SE542861C2 - Method of producing a core material for a laminated board, and laminated board comprising such core - Google Patents

Abstract

The present disclosure provides a method of producing a core material (1) for a laminated board (2). The method comprises providing a sheet (20) of material comprising a corrugated layer and preferably also a planar layer bonded to the corrugated layer, whereby the sheet defines first and second opposite faces, parallel with a sheet main plane (Sp), orienting the sheet such that corrugations extend substantially perpendicular to a feed direction (Df), slitting (21) the sheet along the feed direction, such that a plurality of elongate strips (10a, 10b) are provided, turning (22) the strips 90° about their longitudinal directions, merging (23) the strips first face to second face to form a strip bundle (24), whereby a bundle main plane (Bp1, Bp2) is defined, which is substantially perpendicular to the sheet main plane (Sp) of the individual strips (10a, 10b), arranging the strip bundle (24) to form the core (1) to a predetermined width (Y), and laminating at least one facing sheet (11a, 11b) to the core (1). The strips (10a, 10b) are movable relative to each other until the facing sheet (11a, 11b) has been bonded to the core (1).

Description

METHOD OF PRODUCING A CORE MATERIAL FOR A LAMINATEDBOARD, AND LAMINATED BOARD COMPRISING SUCH CORE Technical Field The present disclosure relates to a method for producing a core forIaminated board materials. Such board materials find applications in fieldssuch as furniture, display/advertising panels and in general construction.

The disclosure also relates to a Iaminated board material which can beproduced according to the method.

BackgroundLaminated board materials having a core based on corrugated paper sheets are well known. ln most cases corrugated paper sheets comprise aplanar sheet and a fluted sheet, which are Iaminated together.

Corrugated paper core based board materials are conventionallyproduced by stacking and laminating together a large number of corrugatedpaper sheets, turning the thus formed block about 90 degrees and sawing theblock into a number of cores having a desired thickness, and laminating thethus formed cores with facing sheets.

However, such production of the core is associated with some dis-advantages, which reduce speed of production and limit production capacity,which in turn lead to a higher cost of the board material.

US3912573 discloses a method of producing a core material for ahoneycomb panel.

However, the method disclosed in US3912573 has a disadvantage inthat the width of the core that can be produced continuously is limited. Forgreater width panels, it is necessary to cut the core into pieces and arrangethem next to each other prior to lamination, which would substantially reduceproduction speed.

Hence, there is a need for an improved method of producing the core,such that the production cost can be reduced.

SummaryA general object is thus to provide an improved method of producing a core for a sandwich panel. Specific objects include increasing productionspeed and flexibility.

The invention is defined by the appended independent claims, withembodiments being set forth in the appended dependent claims, in thefollowing description and in the drawings.

According to a first aspect, there is provided a method of producing acore material for a laminated board. The method comprises providing a sheetof material comprising a corrugated layer and preferably also a planar layerbonded to the corrugated layer, whereby the sheet defines first and secondopposite faces, parallel with a sheet main plane, orienting the sheet such thatcorrugations extend substantially perpendicular to a feed direction, slitting thesheet along the feed direction, such that a plurality of elongate strips areprovided, turning the strips 90° about their longitudinal directions, merging thestrips first face to second face to form a strip bundle, whereby a bundle mainplane is defined, which is substantially perpendicular to the sheet main planeof the individual strips, arranging the strip bundle to form the core to a pre-determined width, and laminating at least one facing sheet to the core. Thestrips are movable relative to each other until the facing sheet has beenbonded to the core.

The sheet may be a so-called corrugated paper or cardboard sheet.Preferably, the corrugated paper sheet comprises one corrugated sheet andone planar sheet, which are laminated together.

The corrugations of the sheet form elongate flutes, which extend alongthe corrugations.

The plurality of strips may be anything from three strips and upward.The width of the strips will be governed by the desired thickness of the coreand thus the number of strips will be determined by the core thickness andthe corrugated sheet width. ldeally, the number N of strips may be on theorder of W/Tc, where W is the width of the sheet material and Tc is thethickness of the core. However, depending on sheet quality, it may be necessary to provide for some excess or scrap along the long side edges ofthe sheet material. ln particular, the strips are movable re|ative one another such that theymay shift re|ative to each other when the bundle is bent in the bundle mainplane. Hence, the strips are not glued or otherwise adhered to each otherbefore they have been arranged to form the core.

Through this method, it is possible to continuously produce a corehaving arbitrary width.

The strips may be maintained continuous and transversely uncut atleast through the arranging step and preferably through the laminating step.

The strip bundle ir-nay--preser-:tpresents a width that is smaller than thepredetermined width of the core, and vRfi-eifeèwarranging the strip bundlecomprises arranging it partially across a length direction of the core and in thecore main plane.

The bundle may be arranged in a substantially crenellated pattern inthe core main plane.

The method may further comprise compressing the core in a directionparallel with the length direction.

The method may further comprise providing at least one guidemember, which is moveable at least across the length direction of the core.

The guide member may be movable along the length direction ofthecore and/or perpendicular to the bundle main plane.

At least two or three guide members may be provided.

The method may further comprise pressing the core in a direction per-pendicular to a length direction of the core.

According to a second aspect, there is provided a laminated boardmaterial, comprising a core formed from strips of a sheet material comprisinga corrugated layer and preferably also a planar layer bonded to the corrugat-ed layer, wherein flutes formed by the corrugated layer extend in a direction substantially perpendicular to a board main plane; and a pair of facing sheetssandwiching the core. A contact surface between adjacent strips issubstantially free from adhesive material.

The adhesive material may be e.g. a polymer resin (e.g. hot meltadhesive, a setting resin), water glass or glue.

The contact surface may be free from adhesive material in a zone thatextends over at least 70 % of a thickness of the core, preferably over at least80 %, at least 90 %, at least 95 % or at least 99%.

Hence, effectively, the only adhesive material present between a pairof adjacent strips is that which has penetrated in connection with theapplication of the facing sheets.

The core may present strips which are bent through at least 90°,preferably at least 135° or about 180°, as seen in the board main plane.

For example, adjacent strips, or even all strips forming a strip bundle,may present the same bend angle but different bending radii.

The core may be formed of a bundle of strips having equal width, saidbundle being bent back and forth in the board main plane.

The new method provides a number of advantages, including in-creased flexibility in laminated sheet format: basically any width can beproduced in a fully automated production line.

Moreover, by eliminating the sawing referred to by way of introduction,enhanced tolerances can be achieved, as sawing-related defects areeliminated.

Brief Description of the Drawinqs Fig. 1 schematically illustrates a process of producing a laminatedboard material.

Fig. 2 schematically illustrates the production process in more detail.

Fig. 3 schematically illustrates a laminated board material which can beproduced according to the present disclosure.

Detailed DescriptionThe methods disclosed herein make use of a corrugated sheet 20 as a starting material. Such corrugated sheet may be supplied in bulk form, e.g. ona reel, or directly from a machine for its production.

Typically, the corrugated sheet may be made from a wood fiber basedmaterial, such as paper. The corrugated sheet may optionally be impregnatedand/or coated in order to reduce its ability to absorb moisture.

The corrugated sheet 20 presents corrugations which provide flutes.Optionally, the corrugated sheet comprises one corrugated sheet and oneplanar sheet, which is bonded to the corrugated sheet.

The corrugated sheet is fed in a feed direction Df from the supply to alongitudinal cutting device 21. The feed direction Df may be substantiallyperpendicular to the longitudinal direction of the corrugations or flutes.Preferably, the feed direction is perpendicular to the direction of thecorrugations, but it is conceivable to feed slightly obliquely or to use a sheet inwhich the corrugations do not extend perpendicular to the longitudinaldirection of the sheet.

Cutting devices 21 are known from e.g. US3912573, which wasreferred to above, and may include knives, saws, rotary cutters, laser, waterjet or other types of cutting techniques.

The number of cutters 21 is selected with regard to thickness of thecore that is to be provided, and thus with regard to the number of strips to beprovided and the width of the sheet.

The cutting device 21 cuts through the sheet, thus dividing it along thefeed direction Df into a plurality of strips 22. However, the strips remainconnected to the supply. That is, there is no cutting in the direction across thefeed direction Df.

Each strip 10a, 10b is then, at 22, turned approximately 90° about itslength direction, i.e. a direction parallel with the feed direction. Preferably, allstrips are turned towards the same direction.

The turning 22 may occur over a certain length in the feed direction Df.This length may be dependent on the width of the strips, and on the flexibility and strength of the material: a wider strip may require a longer length, as maya more brittle or weaker material.

After the strips have been turned, they are merged 23 top surface tobottom surface to form a bundle of strips 24. The bundle 24 will presentprincipal surfaces Bp1, Bp2 which are formed by side surfaces of the strips10a, 10b, and which will be parallel with the principal surfaces of the core 1that is to be produced.

The strips 10a, 10b forming the bundle 24 will not be held together byany adhesive, and thus the strips can move freely relative each other alongtheir length directions. ln one embodiment, where the sheet is supplied in a substantiallyhorizontal orientation, the bundle 24 of strips may be arranged with itsprincipal surfaces Bp1, Bp2 horizontally oriented.

The bundle 24 of strips may be guided by one or more guide membersG1a, G1b, G2, G2a, G2b, G3, G4, which may protrude upwardly through asupport (not shown) on which the bundle 24 is transported, or which may bebrought into contact with the bundle 24 from above.

The guide members G1a, G1b, G2, G2a, G2b, G3, G4 may providemultiple functions: they may collect (G1a, G1 b) and maintain the strips in aheld together bundle; they may push the bundle sideways (G2, G2a, G2b,G3, G4) i.e. in the direction transversely of the feed direction Df and they maypush or hold the bundle towards the downstream direction (G2, G2a, G2b,G3, G4), as seen in the feed direction Df.

Hence, the guide members G1a, G1b, G2, G2a, G2b, G3, G4 may beused to control the layup ofthe bundle 24 to form the core 1.

The laterally outer shape of the core 1 may be defined by rim membersR1, R2, which may run along the feed direction Df. Such rim members maythus define a core width. The rim members R1, R2 may present a portion oftapering width, whereby the core 1 which has been laid up by the guidemembers (G1a, G1b, G2, G2a, G2b, G3, G4) is compressed in a directiontransversely of the feed direction Df.

Once given its intended shape, the core may be provided with facingsheets 11a, 11b to form the laminated board material. The facing sheets may be attached to the core by any conventional type of adhesive or glue.Examples include hot-melt adhesive and setting polymer resins.

Preferably, such glue or other adhesive is applied to the core, e.g. bymeans of a pair of glue rollers 25a, 25b; one 25a applying glue to the upperside of the core and the other 25b applying glue to the lower side of the core. lt is possible to apply glue or other adhesive only to the core, only tothe facing sheets, or to apply glue both to the facing sheets and to the core.

The facing sheets 11a, 11b may be applied continuously, fromrespective reels, or sheet-wise. lt is possible to apply facing sheets only from above or only frombelow, and to then turn the half finished board for application of the next,opposing facing sheet. lt is also possible to apply both facing sheets simultaneously or with aslight offset in the feed direction Df.

The guide members G1a, G1b, G2, G2a, G2b, G3, G4 may be used tolay up the bundle of strips in any desired pattern for forming the core.Specifically, it is contemplated to provide the bundle of strips in a substantiallycrenellated pattern. That is, the bundle of strips will extend across the feeddirection Df, from one side edge of the core, across the entire width of thecore, to the other side edge of the core, bend 180° and then extend all theway back to the first side edge of the core, bend 180°, and so on. ln order to provide such a pattern a first pair ofguide members G1a,G1 b, or a guide member and a rim, may be used to collect the strips to andmerge them into a bundle 24 of strips having the desired width, as describedabove.

A second guide member G2, G2a, G2b may engage the bundle ofstrips downstream of the first guide member G1a, G1 b and push the bundle24 of strips towards one of the side rims R1, R2, such that the bundle is heldbetween the guide member G2, G2a, G2b and the side rim R1, R2. Thebundle is allowed to shift over, and thus be fed past, the second guidemember, at least when it moves in the direction transversely of the feeddirection Df. This second guide G2, G2a, G2b member may then follow in the feed direction, such as to provide some pressure towards the downstreamcore 1 which has already been laid up.

A third guide member G3 may then engage the bundle of strips fromthe side opposite to which it was engaged by the second guide member G2,G2a, G2b. This third guide member may push the bundle of strips towards theopposite side rim, while allowing the bundle to shift over, and thus be fedpast, the third guide member. This third guide member may then follow in thefeed direction, such as to provide some pressure towards the downstreamcore which has already been laid up.

Optionally, a fourth guide member G4 may be provided, may performthe same action as the third guide member G3, but in the opposite sidewaysdirection.

Once the fourth guide member G4 has started to apply pressure in thefeed direction, the second guide member may be disengaged and return torepeat its function.

Then after the second guide member has applied pressure during itssecond cycle, the third guide member will likewise be disengaged and repeatits cycle.

Hence, at any given time, there will be two guide members applyingpressure in the downstream direction (and thus moving together with the laidup core), while a third guide member is in motion.

As another option, the bundle of strips may merely be provided alongthe feed direction. This will limit the width of the board material thus producedto that of the bundle 24. To this end, a single pair of stationary guidemembers G2a, G2b may be used, just a pair of rims R1, R2 or a rim and aguide member.

The finished board material may 2 be characterized as follows.

As there is no adhesion provided between the strips 10a, 10b formingthe bundle of strips 24, each strip 10a, 10b will present a zone, extending inthe thickness direction Y of the board material 2, in which the front and backfaces of the strip is free from adhesive material.

The exact width of this zone is determined by how far the adhesiveprovided when laminating the facing sheets to the core has penetrated into the core. lt is estimated that the adhesive free zone may extend over at least70 % of the core thickness, preferably over at least 80 %, at least 90 % or atleast 95 %.

Where the same type of lamination system has been used for bothfacing sheets 11a, 11b, it is expected that penetration will be very similar onthe two faces of the core 1. Hence, the adhesive free zone will be centeredabout the middle of the core 1, as seen in the thickness direction.

The adhesive free zone will extend substantially continuously along therespective strip. lt is noted that random and/or unintentional occurrence to anextent that is insufficient to impede the relative movement between the stripsmay occur.

Moreover, in boards 2 produced according to the method where thebundles are laid up across the feed direction Df, the board material 2 willexhibit portions where a bundle of strips is bent in a plane parallel with theboard main plane XZ. Such bends may be about 90° or about 180°. Adjacentstrips of a bundle 24 will thus present the same bending angle, but differentbending radii: strips closer to a centre of the bend will have smaller bendingradius and strips further away will have greater bending radius.

Due to the compression in the feed direction Df, strips which are at thepart furthest away from the centre will be substantially parallel with thelongitudinal edge of the board, as seen in the feed direction Df. Hence, theboard material will also present strips 10a, 10b, which are non-parallel witheach other.

Claims (11)

CLAIIVIS

1. A method of producing a core material (1) for a laminated board(2), comprising: providing a sheet (20) of material comprising a corrugated layer andpreferably also a planar layer bonded to the corrugated layer, whereby thesheet defines first and second opposite faces, parallel with a sheet mainplane (Sp), orienting the sheet such that corrugations extend substantiallyperpendicular to a feed direction (Df), slitting (21) the sheet along the feed direction, such that a plurality ofelongate strips (1 Oa, 10b) are provided, turning (22) the strips 90° about their longitudinal directions, merging (23) the strips first face to second face to form a strip bundle(24), whereby a bundle main plane (Bp1, Bp2) is defined, which issubstantially perpendicular to the sheet main plane (Sp) of the individualstrips (10a, 10b), arranging the strip bundle (24) to form the core (1) to a predeterminedwidth (Y), laminating at least one facing sheet (11a, 11b) to the core (1), wherein the strips (1 Oa, 10b) are movable relative to each other untilthe facing sheet (11a, 11b) has been bonded to the core (1), aeel whereirffcftaracterâzed in that the strip bundle presents a width that issmaller than the predetermined width of the core, and wherein arranging thestrip bundle comprises arranging it partially across a length direction (Df, X) ofthe core and in the core main plane (Bp1, Bp2).

2. The method as claimed in claim 1, wherein the strips (10a, 10b) aremaintained continuous and transversely uncut at least through the arrangingstep and preferably through the laminating step. 11

3. The method as claimed in claim 1 or 2, wherein the bundle isarranged in a substantially crenellated pattern in the core main plane (Bp1,Bp2).

4. The method as claimed in elawany of the preceding claims, furthercomprising compressing the core in a direction parallel with the lengthdirection (Df, X).

5. The method as claimed in any one of the preceding claims, furthercomprising providing at least one guide member (G1a, G1b, G2, G2a, G2b,G3, G4), which is moveable at least across (Y) the length direction (Df, X) ofthe core.

6. The method as claimed in claim 5, wherein the guide member (G1a,G1b, G2, G2a, G2b, G3, G4) is movable along the length direction (Df, X) ofthe core and/or perpendicular (Z) to the bundle main plane (Bp1, Bp2).

7. The method as claimed in claim 5 or 6, wherein at least two or threeguide members (G1a, G1b, G2, G2a, G2b, G3, G4) are provided.

8. The method as claimed in any one of claims 2-7, further comprisingpressing the core (1) in a direction (Y) perpendicular to a length direction (Df,X) of the core.

9. A laminated board material, comprising: a core (1) formed from strips (10a, 10b) of a sheet material comprisinga corrugated layer (101) and preferably also a planar layer (102) bonded tothe corrugated layer (101), wherein flutes formed by the corrugated layer extend in a directionsubstantially perpendicular to a board main plane (Bp1, Bp2, XZ); and a pair of facing sheets (11a, 11b) sandwiching the core (1 ); wherein a contact surface between adjacent strips is substantially freefrom adhesive material, 12 characterized in thatthe core (1) is formed of a bundle (24) of strips having equal width, saidbundle being bent back and forth in the board main plane (Bp1, Bp2, XZ).

10. The laminated board material as claimed in claim 9, wherein thecontact surface is free from adhesive material in a zone that extends over atleast 70 % of a thickness of the core, preferably over at least 80 °/-.~, at least90 °/>, at least 95 °/> or at least 99%.

11. The laminated board material as claimed in claim 9 or 10, whereinthe core presents strips (1 Oa, 10b) which are bent through at least 90°,preferably at least 135° or about 180°, as seen in the board main plane (Bp1,Bp2, XZ).