Note: Descriptions are shown in the official language in which they were submitted.
CA 02759345 2011-11-25
Method for the production of an elastic composite material with a textile
surface
Specification:
The invention relates to a method for the production of an elastic composite
material
with a textile surface.
Elastic composite materials with a textile surface are used, among other
things, for the
production of baby diapers, for example as tapes or as an elastic back-sheet,
incontinence articles, feminine hygiene products, and the like. In these
applications, the
textile surface, which must be produced in cost-advantageous manner, has great
importance. In this connection, the textile surface is not allowed to impair
the elasticity of
the film.
Composite materials composed of an elastic carrier film and a nonwoven fabric
that is
laminated on are known. The fabric forms a solid structure that decisively
influences the
stretching behavior of the composite material. Composite materials composed of
an
elastic carrier film and a nonwoven fabric that is laminated on must therefore
be
mechanically activated, by means of mechanical stretching, after the
lamination process.
A method for the production of an elastic composite material with a textile
surface is
known from EP 2 177 654 Al, in which a layer of melt-blown nonwoven is
produced and
glued onto an elastic film without any prior consolidation. In this method,
the nonwoven
layer is not rolled up and unrolled, and no guidance of the nonwoven layer
under tensile
stress is provided. The nonwoven layer can therefore be formed with little
strength and,
in particular, with a low weight per surface area unit, and does not greatly
hinder elastic
stretching of the composite material. For this reason, the composite material
does not
require any subsequent mechanical activation. However, the bond strength
between the
fibers of the textile layer and the elastic film is not yet satisfactory.
Since the work is
conducted with loose fibers, to a great extent, it is not ensured that all the
fibers are
sufficiently anchored in the adhesive matrix. Fibers can unintentionally come
loose from
the composite and be taken in by the user.
Against this technological background, the invention is based on the task of
indicating a
method for the production of a composite material with a textile surface,
which material
is characterized by great stretching capacity, and the textile surface of
which material
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does not contain any loose fibers that come loose from the composite during
use of the
composite material.
The object of the invention and the solution for this task is a method
according to claim
1. In the method according to the invention, first a laminate is produced,
which has
elastic cover layers and a core composed of a nonwoven fabric. The laminate is
subsequently separated into two strips, each of which has a cover layer and an
adhering
layer of nonwoven fabric, by tearing open the core. The method has the
advantage that
the fibers of the textile surface are bound in the nonwoven fabric, and that
when the
core, which consists of a nonwoven fabric, is torn open, no free fibers that
can easily
come loose from the composite are formed. A nonwoven fabric that is slightly
consolidated can be used. The degree of consolidation can be adjusted, for
example
when using calander consolidation, so that the composite material can be
elastically
stretched without subsequent mechanical activation, and so that the stretching
properties are determined by the elasticity of the cover layer.
In order to separate the laminate, the strips are preferably grasped
separately and
pulled apart by applying tensile forces. The strips can be guided over driven
rollers and
wound up separately. It lies within the scope of the invention that the
separation process
is connected with mechanical activation of the elastic cover layer of the
strips,
specifically by means of stretching of the elastic cover layers during the
pulling-off
process. During pulling off and winding up of the strips, the strips can be
stretched in the
transverse direction and/or the longitudinal direction, by means of with
suitable devices.
In particular, the strips can also be passed over profiled rollers in which
over-stretching
of the strips transverse to the take-off direction takes place. In this way,
the stretching
properties of the composite material can be influenced and further improved.
Tearing open the nonwoven fabric can be supported by means of a blade disposed
in
the separation plane.
The laminate with elastic cover layers and a core composed of nonwoven fabric
can be
produced in different ways. Preferably, the nonwoven fabric is laminated in
between two
elastic film webs. However, extrusion lamination, in which the elastic layers
are applied
to the nonwoven fabric by means of extrusion, is fundamentally also possible.
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The elastic cover layers preferably have a layer thickness between 20 pm and
100 pm,
and can consist of a styrene block copolymer or a thermoplastic polyolefin
elastomer. In
addition to mono-films, multi-layer co-extruded films can also be used for the
cover
layers. In particular, perforated or breathable elastic films can also be used
for the cover
layers. When using a breathable elastic film, this important property is
maintained in the
composite material. In place of an elastic film, fundamentally an elastic
nonwoven fabric
that has sufficient tensile strength can also be used.
The nonwoven fabric and the elastic film webs or elastic cover layers are
preferably
glued to one another, whereby polyurethane adhesive and hot-melt adhesives are
particularly suitable. The adhesive can be applied over the entire area or in
patterns, for
example in dots. Full-area application of adhesive is preferred, whereby an
adhesive
application with an application amount between 1 g/m2 and 2.5 g/m2 is
sufficient when
using a solvent-free one-component polyurethane adhesive (1-K-PUR). When using
a
hot-melt adhesive, a higher application weight of 3 g/m2 to 5 g/m2 will
generally be
necessary.
The nonwoven fabric that forms the core of the laminate and is torn open in
the course
of the production process preferably consists of a melt-blown nonwoven. The
fibers of a
melt-blown nonwoven are produced by means of extrusion, and usually exit from
multiple holes of an extrusion nozzle disposed next to one another.
Immediately after
leaving the extrusion nozzle, the viscous polymer strands that exit from the
holes are
impacted with compressed air and stretched. Melt-blown fibers are
characterized in that
they are very thin and guarantee good homogeneous coverage of the elastic
cover
layers even at a low weight per surface area unit, and distinguish themselves
by their
particularly soft appearance. The nonwoven preferably consists of polyolefin
fibers,
particularly polypropylene fibers. The melt-blown nonwoven is only slightly
consolidated
for the method according to the invention, and can be used at a weight per
surface area
unit of 5 g/m2 to 20 g/m2. The degree of consolidation, for example by means
of
calander consolidation, is guided by the desired stretching properties of the
composite
material.
A multi-layer nonwoven fabric with an SMS layer structure (spun-melt-spun) can
also be
used as a nonwoven fabric; this has outer layers composed of a spun-bonded
nonwoven fabric (S) and a center nonwoven layer composed of melt-blown fibers
(M).
The combination of layers composed of a spun-bonded nonwoven fabric and a melt-
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blown nonwoven imparts greater strength in the machine direction (MD
direction) to the
nonwoven fabric. When the pre-finished laminate is torn open, separation of
the
nonwoven fabric within the core layer, which consists of a melt-blown
nonwoven, takes
place. It was found that the material thickness and the weight per surface
area unit of
the strips separated by tearing open the laminate remains constant, within
close
tolerances, if the parting plane runs through a core layer composed of a melt-
blown
nonwoven. High-quality composite material strips are obtained, particularly
strips with a
very high-quality textile surface.
Other nonwoven fabrics can also be used for the method according to the
invention.
However, the quality of the textile surface is poorer, for example if a carded
nonwoven is
used as the core layer of the laminate.
A composite material produced according to the method according to the
invention is
suitable for hygiene articles, for example for sections or closure elements on
baby
diapers and incontinence articles. Furthermore, so-called soft-touch films for
applications outside of the hygiene sector can also be produced according to
the
method according to the invention.
In the following, the invention will be explained using a drawing that
represents an
embodiment merely as an example. The figures schematically show:
Fig. 1 a method for the production of an elastic composite material with a
textile
surface,
Fig. 2 a section through a laminate that is produced as a pre-product, in the
method
shown in Fig. 1,
Fig. 3 separation of the pre-product shown in Fig. 2, in a representation that
is
enlarged as compared with Fig. 1.
The method shown in Fig. 1 serves for the production of an elastic composite
material
with a textile surface, which can be used, for example, as a soft-touch film
or as an
elastic element on baby diapers, incontinence articles, and the like. In the
method, in a
first step, a laminate 1 is produced as a pre-product; this laminate has
elastic cover
layers 2, 2' and a core 3 composed of a nonwoven fabric. Fig. 2 shows the
layer
CA 02759345 2011-11-25
structure of the pre-product. Subsequently, the laminate 1 is separated into
two strips 4,
4' by tearing open the core 3; these strips each have a cover layer 2, 2' and
an adhering
layer composed of nonwoven fabric 5. The strips 4, 4' each form a method
product that
can be used as an elastic composite material, without any subsequent
mechanical
activation.
The core 3 consists of a melt-blown nonwoven or has a multi-layer structure
with outer
layers composed of a spun-bonded nonwoven fabric and a center nonwoven layer
composed of melt-blown fibers. A nonwoven fabric web 6 that forms the core 3
is
laminated in between two elastic film webs 7, and glued to the film webs 7.
The
adhesive 8 is preferably applied, over the full area, to the surface of the
film web 7 that
lies adjacent to the nonwoven fabric. Polyurethane adhesives or hot-melt
adhesives can
be used as the adhesive 8.
The laminate 1 is separated by tearing open the core 3 to form two strips 4,
4'. The
strips 4, 4' are grasped separately and pulled apart by applying tensile
forces. According
to the representation in Fig. 1, the strips 4, 4' are passed over driven
rollers of a take-off
device 9 and wound up separately. Optionally, the take-off device 9 can be
combined
with a stretching device in which the strips 4, 4' are stretched in the
transverse direction
and thereby mechanically activated.
Tearing open the core 3 can be supported by means of a blade 10 disposed in
the
parting plane.
When comparing Fig. 2 and 3, it can be seen that elastic composite materials,
namely
the strips 4, 4', are produced according to the method according to the
invention; these
strips have an elastic carrier as well as a textile surface. The elastic
carrier is formed by
a cover layer 2, 2' of the laminate 1, and gives the composite material its
mechanical
properties. The textile structure is dependent on the nonwoven fabric used in
the core 3
of the laminate 1. Preferably, separation takes place through a nonwoven layer
composed of a melt-blown nonwoven, the fibers of which are thin and form a
high-
quality textile surface during separation. A slightly consolidated nonwoven is
processed
for the production of the laminate 1 that forms the pre-product. No free
fibers that can
come loose when the composite material is used are formed as the result of the
separation of the nonwoven layer in the subsequent step. When the nonwoven
fabric
core 3 is separated, strips 4, 4' are formed, which have constant values with
regard to
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the material thickness and their weight per surface area unit, within close
tolerance
limits.
