HRP930347A2 - Process for the production of wood-fibre boards - Google Patents

Description

The invention relates to the production process of wooden fiberboard, where the raw material is subjected to shredding, and then it is mixed in water under air pressure using an aqueous suspension of binders with glue, and thus the obtained fibrous material, bonded with felt, after drying to the required level of humidity, is sprinkled into the tracks with molds and press under pressure and temperature into plates. The invention particularly relates to such a process for the production of medium-density fiberboards (MDF-boards) and hard fiberboards (HDF-boards), which contain a reduced amount of binder.

The mechanical properties of fibers are determined, in addition to the quality of the shredding process, mostly by the binders used to bind the fibrous material. At the same time, in addition to the increase in the mechanical strength of the panels under the same conditions, there is also an increase in the amount of binder used to bind the fibrous material.

However, since the binder represents an important cost factor in the production of fibers, it is tried, considering the economy of the production of fibers, to use as little binder as possible. Furthermore, efforts are being made to reduce the amount of binders, in order to reduce the burden on the environment, which occurs during the splitting of formaldehyde, especially contained in aminoplastic binders. In the usual process for the production of fiberboards, reducing the amount of binder used leads to a decrease in the strength of the boards produced in this way, as we have already mentioned.

In order to be able to reduce the amount of binder without affecting the strength, until now it has been tried, using various devices when adding the binder to the line with air pressure, to achieve as good a distribution of the glue as possible, i.e. reach as many glued points as possible, which are relevant for the strength of the glued. Binder suspensions with a hard resin content of approximately 50% by mass were also used.

In the field of chipboard production, a process with reduced binder addition has been described, where diluted binder suspensions with a solid resin content of approximately 22 to 30% by mass are used (EP-B-0 010 537). This procedure achieves a more even distribution of the binder among chips of various sizes, and thus saves the amount of binder. In this process, the raw material used is first subjected to shredding and then drying, preferably to a humidity below 2%, before it is mixed with an aqueous suspension of an aminoplast. Chips are glued in a glue mixer. In addition, thickening agents, such as cellulose derivatives, are added to the binder suspension to prevent the binder from penetrating the chips. The humidity of the glued chipboard, which is maintained below 12%, is determined by the amount of water, which is applied by the binder suspension to the chipboard. That publication therefore refers to the usual process for the production of chipboard, where the raw material is first dried and then glued, in contrast to which the invention refers to a dry process for the production of fiberboard, whereby the output material is first glued and then dried.

Until now, with such drying procedures, it has not been possible to produce fibres, which, despite the reduced proportion of binders, would show sufficient strength. In order to achieve sufficient strength according to the current standards, it was necessary to use a mass with always more than 12% of hard resin, which is related on atro (absolutely dry) fibrous material.

One of the objectives of the presented invention is to create the aforementioned process for the production of fiberboards, which would, among other things, achieve an improved utilization of the binder, which is used for gluing the fiber material, so that in order to achieve a certain strength of the panels with a given fiber material in advance, a smaller amount can be satisfied solid resins than before. A further goal of the presented invention is to find such a procedure, which could be carried out without fundamental changes in the existing devices for the aforementioned known procedures, or without significant changes in the time period required for the procedure.

This goal, according to the invention, is achieved by gluing using a suspension with a solid resin content of 20 to 35% by mass or even better from 25 to 35% by mass, while using an amount of binder that is less than 10 % by mass, preferably 7 to 9 % solid resin by mass, in relation to the total, atro (absolutely dry) calculated fibrous material.

According to the invention, by using a highly diluted aqueous binder suspension, it becomes possible to produce fibers through a dry process, the mechanical values of which correspond very well to the set norms, while a significant savings in binders is also enabled, unlike the procedures of the usual technology for the production of panels. Thus, in the process, according to the invention, it is possible to produce fibers with a proportion of solid resin of less than 10% by weight, which would have sufficient strength according to valid standards.

The use of a very diluted binder suspension, provided in the process according to the invention, obviously results in a strong veiling of the fibrous material with the binder, due to which there is a significant increase in glued points, essential for improving the strength of the panels.

A further advantage of this procedure is that, due to the strong dilution of the binder, a cooling effect is obtained on the bonded fibers, because part of the water, which is contained in the binder mixture, immediately evaporates, whereby heat is taken from the entire fiber/binder system. This prevents premature pre-hardening of the binder, which is located on the bonded fiber. This pre-hardening, namely, can also result in a decrease in the strength of the panels.

According to the invention, the presented procedure can be carried out without significant changes in the process technology. Gluing of the fibrous material is done shortly after its exit from the shredding machine (Refiner) into water under air pressure, in the usual way.

Suitable hardening substances are added to the glue suspension, such as ammonium chloride, ammonium phosphate, phosphoric acid, and formic acid, for the purpose of hardening the used binder during the hot pressing process, in amounts known in the art, and which are depending on certain plant conditions. The addition of a special glue booster based on one ligninsulfonate proved to be particularly useful. Furthermore, additional formaldehyde carriers, such as urea, can also be added to the binder suspension. The addition of paraffin emulsions or melted paraffinase to the hydrophobicity (repulsion of water) of the fiber boards is done on the contrary, expediently before entering the shredding machine (Refiner). The fibrous material, which is equipped with a binder in the manner described above, is then dried in a known manner to a residual moisture of a maximum of 12%, preferably 10%, before being pressed after forming in paths with molds in conventional pressure presses into panels.

Pressing into plates can be done in conventional stationary presses at temperatures from approximately 160° to 190°C and pressing up to 35 bar or in Conti-presses with heating plate temperatures up to 235°C and a normal pressing program. The pressing time of the process according to the invention corresponds to the pressing times used so far.

One of the preferred embodiments of the process according to the present invention, which is preferred, consists in first diluting the aminoplastic binder that enters the cartridge with water to a solid resin concentration of approximately 30 to 40% by mass and adding the necessary additives, such as substances of hardeners, glue strengtheners, formaldehyde carriers in a suitable aqueous solution are added to the diluted binder solution only immediately before entering the pipe under air pressure, through the mixing system.

The invention is now explained by examples, without being limited to them.

Example 1

For the production of medium-density fiber boards (MDF-boards), fiber material was used, which was produced in a known way from chopped spruce in a refiner. A mixture containing a binder was added shortly after exiting the Refiner to the air pressure line, through which the fibrous material is taken out of the Refiner. This mixture, which contains a binder, consists of the following:

In the mixing bowl, aminoplastic E1-glue for making fiberboards (HIACOLL MDF 15) was diluted with water to a hard resin concentration of 33% by mass. In another mixing vessel, a solution of 30% urea by mass, 10% ammonium chloride by mass and 2% phosphoric acid by mass was prepared. Using dosing pumps, these solutions were combined via a static mixer in such a ratio that the final glue suspension contained a hard resin concentration of 28.3% by mass. This glue suspension was added to the fibrous material in such a quantity that a sticking factor was obtained with 8.2% of hard resin by mass, referring to completely dry (atro) fiber. The bonded fibrous mixture was then dried in a known manner to a residual moisture of 10% in the mass, then shaped into fibrous mats and pressed into MDF boards in a heating press under the influence of pressure and temperature. The board produced in this way quite well met the requirements of the industrial standard for MDF boards (standard type MDF, formaldehyde content Class A).

Example 2

According to example 1, the fibrous material described was glued in a known manner with the following mixture, which contains a binder:

1,000 kg of HIACOLL MDF, 15,100 kg of urea solution (40% by mass) and 1,000 liters of water were mixed in the mixing bowl, which resulted in a concentration of hard resin in the mixture of 31.4% by mass. In another mixing bowl, 100 kg of HIACOLL K1215 glue booster and 165 I of water were mixed. Both solutions were mixed via dosing pumps in a static mixer in such a mixture ratio that the final concentration of hard resin in the mixture was 27.0% by mass. This mixture was added to the fibrous material in such a quantity that a sticking factor of 7.5% by mass was obtained in relation to the atro (absolutely dry) fibrous material. After drying to the remaining moisture of approx. 10%, molding of fiber mesh and hot pressing resulted in an MDF board, which in all tests met the requirements of the MDF standard type, class A-formaldehyde content according to industry standards for MDF boards.

Example 3

Example 3 is a comparative example.

For gluing the fibrous material, which was carried out as described in examples 1 and 2, an adhesive suspension with the following content was used:

1,000 kg HIACOLL MDF-12,

150 kg of urea solution (40% by mass)

40 kg of ammonium chloride solution (15% by weight) 50 kg of water.

The composition of this adhesive suspension corresponds to the development of the technique. It shows a hard resin concentration of 53.2% by mass. In order to achieve the mechanical values required by the industry standard for MDF boards, 1,000 kg of atro (absolutely dry) fibrous material and 235 kg of glue suspension had to be used for the MDF boards, which were made using this suspension, which corresponded to the factor gluing of 12.5% by mass, referring to atro fibrous material.

Claims (4)

1. The process for the production of fibers, in which the raw material is subjected to shredding, then it is glued in water under air pressure with an aqueous suspension of the binder, and then the bonded fibrous material thus obtained, after drying to the required residual moisture, is sprinkled into the tracks with molds and under pressure and the temperature of the plate press, indicated by the fact that gluing is done with a suspension with a hard resin content of 20 to 35% by mass, and the amount of binder is used, which is less than 10% of hard resin by mass in relation to the total atro calculated fibrous material. 2. The method according to Claim 1, characterized by the fact that the suspension shows a hard resin content of 25 to 35% by mass, and the inserted amount of binder is 7 to 9% of hard resin by mass, in relation to the total atrocalculated fibrous material. 3. The method according to Claim 1 or 2, indicated by the fact that the binder aminoplastic binder is diluted with water to a solid resin concentration of 30 to 40% by mass, to which additives such as hardeners, glue reinforcers and formaldehyde carriers are added in a suitable form of an aqueous solution . 4. The method according to Claim 3, characterized in that the additives are added to the diluted aminoplastic binder immediately before entering the line under air pressure via a mixing system.