NO163728B - PROCEDURE FOR IMPREGNATION OF FRESH WOODWOOD WITH METAL SALTS. - Google Patents

Description

This invention relates to an inexpensive method

for impregnating fresh wood with metal salts and in particular a method for impregnating wood with preservatives and fungicides.

In order to prevent the degradation of wood and timber and thereby increase the useful life, it is common practice to impregnate the wood or timber with a preservative such as creosote dissolved in liquid aromatic hydrocarbons, mixtures of organic compounds dissolved or dispersed in water, or certain compounds dissolved in petroleum distillates. The protection achieved through the application of these agents,

is dependent on a deep and reasonably even penetration of the preservative into the wood or timber. It is also desirable that the treatment is carried out without significant changes in the original dimensions and surface quality of the wood or timber.

The subject of treatment and preservation of wood is treated quite thoroughly in a two-volume treatise entitled "Wood Deterioration and its Prevention by Preservative Treatments", published by Darrel D. Nicholas; Syracuse Wood Science Series 5, Syracuse University Press, Syracuse, N.Y., 1973. Among the examples of wood preservatives described therein are various creosote materials, pentachlorophenol, copper naphthenate, copper 8-quinolinolate, organotin compounds, organomercury compounds, zinc naphthenate, chloro- oxidized hydrocarbons, ammoniacal copper arsenite (ACA), acid copper chromate (ACC), zinc salts such as zinc chloride, zinc oxide and zinc sulfate, chromated copper arsenate (CCA), etc. In volume II, chapter 3, pages 279-298, processes and equipment for treatment of wood. Pressure treatment is described as the most effective method of protecting wood against decay or decay, insects, fire, etc. Treatments carried out without the use of pressure are also treated in this chapter. Dipping is suggested primarily as a satisfactory surface treatment, although some penetration is also observed. Another method that does not involve the application of pressure is the diffusion process carried out on wood that has not been stored. The author states that the method requires a long processing time due to a low diffusion rate.

Although the literature on such wood processing methods

is extensive and covers a period of at least a hundred years, it is a fact that most of the methods that have been described for treating wood with preservatives and resin components, including pressure treatments, do not result in any extensive and uniform impregnation of the material up to the core of the wood, and/or that the methods require a long time to achieve the desired penetration. The problem is particularly acute when treating certain types of fresh or incompletely stored wood, such as soft pine.

The use of liquid aromatic hydrocarbons for the production of impregnation solutions gives the wood a strong odor and leaves the wood with a surface that is oily and difficult to paint. In addition, liquid aromatic hydrocarbons are flammable materials that require special treatment and special safety measures which increase the costs of treating the wood.

Wood that has been treated with organic preservatives dissolved in petroleum distillates has the same disadvantages as wood treated with aromatic hydrocarbons. Using lower-boiling petroleum distillates, such as white spirit, as a solvent does not completely eliminate the disadvantages. Often, a longer period of storage in air will be required after the treatment in order to achieve sufficient evaporation of the solvent if the wood is to be painted. During this storage in air, part of the preservative can migrate to the surface of the wood together with the solvent, and thereby the retention of the preservative in the wood is reduced to below the value that was assumed during the treatment.

A method for using aqueous polyhalophenol-containing systems is described in US Patent No. 4,090,000.

Briefly, this method involves the use of an aqueous solution containing a water-soluble salt of the polyhalophenol and an acid-forming material which can undergo a reaction in the solution leading to the release of an acid that displaces the polyhalophenol from said salt after the wood has been impregnated with the solution .

Regardless of which impregnation solution is used, the most common commercial method for impregnating wood involves subjecting the wood to the action of the preservative under relatively high pressures, such as pressures in the range of 10.5 to 14.1 kg/cm 2 , over a significant period of time , e.g. for 1-24 hours. The method may also require relatively high temperatures, such as temperatures from 75° to 90 or 95°C. Although increases in pressure tend to increase the amount of preservative absorbed by the wood, such increases in pressure can cause penetration to be random or uneven. Also, the application of pressure can cause contraction of the outer layers of the wood, especially after the wood has been weakened and softened through steam treatment. Collapsing of the wood's cells will easily occur, especially when relatively soft, unaged wood with a low specific gravity is treated. When the cells of the wood are folded together in an area, a relatively impermeable layer is formed which limits or even completely blocks the flow of preservatives into the interior of the wood.

It has also been proposed to improve the pressure treatment method by first subjecting the wood to a vacuum treatment. Examples of earlier patents that describe methods for impregnating wood in which vacuum is first used and then pressure are US patent documents no. 2,668,779, 3,200,003 and 3,968,276.

US Patent No. 3,677,805 describes a modification of the pressure treatment. In this method, the wood is immersed in a treatment liquid inside a pressure vessel, and the pressure is increased to the operating pressure, after which the contents of the vessel are subjected to the action of a pulsating pump which produces sinusoidal pressure pulses inside the vessel. In other words, repeated pressure pulses with modulated amplitude are applied to produce variable pressure peaks above and below the pressure maintained in the pressure vessel. This method requires equipment that includes a pulsating pump and a pressure vessel equipped with a pressure relief device.

The prior art described above represents a small selection of the proposals that have been put forward for treating wood with preservatives to prevent deterioration of the wood. Despite these many proposals that have been made in the art, there is still a need for an inexpensive, safe, non-toxic treatment that is effective and results in uniform penetration of the preservatives and other chemicals into the core of the wood.

An improved method for preserving wood has now been found, which does not require any expensive special equipment, and which results in good penetration of the treatment chemicals into the wood. More specifically, the invention provides a method for impregnating fresh wood, where the wood is kept in contact at 5-95°C with an aqueous system containing metal salt and possibly common components such as a flame retardant, a dye, an odorant and/or an insecticide, for a sufficient time for the metal salt to penetrate the wood, and the wood is then removed from the aqueous system. The method is characterized by the fact that an aqueous system is used which contains from 0.2 to 10% by weight of one or more oil-soluble, acidic, neutral or basic metal salts of one or more organic carboxylic acids, one or more anionic or non-ionic surfactants agents or a mixture thereof, and a hydrocarbon solvent in an amount of less than 20% by weight.

The procedure can be carried out under subatmospheric conditions

pressure, at atmospheric pressure or at elevated pressure.

According to the invention, untreated or fresh wood can be impregnated with metal salts which, preferably, act as fungicidal agents (fungicides) when they are incorporated into the wood. The method according to the invention involves the use of an aqueous system, which reduces, although it does not eliminate, the problems associated with many of the previously known methods based on the use of organic solvents which are flammable and often toxic. Moreover, as mentioned above, the method according to the invention is applicable to untreated and fresh wood. Consequently, the method according to the invention eliminates the need for expensive and time-consuming drying and/or storage procedures.

The aqueous systems used in the method according to the invention will contain from 50 to 98% water and in particular from 67 to 83% water.

The other main component of the aqueous systems used in the method according to the invention is at least one oil-soluble metal salt. The solubility of the metal salts used is believed to contribute significantly to the beneficial and desirable results that are achieved. As the organic compound is oil-soluble and mainly hydrophobic, it has no tendency to be extracted or leached from the treated wood, even over a long period of time.

Particularly preferred types of oil-soluble metal salts which are useful in the aqueous systems used according to the invention are the acidic, neutral and basic salts of organic carboxylic acids. These salts are also known in the art as "soaps".

The choice of metal in the salts will depend on which

properties you want to impart to the treated wood, the availability, the costs and the effect. Certain metals are more often used than others in the method according to the invention, and these include copper, zinc, chromium, iron, antimony, lead

and mercury. Salts containing a mixture of the ions of two or more of these metals can also be used.

As mentioned, the salts can be acidic, neutral or basic. The acidic salts contain an insufficient amount of metal cations to neutralize the acid. The neutral acids contain an amount of metallic cation which is just sufficient to neutralize the acidic groups present in the salt anion. The basic salts contain an excess of metallic cations and are often referred to as over-alkaline salts. These acidic, basic and neutral salts are preferably salts of oil-soluble organic carboxylic acids and mixtures of such acids.

The carboxylic acids based on which suitable acidic, neutral

and basic salts can be prepared, include aliphatic, cycloaliphatic and aromatic monobasic and polybasic carboxylic acids. The organic carboxylic acids can be either naturally occurring or synthetic or mixtures of the two types. Examples of naturally occurring acids, although usually refined, include straight and branched chain carboxylic acids and mixtures thereof, such as tall oil acids and cyclic carboxylic acids, such as naphthenic acids. A variety of synthetic carboxylic acids, and particularly aliphatic carboxylic acids or mixtures thereof, are useful, and these generally contain 6 or more carbon atoms.

The metal salts or soaps can be produced by melting or precipitation methods. The soaps are usually prepared in an inert liquid medium, such as a hydrocarbon oil or a solvent. The organic carboxylic acids will usually have at least 6 carbon atoms and can have as many as 30 carbon atoms, but when more than one carboxylic acid is used, a carboxylic acid with down to 2 carbon atoms can be used as one of the acids in the mixture. Examples of usable organic carboxylic acids are acetic acid, propionic acid, butyric acid, isopentanoic acid, hexanoic acid, 2-ethylbutyric acid, nonylic acid, decanoic acid, 2-ethylhexanoic acid, isooctanoic acid, isononanoic acid, neodecanoic acid, lauric acid, palmitic acid, stearic acid, oleic acid, linoleic acid, naphthenic acid and commercially available mixtures of two or more carboxylic acids, such as naphthenic acids, tall oil acids, rosin acids, etc.

Examples of acidic salts are acidic copper salts that contain less than one stoichiometric equivalent of copper per acid equivalent. For metals other than copper, the basic salts or soaps are preferred, because these contain larger amounts of metal. For example, solutions of normal zinc salts of monocarboxylic acids, such as neodecanoic acid, contain approx. 6% zinc, while a solution of a basic zinc neodecanoate can contain up to 16% zinc or more.

Basic metal salts or soaps of carboxylic acids can also be prepared according to methods well known in the art. Examples of neutral and basic salts, metal salt complexes and methods for their production can be found e.g. in US Patent Nos. 2,251,798, 2,955,949, 3,723,152 and 3,941,606. Some of the basic salts have been referred to as complexes, because they are not simple salts. For example, the basic materials described in US Patent No. 3,941,606 are termed "metal carboxylate-alkoxyalcoholaf complexes. For the present purposes, such basic complexes are covered by the term metal salts or soaps as used in the present description and claims.

Specific examples of the salts or soaps that can be used in the method according to the invention are those listed below in table 1 and in the following specific examples.

The production of the above-described metal salts is illustrated in the following examples.

Example B- 1

A mixture of 260 parts of impure neodecanoic acid, in 03

parts propionic acid, 400 parts white spirit, 172 parts copper powder, 91 parts methylcellosolv, 14 parts dipropylene glycol, 70 parts water, 10 parts octylphenoxypolyethoxyethanol (Triton X-15 from Rohm&Haas Company) and 3 parts "Santoflex-77" to-

is prepared and blown through with air while heating to a temperature of approx. 80°C. Under these conditions, a reaction takes place that lasts for approx. 6 hours. A small amount of boric acid (7 parts) is added, and heating is continued at 80°C with air blowing. The reaction is continued at this temperature until 180% acid neutralization has been achieved (a total of 14 hours). The mixture is heated for a further 2 hours at a temperature of approx. 150°C up to 190% acid neutralization. The air blowing ends, and an inert nitrogen atmosphere is used while the mixture is slowly heated to approx. 150°C during 8 hours, while excess water is removed. 4 roughly equal portions of amyl phosphate, which together amount to 176 parts, are added at 3-hour intervals, while a nitrogen atmosphere is maintained and the temperature is kept at approx. 145°C. The mixture is then cooled to approx. 125°C,

allowed to stand to separate excess copper and then filtered.

The filtered product can be heated under vacuum to a temperature of approx. 150°C to remove the white spirit, so that the desired metal concentration is achieved.

The other components from B-2 to B-6 listed in table 1 can be produced in a similar manner to that described above for B-1 or by alternative methods known in the art.

Example B- 7

A mixture of 840 parts distilled naphthenic acid, 176 parts 2-ethylhexanoic acid, 512 parts white spirit, 48 parts "Carbitol" (a diethylene glycol ether from Union Carbide Corp.), 4.8 parts acetic acid, 1.6 parts water and 10.9 parts of an anti-foaming agent is filled into a reactor, and the mixture is heated with stirring to a temperature of approx. 65°C. The mixture is blown through with carbon dioxide, and 214.4 parts of zinc oxide are added to the mixture, which is then heated to a temperature of approx. 105°C. The reaction is continued at this temperature, and the percentage zinc content, the acid value and the percentage water content are checked periodically. If necessary, adjust the acid value to a value from -33 to -38 for 10% zinc. If the water content is higher than 0.4%, the mixture is dewatered.

While stirring, put approx. 100 parts filter aid to the mixture, which is then filtered. The filtrate is a clear liquid which is adjusted to a zinc content with white spirit.

Carboxylate metal salts of the type described above are marketed by Mooney Chemicals, Inc., Cleveland, Ohio, 44113, under the trade names "TEN-CEM", "CEM-ALL", "NAP-ALL", "HEX-CEM", "LIN-ALL " and "NEO-NAP". These solutions in white spirit can be adapted for use in the production of the aqueous systems used according to the invention, by adjusting the content of white spirit (usually by reducing the amount of white spirit) and the solutions are then mixed with water and surfactants as described below.

Water-dispersible solutions/dispersions of metal salts are also marketed by Mooney Chemicals, Inc., under the trade name "HYDRO-NAP". The metal content of these salts varies from 4% to 10%, but these solutions/dispersions already contain the desired surfactants and can be easily mixed with water to form the desired aqueous systems. Mixtures of the carboxylic acid salts, such as those listed in Table 1, can be readily prepared and used in accordance with the invention. For example, a mixture according to the invention is prepared from equal parts of components B-1 and B-6, whereby a mixture containing 8% copper and 5% zinc is obtained. A mixture of 2 parts of component B-1

and 1 part component B-6 will contain 10.7% copper and 3.3% zinc.

Examples of other neutral and basic salts are lead naphthenate, lead neodecanoate, lead-2-ethylhexoate, lead tallate, zinc tallate, chromium-2-ethylhexoate, chromium tallate, chromoleate, antimony octoate, antimonoleate, iron naphthenate, iron tallate, phenylmercury silver oleate, mercury dioleate, etc.

In addition to the metal salts and soaps mentioned above, the aqueous systems used in the method according to the invention also contain at least one surfactant. Preferably, the surfactants are anionic or nonionic surfactants. Many such surfactants are known in the art, see e.g. McCutcheon's "Detergents and Emulsifiers", 1979, North American Edition, published by McCutcheon's Division, MC Publishing Corporation, Glen Rock, New Jersey, USA, especially pages 15-20.

Generally, the nonionic surfactants, such as those containing ether linkages, are particularly useful. Examples of such ether-containing surfactants are those with the general formula:

where R^ is an aryl or alkyl group containing from 6 to 20 carbon atoms, n is two or three, and x is an integer between 2 and 100. Such surfactants are usually prepared by treating fatty alcohols or alkyl-substituted phenols with an excess of ethylene oxide or propylene oxide. The alkyl carbon chain may contain from 14 to 24 carbon atoms and may be derived from a long-chain fatty alcohol, such as oleyl alcohol or stearyl alcohol.

Nonionic polyoxyethylene compounds of this type are described in US Patent No. 3,855,085. Such polyoxyethylene compounds are marketed under the trade name "Surfynol" by Air Products and Chemicals, Inc., Allentown, Pennsylvania, and under the trade names "Pluronic" and "Tetronic " by BASF Wyandotte Corp., Wyandotte, Michigan. Examples of specific polyoxyethylene condensation products are "Surfynol 465", which is a product obtained by converting approx. 10 moles of ethylene oxide with 1 mole of tetramethyldecynediol. "Surfynol 485" is the product obtained by reacting 30 mol of ethylene oxide with tetramethyldecyndiol. "Pluronic L 35" is a product obtained by reacting 22 mol of ethylene oxide with polypropylene glycol obtained by condensation of 16 mol of propylene oxide. Also useful is "Atlox 1045A" from ICI America, Inc., which is a mixture of polyoxyalkylene sorbitol oleate and -laurate.

Surfactants of the type amines, long-chain fatty amines, long-chain fatty acids, alkanolamines, diamines, amides, alkanolamides and polyglycols, which are known in the art, can also be used. One type that has proven to be particularly useful is the group obtained by adding a mixture of propylene oxide and ethylene oxide to diamines. In particular, bonds produced by the addition of propylene oxide to ethylene diamine with subsequent addition of ethylene oxide are applicable,

and such are marketed by BASF Wyandotte Inc. Chemical Group under the trade name "Tetronic".

Humectants of the "Carbowax" type, which are polyethylene glycols with different molecular weights, have also been shown to give good results. For example, "Carbowax No. 1000" has a molecular weight range from 950 to 1050 and contains from 20 to 24 ethoxy units per molecule. "Carbowax No. 4000" has a molecular weight range from 3000 to 3700 and contains from 68 to 85 ethoxy units per molecule. Other known non-ionic glycol derivatives, such as polyalkylene glycol ethers and methoxypolyethylene glycols, which are commercially available, can be used as surfactants in the mixtures used in the method according to the invention.

Anionic surfactants are also useful

in the aqueous systems used. Useful anionic surfactants include the well-known metal carboxylate soaps, organosulfates, sulfonates, sulfocarboxylic acids and their salts as well as phosphates. A number of anionic surfactants are commercially available, and further information on anionic surfactants can be found in "Anionic Surfactants" Parts II and III, published by W.M. Linfield published by Marcel Dekker, Inc., New York, 1976. Examples of anionic surfactants marketed by ICI America, Inc. are "Atlas G-2205" which is an aromatic phosphate, and "Atlas G-3300", which is an alkylaryl sulfonate. Examples of anionic surfactants marketed by the Rohm and Haas Company are "Triton 770", which is a sodium salt of an alkylaryl polyether sulfate, "Triton GR-5M", which is a dioctyl sodium sulfosuccinate, "Triton H-55", which is a phosphate in potassium salt form, and "Triton W-30" and "Triton x-200", which are sodium salts of alkylaryl polyether sulfonates.

Mixtures of the non-ionic and anionic surfactants can be used and are usually used in the aqueous systems used in the method according to the invention. The amount of surfactant contained in the aqueous mixture may vary within wide limits, but is usually from 0.25% to 7.5%, preferably from 1% to 5%.

The aqueous systems used according to the invention usually contain at least 67% water and less than 20% hydrocarbon solvents. Preferably, the amount of hydrocarbon solvent contained in the aqueous mixture is kept to a minimum, and will usually comprise less than 15% of the aqueous system. The metal content in the aqueous systems varies from 0.2 to 10% by weight.

The aqueous systems used in the method according to the invention can be prepared by mixing the metal salt and the surfactants with a sufficient amount of water to give the desired content of the components. Alternatively,

and preferably, the aqueous systems are prepared from water-dispersible additive concentrates containing the desired metal salt, one or more surfactants and a hydrocarbon solvent. As mentioned above, such additive concentrates are marketed by Mooney Chemicals, Inc. under the general trade name "HYDRO-NAP". Moreover, such water-dispersible additive concentrates can be prepared from commercially available solutions of metal salts and white spirit or prepared by mixing the solutions in white spirit with the desired surfactants with or without further addition of hydrocarbon solvents, such as mineral oils. For example, a water-dispersible additive concentrate can be prepared from the metal salt solutions in white spirit illustrated above as examples from B-1 to B-7 by thoroughly mixing the solutions in white spirit with mineral oil and surfactants. A specific example of such a procedure is mixing 800 parts of the product of Example B-7 with 100 parts mineral oil, 75 parts "Atlas G-3300" and 25 parts "Atlox-1045A". Corresponding water dispersible additive concentrations can be prepared from mixtures identified as B-1, B-2, B-3, B-4, B-5, B-6 and B-7 using the same surfactants or other surfactants.

The water-dispersible additive concentrates of the types described above can be transferred to the aqueous systems used in the method according to the invention, by dilution with water. This dilution is usually done using standard mixing methods. This is an appropriate way to carry out the preparation, as the additive concentrate can be transported to the place of use, before the water is added, which reduces transport costs.

The aqueous systems used in the method according to the invention may also contain other additives, which impart desirable properties to the treated wood. For example, the aqueous systems may contain (v) flame retardants, (vi) dyes, (vii) insecticides and (viii) odorants. Generally, these additives can be incorporated into the aqueous systems in the disperse phase or dissolved in the water. The amount of such additives incorporated into the aqueous systems can vary within wide limits, although it is usually satisfactory to use amounts of from 0.5 to 5% of these substances.

Inorganic flame retardant substances are particularly useful in the aqueous systems used. Examples of inorganic substances are diammonium phosphate, monoammonium phosphate, ammonium chloride, ammonium sulphate, borax and zinc chloride. Examples of organic flame retardants are many halogenated compounds and organophosphorus compounds, which can either be dispersed in the aqueous systems as mentioned above or can be made soluble by forming water-soluble salts or solutions of the flame retardant substances, which can then be mixed with the water-dispersible additive concentrates or the aqueous systems. For example, ammonium salts of organophosphorus compounds can be used in the aqueous systems. Specific examples are ammonium salts of bis-dibromopropyl phosphate, diethyl phosphate, bis-(beta-chloroethyl)-phosphate, bis-(1,3-dichloropropyl)-phosphate, etc. Other water-soluble organic flame retardants are aliphatic carboxylic acids containing more than 50% organic bound bromine, alkyl sulfamates, ammonium alkyl phosphates, antimony trichloride together with tertiary amines such as ethanol amines, urea together with ammonium phosphate and urea together with sulfamic acid.

Although the different types of fresh wood that can be treated using the method according to the invention usually have a satisfactory appearance for most purposes, the appearance can be modified if desired through various color effects. Dyes which are either soluble or dispersible in the aqueous systems can thus be incorporated into the aqueous systems. Any of the known oil-soluble, water-soluble or water-dispersible dyes can be used. These dyes are mixed either with the water-dispersible additive concentrates of metal salts described above, or with the aqueous systems, and when the wood is immersed in the aqueous systems containing the dyes, the dyes will penetrate the wood together with the metal salts and produce desirable coloring effects which in many cases will highlight the wood structure. Examples of dyes that can be used are "Bruco Creosote Brown RGY", marketed by Bruce Chemical Co., "Iron Cem-All", marketed by Mooney Chemical Inc., and "Pylaklor Red Brown LX-6249 ", which is marketed by Pylam Dye Co.

Insecticides can also be incorporated into the aqueous systems, and it is preferred that the insecticide is either oil-soluble, water-soluble or easily dispersible in water. Examples of such insecticides are "Dursban TC", which is marketed by Dow Chemical and "Ficam 76WP", which is marketed by BFC Chemicals Inc.

Odorants can also be incorporated into the aqueous systems

which is used in the method according to the invention, and one preferred odorant is pine needle oil. Likewise, other water-soluble or water-dispersible compounds which have a desired odor can be incorporated into the aqueous systems.

The method according to the invention implies that

fresh wood is kept in contact with the aqueous systems for a sufficiently long time for the desired amount of metal salt to penetrate the wood. The contact between the wood and the aqueous system can be achieved by brushing, spraying, painting, immersion, etc. One of the surprising and advantageous features of the present invention is that excellent results have been obtained by immersing the fresh wood in aqueous systems containing such as little as 2% metal in as little as 5 to 10 minutes. Furthermore, subsequent analysis of fresh wood which has been treated according to the method has shown that an excellent uptake of metal salt has been achieved, with very good penetration of the metal salt into the wood.

In a method according to the invention, the aqueous system in which the fresh wood has been immersed can be kept at a temperature of from 5° to 95°C at atmospheric pressure. However, the method according to the invention can be carried out at ambient temperature, which is also preferred, which eliminates the need for equipment or materials for heating or cooling the aqueous systems. In some cases, it may be advantageous to heat the aqueous systems to elevated temperatures in order to increase the rate of penetration.

As mentioned above, the fresh wood, after being brought into contact with the aqueous systems for the desired time, is removed from contact with the aqueous system. The fresh wood treated in this way is then ready for shipping, although it may be desirable in some cases to allow the wood to dry at least partially before shipping.

It is surprising that desirable results can be achieved after such a brief contact between the wood and the aqueous systems. It is assumed that the aqueous systems used in the method according to the invention deposit the desired amount of material on and in the outer layers of the wood during the short-term contact, so that the desired results are achieved even if the metal salts and other additives have not completed their penetration into the wood. After the treated logs have been removed from the aqueous system, the salts and other additives continue to penetrate the wood as the wood is stored or transported. Accordingly, the invention provides a method for treating wood which not only makes use of cheap equipment (such as a large, open container), but a method by which the wood to be treated is kept in the equipment only for a short time.

The method according to the invention can also be used on wood that is contained in a closed container under vacuum or pressure conditions or in a closed container where such conditions alternate. The use of pressure to improve the penetration of various chemicals into all types of wood is well known in the art. According to this technique, the fresh wood is placed in a chamber which is closed and evacuated in a regulated cycle which is determined on the basis of an assessment of the nature of the wood. Usually, the evacuation time will vary from 15 minutes to 1 hour, and the pressure in the closed chamber is brought to approx. 50 mm Hg or lower. The purpose of this step is to remove air and volatile substances from the wood. The diluted aqueous systems used in the method according to the invention are then introduced into the closed container, the quantity of the mixture should be sufficient for the wood to be completely submerged. The container is then pressurized, and the pressure is maintained at a desired level for a given time. Initially, the pressure in the container will decrease as the aqueous system in the container penetrates the wood. The pressure can be increased to maintain a desired pressure level during the penetration period. When the pressure stabilizes in the container, this is an indication that there is no longer any penetration of the liquid into the wood. At this point the pressure can be relieved, the container drained and the wood removed.

The details in connection with the pressure process, including pressure ranges, the concentration of the aqueous mixture, and the alternation between vacuum and pressure can be easily determined by a person skilled in the field for a given type of wood from the examples that follow. While the method according to the invention is followed, the process parameters can be varied to achieve optimal results. For example, the pressures used in the above-described pressure method can be as high as 21.1 kg/cm 2 , although they are usually from 3.5 to 17.6 kg/cm 2 .

The method according to the invention can be used on a wide variety of wood types. The time the fresh wood is in contact with the aqueous systems used will vary depending on the amount of metal salt to be introduced into the wood and the difficulty with which penetration takes place in the different types of wood. Examples of types of wood that can be treated according to the method according to the invention are Western pencil wood, Douglas fir, common spruce, sugar maple, ash, walnut wood, cherry wood, Weymouth pine, red pine, birch, red oak, elm, hickory and linden. Fresh wood is usually defined as wood containing 30% water by weight or more, calculated on a dry weight basis.

Below follows a specific example of the method according to the invention carried out at atmospheric pressure in an open vessel.

Example A

Debarked logs are immersed in an aqueous system prepared by diluting in water zinc-"Hydro-Nap" (TM) from Mooney Chemicals, Inc. containing 8% zinc as zinc naphthenate and stirring to form an aqueous system containing approx. 2.67% zinc. The aqueous system is kept at ambient temperature, and the logs are kept immersed in the aqueous system for approx. 6 minutes. The logs are then removed from the aqueous system and allowed to drip dry. An examination of the canes treated according to this method shows a good uptake of zinc and good retention of the zinc. Furthermore, a subsequent examination of the logs treated according to this method shows an excellent penetration of the zinc salt into the logs, and no significant changes have occurred in the logs' original dimensions and surface structure. The metal salts that have penetrated the logs show resistance to leaching with water.

The following examples illustrate the method according to the invention carried out at elevated pressures in a closed container.

Example B

Logs of red pine are pressure treated in an aqueous system prepared by diluting zinc "Hydro-Nap" (Mooney Chemicals) containing 8% zinc as zinc naphthenate with a sufficient amount of water to form an aqueous system containing approx. 0.57% zinc. The logs are immersed in the system in a closed pressure vessel. The pressure treatment is carried out at a maximum pressure of 19.0 kg/cm 2 for approx. 1 hour. The logs are then removed from the container and allowed to drip dry. The logs treated in this way contain zinc which exhibits good retention properties.

Example C

The procedure according to Example B is repeated, except that the diluted aqueous system contains 0.39% zinc as zinc naphthenate, and that the maximum pressure is 21.1 kg/cm 2 , which pressure is maintained for approx. 2 hours. The logs' weight gain after the treatment is approx. 38%.

Claims (1)

Method for impregnating fresh wood, where the wood is kept in contact at 5-95°C with an aqueous system containing metal salt and possibly common ingredients such as a flame retardant, a dye, an odorant and/or an insecticide, for a sufficiently long time that the metal salt penetrates the wood, and the wood is then removed from the aqueous system, characterized in that an aqueous system is used which contains from 0.2 to 10% by weight of one or more oil-soluble, acidic, neutral or basic metal salts of one or more organic carboxylic acids, one or more anionic or non-ionic surfactants or a mixture of such, and a hydrocarbon solvent in an amount of less than 20% by weight.