State of the art - Crude tall oil is extracted in the sulphate (craft) cooking process of as well soft-as hardwoods.

- Crude tall oil from softwoods has the approximate composition 50% resin acids, 30% fatty acids and 20% more or less non-saponifiable extractives.

- Tall oil from hardwood does not contain any resin acids.

- Because soft-and hardwoods often are mixed in the cooking process a tall oil with variable composition is received: - Resin acids 0-70% - Fatty acids 20-70% - Residue 10-30% Tall oil is industrially distilled (in Sweden by Arizona Chemicals) to resin acids for i. a. coating of paper and fatty acids for i. a. alkyd production. The residue is normally used as a fuel.

Tall oil is an interesting alternative wood preservative. It is known to use tall oil to impregnate wood. A so far not solved problem is that the treated wood products are "sweating"oil an are"sticky"for an unacceptably long period of time. Of that reason tall oil is not used as a wood preservative at present.

In SE-C2-509980 a technique for impregnation of a wood product is described 'where a solid acid anhydride, a vegetable oil, e. g. tall oil, and an alcohol are used as an impregnating agent. The treated wood product is heat treated at a temperature above 150° C to bind the oil. To avoid stickiness from the tall oil it is, thus,

according to this patent necessary to add both a solid anhydride and an alcohol and to heat treat at high temperature. However, the technique has not shown good enough results and has therefore not been commercialised (6 years after priority date).

In SU 589120 impregnation of fibreboard with a tall oil composition is described.

0.5-10%, preferably 1.5%, Mn-salts of fatty or resin acids are added as siccative/catalyst to accelerate oxidation. This is equivalent to an Mn-content of 0.045-0. 9%, preferably 0.14%. On application of this technique in a fibreboard mill it turned out that the boards still were too sticky and the composition thus of no use.

In WO 92/04166 a wood preservative composition is described containing a mixture of two or more metal soaps of long chain unsaturated fatty acids. Despite the fact that several metals are mentioned as useful, copper is the only metal described in the examples and shown to be effective. The composition must contain oleic acid, linoleic acid and linolenic acid in a certain ratio. The object is to replace such preservatives as pentachlorophenol, copper chromium arsenate (CCA), creosote and tributyl tin oxide (TBTo) and to obtain a better effect than by using metal naphthenates against termites and fungi. It is claimed that metal soaps of naturally occurring organic acids such as oleic acid, stearic acid and tall oil acids have been found to be inferior to metal naphthenates. Thus, according to WO 92/04166 a mixture of soaps based on tall oil does not work.

Production of the metal soaps according to WO 92/04166 is described in WO 92/04167. Here only production of copper salts of sunflower oil is described. The metal soaps are dissolved in xylene. The produced copper linoleate solution, containing at least 5% copper, is used for preservation of wood and is shown according to described tests to give good results especially in combination with a additional compound, Cypermethrin.

Object of the invention The object of the invention is to provide an effective wood preservative that gives a dry and useful surface on the preserved wooden object. The preservative should not require toxic ingredients such as organic solvents, copper or biocides.

Another object is to make it possible to use tall oil, tall oil distillates or fatty acids in wood preservatives without problems with stickiness arising.

A further object is to achieve impregnation of wood with a preservative based on tall oil, distillates of tall oil or fatty acids without any substantial heating being required.

Short description of the invention These objects are achieved by means of a wood preservative where tall oil, fatty acids or a mixture of fatty and resin acids are used for impregnation of wood, a part of the fatty and resin acids being saponified to calcium or aluminium salts. The metal content is suitably 1-10 weight % of the amount of oil including acids.

Especially Ca is suitable to use for saponification (of environmental reasons). The preservative thus contains preferably only oil and saponified acids.

Detailed description of the invention The wood preservative according to the invention is based on crude tall oil, a mixture of crude tall oil and an addition of fatty and/or resin acids, or solely resin acids and/or fatty acids. The fatty acids can originate from tall oil or from other sources.

The saponification of a part of the fatty and resin acids to Ca-soaps is preferably brought about by first reacting the tall oil with lime (Ca-hydroxide).

It is also possible to add a soap to the tall oil or the fatty acid/resin acid-mixture, for instance a Ca-soap of a suitable acid with a pKa of about the same magnitude as that of the fatty and resin acids. Thus Ca-soaps of e. g. fatty acids in high concentration can be added to the tall oil or the fatty acid/resin acid mixture.

The amount of Ca-hydroxide can vary between 1 and 10 %, calculated as Ca-metal on the amount of oil. When using aluminium for the saponification an aluminate can be used, for example. Here also the metal amount is 1-10 % calculated on the oil. When a mixture of Ca-and Al-soaps is used the total content of Ca and Al is 1- 10 weight %.

The Ca-and Al-soaps thicken the tall oil and possibly also work as siccatives/catalysts for oxidative cross-linking of the fatty acids in the oil.

The same technique using the reaction with lime can also be applied on pure fatty acid mixtures or on mixtures of fatty acids and resin acids. Turpentine or other natural or synthetic compounds, which improve the preservative effect, can be added, but preferably the preservative only consists of oil and saponified acids.

Suitably the preservative does not contain any solvent.

The technique can also be applied to prevent the"spring back"of compressed wood when it is exposed to wetting.

In the following the invention is described in more detail with reference to illustrative embodiments.

Example 1 Crude tall oil containing about 50 % resin acids and 50 % fatty acids and unsaponifiable substances was heated to 120° C. 7 % Ca-hydroxide dispersed in water was added by instalments under vigorous stirring. When all water had

evaporated the temperature was maintained at 120° for about another 1/2 hour.

Thereafter the mixture was ready for use.

5 cm thick planks of pine composed of both sap-and heartwood were impregnated with the Ca-tall oil mixture. First the planks were evacuated for 1/2 hour in an autoclave at a reduced pressure of about 0.05 atm. Thereafter the Ca-tall oil mixture at 70° C was sucked into the autoclave to completely fill the cylinder. Following this, the pressure was allowed to rise to atmospheric pressure with the planks still submerged in the mixture. The temperature was maintained at 70°. The planks were held submerged for 2 hours whereupon remaining tall oil mixture was drawn from the autoclave. The planks were taken out from the cylinder and allowed to drain in a chamber at 70° over night. Then the surfaces were dry. The oil take-up in the sapwood was about 200 kg/m3. Despite exposure to strong sunshine and an air temperature of more than 30° C the planks remained non-sticky.

Example 2 This time 5 cm thick planks of pine composed of both sap-and heartwood were impregnated with a Ca-tall oil mixture containing 6 % Ca-hydroxide. The oil had been improved by addition of a further 10 % of resin acids. The planks were first evacuated for a 1/2 hour in an autoclave at a reduced pressure of about 0.05 atm. whereupon the Ca-tall oil mixture at 70° C was sucked into the autoclave to completely fill the cylinder. Thereafter the pressure was allowed to rise to 10 atm. with the planks still submerged in the mixture. The temperature was kept at 70°.

The planks were maintained submerged for 2 hours whereupon remaining tall oil mixture was drawn from the autoclave. The planks were taken out from the cylinder and allowed to drain in a chamber at 70° over night. Then the surfaces were dry.

Despite exposure to strong sunshine and an air temperature of more than 30° C the planks remained non-sticky.

Example 3 <BR> <BR> Fatty acids from tall oil (SYLFAT @2S, Arizona Chem. ) were heated to 120° C. 7 % Ca-hydroxide dispersed in water was added by instalments under vigorous stirring.

When all water had evaporated the temperature was kept at 120° for about another 1/2 hour. Thereafter the mixture was ready for use.

5 cm thick planks of pine composed of both sap-and heartwood were impregnated with the Ca-fatty acid mixture in the same way as in example 1 above. The planks were taken out from the cylinder and allowed to drain in a chamber at 70° over night. Then the surfaces were dry. The oil take-up in the sapwood was about 200 kg/m3. Despite exposure to strong sunshine and an air temperature of more than 30° C the planks remained non-sticky.

Example 4 A mixture of 75 % fatty acids from tall oil (SYLFAT @2S) and 25 % resin acids (SYLVAROS @85, Arizona Chem. ) was heated to 120° C. 7 % Ca-hydroxide dispersed in water was added by instalments under vigorous stirring. When all water had evaporated the temperature was kept at 120° for about another l/2 hour.

Thereafter the mixture was ready for use.

5 cm thick planks of pine composed of both sap-and heartwood were impregnated with the mixture in the same way as in example 3 above. 10 % of sulphate turpentine was added to the oil to strengthen the mould resistance. The planks were taken out from the cylinder and allowed to drain in a chamber at 70° over night.

Then the surfaces were dry. The oil take-up in the sapwood was about 150 kg/m3.

Despite exposure to strong sunshine and an air temperature of more than 30° C the planks remained non-sticky.

Example 5 <BR> <BR> Fatty acids from tall oil (SYLFAT @2S, Arizona Chem. ) were heated to 120° C. 5 % Na-aluminate (NaAlO2) dissolved in water was added by instalments under

vigorous stirring. When all water had evaporated the temperature was kept at 120° for about another 1/2 hour. Thereafter the mixture was ready for use.

5 cm thick planks of pine composed of both sap-and heartwood were impregnated with the Al-fatty acid mixture in the same way as in example 1 above. The planks were taken out from the cylinder and allowed to drain in a chamber at 70° over night. Then the surfaces were dry. The oil take-up in the sapwood was about 180 kg/m3. The planks remained non-sticky during a summer of outdoor exposure with periods of air temperature of up to 30° C.

Example 6 18 mm thick compressed pine matchboards for flooring with the density 1.09 g/cm3 were impregnated with the Ca-fatty acid-resin acid mixture from example 4 above.

The boards were first evacuated for 2 hours in an autoclave at a reduced pressure of about 0.05 atm. , whereupon the oil at 70° C was sucked into the autoclave to completely fill the cylinder. Following this, the pressure was allowed to rise to atmospheric pressure with the planks still submerged in the mixture. 4 hours later the planks were taken out of the oil mixture and allowed to drain in a chamber at 50° over night. Then the surfaces were dry. The oil take-up was about 15 % based on the initial weight and the penetration from the surface about 3 mm. No swelling could be registered. The boards were easy to join. After the boards had been dried, re-swelling was negligible when water droplets were applied on surfaces and joints.

The invention is defined in the following claims and shall not be considered as limited to the embodiments above. All modifications and variations within the framework of the claims are possible.