EP0396476B1 - Non woven wet-laid product and process for making the same - Google Patents

Description

For decades, it has been proposed to replace traditional textile tablecloths (fabrics, knits) by so-called "nonwoven" structures which, in general, can be classified into three main categories, resulting from their very manufacturing process, namely nonwovens called "dry", "melted" and nonwovens called "wet". The present invention relates to a new type of material obtained by this latter technique called "wet".

The nonwovens obtained by the wet process consist entirely or in part of chemical fibers which are suspended in water, as in the manufacture of a conventional sheet of paper, and are recovered in the form of a layer. fibrous by bringing said suspension to a drainage system allowing water to be removed.

It has been known for a very long time that the final properties of the product obtained can be adapted by making mixtures of materials, for example by mixing conventional paper fibers in the fibrous suspension with other types of fibers, textile, natural, artificial. , synthetic. In most cases, a suspension is produced comprising a mixture of different fibers (with various additives) so as to obtain a homogeneous sheet.

For certain applications, it has been proposed to produce multilayer articles of the cardboard type, so as to have different properties on the two. sides of the formed sheet, for example a printable or impermeable face and the other fibrous face, or an impermeable face and another face having a high absorbing power or a heat-bonding layer. To give the sheet formed good mechanical properties, consolidation is carried out either by adding to the suspension fibers called "binding" whose properties are revealed later, for example by heat treatment, or by incorporating binders which may have been deposited beforehand. superficially on the fibers. The presence of such binders not only complicates the manufacturing process, but also has the consequence, in certain applications, of altering the textile properties (feel, flexibility, etc.) of the sheet formed.

To reinforce the cohesion of such plies, it could have been envisaged, as has been done in the field of nonwovens obtained by the dry route, to replace the binding materials by a mechanical needling or interlacing treatment, such as for example an interlacing treatment by fluid jets, as described in patents US-A-3,033,721, 3,214,819 and 3,508,308, the latter document describing among other embodiments (cf. example 13) the production of complexes from nonwovens obtained by the wet process.

Tests carried out in this direction on conventional nonwovens obtained by the wet process from a suspension of fibers wholly or partly composed of chemical fibers have shown that if a sheet having improved textile characteristics is obtained compared to an equivalent sheet whose cohesion is obtained by means of binders, that on the other hand, the mechanical characteristics are insufficient for many applications.

Now we have found, and this is what is the subject of the present invention, a new type of nonwoven complex, obtained by the wet method, consisting of a mixture of fibers having different flexibility characteristics, some by compared to others which overcomes the drawbacks of previous solutions and which not only makes it possible to preserve the properties inherent in such fibers, but also results in a sheet whose mechanical characteristics are improved compared to a sheet of equivalent overall composition consisting of 'an intimate mixture of such fibers in the same overall percentages; moreover, the complex according to the invention can be produced according to a simple, economical process, eliminating the presence of additional binders which is also part of the invention and which makes it possible to obtain the material according to the invention directly on a machine production without having to perform an intermediate drying.

If the complex according to the invention consists predominantly of the two types of fibers having different flexibility characteristics from one another, it may of course, optionally include various additives making it possible to modify the properties thereof. depending on the applications.

• . une nappe qui est au moins partiellement à base de fibres relativement rigides en milieu aqueux ;
• . une autre nappe qui comporte au moins une partie de fibres souples en milieu aqueux ;

les deux nappes précitées étant liées entre elles par aiguilletage par fluide, agissant au moins du côté de la nappe de fibres souples, caractérisé en ce que ladite opération d'aiguilletage est réalisée sur la machine de fabrication, alors que les nappes élémentaires sont formées mais non encore séchées.In general, the invention therefore relates to a new type of complex non-woven material obtained by the wet process, consisting of at least two layers of materials superimposed and linked together, comprising:

• . a web which is at least partially based on relatively rigid fibers in an aqueous medium;
• . another layer which comprises at least a portion of flexible fibers in an aqueous medium;

the two aforementioned plies being linked together by fluid needling, acting at least on the side of the ply of flexible fibers, characterized in that said needling operation is carried out on the manufacturing machine, while the elementary plies are formed but not yet dried.

As fibers used in the constitution of the aforementioned elementary layers, polyester fibers, or even viscose fibers, and, as flexible fibers, cellulose fibers from wood pulp are preferably used as rigid fibers. In addition, according to a preferred embodiment of the complex according to the invention, the sheet based on rigid fibers contains a proportion of flexible fibers similar to those used in the constitution of the second sheet. Furthermore, it should be noted that in the sense of the present invention, the "flexibility" or the "rigidity" of the fibers is that which the said fibers have in the medium of the binding fluid and not in their natural state.

• des fibres métalliques pour augmenter la conductivité électrique ;
• des fibres de verre pour augmenter la stabilité dimensionnelle et la résistance au feu ;
• des fibres cellulosiques pour améliorer la dispersion des fibres artificielles ou synthétiques ;
• des charges diverses, telles que charges minérales et/ou organiques peuvent éventuellement être incorporées à l'une ou l'autre des nappes élémentaires pour modifier les propriétés finales du complexe, par exemple l'état de surface après que le complexe ait été lissé ou calandré, de manière à ce qu'il serve de support d'impression.

Furthermore, it can be envisaged to incorporate various additives into one or the other of the plies, making it possible to give them specific properties, such as for example:

• metallic fibers to increase electrical conductivity;
• glass fibers to increase dimensional stability and fire resistance;
• cellulosic fibers to improve the dispersion of artificial or synthetic fibers;
• various fillers, such as mineral and / or organic fillers, can optionally be incorporated into one or other of the elementary plies to modify the final properties of the complex, for example the surface condition after the complex has been smoothed or calendered, so that it serves as a print medium.

• l'une des couches est au moins partiellement composée de fibres relativement rigides en milieu aqueux (polyester par exemple) ;
• l'autre couche comporte au moins une partie de fibres souples en milieu aqueux (fibres de bois de type résineux par exemple),

les deux couches ainsi produites étant soumises, encore à l'état humide, c'est-à-dire avant d'avoir été séchées, à l'action de jets de fluide (eau) s'exerçant au moins sur la face du complexe constitué de la couche à base de fibres souples, l'ensemble ainsi lié étant ensuite séché et rebobiné de manière conventionnelle.For the production of the product according to the invention, a process which also forms part of the invention is implemented, said process consisting, starting from a conventional machine allowing a nonwoven web to be obtained by wet process. of two different layers, to conform two elementary layers from fibrous suspensions, layers which are superimposed on the production machine, said process being characterized in that:

• one of the layers is at least partially composed of relatively rigid fibers in an aqueous medium (polyester for example);
• the other layer comprises at least a portion of flexible fibers in an aqueous medium (wood fibers of the resinous type for example),

the two layers thus produced being subjected, still in the wet state, that is to say before being dried, to the action of jets of fluid (water) exerted at least on the face of the complex consisting of the layer based on flexible fibers, the assembly thus bonded then being dried and rewound in a conventional manner.

For the implementation of such a process, a conventional machine is used for obtaining wet nonwovens, such as for example a machine of the Hydroformer type from the company Voith, modified to include two heads for distributing pasta, this machine being combined with a set of hydraulic binding, also of known type, which allows to apply needle-jet of water under high pressure in order to bind the sheet.

Since such machines have been known for a very long time, they are not described in detail in the remainder of the description.

According to the method according to the invention, the fluid interlacing machine is combined with the machine for forming nonwoven webs, so that the operation of binding the two plies formed is carried out while they are still wet condition and before any drying operation.

It was completely unexpected that by applying such a fluid interlacing technique to a nonwoven complex obtained by the wet process, a complex having a very precise composition (namely a layer based on rigid fibers and the other based on flexible fibers ), the interlacing action being carried out while the complex is not yet dry, so that the interlacing jets act at least on the sheet made of flexible fibers, which it was possible to finally obtain a product whose properties are significantly improved compared to a sheet of equivalent overall composition, produced in a single layer and comprising an intimate mixture of the same fibers in the same overall percentages as is apparent from the exemplary embodiments described below by way of indication and without limitation, FIGS. 1 and 2 illustrating the request being curves respectively showing the characteristics of tear resistance (f igure 1) and tensile (figure 2) for materials produced in accordance with the invention (curve A) and materials having the same overall composition, but produced in a single layer (curve B).

All these examples are made from a conventional paper machine of the Hydroformer Voïth type adapted to have two separate suspension inlets and making it possible to produce a multilayer sheet, machine adapted in accordance with the method according to the invention to allow hydraulic interleaving of the nonwoven structure formed, this binding and consolidation operation of the structure being carried out directly at the outlet (see on) the forming fabric, while the material is still in the wet state and before it passes to the interior of the drying unit that the particular installation includes. In the present case, a conventional hydraulic entanglement binding machine is used. In the following description, the examples are given, it being understood that this is not limiting, by striking the jets of fluid (water) on the upper layer of the sheet therefore receiving the first impact of these jets.

Example 1 :

• pour la couche supérieure : composition à base de fibres relativement souples en milieu aqueux, constituée par une pâte cellulosique à base de fibres de bois de type résineux (Pin Sylvestre par exemple) ;
• pour la couche inférieure : une suspension fibreuse à base de fibres relativement rigides en milieu aqueux constituée de fibres de polyester de 1,7 dtex et 12 mm de longeur.

On a paper machine of the aforementioned type, a nonwoven complex is produced in accordance with the invention from the following fibrous compositions:

• for the upper layer: composition based on relatively flexible fibers in an aqueous medium, consisting of a cellulose pulp based on wood fibers of the resinous type (Sylvester pine for example);
• for the lower layer: a fibrous suspension based on relatively rigid fibers in an aqueous medium consisting of polyester fibers of 1.7 dtex and 12 mm in length.

The two sheets, separately prepared from the above-mentioned compositions, are brought to a spinning belt, superimposed on each other, in an amount such that there is an overall composition comprising 50% of cellulose fibers and 50%. polyester fibers. Before the complex formed has completely dried, the complex is subjected to a fluid interlacing operation at the rate of five successive rows of jets / needles having increasing pressures from 30 bars to 120 bars, the number of jets / needles per meter of width of each row being about one thousand.

On leaving the machine, after drying, a nonwoven having a good look, very good tensile strength, elongation and tearing is obtained. These improved characteristics appear clearly from the appended FIGS. 1 and 2 in which it can be seen on the curves A that for such a percentage, the tensile strength (N / m) is around 1350 for a material according to the invention, whereas in the case where the material is produced in a single layer having the same overall composition (curve B), it is only around 850, and that the tear strength (cN) is, if the reference is made to FIG. 1 of the order of approximately 2600 for a material according to the invention, while it is only slightly greater than 1500 for a material having the same overall composition and produced in a single layer (curve B).

Example 2 :

Example 1 is repeated except that the complex web formed is, before drying, subjected to a fluid interlacing treatment on its two faces. Compared to the previous article, we obtain a product with better mechanical characteristics (resistance to tensile, elongation, tear), but in which the porosity is increased; moreover, there is a higher percentage of fiber losses.

Example 3 :

An article is produced in accordance with the present invention, except that the pastes of the two layers of the complex are modified so that the upper layer is formed from flexible fibers in an aqueous medium (100% cellulose fibers from pine sylvestre), while the layer consists of a mixture of 50% polyester, 1.7 Dtex, 18 mm and 50% birch cellulose.

To improve resistance to certain chemicals, this article is reinforced by an additional treatment in full bath with an emulsion of synthetic polymer (latex type) which is deposited at a rate of approximately 10% relative to the fibrous mass.

The article obtained has, in addition to very good textile characteristics, an improved tear resistance compared to the previous examples.

Comparative examples

These comparative examples are grouped in the appended FIGS. 1 and 2 which are, as said previously, curves for measuring the breaking and tensile strength of the material produced in accordance with the invention (curve A) and of comparative materials having a same overall composition, but made in a single layer (curve B). These curves are made from materials (in one or two layers) weighing overall 65 g / m2 and varying the overall percentage of polyester. The measurements are made according to EDANA standards reference 70.1-75 for tear tests and 20.1-73 for tensile tests.

It is clear from the appended curves that for complex materials comprising the same overall composition of hard fibers and flexible fibers, one being produced in accordance with the invention, the other from an intimate mixture of fibers in the dough. so as to form a monolayer material, that the materials, subjected to an identical interlacing treatment, under the same conditions as for the preceding examples, leads to articles having lower mechanical characteristics and this, for the same grammage and the same overall percentage of fibers.

Of course, the invention is not limited to these exemplary embodiments but it covers all the variants produced in the same spirit, insofar as at least one of the layers of the complex formed comprises at least a portion of fibers. relatively more flexible in an aqueous medium than the other layer. Thus, it can be envisaged to produce articles comprising more than two layers of fibers, for example layers formed of fibers which have, in an aqueous medium, increasingly rigidities going from one face to the other of the material such as, a layer based on wood fibers, then a layer of fibrane, then a layer of viscose, then finally a layer of polyester.

It is obvious that the rigidity and flexibility can be varied as a function of the power of the interlacing jets and their density.

Compared to previous solutions, the new material according to the invention is not only very economical to obtain since it can be produced directly on a production machine without having to carry out an intermediate drying.

However, the main advantage of the new material according to the invention lies in the mechanical characteristics clearly superior to the prior materials, characteristics obtained without deterioration of the textile properties of the plies obtained and above all without the addition of additional binder materials.

As said previously, the invention also covers the case where various additives are added to the material according to the invention, in particular with a view to giving it particular properties, such as good electrical conductivity by incorporating a certain percentage of metallic fibers inside one or other of the elementary layers, improvement of dimensional stability, of fire resistance by incorporation of a certain quantity of glass fibers.

In addition, it could be envisaged to interpose between the two plies before they are linked, additional reinforcing elements such as for example plies based on continuous filaments, textile grids.

The material can also be consolidated with an additional binder of the Latex type or undergo various chemical treatments, such as for example fireproofing, water repellency, coloring treatments, etc. for the final application.

Claims (9)

1. Nonwoven composite material obtained by a wet route, consisting of at least two sheets of superposed fibrous substances bonded together, comprising:

   - a sheet which is at least partially based on fibres which are relatively rigid in aqueous medium;

   - another sheet which comprises at least a proportion of fibres which are flexible in aqueous medium;

   the abovementioned two sheets being bonded together by needling using a fluid, acting at least on the side of the sheet of flexible fibres, characterised in that the said needling operation is carried out on the manufacturing machine when the elemental sheets are formed but not yet dried.
2. Material according to Claim 1, characterised in that the sheet based on fibres which are rigid in aqueous medium is based on polyester fibres, while the sheet based on flexible fibres is based on fibres of wood of coniferous type.
3. Material according to either of Claims 1 and 2, characterised in that various additives are incorporated in the sheets in the aqueous medium for dispersing fibres enabling them to be produced.
4. Material according to Claim 3, characterised in that the additives are metal fibres which make it possible to increase the electrical conductivity.
5. Material according to Claim 3, characterised in that the additives are glass fibres which make it possible to increase the dimensional stability and the fire resistance.
6. Material according to Claim 3, characterised in that the additives are cellulose fibres which make it possible to improve the dispersion of the artificial or synthetic fibres.
7. Material according to one of Claims 1 to 6, characterised in that it has received a treatment which makes it possible to modify its properties, such as treatments by means of a polymeric resin (latex type) or a chemical treatment (flame retardance, colouring, water repellency).
8. Process for the production of a material according to one of Claims 1 to 7, consisting, starting with a conventional machine which makes it possible to obtain a nonwoven sheet by wet route made' of two different layers, in forming two elemental layers from fibrous suspensions, layers which are superposed on the production machine, characterised in that:

   - one of the sheets is at least partially made up of fibres which are relatively rigid in aqueous medium (for example polyester),

   - the other sheet comprises at least a proportion of fibres which are flexible in aqueous medium (for example cellulose fibres of coniferous type),

   the two layers thus produced being subjected, still in the wet state, to the action of jets of fluid (water) acting at least on the face of the composite made up of the layer based on flexible fibres, the assembly thus bonded being subsequently dried and rereeled in conventional manner.
9. Process according to Claim 8, characterised in that the materials are subjected to an additional in-line or out-of-line treatment such as, for example, addition of a polymeric resin (latex type), chemical treatment making it possible to modify its specific properties (flame retardance, colouring, water repellency etc.).

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