NO309075B1 - Form body of impregnated wood, method of manufacture and use thereof - Google Patents

Abstract

The invention concerns a shaped body made of wood which is impregnated with a biodegradable polymer and/or solid natural resin or drying (setting) oil. Wax, fats, salts and/or flame-retardants can also be added to the impregnating agent. The shaped body is pre-heated to a temperature of between 100 and 150 DEG C, optionally placed under vacuum, and immersed in a melt of the impregnating composition. The shaped body remains in this melt - preferably at an excess pressure of between 3 and 20 bar, in particular between 8 and 12 bar - for between 15 and 120 minutes, preferably for between 30 and 90 minutes. The shaped body is then removed from the melt and any remaining melt is eliminated from the surface of the shaped body which is finally cooled.

Description

The present invention relates to a molded body of impregnated wood. Ever since ancient times, wood has been impregnated with various substances, mainly against fungi and insects, in order to reduce water absorption or improve the swelling behaviour, e.g. with tar oil (for bridging wood), paraffin and wax, or with mixtures of montan wax and artificial resin solutions (alkyd resins), whereby however the problem of removing the solvent (e.g. trichlorethylene) from the impregnated wood remains. For the production of bearing discs, wood has also been impregnated with lubricating oil.

This is more successful, particularly for dimensional stabilization and an increase in hardness, with water-soluble phenol or urea-formaldehyde resins. However, these generally only cause a delay, but not a prevention of the swelling, but instead a reduction of the tensile strength. They are therefore usually only used for veneers, which may then be further processed as laminates. In addition, the combination of wood and urea-formaldehyde resin, but also other plastics, leads to duroplastic materials, which after shaping and subsequent cross-linking can no longer be molded thermoplastically, and are also no longer biodegradable and therefore pose a disposal problem.

It has also become known to impregnate veneers with dye and polyethylene or polypropylene glycol, as well as with an aqueous solution of starch, polyvinylpyrrolidone or polyvinyl acetate for the production of colored laminates of glued together individual veneers (JP-A54-117004 or JP-A55-034 931 ), but also the impregnation of only the cut edge of the wood before the veneer planing process with the aim of making the edge firmer, and again with aqueous solutions of starch, gelatin, polyvinyl acetate, sodium alginate, polyvinylpyrrolidone, resol, melamine or urea resin, monomers, such as acrylic or methacrylic acid esters , styrene, vinyl acetate, acrylamide or -nitrole etc. (JP-A54-026317).

Finally, it is also known to impregnate wooden or porous stone materials with an aqueous polyvinyl acetate solution in a vacuum and subsequent application of a small overpressure, whereby wax and/or biocides are optionally added (FR-A2505187).

Other publications also relate to the impregnation of parts of wood with non-biodegradable, polymerisable or cross-linking artificial resins or linseed oil, often from solutions, with the stated disadvantages. These include in particular DE-A1-3942136, FR-A-2647388, JP-A-6071614, JP-54 057 732, W094/11167, US-A-1991752, SU-A1-1701521, JP-A-1174401, SU-A-1288063 and NL-A-23392.

However, all of these methods for the production of impregnated molded bodies from wood have the disadvantage that the removal of the used solvent (also water) is, on the one hand, time- and energy-consuming, and on the other hand, leaves a, albeit to a lesser extent than previously, porous mold body.

The purpose of the present invention is therefore to produce an impregnated, biodegradable molded body of solid wood, the pores of which are largely filled, but which can be produced relatively simply and without special post-processing and which does not have the disadvantages of the usual combinations of wood and plastics in terms of porosity, biodegradability and thermoplasticity. According to the invention, this has been achieved in a surprising way by means of the combination of features stated in the characteristic in claim 1. Particularly advantageous embodiments of the invention are stated in the independent claims.

As a natural resin, a monomer from the group of tall resin, dammar, copal, but also balsam resin or tall oil is used in particular. The oil used is particularly blown (pre-oxidised) linseed oil or Chinese wood oil, possibly with a drying agent (siccative) added. As a fatty acid ester, one used in particular is one that is formed when tallow oil is processed into tallow resin.

For the invention, such polymers, natural resins, oils and fatty acid esters must be selected in particular that are liquid at the loading temperature and preferably do not attack the wood. Particularly preferred are substances which, under the temperature at which the wood is attacked, are relatively low-viscous. A person skilled in the art will choose such a mixture of impregnating agents and any additives, which achieves the desired degree of penetration for impregnating a solid wood component depending on its porosity during the appropriate time, possibly using vacuum and/or pressure. In connection with the invention, the "attack" is to be understood as any undesirable change in the properties, in particular colouring, degradation by chemical reaction, particularly in the case of extreme pH value changes, swelling or shrinkage (if this is undesirable), pore formation etc. It goes without saying that many of the thermoplastic materials used according to the invention may be suitable for impregnating certain types of wood, but not for others. E.g. a little staining may be acceptable for darker types of wood, certain types of wood may be less sensitive to certain pH value changes than others, etc.

In recent years, due to the environmental debate, a number of different, biodegradable materials have been developed on the basis of natural substances and fossil sources, many of which even exhibit a hydrophilic character and as many natural substances, particularly wood, are able to absorb and release water . Corresponding to the relative humidity in the surroundings, these materials contain certain percentages of water and are therefore better suited for the combination than plastic in the usual sense. Their hydrophilic nature makes it easier to penetrate the wood material, whereby the wood's properties are not completely hidden, but only supplemented.

As biodegradable polymers, e.g. the following substances are mentioned: polyhydroxybutyric acids, polycaprolactones, polylactic acids, polyesters based on diols and dicarboxylic acids, polyamides, polyester urethanes, chemically modified natural polymers such as e.g. cellulose acetates.

Other additives, e.g. various fats, oils, waxes, but also lignin or alcohols, especially for the natural resins, oils and fatty acid esters, were used to achieve certain properties in the finished impregnated form body of solid wood, without significantly restricting the thermoplasticity or the biological degradability. In particular, hardened or modified animal or vegetable fat, e.g. hydrogenated vegetable fat, epoxidized oil, wool fat, tallow and salts of various fatty acids, e.g. stearic acid, behenic acid, lauric acid etc. are used.

Finally, different salts can also be used, e.g. phosphates, borates, sulphates, chlorides and silicates as a result of the fact that they can be brought together with the melt into the wood structure. They have a positive effect on the reduction of swelling and shrinking behavior and are also flame retardant and/or fungicidal.

Glycerol is also used as a "solvent", softener or agent to retain moisture. Alkali and alkaline earth resinates function as a drying agent, but also as a wetting agent and emulsifier and thereby promote the penetration of the resins into the wood.

Many of the resins are preferably used in combination with wax and/or a drying oil, which become hard or solid and even brittle at room temperature, but which soften at higher temperatures and preferably then show a significant drop in viscosity, so that processing can take place at temperatures where the wood is not attacked at all or only to a small extent. The brittleness of some of the aforementioned substances is compensated by the fine distribution in the wood matrix.

The viscosity of the impregnating agent should be below 20 dPa at the treatment temperature, more suitably below 10 dPa (the viscosity of glycerol at room temperature), especially below 1 dPa (water has 0.01 dPa at room temperature). While the pores in solid wood are of the order of a few pm, the resins or polymers according to the invention have a size of a few nm. The smaller the molecules, the faster and deeper they penetrate into the wood. At the relevant treatment temperature and duration, the largest, particularly polymeric, particles will only penetrate the uppermost layers of the surface. Precisely that, however, gives the advantage that the surface properties of the shaped body according to the invention, particularly in terms of hardness and optics (e.g. polishing ability) are improved without reducing the thermoplastic formability. Moreover, the diffusion of the smaller molecules at higher temperatures from the interior is effectively prevented.

As growing, preferably growing from nature is used, e.g. carnauba wax, beeswax and montan wax. Waxes exhibit even more favorable processing conditions, such as a generally lower melting temperature and an even greater drop in viscosity when the temperature increases. The combination of wax and resin exhibits good processing and final product properties, due to the fact that the disadvantageous property of cost-effective balsam resin to become sticky at room temperature is compensated by the use of wax. On the other hand, wax alone tends to sweat out at slightly higher application temperatures, which is in turn mitigated by the natural resins present in the mixture.

Linseed oil and Chinese wood oil are before the "drying"

(hardening by polymerisation) already liquid at room temperature, while the viscosity is further lowered by increasing temperature. A linseed oil which has a viscosity of 90 dPa at room temperature exhibits a viscosity drop to 15 dPa at a temperature increase of only 30°C. This low viscosity together with the small molecular size, since it

likewise, first it concerns a monomer, strongly supports the impregnation process. The combination of such an oil with resin enables the production of almost linoleum-like molded bodies in a natural wood matrix. To accelerate the polymerization reaction (drying) of the used oils catalytically, so-called metal soaps based on one or more metals (in combination), particularly cobalt, zinc and manganese resinates, -octoates, are used as drying agents.

-linoleates and -naphthenates.

It was surprising with the combination of biodegradable, partly hydrophilic, thermoplastics and the hydrophilic duroplast wood, that products, molded parts and materials are obtained where the characteristic properties of wood, especially when it comes to water absorption and release, biodegradability, as well as the known, excellent mechanical properties are not lost. The properties of thermoplasticity, better surface and in some cases faster biodegradability were added to the wood. This opens up completely new areas of application for such molded parts.

The swelling and shrinkage of wood is a property that in many cases significantly limits its use, and is reduced by the method according to the invention by at least 50%. Thereby, the extensive processing steps are reduced, e.g. several times of gluing, tongue and groove connections and consideration of expansion joints.

The higher the temperature chosen for the through-impregnation of the solid wood parts, the better the vacuum that can be applied before the impregnation, respectively higher air, gas or steam pressure during or after the impregnation. The more complete the penetration of the wood matrix with the thermoplastic materials takes place all the faster.

A wide variety of wood can be used for the production of the moulds. Whether you work with hard or soft wood, with very thin-walled or stronger wooden parts, depends primarily on the requirements for the end product, e.g. Eucalyptus and poplar wood are used as fast-growing plantation trees primarily for cellulose production or as energy suppliers. Their rapid growth only results in a low total and surface hardness. With the help of the treatment according to the invention, however, these types of wood can also be used for more high-quality applications, e.g. in the floor and window area and thereby replace more expensive and increasingly less available, high-quality natural woods.

A good example of the improvement in the durability of wood is also beech, which with the described melts is easy to load and thereby achieves a significant improvement in durability, stability and resistance to microorganisms.

Wood is by nature only very slightly thermoplastic. The moldings according to the invention are, however, easily accessible for conventional methods of thermoplastic transformation, such as embossing, pressing, bending, forming and the like, such as ordinary plastic components. This thermoplastic transformation goes a long way without destroying the internal wood structure, so that in certain cases even the wood grain is perfectly preserved.

By means of the selection of the type and quantity of the raw materials and any additives as well as the process parameters, such as temperature and pressure, the properties of the shaped body according to the invention can be varied within wide limits. This includes, among other things, the rate of biological degradation, which can even be delayed in relation to wood by using slowly degradable substances. But the specific weight of the molded parts can also be varied over a wide range. This goes from a very small load (density 0.2 t/m<3>), to a fully loaded wooden matrix with approx. 1.5 t/m<3>). An effect that is often desirable, above all with soft wood parts, is the drastic increase of the surface hardness by embedding the substance according to the invention in the wood matrix, so that woods that are naturally soft are also suitable for high-quality floors.

In order to counter the disadvantage of the easy turbidity of the wooden parts which are loaded with resins, waxes and possibly oils, flame retardants are added to the treatment melt, e.g. ammonium phosphate and zinc borate, whereby glycerol can function as a solvent.

A possible method would be complete submersion of the preferably previously evacuated wood part in the molten substance and immediate application of an overpressure, which leads significantly faster to the desired result with complete and even distribution of the thermoplastic substance in the wood matrix. A further improvement of the impregnation method can be achieved by pre-drying the wooden formwork, whereby the liquid substance is also sucked into deeper layers of wood that were previously occupied by water molecules.

The shaped pieces thus obtained can be processed like wood, with the additional property of thermoplastic malleability, although they can still be destroyed as a result of the biological degradability.

A further area of application is open for the finished, possibly thermoplastically modified parts. Any number of examples can be added to the application areas of packaging, furniture manufacturing, flooring, vessel and wood construction, interior development, toys.

Example 1

A 120 mm long, 80 mm wide and 25 mm thick plate of softwood with a density of 420 kg/m<3> was heated to 150°C and immersed in a molten, 150°C hot, low molecular weight polycaprolactone from the company Union Carbide . Depression was practiced for 15 minutes. The slab was then removed from the forge and exposed to a gas pressure of 10 bar in a pressure chamber for 30 minutes to allow the polymeric, biodegradable material to penetrate into the deeper layers of wood. The plate can be shaped continuously at 170°C, whereby water vapor acts as a support.

Example 2

Tall resin ("Sacotan" 85 from the company Krems Chemie, softening temperature 80-85°C) was melted in an open vessel and brought to a temperature of 155°C. In this hot resin melt, parts of wood with a length of 250 mm, a width of 80 mm and a thickness of 15 mm were introduced. This introduction took place in a perforated basket that keeps the individual pieces of wood separate, so that the entire surface of each piece of wood is surrounded by liquid resin, keeps the pieces of wood below the surface of the liquid and extraction of the hot resin melt becomes possible.

After the wooden parts were brought in, as a result of the heating, moisture in the wooden parts began to evaporate and air in them to escape. This process lasted approx. 15 minutes while the temperature of the resin solution was maintained at 150°C. The vessel was then closed and a gas pressure of 9 bar was applied, which should bring the resin into deep layers of wood. After 1 hour of pressure time, the pressure was relieved, and the loaded wooden parts were removed from the resin (125°C) which was still liquid. The amount of resin taken up during this treatment can be determined by weighing the differences.

The resin had distributed homogeneously in the wood matrix. The wood was readily available for the classic woodworking methods. The color changes due to temperature stress and resin penetration (change in light scattering due to filling of voids) of the wood are different depending on the type of wood, but could be determined for each type of wood. The finished wood part (planed) was judged to be slightly sticky.

When bringing in the oven-dried wood which, however, still contained a residual moisture of approx. 10% in the resin melt, a certain foaming was observed which was conditioned by evaporation of the residual water and the expulsion of the excess air, whereby the foaming was not unlike a "frying process" in the food industry. This condition can be reduced or removed completely if, preferably before the wooden parts are immersed in the resin melt, a negative pressure is exerted in the treatment vessel and/or if the wooden parts are preheated.

Example 3

While maintaining the most important test conditions according to example 2, only the wood used was preheated to 150°C before introduction into the resin melt. On the one hand, this causes the wood to dry out, and on the other hand, depending on the temperature, the air in the wood escapes.

The wood pre-treated in this way showed no or only weak foaming, and the pressure vessel could be closed immediately after the introduction of the wood. The fear that this drying could reduce the processing amount of resin could not be confirmed. The determined treatment amounts were almost identical to the amounts in example 2.

Example 4

In order to minimize the discolouration of the wood due to the heat load, a balsam resin was used which begins to soften at 60-65°C and which at 115°C exhibits a low viscosity. The wood was pre-treated for 1 hour at 115°C and introduced into the resin melt of the same temperature. A very short treatment time of just 15 minutes, albeit at a pressure of 15 bar, clearly reduced the discolouration of the wood. The amount of treatment with resin largely corresponded to the data in example 2. Admittedly, it was a bit unpleasant that the resin-laden wooden parts were also a little sticky at room temperature, which is probably connected to the low melting point of the balsam resin.

Example 5

As a negative example of the state of the art, the wooden parts described in example 1 were loaded under similar conditions as in example 2 with exclusively carnauba wax or with a montan wax (melting point 75°C) from the company Schlickum. The melting temperature was 155°C. The wood was pre-dried for 60 minutes at 130°C, and the temperature when the wood was removed was 120°C.

The amount of wax taken up corresponded approximately to the amounts determined for the resin. However, when heating the wax-treated timbers, it was possible from approx. 80°C, an unpleasantly rapid release of the liquid resin from the wood matrix is observed.

Example 6

In order to minimize the lasting disadvantages of the pure wax or pure resin impregnation of the wood, these two materials were combined with each other. Surprisingly, the waxes and resins are infinitely compatible with each other. They form a common, clear melt that has a common softening point. Nor can they be separated from each other upon cooling.

66% tall resin ("Sacotan" 85) and 34% montan wax ("Iscoblend" 207 from the company Schlickum) were melted together and gave a softening temperature of approx. 80°C. The other conditions for treating the wood with this combination corresponded to the conditions stated in the preceding examples. The amount of treatment could be compared with the values stated in the tables in example 2.

The treated timbers thus obtained combined the positive properties of the variants that were treated exclusively with resin or exclusively with wax. The sticky impressions of wood treated with resin alone could be weakened sufficiently by the application of resin. On the other hand, the "melting" of wood that has been treated exclusively with wax is decisively reduced when the temperature rises.

Example 7

In order to accelerate the incomplete and prolonged oxidation of the linseed oil, resins or metal salts of various resin acids are used as well as other drying substances to improve the curing properties. The raw material composition of the biodegradable active substance mixture was 70% linseed oil, 14% zinc resinate, 15% rosin and 1% cobalt octoate. It was kept heated at 150°C until a clear solution formed. The other conditions for the treatment of the wood corresponded to the previous experiments.

The aim of this raw material mixture was to allow the raw materials, which are used in linoleum production, to penetrate into the wood matrix while they are still liquid, respectively as thermoplastic substances, and thereby to connect the properties of wood and linoleum with each other, respectively to actually allow linoleum to form in the wood.

Example 8

A raw material mixture consisting of 30% linseed oil, 15% zinc resinate, 15% rosin, 20% carnauba wax and 19% biodegradable polyester ("Skygreen") and approx. 0.5% manganese resinate was kept heated at 150°C, so that a clear but colored solution was formed. The other treatment conditions corresponded to the conditions in example 2. The raw material combination gave end products with the following properties: Continued drying of linseed oil, also in case of damage to the wood surface.

The resin and wax portion improves the wood's hardness.

The wax portion reduces the stickiness of the linseed oil and resin.

Due to its macromolecular structure, the polyester mainly remains on the surface of the wood.

The timbers were tested for their Brinell hardness perpendicular to the grain direction in accordance with DIN EN 10003-1 and for their bending strength according to DIN 52186:

The treated pieces of wood were placed in a press in which there were already embossing plates that had been preheated to 140°C. The press was closed slowly and held for 2 minutes at a press pressure of 50 bar. The thus reshaped parts had a 2 mm deep embossed waffle pattern with an unbroken, closed surface and undamaged edges. Wood that has been shaped thermoplastically in this way can e.g. used as a stair covering.

Example 9

In order to improve the penetration of the polyester and to achieve the possibility of treating even long pieces of wood, the surface of the wooden parts was perforated with very fine needles to a depth of approx. 3 mm. The treatment conditions and raw material composition corresponded to the previous examples. The penetration depth, also of high-molecular, thermoplastic active substances, can be controlled with the help of the finest perforation. The perforation can be carried out so that macroscopically no surface damage is visible. With this option, the treatment of the wood can also be carried out on significantly larger wood dimensions and also of wood that is naturally difficult to process.

Example 10

If you want to load solid wood completely with thermoplastic active substances, the parts of solid wood are evacuated before the load. Without canceling the negative pressure, work is carried out as described in example 9, with the melt described there being introduced into the evacuated load container. A loading pressure of 9 bar is then maintained at 150°C for 1 hour, whereby the melt is distributed particularly evenly also in the interior of the mold.

Example 11

If you do not want to load solid wood quantitatively, but only modify the cell walls to above all affect the swelling and shrinking behavior, but not change the hardness significantly, you proceed in the following way: The conditions and the raw material mixture corresponded to the same as in example 8. The further untreated wood that has been brought into the loading container is affected before the introduction of the melted active substances for 15 minutes at an air pressure of 4 bar, then work is carried out as in example 8, but without pressure relief. The press-in pressure is set to 15 bar and maintained for 100 minutes. The "pre-tensioning" of the wooden parts under pressure means that, after relaxation, the liquid raw material components are also pressed out as a result of the compressed air escaping, thereby preventing the filling of the cavities. Only the cell walls are loaded with the substances. A later plastic transformation of the parts of solid wood can thereby be carried out even more easily, especially when only the surface is to be shaped by embossing, i.e. by displacement or densification of specific parts.

Example 12

Particular preference is also given to the combination of natural resin, wax and a biodegradable polyester, e.g. in the form of a polylactide. The treatment melt consists of 65% "Erkazit" 415 (from the company Kraemer), 25% "Isco-Blend" 231 (from the company Schlikum) and 10% "EcoPLA" (from the company Cargill). The treatment conditions correspond to the previous examples. The polylactide lays down as a closed coating over the wood surface with only a small (2 mm) penetration depth.

Example 13

The so-called fixation of the "swollen" wood structure by the displacement of the water and the simultaneous introduction of thermoplastic active substances into the cell structure of the wood results in an even more significantly reduced swelling and shrinking behavior. To achieve this, the following procedure is chosen: The wooden parts are conditioned before introduction into the smelting in such a way that the so-called fiber saturation point (water content depending on the type of wood between 12 and 20% water by weight) is reached. The composition of the melt corresponds to the same as in example 9. The melting temperature is 140°C. The wooden parts are quickly introduced into the forge without pre-tempering. The pressure vessel closes quickly without allowing large amounts of water vapor to escape. A pressure of 6 bar is then immediately applied. This somewhat lower pressure is chosen because the wood matrix could easily be deformed due to the presence of significant amounts of water (the wood collapses).

After 120 minutes, the wood is removed at an unchanged melting temperature. During the extraction, a strong outflow of the excess air is observed, but above all of the water vapour. As a result of the simultaneous displacement of the water and replacement with thermoplastic active substances and the fixation of the swelling state as a result of solidification, the swelling and shrinkage behavior of all tested types of wood (beech, alder, birch, maple) could be reduced by at least 75%.

Claims (10)

1. Molded body of impregnated solid wood, characterized in that it is impregnated with at least one largely solvent-free and thermoplastic substance or mixture, which contains a biodegradable polymer, a natural resin and/or an ester of higher fatty acids with polyhydric alcohols and which is solid up to 50°C, but is liquid above 80°C and at a temperature of between 115 and 155°C has a viscosity of below 20 dPa, suitably below 10 dPa, in particular below 1 dPa. 2. Body according to claim 1, characterized in that the biodegradable polymer originates from the group of the following substances: polyhydroxybutyric acids, polycaprolactones, polylactic acids, polyester based on diols and dicarboxylic acids, polyamides, polyesterurethanes, chemically modified natural polymers, such as f .ex. cellulose acetates. 3. Form body in accordance with claim 1 or 2, characterized in that the natural resin originates from the group of the following substances: tall resin, dammar, copal and balsam resin. 4. Body in accordance with one of the preceding claims, characterized in that the fatty acid ester originates from the processing of tallow oil into tallow resin. 5. Shape according to one of the preceding claims, characterized in that the impregnating agent also contains a drying or semi-drying (hardening) oil, in particular blown (preoxidized) linseed oil or Chinese wood oil, possibly with the addition of a drying agent (siccative). 6. Form body in accordance with one of the preceding claims, characterized in that the impregnating agent also contains at least one of the following substances: waxes, in particular carnauba wax, beeswax, montan wax; lignin; higher alcohols; hardened or modified animal and vegetable fats, e.g. hydrogenated vegetable fats and epoxidized oils; wool fat, tallow; salts of various fatty acids, such as e.g. stearic acid, behenic acid, lauric acid; flame retardants, optionally with the addition of a small quantity of a solvent, such as e.g. glycerol. 7. Shape according to one of the preceding claims, characterized in that the impregnating agent consists of 10-60% by weight natural resin, 10-40, preferably 15-35% by weight wax, 10-50, preferably 20-40% by weight drying oil, 0.25-20% by weight of drying agent, in particular cobalt, zinc and manganese resinates, -octoates, -linoleates and -naphthenates, as well as 10-30, preferably 15-25% by weight of a biodegradable polymer. 8. Method for producing a shaped body according to one of the preceding claims, characterized in that the part of wood, which is optionally preheated to a temperature of 100-150°C, is immersed in the melt formed by the impregnating agent and kept there for 10-120 , preferably 30-90 minutes, under pressure and temperature, and then taken out of the melt which is possibly removed from the part's surface, and that the part is finally cooled. 9. Method in accordance with claim 8, characterized in that the forge with the part of the wood is placed under vacuum and/or then brought to an overpressure of 1-100, especially 2-20, bar. 10. Use of a mold body according to one of claims 1-7 for the production of thermoplastically malleable parts of solid wood.