FI91503C - Process for plasticizing wood in particular for processing thereof - Google Patents

Description

91503

The method of softening the wood, especially for design purposes

The present invention relates to a method for softening wood according to the preamble 5 of claim 1, in particular for shaping.

The invention also relates to shaped wood products and to a method for manufacturing such products.

10

In the furniture industry, there is a need for methods by which pieces of wood blanks can be made into the desired shape, which can be used, for example, as components for furniture. In addition to traditional working methods, the wood raw material has long been formed by bending and pressing processes. By these methods, the wood must first be given a soft and plastic feel. According to the prior art, the wood raw material is then impregnated with hot water and / or treated with hot water vapor. However, hot water and steam solutions require long processing times and the shape achieved is not always permanent, for example in a water immersion test.

Softening of wood has also been tried with ammonia treatments. Anhydrous, liquid ammonia or aqueous ammonia is then impregnated into the starting material. Ammonia that has penetrated the wood breaks the hydrogen bonds that are responsible for the natural stiffness of the wood. The wood softens and can be subjected to bending and compression treatments as long as there is ammonia in the fibrous structure.

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The advantage of ammonia treatment is that the rigid basic structure of the wood is restored after the evaporation of the ammonia, whereby a dimensionally stable (i.e. shape-stable) product is obtained, which is especially important in terms of product use in the wood industry. strength.

However, there are some major drawbacks to this prior art. Thus, ammonia has a low boiling point of 2 91503, which adds to the need for cooling and liquefaction equipment required in the process. In addition, it should be noted that ammonia is toxic, which is why it must always be handled with some care.

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In addition to water and ammonia, the use of certain other chemicals to soften wood is also known from the patent literature.

FI patent publication 43008 describes a method for plasticizing wood for shaping, in which method hydrazine is absorbed into the wood and excess hydrazine is removed and recovered during or after the shaping of the wood. After hydrazine absorption, the wood is heated to provide formability. After shaping, a second heat treatment is carried out to remove volatiles and harden the wood. The main disadvantage of this method is that hydrazine is a class I toxin with very toxic fumes. In addition, it has been found that hydrazine-treated wood swells in water immersion like ordinary wood, 20 albeit more slowly. Hydrazine absorption and the subsequent pressing and heat treatment darken the color of the wood.

With regard to the prior art, it should also be noted that chemical methods have also been used to improve the dimensional stability of wood.

JP-A-89,182,002 and 89,226,302 describe the use of a maleic acid-glycerol mixture to improve the dimensional stability of plywood sheets. According to these publications, the surface of the 30 thin veneer layers is treated with the former. . * with the mixture, the veneer is then fixed to the surface of the plywood, heated to a temperature of 170 to 210 ° C and finally the plywood is heat pressed at about 200 ° C to form a laminate. The plywood board produced in this way has a good surface hardness.

35 The JP application publications do not deal at all with the design of massive * · pieces of wood, and the technique described therein 3 91503 is not suitable for softening wood. In our experiments carried out in connection with the present invention, we have seen that in a heat treatment carried out according to the prior art at a temperature of 170 to 210 ° C, the wood does not soften but, on the contrary, hardens.

The object of the present invention is to obviate the drawbacks associated with the prior art and to provide a completely new method, in particular for softening solid wood 10 for shaping.

We have now surprisingly been able to find that by impregnating the wood raw material at least substantially deeper than the surface with a mixture of maleic acid and glycerol, and subjecting the impregnated body to a heat treatment with a substantially lower .

More specifically, the method according to the invention for softening wood is mainly characterized by what is stated in the characterizing part of claim 1.

The product, in turn, is characterized by what is stated in the characterizing part of claim 9.

The method according to the invention for producing shaped wood products from wood raw material is characterized by what is set forth in the characterizing part of claim 10.

• The term "shaped wood product" according to the present invention means a product made of wood which has first been at least partially placed in a moldable or plastic state. Usually, in this state, the product is shaped into the desired shape, after which the product is allowed to cure at least on its surface to be dimensionally stable. For the purposes of this application, "shaping product" also means products which have not been deformed during processing but whose shape stability and in particular their surface hardness have been improved. This can be done by softening, in particular, the surface of the body according to the invention with a maleic acid / glycerol mixture and a heat treatment, after which the surface is allowed to dry and cure with or without a pressure treatment.

By "solid wood product" in this application is meant that the product to be manufactured has at least a moderate thickness, usually greater than about 5 mm.

The wood product can then be a solid (solid) piece of wood made of solid wood or it can comprise a layered product formed from wood veneers or chips, e.g. by pressing (e.g. chipboard or fibreboard). The wood product 15 may also consist of a structure in which uniform layers of wood are adhered together to form a laminate. In the latter cases, a solid wood product means a layered or laminate product which can be impregnated either before or after it is formed into a product.

In the context of the present invention, it has been found that the softening of wood by a mixture of maleic acid and glycerol involves several reactions. Maleic acid reacts with the primary and secondary hydroxyl groups of cellulose to form ester bonds. The esterification reaction then takes place mainly between wood, maleic acid and glycerol. Other reactions include crosslinking by the addition of radicals to the double bond of the maleic acid residue or the formation of ether bonds between hydroxyl groups.

Based on the above, the wood product of the invention contains at least some ester compounds whose acid moieties consist essentially of maleic acid and the alcohol moieties of glycerol, cellulose, hemicellulose or lignin, or combinations thereof.

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The method according to the invention provides wood products with good dimensional stability. In fact, the dimensional stability of the products is often better than that of the wood raw material due to crosslinking, esterification of the hydroxyl-5 groups of the cellulose and swelling of the wood when the maleic acid molecule replaces the hydroxyl groups.

According to a preferred embodiment of the invention, a mixture of maleic acid and glycerol is prepared from maleic anhydride and glycerol. Preferably, these substances are mixed with water, whereby the maleic anhydride is hydrolyzed in aqueous solution to maleic acid.

According to a preferred embodiment of the invention, an aqueous 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 raw 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 varies depending on the application of the wood product and the wood raw material (wood species, wood density and wood moisture). According to the invention, so much solution is always absorbed into the wood as to allow it to penetrate substantially deeper than the surface of the wood product. From the point of view of mechanical shaping, it is important to see that the wood product is also as soft as possible. Thus, 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 preferably absorbed per cubic meter. In connection with the absorption, the moisture content of the wood is preferably kept at a value of 5 to 30%, particularly preferably at a value of about 6 to 7%.

35 According to a particularly preferred method, the impregnation is carried out by removing air from the wood material in a vacuum vessel: · first, air is introduced into the vessel, after which the liquid 6 91503 to be impregnated is fed into the vessel and allowed to soak Alternatively, the wood material is immersed in the impregnation solution for such a time that the solution has time to be absorbed deep into the wood (immersion-5 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.

After impregnation, the wood is heated to a temperature of less than 150 ° C, e.g. at a temperature of about 80 ... 120 ° C. The heating time is typically from a few minutes to a few hours. Usually a treatment of about 30 ... 90 minutes is sufficient. According to a preferred embodiment, the heat treatment is carried out by evaporation at normal atmospheric pressure.

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The impregnation treatment and the heat soften the wood, allowing it to be bent into the desired shape and / or compressed. The bending of the wood after the impregnation-heat treatment is considerable.

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Any equipment known per se can be used for bending.

After bending, the wood is cured, for example in an oven 25 at at least about 150 ° C, usually at about 150 to 200 ° C, preferably at about 170 to 180 ° C. The post-curing time is typically about 10 minutes to 3 hours. During the heat treatment, the volatile components evaporate, which promotes cross-linking reactions in wood.

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Within the scope of the invention, the heat treatment after impregnation and the shaping step of the wood material can be at least partially combined, e.g. by bending the impregnated piece of wood into a rim at the same time as it is treated with hot steam.

Correspondingly, the shaping step and the curing step can be performed simultaneously by compressing the wood, for example in a heat press, whereby it dries at the same time. The density of the wood increases when compressed, which also increases its hardness considerably.

The invention has considerable advantages. Thus, in a preferred embodiment of the invention, the substance used, a mixture of maleic anhydride and glycerol, is water-soluble. No harmful chemical substances are released in the process or during the treatment, as water is released in the reaction and the tools can be washed with water. Treatment of wood with a mixture of maleic acid-10 acid and glycerol improves the dimensional stability of the products. In water immersion, the dimensions of the products change somewhat, but when dried, the wood almost returns to its former shape. From hardened wood, the substance is insoluble in water. The treated wood also does not crack in immersion-drying cycles, nor does it crack under cracks, as in normal bending. The effect of humidity changes on wood living is diminishing.

The structure can be easily bent by breaking it open transversely from the compression side.

20 Treatment changes the color of the wood. The color change varies depending on the amount of absorbent, heating temperature and heating time.

The wood can thus be made to resemble, for example, hardwood. The method according to the invention makes it possible to treat all the usual types of wood used in the furniture industry. Of the domestic raw materials, spruce, pine and birch are mentioned in particular.

The invention will now be considered in more detail by means of a few non-limiting application examples.

Example 1 300 g of maleic anhydride and 100 g of glycerol were weighed into a beaker and mixed with each other. The decanter glass was covered with aluminum foil, after which it was placed in a water bath where it was heated at 100 ° C to melt the mixture. The melt was stirred and heated until it turned into a homogeneous brown-yellowish solution. The solution was heated for an additional 30 minutes, after which it was poured into 600 mL of water to prepare a 40% MG (maleic acid-glycerol) solution.

Example 2 10 Birch pieces measuring 60 cm (length) x 5 cm (width) x 2 cm (thickness) (humidity 6-7%) were impregnated with 40% of the maleic anhydride and glycerol (MG) prepared in Example 1. from a mixture with a mixture ratio of 3: 1.

A good softening effect was obtained by absorbing 120 kg of 15 (amount of active ingredient) of said solution per cubic meter of wood.

The absorbed specimens were steamed for 40-60 minutes.

The specimens were manually bent into an arc or circle with a diameter of 16 cm or 18 cm, respectively. One specimen 20 was bent longitudinally. For comparison, the test piece was impregnated with water and steamed for 40 minutes and bent into an arc. The test pieces were then cured in a mold placed in a larnpo cabinet at 180 ° C for 2 hours.

In the comparative experiment, the birch pieces were treated with hot water in a manner known per se.

The results obtained were influenced by the amount of maleic anhydride-glycerol mixture absorbed. The width of the water-saturated arc 30 changed in the 7-day water immersion test by 4.7% and the width of the arc saturated with a mixture of maleic anhydride and glycerol (MG) by 2.1%. The width of the circles changed by 3%. The changes in thickness were 7% for the water-saturated arc and 6% for the MG-saturated arc, respectively. The thickness of the second 35 specimens bent into a circle increased by 2% and the second decreased by 2%.

The thickness of the longitudinally bent specimen changed by 4% and the width by 1% after 5 days of immersion.

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The water-saturated arc corrected 53% in the 7-day immersion test. The arc treated with MG was 21% correct. The diameter of the circles increased by 11%. The curvature of the specimen 5 bent longitudinally changed by 1.1% after the 5-day immersion test.

After drying following the immersion test, the treated test pieces returned to almost their former dimensions. The arc impregnated with water had elongated 40% of its original length-10, while the arc impregnated with MG corrected only 1%.

The radii of the circles decreased by 1.5 - 4%. The curvature of the specimen bent longitudinally had increased by 1.6% after drying.

Example 2 Pine, spruce and birch pieces were treated with a 40% aqueous solution of maleic anhydride and glycerol. The MG solution was impregnated into the test specimens either by immersion or by pressure cooling. The test pieces were pressed in a heat press at 180 ° C. The hardness of birch pieces treated with MG increased by 35-44% when the amount of 40% MG was 109-457 kg / m3. The MG treatment increased the hardness of spruce by 0 to 31% according to the amount of absorbed MG.

25 The treatment reduced the life of the tree. The tangential Turpo-ama decreased by 40% in pine, 72% in spruce and 87% in birch and the radial swelling in 42% in spruce, 58% in spruce and 60% in birch compared to an untreated or water-saturated control sample.

Example 3 33 Birch bodies were impregnated with 40% MG solution. Two specimens were placed side by side in a press and ♦ 10 91503 of each specimen. The product was a profile reminiscent of a threshold.

In the water immersion test, the change in thickness 5 of the compressed site above 50% was about 22% and the change in thickness at the site compressed by 24% was 8%. During the drying following immersion, no cracks formed in the test piece. Upon drying, the thickness of the compressed test piece was completely restored by 24% and 61% of the compressed site had a thickness change of 6% compared to the initial situation.

Within the framework of the invention, it is also possible to think of solutions that differ from the practical embodiments presented above.

Thus, the annealing and bending steps 1 can be combined and performed at least partially simultaneously. An example is the bending of an impregnated piece of wood into a rim at the same time as it is treated with steam.

As mentioned above, the method 20 according to the invention makes it possible to produce not only bent wooden parts but also laminate structures, veneer and chipboard. In these cases, the small pieces of wood are soaked as above and compressed into the desired piece. If necessary, the pressing and gluing steps can be combined into the same work step.

Claims (14)

1. A process for plasticizing wood in particular for processing thereof, characterized in that the solid wood product to be treated is applied to the surface and at least substantially under it a mixture of maleic acid and glycerol, and then the product is subjected to a heat treatment. at a temperature of not more than about 150 ° C. 2. A process according to claim 1, characterized by using an aqueous solution of maleic acid and glycerol. Process according to claim 2, characterized in that the aqueous solution of maleic acid and glycerol is prepared by forming a mixture of maleic anhydride and glycerol in a ratio of 1:10 - 10: 1 and dissolving said mixture in water to form a solution with a concentration of 1 - 99%. 4. Method according to claim 3, characterized ·. of forming such aqueous solution of maleic anhydride and glycerol, our concentration amounts to about 20-60% by weight and exhibits a weight ratio of maleic anhydride to glycerol of about 1: 5 to 5: 1. 5. A process according to claim 1, characterized in that the raw material is impregnated per cubic meter with at least 20 kg, preferably about 25 - 300 kg and in particular with about 30 - 140 kg of the maleic acid / glycerol mixture. A method according to claim 1, characterized in that the impregnation is carried out by the vacuum pressure method. Process according to claim 1, characterized in that the heat treatment is carried out at a temperature of about 80 ... 120 ° C. 10 8. A method according to claim 7, characterized in that the heat treatment is carried out by steam treatment at normal air pressure. 9. A wood product which is plasticized and formed by the method of claim 1, characterized in that it contains at least a certain amount of ester compounds of the spring acid parts consisting essentially of maleic acid and the alcoholic parts of glycerol, cellulose, hemicellulose or lignin or combinations thereof. A process for making solid wood raw material shaped moldings, characterized by a combination of prior treatment steps: (a) the wood raw material used is impregnated on the surface and below it with a quantity of at least about 20 kg of an aqueous solution of maleic acid and glycerol; spring concentration is about 20-60% by weight and exhibiting a weight ratio of maleic acid to glycerol of about 1: 5 - 5: 1, bC) the impregnated wood material was subjected to a temperature of about 80 ... 120 ° C. c) the plasticized wood material is mechanically machined to the desired shape and d) the wood material processed to the desired shape is subjected to a heat treatment at a temperature of at least about 150 ° C to harden the material at least on the surface. . 91503 11. A method according to claim 10, characterized in that steps (b) and (c) are performed at least partially simultaneously. 12. A method according to claim 11, characterized in that the impregnated wooden piece is bent into a band simultaneously as it is treated with water vapor. The method of claim 10, characterized in that steps (c) and (d) are performed at least partially simultaneously, e.g. in a heat press. 14. A method according to claim 10, characterized in that plasticized cloth chips or veneers are formed into layered structures.