DRYING SECTION

Abstract: Drying section in a machine for the production of a continuous tissue paper web (22), including a pre-drying section having at least one press (1) that includes a first press device (3, 10), and a counter roll (4), being arranged to form a press nip (5) there between, and an endless paper machinery fabric (12) arranged to pass through the press nip (5) together with said web. The press is a hot press (1) having an external heating element (8) arranged to heat a surface section of the counter roll (4). The fabric (12) has a permeable coarse open structure, which defines a surface pattern that will be imprinted into the tissue web (22), and the fabric (12) extends at least to a final drying section for carrying the imprinted web to the final drying section without impairing the structure of the imprinted and pre-dried tissue web.

Description: DRYING SECTION TECHNICAL FIELD The present invention relates to a drying section in a machine for the production of a continuous tissue paper web, including a pre-drying section and a final drying section, said pre-drying section having at least one press that includes a first press device, and a counter roll, which is rotatably journalled in bearings, said first press device and said counter roll being arranged in contact with each other so as to form a press nip there between, and an endless paper machinery fabric arranged to pass through the press nip together with said web. The term "tissue" as used herein is intended to include all kinds of soft hygiene paper, whether creped or not, including but not limited to handkerchief paper, bathroom tissue, and towel. BACKGROUND OF THE INVENTION In the production of soft paper, or tissue at lower basis weights, which e.g. is used for the production of household paper, paper towels and other sanitary products, it is a general requirement that the bulk, i.e. the relation between the weight and the volume of the paper, should be essentially higher than for other types of paper. Paper with a high bulk shows a desired combination of softness and high water absorption levels. The present, commercial technology used to dry a continuous tissue web in a drying section, is to use large diameter cylinders, so called Yankee dryers, which are steam heated internally, or to use cylinders with thermal through-air drying of the web, so called TAD cylinders, which are arranged to blow hot air through the web, either from the inside and out of the cylinder, i.e. with outward flow, or from the outside and in, i.e. with inward flow. Use of Yankee dryers for drying tissue has a major disadvantage in that the smooth surface of the cylinder causes the web to be compressed as it is pressed onto the Yankee dryer by means of a press roll, which is wrapped by a felt that carries the web to the Yankee dryer. This is especially the case since the web still is relatively wet when it is transferred to the Yankee dryer, leading to its structure and bulkiness being impaired by the treatment on the Yankee dryer. Hence, in a conventional drying section for tissue, only limited bulk levels can be reached. Typically, the web is creped from the Yankee dryer, in order to somewhat improve its softness and bulkiness, but generally that improvement is lost when the tissue is used and thereby becomes wet. Furthermore, the Yankee dryer has the disadvantage that it requires a lot of space, that it has a limited capacity, and that it gives high investment costs. This depends on the cylinder being heated from the inside by steam, which heat has to be conveyed through the mantle shell of the cylinder, giving a temperature gradient with a higher temperature on the inside and a lower temperature on the outside. Despite the steam inside the cylinder having a very high temperature, a temperature of only about 95 - 100 °C is reached on the outside. Also, the entire cylinder has to be heated, resulting in a high energy consumption. Due to the relatively low temperature, the web has to be in contact with the Yankee dryer for a long period of time, which means that the cylinder has to have a large diameter. In the development of the drying section for tissue, it has also been suggested to pre-dry the web in a press section, comprising one or more press nips, possibly of shoe press type. The pre-dried web is then finally dried on a conventional drying cylinder, e.g. a Yankee dryer. A paper-making machine of this type, including a pre-drying section and a final drying section, is disclosed in US 5,393,384, the web being carried by an impermeable belt through the drying sections. Although a certain beneficial effect results from this type of system, the pre-drying section can not be made adequately efficient, since only limited linear loads can be used in the press nips, in order not to compress the tissue web and thereby lower the bulk of the web. Consequently, one press is usually not enough, to reach the desired dry content levels in the pre-drying section, why at least two presses have to be used, which requires more space, investment costs and energy. Despite of using at least two presses, the resulting tissue becomes relatively flat and compact, with a bulk that is lower than the desired high bulk. Another problem with this type of presses, is that there always is a certain re- wetting of the web at the outlet from the press nip. Drastically improved bulk levels has been reached by the use of thermal through-air drying cylinders, i.e. TAD cylinders. Typically, the bulk is increased by about 60 - 200 %, compared to the bulk levels that are reached with a conventional press nip followed by a Yankee dryer. Usually, the TAD cylinder is preceded by a suction apparatus, by which an imprinting pattern is achieved in the web in its wet state. The web is thereafter dried in the TAD cylinder, by inward or outward air flow, while retaining the structure/the imprinting pattern and thereby retaining the high bulk, of the web. In the TAD drying, the web structure is, in a matter of speaking, frozen in its structure. The TAD cylinder however has the disadvantage that it requires a lot of space, that it has a limited capacity, and yet that it requires a lot of energy. Moreover, the TAD cylinder requires the use of very large air volumes that have to be handled. Also it gives high investment costs. Another known method to dry a fibre web, is to use so called impulse drying. The wet web is pressed at a high temperature and with a high linear load in a press section, comprising one or more press nips. The technique is described in SE 7803672-0, corresponding to US 4,324,613, and is used in web types other than tissue webs, or for tissue webs with limited bulk. In these patents, there are described maximum specific pressures of 3-8 MPa and surface temperatures, on the counter roll of a press of conventional type, of between about 150°C and 350°C. By conventional type, it is here meant a press nip, in which two rolls with cylindrical cross sections are counter-acting against each other under pressure. The time that the web is kept in this type of press nip, is however only a few milliseconds, due to the short press nip, which is a time that is too short for the beneficial effects of the high pressure pressing at a high temperature to be fully developed. Therefore, it has also been suggested to use impulse drying in a heated shoe press, where the press nip is extended to about 20 - 30 cm, giving much longer times for the web in the nip. US 5,556,551 discloses such an impulse drying process for drying voluminous paper webs, such as e.g. toilet paper. The web and a water absorbing felt are fed into a press nip with a shoe press. The web may be heated by steam, prior to its entry into the nip, or the smooth surface of the counter roll may be heated, prior the nip. Delamination, caused by the sudden expansion of flash steam, when the web leaves the high pressure nip, is stated to improve the volume and softness of the web. The dried web is creped from the counter roll by a scraper. High bulk levels can not be reached by the process of US 5,556, 551, since the web will be compressed in the nip, between the absorbing felt which has a flat surface, and the smooth surface of the counter roll. Yet another known method to dry tissue web, is to use a drying cylinder, such as a Yankee dryer, as the counter roll in a press nip. The roll, which co-acts with the counter roll, may also be equipped with a press shoe. Systems of this type are shown in DE 196 54 345 (Fig. 5) and DE 43 21 403 (Fig. 11). In the latter document, it is also generally stated that the press shoe may include a heating device. In US 3,806,406, there is shown a system for the formation of a tissue web, which system too is of the type with a press nip between a first roll and a counter roll which is a Yankee dryer. Here, there has been made effort to avoid compressing of the high bulk tissue web, in that the surface of the Yankee dryer is showing a relief pattern, with depressions and elevated parts there between. Thereby, it is essentially only the parts of the web which abut the elevated parts of the cylinder surface, that are pressed together in the press nip, the intermediate parts being relatively unaffected. The web is thereby provided with an imprinting pattern, consisting of parts which are pressed together and other parts which are not pressed together, corresponding to the pattern of the cylinder surface. Despite several methods, devices and systems being known for drying tissue webs, there is no commercially available drying section that gives a high bulk, high water absorption levels, a good softness, and a distinct imprinting pattern, in the web, at the same time as it only requires a relatively small space, gives relatively low investment and energy costs, and yet has a high capacity and good reliability. DESCRIPTION OF THE INVENTION It is an object of the present invention to eliminate or lessen the problems of prior art. Accordingly, it is an object of the present invention to provide a drying section for soft paper, or tissue, which only requires a relatively small space, gives relatively low investment and energy costs, and yet has a high capacity and good reliability, and which retains the high bulk, the water absorption levels, the softness, and a distinct imprinting pattern, of the web. Moreover, it is an object of the invention to provide a drying section by which bulk values of the same high levels as the bulk values for TAD dried tissue webs, can be obtained, without TAD cylinders necessarily having to be used. Thereby, the tissue web, which has been dried in a drying section according to the invention, will exhibit an essentially retained high bulk and an essentially retained structure, including its imprinting pattern, even when wetted in connection with use thereof. In a matter of speaking, the tissue web will remember how its has been dried, whereby it keeps its good bulk and structure properties when it is used. Accordingly, there is presented a drying section in a machine for the production of a continuous tissue paper web, including a pre-drying section and a final drying section, said pre-drying section having at least one press that includes a first press device, and a counter roll, which is rotatably journalled in bearings, said first press device and said counter roll being arranged in contact with each other so as to form a press nip there between, and an endless paper machinery fabric arranged to pass through the press nip together with said web, being characterised in that said press is a hot press having an external heating element arranged to heat a surface section of the counter roll, said fabric has a permeable coarse open structure, which defines a surface pattern that during the passage through the press nip will be imprinted into the tissue web, and said fabric extends at least to the final drying section for carrying the imprinted web to the final drying section without impairing the structure of the imprinted and pre-dried tissue web. Since the terms "impulse dryer" and "impulse drying" imply that water in the web evaporates so violently that the formed steam blows out liquid water from the web, the more generic terms "hot press" and "hot pressing" are used to describe the present invention. According to one aspect of the invention, a clothing, preferably a press felt, is arranged to run in a loop about a plurality of guide rolls and to pass through the press nip, together with said fabric, which clothing has the ability to receive liquid and to carry it away from the web. Other known means for receiving and carrying the liquid away are also conceivable. The endless paper machinery fabric, is preferably an imprinting fabric or a TAD fabric, and is arranged to pass through the press nip, together with said web. A TAD fabric is a fabric that takes the web through a TAD unit. According to another aspect of the invention, in every location in the drying section where the web is pressed or subjected to a load between two surfaces, such as the web being carried on the surface of a roll or cylinder, with a fabric or clothing surface on its opposite side, or the web being subjected to a linear load between two surfaces in a press nip, at least one of said two surfaces exhibits a structured/coarse surface. In the case of the structured/coarse surface being a fabric or a clothing, it is a permeable, preferably imprinting fabric or clothing. In the case of the structured/coarse surface being the mantle surface of a roll or cylinder, it is a surface with a relief, preferably imprinting pattern. By this aspect, the web will never be completely compressed between two flat or smooth surfaces in the drying section, whereby it will retain a high bulk, a good softness and good water absorption levels, the structure of the web being essentially retained even when it is re-wetted when used. According to another aspect of the invention, the press is arranged to give an outgoing dry content of 40 - 60 %, preferably 45 - 55 % in the web, when the incoming web to the press has a dry content of 10 - 30 %, preferably 20 - 30 %. Accordingly, the dry content of the web is raised 10 - 50 % units in the hot press nip. Possibly, but not preferably, more than one press nip may be used in the pre-drying section, the additional press nip(s) being of conventional wet press type, or of impulse drying type. The press nip is preferably arranged to provide a linear load of 200-800 kN/m, preferably 300-600 kN/m between the first press device and the counter roll. The counter roll may have a smooth surface, at least if the fabric which carries the web through the nip has a structured, imprinting surface. Alternatively, the mantle surface of the counter roll may have a patterned, imprinting surface, with depressions with a depth of preferably 0.1 - 2.0 mm, and parts between the depressions, i.e. elevated parts, preferably having a width of 1 - 5 mm. The surface area of the elevated parts, i.e. the surface area which will be in contact with the web, constitutes 20 - 50 % of the total surface area of the mantle surface, measured at the circumference of the mantle. If both the permeable fabric, and the counter roll, are provided with imprinting patterns, the tissue product will beneficially be imprinted on both sides. Preferably, the counter roll has a diameter of 2.0 - 3.6 m. The counter roll may be a solid, cylindrical body, or may comprise a heatable, preferably exchangeable, rotatable sleeve, which is arranged to surround a rotatable roll body, preferably to loosely surround the roll body, in order to allow free expansion of the sleeve in relation to the roll body, in connection with said external heating. In that embodiment of the invention, the sleeve is heated by the external heating element, at a surface section of the sleeve. The sleeve and the roll body inside the sleeve, are eccentrically arranged in relation to each other, such that the sleeve is in contact with the first press device in the press nip, and also is in contact with the roll body in the press nip, so that a linear load is conveyed from the roll body to the nip, via the sleeve. The rotation of the sleeve is driven by the rotation of the roll body, the friction between the roll body end the sleeve forcing the sleeve to rotate with the same peripherical speed as the roll body. By this construction, there is avoided temperature related stress in the counter roll. Such stress may otherwise occur, due to the outer layer of a solid, externally heated roll being hotter than the inner layers of the roll, which layers are without distinct border lines. Due to this, the outer layer will expand more than the inner layer, with temperature stresses as the result. Also, in solid rolls, it may be hard to maintain the geometrical shape of the roll across the machine direction, due to difficulties in maintaining the same temperature in the mantle surface as in the gables. With a sleeve, which is loosely arranged around the roll body, this type of problems are avoided. Another advantage with the exchangeable sleeve, is that the imprinting pattern may be exchanged relatively simply, by changing sleeves. According to yet an aspect of the invention, the first press device may be a first roll and/or may be provided with a press shoe in said press nip. Optionally, the press is arranged to carry, and thereby dry, the web on the surface of the counter roll, for at least 90°, preferably at least 180°, and at most about 300° of the circumference of the counter roll, downstream said press nip. It is however also conceivable that the pre-drying section is arranged to lead the web away from the first press device and the counter roll, essentially immediately after/downstream the press nip. One advantage which may be obtained by leading the web away from the rolls essentially immediately after the press nip, is that there may be used a higher temperature on the counter roll, without risk of the (synthetic) fabric being destroyed. Preferably, said surface section of the counter roll is arranged to be heated by the external heating element, to a temperature of at least 150 °C, preferably 200 - 300 °C. The external heating element is arranged at a location other than where the web is carried by the counter roll, preferably just prior the press nip. According to another aspect of the invention, release means, preferably consisting of pressurised airknives, are arranged to release the web from the surface of the counter roll. The final drying section may comprise a Yankee dryer, a thermal through-air drying cylinder, or their combination. Also, the thermal through-air drying cylinder, if such is used, may be arranged with inward flow, or with outward flow. Of coarse, also other drying means may be used for the final drying of the web. By the combination, according to the invention, of a pre-drying section based on hot pressing technique, and a final drying section, which may include a drying cylinder, such as a Yankee dryer or a TAD cylinder, or other drying means known in the art, and with the web never being compressed between two flat or smooth surfaces in the drying section, there is, most importantly, obtained a tissue web with very high bulk levels and with structural properties very similar to the structural properties of TAD dried tissue webs. Thus, there will be obtained a tissue web which has a better structure, and which is pre-dried to a higher dry content, before the final drying of the web. This, in its turn, means that an imprinting pattern of the web, will not be impaired when it is conveyed to a drying cylinder, such as a Yankee dryer. At the same time, the energy demand is decreased in comparison with the energy demand for TAD drying, and the investment cost and space requirement is lowered. The efficient drying in the pre-drying section, ensured by the press nip with hot pressing, makes it possible to increase the speed of the tissue paper machine. Alternately, it decreases the need for large diameter drying cylinders in the final drying section, whereby diameters that are smaller than conventional, may be used in the drying cylinder(s). If a TAD cylinder is used in the final drying section, it may be smaller and will use smaller air flows. In the reconstruction of existing paper-making machines, the capacity may be increased, without requiring any extra space, and also the efficiency and reliability of the machine will be improved. DETAILED DESCRIPTION In the following, the drying section of the present invention will be described with reference to the drawings, of which: Fig. 1 is a schematic illustration of a first embodiment of the invention, comprising a press with the web wrapped around the counter roll, followed by a Yankee dryer, Fig. 2 is a schematic illustration of a second embodiment of the invention, comprising a press without web wrap around the counter roll, followed by a Yankee dryer, Fig. 3 is a schematic illustration of a third embodiment of the invention, comprising a press with the web wrapped around the counter roll, followed by a TAD cylinder with inward air flow, Fig. 4 is a schematic illustration of a fourth embodiment of the invention, comprising a press without web wrap around the counter roll, followed by a TAD cylinder with inward air flow, Fig. 5 is a schematic illustration of a fifth embodiment of the invention, comprising a press with the web wrapped around the counter roll, followed by a TAD cylinder with outward air flow. Fig. 6 is showing a preferred embodiment of a counter roll. Corresponding objects in the various figures are denoted with the same reference numerals. In the embodiment shown in Fig. 1 a pre-drying section includes a hot press, which is generally denoted with the reference numeral 1, and a final drying section with a drying cylinder 2, which in this first embodiment is a Yankee dryer. The hot press 1 that sometimes not quite adequately is called an impulse dryer comprises a first roll 3, a counter roll 4, which together with the first roll 3 forms a press nip 5, and an endless papermaking machinery fabric 12, which is in direct contact with the web 22. The fabric 12 has the ability to receive liquid, in liquid phase or in gas phase. The wet web 22 is being imprinted by the imprinting fabric 12, whereby a vacuum device 30 preferably sucks the web onto, and partially into, the permeable coarse open structure of the fabric, at a location prior to the press 1. Accordingly, the web 22 is arranged on the fabric 12 on the side of the fabric which is opposite the vacuum device 30, in the figure. The counter roll 4 is made of a solid cylindrical body, provided with shaft pivots (not shown), for rotatable journalling in bearings (not shown) by a motor (not shown). The counter roll 4 is provided with a, movable (e.g. oscillating) or stationary, external heating element 8, which heating element is arranged to heat a surface section of the roll 4, just prior to the entry of that surface section into the press nip 5. The heating may be effected by induction heating, heating by gas burner, or other means, known per se in impulse drying. The web 22 is arranged to wrap an essential part of the circumference of the counter roll 4, thereby additionally drying the web on the hot surface of the roll, after the press nip 5. A ventilation hood 9 is arranged to ventilate at least a part of the surface of the counter roll 4, at a location where the web is carried by the roll. The web will release readily from the surface of the counter roll at temperatures of above 200 °C. This is especially the case since the web is relatively firmly held by the mesh structure of the fabric 12. If necessary, release means, such as airknives or similar (not shown), may be arranged to aid in the releasing of the web from the roll surface. If needed, the mantle surface of the counter roll 4, may be cleaned by a cleaning means, such as a doctor blade, a brush (preferably a metal brush), or by airknives (not shown). The impulse drying, in the heated press nip 5, may result in beneficial effects on the bulk. One theory, which is not a binding theory, is that this is caused by the sudden expansion of flash steam, when the web leaves the high pressure nip. Thereby, there is attained an advantageous increase in bulk/volume and softness of the web. Optionally, the temperature of the web 22 may be increased before the press nip 5, by one or more steam blow boxes (not shown) being arranged on the free side of the web. Pre-heating of the wet web gives the water a lower viscosity, which facilitates the pressing of the water from the web in the press nip 5. The mantle surface of the counter roll 4 is preferably, but not necessarily, provided with an imprinting pattern, whereby the web 22 will be imprinted on the side thereof that faces the mantle of the counter roll 4. The imprinting pattern is preferably of the type shown in another patent application, which is filed with the same priority date as the present patent application, by the same applicant, which other patent application has the title "Press". Since the fabric 12 is provided with an imprinting pattern, the web will, in this case, be imprinted on both sides. In addition to the advantage of having the web imprinted on both sides, which increases its bulk and softness, the pattern of the mantle surface of the counter roll 4 leads to the web essentially only being compressed, by the press nip 5, in the parts of the web that are affected by the elevated parts of the imprinting pattern, i.e. the parts between the depressions of the pattern. The intermediate parts, i.e. the parts that correspond to the depressions of the pattern, are relatively unaffected. In these parts, the tissue web will however be allowed to expand by the steam in the depressions, giving a tissue of high bulk. The web is thereby provided with an imprinting pattern, consisting of parts which are pressed together and other parts which are not pressed together, corresponding to the pattern of the surface of the roll. Even if the mantle surface of the counter roll 4 is smooth, there will be achieved a similar effect, due to the open mesh structure of the fabric. In the shown embodiment, the hot press 1 is a shoe press, with an extended press nip 5, the first roll 3 being a shoe press roll, which comprises a press shoe 10. The mantle of the first roll 3 thereby consists, as is conventional for a shoe press roll, of an impermeable, flexible jacket 11. The press shoe 10 has a concave surface (of the type denoted with the reference numeral 23 in Fig. 6),- to follow the convex surface of the counter roll 4, whereby the extended nip 5 is formed. The flexible jacket 11 of the first roll 3 runs through the press nip 5, in sliding contact with the concave surface of the press shoe 10. As an alternative, a press belt may be substituted for the flexible jacket 11 and may run in a loop about a plurality of guide rolls (not shown), the press shoe being mounted in the loop. The clothing 6 of the shoe hot press 1 is arranged to run in a loop around a plurality of guide rolls 7, and through the extended nip 5. The web 22 is carried by the fabric 12 and is led together with the clothing 6, to the press nip 5. The web is departed, together with the fabric, from the clothing after the press nip, in order to lie on the surface of the counter roll 4, as is described above. Usually, the clothing 6 consists of a press felt, but there may also be used a permeable belt, which has through apertures, and possibly depressions between the apertures, or there may be used an impermeable belt with depressions of suitable depth, shape and extension. The apertures and depressions are arranged to receive liquid and to carry it away from the web and out of the press nip 5. As an alternative, there may be used a suction device or any other known means for carrying and withdrawing the moist from the press nip. Instead of, or in combination with, the permeable or impermeable belt, there is used a permeable imprinting fabric 12 to carry the web, at least through the pre-drying section. The fabric is preferably made of a synthetic and/or metal material and has an open coarse structure of about 35-50 mesh, both in the machine direction and in the cross direction. The shown hot press 1, with a press shoe 10, is the preferred embodiment, but also other types of hot press devices, such as a conventional roll press, for example, having a cylindrical press roll that co-operates with the hot counter roll 4 to form a press nip, may be used in the invention. From the hot press 1, i.e. after the web 22 has been released from the surface of the counter roll 4, the web, and preferably also the fabric 12, is led, optionally via one or more guide rolls 13, to a drying cylinder 2 or other drying equipment, for final drying. In the shown first embodiment, the drying cylinder 2 is a Yankee dryer. The web 22 is led into a transfer nip 14, between the drying cylinder 2 and a transfer roll 15 of conventional cylindrical type. The linear load of the transfer nip 14 is very low. It is essentially only enough to transfer the web onto the drying cylinder. The web follows the Yankee dryer around a greater part of its circumference, and is thereby dried by the warm mantle surface thereof. The Yankee dryer is of a conventional type, including a hood and attributes, known per se. Possibly though, it may have a somewhat smaller diameter than a conventional Yankee dryer. When the drying is completed, the web may be creped off from the mantle surface of the dryer, with the aid of a creping doctor 16. Alternatively, it is being led away without being creped. If needed, the Yankee dryer may be followed by a light calender for improving a tactual feeling, or by other drying means, such as e.g. a trough-air drying cylinder (TAD cylinder) or some corresponding means. In Fig. 2, there is shown a second embodiment of the invention, comprising a hot press 1 without web wrap around the counter roll 4, followed by a Yankee dryer 2. Here, the web passes through the nip of the first roll 3, which may be of shoe press type with an extended nip, and the heated counter roll 4. The web 22 is thereafter conveyed from the nip 5, to the Yankee dryer 2, by the fabric 12, without being carried around the circumference of the counter roll 4. The web 22 is released from the roll 4 of the hot press 1, essentially directly after the press nip 5, e.g. by airknives. The external heating element 8 may be arranged to heat the surface of the counter roll 4, at a location about 30° - 300° prior the press nip. Accordingly, it may also be arranged in the vicinity of the outlet from the press nip, which is possible since the heat loss from the surface of the counter roll is relatively small before it comes in contact with the wet web in the press nip 5. Other than this, the shown, second, embodiment is of the same type as the one shown in Fig. 1. In Fig. 3, there is shown a third embodiment of the invention, comprising a hot press 1 with the web wrapped around the counter roll 4, followed by a thermal through-air drying cylinder (TAD cylinder) 17. The pre-drying section, comprising the hot press 1, is of the same configuration as the pre-drying section of Fig. 1. From the hot press 1, the web 22 is led, optionally via one or more guide rolls (not shown), on the fabric 12, to a drying cylinder 17. The web is arranged to be carried around an essential part of the circumference of the drying cylinder, on the surface of the drying cylinder, with the fabric 12, which is permeable, there between. The drying cylinder 17 is arranged to, via a not shown hood, draw air of temperatures up to 220 °C and velocities of about 5-10 m/s, through the web, the fabric 12 and the mantle surface of the cylinder, i.e. with an inward air flow, whereafter the air flow leaves the cylinder via a gable thereof and is recirculated with the aid of a circulation fan. Thereby, the web is dried by the through- flowing air. The web is finally dried on the TAD cylinder 17, it being conveyed, by the fabric 12, after the TAD cylinder, via one or more guide rolls 18, to a reel (not shown) for winding into a tissue paper roll. Alternatively, the web is conveyed after the TAD cylinder, to other drying means, such as a Yankee dryer or the similar, for additional drying. In Fig. 4, there is shown a fourth embodiment of the invention, comprising a hot press 1 without web wrap around the counter roll 4. The hot press 1 is of the same type as the one shown in Fig. 2. After the hot press 1, the web 22 is optionally transferred from the fabric 12 to a second fabric 19, which here is a TAD fabric, via one or more pick-up devices 33, and further to a drying cylinder 17. In this embodiment, the drying cylinder 17 is a TAD cylinder of the same configuration as the one shown in Fig. 3. After the TAD cylinder the web is conveyed to further drying, such as a Yankee dryer (not shown), or it is conveyed to a reel (not shown) for winding. In Fig. 5, there is shown a fifth embodiment of the invention, comprising a hot press 1 with the web wrapped around the counter roll 4, as in Fig. 1. After the hot press 1, the web 22 is conveyed, optionally via one or more guide rolls (not shown), to a TAD cylinder 17. In this embodiment, the TAD cylinder 17 is arranged with outward air flow, i.e. through the mantle surface of the cylinder, through the web, in order to dry the web, and through the fabric. The web is thereby arranged to be carried around an essential part of circumference of the mantle surface of the cylinder, between the permeable fabric 12 and the cylinder 17. In Fig. 6, there is shown that the counter roll 4, in an especially preferred embodiment, is provided with a heatable, preferably exchangeable, sleeve 25, which is arranged to surround a roll body 27, preferably to loosely surround the roll body, in order to allow free expansion of the sleeve 25 in relation to the roll body 27, whereby undesired stresses are avoided. The sleeve 25 is movable, and arranged to continuously transmit heat to the web 22, when the web passes through the press nip 5. The sleeve 25 is heated from the outside by the external heating element 8. The sleeve 25 is preferably cylindrical, and surrounds at least the axial part of the cylindrical roll body 27, which is active in the press nip 5. The sleeve 25 is free from mechanical, adhesive, or any other type of permanent, fixing connection, which would prevent a free expansion of the sleeve 25, axially and/or radially, in relation to the cylindrical roll body 27, outside the press nip 5, i.e. where the heating takes place. The roll body 27 is arranged to press against the sleeve 25 at a location within the zone of the press nip 5, i.e. within the zone of the press shoe 10. The pressure between the sleeve 25 and the roll body 27 is high enough for the sleeve to be rotated by the roll body, with the same peripherical speed at the location of contact. The sleeve 25 is arranged to rotate about its own centre axis, which is eccentric in relation to the axis of rotation of the roll body 27. The sleeve 25 may be rigid and stabile in shape, or flexible, and thus not stabile in shape. Generally, if it is rigid, it has a wall thickness of 5-100 mm, preferably 15-40 mm. By making the wall thickness of the sleeve 25 thick enough, the mantle surface of the sleeve can be treated as the surface of a conventional press roll, whereby it may be cleaned by a cleaning means, such as a doctor blade, a brush (preferably a metal brush), or by airknives (not shown). If the sleeve 25 is flexible, it may be a soft, flexible cylinder, with a wall thickness of 0.4-5.0 mm, preferably 0.8-2.3 mm. Due to the sleeve 25 being flexible, a doctor blade for cleaning may be arranged at a suitable location, so that the sleeve 25 is bent towards the roll body 27, which will act as a support. The sleeve may also, in yet an embodiment, be permeable, which decreases the risk of the web sticking to the mantle surface of the sleeve. The mantle surface of the sleeve may, thereby, be provided with through apertures and/or depressions, which constitute an imprinting pattern for the web. The pattern of the surface is of the same sizes as has been previously described in connection with the counter roll. The releasing of the web may also be facilitated by using airknives (not shown), for directing an intense air flow on the web, directly or through the sleeve. The type of hot press 1 shown in Fig. 6, may be used in connection with any of the embodiments shown above. Accordingly, although not shown, it may also be used with the web wrapped around the sleeve 25, in the same way as the web is wrapped around the counter roll 4 in Figs. 1, 3 and 5. By the embodiment shown in Fig. 1 and 2, the tissue web will be given good properties, such as bulk and structure, in the pre-drying section, at the same time as it is pre-dried to such an extent that the properties not will be impaired by the final drying, although a conventional Yankee cylinder is used for the final drying. Thus, the web will exhibit qualities which are comparable with the qualities of a TAD dried web, without using TAD drying. The same is true for the embodiments shown in Fig. 3, 4 and 5, although a TAD cylinder is used here. The used TAD cylinder may however be smaller than what usually is used for TAD cylinders, and may use smaller air flows than what is conventional. The invention is not limited to the embodiments described above, but may be varied within the scope of the claims. Accordingly, a person skilled in the art will easily see how the different parts of the drying section, as described, may be combined in various ways. For example, the TAD cylinder of Fig. 5 may be combined with a press without web wrap around the mantle surface of the counter roll. Further, the final dryer does not have to include a Yankee dryer and/or a TAD cylinder but may include a flat through- air drying system, or the drying system marketed under the trademark CONDEBELT by Valmet Corporation, and also infrared heaters may be used.

Claims: CLAIMS 1. Drying section in a machine for the production of a continuous tissue paper web (22), including a pre-drying section and a final drying section, said pre-drying section having at least one press (1) that includes a first press device (3, 10), and a counter roll (4), which is rotatably journalled in bearings, said first press device and said counter roll being arranged in contact with each other so as to form a press nip (5) there between, and an endless paper machinery fabric (12) arranged to pass through the press nip (5) together with said web, characterised in that said press is a hot press (1) having an external heating element (8) arranged to heat a surface section of the counter roll (4), said fabric (12) has a permeable coarse open structure, which defines a surface pattern that during the passage through the press nip (5) will be imprinted into the tissue web (22), and said fabric (12) extends at least to the final drying section for carrying the imprinted web to the final drying section without impairing the structure of the imprinted and pre-dried tissue web. 2. Drying section according to claim 1, characterised in that at least one suction member (30) is provided upstream of the press nip (5) for sucking the wet tissue paper web (22) into the coarse structure of said fabric (12). 3. Drying section according to claim 1 or 2, characterised in that an endless clothing, preferably a press felt (6), is arranged to pass through the press nip (5) together with said web (22) and with said fabric (12) sandwiched between the felt (6) and the web, and to leave the web-fabric-felt sandwich on departure from the press nip (5). 4. Drying section according to any one of the preceding claims, characterised i n that said hot press (1) is arranged to give an outgoing dry content of 40 - 60 %, preferably 45 - 55 % in the web (22), when the incoming web to the press has a dry content of 10 - 30 %, preferably 20 - 30 %. 5. Drying section according to any one of the preceding claims, characterised i n that said press nip (5) is arranged to provide a linear load of 200-800 kN/m, preferably 300-600 kN/m, between said first press device (3, 10) and said counter roll (4). 6 . Drying section according to any one of the preceding claims, characterised i n that said first press device (3) comprises a press shoe (10) in said press nip (5). 7. Drying section according to any one of the preceding claims, characterised i n that said hot press (1) is arranged to carry, and thereby dry, the web (22) on the mantle surface of the counter roll (4), for at least 90°, preferably at least 180°, and at most about 300° of the circumference of the counter roll, downstream said press nip (5). 8. Drying section according to any of claims 1-7, characterised in that said pre-drying section is arranged to lead the web (22) away from said first press device (3, 10) and said counter roll (4), essentially immediately downstream said press nip (5). 9. Drying section according to any one of the preceding claims, characterised i n that the counter roll (4) has a solid, cylindrical roll body. 10. Drying section according to any of claims 1-8, characterised in that the counter roll (4) comprises a heatable, preferably exchangeable, sleeve (25), which is arranged to surround a roll body (27), preferably to loosely surround the roll body (27), in order to allow free expansion of the sleeve (25) in relation to the roll body (27), in connection with said external heating. 11. Drying section according to any one of the preceding claims, characterised i n that said counter roll (4) has an outer diameter of about 2.0 - 3.6 m. 12. Drying section according to any one of the preceding claims, characterised i n that said surface section of the counter roll (4) is arranged to be heated by said external heating element (8) to a temperature of at least 150 °C, preferably 200 - 300 °C. 13. Drying section according to any one of the preceding claims, characterised i n that the mantle of said counter roll (4) has an essentially smooth surface. 14. Drying section according to any one of claims 1-12, characterised in that the mantle of said counter roll (4) has a patterned, imprinting surface, with WO 00/79046 γη PCT/SEOO/00842 depressions with a depth of preferably 0.1 - 2.0 mm, and parts between the depressions preferably having a width of 1 - 5 mm. 15. Drying section according to claim 14, characterised in that the parts between the depressions, i.e. elevated parts of the mantle, have a surface area of 20 - 50 % of the total surface area of the mantle, measured at the circumference of the mantle of the counter roll (4). 16. Drying section according to any one of the preceding claims, characterised i n that release means, preferably including airknives, are arranged to release the web (22) from the surface of the counter roll (4). 17. Drying section according to any one of the preceding claims, characterised i n that said final drying section has at least one drying cylinder (2, 17). 18. Drying section according to claim 17, characterised in that said at least one drying cylinder is a Yankee dryer (2), a thermal through-air drying cylinder (17), or similar, or a combination thereof. 19. Drying section according to claim 18, characterised in that said thermal through-air drying cylinder (17) has a hood that is arranged to blow hot air from outside of the cylinder and in. 20. Drying section according to claim 18, characterised in that said thermal through-air drying cylinder (17) is arranged to blow hot air from inside of the cylinder and out. 21. Method of drying a continuous tissue paper web (22) in a drying section of a tissuemaking machine, said drying section including a pre-drying section and a final drying section, said pre-drying section having at least one press (1) that includes a first press device (3, 10) and a counter roll (4), which is rotatably journalled in bearings, said first press device and said counter roll being arranged in contact with each other so as to form a press nip (5) there between, said method including carrying the wet tissue paper web (22) on an endless paper machinery fabric (12), and running the fabric (12) and the web through said press nip (5), characterised by providing an external heating element (8) and heating a surface section of the counter roll (4) by means of the external heating element (8), WO 00/79046 i o PCT/SEOO/00842 hot pressing the wet web (22) in the press nip (5), using as fabric (12) a fabric having a permeable coarse open structure, which defines a surface pattern that during the passage through the press nip (5) will be imprinted into the tissue web, and extending said fabric (12) at least to the final drying section for carrying the imprinted web to the final drying section without impairing the structure of the imprinted and pre-dried tissue web. 22. Method according to claim 21, char acterised by the web, which is carried on the fabric (12) being heated before its entry into the press nip (5). 23. Method according to claim 21 or 22, characterised by a clothing (6), preferably a press felt, being arranged to run together with the fabric (12) through the press nip (5), in order to receive liquid from the web (22), and to carry it away from the press nip (5). 24. Method according to any of claims 21 -23, characterised by the wet tissue paper web (22) being sucked into the coarse structure of said fabric (12) before the press nip (5), preferably by at least one suction member (30). 25. Method according to any of claims 21-24, characterised by the web being finally dried by a Yankee dryer (2), a thermal through-air drying cylinder (17), or similar, or a combination thereof. 26. Method according to claim 25, c h a r a c t e-r i s e d by the final drying comprising said thermal through-air drying cylinder (17), whereby the fabric (12) carrying the web is arranged to run together with the web (22) on the thermal through-air drying cylinder (17). AMENDED CLAIMS [received by the International Bureau on 08 November 2000 (08.11.00); original claims 1 and 21 amended, other claims unchanged (4 pages)] 1. Drying section in a machine for the production of a continuous tissue paper web (22), including a pre-drying section and a final drying section, said pre-drying section having at least one press (1) that includes a first press device (3, 10), and a counter roll (4), which is rotatably journalled in bearings, said first press device and said counter roll being arranged in contact with each other so as to form a press nip (5) there between, and an endless paper machinery fabric (12) arranged to pass through the press nip (5) together with said web, said press is a hot press (1) having heating element (8) arranged to heat the counter roll (4), said fabric (12) has a coarse open structure, which defines a surface pattern that during the passage through the press nip (5) will be imprinted into the tissue web (22), characterised in that said fabric (12) extends at least to the final drying section for carrying the imprinted web to the final drying section without impairing the structure of the imprinted and pre-dried tissue web. 2. Drying section according to claim 1, characterised in that at least one suction member (30) is provided upstream of the press nip (5) for sucking the wet tissue paper web (22) into the coarse structure of said fabric (12). 3. Drying section according to claim lor 2, characterised in that an endless clothing, preferably a press felt (6), is arranged to pass through the press nip (5) together with said web (22) and with said fabric (12) sandwiched between the felt (6) and the web, and to leave the web-fabric-felt sandwich on departure from the press nip (5). 4. Drying section according to any one of the preceding claims, characterised i n that said hot press (1) is arranged to give an outgoing dry content of 40 - 60 %, preferably 45 - 55 % in the web (22), when the incoming web to the press has a dry content of 10 - 30 %, preferably 20 - 30 %. 5. Drying section according to any one of the preceding claims, characterised i n that said press nip (5) is arranged to provide a linear load of 200-800 kN/m, preferably 300-600 kN/m, between said first press device (3, 10) and said counter roll (4). 6. Drying section according to any one of the preceding claims, characterised i n that said first press device (3) comprises a press shoe (10) in said press nip (5). 7. Drying section according to any one of the preceding claims, characterised i n that said hot press (1) is arranged to carry, and thereby dry, the web (22) on the mantle surface of the counter roll (4), for at least 90°, preferably at least 180°, and at most about 300° of the circumference of the counter roll, downstream said press nip (5). 8. Drying section according to any of claims 1-7, characterised in that said pre-drying section is arranged to lead the web (22) away from said first press device (3, 10) and said counter roll (4), essentially immediately downstream said press nip (5). 9. Drying section according to any one of the preceding claims, characterised i n that the counter roll (4) has a solid, cylindrical roll body. 10. Drying section according to any of claims 1-8, characterised in that the counter roll (4) comprises a heatable, preferably exchangeable, sleeve (25), which is arranged to surround a roll body (27), preferably to loosely surround the roll body (27), in order to allow free expansion of the sleeve (25) in relation to the roll body (27), in connection with said external heating. 11. Drying section according to any one of the preceding claims, characterised i n that said counter roll (4) has an outer diameter of about 2.0 - 3.6 m. 12. Drying section according to any one of the preceding claims, characterised i n that said surface section of the counter roll (4) is arranged to be heated by said external heating element (8) to a temperature of at least 150 °C, preferably 200 - 300 °C. 13. Drying section according to any one of the preceding claims, characterised i n that the mantle of said counter roll (4) has an essentially smooth surface. 14. Drying section according to any one of claims 1-12, characterised in that the mantle of said counter roll (4) has a patterned, imprinting surface, with depressions with a depth of preferably 0.1 - 2.0 mm, and parts between the depressions preferably having a width of 1 - 5 mm. 15. Drying section according to claim 14, characterised in that the parts between the depressions, i.e. elevated parts of the mantle, have a surface area of 20 - 50 % of the total surface area of the mantle, measured at the circumference of the mantle of the counter roll (4). 16. Drying section according to any one of the preceding claims, characterised i n that release means, preferably including airknives, are arranged to release the web (22) from the surface of the counter roll (4). 17. Drying section according to any one of the preceding claims, characterised i n that said final drying section has at least one drying cylinder (2, 17). 18. Drying section according to claim 17, characterised in that said at least one drying cylinder is a Yankee dryer (2), a thermal through-air drying cylinder (17), or similar, or a combination thereof. 19. Drying section according to claim 18, characterised in that said thermal through-air drying cylinder (17) has a hood that is arranged to blow hot air from outside of the cylinder and in. 20. Drying section according to claim 18, characterised in that said thermal through-air drying cylinder (17) is arranged to blow hot air from inside of the cylinder and out. 21. Method of drying a continuous tissue paper web (22) in a drying section of a tissuemaking machine, said drying section including a pre-drying section and a final drying section, said pre-drying section having at least one press (1) that includes a first press device (3, 10) and a counter roll (4), which is rotatably journalled in bearings, said first press device and said counter roll being arranged in contact with each other so as to form a press nip (5) there between, said method including carrying the wet tissue paper web (22) on an endless paper machinery fabric (12), and running the fabric (12) and the web through said press nip (5); heating the counter roll (4) by means of a heating element (8), hot pressing the wet web (22) in the press nip (5), using as fabric (12) a fabric having a coarse open structure, which defines a surface pattern that during the passage through the press nip (5) will be imprinted into the tissue web, c h a r a c t e r i s e d by extending said fabric (12) at least to the final drying section for carrying the imprinted web to the final drying section without impairing the structure of the imprinted and pre-dried tissue web. 22. Methodaccordingto claim 21, characteri sed by the web, which is carried on the fabric (12) being heated before its entry into the press nip (5). 23. Method according to claim 21 or 22, characterised by a clothing (6), preferably a press felt, being arranged to run together with the fabric (12) through the press nip (5), in order to receive liquid from the web (22), and to carry it away from the press nip (5). 24. Method according to any of claims 21-23, characterised by the wet tissue paper web (22) being sucked into the coarse structure of said fabric (12) before the press nip (5), preferably by at least one suction member (30). 25. Method according to any of claims 21-24, characterised by the web being finally dried by a Yankee dryer (2), a thermal through-air drying cylinder (17), or similar, or a combination thereof. 26. Method according to claim 25, characterised by the final drying comprising said thermal through-air drying cylinder (17), whereby the fabric (12) carrying the web is arranged to run together with the web (22) on the thermal through-air drying cylinder (17).

Inventors: KLERELID INGVAR, KLERELID, INGVAR
Applicants: KLERELID INGVAR, VALMET KARLSTAD AKTIEBOLAG, KLERELID, INGVAR, VALMET-KARLSTAD AKTIEBOLAG
Application year: 2000
Main classification: D21F5
IPC codes: D21F3, D21F11