EP2681042A1

EP2681042A1 - Method for forming a web of transversely compacted fibrous material with voluminosity and extensibility increase, and apparatus for implementing the method

Info

Publication number: EP2681042A1
Application number: EP12710546.8A
Authority: EP
Inventors: Giorgio Trani; Marion Sterner
Original assignee: Individual
Current assignee: TRANI, GIORGIO
Priority date: 2011-03-04
Filing date: 2012-02-27
Publication date: 2014-01-08
Also published as: ITVE20110013A1; WO2013050810A1

Abstract

A method for forming webs of transversely compacted fibrous material with voluminosity and extensibility increase, starting from a base web (30) of pliable fibrous material having a water content between 5 and 95%, placed on an endless elastic conveyor belt (2) made to advance along a support structure (4) and subjected to at least one localized temporary transverse extension, characterised by causing a substantially flat section of said belt to extend by passing it in correspondence with at least one pair of extender elements (26) which are fixed with respect to said support structure and act simultaneously and in opposing directions in proximity to the longitudinal edges of said belt (2) in a direction parallel to the surface of said substantially flat section, then depositing said base web (30) of fibrous material on said section just as it starts its elastic return to its initial configuration, then subjecting it during this step to partial drying and moisture removal.

Description

METHOD FOR FORMING A WEB OF TRANSVERSELY COMPACTED FIBROUS MATERIAL WITH VOLUMINOSITY AND EXTENSIBILITY INCREASE, AND APPARATUS FOR IMPLEMENTING THE METHOD

The present invention relates to a method for forming a web of transversely compacted fibrous material with voluminosity and extensibility increase, and an apparatus for implementing the method.

Methods for producing fibrous webs, and particularly paper webs, are known. They consist generally 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 operations aimed at finally obtaining a paper web or more generally a web of fibrous material to be then wound into rolls for subsequent use.

The production of fibrous webs, in particular paper webs of the most varied types, involves a high cost in terms of energy consumption (drying) and requires the use of many types of chemical products as additives to confer particular properties on the various paper types or to facilitate the process.

With regard to energy consumption for drying, it is known that once the web is about 30% dry, it is difficult to remove the water remaining in the web centre, as two drier outer layers have already formed through which the water has to pass.

With regard to the chemical product cost and consumption, various additives are added to the mix during production (for example retention agents, mineral fillers, resins for moisture resistance, etc.) or to the surface (for example adhesives, glaze, etc.).

These products are either added directly to the initial fibre suspension

(to the cellulose pulp in the case of paper) or are applied to the surface of the fibrous web under formation by methods known to the expert of the art. In the first case a part of the additives is lost during the first step of pouring the fibres onto the flat table, creating effluent recovery and disposal problems and the problem of obtaining the correct required additive product concentration with respect to the fibres.

In the second case it becomes difficult for the additives to penetrate to the web centre, and in any event there is greater disuniformity along the thickness.

The subsequent use to which a paper roll is subjected can include printing on the paper web or its transformation via successive passages through paper working machines.

However, both such operations pose 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 the 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. of the 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 higher 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 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.

Methods and apparatus are already known for forming sheets and webs of paper material compacted transversely, i.e. in a direction perpendicular to that which will be defined as the "machine direction". These are based on the known principle of causing a base web of pliable fibrous material, having a high moisture content, to adhere to an elastic conveyor belt, temporarily and locally prestretched transversely, i.e. perpendicular to the advancement direction of said conveyor belt, such that when this returns to its original configuration, the base web of pliable fibrous material, which is to form the fibrous material product web, is compacted transversely such that on the one hand it enables its thickness to be increased and on the other hand enables it to present extensibility characteristics.

This known principle has suggested various practical applications therefor and various apparatus able to implement them.

For example, international patent application WO 2010/015614 describes a method by which the transverse prestretch of the elastic conveyor belt is achieved by using a pair of rollers to urge the belt between a pair of circumferential grooves provided in them. In this manner the interference between the pair of thrust rollers and the transmission roller causes transverse stretching of the elastic belt, this stretch being localized within the interference zone alone and is temporary, in that as soon as the elastic belt abandons this zone it is no longer stressed and rapidly re-assumes its original shape, to entrain with it the base web of paper material positioned on it.

The present invention is based on this known principle and improves it in the sense of simplifying its practical implementation and enabling webs of fibrous material in general, and in particular of paper material, to be obtained with a higher degree of transverse compaction, with the facility to modify it on the basis of requirements and to integrate it with further special characteristics linked to specific uses of the web.

FR 1388160 describes a method comprising the steps of continuously feeding an aqueous fibre suspension onto a continuously moving support to form a web of fibres thereon, reducing the water content of the web, and transversely stretching the support.

An object of the invention is therefore to obtain transversely compacted, stabilized 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 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.

Another object of the invention is to provide a method for modifying the morphology of a fibrous web being processed by facilitating its drying and improving the effectiveness of any additives added to said web. Another object of the invention is to reduce the energy consumption in the drying process of said web.

Another object of the invention is to optimize the consumption of chemical products for modifying the characteristics of said web, including with products not traditionally used in the paper industry.

According to the invention the method of forming webs of transversely compacted fibrous material with voluminosity and extensibility increase is as described in claim 1.

Again according to the invention, the apparatus for implementing the method is as described in claim 18.

The present invention is further clarified hereinafter in the form of some preferred embodiments with reference to the accompanying drawings, in which:

Figure 1 is a schematic perspective view showing the principle on which the method of the invention is based,

Figure 2 is a vertical cross-section through an elastic conveyor belt associated with two extenders shown in the non-active condition, Figure 3 shows it in the same view as Figure 2 but with the two extenders in the active condition,

Figure 4 is a perspective view showing a conveyor belt portion subjected to two successive localized extension steps,

Figure 5 is a perspective view showing a conveyor belt portion also subjected to localized longitudinal stretching in a different embodiment, and

Figure 6 is a perspective view showing a conveyor belt portion subjected to transverse stretching with controlled return. As can be seen from the figures, the method of the invention is applied to an elastic conveyor belt 2 supported by a support structure indicated overall by 4 and consisting of a plurality of inverted U elements 6, with a crosspiece 8 and with a pair of legs 10 provided, at their lower end, with a base 12 for support on and/or fixing to the floor.

The elastic belt 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.

A further bar 14 is fixed lowerly to the crosspiece 8 of each U element

6 to support at each end a guide rail 16 for a plurality of carriages 28 constrained at predetermined distances to the two longitudinal edges of the belt 2 and also supports, in proximity to each end, a roller 18 of vertical axis.

Also fixed to said crosspiece 8 there is a pneumatic cylinder 20 internally housing two pistons with their piston rods 22 emerging from both its ends.

Each of these piston rods 22 supports at its outer end a second guide rail 24 for the said carriages 28 which are constrained to the longitudinal edges of the belt 2, and also supports, in proximity to said end, a roller 26 of vertical axis.

As the rollers 18, 26 of vertical axis are positioned at a distance from the crosspiece 8 of the various U elements 6 which is greater than the distance of the various tubular guide pieces 16, 24, the elastic belt 2 is retained with the carriages 28, provided on its longitudinal edges, by said pieces 16, 24, although being able to slide relative to them, and is maintained bent at said rollers 18, 16 such as to assume a C cross-section, with the opening facing downwards for the upper part and upwards for the lower part, as visible in Figures 2 and 3.

The function of these cylinders 20 is to position the rollers 26 of vertical axis at the desired distance apart, linked to the extent of localized transverse stretch to be imparted to the elastic belt 2. Obviously when the belt 2 during its advancement has overcome the two rollers 26, its natural elasticity returns it to its original configuration.

According to the method of the invention, essentially a continuous base web 30 of pliable fibrous material having a water content between 5 and 95% is deposited on that section of the elastic belt 2 which, after being stretched transversely by passage in correspondence with the pair of rollers 26, begins its return to its original configuration. In practice the belt 2 can totally or partly form the so-called flat table, which in a traditional paper making machine receives the mix originating from the feed box. This fibrous material can consist of cellulose fibres if a paper web is to be obtained, or of cellulose fibres and polymer fibres, or polymer fibres alone, if a non-woven web is to be obtained.

After the base web has been deposited and the belt 2 continues to advance, dragged by suitable drive members, which do not form part of the invention and are not shown in the drawings, the elastic return of the belt into its original configuration entrains with it the base web of fibrous material 30, which in this manner is subjected to transverse compacting and, by virtue of the presence of a roller 32 of horizontal axis in that section immediately downstream of the zone of return to the original configuration, is kept adhering to the elastic belt 2, and at the same time is subjected to partial drying. The base web 30 of fibrous material can undergo in the longitudinal direction an action opposite to that undergone transversely, due to the simultaneous longitudinal re-extension of the released elastic belt 2, if this has a normal Poisson deformation coefficient (for example around 0.5). However, simultaneous longitudinal deformation of the belt 2 can be prevented if this is filled with longitudinally disposed reinforcement fibres (for example Kevlar, carbon), or if it is formed with a material having a Poisson coefficient ideally close to zero.

The elastic conveyor belt 2 can consist of one or more layers of elastomer, possibly expanded, or of single or multiple fabric of elastic yarns or even non-elastic yarns if woven with an elastic weave, or can consist of a layer composed of all of the preceding.

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

The elastic belt 2 is preferably made of a liquid permeable material which, in that section in which it reassumes its original configuration, is provided in its lower surface with a suction port 34 which extends transversely for about the entire width of the elastic belt 2 and has the double function of maintaining the base web 30 of fibrous material adhering to said belt during transverse compaction while at the same time removing a part of the moisture contained therein.

To improve adhesion between the fibrous base web 30 and the surface of the elastic belt 2, said surface can be functionalized such as to present high affinity for cellulose. For example the material forming the elastic belt 2 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 elastic belt 2.

The elastic belt 2 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 elastic belt 2 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 fibrous base web 30 of pliable material to the elastic belt 2, said base web can be pressed against said conveyor belt with 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 fibrous base web 30 to the elastic belt 2.

The invention also provides for the use of fixed or rotatable mechanical pressing elements provided with low friction surfaces, or with felts, or of other endless belts, possibly elastic. In particular, a single felt can be used, maintaining the base web 30 adhering to the conveyor belt 2 during transverse compaction, or two felts can be used, between which the base web 30 is interposed, withdrawn from the conveyor belt 2 on termination of the or of each transverse compaction step. In particular, suitable auxiliary conveyor belts can perform the function of felts for partially removing water from the base web 30 between one transverse stretching step and the next.

In all those cases in which the fibrous base web 30 is interposed between two surfaces, for example the conveyor belt 2 and a felt cooperating with it, or two felts, said surfaces can be driven at the same velocity, or at different velocities, such as to cause a voluminosity increase in the fibrous base web 30 interposed between them.

Both the conveyor belt 2 and the felt or endless belt can also have their surface functionalised such as to present a high affinity for cellulose. In this respect, when the pliable fibrous base web 30 is detached from the upper and/or lower belt, these exert on the base web, which is still very moist and pliable, a traction along the direction of its thickness (direction Z), so increasing its thickness and hence its voluminosity. The affinity of the two surfaces for cellulose can be calibrated differentially to cause preferential detachment from one of the two surfaces and obtain a calibrated traction along the direction Z. Detachment of the base web 30 can also be facilitated by doctor blades, by air blades, or by air blown through the lower and upper belts at the detachment point.

Depending on requirements, the web which leaves this transverse compaction step can be fed to the subsequent stages of a traditional process for obtaining a web of fibrous paper material, or can be subjected to further transverse compaction steps, by a repeat of the aforedescribed method, as best seen in Figure 4. This shows an elastic belt 2 passing through two transverse stretching stations. Each station comprises a transversely extended section of the elastic belt 2, a zone in which the base web 30 of fibrous material falls onto the section in which the belt 2, which has just been extended, begins to return to its original configuration, a squeezing zone in which, immediately downstream of said zone of return to the original configuration, a transverse roller 32 is provided, the function of which is to maintain adhering to the belt 2 the base web 30 of fibrous material which has just been subjected to transverse compaction, and to at least partially remove the moisture contained therein, and a subsequent zone for detaching the already partly transversely compacted web of fibrous material under formation. In this respect, after each transverse compaction step the base web 30 of fibrous material must be detached from the belt 2, so as not to nullify the already achieved transverse compaction when the belt is subjected to the next transverse stretching step. This can be advantageously achieved by causing the base web 30 of fibrous material to advance between two successive compaction steps on a conveyor belt 36 travelling parallel above the belt 2.

It is apparent that if the base web of fibrous material is subjected to several transverse compaction steps, in the end it will be transversely compacted to an extent corresponding to the sum of the individual compaction treatments and hence present a degree of transverse extensibility much higher than that obtainable with a single passage.

The base web 30 of fibrous material can also be subjected before or after any compaction step to wetting or addition of suitable substances for modifying the base web characteristics. This enables the method to be applied to already formed paper webs. Again according to the invention, instead of single extender rollers 26, pairs of extender rollers 26', 26" can be provided, of which that 26" positioned downstream is operated at greater peripheral velocity than that 26' positioned upstream. This can be obtained by using roller pairs 26', 26" of equal diameter, operated at different angular velocities (see Figure 4) or by using roller pairs 26', 26" of different diameter, operated at the same angular velocity (see Figure 5). Independently of the particular embodiment used, in both cases the belt 2 is subjected in that section between the two rollers 26', 26" of each pair to longitudinal stretching, which with the elastic return causes longitudinal compaction of the base web 30 of fibrous material. It follows that this base web 30 on the one hand undergoes a thickness increase, and on the other hand acquires a capacity to extend both transversely and longitudinally.

Independently of whether the elastic belt 2 presents one or two sections in which it is subjected to transverse stretching and possibly also to longitudinal stretching, the base web 30 of fibrous material can be also advantageously subjected in any step of the process, either inside or outside the machine, to different treatments with liquid or powder substances or with atmospheric plasmas. In particular a re-wetting treatment can be provided by spraying or by passage through a bath, the treatment liquid consisting of water, a dye substance or an impermeabilizing or other substance, according to the properties which the paper material obtained is required to present.

As these treatments can involve a certain length of the base web of fibrous material, that section of the conveyor belt 2 subjected to stretching can have a corresponding length, obtainable by several successive pairs of rollers 26. As the width of the conveyor belt 2 can be large, it can be supported on transverse support rollers. These can have a smooth outer surface or be provided with helical ribs winding in opposite directions in the two halves of the rollers, to facilitate and make uniform the transverse stretching of the belt, and also possible longitudinal stretching by being rotated at greater peripheral speed than the speed of advancement of the belt.

In addition to this control of the transverse stretching of the elastic belt 2, the invention also provides for controlling its elastic return and in particular for slowing it down according to requirements. This can in particular be achieved by providing the, or each, transverse stretching station for the belt 2 with not a single pair of rollers 26 spaced apart by a distance corresponding to the extent of transverse stretch to be imparted, but with several pairs of rollers spaced apart by a decreasing distance conforming to the elastic pattern desired. Figure 6 schematically shows this principle.

While for the entire upper and lower straight sections of the endless elastic belt 2 its end longitudinal bands are bent with respect to the central band, which in the upper section receives and supports the base web 30 of fibrous material to be treated, this would not be possible in correspondence with the end return rollers for said elastic belt, given the different radius of curvature of the central band and of the edges of the belt. However in order nevertheless to maintain said belt 2 taut, a different pattern of the guide rails 16, 24 is provided at said return rollers, in order to make up this difference in radius of curvature. In particular, at said return rollers, the guide rails 16, 26 extend externally to the vertical plane to which they pertain in the straight sections of the belt 2. The restraint between the longitudinal edges of the belt 2 and the support structure 4 can also be obtained by thickening the edges of the belt 2 and by longitudinally open tubular guide pieces rigid with the structure 4 instead of by carriages constrained to the belt edges and by guide rails 16, 24 connected to the structure 4.

These guide pieces can be advantageously provided with rolling bearings or with ball bearings or the like, to reduce the inevitable friction, which can be considerable in the case of conveyor belts 2 of considerable length.

Independently of the various forms of localized transverse stretching modalities, under normal conditions the two sections, upper and lower, of the elastic belt 2 extend horizontally overall; however according to the invention they can also extend inclined, preferably upwards, in order to facilitate dispersal of the water left by the fibrous base web 30 during treatment.

Moreover the fact that the fibrous material web under formation can be disposed on a horizontal conveyor belt virtually of any length enables action to be taken along it to carry out any treatment on the web (drying, impregnation, coupling, etc.). In this respect the fibrous material web 30 can be subjected before, during or after any mechanical deformation step, to wetting or to addition of suitable substances to modify the web characteristics. This enables the method to be applied to already formed paper webs, and to optimize the additive addition efficiency, hence limiting liquid effluent production. Incompatibility between he additives in solution or suspension (for example because of pH incompatibility or because they would form a gel or 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 based 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 outside the paper machine). In particular, the additives can be encapsulated in miocrocapsules 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:

- crystalline microcellulose,

- nanocellulose,

- 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 CaC03 crystals),

- polyalkyleneglycols

· barrier towards oxygen and/or water vapour, with additives such as:

- proteins (glutins, milk serum derivatives)

- vinylidene chloride copolymers in accordance with CA 711208,

- nanocellulose

• opacity, with additives such as:

- mineral fillers generated in situ by precipitation,

- kaolin

- mica

• antigrease, with additives such as:

- starch

- nanocellulose

- alginates - carboxy methyl cellulose

- polyvinylalcohol

sizing, with additives such as:

- starch

dust control, with additives such as:

- starch

- nanocellulose

- carboxymethylcellulose

- polyvinylalcohol

water repellence (including for capacitor insulating papers easily soakable in dielectric oils or resins), with additives such as:

- waxes, including natural waxes, preferably in dispersion

- colophony

hydrophilicity, with additives such as:

- polyalkyleneglycols

ink adhesion, with additives such as:

- titanium acetyl acetonate

- silanes

- gum Arabic

- dextrins

- alum

antiadherence, with additives such as:

- silicone resins

adhesive curing rate, particularly polyurethane based, with additives such as:

- zinc stearate - caprolactam

- N-acylureas

- tertiary amines

• colour, with additives such as:

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

- pigments based on optical interference generated by nano layers of polyelectrolytes, such as nano cellulose and polyethylene imine

- colorants, including thermal, electro or photo chromic

· voluminosity, with additives such as:

- microcapsules containing expanding agents activatable by heating

- nanocellulose based foams

- chemical expanding agents

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

• possible heating by induction, with additives such as:

- preferably biodegradable susceptors 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 or wet) and, in particular, by controlling the degree of additive penetration, to increase the tensile strength in papers formed from rigid tubular fibres while maintaining good opacity characteristics and tearing resistance, with additives such as:

- starch

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

- melamine resins cross-linkable by heat

- polyamide resins modified with epichlorohydrin

• oxygen scavengers, with additives such as:

- encapsulated substances to function at the required moment, such as ferrous salts

• electrical conductivity, with additives such as:

- carbon fibres

• antibacterials, with additives such as:

- carbon silver salts

- silver nanoparticles

- titanium dioxide

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

- chitosan

- bacteriocins

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

From the aforegoing it is apparent that the method of the invention is particularly advantageous, in that it is simple to implement, it does not require complex and costly apparatus, it maintains a high fibrous web production rate and is quickly adapted to operational requirements, and in particular to the degree of extensibility required for the paper. In particular it enables both the number of transverse and possibly longitudinal compaction stations to be varied vary quickly and easily, and the extent of compaction obtainable in each station. Moreover the possibility of having the forming fibrous web disposed on a horizontal conveyor belt practically of any length enables action to be taken along it to carry out any treatment on the web (drying, impregnation, coupling, etc.).

The machine implementing the method of the invention can be advantageously combined with traditional crinkling and tampering machines to obtain fibrous webs which can be stretched longitudinally utilizing the properties of the expandable folds, and can also be stretched transversely to utilize the extensibility of the fibrous material in that direction.

Claims

C L A I M S

1. A method for forming webs of transversely compacted fibrous material with voluminosity and extensibility increase, starting from a base web (30) of pliable fibrous material having a water content between 5 and 95%, placed on an endless elastic conveyor belt (2) made to advance along a support structure (4) and subjected to at least one localized temporary transverse extension, characterised by causing a substantially flat section of said belt to extend by passing it in correspondence with at least one pair of extender elements (26) which are fixed with respect to said support structure and act simultaneously and in opposing directions in proximity to the longitudinal edges of said belt (2) in a direction parallel to the surface of said substantially flat section, then depositing said base web (30) of fibrous material on said section just as it starts its elastic return to its initial configuration, then subjecting it during this step to partial drying and moisture removal.

2. A method as claimed in claim 1 , characterised by using extender elements (26) provided at their outer end with at least one rolling element cooperating with the surface of the elastic belt, with which it comes into contact.

3. A method as claimed in one or more of the preceding claims, characterised by causing said extender elements (26) to act on lateral bands of said belt (2) which are bent relative to the surface on which said base web (30) of pliable fibrous material is placed.

4. A method as claimed in one or more of the preceding claims, characterised by securing, by means of carriages, both edges of the elastic belt (2) to guide rails (16, 24) rigid with the belt support structure (4).

5. A method as claimed in one or more of the preceding claims, characterised by using, as the endless elastic conveyor belt (2), all or part of the belt of the flat table of a paper machine.

6. A method as claimed in one or more of the preceding claims, characterised in that during the elastic return of the endless conveyor belt (2) the base web (30) of pliable fibrous material is maintained adhering to it.

7. A method as claimed in claim 6, characterised by maintaining the base web (30) of pliable fibrous material adhering to the endless conveyor belt (2) by using at least one roller (32) of transverse axis parallel to the plane of said belt.

8. A method as claimed in one or more of the preceding claims, characterised by maintaining the base web of pliable fibrous material adhering to the endless conveyor belt (2) by using an endless belt.

9. A method as claimed in one or more of the preceding claims, characterised by using a fluid-permeable elastic conveyor belt (2).

10. A method as claimed in one or more of the preceding claims, characterised by maintaining the base web (30) of pliable fibrous material adhering to the endless conveyor belt (2) by using a vacuum source.

11. A method as claimed in one or more of the preceding claims, characterised by providing, in sequence, several transverse stretchings of said endless conveyor belt (2) and several corresponding elastic returns, said base web (30) of pliable fibrous material being removed from said elastic belt in those sections between the termination of an elastic return consequent on a stretching and the commencement of the elastic return consequent on the next stretching.

12. A method as claimed in one or more of the preceding claims, characterised in that at least one wetting step is associated with at least one step of transverse compaction of said base web of pliable fibrous material.

13. A method as claimed in one or more of the preceding claims, characterised in that in the same step in which the endless conveyor belt is subjected to at least one transverse stretching, it is also subjected to at least one longitudinal stretching, said base web of pliable fibrous material being deposited on said endless conveyor belt after its longitudinal elastic return has initiated.

14. A method as claimed in claim 13, characterised by carrying out the transverse stretching of the endless conveyor belt (2) with extender elements, each comprising on each side of said belt a pair of rollers (26', 26"), of which that positioned upstream has a peripheral velocity substantially equal to the advancement velocity of said elastic belt, whereas that positioned downstream has a greater peripheral velocity.

15. A method as claimed in one or more of the preceding claims, characterised by subjecting the elastic conveyor belt (2) to at least one transverse stretching with several pairs of rollers spaced apart by a distance which decreases in the belt advancement direction.

16. A method as claimed in one or more of the preceding claims, characterised in that, in addition to subjecting the base web of pliable fibrous material to transverse compaction and possibly also to longitudinal compaction, it is subjected to a treatment of impregnation with a substance suitable for providing the obtained fibrous web with corresponding specific properties.

17. A method as claimed in one or more of the preceding claims, characterised in that the endless conveyor belt is rested on transverse rollers provided in the two halves with opposing helical ribs acting in the sense of making uniform the belt transverse stretch.

18. An apparatus for implementing the method claimed in one or more of claims from 1 to 17, characterised by comprising an endless conveyor belt (2) mounted on a support structure (4) and associated with drive means and with at least one pair of extender elements (26) mounted fixed with respect to said support structure (4) and acting simultaneously in a direction substantially parallel to the surface of the belt perpendicular to its advancement direction, and in the opposite direction to cause localized temporary stretching of the belt, the section of contact between said base web (30) of pliable fibrous material and said conveyor belt (2) initiating immediately downstream of the commencement of the elastic return stage of this latter, and being associated with means for at least partially removing moisture.

19. An apparatus as claimed in claim 18, characterised in that the longitudinal edges of said belt (2) are slidingly constrained to said structure (4).

20. An apparatus as claimed in one or more of the preceding claims, characterised in that said extender elements (26) consist of rolling elements cooperating with the surface of the elastic belt, with which they are in contact.

21. An apparatus as claimed in one or more of the preceding claims, characterised in that said extender elements (26) are positioned in correspondence with longitudinal folding lines of said elastic belt which separate a central band thereof, on which said base web (30) of fibrous material is positioned, from lateral bands slidingly constrained to said support structure.

22. An apparatus as claimed in one or more of the preceding claims, characterised in that carriages (28), slidable along guide rails (24) rigid with said support structure (4), are associated with the free edge of said lateral bands of the conveyor belt (2).

23. An apparatus as claimed in one or more of the preceding claims, characterised in that each extender element acting on a side of said elastic belt comprises a pair of rollers (26', 26"), of which that positioned upstream has a peripheral velocity substantially equal to the advancement velocity of said elastic conveyor belt (2), whereas that positioned downstream has a greater peripheral velocity.

24. An apparatus as claimed in one or more of the preceding claims, characterised in that each extender element acting on a side of said elastic belt comprises a plurality of rollers (26), each of which lies at a distance from the corresponding roller acting on the opposite side of the belt which decreases in the belt advancement direction.

25. An apparatus as claimed in one or more of the preceding claims, characterised in that transverse rollers (32) are applied to said support structure (4) to support said elastic belt (2).

26. An apparatus as claimed in one or more of the preceding claims, characterised in that each of said transverse rollers (32) supporting said elastic belt (2) is provided in the two halves with opposing helical ribs acting in the sense of making the belt transverse stretch uniform.

27. An apparatus as claimed in one or more of the preceding claims, characterised in that said elastic belt (2) is formed of material permeable to fluids in general.

28. An apparatus as claimed in one or more of the preceding claims, characterised in that the elastic conveyor belt (2) consists of all or part of the belt of the flat table of a paper machine.

29. An apparatus as claimed in one or more of the preceding claims, characterised in that said support structure (4) comprises several pairs of extender elements (26) acting on successive sections of said elastic belt (2) and also comprises means for removing said base web of fibrous material in each section between the termination of an elastic return consequent on a stretching and the commencement of the elastic return consequent on the next stretching.

30. An apparatus as claimed in one or more of the preceding claims, characterised by comprising wetting and/or impregnation means for said base web of fibrous material.