CH643177A5 - METHOD FOR IMPROVING THE PROPERTIES OF WOOD. - Google Patents

Description

The present invention relates to a method for improving the properties of wood and to a preparation for carrying out the method. The method involves impregnating wood with a resin and optionally with additional chemical wood treatment agents such as wood preservatives and flame retardants.

It is well known that wood expands and contracts depending on the extent of the swelling of its cell walls. The cell walls of the wood show varying degrees of swelling depending on the particular solvent or solvent vapor to which the wood is exposed and the affinity of the wood for this solvent or solvent vapor. For example, exposure to water or water vapor leads to a high degree of swelling and exposure to less polar solvents or solvent mixtures, such as ethanol / xylene mixtures, to dehydration of the cell walls and thus shrinkage of the wood.

In addition, when the cell walls, which are mainly made up of cell chains, are in a swollen state, the wood shows maximum porosity, i.e. the free spaces between the cell chains are large, and the porosity is very low in an unwell state. As a result, the size and quantity of molecules that can be deposited within the cell walls depend on the extent of the swelling of the cell walls.

The properties of wood explained above have already been exploited in various ways in order to impart specific properties to the wood. For example, water-soluble polyglycols, such as polyethylene glycol with a molecular weight of 3000-6000, can be introduced into the cell walls of the wood in a wet or swollen state. This is cited for example in the article "New and Better Ways to Dimensionally Stabilize Wood" by A.J. Stam in “Forest Products Journal”, No. 9 (1959), pp. 3, 107-110, and in the article “PEG of the Woodworker's Heart” by Harry C. Leslie in “Man Society Technology, A Journal of Industriai Arts Education », No. 33 (1), pp. 13-16, September / October, 1973. Such polyglycols show low vapor pressure and, in contrast to water, evaporate only very slowly. As a result, the treatment described is very effective in preventing cracking and cracking in wood. Such treatment is often used

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Woodcuts and statues and the like wood, which therefore have a long lifespan even when stored in a dry atmosphere. However, polyglycols remain water-soluble and are leached out of the treated wood when it is exposed to moisture. The usefulness of such treatment is therefore very limited.

For roughly the same reason, water-soluble phenolic and urea resins with a low molecular weight have also been used for the treatment of wood, as described, for example, in US Pat. Nos. 3,968,276, 3,519,476 and 3,493,417. In order to fix such resins in the cell walls of the wood, a subsequent heat treatment of the wood is necessary to harden the resin in order to make it water-insoluble. Combined use of heat and pressure is very often used to further compact the wood. Such treatment is effective, but requires special equipment and is therefore only suitable for industrial manufacture of special articles where resistance to water or chemicals or structural strength or a combination thereof is required.

Many other polymers have also been used to impregnate wood. Some of these are, for example, the use of acrylic monomers as described in US Pat. No. 3,663,261, polyisocyanates as described in US Pat. No. 3,539,386 and dibromopropyl glycidyl ether as described in US Pat. No. 3,483,021 described. All of these treatments require a secondary treatment of the wood after the impregnation in order to polymerize the monomers in situ to fix them in the wood. The most commonly used secondary treatment is heating the impregnated wood, although when using vinyl monomers, such as acrylic monomers, gamma radiation can also be used. The necessary secondary treatment after impregnation is expensive and cumbersome. As a result, none of these methods have found widespread acceptance in the industry.

Even if the cell walls of the wood are wet or swollen, only molecules of relatively small size can penetrate the cell walls. The size of the molecules that can penetrate the cell walls of the wood depends on the extent of the swelling and the type of wood. Polymers with large molecules cannot penetrate the cell walls even when the wood is swollen. For example, polyvinyl acetate and polyacrylate emulsions have been used for years to produce adhesives and paints for wood. In contrast to condensation polymers, such as the phenolic resins already mentioned, these emulsions are produced by free radical or chain polymerization and contain no significant proportions of components with a low molecular weight. This is for example by F.W. Billmeyer, Jr., in the “Text Book of Polymer Science” by Interscience Publisher, 1966. Accordingly, when wood is treated with such emulsions, its cell walls swell due to the presence of water, but the polymer molecules are too large to penetrate the cell walls even when they are swollen. This gives the wood a protective coating, but its other properties, such as resistance to cracking and cracking, are not affected. It is therefore unsuitable to use polymers with large molecules formed in water to achieve the object of the present invention.

Low molecular weight vinyl resins such as acrylic resins are known, but their utility for treating the cell walls of wood to improve crack resistance, dimensional stability and other properties has not been recognized. Such resins have been proposed, for example, for use in floor polishes as leveling agents.

Alkyd resins are condensation polymers and contain a substantial proportion of low molecular weight components, as can be seen from the polymer science manual cited above. In addition, alkyd resins cross-link and harden through reaction with air, making them solvent-resistant and sometimes infusible. In the past, only alkyd resins soluble in organic solvents were generally commercially available. However, the organic solvents in such alkyd resins do not swell the cell walls of wood. Many of them shrink the cell walls of the wood by displacing water and thus reduce the porosity of the wood.

In about the past decade, alkyd resins soluble in water or a mixture of water and polar solvents have been widely used for industrial applications such as coatings for washing machines, refrigerators, automobiles and the like. However, it was not recognized that they also provide a basis for enabling the properties so urgently required to reduce cracking and cracking, to confer dimensional stability and practically permanent flame resistance and to preserve wood, without secondary treatment by heating after impregnation or need gamma radiation. A simple exposure to air is sufficient for crosslinking to form a polymer in situ. In addition, since they are present in water and have an abundant proportion of small but reactive molecules, they show excellent penetrability into the cell walls of wood.

The invention relates to the method defined in claim 1.

In the preferred embodiment, specific chemical mixtures are permanently deposited in the cell walls of wood fibers, the combination of the chemicals to be deposited being liquefied in water or a mixture thereof with water-miscible solvent in order to swell the cell walls of the wood and thereby maximize the penetration of the chemicals into the To achieve cell wall yourself. The choice of chemicals is such that at least one of the components in the mixture contains molecules of small size which are able to penetrate into the free spaces of the cell walls in the presence of the solvent and under ambient conditions, either in themselves or supported by the presence of other chemicals, which can act as a catalyst, can be converted into a water-insoluble form and at the same time retain other water-soluble chemicals which may be present in the mixture, so that the tendency of the mixture to leach out when the wood is subsequently treated with solutions containing water or water is eliminated or greatly reduced becomes.

Resins used in the preferred embodiment of the process according to the invention which can be converted into a water-insoluble form can be water-dilutable, optionally modified alkyd resins. Examples of such resins are water dilutable long, medium and short oil alkyd resins which are currently commercially available from a number of different manufacturers and are well known in the industrial coating industry. Modified alkyd resins, such as urethane-modified alkyd resins, are also commercially available and are well known to those skilled in the art. These optionally modified alkyd resins are generally in water or a mixture of water

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and polar solvent soluble in almost neutral or slightly alkaline solutions. Suitable polar solvents are, for example, butanol or higher alcohols, ketones, butyl cellosolves, butyl carbitol, propasol, N-methylpyrr-olidone.

As a background, it is known that alkyd resins can be obtained by combining synthetic dibasic acids such as phthalic, isophthalic, trimellitic acid anhydride with synthetic or natural fatty oils, i.e. Glycerides of fatty acids. The commonly used fatty acids or glycerides thereof contain mixtures of fatty acids of varying chain lengths with varying degrees of unsaturation in the chain.

Alkyd resins can also be modified by combining them with various glycols. Glycols commonly used for this purpose are, for example, pentaerythritol, diethylene glycol. More drastic changes in the alkyd properties can be obtained by crosslinking with the addition of isocyanates, such as toluene diisocyanate. Such alkyd resins are usually referred to as urethane-modified alkyd resins. Urethane-modified alkyd resins dry to much harder coatings than non-modified alkyd resins. Other examples of modified alkyd resins are alkyd resins obtainable by reaction with natural resins, such as rosin, or with other synthetic resins, such as phenol, amino, silicone resins, or by reaction with imides, styrene and the like.

The final molecular weight or extent of polymerization of the alkyd resins is regulated by the addition of a controlled amount of excess of one of the reactants, fatty acid or glycol. Accordingly, the finished alkyd resins generally contain small amounts of unreacted hydroxyl and / or acid groups. Alkyd resins made using a relatively low ratio of synthetic polybasic acid to fatty acid are called long oil alkyd resins, using a very high ratio made short oil alkyd resins, and those made using an intermediate ratio are called middle oil alkyd resins.

The alkyd resins of the type described above are soluble in both aromatic and aliphatic hydrocarbon solvents and insoluble in most polar solvents such as water, methanol and butanol. Recently, alkyd resins have been reacted with various chemicals to improve their solubility in polar solvents. This can be achieved by introducing highly polar groups into the alkyd structure. For example, alkyd resin can be made using an excess of acid so that the final product has an acid number in the range of 10-100, preferably 20-60. The acid groups are then partially or completely neutralized using an amine and / or ammonia. Products produced in this way are then soluble in polar solvents such as methanol, butanol, “carbitol”, “butyl cellosolve” (ethylene glycol monobutyl ether) and mixtures of such solvents with water. Mixtures of the solvents listed above may be required to achieve complete solubility. For example, some of these alkyd resins are more soluble in higher boiling solvents, such as "butyl carbitol" (di-ethylene glycol monobutyl ether) or "butyl cellosolve", 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 which have been modified for solubility in polar solvents, which are used in the process according to the invention and are referred to below as “water-dilutable alkyd resins”.

In addition to simple alkyd resins, short, medium or long oil lengths, modified alkyd resins can be used in the process according to the invention by reaction with isocyanates, acrylates or other chemicals usually used for the modification of alkyd resins. These modifications are the same as those which are carried out with organic solvent-based alkyd resins with further modification with neutralizable acid groups in order to achieve solubility in polar solvents.

Note that the present invention is not limited to the modified alkyd resin types discussed above. Any water-dilutable polymeric system can be used which is soluble in polar solvents, mixtures thereof or mixtures of polar solvents with water and for conversion into a water-insoluble form, for example by exposure to air, evaporation of water or volatilization of a water-soluble amine component, under ambient conditions of temperature and pressure. For best results, regardless of the choice, the respective resin should expediently contain at least 5% by weight, preferably 10% by weight, of molecules with a molecular weight below 1000. This enables penetration into the free spaces in the cell walls of the wood. The larger molecules, which are too large to penetrate the free spaces in the cell walls, form a protective and decorative layer on the wooden surface.

While all of the water-dilutable polymer systems of the invention described above can be used generally, it should be appreciated that certain resins may be more satisfactory than others for certain uses. For example, the stability of the resin / solvent system may differ and resin precipitation is more likely to occur in some systems than in others. It has been observed that the choice of resin is more critical for stability in more dilute solutions containing less than about 20% by weight resin. In such solutions, several resins can be tried to select the one with the optimal properties. Example 3 below shows a resin / solvent system which is stable at a low resin concentration for a relatively long period of time.

Like alkyd resins that can be diluted with oil or organic solvents, the optionally modified alkyd resins, which can be diluted with water, react with oxygen in the air and crosslink to form a water-insoluble product. The crosslinking rate can be increased significantly by adding small amounts, generally 0.05-1.0% by weight, of catalyst as a dryer. Suitable driers of this type are, for example, calcium, cobalt, manganese and zirconium naphthenates or chelated salts of calcium, cobalt, manganese and zircon.

Surprisingly, it was found that the above-described, water-diluted alkyd resin solutions penetrate into the cell walls of wood and become water-insoluble as a result of subsequent exposure to air. They can thus serve to stabilize the cell walls of the wood and serve the wood with a greatly improved dimensional stability or a reduced tendency to expand and contract when the moisture conditions change.

Also surprisingly, it has been found that other chemicals that are normally soluble in water or in the alkyd resin solution described above are used in

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Use together with these solutions of optionally modified alkyd resin also penetrate into the cell walls of the wood and are fixed in the wood during the subsequent hardening of the optionally modified alkyd resin and can then no longer be leached out with water.

In addition to imparting dimensional stability, this discovery can thus be evaluated to treat the wood with a number of different chemicals that give the wood a long life and other special properties. Thus, normally water-soluble chemical flame retardants can be used to give the wood stable, non-leachable flame retardant properties. Likewise, water-soluble wood preservatives, both organic and inorganic, can be introduced into the wood, and when the optionally modified alkyd resin is hardened, they are fixed with water so that they cannot be leached out, and the wood retains these compounds even when used under wet and damp conditions.

The invention can be used in various ways. For example, a simple treatment with a solution of a water-dilutable alkyd resin with the addition of an appropriate dryer and subsequent air drying can suffice to achieve resistance to cracking and cracking and dimensional stability of the wood. The proportion of the material deposited in the cell walls of the wood is proportional to the concentration of the material in the treatment solution.

This applies both to the polymeric binder and to other additives such as wood preservatives and flame retardants. The binder polymer can be used in as high a concentration as 70% by weight as well as in a low concentration as 5% by weight. In general, mixtures with a concentration of 5-30% by weight are preferred since the viscosity of the solution is very high above this concentration range. However, very viscous solutions take a long time to penetrate the wood. The viscosity can be reduced somewhat by heating the solution. For purely practical reasons, however, it is more appropriate to work at room temperature using a lower concentration range. While a concentration of about 5% by weight of resin as a binder brings about a significant improvement in the dimensional stability of the treated wood and the fixation of other additives in the wood, a concentration of at least 8% by weight of resin should be used when leaching out Additives by water is sought.

The amount of wood preservative or a mixture of such agents depends on the desired level of protection. Pentachlorophenol can be used, for example, in a concentration range of 0.5-6% by weight, preferably 2-5% by weight. Tributyl-tin adducts, on the other hand, are generally used in a concentration range of 0.1-0.5% by weight. Flame retardants or mixtures of such agents can also be used in a concentration range of 2-15% by weight, depending on what is desired Extent of the protective effect. Other suitable chemical wood treatment agents are, for example, copper 8-quinolinolate and copper ammonium borate.

The wood can be treated simultaneously or sequentially with wood preservatives, flame retardants and resin binders. If the wood is first treated with flame retardant or wood preservative and then with resin binder as described, a higher protective effect can be achieved than with simultaneous treatment. For example, a flame retardant, such as borax, can only be compatible with the resin binder according to the invention up to an application concentration of about 4% by weight, although a larger proportion of borax must be deposited in the wood for the desired flame retardant effect. Under such circumstances, the wood is expediently treated first with 10-15% by weight borax in water and then with the resin binder according to the process described in order to fix the higher concentration of borax in the cell walls.

The resin binder by the process described and other chemical wood treatment agents in the water-miscible solvent can be brought into contact with the wood in any suitable manner. Depending on the type of wood and the desired degree of penetration, conventional methods such as brush or brush painting, spraying, dipping or treating the evacuated wood with the treatment solution under pressure at ambient or elevated temperature are suitable.

Organic and / or inorganic conventional pigments, dyes, thickeners, smoothing agents and extenders, individually or as a mixture with one another, can be added to the treatment liquid used in the process described.

example 1

The improvement in the properties of wood according to the method according to the invention is recognizable by the resistance of the wood to dimensional changes when the moisture content changes and also by the dimensional changes of the wood itself.

Samples of about 1.5 cm3 in size from maple wood were impregnated with a resin solution with a concentration of 20.40 or 60% by weight of resin and air-dried for 2 weeks. The dimensional changes between the moisture-saturated and dry state were then determined on the treated and as a blind test on an untreated sample. The percentages given below were based on the formula

Dimension moisture saturated Dimension calculated after oven drying.

Resin concentration dimension,%

the solution wt .-% tangential radial

0 112.18 105.46

20 110.25 103.86

40 109.24 103.34

60 104.94 101.83

The above test results were obtained by immersing the wood samples in the respective resin solution overnight, then air-drying them for 2 weeks and then immersing them in water again overnight. The samples were then dried in an oven at 150 ° C. to constant weight, usually for about 3 hours.

The table below shows the weight compositions of the resin solutions used in the tests with 20.40 and 60% by weight resin content, respectively.

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Components

60%

40%

20%

medium oil dilutable with water

627.0

412.0

200.0

Alkyd resin, 80% solution in

"Butyl cellosolve"

Ammonium hydroxide, 28%

36.0

24.0

12.0

aqueous solution

"Butyl cellosolve"

34.6

77.6

120.0

water

138.4

310.4

480.0

6% cobalt naphthenate *

4.0

2.7

1.3

18% zirconium naphthenate *

2.0

1.3

0.7

"Active-8" *

2.8

1.9

0.9

BYK 301 **

6.0

4.0

2.0

Total

836.0

824.0

812.0

* These three components are dryers ** BYK 301 is a wetting agent

It is obvious that the impregnation of the wood with the solution has led to a great improvement in the dimensional stability, and that the dimensional stability in the tangential direction is greater. It is also important that the treatment compensates for dimensional changes in both the tangential and radial directions. The improvement in dimensional stability also shows that the polymer really penetrates the cell walls.

Similar results were obtained with the same treatment of other types of wood with the solutions mentioned above.

In these experiments, it was also found that the wood did not return to its original dimensions for one week after treatment with the resin solution and subsequent air drying. The dimensional changes of maple wood after such treatment were expressed in% according to the formula

Length of treated sample, oven dried ^^ Length of untreated sample, oven dried calculated and are listed in the table below.

Resin concentration dimension,%

the solution wt .-% tangential radial

0 0 0

20 103.4 101.45

40 103.86 102.15

60 105.81 102.64

This is an additional indication that the polymer actually penetrates the cell walls of the wood.

Example 2

In addition to imparting dimensional stability, the method according to the invention also results in a great improvement in the resistance of the wood to crack formation. This was demonstrated by the following tests with three equivalent samples of red oak wood:

Sample # 1 was only hurdle-dried and was relatively free from cracking.

Sample No. 2 was hurdle-dried, then saturated with water by immersion for about 20 minutes and then oven-dried. The formation of numerous cracks was shown.

Sample No. 3 was hurdle-dried and then saturated with the resin solution of the following weight composition. After oven drying, only a few small cracks appeared.

Components:

water-dilutable medium-oil-alkyd resin, 80% solution in

"Butyl cellosolve" 248.70

Ammonium hydroxide, 28% aqueous solution 15.00

"Butyl cellosolve" 59.51

Water 493.93

"Tinuvin" 328 * 4.46

6% cobalt naphthenate 1.24

18% zirconium naphthenate 0.62

"Active-8" 1.36

BYK 301 2.60

Total 827.42

* "Tinuvin" 328 is a UV absorber

Example 3

It has already been mentioned that wood preservatives and flame retardants, which are normally leached out of wood by the action of water, for example rain, can be practically fixed in the wood and made non-leachable by the process according to the invention.

Pentachlorophenol is generally used as a preservative for wood. For this purpose, pentachlorophenol is generally dissolved in a solution of aromatic and aliphatic hydrocarbons. Blocks of wood treated with pentachlorophenol lose this preservative very quickly when leached out with water.

A wooden block of 1 cm3 volume was treated with 5% by weight of pentachlorophenol and its chlorine content before and after leaching with water was determined for one month using energy dispersion X-ray analysis (EDXA). The result of the analysis clearly indicated that the leaching treatment had leached most of the pentachlorophenol out of the wood. Another 1 cm3 block of the same wood was treated with a solution containing 5% by weight of pentachlorophenol and 14% by weight of water-dilutable alkyd resin and then air dried for 30 days. This block of wood was then subjected to the same leaching treatment with water for a month and its chlorine content was determined by EDXA before and after the leaching treatment. It was clearly evident from the analysis results that very little chlorine was removed by the leaching treatment, that is to say the pentachlorophenol was fixed in the wood by the polymer.

Using the same procedure, other chemical wood treatment agents, for example flame retardants, cannot be fixed in the leachable material.

The treatment solution used in this experiment was prepared from the combination of mixtures A and B according to the following composition by weight:

Mixture A

Pentachlorophenol 823

"Butyl cellosolve" 3837

Ammonia solution 28% 180

4840

Mixture B

"Aroion" 385 * 955

Ammonia solution 28% 22

"Butyl Cellosolve" 64

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"Cobalt hydrocure" ** 6.5

"Active-8" 4.0

Mixture A 1190

after mixing for 15 min

Add water 2700

Adjust the pH 8.5 with 28% ammonia solution

* Ashland Chemical's water-thinnable alkyd resin

Company ** dryer

Example 4

In this example it is demonstrated that, like the wood preservative according to Example 3, a flame retardant deposited in the cell walls of the wood can be fixed by the resin against leaching with water.

The procedure according to Example 2 was repeated with the exceptions that the treatment liquid described in Example 2 was 42 g, i.e. 5 wt .-%, sodium borate were added. The wood was used in blocks measuring 5 x 10 x 0.5 cm. After impregnation, the blocks were air dried at room temperature for 2 weeks and then cut in half in the transverse direction. One half was washed repeatedly with water and air dried. The water-washed and the unwashed half of the block were exposed to a blowtorch at a distance of 10 cm from the flame at the end of the fiber longitudinal direction. In both halves of the block, it took 8 minutes to start charring. In a comparative experiment with the same block, but not treated as described, under the same flame conditions, the charring started after 4 min.

In the above explanations and examples, the invention is primarily illustrated using water-dilutable alkyd resins. However, as indicated, the process described can be carried out using any water-dilutable polymer system that is soluble in polar solvents or mixtures of polar solvents with water and can then be converted to a water-insoluble form. In this regard, it has been shown that water-dilutable, film-forming resins made from vinyl monomers have advantageous properties for use in processes according to the invention. Such water-dilutable resins derived from vinyl monomers can be converted to a water-insoluble form by evaporating the water to form a film and / or by volatilizing ammonia or an amine which has previously been reacted with acid groups in the resin.

Water-thinnable resins based on vinyl monomers are therefore advantageous since they can be processed into a preparation using much less organic polar solvent than the water-thinnable alkyd resins. Certain types of these vinyl resins even do not require any organic solvent at all and can be made into a formulation using water alone as the solvent, as described in U.S. Patent Application No. 91,029.

In the present case, small amounts of water-miscible organic solvent can be used to obtain a vinyl resin that forms a film under ambient conditions. The use of only small amounts of organic solvent, generally less than 10% by weight, preferably less than 5% by weight, based on the total weight of the preparation, is both in terms of environmental protection and

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economically advantageous. The functional advantages are very significant.

In this connection, the organic auxiliary solvents used to achieve the water-dilutability of the alkyd polymer mixture are also good solvents for some of the natural, dark-colored chemicals present in the wood. As a result, the application of such treatment solutions to the wood brings these dark colored compounds to the surface, which thereby darkens while disturbing the natural beauty. In addition, the water-miscible organic solvents pose difficulties with certain water-soluble chemicals, such as wood preservatives and flame retardants, that are added to the permanent deposition formulation in the wood treated with the particular formulation. With the addition of certain such compounds to a formulation containing large amounts of organic solvent, the mixture is separated into two layers, a resin layer containing cosolvent and a layer containing water and wood preservative and / or flame retardant. This phenomenon precludes the use of most water-soluble compounds for the production of a uniform wood treatment liquid, and systems with a larger proportion of organic solvent can therefore only be used together with chemicals which have an acceptable solubility in the mixture, such as pentachlorophenol or soluble in polar solvents Flame retardants. Compounds of this type are expensive in comparison to water-soluble compounds and are often not equally effective in equal proportions. The use of resins based on vinyl monomers, which enable the use of a relatively small amount of organic auxiliary solvents, avoids the problems described above, which occur in systems with large amounts of organic auxiliary solvents.

Polymers made from vinyl monomers, such as acrylic polymers, both homopolymers and copolymers, are generally obtainable by reactions which result in a relatively narrow molecular weight distribution. Like the alkyd resins, the selected vinyl-based resins should also contain at least 5% by weight, preferably at least 10% by weight, of molecules with a molecular weight below 1000. In the preferred embodiment, it is desirable that the preparation contain a sufficiently large proportion of larger molecules that cannot penetrate into the free spaces of the cell walls of the wood and thus form a protective and decorative surface coating. In this regard, a preferred preparation usually contains a combination of two different vinyl polymers, one of which has small molecules suitable for penetration into the wood and the other relatively large molecules suitable for film formation on the surface of the wood. The larger molecules generally have a molecular weight in the range of 20,000-200,000, and a typical preparation may contain, for example, 95% by weight of molecules in a range of 90,000-110,000.

It has been found that most of the emulsions produced by emulsion polymerization of vinyl-containing monomers are suitable for the preparation of the treatment liquid. Monomers containing a vinyl group are, for example, vinyl acetate, methyl methacrylate, ethyl ethyl acrylate, acrylamide, acrylonitrile, styrene, isoprene, maleic anhydride. These monomers can be polymerized to form homopolymers. Preferably

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however, a carefully selected mixture of monomers is used to regulate properties such as minimum film formation temperature, hardness of the dried film and the like. The polymerization is generally carried out in the absence of oxygen using a free radical initiator such as a peroxide, the monomer or monomer mixture being suspended in water which is stirred and the temperature of which is maintained above the temperature required for the decomposition of the initiator .

Many of the commercially available acrylic emulsions contain organic cosolvents that act as thickening and / or agglomerating agents. When water-soluble wood preservatives or flame retardants are added to these emulsions, flocculation of the emulsion or one or more of the added agents can occur.

Examples of emulsions found useful are listed below. Other emulsions which are film-forming at room temperature or below and stable in the presence of any additives can also be used.

The low molecular weight polymers, either in the form of an emulsion or a clear solution, can be made largely similar to the polymerization reaction described above, except that an appropriate chain transfer component is added to the reaction mixture.

Holiem or low molecular weight emulsion polymers made using an acid such as acrylic or methacrylic acid or a mixture of such acids as part of the monomer mixture tend to form a clear solution when ammonia or an amine is used to make the reaction mixture alkaline to adjust, generally to a pH of 8-8.5.

Although these polymers are soluble in this form, when used as binders and / or film-forming agents they lose the content of ammonia or an amine, if a volatile amine was used to regulate the pH, by evaporation and thus become water-insoluble.

When using a mixture of high and low molecular weight polymers, the low molecular weight polymer, together with water and any other chemical wood treatment agents that may be present, penetrates into the free spaces in the cell walls of the wood and is deposited and fixed there after the water has evaporated. The polymer component with higher molecular weight forms a film on the outer surface of the wood, which protects the wood against environmental influences and beautifies its appearance. The addition of such a film-forming component also enables the addition of pigments and dyes to the treatment liquid, which enables simultaneous treatment in accordance with the invention and coating and / or coloring of the wood using a single treatment liquid. The weight ratio of high to low molecular weight resin is generally in the range from 95: 5 to 50:50, usually from 90:10 to 70:30.

When such pigmented systems are used, the pigments used can also serve as UV absorbers. It is well known that UV radiation degrades wood. Accordingly, the use of pigments acting as UV absorbers serves to extend the life of the wood. The same goal can also be achieved by adding UV absorbers to colorless, clear coatings. Typical UV absorbers are listed in the examples above.

The following examples show typical preparations with resins made from vinyl monomers, which can be prepared with a relatively small amount of organic, polar auxiliary solvent. In Example 5, both the low and high molecular weight resins have multiple acid groups which are neutralized by the ammonium hydroxide used. The result is a readily soluble, water-light, transparent solution. Example 8 explains the possibility of adding inorganic flame retardants and preserving salts to the preparation without phase separation of the preparation due to the relatively low concentration of organic polar auxiliary solvent.

The details of the proportions and the percentages of concentration as well as the ratios in the examples are by weight.

Example 5

"Rhoplex" B-505 * 45.00

"Acrysol" 527 ** 4.44

Ammonium hydroxide, 28% *** 1.00

Water 46.56

“Methyl carbitol” 3.00

Total 100.00

* "Rhoplex" B-505 is an emulsion of an acrylic resin copolymer with a high molecular weight from Rohm & Haas Company, with a solids content of 40% ** "Acrysol" 527 is a solution of an acrylic resin with low molecular weight without further additives from Rohm & Haas Company, with 45% solids content *** The aqueous solution of ammonium hydroxide is used to regulate the pH and to clarify the preparation.

The total resin content of the preparation is 20%. The ratio of «Rhoplex» B-505 to «Acrysol» 527, based on solids, is 9.0: 1.0.

Example 6

"Synthemul" 40-450 * 32.65

"Acrysol" 527 8.88

Ammonium hydroxide, 28% 2.00

Water 52.47

"Butyl carbitol" 4.00

Total 100.00

* "Synthemul" 40-450 is an emulsion of a polyvinyl acetate / acrylic acid copolymer from Reichhold Chemicals Inc., with a solids content of 49%.

The total resin content of the preparation is 20%. The ratio of «Synthemul» 40-450 to «Acrysol» 527, based on solids, is 80:20.

Example 7

E-1630 * 40.00

"Acrysol" 527 4.44

Water 52.06

"Methyl carbitol" 3.50

Total 100.00

* E-1630 is a trial acrylic emulsion from the Rohm & Haas Company, with a solids content of 45%.

The total resin content of the preparation is 20%. The ratio of E-1630 to «Acrysol» 527, based on solids, is 90:10.

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643 177

Example 8

E-1630 40.00

"Acrysol" 527 4.44

Flame retardant * 10.00

"Nylates" -10 ** 2.00

Water 40.56

“Methyl carbitol” 3.00

Total 100.00

* The flame retardant was made by completely neutralizing dimethylamine with phosphoric acid.

** "Nylate" -10 is a wood preservative from the Seymore Chemical Company, whose active component is copper 8-quino-linolate.

Example 9

The preparation according to Example 8 was used for the treatment of two equally large board sections made of cedar wood, each with a base area of 10 × 20 cm. Both board sections were immersed in the preparation for 15 minutes and then left to dry at room temperature overnight.

One of the two board sections was then washed under a flowing water jet for 6 hours and again allowed to dry overnight at room temperature. Then the surface of both board sections was flamed at a distance of 15 cm with a blowtorch.

After the blowtorch was removed, neither of the two board sections burned, but localized charring was visible on both board sections after a flame exposure time of 3 min.

In a blind test using the same flame, but not treated with the preparation

Section of the board burned after 1 min of flame exposure with the blowtorch, and the fire persisted even after the blowtorch was removed.

This test proves that the flame retardant was effective in reducing flame spread and was not made leachable by the treatment described, although the compound used as the flame retardant was originally water-soluble.

Example 10

A block of white oak wood of approximate dimensions 4 x 7.5 x 10 cm was immersed in the preparation according to Example 8 for 12 hours and then air-dried for 24 hours. The same block of wood was left untreated for comparison purposes. The treated and comparative blocks were then immersed in water for 2 hours and then oven dried at 120 ° C.

The evaluation of the two blocks showed that the untreated comparison block cracked in the fiber direction, but the treated block showed no cracks. This proves that the wood had been effectively stabilized by the treatment according to the invention with the preparation according to Example 8.

25th

The same experiment was repeated with the exception that the "Acrysol" 527 was omitted in the preparation according to Example 8. This experiment showed that both the treated block and the untreated comparative block showed crack formation after oven drying. This experiment proves that the acrylic polymer with. high molecular weight alone does not provide effective stabilization of the wood.

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Claims (15)

643177 1. A method for improving the properties of wood, characterized in that the wood is brought into contact with a sufficient amount of a water-dilutable resin in a water-miscible solvent to deposit an effective amount of the resin in the cell walls of the wood, whereby the resin contains molecules of such a size that they can penetrate into the free spaces of the cell walls in the presence of the solvent and that the resin in the cell walls is converted into a water-insoluble form. 2. The method according to claim 1, characterized in that one uses a water-containing solvent. 2nd PATENT CLAIMS 3. The method according to claim 1, characterized in that one uses a resin formed from a vinyl monomer. 4. The method according to claim 2, characterized in that one uses a resin containing at least 5 wt .-% molecules with a molecular weight of less than 1000. 5. The method according to claim 1, characterized in that the wood is additionally brought into contact with a sufficient amount of a chemical wood treatment agent in a water-miscible solvent in order to deposit an effective amount of the wood treatment agent in the cell walls before the resin is deposited in the cell walls converted into a water-insoluble form, and that one fixes the chemical wood treatment agent in the cell walls simultaneously with the conversion of the resin into a water-insoluble form in the cell walls. 6. The method according to claim 3, characterized in that the wood is additionally brought into contact with a sufficient amount of a chemical wood treatment agent in a water-miscible solvent in order to deposit an effective amount of the wood treatment agent in the cell walls before the resin is deposited in the cell walls converted into a water-insoluble form, and that one fixes the chemical wood treatment agent in the cell walls simultaneously with the conversion of the resin into a water-insoluble form in the cell walls. 7. The method according to claim 5, characterized in that the resin and the chemical wood treatment agent are simultaneously brought into contact with the wood in the same water-miscible solvent and are deposited in the cell walls of the wood. 8. The method according to claim 6, characterized in that the resin and the chemical wood treatment agent are simultaneously brought into contact with the wood in the same water-miscible solvent and are deposited in the cell walls of the wood. 9. The method according to claim 5, characterized in that one uses as a chemical wood treatment agent selected from the group of wood preservatives and flame retardants. 10. The method according to claim 6, characterized in that one uses as the chemical wood treatment agent selected from the group of wood preservatives and flame retardants and that the proportion of the water-miscible organic liquid is not more than 10 wt .-%, based to the weight of the resin / solvent mixture. 11. The method according to claim 10, characterized in that the proportion of the water-miscible organic liquid is not more than 5 wt .-%, based on the weight of the resin / solvent mixture. 12. The method according to claim 10 or 11, characterized in that one uses a water-soluble chemical wood treatment agent. 13. Preparation for carrying out the method according to claim 1, characterized in that it is a water-dilutable resin which can be converted into water-insoluble form under the influence of ambient conditions, a water-miscible solvent for this resin and a chemical dispersed in the resin and solvent Contains wood treatment agent and that the resin contains at least 10 wt .-% molecules with a molecular weight of less than 1000. 14. Preparation according to claim 13, characterized in that the chemical wood treatment agent is selected from the group of wood preservatives and flame retardants. 15. Preparation according to claim 13, characterized in that the chemical wood treatment agent is a water-soluble salt and that the preparation contains less than 5 wt .-% of the water-miscible organic liquid.