EP2758592A1

EP2758592A1 - Method for dimensionally compensating webs of fibrous material

Info

Publication number: EP2758592A1
Application number: EP12772416.9A
Authority: EP
Inventors: Marion Sterner
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-09-19
Filing date: 2012-09-17
Publication date: 2014-07-30
Anticipated expiration: 2032-09-17
Also published as: WO2013041957A1; EP2758592B1; EP2758592B8; ITVE20110063A1

Abstract

A method for dimensionally compensating webs of fibrous material, characterised by causing a base web (2) of pliable fibrous material, having a dry content between 3% and 80%, to adhere to an endless conveyor belt 4 of elastic material when this latter is in its unstressed condition, then subjecting said belt and the base web adhering thereto localized transverse stretching, starting from said unstressed condition, and to partial removal of the liquid content, and finally removing said base web from said belt before this latter has commenced its elastic return to said unstressed condition.

Description

METHOD FOR DIMENSIONALLY COMPENSATING WEBS OF FIBROUS MATERIAL

The present invention relates to a method for dimensionally compensating webs of fibrous material.

Production methods for fibrous material, and in particular paper webs, are known. They generally consist of pouring a mix of fibrous material and water onto an endless conveyor belt while in movement. This mix is progressively deprived of its water content thereon and is subjected to a series of traditional procedures which finally lead to the obtaining of a paper web or, in more general terms, to the obtaining of a web of fibrous material, to be then wound into rolls for subsequent uses.

These subsequent uses can consist of printing on the paper web or of its transformation by suitable successive passages through paper working machines.

However both these procedures impose particular requirements: printing generally requires precise formats which are often not submultiples of the width of the continuous web obtained from the paper machine. Likewise, the various manufactured paper products are obtained starting from a continuous paper web which is not always used in the format made available by the paper works, but has to be cut and can involve wastage due to scrap.

Moreover, independently of these problems, very often the products obtained from a continuous paper web do not ensure their dimensional stability, because of the inevitable contraction to which the web is subjected both by the effect of its nature and by the effect of the operations to which it is subjected.

The fibrous web production process on a continuous machine gives the fibres a preferential orientation in the production direction. This preferential orientation causes material anisotropy, i.e. different physico-mechanical properties in the production direction compared with the transverse direction. For example, the tensile strength and the rigidity are greater in the longitudinal direction; elongation, tearing resistance and hygroexpansivity are greater in the transverse direction. Other factors contributing to anisotropy of the paper material are the traction to which the fibrous web is subjected along the continuous machine and the transverse contraction which it undergoes on drying. These factors introduce tensions among the interfibre bonds which are differently distributed in the two directions.

The longitudinal preferentiality in the fibre orientation direction and the consequent anisotropy of the paper web is one of the main causes of paper planarity defects. The problem is highlighted if there is a difference between the relative humidity of the environment and that of the paper at equilibrium. In this respect, the fibres tend to swell more in their length direction. The paper sheets can be deformed and not properly stretched.

For some applications, paper or card of high voluminosity (thickness/surface density ratio) is required. For example, voluminosity increases the paper compressibility, facilitating its adaptation to and contact with an inking form and hence increasing ink transfer in a printing process. Voluminosity is also required in the tissue paper sector to provide softness and liquid absorption capacity.

It is known that uniform fibre distribution (candling) within a paper sheet facilitates glazing and more homogeneous printing. It is easier to obtain homogeneous candling for high surface density. A method would therefore appear advantageous which enables a fibrous base web of higher surface density and uniformity to be deposited and then to widen the base web by lowering its surface density while maintaining an acceptable candling uniformity.

A more isotropic paper with more uniform candling has better tearing and bursting resistance and is particularly suitable for producing bags.

EP 1 ,072,720 describes a production method for a fibrous material web using an elastic conveyor belt which, before receiving a base web of fibrous material of high water content, is subjected to longitudinal stretching such as to undergo a transverse contraction. When the elastic belt is returned to its unstressed condition it causes a corresponding widening of the fibrous material base web.

A drawback of this solution is the limit in the width of the fibrous material web obtainable, which at most can be equal to the width in the rest state of the unstressed elastic belt on which it is positioned.

An object of the invention is to provide a method which enables the width of a continuous web of fibrous material, and more particularly of a continuous paper web, to be modified, and to ensure stability of the thus modified web.

Another object of the invention is to provide a method which enables transversely widened, stabilized and possibly longitudinally compacted webs of fibrous material to be obtained.

Another object of the invention is to provide a method which can be implemented with the same plants used to obtain transversely compacted webs of fibrous material. Another object of the invention is to form a web of fibrous material having high voluminosity, in terms of the thickness/surface density ratio.

Another object of the invention is to form a continuous web of fibrous material having a thickness less than the minimum obtainable with traditional paper manufacturing machines and in any event with a more homogeneous candling, for equal surface density, including at low surface densities.

Another object of the invention is to form a web of fibrous material having a fibre orientation which is more homogeneous and less unbalanced in the machine direction, and consequently with more isotropic properties (mechanical, hygroscopic, dimensional stability, etc.).

Another object of the invention is to form a web of fibrous material having controlled porosity.

Another object of the invention is to form a web of fibrous material having a controlled additive concentration along the web thickness.

Another object of the invention is to form a web of fibrous material the mechanical, optical and porosity characteristics of which can be mutually controlled and balanced more finely and flexibly than with traditional methods.

These and other objects which will be apparent from the ensuing description are attained, according to the invention, by a compensation method as described in claim 1.

The invention also comprises an apparatus for implementing the method as described in claim 22.

The present invention is further clarified hereinafter in terms of some embodiments thereof with reference to the accompanying drawings, in which: Figure 1 shows schematically a portion of elastic conveyor belt on which a continuous base web of fibrous material subjected to the method of the invention is positioned,

Figure 2 shows schematically a section through a first embodiment of an elastic sleeve wrapped about a roller and subjected to localized stretching, Figure 3 shows a second embodiment thereof in the same view,

Figure 4 shows a third embodiment thereof in the same view,

Figure 5 shows a fourth embodiment thereof in the same view,

Figure 6 shows in lateral view a particular curved roller for implementing the transverse stretching of the elastic conveyor belt,

Figure 7 is a section through an elastic conveyor belt associated with means for subjecting the fibrous material base web to transverse stretching and to longitudinal stretching,

Figure 8 is a section through a roller wrapped by an elastic sleeve subjected to two stages of localized stretching,

Figure 9 is a section through an elastic conveyor belt taut between two deviation rollers and subjected to localized stretching at each of these, and

Figure 10 is a perspective view of two continuous fibrous material base webs, one subjected to localized transverse stretching by the method of the invention, and the other subjected by the same conveyor belt to transverse compaction.

As can be seen from the figures, the method according to the invention, shown extremely schematically, starts from a fibrous material base web 2 having a dry content between 3% and 80% and hence a moisture content between 20% and 97%.

This fibrous material base web 2, which could also be coupled to a polymer film, is deposited on a conveyor belt 4 made of elastic material and having at least one portion subjected to transverse extension by any mechanical action, for example a transverse traction at its edges or in proximity thereto, or a forced removal from the sliding plane of a portion thereof retained at its edges.

Figure 1 shows an elastic belt 4 subjected to transverse stretching by the application of traction force at its edges in the direction of the arrows 6, while Figure 2 shows an elastic belt 4 subjected to transverse stretching by the temporary forced introduction of the belt, consisting of a tubular sleeve 4 wrapped about a rigid roller 8, into a pair of circumferential cavities 10 formed in said rolled in proximity to its two ends. This temporary forced introduction can be advantageously caused by interference by a pair of introduction rollers 12, which partly enter said circumferential cavities 10.

Independently of the method by which the conveyor belt 4 is stretched, if before this stretching or at least before its completion a fibrous material base web 2 is deposited on the belt, and which given its high water content is in a pliable state, as the conveyor belt widens it also causes the fibrous material base web to widen by dragging.

At the same time the fibrous material base web undergoes compaction in the longitudinal direction due to the simultaneous longitudinal shortening of the elastic belt, if this has a normal Poisson deformation coefficient (for example around 0.5). However the simultaneous longitudinal compaction of the belt 4 can be prevented if this is filled with fibres disposed longitudinally and resistant to axial compression (for example steel, Kevlar, carbon), or if it is made from a material having a Poisson coefficient ideally close to zero.

The elastic conveyor belt 4 can consist of one or more layers of possibly expanded elastomer, or of single or multiple fabric formed of threads which may be elastic, or non-elastic but woven in accordance with an elastic weave, or finally of a composite layer formed from the preceding.

It can also be permeable to fluids and contain a sponge layer able to absorb and/or release liquids.

Finally, the elastic belt 4 can constitute the belt of the so-called flat table, which in a traditional paper machine receives the mix originating from the head box. In this respect, the pliable material base web 2 can originate directly from the head box of any paper processing machine or can be obtained from an already formed paper web already subjected to wetting until having the desired moisture content. It can also consist of cellulose fibres, if a paper web is to be obtained, or of cellulose and polymer fibres or only of polymer fibres, if a web of non-woven fabric is to be obtained.

To improve adhesion between the base web 2 and the elastic surface of the conveyor belt 4, said surface can be functionalized such as to present high affinity for cellulose. For example the material forming the elastic belt 4 can be made starting from a mixture of elastic material (rubber) and cellulose in the form of fibres, microcrystals (microcrystalline cellulose) or nanofibres (nanocellulose).

Alternatively, the cellulose fibres or nanofibres can be bonded to the elastic surface by suitable binders, such as latex or adhesion promoters based, for example, on silicates and titanates. To improve adhesion between the fibre layer and the rubber, this latter can be subjected to corona treatment or generally to plasma treatment.

An elastic fabric composed partly of cotton can also be used as the material forming the conveyor belt 4.

The conveyor belt 4 can also be covered or impregnated with a gum latex of low glass transition temperature, such as those used for pressure-sensitive adhesives, traditionally used for post-it pads. Finally, the conveyor belt 4 can be covered or impregnated with formulations typically used for increasing the adhesion of the fibre web to the Yankee cylinder used in producing tissue paper.

As an alternative to these methods for improving the adherence of the base web 2 of pliable material to the conveyor belt 4, said base web can be pressed against said conveyor belt by a smooth flat or cylindrical (roller) surface; and said belt can also comprise on its surface a plurality of microhooks to favour the gripping of the base web 2 to the belt 4.

However before the conveyor belt 4 has ceased to be stretched transversely or in any event before it bas begun to reassume its original configuration, the transversely stretched fibrous material base web 2 is withdrawn from the belt, in order not to be subjected to any transverse recompacting.

In this manner the fibrous material base web 2 can be thinned, for equal voluminosity, to an extent often greater than that obtainable by traditional paper- making processes.

In the case of excessive adhesion, to detach the fibrous material base web 2 from the elastic surface a blade of air or water vapour or possibly a doctor blade can be used. If the elastic belt 4 is permeable to fluids, air can be blown therethrough to detach the fibrous base web 2.

Moreover, in order to facilitate correct transverse stretching of the elastic conveyor belt 4, which given its function must be in continuous contact with support and drive rollers, the sliding of the elastic belt on these conveyor rollers is advantageously facilitated by suitable lubricant substances interposed between the two, or by adequately varying the belt thickness and/or by a suitably convex shaping of the conveyor rollers, or by providing these with ball retainers.

Figure 3 is a schematic section through a conveyor belt 4 with different thicknesses, namely thinner in the central band and thicker in the two lateral bands. This is wrapped about a convex roller 8, such that during its introduction into the circumferential cavities 10 it is not subjected to sudden deviations, which could result in abnormal stresses, rapid wear and transverse stretching disuniformity. Moreover the two introduction rollers 12 present a complementary shape and can also have all or part of their surface provided with ball retainers (not shown), which facilitate transverse sliding of the conveyor belt 4 thereon.

As an alternative to, or in addition to the differential profile of the conveyor belt 4, its transverse stretching can be controlled, according to the invention, by making this belt of a material of differential elastic yieldability, i.e. more yieldable in the central band intended to receive the pliable fibrous base web 2 and less yieldable in the lateral bands, to which the traction forces are applied.

All these characteristics, i.e. the differential elastic yieldability of the conveyor belt 4, the convexity of the roller 8 and the presence of ball retainers, which in the drawing have been shown as pertaining to specific embodiments, in reality are mutually independent and can be used independently or in the desired combination, according to requirements.

Figure 4 shows a conveyor belt 4 which besides being of differential thickness in the transverse direction, is stretched by withdrawal from its sliding plane by the presence of two ball retainers 14, on which the belt rests.

In contrast, Figure 5 shows a conveyor belt 4, in which the transverse stretching is caused on the actual belt sliding plane, by virtue of ball retainers 14' of particular form.

Figure 6 shows a conveyor belt 4, which is stretched transversely by using a particular curved stretching roller 16, known as a banana in technical jargon and formed by a plurality of minor rollers 18 mounted on one and the same curved shaft 20.

In one embodiment, not shown in the drawings, transverse stretching of the base web 2 is achieved by traditional templates, in which the inclined discs with hooks are replaced by discs with a rubber-coated edge.

Figure 7 shows a conveyor belt 4, which after being subjected to transverse stretching in one of the previously described manners, is also subjected to longitudinal stretching. This longitudinal stretching is induced by dragging by a roller 22, which rotates at a peripheral velocity greater than the peripheral velocity of the roller 8, about which the belt 4 passes during the transverse stretching stage.

The conveyor belt 4 can also be subjected to several successive localized transverse stretchings, and the fibrous base web 2 be positioned on the conveyor belt before commencement of stretching, and then be removed therefrom when stretching is terminated, and then be newly positioned on the same conveyor belt 4 before commencement of the next stretching and so on, such as to be able to be subjected to several stretchings in sequence.

Figure 8 shows a sleeve-shaped conveyor belt 4 wrapped about a roller 8, with which two pairs of introduction rollers 12 are associated, acting on the belt 4 in two separate positions, such as to subject the base web of pliable material to two successive transverse stretching stages. As stated, after the first stretching stage the base web 2 must be withdrawn from the conveyor belt 4 before it resumes its original configuration, this being achieved by a pair of auxiliary conveyor belts 26, the function of which is to withdraw the base web 2, already partially stretched transversely in the first station, and to bring it into the second station, where it is subjected to the second transverse stretching stage.

Figure 9 shows the same principle, applied however to an elastic conveyor belt 4 taut between two rollers 8, 8'. In contrast to the preceding embodiment, in which the two transverse stretching stages of the base web 2 are implemented at the same roller 8, the two transverse stretching stages are implemented at two different rollers 8, 8' in this case.

If the conveyor belt 4 is made of fluid permeable material and if the, or each, transverse stretching section faces the mouth of an aspirator 24 (see Figures 2-5), transverse stretching of the fibrous base web 2 is more effective both because of the more intense removal of the moisture contained therein, and because of its better adherence to the widening conveyor belt 4.

In order to facilitate adhesion of the fibrous base web to the elastic belt, stretching uniformity, and water removal from the pliable fibrous base web 2, the invention also provides for the use of fixed or rotatable mechanical presser elements provided with low friction surfaces, or of felts or other endless belts, including elastic belts. In particular, a single felt can be used, maintaining the base web 2 adherent to the conveyor belt 4 during transverse stretching, or two felts can be used, between which the base web 2, withdrawn from the conveyor belt 4 at the end of the or of each transverse stretching stage, is interposed. In particular, in addition to performing the function of withdrawing the pliable fibrous base web 2 from the conveyor belt 4 between one transverse stretching stage and the next, the auxiliary conveyor belts 26 already described relative to Figures 8 and 9 can perform the function of felts for partially removing water from the base web 2.

In this latter case, the conveyor belt 4 and the felt 26 cooperating with it can be driven at the same velocity, or at different velocities such as to cause a voluminosity increase of the fibrous base web 2 interposed between them.

Both the conveyor belt 4 and the felt or the endless belt 26 can have their surface functionalized such as to present a high affinity for cellulose. In this respect, when the pliable fibrous base web 2 is detached from the upper belt and from the lower belt, these exert on the base web, which is still strongly moist and pliable, a traction along the direction of its thickness (direction Z), so increasing its thickness and hence its voluminosity.

After the fibrous base web 2 has been pressed between the two belts 26 or between the conveyor belt 4 and the felt 26 cooperating with it, and which have a surface of high affinity for cellulose and behave elastically, they and the interposed base web 2 are simultaneous deformed. Moreover, if the two elastic belts are subjected to stretching at the respective edges, and at the same time a distance is maintained between the two which is at least equal to that preceding the stretching, the base web 2 will simultaneously undergo stretching in the transverse direction and stretching along the Z axis. This is due to the adhesion forces between each face of the base web 2 and the elastic surface of the upper and lower conveyor belts, and also to the transverse stretching and the consequent thinning of the thickness of the two elastic belts.

The stretching of the still moist and pliable fibrous base web 2 along the Z axis is directed to causing a voluminosity increase of said base web; again in this case, detachment of the base web 2 can be facilitated by doctor blades, by air blades or by air blown through the lower and upper elastic conveyor belts at the detachment point.

As generally the widening of a section of the conveyor belt 4, the length of which can be regulated at will, is followed by its more or less rapid return to the original condition, and then by a transverse contraction of the previously widened belt section, this sequence of two sections in which the belt is subjected to transverse stresses in opposite direction, can be advantageously utilized to achieve transverse stretching and hence stabilization of a base web 2 of fibrous material, and transverse compacting of a different base web 2' of fibrous material.

Figure 10 shows this principle schematically. It can be clearly seen that the conveyor belt 4 is subjected in one section to transverse stretching by one of the various methods previously described. In the section upstream of the stretched section, the belt 4 receives the base web of pliable fibrous material, which is then removed from the belt 4 at its point of maximum widening. There, a second base web 2' of fibrous material is deposited on the belt 4, such that its elastic return to the initial configuration causes transverse compaction of the base web 2', useful to provide it with transverse extensibility characteristics.

Depending on the particular use for which the final product is intended, the pliable fibrous base web 2 can also be treated, immediately before, during or immediately after stretching, with additives for conferring particular properties. In this manner it is possible to optimize the additive addition efficiency, hence limiting liquid effluent production. Incompatibility between the additives in solution or suspension (for example because of pH incompatibility or because they would form a gel or a precipitate) can be avoided by adding them in different stages. In this manner for example, a gel could be formed directly within the fibrous base web by adding two gelling components separately, such as alginate and calcium ions.

This additive addition can consist of spraying, of deposition by rollers, of impregnation with liquid formulations released from a sponge layer forming part of the elastic belt, or other methods known to the expert of the art.

The degree of dryness of the fibrous base web is chosen on the basis of the additive to be added, the uniformity of surface distribution, the penetration along the thickness of the base web and/or the final effect to be obtained. In particular, greater control of the degree of surface distribution (including regulated addition) and of the penetration of the additive along the thickness of the fibrous base web can be achieved.

By controlling the porosity and the additive distribution along the base web thickness, it is possible, for example, to finely regulate the surface sizing of a paper web, to optimize its properties of liquid penetration and of resistance to delamination or to dust, depending on the type of printing for which the paper is intended.

Additives in powder form are preferably dispersed in water and mixed with binding agents, such as cationic polymers, nanocellulose, polyglycols, acrylic dispersions, styrene-butadiene dispersions, etc.

Said additives can also be activated by administering energy from the outside (heat, UV or visible radiation, microwaves, electron beam, etc.), and provide the required effect only after activation (including external to the paper machine). In particular, the additives can be encapsulated in microcapsules added to the fibrous base web and of which the capsule shell can be broken successively by applying pressure or heat, in order to cause release of the additive at the required moment.

The various additives must be able to perform their function and be activated, if necessary, without mutual interference.

The additives to be added can provide properties such as:

• porosity control (surface porosity is essential for determining the capacity to filter ink pigments from their carrier and hence for print quality) along the thickness with additives such as:

o crystalline microcellulose,

o nanocellulose,

o mineral fillers generated in situ by precipitation (such as precipitated CaC03 to which a calcium bicarbonate solution is added and water and carbon dioxide removed by heating; the solution can contain binders and/or substances able to influence the morphology of the precipitated

CaCO3 crystals),

o polyalkyleneglycols (porosity increase; see WO 08/131793)

barrier towards oxygen and/or water vapour

o proteins (glutins, milk serum derivatives)

o vinylidene chloride copolymers in accordance with CA 711208,

o nanocellulose

opacity

o mineral fillers generated in situ by precipitation,

o kaolin

o mica

antigrease

o starch

o nanocellulose

o alginates

o carboxy methyl cellulose

o polyvinylalcohol

sizing

o starch

dust control

o starch

o nanocellulose

o carboxymethylcellulose

o polyvinylalcohol water repellence (including for capacitor insulating papers easily soakable in dielectric oils or resins)

o waxes, including natural waxes, preferably in dispersion

o colophony

hydrophilicity

o polyalkyleneglycols

ink adhesion

o titanium acetyl acetonate

o silanes

o gum Arabic

o dextrins

o alum

antiadherence

o silicone resins

adhesive curing rate, particularly polyurethane based

o zinc stearate

o caprolactam

o N-acylureas

o tertiary amines

colour

o pigments in dispersion, particularly titanium dioxide for degree of whiteness

o pigments based on optical interference generated by nano layers of polyelectrolytes, such as nano cellulose and polyethylene imine o colorants, including thermal, electro or photo chromic

voluminosity

o microcapsules containing expanding agents activatable by heating o nanocellulose based foams

o chemical expanding agents

o sodium bicarbonate and weak acids possibly added separately in successive stages

possible heating by induction

o preferably biodegradable susceptors, such as some of those described in US 6348679, able to convert electromagnetic energy at radio frequency or microwaves into heat. In particular the susceptors can be added in mixture with nanocellulose such as to be able to achieve effective drying of this latter.

rigidity and tensile strength (dry and/or wet)

o starch

o nanocellulose

o acrylic resins cross-linkable by photo initiators and UV light

o melamine resins cross-linkable by heat

o polyamide resins modified with epichlorohydrin

in particular, by controlling the degree of additive penetration it is possible to increase the tensile strength in papers formed from tubular rigid fibres while still maintaining good characteristics of opacity and tearing resistance

oxygen scavengers o encapsulated substances to function at the required moment, such as ferrous salts

• electrical conductivity

o carbon fibres

• antibacterials

o carbon silver salts

o silver nanoparticles

o titanium dioxide

o quaternary ammonium salts (or ammonium ions associated with nano cellulose or microcellulose)

o chitosan

o bacteriocins

o various natural extracts (from tea, nutmeg, grapefruit, etc.).

Essentially, the method of the invention is suitable for a great number of applications and in particular to receive additives of various type and properties, able to confer on the final product, and in particular on paper webs, properties and potentialities which previously did not exist.

Finally, depending on the use for which the product is intended, the method of the invention can be combined with traditional treatment methods for the final fibrous web, and in particular with coupling methods and/or methods for stretching coupled webs and/or production methods for extensible material webs, such as those described for example in EP 772522, in EP 824619, in EP 876536, in EP 946353, in US 2624245 or in US 7918966.

The advantages of the method according to the invention are apparent from the aforegoing. In particular it enables a web of fibrous material to be formed:

- with fibre orientation more homogeneous and less unbalanced in the machine direction and consequently with more isotropic properties (mechanical, hygroscopic, dimensional stability, etc.),

- with a controlled porosity,

- with a controlled concentration of additives in the web thickness direction,

- with mechanical, optical and porosity characteristics controllable and mutually balanced in a more finely and flexible manner than with traditional methods.

Moreover the apparatuses according to the invention can advantageously consist of independent modules, which can be added to or removed from the production line as required.

Claims

C L A I M S

1. A method for dimensionally compensating webs of fibrous material, characterised by causing a base web (2) of pliable fibrous material, having a dry content between 3% and 80%, to adhere to an endless conveyor belt 4 of elastic material when this latter is in its unstressed condition, then subjecting said belt and the base web adhering thereto localized transverse stretching, starting from said unstressed condition, and to partial removal of the liquid content, and finally removing said base web from said belt before this latter has commenced its elastic return to said unstressed condition.

2. A method as claimed in claim 1 , characterised by subjecting said belt (4) with said base web (2) adhering thereto to transverse stretching by at least partial forced removal of a portion of said belt, retained at its edges, from its sliding plane while in the unstressed condition.

3. A method as claimed in one or more of the preceding claims, characterised by subjecting said belt (4) with said base web (2) adhering to it to transverse stretching by applying a mechanical traction action to the edges of the belt coplanar with its sliding plane.

4. A method as claimed in one or more of the preceding claims, characterised by causing said belt (4), wrapped about a first substantially rigid roller (8), to undergo stretching by interference by at least one second substantially rigid roller (12) having its axis parallel to the axis of the first roller and acting in the sense of urging said belt (4) into a corresponding circumferential cavity (10) provided in said first roller (8).

5. A method as claimed in one or more of the preceding claims, characterised by causing said base web (2) of pliable material, originating from the head box of a paper making machine, to adhere to said elastic conveyor belt (4).

6. A method as claimed in one or more of the preceding claims, characterised by causing said base web (2) of pliable material, obtained from an already formed paper web, previously subjected to wetting to the desired moisture content, to adhere to said elastic conveyor belt (4).

7. A method as claimed in one or more of the preceding claims, characterised by improving the adhesion of said base web (2) of pliable material to said elastic conveyor belt (4) by functionalizing said belt such as to cause it to present high affinity for cellulose.

8. A method as claimed in one or more of the preceding claims, characterised by using a conveyor belt (4) produced from a mixture of elastic material and cellulose in fibre, microcrystal or nanofibre form.

9. A method as claimed in one or more of the preceding claims, characterised by improving the adhesion of said base web (2) of pliable material to said elastic conveyor belt (4) by subjecting this latter to plasma treatment.

10. A method as claimed in one or more of the preceding claims, characterised by facilitating the detachment of said base web (2) of fibrous material from said elastic conveyor belt (4) by a blade of fluid blown between the two.

11. A method as claimed in one or more of the preceding claims, characterised by using a fluid-permeable elastic conveyor belt (4) and facilitating detachment of said base web (2) of fibrous material from said belt (4) by an air jet blown through this latter.

12. A method as claimed in one or more of the preceding claims, characterised by facilitating the transverse stretching of said elastic conveyor belt (4) by interposing friction reduction means between this latter and the members with which it comes into contact.

13. A method as claimed in one or more of the preceding claims, characterised by using a fluid-permeable elastic conveyor belt (4) and facilitating moisture removal from said base web (2) of fibrous material adhering to said belt (4) by causing that section thereof subjected to transverse stretching to face the mouth of an aspirator (24).

14. A method as claimed in one or more of the preceding claims, characterised by facilitating moisture removal from said base web (2) of fibrous material by causing at least one felt (26) to adhere to said base web (2).

15. A method as claimed in claim 14, characterised by advancing said felt (26) at a velocity different from the advancement velocity of said conveyor belt (4).

16. A method as claimed in one or more of the preceding claims, characterised by subjecting said conveyor belt (4) to longitudinal stretching in addition to transverse stretching.

17. A method as claimed in one or more of the preceding claims, characterised by subjecting said base web (2) of pliable material to stretching along the direction of its thickness.

18. A method as claimed in one or more of the preceding claims, characterised in that during the elastic return stage of said previously transversely stretched conveyor belt (4), a different base web (2') of pliable fibrous material is caused to adhere to it, to be subjected to transverse compaction.

19. A method as claimed in one or more of the preceding claims, characterised by subjecting said base web (2) of pliable material, during any stage of its treatment, to additive addition with agents of various types, possibly activatable by administering energy from outside, able to confer specific properties on the final obtained product.

20. A method as claimed in one or more of the preceding claims, characterised by causing a base web (2) of pliable fibrous material coupled to a film of polymer material to adhere to the conveyor belt 4).

21. A method as claimed in one or more of the preceding claims, characterised by subjecting the conveyor belt (4) to several successive localized transverse stretchings, removing the base web (2) of pliable material from said belt (4) before the commencement of its elastic return stage on termination of each of its transverse stretchings, and casing it to again adhere thereto before its next transverse stretching.

22. An apparatus for implementing the method claimed in one of claims 1 to 21 , characterised by comprising:

- an endless conveyor belt (4) of elastic material,

- a station for feeding a base web (2) of pliable fibrous material having a dry content between 3% and 80% to said belt (4),

- means positioned downstream of said feed station, with reference to the advancement direction of said belt (4), for the localized transverse stretching of said belt,

- means for removing said already transversely stretched base web (2) from said belt (4) before its elastic return into the rest configuration.

23. An apparatus as claimed in claim 22, characterised in that said conveyor belt (4) is made of material which is permeable to fluids and/or is able to absorb them and release them.

24. An apparatus as claimed in claim 22, characterised in that said conveyor belt (4) consists of one or more layers of elastic material, possibly fluid permeable and/or spongy.

25. An apparatus as claimed in one or more of the preceding claims, characterised in that said conveyor belt (4) is made with a material having high affinity for cellulose.

26. An apparatus as claimed in one or more of the preceding claims, characterised in that said conveyor belt (4) is made with a rubber latex of low glass transition temperature.

27. An apparatus as claimed in one or more of the preceding claims, characterised in that said conveyor belt (4) is provided on its surface with a plurality of microhooks facilitating the gripping of said base web (2) of pliable material.

28. An apparatus as claimed in one or more of the preceding claims, characterised in that said conveyor belt (4) is of differential thickness in the direction of its length.

29. An apparatus as claimed in one or more of the preceding claims, characterised in that said conveyor belt (4) consists of a holed elastic sleeve mounted on a first roller of substantially rigid material provided with at least one circumferential cavity (10).

30. An apparatus as claimed in claim 29, characterised by comprising a pair of substantially rigid second pusher rollers (12) having their axis parallel to the axis of said first roller (8) and acting in the sense of causing temporary localized introduction of said elastic sleeve (4) into corresponding circumferential cavities (10) provided in said first roller (8).

31. An apparatus as claimed in claim 29, characterised in that said first roller (8) has a convex profile.

32. An apparatus as claimed in one or more of the preceding claims, characterised by being provided with a conveyor belt (4) made of material permeable to fluids and by comprising at least one suction port (24) facing that surface of said conveyor belt (4) which is opposite that to which said base web (2) of pliable fibrous material adheres.