JP2019184097A - Method of drying lumber - Google Patents

Abstract

An object of the present invention is to improve the drying strength and bending strength of wood which is easy to implement and has a high yield at a practically usable level by positively utilizing the falling characteristics of cells. A wood drying method for drying wood taken into a shape other than the shape of a log, wherein the wood is heated and water is released only from a tangential direction to the annual rings of the wood. A drying step of heating and drying the wood to a predetermined target moisture content while maintaining the wood at a drying temperature at which cells of the wood can fall. In addition, in the case of raw wood or wood that is not saturated, the provision of a water-saturation step enables drying of wood with a high yield equivalent to that of raw wood or wood that is saturated, and improvement in bending strength. I can do it. [Selection diagram] Fig. 1

Description

  The present invention relates to a method for drying wood, and more particularly, to a method for drying wood having cell collapse characteristics.

  In recent years, there has been an increasing demand for hardwood materials such as Sudajii (Itagii, Nagajii), Tsuburajii (Kojii), Kunugi, Konara, Mizunara, oaks and the like. These hardwood materials are expected to be effectively used as building materials such as flooring materials and furniture materials.

  However, these woods are susceptible to damage such as internal cracking in the wood during the drying process, and are difficult to dry in a short period by artificial drying. For this reason, it is often difficult to efficiently put it to practical use.

  The internal crack is described in P. As described in 369, it refers to an internal crack observed when a plate is traversed after drying. In the cross section of wood, when only the inner layer portion shrinks without shrinking the surface layer portion, drying stress acts as a tensile force on the inner layer portion. If this pulling force exceeds the strength of bonding between cells, internal cracks will occur.

  One of the causes of wood internal cracking is known to be cell collapse. The drop of cells refers to a phenomenon in which specific cells and tissues are crushed as moisture (free water) decreases from the cell lumen in the process of drying the wood in the moisture content region above the fiber saturation point.

  This drop of cells is attributed to a tensile force (negative pressure) generated in the free water when the free water (water) in the lumen of the cell decreases. This drop of cells is due to the presence or absence of bubbles in the cell lumen, the presence or absence of a hole in the cell wall that can be vented (whether or not the wall hole has a hole that can be vented), and dryness. It is likely to occur when various conditions such as temperature are met. As described in Non-Patent Document 2, the currently known maximum value of tensile force is 277 atm (286 kgf / cm 2) at 10 ° C.

  The relationship between cell drop and internal cracking is as follows.

  When the state where the cell wall dries from the surface (surface layer) of the wood gradually moves to the inside (inner layer), when the raw material above the fiber saturation point or saturated wood is dried, the cell lumen first begins from the surface layer part. As the free water decreases, the cells fall as the free water decreases, and then the bound water also decreases through the fiber saturation point. In the surface layer of wood, even if the cell drop deformation occurs, the wet deformation is still maintained, so the drop deformation is not dried and fixed, and since the drop deformation once generated, there is an inner layer that has not yet started shrinking, Some will try to return to the original shape. In this drying process, the bound water evaporates first from the surface layer. In general, the bound water is H2O that is adsorbed on the inner surface of the wood in the microscopic voids existing in the cell wall. Therefore, when the drying progresses and the cell wall on the surface layer falls below the fiber saturation point, the bound water is Desorbed (dried) from the inner surface in the void. Therefore, the space is closed and the cell wall becomes dense, the cell wall in the surface layer portion begins to harden, and is dried and fixed in a state where the aforementioned deformation has returned a little. Thereafter, when drying proceeds to the inner layer and shrinkage starts, the hardened surface layer acts as a support rod against the shrinkage of the inner layer as a shell, so that a tensile stress acts on the inner layer portion. When cells fall in the inner layer in this state, the inner layer develops into internal cracks because the amount of shrinkage is larger than that of the surface layer.

  In addition, the following can be cited as the cause of the decrease in cell drop deformation on the surface layer of wood as compared with the cell drop deformation in the inner layer.

  For example, assuming that the drying temperature is set to about 80 ° C. and a material that is prone to cell dropping is dried, the surface layer portion is called a latent heat of evaporation as it dries (moisture evaporation) as soon as drying starts. Since the heat is taken away, the temperature is locally lowered, and therefore the degree of softening of the cell wall in the surface layer portion is small compared to the inner layer, and the surface layer where the temperature is relatively low has a small number of cells (small shrinkage). ) Dried and then fixed (cured). Thereafter, similarly, when drying progresses to the inner layer and shrinkage starts, the hardened surface layer acts as a support rod as a shell, so that a tensile stress acts on the inner layer portion. If cells fall in the inner layer in this state, the inner layer shrinks with a larger amount of contraction than the surface layer, and thus develops into an internal crack.

  Further, it is known that the internal crack due to the drop of the cells extends elongated along the radial direction of the wood. The reason why the internal crack direction coincides with the radial direction of the wood is due to the distribution form of the cell group constituting the wood. One factor is considered to be easily crushed in the direction perpendicular to the radial direction.

  In order to prevent such internal cracks, for example, Patent Document 1 discloses that the temperature and moisture content inside the wood obtained by measuring the temperature and moisture content inside the wood continuously or intermittently during drying. Based on this information, a technique for controlling the temperature and humidity in the drying chamber is disclosed.

  Patent Document 2 discloses a technique that promotes the movement of moisture by heating wood in multiple stages and suppressing the difference in temperature between drying and drying.

  Furthermore, a freeze-drying method for drying by freezing wood and then sublimating water has been proposed in order to dry the cells while preventing the cells from dropping.

JP 2003-80504 A JP 2007-144866 A

Terazawa Jun, “All about Drying Wood” Kaiseisha, October 1, 1994 D. H. Trevena, “Liquid Structure and Properties”, Kyoritsu Shuppansha, 1982, p. 82

  However, in Patent Documents 1 and 2, since measures for preventing internal cracks were taken without fully utilizing the knowledge about cell drop, it was decided to perform complicated temperature control and complicated temperature management. It was difficult. In addition, the techniques of Patent Documents 1 and 2 have not been able to improve the yield to a practical level. On the other hand, in the case of the freeze-drying method, there is a problem that a lot of energy is required for freezing water and sublimating water from ice, which is not suitable for industrial production.

  The present invention has been made in view of the above-mentioned problems, and by actively utilizing the characteristics of cell depression, it is easy to implement, and drying of wood with a high yield at a practical level, An object of the present invention is to provide a method of drying wood that can improve the bending strength.

  Conventionally, as measures for preventing internal cracks, as disclosed in Non-Patent Document 1, various measures have been taken to prevent cell drop. However, as a result of earnest research, the present inventor has conceived that internal cracking can be prevented by positively utilizing the drop of cells, and has completed the present invention.

  That is, the present invention provides a method for drying timber other than logs, wherein the timber is heated, and at least the timber is allowed to be released from water vapor only in a tangential direction with respect to the annual rings of the timber. A method for drying wood, comprising a drying step of drying by heating to a predetermined target moisture content while maintaining a drying temperature at which the cells of the wood may drop. As the shape of the wood, it is only necessary to be able to expose even a part of the mesh surface in the atmosphere, the mesh material or the remedy material may be used, and the mesh surface or the remedy surface may be a curved surface instead of a flat surface. .

  In this embodiment, the wood for which artificial drying is required is a raw wood or a saturated wood, so that many (at least some) soft cells are in a saturated state. It is maintained at a predetermined drying temperature and thereby dried. Therefore, in the process of drying the wood, in the wood having a grid surface, the evaporation of moisture from the surface layer of the grid surface is promoted, and the drying of the grid surface is promoted. Similarly, the movement of moisture in the tangential direction with respect to the annual rings is promoted in the wood having the memorial surface, and the drying proceeds in the depth direction of the material from the wood surface to the tangential direction.

  Here, the grid surface is a cross section (grid) along the radial direction of the wood, and the plate surface is a cross section (plate mesh) perpendicular to the grid surface and along the tangential direction to the annual ring. A surface refers to the cross section (cut end) of the wood. In addition, even if each of the mesh surface, the plate surface, and the mouth end surface is not a flat surface but a curved surface, application of the present technology is not excluded. The wood in the saturated state does not have to be in a state where all the cells are saturated, that is, filled with free water, and many soft cells may be in the saturated state. In this case, whether the parenchyma cells are saturated or not can be estimated from the moisture content of the sample, can be determined by the shrinkage rate by drying the sample, or can be determined from empirical rules, Raw materials and wood that has undergone the water saturation step described below satisfy this condition. In addition, “a state in which the release of water vapor only from the tangential direction with respect to the annual rings of wood” is not a strict meaning, and it is also excluded that some water vapor leaks from the orthogonal direction of the annual rings or the material axis direction. Not what you want.

  In this process, at least many parenchyma of the wood dries in a saturated state, and as the free water filled in the lumen of the parenchyma is moved out of the lumen by evaporation, the tensile force of free water is increased. It acts on the cell wall, causing cell drop. Here, the parenchyma cells (radiated parenchyma cells) constituting the radiation tissue are arranged in a direction perpendicular to the wood fibers and perpendicular to the annual rings (that is, in the radial direction). The cell wall of the parenchyma collapses in the tangential direction due to the drop of the cells, and the whole wood dries while shrinking in the tangential direction. In this case, for example, wood having a grid surface, a plate surface, and a mouth end surface is sealed so that water vapor is difficult to escape on the plate surface and the end surface, so that drying is suppressed, and cell walls are hardened on these surfaces. Is not progressing. For this reason, as the cell wall hardens, the action of a stick is also suppressed against contraction in the tangential direction of the wood. Therefore, even if the cell falls in the parenchyma, the whole wood contracts in the tangential direction in accordance with the drop, so that the drying of the wood proceeds in a state in which the internal cracking is suppressed. Then, when the moisture content falls below the fiber saturation point, curing starts including the grain surface and the mouth end surface, and the wood contracts in a state where the whole is tangentially retracted, and a predetermined target moisture content (for example, outdoor) The average annual moisture content is 15%, and for furniture, the average moisture content is 8% or less. In addition, the cell drop occurs not only in the radial parenchyma cells but also in the axial parenchyma cells and true tree fibers, etc., and even with these cell drop, the occurrence of internal cracks can be suppressed by the same principle, and the wood Can be dried properly. In addition, since the cells are actively depressed rather than preventing the cells from falling, if the number of cells involved in the depression is large, the density of the wood can be increased accordingly, and the bending strength of the wood as it dries Can be improved together.

  Moreover, when wood is a raw material, the cut raw material can be immediately subjected to a drying process as wood to be treated. Usually, if it is a raw material, many parenchymal cells are in a saturated state, that is, the lumen of parenchymal cells is filled with free water.

  Specifically, for example, the method for drying wood according to the present invention is a method for drying wood in which a raw material or wood in a saturated state, which has a grid surface and a plate surface, is dried. In a state in which the release of water vapor only from the direction of the grid surface of the wood is allowed, the wood is maintained at a drying temperature at which the wood cells can drop at a predetermined target moisture content. A drying process for drying is provided.

  In this aspect, since the wood is raw wood or saturated wood, many (at least some) soft cells are saturated and maintained at a predetermined drying temperature from this state, It is dried by it. At this time, since the release of water vapor is permitted only from the direction of the wood surface of the wood (the normal direction of the wood surface), the wood grain surface and the mouth surface of the wood are sealed, etc. Is in a state where it is difficult to remove. On the other hand, the grid surface (in the direction) is in a state where water vapor can escape. Therefore, in the process of drying the wood, the evaporation of moisture is promoted from the surface layer of the mesh surface, and the drying is promoted from the inner layer side of the mesh surface.

  Here, in the wood industry, drying in a shorter period is eagerly desired. In order to satisfy the demands of this industry, in the preferred embodiment of the method for drying wood, the drying step is performed in a tangential direction with respect to the annual rings of the wood (for example, in the case of wood having a grid surface and a plate surface) More preferably, the drying temperature is higher than 100 ° C.

  In this aspect, since the pressing is performed in a direction tangential to the annual rings of the wood (for example, in the case of wood having a grid surface and a plate surface), the cell falls due to the load applied by the compression. Even if it exists, it can suppress reaching an internal crack. Moreover, if the drying temperature is set to a temperature higher than 100 ° C. under atmospheric pressure, evaporation from the tangential direction with respect to the annual rings such as the direction of the grid surface is promoted, and the drying time can be greatly shortened. Therefore, it is possible to obtain a drying material with a high yield by reducing the drying time and suppressing the occurrence of internal cracks at a more practical level in the wood industry. Moreover, since the drying temperature is set to be higher than 100 ° C., the cell wall is softened (the strength is reduced) at a temperature higher than 100 ° C. as compared to the strength of the cell wall in a relatively low temperature state. For this reason, it is possible to further increase the number of cells in which depression occurs. Further, cells that have not been depressed due to the softening of the cell wall (for example, cells adjacent to cells that are deformed by depression) can be compressed by being affected by the depression, and more uniform contraction characteristics can be obtained.

  In a preferred embodiment of the method for drying wood, such as when the drying temperature is set to be higher than 100 ° C., the drying step includes placing the wood in an atmosphere having a relative humidity of 100% except for the grain surface of the wood. Executed. In this aspect, by continuing to heat the wood at a temperature higher than the boiling point of water, the moisture contained in the wood evaporates at a level much faster than the diffusion at 100 ° C. or less, and the drying rate is dramatically increased. It becomes possible. Further, in this case, since the atmosphere other than the wood surface of the wood is in an atmosphere with a relative humidity of 100%, for example, it is possible to suppress the drying on the surface of the plate or the end of the wood, and the refilling rods by making these surfaces into a shell The action can be effectively suppressed. Here, the above-mentioned “relative humidity 100%” is not a strict meaning, and is a concept including approximately 100%.

  The wood drying method according to a preferred aspect further includes a water saturation step of preparing the wood by hydrating the wood in a saturated state prior to the drying step. In this aspect, since the pulling force by water does not act because it contains bubbles and the soft cells in which no drop occurs, the bubbles disappear due to the disappearance of the bubbles with water saturation. In addition, not only parenchymal cells but also other cells such as authentic wood fibers are saturated, so that more cells tend to fall. As a result, cell sag occurs evenly throughout the wood, thereby increasing the degree of shrinkage and increasing the density after drying. Therefore, the bending strength of the dried material increases in proportion to the increase in density. Moreover, it becomes possible to implement the reinforcement | strengthening process of the said timber by using an already dried timber for a water saturation process.

  In the method for drying wood according to a preferred embodiment, after the water saturation step and before the drying step, the wood is kept at the moisture content before heating while maintaining the water content of the wood evenly up to the drying temperature. It further includes an equalizing step to be adapted. Here, “maintaining the moisture content before heating” does not require that the moisture content be completely the same, and includes cases where the moisture content is substantially the same. In this aspect, in the equalization step, which is the first step, the wood is heated to the heating temperature, and the moisture content is maintained at the heating temperature while maintaining the moisture content before heating. At this stage, since the moisture content is maintained in the state before heating, even if the heating temperature is set to a relatively high temperature, free water does not evaporate. Therefore, the tensile force of free water does not act, and the cell does not drop. On the other hand, in soft cells that are saturated, even if some of the lumens contain fine bubbles, these bubbles disappear, so that the lumens are filled with free water, A tensile force accompanying the reduction of free water from the cavity is likely to occur. In this state, in the subsequent drying step, the wood at the same temperature in the equalization step is heated at the same drying temperature. Therefore, in the drying process, the temperature difference between the surface layer portion and the inner layer portion of the wood can be made as small as possible. As a result, not only does the drying proceed in a state where moisture gradient does not easily occur, but the surface layer portion also causes a drop in the inner layer. Parts can also be produced equally.

  As described above, in the present invention, the whole can be contracted in a tangential direction without causing internal cracks while actively utilizing the drop of cells. For this reason, a suitable desiccant can be obtained with high yield without taking complicated temperature control and humidity control, and internal crack prevention measures (measures for preventing cell drop) that involve complicated temperature management and humidity management. Therefore, compared with the prior art, the yield can be increased by drying the wood and suppressing internal cracks by a much simpler thermal management method. Also, the drying time can be shortened.

  Further features, objects, configurations, and advantages of the present invention will be readily understood from the following detailed description that should be read in conjunction with the accompanying drawings.

It is a flowchart which shows the drying method of the wood of this invention. It is a graph which shows typically the conditions of each process in one embodiment of the present invention in the case of processing wood after performing a water saturation process. It is explanatory drawing which shows typically the experiment example of the equalization process based on this invention. It is explanatory drawing which shows typically the effect of the experiment example which performed the drying process through the equalization process of FIG. It is a photograph which shows the mouth end surface of the timber dried through the process of FIG.3 and FIG.4, (A) is the example of this invention permitted to evaporate from a grid surface, (B) is from a plate surface. Comparative Example 1 which was dried while allowing the evaporation of (C) was Comparative Example 2 in which no wrap was used. It is explanatory drawing which shows typically the experiment example which performed the drying process, pressing through the water saturation process of FIG. 1, and the equalization process of FIG. In FIG. 6A, the specific mode of pressing is changed. It is an enlarged photograph which shows the front end of the timber dried through the process of FIG.3 and FIG.6, (A) shows the wood before a process and (B) after a process. It is the microscope picture of the Example dried together using the pressing process, (A) is an enlarged photograph near an internal crack, (B) is the principal part enlarged photograph of (A), (C) is (B). It is a principal part enlarged photograph. It is the graph which measured the relationship between the bending strength and density of the test material by this invention, and a control test material. It is the graph which measured the relationship between the bending elastic modulus and density of the test material by this invention, and a control test material. It is a figure which shows the example which processed through the equalization process and the drying process, after saturating the dried Moso bamboo, (A) is the photograph which shows the front and back of a process, (B) is a cell part. An enlarged view, (C) is an enlarged view of (B).

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  First, the drying method according to the present embodiment suppresses internal cracking by making the occurrence of wood cell drop as uniform as possible, and by drying at a temperature higher than 100 ° C. (boiling point of water) under atmospheric pressure. Provide a method to increase the drying speed. According to this drying method, a drying condition that actively promotes the occurrence of cell drop during the drying process of wood is employed. Moreover, since the drying temperature is set higher than 100 ° C. (boiling point of water) under atmospheric pressure, the drying rate can be dramatically increased. In addition, a dry material having a high density (that is, a high bending strength) can be obtained by positively promoting the occurrence of cell drop during the drying process of wood. Furthermore, even if the drying temperature is not set higher than 100 ° C. (boiling point of water), the same effect can be obtained by increasing the evaporation of moisture from the wood surface by a high-speed air flow.

  The tree species to which the present embodiment is applied are woods having cell drop characteristics, such as sudagii (Itajii, Nagajii), tsuburajii (kojii), Japanese oak, Japanese oak, oak, cedar, red oak, and eucalyptus. It is difficult to enumerate all the woods that have "cell depression characteristics", but in addition to the above-mentioned tree species such as Koujii, there are evergreen broad-leaved wood materials, most of deciduous broad-leaved wood materials, and some coniferous wood materials. For example, cypress, tablin, birch, red oak, birch, itaya maple, kunugi, merachi, apito, matoa, asada, kluin, nara, mayapis, kluin, lonrian (Tristania), parosapis, baikizu and the like.

  The wood of these tree species is, for example, P.A. It is known that internal cracking occurs by the 100 ° C. test method described in 394 and below.

  The test procedure for the 100 ° C test method is to put a raw material plate (test material) that has been sawn to a predetermined size into a constant temperature drier set at 100 ° C. It includes the step of recording the extent of three damages called “cracking”.

  Table 1 shows the test results regarding internal cracks in the test of each tree type based on the above-described treatment. In the 100 ° C. test method, No. 1 was used in ascending order according to the degree of internal cracking. 1-No. 5 (or No. 1 to No. 6). No. No problem regarding internal cracks. In this example, no. The classification of 1 is omitted.

  As described above, the internal crack is mainly caused by the dropping characteristics of the wood cells. In this embodiment, in the experiment based on the 100 ° C. test method, No. 2-No. Wood classified as No. 5 (or No. 6) is the target of processing.

  Next, in the wood processing method according to the present embodiment, as shown in FIG. 1, the processing steps are determined based on whether the wood to be dried is a so-called raw material. That is, when the target wood is not a raw material, a water saturation step described later is performed to adjust the target wood to a saturated water state before proceeding to the next step.

  Judgment as to whether or not it is raw wood may be based on the number of days exposed to the atmosphere after cutting into board or square after cutting or the color of the cross section when wood is newly sawn as a guide. Good. Further, it may be estimated from the moisture content, or may be estimated from an empirical rule based on a plurality of trials.

  Here, the “saturated state” has two states, a cell level and a wood level.

  The “saturated state” at the cell level refers to a state in which the lumen of a cell such as a parenchyma cell is filled with water. In addition, the “saturated state” at the level of wood refers to a state in which the lumens of all the cells constituting the wood such as soft cells and genuine wood fibers are filled with water. In this embodiment, the “saturated state” at the cell level is referred to, and in particular, it is a condition that at least many parenchymal cells are in a saturated state. In the case of normal raw materials, that is, in the state immediately after cutting a tree, many parenchyma cells are in a saturated state, and in that case, when the wood is dried, a treatment for “saturating” ( The present embodiment can be applied without performing the saturation process described later. On the other hand, when it is desired to increase the number of cells that contribute to the drop of cells, even in the case of raw materials, by performing the water saturation process, the water level can be further increased from the level of water saturation to the level of wood. It can also be made.

  In the present embodiment, when the wood having the above-described cell drop characteristics is dried, the cell drop is positively generated, thereby suppressing internal cracks and achieving the object. In actively promoting cell depression, the important point is to cause cell depression evenly throughout the wood. In the present embodiment, in order to equalize the drop of cells, a drying process plan is made based on the flowchart as shown in FIG. 1, and a predetermined process or a process within the process is added as necessary.

  First, after explaining the overall outline of the process, the details of each process will be described.

  Referring to FIG. 1, when making a wood drying schedule, an operator first determines whether the material is raw material according to the purpose of drying the wood (step S1). The criteria for determining whether or not the raw material is as described above, if it is not raw material (including dry materials such as withering) (NO in step S1), the water saturation step of step S2 is performed, If it is a raw material, the process proceeds to step S3 to determine whether or not a strengthening process of the wood strength is necessary. In this step S3, when the reinforcement | strengthening process of the timber strength of the raw material used as object is required (it is YES at step S3), it transfers to the water saturation process of step S2. On the other hand, even if it is a raw material, when a wood intensity | strength process is not required (it is NO at step S3), step S2 is skipped and it transfers to step S4.

  The water saturation step in step S2 is a step for making the whole wood saturated. By carrying out the water saturation step, it is possible to increase the number of cells that contribute to cell drop and to obtain a desiccant with high density and therefore high strength.

  Next, the worker further needs an equalization process both when the water saturation process is unnecessary (NO in step S3) or when the water saturation process of step S2 is executed. Whether or not (step S4). The equalization step is a step of heating the wood in which at least the parenchyma cells are saturated to a predetermined drying temperature and equalizing the temperature of the whole wood including the inner layer and the surface layer to the heating temperature.

  As a criterion for determining whether or not the equalization process is necessary in step S4, the determination is made based on the drying temperature in the drying process, the rule of thumb based on trials, the presence or absence of heat treatment in the water saturation process, the tree species and dimensions of wood, and the like. For example, when the cross-sectional area of the material is relatively small, specifically, when it has a cross-section that falls within a rectangular range of 30 mm in length and width, this equalization step is omitted because it adapts to a predetermined drying temperature in a short time.

  If the equalization process is necessary, that is, if YES in step S4, execution of the equalization process (step S5) is set.

  When the equalization process is unnecessary (in the case of NO in step S4), or when the equalization process of step S5 is executed, execution of the drying process (step S6) is set. A drying process is a process of heating wood and drying it to a predetermined target moisture content.

  And the wood used as a process target is dried based on the drying process plan mentioned above based on FIG.

  The wood to be dried is mainly intended to have a considerable moisture content in advance, such as raw materials, but is not necessarily limited to wood having a high moisture content in advance. For example, the drying method according to the present embodiment can be used for the reinforcement treatment even for wood having a moisture content of about 10%. In that case, what is necessary is just to set so that the water saturation process (step S2) may be performed in step S1, and the wood used as a process target may become saturated.

  Next, each step will be described in detail.

  First, as described above, the water saturation step is a step for water saturation of the whole wood. More specifically, not only parenchymal cells but also many cells such as genuine wood fibers are saturated. In this way, the moisture content of the wood to be processed is increased by using a pressure cooker, a reduced pressure and the like, and the wood is saturated (with the saturation of the cells). In the present embodiment, the water saturation treatment is an example of “a water saturation step of adding wood to a water saturated state”. Such treatment methods include a method in which wood processed into a plate shape is submerged in water for a predetermined period (for a certain period according to tree species, board thickness, material length, etc.), or a method in which pressure is repeatedly applied to wood in room temperature water Examples include a method of boiling wood under atmospheric pressure, a method of boiling wood while heating in a pressure cooker, and the like. In addition, in the case of boiling under atmospheric pressure or boiling in a pressure cooker, a short and repeated treatment is effective.

  By using the water saturation step (step S2), water is supplied to the entire tissue inside the wood, and many cell lumens including parenchyma cells are filled with free water. For this reason, in the drying step, cells that do not fall because the moisture in the lumen contains bubbles will fall due to the disappearance of the bubbles, and the whole wood tissue is likely to fall with more cells. In particular, when boiled in a pressure cooker, not only parenchymal cells but also the lumens of many authentic wood fibers can be filled with free water, and the number of cells involved in depression can be increased.

  For this reason, cells that do not drop due to the inherent free water tensile force, such as canals, are pushed in the tangential direction under the influence of deformation due to the drop of adjacent or nearby cells such as parenchyma cells. It will be in a crushed state. As a result, the degree of crushing of the cell wall increases and the density after drying increases. Therefore, the bending strength of the dried material is increased. Moreover, it becomes possible to implement the reinforcement | strengthening process of the said timber by using for the water saturation process the already dried timber.

  On the other hand, even if water saturation treatment is not performed, for example, in the case of raw materials stored in water or raw materials with measures to prevent drying with a sprinkler, the wood is immediately treated as the wood to be treated. Can be used. Usually, with these woods, the soft cells are in a saturated state, like raw materials, so that the wood can be dried with a desired yield even if the process proceeds to the drying step.

  Next, the equalization process (step S5) of FIG. 1 will be described.

  This equalization step heats the wood in which at least many parenchymal cells are saturated (ie, wood having cell drop characteristics), while maintaining the moisture content of the wood at the moisture content before heating, In this step, the temperature of the wood is evenly adjusted to at least a drying temperature at which the wood cells tend to drop.

  As one of the factors that cause internal cracks due to cell drop, there may be a case where drying proceeds in a state where the temperature of the surface layer of wood is lower than the temperature of the inner layer. In this case, the surface layer part is deprived of heat due to latent heat of evaporation as it dries, and the temperature drops, and when the temperature partially decreases, the degree of cell drop is not uniform and the higher the temperature The degree of cell depression increases, and this imbalance can cause internal cracking. In the equalization process, it is an effective means for correcting the above-mentioned unevenness of the cell drop by equalizing the temperature state of the wood.

  It can be said that the equalization step is preferably performed in an environment where the equalization step and the drying step can be continuously performed using the same drying apparatus.

  In this embodiment, since a drying temperature that positively promotes cell drop is applied, the wood is heated to a relatively high temperature (for example, around 100 ° C.) in the equalization step. In this stage, no cell drop occurs. Therefore, internal cracks due to cell drop do not occur. On the other hand, in soft cells in a saturated state, even when minute bubbles are present in the water in the lumen, these bubbles dissolve and disappear, and a tensile force accompanying evaporation tends to occur. Therefore, by performing the equalization process, drying can proceed while maintaining the temperature of the surface layer of the wood and the temperature of the inner layer evenly, and the internal cracking is suppressed by equalizing the drop deformation of the cells of the surface layer and the inner layer. There is an advantage that you can.

  As a means for heating, for example, by wrapping wood using an appropriate surrounding means such as a mold having airtightness or a wrapping material having heat resistance and airtightness, until the temperature is adjusted to the drying temperature in the drying step (step S6). It is preferable to heat with a heating device such as an oven.

  Next, the drying process (step S6) of FIG. 1 will be described.

  The drying step is a step of drying wood having a moisture content higher than the fiber saturation point (usually having a moisture content of approximately 30% or more) to a predetermined target moisture content. Specifically, the wood (raw material) in which many soft cells are saturated is heated, and this wood is maintained at a drying temperature at which the cells of the wood can be dropped to a predetermined target moisture content. It is a step of drying.

  As the drying temperature, various temperatures can be adopted depending on the tree species or the material size. For example, in the above-mentioned 100 ° C. test method, No. 2-No. The initial drying temperature T0 (55 ° C. for No. 2, 50 ° C. for No. 3, 49 ° C. for No. 4, 49 ° C., No. 5 for each type of tree class classified as No. 6) 48 ° C. in the case of No. 6 and 45 ° C. in the case of No. 6) may be determined as a drying temperature T (= T0 + T1) obtained by adding an arbitrary value T1 to each temperature. As described above, when the drying temperature T is 100 ° C. or lower, it is preferable to dry the air in a state where the air is aerated at a certain speed or more from the viewpoint of shortening the drying time.

  In a preferred embodiment, the drying temperature is a little higher than 100 ° C., which is the boiling point under atmospheric pressure, and for example, 101 to 105 ° C. is suitable. This also allows cells that have not been depressed to be depressed, and can be compressed by the depression deformation of adjacent cells due to the softening of the cell wall, so that more uniform contraction characteristics can be obtained. Internal cracks are unlikely to occur. Moreover, since drying is performed at a temperature higher than 100 ° C., evaporation from the grid surface is promoted, and the drying time can be greatly shortened. Therefore, it is possible to reduce the drying time and obtain a desiccant with a higher yield at a more practical level. In addition, by setting a constant temperature range of about 101 to 105 ° C., it is not necessary to perform complicated temperature control that requires skill as in the past, and the drying apparatus itself can be configured simply, reducing maintenance costs. Cost effects are also expected.

  Thus, the setting of the drying temperature is preferably higher than 100 ° C., which is the boiling point under atmospheric pressure. However, if the temperature is too high, there is a risk of deterioration of wood, etc. It is preferable to keep it. In that case, while suppressing problems such as deterioration of the wood, on the other hand, if the drying temperature is too low, there is a concern that the cell wall will not be softened sufficiently and the cells will not fall down properly. The temperature is preferably set higher than the initial drying temperature set by the 100 ° C. test. The drying temperature is preferably set to be constant throughout the heating period from the viewpoint of simplification of operation.

  As the target moisture content, a value sufficiently lower than the fiber saturation point is selected and depends on the temperature and humidity environment in which the dried product is used. For example, the average moisture content is 12%, or depending on the purpose of use. The following is preferable.

  Furthermore, in the present embodiment, the drying process will be described by taking wood having a grid surface and a plate surface as an example. The drying process is carried out in a state in which water vapor is allowed to be released only from the tangential direction to the annual rings of wood (in FIG. 4, the normal direction of the grid surface 11). That is, the direction orthogonal to the tangential direction of wood with respect to the annual rings (in FIG. 4, the normal direction of the grain surface 12 and the end face) is sealed, and water vapor is difficult to escape. On the other hand, the tangential direction with respect to the annual rings is in a state where water vapor can escape. Therefore, in the process of drying the wood, the evaporation of moisture is promoted from the surface layer in the tangential direction with respect to the annual rings of the wood, and the drying is promoted from the tangential direction side with respect to the annual rings.

  Here, promoting evaporation from the tangential direction with respect to the annual rings of wood effectively suppresses internal cracks due to cell drop compared to promoting evaporation from the direction perpendicular to the tangential direction with respect to the annual rings of wood. Because it can. In other words, cells that cause depression including parenchyma cells collapse along the tangential direction with respect to the annual ring of the wood due to the depression, that is, the timber tends to contract in the tangential direction.

  At this time, if evaporation from the direction perpendicular to the tangential direction to the annual ring of wood is promoted and the cell surface is below the fiber saturation point and the cell wall is cured, this plate surface is used as a refilling rod. It acts to inhibit contraction of the material in the tangential direction, and internal cracks are likely to occur due to the fall of the parenchymal cells in the inner layer.

  On the other hand, by configuring as in the present embodiment, drying from the tangential direction with respect to the annual rings of wood is promoted, and even if the cell surface is below the fiber saturation point and the cell wall is cured, the plate surface and the mouth end Since the cell walls of the surface are not hardened, the tangential shrinkage of the wood due to the drop of the cells is not hindered, and the hardened mesh surface only moves in the tangential direction as a whole. Internal cracks due to curing are less likely to occur.

  Therefore, as in this embodiment, when the drying process allows the release of water vapor only from the tangential direction to the annual rings of the wood, it effectively suppresses the occurrence of internal cracks in the wood due to the drop of cells. can do. Such a way of thinking holds true if the wood cutting is other than log shape. For example, regardless of whether the wood is made of remembrance or wood that has been cut in half, it is possible to use a jig for fixing the material to be dried or a device that presses the grid surface. Processing for remembrance materials is possible.

  Moreover, it is preferable that a drying process is performed by arrange | positioning the said wood in the atmosphere of relative humidity 100% (substantially including 100%) except the tangential direction with respect to the annual ring of wood. In that case, by continuing to heat the wood at a temperature higher than 100 ° C., which is the boiling point of water, the moisture contained in the wood evaporates at a level much faster than the diffusion of moisture at 100 ° C. or less, It becomes possible to increase the drying speed. In the present embodiment, since the release of water vapor from other than the grid surface of the wood is regulated using a mold or a wrap material, this measure makes it substantially based on the above requirements, that is, the tangential direction of the wood with respect to the annual rings. The wood can be dried in a state where the release of water vapor from other than the above is regulated.

  Next, in the drying process, it is preferable to perform the pressing process in parallel. The pressing process refers to a process of applying pressure while wood is subjected to a drying process to prevent internal cracks due to variations in cell drop.

  If the drop of the cells in the wood that occurs as a result of drying occurs ideally and uniformly, the pressing treatment is not necessarily required. However, the degree of occurrence of cell drop in an actual material is not uniform due to various factors. For example, the difference between the sapwood part and the heartwood part of the timber, the difference between the summer timber part (late timber part) and the autumn timber part (early timber part), the existence of the knot and the size of the knot, or when sawing Even if it is dried under the same conditions due to cutting of a cell named true wood fiber by sawing, the internal cracks may be generated differently. Also, when there is a partial decrease in the moisture content in the trunk due to the withering of trees, or when the moisture content on the surface of the wood has become lower than the inner layer after sawing for a while after sawing In the case of timber, etc., even if the wood is cut from an equivalent part into an equivalent size and shape, a large individual difference can occur. All of these cause uneven cell surface deformation and unevenness of the inner layer. For this reason, the cell drop deformation is partially increased, and as a result, internal cracks are generated in that portion.

  Therefore, in a preferred embodiment, a pressing process is performed in the drying process. Although the pressing process is a process of pressurizing the target wood, unlike a conventional press process using a hot press, for example, a weak pressing force of 5 kg / cm 2 or less is sufficient. . This is because the pressing process is a measure for correcting the imbalance of the cell drop and is essentially different from the process of compressing the cell itself by an external force. As an example, Kodii can obtain a desiccant that does not cause damage by applying a pressing treatment at a pressure of 0.66 kg / cm2 and drying for a predetermined period (for example, 1 day) when drying at 105 ° C. It becomes possible.

  On the other hand, the relationship between the pressing process and the grain becomes important. In the present embodiment, the pressing process is performed by pressing the wood in the tangential direction of the annual ring from the grid surface. However, since the pressing direction may be a tangential direction to the annual ring, the pressure is not necessarily applied from the grid surface. It is not necessary. As described above, internal cracks have the characteristic of extending in the radial direction and the center part extending in the tangential direction, so pressing the wood in the tangential direction has the effect of imbalance in cell depression. It is possible to correct the situation and prevent internal cracking more reliably.

  In addition, the pressurization direction in the pressing process may be that the material to be dried is pressed in the tangential direction. Further, in this pressing process, it is preferable to uniformly press the grid surface of the wood, but it is not always necessary to apply pressure to the entire grid surface. The surface may be pressed almost uniformly. Further, as long as it can be pressed, the grid surface may not be a flat surface and may be oblique (it may not be perpendicular to the direction of the annual ring).

  Next, with reference to FIG. 2, an embodiment will be described based on the flowchart of FIG. In the following description, the same members are denoted by the same reference numerals, and duplicate descriptions are omitted. An outline of these embodiments will be described first and then specifically described.

  First, the embodiment of FIG. 2 is an example in which a drying process is performed on a target wood after performing a water saturation process and an equalization process.

  As the wood, Kojyi's square material having a grid surface and a plate surface can be adopted. The moisture content of the wood is set in a saturated state in advance through the above-described saturation process, and the lumens of almost all cells including the soft cells are filled with free water.

  In the equalization process, all of the wood surface, plate surface, and mouth surface of the wood that has been saturated using a mold or wrapping material is enclosed (covered) in a state of maintaining airtightness and placed in a heating device. Heat to adjust the whole wood to the drying temperature. The drying temperature is set to 105 ° C. in this embodiment. The time of the equalization process varies depending on the size of the wood and is set to be longer than the time that allows the temperature of the whole wood to be equalized by the sample. However, it may be determined based on an empirical rule or a measuring device such as a temperature sensor. It is also possible to determine the time by actually measuring the temperature using. After the whole wood is acclimatized to 105 ° C., the drying process is subsequently carried out in the same heating device.

  In this drying step, only the direction of the grid surface of the wood is opened in the heating device so that water vapor is evenly released from the grid surface of each piece of wood to be heated, and then the drying step is performed and dried.

  Specifically, in the drying process, the release of water vapor only from the tangential direction to the annual rings of each timber is permitted by a method such as opening a shutter provided in advance in the mold or punching a wrapping material. The airtightness of the surface (direction perpendicular to the tangential direction with respect to the annual rings of wood) is maintained. In the drying process, a pressing process was performed. In the pressing step, a pressure of 0.7 kg / cm 2 is applied to each piece of wood from the grid surface, and the material to be dried is dried while allowing the release of water vapor from the direction tangential to the annual rings of the wood. As a means for releasing water vapor while applying pressure to the grid surface of the wood, for example, a groove is provided on the lower surface of the lid body that becomes a weight, or a spacer member such as a mesh member is provided between the lid body that becomes the weight and the grid surface. It can be realized by intervening.

  In addition, when each timber is enclosed by the lapping material through the space | gap and discharge | release of the water vapor | steam from surfaces other than a mesh face (a board surface and a face of a wood end) is controlled, a drying temperature is 105 times. Combined with being set to ° C., the part other than the grid face of the wood is executed in a state where it is placed in an atmosphere having a relative humidity of 100%. For this reason, in such an embodiment, by continuing to heat the wood at a temperature higher than the boiling point of water, moisture contained in the wood evaporates at a level much faster than diffusion at 100 ° C. or less, thereby increasing the drying rate. It becomes possible.

  Although it depends on the wood species, the capacity of the heating device, the volume of the wood, etc., the drying temperature is set to 105 ° C., so that the processing time required for drying is about 1 day even for the wood 10 with practical material removal. About 2 days.

  As shown in FIG. 3, in the equalization step, the airtightness of the wood 10 is maintained by the wrapping material 14 surrounding the wood 10, so that the water vapor is generated even in a heated state at a relatively high temperature. Is almost never released from the cell, and no cell depression occurs.

  After shifting to the drying step, as shown in the left-side wood 10 in FIG. 4, the release of water vapor from the mesh surface 11 is permitted by the holes 14 a drilled in the wrapping material 14. Evaporates. In the process from the saturated water state to the fiber saturation point, as the free water decreases, the tensile force of the water in the cell lumen acts on the inner surface of the cell wall and the cell falls. On the other hand, the wood 10 has a grain surface 12 and a mouth end surface (not shown) that are controlled to release water vapor by a mold or a wrapping material 14, so that drying is difficult to proceed on these surfaces. Therefore, the wood 10 is dried while a relatively large number of cells (mainly parenchymal cells) cause a drop and the tangential shrinkage is relatively allowed. And the shrinkage | contraction of the timber 10 arises from the site | part (surface layer side) in which evaporation of free water progressed, and it dries with depression deformation. When the moisture content falls below the fiber saturation point, that is, when the bound water is reduced, the bound water is desorbed (dried) from the inner surface of the very fine voids, so that the voids close and become dense. Then, it is fixed (cured) from the cell wall of the surface layer portion of the cell surface 11.

  As described above, the reduction in the size of the material due to cell drop deformation occurs in the direction perpendicular to the grid surface 11, that is, the tangential direction of the material, and the moisture evaporation from the plate surface 12 and the end surface 13 is small. Therefore, it is not cured (not yet below the fiber saturation point), and therefore the grain surface 12 and the end surface 13 are unlikely to become a shell (shell) that causes internal cracks. Due to this and the load due to the pressing, even if the cell drop is not uniform, the whole is compressed in the tangential direction (vertical direction in FIG. 4) without causing internal cracks. Therefore, the dried wood (drying material) is a material having a high density, a high bending strength, and no cracks.

  In the embodiment of FIG. 2, that is, when the heating temperature is set to 105 ° C., the heating is performed at a temperature equal to or higher than the boiling point under atmospheric pressure, so that the wood can be dried in a relatively short period of time, and cracks are not easily generated. A desiccant with high density (improved mechanical strength) can be obtained.

[Verification by experiment]
Next, an experimental example based on the above-described embodiment will be specifically described.

  First, with reference to FIG. 3, the facility of the experiment example which this inventor implemented is demonstrated.

  In FIG. 3, 1 is a hot air type electric heating oven as a heating device. In the oven 1, a movable mounting table 2 is provided. The mounting table 2 can be pulled out of the oven 1. On the mounting table 2, a plurality of woods 10 (three in the figure) to be subjected to a drying process are placed side by side in a polypropylene tray 3. As shown in FIG. 6, in the oven 1 used in this experiment, a lid for applying a pressing pressure to substantially the entire upper surface of the wood 10 with the wood 10 sandwiched between the tray 3 in the drying process. A body 4 is provided separately. The lid body 4 is provided with a ventilation groove or recess 4a at a position corresponding to the hole 14a of the wrapping material 14 so that steam ejected from the hole 14a can be vented through the ventilation groove or recess 4a. Has been.

  Using the above equipment, a plurality of woods 10 were used as test materials, and experiments were performed a plurality of times. The dimensions of the wood 10 used in the experiment were selected in the range of 15 mm to 25 mm in the tangential direction, 15 mm to 50 mm in the radial direction, and 220 mm to 230 mm in the fiber direction.

(Experiment 1: Verification of drying process)
First, on the premise of the equalization process, in the drying process, compared with the comparative example in which only the grid surface is released and heated, compared with the comparative example dried under other conditions, only the tangential direction to the annual ring of wood The effect of opening was verified.

  Each of the woods 10 used for verification is a raw material of kojyi, and in the example shown in the drawing, each piece is cut into a short rectangular shape of 22 mm (tangential direction) × 17 mm (radial direction) × 220 mm (fiber direction).

  With reference to FIG. 3, each wood 10 has a grid surface 11 along one radial direction of the wood 10, a plate surface 12 along a tangential direction perpendicular to the grid surface 11, and a mouthpiece surface 13 which is a cross section of the wood. Are mounted on the tray 3 on the mounting table 2 with one grid surface 11 facing upward.

  Each wood 10 is covered with a wrapping material 14 having a heat resistance and a pressure resistance as a surrounding means. As a material of the wrapping material, it is sufficient that the heat resistance is 120 ° C. to 130 ° C. (when the drying temperature is set to 130 ° C., the heat resistance temperature is 140 ° C.). Vinylidene chloride, polyvinyl chloride, polypropylene or the like can be used.

  In this state, each wood 10 was subjected to an equalization process. As the conditions for the equalization process, the drying temperature was set to 105 ° C., the temperature of a part of the wood 10 was measured with a sensor (not shown), and the heating was continued until the whole adjusted to 105 ° C. As a result, each timber 10 was heated in a state where the wrap material was expanded with steam.

  Next, referring to FIG. 4, each wood 10 was once taken out from the tray 3, and the conditions of the wrapping material 14 were changed to be examples and comparative examples 1 and 2, respectively, and returned to the oven 1. At this time, it is preferable to quickly perform a series of actions from taking each piece of wood out of the tray 3 and returning it to the oven 1 to suppress a decrease in the material temperature.

  In the embodiment (the left end in FIG. 4), a hole 14a is formed in the upper portion of the wrapping material 14 so that water vapor is released only from the tangential direction of the wood 10 with respect to the annual rings of the wood. Each direction was left closed.

  In Comparative Example 1 (center of FIG. 4), a hole 14b is formed in the side portion of the wrapping material 14 so that water vapor is released only from the direction perpendicular to the tangential direction of the wood 10 with respect to the annual rings. 11 and the direction of the end face 13 were kept closed.

  In the embodiments of the holes 14a and 14b of the example and the comparative example, a plurality of (for example, 10 locations) pinholes were uniformly formed over the entire surface so that the release of water vapor was uniform over the entire surface.

  In Comparative Example 2 (the right end in FIG. 4), the wrapping material 14 was removed, and water vapor was released from any direction of each surface 11-13.

  Next, as shown in FIG. 4, each wood 10 was returned to the mounting table 2 and heated in the oven 1. The heating temperature (drying temperature) was 105 ° C., the heating time was 12 hours, and each wood 10 was dried to a moisture content of 10% or less.

  FIG. 5 shows the experimental results.

  As shown in FIG. 5A, in the example, the shrinkage dimension in the tangential direction was about 27% of the original wood, and a large shrinkage was recognized. On the other hand, the degree of internal cracks was one large crack and about 20 small cracks. 3-No. It was found to be about 4. Considering that the drying temperature is considerably high, it was confirmed that the lapping material 14 significantly suppressed internal cracking.

  Next, as shown in FIG. 5B, in the case of Comparative Example 1 in which only the plate surface 12 was opened, the shrinkage in the tangential direction was almost the same as that in the example. On the other hand, the degree of internal cracks is 4 large cracks and 4 small cracks. It was found to be about 5.

  Further, as shown in FIG. 5C, in the case of Comparative Example 2 in which the wrapping material 14 was removed, almost no shrinkage was observed (about 7% to 8%). Further, the degree of internal cracking was 10 or more thick cracks. 5-No. It was found to be about 6.

(Discussion)
(1) It was recognized that the dimensional change was significantly different from the case where the wrap material was provided (Example, Comparative Example 1). This is because when the wrapping material 14 is not provided (Comparative Example 2), the dry air takes the latent heat of vaporization from the surface of the wood 10 and the surface temperature decreases, so the number of cells participating in the drop of cells is the surface layer. This is because the number of cells in the vicinity decreases, and when a large number of cell groups fall down and do not deform at the same time, it is considered that deformation is likely to return.

  (2) When piercing the wrapping material 14, the hole 14a that opens the tangential direction of the wood to the annual ring is provided (Example), but the hole 14b that opens the direction perpendicular to the tangential direction of the wood to the annual ring is provided. It was confirmed that the degree of damage was lower than in the case (Comparative Example 1). This is considered to be due to the following reasons.

  That is, in the case where the holes 14b that open the plate surface 12 are provided, the drying proceeds from the plate surface 12, so that the surface layer side of the plate surface 12 is formed in a hard shell shape such as a replacement rod that is replaced in the tangential direction. Harden. Thereafter, when the inner layer side is dried, tangential shrinkage on the inner layer side is hindered by the hardened material of the surface layer portion, and the width of the inner crack is considered to increase.

  On the other hand, in the case where the holes 14a for opening the mesh surface 11 are provided, the drying proceeds from the mesh surface 11, so that the wood 10 is dried while allowing tangential shrinkage. Therefore, even if drying progresses to the inner layer side, it is considered that the width of the inner crack is reduced by allowing tangential shrinkage on the inner layer side.

  As is clear from Experiment 1, when the drying process is executed by opening only the tangential direction of the wood with respect to the annual rings, and the wood 10 is completed, the internal cracks can be greatly reduced.

(Experiment 2: Verification of pressing process)
The present inventor further verified the effect of the pressing process in order to more reliably prevent internal cracking even when the wood 10 is dried at a high temperature.

  With reference to FIG. 6A, in the pressing process, the lid 4 was placed on the wood 10 in the drying process, and the weight 5 was suspended to apply a load. The load (pressing pressure) applied to the wood 10 by the weight 5 was 0.66 kg / cm 2. Also in this experiment, the wood 10 is mounted on the mounting table 2 with the grid surface 11 facing upward. The wrap material 14 is formed with holes 14a that allow water vapor to be released only from the tangential direction with respect to the annual rings of wood. The lid 4 is formed with a groove or recess 4a for ventilation that opens the hole 14a, and water vapor is released to the outside of the wrapping material 14 through the groove or recess 4a. Similarly, the mounting table 2 is also provided with a ventilation groove or recess 4b that opens the hole 14a. In this experiment, a cover body 4 having a ventilation groove or recess 4a is used. However, the structure of the cover body is not limited to this, and a uniform pressing pressure is applied to the wood 10. 6B, with reference to FIG. 6B, the wood 10 is brought into contact with the lid and the mounting table through one or a plurality of stainless meshes 23 (for example, # 100), etc. It may be to secure.

  Also in Experiment 2, as in Experiment 1, the drying temperature was 105 ° C. and the heating time was 12 hours.

  FIG. 7 shows the experimental results. FIG. 7A shows the wood before treatment, and FIG. 7B shows the wood after treatment.

  As shown in FIG. 7, in Experiment 2, the tangential dimension of the wood 10 contracted by 39%. Further, no internal crack was found, and No. in the 100 ° C. test method. It was equivalent to 1.

  As another example, the case where the pressing pressure was 0.15 kg / cm 2 among the conditions of Experiment 2 was verified.

  As a result, although the dimension in the tangential direction contracted by 37.3%, fine internal cracks occurred. Damage similar to 2 was observed. Further, in Experiment 2, a desiccant having a flat surface could be obtained, whereas the surface in other examples was unevenly undulated.

  With reference to FIG. 8 (A), in this other Example, when the periphery where the internal crack was generated was verified, a plurality of sites 20 where the cells dropped were confirmed. It can be seen that the cell drop occurs relatively evenly in any part 20.

  With reference to FIG. 8 (B), which is an enlarged view of the main part of FIG. 8 (A), in the part 20, the duct 21 having a relatively small opening diameter is crushed, and the parenchyma 22 is depressed. Is confirmed.

  Referring to FIG. 8C, in which the main part of FIG. 8B is further enlarged, when the enlarged portion of FIG. 8B is further enlarged, the cell wall of the canal 21 is crushed in the tangential direction and flattened. It was confirmed that

(Discussion)
As described above, the degree of occurrence of cell sag in an actual material is not uniform due to various factors. However, Experiment 2 confirms that in the case of Kojyi, it is particularly significant to prevent and suppress internal cracking in parallel with the pressing process at a pressure of about 0.66 kg / cm 2 in the drying process. It was done. When sufficient pressure cannot be obtained, the probability of occurrence of internal cracking is high, but unlike what is conventionally performed in a hot press (for example, 8 kg / cm2 or more), For example, a weak pressure of 5 kg / cm 2 or less is sufficient. On the other hand, based on the results of other examples in Experiment 2, it is considered preferable to set the pressure to 0.15 kg / cm 2 or more in order to appropriately obtain the effect of pressing (suppression of large internal cracks). Further, as verified from FIGS. 8A to 8C, it is considered that when the number of cells in which depression occurs is large, the compressibility of the material to be dried increases and the bending strength increases.

(Measurement result of bending strength)
Under the drying conditions shown in Table 2, sample No. 1-No. 17 and a comparative sample No. 1 by the freeze-drying method shown below. 1-No. 17 was prepared and the relationship between each density and bending strength or bending elastic modulus was measured.

  In addition, in the measurement of these density, bending strength, and a bending elastic modulus, it measures according to JISZ2101. Specifically, the test body is a column whose cross section is a square with a side length (side length) of 10 to 15 mm, and the length is a span plus twice the side length. The span is 14 times the side length of the specimen and a concentrated load is applied to the center of the span. As a general rule, the load surface is a grid surface, and the shape of the steel material used for the load point and the viewpoint complies with the JIS regulations. The average load rate was 14.70 N / mm 2 or less per minute, and the bending strength and the bending elastic modulus were obtained.

  As an example, kojii was dried and measured by the method according to the present invention. That is, the sample No. of Example. 1-No. About each of 17, the water saturation process and the equalization process were implemented, and it was made to dry on the conditions shown in Table 2. In addition, about the drying time, the same time as the said Example was set, and it dried until it became almost completely dry.

  As a comparative example, kojii was freeze-dried and measured. This freeze-drying method is a method in which wood is frozen and depressurized by a vacuum pump, and moisture contained in the wood is sublimated from the ice state and dried. The lyophilization conditions in the comparative example are as follows. The freezing temperature of the material was -46 ° C., a rotary pump was used for decompression, the decompression period was set to 1 to 2 weeks, and the material was dried until the moisture content of the material was almost completely dry.

  The measurement results of the density, bending strength, and bending elastic modulus of the samples of each example and the comparative example are shown in Table 3, and the relationship between the density and the bending strength or bending elastic modulus is shown in FIGS.

  In this measurement result, for the density of the example, the average value of 17 samples is 0.77 (g / cm 3), the standard deviation is 0.09 (g / cm 3), and the variation coefficient is 11.5%. there were. Regarding the bending strength of the example, the average value of 17 samples was 126.7 (MPa), the standard deviation was 36.7 (MPa), and the coefficient of variation was 28.9%. Regarding the flexural modulus of the example, the average value of 17 samples was 13,225 (MPa), the standard deviation was 2,889 (MPa), and the variation coefficient was 21.85%.

  On the other hand, regarding the density of the freeze-dried material as a comparative example, the average value of 17 samples is 0.50 (g / cm3), the standard deviation is 0.04 (g / cm3), and the coefficient of variation is 8.1. %Met. Regarding the bending strength of the comparative example, the average value of 17 samples was 72.9 (MPa), the standard deviation was 14.3 (MPa), and the coefficient of variation was 19.6%. Regarding the bending strength of the comparative example, the average value of 17 samples was 7,577 (MPa), the standard deviation was 1,021 (MPa), and the coefficient of variation was 13.5%.

(Discussion)
As described above, the degree of occurrence of cell sag in the actual material is not uniform due to various factors, and although the examples have large variations in density, bending strength and bending elastic modulus compared to the comparative example, It has been confirmed that carrying out the drying method according to the present embodiment is particularly significant in improving all of the density, bending strength, and bending elastic modulus. This is because each sample of the comparative example was freeze-dried and no cell drop occurred, whereas in each sample of the example, the cell drop occurred due to the free water tensile force. This is presumably because the cell shape was deformed and hardened flat and the density was increased.

  Specifically, with respect to the sample of the example, the density tends to be higher than that of the sample of the comparative example, and both the standard deviation and the variation coefficient are increased. This is because, in the examples, the density increases due to the drop of the cells, and there is an individual difference in the drop of the cells (that is, the variation is large). This is probably because the coefficient of variation has increased.

  Also, regarding the bending strength and the bending elastic modulus, the samples of the examples all were equal or relatively higher than the samples of the comparative examples. In particular, in the examples, when the density increases to about 0.9 (g / cm 3) (for example, sample Nos. 10 to 13 and 15 in the example), the comparative example (for example, sample No. in the comparative example) having a density of about half. .1, 6), the flexural strength and flexural modulus of elasticity tend to be more than doubled.

  As described above, in each sample of the example, internal cracking can be suppressed while positively utilizing the drop of cells, so that a high-strength desiccant can be effectively obtained with a high yield. .

(Experiment 3: Verification with Mosouchiku)
It was verified that the utility of the present invention can be applied not only to broad-leaved trees and the like, but also to Mosouchiku, and the curvature of the ridge can be flattened.

  As a treatment method, the dried moso-chiku is subjected to water saturation treatment, water saturation treatment is performed at a drying temperature (105 ° C.) using a lapping material to fill the cell lumen with water, and then the pressing pressure is set to 0. The drying process was carried out while performing the pressing treatment at a setting of .561 kg / cm 2.

  The state after the processing is shown in FIGS.

  The moisture density before treatment had an air dry density of 0.84 g / cm 3, whereas after treatment, the air dry density was 1.06 g / cm 3.

  As shown in FIG. 11A, it was confirmed that even in the case of Mosouchiku, it can be processed using the drying method of the present invention. That is, it was confirmed that the curved wrinkles before processing (left side in FIG. 11A) became flat with respect to those after processing (right side in FIG. 11A) and no cracks occurred.

  Also noteworthy is the mode of cell depression after drying.

  As shown in FIG. 11 (B), it was confirmed that the parenchyma was depressed throughout the entire tissue even in Mosouchi by the drying method according to the present invention.

  Further, as shown in FIG. 11C, it was confirmed that the cells were almost flattened to such an extent that the cell lumens were almost eliminated.

  Thus, it can be seen that the target wood of the drying method according to the present invention is not limited to hardwood materials and the like, but can also be effectively used for softwood materials and bamboo materials in which cells fall.

  The present invention is not limited to the embodiment described above, and it goes without saying that various modifications can be made without departing from the scope of the present invention.

1 Hot air type electric heating oven (an example of a heating device)
2 Placement table 3 Tray 4 Lid 5 Weight 10 Wood 11 Grain surface 12 Plate surface 13 Wood end surface 14 Wrap material 14a Hole 20 Site where cell drops occur 21 Trachea 22 Parenchyma cell 23 Mesh

Claims (5)

In the method of drying wood, which dries wood cut into a shape other than a log shape,
Heating the wood and allowing the release of water vapor only from the tangential direction with respect to the annual rings of the wood, and maintaining the wood at a drying temperature at which the wood cells may fall down to a predetermined target. A method for drying wood, comprising a drying step of drying by heating to a moisture content. The method for drying wood according to claim 1,
The method for drying wood, wherein the drying step is performed while pressing the wood in a direction tangential to the annual ring of the wood. The method for drying wood according to claim 2,
The said drying process is a drying method of the timber which is a process performed by arrange | positioning the said timber in the atmosphere of a relative humidity of about 100% except the grid surface of the said timber, or an additional surface. In the drying method of the wood of any one of Claims 1-3,
In the case of drying wood that is not raw material or wood that is not saturated, prior to the drying step, the wood is further provided with a water saturation step for preparing the wood by hydrating the wood in a saturated state. Drying method. The method for drying wood according to claim 4,
After the water saturation step and before the drying step, further comprising an equalization step for maintaining the moisture content of the wood at a moisture content before heating, and evenly adjusting the temperature of the wood to the drying temperature. How to dry wood.