Coating processes – Vacuum utilized prior to or during coating – Organic base
Reexamination Certificate
1999-04-28
2001-06-19
Cameron, Erma (Department: 1762)
Coating processes
Vacuum utilized prior to or during coating
Organic base
C427S382000, C427S393000
Reexamination Certificate
active
06248402
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an improvement in methods for treating wood in which the latter is impregnated with a hardening product.
BACKGROUND OF THE INVENTION
It is known that, in the natural state, wood or wood fibers which are in contact with a humid atmosphere tend to be water-logged, going as far as absorbing 100% of their weight with water. Such absorption of water is accompanied by a swelling, characteristic of a reduction in the qualities of cohesion of the material which, in certain cases, may go as far as an advanced disintegration of said material. This is why it is usual to effect, before any wood-fashioning operation, a step of drying which, by eliminating the water therefrom, improves its dimensional stability.
Although the step of drying makes it possible to eliminate the water from the wood, it does not, on the contrary, modify the hydrophilic nature thereof, so that it is again capable of reabsorbing the water eliminated during drying, when it is again located in a humid atmosphere.
In order to reduce the hydrophilic nature of natural wood, and thus to give it a long-lasting dimensional stability, different high-temperature heat-treatment techniques have been proposed.
Among these techniques, it has been proposed to subject the natural wood to different steps of treatment including in particular a drying in open circuit followed by heating and maintaining at a temperature included between about 220° C. and 300° C. for a determined period. Such a technique of treatment, called controlled thermal treatment (curing), makes it possible to give the wood both a hydrophobic nature and an excellent dimensional stability.
It has also been proposed, particularly in order to improve the mechanical properties of the wood, to call upon techniques of treatment which consist in impregnating the wood with a monomer then, such impregnation having been effected, in polymerizing it in situ, employing different techniques to that end, such as in particular the action of a gamma radiation or the action of heat.
The methods of treatment used in the prior state of the art consist in disposing the wood to be treated in a chamber in which a vacuum is created, in filling said chamber with the impregnating monomer, and in applying a high pressure in this chamber so as to cause the monomer to penetrate in the wood. All that remains is to polymerize the monomer.
Although these techniques prove to be satisfactory from the standpoint of improving the mechanical properties of the treated wood, and particularly from that of the hardness, they are much less so from that of the stability by volume of the wood in a humid atmosphere. It has thus been noted that the woods thus impregnated presented the particularity, after a certain time of use, of losing their adherence with the polymer with which they were impregnated, which was translated by this wood swelling.
SUMMARY OF THE INVENTION
The present invention has for an object to propose an improvement in techniques of impregnating woods with hardening products, and particularly by monomers, with a view in particular to giving said woods characteristics of dimensional stability when they are subsequently exposed to a humid atmosphere.
The present invention thus has for its object a method for treating wood of the type in which the wood to be treated is placed in a chamber in which a vacuum is created, where said chamber is filled with a hardening product, in particular a monomer, so as to impregnate the wood by causing the product to penetrate in the space between its fibers, where said product is then hardened, in particular by polymerization, characterized in that the wood-impregnating operation is preceded by a step of controlled thermal treatment (curing).
Interestingly, said product is a monomer which is hardened by polymerization, in particular by action of a radiation or by the thermal route.
Impregnation may be effected immediately after the controlled thermal treatment step, so as to use the remaining heat of the wood in the course of cooling, in order to ensure, by the thermal route, polymerization of the monomer.
It is known that a controlled thermal treatment step consists in subjecting the wood to a thermal treatment under controlled conditions in order to provoke reactions of thermo-condensation at the level of the ligno-cellulosic structure of the wood. A controlled thermal treatment operation is usually carried out in a neutral or reducing atmosphere on previously dried wood, by subjecting the latter to a temperature included between 220° C. and 280° C. for a sufficiently long time for the whole mass of the treated wood to attain the temperature of treatment, and without exceeding this time of treatment. It will be appreciated that, under these conditions, this duration is a function of the nature and thickness of the wood.
Applicants have observed that this operation of controlled thermal treatment had three important effects, namely that of slightly increasing the porosity of the wood, of giving the latter a hydrophobic character, and of improving its wettability with respect to the monomers by modifying the surface tension of the wood. These three effects are used in particular in accordance with the present invention to promote impregnation of the wood by the monomer.
Tests made by Applicants, which will be described in detail hereinafter, have thus made it possible to demonstrate that, by effecting, according to the invention, a controlled thermal treatment operation before impregnation of the product, and particularly a monomer, not only an impregnation greater than that in accordance with the prior state of the art was obtained, but it was no longer necessary, in order to obtain such an impregnation, to pressurize the chamber containing the wood to be treated and the impregnating product.
Applicants have also established that the method according to the invention made it possible to effect an impregnation, by monomers, of varieties of wood which, up to the present time, were reputed to be virtually non-impregnable by the known methods, such as in particular spruce, oak, chestnut, beech.
According to the invention, certain of the swelling agents, such as in particular methanol, which are used according to the prior state of the art prior to the impregnation operation, are no longer necessary, which represents a saving, on the one hand, from the standpoint of cost of the product itself, and, on the other hand, from the standpoint of the cost of carrying out the method.
Polymerization of the monomer may, of course, be effected by employing a plurality of techniques and in particular among the latter by the action of gamma rays, by heating by convection and by heating by micro-waves.
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Tsai et al, Kuo Li Tai-Wan, No. 82, 1970.*
Narayanamurti, Holztechnologie, 13(2), pp 118-21, 1972.*
translation of JP48-056806, Aug. 1973.*
translation of Tsai, Kuo Li, 1970, No. 82, pp 2-13.
Gohar Pierre
Guyonnet Rene
Cameron Erma
NOW - New Option Wood
Young & Thompson
LandOfFree
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