• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    The present invention relates to a process for preparing a modified wood product. More specifically, the invention relates to a method of performing thermal modification, wherein the thermally modified wood is suitable for load bearing use. The present invention also relates to a modified wood product produced using said process.
    公开号:SE1650839A1
    申请号:SE1650839
    申请日:2016-06-15
    公开日:2017-12-16
    发明作者:Källander Björn
    申请人:Stora Enso Oyj；
    IPC主号:
    专利说明:

    |/IODIFIED WOOD PRODUCT AND A PROCESS FOR PRODUCINGSAID PRODUCT Field of the invention The present invention relates to a process for preparing a modifiedwood product. More specifically, the invention relates to a method ofperforming thermal modification, wherein the thermally modified wood issuitable for load bearing use. The present invention also relates to a modifiedwood product produced using said process.
    Background l/lany wood species are susceptible to damage caused by the external environment. Untreated wood that is exposed to moisture and/or soil forsustainable periods of time will become weakened by attacks from varioustypes of microorganisms or insects. lt is therefore of importance to treat theless durable wood in order to increase its resistance against moisture andfungal attack.
    There exist a number of different treatment methods which willincrease the resistance against biological decay of wood. Chemicaltreatments of wood in order to increase the biological durability and strengthhave been used for a long time. l/lany different chemicals may be added.These chemicals are normally called fungicides and they will provide long-term resistance to organisms that cause deterioration of the wood. lf it isapplied correctly, it can extend the productive life of timber by five to tentimes.
    Another known method to improve the resistance of wood is to treatthe wood at high temperatures to thermally modify the wood. The mostcommon method is the Thermowood process, in which the wood is treatedwith superheated steam at atmospheric pressure. The wood is dried toabsolute dryness at a temperature of up to approximately 130 °C, followed bya temperature increase to the temperatures required for obtaining themodification, commonly 190°C to 212°C.
    Thermal modification reduces the hygroscopicity of the wood, leadingto a lower Equilibrium Moisture Content (El/IC). Resistance to biologicaldecay is improved by a combination of reduced El/IC which reduces moistureavailable for fungus, and chemical changes that decreases the possibility forfungi and bacteria to thrive on the wood. The reduction in El/IC also improvesthe dimensional stability of the wood with less shrinkage and swelling asresult. One downside of thermally modified wood is the reduction in strength.Bending strength and surface hardness are reduced, and the wood becomesmore brittle, as a result of the modification process.
    Because of the reduced strength of wood that has been thermallymodified according to the established standard procedures, such wood is notrecommended for load bearing purposes.
    There have been several attempts at reducing the negative influence ofthermal modification on the strength properties, although with little to nosuccess. ln the Plato process, the heat treatment is performed in twoseparate steps, with a first treatment in hot water under elevated pressure,followed by drying to absolute dryness followed by treatment of the wood insuperheated steam at a high temperature. lt has also been suggested to do the actual thermal modification atother pressures than atmospheric. Examples of such methods are forinstance the Firmolin process in which the wood is treated in steam underelevated pressure. By treating the wood under elevated pressure, chemicalchanges such as hydrolysis are initiated at lower temperatures thanatmospheric pressure. An opposite attempt is the recently developedTermovuoto process in which the wood is treated under reduced pressure orvacuum. ln view of the limited success of the state of the art processes, there isa need for an improved modified wood product that does not suffer from thereduced bending strength traditionally associated with thermally modifiedwood.
    Summary of the invention lt has surprisingly been found that by removing water from the wood ata relatively low temperature, prior to exposing the wood to the elevatedtemperatures required for modification of the wood, the undesirable reductionof bending strength can be minimized and the treated wood can even besuitable for load bearing purposes.
    One object of the invention is thus to provide thermally modified solidwood which is suitable for load bearing purposes.
    Another object of the present invention is to provide a process forproducing said modified wood in an efficient way.
    These objects and other advantages are achieved by the process andthe product according to the independent claims.
    One embodiment of the present invention is thermally modified solidwood which is suitable for load bearing purposes. ln one embodiment of thepresent invention, pine or spruce wood is used.
    One embodiment of the present invention is thermally modified solidwood having a characteristic bending strength of at least 18 N/mmz measuredaccording to EN408:201O “Timber Structures. Structural Timber and GluedLaminated Timber. Determination of some Physical and l/lechanicalProperties” The characteristic bending strength is the 5-percentile value forthe population concerned.
    One embodiment of the present invention is thermally modified solidwood which is suitable for load bearing purposes above ground in accordancewith Use Class 3.1 as described in the European standard EN335:2013“Wood Preservatives. Test l/lethod for Determining the ProtectiveEffectiveness against Wood Destroying Basidiomycetes,” The present invention also relates to a process for preparing thermallymodified solid wood, wherein the wood is dried to an average moisturecontent of less than 5% at an average wood temperature of less than 100 °C, followed by an increase in wood temperature to above 140 °C. Averagemoisture content can be determined using methods known in the art. ln oneembodiment of the present invention, the wood is is dried to an averagemoisture content of less than 4% at an average wood temperature of lessthan 100 °C, followed by an increase in wood temperature to above 140 °C. lnone embodiment of the present invention, the wood is is dried to an averagemoisture content of less than 3% at an average wood temperature of lessthan 100 °C, followed by an increase in wood temperature to above 140 °C. ln one embodiment of the present invention, the drying is performed ina mixture of air, steam and other gases, or entirely in steam or in a fluid suchas water or oil. ln one embodiment of the present invention, the drying takes placeunder reduced pressure. ln one embodiment of the present invention, thedrying is performed under vacuum or near vacuum. ln one embodiment of thepresent invention, the drying is performed under elevated pressure. ln oneembodiment, the drying is performed at an absolute pressure below 1013mBar. ln one embodiment, the drying is performed at an absolute pressureabove 1013 mBar. ln one embodiment, the drying is performed at an absolutepressure of approximately 1013 mBar. ln one embodiment of the present invention, the energy for the dryingis transferred to the wood through convection by circulating air, steam, gas,liquid or mixtures of these media. ln one embodiment of the present invention, the energy for the dryingis transferred to the wood through heat from a hot material in contact with thewood or through dielectric heating such as high frequency heating using radiowaves or microwaves. ln one embodiment of the present invention, the treated wood issoftwood. ln one embodiment of the present invention, the treated wood ishardwood. ln one embodiment of the present invention, the wood is fromPinus sy/vestris. ln one embodiment of the present invention, the wood isfrom Picea abies. ln one embodiment of the present invention, the wood to be treated issorted prior to the heat treatment step and wood or planks with certaincharacteristics or properties are included or excluded from the treatmentaccording to the present invention. ln one embodiment of the present invention, the wood treated inaccordance with the present invention has been found to be of strength classC18 or higher according to the European standard EN338:2016 “Structuraltimber - strength classes” prior to treatment. ln one embodiment of the present invention, the wood treated inaccordance with the present invention has been found to be of strength classC22 or higher according to the European standard EN338:2016 “Structuraltimber - strength classes” prior to treatment. ln one embodiment of the present invention, the boards treated inaccordance with the present invention has a minimum local stiffness, prior totreatment, of at least 10 N/mmz when being bent on its flat side. ln one embodiment of the present invention, the wood treated inaccordance with the present invention has a dynamic e-modulus, prior totreatment, of at least 10 N/mmz.
    Brief description of the figures Figure1. Normal schedule for treatment of Thermowood D.
    Figure 2. Special treatment schedule according to the presentinvention. Wood is pre dried at low temperature.
    Figure 3. Stiffness and bending strength determined according to EN408 of untreated planks, planks treated according to normal Thermowood Dschedule, and planks treated according to a special schedule based on the invention.
    Detailed description The bending strength of wood, such as the thermally modified woodaccording to the present invention, can be measured using methods known inthe art. ln particular, the bending strength of dimensional lumber can bemeasured according to EN408 Timber structures - Structural timber and gluedIaminated timber - Determination of some physical and mechanicalproperties. Results from tests according to EN 408 are used to determinecharacteristic values according to European standard EN 384 Structuraltimber - Determination of characteristic values of mechanical properties anddensity. Requirements for different strength classes are defined in Europeanstandard EN 338 Structural timber - Strength classes. All of which arestandards recognized by a person skilled in the art.
    Thermal modification according to the present invention can be doneon pre dried wood as well as green, unseasoned, wood. The initial moisturecontent of the wood used in the process according to the present invention istypically at least 10%. ln one embodiment of the present invention, themoisture content is from 10% to 20%. ln a further embodiment, the moisturecontent is from 11% to 15%, such as from 12% to 14%. ln a furtherembodiment, the moisture content is about 12%. ln one embodiment, themoisture content is close to the fiber saturation point. The moisture content aswell as the fiber saturation point of wood can be determined using methodsknown in the art.
    The time required for the drying step depends on the properties of thewood used, but is generally in the range of from 5 hours to 96 hours forsoftwood.
    During the thermal modification step, the wood is heated at atemperature of from 160°C to 250 °C at atmospheric pressure or at atemperature of from 120°C to 250 °C at a pressure higher than atmosphericpressure. ln one embodiment of the present invention, the wood may bedensified during or after the therma| modification step. The densification maybe done by applying pressure to the wood. The densification may be done ata pressure of 1-3 kg/cmz and the maximum compression should be about10% of the thickness of the wood.
    For densification, it is preferred to apply both pressure and heat, sincethis combination will improve the densification of the wood. The densificationmay be done off-line, on-line or in-line, i.e. in-line with the process accordingto the invention. lf off-line densification is used, it is possible to use a hotpress after the therma| modification step. lf in-line densification is used it ispossible to use roller or plate based systems. The densification can be doneduring the therma| modification step or after the therma| modification step.
    By densifying the wood, the surface of the wood will become more set,i.e. the fibers on the surface have less tendency to react with moisture andretain its original form. This also leads to reduced tendency of fiber looseningon the surface of the wood. The surface density and thus also the hardness ofthe wood will also be improved.
    The produced thermally modified wood can also be used for loadbearing purposes.
    The term “solid wood” as used herein is defined as a solid woodcomponent of any kind of wood species, including finger jointed as well aslaminated products.
    The produced thermally modified wood product can be used for theproduction of many different products, such as cladding, decking, window anddoor profiles, light poles, jetties, joinery, furniture etc.
    Examples Thermal treatment of the material Saw falling 45 x 145 mm Norway spruce planks were heat treated accordingto a standard Thermowood D schedule and according to a special schedule according to the present invention. Both schedules used a 3 h plateau phaseat temperature of 212 °C. One set of planks from the same batch was kept untreated to be used as reference material.
    Standard Thermowood treatment The standard Thermowood D schedule was designed as shown in Figure 1.The 77 h schedule comprises of initial heating to 100 °C, drying phase atincreased temperature up to 130 °C, heating to plateau temperature, 3 htreatment at 212 °C, cooling, and conditioning.
    The climate at the end of HT-drying phase at 130 °C dry bulb temperatureand 99 °C wet bulb temperature corresponds to Equilibrium I/loisture Content(E|/IC) = 1 °/> to 2,5 °/>.
    Special treatment according to the present invention The special treatment schedule is based on the idea to reduce or eliminatehydrolysis of the material by drying it to very low I/IC at low temperature.Drying is done at 90°C dry bulb temperature with wet bulb temperaturegradually reduced to 50 °C, corresponding to E|/IC 25%.
    The low temperature drying phase in the test was 52.5 h, followed by a 28 hHT-drying phase before temperature was increased up to 212 °C. Figure 2 shows the trend curves from the special treatment.
    Results from bending tests The results from the bending strength tests are summarized in Table 1.
    Critical values for approval for load bearing use are marked with bold text.
    Table 1. Summary of test results from EN 408 bending tests Tested property Unit Untreated Normal Thermowoodreference Thermowood according toD presentinvenüonBending strength N/mm2 45,2 32,5 36,94-points edgewiseStrength standard N/mm2 9,6 10,7 12,2deviationCharacteristic N/mm2 28,0 15,2 19,6bending strengthNumber of planks n 22 77 75testedstiffness N/mm2 9,8 10,1 10,6Global E-modulusE-mod standard N/mm2 1,8 1,8 1,9deviationNumber of planks n 22 71 73 tested The test results show that strength values can be further improved by pre- sorting of the raw material prior to treatment. Table 2 shows strength values obtained after removal of planks with low local initial stiffness determined mechanically by a l/letriguard longitudinal machine stress rating equipment: Table 2. Test results from EN 408 bending tests with low stiffness planks removed.Tested property Unit Untreated Normal lmprovedreference Thermowood ThermowoodD DBenuing strength N/mm2 49,0 34,4 39,04-points edgewiseStrength standard N/mm2 9,6 10,7 11,8deviationCharacteristic N/mm2 38,9 16,8 21,0bending strengthNumber of planks n 16 30 32testedstiffness N/mm2 10,6 10,8 11,7Global E-modulusE-mod standard N/mm2 1,1 1,8 1,8deviationNumber of planks n 16 27 32 tested Removal of the planks with the lowest local stiffness gave a slight increase of the bending strength values.
    However, the stress grading was done by mechanical bending flatwise, and the bending tests were made edgewise. By using more advanced stress grading procedures a larger increase of characteristic strength values is expected.
    The improvement in bending strength is illustrated by the diagram in Figure 3. 11 In view of the above detailed description of the present invention, othermodifications and variations will become apparent to those skilled in the art.However, it should be apparent that such other modifications and variationsmay be effected without departing from the spirit and scope of the invention.
    权利要求:
    Claims (14)
    [1] 1. Thermally modified solid wood which is suitable for load bearingpurposes.
    [2] 2. Thermally modified solid wood according to claim 1, having acharacteristic bending strength of at least 18 N/mm2.
    [3] 3. Thermally modified solid wood according to claim 2, wherein thebending strength is measured according to EN408:2010.
    [4] 4. Thermally modified solid wood according to any one of claims 1to 3, which is suitable for load bearing purposes above ground.
    [5] 5. Thermally modified solid wood according to claim 4, wherein thesuitability for use above ground is defined in accordance with UseClass 3.1 as described in the European standard EN335:2013.
    [6] 6. Thermally modified wood according to any one of claims 1 to 5,wherein said wood is pine wood or spruce wood.
    [7] 7. Process for preparing thermally modified solid wood, wherein thewood is dried to an average moisture content of less than 5% atan average wood temperature of less than 100 °C, followed by anincrease in wood temperature to above 140 °C.
    [8] 8. Process according to claim 7, wherein the wood is dried to anaverage moisture content of less than 5% at an average woodtemperature of less than 100 °C, followed by an increase in woodtemperature to above 160 °C at atmospheric pressure, whereinthe wood is maintained at a temperature above 160 °C for at leastone hour, followed by cooling to ambient temperature.
    [9] 9. Process according to claim 8, wherein the wood is dried to anaverage moisture content of less than 5% at an average woodtemperature of less than 100 °C, followed by an increase in woodtemperature to a temperature above 160 °C and below 250 °C atatmospheric pressure, wherein the wood is maintained at a
    [10] 10.
    [11] 11.
    [12] 12.
    [13] 13.
    [14] 14. 13 temperature above 160 °C and below 250 °C for at least one hour,followed by cooling to ambient temperature. Process according to claim 7, wherein the wood is dried to anaverage moisture content of less than 5% at an average woodtemperature of less than 100 °C, followed by an increase in woodtemperature to above 120°C at a pressure higher thanatmospheric pressure, wherein the wood is maintained at atemperature above 120 °C for at least one hour, followed bycooling to ambient temperature. Process according to any one of claims 7 to 10, wherein thedrying is performed at an absolute pressure below 1013 mBar. Process according to any one of claims 7 to 10, wherein thedrying is performed at an absolute pressure above 1013 mBar. Process according to any one of claims 7 to 10, wherein thedrying is performed at an absolute pressure of approximately1013 mBar. Thermally modified solid wood obtainable by the processaccording to any one of claims 1 to 13.
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    SE540196C2|2018-04-24|
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    AU2017283797A1|2018-11-22|
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    WO2017216734A1|2017-12-21|
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    引用文献:
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    法律状态:
    优先权:
    申请号 | 申请日 | 专利标题
    SE1650839A|SE540196C2|2016-06-15|2016-06-15|Thermally modified wood product and a process for producing said product|SE1650839A| SE540196C2|2016-06-15|2016-06-15|Thermally modified wood product and a process for producing said product|
    US16/310,159| US20190329442A1|2016-06-15|2017-06-14|Thermally modified wood product and a process for producing said product|
    EP17812857.5A| EP3471934A4|2016-06-15|2017-06-14|A thermally modified wood product and a process for producing said product|
    AU2017283797A| AU2017283797A1|2016-06-15|2017-06-14|A thermally modified wood product and a process for producing said product|
    CN201780034320.0A| CN109219504A|2016-06-15|2017-06-14|Heat modification Wood products and the method for producing the product|
    RU2019100553A| RU2745502C2|2016-06-15|2017-06-14|Product of modified wood and method of its production|
    CA3023215A| CA3023215A1|2016-06-15|2017-06-14|A thermally modified wood product and a process for producing said product|
    PCT/IB2017/053522| WO2017216734A1|2016-06-15|2017-06-14|A thermally modified wood product and a process for producing said product|
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