Method and device for starch application

Abstract

A method and a device for the application of starch on a moving fiber web, especially on a packaging paper web such as a testliner or a corrugated medium web, include first applying starch to a first roll and/or a second roll and passing the fiber web through a treatment nip formed by the first roll and the second roll. At least one of the first or the second roll, preferably both rolls, have a hardness of 15 P&J (Pusey & Jones) or lower, preferably 5 P&J or lower and most preferably 1 P&J or lower. The starch is applied to the first roll and/or the second roll by a slot die and/or a slide die and then transferred to the fiber web in the treatment nip.

Claims

1. A device for the application of starch on a moving fiber web, the device comprising: a first roll and a second roll positioned to form a treatment nip for the fiber web, said first roll and said second roll each having an outer layer or cover with a hardness of 1 P&J (Pusey & Jones) or lower; and an applicator for applying starch on at least one of said rolls, said applicator including at least one of a slot die or a slide die forming a free-falling curtain of starch with at least one of a solid content between 6% and 25% or a viscosity between 5 mPas and 60 mPas.

2. The device according to claim 1, wherein: said free-falling curtain of starch has at least one of a solid content between 8% and 18%.

3. The device according to claim 1, wherein: said free-falling curtain of starch has a viscosity between 10 mPas and 40 mPas.

4. The device according to claim 1, which further comprises a device for removing an air boundary layer from at least one of said first roll or said second roll.

5. The device according to claim 4, wherein said device for removing the air boundary layer includes at least one of a doctor blade, an air jet, a brush or a foil.

6. The device according to claim 4, wherein said first roll and said second roll have diameters being identical or differing by less than 10%.

7. The device according to claim 4, wherein at least one of said first roll or said second roll has a diameter of between 0.25 m and 2 m.

8. The device according to claim 4, wherein at least one of said first roll or said second roll has a diameter of between 0.7 m and 1.8 m.

9. The device according to claim 4, wherein at least one of said rolls has: said cover and said cover is formed of a metal or a ceramic with a layer thickness of less than 1 mm, or said cover and said cover is formed of a rubber, a polyurethane or a composite material with a layer thickness of between 10 mm and 20 mm.

10. The device according to claim 9, wherein said cover formed of a metal or a ceramic has a layer thickness of between 50 μm and 150 μm.

11. The device according to claim 4, wherein at least one of said first roll or said second roll has at least one sensor for measuring a nip load.

12. The device according to claim 1, wherein at least one roll selected from the group consisting of said first roll and said second roll is a controlled deflection roll.

Description

(1) In the following, the invention is described in more details with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(2) FIG. 1 shows a schematic view of a device according to one aspect of the invention.

(3) FIGS. 2 and 2a shows a schematic view a device according to another aspect of the invention.

(4) FIG. 3 shows a schematic view a device according to another aspect of the invention.

(5) FIGS. 4a and 4b show different embodiments of a roll with sensing means according to another aspect of the invention

(6) In FIG. 1 the device according to one aspect of the invention comprises a first roll 1 and a second roll 2, forming a treatment nip 6. The fiber web 5, which may for example be a testliner (TL) or corrugated medium (CM) web 5, passes through the nip 6. Since the rolls are placed in an oblique position, the web 5 is also moving in an oblique direction, preferably at an angle of about 45° w.r.t. the horizontal line.

(7) Here, the starch is applied by two slot dies 3 to the surface of the rolls 1, 2 in the form of a jet and from here transferred to the web 5 in the nip. In order to achieve an improved transfer of the starch to the web, one roll 1, 2 or even both rolls 1, 2, have a hardness of 15 P&J (Pusey & Jones) or lower. Especially at least one roll may have a hardness of less than 5 P&J or even less than 1 P&J.

(8) The diameter of the rolls 1, 2 is in the example of FIG. 1 chosen to be equal, in the range between 0.7 m to 1.8 m, but can be larger or smaller, depending on the application.

(9) The starch used between can have a solid content between 6% and 25%, preferably between 8% and 18%.

(10) In addition, a viscosity between 5 mPas and 60 mPas, preferably between 10 mPas and 40 mPas of the starch may be chosen.

(11) The nipload of the nip 6 can be set in the range between 30 kN/m and 140 kN/m, preferably between 60 kN/m and 100 kN/m. One roll 1, 2 can for example be chosen to comprise a layer of ceramic or metal, while the other roll may comprise layer of rubber, polyurethane or a composite material.

(12) The typical starch amount that is transferred with a device according to the invention is usually between 2.5% and 6% of the basis weight.

DETAILED DESCRIPTION OF THE INVENTION

(13) FIG. 2 shows an embodiment of another aspect of the invention.

(14) While the device according to FIG. 2 may comprise similar rolls 1, 2 as the device in FIG. 1, they are positioned side by side and the fiber web 5 is moving vertically through the nip. In this embodiment, the starch is applied to each of the rolls 1, 2, by a slot die 3. In contrast to FIG. 1, the starch is applied in the form of a free falling curtain. Therefore, the slot dies 3 are positioned on the upper half of the roll 1, 2, preferably at or near the 12 o'clock position. The device of FIG. 2 also comprises means 9 to remove the air boundary layer from the first roll 1 and the second roll 2. Such means are beneficial to avoid the disturbance of the curtain by the air in the boundary layer and therefore to establish a stable curtain and a uniform starch application. While the device 9 in FIG. 2 is in the form of an air nozzle 9 generating an air jet, there are a variety of possible alternatives like doctor blades, brushes or foils.

(15) All the features concerning roll size, hardness or composition, nip load and starch properties mentioned for the embodiment of FIG. 1 are also valid for the embodiment of FIG. 2.

(16) FIG. 2a shows a very similar device as FIG. 2. The main difference is the direction of rotation of the roll. While in FIG. 2 the impact point of the curtains is relatively close to the treatment nip 6, FIG. 2a shows that this does not have to be the case. It is very well possible to apply the starch to a roll 1, 2 and then transport it for a longer distance on the surface of the roll. FIG. 2a shows an embodiment, where the starch is applied near the 12 o'clock position on the first roll 1, and is then transported on the roll surface in counter clockwise rotation to the treatment nip 6, which is approximately in 3 o'clock position. To demonstrate a possible alternative, the device 9 to remove the air boundary layer is here shown as a foil or a flexible blade.

(17) The embodiment of FIG. 3 is very similar to the embodiment of FIG. 2. It only differs in the way the starch is applied to the rolls 1, 2 by slide dies 3a. The starch is again applied in the form of a curtain. Even though the embodiment in FIG. 3 does not explicitly show means 9 to remove the air boundary layer from the rolls such means 9 can be beneficial in this embodiment as well to stabilize the curtain.

(18) Devices like the embodiments shown in the figures are capable of being used to perform methods according to the present invention.

(19) FIGS. 4a and 4b show a first or a second roll 1, 2, comprising a set of sensor means 11 to measure the nip load. The sensor means 11 can be integrated into the roll cover 20. The sensor means 11 in these examples are connected by a signal carrier 10.

(20) This signal carrier may carry electrical or optical signals, depending on the nature of the sensing means.

(21) In FIG. 4a, the sensing means are all positioned along a line in crossmachine direction. In the embodiment in FIG. 4b, the sensor means are positioned helically around the circumference of the roll 1, 2.

(22) The sensor means 11 may for example be included in the top layer 20 or cover of the roll 1, 2, or be positioned between the top layer and the next following layer.