EP2974841B1 - Method for producing a fibreboard panel - Google Patents

Description

The invention relates to a method for producing a source-reduced fiber board.

Wood-based materials are used, for example, in construction as an insulating, constructive or cladding element as well as flooring.

In the production of wood-based materials, a high level of recycling of the wood can be ensured. Thus, in addition to forest wood, residual wood from industry and used wood finds its use. Wood materials are made from wood shavings, wood chips or wood fibers as well as from sawn timber or veneers of various types of wood with the addition of natural and / or synthetic binders and other additives.

The properties of the wood are known to be significantly determined by the moisture content of the wood. As the absorption of water increases, as a rule the wood moisture increases, the strength and dimensional stability of the wood decrease, and the susceptibility to wood-destroying microorganisms increases.

In the production of wood-based materials, the minimization of the natural disadvantages of wood comes to the fore. The resistance of wood to water is determined by swelling and shrinkage and, due to this dimensional change, can lead to processing problems as well as daily use.

When used outdoors, wood products have the disadvantage, among other things, that the absorption of water into the cell walls leads to a swelling of the wood in all three spatial directions. The recurring sequence of swelling and shrinkage can lead to crack formation in solid wood and to irreversible swelling in wood-based materials such as particleboard and fibreboard. Swelling in frictional bonded wood materials, especially in floor coverings, is particularly problematic. For wood-based materials that have layers glued perpendicular to one another, the wood is obstructed during swelling and shrinkage, so that tensions can arise that lead to plastic deformation. The ingress of water, for example in floor coverings, the frictional connections can be destroyed, it can lead to swelling of the cut edges. The protruding fibers are then mechanically torn off, whereby the flooring has optically clear damage that leads to increased and accelerated wear. Furthermore, this behavior has a crucial importance in building materials. During swelling, in addition to increased stress, an increased internal swelling pressure can arise, which counteracts the external mechanical load and also has an influence on the load capacity of the standing under continuous load wood construction.

Wood generally has as builders mainly cellulose, hemicelluloses and lignin. In the cell wall polymers free hydroxyl groups are found, which can make strong hydrogen bonds with water molecules, which hold the water molecules in the cells and thereby induce swelling.

Various coating methods and other chemical methods for modifying wood or wood surfaces to reduce the penetration of water are known from the prior art.

In " Chemical Modification of Wood "(pages 419-430," Monomers, Polymers and Composites from Renewable Resources ", 1st edition, 2008 ) Belgacem and Gandini describe different chemical treatments of wood to improve the resistance to atmospheric and biological degradation and to achieve lower wettability. Here, wood surfaces are treated with plasma, isocyanates, siloxanes and furfuryl alcohol, and the free hydroxyl groups of the cell wall polymers of the wood material are substituted by esterification with, for example, octanyl chloride or etherified with, for example, glycidyl methacrylate. This is intended to limit the property of the wood to absorb or release water.

In the EP 2 032 323 B1 Wood fibers are hydrophobized with wax dispersions for the production of modified wood materials. As a result, the thickness swelling and the water absorption rate of the wood materials produced with it should be delayed.

A reduction of the swellable fractions in the corresponding wood products is also a known strategy. In this regard, in the DE 102 008 056 650 A1 proposed to wood fibers with wood extraneous components such as glass, metal, ceramic and / or plastics to produce wood-based materials. By this addition non-swelling shares a delayed thickness swelling of the wood panels to be achieved.

The EP 1 762 671 B1 describes a building board, which has a reduced swelling and shrinkage behavior and on which a waterproof final layer of polyurethane, plastic or paint or mixtures thereof is applied.

The EP 2 181 818 A2 describes a process for the production of wood fiber materials and wood fiber materials from wood fibers, which are obtained after plasticization of wood and which should have a reduced emission of volatile organic compounds (VOC). The wood fiber materials are prepared so that the uncut and / or comminuted wood is contacted with a formulation containing at least one compound to establish a neutral to basic pH and at least one complexing agent.

The EP 0 139 530 A3 describes a process for the preparation of lignocellulose-containing composites, films and the like with a di- or polyisocyanate based on a binder system in which a mineral acid is used. For this purpose, in a mixing drum dry, finely divided wood material is first sprayed with a mineral acid (HNO ₃ , HCl, H ₂ SO ₄ ) and then with a gluing agent (PMDI) and finally pressed into a wood material.

The known methods have in common that a delay of the swelling is achieved by the coating and chemical modification. This is presumably due to the fact that a shielding, occupation or substitution of the free hydroxyl groups of the cell wall polymers is carried out and the hygroscopicity is lowered. In this way, presumably the interaction between water molecules and free hydroxyl groups of the cell wall polymers is reduced, thereby achieving a reduction in the swelling rate.

A disadvantage of the measures described above is that this only a delay of the absorption of water is achieved. In addition, the chemical modification described above increases the weight of the wood material, which can be detrimental to processing and suitability as a building material.

The person skilled in various methods of introduction of wood preservatives are known. These include painting, spraying, diving and trough dunking. The use of these procedures depends on ingredients, place of use and later use. A disadvantage of the known methods are either a low penetration depth or an increased workload and long waiting times to further processing. Although the steps of painting, spraying or dipping may require a short period of time, the low penetration is disadvantageous. Although deeper impregnation depths can be achieved in the impregnation of drums and boiler pressure impregnation (impregnation of the wood by alternating underpressure and overpressure), in both cases further complicated working steps must be integrated into the production process. Thus, the methods are either complex, costly and / or may not be readily integrated into the usual in the wood industry process without increasing the time, labor and cost.

The WO 2008/028183 A1 describes a process for producing a medium density fiberboard (MDF) wherein lignocellulosic fibers are pretreated with oxalic acid or oxalic acid derivatives prior to the refining step in a type of digester.

The DE 697 10 748 T2 describes in Example 2 a process for producing an MDF board in which wood chips are treated with dilute sulfuric acid for 6 minutes at a temperature of 184 ° C and a pressure of 10 bar.

A disadvantage of the treatment in Vorkocher is that due to the prevailing heat, the pressure and the high degree of dissociation of the acid, the wood fibers can be severely damaged. Under these hydrolysis conditions, the cellulose contained in the wood can easily be broken down. Not only can this result in a reduction in the quality of the fiber in general, but also the structure of the fiber can be so severely damaged that the fiber material can no longer be suitable for producing a fiberboard.

The invention has for its object to provide an effective, cost-effective method, with the source-reduced wood materials, especially a reduced source fiber board, standard processes used in the wood industry without increased time and cost can be produced.

This object is achieved by a method for producing a fiberboard according to claim 1. Advantageous embodiments of the invention are specified in the dependent claims.

The Erffnung applied to a method for producing a reduced-source fiberboard by gluing lignocellulosic material, wherein the lignocellulosic material is treated prior to gluing with an acid, wherein the treatment is carried out at a temperature of 70 to 200 ° C and a pressure of 1 to 12 bar and wherein the acid is a Brönsted acid selected from the group consisting of phosphoric acid, phosphorous acid, hypophosphorous acid and mixtures thereof, and wherein the acid is an acid having a pKa of less than 4.

The inventive method for producing a reduced-source fiberboard provides that the lignocellulosic material is treated prior to gluing with an acid, wherein the treatment is carried out at a temperature of 70 to 200 ° C and a pressure of 1 to 12 bar. The acid according to the invention is in particular a Bronsted acid selected from the group consisting of phosphoric acid, phosphorous acid, hypophosphorous acid and phosphonic acid.

Surprisingly, it has been found that the swelling capacity of fiberboard can be reduced in a particularly simple and cost-effective manner if the lignocellulose-containing material before gluing under the said pressure and temperature conditions with one of these acids and / or a mixture of the acid and its salts, esters or adducts (hereinafter "acid treatment"). The addition of the acid can be done at any time prior to gluing.

In practice it has been found that good results can be obtained when the addition of the acid to the precooker or digester takes place. Particularly preferred is an addition before the refiner, in particular between the digester and refiner. The addition of the acid may be e.g. in a feed or discharge screw that conveys the lignocellulosic material from the precooker / digester to the refiner. Usually, water is partially or completely squeezed or removed between the digester and refiner steps. Preferably, the acid treatment is carried out on such a pressed or dehydrated lignocellulose-containing material. Such a mixture of pressed lignocellulose-containing material and acid can then be fed to the refiner.

Without wishing to be bound by any particular scientific theory, reducing the swelling capacity is believed to be due to elimination of the free-standing hydroxyl groups of the cell wall polymers mediated by the acid treatment, resulting in less interaction with the water molecules and resulting in hydrophobization of the material.

It is advantageous that the acid treatment can be integrated in a simple manner into the usual processes in the wood industry for the production of fiberboard, i. Complex intermediate steps (e.g., drying) or process interruptions are not required.

It is also advantageous that the acids used according to the invention (for example phosphoric acid) are available inexpensively and readily available.

Lignocellulosic material:
By "lignocellulosic material" is meant any type of material containing lignocellulose.

Lignocellulose according to the invention contains cellulose and / or hemicellulose and lignin.

"Cellulose" is an unbranched polysaccharide consisting of several hundred to ten thousand cellobiose units. These cellobiose units, in turn, consist of two molecules of glucose linked by a β-1,4-glucosidic bond.

"Hemicellulose" is a collective name for various components of plant cell walls. The hemicelluloses are branched polysaccharides with a lower chain length - usually less than 500 sugar units - which are composed of different sugar monomers. Hemicellulose is composed essentially of various sugar monomers such as glucose, xylose, arabinose, galactose and mannose, which sugars may have acetyl and methyl substituted groups. They have a random, amorphous structure and are readily hydrolyzable. Xylose or arabinose consist for the most part Part of sugar monomers with five carbon atoms (pentoses). Mannose or galactose consist mainly of sugar monomers with six carbon atoms (hexoses).

"Lignins" are amorphous, irregularly branched aromatic macromolecules, which occur in nature as part of cell walls and there cause the lignification (lignification) of the cell. They are composed of substituted phenylpropanol units, have a lipophilic character and are insoluble in room temperature in neutral solvents such as water. Precursors of lignin are, for example, p-coumaryl alcohol, coniferyl alcohol and sinapyl alcohol. The molecular weights of lignin are usually between 10,000 and 20,000 g / mol.

The lignocellulosic material may be in a frayed and / or unscreened state. According to a preferred embodiment of the invention, the lignocellulose-containing material is first added in undefiberated state (for example as wood chips) and then undergoes a defibering and / or comminution (for example in the refiner) in the course of the process. However, it is also possible to add the lignocellulose-containing material already in the fiberized state or in a mixture of defibered and undrawn material. The treatment of the lignocellulosic material may be in both defibred, partially defibred, and / or uncorrugated state. The acid treatment is preferably carried out on a lignocellulose-containing material which has a water content of from 30 to 400% by weight, in particular from 40 to 200% by weight, in particular from 50 to 150, based on the total weight of the lignocellulose-containing material.

An example of lignocellulose-containing material which can be used according to the invention are wood particles, for example any form of finely divided wood material, ie in particular wood chips, wood chips, OSB strands, wood fibers and / or wood flour. According to a preferred Embodiments of the invention include the wood particles, especially if they are chips, fibers or strands, substantially or completely native wood. By "substantially" herein is meant up to 80, 85, 90, 95, 98, or 99 weight percent, based on the total weight of the lignocellulosic material. Chips, fibers and / or strands of native wood have proved to be particularly suitable. In one embodiment, the lignocellulosic material may be selected from the group consisting of finely divided wood material, wood fibers, wood shavings, and wood chips.

Engineered wood

The term "wood material" is understood to mean a wide variety of materials that consist of wood or contain wood, examples of wood materials are wood boards, laminates, floor coverings, worktops, table tops, pallets and / or wood shaped parts, in particular composite materials of individual wood particles may be any of cellulose products such as wood particles, especially wood shavings, finely divided wood material, wood strands, wood fibers, wood chips and / or wood veneers.Wood materials disclosed herein are particularly those based on solid wood, veneer materials, chipboard, fiber materials, fiberboard or other composites.

The process disclosed herein is particularly well suited for the production of pressed wood materials, in particular for the production of fiberboard. As a fiberboard is for example a UDF, LDF, MDF, or HDF board into consideration.

Preferably, the fiberboard, or the preliminary or intermediate product of the fiberboard, consists essentially of lignocellulose-containing material. In the "essential" here means up to 80, 85, 90, 95, 98 or 99 wt .-%, based on the Total weight of the wood material. However, it is possible that the fiberboard, or the precursor or intermediate, contains further additives. Depending on the type of fiberboard, the lignocellulosic material which is treated with acid in the process of the present invention may be different. The fiberboard can be produced, for example, by comminuting cellulose-containing materials and then joining the structural elements together. The precursor or intermediate can be selected, for example, from the lignocellulose-containing starting material and / or the structural elements obtained by comminution, such as, for example, the wood particles, wood chips, wood strands, wood chips, wood fibers or wood veneers.

With the method according to the invention, source-reduced fiberboard can be produced. By "reduced swelling" is meant a reduction in swelling compared to the untreated material. By "swelling" is meant the consequences of the contact of the wood fibers with water or water vapor. In particular, a wet swelling and / or a wet expansion can occur due to the contact with water. Swelling is understood to mean swelling capacity or thickness swelling. The swelling capacity can be determined according to European standard EN 317 "Particleboard and fiberboard". Thickness swelling can be determined "after water storage" or ISO 24336 "Laminate floor coverings. Determination of thickness swelling after partial immersion in water".

According to a preferred embodiment of the invention, a reduction of the swelling by at least 10%, based on the untreated material is achieved by the inventive method. The swelling can be determined according to EN 317 or ISO 24336.

According to one embodiment of the invention, the content of the acid is 0.1 to 15% by weight, preferably 0.1 to 10% by weight, in particular 0.1, 0.2, 0.5, 1, 2, 3, 5, 7, 9, 10 or 12% by weight, based on the dry matter (atro) of the lignocellulose-containing material. In one embodiment, the acid may be used in admixture with one of its salts, esters or adducts.

acid

The term "acid" includes Bronsted acids and / or Lewis acids. Examples of usable Brönsted acids described herein are, for example, mineral acids. Acids which can be used according to the invention preferably have a pK _s value of less than 4, preferably less than 3.5, 3, 2.75, 2.5, 2.3 or 2. The acid can be used alone or in combination with one of its salts, esters or adducts.

The Brönsted acids may be selected, for example, from the group consisting of phosphoric acid, phosphorous acid, hypophosphorous acid, phosphonic acid, sulfuric acid, sulfonic acid, p-toluenesulfonic acid, benzenesulfonic acid, sulfosuccinic acid, methylsulfonic acid, methylphosphonic acid and ethylphosphonic acid or mixtures thereof. Preferably, the acid is selected from phosphoric acid, phosphorous acid, hypophosphorous acid and phosphonic acid and mixtures thereof. Particular preference is given to using phosphoric acid, in particular ortho- phosphoric acid. Furthermore, a treatment with a mixture of phosphoric acid and a salt of phosphoric acid has proved to be advantageous. The salts may, for example, be alkali salts, alkaline earth salts and / or ammonium salts.

According to the invention, phosphoric acid, phosphorous acid, hypophosphorous acid or mixtures thereof are used. Practical experiments have shown that this can reduce the risk of strongly acidic reactions with the lignocellulose-containing material and the concomitant reduction in quality of the lignocellulose-containing fiber or of the end product. Another advantage lies that the phosphoric acid is less corrosive, so that the process equipment is less stressed.

Phosphoric acids in the context of this invention are those which have a free HO-P group. Examples of phosphoric acids which can be used according to the invention are orthophosphoric acid, phosphonic acid and / or phosphinic acid. As phosphoric acid is especially ortho- phosphoric acid into consideration. The phosphoric acid can be used as a 10 to 85 wt .-% solution in water. If the treatment with phosphoric acid is carried out in the refiner, it is preferable to use a 50 to 85% strength by weight solution in water, in particular a 70 to 85% strength by weight solution in water. When it is mentioned here of salts of ortho- phosphoric acid, in particular phosphates, hydrogen phosphates and / or dihydrogen phosphates are meant. The salts of phosphoric acid may be, for example, their alkali salts, alkaline earth salts and / or ammonium salts or compounds. Salts of phosphoric acid which can be used according to the invention are also phosphonates and / or phosphinates.

Alkyl esters are particularly suitable as the phosphoric acid esters, the alkyl chain length preferably being 1 to 12 carbon atoms, preferably 1 to 10 carbon atoms, particularly preferably 1 to 5 carbon atoms and very particularly preferably 1 to 3 carbon atoms. The adducts of phosphoric acid may be, for example, di-, tri- or meta-phosphates.

Lewis acids described herein are, for example, boron trifluoride, boron chloride, aluminum trichloride, iron (III) chloride and / or zinc chloride.

The addition of the acid can be done at any point in the process prior to gluing or gluing. A treatment in the preheater and / or in the digester has proved to be advantageous. The treatment may take place under elevated pressure (with respect to atmospheric pressure) and / or under elevated temperature (with respect to room temperature). In the preheater (precooker) the treatment normally takes place under normal pressure and / or at a temperature of up to 100 ° C.

A further embodiment according to the invention provides that the treatment takes place after the digester, in particular in the intermediate stage after the digester and before the refiner or in the refiner.

According to the invention, the treatment is carried out at a temperature of 70 to 200 ° C, in particular 160 to 200 ° C. In one embodiment, the treatment may be carried out at a temperature of 120 to 180 ° C. According to the invention, the treatment is carried out at a pressure of 1 to 12 bar, in particular 2 to 10 bar. In one embodiment, the treatment may be carried out at a pressure of 6 to 9 bar.

In another embodiment, the duration of the treatment may be 0.01 to 15 minutes, especially 0.3 to 5 minutes.

According to a further embodiment of the invention, the acid is added before and / or during the crushing process in the refiner. The treatment of the lignocellulosic material with the acid in a conventional refiner in the industry is usually carried out at a process temperature of 160 to 200 ° C and / or a pressure of 2 to 10 bar, in particular from 5 to 9 bar.

"Refiner" is understood to mean the machine used in the wood industry, which is used for comminution, in particular for grinding of fibers. Examples of suitable refiners are disc refiners, cone refiners or cylindrical refiners. Refiner are for example in the " Taschenbuch der Holztechnik ", Wagenführ / Scholz, 2nd ed. 2012, p. 235 ff , described. In the refiner wood particles are treated at a process temperature of 70 to 200 ° C, in particular at 120 to 180 ° C, and / or a pressure between 1 to 10 bar, in particular at 5 to 9 bar.

By "treating" is meant the processing or contacting of the lignocellulosic material (or a precursor or intermediate thereof) with the acid under the conditions described. The lignocellulosic material may be present in the treatment in un-fibered, shredded and / or partially defibred state.

It has turned out to be advantageous if the treatment of the lignocellulose-containing material with the acid takes place in the preheater, cooker and / or refiner.

In one embodiment of the invention, the acid is added after the precooker or digester. Preferably, this addition of acid takes place before the refiner, more preferably the acid is added to the still hot, lignocellulosic material that has leaked from the digester. This is particularly practical in a feed or discharge screw, which conveys the lignocellulosic material from the pre-cooker or digester to the refiner. The acid may be added according to another embodiment in the refiner and / or between the digester and refiner.

The term "cooker" is understood to mean the machine commonly used in the wood industry, which is used to soften the wood chips under the effect of temperature and excess water. The common wood chips preparation for MDF production by means of a cooker and subsequent refining step is described, for example, in US Pat. Holzwerkstoffe ", Soiné, DRW-Verlag 1995, chapter 1.2.2.6 s.

It is assumed that by the treatment in the presence of moisture, under elevated pressure, under elevated temperature and / or with simultaneous comminution an expansion of the fiber pores and concomitantly an enlargement of the fiber surface occurs, so that the acid used according to the invention can more easily diffuse into the fiber core , This also applies analogously to the lignocellulose-containing Material that has just undergone these conditions, for example, the lignocellulosic material that is transported from the precooker by means of a feed or discharge screw to the refiner. The treatment time with the acid is usually less than 15 minutes, preferably about 2 to 3 minutes are sufficient to allow sufficient diffusion.

In principle, the greater the surface area of the lignocellulose-containing material to be treated (i.e., the precursor or intermediate product of the wood material), the higher the reaction rate of the process according to the invention. The surface is known to increase with decreasing particle size. Thus, in the process according to the invention, a higher reaction rate is achieved if the lignocellulose-containing material to be treated has a small particle size. According to one embodiment of the invention, the material to be treated is brought into contact with the acid with simultaneous comminution.

According to a further embodiment of the invention, the acid treatment takes place during the comminution of the lignocellulose-containing material (for example in the refiner). The fact that the lignocellulosic material undergoes the swelling-reducing treatment, a swelling reduction is ensured down to the core of the entire wood material with low cost and process complexity and within the running of the process chain.

The reaction of the acid, in particular the phosphoric acid, with the surface of the lignocellulosic material may begin with the introduction of the acid in the preheater or the digester or only between the digester and the refiner and in the refiner. Due to the thermomechanical conditions in the refiner, the distribution and / or the reaction is further accelerated. By discharging water in the dryer and / or the further thermally induced drying of the nonwoven fabric during plate formation in the press, the reaction can also be driven forward become. The final reaction is often complete only after the finished plate has cooled in the warehouse.

Another advantage of the method according to the invention is that the diffusion process takes place here within a few minutes. A further advantage is the short treatment time in Vorwärmbehäter, Vorkocher and / or refiner or in between. This is generally not longer than 15 minutes, preferably 0.01 to 10 minutes, particularly preferably 0.1 to 5 minutes, in particular 0.3 to 2 minutes. Thus, the inventive method is compatible with current production processes of the wood industry. It can be used within an ongoing production without significantly changing the productivity of the equipment used.

Particularly good results can be achieved if the process according to the invention is used for producing wood composite materials, in particular a fiberboard.

In principle, various methods for the production of wood-based materials, such as, for example, fibreboards, in particular HDF or MDF boards, are known to the person skilled in the art. As a result, treatment with the acid can be easily made in a variety of production processes, such as a HDF or MDF standard process

1. a) Anwärmen des lignocellulosehaltigen Materials in einem Vorwärmbehälter;
2. b) Aufschluss des lignocellulosehaltigen Materials in einem Kocher;
3. c) Zerkleinerung des lignocellulosehaltigen Materials in einem Refiner;
4. d) Behandlung des lignocellulosehaltigen Materials mit der Säure und/oder einer Mischung aus der Säure und ihrem Salz vor oder in mindestens einem der Schritte a), b) und/oder c); und/oder zwischen den Schritten b) und c);
5. e) Beleimen des lignocellulosehaltigen Materials mit einem Bindemittel;
6. f) optional: Trocknen der Mischung enthaltend das lignocellulosehaltige Material;
7. g) Verpressen der Mischung enthaltend das lignocellulosehaltiges Material zu einem Holzwerkstoff.

The method according to the invention can be designed such that it comprises at least the following steps:

1. a) heating the lignocellulosic material in a Vorwärmbehälter;
2. b) digestion of the lignocellulosic material in a digester;
3. c) comminution of the lignocellulosic material in a refiner;
4. d) treating the lignocellulosic material with the acid and / or a mixture of the acid and its salt prior to or in at least one of steps a), b) and / or c); and / or between steps b) and c);
5. e) gluing the lignocellulosic material with a binder;
6. f) optionally: drying the mixture containing the lignocellulosic material;
7. g) pressing the mixture containing the lignocellulose-containing material to a wood material.

Step a)

In step a), the lignocellulosic material to be processed is preheated to the desired temperature.

Step b)

In step b), the lignocellulose-containing material is digested in the digester under elevated pressure and at elevated temperature. Preferably, a temperature of 160 to 200 ° C and / or a pressure of 1 to 12 bar, in particular from 1.5 to 12 bar, 2 to 10 bar, 3 to 10 bar or 5 to 9 bar, is set.

Basically, steps a) and / or b) take place using an excess of water. The proportion of water in the mixture of water and the lignocellulose-containing material in step a) and / or b) can be from 100 to 400% by weight, in particular from 150 to 300% by weight, based on the total weight of the lignocellulose-containing material.

In one embodiment, the addition of the acid may occur in step a) and / or b). Due to the increased water content in step a) and / or b), the added acid is diluted again. This may be advantageous because, according to Ostwald's law of dilution, the degree of proteolysis increases with increasing dilution. This allows a particularly effective use of the acid used. The reaction of the acid is further enhanced by the increased surface area of the fiberized lignocellulosic material and / or the elevated temperature and consequent pore opening of the fibers.

While in principle by the addition of the acid in step a) and / or b) the swelling properties can be improved, practical experiments have shown that such an addition can have a negative effect on the transverse tensile strength.

The addition of the acid in step a) and / or b) can be problematic since exact dosing is difficult due to the considerable and sometimes fluctuating dilution. It can easily happen that either too little acid is added or too much, which then causes the reaction of the acid with the lignocellulose-containing material to proceed so strongly that it suffers from the quality of the lignocellulose-containing material and thus also the quality of the end product. Due to the dilution effect of the water present, it may also happen that not enough acid penetrates into the lignocellulosic material, which is why in turn the treatment time in step a) and / or b) must be extended.

Intermediate step bc)

After cooking in step b), the lignocellulosic material is fed to the refiner (step c)). This phase between the digester and the refiner is referred to herein as "intermediate step bc)". It has proven to be particularly practical if the acid treatment takes place in this intermediate step bc).

Intermediate step bc) involves the transfer of the lignocellulosic material from the digester to the refiner, but may also include other processes, in particular intermediate storage or further processing of the lignocellulose-containing material. Usually, the defibrated lignocellulose-containing material obtained from step b) becomes the refiner used in step c) by means of a feed or discharge screw fed. Here, the still hot lignocellulosic material is carried out of the digester and transported in the direction of refiner. Since the previous step a) and / or b) has an increased water content, which is not desired in the following process steps, the water from the lignocellulose-containing material is usually at least partially pressed or removed in the intermediate transport step bc). After pressing, the lignocellulosic material typically has a water content of from 50 to 200% by weight, in particular from 75 to 150% by weight, based on the total weight of the lignocellulose-containing material. Preferably, the acid treatment is carried out after such pressing or removal of the water, which takes place after removal from the digester.

Typically, the lignocellulosic material still has an elevated temperature during transport from the precooker to the refiner. This has a positive effect on the acid treatment.

The addition of the acid is particularly preferably carried out in intermediate step bc). The addition of the acid in intermediate step bc) can be carried out by initially squeezing or removing water completely or partially and then adding the acid. In particular, the acid may be added after or during at least partial squeezing or removal of the water from the lignocellulosic material. The treatment time with the acid in intermediate step bc) can be 0.1 seconds to 2 minutes, preferably from 0.5 seconds to 1 minute and particularly preferably from 1 second to 30 seconds.

The disadvantages, as they exist in the addition in step a) and / or b) can be largely avoided by the acid addition in intermediate step bc). By squeezing or removing the water in intermediate step bc), the acid is not diluted so much, which also ensures better dosage and the risk Uncontrolled reactions can be reduced. As the acid is used more concentrated, the treatment time can be reduced, which can have a positive effect on the production costs. In addition, after defibration in step a) and / or b), the lignocellulosic material has an increased surface area and elevated temperature such that the pores of the lignocellulosic material are at least partially opened or widened, allowing the acid to more easily diffuse into the lignocellulosic material.

Practical experiments have further shown that it may be advantageous if the reaction of the acid is completed only after cooling of the finished product in the warehouse. Therefore, it may also be advantageous if the acid is added in intermediate step bc) or step c) and thus can remain in the lignocellulose-containing material in the further process. If the acid is added in step a) and / or b), the acid is at least partially removed by the removal or removal of the water in step c) and can then no longer be available for the reaction.

In a particularly preferred embodiment, the acid used is a Bronsted acid selected from the group consisting of phosphoric acid, phosphorous acid, hypophosphorous acid phosphonic acid and mixtures thereof in intermediate step bc) and / or step c). In particular, the acid can be used in an amount of from 0.1 to 10% by weight, based on the lignocellulose-containing material (atro). Phosphoric acid is particularly preferred according to the invention as the acid. In a further embodiment, the phosphoric acid can be added in admixture with one of its salts, esters or adducts in intermediate step bc) and / or step c).

Step c)

In step c), the lignocellulose-containing material (refiner) is comminuted. According to one embodiment of the invention, the acid is before and / or during the crushing process added in the refiner. The treatment of the lignocellulosic material with the acid in a conventional refiner in the industry is usually carried out at a process temperature of 160 to 200 ° C and / or a pressure of 2 to 10 bar, in particular from 5 to 9 bar. These conditions allow for rapid diffusion of the acid molecules into the core of the lignocellulosic material.

Step d)

The acid treatment can be done in each step before gluing or gluing. The treatment preferably takes place in at least one of the steps a), b), bc) and / or c). The acid treatment may also be carried out before or after at least one of steps a), b), c) and d). Examples of this are the feeding of the acid in feed or Austragsschnecken which carry the lignocellulosic material. Alternatively, the acid may be added directly to the preheater, precooker and / or refiner. Most preferably, the addition of the acid is between steps b) and c), i. in intermediate step bc), and / or during step c). In a preferred embodiment, the acid is added in step bc).

Further, in the practice of the method, multiple treatment of the lignocellulosic material has been found to be advantageous.

In a particularly preferred embodiment, the acid used is a Bronsted acid which is selected from the group consisting of phosphoric acid, phosphorous acid, hypophosphorous acid and phosphonic acid and mixtures thereof. In particular, the acid can be used in an amount of from 0.1 to 10% by weight, based on the lignocellulose-containing material (atro). Phosphoric acid is particularly preferred according to the invention as the acid. In a further embodiment, the phosphoric acid may be added in admixture with one of its salts, esters or adducts.

Steps)

In step e) the lignocellulose-containing material is glued with a binder. Suitable binders are in particular a melamine and / or urea resin.

If this is referred to as "gluing", then it can be understood as wholly or partially wetting with a composition that contains a binder. Such compositions are also referred to by the person skilled in the art as "glue liquor". Gluing can in particular also mean the uniform distribution of the binder-containing composition on the wood particles. The application of the binder-containing composition can be carried out, for example, by impregnation or spraying, in particular in a blowline.

According to a preferred embodiment of the invention, a blow-line connects to the refiner. In addition to the added binders and hydrophobizing agents, surface-modifying agents which neutralize the surface and / or encapsulate the fiber can optionally also be sprayed on in the blowline.

The amount of the binder used in the gluing or gluing is preferably 0.1 to 20 wt .-%, in particular 1.0 to 16 wt .-%, more preferably 4.0 to 14.0 wt .-%, based on the Wood dry weight (solid resin / atro). For many applications, it is particularly practical if the binder in an amount of 0.1 to 15 wt .-% based on the dry weight of wood (solid resin / atro) is used. The application of the binder can be carried out, for example, in the blowline known to the person skilled in the art.

In principle, the method according to the invention is suitable for a multiplicity of binder-wood particle combinations. Examples of binders which can be used according to the invention are aminoplasts, phenoplasts, vinyl acetates, isocyanates, epoxy resins and / or acrylic resins. Particularly preferred binders are urea-formaldehyde resin (UF), melamine-formaldehyde resin, phenol-formaldehyde resin (PF), polyvinyl acetate and / or white glue.

According to a preferred embodiment of the invention, the binder used for the gluing is a system based on urea-formaldehyde resins (UF), melamine-reinforced urea-formaldehyde resins (MUF), melamine-urea-phenol-formaldehyde resins (MUPF), Phenol-formaldehyde resins (PF), polymeric diisocyanates (PMDI) and / or isocyanates used. Preferably, the binder is an aminoplast resin.

The binder used in the process of the invention may further contain hardeners. Alternatively or additionally, the curing can also be carried out by pressing the composite material under the action of heat.

Step f)

Optionally, a drying of the glued mixture containing the lignocellulose-containing material can be carried out between the gluing (step e) and the pressing (step g).

Step g)

In step g), the mixture containing the lignocellulose-containing material is finally pressed into a fiberboard. Basically, the person skilled in various methods are known to glue glued wood particles to form a composite material. Optimum results can be obtained if the pressing is carried out at a pressing temperature of at least about 150 ° C.

The person skilled in various methods are known to produce wood chips by compression. According to one embodiment of the invention, the glued wood particles are pressed in step g) into a wood chip material. Preferably it is in step g) is a hot pressing. Optimum results can be achieved if the press factor during hot pressing is from 2 to 10 s / mm, preferably from 3 to 6 s / mm. Press factor is understood to mean in particular the residence time of the lignocellulose-containing wood chip material in seconds per millimeter thickness or thickness of the finished pressed lignocellulose-containing wood chip material in the press.

Suitable temperatures for the compression in step g) of the process according to the invention or one of its embodiments are temperatures of 150 ° C to 250 ° C, preferably from 160 ° C to 240 ° C, particularly preferably from 180 ° C to 230 ° C. At temperatures in these ranges, the process can be carried out particularly economically.

For economic and procedural reasons, it has proved to be advantageous if a specific pressing pressure (active pressure on the plate surface) of 50 to 300 N / cm ² , is used during pressing. Such pressures ensure a particularly good bonding of the lignocellulose-containing particles together. In addition, a high strength of the lignocellulosic wood chip materials can be achieved with such a pressure.

Also described herein is the use of the method or one of its embodiments for producing a reduced-source wood material.

Herein also described the use of phosphoric acid, one of its salts, esters or adducts for the production of a reduced-source wood material.

Also described herein is a fiberboard obtainable by the method of the invention or one of its embodiments and by further processing the fiber board available laminate, a floor covering, a worktop, table top or pallet.

The invention will be described in more detail by way of example with reference to exemplary embodiments.

example 1

It is produced a reduced-source wood fiber board according to the common in the wood industry MDF process.

The wood chips arrive for hydrothermal pretreatment in a preheating, where they are "pre-steamed" together with 1 wt .-% ortho- phosphoric acid (based on the total amount of water and wood chips) at atmospheric pressure at a temperature of up to 100 ° C. The partially plasticized and modified wood chips then pass through the vibration discharge floor and a screw conveyor in the digester. The pitch of the helix decreases continuously, compressing the chips into a relatively pressure-tight plug. With this plug, the seal takes place to the stove. Here, the chips are "cooked" at a vapor pressure between 6 and 10 bar at 140 to 180 ° C. In the digester, the chips remain about 1 to 6 minutes before being fed by a screw conveyor (discharge screw) and via the feed screw into the refiner and pulverized into fibers at a vapor pressure of 6 to 10 bar. In addition to the added melamine-urea-phenol-formaldehyde resin (binder), further hydrophobing agents as well as surface-modifying agents which neutralize the surface or encapsulate the fiber can be sprayed on in the blowline adjoining the refiner. The glued fibers now enter the dryer and are dried to the desired residual moisture. By spreading rollers, the fibers on a circumferential Forming band scattered and the height of the resulting fiber mat is adjusted by calibration rollers (scalper). After precompression, the endless fiber mat is pressed in a continuous hot press at 200 ° C and 30 bar for about 3 minutes to its desired thickness.

The wood fiberboard thus obtained has a significantly reduced thickness swelling.

Example 2

It is made of a wood fiber board according to the common in the wood industry MDF process.

The wood chips arrive for hydrothermal pretreatment in a Vorwärmbehälter, where they are "pre-damped" at atmospheric pressure of a temperature of up to 100 ° C. The partially plasticized and modified woodchips then pass through the vibration discharge floor and / or a screw conveyor in the digester. The pitch of the helix decreases continuously, compressing the chips into a relatively pressure-tight plug. With this plug, the seal takes place to the stove. Here, the chips are "cooked" at a vapor pressure between 6 and 10 bar at 140 to 180 ° C. In the digester, the chips remain about 1 to 6 minutes before being fed by a screw conveyor (discharge screw) together with ortho- phosphoric acid in an amount of 10% by weight, based on the amount of the wood material, into the refiner and at be pulverized to fibers to a vapor pressure of 6 to 10 bar. In addition to the added melamine-urea-phenol-formaldehyde resin (binder), further hydrophobing agents as well as surface-modifying agents which neutralize the surface or encapsulate the fiber can be sprayed on in the blowline adjoining the refiner. The glued fibers now enter the dryer and are dried to the desired residual moisture. By spreading rollers, the fibers are scattered on a rotating forming belt and the height of the resulting fiber mat is adjusted by calibration rollers (scalper). After precompression, the endless fiber mat is pressed in a continuous hot press at 200 ° C and 30 bar for about 3 minutes to its desired thickness.

The wood fiberboard thus obtained has a significantly reduced thickness swelling.

Example 3:

The swelling-reducing effect of 85% phosphoric acid (m / m) on wood fibers was determined.

The wood fibers were subjected to a pulping process. For this wood chips were cooked in a pre-cooker. The wood fibers were fed from the precooker to the refiner by means of a discharge screw while pressing off water. Even before the wood fibers reached the refiner, phosphoric acid was added. The wood fibers thus obtained were examined for their swelling properties. For this purpose, in a beaker, wood fibers, both the reference fibers (0% phosphoric acid) and those treated with phosphoric acid, were weighed (weighed, EW) and covered with water so that they were completely covered. The proportion of phosphoric acid is given in Table 1 as wt .-% phosphoric acid based on the total weight of wood fibers (atro). After different exposure times, the water of the samples was drained over a paper filter placed on a 800 μm sieve for 15 minutes. Thereafter, the wood fibers were weighed (weight, AW) and the water absorption capacity (WAV) determined as follows: $$\mathit{WAV}=\left[\left(\mathit{AW}-\mathit{EW}\right)*\mathrm{100}\%\right]/\mathit{EW}$$

Further, the swelling reduction of the wood fibers (Samples 1-1 to 3-3) was determined in comparison with the respective reference plates 1 to 3.

The swelling was calculated as follows: $$\left[\mathit{WAV}\left(\mathbf{REFERENCE}\right)-\mathit{WAV}\left(\mathit{sample}\right)\right]*\mathrm{100}/\left[\mathit{WAV}\left(\mathbf{REFERENCE}\right)\right]$$

The weights, weights, exposure times and the results are listed in Table 1 below. <b> Table 1: </ b> sample number Proportion of phosphoric acid EW AW WAV exposure source reduction [Wt .-%] [G] [G] [%] [Min] [%] Reference 1 0 2.1103 37.127 1,659.3 30 Reference 1 Reference 2 0 2.1361 38.865 1,719.4 150 Reference 2 Reference 3 0 3.2543 61.2541 1,782.3 390 Reference 3 number 1 2.5 2.4143 36.919 1,429.2 30 13.8 No. 2 2.5 2.5567 41.7506 1533 150 10.8 No. 3 5 3.1985 45.899 1335 30 19.5 No. 4 5 2.6354 40.864 1,450.6 150 15.6 No. 5 5 2.5597 42.1079 1545 390 13.3 No. 6 10 2.8525 40.2027 1,309.4 30 21.1 No. 7 10 2.6235 41.725 1,490.4 390 16.4

Overall, there was a significant swelling reduction of the treated with phosphoric acid wood fibers (samples 1 to 7) compared to the untreated wood fibers (reference 1 to 3).

Claims (12)

1. Method for producing a fibreboard with reduced swelling by gluing lignocellulose-containing material, wherein the lignocellulose-containing material is treated with an acid prior to gluing, wherein the treatment takes place at a temperature of 70 to 200°C and a pressure of 1 to 12 bar and wherein the acid is a Bronsted acid selected from the group consisting of phosphoric acid, phosphorous acid, hypophosphorous acid and mixtures thereof, and wherein the acid is an acid with a pKa-value of less than 4.
2. Method according to claim 1, wherein the acid is used in a quantity of 0.1 to 10 wt.-% in relation to the lignocellulose-containing material (atro).
3. Method according to any one of the preceding claims, wherein the acid is used in a mixture with one of its salts, esters or adducts.
4. Method according to any one of the preceding claims, wherein as the acid an acid is used with a pKa-value of less than 3 or less than 2.5.
5. Method according to any one of the preceding claims, wherein the treatment is performed at a temperature of 120 to 180°C.
6. Method according to any one of the preceding claims, wherein the treatment is performed at a pressure of 6 to 9 bar.
7. Method according to any one of the preceding claims, wherein the duration of the treatment is 0.01 to 15 minutes, in particular 0.3 to 5 minutes.
8. Method according to any one of the preceding claims, wherein the treatment is performed in the intermediate stage after the digester and before the refiner.
9. Method according to any one of the preceding claims, wherein the lignocellulose-containing material is present in a defibred and/or non-defibred state.
10. Method according to any one of the preceding claims, wherein the lignocellulose-containing material is selected from the group consisting of fine-particle wood material, wood fibres, wood shavings and woodchips.
11. Method according to any one of the preceding claims, wherein the method comprises at least the following steps:

    a) Preheating the lignocellulose-containing material in a preheating container;

    b) Macerating the lignocellulose-containing material in a digester;

    c) Grinding the lignocellulose-containing material in a refiner;

    d) Treating the lignocellulose-containing material with the acid in step a), b) and/or c) and/or between steps b) and c);

    e) Gluing the lignocellulose-containing material with a binder;

    f) Optionally: Drying the mixture containing the lignocellulose material;

    g) Pressing the mixture containing the lignocellulose-containing material into a fibreboard.
12. Method according to any one of the preceding claims, wherein the fibreboard is a UDF, LDF, MDF or HDF board.