Field of invention

The present invention relates to a laminate and to a method for producing such a laminate.

Technical Background

Light-weight boards based on a core sandwiched between facing sheets are widely used as building elements. These boards are often based on wood fiber materials, such as paper or paper board.

EP1714776A1 discloses a light-weight wood fiber based board comprising a core that is sandwiched between upper and lower facing sheets. The paper sheets forming the core are corrugated and stacked, so as to form flutes or channels, which flutes or channels are tilted in relation to the facing sheets. Such a construction gives rise to an increased strength, since the effective contact between the walls of the structure is increased.

Due to its durability and strength, a light board material, such as the one described in EP1714776, can advantageously be used in the manufacturing of e.g.

exhibition screen walls, furniture, in-store displays etc. In the manufacturing of such products, the board often needs to be molded to provide a curved surface. Usually, molding is made possible by particle cutting series of grooves in the facing sheets. The disadvantages with this technique are that it is time-consuming and that it has a negative impact on the life-cycle, the strength and the appearance of the end product. Summary of invention

One object with the present invention is to provide a light-weight material, which is strong and durable and which enables curves to be formed in an easy way.

This object, as well as other advantages, is achieved with the laminate according to the present invention. The laminate of the invention comprises a first core formed as a three dimensional body presenting a first face and a second face and a wall structure defining a plurality of channels, each channel having a longitudinal axis intersecting the first face, a first facing sheet laminated onto said first face, and a second facing sheet of a flexible material laminated onto said second face. Said laminate may be referred to as a first laminate .

The laminate according to the invention is light - weighted, strong and durable, and it is easy to form curves in the laminate.

In one preferred embodiment of the invention, the laminate further comprises an additional, second, laminate comprising a second core formed as a three dimensional body presenting a first face and a second face and a wall structure defining a plurality of channels, each channel having a longitudinal axis intersecting the first face. Said second laminate may further comprise a third facing sheet laminated onto said first face of said second core. The additional, second laminate may be laminated onto the first laminate so that the second face of the second core faces the second facing sheet of the first laminate. The arrangement of at least one layer of a flexible material in-between two cores in this way facilitates the molding of the laminate and gives rise to stable curvatures in the laminate. The second laminate may further comprise a fourth facing sheet of a flexible material laminated onto said second face of said second core. The additional, second laminate may be laminated onto the first laminate so that the second facing sheet and the fourth facing sheet are facing each other. In this way, the manufacturing process of the laminate is facilitated since the laminate may be manufactured by laminating two identical (first and second) laminates onto each other.

The laminate according to the invention may be a curved laminate. The formation of curves in the laminate enlarges the field of use of the laminate.

According to one embodiment of the invention, the channels of the core or cores intersect the first face or first faces at an angle (c which is less than 90 degrees, preferably between 45 and 80 degrees. In this way, an exceptionally strong material is produced. The tilted channels of the core in such a structure give rise to a larger surface for the facing sheet to be attached to, which in turn gives a stronger material. Said surface is formed by the cut end portions of the channels forming the core. Moreover, a tilted structure facilitates the formation of curves in the laminate.

Preferably, the flexible material has an elongation of break (stretchability) of at least 5%. Such high stretchability of the material facilitates the molding of the laminate.

The flexible material may be flexible paper, preferably a paper comprising cellulose fibers. In this way, the laminate may be made completely of a renewable material which is environmentally favorable.

In a second aspect, the invention provides a method for manufacturing a laminate. The method of the invention comprises the steps of providing a first laminate comprising a first core formed as a three dimensional body presenting a first face and a second face and a wall structure defining a plurality of channels, each channel having a longitudinal axis intersecting the first face; laminating a first facing sheet onto said first face; and laminating a second facing sheet comprising a flexible material onto said second face.

The method may further comprise providing an

additional second laminate, which second laminate comprises a second core formed as a three dimensional body presenting a first face and a second face and a wall structure defining a plurality of channels, each channel having a longitudinal axis intersecting the first face, and a third facing sheet laminated onto said first face of said second core; applying an adhesive on the second facing sheet of the first laminate; laminating said additional second laminate onto the laminate ; and molding the thus formed (third) laminate by placing the third laminate on a mold and applying pressure while the adhesive is settled.

The additional second laminate may further comprise a fourth facing sheet comprising a flexible material laminated onto the second face of the second core.

According to this embodiment, said additional second laminate is laminated onto the first laminate so that the second facing sheet of the first laminate and the fourth facing sheet of the second laminate faces each other.

The method according to the invention enables curves to be formed in a light-weight material in an efficient manner and avoids the drawbacks of the prior art

technique . Detailed description of the invention

The laminate according to the invention comprises a core presenting a first and a second face. Said core comprises a wall structure defining a plurality of channels and said first face and said second face are formed by the end portions of the channels. The core is preferably made of wood fiber based material, such as paper or paper board.

A first facing sheet is laminated onto the first face of said core. The first facing sheet may be a sheet of paper, cardboard laminate, sheet metal, wood veneer, polymer films or sheets or other materials which is attachable to the core to provide a surface, which may be e.g. smooth, printable and/or water repellant. In one preferred embodiment, the facing sheet is made of paper or cardboard of cellulosic fibers. In this way, the whole laminate can be made of renewable materials.

A second facing sheet is laminated onto the second face of said core. Said second facing sheet comprises, according to the invention, a flexible material. The flexible material facilitates the formation of curves in the laminate.

The laminate comprising a first core and a first and a second facing sheet as described above may be referred to as a first laminate.

In one preferred embodiment, the laminate further comprises a second laminate, comprising a second core presenting a first and a second face, a third facing sheet laminated onto said first face and a fourth facing sheet laminated onto said second face of the core, which fourth facing sheet comprises a flexible material. Said second core may be constructed in the same manner as the first core.

The first and the second core of the laminate may be manufactured by providing a continuous block of material presenting a plurality of channels, which block has a thickness that is greater than the desired thickness of the core and cutting from said block of material pieces that is to form the cores. The block of material may be formed of a plurality of stacked corrugated sheets of wood fiber based material, such as paper or cardboard.

However, other materials may also be used, such as metal sheet, polymer sheets etc. Each sheet in the stack may be adhered to the adjacent sheet by means of an adhesive, preferably a water-based adhesive. Said plurality of corrugated sheets may be interleaved with a plurality of substantially flat sheets. Both the first and the second core may be cut from the same block of material.

The thickness of the core may be between 5 - 65 mm. The thickness of the facing sheets may be between 30 μιη - 5 mm, depending on the material used.

Preferably, said second facing sheet and said fourth sheet are made of flexible materials. Said flexible material may have an elongation of break in MD of at least 5%, preferably of at least 7 %, even more

preferably of at least 10% or of at least 20%.

The flexible material may be flexible paper, such as sack paper or FibreForm® supplied by Billerud.

Edge liners may be attached to the side portions of a cut core, thus to the portions of the core that are connecting the first and the second faces of the core.

Said side portions may have an extension in a plane which is perpendicular to the first and the second faces of the core. Said Edge liners may be of any materials, such as paper, laminate or particle board. The channels defining the wall structure of the first and the second core may have longitudinal axis which intersect the first face of the cores at an angle which is less than 90 degrees, preferably between 45 and 85 degrees. Such a tilted structure gives rise to an increased strength. A core with a tilted wall structure may be provided by cutting a block of material so that the longitudinal axis intersects the first face at an angle which is less than 90 degrees or at an angle between 45 and 85 degrees. This may be accomplished by provision of a block of material in the form of

parallelepiped, presenting two adjacent block faces intersecting at an angle that is equal to the angle at which the longitudinal axis is to intersect the first face. Said block of material may thereafter be cut in a direction parallel with one of the block faces to form a core with a tilted wall structure. In an alternative embodiment, a block of material presenting perpendicular block faces is cut at a cutting angle relative to one of the block faces, which cutting angle is equal to said angle at which the longitudinal axis is to intersect the first face.

Fig. la and lb show schematic perspective views of a core with a tilted wall structure. The core shown in fig. la and lb presents a first face 101 and an in relation thereto parallel, a second face 105. The faces 101, 105 are separated by a core thickness T and there are side portions 110, connecting the faces 101, 105. Fig. lb is a side view of the core 100, showing the side portion 110. Typically, the thickness T of the core 100 is between 8 - 50 mm. The core 100 is constituted of an internal wall structure defining channels 102 that are tilted in relation to the faces 101, 105, i.e. each channel 102 has a longitudinal axis 103 that intersects the faces 101, 105 at an angle a of intersection being less than 90 degrees .

Fig. 2a shows a laminate, 200, according to one embodiment of the invention. The laminate shown in fig. 2a comprises a first core, 201, shown in details in fig. la and lb, a first facing sheet, 203, laminated onto a first face of the core and a second facing sheet, 202, laminated onto the second face of the core, which second facing sheet is made of a flexible material, such as flexible paper. The laminate shown in fig. 2a, may be referred to as a first laminate, 200.

Fig. 2b shows a laminate, 400, according to another embodiment. The laminate shown in fig. 2b comprises a first laminate, 200, described above and shown in fig. 2a. The laminate shown in fig. 2b, further comprises a second laminate, 300, comprising a second core, 301, and a third facing sheet, 303 laminated onto the first face of the core, 300. The second laminate, 300, is laminated onto the first laminate, 200, so that the second facing sheet, 202, of the first laminate, and the second face of the second core, 301, are facing each other. This can be achieved by applying an adhesive on the second facing sheet, 202, of the first laminate and then laminating the second laminate onto the first laminate so that the second facing sheet, 202, of the first laminate, 200, faces the second face of the second core, 301.

Fig. 2c shows yet another embodiment of the

laminate. The laminate shown in fig. 2c comprises a first laminate, 200, described above and shown in fig. 2a and a second laminate, 300, comprising a second core, 301, a third facing sheet, 303, laminated onto the first face of the core, 300, and a fourth facing sheet, 302, laminated onto the second face of the core, 300, which fourth facing sheet, 302, is made of a flexible material, such as flexible paper. The second laminate, 300, is laminated onto the first laminate, 200, so that the second facing sheet, 202, of the first laminate 200, and the fourth facing sheet, 302, of the second laminate are facing each other. This can be achieved by applying an adhesive on the second facing sheet, 202, of the first laminate, 200, and then laminating the second laminate, 300, onto the first laminate so that the second facing sheet, 202, faces the fourth facing sheet, 302. The laminates shown in fig. 2b and in fig. 2c are easily bended to form curves. This may be accomplished by putting the laminate, 400, on a mold before the adhesive applied between the second facing sheet, 202, and second face of the core, 301, or between the second facing sheet, 202, and the fourth facing sheet, 302, has settled and thereafter molding the laminate, 400, e.g. by climbing or pressing, until the adhesive applied between the second facing sheet, 202, and the core, 301, or between the second facing sheet, 202, and the fourth facing sheet, 302, has settled. The adhesive may be any kind of adhesive known in the art. In case a hot-melt adhesive is used, the laminate is molded while the adhesive is settled or solidified by cooling.

Fig. 3 shows a flow chart illustrating a method of manufacturing a curved laminate according to one

embodiment of the invention.

In a first step, 501, corrugated sheets are stacked and adhered using an offset so that a parallelepiped, presenting two adjacent block faces intersecting at an angle that is equal to the angle between the longitudinal axis and the first face, is formed.

In step 502, the parallelepiped is cut into cores with desired thicknesses. The cutting is performed by means of a razor blade in a direction parallel with one of the block faces.

In step 503, a first facing sheet is laminated onto a first face of the core and a flexible paper is

laminated onto a second face of the core. The first facing sheet is according to this embodiment a laminate of craft paper and polyethylene.

In step 504, the laminate formed by steps 501-503 is cut into desired contours so that at least a first and a second laminate is formed.

In step 505, the cut first and second laminates are printed with a desired pattern in a digital printer.

In step 506, a hot melt adhesive is applied to the flexible paper of the first laminate whereupon the first and second laminate is arranged onto each other so that the flexible papers of the first and second laminates are facing each other. In this way, a third laminate is formed by the first and second laminate.

In step 507, the thus formed third laminate is molded into a desired curved form while the adhesive applied between the flexible papers of the first and second laminate is settled by cooling.