METHOD OF IMPREGNATION

Abstract: A process for the impregnation of cellulose-based products, particularly wood, comprising treatment of the product with linseed oil at an increased temperature under pressure in an autoclave, comprising the steps: a) charging the autoclave with the product to be treated, b) charging the autoclave with linseed oil heated to a temperature exceeding the boiling point of water so that the product wil be surrounded by linseed oil, c) applying vacuum to the autoclave while keeping the temperature constant, water in the form of steam and air enclosed in the product being released from the product, d) discharging the linseed oil from the autoclave with simultaneous supply of linseed oil of a temperature lower than the boiling point of water and preferably applying over-pressure to the autoclave, and e) discharging the cold oil from the autoclave which, optionally, for the removal of excess oil from the product is again set under vacuum, whereafter the impregnated product is removed from the autoclave.

Description: METHOD OF IMPREGNATION The present invention relates to a process for linseed oil impregnation of a product based on cellulose, particularly wood, such as lumber, other wood products and the like. The process involves treatment of the prod- uct with linseed oil at an increased temperature under pressure in an autoclave. Even if the present invention is applicable in relation to other cellulose-based products than wood the invention will in the following be described in connection with wood in the form of different types of lumber. Decomposition of wood when used outdoors is almost exclusively caused by fungi and bacteria. The requirement for growth of such micro-organisms is the presence of water. Furthermore, a suitable temperature and access to nutri- tion and oxygen are required. Prevention of decomposition can be based on the elimination of one or more of these conditions necessary for the growth of • the microorganisms. As an example there can be mentioned that if the moisture content is brought down to a value lower than about 20% biological decomposition is substantially prevented. A number of different impregnation processes for the protection of wood are known, and these methods can in principle be divided up into techniques based on the sup- ply of a substance poisonous to the growth of the microorganisms, and techniques whereby the wood is given hy- drophobic properties, for example by impregnation with some kind of oil. In the latter case an impregnation agent is crude linseed oil which can be of hot- or cold- pressed type, both of which by suitable heat treatment are converted into boiled linseed oils. Most of the known methods for oil impregnation of lumber is based on the principle of using overpressure during the impregnation procedure. Moreover, impregnation methods are known which are based on the so called principle "hot and cold-process", i.e. the lumber is initially treated m hot oil and is then transferred into cold oil whereby a certain improved impregnation result is obtained. The known methods are, however, unsatisfactory with regard to obtaining a degree of impregnation resulting m extended protection against attack by microorganisms present m nature, for example micro-organism flora of aggressive brown rot. The present invention has for an ob ect to provide a process for linseed oil impregnation of cellulose-based products, particularly wood, the new process resulting m a substantially improved protective effect, especially m view of the fact that the process enables a higher level of uptake. Another object of the invention is to provide a multi-step process utilizing an initial heating step m which water m the form of vapour and enclosed air is released from the product, and a subsequent step where the result of the water and air release is used to improve the uptake of oil. Yet an object of the invention is to provide a process with alternate use of vacuum m combination with high temperature and then cooling m combination with over- pressure. A particular object of the invention is to make certain m the process that the transition from the vacuum- heating step to the pressure-cooling step takes place continuously so that maximum benefit of this transition will be obtained. For these and other objects which will be clear fror the following description the invention provides for a process for the impregnation of cellulose-based products, particularly wood, with linseed oil, the products being treated with linseed oil at an increased temperature and under pressure m an autoclave. The invention is characterized by the following steps: a) the autoclave is charged with the product to be treated, b) linseed oil heated to a temperature exceeding the boiling point of water is introduced into the auto- clave so that the product is surrounded by linseed oil , c) while keeping the temperature at a constant level the autoclave is put under vacuum, water m the form of steam and air enclosed m the product being released from the product, d) the linseed oil is discharged from the autoclave with simultaneous supply of linseed oil having a temperature lower than the boiling point of water and the autoclave is preferably put under overpressure, and e) the cold oil is discharged from the autoclave which, optionally, for removal of excess oil from the product is again put under vacuum, the impregnated product then being removed from the autoclave. The process according to the present invention is m principle based on the new concept that the switching over of the autoclave from hot linseed oil under vacuum takes place continuously by introducing cold linseed oil simultaneously with dechargmg the hot linseed oil from the autoclave, the autoclave being progressively put un- der overpressure. By this procedure the vacuum m the product generated under heat and autoclaved vacuum is utilized at a maximum so that optimal uptake of linseed oil takes place m connection with the supply of cold linseed oil and putting the autoclave under overpressure. In the present disclosure the expressions "hot linseed oil" and "cold linseed oil" thus mean that the temperature of the oil m the first case exceeds the boiling point of water and m the latter case is lower than the boiling point of water, respectively. In step a) it is suitable to heat the linseed oil to a temperature of about 140-180°C, whereas m the latter step c) it is preferred to put cne autoclave under over- pressure of up to about 15 bar, for example from about 5 to about 12 bar. In the cooling step d) the temperature of the cold linseed oil is suitably maintained within the range about +75 to about +85°C. In the process according to the present invention it is particularly preferred to use for the impregnation a processed linseed oil substantially consisting of lino- lenic acid, linolic acid and oleic acid, mainly in the form of triglycerides , the content of free tocoferol of the linseed oil being less than about 100 ppm. The linseed oil content of free tocoferol is suitably less than about 75 ppm and particularly less than about 50 ppm. Details regarding such processed linseed oil and the proc- ess for the manufacture thereof is found in patent application No. SE 9903621-2 filed simultaneously herewith with the same applicant and the same inventor. The contents of this co-pending patent application is incorporated herein by reference. Finally, the process may in a further final step be dried in an air flow of environmental temperature. The present invention also covers products, particularly wood products, obtained by the process described above . The invention will in the following be further described in connection with no-limiting examples, wherein the percentages given relate to weight if not otherwise stated. EXAMPLE 1 Impregnation procedure In connection with the impregnation procedure there is used Swedish cold-pressed linseed oil from the harvest of 1998. An autoclave is charged with lumber to be treated, in the present case rods which have been distributed and anchored. The autoclave is charged with linseed oil heated to a temperature within the range about 140 to about 180°C, for example about 160°C, and the autoclave is charged so that the lumber is completely surrounded by linseed oil. The temperature is maintained at a constant level while the autoclave is put under vacuum. In view of the high temperature to which the lumber is heated and under the influence of vacuum the water will evaporize and water steam together with air will leave the pore system of the lumber. After finished heat treatment which takes place for a period of about 1 h, the hot oil is continuously replaced with cold oil by pumping the hot oil out of the autoclave at the same time pumping cold oil into the autoclave at the bottom thereof. At the same time as this replacement of hot oil with cold oil the pressure in the autoclave is progressively increased from vacuum to an overpressure of about 10 bar. The temperature of the cold oil is maintained within the range about +75 to about +85°C. In cooling of the lumber a sub-pressure is created in the pore system thereof, whereby impregnating oil more easily impregnates the lumber so as to increase the level of uptake . After finished treatment in the autoclave the lumber is allowed to dry in a cool flow of air at a temperature of about 20°C or lower, whereby excess of oil further penetrates into the lumber. This final step has for a function to prevent that oil by later sweating emerges from the impregnated lumber. EXAMPLE 2 Result of impregnation The lumber made subject to impregnation can be of any type. In Sweden the trend is presently towards the common coniferous trees, namely fir and pine. The lumber can be fresh or dried in different degrees, i.e. contain different amounts of moisture. The time periods of the different process steps will have to be adapted to the parameters of the lumber (dimension, moisture content, type of wood, core and/or sap- wood) and to the uptake level desired. The uptake level can be given in quantity of linseed oil per cubic meter or percent of the dry density of the lumber which is about 450 kg/m 3 , and further with regard to the intended use of the impregnated lumber. The higher the uptake level obtained the better resistance of the lumber and the harder conditions endured by lumber in its practical use . Different types of lumber have been test impregnated in accordance with the process of the invention, and in the following table these types of lumber and the uptake levels obtained are given. TABLE Lumber impregnated to high levels of uptake, i.e. up to 100%, can according to ongoing tests endure long periods of time under quite severe conditions, i.e. freely outdoors in ground or in ground contact . It should be observed that the present invention is not restricted to the specific embodiments exemplified above. Thus, modifications and changes can be carried ou within the frame-work of the invention and such changes and modifications are easily understood by those skilled in the ar .

Claims: CLAIMS 1. A process for the impregnation of cellulose-based products, particularly wood, comprising treatment of the product with linseed oil at an increased temperature un- der pressure in an autoclave, characterized by the steps: a) charging the autoclave with the product to be treated, b) charging the autoclave with linseed oil heated to a temperature exceeding the boiling point of water so that the product will be surrounded by linseed oil, c) applying vacuum to the autoclave while keeping the temperature constant, water in the form of steam and air enclosed in the product being released from the product , d) discharging the linseed oil from the autoclave with simultaneous supply of linseed oil of a temperature lower than the boiling point of water and preferably applying over-pressure to the autoclave, and e) discharging the cold oil from the autoclave which, optionally, for the removal of excess oil from the prod- uct is again set under vacuum, whereafter the impregnated product is removed from the autoclave. 2. A process according to claim 1, characterized in that in step a) the linseed oil is heated to a temperature of about 140 to 180°C. 3. A process according to claim 1 or 2 , characterized in that in step c) the autoclave is set under an over-pressure of up to about 15 bar. 4. A process according to any one of the preceding claims, characterized in that in step d) the temperature of the cold linseed oil is maintained within the range about 75 to 85°C. 5. A process according to any one of the preceding claims, characterized in that in step d) the overpressure is from about 5 bar to about 12 bar. 6. A process according to any one of the preceding claims, characterized in that the impregnation is carried out with a processed linseed oil substantially consisting of linolenic acid, linolic acid and oleic acid, mainly in the form of triglycerides, the contents of the oil of free tocoferol being less than about 100 ppm. 7. A process according to claim 6, characterized in that the contents of free tocoferol of the linseed oil is less than about 75 ppm. 8. A process according to claim 7, characterized in that the contents of free tocoferol of the linseed oil is less than about 50 ppm. 9. A process according to any one of the preceding claims, characterized in that the product in a further final step is dried in an air flow of environmental temperature . 10. Products produced by the process according to any one of the preceding claims.

Inventors: SELDER MIKKEL, SELDER, MIKKEL
Applicants: JAERLAASA FAERGINDUSTRIER AB, SELDER MIKKEL, SELDER, MIKKEL
Application year: 2000
Main classification: B27K3
IPC codes: B27K3