WO2005007369A1

WO2005007369A1 - Method for introducing wax in thermal wood

Info

Publication number: WO2005007369A1
Application number: PCT/DE2004/001471
Authority: WO
Inventors: Hans-Joachim Burger
Original assignee: FRÖHNER, Jürgen; FRÖNER, Reinhard; Gut, Marcus
Priority date: 2003-07-14
Filing date: 2004-07-08
Publication date: 2005-01-27
Also published as: EP1646483A1; DE20310745U1; DE112004001750D2

Abstract

The invention concerns a method for introducing wax in thermal wood which consists in bringing the wax to a temperature higher than melting point and in introducing the thermal wood into the liquid wax. The invention also concerns thermal wood impregnated with wax in its cross-section for at least 30 %, preferably for at least 50 % and more preferably, for at least 75 %.

Description

Process for introducing wax into thermowood

description

The invention relates to a method for introducing wax into thermowood.

The introduction of substances into wood to improve mechanical or biological properties is known per se. For example, DE 19640 873 describes how the mechanical workability of wood can be improved by introducing dispersions or aqueous emulsions of surfactants. Fresh wood, ie wood with a high moisture content, is impregnated. The impregnating agent displaces the water in the wood, here z. B. by greater affinity for cellulose or hemicelluloses. The drying of such impregnated woods often proves to be difficult since the removal of the water can be hindered by the impregnating agents. In order to avoid this drying damage, which ranges from undesirable changes in shape (warping, warping) to tearing and thus loss of mechanical strength, the drying process must be carried out very precisely. If this is not successful, the proportion of rejects is extremely high, since larger and larger quantities of wood are always dried at the same time.

The impregnation of wood that has already dried, for example with a wood moisture content of less than 20% based on the absolutely dry mass (dry) of wood, was not successful in practice because the dry wood is easy to move, ie it is permeable to liquids or gases , is significantly reduced compared to fresh wood.

Attempts to impregnate wood with oils, even at elevated temperatures, have shown that positive effects can only be expected if the liquid oils are oxidized to solids. It is obvious that the time required for this is too long in practical use. The use of polyethylene glycol has also been developed in connection with the treatment of damp wood. The process is extremely lengthy and is only used in the preservation of objects of particular historical importance. Filling wood with acrylic resins (PMMA) results in heavy materials that have little wood properties.

The invention is therefore based on the object of providing a simple method for impregnating wood which can be carried out with low process risks, and of presenting a wood with improved mechanical properties.

This object is achieved with a method for introducing wax into thermowood, in which wax is first heated above its melting point, after which thermowood is introduced into the liquid wax. The wax penetrates the thermal wood and impregnates it. The use of hot wax as a soaking medium is simple and effective.

Thermowood is wood that can only be made weatherproof by intense heat. There are various methods and process steps for the production of thermowood. In the past, softwood was mainly used for this; the process has now also been extended to hardwood, for example beech. For example, a method is known in which the wood is heat-treated at about 200 ° C., preferably at about 215 ° C. or 240 ° C., for about 24 hours with the exclusion of oxygen and without the addition of chemicals.

Another process, known under the Thermowood® brand, which is intended to give domestic woods the quality of tropical woods, involves treating the wood in three phases:

1. At temperatures up to 130 ° C, moisture is almost completely removed from the wood. Water vapor is added, which on the one hand prevents ignition and on the other hand initiates a chemical conversion of the biological material.

2. At temperatures between 185 and 215 ° C, again with the addition of water steam, the wood hard and resistant.

3. Spraying water now lowers the temperature again and levels out the moisture content of the wood to about 4%.

The entire process takes 36 hours.

In the thermowood process, moisture and other volatile components are almost completely removed from the wood and its cell structure changes so that weather, moisture and fungi can no longer harm the wood. This heat treatment makes the wood more resistant to the attack by wood pests and also to the weather. The results outperform the treatment with chemical wood preservatives - and that naturally. Thermowood swells and shrinks less than untreated wood, so it is less prone to changes in shape and size. The wood has an equilibrium moisture content of approx. 8%. The water content is thus greatly reduced, as is the content of resins and wood constituents, which are volatile at the above-mentioned temperature of 215 ° C.

The reasons for the increasing importance of so-called thermowood are:

1.Colour and structure change of native woods such as birch, maple, ash, spruce etc. with the aim of achieving the attractiveness of tropical woods, also to counteract overexploitation.

2. Improvement of the mechanical values. 3. Less change in shape due to moisture.

4. Reducing susceptibility to rot and mold.

5. Avoiding the use of heavy metal chemicals like in the boiler pressure impregnation.

However, the wood is more brittle than before the heat treatment. There was no significant improvement in weather resistance. The waxes that are used to impregnate the thermowood are preferably solid at room temperature. Their melting point is well above room temperature.

Surprisingly, this thermo wood can be easily impregnated with liquid wax. Due to the low water content, the liquid wax can penetrate well into the cavities of the wood and into the cell walls. After cooling, the wax remains in the wood. The wax-impregnated wood is easier to process mechanically and its compressive strength is better than before.

It is to be regarded as a particular advantage that thermowood which has been treated with the method according to the invention is immediately ready for use. It no longer has to be subjected to complex and complicated drying processes. The risk of producing rejects is eliminated or is significantly reduced.

The quality of such wax impregnation of thermowood is far superior to all other impregnation processes, even with the simplest treatment in terms of long-term weather resistance, strength, water stability, workability, environmental compatibility and aesthetics. This can easily be explained in the basic material properties of waxes. There are shrines, death masks and other objects made of wax that have survived for centuries without significant losses.

Significant amounts of wax can be placed in the thermowood. Even impregnation with at least 10 percent by weight (weight) of atro wood shows significantly improved mechanical properties. It is preferred if at least 20% by weight of wax is introduced, particularly preferably at least 30% by weight.

Waxes which contain polyethylene or which consist of polyethylene have proven to be particularly suitable for carrying out the process according to the invention.

These waxes can be melted without special precautions being taken. must, for example against the release of solvents. Waxes made of polyethylene (PE waxes) penetrate wood well, they have a compressive strength that is of the same order of magnitude as wood. PE waxes are therefore well suited to improve the mechanical properties of thermowood. The PE waxes also do not weigh down the wood unnecessarily and they are uncomplicated to process, in particular machining, and to dispose of or recycle the thermowood. To meet the high demands of special wood applications, e.g. B. in instrument making, "wood-hard", pure PE waxes should preferably be used, which have a melting point of approx. 130 ° C and which are low viscosity when heated to 200 ° C. The waxes are inexpensive, the application is simple, it is done without toxic traces and the product is 100% recyclable. An example of such a PE wax is the product "Luwax AH ®" from Tenside (BASF) or PE-Wax A112 from LEUNA Polymer GmbH.

Melting points of suitable waxes are approx. 90 ° C to 120 ° C. According to a preferred embodiment of the method according to the invention, however, the wax is further heated to temperatures of at least 140 ° C., preferably at least 160 ° C., particularly preferably of at least 80 ° C. This ensures that the wax achieves the lowest possible viscosity, which is particularly suitable for penetration into thermowood. Heating beyond the melting point to the above-mentioned temperatures thus ensures that large amounts of wax can be introduced into the thermowood. At these temperatures, it is also ensured that the wax penetrates deep into the thermowood and impregnates all or almost the entire cross section of the thermowood.

According to an advantageous embodiment of the method according to the invention, the thermowood is heated when it is introduced into the liquid wax. It is particularly preferred if the thermowood is introduced into the liquid wax immediately after the heat treatment. Even a wood heated to at least 140 ° C considerably reduces the energy required to apply the wax. If the thermowood has a temperature of at least 160 ° C, preferably at least 180 ° C, this further optimizes the energy requirement for impregnation.

The liquid wax penetrates the thermowood relatively quickly. A dwell time of at least 30 minutes in the liquid wax improves the mechanical properties of the thermowood considerably. Depending on the type of wood and / or the extent to which the mechanical properties are improved, the dwell time can be increased to at least 60 minutes, preferably to at least 120 minutes. The method according to the invention is therefore a relatively short exposure time in comparison to the treatment with thermowood.

The penetration of the wax into the thermowood is effectively supported if the wax is introduced into the thermowood using excess pressure. It has proven to be advantageous to apply a pressure of at least 5 bar in order to introduce the wax faster and deeper into the thermowood. According to a preferred further development of the method, at least 10 bar pressure is applied, particularly preferably at least 20 bar pressure. Higher pressures (up to or even over 150 bar) can be even more advantageous. If this embodiment of the method is chosen, then it makes sense to stack the thermowood in a heatable pressure vessel. If the liquid wax, which has grown to the desired pressure, is then introduced into the kettle via pressure lines, the wax can be introduced into the thermowood in a simple and inexpensive manner.

The invention also relates to a wax-impregnated thermowood in which at least 30% of the wood cross section of the thermowood is impregnated with wax. According to an advantageous embodiment of the invention, at least 50%, preferably at least 75%, of the wood cross section of the thermo wood is impregnated with wax. The deep penetration of the thermo wood with wax ensures a significant improvement in the mechanical properties of the wood, especially the compressive strength.

Worth mentioning in the preparation according to the invention the surprisingly good sound behavior the excellent workability the self-polishing effect the weather resistance - the significantly reduced swelling / shrinkage behavior

The self-polishing effect allows the use of wood treated in this way without any further surface treatment for an estimated decades or centuries. This can be justified by the fact that no z. B. volatile constituents that can be introduced by oxidation.

Particularly surprising for the construction of musical instruments is that, at least in the unpressurized treatment of thermowood, the cooling contraction presumably results in microscopic pores which have the desired moisture absorption of e.g. B. allow condensation without causing swelling of the thermowood.

Finally, according to a further embodiment of the invention, a wax-impregnated thermowood is the subject of the invention, the compressive strength of which is at least 5%, preferably at least 10% above the compressive strength of the natural wood used as the starting material and significantly above that of the non-impregnated thermowood.

The wax introduced into the thermowood can also be colored. This is particularly advantageous if the discoloration of the thermo wood does not satisfy the heat treatment. The use of colored waxes is then simple and safe. The color tones can be permanently corrected, especially by adding wax-soluble dyes to the drinking wax.

Essential features of the invention are explained in more detail below using an example: A spruce wood (thermo wood) with a cross section of 8 x 8 cm and a length of approx. 3 m is conveyed into a heatable pressure chamber and fixed after the heat treatment. The pressure chamber is provided with a feed line and a discharge line for liquid wax. PE wax is heated to 180 ° C and the heatable pressure chamber, which is also heated to 180 ° C, is flooded with the liquefied wax via the feed line with the application of pressure. The pressure is 20 bar. When flooding the pressure chamber, the wood temperature is still 165 ° C. The chamber remains flooded for 45 minutes and is kept at a temperature of 180 ° C. The wax is continuously circulated during the 45 minutes by connecting the supply and discharge lines and switching on a pump. After the 45 minutes have passed, the supply and discharge lines are decoupled and the liquid wax is pumped out of the pressure chamber. Pressure equalization is initiated and the chamber is opened after the equalizing pressure is reached. The thermowood is examined after cooling. The treatment absorbed 25% by weight of wax based on dry wood. After cooling, the compressive strength is approx. 7% higher than the compressive strength of the untreated wood. When planing the wax-impregnated wood, the surface is smoother than when planing untreated thermowood.

The thermal wood treated according to the invention can still be glued well despite the wax content. In this way, plywood, etc. can also be produced with wood that has already been treated with wax. The wood can still be painted well.

Claims

Expectations

1. Procedure for inserting wax in thermowood, with the steps:

- heating wax beyond its melting point and

- Introducing thermowood into the liquid wax.

2. A method for introducing wax into thermowood according to claim 1, characterized in that, based on dry wood, at least lo wt.%, Preferably at least 20 wt.%, Particularly preferably at least 30 wt.% Wax in the thermowood be introduced.

3. The method according to claim 1, characterized in that waxes or mixtures of waxes are introduced into the thermo wood, which contain polyethylene or which consist of polyethylene.

4. The method according to claim 1, characterized in that the wax is heated to temperatures of at least 140 ° C, preferably at least 160 ° C, particularly preferably at least 180 ° C when it is introduced into the thermowood.

5. The method according to claim 1, characterized in that the thermowood is heated to temperatures of at least 140 ° C, preferably of at least 170 ° C, particularly preferably of at least 200 ° C when it is introduced into the liquid wax.

6. The method according to claim 1, characterized in that the thermowood is introduced into the liquid wax for at least 30 minutes, preferably for at least 90 minutes, particularly preferably for at least 120 minutes. η. A method according to claim 1, characterized in that the wax is introduced into the thermowood using pressure, a pressure of at least 5 bar, preferably at least 10 bar, particularly preferably at least 20 bar being applied.

8. Wax-impregnated thermowood, characterized in that at least 30%, preferably at least 50%, particularly preferably at least 75% of the wood cross section are wax-impregnated.

9. Wax-impregnated thermowood, characterized in that the compressive strength of the wax-impregnated thermowood is at least 5%, preferably at least 10%, above the compressive strength of the unimpregnated thermowood.