Technical area:

The present invention relates to a method for producing a laminate. More precisely it relates to the production of high pressure laminates and comprises the following steps: providing an underlayer preferably wooden, application of a number of sheets at one of the sides of the underlayer,such as papersheets which are impregnated with a ther o setting resin such as phenol or melamine, introduction of the in accordance with the above arranged layers into a heat press and application of a high pressure at a high temperature to the grouped layers during compression thereof, so that the layers are joined by means of the thermo setting resin.

Prior art:

Surface materials in the form of so called plastic laminates are produced in accordance with the above-mentioned method and are used within many different areas. Different laminates have been developed having different qualities concerning hardness, abration resistance, structure, colour, pattern etc.

The most durable and hardest plastic laminates are the so called high pressure laminates. These are produced by means of a number of phenol and melamine impregnated papers respecti¬ vely, being compressed under high pressure (5-8 MPa) and during increasing temperature (up to 180°C) . The papers in the top layer are patterned papers plus a transparent wearing course (overlay) .

Nowadays high pressure laminates are normally produced having a thickness of 0,5-1,5 mm and are mainly used as a resistant and decorated surface for applications within the furniture

and building sector. Reguisited plate-like materials are produced as semi-finished products by gluing the high pressure laminate against the chosen framework (normally different forms of particle boards) .

Laminates of lower qualities are produced at lower pressures and in thinner qualities. A simpler form of a laminate surface is provided for when an impregnated paper and the framework are directly joined during exposure to a limited pressure (underneath 3 MPa) and lower temperature (underneath 120 ° C) . This process is called direct laminating and means that the impregnated paper is laminated and applied to the framework directly in the same process. Direct laminating is a cheaper method for applying a surface onto a frame material, compared to the method of first producing a corresponding surface material and thereafter applying it to the framework by gluing.

The German citation DE-A-25 50 768 discloses a process for producing high pressure laminate, where the innermost phenol impregnated layers are exchanged for a particle board mate¬ rial. Hereby the particle "board is subjected to a surplus of a hot setting resin, which is not fully cured, to pressure and heat, whereby the resin turns to liquid state, and at this instant a decoration sheet is added. This method requires a process time of up to 70-90 minutes.

The technical problem:

By the production of a laminate using such a method, at high pressure, an uncontrollable and uneven compression of the framework takes place. Due to the non-homogeneous character of particle boards, are differencies in the density and the thickness obtained, which makes the supporting ability of the material indefinite. The obtained material can therefore not be used as a selfsupporting material without an excessive overdimensioning which is related to the weakest points of the board.

Using this known method also results in too high costs for the production of an acceptable product, caused by the above-men¬ tioned need to overdimension. One could say that the above- described process exchanges a number of phenol impregnated framework sheets for a material of phenol impregnated particle board. Otherwise this process does not deviate from the normal way of production. On page 3 it is clearly described that the intention is not to achieve a form of a direct high pressure laminate but to produce a laminate having a core of impreg¬ nated wooden material as a replacement for the expensive phenol impregnated sheets for the frame work.

Solution:

With a method in accordance with the invention is a pressure range of 5-8 MPa and a temperature range of 120-180°C chosen, and for the underlayer a material is chosen having the proper¬ ties to resist said pressure and heat without any significant deformation and preferably a hard board of eucalyptus wood.

Advantages:

By the invention a method is achieved by which a final cover material is produced by means of direct laminating at high pressures, especially a material for floors, which meets the demands concerning resistance against wear and non-deforma- bility, which such a use requires.

Preferred mode of examples:

The invention relates to a method by which a limited number of phenol or melamine impregnated sheets of paper are directly laminated onto a body by means of heat curing and high pressure. When using the method it is essential that the pressing of the sheets is performed under such circumstances concerning temperature and pressure that the required proper¬ ties of strength are obtained and that the body is accordingly adapted so that it resists these high pressures. Accordingly the method is a mating of physical data and material qualities.

Hence this mating means that the body is chosen in order to resist the pressure and the temperature, which are to be used in order to obtain the desired result by the laminating process. The material however, which can be chosen as body has certain limitations which may not be exceeded, out of practi¬ cal and economical reasons one has to stick to wooden mate¬ rials. Since a certain pressure is necessary in order to obtain a homogeneous laminate and a certain temperature is necessary in order to cure the resin, the time of the process has to be used as a means for adapting the process. To keep this time short is of importance out of economical reasons and reduces the labour costs as well as the cost of capital since the machines can be used more efficient. Furthermore short times of process means that the body of the device is put under less strain since its exposure to pressure and above all to heat is shorter. If the material is exposed to heat for a long time it can lead to a change of its qualities and it can lead to a desiccation.

In accordance with the present invention short processtimes are obtained by adapting the resin to provide for rapid curing.This can be achieved partly by using resins having high ability to react, partly by using a small amount of resin. lso the number of papersheets beeing used is kept on a lower level.The above mentioned will be apparent when describing the following example.

The method is best described by the following example.

Example 1

A body,a framework,is provided for.This body is often made of a euclyptuboard which comprise layers of eucalyptuwood.lt is produced in accordance with known methods,i.e the different layers are joined by exposure to high pressure.

At the laminating process one of the surfaces of the body, is firstly provided with an impregnated paper,secondly with a patterned impregnated paper and finally preferably also a topsheet by means of which the final product can be furnished

with appropriate properties.This latter layer can for instance be a melamine impragnated paper of fine fibres which has a certain transparency.

At the opposite side of the body one preferably places a barrier sheet which also is impregnated.Its object is to equilibrate the construction,so that the forces acting on the body are balanced and to limit deforming movements caused by the environment,e.g varying temperature and humidity.The object of the barrier layer can also be to protect the surface in the same manner as the front layer protectes its surface.

Above it has been mentioned that the used paper sheets are impregnated. This is done using a curable resin based on a urea resin and generally a phenol thermo setting resin or a melamine thermo setting resin. Since phenol resin is cheaper than melamine does one impregnate the innermost sheet which is to be placed closest to the body with phenol ,whereas the patterned sheet and in some cases the superficial sheet is impregnated with melamine since melamine is brighter and its qualities concerning transparency are better, which permits the pattern of the patterned sheet to appear. As mentioned before one strives to shorten the process times. This can be achieved by chosing the resin among such resins, which have increased ability to react and accordingly are cured in a short time and also by deminishing the amount of resin. Above it has been mentioned that preferably two sheets are used, the underlaying sheet and the patterned sheet and furthermore if the demands are such an extra top sheet in order to strengthen the surface. By conventional production of a laminate it is common to use a number of underlaying sheets, core sheets, which obviously is not necessary nore appropriate in this case because of the specific mating in accordance with the invention. Using the exact adaption of above specified features it is possible to achieve pressing times which fall below 2 minutes.

The grouped material comprising its different sheets is placed

in a press. Here it is exposed to a pressure in the range of about 5-8 MPa during a rise of the temperature till a range of about 120-180°C.

Second mode of example:

For certain applications the costs for the material can be made even cheaper by elaminating the barrier sheet. In order to compensate for the longitudinal deformation caused by the laminating of the top layer on one of the sides,is it approp¬ riate to pretreat the body material so that the surface which is to be laminated is given a curved form, a convex form seen from said latter surface. Hereby one can obtain a plane mate¬ rial after the coating even if a barrier layer is not used.

Third mode of example:

Considering its strength the body material is sensitive to being dried up. This can occur during the pressing process with its high temperature. In order to avoid this is it appropriate to treat the materials which are to be used at room temperature and in an environment comprising 50-60 % relative humidity giving it a normal amount of moisture. Furthermore it is appropriate to preheat the body material. Hereby the press time can be shortened and the body material is less influenced.

In order to further de inish the result of drying up it is possible to shorten the press time by using an impregnating material ,for the paper sheets, which ability to react is extreme and/or by using a small amount of resin. This is chosen, at the number of sheet which has been mentioned, so that the press time can be limited to some minutes, preferably less than 2 minutes.

Compared with the corresponding glued laminated material, does a laminate in accordance with the invention obtain a whole lot of advantages. The laminate is more homogeneous due to the higher pressure in the production process and since no layers of glue separate the layers. The amount of material which has

to be used is less since the number of layers in the surface which are required are less, which also leeds to that the undermost barrier sheet of paper, which equilibrates the di'fferencies of tension towards the top layer, can be made in a simpler manner. The process cost are lower since the gluing process is eliminated. As has been mentioned before it is of major economical importance that the pressing times can be shortened.The cost for the capital is also less since it is possible to use laminate presses having short press cycles and since the machines for gluing are excluded.