CA1272854A - Wood preservative - Google Patents

Abstract

Abstract of the Disclosure: An agent for impregnating solid wood by the pressure process, based on a water-dilutable formulation of a copper salt, excess alkanola-mine and, if required, a salt with a fungicidal anion, has a pH of not less than 8 in the concentration usually employed and corresponding to about 1 - 5% by weight of non-aqueous components in the aqueous solution.

Description

~.~7~54 - l - O.Z. 0975/00037 Wood preservative The present invention relates to the provision of agents for the pressure impregnation of (solid) wood, which are based on aqueous formulations of a copper salt, S m~noethanol~ne and, if requ;red, further components, in particular fungicidal salts whose action is attributabLe to the anion, for example salts of boric acid.
To date, chromate-containing, fixing wood pre-servatives have been employed for protecting wood which is exposed to weathering or humidity or, as part of a structure, ;s ;n contact with earth. These wood preserva-t;ves are used in the form of aqueous solutions, eg. from

2 to 6~ solut;ons, depend;ng on the level of risk to which the ;mpregnated wood is subsequently exposed~ the treatment being carried out with the aid of large ;ndus-trial impregnation plants (pressure ;mpregnat;ng process).
For use ;n contact with earth, the agents used are exclusively those which conta;n not only chromate but also copper, owing to the fact that they have to be 2Q effective against wood rot caused by fungiO A d;st;nct;on is made between the CC type (based on copper and chromium), the CC~ type (based on copper, chromium and boron), the CCF type (based on copper, chromium and fluor;ne) and the CCA type (based on copper, chrom;um and arsen;c).
2S Fixing in these wood preservatives is via the chromate part. After ;mpregnat;on, the chromates react with the sonstituents of the wood and are reduced to trivalent chromium compounds; as a result, the pH in the wood increases so that copper compounds and chromium com-pounds are prec;p;tated ;n the wood as water-insoluble compounds and are fixed.
However, chromates, ie. hexavalent chromium com-pounds, constitute a considerable risk for the environment when leakage or weather effects during the fixing process result in these compounds being washed out, so that sur-face water, ground water and tap water are contaminated.
The maximum concentration currently tolerated is, for 74 ~
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- 2 - o.Z. 0975/00037 example, 0.05 ppm. Even if the chromium in the wood is present in trivalent form, it can, bey oxidation, be converted to hexavalent chromium compounds, which may then be washed outoftheash;
thisgivesrisetoproblemswithregardtodisposal.
To date, chromium-free, copper-contain;ng, water-soLuble wood preservatives for large-scale industrial impregnation have been proposed, in which, for example, copper arsenate and borate are converted to a water-soluble alkaline form by complex formation with ammonia~ These agents are fixed in the wood by evaporating the ammonia and as a result of buffering with wood constituents (the pH of the wood itself is about 5). Apart from the odor nuisance, these impregnating solutions, or the concentrates, may lose their stability through the evaporation of the ammonia, so that the solutions are no longer suitable for further impregnation. Furthermore, when the ammonia content is insufficient, penetration of the preservative into the wood is hindered.
Amines having good complexing properties, eg.
ethylenediamine, have also been recommended for wood preservatives containing copper and fluorine, for the protection of wood-based materials, eg. particle boards.
- These agents are mixed into the resin in highly concen-trated form and, together with the resin, are sprayed onto the chips. They are unsuitable for preserving solid wood s;nce the ethylenediamine complexes are stable, even at the p~ of the wood itself t5-6) and do not fix; they are washed out of the wood by ~ater.
Copper is fixed only when water-insoluble organic copper salts can form. For example, wood preservatives which contain copper salts of N-nitrosocyclohexylhydroxyl-amine tnew name: copper salt of N-cyclohexyldioxydiazenium oxide, Cu-HD0) have been described. The Cu-HDO is con-verted, via polyaminPs, eg. ethylenediamine or diethylene-triamine, into wood preservative concentrates, which aredissolved in water in order to carry out impregnation~
They become fixed in the wood as a result of buffering ~. .~

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with the aid of wood constltuents from about pH 7.5.
However, this fixing takes place so rapidly that pene-tration of the Cu-HDO is preven-ted during pressure impreg-nation. For example, even in the case of pine, which can be easily impregnated, the Cu-HDO only penetrates an outer layer of about 10 - 15 mm. Dispersing of the preservative toward the inside falls off rapidly.
If other amines, eg. alkanolamines, in parti-cular monoethanolamine, are used for complexing, the Cu-HDO is completely dissolved only in highly con-centrated solutions; dilution with water to the concen-tration for use precipitates it once again.
We have found that the disadvantages described above can be overcome if use is made of an agent for solid wood preser~ation comprising a water-dilutable formulation of a water-soluble or insoluble, inorganic copper compound, such as copper sulfate, copper fluoro-borate, copper hydroxide, copper borate, copper fluoride, copper carbonate or copper oxychloride, in admixture w it h m on oe t h an o 1 a m i ne p r e s e n t in an amount such that when the formulation composition is diluted with water to a wood treatment concentration of about 1 to 5% of the non-aqueous components in the aqueous solution, a pH of not less than 8 is established in the resulting aqueous composition.
The water-dilutable agents contain the copper in concentrated form, in general in an amount of from 1 to 15~ by weight, calcula-ted as the element.
Suitable concentrates contain, for example, from 5 to 50% by weight of a copper salt, from 5 to 50%
by weight of monoethanolamine, up to 50% by weight of a salt of a fungicidal anion and up to 5% by weight of free alkali, the percentages summing -to 100, and, if desired, minor amounts of other components, such as amines, ammonia, corrosion inhibitors and, if required, ~ .

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- 3a -water, the amount of which can, however, generally be kept small and essentially facili-tates handling. However, t~e present invention also relates to the impregnating solutions of appropriately lower specific concentrations, these solutions being prepared by dilution with water.

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- 4 - O.Z. 0975/00037 Complexing can be carried out in the presence of fungicidal anions, eg. borates or fluorides. Dissolv-ing the copper compounds in the alkanolamine, in particular monoethanolamine, if ne~essary with the addition of water, gives highly concentrated ~ater-soluble pastes or l;quid concentrates which, when dissolved in water, can be used for impregnating ~ood. The pH of the aqueous impregnating solut;ons is 8 or higher, in particular from 9 to 10 (con-centration-dependent). ~hen impregnation is carried out by the pressure process, the copper component penetrates thoroughly into the ~ood. During the impregnation pro-cess, the novel preservatives are buffered by the wood acids present in the wood, the copper being precip;tated ;n the ~ood from abou~ pH 7. From pH 7 - 7.5, the com-1S plex-forming power of the alkanolamines is in fact no longer su~ficient to keep the copper in solut;on, so that the copper is fixed. The extent to which the copper is fixed is of the same order of magnitude as for the pre-v;ous chromate-containing and copper-containing wood pre-ser~ati~es, ie. not less than 85~, and on average from ~ 90 to 95~, of the copper component is fixed in the wood.Fixing is partly dependent on the additional alkanolamine content which is required for adjusting the pH in the case of strong acids or fungicidal anions; a certain effect in respect of pH shift can~ however~ also be achieved by adding~ for example, an alkali metal hydro~ide solution, for example sufficient to produce a pH shift of up to about 1. In g2neral, th;s measure applies to the amount of fungicidal anions or acid radicals; it can also be brought to the required pH, independently of complex formation, by an alkali, ammon;a or another water-soluble amine.
For economic reasons, -the complexing agent is monoethanolamine. The novel wood preservatives may

3~ howeve.r also contain other alkanolamines, eg. isopropanolamine, 1,1- or 1,2-diaminoethanol, am;no-ethylethanolamine, diethanolamine, dimethylethanolamine, . . - . - . . .
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- : ,- -.,: . :: -- - 5 - O.Z. 0975/00037 etc. The amount of alkanolamines added is such that it is sufficient for complex formation with copper (1 g atom of copper generally requires 4 mol equivalents of amine) and, if necessary, for forming alkanolamine salts of the fungi~idal anions additionally used (fluoride, borate or fluoroborate) or esters, so that the aqueous impreg-nating solution is brought to a pH of 8 or higher, prefer-ably from 9 to 10.
To test the invention in practice, the following procedure was adopted: the concentrates, in the amount stated in each case (4 or 3%) were diluted with water, and the product was used to impregnate small pine blocks.
After drying, the stated blocks were washed for 4 weeks with distilled water, the water being changed daily.
The amount of copper washed out was then determined.

A mixture of 33.3% by weight of CuS04.5H20, 33.3% by weight of monoethanolamine and 33.4% by weight of water is dissolved in water in a concentration of 40 9 per liter of water (referred to below as 4% strength solution).
Amount of copper washed out 7.5%~

25 ZO.OX by weight of 3Cu(OH)2.CuCl2, 40.5% by weight of monoethanolamine and 40.0Z by weight of water (4X strength aqueous solution).
Amount of copper washed out 10.5%.

15.0% by weight of Cu(OH)2.CuC03, 16.0% by we;ght of monoethanolamine, 16.0Z by we;ght of aminoethylethanolamine, 25.0% of H3~03 and 35 38.0% of Hzû
t4% strength aqueous solution).
Amount washed out:

7~8~i~

- - 6 - O.Z. 0975/00037 Cu 10.5%
85.5%.

13.5% of Cu(OH)2, 25.0% of boric a~id, 17.5% of monoethanolamine, 17.5% of àminopropanol and 26.5% of water (4~ strength aqueous solution).
Amount washed out:
Cu 7.7%
8 86.5%.
EXAMPLE S
50% of CU(8F4)2 solution (dissoLved in water to give a Sû~ strength solution), 30% of monoethanolamine and 2û% of H2û
(3% strength aqueous solution, defined as above).
Amount washed out:
Cu 10.5%
F 70.0%
8 7S.û~.

16.5% of Cu(OH)2.CuC03, 10X of NH4HF2, 36.0% of monoethanolamine and 3.5X Of H20 ~3X strength aqueous solution).
Amount washed out:
Cu 0.5%
F 78.5%.

15.0% of Cu(OH)2.CuC03, 30% of aminoethanolamine, 25.0% of boric ac;d and 27.0% of HzO
(4% strength aqueous solution)~

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- 7 - O.Z. 0975/00037 Amount washed out:
Cu 12.5~
B 88.0%.

70% of copper borate paste (dispersed in water to give a 50% strength dispersion) and 30% of monoethanolamine (4~ strength aqueous solution).
Amount washed out:
`lO Cu 7~5%
a 85 . 0% .

75% of copper borate paste (dispersed in water to give a 50% strength dispersion) and 25X of monoethanolamine (4% strength aqueous.solution).
Amount washed out:
Cu 6.2%
B 66.1%.

Chromiu~-containing salts:
1a~ Type CC8 Cu content 8.6%
Cr content 13.4~
8 content 4.4%
lb) Type CCF
Cu content 7.7%
Cr content 25.5X
F content 14.5%
30 1a) Type CC8Amount washed out, in %
Cu 8.0 Cr 2.0 . B 93.5 1b) Type CCFAmount washed out, in %
Cu 13.5 Cr 18.5 F 72.5.

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- - 8 - O.Z. 0975/00037 (not according to the invention) 12.0% of CuO, Z2.0% of ethylenediamine, 12.0~ of KHF2 and 54.0% of water dissolved in water to give a 3~ strength solution.
Amount washed out:
Cu 75.5~
F 92.5~.

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Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An agent for solid wood preservation comprising a water dilutable formulation of a) an inorganic copper compound, and b) monoethanolamine, present in an amount such that when the formulation composition is diluted with water to a wood treatment concentration of about 1 to 5% of the non-aqueous components in the aqueous solution, a pH of not less than 8 is established in the resulting aqueous composition.

2. An agent according to claim 1, wherein the inorganic copper compound is selected from the group consisting of copper sulfate, copper fluoroborate, copper hydroxide, copper borate, copper fluoride, copper carbonate and copper oxychloride.

3. An agent according to claim 1 or 2, which further includes a compound having a fungicidal anion.

4. An agent according to claim 1 or 2, which further includes boric acid or a salt of boric acid.

5. A process for preparing a wood impregnating solution which comprises:
- diluting a mixture of (a) an inorganic copper compound and (b) monoethanolamine, with water, and - adjusting, if necessary, the pH of the resulting aqueous mixture to pH 8 or higher with monoethanolamine or alkali metal hydroxide.