SE442101B - PROCEDURE FOR MANUFACTURING FIBER PLATES OF LIGNOCELLULOSALLY MATERIAL - Google Patents

Description

8 "1047" 55.'7 2 areas with dry resin stains resp. areas without spots.

Furthermore, problems arise in transporting the impregnated fiber, since the imperfect fiber impregnation and the high degree of tackiness of the resin used causes lumps of bonded fibers (balls of bonded fibers) to form, which cause serious problems in the transport systems (air or mechanical ) to feed the impregnated fiber to the press.

It is also impossible to impregnate before the fiber has dried. Since the resin hardens quickly, only dry fibers can be impregnated (ie they must have passed the dryer), because transport of the impregnated fiber through a dryer means that gelation takes place in advance, ie. before the material reaches the press.

In order to solve the above-mentioned problems, according to the invention a process of the kind described above is provided, which is mainly characterized in that said binder mixture is prepared from a non-sticky urea-formaldehyde resin with a dry content of between 60% and 70%, preferably 65%, with a viscosity which at 25 ° C and a dry content of 65% is between 150 and 300 cP, and with an amount of free formaldehyde which is less than 1%, preferably between 0.45% and 0.65 76. This resin is added with water in an amount of RO to 55% by weight, based on the resin, further with 0.3% to 0.6% of a catalyst consisting of ammonium chloride or sulphate, and with a retardant computer comprising a solution of ammonia or ammonia and urea, the binder mixture obtained having a resin dry content of between 40 and 45% and a viscosity of less than 15 cP at 25 ° C. The grinder operates at a pressure exceeding 300 kPa and the impregnation moment takes place when the wet fiber leaves the grinder under high pressure and passes on to the dryer which operates at a pressure of approximately 100 kPa, utilizing the fiber expansion in such transport.

In a further development, from 1 to 15% of the urea in the resin is replaced with a product which has a similar chemical behavior, preferably melamine or dicyandiamide.

A fibreboard manufactured according to the invention has important improved properties in comparison with known fibreboards, especially in comparison with chipboards.

The following advantages can be emphasized: '_8 ° ll04755.-v7 3 A homogeneous appearance of the surface and the inside of the plate. This homogeneity even enables castings to be produced in the plate.

Greater flexural strength.

Greater resistance to removal of screws from the fiberboard.

As stated above, the resin used to prepare the binder mixture has a dry matter content between 60% and 70%, preferably 65%, and a viscosity of 150-300 CP at 2 ° C and the dry ice 65 æ.

In some cases it may be of economic interest to produce a similar resin with a lower dry content (eg when the resin is to be used in a place near the place of manufacture and the insignificant increase in transport costs due to the higher product weight may compensated by the decrease in the energy required to concentrate the resin). Such a resin having a dry content of 60% has a viscosity of 80 to 10 ° C at 2 ° C.

Despite these low viscosity values, which (for resins with similar dry contents and formaldehyde and urea contents) indicate that they are resins with low polymerization level and with high levels of free formaldehyde, quite surprisingly, free formaldehyde contents of less than 1% are obtained. and more specifically between 0, # 5 and 0.65% (the determination is carried out in the traditional way with "cold su1fit").

When impregnating the fiber, the binder mixture behaves as if it were not sticky, thus avoiding the formation of lumps or "balls" of bonded fibers, which give rise to serious problems during transport (air or mechanical) of the bonded fibers. Irregularities of the final fiberboard in mechanical properties and appearance are also avoided. which irregularities are caused by some of these clumps or "balls" of bound fibers entering the press.

To impregnate the wet fiber with resin, measuring equipment is needed to regulate the proportions between the fiber and the resin. The commonly used weight ratio is: Weight dry resin = 0_g7 _ 0.11 Weight dry fiber As stated above, the fiber is impregnated while wet. The wet, binder-impregnated fiber vw * vgniïísv s1o47ss = 7 4 must be dried in heat, and if the binder mixture is not in the proper state as it passes through the dryer, it becomes partially or completely gelled, thereby reducing or destroying its bonding ability when it is gelled in the hot table press for making the plate. This problem is solved by preparing a binder mixture in which the resin has been added with an amount of catalyst, usually ammonium chloride or sulphate, which amount is usually between 0.3 and 0.6% and is greater than the amount used in the case of dry matter. fibers.

Q An amount of ammonia solution is also added (if the ammonia used is a commercially available 25% solution, the amount added is 0.5 - 1.5%) or ammonia and urea, which act as retarders. Similarly, the amount of water added is greater than in the impregnation of dry fiber, whereby a mixture is obtained with a resin dry content of between 40 and 45%.

In this way it is ensured that the mixture used for impregnating the fiber is not gelled in advance during the passage through the dryer but gels satisfactorily during the heat pressing operation at which the fiberboard is produced.

With access to this binder mixture, the impregnation can be carried out using the expansion that occurs when the fiber leaves the grinding mill, which generally operates at a high pressure (above 300 kPa), and passes to the inlet LPD, whereby the dryer operates at virtually normal pressure.

The measured amount of resin can be added here without the need for a stirring mechanism.

The impregnation obtained is generally of high quality. This is apparent, among other things, from the fact that there are no spots on the surface of the fibreboard, which are formed by drops of poorly absorbed mixture in the fiber.

Example 1 Preparation of the binder mixture The binder mixture was prepared from a urea resin having a dry content of 65%, a viscosity of 225 cP at 25 ° C and a free formaldehyde content of 0.50% in a mixing vessel equipped with stirring means, in such a manner as to with the weight ratios listed below. 100 parts by weight of the above-mentioned resin were poured into the preparation vessel. Then 40 parts by weight of water and 4 parts by weight of a catalyst were added. The catalyst was prepared as follows: 100 parts of water were added with 27 parts of 25% ammonia which acted as a retarder and 13 parts of ammonium chloride. The previously stirred resin and catalyst binder mixture had a gel time of 3 minutes at 10 ° C and very good stability and thus durability. The viscosity of the mixture thus prepared was 15 cP. Hartstorralten was 45%.

Example 2 Impregnation of wet fiber with a mixture prepared according to Example 1 The fiber used was a mixture of pine and poplar wood chips in an amount of 90 and 10% by weight.

The fiber was pretreated with a paraffin emulsion. The amount of paraffin added over the dry fiber was 1% solid paraffin.

The amount of binder corresponding to 11520 g of wet fiber with a moisture content of 50% was 1107 g and gave 12427 g of bound fiber.

The weight of the bonded fiber, when the fiber had been dried to the right moisture content for the manufacture of fibreboards, was 7000 g. The material thus obtained contained 5660 g of fiber, 498 g of solid resin and 840 g of water.

Example_2 Manufacture of fibreboard using the impregnated fiber of Example 2 Fiber impregnated according to the previous example (fiber dried after impregnation) was used to make fibreboard according to the following procedure.

The impregnated fiber was taken up in a 500 x 500 mm laboratory form. It was pre-cold pressed in a 500 x 500 mm Siempelkamp press for laboratory use for 60 seconds at a pressure of 1472 kPa. The edges of the block were adjusted to the dimensions 450 x 450 mm before hot pressing. 7000 g of impregnated fiber was sufficient to produce a finished fiberboard with the dimensions 450 x 450 x 17 mm and with the density 720 kg / m5. 1 ~ .Poor Qvzatriff ßï04755: 7 6 The pressing of the cold, pre-compressed fiber blocks was carried out in a Siempelkamp press equipped with an automatic ventilation device for laboratory use, both press plates of which had been heated to a temperature of 18000 under a pressure of 2256 kPa.

The press time was 6 minutes. > After grinding the fibreboards, the following result was obtained: Properties of the fibreboard Thickness' loose, O5 mm Density. 715 kg / m5 _¿_ Bending strength 35256 kPa Tensile strength 942 kPa Absorption in water at 2o ° c 11.5% Swelling in water at 20 ° C 5.8% Surface resistance to screw removal r 160 kg Edge resistance s to removal of screws 120 kg The above tests were performed with fiberboard made with densities set to a certain value. They can also be prepared with densities other than those selected. In this case, the tensile strength and the flexural strength varied to a lesser extent. These properties deteriorate at lower densities and improve at higher densities. f!

Claims (5)

is' 8'104755: .7 7 PATENT CLAIMS A process for producing a fiberboard of lignocellulosic material, which process comprises the steps of preparing a binder mixture, providing a lignocellulosic material, tearing this material, boiling the torn material, grinding the obtained product. , impregnation of the fiber with the binder mixture and drying and pressing of the fiber, characterized in that the binder mixture is prepared from a non-stick urea-formaldehyde resin with a dry content of between 60% and 70 to preferably 65%, further with a viscosity between 150 000h 300 GP at 25 ° C for a dry matter content of 65%, and with a free formaldehyde content of less than 1%, preferably between 0,45% and 0,65%, that the resin is added with water 1 an amount of 40 to 55% by weight of the resin, with from 0.3% to 0.6% of a catalyst consisting of ammonium chloride or sulphate, and with a retarding computer consisting of a solution of ammonia or ammonia and urea, the binder mixture obtained having a resin dry content of between 10% and 45% and a viscosity of less than 15 cP at 25 ° C, that the grinder operates at a pressure above 300 kPa, and that the impregnation moment takes place when the wet fiber leaves the grinding mill under high pressure and passes to the inlet of the dryer, which operates mainly at atmospheric pressure, utilizing the expansion of the fiber during this passage. 2. A method according to claim 1, characterized in that the pressing step comprises a cold pre-pressing of the fiber and a hot pressing in a table press. 3. A method according to claim 1, characterized in that the material before impregnation is treated with a paraffin emulsion which gives an amount of solid paraffin of about 1% by weight, calculated on the dry fiber. 4. A method according to claim 1, characterized in that the weight ratio between dry resin and dry fiber is between 0.07 and 0.11. är »_ QQRQUALIñß ß1o47ss = 7 8 l 5. Process according to claim 1, characterized in that the resin part 1 of the urea, which is between 1 and 15%, has been replaced with. a product with similar chemical behavior, preferably melamine and dicyandiamide. '