EP0152369A2 - Process for affording dimensional stability and protection to wood and wood-containing materials - Google Patents

Abstract

Wood from sapwood trees such as beech, birch, maple, poplar and the like, which shows high deformation by shrinkage and swelling and a low natural durability is upgraded. This deficiency can be eliminated by impregnation with tanning agent solutions, which occur as tannins in plants or are produced synthetically. The incorporation of the tanning agents into the cell walls in place of the water which causes the shrinkage and swelling is the salient point for the effectiveness of the process. This effect is accomplished by a heat treatment which is to be matched to the type of wood and type of tanning agent. This heat treatment transforms relatively low-value sapwoods into high-grade special woods which, above all, show a high dimensional stability. They are therefore particularly suitable for use under changing climatic conditions and under outdoor conditions. The field of application includes windows, doors, façades, floors and further uses where a high fitting accuracy is required. It is also suitable for musical instruments and for the manufacture of board products, for example plywood and laminated timber.

Description

The invention relates to a method for producing dimensionally stable wood and wood-containing materials.

Wood changes its dimensions under the influence of changing moisture. This swelling and shrinkage (moisture deformation) leads to the generally known difficulties in wood use, in particular in the case of windows, doors, floors, panel surfaces, etc.

The problem of reducing moisture deformation has been the subject of numerous attempts in science and practice. An overview of this is provided by A. Burmester's BAM Report No. 4 "Dimensional stability of wood against moisture; basics and remuneration procedures" Berlin 1970. The remuneration procedures known so far could only be implemented in practice in a few cases because they have different disadvantages Are connected that limit their applicability. Given the complexity of the problem, it is not possible to develop a universally applicable remuneration process.

The invention has for its object to develop a method for improving the dimensional stability of sapwoods such as maple, birch, beech, poplar, etc., which is inherently a particularly large moisture deformation due to their structure and the lack of core ingredients, so that she and others are therefore excluded from many areas of use.

This object is achieved in that an impregnation is carried out with such substances that can be introduced into the cell wall cavities. Only a few substances are suitable for this. These include the tannins, which are found in plants as natural substances (tannins) and can also be produced synthetically. Tannin is an integral part of the heartwood of many tree species. In the natural conversion of sapwood to heartwood, however, it only has a slight dimensional stabilization because it is only stored in the lumens of the cells and not in the cell walls. According to the current state of knowledge, the technical impregnation of sapwood with tannin solutions also only causes moderate dimensional stabilization. The penetration into the cell walls is limited due to the molecular size of the tannins and can only be promoted to a small extent by soaking the wood in the fiber-saturated state and by extending the soaking time. For practical purposes, however, this dimensional stabilization is not sufficient if you compare it with naturally dimensionally stable types of wood. So far, it has not been possible to store tannin on a large scale in the cell walls.

It has now been found that a decisive improvement in the dimensional stabilization of tannin-soaked wood can be achieved by the action of heat at a certain temperature. In addition to lowering the viscosity of the tannin solution, the porosity of the cell walls is increased to such an extent that the impregnation molecules can fill the cell wall cavities instead of the water causing the moisture deformation. This largely prevents the wood from shrinking during drying. For the penetration of the impregnating substance into the cell walls, its molecular size and the pore size is the Cell walls of importance. The optimal temperature level when exposed to heat is therefore different depending on the molecular size of the respective tannin type and the fine structure of the respective type of wood. It is generally in the range between 20 ° C and 140 ° C.

Tanning agent can be used alone or in a mixture with other substances, e.g. Sugars or salts, including wood preservation or fire protection salts, can be used.

The impregnation of the wood with such solutions is possible in various ways by the usual methods (under pressure or vacuum application and in the immersion method). The effect of heat can be by impregnation with an appropriately heated solution, possibly after preheating the wood. However, it is also possible to carry out the heating only after the solution-saturated wood has been soaked at room temperature or after partial to complete drying. The degree of dimensional stabilization that can be achieved depends on the moisture level during the heat treatment and on its duration and temperature level. Other parameters are the type of impregnation, the solution concentration and the wood moisture before the impregnation.

• 1. die Dimensionsstabilität von Splinthölzern in entscheidendem Maße verbessert wird, so daß geringwertige Hölzer zu hochwertigen Spezialhölzern vergütet werden,
• 2. das Verwerfen und Reißen des Holzes beim Trocknen unterbunden wird,
• 3. der Volumenverlust durch Schwindung und spanabhebende Bearbeitung wesentlich reduziert wird,
• 4. die Tränkung des Holzes bei beliebigem Feuchtigkeitsgehalt mit den üblichen Einrichtungen erfolgen kann,
• 5. der Tränkstoff, insbesondere Tannin, preiswert ist und aus den Rinden einheimischer Bäume gewonnen werden kann,
• 6. mit der Verwendung von Tannin und weiteren Extraktstoffen aus Baumrinde ein wesentlicher Beitrag zur Verwertung dieses bisher wenig genutzten Rohstoffes geleistet werden kann,
• 7. die Widerstandsfähigkeit des vergüteten Holzes gegen Befall durch Pilze und Insekten erhöht wird, wobei Tannin ein für den Menschen ungiftiger Schutzstoff ist, der dem helle Splintholz ein ansprechendes Aussehen verleihto

The advantages that can be achieved with the invention are in particular that

• 1. The dimensional stability of sapwood is improved to a decisive extent, so that low-quality woods are treated to high-quality special woods,
• 2. discarding and tearing of the wood during drying is prevented,
• 3. the volume loss due to shrinkage and machining is significantly reduced,
• 4. the impregnation of the wood with any moisture content with the usual facilities,
• 5. the impregnation material, in particular tannin, is inexpensive and can be obtained from the bark of native trees,
• 6. the use of tannin and other extract substances from tree bark can make a significant contribution to the exploitation of this raw material, which has so far been little used,
• 7. The resistance of the tempered wood to infestation by fungi and insects is increased, whereby tannin is a non-toxic protective substance which gives the light sapwood an attractive appearance

example 1

Beechwood slats, 350 mm long, whose wood moisture content was about 20%, were flooded in an autoclave with tannin solution TL of 70 ° C. After evacuation for half an hour, keeping the temperature of the soaking solution at 70 ° C, the normal air pressure was restored so that the tannin solution penetrated into the wood. The scantlings remained in the 70 ^° C. solution for a further 5 hours and were then removed. Then washers were taken from different lengths, on which the shrinkage was measured. The shrinkage up to the compensation was 0.81% tangentially and 0.57% radially in 20 ° / 86%, 1.80% and 0.97% in 20 ° / 65%. The tangential shrinkage is thus reduced by 85% or 75% compared to untreated beech wood. The test of the bending strength and the modulus of elasticity showed no change; the compressive strength was increased by 10%.

Example 2

Beech wood was soaked in a vacuum process with tannin solution TL. After reaching the maxi from swelling, it was heated at 70 ° C for 5 hours to prevent dehydration. The shrinkage measurement showed a 70% reduction in tangential shrinkage.

Example 3

Maple wood was vacuum-treated with T.L. soaked and dried to fiber saturation. Then, while preventing further drying, a 5-hour heat treatment was carried out at 85 ° C. The shrinkage measured was reduced by 72% compared to the untreated wood.

Example 4

Fresh pine logs with a diameter of 25 cm were soaked in a suction process with heated mimosa bark extract and then dried in a normal climate. A wooden disc removed from it dried without tearing, while the typical V-crack occurred on an untreated disc.

Example 5

Beech wood was soaked in 20% solutions of quebracho extract or synthetic Tanigan LD in a fiber-saturated state and then heat-treated. The greatest shrinkage was achieved for quebracho extract at 90 ° C and for Tanigan LD at 50 ° C.

Claims (4)

1. A method for stabilizing dimensions and protecting wood and wood-containing materials, characterized in that tannins or substances similar to them in their properties are preferably stored in the cell walls by suitable methods. 2. The method according to claim 1, characterized in that wood and wood-containing materials in the highest possible swelling state are soaked with the solutions of the substances in question by otherwise customary methods. 3. The method according to claims 1 and 2, characterized in that the binary storage of the substances in question in the cell walls is carried out by the action of heat in temperature ranges which are each matched to the type of wood, wood moisture content and type of substance. 4. Process according to claims 1 to 3, characterized in that further substances are added to the tannins or these similar substances, e.g. affect the stabilization, fixation and coloring or provide additional protection against fungi, insects and / or fire and weathering.