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(11) | EP 0 279 609 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Manufacturing corrugated board |
| (57) A conventional single faced corrugated board manufacturing plant is modified to produce
corrugated board having two fluted mediums bonded at their flute tips. In addition
to the existing corrugating rolls (10, 11) a further pair of corrugating rolls (34,
35) synchronized with the existing pair are provided so that the corrugated mediums
(22, 23) are contacted at their flute tips. An additional mill roll stand is provided
for the second fluted medium. A carrier roll (36) is provided adjacent to the pairs
of corrugating rolls to take off the bonded fluted mediums and provide support and
prevent uncontrolled movement of the flute to flute structure during the development
of the adhesion bond. Adhesive applicators (37) are provided to apply adhesive to
one of the mediums prior to the flute tip to flute tip bonding and to coat the flute
tips of the bonded fluted structure on the carrier roll for bonding to the inner (21).
An additional guide roll (38) is provided to allow tangential approach for the liner
onto the flute to flute structure carried by the carrier roll. Radiant energy is used
to assist in bonding the inner to the flute to flute tip structure enabling a low
pressure bonding technique to be used. |
[0001] This invention relates to a method of forming sandwich structures, comprising one or more non-corrugated sheet elements (liners) to which are bonded two or more corrugated (fluted) sheet elements (mediums) which are themselves bonded together.
[0002] Australian Patent Application 62323/86 discloses an improved corrugated paper board structure in which two or more layers of corrugated medium (flutes) are bonded together at the peaks of the flutes, and are sandwiched between two outer liners. The disclosures of Application 62323/86 are incorporated herein by reference.
[0003] Patent Specification 62323/86 also discloses a method of forming the structural paper in which two or more separate layers of corrugating medium are corrugated and then brought into flute tip to flute tip contact on synchronised corrugating rollers.
[0004] That method does not address the problem of capital cost in constructing a new corrugating plant for the flute to flute paper board and the likely under utilization of existing corrugating machinery, making conventional flute to liner corrugated boards.
[0005] It is an object of this invention to provide a modification to existing corrugating machinery to enable conventional corrugated board, as well as the new flute to flute corrugated board, to be made. The modification can also be incorporated into the manufacture of new corrugating machinery to enable conventional corrugated board with improved printing properties and visual appearance to be also made.
[0006] Conventional machinery for forming corrugated board incorporates a unit for making single faced corrugated board, that is a liner adhered to a single fluted layer. More complex board constructions can be formed by bonding the exposed flutes to another liner and, if desired, subsequently bonding that to another single faced corrugated board.
[0007] A "single facer" plant normally includes as its essential components:
a) Mill roll stands for liner and corrugating medium.
b) A pair of corrugating rollers for corrugating the medium into a fluted medium.
c) A pair of heated smooth (non corrugated) guide rolls for the liner board.
d) A non corrugated pressure roll for bringing the liner into contact with the second corrugating roller to form the single faced board.
e) An idler roll to guide the formed single faced board to subsequent processing units.
[0008] With conventional single faced board a degree of pressure is applied to ensure secure bonding between the liner and the corrugated medium. This application of pressure creates pressure lines on the outer face of the liner corresponding to the position of the flute tips. The need to apply pressure can adversely affect the strength of the single faced structure and adversely affects the appearance of the board and its suitability for printing.
[0009] It is also an object of this invention to overcome these deficiencies in the conventional product.
[0010] To this end the present invention provides a method for bonding a liner to a corrugated medium or mediums in which adhesive is applied to the flute tips of the corrugated medium. The liner is then brought into contact with the corrugated medium or mediums and the assembled liner and corrugated medium or mediums may be subjected to heat, or other energy or chemical process to initiate or assist in completion of the bonding. This low pressure method of bonding gives superior bond strength (pin adhesion) than is achieved in conventional single-faced board.
[0011] In another aspect this invention provides a modified single face corrugated board making apparatus capable of forming corrugated boards having two fluted mediums bonded together at the flute tips comprising
a) Mill roll stands for two mediums and one liner.
b) Two pairs of corrugating rolls synchronized so that the two fluted mediums are oriented for precise flute tip to flute tip bonding and which may include pressure bonding.
c) A carrier roll juxtaposed to one of the corrugating rolls and adapted to support and constrain continuously the bonded fluted mediums during the development of the adhesive bond. This juxtaposition assists in achieving the required constraint for the joined mediums after bonding of flute tips and before bonding of the first liner.
d) A first adhesive application station adapted to apply adhesive to one of said fluted mediums prior to the flute tips of the said fluted mediums coming into contact.
e) A second adhesive applicator station to apply adhesive to the exposed flute tips of the bonded mediums or to a liner board.
f) A liner applicator roll located adjacent to said carrier roll downstream of said second adhesive applicator adapted to apply a liner board to said bonded fluted mediums.
[0012] This invention also provides the following modification to enable the modified conventional single facer machine to make both conventional single faced board and flute to flute board.
[0013] The modification comprises:
i) Substituting or installing in addition to existing rolls, corrugating rolls synchronised with the existing pair of corrugating rolls (b) in place of the heated guide rolls (c) and pressure roll (d). These new corrugating rolls may substitute for the heated guide and pressure rolls or be installed in addition to existing rolls. One or both heated guide rolls may be used to preheat the second fluting medium.
ii) Providing a mill roll stand for a second fluting medium to be fed through the new corrugating rolls (i), if an existing mill roll stand is not available.
iii) Providing an adhesive applicator to apply adhesive to either a liner or the exposed tips on one side of the flute to flute structure prior to bonding with a liner.
iv) Providing a new guide roll to allow tangential approach of the liner prior to bonding to the flute to flute structure.
(v) Providing very similar treatment of each medium prior to corrugating. This includes the provision of tension control, preheater/preconditioners, heated S wrap drive rolls, and steam box conditioners incorporating a new carrier roll which operates as a take off roll and supports the flute to flute structure holding it in a configuration which
(a) provides an accurately registered support during glue application, and
(b) prohibits uncontrolled movement of the flute to flute structure during development of the glue bond with the liner.
[0014] This modification enables two fluting mediums to be precisely bonded flute tip to flute tip maintained in that orientation and then to be bonded to a liner as a first stage in preparing a flute to flute corrugated board. Where a conventional single faced board is to be formed one fluting medium is simply omitted and the one pair of corrugating rolls the preferred pair being the upper pair, (b), are not utilized. Also the first adhesive applicator is preferably not used.
[0015] In forming the bonded fluted mediums it is necessary to constrain the mediums to maintain the flute orientation of each fluted layer and to maintain the orientation and symmetry of the flute tip to flute tip bonds. This may be achieved by using a grooved carrier roll to take up the bonded mediums and support them until the bond is set. Alternatively a smooth carrier surface can be used in association with vacuum to provide the necessary constraint. Other means for constraining the mediums can also be used such as strings or straps to maintain the flute tips in correct orientation.
[0016] The improved strength characteristics of the double flute construction enable lighter weight board to be made having strengths equivalent to those found in heavier boards of conventional structure. Thus savings in material costs are possible using the flute to flute construction.
[0017] It has been found that boxes formed from flute to flute board exhibit superior durability and strength. The creasing and folding characteristics of board having flute to flute bonding are such that the corner and edge folds of boxes provide added strength to the construction. The flute to flute structure creases in a well defined manner to produce a hinged joint which is superior in strength, flexibility and visual appearance compared with creases in conventional board.
[0018] Bonded fluted mediums according to this invention can be subsequently bonded to any suitable liner material to form light weight structural laminates. The mediums can be manufactured from 100% cellulose fibre or ligno-cellulose fibre or combinations of cellulose, ligno-cellulose and synthetic fibres, or they may be laminated structures.
[0019] The liners or sheet elements may be of any material and structure of varing thickness including, but not limited to, paper board made of cellulose fibres, ligno-cellulose fibres; cellulose, ligno-cellulose and/or synthetic fibre mixtures; natural or synthetic polymers, wood, or metal; or laminates made of bonded layers of any combinations of these materials. Strips or strings of any material may also be fed intermittently, between the mediums across the flutes and thus be bonded at the flute tip to flute tip junction. The inclusion of such strips or strings will constrain the bonded mediums and prohibit expansion of the flute tip to flute tip structure until one or more liners are added and may additionally confer added strength to the board. Bonding may be achieved by use of adhesives or by other means such as, but not limited to, soldering, brazing and fusion welding.
[0020] Where a light weight structural panel for building such as ceiling panels or for use in furniture is required the liners can be wood veneer. In other applications such as air-frame skins for aircraft, the liners may be metal foil or synthetic polymers.
[0021] The modification of a single flute station according to this invention enables in a conventional corrugator, the elimination of the need for pressure application to secure the bond between the liner and the corrugated medium. The use of the heat or other means to complete the bonding process of the first liner to corrugated medium or mediums at the single facer is an innovation and has the advantage of not adversely affecting the strength of the board and of not adversely affecting the appearance of the board by reducing the normal pressure lines.
[0022] A preferred embodiment of this invention will now be described with reference to the drawings in which figure 1 represents a schematic view of a conventional single facer unit; figure 2 shows a schematic view of the unit as modified by this invention for forming a flute to flute structure; figure 3 shows a detailed view of figure 2 and figure 4 shows the modified unit of this invention when used to make conventional single faced corrugated board.
[0023] A conventional single facer unit comprises mill roll stands 4 and 5, a preheater roll 6, a single facer station 7 and a mill roll 8 stand for fluting medium 23.
[0024] The single facer station 7 comprises the corrugating rolls 10 and 11, adhesive applicator 12, pressure roll 13 for pressing the liner against the corrugated medium 23 on roll 11. The liner board 21 is fed from stand 5 over preheater roll 6 to the heated smooth guide rolls 14 and 15.
[0025] The formed single faced board 24 is transferred to idler roll 16 and then to conveyor 17 which transports the single faced board 24 for further processing.
[0026] In the modified unit of this invention one of the mill roll stands 5 is used for a second corrugating medium 22 while an other mill roll stand is used for liner 21. A new guide roll 31 is used to guide the liner onto preheater roll 6 and then under a new guide roll 32, to the S wrap rolls and onto the carrier roll 36.
[0027] For medium 22, a second preheater roll 42 is inserted under preheater roll 6. A new roll guide 43 is used to guide the medium onto the preheater roll 42 and then under a new guide roll 44.
[0028] For medium 23, a further preheater roll 45 is used. This will require a roll guide 46 and a roll guide 47 to guide the medium into the single facer S wrap heated rolls. Steam sprays may be mounted on preheater rolls to precondition the sheet.
[0029] Steam boxes may be located before rolls 10 and 34 to condition the mediums prior to corrugating.
[0030] An automatic splicer may be utilized with each medium coming from roll stands 5 and 8 with the liner coming from roll stand 4.
[0031] The guide roll 14 and pressure roll 13 shown in figure 1 are replaced by corrugating rolls 34 and 35. The heated smooth guide roll 15 is used to preheat the corrugating medium 22. The two corrugated mediums 22 and 23 are adhered together between rolls 35 and 11 which are driven synchronously to ensure precise flute tip to flute tip bonding. This can be achieved by installing a direct drive, meshed gear drive or toothed belt drive between the driven lower corrugating roll 35 and the corrugating roll 11.
[0032] A carrier roll 36 is installed to operate as a take-off roll and to provide support and constraint for the bonded mediums.
[0033] The carrier roll 36 may be constructed as a shell with appropriate drilling for vacuum application to hold the flute to flute structure in position on the carrier roll. Fingers or guides may also be provided to achieve the positioning of the flute to flute structure on the carrier roll and the corrugating rolls.
[0034] As an alternative, the corrugating rolls 11 and 35 can be arranged with a vacuum facility to hold the fluted product in the roll flutes. The area providing the vacuum on roll 35, can be extended to hold the flute to flute structure in the roll flutes and present them in such a way as to achieve a correctly aligned transfer to the carrier roll 36.
[0035] The carrier roll 36 may be a plain or grooved cylindrical surface or may also be provided with spaced bars of metallic or non-metallic materials to carry the flute to flute structure.
[0036] Holding of the flute to flute structure to the carrier roll 36 may also be achieved by use of vacuum, applied from within the carrier roll inner cavity.
[0037] A new adhesive applicator station 37 is located adjacent to the carrier roll 36 to apply adhesive to the flute tips on the exposed face of the flute to flute structure. The surface of the carrier roll may be arranged to provide a positive air pressure at point 49, causing the flute to flute structure to "puff out" ensuring a good transfer of the adhesive to the exposed tips of the structure. The roll 38 guides the liner 21 to join with the flute to flute structure to form one particular example of the structures which are the subject of the invention disclosed in Patent Application No. 62323/86.
[0038] The top liner 21 is assisted in bonding to the flute to flute structure after the glue application by an input of energy in the form of radiant or convected heat, microwave or other energy by the units 39.
[0039] All components may be pre-heated, moistened or pre-treated to accelerate bonding of the component to component interfaces.
[0040] The carrier roll, assisted by positive air pressure from the blow box 40 inside the carrier roll 36, or vacuum from the liner side, will discharge the combined liner and flute to flute structure 25 to transport section 41 preceding the next processing station.
[0041] The transport section 41 may be straight or curved in shape, and if curved, the curve will be arranged to utilise tension forces in the liner to apply gentle pressure to the glue bond. A change in radius will achieve further beneficial bond development.
[0042] The transport section 41 may be provided with a driven carrier belt or belts to transfer the combined liner and flute to flute structure to the next section or next processing unit.
[0043] The carrier roll 36 is driven by a separate synchronised drive, a meshed gear drive or a toothed belt drive from the lower corrugating roll 35 or primary driven roll 11 to ensure it is synchronised with the corrugating roll 35. Precision, of flute tip to flute tip bonding and in the control of transfer from corrugating roll 35 to the carrier roll 36 and in the positional restraint of the flute to flute structure prior to the addition of liner 21 form key elements of this invention.
[0044] As shown in figure 4 the modified unit of this invention can also be used to make an improved form of conventional single faced corrugated board.
[0045] An improved single-faced corrugated board may be produced by ceasing to feed the corrugating medium 23 to the corrugating rolls 10 and 11 and also ceasing to apply glue to glue station 12 while continuing application at glue station 37 to corrugated medium 22. In this case the glue station 37 is moved towards the carrier roll 36 to contact the thinner conventional corrugated sheet and the carrier roll 36 is rotated through one half flute pitch to bring corrugated medium 22 into mesh with carrier roll 36, after leaving corrugating roll 35.
a) mill roll stands for two mediums and one liner.
b) two pairs of corrugating rolls synchronized so that the two fluted mediums are oriented for precise flute tip to flute tip bonding;
c) a carrier roll juxtaposed to one of the corrugating rolls and adapted to support and continuously constrain the bonded fluted mediums during the development of the adhesive bond;
d) a first adhesive application station adapted to apply adhesive to one of said fluted mediums prior to the flute tips of the said fluted mediums coming into contact;
e) a second adhesive applicator station to apply adhesive to the exposed flute tips of the bonded mediums or to a liner board;
f) a liner applicator roll located adjacent to said carrier roll downstream of said second adhesive applicator adapted to apply a liner board to said bonded fluted mediums.
a) The second adhesive applicator is located adjacent the carrier roll and applies adhesive to the exposed flute tips of the bonded fluted mediums.
b) an energy applicator is located ajacent to said carrier roll downstream of the liner applicator roll to promote bonding of the liner to the bonded fluted mediums.