TREATMENT OF WOOD

Abstract

The present invention relates methods for heat treatment of wood. The invention further relates to wood obtainable by the methods of the invention as well as the use of the method for preparing treated wood. The method comprises the step of pressurising said airtight tank (4) to a predefined pressure (P.sub.1) in order to establish a pressurised environment for said wood (6). The method comprises the step of placing said wood (6) in an airtight tank (4) and heating said wood (6) to a predefined temperature (T.sub.2, T.sub.3). The predefined pressure (P.sub.1) is kept so high that the water in the wood (6) cannot evaporate at the predefined temperature (T.sub.2, T.sub.3).

Claims

1. A method for heat treatment of wood comprising the steps of placing said wood in an airtight tank, pressurising said airtight tank to a predefined pressure to establish a pressurised environment for said wood, heating said wood to a predefined temperature by dielectric heating, wherein the predefined pressure during heating prevents water present in the wood from evaporating at the predefined temperature.

2-14. (canceled)

15. The method according to claim 1, wherein the dielectric heating is electromagnetic radiation.

16. The method according to claim 15 wherein a frequency of the electromagnetic radiation is 1-40 MHz.

17. The method of claim 1 wherein the dielectric heating is electromagnetic radiation by means of one or more electrodes.

18. The method of claim 1 wherein the heating is performed for a period of time in the range of 15 minutes to 10 hours.

19. The method of claim 1 wherein the step of pressurising and the step of heating is performed simultaneously, or wherein the step of pressurising is carried out prior to the step of heating.

20. The method of claim 1 wherein the predefined temperature is above the boiling point of water at atmospheric pressure, preferably above 140° C.

21. The method of claim 1 wherein the predefined pressure (P.sub.1) is above 5 bar such as 5-27 bar.

22. The method of claim 1 further comprising at least one of the steps of: cooling said wood, and drying said wood.

23. The method of claim 1 comprising the step of cooling said wood, wherein the cooling is performed by supplying a cooling medium to the tank.

24. The method of claim 23 wherein the cooling medium is a water-containing liquid.

25. The method of claim 23 wherein the pressure during the cooling step is suitably controlled and adapted having regard to the temperature.

26. The method of claim 1 further comprising the step of drying the wood, wherein during thee drying step, the pressure is reduced according to temperature.

27. The method of claim 26 wherein the drying step is performed by reducing the pressure in the tank as the temperature in the tank is reduced.

Description

DESCRIPTION OF THE DRAWINGS

[0059] The invention will become more fully understood from the detailed description given hereof below. The accompanying drawings are provided by way of illustration only, and thus, they are not limitative of the present invention. In the accompanying drawings:

[0060] FIG. 1A shows a first schematic cross-sectional view of an apparatus for heat treatment of wood according to the invention;

[0061] FIG. 1B shows a second schematic cross-sectional view of the apparatus shown in FIG. 1 A;

[0062] FIG. 2A shows a pressure versus time curve of a first method according to the invention;

[0063] FIG. 2B shows a temperature versus time curve of the first method according to the invention;

[0064] FIG. 2C shows a pressure versus time curve of a second method according to the invention;

[0065] FIG. 2D shows a temperature versus time curve of the second method according to the invention;

[0066] FIG. 2E shows a pressure versus time curve of a third method according to the invention;

[0067] FIG. 2F shows a temperature versus time curve of the third method according to the invention;

[0068] FIG. 2G shows a pressure versus time curve of a fourth method according to the invention;

[0069] FIG. 2H shows a temperature versus time curve of the fourth method according to the invention;

[0070] FIG. 3 shows a schematic cross-sectional view of an apparatus for heat treatment of wood according to the invention;

[0071] FIG. 4 shows a schematic cross-sectional view of another apparatus for heat treatment of wood according to the invention;

[0072] FIG. 5A illustrates traditional impregnation wood for comparison. The traditional impregnation was accomplished using vacuum (40 minutes) followed by pressurisation (3 hours);

[0073] FIG. 5B illustrates wood impregnated according to the invention (combination of pressurisation and heating); and

[0074] FIG. 5C illustrates wood fully impregnated according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0075] Referring now in detail to the drawings for the purpose of illustrating preferred embodiments of the present invention, a schematic cross-sectional view of an apparatus 2 of the present invention is illustrated in FIG. 1A.

[0076] FIG. 1A illustrates a schematic cross-sectional view of an apparatus 2 for heat treatment of wood 6 according to the invention. FIG. 1B illustrates another schematic cross-sectional view of the apparatus 2 shown in FIG. 1A.

[0077] The heat treatment apparatus 2 comprises a tank 4 having a cylindrically shaped portion 66 extending along the longitudinal axis X of the tank 4. FIG. 1A illustrates that the cross section of the cylindrically shaped portion 66 is circular. A tube 22 is provided in the top portion of the tank 4. This tube 22 connects the tank 4 with compressor 20 configured to pressurise the tank 4.

[0078] A shaft 28 is rotably mounted to the lower portion of the tank 4. Two roller members 12 are rotably mounted to the shaft 28. FIG. 1B illustrates that four parallel shafts 28 are provided at the lower portion of the tank 4. These shafts 28 and the roller members 12 attached to them constitute a roller conveyer.

[0079] A plurality of wood boards 6 is stacked in the tank 4. The wood boards 6 rest on a lower plate-shaped support member 26 and are sandwiched between the lower support member 26 and an upper plate-shaped support member 24.

[0080] A first electrode 8 is provided at the upper support member 24, while a second electrode 10 is provided at the lower support member 26.

[0081] The tank 4 comprises a first closed end portion 68 and another end portion 70. An opening is provided at the end portion 70. The end portion 70 comprises a tank door 30 rotably attached to the remaining portion of the tank 4 by means of a joint 32. Accordingly, the tank door can be opened in order to fill wood 6 into the tank 4 or to remove heat-treated wood 6 from the tank 4. The use of the roller conveyer 12, 28 eases these processes.

[0082] When wood boards 6 have been arranged in the tank 4, and the tank has been closed, the heat treatment may be initiated. The heat treatment is carried out by means of heating by electromagnetic radiation through one or more electrodes.

[0083] Although not shown, the electrodes 8, 10 may be electrically connected to a (high frequency) generator configured to generate the required electromagnetic radiation, e.g. within the range 1-40 MHz, such as 10-30 MHz, e.g. about 13.56 MHz. It may be preferred that the frequency of the electromagnetic radiation is approximately 13.56 MHz or approximately 27.12 MHz, since it has been shown that the heating of wood is very efficient at these frequencies.

[0084] Generation of heat will, however, not be initiated before the pressure in the tank 4 exceeds a predefined pressure level e.g. between 5-27 bar, such as 20 bar. The predefined pressure level is determined on the basis of the required heating temperature in such a manner that the water in the wood will not boil (change into a gas). This requires that the pressure is kept above a pressure level depending on the heating temperature.

[0085] Since the tank 4 is a pressurised chamber, the water (in the wood) can be heated far beyond the standard 100° C. without boiling. In other words, the pressured tank 4 is capable of keeping the water in liquid phase at high temperatures.

[0086] The compressor 20 may be controlled by a control member (not shown) e.g. shaped as a control box electrically connected to the compressor and to one or more pressure sensors (not shown).

[0087] The heating may be initiated when the desired pressure is established in the tank 4. Once the desired temperature is reached, this temperature may be maintained for a predefined period. It is possible to change the temperature and/or pressure in the tank once or several times and maintain a fixed temperature and/or pressure for a predefined period.

[0088] It may be an advantage to arrange a pressure sensor (not shown) in the tank 4 or in the tube 22. A pressure sensor may be applied to detect the pressure and thus to control the wood treatment process.

[0089] By using high frequency electromagnetic radiation, it is possible to conduct a homogeneous heating of the wood. Hereby, it is possible to provide a homogeneous wood quality.

[0090] FIG. 2A illustrates a pressure 62 versus time 60 curve 72 of a first method according to the invention. Pressure 62 is plotted against time 60.

[0091] The curve 72 has a first section I, in which section I the pressure 62 is kept at a constant level P.sub.1. The curve 72 has a second section II, in which section II the pressure is reduced (linearly) with a constant rate. The duration of the first section I is t.sub.3, while the duration of the second section II is t.sub.4−t.sub.3.

[0092] FIG. 2B illustrates a temperature versus time curve 74 corresponding to the method referred to with reference to FIG. 2A. The curve 74 comprises a first section I in which the temperature 64 is linearly increased from a first temperature T.sub.1 to a second temperature T.sub.2. When the temperature T.sub.2 has been reached at the time t.sub.1, the temperature T.sub.2 is maintained to time t.sub.2. The constant temperature period is the second section II of the curve 74.

[0093] At time t.sub.2 the temperature 64 is linearly decreased until a temperature T.sub.1 is reached at the time t.sub.3. This time period corresponds to the third section III of the curve 74. The temperature T.sub.1 is kept constant in the fourth section IV of the curve 74 extending between time t.sub.3 and time t.sub.4.

[0094] When comparing FIG. 2A and FIG. 2B one can see that a high pressure P.sub.1 is maintained during the complete high temperature phase (section II). This means that the water in the wood will not evaporate. Accordingly, the desired structural changes of the wood will occur.

[0095] FIG. 2C illustrates a pressure versus time curve 72 of a second method according to the invention.

[0096] The curve 72 has a first section I, in which the pressure 62 is kept at a constant level P.sub.1. The curve 72 has a second section II, in which the pressure is reduced with a decreasing rate. The duration of the first section I is t.sub.5, whereas the duration of the second section II is t.sub.6−t.sub.5.

[0097] FIG. 2D illustrates a temperature versus time curve 74 corresponding to the method referred to with reference to FIG. 2C. The curve 74 comprises a first section I in which the temperature 64 is linearly increased from a first temperature T.sub.1 to a second temperature T.sub.2. When the temperature T.sub.2 has been reached at the time t.sub.1, the temperature T.sub.2 is maintained to time t.sub.2. The constant temperature period is the second section II of the curve 74.

[0098] At time t.sub.2 the temperature 64 is linearly increased until a temperature T.sub.3 has been reached at the time t.sub.3. This time period corresponds to the third section III of the curve 74. The temperature T.sub.3 is kept constant in the fourth section IV of the curve 74 extending between time t.sub.3 and time t.sub.4. The temperature 64 is linearly decreased during the fifth section V of the curve 74 extending between time t.sub.4 and time t.sub.5. Hereafter a sixth section VI (between time t.sub.5 and t.sub.6) with a constant temperature T.sub.1 follows.

[0099] FIG. 2E illustrates a pressure 62 versus time 60 curve 72 of a third method according to the invention. Pressure 62 is plotted against time 60.

[0100] The curve 72 has a first section I, in which section I the pressure 62 is kept at a constant level P.sub.1. The curve 72 has a second section II, in which section II the pressure is reduced with an increasing rate. The duration of the first section I is t.sub.3, while the duration of the second section II is t.sub.4−t.sub.3.

[0101] FIG. 2F illustrates a temperature versus time curve 74 corresponding to the method referred to with reference to FIG. 2E. The curve 74 comprises a first section I in which the temperature 64 is increased from a first temperature T.sub.1 to a second temperature T.sub.2. When the temperature T.sub.2 has been reached at the time t.sub.1, the temperature T.sub.2 is maintained to time t.sub.2. The constant temperature period is the second section II of the curve 74.

[0102] At time t.sub.2 the temperature 64 is decreased until a temperature T.sub.1 is reached at the time t.sub.3. This time period corresponds to the third section III of the curve 74. The temperature T.sub.1 is kept constant in the fourth section IV of the curve 74 extending between time t.sub.3 and time t.sub.4.

[0103] FIG. 2G illustrates a pressure versus time curve 72 of a fourth method according to the invention.

[0104] The curve 72 has a first section I, in which the pressure 62 is kept at a constant level P.sub.1. The curve 72 has a second section II, in which the pressure is reduced with a decreasing rate. The duration of the first section I is t.sub.3, whereas the duration of the second section II is t.sub.4−t.sub.3.

[0105] FIG. 2H illustrates a temperature versus time curve 74 corresponding to the method referred to with reference to FIG. 2G. The curve 74 comprises a first section I in which the temperature 64 is increased from a first temperature T.sub.1 to a second temperature T.sub.2. When the temperature T.sub.2 has been reached at the time t.sub.1, the temperature 64 is further raised until time t.sub.2. The period is the second section II of the curve 74.

[0106] At time t.sub.2 a slight temperature increase is followed by a temperature decrease until a temperature T.sub.1 has been reached at the time t.sub.3. This time period corresponds to the third section III of the curve 74. The temperature T.sub.3 is kept constant in the fourth section IV of the curve 74 extending between time t.sub.3 and time t.sub.4.

[0107] The methods explained with reference to FIG. 2 applies a pressure P1 that ensures that the water in the wood does not evaporate all though a high temperature is maintained in the tank. Accordingly, it is possible to provide the desired heat-induced structural changes in the wood.

[0108] FIG. 3 illustrates a schematic cross-sectional view of an apparatus 2 for heat treatment of wood 6 according to the invention.

[0109] The heat treatment apparatus 2 comprises a tank 4 having a cylindrically shaped portion extending along the longitudinal axis X of the tank 4. A first tube 56 and a second tube 56′ are provided in the top portion of the tank 4. The first tube 56 connects the tank 4 with a reservoir 42 and a compressor 52 via a tube 54. The compressor 52 is configured to pressurise the tank 4.

[0110] A valve 48 is provided in the tube 54 between the compressor 52 and the tank 4. The valve is configured to establish and disconnect fluid communication between the compressor 52 and the tank 4. The compressor 52 may be controlled by a control member (not shown) e.g. shaped as a control box electrically connected to the compressor 52 and to one or more pressure sensors (not shown).

[0111] Another valve 46 is provided between the reservoir 42 and the tank. The valve 46 is adapted to establish and disconnect fluid communication between the reservoir 42 and the tank 4. The reservoir may contain any fluid of interest e.g. a wood preservation liquid.

[0112] A pump 58 is connected to the tube 56′. A valve 50 is provided between the pump 50 and the tank 4. By means of the valve 50 it is possible to establish fluid communication between the tank 4 and the pump 58. On the other hand, by closing the valve 50, it is possible to shut off the connection between the tank 4 and the pump 58. A reservoir 44 is provided above the pump 58. The reservoir 44 is in fluid communication with the pump 58. Accordingly, the pump 58 may be used to pump e.g. a cooling fluid from the reservoir 44 into the tank 4 and to pump the fluid back into the reservoir.

[0113] Ten shafts are rotably mounted to the lower portion of the tank 4. A number of roller members 12 are rotably mounted to the shafts. The shafts and the roller members 12 attached to them constitute a roller conveyer for easing transport of wood into the tank 4 and out of the tank 4.

[0114] A plurality of wood boards 6 is stacked in the tank 4. The wood boards 6 are resting on a lower plate-shaped support member 26. The wood boards 6 are sandwiched between the lower support member 26 and an upper plate-shaped support member 24.

[0115] A first group of electrodes 8, 8′, 8″ and a second group of electrodes 10, 10′ have been inserted into the batch of stacked wood 6. The groups of electrodes are electrically connected to a HF (high frequency) generator 18 by cables 14, 14′ and 16, 16′ in such a manner that, when operating the generator 18, the first group 8, 8′, 8″ has a polarity being opposite to that of the second group 10, 10′. The electrodes 8, 8′, 8″, 10, 10′ are arranged in such a way that two neighbouring electrodes have opposite polarity.

[0116] The electrodes 8, 8′, 8″, 10, 10′, the associated cables 14, 14′ and 16, 16′ and the HF-generator 18 constitute an electrode system, which is capable of producing electromagnetic radiation in the frequency range of approximately 10 MHz to approximately 30 MHz.

[0117] The plate-shaped upper support plate 24 and the lower plate-shaped support plate 26 are connected by a first clamp 38 and a second clamp 40. The clamps 38, 40 provide a compression force pressing the two support plates 24, 26 together. The compression force will counteract deformations, such as twisting and bending, of the wood boards 6 caused by the heating process. The clamps 38, 40, and the upper 24 and lower 26 support plates constitute a compression system configured to prevent deformations of the wood 6 during the heating process.

[0118] The tank 4 comprises a first closed end portion 68 and another end portion 70. An opening is provided at the end portion 70. The end portion 70 comprises a detachable tank door 34 configured to be detachably attached to the remaining portion of the tank 4. A sealing member shaped as an O-ring 36 is provided next to the door 34.

[0119] The tank door 34 can be removed in order to fill wood 6 into the tank 4 or to remove heat-treated wood 6 from the tank 4. The use of the roller members 12 eases these processes.

[0120] After arranging the wood boards 6 in the tank 4 and closing the tank, the heat treatment may be initiated. The heat treatment is carried out by means of the electrode system, which is capable of producing electromagnetic radiation in the frequency range of approximately 10 MHz to approximately 30 MHz.

[0121] The heat generation will not be initiated before the pressure in the tank 4 exceeds a predefined pressure level e.g. between 5-27 bar, such as bar. Examples of such treatment method are illustrated in FIG. 2.

[0122] It may be an advantage to arrange a pressure sensor (not shown) in the tank 4 or in one of the tubes 54, 56. Accordingly, the pressure sensor may be applied to detect the pressure and thus to control the wood treatment process.

[0123] By using high frequency electromagnetic radiation, it is possible to conduct a homogeneous heating of the wood. Hereby, it is possible to provide a homogeneous wood quality.

[0124] FIG. 4 illustrates a schematic cross-sectional view of an apparatus 2 for heat treatment of wood 6 according to the invention. The apparatus 2 basically corresponds to the apparatus 2 shown in FIG. 3.

[0125] The apparatus 2 comprises a tank 4 having a central cylindrically shaped portion extending and two end portions 68, 70. The first end portion 68 is an integrated part of the tank 4. The second end portion 70, however, is configured to be detachably attached to the opposite (open) portion of the tank 4. The second end portion 70 comprises a door 34 and an O-ring 36 adapted to be applied for the purpose of sealingly attach the door 34 to the remaining portion of the tank 4.

[0126] A first tube 56 and a second tube 56′ are provided in the top portion of the tank 4. The first tube 56 connects the tank 4 with a reservoir 42 and a compressor 52 via another tube 54. The compressor 52 is adapted to pressurise the tank 4.

[0127] A compressor valve 48 is arranged in the tube 54 between the compressor 52 and the tank 4. The compressor valve 48 is configured to establish communication between the compressor 52 and the tank 4 and to disconnect this fluid communication. The compressor 52 may be controlled by any suitable control member (not shown), such as a control box, which is electrically connected to the compressor 52 and optionally to one or more pressure sensors.

[0128] A reservoir valve 46 is provided between the reservoir 42 and the tank 4. The reservoir valve 46 is configured to establish communication between the reservoir 42 and the tank 4 and to limit or completely shut off this fluid communication. The reservoir 42 may contain any fluid of interest e.g. a wood preservation liquid. The apparatus 2 may be configured to perform several treatment processes including impregnation of a wood preservation liquid.

[0129] A pump 58 is connected to the tube 56′. A pump valve 50 is arranged between the pump 50 and the tank 4. It is possible to establish fluid communication between the tank 4 and the pump 58 by means of the pump valve 50.

[0130] Further, by at least partly closing the valve 50, it is possible to decrease the flow or even completely shut off the connection between the tank 4 and the pump 58. A reservoir 44 is provided above the pump 58. The reservoir 44 is arranged in fluid communication with the pump 58. Therefore, the pump 58 can be used to pump e.g. a cooling fluid from the reservoir 44 into the tank 4 and to pump the fluid back into the reservoir 44.

[0131] Ten shafts are rotably mounted to the lower portion of the tank 4. A number of roller members 12 are rotably attached to the shafts. The shafts and the attached roller members 12 constitute a roller conveyer configured to ease the transport of wood into the tank 4 and out of the tank 4.

[0132] A plurality of wood boards 6 is stacked in the tank 4. The wood boards 6 are resting on a lower plate-shaped support member 26. The wood boards 6 are sandwiched between the lower support member 26 and an upper plate-shaped support member 24.

[0133] A first group of electrodes 8, 8′, 8″ and a second group of electrodes 10, 10′ have been inserted into the batch of stacked wood 6. The groups of electrodes are electrically connected to a HF (high frequency) generator 18 by cables 14, 14′ and 16, 16′ in such a manner that, when operating the generator 18, the first group 8, 8′, 8″ has a polarity being opposite to that of the second group 10, 10′. The electrodes 8, 8′, 8″, 10, 10′ are arranged in such a way that two neighbouring electrodes have opposite polarity.

[0134] The electrodes 8, 8′, 8″, 10, 10′, the associated cables 14, 14′ and 16, 16′ and the HF-generator 18 constitute an electrode system, which is capable of producing electromagnetic radiation in the frequency range of approximately 10 MHz to approximately 30 MHz.

[0135] The plate-shaped upper support plate 24 and the lower plate-shaped support plate 26 are connected by a first clamp 38 and a second clamp 40. The clamps 38, 40 provide a compression force pressing the two support plates 24, 26 together. The compression force will counteract deformations, such as twisting and bending, of the wood boards 6 caused by the heating process. The clamps 38, 40, and the upper 24 and lower 26 support plates constitute a compression system configured to prevent deformations of the wood 6 during the heating process.

[0136] After arranging the wood boards 6 in the tank 4 and closing the tank, the heat treatment may be initiated. The heat treatment is carried out by means of the electrode system, which is capable of producing electromagnetic radiation in the frequency range of approximately 10 MHz to approximately 30 MHz.

[0137] The heat generation will not be initiated before the pressure in the tank 4 exceeds a predefined pressure level e.g. between 5-27 bar, such as bar. Examples of such treatment method are illustrated in FIG. 2.

[0138] It may be an advantage to arrange a pressure sensor (not shown) in the tank 4 or in one of the tubes 54, 56. Accordingly, the pressure sensor may be applied to detect the pressure and thus to control the wood treatment process.

[0139] By using high frequency electromagnetic radiation, it is possible to conduct a homogeneous heating of the wood. Hereby, it is possible to provide a homogeneous wood quality.

[0140] The method of the invention is further illustrated by the following nonlimiting examples.

EXAMPLES

Example 1

[0141] All tests were conducted and approved by The Danish Technological Institute in Denmark where a laboratory machine owned by DWT A/S was installed. Tests were performed using logs of wood (Pine, Spruce, Oak and Meranti Mahogany) with dimensions 1200×45×95 mm having a moisture content of 20-25%. The logs of wood were subjected to treatment with a selection of solutions (liquids) selected from water containing colour pigment, alum (5%, 10%, 20%), boric solution (20%), and copper, respectively. The logs of wood were treated using the method of the invention by which the logs of wood were subjected to a pressuring step, and a heating step. The results are presented in Example 2.

Example 2

[0142] The logs of wood treated according to Example 1 were analysed for uptake of different liquids at various concentrations. The results are indicated in Table 1. “Full imp.” denotes “full impregnation”. The uptake of the various solutions were determined on the basis of the weight of the logs before and after being treated using the method according to the invention.

TABLE-US-00001 TABLE 1 Test results. Spruce Meranti Liquid Pine (25%) Oak Mahogany Water with colour 579 kg/m.sup.3 478 kg/m.sup.3   340 kg/m.sup.3 307 kg/m.sup.3 pigment Alum 5% solution Full imp. Full imp. Alum 10% solution Full imp. Full imp. Alum 20% solution Full imp. Full imp. Boric solution 20% Full imp. Wood tar/linseed +300 kg/m.sup.3 oil 50/40 Copper Full imp. 438 kg/m.sup.3 (Celcure AC800)

[0143] The results confirms that the method according to the invention can be controlled so as to provide complete or partial absorption of liquids through the wood. The laboratory plant has further proven a stable production of Spruce and Pine wood, where alum, and copper have been recorded by more than 400 kg per m3 of wood.

[0144] Tests performed document that the method of the invention makes it possible to achieve full impregnation into heartwood. Test performed further document that the method of the invention makes it possible to applicate both water-based and oil-based liquids to wood and achieve full impregnation into heartwood.

Example 3

[0145] The impregnation depth is a very important parameter in the treatment of wood. The impregnation depth determines the possible uses of the wood and the durability thereof. Most countries apply very strict regulations to outdoor uses of impregnated wood as well as to fire resistance, durability and resistance towards rot and fungi. Furthermore, impregnated wood must also fulfil demands as regards environmental issues and human health issues due to the use of chemicals and biocides in the impregnation process.

[0146] In general, the following impregnation depths are required: [0147] Full impregnation of Spruce wood (25% humidity) and Pine heartwood, which both cannot be impregnated using traditional treatments. [0148] Full impregnation for manufacturing of wood being fire resistant, having extremely long lifecycle (marina piles) and for building structural elements. [0149] 6 mm impregnation for manufacturing of wood with increased durability and fire resistance performances, for outdoor application in several (most common) field of application. [0150] 3 mm impregnation for manufacturing of wood with improved characteristics included aesthetics, for instance for furnishing and flooring.

[0151] The logs treated and analysed in Example 1 and 2 were subjected to inspection as regards impregnation depth. The results are shown in FIG. 5. FIG. 5A illustrates traditional impregnation wood for comparison. The traditional impregnation was accomplished using vacuum (40 minutes) followed by pressurization (3 hours). FIG. 5B illustrates wood 84 impregnated according to the invention (combination of pressurisation and heating). FIG. 5C illustrates wood 84 fully impregnated by the method according to the invention. Accordingly, the sapwood 80, the heartwood 76 and the pith 82 of the heat treated wood 84 can be impregnated by using by the method according to the invention. Moreover, gnarl 78, 78′ (not shown) can be impregnated by using by the method according to the invention.

[0152] In FIG. 5A it can be seen that the impregnation depth D corresponds to approximately one sixth of the thickness of the wood. This means that only the periphery of the wood is impregnated. Accordingly, only a portion of the sapwood 80 is protected by the impregnation. Neither the heartwood 76, the pith 82 nor the gnarl 78, 78′ are impregnated.

[0153] As the tests performed document, the method of the invention provides the following benefits: [0154] Full impregnation of wood both with oil-based, salt-based and water based solutions. [0155] Full impregnation of softwood like wet Spruce (25% humidity) and Pine. [0156] Full impregnation of hardwood like Mahogany and Oak. [0157] Full penetration to heartwood (+50 mm). [0158] Impregnation can be achieved without pre-drying the wood. [0159] Handling of wood tar and linseed oil as paint is usually not adequate for the modern building industry. Ideally, wood tar and linseed oil should be applied 3-5 times on the particular wood surface with a drying range of one week per supply. The method of the invention allows full application of wood tar and linseed oil directly into the raw wood in the treatment process.

LIST OF REFERENCE NUMERALS

[0160] 2 Wood treatment apparatus [0161] 4 Tank [0162] 6 Wood [0163] 8, 8′, 8″, 10, 10″ Electrode [0164] 12 Roller member (roller conveyer) [0165] 14, 16 Cable [0166] 18 HF Generator [0167] 20 Compressor [0168] 22 Tube [0169] 24 Upper support member [0170] 26 Lower support member [0171] 28 Shaft [0172] 30 Door [0173] 32 Joint [0174] 34 Door [0175] 36 Sealing member (O-ring) [0176] 38, 40 Clamp member [0177] 42, 44 Reservoir [0178] 46, 48, 50 Valve [0179] 52 Compressor [0180] 54, 56, 56′ Tube [0181] 58 Pump [0182] 60 Time [0183] 62 Pressure [0184] 64 Temperature [0185] P.sub.1 Pressure [0186] T.sub.1, T.sub.2, T.sub.3 Temperature [0187] t.sub.1, t.sub.2, t.sub.3, t.sub.4, t.sub.5, t.sub.6 Time [0188] X Longitudinal axis [0189] 66 Cylindrical portion [0190] 68, 70 End portion [0191] 72, 74 Curve [0192] 76 Heartwood [0193] 78, 78′ Gnarl [0194] 80 Sapwood [0195] 82 Pith [0196] 84 Heat treated wood [0197] D Impregnation depth [0198] I, II, III, IV, V, VI Section