DE60003086T2 - METHOD FOR PRODUCING A COMPOSITE FLEECE MATERIAL AND PRODUCED MATERIAL - Google Patents

Abstract

The invention concerns a method for producing a complex nonwoven fabric which consists in continuously producing a complex wherein a first web of a cellulosic fibres (4) is continuously sandwiched between two webs of spunbonded filaments (2, 7), and which consists in: producing a first web of spunbonded filaments (2), the bundle of extruded and drawn filaments being received on a mobile conveyor belt (3) in the form of a non-bonded lap; depositing on said web 92) by airlaid process a second web of cellulosic fibres (4); depositing on the textile web (4) a second web (7) of non-bonded continuous filaments; transferring the resulting complex onto an installation (9) for water-jet bonding and hydro-entanglement consolidation; and in drying the nonwoven mixed product and then recuperating it, for example in the form of a cloth wind-up (18).

Description

For decades, it has been proposed to replace conventional textile webs (woven fabrics, knitted fabrics) with so-called "non-woven" structures (nonwoven structures).

In general, such nonwoven structures can be divided into three broad categories, which result from their manufacturing process itself, namely the so-called "dry" nonwoven structures, which are formed by carding and/or by air, the latter technique being usually referred to as "airlaid technique", the nonwoven structures which are produced "fused", a technique usually referred to as "spunbond", and the so-called "wet" technique, which is derived from the techniques of the paper industry.

Moreover, it has long been known that it is possible to adapt the final properties of the product obtained by producing mixtures of materials, for example by bonding together several nonwovens made up of fibres of different types, such as natural, artificial or synthetic fibres.

The invention relates to a new process which makes it possible to produce such a nonwoven product type which is made from a mixture of fibres of different types and which is referred to in the following description as "mixed fibre nonwoven" or "composite fibre nonwoven".

PRE-PUBLISHED TECHNIQUES

Numerous proposals have already been made for producing mixed or composite fibre webs by bonding together webs of artificial or synthetic fibres and a web of cellulose fibres. The bonding of the various components to one another can be carried out in various ways, for example by means of binding agents, by mechanical needling or by hydraulic entangling, the latter technique being known for a long time and being described in particular in patent US 3 508 308. This document describes in particular the manufacture of mixed webs made by the "airlaid" technique by intimately mixing fibres, for example a mixture of synthetic fibres (polyester or acrylic) and rayon fibres (see Examples 10 and 11). It also describes (see Examples 12 and 13) the manufacture of complexes comprising a central layer formed by continuous filaments and two outer layers based on fibres, in particular polyester, distributed by air, the various layers being bonded together by the action of jets of a fluid.

It has also been proposed, as is clear from EP 423 619, to produce absorbent fabrics by bonding a web formed by continuous filaments and a web formed by a mixture of cellulose fibres, in particular wood fibres, also by means of water jets.

Finally, it is known to produce nonwoven fabrics by sandwiching a fibrous web between two nonwovens of continuous filaments already consolidated by heat calendering, the final bonding of the various layers also being ensured by the action of water jets.

This latter relatively simple deployment technique has numerous significant disadvantages, namely:

- the fact that the nonwovens made of continuous filaments (spunbond) are already consolidated by a heat calendering treatment prevents a close mixing of these filaments with the wood fibres of the nonwoven, which is applied by air, thus reducing the absorption capacities of the complex and creating a rough product with a lack of softness;

- moreover, in order to ensure satisfactory cohesion between the layers and to avoid delamination of the complex, it is necessary to use very high fluid velocities during the solidification phase by water jets, since the calendering points of the spunbond nonwovens prevent any mobility of the synthetic filaments; these high speeds of the water jets generate additional costs in terms of energy consumption as well as an increased loss of cellulose fibres;

- the connection points between the filaments obtained by calendering can represent up to 20 to 25% of the surface of the nonwovens based on continuous filaments and thus represent just as many obstacles to the passage of the water jets;

- finally, the fact that the continuous filaments are not mobile gives the material great rigidity, which loses its textile properties and resembles paper rather than a real textile.

DESCRIPTION OF THE INVENTION

An improved process has now been discovered, which is also the object of the present invention, and which makes it possible to continuously produce perfectly bonded mixed fiber nonwovens that have high mechanical properties while retaining the appearance, feel and softness of a conventional textile, such as a fabric.

The solution to such a problem is achieved by combining previously published techniques in a very precise way, which are used continuously and under very precise conditions, namely:

- Techniques for the production of nonwoven webs made from short fibres, the distribution of which is achieved by means of air technology (airlaid technology);

- Techniques for producing webs obtained by direct spinning (spunbond) and

- Solidification of the formed complex by the action of water jets.

In general terms, the process according to the invention consists in continuously producing a complex in which a nonwoven fabric based on cellulose fibres is sandwiched between two nonwoven fabrics of continuous filaments, the process consisting in:

- producing a first nonwoven fabric of continuous filaments, whereby the bundle of extruded and stretched continuous filaments is taken up on a mobile conveyor belt in the form of a non-bonded web;

- to lay a second fleece made of cellulose fibres on this fleece by means of air technology;

- placing a second non-woven web of unbonded continuous filaments on top of the non-woven web;

- to forward the complex formed to a facility for connection by water jets and to consolidate the unit by hydraulic confusing; and

- to dry the mixed fibre fleece produced and then remove it, for example in the form of a winding.

According to a preferred embodiment of the process according to the invention, the cellulose fibers used to produce the complex are wood fibers and their application is carried out by compressed air diffusion.

Moreover, even if it is possible to carry out only one joining treatment by water jet, the complex is preferably subjected to two successive treatments acting on the two opposite faces of the complex.

The invention also relates to a type of nonwoven product obtained by using this process.

Such a mixed fibre nonwoven fabric, which is thus formed from a mixture of fibres of different types, is characterized in that it is composed of a layer of natural fibres, in particular wood, which is inserted between two nonwoven webs formed from extruded and stretched filaments based on synthetic material, the Cohesion of the different layers is achieved by confusing them thanks to the action of water jets.

SUMMARY DESCRIPTION OF THE DRAWINGS

The invention and the advantages arising from it will be better understood with the help of the following examples of embodiments, which are indicative and non-limiting in nature and are illustrated by the accompanying drawings, in which:

- Fig. 1 is a schematic view of a plant for producing a complex material according to the process of the invention;

- Figures 1a, 1b, 1c and 1d are enlarged views of the encircled zones of this Figure 1.

REALIZATION OF THE INVENTION

A composite fiber fleece is continuously produced on a production line as shown in Fig. 1.

For this purpose, a first nonwoven fabric (2) is produced from continuous filaments by melting, spinning and stretching using a production unit designated by the general reference symbol (1), the filaments being arranged and distributed on a mobile conveyor belt (3).

If necessary, this first fleece (2) can be subjected to compaction immediately after formation by means of a pressure roller or by the action of jets coming from a ramp of hydraulic spray nozzles.

The continuous filaments of this first nonwoven fabric (2) can be based on a polymer formed from polypropylene, polyester or other synthetic materials such as polyethylene, polyamide, this list being non-limiting. The continuous filaments can possibly be formed from so-called "bicomponent"filaments. such as those produced by co-extrusion of polypropylene and polyethylene.

The web (2) of unconnected continuous filaments is then passed under a unit designated by the general reference (4) which enables, by air, to apply to the surface of the first web (2) discontinuous fibres (4) of a different type, and in particular cellulose fibres, in particular wood.

The cellulose fibers are applied to the surface of the first nonwoven fabric (2) by means of an air stream. Preferably, the nonwoven fabric of filaments (2) is held on the conveyor belt (3) by means of suction (5). Subsequently, the fibers (4) are preferably arranged between the unconnected filaments of the nonwoven fabric (2) under the effect of suction, resulting in excellent integration of the two components.

The complex (2,4), still held by the conveyor belt (3), is then passed under a second zone (6) for the formation of a second web (7) of continuous filaments, also of synthetic type, of the same type or of a different type to that of the first web (2).

A pressure roller (8) is preferably provided after this zone for arranging the fleece (7) and makes it possible to ensure compaction of the whole for the purpose of transporting it to the hydraulic connection plant, designated by the general reference (9) and following the production plant.

Possibly this compaction process could be carried out with the help of a ramp of hydraulic spray nozzles.

The complex is then introduced into the hydraulic connection zone (9) on a conveyor (10) on which the processes of compaction and pre-moistening of the unit are carried out successively by means of an upper conveyor (11) tangential to the lower conveyor (10) and inside which a hydraulic spray nozzle (12) is arranged.

After compaction and pre-wetting, the complex is subjected to the action of a succession of water jets (13) supplied by several hydraulic spray nozzles arranged in series.

These water jets (13) consolidate the whole formed by the various layers of the complex and give the upper layer good abrasion resistance.

The structure thus treated is then transferred, inverted, to a roller (14) or other conveyor connected to several spray nozzles (15) which also deliver jets of water to the other side of the complex, thus reinforcing the consolidation of the entirety of the layers, while giving the layer opposite the jets good resistance to abrasion.

The complex obtained in this way is then passed on to a squeezing conveyor (16) on which it is squeezed by means of a suction box connected to a vacuum generator.

It is then dried using an air-passing roller (17) and then removed in a conventional manner, for example in the form of a coil (18).

Example

A product according to the invention is manufactured as follows.

A nonwoven fabric of continuous filaments (2) weighing 15 g/m² is produced on a device sold by the patent applicant under the name "Spunjet" which enables a nonwoven web to be produced by extruding, stretching and distributing continuous filaments.

In this embodiment, the polymer extruded is polypropylene, such as that sold by AMOCO under the name 100 ZA 35.

The resulting fleece is made up of 7000 filaments per meter of width and is manufactured at a speed of 250 meters per minute. The diameter of the filaments after stretching is approximately 15 micrometers.

A suction device arranged opposite the stretching gap (20) makes it possible to precisely control the application of the filament and its regularity on the conveyor belt (3).

Above the same conveyor (3) there is a unit (4) which allows the discontinuous fibres to be distributed by air on the previously formed web (2).

Such a fibre distribution unit can be formed by a conventional installation such as that sold by the company M&J. In the concrete example, 35 g/m² of cellulose fibres, in particular wood fibres sold by the company KORSNAES, are applied to the nonwoven fabric of continuous filaments (2), these wood fibres, with a length of approximately 3 mm, usually referred to by the term "fluff paste".

A suction box (5) is arranged under the conveyor under the entire surface of the air distribution head (4). This suction head (S) is connected to a vacuum generator which enables the wood fibres to be evenly distributed while maintaining the homogeneity of the fleece of continuous filaments (2).

A pressure roller (not shown), the speed of which is synchronized with the conveyor belt (3), compacts the unit thus formed.

After compaction, a second nonwoven fabric of continuous filaments weighing 15 g/m² and of the same type as the first nonwoven fabric (2) is applied to the surface of the complex.

This fleece can be formed either on the same conveyor (3) or on an independent conveyor.

This fleece (7) is thus distributed on the layer of cellulose fibers (4). Preferably, the transfer is carried out in a positive manner by using a suction box (5a) arranged under the main conveyor opposite the transfer point.

The structure obtained, which weighs 65 g/m², is compacted, if necessary, using a roller (8). This compaction can be carried out, if necessary, using an additional ramp of hydraulic spray nozzles.

The complex is then forwarded on the conveyor device (10) of the hydraulic connection unit (9).

Such a connection unit comprises a main conveyor (10), above which an upper conveyor (11) is arranged, which is tangent to it, and inside which a hydraulic spray nozzle (12) is provided, which delivers 4000 water jets per meter, these jets having a diameter of 130 micrometers and a speed of 34 meters per second.

The "sandwich" thus compacted and moistened is treated on its upper surface by six hydraulic spray nozzles (13) arranged in series, which project water jets of 120 microns in diameter, 0.6 mm apart from each other and at speeds of 110, 125, 140, 140, 140, 140 m/second respectively.

The treated complex is then passed on to a roller (14) while being turned over, around which four hydraulic spray nozzles (15) are arranged, which emit water jets of 120 micrometers in diameter, which are separated from each other 0.6 mm apart and have speeds of 125, 140, 140, 140 m/second respectively.

The complex solidified in this way is passed on to a squeezing conveyor (16) where it is squeezed through a suction box in which a vacuum of 400 mbar prevails.

The unit is then dried at a temperature of 120ºC by an air-passing roller (17) and then removed at (18).

At the exit from the production plant, it can be observed that the product obtained weighs approximately 60 g/m², has excellent homogeneity, a good feel to the touch, great softness and excellent abrasion resistance both when dry and when wet. Its water absorption capacity is high, at approximately 850%.

Such water absorption capacity is comparable to mixed fiber nonwovens made from discontinuous fibers and produced by carding.

However, the abrasion resistance in both dry and wet conditions, as well as the mechanical properties, are significantly better.

Such a product is perfectly adapted to various applications, such as industrial and domestic wiping products, impregnated linen, surgical gowns and fields, these applications being indicative and not limiting.

Claims (4)

1. Process for producing a complex nonwoven material, which consists in continuously producing a complex in which a fibrous nonwoven based on cellulose fibers (4) is sandwiched between two nonwovens of continuous filaments (2, 7), and which consists in: - producing a first nonwoven fabric (2) from continuous filaments, whereby the bundle of extruded and stretched continuous filaments is taken up onto a mobile conveyor belt (3) in the form of a non-connected web; - to lay a second fleece (4) made of cellulose fibres on this fleece (2) by means of air technology; - placing a second fleece (7) made of non-bonded continuous filaments on the nonwoven fabric (4); - to forward the complex thus formed to a plant (9) for connection by water jets and to consolidate the unit by hydraulic confusion; and - to dry the mixed fibre fleece produced and then remove it, for example in the form of a winding (18). 2. Method according to claim 1, characterized in that the cellulose fibers (4) used in the manufacture of the complex are wood fibers. 3. Process according to one of claims 1 and 2, characterized in that the complex is subjected to two successive bonding treatments by water jets acting against the two opposite faces of the complex. 4. Mixed fibre nonwoven fabric obtained by using the method according to one of claims 1 to 3, characterized in that it is composed of a layer (4) of natural fibres, in particular wood, sandwiched between two nonwoven webs (2, 7) formed from extruded and stretched continuous filaments based on synthetic material, the Cohesion of the different layers is achieved by confusing them thanks to the action of water jets.