EP0880430A1

EP0880430A1 - Wood fibre damp slab

Info

Publication number: EP0880430A1
Application number: EP97950187A
Authority: EP
Inventors: Matthias TRÖGER; Ulrich SCHÖPF; Uwe Lange
Original assignee: Hofa Homann & Co KG GmbH
Current assignee: Fritz Homann & Co KG GmbH
Priority date: 1996-11-15
Filing date: 1997-11-13
Publication date: 1998-12-02
Also published as: WO1998022267A1; DE19647240A1; JP2001506549A; DE19647240B4

Abstract

The object of the invention is to provide a novel wood fibre damp slab which is economic to produce, as far as the parameters energy consumption, water consumption and timing are concerned, and whose density and resulting technical properties such as heat insulation, resistance to pressure and the like can be very accurately adjusted. After a refiner process that follows a pulping process, wood fibres whose humidity content is unaltered are mixed with a binder, spread on a moulding station by a dispenser, shaped in their width and thickness, and after the binder is activated, dried to form a slab. The wood fibre damp slab has < 150 kg/m<3> bulk density and </=0.045 W/(m x K) heat conductivity.

Description

Wood fiber insulation board

The invention relates to an insulation board made of wood fibers, in particular for thermal insulation, whereby mats are also to be understood.

When manufacturing fiberboard, a basic distinction is made between paper fiber or cellulose fiber, mineral fiber and wood fiber starting materials.

Wood fiber boards are currently manufactured using two fundamentally different processes. On the one hand, this is the so-called wet process, according to which soft wood fiber boards and hardboard (HDF) are produced, and on the other hand, a wood fiber drying process, according to which so-called MDF or HDF boards are manufactured.

The wood fiber board production process has in common the production of wood fibers. This is usually done in such a way that wood chips are first defibrated into wood fibers using a defibration system. One speaks of thermal-mechanical digestion, whereby after thermal digestion the wood chips are mechanically defibrated under pressure under the influence of temperature. In a so-called refiner, the cooked or steamed wood chips are fed to a pair of grinding disks via a screw and released after they have been shredded. Steam and wood fibers are usually separated in a cyclone, which come out of the refiner as a mixture due to the thermal-mechanical digestion. In the now classic wet process, the wood fibers are mixed with liquid, usually water, glue and the like to a pulp. This slurry is spread out in shaping stations, usually with a long screen dewatering device, shaped and compacted and dried in a press. In the production of soft wood fiber boards, the water is partly squeezed out with ironing rollers and the remaining water is evaporated with overflow or nozzle dryers. The press for the production of hardboard has at least one of the press surfaces with sieve-like openings for the steam outlet. Thus, the moisture in the wet pulp can escape over the surface and the edges. For this purpose, the nonwoven fabric to be dried must of course remain in the press for a certain time, so that the production process is lengthy. The dwell time in the dryers used in the manufacture of soft wood fiber boards is very long due to the low heat transfer into the board. The addition of liquid, the need to apply a great deal of energy to evaporate the liquid and the long residence time in the drying phase make the wet production processes for wood fiber boards comparatively uneconomical.

For this reason, at least to significantly reduce the time factor and to provide a continuous plate making process, the dry process has been developed. This differs from the wet process in that the fibers are glued and dried before being used for shaping. After drying, the fibers are sprinkled and, after being shaped, cured in a press which no longer has to have the evaporation openings in the press surface. The low residual moisture is evaporated here via the side edges. The dwell time of the fiber material in the drying press is therefore considerably shorter. This significantly reduces the production time after spreading. However, pre-drying of the fibers before curing is still required.

A disadvantage of both methods described is the large amount of energy required for fiber drying, be it in the dry process after defibrating or in the wet process after shaping. Another disadvantage is the unfavorable water balance, especially in the wet process. The pulpy consistency inevitably results in a lower one in the wet process Limit for the bulk density, which cannot be undercut. In addition, there is an upper limit with regard to the thickness of the plates produced by the wet process, since the heat is supplied only via the surfaces of the plates and from a certain thickness, at least with reasonable energy expenditure, complete drying would no longer be possible. Due to the boundary conditions, the thermal conductivity is also limited, i.e. λ values> 0.045 W / mK result. The degree of moisture of the boards produced by the drying process must be set very precisely, otherwise tears or bursts occur on the board due to the drying process. Dehumidification can only take place by evaporation, so that the water in the plate is heated by the high temperature and the high pressure to a temperature above the boiling point at atmospheric pressure. Another disadvantage of the boards produced in the dry process is the unfavorable distribution of the binder, which usually has to be done after blower tube gluing, since otherwise an adequate board bond can no longer be guaranteed. In addition, only water-soluble binders can be used in both processes.

The wood fiber boards produced according to the described and previously implemented processes are, due to the described limits, lower bulk density limit and upper thickness limit on the one hand and lower limit of the thermal conductivity on the other hand, solid boards for interior construction, furniture construction, mold construction and the like in a manner known per se. The known panels are unsuitable for use as a thermal insulation element.

Starting from this prior art, the present invention is based on the object of specifying a wood fiber board which is economical in terms of the parameters of energy expenditure, water consumption and time control during manufacture and in terms of density and the resulting technical properties such as thermal insulation,

Pressure resistance and the like can be adjusted very precisely, can also be produced using non-water-soluble binders, and can be used as an insulation board. For the technical solution to this problem, the invention proposes a wood fiber insulation board containing at least one binder mixed with wood fibers, which are applied to a molding station, shaped in terms of width and basis weight and shaped and cured after activation of the binder to form a board , wherein the plate has a bulk density <1 50 kg / m ³ with a thermal conductivity <0.045 W / (mx K).

The wood fiber insulation board according to the invention falls below any lower density previously known for wood fiber boards with a massive reduction in thermal conductivity at the same time, so that it can be used excellently as a heat insulation element. The term "board" in connection with the invention does not exclude that the wood fiber insulation board can also have mat properties.

Hitherto known wood fiber boards manufactured by conventional methods have a bulk density above 1 70 kg / m ³ and thermal conductivities around 0.05 to 0.06 W / (mx K). Compressive stresses are known to be above 85 kN / m ² and the modulus of elasticity is above 1 million N / m ² . Tear strengths are above 20 kN / m ² .

Advantageously, the wood fiber insulation board according to the invention has a bulk density <1 50 kg / m ³ with a thermal conductivity <0.045 W / (mx K). The tear-off strength is particularly advantageously <10 kN / m ² and the compressive stress <65 kN / m ² , which results in the required softness for thermal insulation elements with sufficient tear-off strength. The pressure modulus is particularly advantageously 650,000 N / m ² .

The thermal insulation board according to the invention can be produced in an extremely economical manner with slight modification of previously known processes and has excellent thermal insulation properties.

It has surprisingly been found that when other process steps are adapted, neither fiber moistening to set a wet process nor fiber drying after the steam separation phase following the refiner process are required. The fibers obtained from the refiner, It goes without saying that these are separated from the steam, can be sprinkled, shaped and dried after mixing with a binder. The water balance is practically not burdened, since no further moisture has to be added. From the energy point of view, an artificially added moisture level does not have to be dried, nor does the residual moisture contained in the fibers have to be dried out before curing. From the point of view of time control during production, there are considerable advantages over the wet process, which come close to the area of the dry process, so that continuous production is possible.

For the purposes of the present invention, the fact that the fibers are unchanged in terms of moisture content means that no active measures need to be taken to set a specific moisture level. If the fibers are stored or otherwise kept ready after defibration and there are slight changes in moisture content, this is of no importance for the implementation of the method.

It is advantageously proposed that the binders be mixed dry with the fibers. This results in a very good distribution. Alternatively, it is also possible to introduce and distribute moist binders. From a ecological point of view, it is particularly advantageous to use natural or near-natural binders. The process can be controlled very precisely and accelerated considerably if, according to an advantageous proposal of the invention, steam-activatable binders are used.

During the molding process after spreading the fiber / binder mixture, prepresses can be carried out in order to set the desired density ratios with great accuracy.

The binding agents are advantageously activated by means of steam which flows through the scattered fiber material strand. This flow ensures complete binder activation. With regard to curing or drying, the invention proposes in a particularly advantageous manner that a drying medium flows through the spread and preformed fiber material. It is advantageously proposed to let hot air flow through the main surfaces of the preformed material. During the flow, a pressing process can advantageously be used to calibrate the wood fiber board.

The invention provides a simple, economical method which can be controlled very precisely with regard to the attainment of technological properties, with which insulating boards with densities far below 1,50 kg / m ^{3 can be} produced, that is to say up to around 60 kg / m ³ . In addition, virtually any thickness can be created if through-flow drying takes place. The board can be produced with natural or near-natural binders such as lignin, damar resins and the like, so that water-insoluble binders can also be used. Thermal conductivities (λ) can be set below 0.040 W / mK. The pressure capacities can be set very high, so that the panels produced by the method according to the invention can also be used for insulating walk-in or other load-bearing areas.

In addition, it is possible to mix additives during different process stages, for example to be able to meet fire class requirements.

The process according to the invention is extremely economical compared to the conventionally known wood fiber board production processes, enables the production of a board type which is completely new in terms of thickness, density and technological properties and can be varied from an ecological point of view.

The fiberboard produced by the described method differs considerably from previously known fiberboard. This plate can be varied widely in terms of density and can also assume very low densities. In addition, very large thicknesses can be set become. The insulation properties can be set very precisely, as can the compressive strength properties.

Further advantages and features of the invention result from the following description with reference to the figures. Show:

Figure 1 is a flow chart to explain an embodiment of the manufacturing process.

Wood chips 1 are subjected to fiberization 2 in a manner known per se, mechanical shredding of the wood chips 1 taking place under pressure and temperature after thermal digestion. In the so-called refiner 2, the wood chips 1 are fed to a pair of grinding disks via a screw and are applied after the defibrating. The steam is then discharged in station 3, which can usually be done using a cyclone in which the steam and wood fibers are separated. The fibers are then stored in a fiber storage 4.

It is important to note that there is no fiber drying or moistening. The fibers are stored and processed as they come out of the refiner, without taking any measures to change or influence the moisture content.

By means of a belt scale 5, the required amounts of wood fiber are recorded, which are fed from the fiber storage 4 to a mixer 1 1. At the same time, binders A, B and C are fed from stocks 6, 7 and 8. The binder quantities are recorded by means of belt scales 9; if necessary, individual binders can also be processed further, for example within a fine mill 10. The number of binders and the type of further processing are given only by way of example and can be varied as required. Other additives can also be added at this point.

In the mixer 1 1, the refiner-moist wood fibers are mixed with the necessary binders. The material is scattered and shaped in a spreading and forming station 12. Forming is understood to mean, among other things, the formation of side edges, uniform spreading and, if necessary, pre-pressing.

In a subsequent stage 1 3, for example a damper, the binder is activated by means of steam, hot air or other activation media. This is preferably done by means of flow.

In the dryer zone 14 there is a pre-pressing and a drying of the plates formed. This can be done, for example, by means of hot air flow, for which purpose a press can be used at this point, which has at least one of the press surfaces in the form of a screen.

The dried plate is then formatted or assembled in a station 1 5.

Reference list

1 wood chip

2 defibration, refiner

3 steam discharge

4 fiber storage

5 belt scale wood fibers

6 binder A

7 binder B

Binder C

Belt scales

10 fine grinder

1 1 mixer

12 Material scattering and shaping

1 3 dampers

14 Dryer zone 5 plate formatting

Claims

Claims:

1 . Wood fiber insulation board containing wood fibers mixed with at least one binder, which are applied to a molding station, shaped in terms of width and basis weight, and shaped and cured after activation of the binder to form a board, the board having a bulk density <1 50 kg / m ³ with a thermal conductivity ≤ 0.045 W / (mx K).

2. Wood fiber insulation board according to claim 1, characterized in that it has a tear-off strength ≤ 1 0 kN / m ² .

3. Wood fiber insulation board according to one of the preceding claims, characterized in that it has a compressive stress ≤ 65 kN / m ² .

4. Wood fiber insulation board according to one of the preceding claims, characterized in that it has a pressure modulus of elasticity <650,000 N / m ² .

5. Wood fiber insulation board according to claim 1, characterized in that the binder is mixed in in the dry state

6. Wood fiber insulation board according to one of the preceding claims, characterized in that it contains natural or near-natural binders.

7. Wood fiber insulation board according to one of the preceding claims, characterized in that it contains steam-activatable binders.

8. Wood fiber insulation board according to one of the preceding claims, characterized in that it is subjected to at least one pre-pressing during the molding process.

9. Wood fiber insulation board according to one of the preceding claims, characterized in that it is flowed through with steam for binder activation.

10. Wood fiber insulation board according to one of the preceding claims, characterized in that the applied and shaped fiber material is flowed through for drying with hot air.