B AC KG ROU D OF THE INVENTION

[0001] This invention relates generally to timber modification and more particularly to the enhancement of timber properties and applications through appropriate treatment and lamination.

[0002] Generally hardwood timbers, because of their aesthetic appeal and durability, are in higher demand than softwood timbers. Hardwood timber supplies are under threat because of unsustainable rates of deforestation. Softwood timbers though are regarded as renewable resources and are more readily available. Softwood timbers however do not normally have the durability nor appeal of hardwood timbers.

[0003] The usage of softwood timbers can be readily enhanced by means of gluing, joining and laminating because adhesives that are used to bond lamellae together can penetrate porous structures of the softwoods and form a bond that is satisfactory for long-term use. However laminated softwood timber is susceptible to rotting and eventual delamination as timber adjacent adhesive areas degrades.

[0004] A laminated product formed from hardwood is not necessarily superior to a laminated softwood product. Hardwood timber has a high density and is relatively non-porous and, consequently, an adhesive is not readily able to penetrate into the timber and create a long- term bond. Thus, although a hardwood product may not decompose as rapidly as a softwood product, delamination may occur rather rapidly - a feature which makes a laminated hardwood product not particularly suitable for an outdoor application. [0005] An object of the present invention is to address, at least to some extent, the aforementioned situation.

SUMMARY OF THE INVENTION

[0006] In a general sense the invention provides a method of producing a laminated timber product which includes the steps of thermally modifying softwood timber, laminating together sections of the thermally modified timber and impregnating the resulting lamination with a suitable wax or wax blend.

[0007] In the first step the timber is thermally modified to improve the durability of the timber and to darken its colour. This step also facilitates the impregnation of cells in the timber, by the wax or wax blend, during the last step.

[0008] Thermo-treated softwood is used as the raw material input for the process. This wood is procured in a suitable thickness e.g. 25mm or 38mm thick. The raw material is cut into suitable widths according to required dimensions of an end product i.e. a finished laminated beam. If sufficient solid lengths are not available the relatively short lengths are finger-jointeo or butt-jointed to required lengths e.g. by using a suitable waterproof adhesive of type 1 according to EN 301 ( D4) to produce appropriate lamellae.

[0009] The lamellae are machined, according to requirement, to a thickness of not less than 16mm and not more than 50mm. Thereafter a suitable waterproof adhesive is applied by means of brush, a roller or an automated glue spreading machine, with a dosing of between 00-200g/m ² to the surface of each lamella which is to be adhered to another lamella. [0010] Where possible, while stacking the lamellae on a gluing press, the growth rings of adjacent individual lamellae should face in opposite directions to add to the stability of the finished product. If butt or finger joints are present it is important to stagger the joints when stacking the lamellae in the gluing press. The lamellae are then pressed together by means of a manual or automated hydraulic laminating press with a pressure of not less than 0.6N/mm ² .

[0011] The lamellae, under pressure, are held in the hydraulic press for a drying time period specified by the manufacturer of the adhesive which has been used. The drying time can be affected though by seasonal temperature and humidity variations. [0012] The timber, once laminated, may be subjected to a high-pressure vacuum impregnation process using a high-melting point synthetic or natural wax.

[0013] This process may include the following sequence of operations:

(1 ) placing the laminated timber in a sealed pressure vessel;

(2) creating a negative pressure in the pressure vessel; (3) raising the temperature in the pressure vessel to vaporise moisture remaining in the timber;

(4) introducing a protective composition into the pressure vessel to cover the timber;

(5) allowing moisture in the vessel to escape to atmosphere; and (6) sealing the pressure vessel and subjecting the timber and the protective composition to one or more pressure cycles wherein, in each cycle:

(a) the pressure in the pressure vessel is raised to a value in the range of 7 to 12 bar for a predetermined time period; and (b) the pressure in the pressure vessel is reduced to atmospheric level and an interior of the pressure vessel is then exposed to atmosphere to allow moisture inside the vessel to escape to atmosphere.

[0014] The number of cycles employed to impregnate the timber with the protective composition may depend, at least, on the dimensions of the laminated timber. [0015] The protective composition in the pressure vessel may be drained to a level below the lowest level of the laminated timber and, thereafter, the vessel may be sealed. A reduced pressure environment may then be established inside the vessel for a period of from 2 to 5 minutes in order to draw excess protective composition from the timber.

[0016] Numerical values given in this specification are exemplary only and are non-limiting. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The invention is further described by way of example with reference to the accompanying drawings in which:

Figure 1 is a block diagram representation of successive steps in implementing the method of the invention, and Figures 2, 3 and 4 illustrate details of equipment used and processes implemented while carrying out the method of the invention.

DESCRIPTION OF PREFERRED EMBODIMENT

[0018] In broad terms the method of the invention allows for the lamination of modified softwood, e.g. coniferous timber, which is subsequently treated so that an end product has properties similar to that exhibited by an unlaminated hardwood. This is achieved in three specific steps:

1. thermal modification of selected coniferous softwood by heating in a kiln specifically designed to reach elevated temperatures under regulated humidity conditions; 2. optimization and lamination of individual sections or boards of the softwood produced in step 1 using suitable timber adhesives to create a laminated product according to requirement; and

3. a high pressure/vacuum impregnation of the laminated product with a high melting point synthetic or natural wax, or a wax blend. [0019] Figure 1 illustrates in block diagram form three steps 10, 12 and 14 which are successively implemented. In the first step 10 (see Figure 2) the selected coniferous timber 20 is thermally modified to enhance its durability and to darken its colour. This step also facilitates impregnation of the cells, with wax, during the third step 14, as is hereinafter described. [0020] Figure 2 shows a thermal treatment oven 22 into which the timber 20 is placed. High speed fans 24 are connected to the oven. A suitable control device 26 is used to regulate the temperature inside the oven 22, the operation of the fans 24, and to control a humidity source 28 which is coupled to the oven.

[0021] The fans 24 are designed to circulate heated air at a high speed throughout the oven 22. Temperature sensors (not shown) provide control signals to the controller 26 which functions to ensure that all locations inside the oven are subjected to the same degree of heat. As may be necessary steam and water are provided from the humidity source 28 to maintain a desired level of humidity in the oven 22 and to help with cooling, when required.

[0022] During a first phase of step 10 the timber 20 is placed in a stack which is fastened with straps to restrict timber movement during treatment. The timber is dried at a temperature of from 100°C to 130°C for a period that is dependent on the timber dimensions. The conditioning of the timber requires that the moisture content must be reduced to 5% or below and that the internal core temperature of the timber reaches a value of about 00°C. Thereafter the timber is subjected to a temperature of from 180°C to 230°C for a period which is also dependent on the timber dimensions. This elevated temperature may be maintained for a period of up to 180 minutes depending on the degree of shading to be imparted to the timber. The longer the timber is kept at an elevated temperature the darker the timber becomes.

[0023] Steam is introduced into the oven 22 at various intervals. This is done in order to saturate the cooler outer sides of the timber slightly. The steam effectively cools the outer sides of the timber and helps to reduce a temperature differential in the timber which could cause surface cracking. [0024] The timber 20 is thereafter cooled in a controlled manner. Water and steam are used to reduce the core temperature of the timber gradually. The cooling phase can endure for up to 300 minutes depending on the timber dimensions. Once the core temperature is below 40°C the cooling step is completed. At the end of the first step 10 the timber has a moisture content of from 5% to 8%.

[0025] Referring to Figure 3, in the step 12 the timber produced in the step 10 is planed (30), top and bottom, to a uniform and predetermined thickness. A timber selection can be made depending on the grading and appearance needed of the end product. Short lengths of timber can be joined together using a butt or finger-joint to produce lamellae of suitable lengths.

[0026] Thereafter an adhesive 32 is spread by an applicator, e.g. a brush, a roller or an automated glue spreading machine, with a dosing of between 100 to 200 g/m ² , onto opposed surfaces 34 of lamellae which are to be bonded together to achieve a product with a desired final dimension. The adhesive-coated timber sections are then held in a manual or automated hydraulic laminating press 36 with a pressure of at least 0,6N/mm ² for at least two hours to allow the adhesive to set.

[0027] In the third step 14 the laminated timber produced in the step 12 is placed in a stack 42 inside a pressure vessel 44 which is sealed - see Figure 4. A negative (reduced) pressure environment is established inside the vessel 44. Steam coils 46 are used to increase the temperature inside the pressure vessel to about 100X. This temperature is high enough to vaporize most of the moisture remaining in the timber stack 42. [0028] At this point a sufficient quantity of a molten natural or synthetic wax or a wax compound 48 is introduced into the pressure vessel in order to cover the timber stack 42 completely. The pressure vessel 44 is exposed to atmosphere initially so that excess water and vapour in the pressure vessel arising from the heated timber is driven off. [0029] Use may be made of a synthetic resin which bonds with the timber acting as an adhesive to reduce blooming and leaching.

[0030] In order to impregnate the timber with the wax compound 48 the timber is subjected to a series of pressure cycles. In each cycle the pressure in the vessel is raised to a value which lies in the range of 7 to 12 bar. Each cycle endures for a period of up to 30 minutes. Thereafter the pressure is released and the pressure vessel is opened to atmosphere to allow moisture to escape. The cycle is then repeated. The number of cycles required to impregnate the timber depends on the timber dimensions.

[0031] After the cyclical impregnation process has been completed the molten wax compound in the pressure vessel 44 is drained to below the level of the stack 42. The vessel is then sealed and a reduced pressure environment is established for a period of from 2 to 5 minutes. This process draws excess wax compound from the timber.

[0032] The product emerging from the pressure vessel 44, after cooling, can be shaped to a desired final form.

[0033] The thermally modified laminated softwood, produced by the method of the invention, has, with respect to the softwood starting material 20, an increased density, improved strength and load-bearing capacity, and the appearance of a dark hardwood. The laminated product has the bonding and strength characteristic of a softwood yet exhibits the durability of a hardwood.