The present invention relates to a method and apparatus for the protection of timber via the use of a wood treatment material.

At present, to protect timber e.g. against decay fungi, the timber is either im¬ mersed in a wood treatment liquid or pressure impregnated, which means hav¬ ing a wood treatment solution soaked into the timber / impregnating the timber with a wood treatment solution in conditions of under- or overpressure in a pressure chamber.

In pressure impregnation, at present mainly copper, zinc, chrome or arsenic salts or a mixture of these is used. However, the use of heavy metals like these is very dangerous, and pressure impregnated timber as waste is hazardous waste.

A further problem with pressure or immersion impregnation are expensive in¬ vestments on equipment and additionally the need to dry the timber again after the soaking.

In immersion impregnation it is at present possible to use wood treatment solu¬ tions that do not contain any substances dangerous to health. A wood treatment solution of this type is disclosed in Fl patent application 20011298. This applica¬ tion describes an environmentally friendly wood treatment solution that does not contain any heavy metals and that contains an impregnating agent consisting of an alkali metal or alkaline earth metal salt of formic acid or propionic acid. Such a salt can be used in an environmentally friendly manner as a wood preserva¬ tive to protect timber especially against decay and termites. In addition, this ma¬ terial has excellent absorption properties, in other words, it soaks into wood faster than e.g. water.

The object of the present invention is to overcome the drawbacks of prior art and to achieve a new type of method and apparatus for the protection of timber. The ^" method of the invention is based on the good absorption properties of new wood treatment materials. These properties are utilized to soak the material into the timber by spraying the material in the form of fine mist e.g. together with the final moistening water into the drying chamber by means of equipment intended

for spreading of the moistening water after the drying and then circulating it in the chamber by means of fans.

The amount of liquid soaked into timber in connection with final moistening may give desired properties to the timber. Thus, by applying the invention, impregna¬ tion of timber can be performed in a drying plant in conjunction with a drying process, and no separate impregnation apparatus is needed.

The details of the features of the invention are presented in the claims below.

In the following, the invention will be described in detail with reference to an ex¬ ample and the attached drawing, wherein Fig. 1 presents a simplified view of the drying chamber of a timber drying plant.

Fig. 1 represents the heat treatment apparatus of a timber drying plant for the drying of timber 1 , comprising a closeable chamber 2 where the timber 1 is ar¬ ranged in a stack with laths between layers. The chamber 2 is provided with a heating unit 3 for heating the air and timber 1 in the chamber 2, a fresh air slide 4 for the supply of air into the chamber 2, an outlet slide 5 for passing the va- pors produced by the heating out of the chamber and a fan apparatus 6 pro¬ vided with an electric motor controlled by a frequency converter for enhancing air circulation in the chamber 2. In addition the apparatus comprises spraying nozzles 8 above the timber stack 1 for spraying final moistening water onto the bundle of timber. The heating unit 3, the slides 4, 5, the spraying nozzles 8 and the fan apparatus 6 are controlled by a control unit 7.

During the drying of timber 1 , the timber is heated to a temperature which is typically about 60 - 80 ⁰ C or in a special hot drying process over 100 ⁰ C in order to dry it (e.g. to a moisture of 10%).

The method of the invention is based on the good absorption properties of the wood treatment material. These properties are utilized to soak the material into the tLmber.by_spraying.t_he material [n _. the form of fine mist together with the final moistening water into the drying chamber after the drying and circulating it in the chamber by means of fans.

The wood treatment solution contains an impregnating agent, which is an alkali metal or alkaline earth metal salt of formic acid or propionic acid.

The alkali metal or alkaline earth metal salt of formic acid or propionic acid may be sodium formate, potassium formate, calcium formate or magnesium formate, and especially potassium formate or calcium formate. It is also possible to use mixtures of the aforesaid salts. The amount of alkali metal or alkaline earth metal salt of formic acid or propionic acid contained in the wood treatment solu¬ tion is e.g. 2-40 weight-%.

It is obvious to the person skilled in the art that different embodiments of the invention are not exclusively limited to the example described above, but that they may be varied within the scope of the claims presented below.