NO117553B - - Google Patents

Abstract

A wood preserving composition comprises a biocidal Cu and/or Zn component, a fluorine component and a chromium-oxygen component in the form of water-soluble compounds in which the chromium has a valency of 6, the fluorine being in the form of a complex boroboro fluoride and/or silico fluoride and the Cr: F atomic ratio being at least 3:6. The composition ingredients may be selected from Cu or Zn oxide and/or salts; Na, K or NH4 borofluoride or silicofluoride, Mg silicofluoride; Na, K and NH4 chromate or dichromate, chromic acid or anhydride; and Cu or Zn borofluoride and/or silicofluoride.

Description

Wood preservative against harmful plant or

animal organisms.

Known" wood preservatives, which are particularly suitable for use on wood that is built up in the open and that has the property of fixing in the wood, consist of alkali fluorides, alkali chromates and/or alkali arsenates or the corresponding ammonium salts.

A particular advantage of such an alkali fluoride-containing wood preservative is that the fixation in the wood proceeds relatively slowly and the overall fluoride is not fixed. It is therefore also suitable for the impregnation of hard-to-impregnable types of wood such as e.g. fir, and next to use in the boiler pressure process as well

suitable for such impregnation processes that require not just hours but days, like various other processes, e.g. trough humidification, etc. A further advantage consists in the fact that part of the fluoride

during the service life of the impregnated wood remains diffusible,

and is thereby able, especially after water access, to penetrate wood zones that were not yet covered by the impregnation process.

The effect of these agents against wood-destroying insects

and fungi from the group Basidiomycetes are, good; however, relatively high dosages are necessary in the case of certain lower types of fungi, which are known as mold rot-producers.

Other wood preservatives are known which are particularly useful for wood which is mainly exposed to attack by mold decay agents; they consist of water-soluble copper and/or zinc salts, predominantly copper sulphate - and alkali chromates and/or chromic anhydride.

These wood preservatives do indeed have a good effect against wood-destroying insects and mold rotting agents, however relatively high dosages are necessary against the wood-destroying substances from the group Basidiomycetes, especially against Poria vaporaria.

A further group of wood preservatives, which are also particularly suitable for use on wood outdoors, and have the property of fixing in the wood, consist of water-soluble copper and/or zinc salts - mainly copper sulphate, arsenate and chromate - alkali chromates and/ or chromic anhydride, alkali arsenates and/or arsenic anhydride. These wood preservatives have a good effect against wood-destroying insects, fungi: from the group of Basidiomycetes and mold decay agents.

Due to their compositions, they fix relatively quickly and completely. They are therefore only suitable for impregnation procedures, which are completed within hours. As no diffusible components remain in the wood after the fixation has been completed, these agents cannot penetrate wood zones, which are not covered by the impregnation process itself. They have therefore only found little use for wood types that are difficult to impregnate, such as e.g. spruce.

It was close to producing mixtures of copper and/or zinc salts - preferably copper salts - with alkali fluorides and alkali chromates. Of such wood preservatives, in addition to a good effect against wood-destroying insects due to the copper and/or zinc salt content, it was expected to have a good effect against mold rotting agents and, due to the content of alkali fluorides, a good effect against Basidiomycetes. At the same time, such salt mixtures should have the advantages of relatively slow and incomplete fixation, with a consequent effect on the applicability for longer-lasting impregnation methods, as well as the advantage of a mobile component part, and thus application in difficult-to-impregnate types of wood such as e.g. spruce. Moreover, such salt mixtures would also be applicable for such purposes where arsenates could not be used for hygienic reasons. In fact, such wood preservatives are mentioned in various patent documents and in the literature. However, they have not come into use as they have a strong corrosive effect on steel. The corrosion properties can only be improved when either the copper and/or zinc salt or fluoride content is lowered so strongly that it becomes practically ineffective.

The invention thus relates to a wood preservative against harmful plant and animal organisms with a content of alkali dichromate and/or chromates and/or chromic acid in amounts corresponding to 10-40 weight percent chromium, water-soluble copper and/or zinc salts in amounts corresponding to 5-30 weight percent of copper and zinc and complex fluorine compounds in amounts corresponding to 5-30% by weight of fluorine,

and the agent is characterized in that the atomic ratio between chromium and fluorine must be at least 3:6, preferably 4-5;6.

The wood preservative according to the invention fulfills the conditions laid down in DIN 52.168 "Prufung von Holzschutz-mitteln. Bestimmung der Korrosionswirkung auf Stahl".

The wood preservative according to the invention is effective

against fungi from the group Basidiomycetes as well as salt mixtures, consisting of alkali fluorides, alkali chromates and/or alkali arsenates. They have the same effects against mold rot-producers as salt mixtures consisting of copper and/or zinc salts, alkali chromates and/or chromic anhydride, alkali arsenates and/or arsenic anhydride. The effect against wood-destroying insects is similar to the effect of the above-mentioned salt mixture.

The fixing speed of the wood preservatives according to the invention is similar to that of salt mixtures, consisting of alkali fluorides, alkali chromates and/or alkali arsenates. They are therefore well suited for various impregnation methods (boiler pressure moistening, fresh juice method, trough moistening, etc.).

A further advantage consists in the fact that, as expected, the total fluoride is not fixed in the wood, but that during the service life of the impregnated wood a part remains diffusible and is thereby able, especially after water access, to penetrate into wood zones that were not covered by the impregnation process itself .

Moreover, it was surprisingly found that not only a part of the fluoride, but also a part of the copper and/or zinc salt remains diffusible and thus the metal components effective against mold decay agents penetrate into the zones that are not covered by the impregnation process itself.

Due to this relatively slow and incomplete fixation, the wood preservative according to the invention is also particularly well suited for wood types that are difficult to impregnate, such as e.g. spruce.

Copper and/or zinc are used as water-soluble salts, preferably as sulphates or as boron fluorides or silicon fluorides.

The complex fluorides can either be used immediately

as boron or silicofluorides of said metal, as alkali boron fluorides or as water-soluble silicofluorides (magnesium, ammonium silicofluorides, etc.).

As water-soluble chromic oxygen compounds, the alkali compounds of chromic acid and polychromic acid are used - especially sodium chromate, potassium chromate, ammonium chromate, sodium dichromate, potassium dichromate and ammonium dichromate, possibly also mixtures of these salts and/or chromic anhydrides. In the case of mixtures containing silicofluorides, due to the higher solubility, ammonium dichromate and/or chromic anhydride are preferably used.

The application concentration of the wood preservatives according to the invention is based on the absorbency of the types of wood to be impregnated, their intended use and impregnation methods.

For use in boiler pressure humidification, e.g. aqueous solutions with a content between 2 and 6 percent by weight of the wood preservative. When impregnating by artisanal methods (e.g. ironing, spraying, etc.), concentrations between 10 and 25 percent by weight are used. For cooling tower maintenance, concentrations between 25 and 5% by weight are used.

The maximum solubility of the wood preservatives according to the invention is above 50% by weight.

The examination of corrosion according to DIN 52.168 was carried out in the following way: 500 ml of the wood preservative was filled into a plastic container and a pre-weighed steel can with a known surface was suspended in this container. The container is kept for 7 days at 20°C, and then the weight loss of the can is determined with reference to its surface.

In the following, the results are reproduced, as in the examples

2, 3 and 7 show that severe corrosion occurs at Cr : F ratios below 3 : 6.

Example 1.

45.3% CuSiFg. 6 H 2 O

54.7% (NH 4 ) 2 Cr 2 O 7 Cr : F - 3 : 6 2 and 4% solutions gave a weight loss of "}1.6 and 25.3 g/m2;

no hole attack.

Example 2.

36.2% Cr02

14.3* Cuo

49i5% MgSiFg . 6 H 2 O Cr : F - 2 : 6

2 and 4%-igé solutions gave a weight loss of 106 g/m2 and macroscopically

noticeable hole attacks.

Example 3.

43.3%CrO3

12.7% CuO..

44.056 MgSiFg . 6 H20 Cr : F = 2.7 : 6

weight loss of 2 and 4% solutions: 155°S 73»9s/m<2>»

macroscopic hole attack.

Example 4.

48.3* CrO3

11.6% CuO

40.1% MgSiFg. 6 H20Cr : F - 3.3 : 6

Weight loss of 2 and 4% solutions: 12 and 1.2 g/m<2>; the

was no hole attack.

Example 5.

53.0%CrO3

10.6% CuO

36.4% MgSiFg. 6 HgO Cr : F 4 : 6 2 and 4% solutions gave a weight loss of 0.3 and 0.5 g/m<2>. No hole attack could be determined.

Example 6.

44.0% CuSiFg. 6 HgO

56.0% Cr03 Cr: F 4: 6

The weight loss of 2 - 20% solutions was between 0.8 and 15.6 g/m<2.>

No hole attack could be determined.

Example 7.

33', 6% CrO3

13.3% CuO

53.1% ZnSiFg. 6 H 2 O Cr : F -2: 6.

Weight loss of 2 and 4% solutions was at 159°g 47»2 g/m<2>. Macroscopic pitting could be seen.

Example 8.

50.3% CrO3 10.0% CuO

39.7% ZnSiFg. 6 H20 Cr : F - 4 : 6 Weight loss of 2 and 4% solutions amounted to 0 and 0.7 g/m<2>.

No hole attack could be observed.

The leaching test showed that a diffusible fluoride as well as a copper part remains in the wood after fixation. Example Q. 44.0% CuSiFg. 6 H 2 O

56.0% CK>3 In Cr : F = 3 : 6

With a 4% solution of this salt mixture, spruce sapwood is fully moistened according to DIN 52.176 sheet 2 and the leachability is determined. 40% of the copper and 50% of the fluorine are washed out.

The limit value of the effect after leaching against wood-destroying fungi from the Basidiomycetes group amounts to 6 kg/m^ compared to those from the mold rot-producing group 11 kg/rn-^.

According to DIN 52.176 sheet 2, the determination of the leachability took place in the following way: 10 normal blocks of spruce sapwood and, as necessary, also the other types of wood considered for the relevant applications are moistened under negative pressure at room temperature (20°C + 2°) with the wetting liquid, whose concentration is adapted to the practical purposes. The liquid absorption is determined by weighing the bricks before and after wetting. After moistening, the blocks are immediately divided into small sticks of 3 m thickness by splitting and, in order to allow the possibly occurring interaction of the moistening substance to run off with each other or with the wood, are treated in the following way: After the moistening, the small sticks remain, during whose moistening organic substances were used solvents or volatile protective substances left in air for 4 weeks. They are then leached as described below: The small sticks moistened with aqueous solutions are stored loose after the moistening for the first 14 days in a closed vessel of 10 to 20 cm height. The cut glass is then opened a little further every day, so that after 14 days it is completely opened and the small rods air-dried. Then leach out. In order to quickly and completely fill the wood cavities with water, the wood is placed in 600 cm^ of distilled water, thoroughly moistened using negative pressure and then brought with the water into a wide-necked glass bottle of 1 liter capacity. After 1 hour, drain off the liquid. The flask then remains standing with each time 600 cm^ constantly renewed distilled water for 2 and 4 hours (1st day), 8 hours (2nd day) and 8 hours (3rd day) as well as finally shaken for 72 hours (4th to 6th day).

During the breaks after the 1st, 2nd and 3rd day, the wood remains without water in the closed bottle.

Depending on the specified time intervals, the water is drained off and analyzed separately.

Example 10.

30.7% Cu(BF4)2

69.3% CK>3Cr : F = 4 6

Weight loss 1.5 to 10% solution amounted to 1.0 to 28.7 g/m . Hole attack could not be determined.

Example 11.

30.5% CuSO4.5H2O

20.8% NH^HF2Cr : F = 4 : 6

48.7% CrO3

Weight loss of 1.5 to 10% solution amounted to 216 to 1,271 g/m . With the exception of the 1.5% resolution, macroscopic hole attacks were observed in all cases.

Example 12.

36.2% CuSiF6.5<H>2<0>

63.8% (NH4)2C<r>207Cr : F = 4 : 6

The determination of the leachability according to DIN 52.176 sheet 2 showed that 4% of the copper and 50% of the fluorine had been washed out.

Corrosion tests were carried out in accordance with DIN 52.168. This norm tolerates a weight loss of up to 60 g/m, but macroscopic pitting is not permitted.

Example 13.

45% potassium bichromate,

50% sodium fluoride,

5% dinitrophenol,

Ratio Cr : f - 1 : 3.9.

(Donna salt mixture corresponds to example 2 1 of the British patent no. 352,272).

Weight loss of a 2% solution: 28.3 g/m<2>.

Weight loss of a 4% solution 0.4 g/m2.

No hole attack.

Example 14.

30.1% potassium bichromate,

33.4% sodium fluoride,

5.0% dinitrophenol,

31.4% copper sulfate,

Ratio Cr : F - 1 : 3.9

(This salt mixture again corresponds to example 2 in the British patent no. 352,272, but a copper salt is added to it in an amount that corresponds to the salts according to the invention).

Weight loss of a 2% solution 242.6 g/m<2>. Weight loss of a 4% solution 216.0 g/m2.

Macroscopic hole attack.

Example 15.

52.4% ammonium bichromate,

43.0% copper silicofluoride,

5.0% dinitrophenol,

Ratio Cr : F « 1 : 2.

(This salt mixture corresponds to the mixture according to the application, to it

is only dinitrophenol added).

Weight loss of a 2% solution 40.7 g/« •

Weight loss of a 4% solution 9*0 g/m<2>.

No hole attack.

Example 16.

39.6% ammonium bichromate,

55.4% copper silicofluoride,

5.0% dinitrophenol,

Ratio Cr : F - 1 : 3.9.

(In this salt mixture silicofluoride is indeed used, but the Cr/F ratio corresponds to the example in British patent no. 352,272).

Weight loss of a 2% solution 3°7»8 sA2»

Weight loss of a 4% solution 212.1 g/m<2>.

Macroscopic hole attacks.

These examples show that the corrosion of salt mixtures containing fluorides, chromates and copper and to which impregnating agents such as e.g. dinitrophenol, is only kept within the limits that are tolerable according to DIN 52.168, when - as according to the present application - complex fluorides are used and a Cr/F ratio is observed in which so much chromate is used that the ratio

at least amounts to 1:2.

Claims (1)

Wood preservative against harmful plant and animal organisms with a content of alkali dichromate and/or chromates and/or chromic acid in amounts corresponding to 10-40 weight percent chromium, water-soluble copper and/or zinc salts in amounts corresponding to 5-30 weight percent copper and zinc and complex fluorine compounds in amounts corresponding to 5"3% by weight fluorine, characterized in that the atomic ratio between chromium and fluorine must be at least 3:6, preferably 4-5:6.