JP2018161802A - Manufacturing method of high durability wood - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide highly durable wood at low cost as a result of easy temperature control without the need for special equipment for processing at a high temperature exceeding 200 ° C. or using an inert gas. It is a method for manufacturing highly durable wood. SOLUTION: The wood is composed of a strong acid and a weak base, and has a step of treating the wood with an aqueous solution of a salt which is substantially neutral to weakly acidic at room temperature, a step of drying the wood, and a step of heating the wood. However, the treatment of the salt with an aqueous solution is a treatment of impregnating wood with the aqueous solution. Further, as the salt, magnesium chloride, calcium chloride, copper sulfate or ammonium sulfate is used. [Selection diagram] None

Description

  The present invention relates to a method for imparting high durability to wood.

  When wood is used in a harsh environment such as outdoors, it has the disadvantages of “rot (deterioration caused by wood decaying fungi)” and “because of damage caused by termites”. In the past, it was common to protect and protect insects by applying and impregnating wood preservatives to wood, but due to increased awareness of the environment and health of users, the durability of wood without relying on chemicals Development of technology that enhances this is desired.

  In recent years, heat treatment technology for improving the durability of wood has been developed in Europe such as Finland and the Netherlands, and wood having high durability has been manufactured and sold. Furthermore, a heat treatment technique called estec treatment has been developed and put into practical use in Japan.

In this type of heat treatment, it is considered that the hemicellulose having low durability among the wood components is decomposed and removed, and at the same time, a part thereof is modified into a highly durable component, thereby improving the durability.
However, in any heat treatment method, heating at 200 ° C. or higher, preferably 220 ° C. or higher is indispensable for imparting practical high durability to wood. For this reason, in the heat treatment step, heating in an inert gas excluding air, heating using superheated steam, heating in supercritical carbon dioxide, and the like are essential in order to prevent burning of wood.

  A method using nitrogen gas as an inert gas is disclosed in Japanese Patent Application Laid-Open No. 56-135004, heating using superheated steam is described in Japanese Patent Application Laid-Open No. 09-502508, and heating in supercritical carbon dioxide is disclosed in Japanese Patent Application Laid-Open No. 2013-2013. -180460, respectively.

JP 56-135044 A JP-T 09-502508 JP2013-180460A

The present inventor performed heat treatment using superheated steam described in Patent Document 2 using cedar sapwood as a test material, and evaluated resistance to wood decay fungi based on standards such as JIS K 1571 In order to exhibit high performance comparable to treatment with antiseptic agents, hemicellulose contained in wood is decomposed and removed in a considerable proportion, and as a result, the weight of wood on a dry basis is 10% or more, Preferably, it had to be reduced by about 15%.
That is, in this heat treatment using superheated steam, it is essential to heat the wood at 200 ° C. for 72 hours or longer, at 220 ° C. for 8 hours or longer, desirably 24 hours or longer, or 240 ° C. for 8 hours or longer. found.

This does not apply only to the superheated steam treatment, and in any of the above-described treatments, treatment for a considerable period of time at a temperature exceeding 200 ° C. is essential for high durability.
In order to impart high durability to wood with conventional technology, excessive energy is required for heat treatment, and it is difficult to control the temperature to maintain the temperature inside the device uniformly or to maintain a predetermined material temperature. The heat-treated wood had to be expensive due to the need for a special device for performing the treatment in a state filled with an inert gas such as nitrogen gas or superheated steam.

  The present invention was devised in view of the above circumstances, and does not require a special apparatus for processing at a high temperature exceeding 200 ° C. or using an inert gas, and temperature control is easy. It aims at providing the manufacturing method of the highly durable wood which can provide highly durable wood cheaply.

  The method for producing a highly durable wood according to the present invention comprises a step of treating wood with an aqueous solution of a salt consisting of a strong acid and a weak base and exhibiting substantially neutral to weak acidity at room temperature, and a step of drying the wood, Heating the wood.

  The treatment with an aqueous salt solution is a treatment in which wood is impregnated with an aqueous solution, applied, sprayed, or immersed in an aqueous solution.

The weight reduction rate of the wood in the heating step is preferably 10% or more and 25% or less, and the concentration of the aqueous salt solution is preferably 0.5% or more and 2% or less.
Moreover, it is preferable that the temperature in the process of heating is 120 degreeC or more and 200 degrees C or less.

  An example of a salt composed of a strong acid and a weak base and exhibiting a neutral to weak acidity at room temperature is magnesium chloride, calcium chloride, copper sulfate or ammonium sulfate.

According to the method for producing a highly durable wood according to the present invention, the concentration of the aqueous salt solution that exhibits neutral to weak acidity at room temperature is 0.5% or more and 2% or less, and the temperature in the heating step is 120 ° C or more and 200 ° C. By making the temperature lower than or equal to 0 ° C., the weight reduction rate of wood due to thermal decomposition and thermal denaturation of hemicellulose for imparting high durability to the wood can be made 10% to 25%.
A wood having a weight reduction rate of less than 10% cannot obtain high durability, and if the weight reduction rate is higher than 25%, the wood is deteriorated in strength. The highly durable wood manufactured by the method has high durability and ensures the strength required for wood.

It is a graph which shows the decay-resistant evaluation result based on JISK1571 with respect to the timber (cedar sapwood) manufactured by the heat processing by superheated steam. It is a graph which shows the decay-resistant evaluation result based on JISZ2101 with respect to the timber (cedar sapwood) manufactured by the heat processing by superheated steam.

  A method for producing a highly durable wood according to an embodiment of the present invention includes a magnesium chloride aqueous solution, a calcium chloride aqueous solution, a copper sulfate aqueous solution, or a salt that consists of a strong acid and a weak base, and is substantially neutral to weakly acidic at room temperature. A step of treating wood with an aqueous ammonium sulfate solution, a step of drying the wood, and a step of heating the wood.

The concentration of the aqueous solution of the salt, which is composed of a strong acid and a weak base and exhibits almost neutral to weak acidity at room temperature, is preferably in the range of 0.5% to 2.0%. When it is 0.5% or less, the effect as an acid catalyst is not exhibited so much. On the other hand, if it exceeds 2.0%, a salt consisting of a strong acid and a weak base, which is almost neutral to weakly acidic at room temperature, has a high hygroscopic property, so that the surface of wood that has been treated is sticky. is there.
In addition, neutral to weakly acidic means the range of pH 4-7.

  Wood is treated with an aqueous solution of a salt (such as an aqueous magnesium chloride solution) composed of such a strong acid and a weak base and exhibiting approximately neutral to weak acidity at room temperature. For this treatment, any of a method in which wood is impregnated with the aqueous solution, wood is coated with the aqueous solution, wood is sprayed with the aqueous solution, and wood is immersed in the aqueous solution is used.

In particular, the pressure injection method is most effective for impregnating wood with an aqueous solution of a salt composed of a strong acid and a weak base and exhibiting almost neutral to weak acidity at room temperature (eg, magnesium chloride aqueous solution).
For example, wood is put in a stainless pressure vessel. At this time, a heavy stone is attached or tied with a rope or the like so as to prevent the wood from floating when the aqueous solution is introduced, and is fixed in the pressure vessel.
The pressure vessel is sealed, and the pressure vessel is depressurized to about 50 to 100 hPa with a vacuum pump. This reduced pressure state is continued for about 30 to 60 minutes.
After that, using the pressure difference inside and outside the pressure vessel, the aqueous solution is injected into the pressure vessel, and after the injection using the pressure difference becomes difficult, the liquid feed pump can be used inside the pressure vessel. As long as it is filled with the aqueous solution. Furthermore, the aqueous solution is fed into a pressure vessel using a plunger pump or the like to obtain a pressurized state of 0.5 to 1.5 MPa.

After maintaining this pressurized state for 1 to 24 hours, the pressure is released.
After releasing the pressure, the liquid feed pump is rotated in the reverse direction to recover an aqueous solution of salt (for example, magnesium chloride aqueous solution) that is composed of excess strong acid and weak base in the pressure vessel, and is almost neutral to weakly acidic at room temperature. Remove the wood from the pressure vessel.
In addition, before taking out a timber from a pressure vessel, the pressure vessel is pressure-reduced and the said excess aqueous solution in the permanent space in wood may be collect | recovered.

In the above-described pressurized injection method, the pressure vessel is made up of a strong acid and a weak base using a pressure difference between the inside and outside of the pressure vessel or a liquid feed pump. Although it was filled with an aqueous solution (for example, magnesium chloride aqueous solution), the inside of the pressure vessel was pressurized to 0.5 to 1.5 MPa by filling the pressure vessel with compressed air using a compressor instead of the aqueous solution. It is also possible to enter a state.
In this case, a stainless steel box-type container is used, and the wood to be treated is fixed with a heavy stone or a rope so as not to float, and after filling the box-shaped container with the aqueous solution, it is put into a pressure container and depressurized with a vacuum pump. Or after putting the box-shaped container which fixed the to-be-processed wood into a pressure vessel, after reducing pressure with a vacuum pump and introducing the said aqueous solution into a box-shaped container, it pressurizes with compressed air.
In this case as well, the pressure is released after maintaining the pressurized state of 0.5 to 1.5 MPa for 1 to 24 hours.
Thereafter, the aqueous solution is collected and the wood is taken out.

Wood made of a strong acid and a weak base and impregnated with an aqueous salt solution (for example, an aqueous magnesium chloride solution) that is substantially neutral to weakly acidic at room temperature is dried by a general wood drying method. That is, natural drying or artificial drying using water vapor or the like is performed on the wood. In the step of drying the wood, the wood is dried to a state where there is no free water or less.
Note that it is more convenient to use artificial drying than natural drying because the time required for the drying process can be shortened.
Moreover, it is also possible to perform this drying process and the heating process performed after that using the same apparatus.

The weight reduction rate of the wood in the heating step is preferably 10% or more and 25% or less, and the concentration of the aqueous salt solution is preferably 0.5% or more and 2% or less.
Moreover, it is preferable that the temperature in the process of heating is 120 degreeC or more and 200 degrees C or less.

  As a method of confirming that durability, especially resistance to wood decay fungi (hereinafter referred to as “decay resistance”) has been developed by heat treatment, JIS K1571 “Wood Preservative—Performance and Testing Method” or JIS Z2101 “Wood” There is an indoor bin test based on “testing method of aging”.

The former is an evaluation test method for wood preservatives, and is a method for evaluating the antiseptic effect when a chemical is impregnated in wood.
Therefore, in order to see the decrease in the antiseptic effect due to the chemicals flowing away, the step of immersing the wood specimen in water before the “antibacterial operation” using wood decay fungi (for example, Prunus edulis, Kawaratake) The “weathering operation” is to be repeated 10 times for the drying process.
In other words, this evaluation test method evaluates the decay resistance under severe environments where wind and rain are always directly applied.

  On the other hand, the latter is a standard that evaluates the decay resistance of wood itself, and is used in places where it is wet, such as under the floor, but is not directly or constantly exposed to wind and rain, because it does not perform weatherproofing and directly performs antibacterial operations. It will be evaluated the decay resistance.

The present inventor performed only heat treatment under various conditions as wood to be treated with cedar sapwood and evaluated the decay resistance by the above-mentioned two methods. As described above, it is clear that there is a clear relationship between the thermal decomposition of the product and the decay resistance.
That is, in the evaluation according to JIS K1571, when the rate of weight loss due to heat treatment was 15% or more, high deterioration was observed (see FIG. 1).
On the other hand, in the evaluation based on JIS Z2101, high deterioration resistance was observed when the weight reduction rate due to heat treatment was 10% or more (see FIG. 2).

  Thereby, it was confirmed that the weight reduction rate of the wood in the heating step is preferably 10% or more and 25% or less.

  In the heating process, it is possible to use a wood dryer capable of high-temperature drying, replacement with superheated steam or nitrogen gas, or a vacuum or close to it, and a dedicated heat treatment that can create an oxygen-free state It is of course possible to use an apparatus.

The wood that has been subjected to the above drying process is placed in an apparatus and placed in an environment of 120 ° C. or more and 200 ° C. or less, preferably 150 ° C. to 180 ° C. for a certain period of time, for example, 2 hours to 72 hours, and wood components, mainly hemicellulose. Cause thermal decomposition and thermal denaturation of
At 200 ° C. or higher, as described above, there is a risk of ignition if it is not replaced with an inert gas or the like, while thermal decomposition hardly occurs at 120 ° C. or lower. Even if inert gas is not used, there is no risk of ignition and the temperature range in which thermal decomposition proceeds moderately is 150 ° C. to 180 ° C.
The weight loss caused at this time is 10% or more, preferably 15% or more, as described above, from the viewpoint of developing durability. On the other hand, when the weight loss increases, the deterioration of the strength of the wood becomes remarkable. Therefore, in consideration of this point, it is 25% or less, preferably 20% or less.
That is, the weight loss due to the heat treatment is 10% to 25%, preferably 15% to 20%.

  The occurrence of thermal decomposition of the wood component can be easily confirmed by measuring the total dry weight before and after the treatment of the wood and confirming that it has been reduced by the treatment. In addition, the fact that hemicellulose has been modified can be inferred from the fact that when Klarson lignin is quantified, the absolute amount thereof is increased by heat treatment as compared with the case of no treatment.

  According to the present invention, “an aqueous solution of a salt consisting of a strong acid and a weak base and exhibiting almost neutral to weak acidity at room temperature” has an effect of promoting thermal decomposition of wood even at a temperature of 200 ° C. or less, and does not use them. Therefore, it was considered that the same phenomenon as that at the time of processing at a high temperature of 200 ° C. or higher was caused. Therefore, under what conditions, the weight reduction rate of wood exceeded 10% or 15% was examined. Conditions and the like at that time are shown in Examples 1 to 12 below.

Example 1)
For wood to be treated, cedar sapwood cut in the tangential direction (T) 30 mm × radial direction (R) 30 mm × length direction (L) 80 mm in an air-dried state is used as a completely dry state at 105 ° C. It was.
A magnesium chloride aqueous solution was used as an aqueous solution of a salt composed of a strong acid and a weak base and exhibiting almost neutral to weak acidity at room temperature. After measuring the weight of the wood (W1), it was placed in a stainless steel vat, poured with a 2.0% magnesium chloride aqueous solution prepared in advance, and submerged in the liquid using a stainless steel weight. . The vat is put into a pressure injection can, deaerated with a vacuum pump, and then under a reduced pressure of about 50 hPa for 1 hour, then under a pressure of 1.3 MPa using a compressor for 2 hours, and further into the solution after decompression. Left a day and night.
After removing wood from the magnesium chloride aqueous solution and measuring the injection amount of the magnesium chloride aqueous solution, it was dried in a blow dryer at 50 ° C. for 3 days, then heated to 105 ° C. and dried for 1 day to be completely dry. .
Then, after measuring the weight of the wood (W2), it was placed in a heat treatment apparatus filled with superheated steam, and the apparatus was adjusted so that the temperature of the wood was 200 ° C., and the treatment was performed for 2 hours. The wood was taken out when the temperature of the wood became 150 ° C. or less and weighed (W3). When the weight reduction rate of the wood due to the heat treatment was determined by the formula (W2-W3) / W1 × 100, it exceeded the target of 15% and became an average of 55.6% for 5 bodies.

Example 2)
Except for the heat treatment temperature of 180 ° C. and the time of 20 hours, the weight reduction rate when the same treatment as in Example 1 was performed was 15.7%.

Example 3)
The weight reduction rate when the same treatment as in Example 2 was performed except that the concentration of the magnesium chloride aqueous solution was 1.0% exceeded the target of 10% and became 13.2%.

Example 4)
Except for the heat treatment temperature of 160 ° C. and the time of 72 hours, the weight reduction rate when the same treatment as in Example 3 was performed exceeded the target of 10% to 12.3%.

Example 5)
The weight reduction rate when the same treatment as in Example 2 was performed except that the concentration of the magnesium chloride aqueous solution was 0.5% exceeded the target of 10% and became 10.4%.

Example 6)
The weight reduction rate when the same treatment as in Example 4 was performed except that the concentration of the magnesium chloride aqueous solution was 0.5% was exactly the target of 10.0%.

Example 7)
The same treatment as in Example 2 was conducted except that a 1.0% calcium chloride aqueous solution was used instead of the magnesium chloride aqueous solution as a salt aqueous solution consisting of a strong acid and a weak base and exhibiting almost neutral to weak acidity at room temperature. The weight loss rate at the time of going over the target 10% was 10.2%.

Example 8)
Except for the heat treatment temperature of 160 ° C. and the time of 72 hours, the weight reduction rate when the same treatment as in Example 7 was performed exceeded the target of 10% and became 10.7%.

Example 9)
The same treatment as in Example 2 was conducted except that a 1.0% copper sulfate aqueous solution was used instead of the magnesium chloride aqueous solution as a salt aqueous solution consisting of a strong acid and a weak base and exhibiting almost neutral to weak acidity at room temperature. The weight reduction rate when it was performed exceeded the target of 15% and became 19.8%.

Example 10)
Except for the heat treatment temperature of 160 ° C. and the time of 72 hours, the weight reduction rate when the same treatment as in Example 9 was performed exceeded the target of 15% and became 21.4%.

Example 11)
The same treatment as in Example 2 was performed except that a 1.0% ammonium sulfate aqueous solution was used instead of the magnesium chloride aqueous solution as a salt aqueous solution consisting of a strong acid and a weak base and exhibiting almost neutral to weak acidity at room temperature. The weight loss rate at that time exceeded the target of 10% and became 14.0%.

Example 12)
Except for the heat treatment temperature of 160 ° C. and the time of 72 hours, the weight reduction rate when the same treatment as in Example 11 was performed exceeded the target of 10% to 14.8%.

  Therefore, the weight reduction rate of the wood in Examples 1 to 12 above is 15.6%, 15.7%, 13.2%, which falls within the range of 10% or more and 25% or less, which is the target of high durability. It became 12.3%, 10.4%, 10.0%, 10.2%, 10.7%, 19.8%, 21.4%, 14.0%, 14.8%.

  Moreover, in Examples 1-12 mentioned above, although magnesium chloride aqueous solution, calcium chloride aqueous solution, copper sulfate aqueous solution, or ammonium sulfate aqueous solution was mentioned as an example of the aqueous solution of the salt which shows substantially neutral to weak acidity at normal temperature, There are aqueous solutions of zinc chloride, nickel chloride aqueous solution, sulfate, nitrate and the like.

Comparative Example 1)
For wood to be treated, cedar sap material cut into a tangential direction (T) 30 mm × radial direction (R) 30 mm × length direction (L) 80 mm in an air-dried state, as in Examples 1 to 12. It was used as a completely dry state at 105 ° C.
After measuring the weight of the wood (W1), it was placed in a heat treatment apparatus filled with superheated steam, and the apparatus was adjusted so that the wood temperature was 200 ° C., and the treatment was performed for 2 hours. The wood was taken out when the temperature of the wood became 150 ° C. or less and weighed (W3). When the weight reduction rate of wood due to heat treatment was calculated by the formula (W1-W3) / W1 × 100, it was 3.2%, which is far below the target 10% or 15%, and the appearance of decay resistance is expected could not.

Comparative Example 2)
Except for the heat treatment temperature of 180 ° C. and the time of 24 hours, the weight reduction rate when the same treatment as in Comparative Example 1 was performed was 4.0%, and the development of the decay resistance could not be expected.

Comparative Example 3)
Except for the heat treatment temperature of 160 ° C. and the time of 72 hours, the weight reduction rate when the same treatment as in Comparative Example 1 was performed was 2.5%, and it was not expected to exhibit the decay resistance.
Thus, when heat treatment was carried out with wood alone without using a catalyst, it became clear that at a temperature of 200 ° C. or less, it was not possible to expect the expression of decay resistance, which far exceeded the target weight reduction rate.

Comparative Example 4)
Instead of an aqueous solution of a salt composed of a strong acid and a weak base and exhibiting neutral to weak acidity at room temperature, a 1.0% aqueous solution of ammonium borate, which is an aqueous solution of a salt composed of a weak acid and a weak base, was used. Other than that, when the same treatment as in Example 2 was performed, the weight reduction rate was 4.3%, and the development of decay resistance could not be expected.

Comparative Example 5)
Except for the heat treatment temperature of 160 ° C. and the time of 72 hours, the weight reduction rate when the same treatment as in Comparative Example 4 was performed was 4.7%, and the development of decay resistance could not be expected.

Comparative Example 6)
Instead of an aqueous solution of a salt composed of a strong acid and a weak base and exhibiting almost neutral to weak acidity at room temperature, a 1.0% aqueous sodium chloride solution which is an aqueous solution of a salt composed of a strong acid and a strong base was used. Otherwise, the weight reduction rate when the same treatment as in Example 2 was carried out was 6.2%, and it was impossible to expect the deterioration.

Comparative Example 7)
Instead of an aqueous solution of a salt consisting of a strong acid and a weak base and exhibiting almost neutral to weak acidity at room temperature, a 1.0% sodium carbonate aqueous solution which is an aqueous solution of a salt consisting of a weak acid and a strong base was used. Otherwise, the weight reduction rate when the same treatment as in Example 2 was performed was 3.2%, and the development of decay resistance could not be expected.

  Thus, in aqueous solutions other than salts consisting of strong acids and weak bases, the effect of promoting decomposition during heat treatment was not observed, and only aqueous solutions of salts consisting of strong acids and weak bases and showing almost neutral to weak acidity at room temperature. The inventors have found that such a catalytic effect is recognized.

  The weight reduction rate of wood in Comparative Examples 1 to 7 is 3.2%, 4.0%, 2.5%, and 4.% that do not fall within the range of 10% or more and 25% or less, which is the target of high durability. 3%, 4.7%, 6.2%, and 3.2%, indicating that high durability is not ensured.

  In the above-described embodiment, the wood is impregnated with an aqueous solution of a salt that is substantially neutral to weakly acidic at room temperature. However, if the aqueous solution can be impregnated, the application of the aqueous solution to wood, Needless to say, spraying of the aqueous solution onto wood or immersion of the wood in the aqueous solution may be used.

Claims (7)

  It comprises a step of treating wood with an aqueous solution of a salt consisting of a strong acid and a weak base and exhibiting almost neutral to weak acidity at room temperature, a step of drying the wood, and a step of heating the wood. A method for producing highly durable wood.   The method for producing a highly durable wood according to claim 1, wherein the treatment with the aqueous solution of the salt is a treatment of impregnating the wood with an aqueous solution.   The method for producing a highly durable wood according to claim 2, wherein the treatment for impregnating the wood with the aqueous solution is any one of impregnation with an aqueous solution, application of the aqueous solution, spraying of the aqueous solution, and immersion in the aqueous solution.   The method for producing a highly durable wood according to claim 1, 2, or 3, wherein a weight reduction rate of the wood in the heating step is 10% or more and 25% or less.   The method for producing a highly durable wood according to claim 1, 2, 3 or 4, wherein the concentration of the aqueous salt solution is 0.5% or more and 2% or less.   6. The method for producing a highly durable wood according to claim 1, wherein a temperature in the heating step is 120 ° C. or more and 200 ° C. or less.   The method for producing a highly durable wood according to claim 1, 2, 3, 4, 5 or 6, wherein the salt is magnesium chloride, calcium chloride, copper sulfate or ammonium sulfate.

Images