FI96930C - Method for fixing modification chemicals and preventing internal cracks in wood pieces - Google Patents

Description

96930

The invention relates to a method according to the preamble of claim 1 for attaching modifying chemicals and preventing internal cracks in wood pieces which are treated at elevated temperatures. The pieces of wood to be treated are massive and large enough for practical needs, e.g. for use in furniture.

10 Softening wood products with modification chemicals, e.g. for shaping, represents a known technique. Traditionally, water and ammonia have been used as plasticizing chemicals, but other chemicals suitable for this purpose are known from the patent application. Thus, FI patent publication 43008 describes a method for plasticizing wood in which hydrazine is used, while the solution according to FI patent publication 15 91503 uses aqueous mixtures of maleic acid.

Immediately after the impregnation treatment in the liquid phase, the modifying chemicals are usually attached to the wood either by heat or by heat and pressure.

20 There are some drawbacks to the prior art. Thus, depending on the concentration (%) of the starting material, a considerable amount of solvent is also absorbed into the wood. If the modification chemical is attached at a high temperature, the modifier will easily come out together with the solvent. In this case, the desired reduction in life and an increase in surface hardness are not achieved. The large temperature difference between the inner and outer surface causes the wood to crack in the pieces to be used. With small specimens, the phenomenon hardly occurs and the problem is not recognized.

. The object of the invention is to eliminate the drawbacks of the prior art and to provide a completely new method for treating wood, by means of which method the modification chemicals can be removed from the wood during the high temperature reaction and at the same time internal cracks can be prevented.

The invention is based on the idea that, before the heat treatment to fix the modifier, the wood product treated with the modifying chemicals is dried so that it does not crack during curing and that no modifying chemicals can escape from it. In particular, the wood product is dried at a temperature below 100 ° C to a moisture content of less than 20%.

More specifically, the method according to the invention is mainly characterized by what is set forth in the characterizing part of claim 1.

The solution according to the invention is suitable for all solvent-based, in particular water-soluble, modifying chemicals which must be applied to wood at an elevated temperature. Typically, ester bonds are formed between the modifying chemicals and the OH groups of the wood upon heat treatment. Among the modifying chemicals, mention may be made of maleic acid and maleic anhydride and maleic acid, which are used in aqueous solution, optionally with glycerol. With maleic acid and maleic anhydride, wood can be softened for shaping (see the above-mentioned FI patent publication 91503). Other examples of modifiers are succinic anhydride and the corresponding acid suitable for thermoplasticization of wood, as well as phthalic anhydride and the corresponding acid.

According to the present invention, a "wood product to be treated" means a wood product whose shape or properties are to be altered. A wood product is desired e.g.

20 is placed in a moldable or plastic state to shape it, or the wood is treated to improve its dimensional stability and in particular its surface hardness. Typically, the product to be treated according to the invention has at least a moderate thickness, usually greater than about 5 mm (= solid piece of wood). It may be a unitary piece of wood made of solid wood, but it may also comprise a layered product (e.g. chipboard or fibreboard) formed from wood veneers or chips, e.g. The wood product may also consist of a structure in which continuous layers of wood are attached to each other to form a laminate. In the latter case, a wood product means a layered or laminate product which can be impregnated either before or after being formed into a product.

In the following, the invention will be described in more detail, using maleic acid and maleic anhydride as examples. It is clear that the method - modified accordingly - can be used for other modification chemicals as well.

30 3 96930

The method according to the invention comprises three steps, the treatment of the wood pieces with a modifying chemical, their drying and their heat treatment (attachment of the modifying chemicals to the wood by means of heat).

In the first step, the pieces of wood are typically impregnated with an aqueous solution of maleic acid or maleic anhydride. Preferably, the treatment agent also contains glycerol. Such a mixture is preferably prepared from maleic anhydride and glycerol. The substances are mixed with water, whereby maleic anhydride is hydrolyzed in aqueous solution to maleic acid. Most preferably, a water-10 solution of maleic acid and glycerol having a concentration of 1 to 99% and a weight ratio of maleic acid to glycerol of 1:10 to 10: 1 is impregnated into the wood starting material. Preferably, a moderately concentrated aqueous solution having a concentration of about 20 to 60% by weight and a weight ratio of maleic acid to glycerol of about 1: 5 to 5: 1 is used. The amount of solution to be absorbed into the wood product varies depending on the application of the wood product and the wood raw material (wood species, wood density and wood moisture). Usually, so much solution is always absorbed into the wood that this can penetrate substantially deeper than the surface of the wood product. From the point of view of mechanical design treatment, it is important that the wood product is also as soft as possible on the inside. Thus, preferably at least about 20 kg, preferably about 25 to 300 kg and particularly preferably about 30 to 140 kg of a mixture of maleic anhydride and glycerol are absorbed per cubic meter. The moisture content of the wood to be impregnated is preferably kept at 5 to 30%, particularly preferably at about 6 to 7%.

* ·

The impregnation can be carried out by first removing air from the wood in a vacuum vessel, after which the liquid to be impregnated is fed into the vessel and allowed to soak at normal pressure or possibly overpressure (so-called vacuum pressure method).

v: Alternatively, the wood is immersed in the impregnation solution for a time until the solution has time to reach. absorbed deep into the wood (immersion method). When it is desired to apply the maleic acid / glycerol solution to the surface layer of the wood alone, the impregnation can also be performed as a surface brush.

.30

After the modification chemical treatment, the wood product is slowly dried at low temperature. in a state where the solvent is removed leaving the active chemical in the wood. Drying is continued until the moisture content of the wood product is at least less than 20%, preferably even less than 15-17%.

4,96930

Drying can be performed at room temperature, but it is preferred to perform it at an elevated temperature below 100 ° C. Preferably the drying is carried out at a temperature of 20 to 99 ° C, particularly preferably at 30 to 95 ° C. For the heat treatment, any device known per se, a drying oven, an oven, etc. can be used, with which the wood cabinet can be dried in the presence or absence of water vapor.

According to a preferred alternative, the drying of the wood product treated with the modification chemical takes place in such a way that the temperatures of the inner part of the wood product and the outer surface of the wood are determined continuously and their difference is also kept reasonably small. Most preferably, said temperature difference is at most about 30 ° C. By "internal temperature" of a wood is meant the temperature that prevails in the wood at some distance from the outer surfaces 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. "Outdoor temperature" means the temperature on or slightly below the surface of the wood. Thus, the "outdoor temperature" in many cases substantially corresponds to the ambient temperature. The temperature is gradually raised so that the thermal space difference between the surface of the wood and the inside cannot increase by more than 30 ° C. Preferably, the temperature difference is kept between 10 and 30 ° C. This solution can be implemented by fitting at least two sensors to the test piece, one measuring the internal temperature of the wood and the other the surface temperature. When drying larger quantities of timber, there are 20 reasons to equip several test specimens with sensors. On an industrial scale, it is advantageous to operate in such a way that, on the basis of the measurement results, a suitable heating program is determined for each timber, which takes into account the effect of the initial moisture on the process.

After drying, the impregnated and pre-dried wood products are subjected to a heat treatment above 100 ° C, preferably at about 100 to 200 ° C.

·. When the substance is used to soften wood, the heat generated in the wood during drying can be utilized. If the wood has cooled after drying, it must be heated above 50 ° C, preferably below 150 ° C, e.g. at a temperature of about 50 ... 100 ° C or even 30 120 ° C. The heating time is typically from a few minutes to another hour of earth. The treatment time varies depending on the thickness of the body to be treated and the amount of absorption, usually about 30 to 90 minutes of treatment are sufficient, but shorter and longer times are also possible. According to a preferred embodiment, the heat treatment is carried out by evaporation at normal atmospheric pressure. The wood containing the modifying chemical is then softened by heat, so that it can be bent into the desired shape and / or compressed. The bending of the wood after the impregnation-heat treatment is considerable.

5

After molding, the modifying chemicals are then attached to the wood product, for example, in an oven at at least about 150 ° C, usually at about 150 to 200 ° C, preferably at about 170 to 180 ° C. The heat treatment time is typically about 10 min ... 3 h; depending on the thickness of the piece of wood and the amount of absorption, longer or even shorter times can be used. During heat treatment, the volatile constituents evaporate, which promotes crosslinking reactions in wood.

However, the attachment can also be carried out directly on the dried wood product, e.g. in a heat press at a temperature above 100 ° C. In the press, the pieces can also be pressed into a pile.

Based on our experiments, the invention achieves considerable advantages. Thus, the treated specimens are penetrated and their surface hardness is significantly increased. The treatment also reduces the life of the wood and improves rot resistance. There are no 20 internal cracks in the wood.

. : In the following, the invention will be examined in more detail with the help of a few application examples.

25 Examples 1-3 illustrate a situation in which the test pieces have been heat-treated at a temperature of more than 150 ° C immediately after impregnation without intermediate drying. In this case, the substance bursts out and there are internal cracks in the pieces. ASE values, which describe a decrease in life, are poor. Examples 4 and 5 illustrate a situation where specimens are dried to less than 20% humidity before adherence at a higher temperature, with no substance exuding.

6 96930

Example 1 (comparison)

When the pine test specimens (size 20 mm x 20 mm x 360 mm) were impregnated with 40% MG solution, the amount of active substance absorbed was 260 kg / m3. In this case, the reduction in survival after two days of 5 water soaking was 40% in the tangent direction and 42% in the radial direction compared to the water-saturated control sample.

Example 2 (comparison) The absorbance of test pieces vacuum impregnated with 40% MG solution was 130 kg / m 3.

Radial swelling was of the same order as for water-saturated samples. Tangential swelling was reduced by 18% compared to the untreated sample.

15 Example 3 (comparison)

Alder and birch pieces 20-23 mm thick, about 50 mm wide and about 1 m long were impregnated with a 30% maleic anhydride-glycerol mixture. The test pieces were cured in a heat press at 160 ° C and at the same time pressed into a pile of about 20%. t 20 After pressing, the thickness of the test pieces was about 18.5 mm. About 70% of the compressed trees cracked at the beginning of evaporation and the substance erupted.

'· <• «• I -

Example 4 Pine and birch pieces with a size of 25x100x500 mm were impregnated with 20, 30 and 40 '> ♦:% MG solution, the amount of active ingredient being 100-300 kg / m 3. After soaking, the test pieces were dried at 70 ° C for 2 to 7 days before the addition of maleic acid at 160 ° C (duration of treatment 2 h). After 1 day of water soaking, tangential swelling (ASE) in birch bodies was reduced by 81–96% and radial swelling by 80–94%. The amount of water absorbed was reduced by 70-95% compared to the untreated sample. The ASE of pine bodies was 70–87% in tangential swelling and 70–85% in radial swelling. The amount of water absorbed was reduced by 37 to 88% compared to untreated wood.

7 96930

Pieces of wood treated as described above are suitable for use in damp rooms, outdoors and indoors, e.g. in bathrooms.

Example 5 5

The intermediate dried pieces in Example 4 were pressed into a pile at about 20% in a heat press at 160 ° C. No material erupted from the specimens and there were no internal cracks. The test pieces were immersed in water for 1 day. The thickness swelling of the birch pieces was 1.2 to 1.6% and the width swelling 0.5 to 1.1%. The thickness swelling of the pine pieces was 1.4 10 to 3.8% and the width swelling 1.2 to 3.6. %. Untreated punched control pieces return to almost their former dimensions after 1 day of water soaking. The Brinell hardness of the birch and pine pieces was 5 to 10.

Thanks to the intermediate drying, the active ingredient does not erupt during compression, so that there is enough of it, and the compression does not recover even in humid conditions.

»« • ·

Claims (14)

1. A process for attaching modifiers to solid wood products and to prevent internal cracking therein, characterized by the combination of the following treatment steps: temperature of below 100 ° C until their humidity is below 20%, and 10. the modified and dried wood products treated with modification chemicals are subjected to a heat treatment performed at a temperature above 100 ° C, to attach modification chemicals to the wood. 2. A method according to claim 1, characterized in that wood pieces are sufficiently large to handle e.g. used in furniture. Process according to claim 1, characterized in that as a modifying chemical an aqueous solution of maleic acid and glycerol is used. 20 Process according to claim 3, 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%. 25 Process according to claim 4, 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. . 30 Method according to any of claims 3-5, characterized in that the wood substance is impregnated with at least about 20 kg per cubic meter, preferably with about 25 - 300 kg and best with about 30 - 140 kg with a mixture of maleic acid and glycerol. ii - ii fiiii mm -1 96930 Process according to claim 1, characterized by reduced succinic anhydride or phthalic anhydride used as modifying chemicals. Process according to any of the preceding claims, characterized in that the desiccation is carried out at a temperature of about 20 ... 99 ° C. 9. A method according to any of the preceding claims, characterized in that the difference between the measured temperatures between the interior of the wood and corresponding to its exterior is poured less than 30 ° C during the pre-drying. 10 Method according to claim 9, characterized by the reduced temperatures in the interior of the wood and correspondingly the exterior of the wood are determined continuously and the temperature of the treatment is adjusted so that the difference between the internal and the external temperature rises to about 10-30 ° C. 15 Process according to any of the preceding claims, characterized in that the dried wood product is subjected to a heat treatment performed at a temperature of 100 - 200 ° C. 20 Method according to claim 11, characterized in that the wood product is heat treated in a heat press. Process according to any of the preceding claims, characterized in that the wood product is subjected to the heat treatment, which aims to attach the modifying chemicals, to a heat treatment at a temperature of about 50-150 ° C to plasticize the wood product for molding. Process according to Claim 13, characterized in that the treated wood product is subjected to a heat treatment at a temperature above 150 ° C to harden at least on the surface.