Field of invention

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

Technical Background

Composite boards, such as particleboards and fiberboards, are widely used as building elements in furniture, floors and walls. Fiberboards are usually formed by layering a mixture of lignocellulosic material and a resin into a mat, consolidating said mat under pressure and curing the resin by applying heat. The physical and/or mechanical properties of fiberboards can be modified by changing the processing conditions e.g. utilizing different types of resins, or changing the type of lignocellulosic fiber, or the pressure under which the mixture is compressed.

Panels of the above described type are usually heavy and cumbersome to handle. In recent years, boards based on a core sandwiched between printable facing sheets have been commonly used to replace such traditional panel material .

US3661099 discloses a pallet deck comprising a board based on a core that is sandwiched between upper and lower facing sheets. Both the core and the facing sheets of said board are paper sheets. The paper sheets forming the core are corrugated and stacked, so as to form flutes or channels, the longitudinal axes of which are

perpendicular to the facing sheets.

EP1714776A1 discloses a light-weight wood fiber based board of the above mentioned sandwiched-type, wherein the 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.

In the art, there are also lightweight panels of sandwiched-types , wherein a core of e.g. honeycomb structure, is sandwiched between medium density

fiberboards (MDF) . The manufacturing of such a board is generally a step-wise procedure. Thus, first a core of a honeycomb structure is manufactured, which core is cut into desired contour, whereafter MDF is been laminated onto said core in a separate process-step. This process is very costly and inefficient.

Summary of invention

One object with the present invention is to provide a method of producing a strong and lightweight panel in a cost-efficient manner.

This object, as well as other advantages, is achieved with the method according to the present invention. The method according to the invention

comprises the steps of providing a 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

laminating a layer of high density fiber board (HDF) onto said first face by means of at least one laminating roll in an on-line process. Preferably, the high density fiber board is supplied to the at least one laminating roll as a continuous web from at least one supply roll.

The method of the invention gives rise to an exceptionally strong and light-weight panel, which is easier to handle and reduces the consumption of materials compared to the panels of prior art. The panel can advantageously be used in furniture, as a temporary wall, as floor, as advertising stand etc. The lamination of high density fiberboard on-line in the process in accordance with the invention involves savings in both time and material.

According to one embodiment of the invention, the channels of the core intersect the first face of the board at an angle (a) 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 HDF 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.

The high density fiber board (HDF) which is

laminated on-line in the process according to the invention may preferably have a thickness of less than 2 mm, preferably between 0,5 and 2 mm or even between 0,5 and 1 mm. It has surprisingly been shown that such a thin HDF may be supplied from a roll in an on-line laminating process .

In one embodiment of the invention, the method further comprises the step of applying a water based adhesive to the first face of the core, prior to the step of laminating the layer of high density fiber board onto the first face of the board. The use of a water based adhesive to attach the high density fiber board to the core gives rise to a strong panel, which is insensitive to heat and which has a high bending resistance.

Moreover, when a water based adhesive is used, the subsequent cutting of the board into a desired contour is facilitated, since clogging of the adhesive on the cutting knives is avoided. Another advantage with the use of a water based adhesive in this way is that the consumption of the adhesive is minimized, since the adhesive is applied on the end portion of the channels forming the first face of the core, i.e. the adhesive is only applied to the parts forming the adhesive bond.

In a second aspect, the invention provides a panel comprising; a 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 layer of hard density board attached to said first face, which layer of hard density board has a thickness of less than 2 mm, preferably between 0,5 and 2 mm. Such a panel is strong and may be manufactured in a cost- efficient manner.

Detailed description of the invention

In accordance with the invention, a high density fiber board (HDF) is laminated onto a first face of a core in an on-line process. Said core comprises a wall structure defining a plurality of channels, which first face is formed by the end portion of the channels. The method of the invention is very cost-efficient and gives rise to a strong, light-weight panel.

The core which is to be laminated 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 a piece that is to form the core. 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 sheet.

Δ high density fiber board (HDF) is, according to the present invention, laminated onto the continuous core on-line in the process. Thus, HDF is continuously supplied from a supply roll to a laminating roll, which laminates the HDF onto the first face of the core. High density fiber board usually has a density of between 850 - 1100 kg/m ³ . The HDF that is to be laminated on the core according to the invention has preferably a thickness of less than 2 mm, more preferably between 0,5 - 2 mm. Such a thin HDF can be supplied continuously from a roll.

According to a preferred embodiment of the

invention, HDF is attached to the core by means of a water based adhesive. Preferably, the water based

adhesive is applied to the first and/or second face of the core, prior to the lamination of the HDF. The water- based adhesive applied on the first face of the core may, e.g., be polyvinyl acetate. The adhesive may be applied to the end portions of the channels by means of

application rollers. This minimizes the consumption of the adhesive. In order to further minimize the

consumption, the adhesive may be foamed, i.e. a gas, e.g. air, may be injected in the adhesive whereby the volume is increased.

A second layer of high density fiber board may also be attached to a second face of the core, which second face is opposite and mutually parallel to the first face. Preferably, the first and the second layers of high density fiber board are attached to the first and second faces simultaneously by means of opposite arranged rollers .

The high density fiber board may be pre-heated prior to laminating the high density fiber board onto the core. The pre-heating of the high density fiber board may be accomplished by means of a heated laminating roll. The laminating roll may be heated to a temperature of 90 - 95 degrees, whereby the temperature of the high density fiber board also reaches temperatures of almost 90 degrees when laminated.

The laminated panel may thereafter be cut to desired contour by means a razorblade or an oscillating knife. Edge liners may be attached to the side portions of the 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. The edge liners may be attached to the core using any known adhesive, e.g. a hot melt adhesive or a water based adhesive.

The channels defining the wall structure of the core may have longitudinal axis which intersect the first face of the core 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. According to the invention, a high density fiber board, preferably with a thickness of less than 2 mm, is laminated onto the first face, 101, and/or to the second face, 105, of the core, (said HDF are not shown in fig. 1) -

Fig. 2 shows a flow chart illustrating a method of manufacturing a board according to one embodiment of the invention .

In a first step, 201, 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 longitidunal axis and the first face, is formed. In step 202, the parallelepiped is cut into a core with desired thickness. The cutting is performed by means of a razor blade in a direction parallel with one of the block faces .

In step 203, a water based adhesive is applied to the first face, 101, and to the second face 105, of the core simultaneously by means of application rollers arranged on mutually opposite sides of the core.

In step 204, HDF is supplied from at least one supply roll to two oppositely arranged laminating rolls and laminated onto the first and second faces of the core .

In step 205, the panel is cut into desired contours.

In step 206, edge liners are attached to the side- edges of the board by means of a hot melt adhesive.

Said steps, 201 - 206, are preferably performed in an on-line process.