DK2957673T3 - Method of drying a cigarette paper web and thus obtaining cigarette paper - Google Patents

Description

The present invention relates to the technical field of making cigarette paper, and more particularly it relates to the operation of drying cigarette paper while it is being made in order to improve its mechanical characteristics .

In conventional manner, a papermaking machine line, in particular a line for making cigarette paper, comprises at the exit from a headbox, a section for dewatering through a felt, followed by a press section, and followed by a section for drying the paper that leads to a winding section.

The prior art proposes numerous solutions for making paper, and in particular for drying paper. For example, US patent No. 6 001 421 describes a machine for drying a strip of paper that includes in particular a predrying section and a coating station followed by a postdrying section. Each pre-drying or post-drying section has a series of groups of dryer drums. Each group of dryer drums has a plurality of dryer drums and a drying felt mounted to press the strip of paper against the dryer drums and to support the strip of paper relative to transfer rolls. Although the technique described in that patent makes it possible to control the tendency of the strip of paper to corrugate or to curl, that patent does not provide teaching for drying a cigarette paper, where cigarette paper is relatively fragile compared with other types of paper.

Likewise, US patent No. 4 882 854 describes a guide roll device for a drying section of a papermaking machine having in particular a drying felt that presses the strip of paper against dryer drums and that supports the strip of paper as it passes around transfer rolls. That patent does not provide pertinent teaching for drying cigarette paper.

Typically, cigarette paper receives additional treatment in a size press, such that the drying section is split upstream and downstream relative to the size press so as to form a pre-drying section and a post-drying section.

One of the characteristics of cigarette paper is its weight, i.e. the magnitude corresponding to its mass per unit area. Typically, cigarette paper possesses weight lying in the range 12 grams per square meter (g/m2) to 45 g/m2, and more precisely in the range 12 g/m2 to 35 g/m2.

Cigarette paper is relatively fragile, which means that the travel speed of the strip of paper needs to be limited in order to avoid breaking it during papermaking. Unfortunately, improving the cost of producing cigarette paper relies in particular on increasing the travel speed of the strip of paper.

Nevertheless, the Applicant has found that increasing the travel speed of the strip of cigarette paper leads to obtaining cigarette paper having mechanical characteristics that are degraded, thereby harming subsequent working of the cigarette paper as made in this way.

The document WO 03/064165 describes a method according to the preamble of claim 1.

The present invention seeks to remedy the drawbacks of the prior art by proposing a novel technique for making cigarette paper that enables the travel speed of the strip of paper to be increased while still enabling cigarette paper to be obtained with very good mechanical characteristics that are suitable for subsequent working of the cigarette paper.

To achieve this object, the invention seeks to propose a drying method for drying a strip of cigarette paper in a drying section of a cigarette papermaking machine line, the drying section comprising a pre-drying section situated at the exit from a press section and the entry to a size press, and a post-drying section situated between the exit from the size press and the entry to a winding section, the drying section having dryer drums, transfer rolls, and at least one drying felt, the method consisting, at least for the pre-drying section, in continuously supporting the strip of cigarette paper with the help of at least one drying felt traveling around all of the dryer drums and of the transfer rolls situated in the pre-drying section in order to form in this pre-drying section a single "Unorun" drying system for driving the strip of cigarette paper at a speed that is substantially constant with a speed variation inferior or equal to 0.1%so as to obtain a cigarette paper having a value of elongation at rupture that is not less than 2.0% and a TEA index that is not less than 2.0 kN.m/m2, said "Unorun" drying system having one or more groups of dryer drums that are associated to support the strip of cigarette paper in continuous manner, each dryer drum group having at least one dryer drum, at least one transfer roll and only one drying felt continuously supporting the strip of cigarette paper, the drying felt being arranged in the form of an endless strip forming a felt circuit and being mounted in such a manner that all of the dryer drums of said group are situated on the outside of the circuit of the felt, and all of the transfer rolls of said group are situated on the inside of the circuit of the felt.

According to another characteristic of the invention, the drying method consists, for the post-drying section, in continuously supporting the strip of cigarette paper with the help of at least one drying felt traveling around all of the dryer drums and of the transfer rolls situated in the post-drying section so as to form, in this post-drying section, a single "Unorun" drying system for driving the strip of cigarette paper at a speed that is substantially constant so as to obtain a cigarette paper having a value of elongation at rupture that is not less than 2.5% and a TEA index that is not less than 2.5 kN.m/m2, said "Unorun" drying system having one or more groups of dryer drums that are associated to support the strip of cigarette paper in continuous manner, each dryer drum group having at least one dryer drum, at least one transfer roll and only one drying felt continuously supporting the strip of cigarette paper, the drying felt being arranged in the form of an endless strip forming a felt circuit and being mounted in such a manner that all of the dryer drums of said group are situated on the outside of the circuit of the felt, and all of the transfer rolls of said group are situated on the inside of the circuit of the felt.

According to another characteristic of the invention, the method consists, in the pre-drying section and/or in the post-drying section, in continuously supporting the strip of cigarette paper with the help of one only drying felt traveling continuously around the dryer drums and the transfer rolls of a section.

According to another characteristic of the invention, the method consists in causing the strip of cigarette paper to travel on a suction transfer roll situated between the size press and the first dryer drum of the post-drying section.

Another object of the invention is to propose a novel cigarette paper presenting mechanical characteristics that are improved, in particular concerning the value of its elongation at rupture and its TEA index, compared with previously known cigarette paper.

Another object of the invention is thus to propose a cigarette paper that possesses a value of elongation at rupture that is not less than 2.0% and a TEA index that is not less than 2.0 kN.m/m2.

Another object of the invention is thus to propose a cigarette paper presenting a value of elongation at rupture lying in the range 2.5% to 3.5% and a TEA index lying in the range 2.5 kN.m/m2 to 3.0 kN.m/m2.

Another object of the invention is thus to propose a cigarette that presents: • porosity lying in the range 10 Coresta units (CU) to 200 CU; • weight lying in the range 12 g/m2 to 45 g/m2; and • a mineral filler content lying in the range 20% to 40%.

Various other characteristics appear from the following description made with reference to the accompanying drawings, which show embodiments of the invention as non-limiting examples.

Figure 1 is a diagrammatic section view of an example of a drying installation in which only the predrying section forms a "Unorun" drying system.

Figure 2 is a diagrammatic section view of another example of a drying installation in which the pre-drying section and the post-drying section form respective "Unorun" drying systems.

Figure 3 is a diagrammatic section view of another embodiment of a drying installation in which the post-drying section is fitted with a transfer roll at its entry.

Figure 4 is a diagrammatic section view of another embodiment of a drying installation in which the pre-drying section has a single circuit for the drying felt.

Figure 5 is a diagrammatic section view of another embodiment of a drying installation in which the or each "Unorun" section comprises drying groups that come into contact in alternation with the bottom and top faces of the felt in order to dry the felt symmetrically.

As can be seen in the drawings, the subject matter of the invention relates to making a strip of cigarette paper 1 in line. Figure 1 shows a first embodiment of a drying section 2 for drying this strip of cigarette paper 1, forming a portion of a papermaking machine that is not shown but is itself well known.

In conventional manner, this drying section 2 is interposed between the outlet from a press section and the inlet of a rolling section, these press and rolling sections not being described in greater detail since they are well known to the person skilled in the art and do not specifically form part of the subject matter of the invention .

The drying section 2 has a size press 3 for treating the strip of cigarette paper 1. Thus, the drying section 2 is made up of a pre-drying section 4 situated between the outlet of the press section and the inlet of the size press 3 and a post-drying section 5 situated between the outlet of the size press 3 and the inlet of a winding section (not shown).

In accordance with the invention, the pre-drying section 4 comprises a single "Unorun" drying system so as to obtain at least 80% of the drying needed by the strip of cigarette paper. Thus, the pre-drying section 4 has a first series of dryer drums 6, transfer rolls 7, and at least one drying felt 8 (a plurality of drying felts 8 in the example shown in Figure 1) each in the form of an endless strip forming a felt circuit and traveling between the cylinders of the felt circuit 9. The dryer drums 6, the transfer rolls 7, and the drying felts 8 are not described in greater detail since they are well known to the person skilled in the art and can be implemented in any appropriate manner.

In known manner, each drying felt 8 travels around a group of dryer drums 6 and at least one transfer roll 7 so that the drying felt 8 extends in contact with the strip of cigarette paper 1 on the outside relative to the dryer drum 6 and on the inside relative to the transfer rolls 7.

In the example shown in Figure 1, the "Unorun" drying system includes, in the pre-drying section 4, a series of four groups of dryer drums, each having a drying felt 8 and a group of two dryer drums 6. Naturally, the predrying section 4 could have a smaller or greater number of groups of dryer drums 6. Likewise, it is possible to envisage using groups of dryer drums with a number of dryer drums that may lie in the range one to more than two. In each group of dryer drums, excepted for the first group of the pre-drying section 4, the number of dryer drums 6 is equal to the number of transfer rolls 7, which transfer rolls are placed in such a manner that two dryer drums 6 are separated by a transfer roll 7. For the first group of the pre-drying section 4, the admission roll is not a transfer roll. For the first group of the pre-drying section 4, if the number of dryer drums 6 is equal to n, the number of transfer rolls is equal to n-1.

Thus, a "Unorun" drying system has a series of groups of dryer drums that are associated to support the strip of cigarette paper 1 in continuous manner. Each dryer drum group has at least one dryer drum 6 and at least one transfer roll 7 for a drying felt continuously supporting the strip of cigarette paper 1 on the outside face of said strip when it passes over each dryer drum 6 and on the inside face of said strip when it passes over a transfer roll 7.

In other words, each dryer drum group of a "Unorun" drying system has only one drying felt continuously supporting the strip of cigarette paper and mounted in such a manner that all of the dryer drums are situated on the outside of the circuit of the drying felt 8, and all of the transfer rolls 7 are situated on the inside of the circuit of the drying felt 8.

Thus, the strip of cigarette paper 1 is in direct contact with all of the dryer drums 6 so as to be interposed between all of the dryer drums 6 and the drying felt, while the strip of cigarette paper 1 is in indirect contact with the transfer rolls since the drying felt 8 is interposed between the transfer rolls 7 and the strip of cigarette paper 1.

It should be considered that the "Unorun" drying system in the pre-drying section 4 acts during the continuous support of the strip of cigarette paper 1 to provide at least 80% of the drying that it needs and preferably 100% so as to limit sufficiently the stretching of the strip of paper while it is still deformable because it is moist (where moisture is the cause of loss of elongation at rupture and of TEA index).

Advantageously, and as can be seen in Figure 1, the circuits of drying felts 8 are mounted to extend over the dryer drums 6. As a result, all of the elements constituting the pre-drying section 4 can rest directly on a solid floor S of the building receiving the papermaking line without needing a basement to be arranged.

As can be seen from the above description, the strip of cigarette paper 1 is supported continuously on the entire pre-drying section 4 with the help of at least one drying felt 8 traveling around the set of dryer drums 6 and of transfer rolls 7 situated in the pre-drying section 4 in order to form a single "Unorun" drying system in this predrying section. In other words, the pre-drying section 4 comprises only one "Unorun" drying system adapted to obtain at least 80% of the drying of the strip of cigarette paper 1.

The use of a single "Unorun" drying system in the pre-drying section enables the strip of cigarette paper 1 to be supported throughout its passage in the pre-drying section 4, thus presents the advantage of reducing or even eliminating breakage of the strip and eliminating the speed differences, referred to as "draw", between the dryer drums 6. Thus, the strip of cigarette paper 1 is driven at a speed that is substantially constant. The travel speed is considered to be substantially constant providing its variation in speed is less than or equal to 0.1%.

The reduction in draw of the strip of paper while the strip of paper is still wet makes it possible to obtain elongation at rupture in traction and TEA indices (Tensile Energy Absorption)that are greater than those obtained with the prior art device.

It is thus possible to obtain cigarette paper with a value of elongation at rupture that is not less than 2% and a TEA index that is not less than 2.0 kN.m/m2. The TEA index (Tensile Energy Absorption) is determined in compliance with TAPPI standard T494 om-01 while the elongation at rupture is defined using the "stretch" magnitude in the same standard.

In the example shown in Figure 1, it should be observed that the post-drying section 5 is made up of dryer drums 6 organized in a top row and in a bottom row, with the strip of paper 1 running between them. While it runs through this post-drying section 5, the strip of paper 1 is supported externally relative to each dryer drum 6 with the help of drying felts 8 arranged above and below the dryer drums.

Figure 2 shows a preferred embodiment variant of the invention in which the post-drying section 5 also has only one second series of dryer drums 6 and of transfer rolls 7 forming a single second "Unorun" drying system around which there travels at least one drying felt 8 in order to support the strip of paper continuously in this post-drying section 5 so as to obtain at least 80% of the drying needed by the strip of cigarette paper. Naturally, this second "Unorun" drying system may be made in any appropriate manner, as explained above for the first "Unorun" drying system with the use of a system 10 for deflecting the path of the web of the strip of cigarette paper 1.

Thus, a "Unorun" drying system comprises a series of groups of associated dryer drums for continuously supporting the strip of cigarette paper 1. Each dryer drum group comprises at least one dryer drum 6 and at least one transfer roll 7 for a drying felt that continuously supports the strip of cigarette paper 1 on the outside face of said strip when it passes over each dryer drum 6 and on the inside face of said strip when it passes over a transfer roll 7. In each group of dryer drums, excepted for the first group of the post-drying section 4, the number of dryer drums 6 is equal to the number of transfer rolls 7, which transfer rolls are placed in such a manner that two dryer drums 6 are separated by a transfer roll 7. For the first group of the post-drying section 4, the admission roll is not a transfer roll. For the first group of the post-drying section 4, if the number of dryer drums 6 is equal to n, the number of transfer rolls is equal to n-1.

In other words, each dryer drum group of a "Unorun" drying system has only one drying felt that continuously supports the strip of cigarette paper, which felt is mounted in such a manner that all of the dryer drums are situated on the outside of the circuit of the drying felt 8 and all of the transfer rolls 7 are situated on the inside of the circuit of the drying felt 8.

Thus, the strip of cigarette paper 1 is in direct contact with all of the dryer drums 6 so as to be interposed between all of the dryer drums 6 and the drying felt, while the strip of cigarette paper 1 is in indirect contact with the transfer rolls, since the drying felt 8 is interposed between the transfer roll 7 and the strip of cigarette paper 1.

Using only one "Unorun" drying system in the postdrying section 5 enables the strip of cigarette paper 1 to be supported continuously over its entire passage through the post-drying section 5. The strip of cigarette paper is driven at a speed that is substantially constant making it possible practically to eliminate draw speed differences between the various dryer drums.

It should be considered that the "Unorun" drying system in the post-drying section 5 then provides continuous support for the strip of cigarette paper, at least 80% of the drying that it needs, and preferably 100% of that drying, so as to limit sufficiently the stretching of the strip of paper while it is still deformable because it is moist (where moisture leads to loss of breaking elongation and of TEA index).

As explained above, the reduction in draw when the strip of paper is still moist throughout the drying section makes it possible to obtain breaking elongations and TEA indices that are better than those obtained with prior art devices. Thus, using a drying section 2 comprising in the pre-drying section 4 only one "Unorun" drying system and in the post-drying section 5 exclusively a single "Unorun" drying system as shown in Figure 2, makes it possible to obtain a value of elongation at rupture lying in the range 2.5% to 3.5% and a TEA index lying in the range 2.5 kN.m/m2 to 3.0 kN.m/m2.

It is thus possible to obtain cigarette paper presenting improved mechanical characteristics that make it easier to work.

The term cigarette paper should be understood as meaning a paper having porosity lying in the range 10 CU to 200 CU, weight lying in the range 12 g/m2 to 45 g/m2, and preferably lying in the range 20 g/m2 to 35 g/m2, and a mineral filler content lying in the range 20% to 40%, typically 30% of calcium carbonate. The values of porosity, weight, and filler content are determined using the following techniques respectively: porosity ISO standard 2965/ weight TAPPI standard T410; filler content TAPPI standard TR413.

In the example shown in Figure 2, it should be observed that in the post-drying section 5, the drying felts 8 are mounted to extend above the dryer drums. As a result, all of the elements making up the pre-drying section 4 and the post-drying section 5 can stand directly on a solid floor S, thus avoiding any need to prepare a basement under at least the drying section 2.

In a preferred embodiment shown in Figure 3, the post-drying section has a suction transfer cylinder 15 at its entry. Thus, the suction cylinder 15 is placed between the exit from the size press 3 and the first dryer drum 6 of the post-drying section 5. The use of a suction drum 15 at the exit from the size press serves to further reduce the stretching of the strip of moist paper.

In Figures 1 to 3, the "Unorun" drying system of the pre-drying section 4 has a plurality of drying felts 8. Figure 4 shows an embodiment example in which only one drying felt 8 is used. In this embodiment variant, the single drying felt 8 bears continuously on the strip of cigarette paper 1 throughout the pre-drying section 4. This drying felt 8 runs around all of the dryer drums 6 and all of the transfer rolls 7. Such a configuration ensures that the strip of cigarette paper 1 has a constant travel speed over the entire pre-drying section 4.

It should be observed that provision may be made for the second "Unorun" drying system forming part of the post-drying section to have only one drying felt 8. This embodiment variant can be used when the "Unorun" drying system forming part of the pre-drying section comprises either a single drying felt 8 or a plurality of drying felts 8.

In another preferred embodiment shown in Figure 5, the "Unorun" drying systems of the pre-drying section 4 and/or of the post-drying section 5 are made up of groups of dryer drums 6 in contact in alternation with the bottom face and with the top face of the strip of cigarette paper 1. The transfers of the paper strip 1 between the groups of dryer drums 6 are provided by a succession of two transfer rolls 7 in order to support the strip of cigarette paper continuously during its travel.

Thus, the groups of dryer drums 6, each including a common circuit for the felt 8, are arranged in such a manner as to procure symmetrical drying of the strip of cigarette paper 1 by coming into contact in alternation with the bottom face and with the top face of the strip of cigarette paper 1. The transfers of the strip of cigarette paper 1 between the groups of dryer drums 6 are provided by a succession of two transfer rolls 7 so as to support the strip of cigarette paper 1 continuously throughout its travel. This provision makes it possible to control the degree of curl of the web as defined by the ISO standard 14968. Such a configuration may be applied to the pre-drying section 4 on its own or to the pre-drying section 4 and to the post-drying section 5.

Claims (8)

A drying method for a cigarette paper web (1) in a drying section (2) of a cigarette paper production line, comprising a drying section (4) located at the output of a press section and the entrance to a glue press (3), and a post-drying section (5) positioned therebetween. the outlet of the glue press (3) and the entrance to a roll-up section, the drying section (2) having a dryer (6), characterized in that the drying section further comprises transfer rollers (7) and at least one drying screen (8), and that the method consists, at least for the pre-drying section (4), to continuously support the cigarette paper web (1) by means of at least one drying screen (8) moving around all the drying drums (6) and the transfer rollers (7) located in the pre-drying section with for the purpose of forming in this pre-drying section (4) a single "Unorun" drying system for operating the cigarette paper web (1) at a speed which is id a substantial constant with velocity variations of less than or equal to 0.1%, thereby obtaining a fracture elongation value of cigarette paper not less than 2% and a TEA index of not less than 2.0 kN. m / m2, said "Unorun" drying system having one or more groups of dryer drums (6) combined to support the cigarette paper web (1) in a continuous manner, each dryer group (6) having at least one dryer drum (6), at least one transfer roller (7) and a single drying screen (8) which continuously support the cigarette paper web (1), the drying screen (8) being formed in the form of an endless web forming a sieve circuit and mounted in such a manner; that all the dryer rollers (6) in the group are located on the outside of the screen for the screen and all the transfer rollers (7) in the group are located on the inside of the screen for the screen. Drying method according to claim 1, characterized in that, for the post-drying section (5), it consists in continuously supporting the cigarette paper web (1) by means of at least one drying screen (8) which moves around all the drying drums (6) and the transfer rollers ( 7) positioned in the post-drying section (5) to form in this post-drying section (5) a single "Unorun" drying system for operating the cigarette paper web (1) at a rate substantially constant with velocity variations less than or equal to 0 , 1%, to obtain a fracture elongation value of cigarette paper not less than 2.5% and a TEA index of not less than 2.5 kN.m / m2, which has "Unorun" drying system one or more groups of drying drums (6) combined to support the cigarette paper web (1) in a continuous manner, each drying drum group (6) comprising at least one drying drum (6), at least one transfer roller (7), and a single t a screen sieve (8) which continuously supports the cigarette paper web (1), the drying screen (8) being arranged in the form of an endless web forming a sieve circuit and mounted in such a way that all the drying drums (6) in the group are positioned on the outside of the screen for the screen and all the transfer rollers (7) in the group are located on the inside of the circuit for the screen. Drying method according to claim 1 or claim 2, characterized in that it continuously supports, in the pre-drying section (4) and / or in the post-drying section (5), by a single dry screen (8) moving continuously about the dryer (6) and transfer rollers (7) in a section. Method according to claim 2 or claim 3, characterized in that it causes the cigarette paper web (1) to move on a suction transfer roller (15) located between the output of the adhesive press (3) and the first dryer (6) in the post-drying section. Method according to any one of claims 1 to 4, characterized in that it comprises, in the pre-drying section (4) and / or in the post-drying section (5), symmetrical drying of the cigarette paper web (1) by alternating contact via groups of dryers ( 6) with the underside and top of the cigarette paper web (1). Cigarette paper obtained by the method according to any one of claims 1 to 4, characterized in that it has a breaking elongation value of not less than 2.0% and a TEA index of not less than 2.0 kN.m. / m 2. Cigarette paper according to claim 6, characterized in that it has a breaking elongation value in the range 2.5% to 3.5% and a TEA index in the range 2.5 kN.m / m2 to 3.0 kN.m. / m 2. Cigarette paper according to claim 6 or claim 7, characterized in that it has: • porosity in the range of 10 CU to 200 CU; • weight ranging from 12 g / m2 to 45 g / m2; and • a mineral filler content in the range of 20% to 40%.