Improved Low Pressure Single Facer

Abstract: A method and apparatus for producing a single face corrugated web (14) from an adhesively bonded liner (13) and medium web (12) without the use of a pressure roll nip where the liner web is joined to the medium web. A heated bonding roll (17) with a fluted outer surface carries the single face web around a circumferential portion sufficient to create a green bond in the glue lines before the web is removed from the roll. The bonding roll may be internally heated or a steam chamber may be positioned around a portion of a lower bonding roll, such that the steam chamber introduces a supply of steam into contact with the single face web while the single face web is in contact with the outer circumference of the bonding roll. An adjustable wrap arm places the freshly glued single face web in contact with the bonding roll and tension in the liner web is controlled to adjust the radial force applied to the glue lines.

Description: The present invention pertains to an apparatus for and a method of forming a single face web of corrugated paperboard, such an apparatus and a method is disclosed in EP 0 737 565 A. In the manufacture of corrugated paperboard, a single facer apparatus is used to corrugate the medium web, apply glue to the flute tips on one face thereof, and to bring a liner web into contact with the glued flute tips of the medium web with the application of pressure and downstream heating to provide an initial bond. A conventional single facer typically includes a pair of fluted corrugating rolls and a pressure roll, which are aligned so the axes of all three rolls are generally coplanar. The medium web is fed between the interengaging corrugating rolls and the adhesive is applied to the flute tips by a glue roll while the medium is still on the corrugating roll. The liner web is immediately thereafter brought into pressurised contact with the adhesive-coated flute tips in the nip between the pressure roll and the corrugating roll. As corrugating nip roll pressures and corrugating speeds have increased, changes have been made in the construction of single facers to maintain the quality of the corrugated medium and to attempt to deal with the problems of high noise and vibration. For example, the load between corrugating rolls at the corrugating nip has required that one of the fluted corrugating rolls be made with a crowned surface to accommodate roll deflection under high nip loads. Deflection as a result of high loading is also believed to be one source of noise and vibration. In a conventional single facer construction, where the two corrugating rolls and the lower pressure roll are in general alignment (their axes lying generally coplanar), corrugating roll loads are transmitted to the pressure roll adding further to the problems associated with high loads and high speeds. This has resulted, in some cases, in manufacturing the pressure roll with a negative crown to match deflections in the corrugating roll which together form the nip for joining the two single face web components. One of the most serious problems in the operation of high speed single facers is the stress applied to the medium web and liner web as the liner is introduced into contact with the medium web under pressure. Because of this pressure induced stress on the corrugated web, the possible thickness of the corrugated paperboard currently is limited such that the individual web components are thick enough to withstand the stress and resist tearing. Tests done with lighter weight web components have shown that the current techniques literally shred the medium web along the lines of the teeth of the corrugating rolls due to the high pressure between the corrugating roll and the pressure roll containing the liner. It has long been presumed that high pressure contact between the pressure roll and the single face web on the corrugating roll was necessary to provide an initial bond which would be fully gelatinised and cured by the residual heat in the two component webs produced by upstream web preheaters and heated corrugating rolls. More recent studies have indicated, however, that a high pressure nipping of the newly joined corrugated medium and single face web actually squeezes moisture from the fresh glue lines at the flute tips and, without moisture, the starch based adhesive cannot gelatinise and no bond will occur at the flute tips. Only the portions of the glue line on the flanks adjacent the flute tips gelatinise and provide the initial tack needed to hold the web together. Even so, the subsequent creation of the necessary green bond, which results from dehydration of the gelatinised glue, requires that adequate heat be supplied over a sufficient length of time. In most prior art single facers, the glued single face web is fed directly from the high pressure nip into the downstream bridge storage and initial dehydration and completion of the green bond is accomplished primarily by the residual heat in the web. However, the initial bond created at the pressure roll nip is often inadequate to assure the integrity of the glue lines as the single face web is flexed and gathered in the bridge storage area downstream from the single facer. Lack of formation of adequate green bond strength may, however, result in a single face web which will not hold together during subsequent processing through the bridge storage area, the double backer, and downstream dry end processing, the result of which may be delamination and the formation of loose back. One recently developed apparatus and process for addressing the prior art problems is disclosed in US Patent 5,614,048. In that apparatus, the liner web is joined to the glued corrugated medium web on the surface of the lower corrugating roll with a pressure roll operating at a very low nip pressure. After joinder, the single face web is wrapped on the surface of the lower corrugating roll over a circumferential portion not exceeding an arc of about 80°. Thereafter, the single face web is taken off the lower corrugating roll and back wrapped (or wound with the liner face of the web) around another heated roll having a smooth outer surface through a larger arc not exceeding about 200°. The use of the second heated roll is necessary to provide adequate heated surface contact which is not available on the heated lower corrugating roll before the freshly glued single face web is removed therefrom. The back wrapping of the web on the heated smooth surface roll downstream from the corrugating roll necessarily takes place before adequate green bond strength has been attained in the glue lines. It is believed that the back wrapping of the single face web at this point cannot apply sufficient pressure to the glued flute tips to optimise the formation of the green bonds. In accordance with the present invention an apparatus for forming a single face corrugated paperboard web from a liner web and a corrugated medium web by corrugating gluing, joining and bonding the liner web and the corrugated medium web on a common roll, said apparatus comprising a large diameter rotary fluted bonding roll forming a corrugating nip with a small diameter fluted corrugating roll, said large diameter bonding roll carrying the corrugated medium web from said corrugating nip, means for applying a starch adhesive to the exposed flute tips of said corrugated medium web on the bonding roll, means for joining the liner web with the medium web on the bonding roll and means for adjustably wrapping the glued single face web around the circumference of the bonding roll surface, wherein said means joins the liner web with the medium web on the bonding roll without significant nipping pressure to create uncured adhesive glue lines between the liner web and said exposed flute tips, means for heating said bonding roll to heat the single face paperboard web to a bonding temperature of at least 93°C (200°F), and, said adjustable wrapping means wrapping the glued single face web around more than half of the circumference of the bonding roll surface downstream of the point of joining the liner web with the medium web, sufficient to permit substantially complete formation of green bonds in said adhesive glue lines, the radial pressure applied to the web around that region of the bonding roll circumference determined by said wrapping means being that induced by web tension. In order to provide adequate resident time of the glued web on the bonding roll, such that the adhesive may completely gelatinise and be transformed well into the green bond region, large bonding roll diameters are required so that the portion upon which the single face web is wrapped will provide a residence time of at least about 500 milliseconds. For example, with a single face web moving through the single facer at 500 cm/sec (1,000 feet per minute), a 122 cm (4 foot) diameter bonding roll will require the web to be wrapped over approximately 240° of the roll circumference. Desirably said small diameter fluted corrugating roll has a diameter not greater than about one third the diameter of the large diameter bonding roll, and, said adhesive applying means and said joining means are positioned adjacent and downstream of said corrugating nip such that the surface of the bonding roll between the corrugating nip and the joining means subtends an arc of less than about 90°. The use of the small diameter corrugating roll allows the apparatus for applying glue to the flute tips and the device for joining the single face liner to the corrugated medium to be placed close to the corrugating nip and to one another along a circumferential portion of the bonding roll not exceeding an arc of about 90°. This, in turn, permits a very large portion of the bonding roll circumference, up to about 270°, to be used for maintaining the single face web in contact therewith to assure adequate formation of green bonds. Preferably said adjustable wrapping means comprises an idler roll adjustably positioned adjacent the glued single face web on the bonding roll with the axis of said idler roll parallel to the bonding roll axis, and, means for positioning said idler roll relative to said bonding roll to wrap a selected length of the glued single face web around the circumference of said bonding roll. Conveniently said idler roll is carried by a wrap arm mounted for movement about an axis coextensive with the axis of said bonding roll, said means for positioning said idler roll moving said wrap arm about said axis. Derisably the adjustable wrapping means is operable to effect a wrap in an arc of up to about 270°. Conveniently said joining means comprises a rotatable liner roll carrying the liner web thereon and forming with the bonding roll a nip for said liner web and the glued medium web. The invention further resides in a method of forming a single face corrugated paperboard web comprising corrugating, gluing, joining and forming, on a common roll, substantially complete adhesive green bonds in a single face corrugated paperboard web which includes a liner web adhesively joined to the glued flute tips of a corrugated medium web, the method comprising the steps of: providing a large diameter heated fluted rotary bonding roll; feeding a medium web into said corrugating nip formed by rotatably engaging the bonding roll with a fluted corrugating roll having a diameter not greater than about one third the diameter of said bonding roll; applying a starch adhesive to the exposed flute tips of the corrugated medium web on the bonding roll as the medium web exits the corrugating nip; joining in the absence of significant nipping pressure the liner web to the glued flute tips of the corrugated medium web on the bonding roll; causing said feeding, applying and joining steps to occur such that the single face web can be wrapped along more than half of the circumference of the bonding roll extending from said corrugating nip; heating the bonding roll to a temperature sufficient to heat the web on the bonding roll to at least 93°C (200°F); wrapping the single face web around the bonding roll downstream from the point of joining of the liner to the medium web, along a circumferential portion of the bonding roll adjustably selected to provide formation of the green bond; and, limiting the radial pressure applied to the web during the wrapping step to that induced by web tension. The accompanying drawing is a schematic side elevation view of a single facer apparatus in accordance with one example of the present invention. Referring to the drawing, the single facer operates to form a corrugated medium web 95 from an incoming medium web 94 and to join it to a liner web 97 to form a composite single face web 100, which function is generally characteristic of prior art single facers. The incoming web 94 is directed into the corrugating nip 93 defined by the interengaging flutes of a large diameter bonding roll 90 and a smaller diameter corrugating roll 92. The medium web 94 is deformed in the corrugating nip 93 to provide the characteristic corrugated medium web 95 which is wrapped around the fluted bonding roll 90. In a manner known in the art, the flute tips of the corrugated medium web 95 being carried on the fluted surface 91 of the bonding roll 90 are contacted by a glue roll 96 having a layer of a typical aqueous starch-based adhesive thereon which is transferred to the flute tips to create continuous glue lines across the flute tips in the machine direction. Just downstream from the glue roll 96 the liner web 97 is brought tangentially into contact with the glued flute tips of the corrugated medium web 95 by a liner delivery roll 98. As will be appreciated by those in the art, any method of conventional preheating, whether by a roll, hot air, or other radiant energy, or other known source, may be employed in preheating the web, or it may be found that preheating is not required in particular applications. The absence of a pressure roll or any means for imposing a joining force on the glue lines between the corrugated medium web and the liner web distinguishes the single facer of the present invention from prior art devices. Recent studies have suggested that pressure rolls in prior art single facers tend to squeeze the adhesive glue lines with sufficient pressure to actually squeeze the water from the starch adhesive. Without water, this portion of the glue line extending right along the flute tip cannot gel, much less form a green bond and cure. This portion is, therefore, completely lost to the bonding mechanism and only the portions of the glue lines on the flanks of the flutes as they curve away from the tips are available to form the actual glue bond. Furthermore, reliance on the residual heat in the two component webs to gelatinise the starch adhesive and to create at least initial dehydration to provide a green bond, is insufficient. As a result, the initially joined single face web leaving the high pressure nip of a conventional single facer has inadequate strength to assure sufficient single face integrity for subsequent downstream handling. In the illustrated apparatus adequate green bond strength of the adhesive joints is created on the bonding roll 90 by applying heat to the freshly joined single face web 100 at a temperature and for a time sufficient to establish a green bond. Green bond strength relies on the removal of water from the adhesive, either by migration into the paper or from evaporative dehydration of the aqueous starch adhesive. The latter is the more significant phenomenon, and is also amenable to manipulation, and, therefore, it is necessary to raise the web temperature significantly above the initial gelatinisation temperature to achieve an adequate green bond strength. In addition, the web must be maintained at the higher temperature level for an adequate length of time. The glued single face web 100 is maintained at a green bond formation temperature and for a necessary period of time on the bonding roll 90 itself. In this manner, the integrity of the single face web is retained and assured by retaining the corrugated medium web on the mating fluted surface 91 of the bonding roll with the outer liner web 97 in intimate (but low pressure) contact therewith. It will be appreciated that, in prior art single facers, directing the single face web away from the transfer roll or pressure roll immediately after nipping contact will preclude the formation of an adequate green bond to maintain web integrity. Although the latent heat in the web may be sufficient to eventually form a green bond, such bond may not occur until the web has been transferred over reversing takeup rolls and the like and into the bridge storage, causing undesirable flexing and disruption of the inadequate bond. Referring again to the drawing, the bonding roll 90 is preferably heated internally with a conventional live steam system of a type well known in the art, whereby for example, live steam is supplied to the interior of the roll by an axially disposed steam supply tube. The bonding roll 90 is heated to provide a temperature at the fluted outer surface 91 sufficient to raise the temperature of the web and adhesive to 93°C (200°F) or higher, and preferably to about 102°C (215°F), to facilitate dehydration and formation of the green bond. In order to achieve sufficient heat transfer to raise the adhesive temperature to that point, the bonding roll surface temperature should be at about 182-193°C (360-380°F) or more. Although green bond formation will begin immediately at the indicated temperature, substantial dehydration of the glue line and adjoining web surfaces must occur before adequate green bond strength is realised. It has been estimated that 80% of the moisture must be removed for full green bond strength. Thus, the single face web 100 is retained on the surface of the bonding roll 90 for a period of time adequate to assure good green bond formation. Although commentators in the art have suggested that green bond formation begins as quickly as 20 milliseconds after component web joinder in the pressure roll nip, it is believed that retaining residence of the single face web on the fluted bonding roll for a much longer period of time, up to about 500 milliseconds, will provide the necessary full green bond strength. In the drawing it will be seen that the single face web can be wrapped substantially more than 180° around the circumference of the bonding roll before the tangential takeoff point where the single face web is back wrapped around a takeoff idler roll 103. The position of the roll 103 may be adjusted to vary the amount of wrap on the bonding roll between the takeoff point and the upstream initial tangent contact point where the liner web 97 is initially joined with the corrugated medium web 95. It should be noted that any known system of takeoff rolls, whether a single or multiple roll design, can be employed to perform the function of takeoff roll 24, as known in the art. As indicated above, in order to provide a 500 millisecond residence time of the single face web on the bonding roll, consideration must be given to the speed of the web through the single facer, bonding roll diameter, and the amount of circumferential wrap available. With respect to the latter consideration, it is obvious that space must be made available for the corrugating roll 92, the glue roll 96 and the liner delivery roll 98 or other means of bringing the liner web 97 onto the bonding roll. By making the diameter of the bonding roll substantially larger, more space is made available for the other components and, simultaneously, the circumference is enlarged to accommodate a longer single face web wrap thereon. With a web speed of 500 cm/sec (1,000 feet per minute), a 122 cm (4 foot) diameter bonding roll 90 will require about 240° of single face wrap to provide a web residence time on the roll of 500 milliseconds. In the embodiment shown, the large diameter bonding roll will easily accommodate this arrangement. The small corrugating roll 92 is provided with a backing device which provides the nipping force and prevents deflection of the roll 92, for example as disclosed in European patent application 0878295. Furthermore, the apparatus eliminates completely a conventional pressure roll of the type typical of prior art single facers in which two relatively large diameter corrugating rolls are aligned with a pressure roll such that the axes of all three rolls lie generally coplanar. Elimination of the conventional pressure roll, in this embodiment as well as in the previously described embodiment, provides a much larger circumferential portion on the bonding roll 90 on which to retain the freshly glued single face web for curing. Just downstream of the glue roll 96, a liner web 97 is brought into contact with the glued medium web 95 on the liner delivery roll 98 which preferably is spaced from the fluted outer surface 91 of the bonding roll 90 by a distance sufficient to preclude any significant nip pressure. The freshly glued single face web 100 is maintained in contact with the heated bonding roll 90 with a wrap arm device including the idler roll 103. The device 101 which allows the single face to be adjustably wrapped around a circumferential portion of the bonding roll of a selected length or arc. The wrap arm device 101 includes a pair of radially extending wrap arms 102 rotatably mounted on the axis of rotation of the bonding roll 90, but adapted to rotate independently thereof. The idler roll 103 is mounted between the radially outer ends of the wrap arms 102, extends the full length of the bonding roll 90 and is positioned to maintain the single face web 100 in engagement with the fluted outer surface 91 of the bonding roll. A wrap arm drive and locating device 104 is utilised to move the idler roll 103 around the outer surface of the bonding roll 90 to selectively adjust the amount of circumferential wrap of the single face web on the bonding roll. As indicated previously, the use of a small diameter corrugating roll 92, as well as a more compact location of the glue roll 96 and the liner delivery roll 98 to position them closer to the small corrugating roll, will provide for as much as about 270° of wrap of the single face web around the bonding roll (see the broken line position in the drawing). From the idler roll 103 on the wrap arm, the single face web is delivered to a downstream web drive 105 from which it is carried to further downstream processing or storage, such as a conventional bridge storage area. Pressure on the glued flute tips as the single face web is carried around the bonding roll 90 is provided directly as a result of the radially inward force generated by liner web tension. Web tension and, therefore, the radial pressure generated on the glued flute tips may be readily varied. For example, the web drive 105 could be operated at a slight overspeed with respect to the speed of the web on the bonding roll 90. Preferably, however, web tension is varied by retarding the liner web delivery roll 98 with the use of a suitable adjustable braking device 106. Thus, tension in the liner wrapped on the bonding roll replaces a conventional pressure roll in the single facer. Furthermore, a substantial portion of the circumference of the heated bonding roll may be utilised to assure an adequate green bond has formed before the single face web is removed form the bonding roll.

Claims: An apparatus for forming a single face corrugated paper board web (14; 100) from a liner web (13; 97) and a corrugated medium web (12; 95) by corrugating gluing, joining and bonding the liner web and the corrugated medium web on a common roll (17; 90), said apparatus comprising a large diameter rotary fluted bonding roll (17; 90) forming a corrugating nip with a small diameter fluted corrugating roll (16; 92), said large diameter bonding roll carrying the corrugated medium web from said corrugating nip, means (20; 96) for applying a starch adhesive to the exposed flute tips of said corrugated medium web on the bonding roll, means (21; 98) for joining the liner web with the medium web on the bonding roll and means (24; 103) for adjustably wrapping the glued single face web around the circumference of the bonding roll surface, the apparatus being characterised in that said means (21; 98) joins the liner web with the medium web on the bonding roll without significant nipping pressure to create uncured adhesive glue lines between the liner web and said exposed flute tips, means for heating said bonding roll to heat the single face paper board web to a bonding temperature of at least 93°C (200°F), and, said adjustable wrapping means (24; 103) wrapping the glued single face web around more than half of the circumference of the bonding roll surface downstream of the point of joining the liner web with the medium web, sufficient to permit substantially complete formation of green bonds in said adhesive glue lines, the radial pressure applied to the web around the region of the bonding roll circumference determined by said wrapping means being that induced by web tension. Apparatus as claimed in Claim 1, characterised in that said small diameter fluted corrugating roll (16; 92) has a diameter not greater than about one third the diameter of the large diameter bonding roll (17; 90), and, said adhesive applying means (20; 96) and said joining means (21; 98) are positioned adjacent and downstream of said corrugating nip such that the surface of the bonding roll between the corrugating nip and the joining means subtends an arc of less than about 90°. An apparatus as claimed in Claim 1 or Claim 2, characterised in that said adjustable wrapping means comprises an idler roll (103) adjustably positioned adjacent the glued single face web on the bonding roll with the axis of said idler roll parallel to the bonding roll axis, and, means for positioning said idler roll relative to the bonding roll to wrap a selected length of the glued single face web around the circumference of said bonding roll. An apparatus as claimed in Claim 3 characterised in that said idler roll (103) is carried by a wrap arm (102) mounted for movement about an axis coextensive with the axis of the bonding roll, said means for positioning said idler roll moving said wrap arm about said axis. Apparatus as claimed in any one of the preceding claims, characterised in that the adjustable wrapping means is operable to effect a wrap in an arc of up to about 270°. An apparatus as claimed in any one of the preceding claims, wherein the joining means comprises a rotatable liner roll carrying the liner web thereon and forming with the bonding roll a nip for said liner web and the glued medium web. A method of forming a single face corrugated paper board web characterised by comprising corrugating, gluing, joining and forming, on a common roll, substantially complete adhesive green bonds in a single face corrugated paper board web which includes a liner web adhesively joined to the glued flute tips of a corrugated medium web, the method comprising the steps of: (1) providing a large diameter heated fluted rotary bonding roll; (2) feeding a medium web into said corrugating nip formed by rotatably engaging the bonding roll with a fluted corrugating roll having a diameter not greater than about one third the diameter of said bonding roll; (3) applying a starch adhesive to the exposed flute tips of the corrugated medium web on the bonding roll as the medium web exits the corrugating nip; (4) joining in the absence of significant nipping pressure the liner web to the glued flute tips of the corrugated medium web on the bonding roll; (5) causing said feeding, applying and joining steps to occur such that the single face web can be wrapped along more than half of the circumference of the bonding roll extending from said corrugating nip; (6) heating the bonding roll to a temperature sufficient to heat the web on the bonding roll to at least 93°C (200°F); (7) wrapping the single face web around the bonding roll downstream from the point of joining of the liner to the medium web, along a circumferential portion of the bonding roll adjustably selected to provide formation of the green bond; and; (8) limiting the radial pressure applied to the web during the wrapping step to that induced by web tension.

Inventors: MARSCHKE CARL R, MARSCHKE, CARL R.
Applicants: MARQUIP LLC, MARQUIP, LLC
Application year: 1997
Main classification: B31F1
IPC codes: B31F1