HRP20010858A2 - Wood-fibre semi-finished product and method for producing the same - Google Patents

Description

The invention relates to a semi-finished product made of wood fibers, which contains pressed wood fibers coated with hot-cured condensation resins, the process of obtaining them, as well as compact panels made of wood fibers, which are composed of these semi-finished products.

Technical condition

Wood fiber semi-finished products, especially in the form of panels, are produced from wood fibers or fibrous material that is partially composed of lignocellulose. These starting materials are separated into individual fibers or bundles of fibers under the influence of heat, moisture and mechanical pressure forces in devices for separating fibers. During the further production process, the fibrous material is glued with condensation resins, then dried and formed into slats. In the further process, these shaped hasurs are pre-compacted and pressed. According to DIN 68753/1976, according to the packed weight of the fiber mats and the applied pressure, hard boards made of wood fibers, so-called HFH-boards, with a raw density of more than 800 kg/m3, as well as medium-density boards made of wood fibers, so-called MDF- can be produced. board, with a density in the range of 350 kg/m3 to 800 kg/m3.

The aforementioned MDF-boards are used in interior construction, especially as visible elements in the manufacture of furniture, for example as three-dimensionally milled panels, as panels for covering ceilings and walls, as well as in the production of doors as so-called "Doorskins".

Due to their high density, HFH panels can also be used in construction, for example as roof substructures or in the construction of floors as load-bearing panels for so-called laminate floors.

If particularly high requirements are placed on the boards with regard to moisture strength, dimensional stability of the boards both in the longitudinal and transverse directions in case of climate change, low swelling value and low water absorption capacity especially in the edge parts, bending strength and E-modulus of bending according to EN 438/1 for decorative "High Pressure Laminates", however, those panels made according to EN 622/5 are not or are only conditionally suitable for interior construction. Panels with quality requirements corresponding to EN 438/1 find multiple outdoor applications, for example as decorative surfaces for cladding balconies and facades, but also for indoor use, for example as furniture in wet conditions.

In order to fulfill the requirements according to EN 438/1, we mainly work with materials pressed in layers, consisting of several layers of paper impregnated with condensation resins. Their production is carried out at elevated pressure and elevated temperature, so that the finished panels are labeled as so-called "High Pressure Laminates" (HPL). These HPL-boards are characterized by particularly good mechanical strength as well as satisfactory moisture strength values. The mechanical strength values can be influenced primarily by using a large number of papers impregnated with condensation resins in the production process.

The pressed material in layers produced by this process has the disadvantage that dimensional stability is low in changing climatic conditions. The cause of this unsatisfactory dimensional stability probably lies in the structure of the core layer of that well-known layered pressed material, because it is made of sodium-hard paper. Natron-hard papers consist of fibers, which are arranged 60-80% in the longitudinal direction and 20 to 40% in the transverse direction to the longitudinal direction of the paper strip. The predominant orientation of the fibers in the longitudinal direction of the paper strip has the consequence that the material for pressing in layers under changing climatic conditions is subject to strong changes in dimensions in the longitudinal and transverse directions.

Thus, for example, EP-A-35 133 describes a process for the production of decorative HPL-laminates, in which a core layer of fibers such as cellulose is formed from impregnated phenol-formaldehyde resins. The proportion of resins is 20-35% by weight; fibers like cellulose have an average length of 0.5-2.5 mm. Further layers of at least one decorative paper as well as one transparent cover sheet are continued on this core layer.

Furthermore, EP-A-81 147 describes the production of decorative building panels for external use, in which a core layer of wood and/or cellulose fibers with a maximum length of 20 mm is formed, and in which these fibers are coated with heat-cured phenolic with formaldehyde resins in an aqueous solution, so that a resin content of more than 150-900 g per 1000 g of dry fibers is achieved. The density of these construction panels is in the range of 1100-1500 kg/m3.

For the production of the core layer according to this well-known procedure, a relatively high proportion of phenol-formaldehyde resins is required in comparison to the used sodium-solid papers or atro-wood fibers, which on the one hand, conditioned by the emission of free phenols or monomer compounds of phenols, requires demanding aeration or exhausting of the device for production in order to achieve the required MAK-values prescribed by the environmental protection service, and on the other hand, due to the impregnation and drying of the used sodium-solid papers, i.e. the drying of wood fibers and their hardening by heat, there is a necessary and expensive thermal afterburning of the exhaust air containing phenol , as a consequence.

Description of the invention

The task of the described invention is to avoid the previously mentioned bad properties that relate to the properties of the product and the management of the process.

According to the invention, it is proposed that a semi-finished product made of wood fibers of the type described above, which is characterized by the fact that the degree of adhesion of wood fibers is 30 to 60% of solid resins in the form of mixtures of condensation resins or mixtures of condensation resins (copolymers) in relation to 100% atro-fibers , where the share of solid resins in melamine-formaldehyde resins as condensation resins is a maximum of 45%, with respect to atro-wood fibers, and the share of solid resins in phenol-formaldehyde resins as further condensation resins is less than 15% compared to atro-wood fibers, and that they are wood fibers, which are coated with hot-hardened melanin- and phenol-formaldehyde resins, additionally covered with a layer of wax.

This task can be solved in a particularly satisfactory way by using melamine-formaldehyde resins with a degree of condensation of 1.4 to 1.6 measured on cold water tolerance.

Lower emission values with respect to monomeric compounds of phenol can be achieved if phenol-formaldehyde resins are used with a maximum free phenol content of 0.5% and a B-time of 48 s. The B-time is the time during which the liquid phenol-formaldehyde at 150°C, the resin turns into a solid state by polycondensation, in which it can no longer go into a melting or swelling state, into the so-called C-state.

By reducing the proportion of phenol-formaldehyde resin in the applied mixtures of condensation resins or mixtures of condensation resins (copolymers), according to the invention, no subsequent inclusion of air cleaning procedures or air combustion procedures is necessary.

The long-known device for air spraying has proven to be particularly useful for the uniform orientation of the fibers in the longitudinal and transverse directions, in the production of continuous fibrous mats and mats of the same shape if the semi-finished wood fiber product according to the invention consists of wood fibers with an average length of 1.0 up to 1.4 mm and an average diameter of 0.02 mm. In this way, not only in the longitudinal but also in the transverse direction of the semi-finished product made of wood fibers, a satisfactory dimensional stability is achieved under changing climatic conditions.

Very good strength values are achieved with semi-finished wood fiber products according to the invention when their density lies in the range of 800-1000 kg/m3.

For the production of the above-mentioned semi-finished product from wood fibers according to the invention, the raw material is separated into individual fibers, then glued with condensation resins in the exhaust line, and the thus obtained glued fibrous material, after drying to the required residual moisture, is spread into scraping belts under pressure and at a certain temperature is pressed into a semi-finished product. According to the invention, this process achieves a degree of adhesion of wood fibers within the exhaust pipe of 30-60% solid resin in the form of mixtures of condensation resins or mixtures of condensation resins (copolymers), whereby the resins inside the exhaust pipe are distributed on the wood fibers in such a way that the proportion of solid resin in melamine-formaldehyde resin as a condensation resin is a maximum of 45%, and the share of solid resin in phenol-formaldehyde resin as a further condensation resin is less than 15% compared to atro-wood, and in the exhaust water a wax emulsion is applied to the glued fibers with melamine- and phenol-formaldehyde resins.

The advantage is in the application of melamine- and phenol-formaldehyde resins in the exhaust water in the form of a mixture or one after the other as individual components or in the form of mixtures of condensation resins (copolymers).

The residual moisture after drying the glued wood fibers in the preferred embodiment is at least 16%. This has the advantage on the one hand of rapid heat transfer during the pressing process when making semi-finished products from wood fibers, and on the other hand of achieving a residual moisture of max. 8% in the fully finished semi-finished product. Semi-finished products made of wood fibers with a residual moisture of up to 8% ensure that the condensation resins have not yet reached the C-state, which is desirable and necessary only in the next processing step. The degree of condensation of the resin can be controlled and regulated through the remaining moisture in the wood fiber semi-product.

Semi-finished products made of wood fibers, in the form of boards, sanded, cut into formats and stored in an air-conditioned manner, can according to the invention be pressed individually or in the form of multi-layer construction into decorative compact fiber boards with a single or multi-layer construction of decorative paper based on melamine resins, for example in multi-layer press with return cooling under similar conditions as classic HPL panels. A particular advantage is the use of phenol-impregnated natron-hard papers in pressed layers as so-called binding films between individual wood fiber semi-products in order to join them by hot tempering and be water-repellent.

The advantage of using wood fiber semi-products for the production of decorative fibrous compact panels according to the invention consists in the fact that, after additional densification up to 1400 kg/m3 and reaching the C-state of the applied condensation resins under pressure and at a certain temperature during the application of the decorative layer on multistage press with return cooling, completely finished fibrous compact panels with satisfactory values of mechanical strength as well as moisture strength can be produced.

Guidelines for carrying out the invention

The invention will now be explained in more detail on the basis of a sketch of the procedure as well as an example of implementation.

Example 1

Chopped steaks are made in a familiar way, consisting of 50% beech and 50% spruce. The use of spruce and beech is suitable because of this, because both types of wood have a relatively high proportion of sclerenchyma fibers (tissue that provides strength), and this enables better utilization of the fibers. The use of beech wood contributes on the basis of specific fiber properties, such as short length and smaller diameter as well as increased specific weight, significant improvement of surface quality and edge quality while simultaneously optimizing physical properties, especially swelling and water absorption values.

According to the procedure, the chopped steaks are fed through the rinser l and the dewatering auger 2 into the chopped material hopper 3a, from which they are delivered to the preheater 3c via the clogging auger 3b. In the preheater 3c, the chopped steaks are thermomechanically processed for approximately 5 minutes using water vapor at a pressure of 8 to 12 bar and then in the defibrator 3d they are separated into fibers with a length of 0.1 to 22 mm. The fibers consist of 60 to 80% of fibers with a length of 0.5 to 3 mm, ca. 19 to 39% of fibers less than 0.5 mm in length (fines) and ca. 1.0% of fibers with a length of 3 to more than 20 mm (shives). The average length of the fibers is approx. 1.0 to 1.4 mm.

Thus produced, individual or connected, wet fibers are transferred from the defibrator 3d via the exhaust pipe 4 by a turbulent current at ca. 6 to 8 bar in the exhaust line and with a speed of 50 to 100 m/s into the dryer 5. The pasting is carried out in the exhaust line 4, for example in a completely specific order. First, in relation to atro-wood fibers, 75% of liquid melamine-formaldehyde resin with a proportion of solid particles of 50% (that is 37.5% of solid resin in relation to atro-wood fibers) is injected through the nozzle 4a for impregnation or saturation fibers. Then 35.7% of liquid phenol-formaldehyde resin with a proportion of solid particles of 35% (that is 12.5% of solid resin in relation to atro-wood) is injected via nozzle 4b, which is located at a distance of 4 m from the first nozzle (4a), for wrapping already previously impregnated or saturated fibers. Via nozzle 4c, which is located at a distance of 4 m from nozzle 4b, 4% liquid wax emulsion with a fiber content of 50% (2% solid wax in relation to atro-wood) is introduced in relation to the fibers as a hydrophobing agent or separation agent.

The wet fibers, impregnated with melamine-formaldehyde resin, made with phenol-formaldehyde resins and mixed with wax emulsion, are then dried to 16% residual moisture in dryer 5 using a stream of hot air at 100° to 140°C and an air speed of 10 to 30 m/s. The dried fibers are stored in the fiber container 6, and then, by means of the air sprayer 7, they are continuously spread in the form of a uniform pile of fibers on the forming belt 8a and in the pre-press 8b they are cold pre-compacted to one fifth of the initial volume. Using a spray device, 8e is uniformly applied at 1% of water, in relation to the weight of the mesh, on the underside and the top of the fiber mesh. The cold pre-compacted and moistened fiber mat 12, after passing the metal detector 8d in this case and the edge sides are processed in the hemming station 8c, is processed in a continuous hot press 9 under a pressure of 15 to 30 bar and a temperature between 180° to 200° C. they are pressed and shaped into highly glued semi-finished products from wood fibers with a density of 850 ±50 kg/m3, residual moisture of 8% and calibrated to a thickness of 3.0 mm.

In the further hemming station 10 and the cutting station 11, for example, the 3 mm calibrated semi-finished wood fiber 13 is formatted. The wood fiber semi-products 13 produced in this way are conditioned during storage and then in a further process that is not shown in the sketch, they lead to a compact wood fiber product.

These wood fiber semi-products 13 can be used in the production of decorative fiber compact panels, which are passed through a multi-stage press with return cooling at a temperature of, for example, 145°C and a pressure of, for example, 55 kp/cm2.

For the production of a decorative compact fiber board with a thickness of 9 mm, three semi-finished products made of wood fibers, calibrated and formatted to a thickness of 3 mm, are used. For example, solid paper impregnated with phenol-formaldehyde resins is used as a binding layer between individual layers.

Well-known decorative papers impregnated with melamine resin are used for the production of decorative outer layers. To increase wear resistance, so-called overlay papers can be laid over them.

The decorative compact board made of wood fibers produced in this way has a density of 1205 kg/m3 and a bending strength of 106 MPa. These values correspond to the usual HPL-materials used in construction and furniture production in layers of type S, EN 438/1.

Furthermore, the compact board made of wood fibers shows only a small ability to absorb water, which can be explained by the impregnation of the fibers and the multi-layer wrapping of the fibers using, in this case, the applied melamine- and phenol-formaldehyde resins during gluing, as well as the additional application of wax emulsion.

Example 2

Semi-finished products from wood fibers and then decorative compact panels from wood fibers are produced as in example 1, where the starting point is the same level of adhesion (50% solid resin compared to atro-wood) and the same ratio of the glue mixture. The difference from example 1 consists in the fact that the melamine- and phenol-formaldehyde resin are mixed in a weight ratio of 3:1 ("matching") before gluing and are applied to the wood fibers in the exhaust water using nozzles 4a to 4c. Despite this change in the procedure, identical values can be achieved as in example 1, for example with regard to moisture strength, which again can be connected to the mutually coordinated chemical and physical action of the applied melamine- and phenol-formaldehyde resins and thus the achieved values of fiber impregnation and by multiple wrapping of wood fibers.

Example 3

Semi-finished wood fiber products and then compact wood fiber panels are produced, as stated in example 2, starting from the same overall degree of adhesion - 50% hard resin in relation to atro wood - and the same numerical ratios.

The difference according to example 2 consists in the fact that the melamine- and phenol-formaldehyde resin as a mixture of condensation resin (copolymerizate), as is already known, reacts with formaldehyde in the appropriate molar ratio, whereby the weight ratio in the mixture of condensation resin between melamine - and phenolformaldehyde resin of 3:1 and this is applied to wood fibers using nozzles 4a to 4c.

Despite this change in the process, almost identical values can be achieved, for example with regard to moisture strength, as in examples 1 and 2, which is again conditioned by the coordinated chemical and physical interaction, and the selected molar ratios in the mixture of condensation resin (copolymerizate) and thereby achieved impregnation and multiple wrapping of wood fibers.

Business application

Semi-finished products made of wood fibers according to the invention have stable dimensions even in changing climatic conditions, which can be connected with the interaction between the wood fibers and the adhesive in the form of condensation resin mixtures (copolymerizate). Compact panels produced from these semi-finished products are used for interior and exterior construction.

These panels can be coated with decorative papers, which can be dispensed with in the technical field, without negatively changing the properties mentioned above.

Furthermore, it is also possible to reshape compact wood fiber panels in a known manner.

In conclusion, one example of the invention can be described as follows:

The invention relates to semi-finished products made of wood fibers consisting mainly of pressed wood fibers, which were made with hot-cured condensation resins. The degree of adhesion of wood fibers is 30 to 60% of solid resin in the form of mixtures of condensation resins or mixtures of condensation resins (copolymers) in relation to 100% atro-fibers, where the proportion of solid resin in melamine-formaldehyde resin as condensation resin is a maximum of 45 % compared to atro-wood, and that the proportion of solid resin in phenol-formaldehyde resin as a further condensation resin is less than 15% compared to atro-wood. Semi-finished products made of wood fibers according to the invention have stable dimensions even under variable climatic conditions, which can be connected to the coordinated chemical and physical interaction between wood fibers and the adhesive in the form of condensation resin mixtures or condensation resin mixtures (copolymers). Compact panels produced from these semi-finished products are used for interior and exterior construction.

Claims (7)

1. A semi-finished product made of wood fibers, which contains pressed wood fibers, which were made with hot-cured condensation resins, characterized by the fact that the degree of adhesion of wood fibers is 30 to 60% of hard resin in the form of mixtures of condensation resins or mixtures of condensation resins (copolymers) in the ratio of atro - wood fibers, and that the proportion of solid resins in melamine-formaldehyde resin as a condensation resin amounts to a maximum of 45%, considering atro-wood fibers, and the proportion of solid resins in phenol-form 2. aldehyde resin as a further condensation resin less than 15% in relation to atro-wood fibers, and that these wood fibers are made with hot-hardened melamine-formaldehyde resins, additionally made with a layer of wax. 3. A semi-finished product made of wood fibers, according to claim 1, characterized in that the average length of the wood fibers is in the range of 1.0 to 1.4 mm, and that the average diameter of the wood fibers is 0.02 mm. 4. Semi-finished wood fiber product, according to claim 1 or 2, characterized in that the density of the semi-finished wood fiber product is in the range of 800 to 1000 kg/m3. 5. The process for the production of semi-finished products from wood fibers, in which the raw material is subjected to a process for breaking it down into individual fibers, then it is pasted with condensation resins in the exhaust water, and the thus obtained pasted fibrous material, after drying to the required residual moisture, is distributed into strips for scraping and under pressure and at a certain temperature, it is pressed into semi-finished products, indicated by the fact that the wood fibers inside the exhaust pipe are coated with 30-60% of solid resin in the form of mixtures of condensation resins or mixtures of condensation resins (copolymers) in relation to atro-wood fibers, and that the condensation the resins inside the exhaust line are distributed on the wood fibers in such a way that the proportion of solid resin in the melamine-formaldehyde resin as a condensation resin amounts to a maximum of 45%, and the proportion of solid resins in the phenol-formaldehyde resin as a further condensation resin is less than 15% compared to atro- wood fibers, and that in the exhaust water on wood fibers, pasted with melanin-i f with enol-formaldehyde resins, wax emulsion is additionally applied. 6. The method according to claim 4, characterized in that the deposition of melanin-and phenol-formaldehyde resins in the exhaust water is carried out in the form of a mixture or one after the other as individual components or in the form of mixed condensation resins (copolymers). 7. Compact boards made of wood fibers with a layer of decor paper applied on one or both sides, characterized by the fact that the compact board made of wood fibers contains at least one semi-finished product made of wood fibers according to one of claims 1 to 3, and that the condensation resins, on the glued wood fibers by pressing with at least one layer of decor paper at elevated pressure and temperature, passed from the B-state to the C-state.