Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Pattern Densified Fabric Comprisinq Conjugate Fibers
Backqround Of The Invention
rlethods of compression embossing fibrous webs are known in
the art. Methods of heat embossing fibrous webs including
fibrous webs comprising the m oplastic fibers are also
known. In general, the heat embossing is done by means of
heated rollers, with the fibrous web traveling through the
nip between the counterrotating heated rollers. To
maintain a good through-put speed, the rollers are usually
heated a few degrees higher than the melting point of the
thermoplastic fibers in the web or the temperature desired
in the embossing process. This is necessary so that the
web traveling quickly through the nip achieves the desired
temperature.
Fabrics which have been heat embossed and in particular
fabrics which have been heat embossed in a pattern by
patterned rollers often display damage from excessive
heat. In particular, in order to achieve heat suf-ficient
to fuse the fibers in the patterned regions, the fibers
immediately adjacent the patterned regions are heated to a
temperature sufficient to cause shrinkage and damage. The
heat radiated to the fibers next adjacent the patterned
area also shrinks the web blurring the line of demarkation
of the pattern. In the method of the present invention, a
combination of heat and pressure is used to compact the
fibers in the patterned regions in the web. This combina-
tion of factors does not effectively radiate to the fibersnext adjacent the pattern region of the fabric, creating a
fabric with very sharp pattern delineation and high loft
adjacent the pattern region.
It is also old in the art to cold emboss to form or
laminate fibrous layers. Cold embossing of moist fibrous
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layer produces a compacted product which exhibits deforma-
tion of fibers and hydrogen bonding. Paper toweling is
often made by such a method. The compaction achieved with
cold embossing can be undone with water. In the method
and fabric of the present invention, the compaction of the
fibrous web may not be reversed or undone by the applica-
tion of water.
Summary Of The Invention
The present invention comprises a method of pattern embos-
sing a nonwoven web of fibers comprising conjugate fibers
and the fabric formed thereby. The method comprises heat
embossing the web at a temperature slightly below the
softening point of the low melting point component of the
conjugate fiber, and with the combination of pressure and
temperature sufficient to cause cold flow of at least the
low meltin~ point component of the conjugate fibers to
deform and compact the conjugate fibers compacting the
fibers of the web in only the patterned regions. The
fabric formed according to the method has a very sharp
pattern delineation and high loft immediately adjacent the
pattern. The web contains at least 15 percent conjugate
fibers. In a preferred embodiment, the conjugate fibers
2S are a sheath/core of high density polyethylene/polyester
fibers.
Description Of The ~rawing:
The Figure is a photomacrograph showing a cross-section of
a fabric prepared according to the method of the present
invention.
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Detailed Description Of The Invention
The present invention comprises a method of embossing a
web comprising at least 15 percent conjugate fibers and
the fabric formed thereby. The conjugate fibers comprise
a low melting point component and a high melting point
component, and preferably comprise a sheath/core
polyethylene/polyester fiber.
Preferably, the conjugate fibers employ high density poly-
ethylene, that is, linear polyethylene that has a density
of at least about 0.94, and a Melt Index ("M.I.") by ASTM
D-123~(E) (190C., 2160 gms.) of greater than 1, preferab-
ly greater than about 10, and more preferably from about
20 to about 50. Usually the fibers will be composed of
about 40 to 60 weight percent, and preferably 45 to 55
weight percent, polyester, the remainder being
polyethylene.
The abrics of the invention are produced by first forming
a fibrous web comprising a loose array of the conjugate
fibers, as by carding, air laying, or the like. The exact
weight of the fibrous web has not been Eound to be narro~-
ly critical, although useful weights have been found
within the ran~e from about 0.2 to about 4.2 ounces per
square yard. This web is then conveyed to the nip of the
embossing rollers.
According to the method of the present invention, a combi-
nation of heat and pressure is applied at the embossing
nip combined to cause the low melting point component of
the conjugate fibers of the web to cold flow. The method
of the present invention encompasses usin~ patterned
embossed rolls generally known in the art. The pattern
embossed rollers have raised patterned surface areas which
contact ànd compress the web as it passes through the nip
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of a pair of counterrotating pattern emboss rollers. In
the conventional heat embossing operation, the rollers are
heated to a temperature many degrees above the effective
temperature needed at the nip. This is necessary to main-
tain a good through-put speed of the web. The elevated
temperature assures that during the short amount of time
that the web spends in the nip, the effective temperature
within the web is reached.
In the method of the present invention, the rollers are
heated to a temperature below the softening point of the
low melting point component of the conjugate fiber of the
web which is to be processed through the nip of the rol-
lers. As the web passes through the nip, the combination
of heat and pressure applied by the patterned embossed
rollers causing at least the low melting point component
of the conjugate fibers of the web to cold flow and
deform and compact the conjugate fibers, compacting the
fibers in the web, in only the patterned regions. By
using a combination of pressure and temperature, the
method of the present invention avoids fiber shrinkage and
web damage in the regions immediately adjacent the
patterned regions normally caused by the radiation of heat
from the super heated rollers used when heat alone is used
to fuse the fibers of the web.
The fibrous webs used in practicing the method according
to the present invention comprise at least 15 percent
conjugate fibers and preferably sheet/core high density
polyethylene/polyester conjugate fibers. Examples of
other conjugate fibers which may be used in the method of
the present invention are copolyester/polyester and
nylon 6/nylon 66 fibers. Optionally, before passing to
the nip, the web may be heated with heated air at a
temperature sufficient to fuse the conjugate fibers to
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each other and to other fibers in the web to strengthen
the fabric in the remaining, unpatterned regions.
Figure 1 illustrates a microscopic cross-section of a
fabric formed according to the present invention. The
fabric shown generally at 10 has embossed densified
regions 12 created by the deforming and compacting of the
conjugate fiber, compacting all the fibers in the web in
only the pattern embossed region. The deformation and
compaction of the conjugate fibers are accomplished by a
combination of heat and pressure. In the method of the
present invention, the heated embossed rollers are heated
to a ter;lperature slightly below the softening point of the
low melting point component of the conjugate fibers.
Sufficient pressure is applied in the patterned area to
permanently deform the low melting point component of the
conjugate fiber and hence the conjugate fiber. Any other
fibers in the patterned regions of the web are compacted
and the web is maintained in a densified state by the
deformation of the conjugate fibers. The patterned
regions display an opacity that is believed due to the air
fiber interfaces. One could speculate that the deforma-
tion of the conjugate fibers is caused by cold flow of at
least the sheath and perhaps the core of the fibers. In
the regions 1~ immediately adjacent the densified
patterned regions, the fabric shows a very high loft and
individual fibers 16 are seen. The high loft delineates
the pattern of the fabric and indicates a lack of fiber
damage in the regions immediately adjacent the patterned
regions.
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