Method and apparatus for producing transversally extensible tapes of fibrous material.

Abstract

Method for producing a transversely extensible fibrous material tape characterized in that: - a belt-like support (2,2'), which is elastically extensible at least in the transverse direction, is advanced in the longitudinal direction and is provided with at least one longitudinal band of its surface by a plurality of longitudinally protruding ribs (12,12') parallel to said longitudinal direction and substantially equidistant from one another, is subjected to localized transverse stretching, - a layer (14) of moldable fibrous material with a dry content ranging between 18% and 70%, preferably between 40% and 60%, is deposited on the surface of the prestretched section of said belt-like support (2,2') affected by said protruding longitudinal ribs (12,12'), - said belt-like support (2,2') is released to allow it to return elastically to its original configuration and to drag with it said layer (14) of moldable fibrous material, which is thus compacted transversely, - the transversely compacted fibrous material layer (16) is then removed from said belt-like support (2,2').

Description

[0001] METHOD AND APPARATUS FOR PRODUCING TRANSVERSALLY EXTENSIBLE TAPES OF FIBROUS MATERIAL.

[0002] The present invention relates to a method and an apparatus for producing transversally extensible tapes of fibrous material, in particular tapes of paper.

[0003] Methods and apparatuses are known for producing paper tapes extensible in the transverse direction. These involve placing a paper tape having a dry content generally ranging from 18% to 70% on a support consisting of a continuous elastic belt or of an elastic sleeve previously stretched locally in the transverse direction, so that after this support is released and elastically returns to its original width, it drags the paper tape along with it and compacts it transversely. Once the transversally compacted paper tape has been removed from the elastic support that compacted it, it can be conveyed to other processing steps, such as drying or other, but at the end it exhibits a transverse extensibility whose extent is linked to the extent of the compaction to which it was previously subjected.

[0004] Know methods for producing paper tapes extensible in the transversal direction are disclosed in WO2013 / 050810 and in W02010 / 015614.

[0005] The traditional elastic supports on which the paper tape to be compacted is placed can consist of a fluid-permeable continuous belt stretched between return rollers or of a tubular sleeve of liquid-permeable and transversally elastic fabric, to which the paper tape is preferably adhered by suction; or they can consist of a continuous belt or a tubular sleeve of a liquid-impermeable and transversally elastic material, on which the paper tape is placed and made to adhere thanks to its moisture content or under controlled pressure.

[0006] A drawback of these traditional techniques lies in the fact that the transverse shrinking of paper tapes of various types occurs in a disordered manner with the formation of microfolds distributed more irregularly as the basis weight and dry content of the paper increase. The reason for this irregularity is linked to the inevitably non- uniform fiber density of different zones of the paper tape, and therefore to the equally non-uniform compaction of the fibers in the various zones, and to the different extensibility of the zones themselves, which is related to the transverse compaction to which they were previously subjected. In turn, this non-uniform compaction leads to mechanical performances of the tape that are not uniform across its entire width, and in particular to different elongations in different zones, breaking points, etc., in addition to difficult or even impossible printability.

[0007] Another drawback lies in the fact that, in the case where the paper tape to be transversally compacted must be kept adhered to a permeable support during its transverse compaction by suction, this suction is difficult to regulate, whereas in the case it must be kept adhered to a non-permeable support, it is necessary to process a paper tape with a low dry content and with possible additions of water or steam, which make the tape itself very fragile and difficult to handle.

[0008] Due to these drawbacks, currently existing methods have proven to be unsatisfactory and, in practice, have been little used.

[0009] The purpose of the invention is to propose a method and an apparatus for producing transversally extensible tapes of fibrous material capable of overcoming all these drawbacks existing in the prior art.

[0010] In particular, a purpose of the invention is to propose a method for producing tapes of fibrous material, in particular paper, transversally extensible and exhibiting a high degree of uniformity in this transversal extensibility.

[0011] Another purpose of the invention is to propose a method that can be implemented in a simple and cost-effective manner.

[0012] Another purpose of the invention is to propose a method that can be implemented with limited modifications to current methods.

[0013] Another purpose of the invention is to propose a method that guarantees optimal and consistent results over time.

[0014] Another purpose of the invention is to propose a method that allows the production of fibrous material tapes with different transversal extensibility characteristics from tape to tape depending on the requirements imposed by their use, but homogeneous across the entire width of the tape.

[0015] Another purpose of the invention is to propose a method that allows the production of fibrous material tapes with excellent printability characteristics.

[0016] Another purpose of the invention is to propose a method suitable for implementation both with a flat paper machine and off-line.

[0017] Another purpose of the invention is to propose an apparatus for implementing the method.

[0018] All these purposes, and others that will become apparent from the following description, can be achieved according to the invention with a method for producing transversally extensible tapes of fibrous material as defined in claim 1 , and with an apparatus for implementing the method as defined in claim 9.

[0019] The present invention is further clarified below in some of its preferred embodiments of practical implementation, provided by way of purely illustrative and non-limiting example with reference to the attached drawing sheets, in which: figure 1 partially shows in the partial and schematic section l-l of fig. 2 an apparatus for implementing the method according to the invention in a first embodiment, figure 2 shows it in vertical section I l-l I of fig. 1 , figure 3 shows it in perspective view and partially in transparency, figure 4 shows it in the same view as fig. 1 , in a different embodiment, figure 5 shows it in the same view as fig. 2, in this second embodiment, figure 6 shows it in the same view as fig. 3, in this second embodiment, and figure 7 shows it schematically in perspective view in a third embodiment.

[0020] In a first embodiment of the method according to the invention, the apparatus implementing it is illustrated in figures 1-3. It includes an elastic belt 2, advantageously made, for example, of a cylindrical sleeve, which has a certain elasticity in the axial direction and is constrained at the edges to two rigid discs 4. These discs are rotationally fixed to a shaft 6 and are simultaneously articulated to it so that, as it rotates, they always maintain the same orientation, causing the edge portions, which in fig. 1 are located at the top, to be spaced further apart, and the edge portions, which in the same fig. 1 are located at the bottom, to be brought closer together. This can be achieved, for example, by means of fixed rollers with a vertical axis pressing externally on the discs 4 to maintain them with a constant inclination relative to the axis of the shaft 6, which are not shown in the drawings for simplicity of representation.

[0021] In this way, as the shaft 6 and the two discs 4, rigidly fixed to it, rotate, the sleeve 2 is cyclically subjected to a transverse stretching on a section parallel to the shaft 6 and a transverse elastic contraction on the diametrically opposite section.

[0022] The sleeve 2 can be advantageously wound around a perforated rigid cylinder 8, which is also rotationally fixed to the shaft 6 and houses within it a fixed suction chamber 10, connected to a vacuum source (not shown), and having its suction surface facing a portion of the perforated cylindrical surface of the rigid cylinder 8.

[0023] In fig. 2, a suction chamber 10 is shown, which is substantially semicylindrical, meaning that its suction surface extends over approximately 180°. For ease of representation in the drawing, it forms the lower part of the rigid cylinder 8, although its position and angular extent can evidently differ.

[0024] In the embodiment shown in fig. 2, as the cylinder 8 and the elastic sleeve 2 rotate, only the part of these elements that is instantaneously in its lower position is exposed to the suction chamber 10, which exerts a vacuum effect on the corresponding portion of the sleeve 2 when it is transitioning from the condition of maximum transverse stretching to the condition of elastic return to its original resting configuration.

[0025] In an alternative embodiment, not shown in the drawings, the rigid cylinder 8 is fixed, while the elastic sleeve 2 is driven in rotation relative to it. In this case, it is sufficient for the cylinder 8 to have a perforated lateral surface only in the part facing the suction opening of the suction chamber 10.

[0026] The elastic sleeve 2 can be made of a fabric that, due to its nature, is permeable to fluids, and in this case, its weft threads are advantageously elastic, while its warp threads (non-elastic or only slightly elastic) are thicker than the weft threads and, due to their greater protrusion, form a sort of circumferential ribs 12 on the sleeve 2. Alternatively, the warp threads of the fabric forming the elastic sleeve 2 are not thicker than the weft threads, but thin tapes of material forming the circumferential ribs 12 are applied to the fabric, for example, by adhesive.

[0027] The sleeve 2 can also be made of a continuous layer of a material that is elastically extensible in the transverse direction and preferably micro-perforated. In this case, the ribs 12 are made up of thin, evenly spaced circumferential bands that are more thickened compared to the remaining material forming the sleeve 2.

[0028] The invention may also involve the use of a sleeve 2 that features both of the configurations described above, i.e. , a sleeve formed from a continuous, transversally elastic layer, reinforced with a fabric structure where the warp threads protrude more from the elastic layer.

[0029] The base materials of this elastic sleeve can, for example, include one or more layers of elastomer, possibly expanded, or a single or multiple fabric layers of elastic threads or even non-elastic threads woven in an elastic weave, or a composite layer of the aforementioned materials, or finally an elastomeric structure with a plurality of metal or plastic springs embedded within it.

[0030] Regardless of the specific embodiment of the elastic sleeve 2, on the portion of the sleeve that is in the condition of maximum transverse stretching, which in fig. 1 corresponds to its top, a layer 14 of fibrous material mixture is deposited, with a dry content between 18% and 70%, preferably between 40% and 60%. As the cylinder 8 and the elastic sleeve 2 rotate, the progressive elastic return of the sleeve to its original resting configuration causes the progressive transverse compaction of the fibrous layer 14, which adheres to the sleeve 2, also aided by the vacuum created by the suction chamber 10, where provided. If the method according to the invention is implemented within a paper machine, the dry content values of the fibrous layer 14 are naturally present in the respective position of gradual paper drying.

[0031] During the elastic return of the sleeve 2, thanks to the presence of the protruding ribs 12, the compaction of the fibrous layer 14, which adheres to the sleeve itself, occurs in a regular and uniform manner across the entire width of the layer, ensuring a substantial uniformity in the transverse extensibility characteristics of the final fibrous tape 16, once removed from the sleeve 2.

[0032] In the embodiment shown in figures 4 - 6, the apparatus for implementing the method according to the invention still includes an elastic sleeve 2, which in this embodiment is not permeable to fluids but is always equipped, at least on the outer surface, with protruding circumferential ribs 12, and is always wound around a rigid cylinder 8. In this case, creating a vacuum inside the cylinder 8 wrapped by the elastic sleeve 2 would not be useful, and the adhesion of the fibrous layer 14 during the shrinking process is facilitated if the dry content of the fibrous layer is less than 50%, or if it is treated with a jet of hot steam, or if it is lightly pressed against the elastic sleeve 2 by one or more rollers (not shown).

[0033] At the end of this compaction phase, the transversally compacted fibrous layer 16 can be removed from the sleeve 2 and sent to subsequent processing stages, such as drying, etc. It will have a transverse extensibility that is greater the more it has been transversally compacted, and in any case, it will be quite uniform, thanks to the uniform compaction provided by the longitudinal ribs 12.

[0034] In an alternative embodiment, the elastic sleeve, on which the fibrous material layer to be transversally compacted is deposited, can be replaced by a continuous belt closed in a loop, supported by guide rollers and following a path dictated by the configuration of the system on which the belt itself is mounted. In figure 7, a portion of this continuous belt 2’ is illustrated, which could also be the belt of the so-called flat table, which in a traditional paper machine receives the slurry from the head box. In the same figure, the direction of movement of the continuous belt is indicated by the arrow 18, and a portion of the elastic belt 2’ is shown, featuring transverse elasticity and equipped with a plurality of longitudinal ribs 12’.

[0035] In a certain section of its path, the belt 2’ is subjected to transverse stretching using any known method, so that it widens and substantially uniformly distances the longitudinal ribs 12’. Preferably, when the belt 2’ reaches its maximum widening, the fibrous slurry layer 14 is deposited on it. With the subsequent elastic return of the belt 2’ to its original configuration, the transverse compaction of the fibrous layer is caused in a significantly uniform manner, thanks to the presence of the protruding longitudinal ribs 12’.

[0036] It may be advantageously foreseen that beneath the section of the belt 2’ that is narrowing, there is an aspirating plane that integrates the effect of depression with the natural tendency of the layer 14 to adhere to the belt itself during narrowing, due to gravity and its plasticity.

[0037] In any case, regardless of whether the method according to the invention is carried out using an elastic sleeve 2 or a continuous elastic belt 2’, it always has very low or essentially no elasticity in the longitudinal direction.

[0038] The method described here involves treating the fibrous slurry layer 14 when it is undergoing the process of progressive drying, and more particularly when its dry content is between 18% and 70%, preferably between 40% and 60% dry. This occurs within the process where the slurry of fibrous material exiting the head box is deposited on the flat table of a paper machine to undergo the traditional drying process. However, the invention also contemplates performing the treatment on a pre-formed paper tape, with a dry content of 90% - 98%. In this case, the invention provides for the paper tape to be pre-treated with a rewetting process to reduce its dry content to a level suitable for undergoing the previously described transverse compaction treatment.

[0039] In all the embodiments now disclosed, it is also possible for the sleeve 2, 2’, on which the fibrous slurry layer 14 is deposited, instead of being entirely made of elastically extensible material, to include a central band of elastically extensible material and two lateral bands of non-extensible material. These lateral bands do not perform any compaction function on the fibrous layer 14 but serve to focus the transverse compaction solely on the portion of the slurry layer that is subjected to the treatment.

[0040] Moreover, the method according to the invention can also be combined in succession with other treatments, such as the treatment to make the paper tape extensible in the longitudinal direction as well (the so-called Clupak process, creping, etc.).

Claims

C L A I M S1. Method for producing a transversely extensible fibrous material tape characterized in that: a belt-like support (2,2'), which is elastically extensible at least in the transverse direction, is advanced in the longitudinal direction and is provided with at least one longitudinal band of its surface by a plurality of longitudinally protruding ribs (12, 12') parallel to said longitudinal direction and substantially equidistant from one another, is subjected to localized transverse stretching, a layer (14) of moldable fibrous material with a dry content ranging between 18% and 70%, preferably between 40% and 60%, is deposited on the surface of the prestretched section of said belt-like support (2,2') affected by said protruding longitudinal ribs (12, 12'), said belt-like support (2,2') is released to allow it to return elastically to its original configuration and to drag with it said layer (14) of moldable fibrous material, which is thus compacted transversely, the transversely compacted fibrous material layer (16) is then removed from said belt-like support (2,2').

2. Method according to claim 1 , characterized in that a belt-like support is used, which is an elastic sleeve (2) rotated relative to a fixed rigid cylinder (8) and is cyclically subjected during its rotation to stretching in the direction of the sleeve's axis and to a subsequent release to allow it to return elastically to its original configuration.

3. Method according to claim 1 , characterized in that a belt-like support is used, which is an elastic sleeve (2) rotated integrally with a fixed cylinder (8) and is cyclically subjected during its rotation to stretching in the direction of the sleeve's axis and to a subsequent release to allow it to return elastically to its original configuration.

4. Method according to one or more of the preceding claims, characterized in that the adherence of said layer of fibrous material (14) to said belt-like support (2) is facilitated by creating a vacuum inside said rigid cylinder (8), which has openings at least on part of its surface, to which the belt-like support (2), made at least partially of fluid-permeable material, faces during its elastic return phase.

5. Method according to claim 1 , characterized in that an elastic belt-like support (2') is used, made of elastic material stretched between guide rollers and subjected, on a section of it, to localized transverse tension followed by a release to allow it to return elastically to its original configuration, and the layer of fibrous moldable (14) is deposited on the section of said belt (2'), where this elastic return occurs.

6. Method according to one or more of the preceding claims, characterized in that an elastic belt-like support (2,2’) is used, which is a fabric with longitudinal threads (12,12’) protruding from the surface intended to come into contact with said layer of fibrous material (14).

7. Method according to one or more of the preceding claims, characterized in that said layer of fibrous material (14) is pressed against said elastic belt-like support (2,2’) with rollers or a jet of hot steam during the elastic return phase of said support to its original configuration.

8. Method according to one or more of the preceding claims, characterized in that a layer of fibrous material (14), obtained from a pre-formed paper web, having a dry content between 90% and 98%, is deposited onto the surface of the prestretched portion of said tbelt-like support (2,2’) affected by said protruding longitudinal ribs (12,12’) and is previously subjected to a rewetting treatment to bring its dry content to a value between 18% and 70%, preferably between 40% and 60%.

9. Apparatus for producing a transversely stretchable fibrous web, characterized in that it comprises: an elastic belt-like support (2,2') driven in motion along a longitudinal direction and having, on at least one longitudinal section of its surface, a plurality of longitudinally protruding ribs (12,12'), parallel to said longitudinal direction and substantially equidistant from each other, means for subjecting said elastic belt-like support (2,2') during its movement to localized transverse stretching followed by a release that allows it to return elastically to its original configuration, means for depositing a layer of moldable fibrous material (14) on the surface of a transversely stretched section of said elastic belt-like support (2,2'), having a dry content ranging from 18% to 70%, preferably between 40% and 60%, means for removing the layer of fibrous web (16) from said elastic belt-like support (2,2') after it has undergone its transverse compaction.

10. Apparatus according to claim 9, characterized in that said elastic belt-like support consists of an elastic sleeve (2) with its edges fixed to two disks (4) that are kept inclined with respect to each other in a constant manner and are rotatably fixed to a shaft (6), so that said elastic sleeve (2) is cyclically subjected to localized stretching in the axial direction, followed by elastic return to its original configuration.

11. Apparatus according to claim 10, characterized in that said elastic sleeve (2) is externally wound around a rigid cylinder (8).

12. Apparatus according to claim 11 , characterized in that said elastic sleeve (2) is made of fluid-permeable material and said rigid cylinder (8) is hollow inside, housing a vacuum source (10) within it, and is provided at least on the part of its lateral surface, where the elastic return of said sleeve (2) to its initial configuration occurs, with openings for communication with said vacuum source (10).

13. Apparatus according to claim 11 , characterized in that said rigid cylinder (8) rotates integrally with said shaft (6) and has its entire lateral surface perforated.

14. Apparatus according to one or more of claims 9 to 13, characterized in that said elastic belt-like support (2,2') is made of a fabric comprising elastic weft threads and non-elastic warp threads (8) with a greater diameter, protruding at least from the surface intended to come into contact with said layer of fibrous material (14).

15. Apparatus according to one or more of claims 9 to 13, characterized in that said elastic tape-like support is made of a continuous transversely elastic layer, reinforced with a structure similar to a fabric with warp threads protruding more from the elastic layer.

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