JP2008307790A - Wood drying method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wood drying method which can inhibit the surface cracking of wood due to drying and produce the wood which is almost free from the color change of wood attributed to drying and keeps a high residual rate of a wood aromatic component after drying process. <P>SOLUTION: Prior to performing a main drying of the wood, e.g. low temperature decompression drying etc., a cooking process and a high temperature pretreatment drying process of the wood are performed successively. In the high temperature pretreatment drying process, the wood is kept, for example, at 140°C dry-bulb temperature and 95°C wet-bulb temperature for 2 to 5 hours. Consequently, it is possible not only to inhibit the surface cracking of the wood due to drying but also subdue the wood color change attributed to drying and increase the residual rate of a wood aromatic component after drying process. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a wood drying method, and more particularly to a wood drying method that suppresses surface cracking of wood due to drying, has little change in material color due to drying, and has a high residual ratio of aroma (essential oil) component after drying.

A general method for drying wood is high-temperature drying in which the wood is heated at 100 ° C. or higher (for example, cited document 1). Since high-temperature drying has high thermal efficiency, the drying time can be shortened and the production cost can be reduced. Moreover, during drying, a drying set that suppresses free shrinkage of the wood by a tensile force caused by high-temperature drying occurred in the surface layer portion of the wood, and cracks on the surface of the wood were reduced. However, such high-temperature drying has a problem that the color and aroma inherent to wood are impaired.
Thus, in order to improve these problems, conventionally, a low temperature drying method (for example, Patent Document 2) for drying wood at less than 100 ° C. is known. In Patent Document 2, since the wood is dried at a temperature as low as less than 100 ° C. in this way, the original color and fragrance of the wood are hardly impaired during drying.

JP-A-1-114686 JP 2007-045053 A

  However, in the low-temperature drying method, since the wood is dried at a low temperature of less than 100 ° C., the advantages of the high-temperature drying are eliminated, the drying time becomes long, the production cost increases, and the drying set cannot be expected. Cracks were increasing on the surface of the wood.

  Therefore, as a result of earnest research, the inventor performed the steaming step and the pretreatment drying step at high temperature in order before performing the main drying (low temperature drying) on the wood, and the advantages of high temperature drying and low temperature drying. As a result, the present invention was completed.

An object of the present invention is to provide a method for drying wood, which suppresses surface cracking of wood due to drying, has little change in color of the wood due to drying, has a high residual ratio of scent components of wood after drying, and has low production costs. Yes.
Another object of the present invention is to provide a wood drying method that can shorten the drying time as compared with the case of conventional low temperature drying alone.

  The invention according to claim 1 includes a step of steaming wood, a step of drying the steamed wood at a high temperature pretreatment, and a step of main drying the wood after the high temperature pretreatment drying. It is.

According to the first aspect of the present invention, the steaming process and the high-temperature pretreatment drying process of the wood are sequentially performed on the wood before the main drying of the wood. Thereby, surface cracks of the wood due to drying can be suppressed, the color change due to drying is small, the residual ratio of the scent component of the wood after drying is high, and the production cost can be reduced.
Wood can be cooked to increase the temperature without evaporating the surface. In the subsequent high temperature pretreatment drying step, the wood is held at a dry bulb temperature of 140 ° C. and a wet bulb temperature of 95 ° C. for 2 to 5 hours, for example. As a result, a tensile drying set is formed on the surface layer without being exposed to high temperatures for a long time inside the wood, and surface cracks in the drying process are suppressed. Thereafter, the wood is dried. Since it comprised in this way, the produced dry wood has the advantage of high temperature drying, and the advantage of low temperature drying.

Examples of the wood include cedar, cypress, and larch. The wood may be square, log or board. The size of the wood is arbitrary.
Wood steaming refers to a method of heating wood in which high-pressure heated steam is supplied into the saturated steam atmosphere of the drying chamber, the wood stored in the drying chamber is heated and maintained at a constant temperature with a relative humidity of approximately 100%. .

The high-temperature pretreatment drying of wood means that the wood is dried by heating to 100 ° C. or more in a shorter time than the main drying before the wood is fully dried. Maintaining 100 ° C. or higher in the high temperature pretreatment drying may be the entire time of the high temperature pretreatment drying. Further, the temperature may be temporarily set to 100 ° C. or higher, and the others may be dried at less than 100 ° C.
Examples of the conditions for the high temperature pretreatment drying include a dry bulb temperature of 140 ° C. and a wet bulb temperature of 95 ° C., and holding for 2 to 5 hours.

As a heat source in the high-temperature pretreatment drying, for example, a steam boiler using oil, wood chips or the like as fuel can be employed.
The main drying of wood refers to the main drying step of wood in the wood drying method, and for example, low temperature drying, reduced pressure drying, low temperature reduced pressure drying, natural drying and the like can be employed.

  The invention according to claim 2 is the wood drying method according to claim 1, wherein, in the high temperature pretreatment drying step, the dry bulb temperature is 140 ° C. and the wet bulb temperature is 95 ° C., and is maintained for 2 to 5 hours. .

  According to the second aspect of the present invention, in the high temperature pretreatment drying step, the wood is held at a dry bulb temperature of 140 ° C. and a wet bulb temperature of 95 ° C. for 2 to 5 hours, so there is little change in fragrance and material color. Surface cracking can be suppressed.

When the dry bulb temperature is less than 140 ° C., a sufficient drying set is not formed, and crack suppression is not sufficient. Moreover, when it exceeds 140 degreeC, the change of a fragrance, material color, and an internal crack will generate | occur | produce.
When the wet bulb temperature is less than 95 ° C., the material temperature is low and the formation of the drying set is insufficient. On the other hand, when the temperature exceeds 95 ° C., the material color changes and the surface evaporates slowly and the formation of the drying set becomes insufficient.
When the holding time is less than 2 hours, the formation of the drying set is insufficient. Moreover, when holding time exceeds 5 hours, a change of a fragrance, a material color, and an internal crack will generate | occur | produce.

  The invention according to claim 3 is the wood drying method according to claim 1 or 2, wherein the step of performing the main drying includes a step of drying the wood at a low temperature under reduced pressure.

  According to the invention described in claim 3, since the low-temperature reduced-pressure drying is performed in all or a part of the main drying process, the drying time is shortened compared to the case where the conventional wood is dried only by the low-temperature drying. Cost can be reduced.

  The invention according to claim 4 is the wood drying method according to claim 3, wherein the low-temperature vacuum drying process repeats heating under reduced pressure at a pressure of normal pressure to −90 kPa and a temperature of 30 ° C. to 60 ° C.

  According to the invention described in claim 4, during the low-temperature vacuum drying, the pressure is reduced from normal pressure to -90 kPa, and the temperature is repeated from 30 ° C to 60 ° C for a short time without impairing the scent or the material color. Can be dried.

If the ultimate degree of vacuum during low-temperature vacuum drying is less than -90 kPa, there is a disadvantage that drying is delayed. Moreover, when it exceeds -90 kPa, an apparatus price will become high on an apparatus body structure.
If the heating temperature at the time of low-temperature vacuum drying is less than 30 ° C., the drying is slow. Moreover, when it exceeds 60 degreeC, a fragrance and material color will be impaired.

  The invention according to claim 5 is the wood drying method according to any one of claims 1 to 4, wherein the wood is any of cedar, cypress, larch square, log, and board. is there.

  The wood can be cedar, cypress or larch. Among these, since the palatability of a fragrance and a material color is strong, the effect of this invention becomes the most remarkable in the case of a cedar and a cypress. The form of the wood may be square, log or plate.

  According to the first aspect of the present invention, the steaming step and the high temperature pretreatment drying step of the wood are sequentially performed on the wood before the main drying of the wood, so that the surface cracking of the wood due to the drying is suppressed. In addition, the material color change due to drying is small, the residual ratio of the scent component of the wood after drying is high, and the production cost can be reduced.

  In particular, according to the second aspect of the present invention, as the high-temperature pretreatment drying conditions, the holding at a dry bulb temperature of 140 ° C. and a wet bulb temperature of 95 ° C. for 2 to 5 hours is adopted. Less surface cracks can be suppressed.

  In addition, according to the invention described in claim 3, since the low-temperature reduced-pressure drying is performed in all steps or a part of the main drying, the drying time is shortened as compared with the case of only conventional low-temperature drying, Production costs can be reduced.

  Furthermore, according to the invention described in claim 4, during the low-temperature vacuum drying, the drying time is reduced only by the pressure reduction and heating function by repeating the pressure reduction from normal pressure to -90 kPa and the temperature from 30 ° C to 60 ° C. The production cost can be reduced.

  Examples of the present invention will be specifically described below.

In FIG. 1, 10 is a wood drying apparatus to which the wood drying method according to Embodiment 1 of the present invention is applied. The wood drying apparatus 10 has a drying chamber 11 in which the wood A is stored and dried. As the wood A, two kinds of cored squares of cypress and cedar are adopted.
In the drying chamber 11, a dry bulb thermometer 12 for measuring the indoor dry bulb temperature, a wet bulb thermometer 13 for measuring the indoor wet bulb temperature, a pressure gauge 14 for measuring the indoor vapor pressure, and a boiler are generated. High-pressure steam injection means 15 for supplying high-pressure steam to the drying chamber 11, a heater 16 for heating the internal air of the drying chamber 11, and an exhaust gas pipe 17 that communicates with the drying chamber 11 and exhausts the internal air in the drying chamber 11 ( An on-off valve 18) and a decompression pump 19 for decompressing the drying chamber 11.

Next, a wood drying method using the wood drying apparatus 10 will be described with reference to the flow sheet of FIG.
The wood drying method includes a step of steaming the wood A, a step of pre-drying the steamed wood A at a high temperature, and a step of drying the wood A after the high-temperature pre-treatment drying at a low temperature under reduced pressure (main drying). . Hereinafter, each process will be described.
In FIG. 1, raw wood A (cypress, cedar) is carried into the drying chamber 11, and the drying chamber 11 is sealed. Next, the high-temperature high-pressure steam (160 ° C., 640 kPa) generated in the boiler is supplied to the drying chamber 11 for a certain period of time by opening the on-off valve 18 to the internal air of the drying chamber 11 by the high-pressure steam injection means 15. Thereby, the air in the drying chamber 11 becomes high temperature in a high humidity state. The drying chamber 11 is gradually maintained at a high temperature and high humidity by high-temperature and high-pressure steam, and the wood A stored in the drying chamber 11 is heated to a predetermined temperature by suppressing surface evaporation. The temperature in the drying chamber 11 is measured by a dry bulb thermometer 12 and a wet bulb thermometer 13, and the pressure in the drying chamber 11 is measured by a pressure gauge 14.

When the wood A is cooked, the high pressure steam injection means 15 is controlled by, for example, a microcomputer based on the data obtained from the two thermometers 12 and 13 and the pressure gauge 14 so that the drying chamber 11 has a certain cooking condition. Control.
Specifically, when the temperature of the drying chamber 11 reaches, for example, 95 ° C. for both the dry bulb temperature and the wet bulb temperature, and the drying chamber 11 is filled with saturated steam, the on-off valve 18 is closed. After that, the supply of water vapor by the high-pressure steam injection means 15 is continued, and the drying chamber 11 is filled with saturated water vapor. Therefore, excess water becomes condensed water and accumulates at the bottom. Thereafter, the injection of high-pressure steam into the drying chamber 11 by the high-pressure steam injection means 15 and the operation of stopping the supply of steam are repeated several tens of times for 3 hours, and the wood A is cooked.

Next, the high temperature pretreatment drying process of the wood A after cooking will be described.
In the high-temperature pretreatment drying step, the on-off valve 18 is opened, and the high-pressure steam in the drying chamber 11 is exhausted from the exhaust pipe and replaced with normal-pressure external air. At the same time, the internal air of the drying chamber 11 is heated by the heater 16, and the dry bulb temperature is 140 ° C. and the wet bulb temperature is 95 ° C., and is held for 2 to 5 hours. Thus, the wood A is subjected to pretreatment drying at a high temperature for a short time before the main drying (low temperature reduced pressure drying).

Next, the low temperature reduced pressure drying (main drying) process of the wood A using the wood drying apparatus 10 will be described.
In the low temperature reduced pressure drying process, the on-off valve 18 is closed, the pressure reducing pump 19 is operated, the internal air of the drying chamber 11 is forcibly exhausted, and the drying chamber 11 is depressurized. Specifically, the pressure in the drying chamber 11 is set to −90 kPa, and when the temperature in the drying chamber 11 is lowered to 30 ° C., the pressure is returned to the normal pressure, and the heater 16 is heated to 60 ° C. to reduce the pressure to −90 kPa again. The above steps are repeated until the wood A is dried to a predetermined moisture content.

Thus, since the steaming process and the high-temperature pretreatment drying process of the wood A are sequentially performed on the wood A before the main drying of the wood A, the surface cracking of the wood A due to drying can be suppressed. Further, since the material color change due to drying is small, the residual ratio of the scent component of the wood A after drying is high, and the drying time is shortened, the production cost can be reduced as compared with conventional vacuum drying.
In addition, as a high temperature pretreatment drying condition, since the holding at a dry bulb temperature of 140 ° C. and a wet bulb temperature of 95 ° C. for 2 to 5 hours is adopted, there is little change in the material color and the scent component of the wood A after drying remains. The effect that the drying set for surface crack suppression is formed in a state with a high rate is acquired.
Furthermore, since the low-temperature vacuum drying is performed after the high-temperature pretreatment drying, the drying time is shortened and the production cost can be reduced as compared with the conventional case of only the low-temperature drying without the high-temperature pretreatment drying.
And since it was made to repeat the reduced-pressure heating of 30 to 60 degreeC at -90kPa at the time of low-temperature pressure reduction drying, the effect that drying time is shortened also at low temperature is acquired.

Here, (1) surface cracking, (2) material color change, and (3) scent component for dry wood in the wood drying method of the present invention involving a high temperature pretreatment drying step and the conventional wood drying method. Report the test results compared.
(1) Surface cracking test of dry wood As wood for the sample, cedar and cypress cored squares (130 mm × 130 mm × 500 mm) with a sealed end were adopted. A constant temperature and humidity machine (Espec K series) was used as the dryer. The drying conditions are as shown in Table 1 below. In Table 1, DBT is the dry bulb temperature. WBT is wet bulb temperature. Steaming is steaming drying under the condition of 95 ° C. for both DBT and WBT. The pretreatment is high temperature pretreatment drying under conditions of DBT 140 ° C., WBT 95 ° C., cypress for a few hours, and cedar for 3, 5, and 7 hours. The finish drying is hot air drying under the conditions of DBT 60 ° C. and WBT 45 ° C. for examining only the crack prevention effect of the high temperature pretreatment.
As a test for the surface crack of wood, the surface crack area per column was evaluated.

  Regarding the occurrence of surface cracks in hinoki cypress wood, cracks occurred on the wood surface by high-temperature and low-humidity treatment at 120 ° C. for 3 hours. Little happened (graph in Fig. 3). In addition, when the cedar square was tested in the same manner, cracks occurred on the wood surface at 140 ° C. for 3 hours, but no cracks occurred at 140 ° C. for 5 hours and 140 ° C. for 7 hours (graph in FIG. 4). . 3 and 4 are dry bulb temperatures.

(2) Material color change test of dry wood Next, a material color change test is performed on the cypress core-supported square material dried under the drying conditions shown in Table 1 and the cedar sapwood obtained by processing the cedar square material. Report the results.
As a test method for the material color change, evaluation was performed by an L * a * b * color system using a colorimeter.
Tight drying here means low-temperature and vacuum drying while pressing the surface of the four column members with a spring clamp so that surface cracks do not occur during drying.
Moreover, high-temperature drying means the drying performed on 95 degreeC steaming conditions for 5 hours, DBT120 degreeC and WBT90 degreeC for 24 hours, and then DBT80 degreeC and WBT50-60 degreeC for 96 hours.

The graphs of FIGS. 5 to 7 show changes in the material color in the drying process of hinoki cornwood. It can be seen that in tight drying, where the surface of the wood is tied with a clamp, the material color hardly changes from the drying process to after the molding process. Molder processing is a type of processing that increases the smoothness of the surface of wood. In the drying of the present invention, as in the case of high-temperature drying, it was found that the L * value (lightness) was lowered by drying, but the L * value was recovered by applying a molder process thereafter.
The graphs of FIGS. 8 to 10 show the material color change in the drying process of the cedar sapwood. The sapwood is wood called white flakes on the outer peripheral portion of the colored core material in the inner layer portion of the log. In tight drying, there was almost no change in the color of the raw material (wood before drying) during the drying process. In the high temperature pretreatment drying, the L * value is lowered by drying as in the high temperature drying, but the cedar sapwood of the present invention had the L * value similar to that of the raw material after the molding process.
As described above, it was found that if high-temperature pretreatment drying was performed before the main drying of the wood, there was an effect of suppressing cracking of the wood surface, and the material color after molder processing was better than that of high-temperature drying.

(3) Qualitative / Quantitative Test of Scented Component of Dried Wood Next, the results of a qualitative / quantitative test of the scented component by collecting volatile components are reported for the cedar squarewood dried under the drying conditions shown in Table 1.
In Tables 2 and 3, the surface layer refers to the surface layer of wood, the center refers to the center of the wood, and the raw material refers to naturally dried wood. In addition, after drying in Table 2 means after drying of the present invention accompanied by high temperature pretreatment drying, and after drying in Table 3 means after conventional high temperature drying.

experimental method:
Approximately 150 liters of compressed air was injected into the Tedlar bag and the sample was placed in a gas wash bottle. Thereafter, the Tedlar bag, the gas cleaning bottle, and the mini pump were communicated in this order by the silicon tube. Thereafter, in order to replace the air in the gas washing bottle with compressed air, about 0.5 liters of air was sucked. Thereafter, an adsorption pipe (adsorption pipe 1 near the gas washing bottle and adsorption pipe 2 near the gas pump was used as the adsorption pipe 2) was placed between the gas washing bottle and the mini pump, and compressed air was sucked in for 20 hours continuously. Volatile components were collected.
When the suction was completed, the adsorption tube was divided with a file, and the activated carbon inside was collected in a test tube and immersed in 1 ml of acetone. One day later, the supernatant was collected, and Eicosane (internal standard) was added to the supernatant and analyzed by GC-MS.

<Mini pump value>
Raw material TIME = 20 hr TOT = 144.00 liters F_AV = 0.120 L / min
Wood after drying TIME = 20 hr TOT = 144.00 liters F_AV = 0.119 L / min
<Sample size>
Raw material 6.9 × 3.5 × 2 (cm) Surface area: 89.9 (cm ² )
Wood after drying 7 × 3.5 × 2 (cm) Surface area: 91 (cm ² )

<Analysis conditions>
Analytical instrument: SHIMADZU QP5050
Column: DB-5, 30 m × 0.25 mmφ, 0.25 μm
Temperature rising:
40 ° C. (1 min. Hold) → 245 ° C. (10 ° C./min., 18 min. Hold) → 320 ° C. (10 ° C./min., 1 min. Hold)
Split ratio: 1/5, EIMS range: 50-500 m / z, injection volume: 1 ml.

[Quantitative]
Quantification was performed as follows using the calibration curve created immediately before.
<How to determine the equivalent amount (μg) of β-caryophyllene>
β-carophyllene equivalent amount (μg) = (1) × 0.9 ((2)) × 1 / 0.962 ((3)) × 1/1000 ((4)) × 1000 × 1000
Here, (1) is β-caryophyllene equivalent concentration (μl / ml),
(2) is β-caryophyllene specific gravity: 0.9 (mg / μl),
(3) is the amount actually adsorbed calculated from the collected amount of the adsorption tube: 1 / 0.962,
(4) is GC-MS injection amount: 1/1000 (ml).
Since 1 ml of acetone was used at the time of solvent desorption, it is multiplied by 1000.

  As shown in Table 2, in the present invention with high temperature pretreatment drying, the volatile component content was almost unchanged or rather increased in the surface layer and the center of the wood as compared with the raw material. This becomes clear when compared with the high temperature drying in Table 3. That is, it is shown that when the new dryer for the present invention is used, drying with the volatile components of wood remaining is possible. In addition, the data of the surface layer portion and the central portion include an increasing component and a decreasing component as compared with the raw material. It shows that terpenes having these similar structures are present while being converted to each other during the drying process.

  As shown in Table 3, in the conventional high-temperature drying, a 30% reduction in volatile components was observed in the surface layer portion of the cedar square wood due to this high-temperature drying. However, there was almost no change in the amount of volatile components at the center of the cedar square. Moreover, in the surface layer part of wood, most terpenes decreased, but β-cadinene and zonarene increased. In addition, β-cdadinene and zonarene also increased in the center of the wood. Furthermore, in the surface layer portion of the wood, the decreased α-murolene and δ-cadinene increased. Although there is such a behavior, it has been found that most of the volatile components in the surface layer are lost during high-temperature drying. On the contrary, inside the wood, although the terpene composition was affected, it was confirmed that there was little change in the total amount of volatile components.

1 is an overall configuration diagram of a wood drying apparatus to which a wood drying method according to Embodiment 1 of the present invention is applied. It is a flow sheet which shows the wood drying method which concerns on Example 1 of this invention. It is a graph which shows the generation | occurrence | production situation of the surface crack of a cypress material in each process of the wood drying method which concerns on Example 1 of this invention. It is a graph which shows the generating condition of the surface crack of a cedar material in each process of the wood drying method which concerns on Example 1 of this invention. It is a graph which shows the material color condition of the cypress material in each process of the wood drying method which concerns on Example 1 of this invention. It is a graph which shows another material color condition of the cypress material in each process of the wood drying method which concerns on Example 1 of this invention. It is a graph which shows the other material color condition of the cypress material in each process of the wood drying method which concerns on Example 1 of this invention. It is a graph which shows the material color condition of the cedar material in each process of the wood drying method which concerns on Example 1 of this invention. It is a graph which shows another material color condition of a cedar material in each process of the wood drying method which concerns on Example 1 of this invention. It is a graph which shows the other material color condition of a cedar material in each process of the wood drying method which concerns on Example 1 of this invention.

Explanation of symbols

  A Wood.

Claims (5)

Steaming wood,
A step of high-temperature pretreatment drying of the cooked wood;
A step of drying the wood after the high temperature pretreatment drying.   The wood drying method according to claim 1, wherein in the high-temperature pretreatment drying step, the dry bulb temperature is 140 ° C and the wet bulb temperature is 95 ° C and is maintained for 2 to 5 hours.   The wood drying method according to claim 1, wherein the step of performing the main drying includes a step of drying the wood at a low temperature under reduced pressure.   The wood drying method according to claim 3, wherein the low-temperature vacuum drying process repeats heating under reduced pressure at a pressure of normal pressure to −90 kPa and a temperature of 30 ° C. to 60 ° C. 5.   The wood drying method according to any one of claims 1 to 4, wherein the wood is one of cedar, cypress, larch square, log, and board.

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