Wood treating method

Abstract: There are available as chlorine base organic solvents for cleaning by vapor-defatting methylene chloride (CH₂Cl₂), trichloro ethylene (CHCl=CCl₂), perchloroethylene (CCl₂=CCl₂), 1,1,1-trichloroethane (CH₃CCl₃) and flon 113 (CCl₂FCClF₂), etc., of which mainly used is a methylene chloride (CH₂Cl₂) solvent. By vaporizing said methylene chloride solvent and permeating its vapor into the wood to be treated 10, to melt the tough lignin in the cell structure, thereby perforating the cell membranes, and undermine the valve action of portholes of the false vessels or vessels, fleeing of the cell water confined inside the cells and lumens is facilitated through said perforations and the porthole valves. By perforating the cells and undermining the valve action of the portholes, the fleeing of the free water confined therein, when drying the treated wood by hot air or sun's heat, is facilitated, for the benefit of very rapid drying. Besides, easy penetration of fine dye grains into the wood through said perforations and portholes enables its coloration to deep layers of wood.

Description: Field of the Invention: The present invention relates to a method for defatting, coloring and drying wood. By the conventional method for treating wood by defatting, drying and coloring and so forth, such parts of wood as cellulose, hemicellulose and lignin, which compose its cell membranes, can hardly be melted out in any way. If excess water in wood were tried to be abruptly evaporated in a short time, the shape of wood would be notably altered, so that it became unsuitable to be processed into the designated wood products. Therefore, it was only possible to perform this treatment by drying wood, taking such a long time as about one year and with care not to alter the shape of wood. Enormous energy and time are expended for the work of drying wood, so that the quantity of treatable products is naturally limited. Such and other many problems have arisen. Lignin itself is a material which was difficult to decompose or dissolve, its composition being not chemically clarified. When coloring wood, the dye permeates only to its thin surface layer. Thus whether wood is dried by the sun's heat or artificially, reducing the water content of wood to the saturation point of fibers can relatively easily be done by removing free water which is not confined in cells, but the free water confined in the cell membranes, which are tightly closed by lignin being a chemical component with high molecular phenols as its basic component material, can hardly be removed. As a tree has been felled, the pore holes of the false vessels and vessels of wood close, as if acting as valves, whereby the free water is confined within them. If the surface is abruptly dried, while drying wood, the aforementioned pore holes of the false vessels and vessels close, acting as valves, whereby movement of free water content in lumens is stopped, bringing about a state in which the moisture remaining in the lumens does not evaporate, however high the temperature is raised thereafter, a surface hardened state. As above-described, the wood, after the parent tree has been felled, performs the act of confining water content in its cells and lumens by means of lignin. Accordingly, its water content can hardly be evaporated by drying by sun's heat or hot air, thus requiring long time for its drying. Heretofore, the techniques for subjecting wood to special treatments for improvements in putrefaction resistance, durability and design-ability, while maintaining the proper properties of wood, are believed to be well known. They include such techniques as appear in Japanese Patent Laid-Open Nos. Sho 49-116204, 51-136803 and 61-37402 and Japanese Patent Publication No. Hei 1-38641. A method for drying wood veneer with jets of a pure superheated chlorinated aliphatic hydrocarbon solvent which is heated to at least 100°C is described in US-A-4 106 209. This process is perfomed in a housing through which the veneer is continuously moved on an endless belt. A wood drying process wherein wood is subjected to a saturated atmosphere of an inert organic vapour like a halide at a high temperature and under a low pressure is disclosed in US-A-2 273 039 and US-A-2 435 219 as a CIP application of this patent discloses a similar wood drying process, wherein the wood is subjected to a highly heated vapor composition at a temperature in the range of 118° to 250°C and containing not less than 65% by weight of the organic vapour like the halide and not more than 35% by weight of water vapour. This water content, however, is not created by mixing water and solvent and heating the mixture for vaporization, but is rather acchieved in that only a smaller portion of the vapor containing the water evaporated from the wood is handled and reclaimed during the drying operation. Summary of the Invention: The problem the present invention is to solve is as above-described. According to the present invention there is provided a wood treating method, comprising the following steps: providing a mixture of methylene chloride solvent and water, said water accounting for approximately 90% of said mixture; heating said mixture at 100°C to 140°C, preferably 100°C to 130°C, so that vapors of said methylene chloride solvent and said water are simultaneously generated; confining wood to be treated and said vapors of said mixture in a pressure container which is hermetically sealed; permeating said vapors of said mixture into cells of said wood; and melting oil and fat contents in cell membranes of said cells by said vapors thereby creating perforations in said cell membranes. Preferred embodiments of this method are defined in the sub-claims. By creating the perforations in the cell membranes fleeing to outside of the free water confined within through said perforations of the cells and the pore hole valve parts is facilitated. The perforations of the cells and the collapse of the valve action of the pore holes permit fine molecules of a dye to easily penetrate into the cell membranes, thereby enabling easy coloration deep into the interior of wood. In a preferred embodiment of the wood treating method the wood is repeatedly subjected to compression by heating and decompression by cooling, thereby promoting the melting of the oil and fat components of the wood in the wood treating process. The wood treating method further comprises drying the treated wood. The wood treating method still further comprises coloring wood by permeating a fine grained dye thereinto. Brief Description of the Drawings: FIG. 1 is a front sectional view of a treating apparatus for use in exercising the wood treating method of this invention; FIG. 2 is a plan view of the treating apparatus with its top cover removed for use in exercising the wood treating method of this invention; FIG. 3 is a schematic sectional view of the treating apparatus far use in exercising the wood treating method of this invention, showing its preparation for the treating work by use thereof; FIG. 4 is a schematic sectional view of the treating apparatus for use in exercising the wood treating method of this invention, showing the treating work by use thereof; FIG. 5 is a schematic sectional view of the treating apparatus for use in exercising the wood treating method of this invention, showing the treating work by use thereof; and FIG. 6 is a schematic sectional view of the treating apparatus for use in exercising the wood treating method of this invention after accomplishment of the treating work by use thereof. Description of a Preferred Embodiment: In reference to FIGS. 1 and 2, the composition of the treating apparatus for use in exercising the treating method of this invention is described. A wood treating pressure container A is made of stainless steel and is composed of a cylindrical body 1 and a dome shaped top cover 2 placed thereon, said done shaped top cover 2 being mounted on the body 1 by screwing a plurality of closing bolts 3 into a plurality of bolt holes 1e, 1e, ... of a flange 1d located at the top of the body 1, and further the inside of the body 1 being composed of 3 compartments of a solvent tank 1a, a treating chamber 1b and a cooling chamber 1c. In the following a wood treating process employing methylene chloride solvent at a low temperature of 40°C is described. Although this process is not covered by the present invention it serves to explain certain principles and effects of the process of the present invention, which different from this explanatory process employs a mixture of methylene chloride solvent and water, said water accounting for approximately 90% of the mixture, and in which the mixture is heated at 100°C to 140°C. The aforementioned solvent tank 1a is, as shown in FIGS. 1 and 2, arranged under a floor of the body 1 and is fully filled with a methylene chloride solvent B, being a chlorine base organic solvent for cleaning by vapor-defatting. As other organic solvents than methylene chloride (CH 2 Cl 2 ) for cleaning by vapor-defatting, there are available trichloroethylene (CHCl=CCl 2 ), perchloroethylene (CCl 2 =CCl 2 ), 1,1,1-trichloroethane (CH 3 CCl 3 ) and flon 113 (CCl 2 FCClF 2 ). In this embodiment, the methylene chloride (CH 2 Cl 2 ) solvent B is used. A heat supply pipe 4 for heating said methylene chloride solvent B to boil is arranged from outside the tank for uniformly warming the whole of the tank interior. Besides, there are respectively connected to the solvent tank 1a a solvent return pipe 6 for returning into the solvent tank 1a the methylene chloride solvent B, which has been recovered by distillation at the cooling chamber 1c and then refined in a water separator 5, and a solvent drain pipe 8 for draining the methylene chloride solvent B out of the solvent tank 1a after accomplishment of the first half of the treating operation, to store it in a solvent storage tank 7. The aforementioned solvent tank 1a and the treating chamber 1b are partitioned by a drain-board floor 9. Inside said treating chamber 1b, the vapor of the methylene chloride solvent B which has been heated to boil at such a low temperature as about 40°C in the solvent tank 1a is accumulated, forming a solvent vapor layer C of methylene chloride. During the treating operation, a highly ventilative wood transport container 11 holding wood blocks 10 to be treated is mounted on the drainboard floor 9 of the treating chamber 1b. The methylene chloride (CH 2 Cl 2 ) solvent B, which boils at about 40°C, may be readily vaporized and this vapor has the effect of defatting the oil and fat components of wood. The cooling chamber 1c provided in such a way as to form a border D between air/vapor over the aforementioned treating chamber 1b is designed to recover by distillation the excess solvent vapor which has come up from the treating chamber 1b. It is so composed that with the temperature of said cooling chamber 1c always preset not higher than 40°C, the B.P. of the methylene chloride solvent B, by means of cooling water 12, the vapor of the methylene chloride (CH 2 Cl 2 ) solvent B coming up from the treating chamber 1b condenses there, accumulates in a condensate and water receiving trough 13, is then fed through a condensate pipe to a water separator installed on one side of the body 1, to be refined, and returned to the solvent tank 1a. Referring to FIGS. 3 to 6, the treating work is described hereunder: First, as shown in FIG. 3, a wood transport container 11 holding the wood blocks 10 to be treated is carried in by a crane 16, to be mounted on the drainboard floor 9 inside the apparatus body 1 in the state of the cover 2 of the wood treating pressure container A being taken off. Then as shown in FIG. 4, the top cover 2 is screw-fitted to the body by closing bolts, 3, 3, ..., to hermetically seal the interior of the wood treating pressure container A. As the power switch for the heat supply pipe 4 is turned ON, the heat from the source goes on being transmitted to the whole of the heat supply pipe interior, whereby the methylene chloride solvent B inside the solvent tank 1a is heated to boil, forming a solvent vapor layer C. Then the solvent vapor infiltrates into the interior of the wood blocks 10 to be treated in the wood transport container 11, which are in the state of being left in said solvent vapor layer C. Then the free water not confined is thereby expelled out and the vapor melts the lignin which firmly blocks the cellulose and hemicellulose composing the cells of wood. This treatment work is continued for several hours. Then not only is the power switch for the heat supply pipe 4 turned OFF, but the methylene chloride solvent B inside the solvent tank 1a, which is no longer necessary for the latter half of the treatment work, is totally transferred into the solvent storage tank 7. By the above-mentioned treatment, works are done of expelling the unconfined free water which is contained in the wood blocks to be treated 10 and of melting its oil and fat components, whereby the oil and fat components of wood are eluted by the methylene chloride (CH 2 Cl 2 ) solvent B, together with its water content. As this defatting treatment has been accomplished, the oil and fat parts in the wood are dissolved out, bringing the wood into a state of its cells being perforated and the pore hole valves being broken down. Next comes the work of reducing the water content to a predetermined value, as shown in FIG. 5. In this operating example, the water content is reduced by hot air drying, but this may be done by sun's heat. In the case of hot air drying, the drying work of driving the water content out of the interior of the wood by means of hot air is carried out. This drying work expells the solvent vapor which has infiltrated into the interior of the wood blocks 10 to be treated and drives out the confined free water through the perforated cells after oils and fats have been melted out and the pore hole valve parts of the false vessels and vessels. For this purpose, a hot air feed pipe 15 located on the top cover 2 is opened, to feed hot air into the interior of the wood treating pressure container A. By said hot air, the solvent and water content, which have infiltrated into the interior of the wood blocks 10 to be treated, are evaporated and the free water, which has been confined inside the cells and in the false vessels and vessels, is also evaporated. By continuing this work for several hours, the solvent of methylene chloride and the confined free water can be completely evaporated from the interior of the treated wood blocks 10. Upon completion of all treating works, the dome shaped top cover 2 is again opened, as shown in FIG. 6, and then the wood transport container 11 is carried out of the wood treating pressure container A by means of a crane 16. During the treating operation, as shown in FIG. 4, the solvent storage tank 7 is brought upward, to hold equal the level of the methylene chloride solvent B in the solvent tank 1a and the solvent storage tank 7, and upon completion of the first half of the treatment work, the solvent storage tank 7 is brought downward, to facilitate recovery of the methylene chloride solvent B in the solvent tank 1a. Then the solvent is recovered through a solvent drawing out pipe 8. By this wood treating work, the wood is defatted by the methylene chloride solvent B, the tough lignin in the cell structure is melted, thereby perforating the cell membranes, and the pore hole valves of the false vessels and vessels are broken down. In that way the process of driving out the confined free water through said perforations and pore hole valves is facilitated. Thereafter, the coloring of the wood is made by infiltrating a fine grained dye through these perforations and pore holes. By the usual coloring method, the dye failed to penetrate into the interior of the wood because of its cells being firmly bound by lignin. In the method as above-described, the methylene chloride solvent B melts out the tough lignin in the cell structure and undermines the pore holes' valve action, to bring about a state which ensures easy fleeing of the confined water through said perforations and the pore hole valves, thereby enabling coloring the wood with the same dye deep into its interior. The coloring operation with said dye may be performed by dipping in a dye bath the wood blocks which have been subjected to the defatting treatment, but it may also be permeated as a vapor, as above-described, with the fine grains of the dye mixed with the methylene chloride solvent B. In the wood treating pressure container A of this invention, safety valves 17 aid 18 are provided respectively on the top cover 2 and the solvent tank 1a, so that should an abnormal pressure develop in the interior of the wood treating pressure container A during the treating work, they would open to reduce the pressure, thereby keeping its inside pressure always constant. Besides, the methylene chloride solvent B and the wood blocks 10 to be treated are hermetically sealed in the interior of the wood treating pressure container A and heated by a heat supply pipe 4 or otherwise heated by some heat source from outside, thereby to vaporize the methylene chloride solvent B at a rate of about 6 kg/cm 2 . The supply of heat to the heat supply pipe 4 is suspended about 1 hour later, to return the methylene chloride solvent B to its aqueous solution and the pressure is lowered to about the atmospheric pressure. The operation of compression by heating 1 hr later and decompression by cooling 1 hr later is repeated several times, whereby the defatting treatment by the vapor of the methylene chloride solvent B may be further promoted. When the methylene chloride solvent B only is put in the solvent tank 1a inside the wood treating pressure container A and evaporated by heating, it may be vaporized at about 40°C, but because the surfaces of the wood blocks to be treated 10 are hardened at the initial period of the wood treatment, there arises a situation of penetration of methylene chloride solvent B into the cells being thwarted. To counter this situation, according to the method of the invention, mixing about 90 % of water with the methylene chloride solvent in the solvent tank 1a and then heating this mixture to 100 - 140°C, thereby explosively vaporizing water and the methylene chloride solvent B, is effective. Thus by mixing steam and vapor of methylene chloride and permeating the mixture into the wood blocks 10 to be treated, the cells of said surfaces of the wood blocks 10 to be treated are opened and through the openings, the vapor of the methylene chloride solvent B is permeated, whereby the effect of promoting the defatting treatment is achieved. When the wood block 10 to be treated, after defatted by the methylene chloride solvent B, are dried, using hot air, their water content goes down to the equilibrium value in several hours, but even by drying them with sun's heat, it takes only about 2 weeks to reduce the water content to the equilibrium value. As the defatting work of wood has ended with use of the methylene chloride (CH 2 Cl 2 ) solvent and water, the methylene chloride (CH 2 Cl 2 ) solvent and water again return to liquid, but besides them, the oil and fat contents in the wood also remain in this liquid in a separated state. Accordingly, the liquid is in the state of being separated in 3 layers of water, oil and fat components and methylene chloride. Then the oil and fat components of wood may be physically separated, from which to obtain a natural resin material. Since the present invention is composed as hereabove described, following effects are achieved: The vapor of the methylene chloride (CH 2 Cl 2 ) solvent B, a chlorine base organic solvent for cleaning by vapor-defatting, acts on the oil and fat components of wood, to defat and melt them, thereby partly perforating the cells of wood which are containing cell water and breaking down the pore hole valves of the false vessels and vessels. In this way, fleeing of the free water contained therein which was hitherto difficult to extract and conversely penetration of dye are facilitated. Accordingly, this method drastically retrenches the wood treating time from one year unit to several days unit, as compared with the conventional method, thus enabling large amount of wood to be treated with enormous savings in time and energy. The wood after treated, as compared with that before treated, has a volume that has been expanded, rather than shrunk, and its strength not reduced at all. The methylene chloride solvent, a chlorine base organic solvent for cleaning by vapor-defatting which is used for large cutback on the treatment time is a highly safe chlorine base solvent which does not injure wood and moreover has such a low B.P. as 40 o C, so that even when feeding hot air into the interior of the wood treating apparatus as a finishing step of the treatment work or when recovering it by distillation, the time and energy may be saved. According to this invention, a fine grained dye is mixed with methylene chloride or loaded on the gas of methylene chloride, for said fine grained dye to be carried into the cells of wood. In this way, it has become possible to obtain a wood with a nearly uniform grain color. In the conventional coloring method, wood is colored by dipping in a bath of a molten dye, but the cell's defence is firm, with the wood's lignin remaining unmelted, thus permitting the dye to penetrate only to the surface, resulting in this colored layer. Therefore, if the surface of the wood was shaved or otherwise removed, the colored layer was stripped, exposing the former wood grain deprived of the effect of coloration. However, when as in the method of this invention, the wood is dyed, after defatting it, the coloration can be made deeper by letting the fine grained dye penetrate into the cells, thereby enabling the colored layer to be left unremoved, even if the surface is shaved. In this invention, "wood" contains "chip" for pulp industry.

Claims: A wood treating method, comprising the following steps: providing a mixture of methylene chloride solvent and water, said water accounting for approximately 90% of said mixture; heating said mixture at 100°C to 140°C, preferably 100°C to 130°C, so that vapors of said methylene chloride solvent and said water are simultaneously generated; confining wood to be treated and said vapors of said mixture in a pressure container which is hermetically sealed; permeating said vapors of said mixture into cells of said wood; and melting oil and fat contents in cell membranes of said cells by said vapors thereby creating perforations in said cell membranes. A wood treating method as defined in claim 1 further including the step of: repeatedly subjecting said wood to be treated to compressed vapors of said mixture and decompressed vapors of said mixture, wherein said repeatedly subjecting process comprises: heating the mixture of said water and said methylene chloride to 100°C to 140°C thereby increasing the pressure of said vapors of said mixture to create said compressed vapors of said mixture; suspending the operation of heating said mixture to create said decompressed vapors of said mixture. A wood treating method as defined in claim 1 or 2 further including the step of drying the wood which has been treated. A wood treating method as defined in claim 1 or 2 further including the step of coloring the wood which has been treated by permeating a fine grained dye into the wood.

Inventors: HASHIMOTO YOTARO, HASHIMOTO, YOTARO
Applicants: EIWA CO LTD
Application year: 1993
Main classification: B27K5
IPC codes: B27K5