Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21G—CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES
  • D21G1/00—Calenders; Smoothing apparatus
  • D21G1/006—Calenders; Smoothing apparatus with extended nips
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H23/00—Processes or apparatus for adding material to the pulp or to the paper
  • D21H23/02—Processes or apparatus for adding material to the pulp or to the paper characterised by the manner in which substances are added
  • D21H23/22—Addition to the formed paper
  • D21H23/30—Pretreatment of the paper
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H27/00—Special paper not otherwise provided for, e.g. made by multi-step processes
  • D21H27/30—Multi-ply
  • D21H27/38—Multi-ply at least one of the sheets having a fibrous composition differing from that of other sheets
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H11/00—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only
  • D21H11/02—Chemical or chemomechanical or chemothermomechanical pulp
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H11/00—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only
  • D21H11/08—Mechanical or thermomechanical pulp
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H11/00—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only
  • D21H11/14—Secondary fibres
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H19/00—Coated paper; Coating material
  • D21H19/80—Paper comprising more than one coating
  • D21H19/82—Paper comprising more than one coating superposed
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H19/00—Coated paper; Coating material
  • D21H19/80—Paper comprising more than one coating
  • D21H19/84—Paper comprising more than one coating on both sides of the substrate

Definitions

• the invention relates to a coated board product and its production.
• An object of the invention is to improve the quality of board products, especially boxboard, and the economy of producing the same.
• Board is required to have a certain surface quality for ensuring a desired gloss and print quality, a stiffness and tear resistance for securing the functionality of a package. Since board is produced in large quantities in a board mill, the efficient use of raw material is also important. These demands are somewhat contradictory to each other. Board can be provided with a sufficient gloss by calendering the board by compressing it in a nip, often moistened and heated in a certain manner. The surface fibers and coating of board are preferably pressed smooth by this compression, yet without compacting the middle ply of board. The compaction of a middle ply undermines board stiffness and reduces tear resistance. The compaction of a middle ply is often referred to as a loss of bulk. In this case, bulk is understood as being an inverse value to density and a loss thereof is thus equal to a densifying compaction of paper or board.
• the filler ply consists often of mechanical pulp, typically groundwood (GW), but in many cases also pressure groundwood (PGW) and chemithermo-mechanical pulp (CTMP), or the filler ply can also be made by using broke.
• the face of board is generally coated twice and the back once. Coating and sizing are used for providing desired properties.
• a typical basis weight range for boxboards is 180-350 g/m 2 .
• the necessary basis weight depends on a required stiffness of the container, a lighter board being sufficient for small boxes.
• Successful conservation of board bulk in surface treatment to produce thereby board of a higher stiffness results in savings of raw material and energy by enabling the use of board of a lesser basis weight.
• Typical applications for board include cigarette packages, pharmaceutical packages, postcards, cardboard covers for books, various food packages.
• Boxboards are often smoothed with a Yankee cylinder prior to coating, which provides a good bulk and stiffness, the surface properties being also good, the drying shrinkage along the edges being likewise small, yet the use of a Yankee cylinder is limited by speed restraint, space demand for equipment and the enormous size of a Yankee cylinder in a high-speed machine.
• Another typical treatment method involves a wet-stack calender, the drawbacks of which include problems regarding runnability and a controlled application of water and, in addition, extra costs are incurred by the necessity of drying the board before and after a calendering process.
• a machine calender is often used together with other calenders, the machine calender referring to a hard calender with no elasticity in its rolls. The use of a machine calender as the sole surface treatment method is not advisable.
• a soft calender refers to a soft-nip calender, wherein the calender roll has a surface which is elastic, the surface having possibly a hardness in the same order as the surface hardness of wood, yet being elastic.
• the coated container board of the invention comprises two or more plies of fiber, wherein the outside plies consist of bleached chemical pulp and the inner plies of mechanical pulp or chemithermo-mechanical pulp or broke.
• boxboard is treated with a long-nip calender prior to coating or during its coating process in order to upgrade the board qualities over what is known before and, in addition, the production runnability is improved and the production method is not subject to a speed restraint the same way as a Yankee cylinder.
• a long-nip calender suitable for making a board of the invention has been described for example in the Applicant's patent US6164198.
• a calender suitable for the surface treatment of a board of the invention includes a fixed support element, around which is a tubular jacket.
• a heated counter-element is disposed on the other side of the tubular jacket from the support element, such that a web passes through between said counter- element and the tubular jacket.
• the fixed support element is provided with load elements, applying the jacket against the heated counter-element and thereby enabling a calendering process between the jacket and the counter- element.
• the jacket has its opposite ends secured to end walls mounted rotatably relative to the support element, the rotary motion of the end walls being delivered by a separate drive motor, which is independent of a motion of the fibrous web in order to avoid overheating of the jacket.
• a method of the invention for conditioning the surface of coated or uncoated board with a surface conditioning device is in turn characterized in that the method comprises feeding a fibrous web through a long nip established by a roll and a counter-roll, the former being in the form of a tubular-shaped flexible jacket. Across the extent of the nip the jacket deflects and thereby presses into contact with the counter-roll over a long stretch.
• the board treated with the method is lighter than currently available boards, while stiffness and surface properties are equal to those of currently available boards.
• the solution enables a running speed substantially higher than what is accomplished with a Yankee-cylinder equipped board machine.
• the runnability is better, this also contributing to improved quality and reducing waste.
• Web speed in the calender may be higher than 600m/min, preferably higher than 800m/min, and still more preferably 1000 m/min, yet lower than 4000 m/min. Thus, the calender does not restrict the speed of a board machine.
• the above-mentioned heated roll has a temperature of 150-350°C, preferably higher than 170°C, most preferably about 200-250°C.
• Linear pressure in the nip is within the range of 100-500 kN/m, preferably less than 400, most preferably about 50-300 kN/m. Maximum pressure in the nip is 3- 15 MPa, preferably less than 13 MPa, most preferably about 0,5-8 MPa.
• Fig. 1 is a sectional view of a long-nip calender, provided with a long nip between an enclosed shoe calender and a counter-roll.
• Fig. 1A is a partial enlargement of fig. 1.
• Fig. 2A is a partial sectional view of the device shown in fig. 1, along the roll axis and depicting a drive mechanism.
• Fig. 2B shows the operation of press shoes in a longitudinal section.
• a board web 80 travels through an extended and heated nip 1.
• the nip 1 is established by means of an enclosed shoe roll 10 present under the web 80.
• Above the web 80 is a heatable counter-roll 22.
• the enclosed shoe roll 10 comprises a flexible jacket 12 impervious to liquid.
• the jacket consists for example of fiber-reinforced polyurethane.
• the stationary fixed support element 14 carries at least one load shoe 18. Between the load shoe 18 and the support element is an actuator 20, such as a hydraulic cylinder, for urging the concave load shoe 18 and thereby also the flexible jacket 12 against the counter-roll 22.
• the jacket 12 is forced out of its normal unloaded position 11 in a direction away from the center of the enclosed shoe roll.
• the jacket 12 is fastened at both ends thereof to end walls 24, 26, thus creating a sealed compartment 13 (see fig. 2).
• at least one detector device 99 is mounted in communication with the web 80 for detecting web breaks.
• the detector device 99 is connected to a control device 98 for controlling the operation of a calendering process in dependence of the web being broken or not.
• the heatable counter-roll 22 is accompanied by a disengagement mechanism, comprising a lever 95 pivotable by means of a hydraulic cylinder assembly 94 and provided with a pivot point 96 for pivoting the lever thereon.
• the disengagement mechanism presses the counter-roll 22 to an engagement with the nip 1 and disengages it from the nip 1.
• a pressurized oil which develops a hydrostatic pressure throughout the nip and presses the jacket to an engagement with the counter-roll 22 over the entire extent of the nip 1.
• the oil protects the jacket from being damaged by lumps and a temperature rise.
• end walls 24, 26 are rotatably mounted on stub shafts 16, 17 of the support element 14.
• the end walls are preferably not integral but divided into a static part and a rotating part as shown in fig. 2B).
• a cylindrical shaft 32 is arranged rotatably via bearings 34.
• a support column 36 is arranged to the cylindrical shaft via self- aligning bearings 38, which allow spherical movement to allow the deformation/bending of the support element 14 when heavily loaded.
• One of the end walls 24 is fixedly attached to the cylindrical shaft.
• a drive transmission 40 is fixedly attached to the cylindrical shaft outside the end wall, in the shown embodiment a cog wheel.
• the cog wheel is connected to a transmission 42 and in turn a drive 44.
• a cog wheel 46 is fixedly attached to the cylindrical shaft inside the end wall.
• a drive shaft 48 is arranged inside the jacket and parallel to the support element 14. The drive shaft 48 is supported by bearings 50 arranged in bearing houses 52 attached to the support element.
• cog wheels 54 are arranged at each end of the drive shaft. Preferably these cog wheels have a prolonged toothed portion to allow axial movement of the intermeshing cog wheel which is attached to the end wall.
• a further cog wheel 56 is fixedly attached to the second end wall 26 inside the jacket. Both cog wheels inside the jacket mesh with the corresponding cog wheel on the drive shaft.
• the second end wall 26 is rotatably arranged on the second stub shaft 17.
• the second stub shaft is in turn fixedly attached to a second support column 58.
• the operation is as follows.
• the driven heated roll 22 is in interaction with the fibrous web and the flexible jacket 12 by means of a desired pressure being exerted by the load shoe 18, thereby causing a friction based drive of both the fibrous web and the flexible jacket. Accordingly, during normal operation the forces exerted in the nip provide for rotation of the enclosed shoe roll.
• the independent drive of the enclosed shoe roll 10 is to be used for instance at the startup of the calendering surface. At the start, the nip gap is not closed, but the roll 22 has been moved out of contact with the nip 1.
• the drive arrangement 44 of the enclosed shoe roll 10 is activated to accelerate the first end wall 24 via transmissions.
• the rotation of the end wall causes the inner first cog wheel 46 to rotate, and subsequently the drive shaft 48.
• the drive shaft transmits the rotation to the second end wall 26 via the second inner cog wheel 56.
• the both end walls are thus accelerated and rotate at the same speed until a desired peripheral speed is obtained, which is normally equal to the speed of the fibrous web.
• the nip is closed by activating the hydraulic piston 94 to pivot the lever 95 and thereby moving the counter-roll 22 into the nip and subsequently the load shoe 18 is urged against the heated roll 22 by means of its actuators 20.
• Fig. 2B also shows a more preferred design of arranging the support element and the end walls.
• the end walls are divided into an inner part 24A; 26A connected non-rotatably to the support element 14, a rotational part 24B; 26B, and a bearing assembly 24C; 26C therebetween.
• the support element 14 is at its ends arranged with self-aligning bearings 23, 25 to allow a deflection of the support element 14.
• a drive 44 having a shaft 19B.
• a disc 19 having a rubber layer at its peripheral end 19A.
• the outer ends of the flexible jacket 12 are fixedly attached between an annular ring 15, acting as a replaceable force transmitting device, and the periphery of each end wall.
• the ring 15 is fixedly attached to the end wall.
• the drive arrangement 44, 19 is movable in and out of contact with the force transmitting device 15. When it is desired to accelerate the enclosed shoe roll 10, the drive arrangement is moved such that the rubber layer 19A comes into frictional engagement with the force transmitting device 15.
• Fig. 2B further illustrates in a schematic view one preferred functional embodiment of the load shoe 18.
• the load shoe 18 is not disposed diametrally relative to the drive shaft, but perpendicularly as in fig. 2A.
• Shoe calenders can be driven at notoriously high speeds and, furthermore, by the application of an elevated temperature, e.g. about 250°C, and by taking into account a long dwell time in the calendering zone, the resulting gloss finish will be equal to what is achieved in a slower solution using a Yankee cylinder.
• the board is provided with improved bulk.
• the results include savings of production space in a mill, the elimination of a production limiting Yankee cylinder, and the provision of a more manageable, more easily controlled system.
• reference board and pilot-calendered board were coated twice in a blade coating station, the total amount of coating being about 24 g/m 2 .
• test results represents a progressive step, regarding for example the quality and production economy of boxboard.
• pilot tests provide results inferior to those obtained in the ultimate environment, so even on the basis of these preliminary tests, it is possible to draw a conclusion that the method is capable of producing board that is better than before and at the same time more easily and economically producible.
• the method is applicable to considerably higher speeds than a Yankee cylinder.

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Citations (3)

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• 2002
  • 2002-11-27 FI FI20025053A patent/FI116080B/sv not_active IP Right Cessation
• 2003
  • 2003-11-14 AU AU2003282138A patent/AU2003282138A1/en not_active Abandoned
  • 2003-11-14 JP JP2004554575A patent/JP2006508269A/ja active Pending
  • 2003-11-14 WO PCT/FI2003/000871 patent/WO2004048689A1/en active Application Filing
  • 2003-11-14 US US10/533,038 patent/US20060124262A1/en not_active Abandoned
  • 2003-11-14 DE DE10393788T patent/DE10393788T5/de not_active Withdrawn

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