PROCESS AND MACHINE FOR THE MANUFACTURE OF A PAPER WEB THAT IS SMOOTH ON ONE SIDE

Abstract

A method to manufacture a fibrous web in the form of a paper web, which is smooth on one side, by a papermaking machine having a forming area, a pressing area and a drying area. The method including picking up the paper web from the forming area by a water absorbent first press felt; guiding the paper web together with the first press felt and a smooth transfer belt through a first press nip. The smooth transfer belt being configured to substantially not absorb any water. The first press nip being a part of the pressing area. The first press felt being configured to be separated and led away from the paper web immediately after the first press nip. The method further including the steps of leading the paper web together with the smooth transfer belt away from the first press nip; and subsequently leading the paper web from the smooth transfer belt by way of a conditioned water absorbent second press felt, the second press felt not passing through the first press nip; and subsequently guiding the paper web together with the second press felt through a second press nip, the second press nip being associated with the drying area.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention pertains to a process as well as a machine for the manufacture of a paper web of paper that is smooth on one side.

2. Description of the Related Art

The production of paper, that is smooth on one side, and which has a basis weight (gsm=grams per square meter or g/m²) of conventionally 20 g/m² up to 80 g/m², or in particular 16 g/m² up to 40 g/m², is nowadays mostly conducted with so called MG-machines (MG=machine smoothened or flattened). The web, which has a comparatively low dry content, is transferred by the use of a pressure roller onto the smoothing cylinder or Yankee cylinder, respectively. The production output of such a machine is limited though by the evaporative capacity of the cylinder and the hood associated with it. There is however the already known practice of wet pressing before the smoothing cylinder. The low basis weight of the paper web requires the use of its enclosed guidance. The presses are, in this instance, covered with felt on both sides of the web, which is why the attainable dry content is limited by remoistening.

According to a method as well as a machine of the type initially referred to, known from WO 99/31319, the web of paper that is being processed is transferred by way of a transfer felt from the press area on to the drying area, which was previously guided through a nip that is associated to the press area. In this case the light weighted web can be remoistened, which is quite undesirable.

Following a method and a machine, both of the initially described kind, and known from DT 24 43 099 A1, a web of paper, which is being processed, runs after the first press nip onto a felt, which can cause remoistening of the web, which is undesirable. It is a further disadvantage that the press area does not contain a covering to provide a support for the web.

Another method as well as an associated machine is devised for the manufacture of voluminous tissue, known from WO 00/14330. In this machine the web is led through a press nip together with a smooth belt, and the web is subsequently taken from the smooth belt by a structured screen. Following this stage the web is passed onto a Yankee cylinder without any applied contact pressure by a transfer roller.

What is needed in the art is a more efficient, cost-effective method of producing a paper web that is smooth.

SUMMARY OF THE INVENTION

The basic objective of the present invention is to provide a better method as well as an improved machine, which is not disadvantaged by the before mentioned issues. The present invention provides an efficient, mechanical drainage for the web before the thermal drying is initiated inside the drying area, and provides a contained guidance of the web to prevent it from breaking, from the forming area up to the drying area, and in particular, to the smoothing cylinder or Yankee cylinder both of which are associated with the drying area.

The present invention includes a method for producing a paper web, which is smooth on one side, by way of a machine having a forming area, a press area, and a drying area. The paper web to be produced is taken up by way of a water-absorbent first press felt from the forming area and guided together with the first press felt and an at least substantially non-water-absorbent smooth transfer belt through a first press nip associated with the press area. The first press felt is guided away from the paper web directly after the first press nip, while the paper web is guided away from the first press nip together with the smooth transfer belt. The paper web is subsequently taken up from the smooth transfer belt by way of a particularly conditioned, water-absorbent second press felt that is not guided through the first press nip and subsequently, along with the second press felt, guided through a second press nip associated with the drying area.

The more efficient mechanical drainage of the web, which takes place before the thermal drying is initiated inside of the drying area, brings on a noticeable increase in production capacity. In addition the method provides a contained guidance of the web and prevents it from breaking from inside of the forming area or the screen, respectively, up to the smoothing cylinder or Yankee cylinder, located in the drying area.

According to one embodiment of the method of the present invention, the first felt is led away from the web of paper immediately following the first press nip at an angle >0°, preferably >10°, with respect to the web of paper or to the transfer belt.

It is of further advantage if the first press nip, which is associated with the press area, is in the form of a shoe press.

It is preferred if the first press felt passes through the first press nip as a top felt, while the smooth transfer belt passes through this first press nip as the lower belt.

For webs of lower basis weights the drainage capacity of a simple shoe press covered with felt is sufficient. It is hereby possible to attain a dry content of >40%. Since the web is separated from the first press felt immediately following the first press nip before it follows the smooth transfer belt, the chance for remoistening is reduced to a minimum.

Advantageously, the web of paper is picked up from the smooth transfer belt by a pick-up roll, where a second press felt, which is wrapped around this pick-up roll, takes it from the smooth transfer belt. Subsequently the web of paper is guided together with the second press felt through the second press nip, which is associated with the drying area.

According to one embodiment of the method proposed by the present invention, the second press nip, which is associated with the drying area, is formed between a press element and a smoothing cylinder and/or Yankee cylinder.

The press element can include a suction roll, a pick-up roll, around which the second press felt is wrapped, a massive roll, or a shoe press unit, in particular, a shoe press roll.

In any case, contrary to conventional practices, it is preferable to use a well conditioned second press felt, which will make it possible to improve the dry content to levels of 50% or above. As a result less water needs to be subsequently evaporated. If hereby the same evaporation capacity were maintained then the overall production capacity increases, or if the same production capacity were maintained then the costs specific to drying would decrease, for example, less gas would be needed to operate the heating hood which is associated with the smoothing cylinder and/or it would than be possible to employ a smaller smoothing cylinder.

It is of further advantage if the smooth side of the paper web, which previously faced the smooth transfer belt, would be passed with its smooth side facing the smoothing cylinder or the Yankee cylinder.

This method of the present invention is particularly applicable to the production of smooth webs of paper that are smooth on one side, and which have a basis weight in the regime of 20 g/m² up to 80 g/m² and, in particular, in the range of 16 g/m² up to 40 g/m².

The method of the present invention for producing a paper web that is smooth on one side is achieved with a machine, which includes a forming area, a press area, and a drying area, where the paper web to be produced is taken up by way of a water-absorbent first press felt from the forming area and guided together with the first press felt and a substantially non-water-absorbent smooth transfer belt through a first press nip associated with the press area. A first press felt is guided away from the paper web directly after the first press nip, while the paper web is guided away from the first press nip together with the smooth transfer belt. The paper web is subsequently taken up from the smooth transfer belt by way of a particularly conditioned, water-absorbent second press felt, which is not guided through the first press nip, but which is subsequently along with the second press felt guided through a second press nip associated with the drying area. The machine proposed by this invention is particularly intended to facilitate the method proposed by the invention.

Some preferred preparations are intended to condition the second press felt. This second press felt is preferably not structured.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic, partial representation of the components of an embodiment of the machine of the present invention to produce a paper web that is smooth on one side;

FIG. 2 is a schematic enlarged representation of the press area of the machine of FIG. 1;

FIG. 3 is a schematic, partial representation of the drying area of the machine of FIG. 1; and

FIG. 4 is a schematic, partial representation of the drying area of another embodiment of the machine of FIG. 1.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly to FIG. 1, there is depicted a schematic, partial representation of the components of one embodiment of a machine 10 to manufacture a fibrous web 12 in the form of a paper web 12, which is smooth or machine-glazed on one side, with a forming area 14, a press area 16 and a drying area 18.

Paper web 12 is taken up from a screen 24, which is located in forming area 14 of machine 10 by way of a water-absorbent first press felt 20, which is located in an area where press felt 20 is wrapped around a pickup roll 22, and from where paper 12 is guided together with first press felt 20 and an at least substantially non-water-absorbent smooth transfer belt 26, through a first press nip 28, which is associated with press area 16. Immediately after first press nip 28 first press felt 20 is guided away from both paper web 12 and smooth transfer belt 26, respectively, while paper web 12 is guided by smooth transfer belt 26 away from first press nip 28.

Paper web 12 is subsequently taken up from smooth transfer belt 26 by way of a preferably conditioned and specifically not structured, water-absorbent second press felt 30, which is not guided through first press nip 28. Further along paper web 12, along with second press felt 30, is guided through a second press nip 32, which is associated with drying area 18. Contact pressure is again exerted inside of second press nip 32.

Now, additionally referring to FIG. 2 there is depicted again press area 16 of machine 10, this time in an enlarged representation similar to FIG. 1. First press felt 20 is herein led away from paper web 12 immediately following first press nip 28 at an angle a >0°, preferably >10°, with respect to paper web 12 or to transfer belt 26, respectively.

It can be seen from FIGS. 1 and 2 that press nip 28, which is part of press area 16, can be in the form of, a shoe press 28. In the present case shoe press 28 includes, an upper shoe press unit, in particular, a shoe press roll 36 and a lower counter roll 38. First press felt 20 can be in the form of a top felt and smooth transfer belt 26 can be, guided as a lower band through first press nip 28 (compare FIGS. 1 and 2). Paper web 12 is picked up from smooth transfer belt 26 in the vicinity of a second pickup roll 40 by second press felt 30, which wraps around second pickup roll 40.

Second press nip 32, which is associated with drying area 18, is formed in between a press element 42 and a smoothing cylinder and/or Yankee cylinder 44. The embodiment shown in FIGS. 1 and 2 depict a press element 42, which is in the form of a suction roll that is separate from pick-up roll 40.

Now, additionally referring to FIG. 3 there is shown a partial schematic diagram of drying area 18 of another embodiment of machine 10, where press element 42 is formed by pickup roll 40, around which second press felt 30 is wrapped. The combination of a pick-up roll 40 and a suction roll together with smoothing cylinder 44 forms second press nip 42, which represents a press element 42. Otherwise this particular adaptation is arranged in the same way as was the adaptation in FIG. 1. The corresponding components in each figure are identified with the same reference symbols.

Now, additionally referring to FIG. 4 there is shown another partial, schematic diagram of drying area 18 of another embodiment of machine 10, where press element 42 is formed by a shoe press unit 42, in this particular instance, a shoe press roll 42.

For all practical purpose the press element 42 can be formed, for example, by a massive roll 42.

In all of the versions that were presented paper web 12 is passed on to the smoothing cylinder or Yankee cylinder 44, with its smooth side, which it attained from prior contact with smooth transfer belt 26, facing to smoothing cylinder 44or Yankee cylinder 44.

As can be ascertained from FIG. 1 there is a drying hood 46 associated with smoothing cylinder 44 or Yankee cylinder 44.

While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.

LIST OF REFERENCE SYMBOLS

• 10 machine
• 12 web of paper
• 14 forming area
• 16 press area
• 18 drying area
• 20 first press felt
• 22 first pickup roll
• 24 screen
• 26 smooth transfer belt
• 28 first press nip
• 30 second press felt
• 32 second press nip
• 34 shoe press
• 36 shoe press roll
• 38 counter roller
• 40 second pick-up roll
• 42 compression element
• 44 smoothing cylinder, Yankee cylinder
• 46 drying hood

Claims

1. A method to manufacture a fibrous web in the form of a paper web, which is smooth on one side, by a papermaking machine having a forming area, a pressing area and a drying area, the method comprising the steps of: picking up the paper web from the forming area by a water absorbent first press felt;guiding the paper web together with said first press felt and a smooth transfer belt through a first press nip, said smooth transfer belt being configured to substantially not absorb any water, said first press nip being a part of the pressing area, said first press felt being configured to be separated and led away from the paper web immediately after the first press nip;leading the paper web together with said smooth transfer belt away from said first press nip;subsequently leading the paper web from said smooth transfer belt by way of a conditioned water absorbent second press felt, said second press felt not passing through said first press nip; andsubsequently guiding the paper web together with said second press felt through a second press nip, said second press nip being associated with the drying area.

2. The method of claim 1, further comprising the step of immediately separating said first press felt from the paper web after the paper web passes through said first press nip, said first press felt assuming an angle a >0° with said smooth transfer belt and the paper web as said first press felt is led away from the paper web.

3. The method of claim 2, wherein said angle a >10°.

4. The method of claim 1, wherein said first press nip is associated with the press area, said first press nip being formed by a shoe press.

5. The method of claim 1, wherein said first press felt is a top felt, said smooth transfer belt being a lower band relative to the paper web as the paper web travels through said first press nip in said guiding step.

6. The method of claim 5, wherein the paper web is picked up from said smooth transfer belt proximate to a pickup roll by said second press felt, said second press felt wrapping around said pickup roll.

7. The method of claim 6, wherein said second press nip is formed in between a press element and one of a smoothing cylinder and a Yankee cylinder.

8. The method of claim 7, wherein said press element is a suction roll.

9. The method of claim 7, wherein said press element is said pickup roll.

10. The method of claim 7, wherein said press element is a massive roll.

11. The method of claim 7, wherein said press element is a shoe press unit.

12. The method of claim 11, wherein said shoe press unit is a shoe press roll.

13. The method of claim 7, wherein the paper web is passed on to one of said smoothing cylinder and said Yankee cylinder with the smooth side of the paper web facing one of said smoothing cylinder and said Yankee cylinder, the paper web having attained the smooth side from prior contact with said smooth transfer belt.

14. A machine to manufacture a paper web that is smooth on one side, the machine comprising: a forming area;a press area downstream from said forming area in a direction of the paper web movement;a drying area downstream from said press area in said direction;a water absorbent first press felt configured to pick up the paper web from the forming area;a smooth transfer belt, the paper web being guided together with said first press felt and said smooth transfer belt through a first press nip in said press area, said smooth transfer belt not substantially absorbing any water, said first press felt being immediately separated from the paper web after the paper web goes through said first press nip, said smooth transfer belt being configured to carry the paper web away from said first press nip; anda conditioned water absorbent second press felt configured to pick up the paper web from said smooth transfer belt, said second press felt not passing through said first press nip, said second press felt traveling with the paper web in said direction through a second press nip, said second press nip being associated with the drying area.

15. The machine of claim 14, wherein said first compression felt assumes an angle a >0° relative to said smooth transfer belt and the paper web after traveling through said first press nip in said direction.

16. The machine of claim 15 wherein said angle a >10°.

17. The machine of claim 15, wherein said first press nip is formed by a shoe press.

18. The machine of claim 15, wherein said first press felt is a top felt, said smooth transfer belt being a lower band, the paper web traveling through said first press nip between said top felt and said lower band.

19. The machine of claim 15, further comprising a pickup roll with said second press felt wrapping thereabout, said second press felt being configured to pick up the paper web from the smooth transfer belt in the vicinity of said pickup roll.

20. The machine of claim 19, further comprising: a press element; andone of a smoothing cylinder and a Yankee cylinder, said second press nip being formed between said press element and one of said smoothing cylinder and said Yankee cylinder.

21. The machine of claim 20, wherein said press element is a suction roll.

22. The machine of claim 20, wherein said press element 42 is said pickup roll.

23. The machine of claim 20, wherein said press element is a massive roll.

24. The machine of claim 20, wherein said press element is a shoe press unit

25. The machine of claim 24, wherein said shoe press unit is a shoe press roll.

26. The machine of claim 20, wherein the paper web is passed on to one of said smoothing cylinder and said Yankee cylinder with the paper's smooth side, which it attained from prior contact with said smooth transfer belt, facing one of said smoothing cylinder and said Yankee cylinder.