Method of making wet-pressed fiberboard of high resistance to bending

<td colspan="2">SWEDEN [B]</td><td colspan="2">(11) PUBLISHING LETTERS</td><td> 7406675-4</td>

<td> (19)</td><td>SEE</td><td>(51) International class^{* 2 * * 5 * * * * 10}</td><td></td><td>0 21 J 1/16</td>

<td></td><td> ® ®|</td><td>(44) The application laid out and the application</td><td> 79-02-05</td><td>Publication 406 337</td>

<td></td><td>w I</td><td>publication paper</td><td></td><td>number</td>

<td></td><td></td><td>'(41) Application widely available</td><td> 75-11-21</td><td></td>

<td></td><td></td><td>(22) The patent application was filed</td><td> 74-05-20</td><td></td>

<td colspan="2">PATENT AND</td><td>(30) Priority information</td><td></td><td></td>

<td colspan="2">Registration Office</td><td colspan="2">(32) Date (33) Country (31) No</td><td></td>

The numbers in brackets indicate international identification code, INID code. Letters in chiams indicate international document code.

. (71) Applicant: EL BACK, LIDINGÖ, SE (72) llppf in below: Search.

(74) 0mbuds: Hammar ij (54) Name: Process for the production of hydrogen-pressed fiberboard material

The present invention relates to wet pressed sheet materials made of fibers, in particular fibers of lignocellulosic material such as wood.

The invention aims to provide a process for producing sheet material of the stated kind, which has low density, but at the same time bends rigidity, which at the same thickness is considerably higher than that of known sheet material of substantially the same density.

The object of the invention is achieved by making the wet-pressed sheet material made of fibers so that at least in one of the two main directions of the plane, normally in the machine direction, it consists of strip-shaped surface portions of at least two different densities and / or different mass, the present in optional widths. .

The process according to the invention basically consists in the manufacture of fibreboard¹ by applying a fiber suspension in a layer and pressing this layer into a bonded disk-shaped product having substantially uniform thickness the supply of

7406675-4 fibrous material for different parts of the layer is varied so that after the final pressing, the sheet material has at least one direction in the plane of the sheet having strip-shaped surface portions of different characteristics.

According to the invention, this result is achieved by applying the fiber material to the layer in varying amount over its surface, so that after pressing the sheet material obtains strip-shaped surface parts of different density.

There are a number of advantages of having surface parts in the disc with low and high density, respectively. The primary advantage is, as already mentioned, that it is possible in this way to build discs with high bending stiffness without increasing too much density. If you properly align surface parts with high density to the end purpose of the disc, you can achieve a particularly good edge density in future cutting surfaces compared to the other parts of the disc. With this high density on the edge, this edge becomes more easily painted and provides significantly increased fastening for screws, fasteners, etc. Especially when screws are to be fastened to or at the saw edge, e.g. when installing cabinets, etc., of fibreboard, or where hinges are to be fastened in cupboards. This also applies to wall panels which, in their sides, must be provided with groove and tongue or with a spring and thus must be attached to these edges.

If, in this way, low and high density surface parts are to be adapted to the finished formats from the finished sheet for furniture or wallboard manufacture, then a wide range of strip and grid patterns with high and low density can be envisaged. This is especially true in the machine direction where it is very easy to vary these designs.

Conveniently, the surface of the disc contains strip-shaped surface portions of two different densities, the density of the denser surface portions being at least 20% and preferably at least 30% greater than that of the less dense surface portions. The latter may thereby have the density which is normal in currently manufactured medium-hard fiber sheets, i.e. about 500 - 750

0 kg / m, while the denser surface parts have a density in the range 750 - 900 kg / m³.

In order to achieve the desired increased bending stiffness without excessive increase in the average density of the sheet material, it is most convenient that the denser material constitutes a smaller part of the whole sheet material, and for this purpose the two materials of different densities are preferably distributed so that the higher parts with higher density. density is 10 - 50%, preferably 15 - 30%, of the surface of the sheet material.

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It is also advisable to build the denser portions of the board of more qualified raw material than the less dense portions, e.g. more well-ground fiber raw material. It is also advisable to add these parts with a higher content of adhesive, such as thermosetting resin, than the other parts.

Methods for producing wet sheets are well known in the art. A suspension of fibers, eccentrically fitted with binder, is laid out through an inlet box as a layer on a movable wire in a sheet forming machine, whereupon the layer is partially dewatered on the wire to obtain a coherent web. The web is edge cut and cut into sheets, which are then pressed under high pressure and at high temperature so that the finished slices are obtained.

In the manufacture of fiber discs according to the present invention, in order to vary the density in strips along machine direction, a suitably arranged inlet boxes can be arranged, where two flow streams alternate with each other and flow out on the wire at equal speed, the two flow streams having different concentration and / or containing fibers. different nature. To the inlet box, these two stock streams are fed separately and are initiated, for example, from different sides or with one stream from the side and the other straight from behind. Such a manufacturing method provides an opportunity to have different raw materials in these two stock streams, e.g. a more highly qualified fiber raw material in the one to provide a high density surface, and a less qualified bark-containing waste material in low density surface parts. The method also provides the possibility of adding a thermosetting resin, e.g. phenolic resin, to the stocking stream which will give surface parts of higher density. In a particular embodiment of the invention, the wafer is also made with a middle layer extending over its entire extent which has the higher amount of binder.

A simpler procedure when it comes to producing surface parts with different densities is to vary the lip setting in the inlet box outlet to the wire, thus varying the amount of stock flowing in different parts across the machine width. As long as the speed of sheet forming is low and especially when sheet forming takes place at high concentration and with heavy dewatering at the beginning of the wire section, this manufacturing method has the prerequisites to succeed. Higher density surface parts across the machine direction can be provided by a chute which is at an angle to the machine direction adapted so that a small portion of the chute is opened downward for outlet of the stock, and this opening moves over the machine direction at a speed which

7406675-4 is adjusted to the speed of the machine so that the pulping is perpendicular to the machine direction.

Without limiting the scope of the invention, here are given some examples of boards made with surface parts of different properties and methods of making them.

Example 1

On a wallboard machine for the production of medium hard boards with a clean cut machine width of 125'cm and with a sheet forming width of 132 cm, the inlet box was arranged so that two stock streams could. supplied and leave the inlet box at equal speed. One stock flow had a concentration of 2.4%, the other a concentration of 3.4%. Mass dewatering resistance was 25 Defibrator seconds.

In the sheet forming, the pulp with the higher concentration was filmed in each 10 cm outer strip on each side and in addition in three strips of 5 cm evenly distributed over the width at a distance of 25 cm from each other and from the outer strip with high density. At the same time, four strips of 25 cm width with stock were added with the lower concentration. Dewatering took place on wet suction boxes and without mixing the stock flows to a substantial extent with the product 20 draw. To the stock with the higher density was added 0.5% phenolic resin dry-based on dry-pulped mass. The sheets were pressed to 10 mm thickness in a multi-stage press with 220 ° C press temperature against heel and with 24 minutes total press time. The sheet had previously been cleaned to a width of 129 cm. After curing for 4 hours at 155 ° C, the sheet is finely cut to 124 cm. The finished cut was 3 completely flat, had a total density of 650 kg / m, overall. 3 3 where surface parts with a density of 850 kg / m and with 600 kg / m were generally found in the above strip form patterns. Flexural rigidity in the area of ​​elastic stress was 25% higher than that of a homogeneous slab of density 650 kg / m³.

Example 2

On a similar machine as in Example 1, but with only a normal inlet box for the machine for only one pulp type, the outlet portion of the box had been rebuilt so that large variations in outlet height could be achieved with the lip. In 5 cm wide strips of 10 cm apart, the lip height, ie the opening from the outlet box, was increased by 50% in addition to adjacent surface parts. The pulp concentration in the inlet drawer was 4.1%, surface pulp was applied at 200 g / m of a high-ground fiber raw material, while the matrix consisted of sawdust pulp with a dewatering resistance of 26 Defibrator seconds. Medium hard fiber boards about

7406675-4 mm thickness was made in the same manner as in Example 1 and 3 strip shaped surface parts were obtained with a density of 500 and 8 mm respectively. 700 kg / m. The boundary between these surface parts was not as sharp as in Example 1, but they were 1/3 respectively. 2/3 of the surface each and the disc was completely flat.

The average density of the disc was 570 kg / m. The stiffness as above was 30% higher compared to a homogeneous slab made with a density of 570 kg / m 2.

Example 3

Wet sheets according to Example 1 had, after machine dewatering and prior to pressing, been equipped with strips with machine-made stock for the purpose. Additional 2

750 g measured per m is paved in strips of 15 cm width across the machine and with a mutual distance of 35 cm. Such a wet sheet was wet-pressed again and followed through the manufacturing process. Discs were cleaned so that they received a high-density edge strip around. Thus, improved edge density was obtained, which manifests itself in low color consumption at the edges. The screw strength at the edge was tested according to the method in Medd.

STTI (1971) (FS: 9B) and found in the strips along the machine direction to be 25% higher than for a disc with the same overall average density.

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