WO2023012843A1

WO2023012843A1 - Machine and process for the production of structured paper

Info

Publication number: WO2023012843A1
Application number: PCT/IT2022/050219
Authority: WO
Inventors: Luca Ghelli; Gaetano PASSANISI; Paolo Raffaelli
Original assignee: Toscotec S.P.A.
Priority date: 2021-08-03
Filing date: 2022-07-27
Publication date: 2023-02-09
Also published as: EP4381127A1; IT202100020858A1

Abstract

Paper making machine comprising a forming zone in which a layer of fibrous material is formed, a zone for forced removal of water from the fibrous web downstream of the forming zone, and a drying zone downstream of the forced water removal, wherein a structured wire (4) configured to support and transport the layer of fibrous material through the forced water removal zone is arranged, and the structured wire (4) has an inlet section of entrance in the forced water removal area and an exit section from the same zone. In the forced water removal zone there is a pressing zone (ZP) for the layer of fibrous material supported by the structured wire (4) in proximity of said entrance section, in the pressing zone (ZP) being arranged and acting pressing means configured to compress the layer of fibrous material supported by the structured wire (4). Downstream of the pressing zone (ZP), with respect to a direction (MD) followed by the fibrous web inside the machine, there are additional devices for forced removal of the water from the fibrous web.

Description

TITLE

Machine and process for the production of structured paper.

DESCRIPTION

The present invention relates to a machine and a process for the production of structured paper.

It is known that, in general, paper machines, for example for the production of tissue paper from which products such as paper napkins, toilet paper, kitchen paper, handkerchiefs and similar products are obtained, use a fibrous mixture containing cellulosic fibers in aqueous suspension and, in general, additives intended to give the finished paper certain chemical-physical characteristics and improving the operating conditions of the production process. The mixture, with a low fiber content with respect to the water, is distributed by means of an headbox on a forming system which that comprises a forming wire possibly associated with a felt or another wire. A layer of fibrous material is therefore generated from the mixture after a progressive removal of the water which determines a higher percentage content of fibers. Subsequently, the layer of fibrous material is transferred to a drying system which for example comprises a Yankee cylinder, around which the cellulosic layer is passed to determine its drying. The web of cellulosic material is then detached from the Yankee to be wound in the form of a reel or subjected to other processes.

Machines that produce structured paper use a structured wire for conveying the fibrous layer, generally known as “ textured” belt ”or“ textured wire", which is forced to pass through a high vacuum area (molding box) which facilitates the formation of a three-dimensional structure in the fibrous layer substantially corresponding to the structure of the conveying wire. The formation of the three-dimensional structure is obtained in correspondence with the passage of the sheet between the a forming wire and a structured wire, in the case of machines with double- wire formation, exploiting the different speed of the two wires (forming wire faster than the structured wire, in order to constrain the fibers to bundle up and penetrate into the cavities of the structured wire). This step is usually called "rush transfer".

In the case of crescent former machines, in which the "rush transfer" is not provided, the wire cloth itself replaces the felt and the fibrous mixture penetrates into the structure of the structured wire in the area of the forming cylinder under the pressure of the external forming wire. Also in this case there is a high vacuum box (molding box) which consolidates the fibers in the cavities of the structured wire.

According to the methods described above, the forcing of the sheet supported by a structured wire through a pressing section involves a limited forcing of the fibers (now already arranged) inside the cavities of the structured wire. The main effect is the creation of a greater compression of the fibers along the reliefs of the structured wire. In this way, the paper has a high mechanical resistance due to the weft made up of the most compacted fibers, while the characteristics of bulk, thickness and absorption capacity are guaranteed by the least compressed parts of the sheet.

The present invention relates, in particular, to the removal of water from the fibrous layer in a paper making machine using a structured wire. Even more particularly, the present invention relates to the steps of removing water from the layer of fibrous material and forming the final structure of the paper ply in machines that use a structured wire and it aims at improving the related processes both in terms of energy efficiency and in terms of quality of the finished product. Another object of the present invention is to provide a system for the production of structured paper alternative to existing systems. Still another object of the present invention is to provide a machine which, in addition to ensuring the aforementioned advantages, is easily configurable to produce structured paper using variously configured devices for removing water from the fibrous layer, thus ensuring production flexibility in li. with the current industrial needs.

This result has been achieved, in accordance with the present invention, by means of a machine and a process having the characteristics indicated in the independent claims. Other features of the present invention are the subject of the dependent claims.

Thanks to the present invention, it is possible to produce structured or textured paper by reducing the overall thermal and electrical power required for this production, thanks to the fact that the pressing area of the fibrous layer is arranged as far upstream as possible along the path followed by the fibrous layer supported by the structured wire, in order to take advantage from the pressing which is in fact operated on the fibrous layer supported by the structured wire when the level of dryness is minimal. Furthermore, a machine according to the present invention can be set up according to a wide range of operating configurations according to the specific needs of use.

These and further advantages and characteristics of the present invention will be better understood by every person skilled in the art thanks to the following description and the attached drawings, provided by way of example but not to be considered in a limiting sense, in which:

• Fig.l represents a schematic side view of a machine for the production of structured paper according to a first embodiment of the present invention;

• Figs. 2-5 are enlarged details of Fig.l, in which some parts are not represented to better highlight others;

• Fig.6 represents a schematic side view of a machine for the production of structured paper according to a second embodiment of the present invention;

• Figs . 7-8 are enlarged details of Fig.6, in which some parts are not represented to better highlight others;

• Fig.9 represents a schematic side view of a machine for the production of structured paper according to a third embodiment of the present invention;

• Fig. 10 represents a schematic side view of a paper production machine structured according to a fourth embodiment of the present invention;

• Fig.11 represents a schematic side view of a machine for the production of paper structured according to a fifth embodiment of the present invention.

The following description provides exemplary embodiments of a machine in accordance with the present invention.

Reduced to its essential structure and with reference to the accompanying exemplary drawings, a machine according to the present invention comprises, in general: a formation zone, in which means are provided for feeding a fibrous suspension, of known composition, and means configured to receive said suspension and transport it along a predetermined path causing a progressive dehydration of the layer of fibrous material thus produced; a zone of forced water removal downstream of the formation zone; a drying zone downstream of the forced water removal zone, in which means are provided for drying the layer of fibrous material formed in the formation zone; a paper web collection zone downstream of the drying zone, in which web collection means are provided which are suitable for collecting the web according to a predefined configuration, for example in the form of reels.

For example, the means for feeding the fibrous suspension comprise a headbox (1), known per se.

With reference to the example shown in Figs. 1-5, the means for forming the layer of fibrous material comprise two wires (2, 3), with a formation wire (2) and a conveyor belt (3) between which the fibrous suspension delivered by the headbox (1) is fed. The forming wire (2) and the conveyor belt (3) can be of the type normally used in continuous machines for the production of paper, so that the belt (3) can also be a wire. In this case, the aqueous suspension is fed from the headbox into an area (A) where the forming wire (2) and the conveyor belt (3) converge. According to a per se known configuration, the conveyor belt (3) is guided on a corresponding cylinder (30) arranged immediately downstream of the headbox (1) and, in a position opposite to the cylinder (30) with respect to the wire (2 ) and the belt (3), there is a duct (200) for the water removed by centrifugation and drained through the wire (2) which water collection area develops along an arc of predetermined width of the path followed by the same wires downstream the headbox (1). The forming wire (2) is on a closed path (P2) defined by a plurality of rollers (21) arranged in predetermined positions along this path and having the function of driving, keeping in guide and tensioning the wire. The movement of the formation wire (2) along the path (P2) is indicated by the arrows “F2” in the drawings. One or more rollers (21) can be motorized or rotated by motor means (not visible in the drawings). The rollers (21) can also be dragged (all or some) by the friction exerted by the wire (2) wrapped around them and moved by other means such as the cylinder (30), which, in turn, can be motorized.

Similarly, the conveyor belt (3) is on a respective closed path (P3) defined by a plurality of rollers (31) arranged in predetermined positions along this path and having the function of driving, keeping in guide and tensioning the belt. (3). The movement of the transport belt (3) along the path (P3) is indicated by the arrows “F3”. One or more guide rollers (31) can be motorized or rotated by motor means (not visible in the drawings). The rollers (31) can also be dragged (all or some) by the friction exerted by the belt (3) wound around them and moved by other means such as the cylinder (30) which, in turn, can be motorized.

Along said paths (P2, P3) spray or needle washing devices can be arranged, oscillating in the direction transversal to the motion of the belts or fixed (D2, D3) acting on the wire (2) and on the belt (3), as well as on the rollers (21 , 31 ), in a manner known per se.

The paths (P2, P3) of the wire (2) and of the belt (3) have a common section downstream of the headbox (1), between said convergence area (A) and a point (AD) at which these paths diverge.

Along the path (P3) of the conveyor belt (3), suction boxes (32) acting on the internal side of the same belt (3), i.e. on the side facing the inside of the path (P3), can be arranged.

The conveyor belt (3) conveys the layer of fibrous material, which is produced downstream of the headbox (1), towards and up to a structured wire (4) arranged downstream with respect to the direction (MD) followed by the fibrous material inside the machine.

The structured fabric (4) is closed in a loop along a respective path (P4) having a branch where an outlet side of the conveyor belt (3) converges. The path of the structured wire (4) is defined by a plurality of corresponding rollers (41) on which the structured wire (4) is guided. In the drawings, the reference “CF” indicates the area of the machine where the conveyor belt (3) and the structured wire (4) converge. In the “CF” zone the layer of fibrous material is transferred from the conveyor belt (3) to the structured wire (4). The latter is constituted, in a per se known way, by a flexible support having an external side on which depressions are formed, consisting for example of pockets of predetermined shape and size, and reliefs that give the cellulosic layer that is transferred thereon a substantially three-dimensional structure, i.e. a non-planar structure. The inner side of the wire (4) is the one facing the inside of the path (P4). The arrows “F4” show the movement of the wire (4) along the path (P4). One or more rollers (41) can be motorized or rotated by motor means (not visible in the drawings). The rollers (41) can also be dragged (all or some) by the friction exerted by the structured wire (4) wrapped around them and moved by other means such as by the friction between the motorized drying cylinder (6) and the pressure element (60) described below.

For example, the structured wire (4) can be of the type described in US8328990B2. In the area (CF) the transfer of the layer of fibrous material from the conveyor belt (3) to the structured wire (4) preferably takes place in "rush transfer" mode, i.e. with a predetermined difference between the speed of the conveyor belt (3), faster, and the speed of the structured wire (4), slower. In this way, the fibers of the paper being formed are forced to fill the cavities of the structured wire, realizing the so-called structuring of the paper, i.e. the passage from a substantially planar structure to a non-planar structure. For example, the speed difference between the conveyor belt

(3) and the structured wire (4) is less than 8% (preferably between 2% and 5%) for low weight paper such as toilet paper, while it is between 7% and 25% (preferably between 10% and 15%) for paper with greater weight such as paper of the towel type. In this phase the dry content of the sheet (percentage by weight of the fibers in the fibrous material transferred to the structured wire 4) is comprised between 10% and 30% and more preferably between 15% and 20%.

In correspondence with said transfer area (CF), a suction box (42) can be arranged which serves to facilitate the transfer from the conveyor belt (3) to the structured wire

(4) and to further force the seating of the fibers in the cavities of the latter (4). The suction box (42) is arranged inside the path (P4) followed by the structured wire (4). Preferably, downstream of the suction box (42), with respect to the direction (F4) of motion of the structured wire (4), a further suction box (43) is arranged to further facilitate the adhesion of the fibrous material in the cavities of the structured wire (4). Along the path of the structured fabric (4) there is a pressing zone (ZP) of the layer of fibrous material supported by the structured wire (4) immediately downstream of the transfer zone (CF), i.e. in the as much as possible initial position of the path followed by the fibrous material supported by the structured wire (4) compatibly with the structural and mechanical constraints imposed by the machine architecture. In this example, in the pressing area (ZP) there is a press consisting of two rollers (Pl, P2) which form a pressure nip in cooperation with a counter roll (C5). Each of said rollers (Pl , P2) can be, for example, a perforated roller equipped with a suction sector or a non-suction roller. The counter-roller (C5) can be a perforated suction roller (preferable solution if combined with a non-suction roller) or a non-suction roller. The structured wire (4) passes between the rollers (Pl, P2) and the counter-roller (C5). The rollers (Pl, P2) are each mounted on a corresponding support (SI, S2) on which an actuator (Al, A2) is connected which allows the support to be pushed towards the counter-roller with the required pressure. The counter-roller (5C) is inside the closed path of a felt (5). On the path followed by the felt (5) are positioned conditioning, tensioning and guiding devices of the type commonly used to condition, tension and guide the felts in machines for producing paper and indicated as a whole with the reference "50" in the attached drawings. In the drawings, the arrows “F5” indicate the movement of the felt (5) along the respective path. The felt (5) comes into contact with the fibrous material, while the rollers (Pl, P2) come into contact with the structured wire (4) from the opposite side, i.e. with the internal side of the latter.

Downstream of the pressing zone (ZP), along the path of the structured fabric (4), a capillary roller (44) is arranged. The capillary roller (44) is a per se known device, for example of the type described in US5701682 to which reference can be made for a more detailed description. In practice, the capillary roller (44) is a roller for the dehydration of fibrous webs, in particular for the dehydration of fibrous webs in paper production machines, consisting of a drum (45) rotating around an axis transverse to the direction (MD) followed by the fibrous material to be dehydrated and provided with a capillary membrane (46) on its surface, with which the layer of fibrous material comes into contact. The capillary membrane is preferably made up of a very fine mesh metal fabric with a structure comparable to that of a perforated surface with an equivalent diameter of the holes comprised between 2 pm and 20 pm, preferably between 4 pm and 8 pm. The capillary membrane can also be a very fine mesh made of plastic materials or made by suitably perforated membranes. The membrane can be made of a single layer or multiple layers with progressively coarser meshes or perforations (in the sense that the equivalent diameter of the permeable areas of the mesh or of the passage holes increases) increasing from the external surface of the membrane towards the internal surface. The layer of fibrous material intended to be transformed into paper, which contains free water between the fibers, being transported by the structured wire (4), comes into contact with the capillary membrane (46) which must be saturated with water to produce a condition of continuity between the water of the membrane and the water of the fibrous material. By capillarity, a certain amount of water is consequently removed from the fibrous material and attracted by the capillary holes (or by the permeable spaces between the meshes, of capillary size) of the membrane (46). A suction is produced inside the drum (45) which keeps active the process of removing water from the fibrous material by capillarity. The extent of the suction in the drum (45) depends on the specific nature of the membrane (46) and, generally, is comprised between -50kPa and -lOkPa, preferably between -25kPa and -20kPa. In practice, said suction is of such a magnitude as to ensure the complete evacuation of the water from the pores of the capillary membrane without however causing suction of air from the outside. In general, this system is all the more efficient the higher the suction produced in the drum (45), as long as it is lower than the maximum value ("break- through pressure") characteristic of the capillary membrane used, since this allows to maintain active the process of capillary removal of the water that passes from the layer of fibrous material to the capillary membrane. The advantage in using this system derives from the fact that the passage of water from the sheet to the drum (45) occurs without air flow. The capillary passages always remain full of water (during contact with the paper) and the vacuum produced inside the drum (45) in the sector in contact with the paper serves only to keep active the movement of water from the sheet towards the inside the drum. The lack of an air flow reduces the energy consumption of the vacuum creation systems, whose task remains solely that of maintaining the vacuum level established in order to support the process of capillary removal of water from the layer of fibrous material.

According to a configuration that is less advantageous from the energetic point of view, the drum (45) can have, inside it and in correspondence with the final part of the contact with the sheet, a suction sector in which a vacuum level higher than the "break- through pressure" is applied: in correspondence with this sector there is also the passage of air through the membrane. This configuration may be preferable when a higher concentrated dehydration capacity in the sector (Zl) is required even if it implies a lower overall energy efficiency.

In accordance with the example shown in Figs.1-5, the structured wire (4) conveys the fibrous material around an inlet roller (47) placed near or in contact with the capillary roller (44). The vacuum sector of the capillary roller (44) begins at the point of tangency of the structured wire (4) with the capillary roller (44). The inlet roller (47) can be pressed against the capillary roller (44) to form a nip useful to facilitate the creation of continuity between the water of which the capillary membrane is saturated and the water contained in the layer of fibrous material conveyed by the structured wire (4). The water continuity between the layer of fibrous material and the capillary membrane facilitates the activation of the dehydration process due to the capillary effect. The fibrous material detaches from the capillary membrane following the path of the structured wire (4), guided by an exit roller (48). The exit roller (48) can also be pressed against the capillary membrane, in this case in order to facilitate the detachment of the forming paper from the membrane and the maintenance of its adhesion to the wire (4). The inlet roller (47) can be replaced by a pressure cylinder that can be a perforated pressure cylinder equipped with a blowing sector in correspondence with the possible area of pressure with the membrane, in order to favor the contact of the layer of fibrous material with the wet membrane. The output roller (48) can be replaced by a pressure cylinder that can be a perforated pressure cylinder equipped with a blowing sector in correspondence with the possible area of pressure with the membrane, in order to facilitate the detachment of the sheet from the membrane (46) and the restoration of its adhesion with the wire (4).

Both rollers (47) and (48) can be mounted on movable supports to adjust, by means of suitable actuators, the pressure they exert on the membrane of the capillary roller. Subsequently, the paper leaving the area where the capillary roller (44) acts, adheres to the surface of a Yankee (6), preferably a steel Yankee, with the aid of a transfer roll (60). The latter is a rubber-coated roller with smooth or ribbed coating or with blind holes or with one or more of these combined characteristics, which is pressed against the surface of the Yankee (6) with a linear pressure comprised between 40 kN /m and 120 kN/m, preferably between 50 kN/m and 80kN/m.

The transfer roll (60) is used to facilitate the adhesion of the paper to the surface of the Yankee (6) which in turn determines a further removal of the water from the paper by evaporation according to a mechanism known per se. The transfer roll (60) exerts just enough pressure on the paper to detach it from the structured wire (4) when adhering to the Yankee (6) in order not to exert a crushing action which otherwise would reduce the bulk of the paper thus produced.

The adhesion of the paper to the Yankee (6) is favored by the organic coating sprayed on the surface of the Yankee immediately upstream of the transfer roller (60) by means of sprayers arranged in a suitable position for this purpose. The coating, the composition of which is known to those skilled in the art, contains adhesive substances suitable for overcoming the resistance of the paper to detachment from the structured wire (4).

Finally, the paper is removed by scraping at the end of the drying process on the Yankee (6).

The drawings also show a hood (61), known per se, arranged on the Yankee (6).

The paper leaving the Yankee can then be subjected to other processes in a station (FP) downstream of the Yankee (6), such as winding.

With reference to the example shown in Figs. 6-8, the formation of the layer of fibrous material takes place between two wires (2, 4), one of which is a structured wire (4). Also in this case, the use of a headbox (1) is envisaged but, unlike the example described above, the structured wire (4) does not receive the layer of fibrous material from an intermediate conveyor belt. Also in this case, the structured wire (4) develops along a closed path which allows the layer of fibrous material to be transported through a succession of stations in which a progressive dehydration of the material itself occurs. In this example, along the path of the structured wire (4) there is a pressing zone (ZP) for pressing the layer of fibrous material supported by the structured wire (4) immediately downstream of the formation zone, i.e. at the initial position of the path followed by the fibrous material supported by the structured wire (4) compatibly with the structural and mechanical constraints imposed by the machine architecture. In this example, in the pressing area (ZP) there is a press consisting of a roller (Pl) which forms a pressure nipple in cooperation with a counter-roller (C5). As in the example described above, the roller (Pl) can be, for example, a perforated roller equipped with a suction sector or a non-suction roller. The counter roller (C5) has already been described. The structured wire (4) passes between the roller (Pl) and the counter-roller (C5). The roller (Pl) is mounted on the support (SI) to which is connected the actuator (Al) that, as in the example described above, allows the support to be pushed towards the counter-roller with the required pressure. The counter-roller (5C) is inside the closed path of a felt (5). Before the pressing area as described above, it is also possible to arrange suction boxes whose main function is to determine the correct quantity and the correct distribution of the water inside the sheet and the structured wire (4), in order to prepare the sheet to the pressing action. Also in this example, on the path followed by the felt (5) are positioned conditioning, tensioning and guiding devices of the type commonly used for conditioning, tensioning and guiding the felts in machines for producing paper and generally indicated with the reference "50" in the drawings. In the drawings, the arrows “F5” shows the movement of the felt (5) along the respective path. The felt (5) comes into contact with the fibrous material, while the roller (Pl) comes into contact with the structured wire (4) from the opposite side, i.e. with the inner side of the latter. The references “P2”, “F2” and “20” have the same meanings described above.

Downstream of the pressing zone (ZP), along the path of the structured fabric (4), there is a capillary roller (44) whose structure and function are identical to those described above. Also in this case, the material leaving the area where the capillary roller (44) acts is conveyed to a Yankee (6) and the paper leaving the Yankee can then be subjected to other processes in a station (FP) downstream of the Yankee (6), such as winding.

With reference to the example shown in Fig. 9, the means for forming the layer of fibrous material comprise two wires (2, 3), with a formation wire (2) and a conveyor wire (3) between which is fed the fibrous suspension dispensed by the headbox (1) as in the example described with reference to Figs. 1-5 but only one pressure roller (Pl) is arranged in the pressing area as in the example described with reference to Fig. 6-8.

With reference to the example shown in Fig. 10, the means for forming the layer of fibrous material comprise two wires (2, 3) with a formation wire (2) and a conveyor wire (3) between which is fed the fibrous suspension dispensed by the headbox (1) and in the pressing area (ZP) a double press (Pl, P2) acting on the structured wire (4) is arranged, as in the example described with reference to Figs. 1-5, but downstream of the pressing area (ZP) there is a TAD hot air drying area (TD) crossed by the structured wire (4) upstream of the Yankee (6).

With reference to the example shown in Fig. 11, the means for forming the layer of fibrous material comprise two wires (2, 3) with a formation wire (2) and a conveyor wire (3) between which is the fibrous suspension dispensed by the headbox (1) and downstream of the pressing area (ZP) there is a TAD hot air drying area (TD) crossed by the structured wire (4) upstream of the Yankee (6) similar to the example shown in Fig. 10, but in the pressing area (ZP) a single press (Pl) acting on the structured wire (4) is arranged as in the example described with reference to Figs 6-8.

However, further configurations for the dehydration mechanisms of the layer of fibrous material downstream of the pressing zone (ZP) are possible. For example, downstream of the pressing zone (ZP), both a capillary roller and a complete or partial hot air TAD section (i.e. with a smaller number of TAD drums) can be arranged upstream of the Yankee. Furthermore, depending on the desired machine configuration, the final drying section may consist of drying systems other than a Yankee.

With reference to all the examples described above, the zone (ZP) for pressing the layer of fibrous material supported by the structured wire (4) is arranged in the position as initial as possible of the path followed by the fibrous material supported by the structured wire (4) compatibly with the structural and mechanical constraints imposed by the machine architecture.

In the examples described above with reference to the attached drawings, a press consisting of one or more rollers (Pl, P2) forming a pressure nip in cooperation with a counter-roller (C5) is arranged in the pressing area (ZP). It is understood, however, that the means used for pressing the fibrous layer in the zone (ZP) of the machine may be of any other type. For example, a shoe press, a blind-holes press combined with a counter-roller, or even a suction press combined with a counter-roller can be used, providing that, when suction is used, this will be preferably operated on the felt (5) side.

In practice, in accordance with the present invention, said pressing zone (ZP) of the layer of fibrous material supported by the structured wire (4) is arranged at an initial part of the path followed by the layer of fibrous material supported by the structured wire (4), upstream of the drying section (which in the examples described above is identified by the Yankee 6) and of other sections of dehydration of the layer of fibrous material that are upstream of the drying section.

In the examples described with reference to figures 1-5, 6-8, 10 and 11, the pressing zone is placed immediately after the transfer of the layer of fibrous material from the conveyor belt (3) to the structured wire (4), while in the other examples described above the pressing zone is placed immediately after the forming zone. This allows the pressing to be exploited as much as possible before other dehydration systems intervene on the layer of fibrous material supported by the structured wire (4). A technical advantage is that use is made of the efficiency of mechanical pressing, the efficiency of which is greater the greater the water content in the sheet. The inventors have in fact observed that using pressure to remove water when the degree of dryness had already been increased by means of other systems such as hot air drying (TAD section) or removal by capillarity would reduce the overall energy efficiency of the system, since this would not allow to obtain the maximum result from the pressing and would use less efficient systems (such as TAD and capillary roller) to remove a portion of water that would be easily removed by pressing.

Inside the pressing zone (ZP) and in the zones following the pressing zone, it is possible to set up auxiliary systems, known per se, such as hot air blowing caps connected to the discharge of the Yankee hood or to turbo blowers enslaved to the vacuum system of the machine (in which the hot exhausted air is possibly enriched with steam to increase the effectiveness of heat transmission to the paper) to further promote drying both before the press (Pl; P2) and before the subsequent drying stations. These systems can be coupled to the pressing elements (Pl; P2) or arranged immediately upstream of them. The purpose of these systems, in fact, is not so much to remove water from the sheet, but to increase the temperature of the water contained in the sheet, consequently reducing its viscosity. In this way, the water removal action exerted by the pressing zone or by the downstream components is improved.

Ultimately, a paper making machine according to the present invention is a machine comprising a forming zone in which a layer of fibrous material is formed, a zone for forced removal of water from the fibrous web downstream of the forming zone , and a drying zone downstream of the forced water removal zone, wherein a structured wire (4) configured to support and transport the layer of fibrous material through the forced water removal zone is arranged, wherein the structured wire (4) has an inlet section of entrance in the forced water removal area and an exit section from the same area, and wherein in the forced water removal area there is a pressing area (ZP) for the layer of fibrous material supported by the structured wire (4) in proximity to said entrance section.

A process for producing paper in accordance with the present invention is a process comprising a formation step in which a layer of fibrous material is formed, a step of forced removal of water from the fibrous web downstream of the forming step, and a drying phase downstream of the forced water removal phase, wherein a structured wire (4) is used to support and transport the layer of fibrous material during the forced water removal phase, and wherein, in the phase of forced removal of water, a step of pressing the layer of fibrous material supported by the structured wire (4) is preliminarily carried out.

In practice, the details of execution can in any case vary in an equivalent way as regards the individual elements described and illustrated, without thereby departing from the solution technique adopted and therefore remaining within the limits of the protection granted by this patent in accordance with the following claims.

Claims

1) Paper making machine comprising a forming zone in which a layer of fibrous material is formed, a zone for forced removal of water from the fibrous web downstream of the forming zone, and a drying zone downstream of the forced water removal, wherein a structured wire (4) configured to support and transport the layer of fibrous material through the forced water removal zone is arranged, and the structured wire (4) has an inlet section of entrance in the forced water removal area and an exit section from the same zone, characterized in that in the forced water removal zone there is a pressing zone (ZP) for the layer of fibrous material supported by the structured wire (4) in proximity of said entrance section, in the pressing zone (ZP) being arranged and acting pressing means configured to compress the layer of fibrous material supported by the structured wire (4), and in that further downstream of the pressing zone (ZP), with respect to a direction (MD) followed by the fibrous web inside the machine, there are additional devices for forced removal of the water from the fibrous web.

2) Machine according to claim 1 characterized in that pressing means are provided in said pressing zone comprising a press consisting of one or more rollers (Pl, P2) which form at least one pressure nip in cooperation with a counter-roller (C5).

3) Machine according to claim 1, characterized in that in said pressing zone, pressing means are arranged selected in a group comprising: a shoe press with counter-roller, a blind-hole press with counter-roller, or a suction press with counter-roller.

4) Machine according to one or more of the preceding claims, wherein the pressing means are associated with suction means suitable for sucking water from the fibrous web subjected to compression, characterized in that said suction means are arranged and acting through a felt (5) with which the fibrous web is in contact.

5) Machine according to claim 1 characterized in that said additional forced water removal devices downstream of the pressing zone (ZP) comprise a capillary roller (44) and/or a hot air TAD section (TD). 6) Machine according to claim 1 characterized in that in said drying zone there is a Yankee (6).

7) Process for the production of paper comprising a formation phase in which a layer of fibrous material is formed, a phase of forced removal of water from the fibrous web downstream of the formation phase, and a drying phase downstream of the phase of forced water removal, in which a structured wire (4) is used to support and transport the layer of fibrous material during the forced water removal phase, characterized in that in the forced water removal phase it is preliminarily operated a step of pressing the layer of fibrous material supported by the structured wire (4) and in that, after said pressing phase, the fibrous web is subjected to at least one further step of forced removal of water.

8) Process according to claim 7 characterized in that said pressing phase is operated by pressing means comprising one or more rollers (Pl, P2) which form at least one pressure nip in cooperation with a counter-roller (C5).

9) Process according to claim 7 characterized in that said pressing phase is operated by pressing means selected in a group comprising: a shoe press with counter-roller, a blind-hole press with counter-roller, or a suction press with counter-roller.

10) Process according to claim 7 characterized in that said at least one additional phase of forced water removal is operated by a capillary roller (44) and/or a hot air TAD section (TD).

11) Process according to claim 7 characterized in that said drying phase is operated by a Yankee (6).