EP2078599A1 - Chipboard and method for producing same - Google Patents

Abstract

Production of board from cellulose-containing particles comprises mechanically cutting chips from cellulose-containing material in a first step, drying the chips, and mechanically cutting the chips at least partly into micro-chips which are glued and used to produce micro-chip board. The chipboard is produced at least partly from the micro-chip material by pressing and heating. An independent claim is also included for a board made of cellulose-containing material. Preferred Features: The board is completely made of the micro-chip material. A middle layer is made of chipboard material and the two outer layers of microchip material.

Description

The present invention relates to a method for producing a plate at least partially from micro-chip material and to a plate which has been produced by the method.

The production of conventional chipboard is known. From wood chips are produced by a cutting of solid wood or wood waste, such as wood chips, from the sawing industry. The cutting takes place in the state of the initial moisture of the wood, which depending on the origin of the wood and the season can be between 60 and 150% based on the wood dry mass. Subsequently, the wood chips are dried to a moisture content between 1.5 and 3% and fractionated by screening for top layer and middle layer material, for which Table 1 shows by way of example a sieve fractionation. Table 1 shows the diameters of the chips, the values of the table being understood to mean that, for example, for covering layer material, 95.8 mass% of the material to be screened passes through a sieve with a mesh size of 2.0 mm or 8.4 mass% through the screen mesh area from 1.4 to 2.0 mm.

The term diameter is to be understood in the indication of a sieve fraction that the diameter in each case indicates the smallest diameter in a cross section in any direction of the particle or chip. Because in a screening, the particles to be sieved are moved so that too elongated particles are erected and come along the longitudinal extent through the sieve.

In Table 1 it can be seen clearly that the maximum of the distribution of the diameter of the chips for the cover layer in the range 0.4 mm to 1.0 mm, while for the middle layer, the maximum is in the range 2.0 to 4.0 mm , It is therefore possible to clearly differentiate the composition of the two different layers from the dimensions of the chips.

Before the mats are formed, the shavings are mixed separately into cover layers and middle layer in mixers with binder, hardener, wax emulsion and optionally additives and fed to the spreading machine, which forms a multi-layered chip cake mirroring the center of the board. The chip cake consisting of lower cover layer, a middle layer and an upper cover layer (three-layer or multilayer boards). But a multi-layered structure can also be completely missing, then one speaks of single-layer plates. By hot pressing, a stable chipboard is pressed under the action of pressure and temperature, by curing the binder, which can meet the requirements of the European standard EN 312-3, shown in Table 2.

The production of fiberboards by the dry process is known. The wood particles, so-called wood chips, are softened by the action of pressure and temperature in a saturated steam atmosphere and then separated in a refiner into fine particles, the fibers. This process is also called defibration.

Since MDF fibers are prone to clumping or felting, screening with screening machines such as chips is not possible to determine the size of the fibers. Therefore, the diameters of MDF fibers were determined by means of a laser particle counter. For this purpose, the sample material was homogeneously mixed with water to form an approximately 2% dispersion and fed to the PQM 1000 measuring device. The measured quantities were the number of fibers, with a certain length and a certain diameter, from which the mass fractions could then be calculated as a function of the fiber diameter. The results are shown in Table 3.

The fibers leave the refiner together with water and steam via a pressure pipeline, the so-called blowpipe - also called blow-line. In this tube there are several leads for supplying binder, hardener, emulsion and other additives.

The fiber-binder mixture thus obtained is transferred to the dryer - usually a tubular electric dryer in which the fibers are dried by the action of convective heat to a final moisture content of 8 to 15%. The result is binder-provided wood fibers from which a fiber cake is subsequently formed. By hot pressing a stable plate (medium-density fiberboard MDF or high-density fiberboard HDF) is pressed under the action of pressure and temperature, by curing the binder. The panels comply with the requirements of European standard EN 622, Part 5, which defines the properties of MDF and whose values are shown in Table 4.

A fiberboard, in contrast to a chipboard, is distinguished by a very homogeneous density distribution over the plate thickness and over a very homogeneous surface. If the direct coating of chipboard makes high demands on the preparation of particle board surface quality, such as. can be achieved by trowelling, so an MDF board can be painted with conventional painting techniques without pretreatment as a chipboard. The reason for this is on the one hand the high isotropy of the MDF surface, which is ensured by the fineness and / or fiberiness of the wood, and on the other hand by the homogeneous suction behavior of the surface.

The manufacturing costs of a fiberboard, however, are significantly greater than those of a chipboard. Both the system costs distinguish them significantly and the required power and heat requirements.

Another disadvantage in the production of fiberboard is that the fibers are not pourable Good and thus are expensive to handle. Thus, for example, the conventional mixers used for particle board production can not be used for gluing the fibers. The fibers are very flexible due to their elongated rod-like shape with small thickness and have the so-called Curleffekt. As a result, juxtaposed fibers entangle and matt easily, which makes pouring or sieving impossible for fractionation.

Moreover, a disadvantage of the fiberboard is that because of the high process temperatures, the color of the fibers and thus of the finished fiberboard is dark. The dark color makes a color coating difficult, for example by painting, when a light color, for example white, is to be achieved as the surface color.

The present invention is therefore based on the technical problem of specifying a method for producing a chipboard and a chipboard itself, wherein the chipboard has properties of an MDF board without the use of expensive MDF manufacturing process.

The aforementioned technical problem is solved according to the invention by a method having the features of claim 1 and by a plate having the features of claim 6. Further advantageous embodiments are specified in the subclaims.

• in einem ersten Schritt wird zellulosehaltiges Material mechanisch zerspant und anschließend werden die Späne getrocknet.
• die Späne werden zumindest teilweise mechanisch mikrozerspant und die Mikrospäne werden beleimt.
• aus dem Mikrospanmaterial wird ein Mikrospankuchen hergestellt.
• durch Anwendung von Druck und Temperatur die Platte zumindest teilweise aus dem Mikrospanmaterial hergestellt wird.

The process according to the invention for producing a plate of cellulosic particles has the following steps:

• In a first step, cellulosic material is machined mechanically and then the chips are dried.
• the chips are at least partially mechanically micro-machined and the micro-chips are glued.
• from the microspan material, a micro chip cake is produced.
• by applying pressure and temperature, the plate is at least partially made of the micro-chip material.

According to the invention, it has thus been recognized that the wood is not defibred in the moist state after thermal digestion as is usual for MDF, but is micro-machined in the dried state. This results in a diameter distribution of the micro-chips, which is in the range of the diameter distribution of the fibers. Thus, with less technical effort essentially the same mechanical properties as in conventional MDF boards can be achieved.

The plate according to the invention consists of a cellulosic material with a proportion of cellulosic chips and a proportion of binders. Microplated material is provided within at least one plate layer, the chips having a proportion of micro-chips with a diameter of less than 1.0 mm, which is at least 75%, in particular at least 80% and preferably at least 90% of the chips.

A further preferred embodiment of the invention even includes a proportion of greater than 95% chips with a diameter of less than 1.0 mm. It is also possible to produce a plate containing over 98% of micro-chips smaller than 1 mm in diameter.

The plate according to the invention thus differs from the prior art, which is larger in the at least one layer, the proportion of micro-chips than conventional chipboard. It generally applies that the properties of the chipboard are better, the greater the proportion of chips under a diameter of less than 1 mm.

In a preferred manner it is provided that in the micro-chip material the chips have a proportion of micro-chips with a diameter of less than 0.6 mm, which is at least 50%, in particular at least 65% and preferably at least 80% or even at least 85% of the chips.

In particular, one can characterize the plate such that in the micro-chip material the chips have a proportion of micro-chips with a diameter of less than 0.4 mm, which is at least 35%, in particular at least 50% and preferably at least 60% of the chips.

In any case, the proportion of small chips, so the micro-chips compared to the prior art is so high that the properties of such micro-chipboard are similar to the properties of MDF boards. The properties of the micro-chipboard are the better, the greater the proportion of smaller micro-chips.

The plate may preferably consist entirely of the microspasm material so that a homogeneous distribution of the micro-chips within the plate results. In contrast, it is also possible that the plate has a middle layer, which consists of a conventional chip material, while the two outer layers consist of the micro-chip material. This ensures that the cheaper material of the chipboard is used in the middle, while the more expensive material of the micro-chips is used at the bottom and the top, in particular to be able to exploit the improved surface properties can. The The inventive method is then designed accordingly, wherein only a part of the plate is made from the micro-chip cake.

For the production of the micro-chip material, wood parts are machined analogously to chipboard production and dried to a residual moisture content of 2-5%, in particular 4-4.5%. Subsequently, the dry fiber is carried out in a fiber mill, which is for example by means of special V-groove strips and baskets in a position to produce fibers from the chips. In order to be able to better illustrate the differences from the conventional fibreboard in the following, the particles produced in the dry fiber are called micro-chips, which can also be derived from the properties of the micro-chips described below.

A first distinguishing feature compared to fibers is that the micro-chips represent a pourable and pourable good. In contrast to the fibers for a production of a fiberboard so the micro-chips can be fractionated by a sieving.

The microspheric mixture obtained in this way has the following exemplary microspan size distribution which has been obtained by sieve analysis with sieves of corresponding mesh size. Table 5 shows the measurement results for the diameter of the micro-chips over several samples. The result is a diameter distribution which is close to the diameter distribution for fibers shown in Table 3. Further measurement results are explained in more detail in the examples discussed below.

The micro-chips are subsequently glued, and due to the nature of the micro-chips, conventional mixers used in the chipboard industry can be used. In contrast to fiber plate technology (blow-line gluing), due to the low processing temperature, no damage to the binder occurs, which is reflected in a lower binder requirement. For the gluing of the microprecipitants, it has proved to be advantageous that a proportion of binder, based on the dry weight of the microprecipitants, of at least 12%, preferably 15-25%, is emphasized. The value of the binder content varies depending on the dust content of the chips, which occurs increasingly in the production of micro chips.

The production of the micro chip cake is done in analogy to chipboard production. Again, no special devices are needed and it can be used on spreaders of the prior art. For pressing the panels, one-floor presses, multi-daylight presses, continuous presses such as conti-roll systems or calendering machines can be used.

Another advantage of the method according to the invention compared to the MDF technology is that a grinding of the micro-chipboard is possible immediately after pressing. After hot pressing, MDF boards are stored for 2 to 5 days in the maturing warehouse before they can be sanded and subsequently processed. This circumstance is detrimental to the production logistics as well as to the manufacturing costs due to the necessity corresponding storage capacities and through the longer capital tie-up in the maturing warehouse.

The mechanical technological properties of the micro-chipboard according to the invention correspond to the requirements for MDF boards by the dry process, as shown in Table 4 of EN 622, Part 5 above. There are no restrictions on the plate thickness. Thus, depending on the pressing process, sheets from 1.0 mm (for example calender presses) to more than 40 mm thick (platen press or conti-roll press) can be produced. Especially with thick slabs, the homogenous density distribution over the slab thickness, comparable with an MDF slab, offers advantages in edge processing. Particle boards with a marked density minimum in the center of the board and the coarse chip structure of the middle layer chips on the other hand do not provide adequate conditions, for example, for direct paintability of the board edges.

Also, cutting three-dimensional relief-like processing of the edges or the surface possible, as is necessary, for example, for imitation of filled door leaves. In the process, relief-like structures are milled into the plate surface, whereby the processing surfaces can be directly painted without the complexity of surface treatment, due to the closed nature of the material, comparable to MDF. Such machining is not possible with chipboard due to the porous center layer without complex pore-filling machining. Another area of use is the use of such plates, in particular with low strength (2.5 to 3.5 mm) as door decks. The advantage here is the good paintability of the surface while still comparatively low plate costs. Also, use as a support plate for laminate floor is possible.

The invention will be explained in more detail below with reference to examples. To show the Fig. 1 and 2 a graphical comparison of the values from Tables 1, 3 and 6, wherein the Fig. 2 a section of the in Fig. 1 represents shown diameter range.

Example:

Chips from the production of thin chipboard by the calender process are mikrozerspant after drying the same by means of a fiber mill. The mill is characterized by special V-slot bar fittings that leave a narrow gap between stator and rotor of the mill. This can affect the Mikrospangeometrie. The microsphering mixture thus obtained shows the sieve fractionation shown in Table 6.

After dry microsizing, the microsphering mix is mixed with 12% (solids to dry weight micro-chips) of a conventional urea-formaldehyde binder. Furthermore, 0.8 percent by weight of hardener based on solid binder based on ammonium sulfate and about 1.2% paraffin emulsion (solid wax based on dry weight micro-chips) are added in the form of a 60% emulsion. The mixture of the individual components with the micro-chips is carried out in a conventional continuous mixer, as it is used for the production of chipboard.

Subsequently, a micro-chip mat is formed using a spreader with wind and throw separation. The microspheric cake thus obtained is then pressed in a calender press under the action of pressure and temperature to form a stable plate having the mechanical technological properties shown in Table 7.

In the Fig. 1 and 2 the diameters are shown in cumulative distributions. One recognizes, on the one hand, the shavings of the conventional chipboard that are shifted to larger diameters, the values for the middle layer and the outer layer are shown. On the other hand, the curves for the micro-chips and the MDF fibers are very close to each other.

Therefore, a chipboard of the invention can be easily distinguished from a conventional chipboard by analyzing the size distribution of the chips.

Although the diameter values for the micro-chips and for the MDF fibers are very close to each other, the micro-chips and the fiber can nevertheless be very well distinguished from each other. Because the fibers have, in contrast to the micro-chips on a much longer form, while the micro-chips have a more cubic or almost cubic shape. Cubic shape means that the dimensions of the micro-chips in length, width and thickness are substantially similar. Incidentally, in contrast to the fiber, the cubic shape makes it possible for the micro-chips to be a free-flowing and pourable material.

In order to distinguish a microplate from an MDF or HDF board, the following test can be performed become. Material of the plate to be examined is treated in an acid bath in order to dissolve the aminoplast resin acting as a binder. Thereafter, the detached material is dried and mechanically sieved. If the material can be sieved, ie if it is sieve-capable, it results from the fact that the plate consists at least partially of micro-chips. If, on the other hand, a coherent, possibly tangling, mass is formed, then it can be assumed that it was a fiberboard.

An essential criterion for the good paintability of the chipboard according to the invention is the limited absorbency of the surface. This is essentially determined by the small size of the chips, by the binder content and the calendar process additionally by the location of the heating drum. The lower the absorbency, the better the paintability.

The absorbency can be quantified by means of the toluene test specified in EN 382-1: 1990 10 01 (Fibreboard, Determination of surface absorption, toluene test). It is applied a defined amount of toluene on the arranged at a certain angle to the horizontal specimens and the distance which the resulting droplets travels until it is completely absorbed by the substrate, then determined as a measure of the absorbency.

The following values show a comparison between the preferably to be coated surface (heating drum side) of a chipboard according to the invention with a conventional chipboard with the above-mentioned cover layer material - each produced in the calendering process. The performed Investigations showed the same pretreatment (1 grind with grain size 100): Micro chipboard conventional chipboard min 290mm 120mm Max 560mm 150mm medium 427mm 131mm

The chipboard according to the invention therefore has a significantly lower absorbency than a conventional chipboard. The chipboard according to the invention can therefore be painted better than a conventional chipboard.

tables:

Table 1: Diameter distribution of the chips for a conventional chipboard, D - mesh width % Figures in weight percent: topcoat middle class D in mm % total % total 10.0 0.0 0.6 100.0 8.0 1.0 100.0 17.0 99.4 4.0 3.2 99.0 40.5 82.4 2.0 8.4 95.8 7.7 41.9 1.4 22.7 87.4 14.1 34.2 1.0 47.9 64.7 16.1 20.1 0.4 9.6 16.8 2.7 4.0 0.2 7.2 7.2 1.3 1.3 0.0 0.0 0.0 0.0 0.0 Table 2: Mechanical material properties of a conventional chipboard Requirement Thickness range (mm, nominal size) properties test methods unit 3 to 4 > 4 to 6 > 6 to 13 > 13 to 20 > 20 to 25 > 25 to 32 > 32 to 40 > 45 flexural strength EN 310 N / mm ² 13 15 14 13 11.5 10 8.5 7 Flexural modulus EN 310 N / mm ² 1800 1950 1800 1600 1500 1350 1200 1050 transverse tensile strength EN 319 N / mm ² 0.45 0.45 0, 40 0.35 0.30 0.25 0.20 0.20 soundness EN 311 N / mm ² 0.8 0.8 0.8 0, 8 0.8 0.8 0.8 0.8 Table 3: Diameter distribution of the fibers for a conventional MDF board, D - mesh width % Figures in weight percent: D in mm % total 1.0 16.9 100.0 0.6 38.9 83.1 0.3 36.9 44.2 0.2 7.3 7.3 0.0 0.0 0.0 Table 4: Mechanical material properties of a conventional MDF board Nominal thickness range (mm) properties test methods Unit 1.8 to 2.5 > 2.5 to 4.0 > 4 to 6 > 6 to 9 > 9 to 12 > 12 to 19 > 19 to 30 > 30 to 45 > 45 Thickness swelling 24 h EN 317 % 45 35 30 17 15 12 10 8th 6 transverse tensile strength EN 319 N / mm ² 0, 65 0, 65 0.65 0, 65 0.60 0.55 0.55 0.50 0.50 flexural strength EN 310 N / mm ² 23 23 23 23 22 20 18 17 15 Flexural modulus EN 310 N / mm ² - - 2700 2700 2500 2200 2100 1900 1700 Table 5: Diameter distribution of the micro-chips for a micro-chip material according to the invention with data on the fluctuation widths over several samples, D - mesh width % Figures in weight percent D in mm Percentages by weight > 1 0 - 0.6 0, 8 - 1.0 1.5 - 2.0 0, 6 - 0.8 7 - 10 0.5 - 0.6 8 - 11 0.4 - 0.5 13 - 17 0.3-0.4 15-19 0.2-0.3 14 - 20 <0.2 25 - 40 Table 6: Diameter distribution of the micro-chips for a micro-chip material according to the invention, D - mesh width % Figures in weight percent D in mm % total 1.4 0.5 100.0 1.0 1.7 99.5 0.8 9.3 97.8 0.6 10.2 88.5 0.5 15.0 78.3 0.4 17.8 63.3 0.3 16.8 45.5 0.2 28.7 28.7 0.0 0.0 0.0 Table 7: Mechanical material properties of an inventive Micro chipboard Thickness: 3,2mm Thickness swelling 24 hours: 25% transverse tensile strength: 0.72 N / mm ² Bending strength: 26.3 N / mm ² Flexural modulus of elasticity: 3,200 N / mm ²

Claims (8)

Plate made of a cellulosic material, with a content of cellulose containing chips and - containing a proportion of binders, microspan material being provided at least within a plate layer, the chips comprising a proportion of glued micro-chips having a diameter of less than 1.0 mm, which is at least 75% by weight, and a proportion of glued micro-chips having a diameter of less than 0 4 mm, which is at least 35% by weight. Plate according to claim 1, characterized in that the plate is made entirely of microspan material. Plate according to claim 1 or 2, characterized in that a middle layer of chipboard material and the two outer layers are made of the micro-chip material. Plate according to one of the preceding claims, characterized in that the gluing of the micro-chips with a binder content based on the dry weight of the micro-chips of at least 12 wt .-% is carried out. Plate according to claim 4, characterized in that the gluing of the micro-chips with a binder content based on the dry weight of the micro-chips of 15 to 25 wt .-% has taken place. Plate according to one of the preceding claims, characterized in that the chips in the plate layer have a proportion of micro-chips with a diameter of less than 1.0 mm, of at least 80% by weight, preferably at least 90% by weight, of the chips is. Plate according to one of the preceding claims, characterized in that the chips in the plate layer have a proportion of micro-chips with a diameter of less than 0.6 mm, which is at least 50 wt .-%, in particular at least 65 wt .-% and preferably at least 80 wt .-%, the chips is. Plate according to one of the preceding claims, characterized in that the chips in the plate layer have a proportion of micro-chips with a diameter of less than 0.4 mm, of at least 50% by weight, preferably at least 60% by weight, of the chips is.

Images