DEVICE AND METHOD FOR PRODUCING A FIBROUS WEB

Abstract

A device for producing a fibrous web, in particular a tissue web, includes a first press having a first felt and a second felt, both of which are guided through a press nip of the first press. A Yankee cylinder dries the fibrous web and a transfer press transfers the fibrous web to the Yankee cylinder. The second felt is also guided through a press nip of the transfer press. A paper-contacting side of the second felt is formed of a nonwoven layer which includes at least 80 wt. %, in particular at least 90 wt. % of nonwoven fibers formed of polyamide or polyamides and having a fineness of 6.7 dtex or less, in particular 3.3 dtex or less. An associated method for producing a fibrous web, in particular a tissue web, is also provided.

Claims

1-8. (canceled)

9. A device for producing a fibrous web or tissue web, the device comprising: a first press having a press nip, a first felt and a second felt, said first and second felts both being guided through said press nip of said first press; a Yankee cylinder for drying the fibrous web; a transfer press for transferring the fibrous web to said Yankee cylinder, said transfer press having a press nip, said second felt being guided through said press nip of said transfer press; and said second felt having a paper-contacting side formed of a nonwoven layer including at least 80 wt. % of nonwoven fibers formed of polyamide or polyamides having a fineness of 6.7 dtex and less.

10. The device according to claim 9, wherein said nonwoven layer includes at least 90 wt. % of said nonwoven fibers formed of polyamide or polyamides, and said fineness is 3.3 dtex or less.

11. The device according to claim 9, wherein said second felt also includes further nonwoven layers having nonwoven fibers, and at least 90 wt. % of said nonwoven fibers of all of said nonwoven layers have a fineness of 6.7 dtex and less.

12. The device according to claim 11, wherein at least 90 wt. % of said nonwoven fibers of all of said nonwoven layers have a fineness of 3.3 dtex or less.

13. The device according to claim 11, wherein at least some of said nonwoven fibers are materially bonded or adhesively bonded or welded or fused to one another in at least one of said nonwoven layers or in all of said nonwoven layers of said second felt.

14. The device according to claim 9, wherein said second felt has an air permeability of less than 5 cfm (approximately 142 l/min).

15. The device according to claim 14, wherein said air permeability of said second felt is 0 cfm.

16. The device according to claim 9, wherein said first felt has a paper-contacting side formed of a nonwoven layer including at least 80 wt. % of nonwoven fibers having a fineness of more than 6.7 dtex.

17. The device according to claim 17, wherein at least 80 wt. % of said nonwoven fibers of said nonwoven layer of said paper-contacting side of said first felt have a fineness of 11 dtex and more.

18. The device according to claim 9, wherein said first press is a shoe press.

19. A method for producing a fibrous web or a tissue web, the method comprising steps of: transporting the fibrous web on a first felt to a first press; pressing the fibrous web in the first press between the first felt and a second felt; transporting the fibrous web with the second felt from the first press to a Yankee cylinder; using a transfer press to transfer the fibrous web from the second felt to the Yankee cylinder; guiding the second felt through a press nip of the transfer press; and providing a paper-contacting side of the second felt formed of a nonwoven layer including at least 80 wt. % of nonwoven fibers formed of polyamide or polyamides and having a fineness of 6.7 dtex and less.

20. The method according to claim 19, which further comprises providing the nonwoven layer with at least 90 wt. % of the nonwoven fibers formed of polyamide or polyamides and having a fineness of 3.3 dtex or less.

21. The method according to claim 19, which further comprises carrying out the pressing in the first press at more than 200 kN/m.

22. The method according to claim 21, which further comprises carrying out the pressing in the first press at between 400 kN/m and 600 kN/m.

Description

[0032] The invention is explained below by means of schematic figures; however, the invention is not limited to the examples shown here. In particular:

[0033] FIG. 1 shows a detail of a device according to one aspect of the invention

[0034] FIG. 2 shows by way of example a machine for producing a tissue web with a device according to a further aspect of the invention.

[0035] FIG. 1 shows the part of a device for producing a fibrous web 1 that is important for the present invention. Here, the fibrous web 1 is transported to the first press 20 while being supported on a first felt 10. In this case, it is not essential to the present invention whether the fibrous web 1 has been formed on the first felt 10 or whether it has been transferred to the first felt 10 after forming. The first press 2 is illustrated by way of example in FIG. 1 as a shoe press. The web passes through the press nip of the first press 2 in a sandwich between the first felt 10 and a second felt 20 and is dewatered as it does so. Common press loads in this context are above 200 kN/m, often between 400 kN/m and 600 kN/m. Here, the paper-contacting side of the second felt 20 consists of a nonwoven layer which comprises at least 80 wt. %, often also 100%, of nonwoven fibers which consist of a polyamide or polyamides and have a fineness of 6.7 dtex and less, in particular 3.3 dtex or less.

[0036] After leaving the press nip of the first press 2, the fibrous web 1in particular a thin tissue web 1does not adhere to the first felt 10 but to the second felt 20. This is due to the surface of the second felt 20, which is comparatively smooth for a felt. In the example shown in FIG. 1, the fibrous web 1 then hangs below the second felt 20. In this way, it is transported onward in the direction of the Yankee cylinder 4. The transfer from the second felt 20 to the Yankee cylinder 4 is accomplished by means of a transfer press 3. This transfer press 3 does not have any significant dewatering tasks. It is intended principally to press the second felt 20 with the fibrous web 1 against the Yankee cylinder 4 with comparatively slight pressure, ensuring that the fibrous web 1 travels along with the highly smooth surface of the Yankee cylinder 4 and is dried further there by the action of heat.

[0037] In the schematic illustration of FIG. 1, the depiction of components which are not essential for understanding the concept has been dispensed with. In practical applications, a large number of further units can also be provided, in particular cleaning devices such as, for example, scrapers, felt conditioners, sensors or the like.

[0038] FIG. 2 shows, by way of example, a tissue machine with a device according to a further aspect of the invention, in particular with the device shown in FIG. 1.

[0039] From a headbox 40, the fibrous suspension is brought into a forming section, where the initial dewatering takes place. In this case, the formation of the fibrous web 1 takes place between the first felt 10 and a dewatering screen 30. Dewatering elements, such as a suction roll 50 or suction boxes (not shown in the figure), are usually provided here. The fibrous web 1 is then transported on the first felt 10 with a still relatively high moisture content to the first press 2. As described with regard to FIG. 1, the fibrous web 1 is further dewatered in the first press 2 by pressing between the first felt 10 and the second felt 20. When it leaves the press nip, the fibrous web 1 no longer continues to run with the first felt 10, but instead adheres to the second felt 20 and is transported onward from the latter to the Yankee cylinder 4. It can be advantageous here for a stable process if the paper-contacting side of the first felt 10 consists of a nonwoven layer which comprises at least 80 wt. % of nonwoven fibers which have a fineness of more than 6.7 dtex, in particular 11 dtex and more.

[0040] By means of a transfer press 3, the fibrous web 1 is transferred to the surface of the Yankee cylinder 4. Further drying of the fibrous web 1, that is to say in this case the tissue web 1, is performed by means of the usually steam-heated Yankee cylinder 4. In most cases, a hood 5 is provided, through which hot air is blown onto the tissue web 1. After the tissue web 1 has been removed from the Yankee cylinder 4usually by means of crepe scrapers (not shown explicitly here)the tissue web 1 is wound up with a reel 60 to form rolls, which can undergo further processing.

LIST OF REFERENCE SIGNS

[0041] 1 fibrous web [0042] 2 first press [0043] 3 transfer press [0044] 4 Yankee cylinder [0045] 5 hood [0046] 10 first felt [0047] 20 second felt [0048] 30 dewatering screen [0049] 40 headbox [0050] 50 suction roll [0051] 60 reel