PL234952B1 - Method for manufacturing fibreboards in the dry forming technology - Google Patents

Abstract

The method of producing fibreboards in the dry forming technology, in which chips of wood material are defibrated, the mass of fibers is glued, a carpet is formed from the dried mass, which is then pressed, and the produced boards are cooled down and, optionally, sanded. that a priming mixture consisting of wood dust and starch in a weight ratio of 1 : 2 ÷ 2.5, calculated as granular starch, and water in such an amount that the viscosity of the priming mixture is 200 - 400 mPa•s, with the priming mixture being applied in the amount of 20 - 40g/m2.

Description

Description of the invention

The present invention relates to a method for the production of dry formed fibreboards with a smooth surface.

Fibreboards are made from defibrated wood tissue by fulling it and shaping it at the appropriate temperature and under normal or increased pressure. The natural adhesion properties of the fibers are increased by adding a synthetic adhesive. The fibers are arranged in different directions, which provides the board with alignment of quality and strength characteristics. There are basically two technologies for the production of boards: dry and wet. In the dry method, wood material is made into wood chips, which are then subjected to fiberisation, the obtained fibers are glued with a glue resin (usually urea-formaldehyde or melamine-urea-formaldehyde resin), dried, and a carpet is formed, which is then pressed and cooled. In the final stage, the boards are formatted, and the boards with a thickness of several millimeters are sanded before their surface is refined.

MDF boards, including HDF, are usually refined before they are intended for specific applications. The refinement consists in covering the board surface with veneers, laminates, foils or varnishes. In the context of these types of refinements, the surface quality of the boards is assessed by testing the roughness and absorption of liquids (water and / or toluene). It is well known that the smoother and less liquid-absorbing the surface of the plates, the smaller the amount of paint and varnish materials is needed to refine it. Already at the stage of production of the boards, the aim is to make their surfaces as smooth as possible, mainly by using the appropriate size of wood fibers, their humidity and appropriate parameters for pressing the carpets. Roughness of raw surfaces of boards to be varnished should be Ra 1.5-3.5 µm, and boards whose surfaces are covered with foil should be up to 5.0 µm. If the roughness is greater, MDF boards are ground. In turn, before the actual painting stage, primers are applied to the surfaces of MDF and HDF boards.

From the patent application US6010793 an OSB board made of wood material is known, which comprises a top layer containing a powdered filler and an isocyanate resin. Calcium carbonate is used as a powdered filler in the form of a powder. On the other hand, European patent EP1749587 discloses a method of producing a building board made of wood material, in particular an OSB board, with an upper covering layer and a lower covering layer, according to which, after pressing the board, at least the upper covering layer is coated with a soluble water of the varnish and the coating is supplemented with additional materials and / or fillers immediately after its application. Preferably, the filler is quartz sand particles, but may also be wood flour. The coating is cured, preferably with heat from the plate itself. The effect of using this method is to level the unevenness of the covering layer of the slab. Another solution aimed at leveling the surface of the board made of wood material is presented in the patent description PL202330. The board described there, between the OSB core and the phenolic resin impregnated paper covering this core, has a layer of fine chips or fibers, filling in the roughness of the outer surface of the core, and on it is applied a filling substance based on acrylates or phenol, filling in the irregularities of the surface of the layer. from chips or fibers.

In the solutions described above, it is envisaged to use chemical binders: isocyanate resin, water-soluble varnishes, acrylic or phenolic resins. Meanwhile, given the desire to eliminate the negative impact of wood-based products on humans and the environment, both in the context of production technology and product use, it is important to look for ecological and health-friendly solutions. The present invention is part of this trend.

The method of manufacturing fibreboards using the dry forming technology, according to the invention, is characterized in that a priming mixture consisting of wood dust and starch in a weight ratio of 1: 2: 2.5, based on the weight ratio, is applied to the surface of the fiber carpet, prior to the pressing step. granular starch and water in such an amount that the viscosity of the priming mixture is 200-400 mPa · s. The priming mixture is applied in the amount of 20-40 g / m ² .

The priming mixture is prepared by pasting the starch, then mixing it with wood dust in the given weight ratios and adding enough water that the mixture can be applied evenly to the surface of the carpet by means of the application device.

PL 234 952 B1

Preferably, wood dust from pine or other coniferous species is used.

Preference is given to using starch glued at a temperature of 65-70 ° C.

The amount of priming mixture depends on the quality of the wood fibers used in the production of the boards and the properties of the boards. The amount and composition of the priming mixture results, on the one hand, from the necessity to give the mixture an appropriate viscosity, depending on the device applying this mixture to the fibers, and on the other hand, the viscosity of the mixture cannot be too high so that the water contained in it does not significantly increase the moisture content of the fibers. in the carpet, which should be 6-9%.

In the priming mixture, wood dust acts as a filler for the space between the fibers constituting the surface of the manufactured board. Starch, as a polysaccharide, was used as a substance to "strengthen" the fine grains of the filler and as a filler connector with the wood fibers of which the carpet is made. In turn, the water introduced for starch pasting and is the carrier of these two mixed components, allowing the mixture to be evenly sprayed on the surface of the carpets, and additionally, it also acts as a plasticizer of wood particles (dust and fibers) in the process of pressing the carpets and thus facilitates their bonding. The amount of water in the mixture should be regulated depending on the pressing parameters of the boards produced.

The method according to the invention allows for the reduction of surface roughness and liquid absorption (water and toluene) of the finished boards. As a result of applying the priming mixture to the surface of the fibrous carpets, the roughness (Ra) of the boards can be reduced by 2-3 times, the surface water absorption by 20-30%, and the toluene absorption by 80-100%.

The influence of the priming mixture on the strength properties of the boards depends on the density of the boards produced. In the case of high-density boards (approx. 900 kg / m 3), a statistically significant increase in strength properties is observed, in the case of lower-density boards (approx. 700 kg / m ³ ), some decrease in strength properties may occur, but the decrease is statistically insignificant. The priming mixture has no significant effect on the swelling of the boards.

The advantages of the method are the simple method of applying the mixture on the rugs, without the need to introduce changes in the production process, and the use of generally available, environmentally friendly substances to prepare the mixture.

The method according to the invention is illustrated in the examples.

P r z k ł a d 1

Pine wood fibers, obtained in industrial conditions, were glued with melamine-urea-formaldehyde resin in the amount of 13.5% (in relation to the weight of completely dry fibers, z.m.) with a gun. A hydrophobic agent was applied to the fibers - a paraffin emulsion in the amount of 1% of paraffin in relation to z.s.m. fibers, also with a gun.

After chemicals were applied to the fibers, they were formed into carpets in a molding box. A priming mixture (MG) with a composition of 2.8% of dust, 6.2% of dry starch and 91.0% of water, with a viscosity of 250 mPa, was sprayed onto the surfaces of the formed carpets.

MG was sprayed in an amount of 20 or 40 g / m ² (the amounts of the mixture were determined in preliminary studies). The carpets were pre-pressed in a plate press at ambient temperature, and then in a press whose shelves had a temperature of 180 ° C and a pressure of 2.5 MPa for 90 seconds.

Plates predetermined density of 890 or 700 kg / m ³ and a thickness of 3 mm or 4 mm (respectively) were produced in the laboratory. The tests of the surface of the slabs consisted of determining the roughness of the slabs using the Mitutoyo SJ-201 method (surface roughness Mitutoyo SJ-201), surface absorption - water EN 382-2 / 2001 and surface absorption - toluene EN 382-2 / 2001 ). The strength properties and swelling of the boards were determined in accordance with the requirements of PN-EN 622-5 / 2010. The data presented in the tables are average results from 10 determinations.

Potato starch was used in the process, gelatinized in such a way that about 1.25 kg of water at 18 ° C was added to 1 kg of granular starch while mixing, and after mixing the two components, about 11.25 kg of water at 65-70 ° C was added.

P r z k ł a d 2

The panels obtained according to example 1 were tested for surface roughness, water and toluene absorption. For comparison, panels obtained in the same conditions were tested, without the primer layer applied.

The surface properties of the boards are presented in Table 1, and their strength and swelling properties in Table 2.

PL 234 952 Β1

Table 1

Properties of the surface of the plates

Plate density / quantity MG (kg / m ³ ) / (g / m ² ) Ra μιη WA g / m ² TA mm 890/0 5.77 126 144 890/20 4.32 112 > 283 890/40 4.70 97 282 700/0 8.10 140 134 700/20 2.66 104 > 283 700/40 1.96 96 > 283

Ra (Arithmetic mean deviation of the profie) - arithmetic mean deviation of the profie

WA (Water absorption) - water absorption

TA (Toluene absorption) - toluene absorption

Table 2

Strength properties and swelling of boards

Plate density / quantity MG (kg / m ³ ) / (g / m ² ) MOR N / mm ² IB N / mm ² TS % 890/0 33 0.7 14 890/20 41 0.7 19 890/40 44 0.7 18 700/0 29 0.4 12 700/20 22 0.4 10 700/40 24 0.4 12

MOR (Modulus of rapture) - static bending strength IB (Internal bond) - stretching perpendicular to the plate planes TS (Thickness swelling) swelling after 24 h soaking

Claims (3)

1. Method for the production of fibreboards using the dry forming technology, in which the wood chips are defibrated, the mass of fibers is glued, a carpet is formed from the dried mass, which is then pressed, and the boards produced are cooled and, possibly, sanded, characterized by in that a primer mixture consisting of wood dust and starch in a weight ratio of 1: 2: 2.5, based on granular starch, and water in such an amount, is applied to the surface of the fiber carpet, before the pressing step, so that the viscosity of the priming mixture was 200-400 mPa · s, the primer mixture was applied in an amount of 20-40 g / m ² . 2. The method according to p. The process of claim 1, wherein the wood dust is pine and / or other coniferous wood. 3. The method according to p. The method of claim 1, wherein plywood potato starch is used.