DE3044221A1 - METHOD FOR THE DIMENSIONAL STABILIZATION OF PRESS-COMPRESSED WOOD MATERIALS - Google Patents

Description

ROTGERSWERKE Aktiengesellschaft, D-6000 Frankfurt Pat-795-R

Patent application
15th

Process for dimensional stabilization of compression-molded Wood-based materials

The invention relates to a method for remuneration of wood-based materials, which are compacted by a pressing process have been.

The natural change in dimensions of wood and wood products with changing wood moisture levels is a disadvantage of this group of materials. The dimensional stability can be improved by constructive, chemical and physical measures. There are numerous proposed solutions in practice and in the literature.
As a particularly economical method 2263758 a method for the dimensional stabilization of wood at temperatures between 120 and 18O ⁰ C in a gas atmosphere at gas pressures up to 15 bar is described in DE-PS. at

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Under these process conditions, improvements in dimensional stability of 50-70 % can be achieved within a few hours. However, in the case of solid wood, the risk of cracking when the wood is damp is great. For this reason, 2,916,677 timber is used with a timber output moisture content of below 10% and annealed at temperatures between 160 and 24O ⁰ C in a gaseous atmosphere under pressure in the process according to DE-OS.

In wood-based materials that have been compacted by a pressing process, such as chipboard or fiberboard, plywood or laminated wood, the disadvantage of the natural dimensional change of the wood in the plane of the board is only very slightly effective, but perpendicular to the plane of the board there is an extremely high thickness swelling when moisture is absorbed of up to 30 % , which far exceeds the natural swelling of wood. The reason for this great swelling in thickness is the tendency of the wood fibers and laminates to return to their original position before pressing and compacting.

Attempts have therefore been made to stabilize the dimensions of To achieve chipboard by using wood chips according to the method according to DE-PS 2 263 758 or DE-OS 2 916 677 by means of heat and Compensates for pressure and uses these treated chips to manufacture chipboard.

However, this way of working is associated with a significant fire. associated with danger. In addition, the chips are used in the heat-pressure treatment brittle, so that difficulties arise in the manufacture of the chipboard.

i _m The method according to DE-OS 1,453,382 to boiling glued wood-based panels with humid air under pressure at

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Temperatures between 70 and 150 ⁰ C treated. Due to the necessary treatment duration of one or even several days, this process is extremely uneconomical. In addition, the reduction in the swelling in thickness is relatively slight and has to be achieved through the additional application of a water-repellent agent. on the chips to be improved.

The task, therefore, was a safe, economical one To find a method for dimensional stabilization of wood-based materials that have been compacted by a pressing process with which an optimal swelling resistance of the treated wood-based material is achieved within a short treatment time.

The object is that the compacted by a pressing wood materials at temperatures of 160 - 22O ⁰ C are treated in a gas atmosphere, · which has been compressed to between 4 and 15 bar.

Although it was originally believed that among the inventive Process conditions the gluing of the wood-based materials would be destroyed, that the handling of preformed parts, combined with a uniform reconditioning, difficult and that would be irreparable due to uneven tensions If there were distortions, it was found that, under the conditions according to the invention, wood-based materials such as chipboard and plywood can be remunerated easily and without problems and that the changes in shape during the Treatment process can be negligibly small. By tempering at high pressures and temperatures the state is stabilized after the wood-based material has been compacted; the tendency of the fibers to spring back in the initial state is very much reduced. Simultaneously

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ORIGINAL INSPECTED

the wood fibers, as described in the patent specifications DE-OS 2 916 677 and DE-PS 2 263 758 * in their swelling behavior improved. Therefore, with the method described, the process for plywood and chipboard already increases relatively low moisture deformation in the plate levels even further. This is an advantage especially for large or very large areas long components.

It is a further advantage of the method according to the invention that tempered wood-based materials are obtained whose thickness swell under the influence of moisture is less than the swelling in thickness of wood-based materials, which are made in accordance with DE-PS 2,263 and DE-OS 2 916 677 treated wood chips have been produced.

The reduction in the swelling in thickness achieved allows Improve and expand the possibilities of using dimensionally stable profiles based on chipboard. The production of plastic-coated window profiles based on Plywood or chipboard. Because of the decrease in the flexural strength of the wood-based materials after this process Among the chipboards, the types with high flexural strength such as OSB panels are preferred.

An essential prerequisite for the process is the temperature resistance of the wood material used Binder. Phenolic resins are preferably used here. Urea resins cannot be used.

Wood materials are less sensitive to cracking than solid wood. Therefore the water content can be varied in the range of 0 - 20 %. As a rule, the larger the smallest wood dimension the board thickness, the lower the water content should be. The dimensional stability of the tempered board is always better, the lower the wood moisture content. on the other hand

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wood dimensional stabilization is better at high levels of moisture. The optimal range of wood moisture is therefore between 4 and 12 %.

The wood materials are in a reaction vessel in a compressed gas atmosphere at temperatures of 160 - treated 22O ⁰ C. The working pressures are generally between 4 and 15 bar, in particular between 6 and 12 bar.

The duration of treatment is usually between 0.5 and hours; it is in general <
Temperature is selected.

'" Hours; in general, the higher the hours, the shorter the hours

Particularly good results, especially with regard to .the avoid tension and partial pressure gradient, can ^ ⁵ are achieved when enriches the escaping in the thermal treatment of the wood products in the reaction vessel. This can be achieved, for example, by a high degree of filling of the reactor, that is to say by a low ratio of reactor volume to wood volume, preferably lower

^c as 7, and / or by adding wood condensate and / or one or more wood condensate ingredients.

Of the ingredients present in the wood condensate, such as e.g. formic acid, acetic acid, furfural, furfuryl alcohol,

"Methanol, or even water, is especially acetic acid and / or formic acid are suitable. Also higher alkanecarboxylic acids, in particular with up to 6 carbon atoms, or also the anhydrides of the acids, e.g. acetic anhydride, are possible as additions. The additives can be entered into the reaction space before the heat treatment, or are preferably added during

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■ ν

fed to the treatment of the reactor from the outside. Another possibility is also that to be treated Soak wood with additives before treatment.

The amount of additive is generally not critical. As a rule, the sum of the partial pressures should not be 12 bar exceed; Under no circumstances should concentrations be reached at which there is already partial condensation the additives takes place in the reaction vessel.

For safety reasons and for oxidative wood degradation to suppress the oxygen concentration in the reaction vessel Do not exceed 5 percent by volume. To ensure that the treated wood is tinted as light as possible, it is advisable to switch off oxygen completely; one then works in an inert gas atmosphere, e.g. under nitrogen.

The preferred reaction vessel (reactor) is an autoclave made of corrosion-resistant material, e.g. 1.4571 or 1.4541 steel is used. The size and sizing is aimed depending on the size of the woods to be used. The heat is preferably supplied via the reaction vessel built-in heating coils through superheated steam of e.g. 40 bar. To improve the heat exchange from the heat carrier in the gas atmosphere and from the gas atmosphere into the wood there is a gas circulation in the reaction chamber, e.g. by means of a fan or a blower, as proven expedient.

Relaxing and cooling the reactor and its contents must be done slowly to avoid product damage.

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The respective time span depends on the product. For chipboard with a thickness of 16 mn, for example, 10 bar can be reached within 15 minutes relaxed to 1 bar and from ambient air temperature to room temperature be cooled down.

Examples Example 1 (with comparative example)

Beech plywood in the dimensions 50 100 χ 1000 mm (radial χ tangential χ axial), which was made from 1.2 mm peeled veneers glued with phenolic resin, was ^{treated at 195 °} C. in an N ₂ atmosphere with a total pressure of 10 bar of the circulated gas. The initial moisture content of the wood was 5 %. After a treatment time of 2 1/2 hours, the reactor was within 20 min relaxed. And cooled to about 7O ⁰ C.

Table 1 shows the properties of the laminated timber treated in this way in comparison to unmodified beech laminated timber. The swelling was determined in each case after 14 days of storage of the specimens in water at 2O ⁰ C. Table 1

Beech plywood Beech plywood unpaid hardened and tempered Diche (kg / m ³ ) 850 770 tangential swelling {%) 10 . 3.2 radial swelling {%) 16 2.8 axial swelling (%) 0.25 0J5 Ε module (N / mm ² ) 14000. 13000 Bieafestiakeit 160 100

(The table contains statistical mean values)

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Example 2

Beech plywood, produced from 4 mm peeled veneers with phenolic resin gluing in the dimensions 50 100 1000 mm, is treated and examined as indicated in Example 1. The initial moisture content of the panels was 8 %. Table 2 shows the properties of the plywood treated in this way in comparison to untreated plywood.

Table 2 Beech plywood Beech plywood unpaid hardened and tempered 710 630 Density (kg / m ³ ) 10.2 3.6 tangential swelling (%) 8th 2.2 radial swelling {%) 0.25 0.15 axial swelling {%) 11300 13300 Ε module (N / mm ² ) 122 65 Flexural strength (N / mm ² )

A commercially available chipboard, glued with phenolic resin and having a panel thickness of 16 mm, was ^{treated for 2 1/2 hours at 195 °} C. and 10 bar gas pressure in a circulating nitrogen atmosphere. The initial moisture content was 10 %. Table 3 shows the corresponding test values in comparison with those of an untreated chipboard.

-Jt- after - - 304422 H Table 3 Chipboard Chipboard (N / mm ² ) unpaid hardened and tempered Density (kg / m ³ ; 720 630 Swelling in thickness Water storage a) 24 h / 2O ⁰ C 14th 3.2 b) 1 h / 100 ^° C 18.5 5.7 Flexural strength 25th 12th

Transverse tensile strength according to ο

Boil test V 100 (N / imr) 0.15 0.15

according to DIN 68763

Example 4

ο

4 mm thick hardboard are tempered for 1 hour at 195 ° C. in an N ₂ atmosphere. The total gas pressure is 10 bar. The initial moisture content of the hardboard is 10 JS. Table 4 shows the corresponding test values in comparison with those of a non-tempered hardboard.

Table 4. ·

Hardboard Hardboard unpaid hardened and tempered Swelling after 24 hours of water storage at 2O ⁰ C (%) a) swelling in thickness 30th 15th b) swelling of the surface • 1.2 1.0 Flexural strength (N / mm) 55 38 Ε module (N / mm ² ) 6000 6000 Density (kg / m ³ ) 1060 1020

Example 5

The tempering of a chipboard with oriented chips (OSB type) was ^{treated at 195 °} C., 10 bar N ₂ atmosphere for 1 h. The OSB panel used is of the 1-ply type, ie there is only one uniform layer and chip orientation. The thickness is 3.6 mm.

Table 5 shows the corresponding test values in comparison with those of a non-tempered OSB panel.

Tabel

OSB panel OSB panel untreated treated Density (kg / m ³ ) 650 600 Swelling after 24 hours of water storage at 2O ⁰ C (%) a) swelling in thickness 29 11 b) swelling in fiber 0.28 0.20 direction Flexural strength (along the . Fiber) (N / mm ² ) 47 35 Ε module (along the fiber) (N / mm ² ) 6650 7200

Claims (8)

30U221 ROTGERSWERKE Aktiengesellschaft, D-6000 Frankfurt a.M. Pat-795-R Patent claims 15 1. Process for the dimensional stabilization of wood materials that have been compacted by a pressing process, by heat-pressure treatment, characterized in that the wood-based materials at temperatures of 160 - are treated 22O ⁰ C in a Gasatmiosphäre, the compacted to between 4 and 15 bar has been. 2. The method according to claim 1, characterized in that that the gas atmosphere is compressed to 6 to 12 bar. 3. The method according to claim 1 and 2, characterized in that that the treatment time is 0.5 to 8 hours. 4. The method according to claim 1 to 3, characterized in that that the water content of the wood-based material is between 0 and 20% by weight. -2-35 5. The method according to claim 1 to 4, characterized in that that the water content of the wood-based material is between 4 and 12% by weight. 6. The method according to claim 1 to 5, d a d u r c h g e indicates, that the gas atmosphere is circulating will.. 7. The method according to claim 1 to 6, characterized in that that the treatment of the wood '' The wood degradation products and water produced by the material are targeted are enriched in the gas atmosphere. 8. The method according to claim 1 to 7, characterized g e mark chnet that inert gases in the gas atmosphere '^ like nitrogen are enriched and atmospheric oxygen under 5% by volume is present.