Method for producing particles for the manufacture of a material board, and material board

Abstract

The invention relates to a method for producing particles for the manufacture of material boards, wherein the particles are fibres or contain fibres, and wherein the particles are created from vegetable starting products in a treatment process which comprises at least a thermal process step for breaking down the starting products. A material mixture of at least two different plant types is used as starting products, and the different starting products of the material mixture are broken down in a common treatment process which comprises at least the thermal process step, wherein the starting products of the different plant types are selected and / or are pretreated such that in the common treatment process, particles with homogeneous properties are created.

Description

[0001] Method for producing particles for the production of a material plate and material plate

[0002] Description:

[0003] The invention relates to a method for producing particles for the production of material plates, wherein the particles are fibers or contain fibers and wherein the particles are produced from plant starting products in a treatment process which comprises at least one thermal process step for digesting (or softening) the starting products, e.g. in a cooker.

[0004] Furthermore, the invention relates to a method for producing a material plate with such particles or from such particles, wherein a mat is produced from the particles produced in this way, which are preferably provided with a binder or are mixed with a binder, and wherein the material plate is produced from the mat using pressure and / or heat, e.g., in a press. Finally, the invention relates to a material plate.

[0005] The particles that form the basis for the production of such a material board are preferably plant particles, in particular lignin-containing particles that are obtained from annual plants (e.g. straw or grasses) or preferably from perennial plants (in particular wood). The particles are preferably fibers, in particular plant fibers, e.g. wood fibers. Alternatively, they are particles that contain a large number of fibers, e.g. chips, preferably wood chips. A material board that is made from fibers, e.g. wood fibers, is also referred to as a fiberboard, e.g. wood fiberboard, which can be an MDF board (Medium Density Fibers), for example. If the board is made from chips, it is referred to as particle board. In principle, the use of long chips or strands is also possible, namely as OSB board (Oriented Strand Board).

[0006] A mat is created from the (lignin-containing) particles, for example, scattered as a grit mat or applied in a slurry-like manner. The mat is then pressed into the board, for example, in a press using pressure and, if necessary, heat. Production can be continuous or intermittent. In the case of continuous production, a continuously operating press is generally used, e.g., in the form of a double-belt press. For intermittent production, intermittent presses are used, e.g., single-opening presses or multi-opening presses.

[0007] The starting products, e.g., wood chips, are produced by chopping the raw material, e.g., tree trunks. In the case of fiber production, the starting products, e.g., wood chips, are subsequently broken down in a thermal process step or a hydrothermal process step, e.g., by cooking in a digester. To obtain the fibers that form the particles, they can then be defibrated in a so-called refiner, in which the previously softened or broken down wood chips are mechanically defibrated. The digester-refiner unit is also referred to in practice as a refiner plant.

[0008] Material boards, and in particular wood-based boards, and their production have long been known in a wide variety of forms and are of great practical and economic importance. The mechanical properties of the material board that are relevant to the user, such as stiffness, flexural strength or flexural elasticity, are largely determined by the selection and production of the fibers and their properties, as well as by their local arrangement within the material board in question. The selection of the plant varieties used to produce the particles, along with the type of gluing, also plays a decisive role. Material boards are often made up of multiple layers, e.g., outer cover layers and one or more inner middle layers, with different particle types, particle sizes, orientations, etc. being used for the individual layers if necessary.

[0009] In order to best meet the requirements of a material board and, for example, individual layers of a material board, but also for cost reasons or to ensure consistent raw material availability, material boards are often produced using fibers originating from different plant types and varieties. A disadvantage is that the source plants can have different processing requirements depending on their degree of relatedness.

[0010] Since the production of material boards is often tied, at least in part, to the structure of continuous manufacturing processes for cost reasons, and interrupting continuous industrial processes is always associated with high costs, it is accepted in practice that during the production of particles from different plant species, at least some of the particles do not fully develop the properties desired for material board production. This leads to the particles being incorporated into the actual production process of the material board in at least an incomplete quality. Material boards and methods for their production are known, for example, from DE 10 2019 121 476 A1 and DE 10 2019 121 471 A1.

[0011] DE 10 2017 120 033 A1 describes the production of fibers from plant material for panel production. Straw, for example, is provided as the starting material. After preliminary shredding in a straw chopper, for example, it is shredded in a first shredding device, such as a hammer mill. After a classifying process, a second shredding step can take place in a fiberizing device, also known as a refiner system. This device comprises a digester on the one hand and a refiner on the other. The particles are softened and broken down in the digester using steam pressure and are then mechanically ground in the refiner.

[0012] A process and plant for processing wood for the production of MDF boards is also described in DE 10 2010 034 763 B3. There, too, wood chips are first produced, which are then transported to a bunker and pre-cooked using superheated steam. From the bunker, the wood chips are conveyed to a digester via a screw conveyor. In the digester, the wood chips are then digested using superheated steam. The digested wood chips are then shredded into wood fibers in a refiner.

[0013] Alternatively, EP 3059 056 A1 discloses a process for producing wood fibers or wood fiber boards, in which wood is chopped into wood chips and then the wood chips are hydrothermally pretreated with steam in a pre-steaming vessel at a temperature of 100 °C to 180 °C and a pressure of 1 to 10 bar. The pre-treated wood chips are then ground into fine wood particles in a refiner in the presence of steam at a temperature of 150 °C to 200 °C and a pressure of 4.5 to 16 bar. The fibers obtained in this way can be glued and dried and are then available for the production of the board by pressing. In this process, the grinding of the pre-treated wood chips into wood particles, e.g. fibers, is carried out in the presence of one or more surfactants.

[0014] Furthermore, DE 10 2021 100 288 A1 describes a method for producing a dimensionally stable object from renewable biomass, wherein the object is in particular a container. Renewable biomass is provided, comminuted, and mixed with water. This is followed by a pretreatment to convert the biomass into fiber. This is followed by a shaping process that includes thermal treatment. The raw materials of the renewable biomass are selected from at least one or a combination of long-fiber lignocellulose-containing plants, in particular grasses, cereals, straw, bast, leaf, seed and seed pod fibers and / or wood, particularly preferably from miscanthus, hemp, straw, oat husk, flax, sisal, and / or bamboo.

[0015] Furthermore, EP 2 142 348 B1 discloses a process for producing bleached cellulose-containing particles, wherein cellulose-containing raw materials are ground in a refiner to form cellulose-containing particles, with a bleaching agent composition being added. Pretreatment in a digester may be provided. Wood, bagasse, or straw can be used as raw materials for the cellulose-containing particles.

[0016] Another method for producing a material plate is described in DE 10 2021 001 806 B3. Based on the prior art, the object of the invention is to provide a method by which high-quality material plates or particles for the production of such material plates can be produced in an economical manner.

[0017] This object is achieved according to the invention by a method for producing particles having the features of patent claim 1 and by a method for producing a material plate having the features of claim 12. In a generic method of the type described at the outset, it is provided that a material mixture of at least two different plant types is used as starting products and that the various starting products of the material mixture are digested in a common treatment process which comprises at least the thermal process step, wherein the starting products of the various plant types are selected and / or pretreated (before the common treatment process) in such a way that particles with homogeneous properties are produced in the common treatment process.

[0018] The thermal process step may, in particular, be a thermal or hydrothermal treatment in a digester. In this case, the starting products of the various plant types are selected and / or pretreated in such a way that they are digested in the thermal process step in a (common) digester, preferably with identical cooking times.

[0019] The invention is based on the finding that, particularly from an economic point of view, it is advantageous to use plant-based starting materials from different plant types, which form the basis for producing the particles (e.g., fibers). Within the scope of the invention, the term "plant type" is to be understood generally, meaning, in principle, different plant types, such as annual plants on the one hand, or perennial plants on the other. However, it is also understood in a narrower sense, for example, by using wood from different tree species, e.g., conifers on the one hand, and deciduous trees on the other, or even different coniferous or deciduous trees.

[0020] The invention has recognized that material plates with high quality and in particular good mechanical properties can be produced economically even on the basis of different starting products or on the basis of starting products from different plant types and that in particular a common or uniform thermal treatment of the various starting products, e.g. in a digester or a refiner plant, is possible if a suitable selection and / or particularly preferably a suitable pretreatment of the different starting products or particles takes place beforehand.

[0021] For example, it is possible to pretreat different starting products—e.g., starting products from a first plant type on the one hand and a second plant type on the other—in different ways before the thermal processing step, or to pretreat only one of the starting products (or one plant type) and not the other (or the other). By carefully selecting individual or multiple pretreatment steps, the starting products can be homogenized for the subsequent thermal processing step, particularly for cooking and subsequently breaking down the products into fibers.

[0022] For example, if two different types of wood are used, one of which would actually need to be cooked for a longer time to open up the fibers, and for this reason, parallel processes would have to be carried out, for example, in two different cookers, the invention proposes, for example, pretreating the wood intended for the longer cooking time in a suitable manner so that both types of wood can then be thermally treated in the same cooker. This makes it possible, for example, to pretreat two different types of wood or even other plant types in different ways during pretreatment, e.g., by pre-shredding, in order to subsequently obtain fibers with homogeneous properties in a single thermal treatment step.Depending on the type of raw materials used, this can also be achieved by pretreating only one of the raw materials, while pretreatment is not required for the other raw material.

[0023] In principle, it is possible to pretreat one or both starting products or several starting products mechanically, e.g. to crush them mechanically and preferably to crush them mechanically in different ways.

[0024] In a further embodiment, however, it is also possible to pre-shred one of the starting products or a starting product of a plant type prior to the thermal process step not mechanically, but contactlessly, in particular using pressure shock waves. The comminution of material and also of wood materials by pressure shock waves is generally known from the prior art (cf. DE 10 2021 001 806 B3). This is a contactless or non-mechanical comminution process in which shock waves are generated within the material and lead to comminution of the material without mechanical influences. A suitable device is marketed by the applicant, for example, under the name "EcoPulser," and this technology can be used within the scope of the invention. It is interesting to note that comminution by means of shock waves can be used, for example, for one of the wood species used, e.g.when a particularly hard and therefore potentially expensive type of wood is used, which usually has to be shredded to balance the cooking properties. In particular, it must achieve a higher degree of shredding than, for example, a softer type of wood, such as a coniferous wood. If mechanical shredding is chosen in this case, this can destroy the fiber chains, which can then no longer contribute, or no longer fully contribute, to the stability of the board. If shredding using shock waves is used instead, macroscopic shredding takes place and thus balances the cooking properties without destroying the fiber chains. This leads to the separation of fiber and matrix, so that the matrix is ​​completely preserved. It is interesting to note that shredding using shock waves, for example,can only be used for one of the wood species used, while mechanical shredding is used for the other wood species, or (further) shredding is omitted entirely. Nevertheless, the starting products pretreated in this way are subsequently fed to the same thermal process step, i.e., the thermal treatment takes place in the same plant or in the same facility.

[0025] Part of the plant, e.g. in the same digester and the same refiner, preferably with identical treatment times.

[0026] Comminution by means of pressure shock waves can be considered not only for one plant type, but also for several or all plant types in order to fully achieve the advantages of processing with pressure shock waves. The product prepared by pressure shock waves leads to economic and qualitative advantages in fiber production. The product, i.e. the starting product, usually consists, among other things, of bundles of arranged cellulose fibers / hemicellulose fibers that are embedded in a matrix of lignin molecules. The lignin serves mainly as a support material and is essentially responsible for the compressive strength of the fabric in the bundle. In contrast, the embedded cellulose fibers / hemicellulose fibers ensure the tensile strength and flexural strength of the fabric in the bundle. In order to utilize the properties of these fibers in the wood products industry, the lignin matrix must be dissolved as far as possible and the cellulose or hemicellulose fibers must be removed.Hemicellulose must be exposed accordingly. This can be achieved, among other things, through a thermomechanical process in a refiner or pressure refiner. The pulping of the product in the pressure refiner occurs through plasticization of the lignin and the mechanical extraction of the cellulose fibers / hemicellulose fibers from the product using grinding discs. The quality / properties / consistency of the resulting fiber depends on many factors, which are influenced almost exclusively by the product fed into the pressure refiner. The prior process-technical impact on the product in the form of homogenization using pressure shock waves leads to a reduced influence on the thermomechanical process (in the pressure refiner). Consistent process parameters in the pressure refiner, in turn, lead to more economical fiber production and consistent fiber composition.

[0027] In the shredder, which operates with pressure shock waves, pressure shock waves are generated to break up, i.e., disintegrate, the fiber structure. At the same time, organic and inorganic substances are dissolved. The pressure shock waves cause the fiber agglomerate to break up and open, preferably in the longitudinal direction of the fiber. The bond between, among other things, the cellulose, hemicellulose, and the lignin, which serves as structural reinforcement, is weakened. The breakup of the fiber agglomerates leads to better permeability of the product in the pre-cooker, which results in faster heating / through heating and an increase in moisture content of the product before it is fed into the cooker through the screw conveyor. This results in advantages such as:faster and more even heating, faster and more even heating through, faster and more even temperature increase, more even wetting and moistening, lower moisture fluctuations, shorter residence time, higher throughput, more even process, etc. The product from the pre-cooker prepared in this way leads to further advantages in the pressure area of ​​the refiner or after passing through the grinding discs, e.g. more even fiber quality, better fiber quality, better fiber fibrillation, higher long fiber content, shorter cooking time, reduced risk of overcooking, higher throughput, lower grinding energy, gentle mechanical dissolution of the fiber composite, fewer fiber splinters, fewer fines, lower proportions of inorganic foreign bodies, lower proportions of organic foreign bodies (e.g. bark, bark or the like).A particular advantage is the equalization of the cooking time of different crop species (e.g. hardwood, softwood, bamboo, annual plants such as rice straw, hemp, bagasse, oil palm, etc.) with different proportions of organic or inorganic substances.

[0028] The frequencies resulting from the pressure shock waves break down the inorganic substances or their crystalline structures, leading to the dissolution of organic substances. These substances can optionally be separated from the processed material in a cleaning process (sieving, sifting, washing, etc.). This leads to advantages such as purer fiber quality, improved fiber properties, more homogeneous fiber production, lower grinding energy, gentler mechanical disintegration of the fiber composite, fewer fines, less binding agents, lower levels of inorganic foreign matter, lower levels of organic foreign matter, less wear on the grinding discs, less wear on downstream processing machines and tools, and improved product processability.

[0029] The starting materials used in the invention are, in particular, wood chips obtained from raw materials such as tree trunks, e.g., by mechanical comminution. The starting materials are then broken down and, in particular, shredded in the manner described.

[0030] Particularly advantageously, in addition to or as an alternative to raw material obtained from tree trunks or small-sized wood and / or annual plants such as grasses, in particular straw, starting material obtained from at least partially pre-formed material panels is also used for the present process. It is conceivable that the at least partially pre-formed material panel already contains two different plant types, and that at least two differently formed material panels are used as raw material suppliers, the components of which are differently formed and which together comprise at least two different plant types. It is also conceivable that one plant type is obtained from a fresh material, i.e. a tree trunk,

[0031] Small wood or in particular stalks from annual plants, such as grasses, in particular straw, while the other plant type is obtained from a recycled material in the form of an at least partially pre-formed material plate or a hand- or machine-formed plant part, in particular a tree trunk.

[0032] Such a design of the process can contribute to a particularly ecological production of a material board, as it makes an important contribution to enabling the inexpensive production of a high-quality material board that can use the qualities of individual plant types in a targeted and coordinated manner to achieve predetermined goals, without requiring various energy-consuming and costly cooking processes. In addition, by using recycled material, important resources can be conserved and, in densely populated areas of the world, energy-intensive transport costs can be reduced.

[0033] For pulping or defibration, generally known processes and equipment can be used. For example, the starting materials are preferably digested in a digester, e.g., with steam at a predetermined temperature. This can be followed by comminution, e.g.

[0034] Subsequent defibration in a refiner. The combination of digester and refiner is also referred to in practice as a refiner system. This can be a pressure refiner system. The subject matter of the invention is not only the described manufacturing process, but also the material board produced using such a process. The product of the process is therefore also protected. The invention is explained in more detail below with reference to a drawing, which represents only one exemplary embodiment.

[0035] The single figure shows a schematic and highly simplified system with which particles for the production of a material plate are produced in the manner according to the invention.

[0036] In the simplified representation of the plant, feedstocks from different plant types are provided in separate bunkers 1a and 1b, respectively. For example, wood chips from a first plant type are stored in a first bunker 1a, and wood chips from a second plant type are stored in a second bunker 1b. These can, for example, be wood chips from different wood species.

[0037] The wood chips are broken down and fiberized in a refiner 2, i.e., the wood chips are converted into fibers for board production. For this purpose, the refiner 2 contains a digester 3 and a refiner 4.

[0038] In digester 3, the wood chips are thermally or hydrothermally treated, e.g., using superheated steam at high pressure and high temperature. The wood chips thus digested are then shredded in refiner 4, e.g., by mechanical comminution.

[0039] The wood fibers obtained in the refiner 4, which are in a wet state, are then dried in a dryer 5 and then optionally provided with a binder in a gluing device 6 or mixed with a binder. The glued fibers can finally be stored in another bunker 7 and are thus available for the production of a mat for the manufacture of a material board. The production of the mat and the manufacture of the material board itself, which takes place, for example, in a press, are not shown in Fig. 1. Conventional manufacturing processes and systems are used for this.

[0040] It is particularly important that the starting products from the two different plant types are processed in the same refiner plant 2, even though fundamentally different thermal conditions, e.g. different cooking times or different temperatures and / or pressures, would be appropriate for the different plant types. In order to balance the properties and to be able to carry out the thermal treatment in the same plant and the same process, a selective pretreatment is carried out according to the invention. This is illustrated in the figure by the fact that a pretreatment device 8 is provided for only one of the plant types, e.g. mechanical pre-shredding or pre-shredding by means of pressure shock waves. In this way, the starting products are homogenized, which enables thermal treatment in the same thermal process step and in the same plant.Alternatively, a pre-treatment, e.g. pre-shredding, can be provided for both plant types, so that each plant type then undergoes its own pre-treatment, through which homogenization can be achieved.

Claims

Patent claims: 1 . A method for producing particles for the production of material panels, wherein the particles are fibers or contain fibers and wherein the particles are produced from plant starting products in a treatment process which comprises at least one thermal process step for digesting the starting products, characterized in that a material mixture of at least two different plant types is used as starting products and that the different starting products of the material mixture are digested in a common treatment process which comprises at least the thermal process step, wherein the starting products of the different plant types are selected and / or pretreated in such a way that particles with homogeneous properties are produced in the common treatment process.

2. Method according to claim 1, characterized in that the starting products of the different plant types are pretreated separately and differently before the common thermal process step or that only the starting products of one plant type are pretreated.

3. Method according to claim 1 or 2, characterized in that the starting products of at least one plant type are mechanically pre-shredded before the thermal process step.

4. Method according to one of claims 1 to 3, characterized in that the starting products of at least one plant type are pre-comminuted without contact, in particular with pressure shock waves, before the thermal process step.

5. A method according to any one of claims 1 to 4, characterized in that wood chips are used as starting products, which are obtained, for example, from raw material, e.g. tree trunks, by mechanical comminution.

6. Process according to one of claims 1 to 5, characterized in that the starting products are digested in the thermal process step in a cooker, e.g. with steam at a predetermined temperature.

7. The method according to any one of claims 1 to 6, characterized in that the particles broken down or softened in the thermal process step are subsequently reduced to particles in a refiner, e.g. shredded into fibers.

8. A process according to any one of claims 1 to 7, characterized in that wood from different tree species is used as starting products.

9. A process according to any one of claims 1 to 7, characterized in that starting materials from annual plants, e.g., straw, and perennial plants, e.g., wood, are used.

10. A process according to any one of claims 1 to 9, characterized in that starting materials from different plant types are used, whose lignin content is the same or very similar.

11. A method according to any one of claims 1 to 10, characterized in that the starting products of the various plant types are selected and / or pretreated in such a way that they are digested in the thermal process step in a cooker with an identical cooking time.

12. A method for producing a material plate, wherein particles are produced by a method according to one of claims 1 to 11 and wherein a mat is produced from these particles and wherein the material plate is produced from the mat by applying pressure and / or heat, e.g. in a press.

13. The method according to claim 12, characterized in that the particles are provided with a binder or are mixed with a binder and the mat is produced from these particles.

14. A material plate produced by a process according to claim 12 or 13.

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