SI9210125A - Process for the production of wood-fibre boards - Google Patents

Abstract

In a process for producing wood-fibre boards, the raw material is first defibrated, then mixed with aqueous binder liquor in a blast pipe. The binder-coated fibrous material thus obtained is dried to the required residual-moisture content and then spread out into strips which are converted by the action of pressure and heat into boards. The mixing procedure is carried out using a liquor containing 20-35 % by wt. of solid resin, and the amount of binder used, relative to the total dry weight of the fibre material, is less than 10 % by wt.

Description

OSTERREICHISCHE HIAG WERKE Gesellschaft m.b.H.

The process of making wood fiber boards

The invention relates to a method of manufacturing wood fiber boards, in which the raw material is subjected to dehumidification, then it is glued in a blower line with an aqueous solution of binder and the resulting adhered fibrous material is then dried into the lines of planar fill after drying to the necessary residual humidity. under pressure and temperature squeezes into panels. In particular, the invention relates to such a process for making medium-sized fibreboards (SGV boards; MDF - mitteldichte Faserplatten) and hard fibreboards (TGV boards; German HDF - Hartfaserplatten) containing a reduced amount of binder.

The mechanical properties of the wood fiber boards are determined, in addition to the quality of the stretching operation, in a significant part by the binder used to bond the fiber material. Under the remaining constant conditions, an increase in the mechanical strength of the plates is related to an increase in the amount of binder introduced for bonding the fibrous material.

However, since the binder material is a significant cost factor in the manufacture of fiber boards, there is a tendency to invest as little binder as possible in the cost-effectiveness of fiber board production. It further seeks to reduce the amount of binder in order to reduce the environmental burden of formaldehyde cleavage occurring in particular with aminoplastic binders. In conventional wood fiber board manufacturing processes, however, a decrease in the amount of binder put in, as mentioned above, leads to a decrease in the strength of the boards so made.

In order to reduce the amount of binder without damaging the strength, it has hitherto been attempted to achieve a good distribution of adhesive by using various apparatus to add a binder in the blowing line. they wanted to reach as many points (points) as possible, which are crucial for the strength of the evil. The solutions of the binder with a solid resin content of about 50% by weight were further used.

In the area of wood chip boards, a process with a reduced amount of added binder has already been described according to which a diluted binder solution with a solid resin content in an amount of preferably 22 to 30% by weight is used (EP-B 0 010 537). This process results in a more even distribution of the binder across sections of vastly different sizes and thus saves on the amount of binder. The raw material used in this process is first divided into chunks and then subjected to drying to a moisture content of preferably less than 2% before being bonded with an aqueous solution of a particular aminoplast. The slices are coated with glue in a blender mixer. In addition, thickening agents such as cellulose derivatives are added to the binder solution to prevent the binder from penetrating the material of the cuts. The moisture content of the adhered snippet material held below 12% is determined by the amount of water applied to the snippet material with a binder solution. The said publication therefore relates to a process which is customary for the manufacture of slabs of cuttings, after which the raw material is first dried, then glued, and the invention relates to dry processes for the manufacture of fibreboards, in which the starting material is first glued, then dried.

Such dry processes have so far failed to produce fibreboards which, despite their low content of binder, have sufficient strength. In order to achieve sufficient strength according to the applicable technical standards, it has hitherto been necessary to install a solid resin in the fiber boards (both SGV and TGV boards), whose proportion is a.s. (absolutely dry) fibrous material always exceeded 12% by weight.

It is an object of the present invention to provide the aforementioned process for the manufacture of wood fiber boards, by which, inter alia, the improved utilization of the binder used to adhere the fibrous material is achieved so that to achieve a certain strength of the plate at a predetermined fiber material work with less solid resin than before. It is a further object of the present invention to create such a process that will be practicable without altering the principle of apparatus devices such as are available to perform the above known procedures, or without substantially altering the time required to carry out the process.

This object of the invention is achieved by adhering to a solution having a solid resin content in an amount of from 20 to 35% by weight, preferably from 25 to 35% by weight, while adding a binder in an amount of less than 10% by weight .%, preferably 7 to 9% by weight of solid resin, taken as a total, per ac condition calculated fiber material.

Using the characteristic of the invention, heavily diluted aqueous binder solutions, it is possible to dry wood fiber boards, whose mechanical values correspond very well to the requirements of the technical norms, in a dry process, in comparison with the plates made according to the process method from everyday life. technology, while allowing significant binder savings. Thus, according to the method of the invention, it is possible to produce wood fiber boards with a solid resin content of less than 10% by weight, having sufficient strength according to the applicable technical standards.

Using the method of the present invention, the heavily diluted binder solutions obviously provide an extremely complete coating of the fiber material with the binder, thereby greatly multiplying the adhesion points that are so important for restoring the strength of the plates.

A further advantage of this process is that a strong dilution of the embedded binder to the bonded fibers exerts a cooling effect, since part of the water from the binder mixture is immediately evaporated, thereby dissipating the fiber / binder system as a whole. This will prevent premature hardening of the binder located on the bonded fibers, and premature hardening could also result in a decrease in the strength of the panel.

The present method of the invention can be carried out without substantially altering the procedural technique. The fiber material is peeled off just after the material is exited from the refiner in the blower line in the usual way.

Appropriate solids, such as ammonium chloride, ammonium phosphate, phosphoric acid, formic acid, are added to the adhesive solution to solidify the binder used during hot pressing operations, in amounts known in the art, which depend on the particular conditions of the device. The addition of a special lignin sulfonate based adhesive enhancer has also proved particularly advantageous. Further, additional formaldehyde traps such as urea may also be added to the binder solution. However, paraffin emulsion or molten paraffin to achieve the hydrophobicity of the fiber boards is added well before entering the refiner.

The fiber material, which was equipped with the binder as described above, is then dried in a known manner to a residual moisture content of not more than 12%, preferably not more than 10%, before being pressed into flat lines of uniform thickness by spreading them into plates in conventional presses in the hot.

The material can be pressed into panels or in conventional stationary presses at temperatures from about 160 to 190 ° C and pressures down to 35 bar or in counter presses at temperatures up to 235 ° C and conventional pressure programs. The compression times of the process according to the invention correspond to the compression times that have been used so far.

A preferred embodiment of the process of the present invention is that the ready-to-use aminoplastic binder is first diluted with water to a solid resin concentration of about 30 to 40 wt.% And the necessary additives such as solids, adhesive enhancer, formaldehyde trap , in a suitable aqueous solution, is added to the diluted binder solution only immediately before entering the blower line via the mixing line.

The invention will now be further explained on a case by case basis, without being limited thereto.

EXAMPLE 1

For the production of medium-sized fiber boards (SGV panels), we used fiber material, which was obtained in a well-known way from finely chopped pines in a refiner. Immediately after leaving the refiner, a mixture containing the binder was dosed into the blowing line through which the fibrous material was discharged from the refiner. We have assembled this binder containing compound as follows:

In the mixing vessel, the aminoplastic El fiber board adhesive (HIACOLL MDF 15) was diluted with water to a concentration of 33% by weight of solid resin. A solution of 30% by weight of urea, 10% by weight of ammonium chloride and 2% by weight of phosphoric acid was prepared in another mixing vessel. With the aid of the dosing pumps, the two solutions were combined in a static mixer in such a proportion that the final adhesive solution contained a concentration of 28.3% by weight of solid resin. This adhesive solution was added to the fiber material in such a quantity that the adhesive factor was obtained

8.2% by weight of solid resin, taken with respect to absolute dry (a.s.) fiber. The adhered fiber mixture was then dried in a known manner to a residual moisture content of 10% by weight, formed into a planar fill of uniform thickness and pressed into a SGV plate under the influence of pressure and temperature. The plate produced in this way was very well suited to the requirements of the industry standard for SGV panels (standard type MDF [= SGVj, formaldehyde content A class).

EXAMPLE 2

The fiber material from the first example was in a known manner glued to the following mixture containing the binder:

1,000 kg of HIACOLL MDF 15, 100 kg of urea solution (40% by weight) and 1,000 1 of water were mixed in the mixing vessel so that the solid resin concentration of this mixture was 31.4% by weight. In a second mixing bowl, 100 kg of HIACOLL K1215 adhesive enhancer and 165 l of water were mixed. The solutions were mixed through a metering pump and a static mixer in such a mixture ratio that the final solid resin concentration in the mixture was 27.0% by weight. This mixture was applied to the fiber material in an amount to obtain a peel factor of 7.5% by weight taken on a.s. fiber material. After drying to about 10% residual moisture, forming a planar fill of uniform thickness, and pressing in hot, an SGV plate was obtained which, in all test values, corresponded very well to the standard MDF type (= SGV), the formaldehyde content of A grade according to the industry standard for MDF (= SGV) panels.

EXAMPLE 3

Example 3 is a comparative example.

To adhere the fiber material, which was carried out as described in Examples 1 and 2, we used an adhesive solution of the following composition:

HIACOLL MDF-12 urea solution (40% by weight)

1,000 kg 150 kg ammonium chloride solution (15% by weight) 40 kg water kg

This adhesive solution in its composition corresponds to the state of the art. It has a solid resin concentration of 53.2% by weight. In order to achieve the mechanical values of MDF (= SGV) panels made using this solution, ie the values prescribed by industry standards for MDF (= SGV) panels, we had to per 1,000 kg a.s. to incorporate 235 kg of adhesive solution into the fibrous material, which corresponds to the adhesive factor of 12.5% by weight taken on a.s. fiber material.

Claims (4)

Patent claims 1. A process for the manufacture of wood fiber boards in which the raw material is subjected to bifurcation, then adhered in a blower line with an aqueous binder solution, and the resulting adhered fibrous material is then sprayed onto the surface of the filler after drying to the required residual humidity and pressurized. and the temperature is compressed into panels, characterized in that it is bonded with a solution having a solid resin content in an amount of 20 to 35% by weight, while adding a binder in an amount of less than 10% by weight of the solid resin, taken relative to the total , on ace condition calculated fiber material. Process according to Claim 1, characterized in that the solution has a solid resin content of 25 to 35% by weight and the amount of binder incorporated has 7 to 9% by weight of solid resin, taken relative to the total, on a.s. condition calculated fiber material. Method according to claim 1 or 2, characterized in that the binder with water to a concentration of solid resin is 30 to 40% by weight of a diluted aminoplastic binder, to which are added additives as solids, adhesive enhancer and formaldehyde trap in a suitable aqueous solution. A method according to claim 3, characterized in that the additives are added to the diluted aminoplastic binder immediately before entering the blowing line via the mixing line. OSTERREICHISCHE HIAG WERKE Gesellschaft m.b.H. For her: LJUBLJANI λ 22223-PR.0-ing.SK-I / 95 Summary A method of manufacturing wood fiber boards is described, in which the raw material is subjected to a bifurcation, then it is adhered in a blower line with an aqueous solution of binder, and the resulting adhered fiber material is then sprayed onto the surface of the filler after drying to the required residual humidity and pressurized. and compresses the temperature into panels, adhering to a solution having a solid resin content of from 20 to 35% by weight, and adding a binder in an amount of less than 10% by weight of the solid resin taken as a condition calculated fiber material.