NO794319L - PROCEDURE FOR TREATMENT OF TREE AND PREPARATION FOR USE IN THE PROCEDURE - Google Patents

Description

"Procedure for treating wood, as well as preparations for use in the process".

The invention relates to the treatment of wood for improvement

of its properties. More particularly, it relates to the impregnation of wood with resin and possibly with various additives, e.g. preservatives and fire retardants.

It is a fact that wood expands and contracts depending on the degree of swelling in its cell walls. The cell walls of wood exhibit varying degrees of swelling depending on the particular solvent or solvent vapor to which it is exposed, and its affinity for this

solvent or this solvent vapor. thus exposure to water or water vapor causes a high degree of swelling,

and exposure to less polar solvents or solvent mixtures, e.g. ethanol/xylene mixture, causes its cell walls to dehydrate, resulting in shrinkage.

In addition to this, the tree's cell wall, which consists mainly of cellular chains*, has maximum porosity when it is swollen, i.e. that the free space between relevant cellular chains is large, and when it is not swollen, the porosity is very low. Consequently, the size and amount of molecules that can be deposited in the tree's cell walls depends on the degree or swelling in the cell walls.

The above properties of wood have been used in a number of ways to provide specific properties in wood. Thus, water-soluble polyglycols, e.g. polyethylene glycol, which has a molecular weight of approx. 3000-6000, introduced into wooden cell walls in a wet or swollen state. (See "New and Better Ways to Dimensionally StabilizeWood", A.J.Stam>Forest Products journal, 9(1959):3,107-110, and "PEG of the Woodworker'sHeart", Harry C. Leslie, Man society Technology, AJournal of Industrial ArtsEducation, 33(1):13-16, Sept. and Oct., 1973.) Such polyglycols have a low vapor pressure and, unlike water, evaporate only very slowly. Consequently, the above treatment is very effective in preventing cracking and cracking of wood. Such a treatment is often used for the treatment of wooden carvings, statues etc. and gives these wooden objects a long life even when they are stored in a dry atmosphere. However, polyglycols remain water soluble and will leach out when wood treated with them is exposed to wet conditions. useful-

the effectiveness of this treatment is therefore very limited.

Using much the same idea, low molecular weight water-soluble phenolic and urea resins have been used for the treatment of wood. (See US Patent Nos. 3,968,276, 3,519,476

and 3,493,417). In order to fix these resins in the cell walls of the wood, subsequent heat treatment is required to harden the phenolic resin so that it is rendered insoluble. Very often a combination of heat and pressure is used to further densify the wood. Such a treatment, although effective, requires special equipment and is therefore only carried out for the industrial production of special articles where resistance to water or chemicals or structural strength or a combination of these is needed.

Many other polymers have been used for impregnating wood. Some of these include the use of acrylic-type monomers (US Patent No. 3,663,261), polyisocyanate (US Patent No. 3,539,386) and dibromopropyl glycidyl ether (US Patent No. 3,483,021). All these treatments require a secondary treatment of wood after the impregnation step for polymerization of the monomers in situ for fixation in the wood. The secondary treatment most often used is to heat the impregnated wood, although, in the case of vinyl-type monomers, e.g. acrylic, can also use gamma ray exposure. The requirement for a secondary treatment after the impregnation is expensive and troublesome. Consequently, none of these techniques have found particular acceptance in the industry.

Even when the wood's cell walls are in a wet or swollen state, only relatively small molecules can penetrate the wood's cell walls. The actual size of the molecule that will penetrate the tree's cell walls depends on the degree of swelling and the type of wood. Polymers that have a large molecular size will not penetrate even a swollen wood cell wall. Thus, e.g. Polyvinyl acetate and polyacrylate emulsions have been used for years to make adhesives and paints for wood. Different condensation polymers, e.g. the phenolic resin mentioned earlier, these emulsions are produced by free radical or chain polymerization and do not contain any particular amounts of low molecular weight components. (See Text Book of polymer Science, F.W. Billmeyer, jr<T>., Interscience Publisher, 1966).

Consequently, when wood is treated with these emulsions, it swells

the wood's cell walls due to the presence of water, but the polymer molecules are too large to penetrate even the swollen wood cell wall. Consequently, the wood receives a protective coating, but its other properties, e.g. resistance to cracking and cracking is not affected. It is therefore not useful to use a water-borne polymer with a large molecular size to achieve the purpose according to the invention.

Low molecular weight vinyl resins, e.g. acrylic resins, are known, but their applicability for treating wooden cell walls to improve crack resistance, dimensional stability and other properties has not been recognized. For example, such resins have been proposed for use in building materials as a leveling aid.

Alkyds are condensation polymers and contain a significant amount of low molecular weight components (polymer science textbook, see above). Furthermore, alkyds and hardeners are cross-linked, i.e. that they become solvent-resistant and partially infusible, upon reaction with air. Previously, only alkyds that were soluble in organic solvents were standard materials in the trade. The organic solvents in these alkyds do not swell the wood cell walls. Many of them actually shrink the wood cell walls by displacing water and reduce the porosity of the wood.

In the last decade or so, alkyds that are soluble in

water or in a water-polar solvent mixture has been widely used in industrial finishing, e.g. as a coating for washing machines, refrigerators, cars, etc. However, it was not realized that they also form the basis for providing the highly sought-after properties with regard to reducing cracking and spalling, introducing dimensional stability,

and capable of providing the wood with virtually permanent fire retardant and preservative treatment> without any secondary post-impregnation treatment with respect to heating or exposure to gamma rays. Simple exposure to air is sufficient to crosslink them to form a polymer in situ. Furthermore, as they are in water, and contain a considerable amount of small but reactive molecules, they have excellent penetration into the cell walls of the tree.

in the preferred embodiment of the invention, specific chemical mixtures are permanently deposited in the cell walls of wood fibers, the combination of chemicals to be deposited having been solubilized in water or water/water-miscible solutions.

agent combinations, so that the tree's cell wall will swell and thus provide maximum penetration of the chemicals into the wall itself. The chemicals that are selected are such that at least one of the components in the mixture comprises molecules of small size* which are able to enter the free space in the cell walls in the presence of the solvent, and which are able to be converted under ambient conditions , either by itself or aided by the presence of other chemicals that can serve as catalysts,

into a water-insoluble form, whereby at the same time other water-soluble chemicals that may be present in the mixture are captured, thereby eliminating or greatly reducing the tendency of the entire mixture to leak out upon subsequent treatment of the wood with water or aqueous solutions.

The chemical capable of being converted into a water-insoluble form used in accordance with the invention may be a water-dilutable alkyd or a modified water-dilutable alkyd. Examples of such alkyds are water-dilutable alkyds with long, medium or short oil length which are currently commercially available from a number of different producers* and which are well known in the industrial coating area. Modified alkyds* e.g. urethane modified alkyds* are also commercially available and well known in the art. Such alkyds or modified alkyds are generally soluble in water or water-polar solvent mixtures in near-neutral or weakly alkaline solutions. Examples of polar solvents are butanoic or higher alcohols, ketones, butyl "cellosolve", butyl carbitol, propasol and N-methyl-pyrrolidone.

For the sake of background, it is mentioned that it is known that alkyd resins are produced by combining synthetic dibasic acids, e.g. phthalic anhydride*isophthalic anhydride, trimellitic anhydride, with synthetic or natural fatty acid oils, e.g. glycerides of fatty acids. The fatty acids or their glycerides that are used generally contain mixtures of fatty acids of varying chain lengths and varying degrees of unsaturation

hot in the chain.

Alkyds can be further modified by combining them with different glycols. Examples of glycols that are usually used are pentaerythritol diethylene glycol. More drastic changes in the alkyd's properties can be produced by cross-linking them by adding isocyanates, e.g. toluene diisocyanate. The latter alkyds are usually called urethane-modified alkyds. Urethane-modified alkyds dry to a much harder coating than alkyds that have not been so modified. Other examples of modified alkyds include modification by reacting them with natural resins, e.g. rosin, or with other synthetic resins, e.g. phenol resins, amino resins, silicone resins, or by reacting them with imides, styrene and the like.

The final molecular weight or degree of polymerization of the alkyds is regulated by adding regulated amounts of an excess of one of the reaction partners - fatty acids or glycols. Accordingly, the finished alkyds generally contain small amounts of unreacted hydroxyl or acid groups or both. Alkyds made using relatively low ratios of synthetic polybasic acid to fatty acid are called long oil length alkyds, those made with a very high ratio are called short oil length alkyds, and those made with an intermediate ratio are called alkyds with medium oil length.

The alkyd resins of the above type are soluble in both aromatic and aliphatic hydrocarbon solvents, and they are insoluble in most polar solvents such as water, methanol and butanol. In recent times, alkyd resins have been reacted with various chemicals to improve their solubility in polar solvents. This can be remedied by introducing strongly polar groups into the alkyd structure. As an example of this, alkyd can be made by using an excess of acid whereby the finished product has an acid number that varies from approx. 10 to 100, preferably approx. 20 to 60. The acid groups are then partially or completely neutralized using an amine or ammonia or a combination of amines and ammonia. The products produced in this way are then soluble in such polar solvents as methanol, butanol, carbitol, butyl-"Cellosolve" (ethylene-

glycol monobutyl ether) and mixtures of such solvents

with water. To achieve full solubility, it may be necessary to use mixtures of solvents of the above type. For example, some of these alkyds have greater solubility in higher-boiling solvents, e.g. butyl carbitol (diethylene glycol monobutyl ether) or butyr-Mcellosolve", and the addition of such solvents can increase the amount of water that can be used as part of the solvent system. It is these alkyd resins that have been modified for dissolution in polar solvents that are useful in connection with the present invention and which are referred to here as water-dilutable alkyds.

Apart from simple alkyds, with short, medium or long oil length, alkyds which have been modified by reaction with isocyanates, acrylic compounds or other suitable chemicals which are usually used for modifying alkyds, can be used for carrying out the invention. These modifications are the same as those used with organic solvent-based alkyds and which have been further modified with neutralizable acid groups for solubility in polar solvents.

It should be noted that the present invention is not limited to the types of modified alkyds discussed here. Any water-dilutable polymeric system which is soluble in polar solvents, or mixtures of polar solvents,

or mixtures of polar solvent and water, and which can be converted into a water-insoluble stage, e.g. by curing by exposure to air, by evaporation of water, or by volatilization of a water-solubilizing amine component under ambient conditions with regard to temperature and pressure, can be used for carrying out the invention. To achieve the best results, the resin you choose should contain at least 5% by weight of molecules that have a lower molecular weight than approx. lOOO*preferably 10% by weight of molecules having a molecular weight below. about. 1000. This will induce entry into the free space in the tree's cell wall. The large molecules that are. too large to enter the free space in the tree's cell wall, form a protective and decorative layer on the tree's surface.

Although all water-dilutable polymeric systems as described above are useful on a broad scale in the present invention, it should be understood that some resins may be more satisfactory than others for a particular purpose. For example, stability of the resin/solvent systems differs, and resin precipitation can occur more quickly in some systems than in others. It has been observed that the choice of resin is more critical with regard to stability in more dilute resin solutions containing less than about 20% by weight of resin. In such solutions, several resins can be tested to select one with optimal properties.Example 3, given below, illustrates a resin/solvent system that has relatively long-term stability at low resin concentrations.

Like oil- or organic solvent-dilutable alkyds, water-dilutable alkyds or modified alkyds react with oxygen in the air and cross-link to form a water-insoluble product. The degree of cross-linking can be increased significantly by adding small amounts, generally 0.05 - 1.0% by weight, of catalysts as drying agents. Examples of drying agents that can be used are calcium, cobalt, manganese and zirconium naphthenates or gelated salts of calcium, cobalt, manganese or zirconium.

It has surprisingly been found that the above water-dilutable alkyd solutions, when applied to wood, penetrate the wood's cell wall and upon subsequent exposure to: air become water-insoluble. They can therefore be used to stabilize the wood's cell walls and thus provide greatly improved dimensional stability or a reduced tendency to expand and contract with changes in humidity.

It is also surprising to find that other chemicals which are normally water-soluble or soluble in the above-mentioned alkyd solution, when used in conjunction with these alkyd or modified alkyd solutions, also penetrate through the cell walls of the wood and upon subsequent air curing of the alkyd or the modified alkyd is fixed in the wood and is essentially water-non-leachable.

Therefore, in connection with providing dimensional stability to wood, this discovery can be used for treating wood with a variety of chemicals that give the wood long-lasting and other special properties. Thus, normally water-soluble fire retardants can

chemicals are used to give treated wood permanent non-water-leachable fire-retardant properties. Likewise, water-soluble can

wood preservatives, both organic and inorganic, are introduced into wood and upon curing the alkyd or the modified alkyd become non-leachable and thereby give the wood the ability to retain these compounds, even under wet and humid conditions of use..

The invention can be used in a number of ways. If it e.g. if it is desired to give wood crack resistance and dimensional stability, a single treatment with a solution of one water-dilutable alkyd containing suitable drying agents followed by air drying may be sufficient. The amount of material deposited in the tree's cell walls is proportional to the concentration of the material in the treatment solution. This alludes to the binder polymer as well as other ingredients, e.g. wood preservatives or fire retardants.

The binder polymer used can be as concentrated as approx. 70% by weight or as low as approx. 5% by weight in concentration. In general, mixtures of approx. 5% by weight and up to approx.

30% by weight, then above this concentration range the viscosity of

the solution becomes very high. Highly viscous solutions take a long time to penetrate the wood. The viscosity can be lowered somewhat by heating the solution. However, from a purely practical point of view, it is more convenient to use room temperature and lower concentration ranges. Even ora concentrations of approx. 5% by weight of resin binder shows decided improvement in dimensional stability of treated wood and by fixing other additives therein, a concentration of at least approx. 8% by weight resin is used if one strives for substantial avoidance of water leaching of additives.

The amount of wood preservative or mixtures of wood preservatives used depends again on the degree of protection desired. Pentachlorophenol e.g. can be used in concentration ranges of approx. 0.5-6% by weight, preferably approx. 2-5% by weight. Tributyltin oxide adducts, on the other hand, are used in concentration ranges of approx. 0.1-0.5% by weight. Likewise, fire retardants or mixtures of fire retardants can be used in concentration ranges of approx. 2-15% by weight, again depending on the degree of protection required. Other wood treatment chemicals included are copper 8-quinolinolate and copper ammonium borate.

The wood can be treated sequentially or simultaneously with preservatives, fire retardants and resin binder. If the wood is first treated with a fire retardant or wood preservative and then with the binder in the present system, higher levels of protection can be achieved than

what would be possible with a simultaneous treatment. E.g. can such a fire retardant as borax be compatible with the present binder system up to only 4% by weight,

and a larger amount is needed for deposition in the wood for the level of fire protection desired. Under such circumstances, the wood could first be treated with 10-15% by weight borax in water and then with the binder in the present system for. fixation of the higher concentration of borax in the cell walls.

The resin binder and other wood treatment chemicals can be brought into contact with the wood by any suitable technique. Such conventional methods as brushing, spraying, dipping or exposing the wood to a vacuum followed by the treatment solution under pressure at ambient or elevated temperature are all included here, depending on the wood and the degree of penetration desired.

Conventional pigments, dyes, thickeners, flattening agents and emollients, both organic and inorganic, can be included in the recipes as desired.

in

Example 1

The improvement of wood properties by means of the present invention is reflected in the wood's resistance to dimensional changes with changes in moisture content, and also the dimensional change in the wood itself. For samples of maple (English: maple) of 1.5 cm 3 impregnated with resin solutions of concentration 20, 40 bg 60% by weight and air-dried for 2 weeks, the following percentage changes in dimensions at saturation moisture level and in the dry state were found.

The above results were obtained by soaking the wood samples overnight in the resin solutions mentioned in the following table. After the 2-week air-drying period, they were again soaked in water overnight. Oven drying took place at 150°C until constant weight was achieved - usually within approx.

3 hours.

It is obvious that impregnation of wood with the solution has resulted in great improvements in dimensional stability and that the dimensional stability provided in the tangential direction is greater. It is also significant that the treatment results in equalizing the dimensional changes in both tangential and radial directions. The improvement in dimensional stability also shows that cell wall penetration is present

of the polymer.

Similar results were obtained when samples of American linden, Pinus lambertiana and yellow poplar were treated with the above solutions.

During this investigation, it was also found that the tree after

treatment with the resin solution, followed by air curing for 1 week, did not return to its original dimensions. Percentage change in dimensions due to such treatment of salary is given below.

This is further proof of the fact that the polymer really penetrates the wood cell walls.

Example 2

Apart from providing dimensional stability, the present treatment of wood also results in greatly improved crack resistance. This was shown by taking 3 equivalent samples of red oak.

Sample No. 1 was only dried in a calcining oven and is relatively free of cracks.

Sample No. 2 was dried in a calcining oven, water saturated by soaking in water. for about. 20 minutes and then oven dried. T-all-rich cracks are visible.

Sample No. 3 was dried in a calcining oven and then soaked in the polymer system indicated in the table below. After oven drying, only a few small cracks are visible.

Example 3

It has previously been mentioned that wood preservatives

and fire retardants that normally leach out of wood when exposed to water, e.g. rain, can be substantially fixed in the wood and made non-leachable by means of the present invention.

Pentachlorophenol is usually used as a preservative for wood. For this purpose, pentachlorophenol is generally dissolved in a solution of aromatic and aliphatic hydrocarbons. Pieces of wood that have been treated with pentachlorophenol lose the preservative at a very high rate when leaching with water, thus a • 1 cm 3 piece of wood was treated with 5% by weight of pentachlorophenol, and its chlorine content was analyzed before and after leaching with water (1 month) under application of "Energy-Dispersive" X-ray analysis (EDXA). Analysis with regard to the absence of chlorine in the leached sample clearly shows that most of the pentachlorophenol was leached. Another 1 cm piece of wood was treated with a solution of 5 wt% pentachlorophenol and 14 wt% water-dilutable alkyd. The piece of wood was air-dried for 30 days. Again, the chlorine content was analyzed using EDXA before and after the water leaching (1 month). The results clearly show that very little chlorine had been lost - the polymer had fixed the pentachlorophenol in the wood. This same method can be used to add other chemicals to wood, e.g. fire retardants, and to make them non-leachable.

the treatment solution was prepared from the combination of mixtures A and B indicated in the following table.

Example 4

This example shows that a fire retardant, like the preservative from example 3, can be deposited inside cell walls and fixed against water leaching by means of the resin.

The procedure from example 2 was repeated, with the exception that 42 g (5%) of sodium borate was added to the binder mixture from example 2. The pieces of wood used had the dimensions 5 cm x 10 cm x 1/2 cm. After processing the piece of wood, it was air-dried at room temperature for 2 weeks. It was then cut up to half width.' One of the halves was repeatedly washed with water and air dried. The water-washed and the unwashed parts of the piece of wood were exposed to a lighted torch. which was held at a distance of 10 cm from the end on the side of the piece of wood that had annual rings. For both pieces of wood, it took 8 minutes before charring began. In comparison, an untreated piece of wood under identical conditions began to

char within 4 minutes.

The foregoing description and the experiments that have been carried out primarily illustrate the present invention with water-dilutable alkyd resins. As indicated, the invention can be practiced with any water-dilutable polymer system that is soluble in polar solvents or mixtures of polar solvents and water when they can then be converted to a water-insoluble stage. In this regard, water-dilutable film-forming resins prepared from vinyl monomers have been shown to have advantageous properties

in connection with the invention. These vinyl monomer-derived water-dilutable resins are converted to a water-insoluble form by water evaporation and filtration and/or by volatilization of ammonia or an amine which has been reacted with acid groups in the resin.

The vinyl monomer-based water-dilutable resins are advantageous in that they can be mixed with much less organic polar solvent than the water-dilutable alkyd resins. In fact, certain types of these vinyl resins do not require any

organic solvent at all and is combined with water exclusively as a solvent as is obvious and claimed to be protected in the concurrent application no.

In the present case, small amounts of water miscible organic solvent can be used to provide a vinyl resin which will form a film under ambient conditions. The use of only small amounts of organic solvent (generally less than about 10% by weight, and preferably less than 5% by weight, calculated on the entire mixture) has both environmental and economic advantages. The functional benefits are the most significant.

In this connection, the organic carbon solvents used to give the alkyd polymer mixture water-dilutability are also good solvents for some of the dark colored chemicals that are naturally present in the wood. Consequently, applying these solutions to wood brings these dark-colored compounds to the surface, darkening the wood and detracting from its natural beauty. In addition, the water-miscible organic solvents create difficulties with respect to certain types of water-soluble chemicals, e.g. wood preservatives and fire retardants, which are added to the product for. permanent disposition in the wood that has been treated with the preparation. Addition of certain of these compounds to a preparation containing large amounts of organic solvent separates the mixture into two layers - a resin-cosolvent layer and a water/wood preservative and/or fire retardant layer. This phenomenon precludes the use of most water-soluble compounds for the composition of a uniform wood treatment solution, and the systems that contain larger amounts of organic solvent are thus only useful when they are used in connection with chemicals that have a reasonable degree of solubility in the mixture, e.g. .ex. pentachlorophenol or fire retardants soluble in polar solvents. Such compounds are expensive compared to water-soluble compounds and are often not as effective in the same quantities. The use of resins formed from vinyl monomers which allow the use of a relatively small amount of organic co-solvents avoids the aforementioned problems which are for

the hand in systems that require larger amounts of organic co-solvents.

Polymers formed from such vinyl polymers as acrylic polymers, both copolymers and homopolymers, are generally produced by reactions that result in a relatively narrow molecular weight distribution. As is the case with the alkyd resins, the selected vinyl-based resin should contain at least 5% by weight of the resin molecules present having a molecular weight lower than

about. 1000 and preferably at least approx. lo weight% of resin molecules that have a molecular weight below approx. 1000. In the preferred embodiment, it is desired to include sufficiently large molecules in the preparation which cannot penetrate the wood cell wall and therefore form a protective and decorative surface coating. For this purpose, the preferred preparations will usually include

combine two different vinyl polymers, one that has the small molecules for penetration into the wood, and the other that has relatively large molecules for film formation on the surface of the wood. The larger molecules will generally have a molecular weight of approx. 20,000--200,000, with a typical composition having 95% of the molecules in a molecular weight range of 90,000-110,000.

It has been found that most emulsions made by emulsion polymerization of vinyl-containing monomers can be used for composition of the treatment solution. Examples of monomers containing a vinyl group are vinyl acetate, methylmethacrylate, ethylethacrylate, acrylamide, acrylonitrile, styrene, isoprene, and maleic anhydride. These monomers can be polymerized in themselves to form homopolymers. Preferably, however, a judiciously selected mixture of monomers is used to regulate such properties as the minimum film-forming temperature, the hardness of the dried film, etc. The polymerization is generally carried out in the absence of oxygen using a free radical initiator, e.g. a peroxide, the monomer or monomer mixture being suspended in water, by agitation and its temperature regulated above the temperature needed to cleave the initiator.

Many commercial acrylic emulsions contain organic carbon solvents that serve as thickeners and/or coalescing agents. If water-soluble wood preservatives or fire retardants are added to these, flocculation of the emulsion or one or more of the additives may occur.

Examples of emulsions that have been found suitable will be given later. Other emulsions which are film-forming at or below room temperature and are stable in the presence of the additives can be used.

The low molecular weight polymers, either in emulsion form or as clear solutions, are synthesized in much the same way as the polymerization reaction described above, except that a suitable chain transfer ingredient is included in the reaction mixture.

Emulsion polymers of high or low molecular weight, when made using an acid, e.g. acrylic or methacrylic acid, or a mixture of such acids, as part of the monomer mixture, tend to form clear solutions when amines or ammonia are added to them to raise their pH to the alkaline range, generally above 8 or 8.5.

Although they are soluble in their form, when they are used as binders or film-forming agents, they lose ammonia or the volatile amine (if a volatile amine is used to adjust the pH value) on evaporation and become water-insoluble.

When a mixture of a high molecular weight polymer and a low molecular weight polymer is used, the polymer permeates . with low molecular weight, together with water and the additives, the cell walls of the wood and is deposited therein by evaporation of water. aesthetic appeal. the incorporation of this surface-forming component also enables the addition of pigments and dyes to the treatment solution, thus constituting a wood treatment and a wood coating or stain system in a single mixture, the weight ratio between high molecular weight resin and low molecular weight resin will generally be of from 95:5 to 50:50 and more commonly from approx. 90:10 to 70:30.

If such pigmented systems are used, the pigments also serve as ultraviolet (UV) light absorbers. It is well known that UV light degrades wood. Consequently, incorporating the pigment further serves to increase the life of the wood. In clear coatings, the same purposes can be achieved by adding UV absorbers. Typical examples of UV absorbers are given in the preceding examples.

The following examples illustrate typical recipes where resins formed from vinyl monomers are used and which can be combined with a relatively small amount of organic polar solvent. In example 5, both the high and low molecular weight resins have a majority of acid groups which are neutralized with the ammonium hydroxide. The result is a very soluble, water-white transparent solution. Example 8 illustrates the ability of the mixture to incorporate inorganic fire retardant and preservative salts without causing phase separation due to the relatively low concentration of organic polar cosolvent.

Example 5

Example 6

Example 7

Example 9

The recipe from example 8 was used for application to two pieces of yellow cedar with the dimensions 10 cm x 20 cm.

The wood was soaked in the preparation for 15 minutes and then allowed to air dry overnight at room temperature. One of the pieces of wood was then washed under running tap water for 6 hours and again dried overnight at room temperature. The pieces of wood were then exposed to the flame from a blowtorch held approx. 15 cm above their surface. Neither of the two pieces of wood supported the flame after the blowtorch was removed. However, local charring was visible after a period of 3 minutes. In a control piece of wood that was not treated at all, the wood caught fire within 1 minute of being exposed to the flame, and the fire continued to burn after the blowing match was removed. This experiment shows that the fire retardant was effective in reducing the spread of the flame and had become non-leachable even though it was originally a water-soluble compound.

Example lo

A piece of white oak with the approximate dimensions

3.8 cm x 7.6 cm x 10 cm was soaked in the preparation from Example 8 for 12 hours and was air dried for 24 hours. A piece of wood of identical size was used as an internal control. The treated piece of wood and the control piece were then soaked in water for 2 hours and dried in a drying cabinet at approx. 120°C. When examining these dried pieces of wood, it turned out that the untreated piece of wood had cracked

along the radiation cells while the treated piece of wood showed no cracking whatsoever." This test shows that the preparation from example 8 had stabilized the wood effectively.

The entire experiment was repeated, with the exception that "Acrysol 527" was omitted from the recipe of Example 8. In this case, it was found that both the control sample and those. treated pieces of wood cracked during oven drying. This experiment shows that the acrylic polymer with a high molecular weight did not alone stabilize the wood effectively. 1. Process for treating wood to improve its properties, characterized by contacting the wood to be treated with sufficient water-dilutable resin in a water-miscible solvent to deposit an effective amount of said resin in the cell walls of the wood, the resin containing molecules of a size that can enter the free space in the cell walls in the presence of the solvent, and to convert the resin in the cell walls into a water-insoluble form under ambient conditions. 2. Method as stated in claim 1, characterized in that a solvent which includes water is used.

3.Procedure as stated in claim 2>characteristics

provided that a solvent is used which includes a water-miscible organic liquid.

4. Method as stated in claim 3, characterized in that an alkyd is used as resin which can be cured by exposure to air so that it becomes water-insoluble. 5. Method as stated in claim 3, characterized in that a resin is used which is formed from a vinyl monomer. 6. Method as stated in claim 5, characterized in that a resin is used which is formed from an acrylic monomer. 7.. Method as stated in claim 5, characterized in that a resin is used that comprises a film-forming emulsion, water-insoluble by evaporation of solvent. 8. Method as stated in claim 5, characterized in that a resin containing amine- or ammonia-neutralized acid groups is used to provide water solubility, volatilization of the amine or ammonia which causes the resin to become water-insoluble.

9. Method as stated in claim 2, characterized by the fact that a resin is used which contains at least approx. 5% by weight of molecules with a molecular weight of less than approx. 1000.

10. Method as stated in claim 9, characterized in that a resin is used which contains at least approx. lo weight% of molecules that have a molecular weight of less than approx. 1000. 11. Method as stated in claim 10, characterized by the fact that a resin is used which contains a significant proportion of molecules whose molecular size is larger than what can enter the free space in the cell walls, and selected for formation of a surface film on the wood. 12. Method as stated in claim 11, characterized in that a resin is used with molecules of larger molecular size, with a molecular weight of approx. 20,000-200,000. 13. Method as stated in claim 9, characterized in that the resin is used in resin/solvent- the combination in a weight% of approx. 5-70. 14. Method as stated in claim 10, characterized in that the resin is used in resin/solvent- the combination in a weight% of approx. 5-30. 15. Method as stated in claim 14, characterized in that the resin is used in the resin/solvent combination in a weight% of at least approx. 8. 16. Method as stated in claim 3, characterized in that a further wood treatment chemical in a water-miscible solvent is brought into contact with the wood to deposit an effective amount of the chemical in the cell the walls of the wood before the resin in the cell walls is converted into a water-insoluble form, and then the wood treatment chemical is fixed in the cell walls by converting the resin into a water-insoluble form. 17..Procedure as set forth in claim 5, characterized in that a further wood treatment chemical in a water-miscible solvent is brought into contact with the wood to deposit an effective amount of the chemical in the cell walls of the wood before the resin in the cell walls is converted into "a water-insoluble form, and then the wood treatment chemical is fixed in the cell walls by converting the resin into a water-insoluble form. 18. Method as stated in claim 16, characterized in that the wood treatment chemical is used in the presence of the same solvent as the resin and is simultaneously brought into contact with the wood, whereby the wood treatment chemical and resin is deposited in the cell walls together. 19. Method as stated in claim 17, characterized in that the wood treatment chemical is used in the presence of the same solvent as the resin and is simultaneously brought into contact with the wood, whereby the wood treatment chemical and resin are deposited in the cell walls together 20. Procedure as an given in claim 16, characterized in that a wood treatment chemical is used which is selected from among wood preservatives and fire retardants. 21. Method as stated in claim 17, characterized in that a wood treatment chemical is used which is selected from among wood preservatives and fire retardants and that the water-miscible organic liquid does not amount to more than approx. lo wt% of the resin/solvent combination. 22. Method as stated in claim 21, characterized in that the water-miscible organic liquid is used in an amount that does not amount to more than approx. 5% by weight of the resin/solvent combination. 23. Method as stated in claim 21 or 22, characterized in that a water-soluble wood treatment chemical is used.

24*. Wood treatment preparation, characterized in that it comprises a water-dilutable resin which can be converted into a water-insoluble form upon exposure to ambient conditions, a water-miscible solvent for the resin, as well as an effective amount of a wood treatment chemical dispersed in the resin and the solvent, the resin containing at least approx. lo wt% of

molecules that have a molecular weight less than approx. 1000.

25. Preparation as stated in claim 24, characterized in that the solvent includes water and a water-miscible

■organic liquid.

26. Preparation as stated in claim 25, characterized in that the resin is polymerized vinyl monomers. 27. Preparation as specified in claim 26, characterized in that it contains less than approx. lo weight% of water-miscible organic liquid. 28. Preparation as stated in claim 24, characterized in that the resin is present in the resin/solvent combination in a weight% of approx. 5-70. 29. preparation as stated in claim 28, characterized in that the resin is present in a weight% of approx. 8-30. 30. Preparation as specified in claim 24, characterized in that the wood treatment chemical is selected from among wood preservatives and fire retardants. 31. Preparation as specified in claim 26, characterized in that the wood treatment chemical is a water-soluble salt and that the preparation contains less than approx. 5% by weight water-miscible organic liquid. 32. preparation as stated in claim 27, characterized in that it contains a significant proportion of molecules that have a molecular size that is larger than what can penetrate into the free space in the cell walls of the wood, selected for the formation of a surface film on wood which has been treated with the preparation. 33. Wood processing preparation as stated in claim 32, characterized in that the weight ratio between high molecular weight resin and low molecular weight resin is approx. 95:5 to 50:50. 34. Preparation as stated in claim 33, characterized in that the weight ratio between high molecular weight resin and low molecular weight resin is approx. 90:10 to 70:30. 35. Wood treatment preparation as stated in claim 34, characterized in that the resin contains an acrylic copolymer. 36. preparation as stated in claim 32, characterized in that the resin is present in the form of an emulsion. 37. Preparation as specified in claim 32, characterized in that the resin contains sufficient acid groups for solubility in alkaline solution.