EP1440779B1 - Method for impregnating gaspermeable solids with an impregnation agent - Google Patents

Abstract

The impregnating process consists of putting the solid in an autoclave; introducing a gas up to a preset pressure; setting the pressure equalization in the solid to a preset protective pressure; introducing a liquid impregnator; raising the pressure in the autoclave to above the protective pressure to facilitate impregnation; and reducing the pressure in the autoclave to ambient pressure.

Description

The invention relates to a method for impregnating wood-based materials with a liquid impregnating agent.

The method is directed to the impregnation of wood and wood materials, which are penetrated by a compressed gas. The aim of the process is to improve the technical or aesthetic properties of the wood-based material. The impregnation of wood and wood-based materials makes particularly high demands on the process management because of the complex structure and the poor path for an impregnation medium

State of the art

The impregnation of wood with impregnating agents for increasing the durability, for improving mechanical properties, for coloring or for unlocking the wood structure has long been carried out. The impregnation of wood is usually done with liquid impregnants. Accordingly, there are many studies on this subject dealing with the influence of the wood properties, the impregnating agents, the impregnation pressure and the soaking time on the impregnation of the wood.

The applied in the known impregnation process pressure is usually limited to about 15 bar, since up to this load usually no damage to the wood occur. Only a few studies are concerned with higher impregnation pressures up to about 80 bar (usually referred to as high-pressure impregnation): it is reported on the uptake and distribution of the impregnating agent in species that withstand these higher pressures largely without recognizable damage; any structural changes are mentioned as cell collapse or cracking (TAMBLYN 1953, ELLWOOD 1956, DALE 1960, SIAU 1970). Processes which work not only with overpressure but also with vacuum are shown, for example, in WO 98/46403. The application of vacuum requires considerable expenditure on equipment in technical application.

Because of their widespread distribution in Europe and their high yield, the softwood species spruce (Picea abies, karst.), Sitka spruce (Picea sitchensis Carr.), Pine (Pinus silvestris, L.) and larch (Larix decidua Mill.) Are of particular wood economic importance , With the exception of pine sapwood, the poor pathway for liquids is common to all, which presents a high resistance to impregnation and thus carries the risk of cell damage at high pressures. Similarly difficult conditions exist for hardwood species such as oak (Quercus robur L.) and various poplar (Populus sp.) And birch (Betula sp.) . In contrast, beech (Fagus sylvatica, L.) is relatively easy to impregnate. Further details on the impregnability of selected wood species of particular importance for Europe are contained in DIN EN 350-2: 1994-10.

Since wood in the dry state (below the fiber saturation point) is even more difficult for liquids (PHILLIPS 1933; DIN EN 350-2: 1994-10), only unsatisfactory watering results have hitherto been achieved with large-scale processes (eg vacuum-pressure process) (BELLMANN 1968). Required penetration depths (RAL-RG 411 1980) are achieved by complex mechanical pretreatment such as mechanical slot perforation, mechanical needlestick perforation, fluid jet perforation or laser perforation and subsequent vessel pressure impregnation or by impregnation with the alternating pressure method. In addition to the additional costs for the perforation, especially the perforation openings are to be classified as disadvantageous for the visual appearance. The perforations themselves represent undesirable structural changes.

Impregnation pressures of more than the usual 15 bar in practice have an effect on the macrostructure and microstructure of the wood structure. For this purpose, the influence factors Wegsamkeit and strength of the wood are essentially decisive. Is the impregnation pressure above the strength of the wood, d. H. if the density is too low, it comes in hard-to-reach woods, such. B. spruce, to structural changes that affect in the form of short radial and tangential cracks. Also, the so-called "washboard effect", in which the early wood cells are compressed and the latewood cells largely withstand the impregnation pressure and do not change their shape, can be explained by the different firmness of early and latewood.

At an impregnation pressure of 80 bar, coniferous trees regularly suffer from cell upsets and cracks caused. The question of a critical impregnation pressure, in which these use, is very difficult to assess. The previous findings from the literature, however, allow the conclusion that scattered-porous woods, as z. B. in some hardwood species such. As eucalyptus occur, with a moderate to heavy bulk density and uniform distribution over the tree ring width, even with low Wegsamkeit a impregnation pressure of 80 bar can withstand. For conifers, this limit is about 30 bar. The spread of liquids in the wood is limited by the relatively high viscosity of liquids.

However, the pressure limits of 30 bar or 80 bar can be overcome if compressed gases are used as the carrier medium for the impregnants instead of liquids, which are compressed to near or above the so-called critical point and thereby liquid-like densities still comparatively low Possess viscosities. Such compressed gases are referred to as supercritical fluids.

The use of supercritical carbon dioxide (sc.CO ₂ ) has been described by SMITH, MORELL, SAHLE-DEMESSIE and LEVIEN (1993) and its effect under conditions of 135 and 245 bar and 40 ° and 80 ° C, respectively, on the flexural strength of spruce limestones examined. Neither the modulus of elasticity nor the fracture work showed significant differences to untreated wood after treatment with sc. CO ₂ . A comparable method for impregnating the other substrates mentioned above, such as ceramic, leather, paper or wood by means of sc. CO ₂ teaches DE OS 42 02 320.

An essential prerequisite for the impregnation, however, is a sufficiently high solubility of the impregnating media in the compressed gases, which, however, is the case for most impregnating media of conventional pressure impregnation of the boiler, such as, for example, Copper, chromium or arsenic salts, but also in many colors or flavors is not given.

In addition, the treatment of natural products with compressed gases can also easily lead to an extraction of ingredients. Since, for example, resins from resin-rich woods dissolve relatively well in sc CO ₂ , special methods are required to avoid undesirable consequences, such as the escape of the resin from the wood. Be on this topic described in WO 00/27601 and WO 00/27547 alternating pressure method to impregnate with sc. CO ₂ resin rich wood with organic wood preservatives. As impregnating propiconazole and tebuconazole and copper naphthenate, copper linolate and similar derivatives are described. FR 2 770 171 describes a basic form of supercritical impregnation. The pressure is raised starting from the ambient pressure continuously up to the supercritical range and possibly varied there. Processes of this kind often lead to damage to the material to be impregnated, because material-typical strength properties are not taken into account, or only a few materials can be processed without damage using these processes.

Another problem is that when impregnated by compressed gases often only the surface is good, the interior of the impregnated material, however, is insufficiently impregnated. This phenomenon is described in DE OS 100 41 003. As a remedy, an alternating pressure method is shown, which consumes more time for the pressure build-up than during pressure reduction. The pressure of the density of the compressed gas used is varied and thus its dissolving power compared to the impregnating medium. The process can be modified by addition of auxiliaries of up to 20% by weight to the gas (mixture).

Presentation of the invention

The object of the invention is, with a Druckimprägnierverfahren even with difficult to impregnate wood materials such. Spruce wood, an impregnating medium for changing the spectrum of properties (biological, chemical, physical or other properties) to bring into the interior of the solid or impregnated material without the structure, e.g. by previous perforation or by cell collapse and / or cracking.

Surprisingly, it has been found that with the impregnation method according to the invention liquid impregnation media can be introduced into wood materials at pressures well above the known cell collapse limit, without causing structural damage. This is achieved when first a protective pressure is built up to protect the wood material with a gas inside the porous wood material, before the liquid impregnating medium is added. The Height of the protective pressure is selected depending on the wood material to be impregnated and the gas used or impregnating medium if necessary and then specified for the implementation of the method. After adjusting the protective pressure, the pressure can be moderately further increased without causing cell collapse. When relaxing a likewise regulated procedure is necessary in order to avoid tearing of the wood material by internal overpressure, which occurs when the pressure in the autoclave is reduced too quickly.

In principle, this process can be carried out with any gases and various liquids. With gases whose critical state points in the moderate pressure-temperature range, that is preferably between 20-150 bar and 20 -150 ° C, such. With ethane, ethene, propane, propene, carbon dioxide or some halogenated alkanes, by dissolving a portion of the compressed gas in the liquid impregnation medium, a reduction in viscosity can be additionally achieved and thus improved penetration into the wood material. The load, ie the proportion of the impregnation medium which remains in the wood material after impregnation, is particularly high in the process according to the invention.

With this new impregnation process, which focuses on building up a protective pressure before the actual impregnation, a complete impregnation with high loadings over the entire cross-sectional area has become possible for the first time, even for hard-to-reach wooden materials.

In order to achieve an improved and uniform penetration of the impregnating medium into the wood-based material, it is possible to add a residence phase after the introduction of the impregnating medium into the autoclave, during which the pressure in the autoclave may change, if necessary. Such alternating pressure phases, as well as a circulation of the impregnating medium, promote an accelerated and homogeneous distribution of the impregnating medium in the wood material. In the alternating pressure phases, a pressure change is preferably made by lowering the pressure in the autoclave and then raising the pressure to the previous maximum pressure.

The new process differs significantly from the prior art in several respects. On the one hand, it allows at high pressures, in particular in the range of 15 bar to 300 bar, the use of conventional solvents (water, organic substances such as alcohols, ketones, esters, synthetic, mineral, vegetable or animal oils) as the basis for the liquid impregnating medium. The dissolving power of these solvents remains almost unchanged even at high pressures. It is thus much higher than the dissolving power of most compressed gases.

This allows the use of known and proven solvents with high or to the desired level adjustable solubility against the various active ingredients, which bring about the desired improvement in the product property of the solid. On the other hand, the use of known, conventional solvents far surpasses the very limited dissolving power of compressed gases in relation to many active substances. The solvency can be estimated in a simple approximation depending on the dielectric constant. This is for conventional liquid solvents such as water 80.4, methanol 32.6 and ethanol 24.3. For sc CO _2, on the other hand, the dielectric constant is between 1.1 and 1.6.

Solids may be added to the liquid impregnation medium, provided that they can penetrate into the solids to be processed. For example, nano-silicates having dimensions smaller than the penetration paths present in wood structures are suitable. Nanosilicates can be dispersed in alcohols, preferably in ethanol. This mixture is then an impregnation medium, which can be introduced after application of the protective pressure in wood. After completion of the impregnation, the alcohol evaporates and remains with nanosilicate solidified and hydrophobic wood.

The setting of a protective pressure of 15 to 100 bar is carried out without altering or damaging the physical properties or the structure of the wood-based material. Likewise, the increase in pressure during or after introduction of the impregnation medium, without causing damage to the wood material happens because this wood material is exposed to the construction of the protective pressure only a relatively small pressure difference.

The protective pressure is increased after the introduction of the impregnating medium by an amount of 30 to 200 bar, ie to a maximum of 300 bar. The pressure increase takes place at a rate of increase of 5 bar / hour to 150 bar / hour. The rate of increase is chosen inter alia as a function of the permeability of the wood-based material, the type of protective gas and the liquid impregnating medium.

• dem Schutz des zu imprägnierenden Holzwerkstoffs vor biologischer Besiedelung oder Abbau dienen, wie z. B. Biozide, speziell Insektizide oder Fungizide auf organischer Basis (zunächst Lindan und Pentachlorphenol, heute Triazole oder Biozide auf anorganischer Basis, wie z. B. Borsalze).
• dem Schutz vor Schädigung durch UV-Licht dienen, wie z. B. organische UV-Schutzmittel z. B. auf Epoxidbasis oder anorganische UV-Schutzmittel, wie z. B. Zinkoxid oder Titandioxid
• der Hydrophobierung dienen, wie z. B. auf organischer Basis, wie z. B. natürliche, synthetische oder mineralische Wachse wie Bienenwachs, Parafin, Montanwachs und Ölen, wie z. B. Lein- und Rapsöl als Vertreter pflanzlicher Öle, Mineralöle oder synthetische Öle z. B. auf Silikonbasis. Die Hydrophobierungsmittel können auch anorganischer Natur sein und z. B. aus Silikaten, insbesondere Nanosilikaten, Siliciumdioxiden, Bentoniten oder Alumiumoxiden bestehen.
• der Verfestigung dienen, wie natürliche und/oder synthetische Polymere, wie z. B. Balsamharze oder Polyolefine oder vernetzbare Monomere, wie z. B. Harnstoff, Phenol, Melamin oder Isocyanate oder die vorgenannten Silikate, insbesondere in der Form von Nanosilikaten
• der Farbgebung dienen, wie z. B. anionische, kationische oder Säurefarbstoffe, Reaktivfarbstoffe, Metallkomplexfarbstoffe oder Fluoreszensfarbstoffe, wie z. B. Fluoreszein
• der Geruchsgebung dienen, wie z. B. verschiedene aromatisch riechende natürliche Öle, wie z. B. Zedernöl, Sandelholzöl, Lavendelöl oder auch Limonen.
• dem Flammschutz dienen, wie z. B. Phosphate, insbesondere Ammoniumphosphat oder Borverbindungen.

As active ingredient in the impregnating medium, it is possible to use those substances which

• serve the protection of wood material to be impregnated against biological colonization or degradation, such. B. biocides, especially insecticides or fungicides on an organic basis (first lindane and pentachlorophenol, triazoles today or biocides on an inorganic basis, such as boron salts).
• to protect against damage from UV light, such. B. organic UV protection agents z. For example, based on epoxy or inorganic UV protection agents such. As zinc oxide or titanium dioxide
• serve the hydrophobing, such as. B. on an organic basis, such as. As natural, synthetic or mineral waxes such as beeswax, paraffin, montan wax and oils, such as. As linseed and rapeseed oil as representatives of vegetable oils, mineral oils or synthetic oils z. B. silicone-based. The water repellents may also be inorganic in nature and z. B. of silicates, in particular nanosilicates, silicas, bentonites or Alumiumoxiden exist.
• serve the solidification, such as natural and / or synthetic polymers, such as. As balsam resins or polyolefins or crosslinkable monomers, such as. As urea, phenol, melamine or isocyanates or the aforementioned silicates, especially in the form of nanosilicates
• the color serve, such. As anionic, cationic or acid dyes, reactive dyes, metal complex dyes or fluorescent dyes, such as. B. fluorescein
• serve the odor, such as. B. various aromatic-smelling natural oils such. As cedar oil, sandalwood oil, lavender oil or limonene.
• serve the flame retardant, such. For example, phosphates, in particular ammonium phosphate or boron compounds.

Experimental procedure and examples

The process according to the invention was tested in a high-pressure autoclave apparatus on various types of wood (fir, spruce, pine, birch and beech). The gases used are mainly carbon dioxide, but also nitrogen and R ₁₃₄ a (halogenated alkane). The impregnation medium is in each case composed of a solvent with the active ingredient dissolved therein. In order to enable an optically simple evaluation of the test results, a dye was added as active ingredient to the impregnating medium first.

The core of the apparatus is a 1.8 liter high pressure stirred autoclave. It is designed for a maximum operating pressure of 350 bar at 300 ° C. Depending on the size of the specimens, a frame can optionally be used, on which various samples can be placed on three levels. The gas is introduced into the autoclave via a pressure converter driven by compressed air. The liquid impregnating medium is pumped with a high-pressure pump against a previously inserted protective pressure in the autoclave. The compressed gas passes through the pumped impregnating medium and reduces its viscosity. By means of a pneumatically driven propeller stirrer, the gas-containing liquid impregnating medium can be circulated in the autoclave. The heating of the autoclave is done electrically from the outside via a heating jacket, which is connected to the temperature control.

Satisfactory impregnations, however, were always achieved only when pressure was first applied to the wood samples by means of a gas. For this purpose, the wood introduced into the autoclave were put under gas pressure for a certain time, so that a corresponding protective pressure could build up inside the porous solid wood. Then the impregnating medium, ie the active substance dissolved in a liquid base, was pumped in until the wood samples were surrounded on all sides by the liquid. Finally, the pressure was slowly further increased by renewed addition of the gas and then lowered again by lowering the liquid and subsequent expansion of the compressed gas to atmospheric pressure. Again, this step must not be too fast, so that the wood will not suffer any structural damage, e.g. Cell collapse or cracking experiences.

Phase 1:

Druckaufbau mit Schutzgas (ggf. nach Evakuierung)

Phase 2:

Verweilzeit bei Schutzgas-Druck

Phase 3:

Zudosierung des Imprägniermediums (ggf. mit leichtem Druckanstieg verbunden)

Phase 4:

Drucksteigerung durch weitere Zudosierung von Gas

Phase 5:

Verweilzeit bei höchstem Druck oder bei Druckwechselstufen

Phase 6:

Druckabsenkung (ggf. noch Evakuierung)

A typical pressure curve is shown schematically in FIG. 1 for the entire process. The procedural steps are divided into the following phases:

Phase 1:

Pressure build-up with inert gas (possibly after evacuation)

Phase 2:

Residence time at inert gas pressure

Phase 3:

Addition of the impregnation medium (possibly combined with slight increase in pressure)

Phase 4:

Pressure increase by further metered addition of gas

Phase 5:

Dwell time at highest pressure or at pressure change stages

Phase 6:

Pressure reduction (possibly evacuation)

The longest time interval of the process typically falls on the impregnation step with increasing pressure (phase 4). The residence time is required when a larger penetration of the workpiece with the impregnating medium is to be ensured for larger workpieces. Phase 5 can be carried out either at constant pressure or during pressure changes with individual reductions below the maximum pressure.

example 1

The staining medium used was neozapon red 335 dissolved in ethanol. Spruce and beech with the dimensions 2 x 4 x 19 cm were used as woods. The brain surfaces of the woods were sealed with epoxy resin. Over 40 minutes, the pressure was increased by CO ₂ - supply up to 50 bar. It turned after the pressure build-up a temperature of about 60 ° C. The woods lingered under these conditions for 1 hour under protective gas pressure. The dye solution was added within 20 minutes. The pressure in the autoclave increased to 65 bar. By adding gas, the pressure was increased to 115 bar over a period of 1 hour and 50 minutes. During the duration of the pressure increase the mean temperature was 58 ° C. At a pressure of 115 bar, the wood stayed in the pressure vessel for 15 minutes. Subsequently, the autoclave contents were drained and after 80 minutes, ambient pressure was reached. The temperature dropped to 50 ° C during the pressure drop.

Both woods were recognizable not deformed. The birch wood was also completely dyed through. No colorant had penetrated the wood over the closed areas of the spruce. Laterally, however, the color was up to about 1cm deep into the wood.

Example 2

In a further experiment, a commercial impregnating agent, a spray and brush pick type S 9900 Fa. Zweihorn water-alcohol-based was used. To carry out the experiment, a sample of pine wood with the dimensions 4.5 cm x 4.5 cm (wood cross section) x 20 cm (length in the fiber direction) was inserted into the autoclave. The autoclave was then filled with CO ₂ , which acts as compressed gas, for about 15 minutes at a pressure of 50 bar at a temperature of about 50 ° C. The set pressure was maintained for about 15 minutes to ensure the formation of the protective pressure inside the wood. In the subsequent phase of the impregnation process, the liquid impregnating agent was conveyed into the autoclave in about 15 minutes by means of the high-pressure pump integrated in the system. In order to avoid an increase in pressure during the metering of the impregnating medium, the gas phase was reduced by a valve attached to the top of the autoclave. In the actual impregnation step of the process, the pressure in the autoclave was increased to 100 bar over a period of 120 minutes. The relaxation of the autoclave to normal pressure was realized in 50 minutes.

The wood samples taken from the autoclave after the experiment were undamaged after the treatment and impregnated penetratingly, except for a few places.

Example 3

This experiment was carried out with Neozapon Red 355 dissolved in ethanol and with CO ₂ as compressed gas. For this, fir wood with the dimensions 4.5 cm x 4.5 cm (wood cross section) x 20 cm (length in the fiber direction) was introduced into the high-pressure stirred autoclave. At the beginning of the experiment, the wood introduced into the autoclave is pressurized with CO ₂ and a pressure of 50 bar is set at a temperature of about 50 ° C. within about 15 minutes. Subsequently, the pressure was maintained for about 15 minutes, thus allowing the construction of a protective pressure inside the wood. Thereafter, the dyeing medium was pumped in within about 20 minutes while maintaining the pressure of 50 bar. The isobaric dosing of the dye solution was accomplished by repeatedly venting gas through a top of the autoclave attached drain valve. Subsequently, the pressure was increased for 2 hours at an increase rate of 25 bar / h to 100 bar. After reaching the selected maximum pressure was released within 50 minutes by draining the liquid and the gas to ambient pressure.

The used fir wood was undamaged and almost uniformly colored after the treatment.

Example 4 (not according to the invention)

2 pieces of beech wood measuring 4.5 x 4.5 cm in cross-section and 15 cm in length was set with nitrogen to a protective pressure of 45 bar. Nanosilicate dispersed in ethanol (20% nanosilicate, 80% ethanol) was then added and the pressure was increased stepwise to 70 bar. The pressure increase was 5 bar per 5 minutes. The relaxation to ambient pressure took place in 10 minutes. It was achieved a loading of about 50% nanosilicates, based on the wood substance used.

As a result of the vacuum drying, the second sample crystallized out of the nano silicates on the beech wood surface.

Example 4 shows that wood can also be impregnated by means of liquid impregnating media with solids, provided that they have adequate dimensions. The introduction of nanosilicates hardens the wood z. B. against insect infestation and it hydrophobic wood. Impregnation with CO ₂ leads to precipitation of nanosilicates, surprisingly, the impregnation works well when nitrogen is used.

bibliography

• BELLMANN, H. (1968): Pretreatment of wood for pressure impregnation. Journal of the Institute of Wood Science 20, 54-62
• DALE, F.A. (1960): First commercial high-pressure plant starts production. Forest Products Newsletter No. 265, CSIRO, Melbourne
• DE OS 4202320 (1992): D. Knittel, W. Saus, R. Benken, H.-J. Buschmann and Schollmeyer E. (Knittel, D .; Saus, W. Benken, R., Buschmann, H.-J, Schollmeyer E.), Process for Impregnating Substrates.
• DE OS 10036566 (2000): A. Dürkop (Baur, Gaebel GmbH, 50986 Cologne), impregnating medium for wood.
• DE OS 10041003 (2000): J. Heidlas, Z. Zhang, K. Stork, J. Wiesmüller, M. Ober and J. Obersteiner (SKW Trostberg AG, 83308 Trostberg), Process for impregnating a carrier matrix with solid and / or liquid Compounds using compressed gases and substances so impregnated.
• DIN EN 350-2: 1994-10: Durability of wood and wood products - Natural durability of solid wood - Part 2: Guide to the natural durability and impregnability of selected wood species of particular importance in Europe.
• ELLWOOD, E.L. (1956): Progress Report No. 1, 8 pp, CSIRO, Div. of For. Prod., Melbourne
• PHILLIPS, E.W. (1933): Movement of the pit membrane in coniferous woods, with special reference to preservative treatment. Forestry 7, 109-120
• SIAU, J.F. (1970): Pressure impregnation of refractory woods. Wood Science, 3, 1, 1-7 TAMBLYN, N. (1953): Problems of Rail Sleeper Preservation in Australia II. Forest Products Newsletter No. 194, Commonwealth Scientific and Industrial Organization (CSIRO), Melbourne
• WO 00/27547 (1999): O. Henriksen (FLS Miljo A / S, DK-2500 Valby), A method of performing an impregnating or extracting treatment on a resin-containing wood substrate.
• WO 00/27601 (1999): O. Henriksen (FLS Miljo A / S, DK-2500 Valby), A method of performing an impregnating or extracting treatment on a resin-containing wood substrate
• WO 01/53050 (2001): MH Schneider (Woodtech Inc., Fredericton, New Brunswick E3A ₇ J ₃ (CA)), Wood impregnation.

Claims (12)

1. A method of impregnating a wood material with a liquid impregnating medium, comprising the steps of:

   introducing the wood material into an autoclave,

   - feeding-in a gas up to a predetermined pressure, and

   - reducing the pressure in the autoclave until ambient pressure is reached,
   characterized by the steps of, before reducing the pressure in the autoclave until ambient pressure is reached,

   - adjusting the pressure compensation within the wood material to a predetermined protection pressure, and

   - feeding-in a liquid impregnating medium, and finally

   - increasing the pressure in the autoclave by an amount of between 30 bar and 200 bar above the predetermined protection pressure for introducing the impregnating medium into the wood material.
2. The method according to claim 1, characterized in that the pressure in the autoclave is increased as the liquid impregnating medium is fed-in.
3. The method according to claim 1, characterized in that, after introducing the impregnating medium, a holding time follows, during which the wood material to be impregnated either remains within the autoclave under unchanged conditions, or during which the wood material to be impregnated is subjected to phases of changing pressure.
4. The method according to claim 1, characterized in that a gas is used having a critical point at a pressure of between 20 bar and 150 bar and a temperature of between 20°C and 150°C.
5. The method according to claim 1, characterized in that a gas is used which reduces the viscosity of the impregnating medium, preferably carbon dioxide or nitrogen.
6. The method according to claim 1, characterized in that the predetermined pressure within the autoclave before introducing the liquid impregnating medium is between 15 and 100 bar.
7. The method according to claim 1, characterized in that the pressure at the time of or after introducing the impregnating medium is increased above the predetermined protection pressure.
8. The method according to claim 1, characterized in that the pressure for introducing the impregnating medium is increased above the predetermined protection pressure at a rate of between 5 bar per hour and 150 bar per hour.
9. The method according to claim 1, characterized in that the liquid impregnating medium contains at least one substance which improves the biological, chemical, physical or other characteristics of the wood material.
10. The method according to claim 1, characterized in that the solvent in which the impregnating medium is dissolved has a higher solvent power, with respect to the impregnating medium, than the gas in its gaseous or superfluid state which is used for building up the protection pressure.
11. The method according to claim 1, characterized in that the liquid impregnating medium includes solid materials, in particular nanosilicates.
12. A wood material impregnated by the method according to at least one of the above claims 1 to 10.

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