Process for the consolidation of non woven fibrous structure and machinery to implement the process

Abstract: A process for the consolidation of fibrous non woven structure, characterised in that, after having placed the fibrous structure to be consolidated on a pierced surface conveyor, its superior face is run over by blown air jets and, at the same time, undergoes a suction through said pierced conveyor, the blowing pressure and the suction depressure being settled so that the loss of head caused by the web, together with the supporting conveyor, causes a sensible expansion of the air flow pipe, near to the web itself.

Description: The present invention relates to a process for the consolidation of non woven fibrous structure and a machinery to implement the process. Various industrial fields use, for very different aims, non woven materials of various thicknesses and shapes. Non woven materials are generally made of natural or synthetic fibers, that are firstly carded and placed on a mobile surface, so to generate a disorderly structure, called web, with uniform thickness. Later, this web is passed through cohesioning fluid jets, generally hot air or cold water. In the first case the hot air softens or melts the web fibers, cohesioning them, while in the second case, the cold water opens the fibers with violence so to interlace them. The machinery using hot air as cohesioning fluid, generally includes a conveyor, with pierced surface, moving the web through a suction fan, which generates individual, very strong hot air jets. These jets, heated by the closeness to a heating source placed over the belt conveyor, soften or melt the web fibers met in their walk, taking them away and creating holes. A main drawback of these machines consists in that the web thus obtained undergoes a certain loss of weight. Another drawback is the difficulty to control the speed, the capacity and the temperature of the air flow and consequently the pressure on web. This fact can create problems on the control of fibers softening and fusion as well as on the final product quality. The machineries using cold water jets as cohesioning element are substantially similar to the previous one above described, for what regards their working, but they create a different cohesioned structure. The water jets, in fact, do not create holes, as it occurs with hot air jets, by taking away the fibers met in their walk, but they open and at the same time interlace fibers among them. The structure thus obtained on one hand has more resistance, and on the other hand has no loss of weight after the cohesioning process. The main drawback of this machinery is that the water jets must have a very high pressure to move, open and interlace the web fibers, expecially when very thick. For this reason, very powerful and expensive compressors must be used. Further, the cohesioning process wets the web, that must consequently be furtherly worked and dried with the usage of expensive dryers. EP-A- 0 284 462 describes a process of thermobinding non wowen fibrous structure wherein the fibrous structure is placed on a band made of plastics monofibers having a melting point at least 80°C higher than the melting point of the non wowen fibrous structure. According to the invention, all these drawbacks are eliminated by a process for the consolidation of fibrous non woven structures, characterised in that, after having placed the fibrous structure to be consolidated on a pierced surface conveyor, its superior face is run over by air jets while, at the same time, it undergoes a suction through the said pierced conveyor, the blowing pressure and the suction depressure being settled so that the loss of head caused by the web together with the supporting conveyor, causes a sensible expansion of the air flow pipe near to the web itself. To implement the process, the invention foresees a machinery including: two pierced conveyors running, at least for a short portion, facing each other and working with similar peripherical speed to let the structure to be consolidated go on. a compressor placed on the same side of one of the two conveyors, opposite to the structure to be consolidated said compressor being able to generate various air jets, which pass through both the two conveyors and the structure, a suction pump placed opposite to the other conveyor opposite to the structure and provided in the suction pipe, with an air jet conveyor, the pressure of said pump being less than that of the air compressor. The invention is herebelow further clarified with reference to the enclosed drawings in which: Figure. 1 shows in front view the machinery for the consolidation of fibrous nonwoven structures; Figure. 2 shows it in a second embodiment; Figure. 3 shows it in a third embodiment, and Figure. 4 shows it in a fourth embodiment. As can be seen from the drawings, the machinery includes, in the embodiment shown in figure 1, a belt conveyor, generally consisting of a net, maintained in tension between rolls 3 bound to the machine frame (not shown in the drawings). Inside the belt conveyor 1, a suction box 5 is provided, with a slit 7 running crosswise it, whose clearance can be settled by traditional methods. The suction box 5 is connected, through a pipe 9, to a pump 11. Near to the slit 7 of suction box 5, over the belt conveyor 1, another conveyor is provided, consisting of a pierced cylinder 12, supported by rolling and suspension tools, bound to the machine frame. Inside the pierced cylinder 12, a blowing box 16 is mounted: it has substantially a shape like a parallelepiped, with a slit 17 tapered towards downside and facing the corresponding slit 7 of the suction box 5. The blowing box 16 is connected, through a pipe 21, to a compressor 23. Inside the blowing box 16, or at the oulet of the compressor 23, a heating source 25, for example consisting of an electric resistance, can be placed. The pierced cylinder 12 is driven so that its tangent speed is egual to the advancing speed of the belt conveyor 1. The machine operates as follows: a web, made of simple loose fibers, is conveyed to the conveyor 1 and passes on it and under the cylinder 12 and the suction box 5. When the fibers free of web are between the slit 17 of the blowing box 16 and the slit of the suction box 5, they are run over by the air blow generated by the compressor 23 that, passing through the pierced cylinder 12, shares in various minor jets. The air blown inside the blowing box 16 is heated by the closeness with the heating source 25. The air jets press the web in different ways, depending on resistance and shape of the conveyor 1. They pass through the web in preferential zones, depending on the structure of the conveyor 1 and are sucked in by pump 11. The blowing pressure and the suction depression can be settled, so that the loss of head, caused by the web and the conveyor supporting it, creates a sensible expansion of the air flow pipe near to the web itself. The expansion opens the fibers and welds them through melting or softening. From the above, it results that the process according to invention and the machinery that allows its application have numerous advantages and in particular: they allow to obtain a web with a stronger mechanical structure; they allow to improve fiber distribution depending on the thickness and the kind of structure to obtain, as well as on the density and features of the fibers used; they allow a sensible decrease in production cost and time. they allow to build a machine with low management and manufacturing costs. In the embodiment shown in figure 2, the machinery includes two units for the consolidation of web, similar in all its parts to the one already described. In particular, it includes a conveyor 1 innerly provided with two suction boxes 5 and 5′, with slits 7, 7′, running crosswise it, whose width can be settled with tradional methods. These suction boxes 5 and 5′ are connected through pipes 9 and 9′ to suction pumps 11, 11′. Near to the slits 7 and 7′ of suction boxes 5 and 5′, over the belt conveyor 1, two pierced drums 12, 12′ are provided. Inside the pierced drums 12, 12′, two blowing boxes 16,16′ are assembled, with slits 17,17′ tapered towards downside and facing the corresponding slits 7, 7′. The boxes 16,16′ are connected to compressors 23,23′. Inside the blowing box 16′, or at the oulet of the complessor 23′, a heating source 25 can be placed, for example represented by an electric resistance. The machinery operates as follows: as previously, the web passes, by means of the conveyor 1, in the slit of the first unit foreseen among slit 17 and suction box 5. When the fibers free of web are between the slit 17 of the empty casing 16 and the slit 7 of the suction box 5, they are run over by various cold air jets, generated by the compressor 23. These jets pass through the web, they press it and are sucked in by pump 11. Later, the fibrous structure, already pierced in various points, passes through the second unit, whose pierced cylinder is synchronized with the rotating movement of the previous unit cylinder. When the web fibers already interlaced are between the slit 17′ of the blowing box 16′ and the slit 7′ of the suction box 5′, they are run over by hot air jets generated by the compressor 23′. These jets pass through the web in its holes, previously created by the cold air jets, furtherly opening the fibers and welding them by local melting or softening. This second embodiment presents the same advantages of the machinery previously described and provided with a single consolidation unit, but it allows a more uniform and defined consolidated structure. The use of only hot air jets to open and weld web fibers can cause a disorderly melting or softening of fibers. The disorder depends on the different resistance to the moving of fibers, especially present in thick webs, that causes differences in the period of contact between the hot air jet and the fiber. In the web already pierced, instead, the hot air jet does not meet particular resistances in its passing through the web; instead, it passes over the fibers uniformerly all along the thickness of web. The embodiment shown in figures 3 and 4 have the same advantages of the previously described machinery, while they differ for the presence of two consolidation units; in particular the blowing boxes 16 and 16′, placed inside a single pierced cylinder or a pierced closed-ring-like conveyor. In the first case, the conveyor 1 is partially adapted to the circumference of cylinder 12 to allow the web to be first run over by the cold air jets and later by the hot ones.

Claims: A process for the consolidation of a fibrous nonwoven structure to be bonded on a net conveyor (1) characterised by comprising: passing the fibrous structure through a gap between a pierced rotating cylinder (12, 12') and a facing slitted box (5, 5'), wherein said pierced rotating cylinder has a central rotating axis and said facing slitted box (5, 5') includes a slit (7) running crosswise the net conveyor (1) and that is parallel to said central rotating axis, and said pierced rotating cylinder (12) has a tangential speed substantially equal to the net conveyor's speed; running over the upper surface of the fibrous structure by heated blown air jets coming from apertured zones of the pierced rotating cylinder (12); subjecting the other surface of the fibrous structure to the action of a suction means (11, 11') connected to said slitted box 85, 5'); the heated blown air jets and the suction means being settled such that the loss of head through the gap causes a substantial expansion of the heated blown air jets near the fibrous structure. A process for the consolidation of a fibrous nonwoven structure according to claim 1, characterised in that the fibrous structure to be consolidated is run over by said heated blown air jets to open and at the same time weld the fibers of the fibrous structure. A process for the consolidation of a fibrous nonwoven structure according to claim 1, characterised in that the fibrous structure is passed between a pierced rotating cylinder (12) blowing cold air jets and facing slitted suction box (5) before the fibrous structure is subjected to consolidation, such that the cold air jets open the fibrous structure prior to the application of the heated blown air jets. Machinery to implement the process according to claims 1-3 characterised by comprising: a net conveyor (1) for supporting the fibrous structure to be consolidated, a rotating pierced cylinder (12, 12') overlying said conveyor and having tangential speed substantially equal to the speed thereof, a compressor (23) placed on the same side of the pierced cylinder, opposite the structure to be consolidated, said compressor feeding said rotating cylinder to generate air jets which pass through the structure, a suction box (5) under the net conveyor and provided with a slot (7) running crosswise the net conveyor, said suction box being connected to a suction pump (11), the pressure of said pump (11) being less than that of the pressure of the compressor (23).

Inventors: GOVERNALE CLAUDIO, GOVERNALE, CLAUDIO
Applicants: GOVERNALE CLAUDIO, GOVERNALE, CLAUDIO
Application year: 1990
Main classification: D04H1
IPC codes: D04H1