Nonwoven web and method of making same

Abstract

A nonwoven web is made by first depositing fibers as a nonwoven web in a deposition area, then conveying the web away from the deposition area in a web-travel direction, preconsolidating the web in the path, and passing the preconsolidated web between a pair of rollers that compress and final consolidate the preconsolidated web, One of the rollers is separated from the web such that final consolidation of the web at a starting level is stopped and at the same time or immediately beforehand upstream preconsolidation of the web increased. After separating the one roller from the web, another roller is engaged with the web at the consolidation station and then final consolidation is recommenced, whereupon upstream preconsolidation of the web is reduced back to the starting level.

Claims

1. A method of making a nonwoven web, the method comprising the steps of: depositing fibers as a nonwoven web in a deposition area; conveying the web along a path away from the deposition area in a web-travel direction; preconsolidating the web in the path; passing the preconsolidated web between a pair of rollers that compress and final consolidate the preconsolidated web; separating one of the rollers from the web such that final consolidation of the web is stopped and at the same time or immediately beforehand increasing upstream preconsolidation of the web; after separating the one roller from the web, bringing another roller into engagement with the web at the consolidation station and thereby recommencing final consolidation; and on recommencing of final consolidation, reducing upstream preconsolidation of the web.

2. The method defined in claim 1, wherein preconsolidation is effected with a predetermined level of compression of the nonwoven web and, during separation of the one roller from the web, the level of compression is increased.

3. The method defined in claim 1, further comprising the step of: stretching the fibers prior to deposition.

4. The method defined in claim 1, wherein the fibers are continuous spun filaments deposited as a spun-consolidated nonwoven web or as a melt-blown nonwoven web.

5. The method defined in claim 1, wherein the preconsolidater has at least one pressure roller that bears on the nonwoven web with a pressure that is increased during calender-roller exchange by increasing a temperature and/or a compaction pressure or a line pressure of the pressure roller.

6. The method defined in claim 5, wherein the preconsolidater has at least one additional preconsolidating component that is activated against the nonwoven web during calender-roller exchange for additional preconsolidation of the nonwoven web.

7. The method defined in claim 5, wherein the at least one additional preconsolidating component is at least one press roller that is brought into contact with the nonwoven web during calender-roller exchange for additional preconsolidation of the nonwoven web.

8. The method defined in claim 5, wherein the at least one additional preconsolidating component is a spray adhesive applicator with which adhesive or spray adhesive is applied to the nonwoven web for additional preconsolidation of the nonwoven web.

9. The method defined in claim 5, wherein the at least one additional preconsolidating component projects hot air against the nonwoven web during calender-roller exchange for additional preconsolidation.

10. The method defined in claim 1, further comprising the step during calender-roller exchange of: increasing a web-travel speed of the nonwoven web between the deposition area and a downstream receiving device for the nonwoven web.

11. The method defined in claim 10, wherein a rotational speed of at least a portion of a roller provided between the deposition area and the receiving device and in contact with the nonwoven web is increased during calender-roller exchange.

12. The method defined in claim 1, further comprising the step of: winding a downstream end of the nonwoven web continuously in a compensator unit with at least one dancer roller during calender-roller exchange.

13. The method defined in claim 1, further comprising the step of: monitoring a nonwoven web and controlling preconsolidation with or without feedback during calender-roller exchange.

14. The method defined in claim 1, further comprising the steps of: using a screen deposition belt as a deposition area for the fibers, separating the nonwoven web from the screen deposition belt before transfer to the at least one calender roller, and assisting separation of the nonwoven web during calender-roller exchange by an additional stripper.

15. The method defined in claim 1, wherein at least one additional take-off roller activated during calender-roller exchange effects the separation of the nonwoven web from the screen deposition belt by contact with the nonwoven web, and the additional take-off roller contacts a cooling roll in order to cool the nonwoven web while forming a take-off nip for the nonwoven web.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing whose sole FIGURES is a schematic view of the instant invention.

SPECIFIC DESCRIPTION OF THE INVENTION

(2) An apparatus for making a spun-consolidated nonwoven web 1 from continuous filaments 2, preferably of a thermoplastic synthetic resin, has a spinning device or spinneret 3 and, downstream therefrom in a filament-travel direction FD, a cooler 4. A stretcher 5 for stretching the filaments 2 follows the cooler 4 in the filament-flow direction FD. Preferably, this stretcher 5 has an intermediate passage 6 that converges in the direction of flow FD of the filaments 2, as well as an adjoining stretching passage 7. Recommendably, the assembly of the cooler 4 and the stretcher 5 is a closed system. Apart from the supply of cooling air or process air in the cooler 4, no further air supply is provided in this closed system. According to a preferred embodiment, a diffuser 8 is downstream of the stretcher 5 in the direction of flow FD of the filaments 2.

(3) Advantageously, the filaments 2 are deposited downstream of the diffuser 8 on a screen deposition belt 9 to form the nonwoven web 1. Preferably, the screen deposition belt 9 circulates continuously to advance the mat 1 thus formed in a horizontal travel direction TD perpendicular to the vertical filament direction FD.

(4) Recommendably, the deposited nonwoven web 1 is preconsolidated between two pressure rollers 11 in a preconsolidater 10. Advantageously, the preconsolidated nonwoven web 1 is then final consolidated in a calender 12 with a first upper calender roller 13 and a lower calender roller 14. The drawing shows that the first upper calender roller 13 is exchanged during an ongoing process operation for a second upper calender roller 15 (calender-roller exchange). The first upper calender roller 13 is pivoted away from the nonwoven web 1, and the second upper calender roller 15 in brought into contact with the lower calender roller 14 only thereafter. This results in a period of time in which no calendering of the nonwoven web 1 takes place. Accordingly, the transporting tension applied by the calendering apparatus 12 to the nonwoven web 1 drops. As a result, the other conveying components for the nonwoven web 1 must apply greater force, more particularly greater tension. This can result in damage or to tearing of the nonwoven web 1.

(5) According to the invention, in order to remedy this situation, the preconsolidation of the nonwoven web 1 is increased during calender-roller exchange, and this increased preconsolidation is advantageously reduced again after the second upper calender roller 15 is installed.

(6) In this embodiment according to the drawing, the preconsolidater 10 has two pressure rollers 11 that act on the nonwoven web 1. It lies within the scope of the invention for the preconsolidation to be increased with the pressure rollers 11 during calender-roller exchange. Preferably, the temperature and/or the compaction pressure of the pressure rollers 11 is increased for this purpose.

(7) According to a preferred embodiment, the preconsolidater 10 has at least one additional preconsolidating component 17 that is activated during calender-roller exchange for additional preconsolidation of the nonwoven web 1. According to one embodiment according to the drawing, the additional preconsolidater can also be is a hot-air final consolidater 16 with which hot air is applied to the nonwoven web 1 during calender-roller exchange for additional preconsolidating. A spray nozzle 18 is also usable.