CA2243078C - Wood fiber insulating panel - Google Patents

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/m3 bulk density and <=0.045 W/(m × K) heat conductivity.

Description

WOOD FIBER INSULATING PANEL

The present invention relates to a dampening or insulating panel or slab of wood fibers, especially for thermal insulation, with the terminology also being intended to cover mats.

During the manufacture of fiber panels, a distinction is principly made between the starting materials of paper, i.e. cellulose, fibers, mineral fibers, and wood fibers.

At the present time, wood fiber panels are manufactured pursuant to two fundamentally different processes. These involve on the one hand the so-called wet process, pursuant to which wood soft fiber panels and wood hard fiber panels ( HDF) are produced, and on the other hand a wood fiber dry process, pursuant to which so-called MDF panels or HDF panels are produced.

Common to the wood fiber panel manufacturing processes is the production of the wood fibers. This is conventionally effected by first grinding wood chips to wood fibers with a grinding unit. This refers to thermal-mechanical treatment, whereby after thermal treatment a mechanical grinding of the wood chips under pressure and temperature effect takes place. In a so-called refiner the cooked or steamed wood chips are conveyed by a screw conveyor to a pair of grinding disks, and are brought out after the grinding. The separation of steam and wood fibers is conventionally effected in a cyclone; due to the thermal-mechanical treatment, the wood fibers UT TRSL of PCT/EP97A26338 - Trt7per et 8f - HOFA Homann GmbH & Co. KS - 98 075!

leave the refiner as a mixture.

Pursuant to the in the meantime classic wet process, the wood fibers are blended with liquid, normally water, adhesive and the like to a paste. This paste is introduced into shaping stations, conventionally with a wet machine, is shaped, and is compressed and dried in a press. During the manufacture of wood soft fiber panels, the water is partially pressed out with colander rollers and the remaining water is evaporated with flow-over or jet dryers. The presses for the manufacture of wood hard fiber plates has sieve-like openings for the discharge of steam in at least one of the press surfaces. In this way, the moisture found in the wet fiber paste can escape via the surface and the edges. For this purpose, the fiber material that is to be dried must of course remain for a certain period of time in the press so that the manufacturing process becomes time-consuming. The retention time in the dryers used for the wood soft fiber panel manufacture is very long due to the low heat transfer into the panels. Due to the addition of liquid, the requirement for applying a great deal of energy to evaporate out the liquid, and the long retention time in the drying phase, the wet manufacturing processes for wood fiber panels are relatively uneconomical.

For this reason, at least to significantly reduce the time factor and to provide a continuous panel manufacturing process, the dry LIT TRSL of PCTlEP97iU8338 - TrlJger et al - HOFA Homann GmbH & Co. KS -a t 1 process was developed. This differs from the wet processes in that adhesive is added to the fibers and they are dried prior to introduction for shaping. After the drying, the fibers are spread out and after shaping are cured or hardened in a press that now no longer has to have the evaporation openings in the press surface.
The evaporation of the slight residual moisture is in this way effected via the side edges. The retention time of the fiber material in the drying press is consequently considerably shorter. Thus, the production time after the spreading out is significantly reduced.
However, the preliminary drying of the fibers prior to the curing is still necessary.

A drawback of both of the described processes is the large amount of energy consumption which is required for the fiber drying, be it in the dry process after the grinding or in the wet process prior to the shaping. A further drawback is the unfavorable water and evaporation condition, especially with the wet process. Due to the paste-like consistency, there necessarily results with the wet process a lower limit for the gross or bulk density, below which it must not drop. Furthermore, there is an upper limit with regard to the thickness of panels produced by the wet process since the addition of heat can be effected only via the surfaces of the panels and therefore after a certain thickness, at least at a reasonable energy consumption, no complete thorough drying is any longer possible. Due to the limiting conditions the thermal conductivity is LIT TRSL of PCT/EP97N8338 - TiCger et al - HOFA Homann GmbH & Co. KS - 98 0751 also limited, in other words, a values z 0.045 W/mK result. With panels produced according to the dry process the moisture content must be established very exactly since otherwise the drying process causes splitting or cracking on the panels. The removal of moisture can be effected only by evaporation, so that the water found in the panel is heated by the high temperature and the high pressure to a temperature that is above the boiling point at atmospheric pressure.
A further drawback of the panels produced by the dry process is the unfavorable binder distribution that conventionally must be effected pursuant to blast tube gluing, since otherwise an adequate panel bonding can no longer be ensured. Furthermore, with both processes only water soluble binders can be used.

Due to the described limits of lower gross density and maximum thickness on the one hand, as well as the lower limit of the thermal conductivity on the other hand, the wood fiber panels manufactured pursuant to the described and previously realized processes are in a known manner compact or dense panels for interior construction, furniture construction, mold construction and the like. The heretofore known panels are not suitable for use as a thermal insulating element.

Starting from this state of the art, it is an object of the present invention to provide a wood fiber panel that with respect to the perimeters energy consumption, water consumption and timing is LIT TRSL of PCT/EP97108338 - Trtlger et af - HOFA Homann GmbH & Co. KS - 98 economical to produce, with the density of the panel and the resulting technical properties such as thermal insulation, resistance to pressure and the like being adapted to be established very accurately. The wood fiber panels are also to be able to be produced using non water-soluble binders, and are to be usable as insulating panels.

As a technical realization of this object, the present invention proposes a wood fiber insulating panel containing wood fibers mixed at least with a binder, wherein the wood fiber mixture is introduced to a shaping station where they are shaped relative to width and weight per unit area, wherein after activation of the binder the wood fiber mixture is molded in thickness to form a panel and is hardened or cured, and wherein the panel has a bulk or gross density of 1 150 kg/m3 at a thermal conductivity of s 0.045 W/(m x K).

The inventive wood fiber insulating panel falls below all gross density limits known up to now for wood fiber panels while at the same time significantly reducing the thermal conductivity, so that it can be outstandingly used as a thermal insulating element. The use of the term "panel" in conjunction with the invention does not preclude the wood fiber insulating panel from also having mat characteristics.

Heretofore known wood fiber panels manufactured pursuant to LIT TRSL of PCTiEP97R7B338 - Troger et al - HOFA Homann GmbH & Co. KS - 98 075 f conventional processes have gross densities above 170 kg/m3 and heat conductivities of about 0.05 to 0.06 W/(m x K). As is known, compressive stresses are above 85 kN/m2 and the pressure-E-modulus is above I million N/mZ. Breaking or separation strengths are above 20 kN/m2.

The inventive wood fiber insulating panel advantageously has a gross density { 150 kg/m3 at a heat conductivity of ~ 0.045 W/(m x K). The breaking strength is particularly advantageously ~ 10 kN/m2 and the compressive strength ~ 65 kN/m2, as a result of which, at adequate breaking strength, the softness required for thermal insulating eJements results. In a particularly advantageous manner, the pressure-E-modulus is :5 650,000 N/m2.

The inventive thermal insulating panel can be produced in an extremely economical manner with slight modification of known processes, and has excellent thermal insulating properties.

It has been surprisingly established that with the adaptation of other process steps neither a moistening of fibers to establish a wet process nor a fiber drying pursuant to the steam separation phase are required after the refiner process. The fibers as they are obtained from the refiner, whereby it is self understood that these fibers are separated from steam, can after being mixed with a binder be spread, shaped and dried. The water balance is practically LIT TRSL of PCT/EP97108338 - Tn7qer et al - HOFA Homann GmbH & Co. KS - 98 , . , .

unaffected since no further moisture has to be supplied. From a stand point of energy, neither an artificially supplied moisture level has to be dried, nor does residual moisture contained in the fibers have to be dried out prior to curing. From the stand point of timing during the manufacture, considerable advantages result relative to the wet process, with such advantages being close to those of the dry process, so that continuous manufacture is possible.

The fact that the fibers are not changed with regard to the moisture content means, in the context of the present invention, that no active measures have to be carried out to establish a specific moisture level. To the extent that the fibers are stored after the grinding or are otherwise kept available, and hence undergo slight changes in moisture content, is of no significance for carrying out the process.

It is advantageously proposed that the binder be mixed in a dry state with the fibers. In this way, a very good distribution results.
Alternatively, it is also possible to introduce moist binder and to distribute it. Particularly advantageous from an ecological stand point is the proposal to use natural or nearly natural binder. The process can be controlled very exactly, and can be considerably accelerated if pursuant to an advantageous proposal of the invention binder is used that can be activated by steam.

UT TRSL of PCTIEP97106338 - TnSger et a/ - HOFA Homann GmbH & Co. KS - 98 0751 , . . , During the shaping process after the spreading of the fiber/binder mixture, pressings can be effected in order with great exactness to establish the desired density characteristics.

The activation of the binder is advantageously effected by means of steam, which flows through spread out fiber material. This flowing-through ensures a complete binder activation.

With respect to the curing or drying, it is inventively proposed in a particularly advantageous manner that a drying medium flow though the spread-out and preshaped fiber material. It is advantageously proposed that hot air be allowed to flow transverse to the main surfaces of the preshaped material. A pressing process can advantageously take place during the flow-through, which serves for sizing the wood fiber panel.

A simple, economical process is provided with the invention that can be controlled very exactly with regard to obtaining technological properties, with insulating panels having densities well below 150 kg/m3, in other words to about 60 kg/m3, being producible with this method. Furthermore, any desired thickness can be established if a flow-through drying takes place. The panels can be manufactured with natural or nearly natural binders such as lignin, dammar resins, and the like, so that water insoluble binders can also be used.
Thermal conductivities ()) below 0.040 W/mK can be established.
LIT TRSL of PCT/EP97176338 - TrHger et al - t-fOFA Homenn GmbH & Co. KS - 98 The resistance to pressure can also be set very high, so that the panels produced pursuant to the inventive process can also be used to insulate traversable or otherwise load-carrying regions.

There is furthermore the possibility of adding in during various method steps additives, in order, for example, to be able to fulfill fire classification requirements.

In contrast to the conventional known wood fiber panel manufacturing processes, the inventive process is extremely economical, enables the manufacture of a completely new type of panel with respect to thickness, density and technological properties, and can be varied from an ecological stand point.

The wood fiber panel manufacture pursuant to the process described differs significantly from heretofore known wood fiber panels. The present panel can vary greatly with respect to density and can also have very low densities. Furthermore, very great thicknesses can be established. The insulating properties can be established very exactly, as can the resistance to pressure.
Further advantages and features of the invention can be seen from the following description in conjunction with the drawing. Shown is:
Figure. 1 a flow diagram to explain one exemplary embodiment of the manufacturing process.

UT TRSL of PCT/1=P97108338 - Trllger et a! - HOFA Homann GmbH & Co. KS - 98 , . . .

Wood chips or shavings I are subjected in a manner known per se to a pulping or grinding process 2, whereby after thermal treatment a mechanical grinding of the wood chips I under the effect of pressure and temperature is effected. In the so-called refiner 2, the wood chips 1 are conveyed to a pair of grinding disks via a screw conveyor, and after the grinding are brought out. Subsequently, the steam extraction occurs in the station 3, which is conventionally effected by a cyclone in which the separation of steam and wood fibers is effected. The fibers are then stored in a fiber storage means 4.

It is important to note that neither a fiber drying nor a moistening is effected. The fibers are stored and further processed, in the state in which they exit the refiner, without having to undertake measures for altering or influencing the moisture content.

By means of a conveyor type weigher 5, the required quantities of wood fibers are picked up, and are conveyed from the fiber storage means 4 to a mixer 11. At the same time, the binders A, B and C
are conveyed from the supply containers 6, 7 and 8. The quantities of binders are picked up by conveyor type weighers 9, and if necessary individual binders can also be further processed, for example within a pulverizer 10. The indication of the number of binders and the type of further processing is provided by way of example only, and can be varied as desired to fit particular needs.
UT TRSL of PCT/EP97105338 - Tiager et al - HOFA Homann GmbH & Co. KS - 98 0751 Further additives can also be mixed in at this location.

Mixing of the refiner-moist wood fibers with the required binders takes place in the mixer 11.

Spreading and shaping of the material is effected in a spreading and shaping station 12. Shaping means, among other things, a formation of side-edges, a uniform spreading out, and possibly a preliminary pressing.

In a subsequent stage 13, for example an autoclave or steamer, the activation qf the binder is effected by means of steam, hot air or other activation media. This expediently occurs by means of flow-through.

An initial pressing and a thorough drying of the panels or slabs that are formed takes place in the dryer zone 14. This can be effected, for example, by means of hot air flow-through, forwhich purpose, for example, a press can be used at this location that has at least one of the pressed surfaces in the form of a sieve.

The finish-dried slabs or panels are subsequently formatted or fabricated in a station 15.

LIT TRSL of PCTiEP97ro6338 - Troger et a! - HOFA Homann GmbH & Co. KS - 98 , . . .

List of Reference Numerals 1. Wood chips 2. Pulping or grinding/refiner 3. Steam extraction 4. Fiber storage means 5. Conveyor type weigher for wood fibers 6. Binder A
7. Binder B
8. Binder C
9. Conveyor type weighers 10. Pulverizer 11. Mixer 12. Material spreading and shaping 13. Autoclave or steamer 14. Drier zone 15. Slab or panel formatting LIT TRSL of PCT/EP97108338 - Trdger et a! - HOFA Homann GmbH & Co. KS - 98

Claims (10)

Claims:

1. A method for producing a wood fiber insulating panel having a gross density of <150 kg/m3 at a thermal temperature conductivity <=50.045 W/(m ×
K), comprising the following steps:

- obtaining a refiner moist wood fiber;

- adding a binder to the refiner moist wood fiber;

- mixing the wood fiber and the binder to obtain a mixture;

- spreading and shaping the mixture to produce a shaped form;
- activating the binder; and, - pressing the shaped form after activation into a final shape.

2. The method according to claim 1, characterised in that the binder is mixed in dry state.

3. The method according to claim 1 or 2, characterised in that the binder is a natural or a nearly natural binder.

4. The method according to claims 1, 2 or 3, characterised in that the binder can be activated by steam.

5. The method according to claims 1, 2, 3, or 4, characterised in that the step of pressing the shaped form after activation into a final shape involves at least one preliminary pressing.

6. The method according to claim 1, 2, 3, 4, or 5, characterised in that the steam flows through the introduced and shaped fiber material for activating the binder.

7. The method according to claim 1, 2, 3, 4, 5, or 6, characterised in that hot air flows through the introduced and shaped fiber material for drying.

8. A wood fiber insulating panel produced by the method according to any one of claims 1-7, characterised in that it has a breaking strength of <=10 kN/m2.

9. The wood fiber insulating panel according to claim 8, characterised in that it has compressive strength of <=565 kN/m2.

10. The wood fiber insulating panel according to claims 8 or 9, characterised in that it has a pressure-E-modulus of <=5650,000 N/m2.