattern shown in Fig. 4a, and having a paper side surface as shown in
Figure 4b.
Figure 5a is a 24-shed weave diagram for a double layer embossing fabric in a
fifth
embodiment of the invention. In this embodiment, the warp yams are arranged in
groups
consisting of three yams, and the fabric is woven using a double beam loom.
Figure 5b is a
diagram showing an approximation of the paper side surface embossing pattern
of a fabric
woven according to the overall 24-shed pattern shown in Figure 5a; and Figure
5c is a
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depiction of a three-dimensional representation of a fabric constructed
according to the
weave diagram shown in Figure 5a.
Figure 6a is a 24-shed weave diagram for a double layer embossing fabric in a
sixth
embodiment of the invention. In this embodiment, the pattern also includes
pairs of weft
binder yarns, and the warp yams are arranged in groups consisting of two yams.
The fabric
is woven using a double beam loom. Figure 6b is a diagram showing an
approximation of
the paper side surface embossing pattern of a fabric woven according to the
overall 24-shed
pattern shown in Figure 6a; and Figure 6c is a depiction of a three-
dimensional
representation of a fabric constructed according to the weave diagram shown in
Figure 6a.
Figure 6d is a photograph of a tissue sheet sample formed and embossed on a
fabric woven
according to the pattern shown in Fig. 6a.
Figure 7a is a 24-shed weave diagram for a double layer embossing fabric in a
seventh
embodiment of the invention. In this embodiment, the warp yams are arranged in
groups
consisting of two yarns, and the fabric is woven using a double beam loom.
Figure 7b is a
diagram showing an approximation of the paper side surface embossing pattern
of a fabric
woven according to the overall 24-shed pattern shown in Figure 7a; and Figure
7c is a
depiction of a three-dimensional representation of a fabric constructed
according to the
weave diagram shown in Figure 7a. Figure 7d is a photograph of a tissue sheet
sample
formed and embossed on a fabric woven according to the pattern shown in Fig.
7a.
In Figures 3a, 4a, 5a, 6a and 7a, the weave diagrams show the
interrelationship between the
warp and weft yarns and the basic construction of the fabrics. In the
diagrams, each vertical
row of filled squares and white (or blank) squares represents a warp yam and
each
horizontal row of filled and white / blank squares represents a weft (or pick)
yam; thus, each
square represents an intersection of a warp and weft yarn. A filled square
indicates that a
warp yam is raised (or passes) over a weft yarn at that point of intersection;
a white or blank
square indicates that the warp yam is below the weft yam at that intersection.
As the
diagrams are presented on the respective pages, the warp yarns are numbered
from left to
right, and the weft yarns are numbered from top to bottom.
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