SE509068C2 - Process for binding modification chemicals to solid wood products and to prevent cracking in these - Google Patents

Abstract

The invention concerns a method for binding modification chemicals to massive wood products. According to the invention, the wood products are first treated with the modification chemicals, such as aqueous solutions of maleic acid or maleic anhydride, and then the wood products are redried at a temperature of less than 100 DEG C until their humidity has decreased below 20 %. Finally, the wood products which thus have been treated with modification chemicals and predried are subjected to a heat treatment carried out at a temperature of more than 100 DEG C in order to bind the modification chemicals to the wood. The heat treatment can be carried out in a heat press. The invention makes it possible to avoid internal cracks in wood products which are big enough for practical purposes such as for use in various pieces of furniture.

Description

15 20 30 509 068 2 at the same time prevent the occurrence of internal cracking in the wood.

The invention is based on the idea that a wood product treated with modifying chemicals is dried so long that no cracks are formed during the curing of the product and that no modifying chemicals seep out. In particular, the wood product is dried at a temperature below 100 ° C, until the moisture content is lower than 20%.

More specifically, the inventive process is characterized mainly by what is stated in the characterizing part of claim 1.

The process of the present invention is suitable for all solvent-based, in particular water-soluble, modifying chemicals intended to bind to the wood at high temperatures. Typically, ester bonds are formed between the modifying chemicals and the OH groups of the wood (eg cellulose and / or hemicellulose) in connection with the heat treatment. Examples of suitable modifying chemicals are maleic acid and maleic anhydride, as well as maleic acid, which is used in aqueous solutions possibly together with glycerol. With maleic acid and maleic anhydride, the wood can be plasticized for shaping (cf. the above-mentioned FI patent number 91503). Examples of other modifying chemicals are succinic anhydride and the corresponding acid, which are suitable for thermoplasticization of wood, as well as fl alkanoic anhydride and the corresponding acid.

In a particularly preferred embodiment, the wood product is impregnated substantially more deeply than just on the surface with maleic anhydride, with a mixture of maleic anhydride and glycerol, with succinic anhydride or with fi-anhydride.

By "pretreatment intended wood product" is meant within the scope of the present invention a product made of wood, the shape or properties of which it is desired to change. For example, it is desired to bring the wood product into a moldable or plastic state to shape it. or the wood is treated to improve the dimensional stability of the wood or in particular its surface hardness. According to the invention, the product intended for treatment typically has at least a moderate thickness, which is usually greater than about 5 mm (= solid piece of wood). It may comprise a coherent solid wood fabric, but also a laminated product (15 lx) us (eg a clamping board or a fibreboard) made of wood veneer or wood groove. The wood product can also consist of a structure, the individual layers of wood of which are attached to each other to form a laminate. In the latter cases, wood product refers to the layered or laminated product to be manufactured and which can be impregnated either before the product is designed or there.

In the following, the invention is described in more detail with maleic acid and maleic anhydride as examples. It should be noted that the procedure, with appropriate modifications, can also be applied to other modification chemicals.

The invention comprises three steps, namely treatment of the pieces of wood with modifying chemicals, drying of the pieces of wood and heat treatment of the pieces of wood (bonding of the modifying chemicals to the wood using heat).

During the first step, the pieces of wood are typically impregnated with an aqueous solution of maleic acid or maleic anhydride. Preferably, the modifier also contains glycerol.

This mixture is preferably prepared from maleic anhydride and glycerol. The substances are mixed with water, whereby maleic anhydride is hydrolyzed in the aqueous solution to maleic acid. Preferably, the woody material is impregnated with an aqueous solution of maleic acid and glycerol having a concentration of 1 - 99% and a weight ratio of 1:10 - 10: 1 between the maleic acid and the glycerol. Preferably a rather concentrated solution is used with a concentration of about 20 - 60% by weight and a weight ratio of about 1: 5 - 5: 1 between the maleic acid and the glycerol. The amount of solution with which the wood product is impregnated depends on the purpose for which the wood product is intended and on the wood raw material (type of wood, wood wood and wood moisture). Usually the wood material is impregnated with so much solution that it penetrates significantly deeper into the wood product than just below the surface. If the wood product is to be subjected to a mechanical design treatment, it is important that the inner parts of the wood product are as soft as possible. Thus, the wood is preferably impregnated with at least about 20 kg, preferably with about 25 - 300 kg and most preferably with about 30 - 140 kg of a maleic anhydride and glycerol mixture per cubic meter of wood. The moisture or moisture content of the wood intended for impregnation preferably amounts to 5 - 30%, in particular to about 6 - 7%. 10 15 20 25 30 509 068 4 The impregnation can be carried out in such a way that in a pressure vessel under reduced pressure the lye is first removed from the wood material, where the impregnation solution is fed into the vessel and the solution is allowed to penetrate under normal pressure or possibly under high pressure. . Alternatively, the wood material can be immersed in the impregnation solution for such a long time that the solution has time to penetrate deep into the wood (lowering procedure). If the solution of maleic acid and glycerol is to be applied only to the surface of the wood product, the impregnation can also be carried out by surface coating.

After treatment with the modifying chemicals, the wood product is slowly dried at a low temperature, removing the solvent and depleting the active chemical in the wood.

The drying is allowed to proceed until the moisture content of the wood is lower than 20%, preferably also lower than 15-17%. The drying can be carried out at room temperature, but preferably at an elevated temperature lower than 100 ° C. Preferably, the drying is carried out at a temperature of between 20 and 99 ° C, particularly preferably between 30 and 95 ° C. In the heat treatment, any per se known heating device can be used, by means of which the piece of wood can be dried in the presence or absence of water vapor, for example a drying oven, an incubator or the like.

According to a preferred form of drying, the drying of the wood product is carried out in such a way that the temperatures of the inner parts of the wood product and of the surface of the wood are determined continuously and that the difference between them is kept reasonably small. Preferably, the temperature difference does not exceed 30 ° C. The term "the internal temperature of the wood" refers to the temperature of the wood at a certain distance from the surface of the wood. Depending on the shape of the piece of wood, the "internal temperature" is typically measured at a depth of at least about 2 - 5 cm. "External temperature" refers to the temperature of the wood surface or something dänmder. In many cases, the “external temperature” corresponds to the ambient temperature. The temperature is gradually raised in such a way that the temperature difference between the surface of the wood and its interior does not exceed 30 ° C. Generally, the temperature difference is maintained at a level of 10-30 ° C. This embodiment can be realized in such a way that at least two sensors are arranged on a test piece, one of which measures the internal temperature of the wood and the surface temperature of the other wood. When drying large quantities of wood products, prov your test pieces should be equipped with sensors. On an industrial scale, a heating program for each group of wood products can be determined, taking into account the potential of the starting moisture in the process.

After drying, the impregnated and dried products are subjected to a heat treatment, which is carried out at a temperature of over 100 ° C, preferably of about 100 - 200 ° C.

When the scar is used for plasticizing wood, you can use the heat in the wood generated during drying. If the wood has cooled down after drying, it must be reheated to a temperature above 50 ° C, preferably below 150 ° C, e.g. to about 50 - 100 ° C or up to 120 ° C. The warm-up time is between a couple of minutes and a few hours. The treatment time depends on the thickness of the piece and on the amount of impregnation solution, usually a 30 - 90 minute treatment is enough, but even shorter or longer times are possible. According to a preferred embodiment, the heat treatment is performed by steaming under normal pressure. The wood containing modifying ceramics is then plasticized by the action of heat, whereby it can be bent into the desired shape and / or compressed. The bending of the wood after the impregnation and heat treatment is considerable.

After shaping the wood, the modifying chemicals are bound to the wood product, for example in an incubator, at a temperature of at least 150 ° C, usually about 150 - 200 ° C, preferably about 170 - 180 ° C. The time for the heat treatment is typically between about 10 minutes. and 3 hours; depending on the thickness of the piece of wood and the amount of impregnation solution, longer or shorter times can also be used. During the heat treatment, volatile constituents evaporate, which initiates crosslinking reactions in the wood.

The binding can also be performed directly on a dried wood product, e.g. in a thermocompressor or a heat press at temperatures above 100 ° C. The pieces can also be compressed in the press.

Based on our tests, significant benefits are achieved with the present invention. Thus, the specimens become completely colored and considerably harder on the surface. The treatment also reduces the swelling of the wood and improves its stability against rot. The wood has no internal cracks.

In the following, the invention is described in more detail by means of some application examples. Examples 1 - 3 describe a situation where the test pieces are immediately after the impregnation subjected to a heat treatment at a temperature of 150 ° C without intermediate drying. Then the substance seeps out and internal cracks form in the pieces. The ASE values for reduced swelling are poor. Examples 4 and 5 describe a situation where the specimens are dried until they have a moisture content of less than 20% before the bonding takes place at a high temperature; the substance does not leak out.

Example 1 (comparison) When pine pine specimens (size: 20 mm x 20 mm x 360 mm) were impregnated with a 40% MG solution, the amount of active sleeve absorbed was 260 kg / m 3. The ASE value for reduced swelling in the tangential direction amounted to 40% after a two-day immersion in water, and in the radial flow to 42% compared with a control piece saturated with water.

Example 2 (comparison) The absorption of specimens vacuum-impregnated with a 40% MG solution was 130 kg / m 3. The swelling in the radial flow decreased by 18% compared with an untreated sample.

Example 3 (comparison) Wood pieces of alder and birch with a thickness of 20 - 23 mm, a width of about 50 mm and a length of about 1 m were impregnated with a 30% mixture of maleic anhydride and glycerol. The specimens were cured in a heat press at a temperature of 160 ° C and compressed by about 20%. The compression was about 18.5 mm thick. Cracks formed in about 70% of the compressed pieces of wood during the initial stage of steaming and the substance leaked out. 10 4 20 25 509 068 Example 4 Samples (25 x 100 x 500 mm) of pine and birch were impregnated with MG solutions with different concentrations of 20, 30 and 40% in amounts of 100 - 300 kg of active substance per cubic meter. After impregnation, the specimens were dried at a temperature of 70 ° C for 2 to 7 days before the maleic acid was bound to the wood at a temperature of 160 ° C (treatment time: 2 hours). After immersion in water for 24 hours, the tangential swelling (ASE) of the birch pieces decreased by 81 to 96% and the radial by 80 to 94%.

The amount of water absorbed decreased by 70 to 95% compared to an untreated piece. The ASE swelling of the pine pieces amounted to 70 - 87% in the tangential direction.

The amount of water absorbed decreased by 37 - 88% compared to untreated wood.

The pieces of wood treated in the above-mentioned manner are suitable for use in wet areas indoors and outdoors, for example in bathrooms.

Example 5 The intermediate dried pieces of Example 4 were compressed by about 20% in a heat press at a temperature of 160 ° C. No substance leaked out of the specimens and no cracks could be observed to have occurred in it. The specimens were placed in water for 24 hours. The thickness swelling of the birch pieces amounted to 1.2 - 1.6% and the swelling of the width to 0.5 - 1.1%.

The thickness swelling of the pine pieces amounted to 1.4 - 3.8% and the swelling of the width to 1.2 - 3.6%. The untreated compressed control pieces almost completely regained their original dimensions or a one-day irrigation. The brinell hardness of the birch and pine pieces was 5 - 10.

Due to the intermediate drying, no active substance leaked out during the compaction. A sufficient amount of the substance is thus retained and the compression is not canceled even in wet conditions.

Claims (15)

10 15 20 25 30 509 068 Patent claims: A method for binding modifying chemicals to solid wood products and to prevent internal cracking in them, characterized by a combination of the following steps: i - the wood products are treated with the modifying chemicals, - after the treatment the wood products are dried at a temperature below 100 ° C, until their fi content is lower than 20%, and - the wood products treated and dried with the modifying chemicals are subjected to a heat treatment carried out at a temperature of over 100 ° C to bind the modifying chemicals to the wood. Method according to claim 1, characterized in that pieces of wood which are large enough to be used, e.g. in furniture. 3. A method according to claim 1 or 2, characterized in that the wood products are treated with solution-based chemicals, which can form ester bonds with the OH groups of the wood. Process according to one of the preceding claims, characterized in that an aqueous solution of maleic acid and glycerol is used as the modifying chemical. Process according to claim 4, characterized in that the aqueous solution of maleic acid and glycerol is prepared by forming a 1:10 - 10: 1 mixture of maleic anhydride and glycerol, which is dissolved in water to form a solution with a concentration of 1 - 99%. Process according to Claim 5, characterized in that an aqueous solution of maleic anhydride and glycerol is formed, the concentration of which is about 20 to 60% by weight and which has a weight ratio of maleic anhydride to glycerol of about 1: 5 to 5: 1. Process according to one of Claims 4 to 6, characterized in that the wood substance is impregnated with at least about 20 kg, preferably with about 25 to 300 kg and particularly preferably with about 30 to 140 kg of the mixture of maleic acid and glycerol per cubic meter of wood. 10 15 20 25 509 068 9 Process according to Claim 1, characterized in that succinic anhydride or phthalic anhydride is used as modification chemicals. Process according to one of the preceding claims, characterized in that the pre-drying is carried out at a temperature of about 20 - 99 ° C. 10. A method according to any one of the preceding claims, characterized in that the difference between the temperatures in the interior of the wood and on its outer surface is kept at a level of less than 30 ° C during pre-drying. Method according to claim 10, characterized in that the temperatures in the inner parts of the wood and on the outer surface of the wood are measured continuously and the temperature for the treatment is adjusted so that the difference between the inner and the outer temperature amounts to about 10 30 ° C. Method according to one of the preceding claims, characterized in that the dried wood product is subjected to a heat treatment carried out at a temperature of 100 - 200 ° C. 13. A method according to claim 12, characterized in that the wood product is heat treated in a heat press. 14. A method according to any one of the preceding claims, characterized in that the wood product is subjected to a heat treatment at a temperature of about 50 - 150 ° C before the heat treatment for bonding the modification chemicals to plasticize the wood product for shaping. 15. A method according to claim 14, characterized in that the shaped wood product is subjected to a heat treatment at a temperature of over 150 ° C in order to harden at least on the surface.