SE513336C2 - MDF fiber board, methods of making the same, and the use of recycled cellulose fibers for the manufacture of such fiber boards - Google Patents

Abstract

Fiberboard comprises cellulose fibers and a bonding agent. The cellulose fibers are recovered from recycled foodstuff packaging cardboard. An Independent claim is also included for production of fiberboards using cellulose fibers recovered from recycled foodstuff packaging cardboard (31), to be mixed with a bonding agent (45). The mixture is pressed into boards, using heat and pressure.

Description

513 336 2 quality, so-called chemical pulp, often with a mixture of CTMP pulp, it is all the more important to find recycling solutions for this particular type of waste. Due to current food regulations and other quality requirements, the use of high quality new fibers in liquid board is highly desirable and even necessary.

It is then considered a great waste of natural resources to have to leave food packaging including liquid cardboard directly for incineration, as is predominantly the case today.

A process based on dry delamination and separation of different materials in composites, has recently been developed by a company based in Switzerland, namely Result Technology AG. Their technology is based on different materials behaving differently under the influence of strong shear and frictional forces, and that these forces exceed the adhesion and the cohesive forces between the different materials in the composite, which are therefore delaminated so that the materials are separated from each other. The shear forces are forced by means of high acceleration and strong, turbulent air currents and thus do not mean that the composite material has to be mechanically ground or pulverized. For papers, this is important because their length and quality can thus be preserved largely unchanged and reused in new high-quality products. The principles of this acceleration and separation technique are described in, among others, the European patent EP-B-751831, the international patent application WO97 / 26994 and the German patent application DE-A-19637550.

With this new technology, the paper fibers can thus be separated from the polymer and metal materials in a simple and rational way. Polymer and metal can be further separated from each other using the same technique in a wider process step to obtain pure metal and pure polymer, which can be recycled or incinerated independently. In order to make this new process technology profitable, however, it is necessary to be able to find sales for the various recycled materials and in a simple and flexible way connect recycling processes to new areas of use worldwide. Liquid cardboard laminates are used in most countries around the world today, and there is a demand for a global recycling solution for these materials today. As the world's population increases, so does the consumption of liquid board, as such packaging containers are today the only way in many countries to transport and distribute food with good sustainability in an economically and environmentally beneficial way, especially in countries with hot climates and generally poor financial resources.

The fibreboard industry, especially in the manufacture of medium density fibreboards, so-called MDF boards with a density from about 600 to about 800 kg / m3, has use for relatively high quality cellulose fibers. (Low-density MDF (approx. 450-600 kg / m3) and thin MDF (approx. 800-1000 kg / m3) are also available). For special production of MDF boards, recycled fibers of the traditional type are unsuitable and cellulosic fibers are obtained primarily from waste from the forestry industry in the form of wood chips, veneer waste and sawdust. These are ground, refined and converted into pulp in a wet and energy-intensive process. The wet pulp must then be dried before it can be used further for the manufacture of fibreboard. The fibrous mass still has a high moisture content when a binder of a curable polymer is added, usually a urea-formaldehyde resin, to achieve even distribution and mixing of the curable polymer resin in fi berm pulp. Then the pulp is further dried and formed into a fi berm mat which is compressed into fibreboard pressure and heat.

The use of fibreboard and in particular MDF board is steadily increasing throughout the world. Its good properties during processing, such as sawing and milling, but also paintability, make the board material especially suitable for the furniture and interior design industry, for example in wood panels, floor coverings, cabinet doors, etc.

World consumption of MDF boards has increased by about 12.7% annually since 1989 and production capacity has increased from about 6 million m3 in 1991 to about 20 million m3 in 1997. With an MDF density of about 750 kg / ms, this corresponds to about 15 million tonnes, which should be compared with the total production of beverage cartons amounting to about 3 million tonnes. The market for such fibreboard materials is thus very expansive and the demand for cellulose fibers of relatively high quality will therefore also increase sharply in the future.

The fibreboard industry has for a long time been confronted with and solved major environmental problems in connection with binder formulation and glue pressing of boards of different qualities. The use of formaldehyde has been optimized and environmental approval has been obtained in accordance with the German 'Ef' standard, while maintaining the quality properties of the fibreboards. In fiber and MDF board production, it is very important that the fiber material is as homogeneous as possible throughout the board. This also presupposes an even quality of the fibers and a homogeneous mixture of fibers with binder.

Fiberboard already plays a major role in terms of the environment and resources, as it takes advantage of and refines waste from the wood and furniture industry by transforming it into valuable fiber panels and so-called chipboard. However, it is highly desirable for the disc and MDF industry to be able to further improve its reputation and image in terms of health and environmental impact. Efforts have been made to develop processes for the use of used fis, so-called "urban esbres", but so far it has not been possible to use recycled fibers as a raw material for MDF fibreboards.MDF-513 336 4 U.S. Patent No. 4,072,273 describes a conventional recycling process that results in shorts of too poor quality for MDF manufacturing, a mechanically violent process that destroys the servers ("servers cutting", "abrading", "trashing", "scrubbing", "scraping" etc.) and is adapted for recycling of waste materials containing gravel, pebbles, glass, hard plastic and other. The recycling process is wet, ie the fibers are separated from each other by the addition of water.

There is thus a need to be able to utilize the above-described new simple and rational recycling process in combination with new markets and partners for the use of recycled cardboard as well as other materials included in cardboard laminate, while there is a need to be able to further increase profitability and capacity and raise the environmental profile of the disc industry.

Since erskboard boards have traditionally been made from wood chips and shavings as starting material, a wet pulp process has been linked to board production.

The starting material has had a high moisture content, which has determined the conditions for, and facilitated, the addition and mixing of binder resin before pressing.

An object of the present invention is therefore to provide a cost-effective, environmentally friendly and resource-efficient MDF-type high-quality disc.

Another object of the invention is to provide a new process for the manufacture of fibreboards and MDF-type wood boards. Yet another object of the invention is to provide a new integrated, cost-effective, environmentally friendly, resource-efficient and rational process that connects the recycling of liquid board by acceleration and turbulent air currents according to the Result® technology with the production of high-quality MDF-type fiber boards.

A further object of the invention is to provide a new use for liquid board cartons, recycled using the new dry delamination and separation technology by means of acceleration and turbulent air currents.

These objects are achieved with a fibreboard having the characteristic stated in the characterizing part of claim 1 and by means of the method specified in the characterizing part of claim 8. Variations and preferred embodiments of the bearing disc and the method according to the invention appear from subclaims 2-7 and 9-18, respectively.

According to another aspect of the invention, there is further provided a new use of liquid board cartons for fiberboard according to claim 19. In another aspect of the invention further provided a new use of liquid board fibers for fiberboard according to claim 19.

The above-mentioned new recycling technology from "Result Technology AG" in Switzerland, is thus based on delamination of fibrous layers from other composite / laminate layers and separation of cellulose fibers from the other materials included in the composite by means of a dry, mechanical process, which does not mean that the materials are ground broken into too small particles that are difficult to separate. By high-speed rotation of the composite material, a bimodal distribution of materials with different particle sizes is obtained. When laminated materials are subjected to acceleration and strong, turbulent air currents (air vortices), the different materials react in different ways and assume different morphology after the accelerator treatment. Because the shear forces of the different materials in different directions delaminate them from each other. Fibers separate from each other and adjacent layers. Plastic layers tend to stretch and pull out into flakes while metal layers instead contract and assume a globular shape. Due to the different geometry and density of the separated materials, they can then be easily separated from each other by means of different screening and air separation methods.

The composite material may be dry as well as relatively moist at the starting point of the delamination process, for example having a moisture content of about%. The material is cut in a first step by means of a rotating cutting knife or the like, into small pieces of the order of 50 x 50 mm, or less. The small pieces are then fed into an acceleration unit, ie a centrifuge, vertically mounted rotor or the like. The acceleration unit usually comprises different devices and functions in order to be able to adjust and develop different acceleration levels. The high-speed rotation produces strongly turbulent currents and high acceleration at the edge of the device. The strong forces of the swirling air currents delaminate the different layers from each other in the interfaces and then deform the structure of the different components to different geometric shapes and dimensions. Important parameters for regulating the acceleration process are how the material has been pre-treated and cut, rotational speeds, pressure conditions, air fate as well as dimensioning of the accelerator and associated equipment. the settings for the delamination process must be adapted to each individual material and each individual composite composition, due to the different properties and dimensions (thickness, etc.) of the materials included in the composite. It has thus been found that a special choice of the different parameters for separation of fibrous layers from other laminate layers of plastic, possibly in combination with metal foil, differs from the parameters relevant for separation and partial annealing of these plastic layers from each other coh 513 336 6 from the possible metal layers. Fiber bonds can dissolve very gently, separating the fibers from each other and from adjacent layers, leaving the accelerator as a dry, fluffy fibrous material. In a later step under acceleration conditions, the remaining plastic layers are separated from any metal layers.

Separation of the different materials from each other usually takes place first and foremost by means of sieving methods and / or combinations of sieving and electrostatic separation methods. Separation in fluidized beds is also a possible alternative or complement to screening. Delaminated liquid board laminate can advantageously be divided into its constituents by sieving fibers and other materials, and in a later stage by sieving in combination with electrostatic charging of polymer against metal.

Fiberboard manufacturing processes are well known to those skilled in the art.

For example, processes for the manufacture of MDF fiberboard have been developed by both Sund's defibrator and by Kvaerner. These are based on the same type of process and comprise substantially the same process steps and for further description of this prior art reference is made to an example of an MDF manufacturing process as described in Figure 1.

The said binder in the form of a curable polymer is preferably a urea-formaldehyde resin of known type with E1 approval, ie an approved low content of formaldehyde, in particular for the manufacture of MDF boards. It is generally believed that urea-formaldehyde cures by crosslinking, but other physical forms of bonding in the material have also been discussed. The binder can also be based on phenol-formaldehyde resin for the production of harder hardwood sheets or on melamine-formaldehyde resin, or for certain uses, on isocyanate-containing prepolymers, for example of the PMD1 type (including methylene diisocyanate) to completely avoid formaldehyde content. Due to the heated debates of the last decade about the health effects of formaldehyde in home and interior design environments, the latter or other types of formaldehyde-free binders are sometimes preferred.

The invention will now be described in more detail with reference to the accompanying drawings in which Figure 1 schematically shows examples of a process for manufacturing fibreboards, in particular MDF boards according to the prior art, Figure 2 schematically shows an example of a fiberboard according to the invention, Figure 3 schematically shows a preferred method according to the invention. Although the invention is described in more detail with reference to particular embodiments shown in the drawings, it will be apparent to those skilled in the art that various modifications and variations may be made without departing from the spirit of the invention as defined in the appended claims.

Figure 1 thus schematically shows a traditional way of manufacturing fiboard boards, in particular MDF boards with the general designation 10.

Wood is fed into a wood chip or a so-called "chip" 11. Alternatively, finished wood chips and shavings, which have been obtained from sawmills and other wood industries, are used. Chips and chips are sieved in a sieve 12 to reduce the amount of contaminants, such as pebbles, nails and other objects, in the chips. The screened chips are fed to a chip washer 13 in which residual contaminants are washed away, such as gravel, etc. A chip washer facilitates subsequent process steps and prevents the chips from wearing on the equipment in the next operation where the chips are defibrated. De-curing 14 takes place by first steaming the chips up to a temperature of about 80 ° C to soften the chips and to facilitate later extraction of, for example, raisin resin. The chips are then broken down into fibers by means of a feed screw and a subsequent pressurized rafter. The released fibers are dried in a dryer 15 and passed to a berry silo 16. Before use for pressing berry sheets, the fibers are fed through a berry spreader 17 (so-called "fiber sieves") where they are mixed with polymeric resin binder. still a relatively high moisture ratio which may be maintained by the supply of hot steam, which may facilitate mixing of fibers and polymer resin.The resin-mixed fibers are then fed to a mat former 18 for preparation for pressing, after which the obtained mat is pre-pressed into a pre-press 19 under lighter pressure and weaker heat to evaporate some of the moisture contained in the bers, divert air contained in the mat and heat the berm mat.

As a result, higher capacity is obtained in the subsequent continuous press. In the next step, the pre-pressed mat is thus fed through a continuous press 20 and after pressing is sawn up into discs of suitable size in a sawing station 21. The sawn fiber discs are passed on to a cooling device 22 to cool the press-hot discs without they cool or change dimension due to uncontrolled cooling. The cooled fibreboards are stored temporarily or for a longer period of time at 23 and are polished before delivery in a polishing station 24 and cut to the desired size in a cutting station 25, to obtain ready-to-deliver disc product 26 .

In general, MDF and other board production is relatively energy intensive and various systems and devices for recovering heat energy are included in the process.

Figure 2 schematically shows a homogeneous carrier board with the designation 2a according to the invention, in particular a medium density carrier board (MDF). It shows how fibers 2b of uniform quality and length distribution occur in homogeneous mixture with the bonding resin 2c of a cured polymer without the presence of so-called resin stains due to accumulations of the polymer in the fibreboard.

Figure 3 schematically shows a preferred method of manufacturing fibreboard, in particular MDF board, according to the invention, with the general designation 30. collected cardboard waste from emptied food packages 31 comprising laminate layers of cardboard and for example of polyethylene and aluminum, fed into a cutting device 32 to small pieces of even size, for example from about x 20 mm to about 60 x 60 mm in size. The device may consist of one or more rotating knives which quickly and efficiently cut the fed packaging containers. The shredded packaging laminate pieces are passed on to a first accelerator 33, i.e. a high speed rotor, centrifuge or similar device. In the accelerator, which is dimensioned for the purpose of being able to delaminate such laminated packaging materials, air flow, rotor speed and pressure conditions are adjusted so as to each other and detach from adjacent layers in the laminate. A mixture of polyethylene / aluminum foil and loose release fibers is obtained, which mixture is passed on to a screening device or screening station 35 for separating fibers from other polymer and metal materials. A cyclone for air separation can be arranged integrally in connection with the accelerator or in a separate step 34, before the screening station. Since the fibers have completely different geometric shapes and weight properties compared to the plastic and metal material, the fibers 36 can be separated and passed on to a fiber silo 42. The remaining plastic and metal material 37, in this specific case polyethylene and aluminum, can be passed on to a second accelerator 38, in which air flow, rotor speed and pressure conditions are adjusted so that desired shear forces are achieved and the polyethylene is stretched into thin plastic flakes, while the aluminum is contracted into spherical particles and thereby delaminated from the polyethylene layer. The mixture of plastic flakes and aluminum particles is then fed further to a screening device 39, if applicable combined with a device for electrostatic separation of plastic from metal 39 '(not shown). A first stream of polyethylene ions 40 and a second stream of spherical aluminum particles 41 are obtained. The polyethylene fraction can advantageously be incinerated and thus converted into energy in the energy-intensive manufacturing process for fibreboard, in particular in the manufacture of MDF board.

The aluminum fraction is almost pure and can advantageously be sold for reuse in the aluminum industry. In this way, a complete solution is obtained for recycling cardboard-based food packaging. For fibreboard manufacturing, it is also not as important that the recycled fibers are bleached, since fibreboards are usually painted or hidden behind panels of veneer or impregnated decorative paper. 513 336 9 For some recycled uses, bleached recycled fibers are required, so they may be easier to sell. Since food cardboard is usually printed and coated with a decorative layer, unbleached cardboard works just as well. An additional environmentally beneficial effect is thus achieved by using recycled unbleached food cartons for MDF production.

The dry separated fibers 36 can be led directly, or after storage, from the silo 42 to a mixing station in the form of a circulation tube 43 which is passed through by air at a relatively high speed 44. The fibers are allowed to circulate in the circulation tube until homogeneously mixed with other additives. obtaining a fiber mass which can then be pressed into fibreboard. The flowing air 44 preferably has a velocity of about 18-25 m / s, most preferably about 20 mls. Other additives preferably consist of a curable polymer or pre-polymer 45 of the type urea-formaldehyde of the E1-approved type, possibly with a certain content of melamine resin. Where applicable, the recycled cardboard fibers can be mixed with other types of MDFs 46 in order to be able to tailor the properties of the final product if necessary. The blended polymer mass is substantially dry, as only about 10-15% by weight, preferably about 12% by weight, per oven dry end product of the curable polymer 45 is added to the dry fibers 36. Mixing can be performed as a batch or continuous process ". The mixing device is designed as a mixing and circulating stub, preferably for continuous supply of fibers and polymer resin and continuous extraction of homogeneously mixed pulp 47. The homogeneously mixed fibrous pulp 47 is passed on to a carpet forming device 18 to transform the fibrous mass into a fibrous mat, which fiber mat is then further processed as described in Figure 1 in subsequent pre-press 19, continuous press 20, saw station 21 and cooling station 22.

Recycled fibers from packaging generally have a higher pH than conventional MDF fibers. However, this has not been shown to cause any problems in the MDF manufacturing process. Compatibility with urea-formaldehyde (UF) resin (E1-type prepolymer) was tested and gel times of blends of the recycled fibers and about 12% by weight of UF were measured. It was found that the gel times were maintained with the same addition of catalyst compared to softwoods (conifers), and in some even shortened.

Especially when a UF resin of the MR type was used, ie moisture resistant UF with a content of melamine resin of about 2-20% by weight, greatly shortened gel times were achieved, which indicates that further process advantages in the form of shorter pressing times and / or reduced addition of catalyst to curable resin / pre-polymer can be achieved. 513 336 After mixing as above in flowing air in a circulating tube and subsequent pressing into fi sheets, it was found that polymer resin stains could be completely avoided and that the mixture is therefore almost completely homogeneous.

Dry mixing of polymers with polymer resin has not previously worked well in the prior art, since accumulations of polymer stains always appear to occur.

According to known techniques, work has been done on spraying the polymer resin solution on the dry fibers, whereby non-decorative polymer stains always occur. To 99%, therefore, all MDF production consists of polymer additives for wet or moist cellulose beads.

Other mixing devices may be conceivable according to the invention, but devices based on mechanical mixing of fibers and polymer resin have been excluded, as they do not work well enough, ie mix homogeneously enough. Blending by air flow methods appears to be the solution to obtain homogeneous fi-polymer mixtures. Particularly and preferably, air flow through an orbital tube is used as described above, as this works particularly well.

Mixtures of recycled food carton fibers and ordinary soft-wood MDFs were tested in the flow-filled air circulation tube, in amounts of about 10, 20, 80 and 90% by weight of MDFs, respectively. The fiberboard pressed by the blends clearly showed that blending of other types of MDF fiber is entirely possible in order to possibly be able to adjust the properties of the resulting fiberboard.

A process with obvious advantages both economically, environmentally and in terms of quality, for the production of erskber boards and in particular MDF boards, is obtained.

The entire wet fiber handling according to Figure 1 up to the carpet forming station 18 can in this way be replaced with only a dry delamination process, which delamination process is both cost-effective and environmentally friendly as it gives rise to reduced emissions to air and water. The need for wastewater treatment is greatly reduced or even eliminated, as a dry fiber production process is used. Energy use is also greatly reduced, as no steam heating or chip washing is needed. Emissions to air are reduced according to the invention, since the recycled cardboard fibers do not need to be dried. MDF or fiberboard production will also be more environmentally friendly because it uses recycled fibers and does not require felling of new forest.

From the above description it thus appears that the invention in a simple manner and with simple means fulfills the set objectives and provides cost-effective, environmentally friendly and resource-efficient MDF fiber boards of high quality. The invention also provides an economical and rational process for the manufacture of such fibreboards as well as a new use for cellulosic fibers recycled from cardboard-based food packaging.

Claims (19)

515,336 Patent claims A MDF-type (2a) type (2a) baseboard (2a) comprising cellulose sheets (2b) of the required quality and length and a binder (2c), characterized in that the cellulosic fibers are mainly recovered from carton-based food packaging so that they are recycled. maintained quality and length. A carrier sheet according to claim 1, characterized in that the sheets are recovered by layer delamination and separation of the cellulose sheets from other layers of polymer and, where applicable, metal, by means of shear and vortex forces from swirling air currents in a centrifugal accelerator. A fibrous sheet according to claim 1 or 2, characterized in that the binder (2c) comprises a curable polymer selected from a group consisting of urea-formaldehyde polymer, melamine-formaldehyde polymer, phenol-formaldehyde polymer, an isocyanate-curing polymer or a mixture of some of these polymers. A fibrous sheet according to any one of claims 1-3, characterized in that the binder (2c) comprises a urea-formaldehyde resin. A fibrous sheet according to any one of claims 1-4, characterized in that the binder (2c) comprises a mixture of a urea-formaldehyde polymer and about 2-20% by weight of melamine resin ("UF MR"). A fibreboard according to any one of claims 1-5, characterized in that the binder (2c) constitutes about 10-15% by weight, preferably about 12% by weight, of the fibreboard, calculated per dry weight. A fibrous sheet according to any one of claims 1 to 6, characterized in that the cellulose fibers and the binder are homogeneously mixed so that no accumulations of binder are visible in the fibreboard. A method of producing an MDF-type disc comprising cellulose fibers of the required quality and length and a binder, characterized in that the cellulose fibers are mainly recovered from carton-based food packages (31) so that they are substantially maintained in quality and length and then mixed with 513 336 IB. binder, which means that the mixture is then compressed into a disc-shaped object. A method of producing a carrier sheet according to claim 8, characterized in that the sheets are recovered by layer division and separation of the cellulose sheets from the other layers of polymer and, where appropriate, metal, by means of shear and vortex forces from swirling air streams in a centrifuge. / accelerator (33). A method of preparing a carrier sheet according to claim 8, characterized in that the binder (45) comprises a curable polymer selected from a group consisting of urea-formaldehyde polymer, melamine-formaldehyde polymer, phenol-formaldehyde polymer, an isocyanate-curing polymer or a mixture of some of these polymers. A method of making a disc according to any one of claims 8 or 9, characterized in that the binder (45) comprises a mixture of urea-formaldehyde polymer and about 2-20% by weight of melamine resin (UF MR). A method of producing a sheet according to any one of claims 8-10, characterized in that binder (45) is added to the sheets (36) in an amount of about 10-15% by weight of the sheet material, preferably about 12% by weight. , calculated per dry weight. A method of producing a iva board according to any one of claims 8-11, characterized in that the fi boards (36) are almost dry when the binder (45) is added. A method of making a cover sheet according to any one of claims 8 to 12, from cellulosic sheets recovered from board-based laminates in food packaging, at least comprising the following steps: a) the backing layer is delaminated from other laminate layers and the cellulosic boards are separated from other polymeric materials; where applicable, metal, in the dry state (33) by applying shear and vortex forces from swirling air currents in a centrifuge / accelerator b) the cellulose bricks are separated from the mixture of separated bricks and other materials (34, 35) c) the dry cellulose bricks (36 ) is mixed (43) with a binder (45) d) the mixture is compressed (20) under heat supply and pressure to cure the binder, to form a disc. 513 336 lt-r Method of producing a carrier sheet according to one of Claims 8 to 14, characterized in that the cellulose fibers (36) are separated from the other separated materials by means of screening and / or air separation (35, 34). A method of preparing a flberboard according to any one of claims 8-15, characterized in that the cellulosic fibers (36) and the uncured binder (45) are homogeneously mixed (43) so that no accumulations of unmixed binder are visible in the cured fiboard. Method of producing a carrier sheet according to one of Claims 8 to 16, characterized in that the cellulose fibers are mixed with the binder by means of flowing air (44) in a revolving tube (43). A method of producing a carrier disk according to claim 17, characterized in that the flowing air (44) has a velocity of about 18-25 m / s, preferably about 20 mls. Use of cellulose recycled from cardboard-based food packaging for the manufacture of medium-density MDF boards.