U.S. patent application number 10/116877 was filed with the patent office on 2002-10-31 for method for the production of nonwoven webs, the cohesion of which is obtained by means of fluid jets.
This patent application is currently assigned to RIETER PERFOJET. Invention is credited to Noelle, Frederic.
Application Number | 20020160681 10/116877 |
Document ID | / |
Family ID | 9550742 |
Filed Date | 2002-10-31 |
United States Patent
Application |
20020160681 |
Kind Code |
A1 |
Noelle, Frederic |
October 31, 2002 |
Method for the production of nonwoven webs, the cohesion of which
is obtained by means of fluid jets
Abstract
The invention concerns a method for producing a nonwoven web
formed at least partly with hydrophilic elementary fibers which
consist in: producing by carding a textile layer (10) which is then
compressed and moistened; subjecting it to a bonding treatment
using water jets acting at least against one of its surfaces; and
transferring said bonded layer to a unit (32, 33) to be dewatered
and dried. Said method is characterised in that, after the bonding
treatment (20) with water jets and before drying and delivery, the
pre-bonded and moistened layer is transferred to a supplementary
unit (28) to be treated by the action of one or several series of
water jets, said unit comprising a mobile suction surface in the
form of a drum covered with an open-work structure (30) consisting
of a wire-mesh fabric, comprising successive raised and recessed
zones.
Inventors: |
Noelle, Frederic; (Saint
Nazaire Les Eymes, FR) |
Correspondence
Address: |
HESLIN ROTHENBERG FARLEY & MESITI PC
5 COLUMBIA CIRCLE
ALBANY
NY
12203
US
|
Assignee: |
RIETER PERFOJET
Montbonnot
FR
|
Family ID: |
9550742 |
Appl. No.: |
10/116877 |
Filed: |
April 5, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10116877 |
Apr 5, 2002 |
|
|
|
PCT/FR00/02633 |
Sep 22, 2000 |
|
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Current U.S.
Class: |
442/408 ;
442/361; 442/415; 442/416 |
Current CPC
Class: |
Y10T 442/637 20150401;
Y10T 442/698 20150401; Y10T 442/697 20150401; D04H 3/11 20130101;
D04H 5/02 20130101; D04H 1/4258 20130101; D04H 18/04 20130101; Y10T
442/689 20150401; D04H 1/495 20130101; D04H 1/492 20130101 |
Class at
Publication: |
442/408 ;
442/415; 442/361; 442/416 |
International
Class: |
D04H 001/46; D04H
003/10; D04H 005/02; D04H 001/00; D04H 003/00; D04H 005/00; D04H
013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 5, 1999 |
FR |
FR-99.12601 |
Claims
1. A method for producing a nonwoven consisting at least partially
of hydrophilic elementary fibers, which involves continuously:
producing a fibrous web (10) by carding or another conventional
technique; compressing and moistening said web; subjecting the
moistened and compressed web to a bonding treatment by means of
water jets acting at least against one of its faces, the web being
supported by a rotary drum comprising randomly distributed
microperforations, a partial vacuum being applied to the interior
of said drum; transferring said bonded web to an assembly (32, 33)
making it possible to drain and dry it before it is received, in
particular in the form of a wound package, characterized in that,
after bonding treatment (20) by means of water jets and before
drying and reception, the prebonded and moistened web is
transferred to an additional assembly (28) for treatment by the
action of one or more series of water jets, said assembly
comprising a movable suction surface taking the form of a drum
covered with a removable sleeve defining an open-work structure
(30) consisting of a woven bronze-wire cloth and shaped to have a
succession of raised and recessed zones, the raised zones being
obtained by embossing, the ratio of emptiness in relation to the
surface being between 10 and 50%, and the overall height between
the bottom of the recessed parts and the upper part of the raised
zones being between 0.5 and 2 mm.
2. A nonwoven web obtained by bonding by means of jets of water
under pressure from elementary viscose fibers having a succession
of raised and recessed designs.
3. A nonwoven web obtained by bonding by means of jets of water
under pressure from elementary fibers comprising a mixture of
absorbent artificial fibers and of synthetic fibers having a
succession of raised and recessed designs.
4. A nonwoven web obtained by bonding by means of jets of water
under pressure from elementary chemical, artificial and/or
synthetic fibers taken alone or in a mixture and associated with
natural fibers such as wood fibers, having a succession of raised
and recessed designs.
5. The use of nonwoven webs as claimed in one of claims 2 to 4, as
wiping material or support for wet wipes.
Description
TECHNICAL FIELD
[0001] For decades, it has been proposed to replace traditional
webs (woven fabrics, knitted fabrics) by what are known as
"nonwoven" structures which, in general terms, may be classified in
three large categories by virtue of the actual process for
manufacturing them, to be precise nonwovens known as "by the dry
way" and "by the melted way" and nonwovens known as "by the wet
way".
[0002] In the rest of the description, the present invention will
be described as applied to obtaining nonwovens by the technique
known as "by the dry way", but it is clear that it is not limiting
and that, if appropriate, it could be applied to the other two
categories of nonwovens.
[0003] One of the main problems which arises during the production
of nonwovens is that of achieving the cohesion of the structure in
order to give the products mechanical characteristics according to
the application in question, while maintaining or imparting
particular physical characteristics, such as bulk, handle,
appearance, etc.
[0004] Among the techniques proposed hitherto, such cohesion is
obtained by the intermingling of the fibers in the thickness of the
web by means of the action of fluid jets and, more particularly, of
jets of water under pressure.
[0005] Such a technique of treatment by means of water jets has
been proposed for decades, as may be gathered from the patents U.S.
Pat. Nos. 3,214,819, 3,508,308 and 3,485,706.
[0006] In general terms, this technique involves carrying out the
interlacing of the elementary fibers with one another by means of
the action of jets of water under pressure which act on the fibrous
structure in the manner of needles and make it possible to reorient
part of the fibers forming the web in the direction of
thickness.
[0007] Such a technology has been widely developed at the present
time and is used not only for producing what are known as
"spunlace" structures for textile use, such as, in particular for
applications in the medical and hospital fields, for wiping,
filtration and wrappings for teabags, but also for making tiny
perforations in continuous supports such as paper, cardboard,
films, even sheets of plastic or the like and the articles obtained
may be regular and homogeneous and take the form of a plane sheet
which, if appropriate, may have perforations, as may be gathered
from the patent U.S. Pat No. 3,508,308, and even, if appropriate,
comprise designs resulting from the reorientation of the fibers,
this being essentially for an esthetic purpose, as may be gathered
from U.S. Pat. No. 3,485,706.
[0008] As regards the applications of such products of the
"spunlace" type, it has been known for a very long time that the
final properties of the product obtained can be adapted by
producing mixtures of material, for example by combining with one
another a plurality of webs consisting of fibers of different
types, for example of natural, artificial or synthetic fibers, even
from webs in which the fibers are previously mixed, reinforcements
(woven or nonwoven nettings, webs of the "spunbond" type, etc.)
being capable, if appropriate, of being incorporated into the
nonwoven structure.
[0009] Of the numerous applications of nonwovens, mention may be
made of wiping products known as "wet wipes", and of products in
the hygiene field.
[0010] In addition to good mechanical characteristics both in
length and in width, also both in the dry state and in the wet
state, such products must also have the essential characteristic of
having a good capacity for the absorption and retention of the
liquid or treatment product which they support or which they must
absorb. Moreover, they must have good dimensional stability and be
flexible, soft, bulky and pleasant to handle.
[0011] The invention is particularly suitable for producing such
articles, and, in the rest of the description, it will be described
more particularly for obtaining such products.
[0012] Prior Art
[0013] Hitherto, to produce wiping cloths or wet wipes, it has been
conceivable to use nonwoven webs consisting entirely of absorbent
fibers, such as cellulose fibers, particularly viscose fibers. In
order to give the product good mechanical characteristics, a
mixture of synthetic fibers (polyester, polypropylene) and of
artificial fibers (viscose) is preferably used.
[0014] To produce such articles consisting of a mixture of fibers,
either an intimate mixture of said fibers can be produced, which is
converted into a homogeneous unitary web, or the combination of two
webs previously produced is carried out, to be precise, one web
based on discontinuous fibers or on continuous synthetic filaments
(polyester, polypropylene) and the second based on artificial
fibers (viscose), and said webs are combined by hydraulic
entanglement.
[0015] It has also been proposed, in order to produce such
articles, to replace the artificial fibers which give the web the
capacity for the absorption and retention of the liquid with
natural cellulose fibers, such as wood fibers, incorporated in the
same proportions as the prior products based on artificial or
synthetic fibers, said natural cellulose fibers being entangled
with the chemical fibers likewise by treatment by means of water
jets.
[0016] Such a product has good mechanical resistance
characteristics, essentially afforded by the synthetic fibers, and
good liquid absorption and retention characteristics imparted by
the cellulose fibers.
[0017] French patents FR-A-2 730 246 and 2 734 285, these patents
corresponding respectively to the patents U.S. Pat. Nos. 5,718,022
and 5,768,756, describe solutions which make it possible to
successfully treat hydrophobic fibers or mixtures of these fibers
with other hydrophilic fibers or even webs consisting entirely of
natural fibers by means of water jets.
[0018] In general terms, according to the teachings of these
documents, the treatment involves treating a basic web composed of
elementary fibers of the same type or of different types,
compressing and moistening this basic web and then intermingling
the fibers by means of at least one rack of contiguous jets of
water under high pressure acting on the basic web.
[0019] For this purpose, the basic web is advanced positively on an
endless porous support in motion, and it is brought onto the
surface of a perforated rotary cylindrical drum, to the interior of
which a partial vacuum is applied.
[0020] The basic web is compressed mechanically between the porous
support and the rotary drum which both advance substantially at the
same speed.
[0021] Immediately downstream of the compression zone, a water
curtain is directed onto the web and passes successively through
the porous support, the compressed basic web and the supporting
perforated drum which sucks up the excess water.
[0022] The elementary fibers are intermingled continuously, still
on the rotary cylindrical drum, by the compressed and wetted web
being subjected to the action of at least one rack of jets of water
under high pressure. In general, bonding is carried out by means of
a plurality of successive racks of water jets which act either on
the same face or alternately against the two faces of the web, the
pressure within the racks and the velocity of the jets discharged
varying from one rack to the next and usually progressively.
[0023] Moreover, it is appropriate to note, as may be gathered from
FR 2 734 285, that the perforated roller preferably comprises
randomly distributed micro-perforations.
[0024] If appropriate, after this bonding treatment, the nonwoven
structure may be subjected to a second treatment applied to the
reverse face.
[0025] Presentation of the Invention
[0026] A method has been found, this being the subject of the
present invention, which not only makes it possible to produce
absorbent nonwovens having excellent physical properties (tensile
strength, tearing strength, abrasion resistance) and a good
capacity for the absorption and retention of liquid similar to
articles of the same composition obtained according to the
teachings of FR-2 734 285 but which, moreover, has, in relation to
such articles, a more pleasant handle and increased bulk.
[0027] In general terms, therefore, the invention relates to a
method making it possible to produce a novel type of nonwoven
consisting at least partially of hydrophilic elementary fibers,
which involves continuously:
[0028] producing a fibrous web by carding or another conventional
technique;
[0029] compressing and moistening said web;
[0030] subjecting the moistened and compressed web to a bonding
treatment by means of water jets acting at least against one of its
faces, the web being supported by a rotary drum comprising randomly
distributed micro-perforations, a partial vacuum being applied to
the interior of said drum;
[0031] transferring said bonded web to an assembly making it
possible to drain and dry it before it is received, in particular
in the form of a wound package.
[0032] The method according to the invention is characterized in
that, after bonding treatment by means of water jets and before
drying and reception, the prebonded and moistened web is
transferred to an additional assembly for treatment by the action
of one or more series of water jets, said assembly comprising a
movable suction surface taking the form of a drum covered with an
open-work structure consisting of a woven metal-wire cloth and
shaped to have a succession of raised and recessed zones.
[0033] For implementing the method according to the invention, the
first treatment by means of water jets is carried out according to
the teachings of FR-A-2 730 246 and FR-A-2 734 285, the content of
which is incorporated in the present description as required.
[0034] The additional treatment by means of jets which is carried
out before the drying of the web is obtained, as mentioned above,
by causing it to pass onto the surface of a perforated rotary
cylindrical suction drum. In a known way, such a drum consists of a
honeycomb structure which is covered with a perforated plate and
which rotates about a second hollow fixed coaxial cylindrical drum
connected to a partial vacuum source in order to form a suction box
below the zones where the water jets act. According to the
invention, said drum is covered with a likewise perforated or
intrinsically porous structure having raised and recessed zones,
this structure preferably consisting of a woven fabric taking the
form of a removable sleeve.
[0035] By virtue of such a design, it is therefore easy, simply by
changing this sleeve, to modify the appearance and characteristics
of the product obtained.
[0036] As covering structure, preferably used for the suction drum
will be a woven cloth which is produced, for example, from bronze
wires, and which has the characteristic of being capable of being
embossed.
[0037] In such a structure, the ratio of emptiness in relation to
the surface is between 10% and 50%, and the overall height between
the bottom of the recessed parts and the upper part of the raised
zones is generally between 0.5 mm and 2 mm.
[0038] The configuration of the raised and recessed portions which
such a cloth will have may be of any type, for example, may take
the form of herringbones, of designs with exact contours (circular,
square) or a crimped, crinkled, etc. appearance.
[0039] In a variant according to the invention, before treatment on
the embossed surface, the complex may, if appropriate, receive a
second bonding treatment by means of jets, which is carried out in
a similar way to the preceding treatment, but on the opposite
face.
[0040] After treatment, the nonwoven, still in the wet state, is
transferred to a squeezing-out zone, followed by a drying zone
consisting of a through-air drum. Finally, it is received in the
form of a wound package.
[0041] Such a method can be implemented for fibrous webs of any
composition produced from natural, artificial and/or synthetic
fibers taken alone or in a mixture. For the production of absorbent
nonwovens, it is conceivable to produce a web consisting entirely
of viscose fibers.
[0042] Preferably, however, a mixture of absorbent artificial
fibers (viscose) and of synthetic fibers, such as polyester or
polypropylene, will be used.
[0043] In such mixtures, the linear density of the elementary
fibers and their length are preferably similar and, for example,
are between 1 dtex and 3.3 dtex, the length being between 20 mm and
60 mm.
[0044] It is also conceivable to adapt the method so as to
incorporate natural fibers, such as wood fibers, into the web, for
example by pneumatic lapping followed by hydraulic bonding by means
of racks of jets acting against the face on which the wood fibers
were distributed.
[0045] This operation of pneumatic lapping and bonding is carried
out before shaping treatment on the embossed assembly, the jets of
this assembly preferably acting against the surface covered with
wood fibers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] The invention and the advantages which arise from it will be
understood more clearly, however, from the following exemplary
embodiments given as a nonlimiting indication and illustrated by
the accompanying diagrams in which:
[0047] FIG. 1 is a diagrammatic view of the whole of a production
line for a nonwoven web according to the invention, the cohesion of
which is imparted by the action of jets of water under pressure,
FIGS. 1a and 1b being enlarged views of the zones circled in this
FIG. 1, and FIG. 1c illustrating the structure of a conventional
bonding zone used within the framework of the comparative examples
which will be given later;
[0048] FIG. 2 is a diagrammatic view of a production line for a
nonwoven web produced according to the invention, making it
possible to produce mixed webs, synthetic fibers/wood fibers, FIGS.
2a, 2b, 2c and 2d being enlarged views of the zones circled in FIG.
2;
[0049] FIG. 3 is a reproduction of an embossed structure used
within the scope of the invention, and
[0050] FIG. 4 is a reproduction of the effect obtained on the final
product;
[0051] FIG. 5 is another embodiment in which the embossed surface
makes it possible to obtain a recessed and raised effect of the
"crinkled" type.
IMPLEMENTATION OF THE INVENTION
[0052] Referring to the accompanying figures, and more particularly
to FIGS. 1, 1a and 1b, a production line making it possible to
produce a nonwoven in accordance with the method according to the
invention is composed essentially of an assembly, designated by the
general reference (1), making it possible to produce, by carding or
another similar technique, a web which may consist either entirely
of artificial fibers, particularly viscose, or of a mixture of
artificial fibers and of synthetic fibers, such as polyester or
polypropylene.
[0053] At the exit of the zone for shaping the web (10), the latter
is transferred onto a porous conveyer belt (11) consisting, for
example, of an endless cloth which is produced from synthetic
monofilament, in particular from polyester, and which has a
porosity of between 30 and 60%, that is to say a ratio between the
solid areas and the empty areas of between 30 and 60%, preferably
around 50%.
[0054] This porous support (11) is associated, in a way similar to
the teachings of FR-A-2 730 246, with an assembly for treatment by
water jets, making it possible, on the one hand, to ensure the
compression and wetting of the web (10) formed and, on the other
hand, to subject this web to the action of racks of water jets.
Such an assembly comprises essentially a rotary cylindrical drum
designated by the general reference (20), in bearing contact
against the surface of the conveyer belt (11).
[0055] A first rack of water jets (21) is arranged below the
support (11) and makes it possible to carry out the prewetting of
the web (10). This rack is arranged at a distance of between 70 and
100 mm from the porous support (11) and forms a water curtain
making it possible to wet the compressed web and bringing about a
first slight intermingling of the web.
[0056] The drum (20) is composed of a conventional rotary cylinder
with a honeycomb structure (not illustrated in the accompanying
figures), which is covered with a metal film (22) comprising
microperforations distributed randomly on its surface or with a
woven structure. This rotary cylinder surrounds a second hollow
fixed coaxial cylindrical drum (23) connected to a partial-vacuum
source so as to form a suction box, suction being applied through
slits (26) located opposite the active zone of the water jets.
[0057] After prewetting by means of the rack (21), and as may be
gathered from FIGS. 1 and 1a, the web (10) is subjected to the
action of jets of water under pressure (27) coming from two
conventional racks (24, 25).
[0058] If appropriate, it would be conceivable to have only a
single rack (24) or more than two successive racks associated with
the drum (20).
[0059] These racks (21, 24, 25) are formed from contiguous
injectors arranged at predetermined distances from one another.
[0060] Opposite each rack (21, 24, 25) the drum comprises a slit
(26) which extends over the entire length of a generatrix, the
width of which is generally between 5 mm and 30 mm and through
which the water of the jets (27) is recovered.
[0061] After bonding on the assembly (20), the web is subject to
the action of a second assembly (28) which is produced according to
the invention, and the general structure of which may be gathered
from FIG. 1b. This assembly (28) consists of a rotary suction drum
(29), which likewise consists of a honeycomb cylindrical structure,
not illustrated in FIG. 1b, and which does not support a
microperforated band, as in the case of the treatment assembly
(20), but, instead, a covering consisting of an open-work plate
(29). As an indication, the perforations of this plate (29) may
have a diameter of 3 mm, the center distance between two
consecutive orifices being 4 mm, and the orifices being offset from
one row to the next.
[0062] According to the invention, the perforated surface (29) is
covered with a sleeve-shaped open-work structure (30) having a
succession of raised and recessed zones.
[0063] This open-work structure (30) consists of an open-work cloth
made from metal wires, more particular from bronze wires, having an
aperture ratio of between 10% and 50%, said cloth having been
embossed, as may be gathered from FIGS. 3 and 5, in order to
comprise a succession of raised and recessed zones. These raised
and recessed zones may have a regular structure, for example a
herringbone shape, as illustrated in FIG. 3, or a configuration
forming irregular designs, giving, for example, a crinkled
appearance, as illustrated in FIG. 5.
[0064] As may be gathered from FIG. 1b, during its passage through
this additional treatment zone (28), the prebonded web is
restructured by the action of one or more series of jets coming
from conventional hydraulic injectors, of which there are two in
the present instance. Under the action of these jets, the web
matches the configuration of the raised and recessed zones of the
open-work structure (30). After treatment, the treated web (31) is
delivered onto a conveyer (32), where the water is eliminated, for
example with the aid of a suction box arranged below the conveyer
(32), the treated web then being dried by passage over a
through-air cylinder (33) having a temperature of the order of
150.degree. C., before being received in the form of a wound
package (34).
[0065] FIG. 2 illustrates a second embodiment of a production line
for a nonwoven, making it possible to produce mixed webs, synthetic
fibers--cellulose fibers, for example wood fibers, which is
designed for implementing the method according to the
invention.
[0066] FIGS. 2a, 2b, 2c and 2d are enlarged views of the treatment
zones circled in FIG. 2.
[0067] In general terms, such a production line is produced
according to the teachings of the document FR-A-2 781 818, which
makes it possible to produce nonwovens consisting of a mixture of
elementary fibers of different types and, more particularly, of a
mixture of synthetic fibers which is associated with cellulose
fibers, in particular wood fibers.
[0068] In general terms, in such an installation, a mixed non-woven
is produced in the following way. First of all, a first web (10) is
produced, by carding (1) or another conventional technique, from
chemical fibers. The fibrous web (10) produced is then subjected to
a bonding treatment by means of water jets on a first treatment
assembly designated by the reference (40).
[0069] In this treatment phase, the two faces of the fibrous web
(10) are subjected to the action of water jets by passage around
two suction cylinders, the first comprising microperforations on
the surface and the second being covered with a coarse cloth, as
may be gathered from FIG. 2a.
[0070] After the web has been treated, it is transferred onto a
conveyer (50), and natural fibers (52), such as wood fibers (cf.
FIG. 2), are deposited on the surface of said web (10).
[0071] The complex structure, web of synthetic fibers (10) which is
covered with natural fibers (52), is then subjected to the action
of a new series of water jets by means of an assembly, designated
by the general reference (53), positioned above a second conveyer.
This treatment ensures not only the bonding, but also the
prewetting of the web, necessary for implementing the method
according to the invention.
[0072] The complex structure thus produced is subsequently treated,
according to the invention, on an assembly, designated by the
general reference (28), illustrated in FIG. 2d, this assembly being
similar to that illustrated in FIG. 1b and described above. After
treatment, a mixed nonwoven (31) is obtained, comprising raised and
recessed designs, which is received on a belt (32) in order
subsequently to be dried at (33) and received at (34).
EXAMPLE 1
[0073] The method according to the invention is implemented on an
installation, as illustrated by FIGS. 1, 1a and 1b, for the purpose
of producing a product according to the invention consisting of a
single type of hydrophilic fibers, to be precise viscose
fibers.
[0074] To this effect, a web (10) is produced, weighing
approximately 65 gm.sup.2 and composed of 100% viscose fibers of
1.7 dtex and with a length of 38 mm, this web being produced at a
speed of 50 m/min by a card for nonwovens (1).
[0075] This web (10) is transported by a conveyer belt (11) to a
hydraulic bonding unit of the type sold under the designation
"Jetlace 2000", designed for implementing the method according to
the invention.
[0076] The web (10) is compacted between the transport conveyer
(11) and a first bonding cylinder (20), covered with a
microperforated casing, the holes being arranged randomly, as
described in French patent 2 734 285. During compaction, the web is
wetted by means of the rack (21) located behind the transport
conveyer, just after the compacting point, said rack being arranged
perpendicularly to the generatrix of the cylinder.
[0077] The web thus compacted and wetted is then subjected to the
action of two successive hydraulic injectors (24, 25) projecting
water jets (27) with a diameter of 120 microns at increasing
velocities of 100 and 125 m/second, the water jets being spaced 1.2
mm from one another.
[0078] After bonding treatment, the bonded web undergoes additional
treatment according to the invention (FIG. 1b) by being passed over
a cylinder, likewise covered with a perforated casing (29) on which
is arranged a sleeve consisting of a bronze fabric (30) comprising
15 wires/cm and 15 wefts/cm, having a diameter of 0.24 mm and
possessing an emptiness ratio of 40.8%.
[0079] This bronze sleeve (30) is embossed so as to have a
herringbone design (as illustrated in FIG. 5), the depth of which
is of the order of one and a half millimeters (1.5 mm).
[0080] The fibrous web is subjected to the action of two successive
hydraulic injectors delivering jets with a diameter of 120 microns
at a velocity of 200 m/second, the jets being spaced 0.6 mm from
one another.
[0081] The web is subsequently transferred onto a suction belt (32)
connected to a vacuum generator, then dried at a temperature of
145.degree. C. in a through-air oven (33), in order finally to be
received, for example, in the form of a wound package (34).
[0082] A nonwoven is obtained, which weighs approximately 60
g/m.sup.2 and has a herringbone design (35), as illustrated in FIG.
4, this design having excellent definition. It is permanent and
friction-resistant.
EXAMPLE 2
[0083] The treatment conditions are the same as those given in
example 1.
[0084] A product consisting of a 70/30 mixture of viscose and
polyester fibers is produced.
[0085] The fibers have a linear density of 1.7 dtex and a length of
38 mm.
[0086] The web formed weighs approximately 65 g/m.sup.2 at the exit
of the card and 60 g/m.sup.2 after treatment.
EXAMPLE 3
[0087] This example illustrates an actual embodiment of a nonwoven
according to the invention, consisting of a mixture of synthetic
fibers and of natural fibers, and, more particularly, of cellulose
fibers, especially wood fibers.
[0088] According to this exemplary embodiment, a production line,
as illustrated in FIG. 2, is used, which, in general terms, is
produced according to the teachings of the document FR-A-2 781 818,
except that it comprises, before drying at (33), and after bonding
and prewetting treatment carried out by means of the jets (53), an
additional assembly (28) for treatment by the action of water jets,
said assembly comprising a movable suction surface taking the form
of a drum covered with an open-work structure (30) and consisting
of a woven metal-wire cloth shaped so as to have a succession of
raised and recessed zones.
[0089] In this exemplary embodiment, a first web (10) is produced
at 60 m/min, weighing 30 g/m.sup.2 and consisting of polyester
fibers of 38 mm and of 1.7 dtex, said web being introduced to a
hydraulic bonding unit of the type sold by the applicant under the
designation "Jetlace 2000", by means of a transport conveyer
(11).
[0090] The web is compacted between this conveyer and a first
assembly, designated with the general reference (40), which
comprises a bonding cylinder covered with a microperforated casing,
the holes of which are arranged randomly. After compaction, the web
is prewetted by means of a rack located behind the transport
conveyer (11), just after the compacting point, and arranged
perpendicularly to the generatrix of the cylinder.
[0091] The web thus compacted and wetted is subjected to the action
of two hydraulic injectors projecting water jets with a diameter of
120 microns at increasing velocities of 78 and 94 m/s, the water
jets being spaced 1.2 mm from one another.
[0092] The web is then introduced to the assembly designated by the
general reference (48), which comprises a second cylinder covered
with a coarse cloth consisting of 9 wires per centimeter, made of
bronze, with a rectangular cross section with sides of 0.3 mm by
6.64 mm in the warp direction and of 9 wires per centimeter,
likewise made of bronze, with a diameter of 0.46 mm in the weft
direction.
[0093] Two hydraulic injectors are arranged above this cylinder.
They project onto the web water jets with a diameter of 120 microns
at velocities of 100 m/s, the jets being spaced 0.5 mm from one
another.
[0094] The web is then squeezed out with the aid of a suction box
connected to a vacuum generator.
[0095] The product at the exit of this conveyer has a crimped
appearance of the pyramidal type, with different fiber density
zones.
[0096] The web is then introduced to a pneumatic lapping machine
(51) which deposits 35 g/m.sup.2 of cellulose fibers.
[0097] After these fibers have been deposited, the web is
introduced onto another conveyer (54), above which are arranged
four hydraulic injectors (53) projecting water jets with a diameter
of 120 microns, spaced 0.6 mm from one another, at velocities of
150 m/s.
[0098] The product thus obtained therefore takes the form of a
prebonded and moistened web which is subsequently transferred to an
additional treatment assembly, designated by the general reference
(28). Such an assembly comprises a cylinder covered with a bronze
sleeve which is identical to that used in example (1) and which is
embossed so as to have a herringbone design.
[0099] The fibrous web is subjected to the action of two successive
hydraulic injectors delivering jets with a diameter of 120 microns
at a velocity of 60 m/s, the jets being spaced 0.6 mm from one
another.
[0100] The product thus obtained by the method according to the
invention is subsequently transferred onto a suction belt (32)
connected to a vacuum generator and is then dried at a temperature
of 160.degree. C. in a through-air oven, in order, finally to be
received in the form of a wound package (34).
[0101] After drying, a complex having raised and recessed designs,
which is illustrated in FIG. 4 is obtained.
COMPARATIVE EXAMPLES
[0102] The same examples as above are produced, with the exception
of the following differences.
[0103] As regards examples 1 and 2, these are produced on an
installation in which the treatment assembly (28), as illustrated
in FIG. 1b, is produced by means of a second series of jet
treatments, as illustrated in FIG. 1c, that is to say on a
conventional suction drum, the surface covering of which consists
of a microperforated film (22) similar to that used for the
prebonding treatment.
[0104] Where example 3 is concerned, this is produced on a
production line, as illustrated in FIG. 2, but not comprising a
treatment assembly (28).
[0105] Proceeding in the same way, nonwovens are obtained which
have the same composition and virtually the same weight as those
produced according to the invention, but do not comprise any
designs.
[0106] The products obtained according to the invention and those
of the comparative examples are tested in order to determine the
thickness, the density, resistance in the longitudinal direction
(SL) and in the transverse direction (ST), elongation in the
longitudinal direction and in the transverse direction and the
water absorption rate.
[0107] The results are collated in the following table.
1 TABLE Example 1 Example 2 Example 3 Characteristics Comparative
Comparative Comparative Weight g/m.sup.2 60 60 60 60 55 55
Thickness in mm 0.71 0.50 0.82 0.58 0.61 0.44 Density in g/cm.sup.3
0.085 0.12 0.073 0.103 0.090 0.125 Resistance dry 115 120 112 114
108 110 in the longitudinal wet 58 59 98 92 99 101 direction (SL)
N/50 mm Resistance dry 21 20 18 22 21 19 in the transverse wet 15
14 17 20 18 17 direction (ST) N/50 mm Elongation dry 25 29 30 27 31
30 in the longitudinal wet 26 28 35 33 30 29 direction (SL) in %
Elongation dry 123 134 129 133 185 189 in the transverse wet 99 100
124 126 184 185 direction (ST) in % Absorption rate g/g 928 906 850
826 833 824
[0108] As compared with products produced conventionally, and as
may be gathered from the above table, the materials produced
according to the invention, have the advantage of being much
thicker for an equal weight.
[0109] Moreover, their resistance both in the longitudinal
direction and in the transverse direction are comparable to those
of products produced conventionally, thus ensuring that they have
stability and resistance during use.
[0110] In addition to their increased thickness, the novel products
have an agreeable and favorable textile appearance which increases
their commercial value.
[0111] Of course, the invention is not limited to the actual
exemplary embodiments given above, but embraces all their variants
produced in the same spirit.
[0112] Moreover, although, in the examples given, an embossed
bronze fabric comprising 15 wires in warp and in weft, of which the
diameter is 0.24 mm and the aperture ratio 40.8%, is used, it will
be conceivable to use other types of embossed structures.
[0113] As an example, when products similar to those given in the
quoted examples are produced, which do not have a "herringbone"
appearance as illustrated in FIGS. 3 and 4, but, instead, a
"crinkled" appearance, as illustrated in FIG. 5, it was found that
higher definition and an increase in the relief of the designs were
obtained, using an embossed fabric produced from bronze wires with
a smaller diameter and having a greater wire density.
[0114] As an indication, in order to produce such fabrics, the
embossed bronze cloth has 23.5 wires/cm both in warp and in weft,
said wires having a diameter of 0.19 mm and the aperture ratio
being 30.5%.
[0115] Furthermore, as indicated above in the description and as
illustrated in FIG. 2, the method according to the invention may
also be implemented in order to obtain mixed nonwovens consisting
of a mixture of fibers of different types.
* * * * *