Method of manufacturing a wet-laid nonwoven fabric

Abstract

A method of manufacturing a wet-laid nonwoven web includes the following steps: feeding a pulp suspension onto a forming screen for depositing a fibrous web thereon, wherein the pulp suspension has industrially produced, inorganic fibers or fibers of synthetically produced polymers and the pulp suspension is substantially free from binders, such as chemical binders, and hydraulic consolidation of the fibrous web to generate the nonwoven web through water jet needling of the fibrous web.

Claims

1. A method of manufacturing a wet-laid nonwoven web, the method comprising the following steps: providing a pulp suspension of industrially produced, inorganic fibers or fibers of synthetically produced polymers, the pulp suspension being substantially free of binders; feeding the pulp suspension onto a forming screen for depositing a fibrous web thereon; consolidating the fibrous web by hydroentanglement of the fibrous web to produce the nonwoven web; providing the pulp suspension with binder fibers or feeding binder fibers into the fibrous web before or during the consolidating step; and the fibers having a decomposition point or melting point above 300° C., the material of the fibers have a modulus of elasticity of at least 10 GPa, and the binder fibers have a modulus of elasticity that is lower than 10 GPa.

2. The method according to claim 1, wherein the material of the fibers is selected from the group consisting of glass, metal, mineral, ceramic, and carbon.

3. The method according to claim 1, wherein the fibers have a mean length of 2 to 40 mm.

4. The method according to claim 1, wherein the binder fibers are plastic fibers selected from the group consisting of thermoplastic fibers and fire-resistant fibers, and/or the binder fibers are selected such that their decomposition or melting point is at least 300° C.

5. The method according to claim 1, which comprises consolidating the fibrous web by a final hydraulic consolidation at the forming screen to form the nonwoven web in substantially finished form.

6. The method according to claim 1, wherein the consolidating step comprises performing a hydraulic pre-consolidation by water jet needling at the forming screen, and effecting a final consolidation in an additional process step outside the forming screen.

7. The method according to claim 1, wherein the consolidating step comprises hydraulically consolidating by water jetting and subsequently chemically consolidating the nonwoven web.

8. The method according to claim 7, wherein the step of chemically consolidating the nonwoven web comprises impregnating with a binder.

9. The method according to claim 1, which comprises mechanically dewatering the nonwoven web by way of a press, or dewatering by subjecting the nonwoven web to vacuum dewatering, or thermally dewatering by way of a dryer.

10. An apparatus for manufacturing a wet-laid nonwoven web, the apparatus comprising: an inclined wire former having a forming screen for producing a fibrous web by depositing a pulp suspension on the forming screen; and a first hydraulic consolidation device associated with said forming screen a configured for hydraulically consolidating the fibrous web into a nonwoven web; and the apparatus being configured carry out the method according to claim 1.

11. The apparatus according to claim 10, further comprising a support screen arranged downstream of said forming screen in a direction of travel of the nonwoven web being manufactured, and a second hydraulic consolidation device associated with said support screen in order to finally consolidate the fibrous web after having been pre-consolidated by said first hydraulic consolidation device.

12. The non-woven fabric according to claim 10, formed of a nonwoven web manufactured according to claim 1.

13. A method for converting an apparatus for manufacturing a wet-laid nonwoven web, the apparatus having: a forming section with a former and at least one forming screen associated therewith; and a binder section with a binder application unit for impregnating the nonwoven web with a binder; the method comprising the following steps: mounting a consolidation device, having at least one water jet nozzle, for hydraulically consolidating a fibrous web to a nonwoven web in a vicinity of the forming screen; and deactivating or removing the binder section from the apparatus.

14. A nonwoven web, comprising: a water jet-consolidated nonwoven web made from a wet-laid fibrous web laid from a pulp suspension substantially free of binders, the wet-laid fibrous web containing industrially produced inorganic fibers or fibers made from synthetically produced polymers; the nonwoven web having the characteristics of having had binder fibers applied thereto before or during the water jet-consolidation; and the fibers have a decomposition or melting point of above 300° C., the material of the fibers has a modulus of elasticity of at least 10 GPa, and the binder fibers have a modulus of elasticity that is lower than 10 GPa.

15. A non-woven fabric for high-temperature application, the fabric comprising: a wet-laid and hydroentangled nonwoven fabric formed of industrially produced inorganic fibers or fibers of synthetically produced polymers and being free of binders, said fibers having a decomposition or melting point of above 300° C.; the nonwoven fabric having the characteristics of having had binder fibers applied thereto before or during the water jet-consolidation; and said fabric being configured for use in high temperature applications of at least 300° C., the material of the fibers has a modulus of elasticity of at least 10 GPa, and the binder fibers have a modulus of elasticity that is lower than 10 GPa.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) The invention will be explained in greater detail below with reference to the drawings, without limiting its generality. The drawings show the following:

(2) FIG. 1 a highly schematic representation of an apparatus according to the invention in a side view according to a first embodiment;

(3) FIG. 2 a highly schematic representation of an apparatus according to the invention in a side view according to another embodiment.

DESCRIPTION OF THE INVENTION

(4) FIG. 2 shows, schematically and therefore not to scale, a side view of an apparatus according to the invention for wet-laying a nonwoven web. The apparatus comprises a former, which in this case is designed as inclined wire former 1. An infinite forming screen 2, which here moves on rollers, is associated with the former. This fabric revolves relative to the stationary inclined wire former 1. A headbox 1.1 is arranged above the forming screen 2. The latter is associated with the inclined wire former 1. A pulp suspension may be fed to the headbox 1.1, and may be applied to the forming screen 2, more precisely on the upper side thereof, via an outlet of the headbox 1.1. The pulp suspension usually has a water-fiber mixture. The forming screen 2 is designed so as to let the water through. Below the forming screen 2, on the side facing the headbox 1.1, a dewatering box 1.2 is arranged for discharging the water from the pulp suspension. The dewatering box 1.2 is associated with the inclined wire former 1.

(5) In normal operation of the apparatus, the pulp suspension passes through the outlet of the headbox 1.1 to the forming screen 2 that is moving past on the rollers relative to the headbox 1.1 and dewatering box 1.2. The water flows through the forming screen 2 into the dewatering box 1.2. The fibers from the pulp suspension continue to hang onto the forming screen 2 and are transported along with it. In this way, a corresponding fibrous web F is continuously stored or formed on the forming screen 2.

(6) In a first section, the forming screen 2 is—viewed in its own direction of travel or in the direction of travel of the fibrous web F—inclined upward from the horizontal. In this first stretch, the inclined wire former 1 is arranged, i.e. the fibrous web F is formed in this section. The first section is bounded by the upper rollers, which come immediately after one another in the direction of travel of the support screen 2. At least two such upper rollers are furnished for this purpose. In the illustration shown, the forming screen 2, which circulates in the clockwise direction, thus rises in the first section, from bottom left to top right.

(7) The fibrous web F is still fed past after being formed on the forming screen 2, to be hydraulically consolidated under the consolidation device 4. A plurality of water jet nozzles 4.1, here situated above the forming screen 2, and an outlet 4.2 for water, situated below the forming screen 2, are associated with the consolidation device. In this case, as shown, the forming screen 2 circulates horizontally, or at least partially substantially parallel to the horizontal plane in the region in which the water-jet nozzles 4.1 and the outlet 4.2 are arranged. According to this embodiment, the fibrous web F undergoes final consolidation on the forming screen 2, to form the nonwoven web V.

(8) The former thus constitutes the forming section of the apparatus. In the direction of travel of the nonwoven web V being manufactured, in this case, a binding section of the apparatus directly abuts the forming section. This section comprises an application apparatus 7, which is arranged above a transport screen 5 that extends horizontally or at least partially substantially parallel to the horizontal plane. The nonwoven web V, having undergone final hydraulic consolidation, may be impregnated with a chemical binder by means of the application apparatus 7. In the direction of travel of the nonwoven web V being manufactured (from left to right in the view of FIG. 2), for example a thermal drying device may be attached directly to the binder section, in order to dry the nonwoven web V (not shown) that has been provided with binder.

(9) FIG. 1 shows a refinement of the embodiment from FIG. 2. There, substantially the same components are shown and correspondingly designated as in FIG. 2. In addition, however, an additional consolidation device 4 is arranged. Viewed in the direction of travel of the nonwoven web V being manufactured, this device follows immediately after the forming screen 2. The additional consolidation device 4 likewise comprises a plurality of water jet nozzles 4.1, which here are arranged above a support screen 3 and an outlet 4.2 for water, which is arranged below a support screen 3. Thus, viewed in the direction of travel of the nonwoven web being manufactured, the additional consolidation device 4 comes after the forming section and upstream of the optional binder section (respectively immediately before and after).

(10) As shown in the two drawings, in the direction of travel of the nonwoven web being manufactured, the (first) hydraulic consolidation device 4 is associated with a pre-consolidation device 6. In principle, this may be set up analogously to the hydraulic consolidation device 4, but may be operated at a lower pressure than the consolidation device 4, which is for example only 5 to 25 bar. The respective consolidation device 4, in contrast, may be operated at a pressure of 15 to 400 bar.

(11) As shown in the drawings, the fibrous web F is consolidated from one side, in this case the upper side, namely the side facing away from the forming screen 2 or the support screen 3. In principle, it would also be conceivable to additionally strengthen the fibrous web F from its lower side. To that end, according to FIG. 1, in the direction of travel of the nonwoven web V being manufactured, the additional consolidation device 4 could directly be followed by a further consolidation device, not shown. In the aforementioned direction of travel, this device could be placed upstream of the binder section shown in the drawings. In the embodiment of FIG. 2, in the same direction of travel, the device would be directly downstream of the forming screen 2 or forming section. Such a consolidation device could comprise a cylinder that at least partially wraps around the fibrous web F to (finally) consolidate the web. In turn, a plurality of water jet nozzles are then directed onto the cylinder, in order to apply water jets from below onto the fibrous web that has been partially fed around the cylinder.

(12) Irrespective of the illustrated embodiment, the rigid fibers according to the invention are mixed into the pulp suspension. In this case, the pulp suspension may be substantially free of any added (chemical) binder. Preferably, binder fibers may also be added to these fibers—either already in the pulp suspension, or shortly before the (first) hydraulic consolidation. As stated initially, the binder fibers may be designed to be comparatively flexible compared to the fibers according to the invention, so that their entanglement provides a higher overall strength for the nonwoven web during hydraulic consolidation.

(13) In principle, and irrespective of the illustrated embodiment, the binder section could be dispensed with. Thus, a conventional apparatus for manufacturing such a nonwoven web usually comprises the components shown in FIGS. 1 and 2, but does not comprise any (pre-)consolidation devices 4 and 6. To convert such a conventional apparatus in accordance with the invention, the aforementioned (pre-)consolidation devices 4 and 6 are now mounted at the aforementioned locations, and then the binder section is preferably removed. Alternatively, instead of this, a conventional transport screen may for example be provided. Thus, conventional apparatuses that provide thermal or chemical bonding of the fibers to manufacture a nonwoven web without hydraulic consolidation may be provided. Such a conventional apparatus may be quickly, easily and cost-effectively converted to an apparatus according to the invention.

LIST OF REFERENCE SIGNS

(14) 1 Inclined wire former 1.1 Headbox 1.2 Dewatering box 2 Forming screen 3 Support screen 4 Consolidation device 4.1 Water jet nozzles 4.2 Outlet 5 Transport screen 6 Pre-consolidation device 7 Applicator F Fibrous web V Nonwovenweb