Method for producing a wet-laid nonwoven fabric

Abstract

A method for producing a wet-laid nonwoven fabric web includes the following steps: providing a fibrous web of industrially generated inorganic fibers, or fibers from synthetically generated polymers, and thermally drying the fibrous web in an alternating manner by infrared radiation and hot air, in order for the nonwoven fabric web to be generated.

Claims

1. A method of producing a wet-laid nonwoven fabric web, the method comprising the following steps: a) providing a fibrous web formed of industrially generated inorganic fibers, or fibers from synthetically generated polymers; and b) thermally drying the fibrous web by alternatingly subjecting the fibrous web to infrared radiation and to hot air, to generate the nonwoven fabric web, and thereby blowing the hot air onto the fibrous web with air blowers that aspirate fresh air.

2. The method according to claim 1, which comprises providing a fibrous suspension of industrially generated inorganic fibers, or fibers from synthetically generated polymers, and producing the fibrous web by feeding the fibrous suspension onto a forming screen for depositing the fibrous web on the forming screen.

3. The method according to claim 1, which comprises selecting fibers with a decomposition or melting temperature of at least 300° C.

4. The method according to claim 1, which comprises using fibers having an elasticity modulus of at least 10 GPa.

5. The method according to claim 4, which comprises selecting the fibers from the group consisting of glass, metal, mineral, ceramics, carbon, and combinations of the afore-mentioned materials.

6. The method according to claim 1, wherein the fibers have an average length from 2 to 40 mm.

7. The method according to claim 1, which comprises chemically solidifying the fibrous web prior to thermal drying.

8. The method according to claim 7, which comprises chemically solidifying the fibrous web by soaking the fibrous web with a binding agent.

9. The method according to claim 1, which comprises heating the fresh air by heat exchange with thermal energy contained in exhaust gas generated by the infrared irradiation.

10. A drying device for producing a wet-laid nonwoven fabric web, the drying device comprising: a forming screen for carrying a fibrous web formed from a fibrous suspension of industrially generated inorganic fibers, or fibers from synthetically generated polymers; a plurality of combination dryers disposed along the forming screen in a running direction of the fibrous web to be dried; each of said combination dryers including at least one infrared dryer and at least one hot air dryer, and said hot air dryer of each said combination dryer being disposed downstream of said infrared dryer in the running direction of the fibrous web to be dried, and being configured to aspirate fresh air.

11. The drying device according to claim 10, wherein said infrared dryer is a gas-fired infrared dryer.

12. The drying device according to claim 11, wherein said infrared dryer has a plurality of gas-fired infrared radiators and at least one suction nozzle for suctioning off exhaust gases generated within said infrared dryer.

13. The drying device according to claim 12, wherein said hot air dryer includes at least one blower nozzle for directing hot air onto the fibrous web to be dried.

14. The drying device according to claim 13, wherein said at least one suction nozzle of said gas-fired infrared dryer is fluidically connected to said at least one blower nozzle of said hot air dryer such that the exhaust gases generated within said infrared dryer and suctioned off by way of said suction nozzle are available to be fed to said at least one blower nozzle of said hot air dryer, and to deliver the exhaust gases onto the fibrous web to be dried.

15. The drying device according to claim 10, wherein a heating temperature or a heating output of said combination dryers, when viewed in the running direction of the fibrous web to be dried, is dissimilar.

16. The drying device according to claim 15, wherein the heating output or the heating temperature of said combination dryers, when viewed in the running direction of the fibrous web to be dried, increases from one combination dryer to a following combination dryer.

17. The drying device according to claim 10, wherein said combination dryers are configured for setting a heating temperature or a heating output thereof independently of one another.

18. The drying device according to claim 10, wherein said forming screen and said plurality of combination dryers in the drying installation are configured for carrying out the method according to claim 1.

19. The drying device according to claim 10, wherein said hot air dryer is configured to aspirate fresh air, to heat the fresh air with thermal energy contained in exhaust gas generated by said infrared dryer, and to blow the heated fresh air onto the fibrous web to be dried.

20. A drying device for producing a wet-laid nonwoven fabric web which is generated by depositing a fibrous web from a fibrous suspension containing industrially generated inorganic fibers, or fibers from synthetically generated polymers, the drying device comprising a plurality of combination dryers disposed along the drying device in a running direction of the fibrous web to be dried, wherein each said combination dryer includes at least one infrared dryer and at least one hot air dryer, and said hot air dryer of one and the same combination dryer in the running direction of the fibrous web is in each case disposed downstream of the infrared dryer of one and the same combination dryer, and wherein said hot air dryer is configured to aspirate fresh air, to heat the fresh air with thermal energy contained in exhaust gas generated by said infrared dryer, and to blow the heated fresh air onto the fibrous web to be dried.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) The invention will be explained in more detail hereunder with reference to the drawings and without limiting the generality. In the drawings:

(2) FIG. 1 shows a highly schematic partial illustration of a machine for producing a nonwoven fabric web, in a lateral view; and

(3) FIG. 2 shows a highly schematic illustration of a drying device according to the invention, according to one embodiment, in a three-dimensional view.

DESCRIPTION OF THE INVENTION

(4) Part of a machine for wet-laying a nonwoven fabric web is illustrated in a lateral view in a schematic manner and therefore not-to-scale in FIG. 1. The device comprises a former, presently embodied as an inclined screen former 1. Said inclined screen former 1 is assigned a continuous forming screen 2 which here revolves on rollers. Said forming screen 2 revolves relative to the stationary inclined screen former 1. A headbox 1.1 is disposed above the forming screen 2. Said headbox 1.1 is assigned to the inclined forming screen 1. A fibrous suspension is capable of being fed to the headbox 1.1, said fibrous suspension by way of an outlet of the headbox 1.1 being capable of being applied to the forming screen 2, more specifically to the upper side of the latter. The fibrous suspension typically comprises a water/fiber mixture. The forming screen 2 is embodied such that said forming screen 2 allows water to pass through. A dewatering box 1.2 for discharging the water of the fibrous suspension is disposed below the forming screen 2 on that side that faces the headbox 1.1. The dewatering box 1.2 is assigned to the inclined screen former 1.

(5) In the intended operation of the device, the fibrous suspension, by way of the outlet of the headbox 1.1, makes its way onto the forming screen 2 which by way of the rollers moves relative to the headbox 1.1 or to the dewatering box 1.2, respectively. The water flows out through the forming screen 2 into the dewatering box 1.2. The fibers from the fibrous suspension herein are trapped on the forming screen 2 and are transported onward conjointly with the latter. A corresponding fibrous web F is continuously deposited or formed, respectively, in this manner on the forming screen 2.

(6) The forming screen 2, when viewed in the running direction thereof, or in the running direction of the fibrous web F, respectively, in a first portion of the distance is inclined upward, counter to the horizontal. The inclined screen former 1 is disposed in this first portion of the distance, that is to say that the fibrous web F is formed on said portion. The first portion of the distance herein is delimited by the upper rollers which are directly successive in the running direction of the supporting screen 2. To this end, at least two such upper rollers are provided. In the illustration shown, the forming screen 2, presently revolving in the clockwise direction, thus in said first portion of the distance ascends from the bottom left to the top right. The former could also be embodied in a manner other than the inclined screen former 1 illustrated.

(7) The former including the forming screen 2, the headbox 1.1 and the dewatering box 1.2, is part of the forming section of the machine for producing the nonwoven fabric web V from the wet-laid fibrous web F. In the running direction of the fibrous web F to be produced, a bonding section of the machine presently directly adjoins the forming section. Said bonding section presently comprises an application device 7 which is disposed above a transporting screen 5 which runs horizontally, or at least in portions runs substantially parallel to the horizontal plane, respectively. The nonwoven fabric web V can be soaked with a chemical binding agent by means of the application device 7. However, the application device 7 could also be embodied in a manner deviating from the embodiment shown.

(8) For example, a drying device 3 (see FIG. 2) for drying the fibrous web F provided by means of the binding agent can directly adjoin the bonding section in the running direction of the nonwoven fabric web V to be produced, said running direction of the nonwoven fabric web V simultaneously corresponding to the running direction of the fibrous web F (in the view of FIG. 1 from left to right). Directly means that the impregnation of the fibrous web F by means of the binding agent is performed directly prior to the drying of the fibrous web F without any other processing or finishing steps of the fibrous web F taking place in the meantime.

(9) In principle, it would be conceivable for the binding agent application to take place already on the forming screen 2. To this end, the application device 7, when viewed in the running direction of the fibrous web F, would be disposed behind the former. The latter in such a manner that said application device 7 dispenses the binding agent from above onto the fibrous web F that is deposited on the forming screen 2. Alternatively, it would also be possible for the fibrous web F to be impregnated with the binding agent in that such a binding agent is added to the fibrous suspension before the latter is applied to the forming screen 2.

(10) A drying device 3 according to the invention, such as could adjoin the bonding section of FIG. 1 in the running direction of the fibrous web F, is illustrated in FIG. 2. As is indicated by the arrow, the fibrous web F generated in the forming section first makes its way into the drying device 3. When the fibrous web F leaves the drying device 3, said fibrous web F is finally solidified so as to form the actual nonwoven fabric web V.

(11) The length of the drying device 3, thus the length of the action of heat on the fibrous web F to be dried, is also referred to as the drying distance.

(12) The drying device 3 comprises at least one combination dryer 4. In the present case, four combination dryers 4 which are successively disposed in the running direction of the fibrous web F, are provided. Said four combination dryers 4 are disposed so as to be directly contiguous to one another. This means that when the fibrous web F to be dried leaves a first combination dryer 4, said fibrous web F makes its way directly into the following combination dryer 4, when viewed in the running direction.

(13) Each of the combination dryers 4 comprises in each case one infrared dryer 6 and one hot air dryer 8. All combination dryers herein are specified such that, when viewed in the running direction of the fibrous web F, drying is performed in an alternating manner by means of infrared radiation from the associated infrared dryer 6, then by means of convection by the corresponding hot air dryer 8, in a corresponding manner again by means of heat radiation, and so forth. As soon as the fibrous web F, when viewed in the running direction thereof, has left the first combination dryer 4, said fibrous web F makes its way into the second combination dryer 4. Said fibrous web F therein, again when viewed in the running direction of said fibrous web F, is first dried by the corresponding infrared dryer 6, then by the corresponding hot air dryer 8. In other words, in each case when viewed in the running direction of the fibrous web 7 through the drying device 3, one hot air dryer 8 assigned to the first combination dryer 4 is in each case disposed between an infrared dryer 6 of a first combination dryer 4 in the running direction, and between an infrared dryer 6 of a further combination dryer 4 that directly follows in the running direction. It could also be said that the fibrous web F along the drying distance is dried in an alternating manner by means of heat radiation, then by means of convection, in turn by means of heat radiation, and so forth. To this end, the combination dryers 4 are successively disposed in a corresponding manner along the drying distance.

(14) The infrared dryer 6 of a respective combination dryer 4 can be embodied as a gas-fired infrared dryer. To this end, the infrared dryer 6 can comprise one or a plurality of infrared radiators (not shown). The exhaust gases generated by means of the infrared radiator can in this instance be suctioned from the infrared dryer 6 by way of one or a plurality of suction nozzles 9 that are assigned to the infrared dryer 6, only one of said suction nozzles 9 being purely schematically indicated here. The at least one suction nozzle 9 can be disposed within a housing that surrounds the infrared dryer 6.

(15) The respective hot air dryer can comprise one or a plurality of blower nozzles 10, of which likewise only one is illustrated in a purely schematic manner here. The at least one blower nozzle 10 serves inter alia for feeding heated air to the fibrous web F in order for the latter to be dried. To this end, the at least one blower nozzle 10 can be fluidically connected to a fresh air intake (not shown), on the one hand. Moreover, a fluidic connection can be provided between the at least one suction nozzle 9 and the at least one blower nozzle 10 of one and the same combination dryer 4. By means of said fluidic connection, the thermal energy contained in the exhaust gas of the infrared dryer 6 can be utilized for heating the fresh air, or for drying the fibrous web F also by means of the thermal energy of the exhaust gas of the respective infrared dryer 6, respectively.

(16) Independently of the embodiments illustrated in the figures, it is in principle advantageous for the drying device 3 to be specified in such a manner that the heating temperature or the heating output of the individual combination dryers 4, when viewed in the running direction of the fibrous web F to be dried, is dissimilar, or is capable of being set in a mutually independent manner, respectively. The drying output can thus be adapted in an optimal manner to the fibers of the fibrous web F to be dried, and the optimal strength of the nonwoven fabric web V to be produced can thus be set in a targeted manner. It has been demonstrated herein that it is advantageous for the drying device 3 to be specified in such a manner that the heating output or the heating temperature, when viewed in the running direction of the fibrous web F to be dried, increases from one combination dryer 4 to the next combination dryer 4. In other words, a temperature profile can be imposed on the entire drying device 3 in the running direction of the fibrous web F to be dried, thus when viewed across the entire drying distance, said temperature profile being kept constant in the operation of the drying device 3. Within the respective combination dryer 4, the temperature both in the infrared dryer 5 as well as in the hot air dryer 8 can be set so as to be constant. For example, the temperature profile can increase in steps from the first to the second and toward the third combination dryer 4 in the running direction of the fibrous web F to be dried, for example, and drop again in the fourth (last or further) combination dryer 4. Since the moisture content of the fibrous web F continuously decreases when passing through the drying device 3, a lower heating output is also required toward the end of the drying within the drying device 3. Depending on the type of the fibers of the fibrous web F, a corresponding temperature profile can be predefined for the drying device 3 and thus for the combination dryers 4, in order for the fibrous web F in this instance to be dried in an optimal manner so as to form the nonwoven fabric web V.

(17) Independently of the embodiments illustrated, the fibrous web F according to the invention is solidified in a purely chemical manner such that the final nonwoven fabric web V is created. This takes place by the addition and the subsequent drying of the chemical binding agent contained in the fibrous web F.

(18) The final strength of the nonwoven fabric web V can be achieved in a comparatively short time by means of the present invention. The nonwoven fabric web can thus be transferred faster than to date by way of a free draft to another belt such as a transport belt for further processing or winding in a further section of the machine for producing such nonwoven fabric webs, without said non-woven fabric web breaking.

(19) It has been demonstrated that the invention displays the advantages mentioned at the outset particularly positively in the case of nonwoven fabrics produced from inorganic fibers such as glass fibers.

LIST OF REFERENCE SIGNS

(20) 1 Inclined screen former 1.1 Headbox 1.2 Dewatering box 2 Forming screen 3 Drying device 4 Combination dryer 5 Transporting screen 6 Infrared dryer 7 Application device 8 Hot air dryer F Fibrous web V Nonwoven fabric web