Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F11/00—Processes for making continuous lengths of paper, or of cardboard, or of wet web for fibre board production, on paper-making machines
  • D21F11/14—Making cellulose wadding, filter or blotting paper

Definitions

• the present invention relates to a paper machine for manufacturing a fibrous soft paper web, including:
• a wet section having a headbox; a forming roll; and inner an outer clothings running around the forming roll, between which clothings the fibrous web is formed;
• a press section having at least one shoe press having a shoe press roll and a counter roll, said rolls forming an extended press nip, a substantially impermeable belt and a press felt, the substantially impermeable belt and tne press felt running through the extended press nip with the fibrous web enclosed therebetween;
• a drying section having a drying cylinder and a transfer member which, together with the drying cylinder, forms a transfer nip for transfer of the fibrous web to the drying cylinder.
• the invention also relates to a method of manufacturing a fibrous soft paper web m a paper machine, said machine including:
• wet section having a headbox; a forming roll; and inner and outer clothings running around the forming roll, between which clothings the fibrous web is formed;
• a press section having a least one shoe press having a shoe press roll and a counter roll, said rolls forming an extended press nip, a substantially impermeable belt and a press felt, the substantially impermeable belt and the press felt running through the extended press nip with the fibrous web enclosed therebetween;
• a drying section having a drying cylinder and a transfer member which, together with the drying cylinder, forms a transfer nip for transfer of the fibrous web to the drying cylinder.
• a paper machine of the type described above is disclosed in US-5, 393 , 384 , see particularly Figure 6.
• the paper machine shown therein has a belt impermeable to water, which runs in a loop through an extended press nip formed by a shoe press roll and a counter roll.
• a press felt is conducted directly to the press nip, where it runs together with the impermeable belt and the paper web.
• the paper web is transferred from a forming fabric to the impermeable belt, which is to carry the paper web on its under side up to the press nip and thence to the drying cylinder.
• the impermeable belt thus carries the paper web a relatively long distance after the paper web has been transferred from the forming fabric to the impermeable belt.
• the adhesion force between the impermeable belt and the paper web is greater than that between the press felt and the paper web.
• the impermeable belt in question is not compressible and has a smooth, web-carrying surface.
• DE-195 48 747 describes a paper machine for manufacturing creped tissue paper, which is provided with a press comprising a shoe press roll, a counter roll and a suction roll, the counter roll forming a first press nip with the suction roll and a second extended press nip with the shoe press roll .
• a felt passes through the two press nips together with the paper web and then carries the paper web with it to a Yankee dryer, to which the paper web is transferred when the felt and the paper web pass around a transfer roll forming a non-compressing nip with the Yankee dryer.
• Suction zones for dewatering the felt are provided before and after the first press nip, the suction zone before the press nip being situated within the suction roll whereas the suction zone after the press nip is in a side loop in which the felt runs alone and joins the paper web again at the entry to the second press nip.
• One drawback with such a paper machine is that the paper web is exposed to rewetting by the wet felt before it reaches the Yankee dryer.
• US-5, 298, 124 describes a compressible transfer belt for use in a paper or board machine in order to eliminate open draws of the paper web and to easily release the paper web so that it can be transferred to a fabric or belt .
• the transfer belt carries the paper web through the press section, which comprises one or more press nips, and on to the drying section which comprises a plurality of drying cylinders and a belt passing in a loop around a transfer roll which forms a nip with the transfer belt.
• Each press is also provided with a felt passing through its press nip and enclosing the paper web between it and the transfer belt .
• the impermeable transfer belt is also designed so that a liquid film formed in the press nip between the transfer belt and the paper web breaks up when the pressure on the transfer belt ceases after the press nip, so that its release properties increase and the paper web can thus more easily be transferred to a fabric or another belt running in a loop.
• US-5, 298, 124 offers an excellent description of the tasks a transfer belt cooperating with a press felt shall perform in a satisfactory manner, and also of the properties and design of such transfer belts, which then were described in patent specifications US-A-4 , 483 , 745 , 4,976,821, 4,500,588, 5,002,638, 4,529,643 and CA-A-1, 188, 556.
• the critical tasks are a) to remove the paper web from the press felt without causing instability problems; b) to cooperate with the press felt in one or more nips to ensure optimal dewatering and high quality of the paper web; and c) to transfer the paper web in a closed draw from a press in the press section to a paper receiving fabric or belt in the following press or presses of the press section or to a pick-up fabric in the drying section.
• the transfer belt for the press section of a paper machine described in US-5, 298, 124 has a web-contacting surface which is substantially impermeable to water and air and has pressure-responsive microscale topography. Under influence of the pressure in a press nip in the press section, the transfer belt is compressed so that the microscale roughness of said surface is decreased, whereupon the surface becomes much smoother and allows the formation of a thin, continuous film of water thereon.
• a belt of the type described in US-5, 298, 124 is also well suited for use in a paper machine according to the invention, for transferring a soft paper web in closed draw from a shoe press nip in the press section to a Yankee dryer in the drying section of the soft paper machine.
• a shoe press nip results in a high degree of dewatering.
• the object of the present invention is to provide an improved paper machine and an improved method of manufacturing soft paper, said paper machine and said method enabling the manufacture of a fibrous web with high dry solids content before the drying cylinder in order to enable a high production rate to be achieved at reasonable cost, and to reliably transfer the fibrous web to the drying cylinder although the fibrous web is carried to the drying cylinder by an impermeable belt.
• the press felt is arranged to carry the fibrous web to the press section from the forming roll or from a point situated downstream of the forming roll and upstream of the press section;
• the substantially impermeable belt and the web-carrying press felt are arranged to run together not until they enter the press section to enclose the fibrous web between them, the substantially impermeable belt being arranged to run directly to the press section;
• the substantially impermeable belt is arranged to run from the shoe press to the drying cylinder to carry the fibrous web to said transfer nip;
• the press felt is arranged to run in a direction away from the substantially impermeable belt at a point immediately after the extended press nip and before a water film formed in the extended press nip on the substantially impermeable belt breaks up;
• a device for applying adhesive is arranged before said transfer nip to apply a continuous adhesive layer on the envelope surface of the drying cylinder and/or on the fibrous web.
• a transfer belt according to US-A-5, 298, 124 which is intended for pressing in a press section and usable for transferring a paper web from the press section to a drying fabric, is useful with advantage for transferring a soft paper web from a shoe press nip directly to a Yankee dryer or other drying cylinder.
• the conditions at a Yankee dryer are completely different from those in a press nip. With a Yankee dryer no pressing of the soft paper web occurs for direct dewatering. Rather it is a question of supporting the soft paper web to the envelope surface of the Yankee dryer so that the fibers of the soft paper web adhere efficiently to the surface of the Yankee dryer thereby achieving good heat transfer to the paper web.
• Figure 1 shows a paper machine according to a first embodiment of the invention.
• Figure 2 shows a paper machine according to a second embodiment of the invention.
• Figure 3 shows a paper machine according to a third embodiment of the invention.
• Figure 4 shows a paper machine according to a fourth embodiment of the invention.
• Figures 1-3 show schematically parts of a paper machine for manufacturing a fibrous web 1 of soft paper such as tissue and other sanitary paper products.
• Each of the paper machines comprises a wet section 2, a press section 3 and a drying section 4.
• the wet section 2 comprises a headbox 7, a forming roll 8, an endless, carrying, inner clothing 9 and an endless, covering outer clothing 10 consisting of a forming fabric.
• the inner and outer clothings 9 and 10 run, each in its own loop, around a plurality of guide rolls 11 and 12, respectively.
• the drying section 4 comprises a drying cylinder 5 covered by a hood 30.
• the drying cylinder is suitably a Yankee dryer.
• a creping doctor 21 is arranged to crepe the fibrous web 1 off the Yankee dryer 5.
• An application device 31 is provided for applying of a suitable adhesive on the envelope surface of the Yankee dryer 5 immediately before the transfer nip.
• the press section 3 comprises a shoe press with a shoe press roll 14 and a counter roll 19, these rolls 14 and 19 forming an extended press nip with each other.
• the press section also comprises an endless press felt 15 which runs in a loop around guide rolls 6, and an endless, substantially impermeable transfer belt 16.
• the substantially impermeable belt 16 runs in a loop around the counter roll 19, a transfer roll 17 and a plurality of guide rolls 18.
• the transfer roll 17 forms a transfer nip with the Yankee dryer 5 with low linear pressure, i.e. about 30-60 kN, through which transfer nip the substantially impermeable belt 16 thus passes.
• the press section 3 also includes a roll press, the rolls of which consisting of a suction press roll 13 and said counter roll 19 to form a press nip through which the substantially impermeable belt 16 and the press felt 15 pass together with the fibrous web 1.
• the press felt 15 is conducted away from the fibrous web 1 and the substantially impermeable belt 16 in a side loop around the suction press roll 13 and two guide rolls 32.
• the press felt 15 rejoins the fibrous web 1 and the substantially impermeable belt 16 immediately before the extended press nip.
• suction devices may be arranged within this side loop of the press felt 15 in order to increase the capacity of the press felt to absorb water at the entrance to the extended press nip.
• the inner clothing 9 of the wet section 2 is a felt conveyed to the press section 3 to be also used as press felt 15 and which thus runs in a loop back to the forming roll 8.
• the inner clothing 9 of the wet section 2 is a fabric, in which case the press felt 15 runs around a pick-up roll 20 arranged close to the loop of the fabric 9 so that press felt 15 and fabric 9 run in contact with each other to transfer the fibrous web from the fabric 9 to the press felt 15.
• the pick-up roll 20 may be provided with a suction shoe (not shown) .
• the pick-up roll and suction shoe may be replaced by a pick-up suction box.
• FIG 4 shows schematically parts of a paper machine according to a further embodiment of the invention. It is similar to that shown in Figure 1 with the exception that the press felt 15 is not led in a side loop between the two press nips, but instead accompanies the counter roll 19 so that the fibrous web 1 is held enclosed between the substantially impermeable belt 16 and the press felt 15.
• the counter roll 19 is a smooth roll and is arranged in a loop of the substantially impermeable belt 16.
• the positions of rolls 14 and 19 are reversed, i.e. the shoe press roll 14 is arranged in a loop of the substantially impermeable belt 16 and the counter roll 19 in the loop of the press felt 15.
• the counter roll may be a suction roll, a grooved roll or a blind-drilled roll.
• the substantially impermeable and elastically compressible transfer belt 16 is of the type described in US-5, 298, 124, for instance.
• the substantially impermeable belt 16 used in the paper machines according to the invention is compressible under the influence of the press forces prevailing in the press nips.
• the substantially impermeable belt 16 thus assumes an uncompressed state upstream and downstream of a press nip and a compressed state when it passes a press nip, the surface, the web-carrying surface, facing the fibrous web having a high degree of roughness in the uncompressed state of the substantially impermeable belt and a lower degree of roughness in the compressed state of the substantially impermeable belt so that the web-carrying surface in the compressed state of the substantially impermeable belt is sufficiently smooth for a continuous liquid film to be formed on the web-carrying surface when the substantially impermeable belt, together with press felt and fibrous web, passes through the press nip and so that the web-carrying surface in the uncompressed state of the substantially impermeable belt is sufficiently rough to permit the continuous liquid film to break up after the substantially impermeable belt has expended in thickness direction.
• the R z -value is more specifically the ten-point height which is defined in said ISO norm as the average distance between the five highest peaks and the five deepest volleys in the reference length measured from a line parallel to the mean line and not crossing the surface profile.
• the substantially impermeable transfer belt preferably has an air permeability of less than 6 m /m /minute, measured in accordance with the procedure described in "Standard Test Method for Air Permeability of Textile Fabrics, ASTM D 737-75, American Society of Testing and Materials".
• the polymer coating of the substantially impermeable belt may advantageously comprise a polymer composition such as acrylic polymer resin, polyurethane polymer resin and polyurethane/polycarbonate polymer resin composition.
• the polymer coating may also contain particles of filler with a different hardness from the polymer material and which may consist of kaolin clay, polymer material or metal, preferably stainless steel.
• the transfer belt included in the paper machine according to the invention is manufactured in the manner also described in US-5 , 298 , 124. Thanks to the use of the above polymer composition, a surface layer is achieved on the belt which is elastically compressible. After the actual surface working in the manufacturing process a surface is obtained which gives a controlled topography. The compressibility and topography of the surface layer are not noticeably affected by possible wear during operation.
• the dense polymer surface is easy to keep clean and can stand being cleaned with a doctor blade directly on the belt surface. To ensure that the belt will not age at the edge portions running against the Yankee dryer outside .the paper web, this must be taken into consideration when selecting material and the combinations which withstand heat best must be chosen. Otherwise edge cooling must be effected by spraying water on the edge, for instance, immediately before or after passage of the Yankee dryer.
• the carrier in the transfer belt is endless and includes also types of base elements which can in some way be made endless.
• the term also particularly covers an openable base element provided with a seam, which element is made endless first when it is installed in the paper machine with the aid of a suitable seam.
• the carrier may consist, for instance, of a multi-layered woven fabric produced from polymer monofilaments such as polyester, polyamide and the like.
• the base element may also consist of a fibrous web (non-woven) held together by binder, combined wound yarns, polymer foil/film, warp knitting or the like. The requirement is that the carrier is form- stable both in machine direction and transverse thereto, so that it contributes to stability of the belt upon mechanical stress in these directions.
• the carrier is to be completely enclosed in the polymer coating, this can either be applied on one side with complete bleeding through to the reverse side, or it may be applied first on one side and then on the other. Configurations may occur requiring particularly thin belts, in which case it may be advisable to apply the coating only from one side with restricted through-bleeding. In this case it is essential that the non-coated surface of the base element is wear-resistant and easy to keep clean.
• the paper machine according to the invention produces a fibrous web with a high dry solids content before the drying section, i.e. up to 55%, which should be compared with the dry solids contents of up to 45% achieved with paper machines in use today.
• This improvement can be utilized either to run the paper machine at a higher production or to reduce the energy consumption in the drying section. It also enables a reduction in the diameter of the drying cylinder.
• a guide roll may be arranged if desired in the loop of the substantially impermeable belt 16 immediately before the transfer roll 17.
• a transfer member consisting of the transfer roll 17.
• the transfer roll is replaced by the substantially impermeable belt itself which is allowed to run around a predetermined part of the drying cylinder, e.g. within a sector angle of 30-60, to form an extended transfer nip with the drying cylinder.

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Citations (3)

• 1998
  • 1998-03-20 SE SE9800948A patent/SE511702C2/sv not_active IP Right Cessation
• 1999
  • 1999-03-12 JP JP2000538082A patent/JP3764050B2/ja not_active Expired - Fee Related
  • 1999-03-12 KR KR1020007010373A patent/KR100554340B1/ko not_active IP Right Cessation
  • 1999-03-12 DE DE69910194T patent/DE69910194T2/de not_active Expired - Lifetime
  • 1999-03-12 AT AT99912198T patent/ATE246745T1/de active
  • 1999-03-12 EP EP99912198A patent/EP1075567B1/en not_active Expired - Lifetime
  • 1999-03-12 WO PCT/SE1999/000382 patent/WO1999049132A1/en active IP Right Grant
  • 1999-03-12 BR BRPI9908983-1A patent/BR9908983B1/pt not_active IP Right Cessation
  • 1999-03-12 CA CA002323636A patent/CA2323636C/en not_active Expired - Fee Related

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