Woodworking – Process – Mechanical cutting or shaping
Reexamination Certificate
1997-09-25
2001-06-26
Bray, W Donald (Department: 3725)
Woodworking
Process
Mechanical cutting or shaping
C144S271000, C144S361000, C427S397000, C427S440000, C428S292400, C428S359000
Reexamination Certificate
active
06250350
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of impregnating wood with liquid, and particularly, to a method of efficiently impregnating conifers such as sugi (Japanese cedars) and karamatu (Japanese larches) with liquid containing preservatives, fire retardants, resin, etc., to improve the physical properties such as decay resistance and fire retardancy of the wood.
2. Description of the Related Art
Techniques of infiltrating chemicals such as preservatives and insecticides into wood tissue are widely carried out to suppress the biological deterioration of the wood and improve the durability thereof. Infiltration of fire retardants and resin into wood tissue is also achieved to improve the fire retardancy and water resistance of the wood. These chemicals and resin are dissolved or dispersed in water or organic solvents and are used in a liquid state.
A known method that is practical to efficiently infiltrate liquid into wood tissue is a vacuum-pressure treatment. This method dries wood to be treated up to a proper moisture content, puts the wood in an airtight vessel, reduces pressure in the vessel to remove air from the cells and conducting vessels of the wood, introduces liquid into the pressure-reduced vessel, and pressurizes the liquid so that the wood is impregnated with the liquid.
Since the vacuum-pressure treatment infiltrates pressurized liquid into wood through the fine cells and conducting vessels of the wood from which air has been removed, the liquid receives large resistance from the cells and conducting vessels when it passes therethrough. If the wood is axially large, the liquid takes a long time to penetrate the wood and sometimes hardly reaches the heartwood.
Accordingly, methods are studied to pretreat wood, to change the fine structure thereof so that the wood may easily be impregnated with liquid. One of the methods is a compression-recovery method. This method employs metal molds to compress wood orthogonally to the fiber axis of the wood, thereby promoting the separation of pit covers tori from pits or breaking of closed pits in the conducting vessels of the wood. This may form and expand effective paths for passing liquid in the wood. The compressed wood is transferred from the metal molds into liquid so that the wood may undergo volume relaxation and recover the shape thereof in the liquid. This produces suction force to promote penetration of the liquid into the wood. For example, Mokuzai Gakkaishi (a journal issued by the Japan Wood Research Society) reports in Vol. 41, No. 9, 1995, pp. 811 to 819 that the compression-recovery method expedited liquid penetration on seven kinds of conifers and broadleaf trees.
The compression-recovery method compresses wood in metal molds, cools the wood so that the wood temporarily keeps a compressed state, transfers the wood from the metal molds into liquid, makes the wood recover the shape thereof in the liquid, and employs the recovering force of the wood to infiltrate the liquid into the wood. Consequently, this method needs at least the following six steps of:
1) placing wood to be treated into the metal molds;
2) adjusting the wood to a predetermined temperature;
3) driving the metal molds with, for example, hydraulic pressure to compress the wood;
4) cooling the compressed wood in the metal molds and taking the wood out of the metal molds;
5) immersing the wood, which temporarily keeps the compressed state, in liquid of a predetermined temperature and letting the wood relax the volume thereof and recover the shape thereof; and
6) taking out the liquid-impregnated wood.
In this way, the conventional compression-recovery method needs the step of employing metal molds to compress wood to be treated, the step of temporarily holding the compressed state of the wood, the step of transferring the wood from the metal molds into liquid, etc. Compared with the conventional vacuum-pressure treatment, the compression-recovery method involves such troublesome steps and needs expensive metal molds and an apparatus for driving the metal molds, to increase fixed and manufacturing costs. Accordingly, the compression-recovery method is impractical, and the metal molds easily damage the surface of wood to be treated.
SUMMARY OF THE INVENTION
In view of these problems, an object of the present invention is to provide a method of efficiently and economically impregnate wood with liquid based on the compression-recovery method.
In order to accomplish the object, the invention of claim
1
puts dried wood in a pressure vessel, immerses the wood in liquid contained in the pressure vessel, pressurizes the liquid to compress the wood while keeping the temperature of the wood at or above the softening point of the wood, and reduces pressure in the pressure vessel so that the wood may undergo volume relaxation in the liquid and be impregnated with the liquid.
As stipulated in claim
2
, it is preferable to keep the temperature of the wood higher than the softening point thereof while the wood is being compressed in the liquid and relaxing the volume thereof in the liquid.
As stipulated in claim
3
, it is preferable, after the dried wood is put in the pressure vessel or after the wood is immersed in the liquid, to reduce or remove air contained in the wood by reducing pressure in the pressure vessel, and then, pressurize the liquid to compress the wood.
As stipulated in claim
1
, the present invention compresses wood with the hydrostatic pressure of liquid and lets the wood relax in volume and recover the shape thereof in the liquid so that the liquid may infiltrate into the wood. Accordingly, the present invention needs no metal molds nor troublesome steps of placing and removing the wood into and from the metal molds and transferring the wood from the metal molds into liquid. The present invention is capable of reducing the costs related to the metal molds and an apparatus for opening and closing the metal molds.
The present invention compresses wood at a temperature higher than the softening point of the wood so that the wood is sufficiently soft to be easily and surely compressed. This results in quickly and surely separating tori from pits or breaking closed pits in the conducting vessels of the wood and easily, surely, and quickly impregnating the wood with liquid during volume relaxation of the wood. In addition, as stipulated in claim
2
, the volume relaxation takes place at a temperature higher than the softening point of the wood so that the wood is sufficiently soft to relax in volume and recover the shape thereof. Namely, the volume relaxation takes place smoothly, and the wood substantially recovers the original shape thereof. At this time, the wood produces large suction force to more efficiently draw the liquid even into the heartwood.
As stipulated in claim
3
, the present invention puts dried wood in the pressure vessel, and before compressing the wood, reduces pressure in the pressure vessel, to reduce or remove air from the wood. This sort of air is present in the cells and conducting vessels of the dried wood and is considered to hinder the compression, volume relaxation, and liquid impregnation of the wood, if it is not removed. By removing such air, the invention of claim
3
makes the compression and volume relaxation of the wood easier and further improves liquid penetration to the wood.
A method according to the present invention includes a compression step and a volume relaxation step. These steps will be explained in sequence.
The compression step puts dried wood in a pressure vessel and immerses the wood in liquid contained in the pressure vessel. The liquid may be put in the pressure vessel before or after placing the wood in the pressure vessel. The liquid in the pressure vessel is pressurized by a unit to be explained later, to increase pressure in the pressure vessel. The pressure applied to the liquid, i.e., the hydrostatic pressure of the liquid compresses the wood. When the pressure reaches a certain level, the wood starts to shrink, and therefore,
Arakawa Tamio
Funato Masahiro
Hoshino Akiko
Muraki Toshio
Arent Fox Kintner Plotkin & Kahn
Bray W Donald
Mywood Kabushiki Kaisha
LandOfFree
Method of impregnating wood with liquid does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of impregnating wood with liquid, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of impregnating wood with liquid will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2457103