Coating processes – Vacuum utilized prior to or during coating – Organic base
Patent
1985-10-02
1987-01-20
Lusignan, Michael R.
Coating processes
Vacuum utilized prior to or during coating
Organic base
118 50, 118429, 427440, B05C 300, B05D 118, B05D 300, C23C 1400
Patent
active
046379525
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATION
This U.S. application stems from PCT International Application No. PCT/NO 85/00007 filed Feb. 1, 1985.
The present invention relates to a method for impregnating wood by means of an impregnating liquid, and an apparatus for carrying out the method.
Treatment of wood materials by pressure impregnation or deep impregnation has been known for some time. The object is to make the wood more resistant to rot, fungus attack and woodboring insects. The impregnating agent is normally a liquid containing various dissolved salts, which usually have a certain toxic effect.
In the method most commonly practiced today, dry wood is placed in a pressure vessel and the tank is subjected to vacuum. The purpose of this is to draw out as much of the air in the cells of the wood as possible. Thereafter, impregnating liquid is introduced at atmospheric pressure into the impregnation tank from a special storage tank. By suction, the wood will then absorb the impregnating liquid. A drawback of this method is that the woody's ability to absorb the impregnating liquid is considerably reduced because it takes a certain amount of time before the wood is completely surrounded by the impregnating liquid. In the interim period, before the materials are completely surrounded by the liquid, the wood will absorb air and the cells of the wood will fill with air instead of the liquid. Therefore, the pressure outside and inside the cell walls will be equalized to a great degree, and the impregnating liquid achieves rather poor penetration into the wood.
Upon closer examination of this known process, it has been observed that in spite of the fact that the wood loses a major part of the gas volume contained in its cells, not all of the volume once occupied by this gas is replaced by the impregnating substance, even after the laterials have been completely submersed in the liquid. Since no deformation of the materials occurs, either, it must be assumed that the remaining volume has been taken up by some substance other than the impregnating liquid.
Logically, this substance must be gas. This gas consists in part of air which is absorbed by the wood as the liquid is being added, as discussed above, but in addition, it is likely that gas is also drawn out of the liquid, according to the law of the solubility of gases in liquids in relation to the gas pressure above the liquid. The cell membranes in wood are of such nature that they can confine, for example, glucose molecules, while allowing water molecules to pass through. In other words, small molecules may more easily pass through the membrane than large molecules. A large proportion of the molecules which pass through the membrane into the cells in the known impregnation method, therefore, will be gas molecules from the impregnating liquid, and this reduces the possibility for the liquid molecules in the impregnating substance to penetrate the cells. This naturally leads to poorer penetration of the impregnating liquid in the types of wood, especially pine, which today are considered impregnable by this method. It also means that other important kinds of wood, such as fir, are now considered unsuitable for pressure impregnation treatment, owing to the difference in cell structure of the two conifers. As a result, only pine wood is treated according to the above-described method in Norway, and this limitation naturally constitutes a serious drawback of the method.
The object of the present invention is to improve this method of impregnating wood materials, with the aim of increasing the depth of impregnation and making it possible to impregnate types of wood which heretofore have been considered unsuitable for treatment by pressure impregnation or deep impregnation.
This object is obtained through a method for impregnating wood by means of an impregnating liquid, wherein the wood is placed in an airtight pressure vessel or impregnation tank from which the air has been completely or almost completely evacuated, and the impregnation liquid, following its int
REFERENCES:
patent: 4337720 (1982-07-01), Hager
patent: 4433031 (1984-02-01), Allen
patent: 4466998 (1984-08-01), McIntyre
patent: 4542046 (1985-09-01), Moldrup
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