EP0496885A1

EP0496885A1 - Method of modifying treatment of timber and the like

Info

Publication number: EP0496885A1
Application number: EP90914969A
Authority: EP
Inventors: Hideaki Takahashi; Kinji Tamakawa; Kiyoshi Sato; Isao Suzuki; Satoshi Yunome; Katsumi Honma; Yasuo Suzuki
Original assignee: KYOGYOKUMIAI SENDAI FANICHIA; MIYAGIKEN
Current assignee: KYOGYOKUMIAI SENDAI FANICHIA; MIYAGIKEN
Priority date: 1989-10-16
Filing date: 1990-10-16
Publication date: 1992-08-05
Also published as: WO1991005643A1; KR920703279A; CA2067824A1; JP2717713B2; JPH03162902A; EP0496885A4

Abstract

Confident that, when cracks occur in a piece of timber due to the heat treatment of the timber, an acoustic emission (AE) should occur, an effective AE signal directly involved with the cracks is discriminated and detected, and, in addition to this, the total (integrated) number of events and the rate of occurrences of AE are monitored while the drying treatment process and the high temperature treatment process are discriminated to thereby put all above evidences together to predict cracks occurring during the processes of the drying treatment and the high temperature treatment, whereby the temperature and humidity are controlled on the basis of the predicted information to thereby control the atmosphere such that the cracks will not occur. Furthermore, in that case, the timber is impregnated with a specific organic solvent medium to conduct the impregnating treatment where the water and the heat react chemically with each other, whereby the interior of the piece of timber is plasticized and the cracks due to the heating treatment are prevented from occurring and the brittleness in the quality of timber due to the high temperature treatment is greatly bettered, thus improving the workability of the timber.

Description

Technical Field

This invention relates to a method of treatment for modifying the characteristics of timber and other wood products, wherein, in applying heat treatment to various worked vegetable materials such as logs, worked timber or bamboo material, etc. (hereinafter referred to as "timber and other wood products" or "timber and the like" depending upon circumstances), while making use of characteristics that the timber and the like naturally have to manufacture worked vegetable materials to which various characteristics are added, this method is adapted to have the ability to prevent cracking in timber and the like subjected to heat treatment, and to improve workability of timber and the like which has a tendency to be deteriorated by application of heat, thus to allow such timber and the like to be worked vegetable materials having a higher quality and more versatile properties as compared to the prior art.

Background Art

Heretofore, technologies to apply high temperature heat treatment to timber and the like to change them to worked material having new characteristics have been already disclosed. Examples of technology of this kind are: a method of applying heat treatment to timber or bamboo material, etc., at a high temperature in the atmosphere of an incombustible gas to process or work the timber so that it is in the form of lignite or fossil wood (Japanese Laid Open Patent Application No. 135004/81), a method of manufacturing smoked bamboo (Japanese Laid Open Application No. 212007/82), and a method of modifying treatment of worked vegetable material such as timber, bamboo material, etc. The inventors of this application are developing to put into practice a new worked vegetable material using these technologies to apply heat treatment to timber and the like to make artificial lignite or fossil wood, artificial smoked bamboo or high temperature heat treated material. Such high temperature heat treated materials, so called new materials, are not only utilized as substitutes for natural lignite or fossil wood in short supply, but also are utilized for combining pieces having light and shading with each other to make up a beautiful wooden mosaic, or are utilized for furniture or facing material by making use of adhesiveness or machine workability which cannot be found in natural lignite or fossil material, and the property to give light and shading in color tone by a temperature difference. Further, in recent years, by making use of the characteristic that such new materials are difficult to rot because they are heat-treated, these new materials are exhibiting usefulness or utility in various fields such as water related facing material such as bath tubs, lavatory or kitchen units, etc.
However, there are many instances where high temperature heat treatment of timber and the like is such that a heat treatment crack may appear during manufacturing, giving rise to the drawbacks that the yield is lowered and/or the workability of the products is deteriorated to a greater degree than as compared to timber and the like to which no heat treatment is applied. For this reason, there has arisen a technical requirement to improve this.
In the course of searching for a cause of "crack" in timber and other wood products subjected to heat treatment and to study methods of preventing this, the inventors have assumed that there should be an acoustic emission (AE), since cracking by drying or heat is a sort of destruction of solid. On the basis of observation of such AE, they began to make studies of a technology to detect a "crack" or predict a "crack" caused by drying or heat. At the same time, they investigated technical literature in regard to the relationship between "crack" of timber and AE. As a result, they noticed a known technology of "Device for predicting and preventing cracking of timber by drying" (Japanese Patent Publication No. 7317/88).
Further, in recent years, the inventors have found that timber can be changed to a material having a flexibility similar to that of plastic by a simple chemical reaction.
The inventors have taken hints from the above facts to conduct studies with a view to realizing prevention of cracking and improvement in workability of material in the high temperature heat treatment of timber and other wood products under more rigorous or severe conditions that of the drying treatment, thus to complete the invention of this application.
It is considered that the cause of a crack occurring in timber, etc. when high temperature heat treatment is applied thereto is mainly due to movement of moisture in the heating and drying process, contraction of tissue, and decomposition of cellulose.
First of all, the following finding was obtained in connection with the cracking of timber, etc. followed by movement of moisture in the heating and drying process and contraction of tissue. Moisture in timber, includes ordinarily free water and combined or absorbed water. During drying, only free water is first dissipated and removed at the surface layer. As drying is developed, combined water will also be removed. In the case of the former movement of free water, capillary phenomenon is dominant. On the other hand, the latter movement of combined water is based on diffusion. In this way, free water and combined water at the surface layer of timber are removed, so the timber is dried. However, the inner layer still remains in a state having a high moisture percentage. Thus, the dry portion attempts to contract, whereas the moisture contained portion resists contraction. As a result, at the former or first part of drying, tensile stress is exerted at the surface layer and compressive stress is exerted at the inner layer. Accordingly as drying is further developed, these stresses become large, and contraction spreads internally. However, since the surface layer is subject to a large tensile stress at all times, permanent deformation takes place in such a manner that the surface layer is not normally contracted. Thereafter, as a result of the fact that as the inside is dried the surface layer attempts to cause a normal contraction, positive and negative stresses are reversed. At the latter part of drying, the surface layer is subject to compressive stress and the inner layer is subject to tensile stress. For this reason, when the tensile stress is greater than the tensile strength of the wooden part, a wood section crack or a surface crack along the surface tissue takes place during the initial part of drying, and an internal crack takes place in the latter part of drying. In addition, surface hardening, and/or the defect called depression also occur with drying. It has been found that they are all directly related to the magnitude of the gradient of a moisture percentage distribution inside the timber or wood. In heat drying, it is required that defects such as various cracks, etc., do not take place, and that the gradient of a moisture percentage distribution inside the wood is made as great as possible to shorten the drying time. To realize this, it is important to take a moisture percentage distribution every hour inside the timber. Further, it is necessary to dry the timber whilst adjusting the temperature or humidity in dependence upon the moisture percentage of the timber being dried. However, since timber tissue is complicated, and various thermal properties are affected by the humidity moisture percentage and vary according to the kind of wood, it is difficult to theoretically take a moisture percentage distribution every hour inside the wood. In addition, since the mechanical strength and/or thickness of a material are also involved in crack occurrence following drying, then in the case of a complicated timber tissue having great anisotropy it is extremely difficult to determine the conditions under which a defect occurs. Accordingly, at present, in the conventional drying treatment, one enters a room in the course of drying to confirm cracking by eye measurement to re-adjust the atmosphere in the room. However, with this method, it is difficult to predict a crack before its occurrence, and it is impossible to find out about a crack occurring inside. In addition, in high temperature heat treatment, as in the invention of this application, and particularly when heating is carried out in an atmosphere of incombustible gas, this method is unable to be carried out.
Further, in the case of high temperature heat treatment, when wood is subjected to high temperatures, the cellulose of the wood begins to dissolve, so that the mechanical strength of the material is weakened. As a result, the wood is apt to crack. Accordingly, in high temperature heat treatment, through a high contraction factor of heat by high temperature and weakened mechanical strength of material, the situation arises where it is extremely difficult to prevent cracking from a technical point of view, as compared to the method of simply drying wood.
In the method of working or processing timber so that it is in the form of lignite or fossil wood (Japanese Laid Open Patent Application No. 135004/81), the method of manufacturing smoked bamboo (Japanese Laid Open Patent Application No. 212007/82), and the method of modifying treatment of worked vegetable material such as timber or bamboo material, which were previously developed, any measure relating to a crack due t heat treatment is hardly considered. For this reason, in the case where these methods are adopted on an industrial scale basis, the most important technical consideration is to allow products to be free from cracks and have high quality, and to manufacture usable products with good yield. Also, cost-effectiveness is important.
In view of this, the inventors have drawn attention to the known technology (Japanese Patent Publication No. 7317/88) to carry out prediction of a crack caused by drying of timber by using AE detection technology to control the ambient temperature and humidity of the timber, thus to prevent cracking. However, in the above known literature, a method is only described of predicting an initial crack in the drying treatment on the basis of the number of accumulated AE and the rate of occurrence of AE. Namely, even in the drying treatment, only prediction of an initial crack of drying in a temperature zone of 30 to 80°C is conducted, and consideration is not made in connection with cracking in the latter part of the drying treatment and/or cracking in high temperature heat treatment above 1000°C. Further, in the method of predicting an initial crack only a procedure is disclosed to know the number of accumulated AE and the rate of occurrence of AE immediately before the timber is cracked to operate control equipment when the AE occurrence rate reaches a limit value to relax the drying condition, thus to prevent a crack. In that case, the correlation between the number of accumulated AE or the rate of occurrence of AE and the occurrence of a crack is effective in the initial part of drying, but the correlation is not necessarily exhibited in the latter part of drying or high temperature heating.
Further, it has been found that, since the occurrence characteristic of AE varies according to the individual circumstances of the wood (timber) subject to treatment, and that the characteristic varies according to the kind of wood (timber), criteria conforming thereto are required. The inventors have noticed, in the course of observing and analyzing the circumstance under which cracks in timber and AE signals occur, that the cracking of timber has a close correlation with the amplitude of an AE signal, thus to pay attention to the amplitude of the electric signal to discriminate and detect an effective signal directly related to crack. Thus, even when a single AE signal is detected, where the amplitude of that AE signal is large, this signal is considered as a dangerous signal for a crack. Further, monitoring of the total number of events (accumulated value) and the AE occurrence rate is conducted on line on the basis of such AE signals to judge the state of the timber, thus to make predictions in the course of treatment. Then, the temperature and humidity are controlled on the basis of this predicted information to control the atmosphere so that no cracking takes place in the timber, etc. This method is applied to the total process of the drying treatment process step and the high temperature heat treatment process step to prevent cracking of timber during treatment, thereby making it possible to manufacture, with good yield, usable modifying-treated products of timber, etc. Namely, a first object is to provide a new technology capable of efficiently manufacturing high temperature heat treated material of a high quality from an industrial point of view.
Further, impregnating technology for timber is widely adopted. However, no example is known where any impregnant is used in advance with a view to preventing cracking in drying or heat treatment. The inventors have found that when a specific organic solvent selected from various impregnants is impregnated into timer, etc., thereafter to apply heat treatment thereto, a chemical reaction takes place inside, whereby internal plasticization occurs so that thermal fluidity is rendered to the material. Thus, the inventors have considered that when this finding is applied, thermal fluidity inside the timber may prevent cracking during heat treatment, thus to develop the invention of this application. Namely, by impregnating a specific organic solvent to implement impregnating treatment to cause hydrothermal chemical reactions, the inside of the timber is plasticized. Thus, there is provided a second object to prevent cracking by heat treatment, to greatly decrease the brittleness of wood caused by the high temperature heat treatment, thus to improve workability.

Disclosure of the Invention

The invention of this application contemplates attaining, by combining the following technical means, the technical solution to prevent the occurrence of cracks during heat treatment and to prevent the lowering of workability as a result of the timber becoming brittle by thermal treatment, which are drawbacks of the method of modifying treatment of timber to implement high temperature heat treatment in the atmosphere of incombustible gas already known as previously described.
As a result of the fact that the inventors have conducted studies on cracking in the case where heat and drying treatment of timber, etc., is implemented, it was made clear that such cracking takes place by movement of moisture, contraction of tissue and decomposition of cellulose by high temperature. It is considered that cracking during heat treatment of timber is one of the forms of destruction of a solid, so an acoustic emission (AE) should be produced similarly as in cracking by drying. Further, it is considered that if that AE signal is detected to know its frequency and signal strength, the information may be processed to make it possible to predict cracking in advance. As the result of study, the inventors have noticed that cracking of timber has a close correlation with the amplitude together with the occurrence rate of AE signals and that one should pay attention to the amplitude of the electric signal to discriminate and detect an effective signal directly connected to cracking. As a result, in the case where the amplitude is large, even when only one AE signal is detected, this signal can be considered as a dangerous signal for cracking. Further, monitoring of the AE accumulated event number and the AE occurrence rate is made on line on the basis of the above AE signal to discriminate phases or stages of drying or heat treatment to analyze and study the meaning of an AE signal detected while making a comparison with a reference value empirically determined in advance to carry out predictive judgement of cracking in the course of treatment to control temperature and humidity on the basis of predicted information to effect a control to relax the atmospheric conditions so that no cracking takes place in timber, etc. It is further made clear that since cracking of timber, etc. is caused by movement of moisture caused by the drying treatment and the heat treatment, and the denaturation of material due to heat, if temperature and humidity are adjusted as a control factor, cracking can be sufficiently prevented.
Further, when an approach is employed to impregnate an organic impregnant in timber and the like thereafter to place it high temperature water at more than 100°C to dissolve it by hydrothermal reaction (hydrolysis), the woody part is chemically changed into a state having thermal plasticity (thermal fluidity). Thus, it is made clear that since the woody part is deformed in correspondence with a difference between the tensile stress and the compressive stress at the surface layer and the internal layer, occurring by application of heat, no cracking takes place. The fact that the woody part is chemically changed into a state having thermal plasticity (thermal fluidity) by impregnation of an organic impregnant decreases the brittleness of the wood caused by the high temperature heat treatment, thus to improve workability.
These three ideas are recited as follows:
First is to improve workability by preventing cracking by impregnation treatment with an organic agent, and by allowing the timber to be chemically modified.
Second is to detect an AE signal to predict cracking of the timber, etc., by the information processing thereof to carry out atmosphere control using, as a control factor, temperature and humidity on the basis of the predicted information, thus to prevent cracking.
Third is to carry out heat and drying treatment and high temperature heat treatment at normal pressure or high pressure while conducting atmosphere control to thereby improve the wood property characteristics and the functional characteristics.
By suitably combining these ideas, this invention contemplates providing a new worked vegetable material in which timber, etc., is efficiently subjected to a modifying treatment so that it has a high quality.
Inventions for which the patent is sought to be granted will now be described in detail.
The first invention for which the patent is sought to be granted resides in a method of first impregnating an organic impregnant, e.g., oxyether such as polyethylene glycol or methyl cellosolve, etc., polyatomic alcohol, phenol, natural rubber, synthetic rubber, or mixtures including them in combination, into various worked vegetable materials, etc., such as logs, worked timber, bamboo material (timber or any other wood product) to allow a hydrothermal chemical reaction (hydrolysis) to take place, thus to carry out the impregnating treatment.
Material which may be subjected to the treatment of this invention is not just timber, etc., but includes all worked vegetable materials such as logs, worked timber, bamboo material, etc. irrespective of the kind of vegetable.
Further, a specific organic impregnant to be impregnated may employ an oxyether such as polyethylene glycol, or methyl cellosolve, etc., polyatomic alcohol such as 1, 4 butanediol, etc., phenol, a natural rubber, synthetic rubber, or mixtures including them in combination.
Changes in the wood properties occurring by the impregnation treatment will now be described.
Chemically, timber is comprised of cellulose of 40 to 50%, hemicellulose of 15 to 25%, lignin of 20 to 30%, and other sub-ingredients. In addition, in cell walls constituting timber, bundles of aggregate of cellulose molecular chains dodge meshes existing in the form of sponge, and hemicellulose are filled into a gap therebetween. Combination of respective compositions is carried in a form as stated above. Further, bundles of aggregates of the cellulose molecular chains are regularly arranged to form crystals. Since these crystals are linear high molecular having a cubic arrangement of regularity and many hydroxyl groups, there is a state where regular hydrogen bonds of hydroxyl groups are apt to occur between adjacent molecules. In addition, 70-% of the entirety of cellulose is in such a state. Since such cellulose has a high melting point of crystal and is thermally dissolved before fluidity takes place even if heat treatment is applied, it does not eventually cause thermal fluidity. It is considered that such a property of timber, etc. allows a crack to be apt to occur by movement of moisture, contraction of tissue, and thermal decomposition of cellulose. However, if chemical modification to substitute acetyl groups (-COCH₃), nitrogen groups, benzyl groups, or lauryl groups, etc. for hydroxyl groups (-OH) of cellulose is caused to take place, internal plasticization takes place in the timber. Thus, thermal fluidity is rendered thereto. Namely, it is considered that if cellulose is changed to a derivative and the degree of hydrogen bonding is weakened, thermal fluidity is provided in the timber. It is further considered that if there is caused to exist a state where crystals of the cellulose are caused to have fluidity, cracking by contraction or by movement of moisture does not take place even if high temperature heat treatment is implemented to such cellulose.
As an actual method, it is imagined to utilize the method that the wood timber thermal fluidity state (thermal plasticity) results from hydrothermal chemical reaction. Namely, as a pre-treatment process, an approach is employed to impregnate a specific organic impregnant in the timber to place it in high temperature water at more than 100°C to allow hydrothermal chemical reaction (hydrolysis) to take place to dissolve a portion of the cellulose or lignin, etc., in the wood to partially cleave several chemical bonds, to change esters in the resin to alcohol, or to implement halogen substitution of lignin aromatic nuclear to provide lignin chloride, etc., thus to provide the state where the woody part has thermal fluidity (thermal plasticity). It is to be noted that it is needless to say that in the case of carrying out high temperature heat treatment at more than 100°C, this treatment is not necessarily required as a pre-processing (hydrothermal chemical reaction), but may be carried out later in a manner doubling as a high temperature heat treatment.
Then, the impregnation-treated timber, etc., after undergoing drying treatment is placed in an atmosphere of more than 90% incombustible gas, and an AE sensor is attached on the timber, etc.
Here, the term "incombustible gas" refers to inert or inactive gas such as argon, krypton or helium, etc., or mixed gas including one or two kinds of ammonium, sulfur dioxide, carbon dioxide and nitrogen.
Attachment of the AE sensor is carried out through a wave guide by taking temperature and humidity into consideration. The attachment position of the wave guide is the test specimen cross section.
Then, an AE that the timber, etc., produces in accordance with a change of the woody structure is detected as an electric signal to analyze its information to predict cracking of the timber, etc. The technology therefor will now be described.
For example, in the case of carrying out processing at a temperature (160 to 170°C) and a pressure (2.0 to 2.4 Kg/cm₂) of a high temperature heat treatment (example 1) as shown in Fig. 1, AE signals sent from the sensor are sorted into each amplitude class. Thus, AE event numbers for each class are represented as shown in Fig. 2. AE signals are amplified at a pre-amplifier and then subjected to a threshold comparison with a net value by a cracking monitor (more than 1V at 80 dB). By amplifying the signals thus processed, the number of AE events is detected. Recording of such AE event data is shown in Fig. 3, and recording of an accumulated AE energy is shown in Fig. 4.
This case shows an example of an experiment where because the moisture percentage prior to treatment is 10 to 12% and for other reasons, "crack" does not take place in a test specimen after experiment.
On the other hand, for example, in the case of carrying out treatment at a temperature (160 to 170°C) and a pressure (2.0 to 2.4 Kg/cm₂) of a high temperature heat treatment (example 2) as shown in Fig. 6, when AE signals sent from the sensor are sorted into each amplitude class, AE event numbers at each respective class are represented as shown in Fig. 7. These AE signals are amplified at the pre-amplifier to detect the number of AE events more than a set value at the cracking monitor. Recording of AE event data of more than 1V is shown in Fig. 8, and recording of an accumulated AE energy thereof is shown in Fig. 9. In this case, because the initial moisture percentage is 28 to 33% and for other reasons, a "crack" takes place at the central portion of a test specimen after experiment as shown in Figs. 10(a) and (b).
By the AE signal data of the experiment example 1 (no crack example) and the experiment example 2 (crack example), it is possible to clearly specify the time point when the timber, etc., is cracked during treatment and the condition at that time. When an approach is employed to collect a large number of such test data to analyze them, it becomes possible to predict a crack from AE data. Namely, even if attention is drawn to the entire AE signals, it is impossible to clearly recognize a crack because there are many noise signals. However, when AE signals having an amplitude more than an empirically determined fixed value (AE signals more than 1V at 80 dB in the case of the experiment example) are recorded, everybody can clearly recognize relative relationship with cracking (Fig. 8). In view of this, attention is drawn to AE signals of more than a specific amplitude to consider occurrence of this signal as a "crack warning". Then, the rate of occurrences (Fig. 8, Fig. 11∧) of a specific amplitude (more than 1V in this experiment example) are plotted, and accumulated AE event numbers are plotted (Fig. 9, Fig. 11□). When such events thus plotted are collected to carry out statistical processing by using conditions such as the kind of wood, initial moisture percentage, heat temperature, or plate thickness, etc. as a parameter, it is made clear that AE signals above a fixed amplitude under a predetermined condition indicate a crack warning limit value (Fig. 8, Fig. 11∧). Further, it is possible to know that there is no cracking when that pattern of the accumulated AE energies is selected, thus to specify a crack warning limit model pattern. In view of this, an approach is employed to compare the model pattern of the specified standard warning limit AE occurrence rate and the crack warning limit accumulated AE event numbers with AE occurrence circumstances actually measured and recorded to analyze the meaning of AE signals at that time point, thus to carry out predictive judgement of cracking of timber, etc.
Then, this invention is directed to a method of treatment for modifying timber, etc., which is adapted to apply temperature so that its gradient is not steep while controlling the atmosphere so that no cracking occurs in the timber, etc., by using temperature and humidity as a control factor on the basis of the above predicted information, thus to carry out a predetermined high temperature heat treatment.
Namely, in the case where predictive judgement of cracking is carried out from the AE data as described above, an approach is employed to inject a large quantity of vapour for a short time, or to stop the operation of the heating unit to lower temperature. By carrying out this approach, an atmosphere in which no cracking occurs in the wood, etc., is provided. As a result, generation of AE is stopped, or AE is generated at a level less than the crack warning standard level empirically determined. Namely, by using temperature and humidity as a control factor, it is possible to carry out the atmosphere control by using temperature and humidity as a control factor. The relationship of temperature, the humidity and the AE generation is shown in model form in Fig. 12.
Further, it is empirically recognized that the main cause of crack occurrence in high temperature heat treatment is not movement of moisture, but contraction or expansion through a sudden temperature change. Accordingly, while gently setting the temperature gradient when temperature is applied or lowered where a crack occurs meets with this purpose, since the limit value of the temperature gradient where a crack occurs varies depending upon the initial moisture percentage, the kind of wood, the plate thickness, and the device, etc., it is required to measure AE in advance under a predetermined condition to set, at all times, the accumulated AE energy increasing rate to less than a limit value (warning limit standard).
The change in the wood property by the high temperature heat treatment will now be described.
In the processing for applying high temperature heat treatment to timber, etc., in this invention, the strength is enhanced or increased with respect to impact, compression or bending by increasing lignin, and the tensile strength is weakened or decreased by reducing cellulose. However, since the crystals of cellulose have a high melting temperature, and are subjected to thermal decomposition before being placed in a thermal fluid state, no thermal fluid state is eventually provided (Fig. 13). Namely, this treatment is featured below. By making use of a property such that the timber does not produce a thermal fluid state, high temperature heat treatment is further carried out under incombustible conditions, i.e., in an atmosphere of incombustible gas to completely remove moisture while retaining tissue of a regular cubic arrangement as it is, and to harden or cure the entirety by thermal denaturation of protein or other ingredients. The wood property is cured or hardened by this treatment, resulting in excellent weather resistance or water proofing. On the other hand, the wood becomes brittle, disadvantageously lowering workability.
In this instance, in this invention, acetyl groups or nitro groups, etc., are substituted for hydroxyl groups of cellulose to change the cellulose to a derivative to weaken the degree of hydrogen bonding, thus allowing the woody part to have thermal fluidity (thermal plasticity). This invention relaxes curing of wood property by this treatment to decrease brittleness, and to recall tenacity or toughness intrinsic to wood thus to improve workability such as cutting property, etc.
In the second invention for which the patent is sought to be granted, an approach is employed to impregnate an organic impregnant, e.g., an oxyethyl such as polyethylene glycol or methyl cellosolve, etc., polyatomic alcohol, phenol, natural rubber, synthetic rubber, or mixtures including them in combination into various worked vegetable materials such as logs, worked timber, or bamboo material, etc., to implement impregnating treatment to cause hydrothermal chemical reaction (hydrolysis). This pre-processing is the same as that of the invention of claim 1.
Then, an AE sensor is attached to the impregnation treated timber, etc. to detect, as a signal, an AE that the timber, etc., produces in accordance with a change of the woody structure to carry out information processing of that signal to detect a crack of the timber, etc., to conduct a heat treatment at a temperature less than 80°C at a normal pressure while carrying out an atmosphere control so that no cracking takes place in the timber, etc., on the basis of the predicted information, thus to implement a drying treatment.
As stated above, also in the drying treatment process, by observing AE signals, it has become possible to always grasp the development circumstances in the course of drying of timber, etc.
Namely, signals sent from the sensor attached to the wood, etc., are amplified at a pre-amplifier, and signals below a set level are cut out at a cracking monitor After such signals are amplified, the number of AE events of a specific amplitude is detected. The AE event data of the specific amplitude is recorded (Fig. 14). When this is illustrated as an accumulated energy, Fig. 15 is produced. The procedure until now is the same as that in the case of AE in the high temperature heat treatment. When a large number of such events are collected to carry out a statistical processing, a standard AE pattern in a timber dry treatment process as shown in Fig. 16 can be provided.
In order to predict a crack of timber, etc., from the standard AE pattern in the drying treatment, the following rules of experience can be obtained:

1. In the case where an AE signal above a fixed amplitude empirically determined appears, this is considered as a precursor or warning of a crack.
2. The drying process is comprised of three stages. It is important to vary the criterion at every stage.

It is considered that the first stage (I) is the stage where vapour is infiltrated or penetrated into the central portion of timber, etc., and the temperature and the moisture percentage become uniform, whereby drying is gradually developed. The moisture percentage at the time when the first and second stages are divided is 25%, and corresponds to a fibre (tissue) saturation point (about 30 to 25%). At a point above the fibre saturation point, moisture in a liquid state exists in timber. At this stage, since cracks occur easily, attention must be sufficiently drawn.
Further, it is considered that the second stage (II) is the stage where moisture absorbed in the form of combined water into the tissue cuts the bond, and begins vaporization. Accordingly, the energy required for reducing the moisture percentage becomes larger than that at the first stage. It is considered that the tensile strength of the wood suddenly increases at this stage, thus to have the ability to tolerate a drying condition more severe than that at the first stage. Accordingly, a drying condition more severe than that at the first stage can be applied. Namely, at the second stage, it is possible to apply a drying condition more severe than that of this experiment. Thus, the drying time can be shortened. The boundary between the second and third stages corresponds to about 15% of the moisture percentage. The state of the moisture percentage of about 15% is considered to an equilibrium moisture percentage, and corresponds to the air dry state.
Since there are many AE of a small amplitude at the third stage, it is considered that the phenomenon that crystal water inside the cell is away from the cell takes place. However, since this AE of small amplitude is not completely related to cracking by drying, it is sufficient to set the drying condition irrespective of the number of AE events. Accordingly, a drying condition setting further more severe conditions than that at the second stage can be made at the third stage. By this experiment, the drying time can be shortened.
In this way, when the dry state is developed and the moisture percentage becomes equal to a value less than 10%, the number of AE of small amplitude is also decreased. Once there results such a state, the heat condition is caused to become much more severe to shift to a high temperature heating state.
Accordingly, the method of predicting a "crack" in the drying process comprises: discriminating at which drying stage a present stage is at while monitoring the AE occurrence rate and the number of accumulated events on line, comparing the discriminated state value with the standard AE occurrence circumstances empirically determined (AE occurrence rate and AE accumulated event number), and the crack warning reference value, thus to carry out predictive judgement of a crack in the process of treatment.
Then, an approach is employed to control the temperature condition and the humidity condition by using, as a reference, an optimum control pattern at that stage empirically determined on the basis of the crack predicted information to effect a control to relax the atmospheric condition so that no cracking takes place, or to allow the temperature condition and the humidity condition to be severe so that there is no loss in the treatment efficiency. In this way, cracking is predicted by analysis of AE signals to carry out drying treatment while conducting the atmospheric control by using the temperature and the humidity as a control factor to dry the wood so that the moisture percentage of the timber, etc., becomes equal to a value less than 10%. In the high temperature heat treatment of the next process step, since material is difficult to be cracked according as the degree of drying becomes large, and the material is not cracked even if the gradient of temperature elevation is relatively steep, it is desirable to dry the wood, etc., until the moisture percentage thereof becomes equal to a value less than 10% thereafter to carry out high temperature heat treatment.
Subsequently, the impregnation-treated dried timber, etc., is placed in an atmosphere of more than 90% incombustible gas to carry out high temperature heat treatment at more than 100°C. When timber, etc., is placed in such a high temperature state, since it would become carbonized, it is preferable to place it in an incombustible gas atmosphere.
Also in this instance, an approach is employed to attach an AE sensor to the timber to detect, as a signal, AE that the timber, etc., produces in accordance with changes in the woody structure to carry out information processing of that signal to predict cracking of the timber, etc., to carry out high temperature heat treatment at more than 100°C under high pressure or normal pressure while conducting the atmosphere control so that no cracking takes place, by using temperature and humidity as a control factor on the basis of the predicted information. The second invention is directed to a method of treatment for modifying wood, etc., in which the above-mentioned approach is adopted. The method of predicting cracking in timber, etc., in this high temperature heat treatment is the same as that of the invention of claim 1. Namely, since occurrence of AE signals having an amplitude more than a predetermined width and a limit value of the temperature gradient where a crack occurs vary depending upon the initial moisture percentage, the kind of wood, the plate thickness, and the device, etc., it is preferable to measure in advance AE under a predetermined condition to specify a limit of crack as a warning limit reference value from the AE occurrence rate and the accumulated AE energy increase rate to compare it with AE occurrence circumstances actually measured to complete the high temperature heat treatment while maintaining it at a value less than a limit value at all times.
Namely, the invention of this application is directed to a method of first carrying out impregnating treatment, to predict cracking of the timber, etc., on the basis of AE signals to dry the timber while controlling the atmosphere so that no crack takes place by using temperature and humidity as a control factor on the basis of predicted information, to subsequently carry out the high temperature heat treatment in consistency.
It is to be noted that Fig. 17 shows, in model form, a standard AE occurrence pattern of the modifying treatment of timber, etc., for carrying out in consistency such dry treatment and high temperature heat treatment.
The third invention to which the patent is sought to be granted is directed to a method of treatment for modifying timber characterized in that "the method of detecting an AE as a signal to carry out information processing of that signal to predict a crack of timber, etc., to control the atmosphere so that no crack takes place in the timber, etc., by using temperature and humidity as a control factor", which is described in the above-mentioned first and second invention is modified as follows. Namely, in the third invention, an approach is employed to detect an AE as a signal to discriminate amplitude of those signals from the total count number of AE to recognize AE signals having an amplitude greater than a predetermined value as a dangerous signal for crack to further carry out monitoring of the number of accumulated AE events and AE occurrence rate to discriminate if the present stage is an initial, medium or later stage, or whether or not the present stage is at a high temperature heat treatment stage to predict a crack while comparing it with a reference value at the discriminated treatment stage to control temperature and humidity on the basis of predicted information to carry out control of the atmosphere so that no crack occurs in the timber, etc. A model pattern of heat temperature/moisture percentage, an accumulated AE energy in that instance, and AE occurrence rate standardized at the time of high temperature heat treatment is as shown in Fig. 11. Further, a model pattern of temperature/moisture rate, an accumulated AE energy in that case, and AE occurrence rate standardized at the time of timber drying treatment is as shown in Fig. 16. In addition, a model pattern of temperature/moisture percentage, an accumulated AE energy in that instance, and an AE occurrence rate in the case of carrying out in consistency dry treatment and high temperature heat treatment is as shown in Fig. 17. Since the way or method of recognizing a dangerous signal by an amplitude from measured AE signals, the way of discriminating between treatment stages, the way of predicting a crack, and the way of controlling the atmosphere were already described in detail in the first and second inventions, their explanation is omitted here.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a graph in which temperature and pressure of the high temperature heat treatment (example 1) are recorded, Fig. 2 is a graph in which AE event number (occurrence rate) for each amplitude class of the high temperature heat treatment (example 1) is recorded, Fig. 3 is a graph in which AE occurrence rate of an amplitude of more than 1V of the high temperature heat treatment (example 1), Fig. 4 is a graph in which an accumulated AE energy of an amplitude more than 1V of the high temperature heat treatment (example 1) is recorded, Fig. 5(a) is an explanatory view showing the state of a test specimen after experiment of the high temperature heat treatment (example 1), and Fig. 5(b) is a cross-sectional view showing the essential part thereof.
Fig. 6 is a graph in which temperature and pressure of the high temperature heat treatment (example 2) are recorded, Fig. 7 is a graph in which AE event number (occurrence rate) for each amplitude class of the high temperature heat treatment (example 2) is recorded, Fig. 8 is a graph in which AE occurrence rate of an amplitude of more than 1V of the high temperature heat treatment (example 2) is recorded, Fig. 9 is a graph in which an accumulated AE energy of an amplitude more than 1V of the high temperature heat treatment (example 2) is recorded, Fig. 10(a) is an explanatory view showing the state of a test specimen after experiment of the high temperature heat treatment (example 2), and Fig. 10(b) is a cross sectional view showing the essential part thereof.
Fig. 11 is an AE occurrence model pattern at the time of high temperature heat treatment, Fig. 12 is a model view showing temperature/humidity control and AE occurrence, and Fig. 13 is a graph showing changes in the wood property at the time of high temperature heat treatment.
Fig. 14 is a graph in which temperature and AE occurrence rate of an amplitude of more than 1V of the drying treatment (example 3) is recorded, Fig. 15 is a graph in which accumulated AE energy of an amplitude of more than 1V of the drying treatment (example 3) is recorded, Fig. 16 shows an AE occurrence model pattern at the time of high temperature heat treatment, Fig. 17 shows an AE occurrence model pattern at the time of drying/high temperature heat treatment, Fig. 18 is a graph in which a temperature change of the high temperature heat treatment in the embodiment 1 is recorded, Fig. 19 is a graph in which AE event number (occurrence rate) for each respective amplitude class of an unprocessed material is recorded. Fig. 20 is a graph in which AE event number (occurrence rate) for each respective amplitude class of the impregnation treated material of the embodiment 1 is recorded, Fig. 21 is a graph in which AE occurrence rate of an amplitude of more than 1V of the unprocessed or non-worked material of the embodiment 1 is recorded, Fig. 22 is a graph in which AE occurrence rate of an amplitude of more than 1V of the impregnation treated material of the embodiment 1 is recorded, Fig. 23 is a graph in which an accumulated AE energy of an amplitude of more than 1V of the unprocessed or non-worked material of the embodiment 1 is recorded, Fig. 24 is a graph in which accumulated AE energy of an amplitude of more than 1V of the impregnation treated material of the embodiment 1 is recorded, Fig. 25 is a graph showing an AE occurrence model pattern and a crack limit control reference by the accumulated AE at the time of high temperature heat treatment of the embodiment 1, Figs. 26(a) and (b) are explanatory views showing the state of a test specimen before and after the high temperature heat treatment according to the embodiment, and Figs. 27(a) and (b) are explanatory views showing a cutting test state of a test timber subjected to temperature heat treatment according to the embodiment 1.

Best Mode for Carrying Out the Invention

Explanation will now be given on the basis of an embodiment for explaining this invention in more detail.

Embodiment 1

A naturally dried (moisture percentage 30%) natural raw timber log material (length of 200 mm x diameter of 80 ) of a maple tree is prepared. This log material is first decompressed at room temperature to carry out deaeration of the timber thereafter to pressure-inject polyethylene glycol at 3 to 5 atm by a pressure pump. Then, the impregnated timber is inserted into high temperature water at more than 100°C to cause hydrothermal chemical reaction. It is to be noted in the case of carrying out high temperature heat treatment at more than 100°C that this treatment is not necessarily required as the pre-processing (hydrothermal chemical reaction), it is a matter of course to carry it out in a manner doubling as a subsequent high temperature heat treatment. The log material pre-treated in this way and the same log material which has not been pre-treated are admitted into a thermal treatment chamber, and an AE sensor is attached to the materials through a wave guide. In actual terms, the thermal treatment chamber internal side terminal of the wave guide is fixed to a section of the test timber by means of wood screws. The wave guide is extended to the outside passing through a measurement hole provided in the thermal treatment chamber. The AE sensor is attached to the externally extended portion of the wave guide, and is connected to a pre-amplifier, a cracking monitor, and a personal computer installed in the vicinity therewith. Then, air is deaerated from the thermal treatment chamber, and nitrogen gas is injected or introduced from an incombustible gas injection unit to provide an atmosphere of 97% incombustible gas. After such a state is provided, a thermocouple is caused to be operative to increase the temperature within the heat treatment chamber, and to inject vapour from a vapour insertion unit, thus to adjust humidity inside the chamber. As shown in Fig. 18, the temperature is raised up to 150°C at a stroke to carry out high temperature heat treatment of about 150 to 160°C for 22 hours thereafter to lower the temperature to a normal temperature in about two hours, thus to complete the treatment in about 24 hours. Occurrence circumstances of AE for that time period was observed. Fig. 19 shows AE event circumstances for each respective amplitude class of the untreated material in that instance. On the other hand, Fig. 20 is a record indicating AE event occurrence circumstances for each respective amplitude class of the impregnation treated material. In both cases, since there are a great quantity of AE signals which are not related to cracking, it is impossible to specify at which time point cracks occur. In view of this, when an approach is used to specify AE having an amplitude of more than 1V with the amplification factor being at 80 dB within one minute intervals to make a record, AE event occurrence circumstances of the untreated material are as shown in Fig. 21, and AE event occurrence circumstances of the impregnation treated material are as shown in Fig. 22. Thus, it has been possible to considerably clearly recognize AE signals related to crack. When one reads these graphs, the untreated material and the impregnation treated material both have the following tendency. Namely, at the initial stage where temperature within the heat treatment chamber rises, a great quantity of AE are produced. At the intermediate state, there is hardly any occurrence of AE. When the temperature begins to lower, AE events take place for a second time. However, the occurrence circumstances of the untreated material and those of the impregnation treated material are extremely different from each other. In the case of the impregnation treated material, there results the circumstances where AE hardly takes place. Namely, this clearly teaches that a crack takes place at the initial stage of heat treatment in the case of the untreated material, whereas no crack takes place in the case of the impregnation treated material. When comparison between Fig. 23 (untreated material) and Fig. 24 (impregnation treated material) indicating an accumulated AE energy is made, the above teaching is more clearly recognized.
In view of this, in the case of implementing high temperature treatment to timber easy to crack as in the case of the untreated material, it is required to predict a crack to control the atmosphere. Its control model is as shown in Fig. 25. Namely, an approach is employed to detect AE as an electric signal to carry out to record and/or analyze that data by means of the personal computer to compare the result thus analyzed with a reference value empirically set in advance, thus to predict a crack in the timber, etc. More particularly, an approach was adopted to record AEs having an amplitude of more than 1V, with the amplification factor being set to 80 dB, within one minute to judge the present circumstances to fall within a crack warning zone when the accumulated event number is above a reference value, or when the amplitude is above a reference to allow the vapour injection unit to be operative to inject a large quantity of vapour into the heat treatment chamber in a short time to adjust humidity in the heat treatment chamber, and to control the operation of the heating unit to adjust temperature within the heat treatment chamber to control the atmosphere so as to maintain the state where no AE takes place from the timber, etc., the occurrence state where the AE signal is below a predetermined reference to allow the heating unit to be operative while carrying out such a control of atmosphere to gradually raise the temperature within the heat treatment chamber, thus to carry out a high temperature heat treatment for four hours at 160 to 180°C so that no cracking takes place in the timber, etc.
As a result, in the case of the impregnation treated material, a satisfactory modifying treatment implemented product in the form of lignite or fossil wood was made up. Reference photograph 3 shows this. In the case of the modifying treatment implemented timber subjected to impregnation high temperature heat treatment, cracking does not take place. On the other hand, in the case of modifying treatment implemented timber which is not subjected to high temperature heat treatment, a large number of radial cracks were confirmed.

Then, a comparative study on cutting property in the wood section of the timber subjected to modifying treatment in the form of lignite or fossil wood was conducted. A1, A2 and B1, B2 of reference photographs 4 show the compared results. In connection with the impregnation/high temperature heat treatment implemented timber and the high temperature heat treated timber which is not subjected to impregnation treatment, a cup byte of a lathe is used to carry out cutting of the wood section at 1580 rpm. As a result, in the case of the formed impregnated/high temperature heat treated timber, cutting quality of an edge tool is improved, and chips are successive in a belt shape (A1 of reference photograph 4). The cutting surface is smooth. Thus, tenacity, workability and strength intrinsic to timber are recalled. On the other hand, in the latter non-impregnated high temperature heat treated timber, the chips are in the form of powder (B1 of reference photograph 4), and the cutting surface is rough (B2 of reference photograph 4). As stated above, in the case of the impregnation/high temperature heat treatment implemented timber, brittleness which was the drawback in the prior art can be reduced to a great degree, and chisel/planer working, wood lathe working, general wood machine planing, wood screw/nail fastening work can be sufficiently implemented thereto. Accordingly, such impregnated/high temperature heat treated timber can be used not only for artistic handicrafts but also furniture stuff, building or construction materials, roofing materials, or marine boards, etc.

TABLE 1

MATERIAL, USE OF HIGH TEMPERATURE HEAT TREATED TIMBER
	USE, PROPERTY	A	B	C
USE	ARTISTIC HANDICRAFTS	⃝	⃝	△
	FURNITURE MATERIALS	⃝	△	⃝
	BUILDING MATERIALS	⃝	X	⃝
	MARINE BOARD MATERIALS	⃝	X	X
FUNCTIONAL CHARACTERISTICS	COLOURING PROPERTY	⃝	X	X
	DIMENSIONAL STABILITY	⃝	⃝	X
	ROT PROPERTY	⃝	⃝	X
	WATER REPELLENT PROPERTY	⃝	⃝	X
MATERIAL CHARACTERISTICS	STRENGTH - TENACITY	⃝	X	⃝
	WORKABILITY (PLANER, SAW)	⃝	X	⃝
	FASTENING CHARACTERISTIC (NAIL, SCREW)	⃝	X	⃝
* A; IMPREGNATED, HIGH TEMPERATURE HEAT TREATED TIMBER B; NON-IMPREGNATED, HIGH TEMPERATURE HEAT TREATED TIMBER C; NATURAL TIMBER ⃝; GOOD △; RELATIVELY GOOD X; NO GOOD

Industrial Applicability

The first invention of this application resides in a method of treatment to modify timber, etc., of impregnating a specific impregnant into timber, etc., to allow an hydrothermal chemical reaction (hydrolysis) to take place, to apply high temperature heat treatment to the timber, etc., in the atmosphere of an incombustible gas, wherein an approach is employed to detect acoustic emissions that the timber, etc., produces in accordance with a change of the timber structure in the high temperature heat treatment to detect cracking of the timber, etc., thus to carry out high temperature heat treatment while controlling the atmosphere so that no cracking occurs in the timber, etc., by using temperature and humidity as a control factor. By impregnation of the organic impregnant, thermal plasticity is rendered to wood property. By the high temperature heat treatment in an atmosphere of incombustible gas, the property of the lignite or fossil wood is rendered thereto. In addition, during treatment, an atmosphere control using AE as a signal, and using temperature and humidity as a control factor is carried out. Accordingly, when the above effects are combined, cracking during treatment becomes null, so the timber, etc., is caused to have a particularly woody property. Thus, the workability is improved to a great extent, and the range of use becomes broader than that in the prior art.
The second invention of this application resides in a method of impregnating a specific organic impregnant into the timber, etc., to allow hydrothermal chemical reaction (hydrolysis), thereafter to carry out a heat drying process. During this drying treatment, an approach is employed to detect AE as a signal to predict cracking of the timber, etc., to carry out atmosphere control by using temperature and humidity as a control factor. Accordingly, there is hardly any cracking during treatment. When the degree of drying is developed to a level less than 10% in this way, the impregnated timber, etc. is subjected to high temperature heat treatment in the atmosphere of an incombustible gas to render it the property of lignite or fossil wood. Also in this instance, during treatment, an approach is employed to detect AE as a signal to predict cracking of the timber, etc., to carry out atmosphere control by using temperature and humidity as a control factor. By adopting such an approach, even in the case of the treatment from green timber having a high moisture percentage, it is possible to carry out in consistency drying treatment and high temperature heat treatment in the state where there is hardly any cracking during treatment. As a result, it has become possible to prevent lowering of yield in the conventional high temperature heat treatment, and to improve the quality of high temperature heat treated timber.
The third invention of this application resides in a method based on the methods of the first and second invention wherein an approach is employed to detect AE as a signal to analyze it to predict cracking to carry out high temperature heat treatment while preventing cracking by conducting the atmosphere control. Particularly, this third invention is characterized in that an approach is employed to have the ability of predicting in advance cracking of timber by analysis of AE. By adopting this approach, it has become possible to industrially and efficiently mass-produce timber, etc. having good yield and free from cracks.

Claims

A method of treatment for modifying the characteristics of timber and other wood products, which comprises the steps of:
impregnating an organic impregnant, e.g. an oxyether such as polyethylene glycol or methyl cellosolve, etc., polyatomic alcohol, phenol, natural rubber, synthetic rubber, or mixtures including them in combination, into various worked vegetable materials, etc., such as a log, worked timber, or bamboo material (hereinafter referred to as "timber or any other wood product") to allow a hydrothermal chemical reaction (hydrolysis) to take place, thus to carry out an impregnating treatment, and
placing the impregnated timber or any other wood product in an atmosphere of more than 90% of an incombustible gas to attach an acoustic emission sensor (hereinafter referred to as an "AE sensor") to the timber or any other wood product to detect, as a signal, an acoustic emission (hereinafter referred to as an "AE") that the timber or any other wood product produces in accordance with a change of the timber structure, to carry out information processing of that signal to predict cracking of the timber or any other wood product, thus to carry out high temperature heat treatment at more than 100°C under high or normal pressure whilst conducting atmosphere control so that no cracking takes place in the timber or any other wood product, by using temperature and humidity as a control factor on the basis of the predicted information.
A method of treatment for modifying the characteristics of timber and other wood products, which comprises the steps of:
impregnating an organic impregnant, e.g. an oxyether such as polyethylene glycol or methyl cellosolve, etc., polyatomic alcohol, phenol, natural rubber, synthetic rubber, or mixtures including them in combination, into the timber or any other wood products,
attaching an AE sensor to the impregnated timber or any other wood products to detect, as a signal, AE that the timber or any other wood product produces in accordance with a change in the timber structure, to carry out information processing of that signal to predict cracking of the timber or any other wood product to carry out heat treatment at less than 80°C whilst conducting an atmosphere control so that no cracking takes place in the timber or any other wood product, by using temperature and humidity as a control parameter on the basis of the predicted information to implement drying treatment, and
subsequently placing the impregnated dried timber or any other wood product in an atmosphere of incombustible gas to attach an AE sensor to the timber or any other wood product to detect, as a signal, an AE that the timber or any other wood product produces in accordance with a change of the timber structure, to carry out information processing of that signal to predict cracking of the timber or any other wood product, thus to carry out high temperature heat treatment at more than 100°C under high or normal pressure while conducting an atmosphere control so that no cracking takes place in the timber or any other wood product, by using temperature and humidity as a control factor on the basis of the predicted information.
A method of treatment for modifying the characteristics of timber and other wood products wherein the method of detecting an AE as a signal to carry out information processing of that signal to predict cracking of the timber or any other wood product to carry out an atmosphere control so that no cracking occurs in the timber or any other wood product, by using temperature and humidity as a control factor claimed in claim 1 or 2, is implemented by detecting AE signals to discriminate amplitudes of those signals to consider an AE signal having an amplitude more than a predetermined value as a dangerous signal for cracking, to carry out monitoring of the number of accumulated events of AE and the rate of occurrences of AE on line to discriminate between a drying stage and a high temperature heating stage to predict cracking while comparing current or present values with reference values at the respective discriminated stages to effect a control by using temperature and humidity as a control factor on the basis of the predicted information, thus to carry out an atmosphere control so that no cracking occurs in the timber or any other wood product.