WOOD-IMPREGNATION PROCESS DESCRIPTION

The present invention relates to a method of impregnation of wood, in particular the wood of broadleaf trees such as chestnut, oak, ash, beech, elm, poplar and walnut, as well as to a process for the preparation of semi-finished and finished products made of wood comprising said method. Furthermore, the present invention relates to articles made of wood obtained with said method and process, where by the term "articles" are meant both semifinished products and finished products.

It is known that articles made of wood, particularly if used in external environments, are subject to a more or less rapid degradation, according to the environment in which they are located, owing to attack by atmospheric agents, such as humidity, UV irradiation, and the like, as well as by biological agents, such as fungi/moulds, insects, marine organisms and the like. There exist in nature species of trees that offer a resistance that is even high to the aggression of the aforementioned agents, but these are in general types of wood that are relatively costly or very costly, normally used for products of high quality and not suitable for applications that must have a contained cost.

To overcome the above drawbacks and to enable use of the aforesaid types of wood also in relatively low-cost applications, the wood is thus normally treated with appropriate chemical substances designed to provide specific protection against one or more of the aforesaid atmospheric and biological agents. Said treatment can be carried out using technologies of a traditional type, for example by dipping or by means of application of said chemical substances with a brush or by spraying. However, such treatment is not able to provide simultaneously satisfactory protection in terms of resistance to fungi and insects, water-repellence, and resistance to UV light.

Instead, better results are obtained using the technology of impregnation in an autoclave, which involves a first step in which the wood is positioned in an autoclave where a vacuum is created, thus freeing the tracheids of wood from air and facilitating the subsequent impregnation. The second step envisages in fact the introduction into the autoclave of the treatment solution so as to cover the material to be treated. Next, pressure is applied so as to force the solution into the wood. At the end of the step of treatment under pressure, the solution is discharged, and a vacuum is once again applied in the autoclave for a given period of time in order to facilitate fixation of the active principles in the wood. After restoring conditions of room pressure in the autoclave, the wood is ready for the subsequent processes.

An example of treatment of wood by impregnation in an autoclave with fire-proof substances is described in the Spanish patent application No. ES 2246157-Al. According to what is described in the above patent, and also according to common practice, an indispensable requisite that must be met by the wood to be treated is represented by its relative humidity, which must be equal to or lower than 15%.

From the standpoint of the species of trees, in applications for exteriors there is widely favoured the use of the wood of conifers, whilst broadleaf trees are generally considered not easily impregnable or not impregnable at all. In the current state of the art in fact, articles for exteriors made of impregnated wood are almost exclusively made with the wood of conifers.

The technology described above, albeit achieving its own tasks, presents some drawbacks, the main one of which being linked to the fact that impregnation occurs only for a thickness of a few millimetres of the surface of the piece to be treated. This obviously has a negative impact on the useful service life of wood for exteriors thus treated, which is normally guaranteed for a period not longer than ten years.

Furthermore, also as a consequence of the fact that, as has been seen, impregnation occurs only on the external surface, normally the cycle of processing of wood envisages that the finished product and not a semi-finished product will be introduced into an autoclave. In the latter case in fact, the subsequent processes for making the finished product would bring to light untreated internal portions of the piece, with the consequent need for further protective treatments.

Treatment by impregnation of the finished product involves, however, a deterioration of the quality of the finish, given that the vacuum-pressure-vacuum cycle necessarily determines non-uniform movements in the wood on account of the non- structural uniformity of wood itself.

On the basis of the above considerations, the main task of the present invention is to provide a method of impregnation of wood, in particular wood of broadleaf trees, such as chestnut, oak, ash, beech, elm, poplar, and walnut, which will enable the drawbacks referred to above to be overcome. A further task of the present invention is to provide a process for the preparation of semi-finished and finished products made of wood that will enable the drawbacks referred to above to be overcome.

In the framework of the above task, a purpose of the present invention is to provide a method of treatment of wood by means of impregnation that will enable an increase in the useful service life of the articles made using wood subjected to said treatment.

A further purpose of the present invention is to provide a method of treatment of wood by means of impregnation that will enable articles characterized by a high degree of impregnation to be obtained also throughout their bulk and not only on the external surfaces.

Yet a further purpose of the present invention is to provide a method of treatment of wood by means of impregnation that will enable simplification of the cycle of processing of wood.

Another purpose of the present invention is to provide a method of treatment of wood by means of impregnation that will enable the use of a plurality of substances for said treatment.

Not the least important purpose of what forms the subject of the present invention is to provide a method of treatment of wood by means of impregnation, as well as a process for processing wood that comprises said method, which will present a high degree of reliability and will be relatively easy to implement and at competitive costs.

The above task, as well as the above purposes and others that will emerge more clearly from what follows, are achieved according to the invention through a method of treatment of wood by means of impregnation in an autoclave, characterized in that the wood to be treated is a wood of broadleafed trees chosen from among chestnut, oak, ash, beech, elm, poplar, and walnut; moreover, said wood is characterized by a content of relative humidity higher than 15%.

In other words, the method of treatment of wood by means of impregnation in an autoclave according to the invention is characterized in that, contrary to what occurs normally, the wood to be treated is chosen from among woods of broadleafed trees, usually considered as not impregnable, having a particular content of humidity. It has in fact surprisingly been found that, working for example with ash that has dried naturally (and hence with a content of humidity comprised between 20% and 22%), it is possible to obtain articles with practically uniform impregnation throughout the entire section of the article itself.

This constitutes a considerable achievement in so far as ash has always been considered a wood unsuitable for making articles for exteriors, given that it is not naturally resistant to the aggression of fungi, termites and woodworm. On the other hand, ash has always been considered a wood unsuitable for the treatment of impregnation in that it presents average impregnability of its sapwood in normal process conditions (i.e., with a content of humidity lower than 15%), whilst the heartwood is not impregnable at all.

The above result is even more surprising if it is considered that, working with a

content of humidity greater than 15%, preferably comprised between 18 and 30%, and even more preferably comprised between 20 and 25%, it is possible to obtain a practically total impregnation of the piece, whereas the wood of conifers can be impregnated only in a region of the thickness of a few millimetres in the proximity of the surface of the piece.

Illustrated in what follows are some preferred embodiments of the invention, without this, however, implying any limit to the scope thereof, as defined in the ensuing claims.

As mentioned previously, the method according to the invention relates to the treatment of a wood of broadleafed trees chosen from among chestnut, oak, ash, beech, elm, poplar, and walnut. Amongst the species of trees mentioned, ash is by far the one preferred. In fact, ash presents mechanical characteristics equal or superior to those of oak, and by far superior to those of the wood of conifers, such as Scotch pine and Monterey pine. With respect to the wood of oak it has the considerable advantage of not containing tannins, which, as is known, when they are released from the wood, create problems of undesirable stains.

The method of treatment can be conveniently carried out in plants of a known type, for example the impregnation plants IMP-VP, produced by the firm I.S.V.E. s.r.l., which comprise: an autoclave that is able to withstand a vacuum as high as -700 mmHg and a pressure of 12 atm; a bath for containing the impregnating solution or, alternatively, a cistern for containing said solution; a bath or cistern for preparation of the impregnating solution; a vacuum pump; and a high-pressure pump.

As regards the type of treatment, the method according to the invention is highly flexible and enables impregnation of the wood with any substance, according to the needs. The treating substances can in fact be protective substances both against atmospheric agents and against biological agents, or else fire-proof substances, or else wood-dyeing substances, or any mixtures thereof. The method according to the invention does not present particular limitations as regards the solvent for the impregnating solution, which can be water or else an organic solvent, according to the needs.

As regards the sequence of steps of the process, the method of treatment according to the invention preferably comprises the following ones: introducing the wood to be treated into an autoclave; connecting the internal volume of the autoclave to a vacuum pump and creating a desired value of vacuum within said autoclave; the period of maintenance of the vacuum varies according to the needs and may for example be comprised between 30 and 90 minutes; introducing into the autoclave the solution that contains one or more treatment substances;

connecting the internal volume of the autoclave to a high-pressure pump and pressurizing the inside of the autoclave itself; also in this case, the period of operation of the pressure pump varies according to the needs and may for example range between 30 and 180 minutes; discharging said solution from said autoclave, for example through a discharge valve positioned on the bottom of the autoclave; connecting the internal volume of said autoclave again to a vacuum pump and creating a desired value of vacuum within said autoclave; the period of maintenance of the vacuum varies according to the needs and may for example range between 20 and 40 minutes; bringing the autoclave back to atmospheric pressure.

As mentioned previously, the method according to the invention enables very high levels of impregnation to be obtained, in particular with ash, given that it is possible in practice to achieve a substantially uniform impregnation throughout the section of the piece. This fact enables radical modifications to be made also in the processing of wood as compared to current practice.

In the current state of the art in fact, since impregnation occurs only at the surface of the pieces, it is necessary to introduce the articles into the autoclave in the form of finished pieces. If a semi-finished product were treated directly, the subsequent necessary processes would bring to light non-treated internal portions of wood, rendering necessary a further treatment of impregnation.

However, the impregnation of the finished product reduces the level of quality of the finish in so far as the wood, and in particular its external surface, is exposed to the alternate action of vacuum and pressure in the presence of liquids, which inevitably modifies the characteristics thereof. For example, the expulsion of knots in areas corresponding to the surface is a phenomenon that frequently occurs and is certainly favoured by the vacuum-pressure- vacuum cycle mentioned above.

The present invention hence relates also to a process for wood processing and for preparing articles made of wood, which is characterized in that it comprises the following steps: prearranging the wood in the form of semi-finished articles; treating the wood by means of impregnation in an autoclave using the method of treatment by impregnation described previously; subjecting the treated wood to a process of drying;

subjecting the dried wood to one or more processing operations for making articles in the form of finished pieces.

Since in fact the penetration of the impregnating substance is complete and deep, the treated wood can be cut, sawn, shaped, or in any way processed according to the needs, without having exposed surfaces that have remained untreated. In this way, the level of finish is the one desired and imparted by the processes to which the piece is subjected, without there being the typical alterations that are encountered with methods of a known type. For determination of the content of relative humidity of wood it is possible to make reference to the standards and equipment normally used in the sector, for example the method UNI9091-2/87.

EXAMPLES

Given by way of example in what follows are the results obtained by the treatment of ash using the method according to the invention.

Eight pieces of ash having the dimensions of 30x15x6 cm were prepared using a naturally dried wood with a content of relative humidity of approximately 22%. The pieces were introduced into an autoclave model IMP-VP, produced by the firm I.S.V.E. s.r.l., in which the vacuum was created and maintained for 60 minutes. Next, an aqueous solution containing a protective substance (Wolmanit CX, produced by the firm Wolman) was introduced into the autoclave in the amount of 3 kg of treating product per 100 1 of water.

The autoclave was pressurized at a pressure of approximately 10-12 bar and kept in said conditions for approximately 1 h. After this period had elapsed, the solution was discharged through a discharge valve, and a vacuum was created in the autoclave. The vacuum was maintained for approximately 15 minutes, after which the autoclave was brought to room pressure, and the pieces treated were taken out.

The pieces were cut in a number of points to expose their transverse and longitudinal sections. In all the cases, it was found that the impregnation was substantially complete and uniform throughout the section. By comparison, a piece of pine, introduced into an autoclave together with the pieces of ash, was found to be impregnated only at the surface of the piece itself and only for a thickness of a few millimetres.

The mechanical characteristics of the pieces of ash thus treated also proved to be very good.

It has been seen how the technical solutions adopted enable the pre-set tasks and purposes to be fully achieved. In particular, the method according to the invention enables

in-depth impregnation of the wood of broadleafed trees used. There derives therefrom the immediate advantage that the useful service life of the articles made using said wood is considerably increased, so much so that for said articles it would be possible to offer guarantees of duration of up to twenty years, as compared to the ten years usually accorded to articles made with the wood of conifers.

A further advantage derives from the possibility of using types of wood, namely the wood of broadleafed trees, for making articles for exteriors, whilst up to now the vast majority of such applications contemplated the use of the wood of conifers.

Furthermore, the method according to the invention enables implementation of a process of wood processing of an innovative type in so far as it enables introduction of the semi-finished product into an autoclave, treatment thereof with the impregnating substance, and, after drying, subjection to the processes of finishing. This leads to an improvement in the quality of the finish and a reduction in the times and in the processing cycles as compared to processes of a known type.

It should be pointed out that articles, semi-finished products, and finished products made with the method and process according to the present invention also fall within the scope of the present invention.

The method of treatment of wood by means of impregnation in an autoclave, as well as the process of wood processing, thus conceived may undergo numerous modifications and variations, all falling within the scope of the inventive idea; in addition, all the various items may be constituted by other technically equivalent ones.

In practice, the materials used, as well as the contingent dimensions and shapes, may be any whatsoever according to the requirements and the state of the art.