US1957873A - Wood preservative - Google Patents

Description

Patented May 8, 1934 PATENT OFFICE WOOD PRESERVATIVE Karl Heinrich Wolman, Berlin-Grunewald, and Hans Pflug, Berlin-Wilmersdorf, Germany, assignors to Grubenholzimpragnierung G. n. b.

H., Berlin, Germany No -Drawing. Application July 10, 1930, Serial No. 467,130. In Germany August 10, 1929 3 Claims. (01. 13478.6)

The present invention relates to improved water-soluble preservatives for wood. It is known, that numerous water-soluble preservatives, such as the salts of hydrofluoric acid and fiuosilicic 5 acid, or the soluble arsensic compounds, for instance the soluble salts of arsenic acid and ar-' senious acid, have a good fungicidal action, but

in practice do not show a protective action, which is in all cases satisfactory and more especially sufficiently durable, since they may easily be leached out of the wood upon water entering the wood in the form of atmospheric deposits,-such as rain or snow or soil water or the like and thus become incapable of protecting the wood against destructive fungi and pests. For the purpose of avoiding this drawback it has already been proposed, to use diflicultly-soluble conrponds for preserving wood. It has been proposed for instance to impregnate the wood successively with two solutions, the ingredients of which react in the wood to form a difiicultly-soluble, preservative compound. Use has also been made of solutions, which when they dry in the wood involve chemical changes between the constituents of the solution, which cause the formation of dificultly-soluble compounds in the wood. Both processes possess, however, certain disadvantages. If two solutions are introduced into the wood, which by their reaction are to form the difiicultly-soluble pre- 0 servatives, there is reaction of the twp solutions is not complete, since the presence of the first solution introduced into the wood hinders the penetration of the second solution, more especially into the deeper layers of the wood. The processes belonging to the second group mentioned above, in which therefore-the wood is only treated with one solution,

from which the, difiicultly-soluble preservative is formed after drying, show the drawback that the 40 solutions are not sufiiciently stable and readily decompose more especially at an increased temperature. If therefore such solutions are kept for some time, it may easily happen that the composition of the solution changes in an undesirable way before impregnation, and the same position may arise if the solutions are heated prior to the impregnation, which is desirable in many cases to facilitate impregnation. V

We have found that these drawbacks can be avoided and at the same time a preservationof the wood which is resistant to leaching out by water can be pbtained, if other compounds such as for instance chromic acid or dichromic acid or salts of these acids, namely potassium chromate, sodium chromate, alkali dichromates,

always the difficulty that the' atives.

potassium dichromate or sodium dichromate, also suitable compounds of the light and heavy metals singly or in mixture are added to the soluble protectives, for instance fluorine compounds, more especially the soluble salts of hydrofluoric acid or fluosilicic acid, arsenic compounds, for instance the soluble salts of arsenic acid and arsenious acid. These former substances are capable on the one hand of diminishing the capacity of the said soluble preservatives to be leached out, andon the other hand of themselves becoming bound to the wood substance in such a way that they are diflicult to wash out. These substances used as additions to the water-soluble preservatives we term in our application fixatives, These fixatives can be dissolved together with the protectives in water. After introduction into the \wood or after the drying of the impregnating solution, the added substances effect a fixing of the preserving media and also themselves become fixed to the wood fibres in such a way that they are difficult to wash out. We use the fixatives in such quantities, that of the preserving agents introduced into the wood at least 30% are fixed to the wood fibres so that they cannot be washed out. We mean by this that the wood treated with the preservatives according to the invention can be treated with water at ordinary tem-' peratnre without more than 70% of-the preservative originally introduced into the wood being able tobe leached out. Preferably we employ the fixatives in amounts of more than 20% of the total amount of the salts. The composition of the preservative can naturally vary within wide limits and depends upon the protective substances and the fixative used. I

Other suitable fungicidal or insecticidal substances or substances reducing the infiammability of the wood, such as for instance nitrated phenols or their salts, phosphates, borates, acetates, salts of ammonium and so on can also be added to the aforementioned mixtures of preservatives and fixative. Use may also be made of a mixture of several preservatives and a mixture of several fix- The new preservatives can be used to impregnate wood in any suitable manner, for instance by saturating in closed vats with the use of vacuum and pressure, by steeping in the impregnating liquid in open troughs, by the so-called inocculation process, by introduction into receptacles, which are placed on or round the wood, by coating and the like. Prior to the impregnation there can be a suitable preliminary treatment of the wood, in which it is subjected for instance in a manner known per se to aelectricity, air or gases. the new impregnating Example 1 1 part of potassium bichromate and 1 part of sodium fluoride are mixed and a 2% aqueous solution prepared from this salt mixture. This solution is used to saturate wood in a closed vat according to the so-called full cell process at 7080 C.

'Example 2 45 parts of potassium bichromate, parts sodium fluoride and 5 parts dinitrophenol are mixed and this salt mixture used in a manner known per se' for impregnating wood in a 1,8% solution.

The excellent effect of the preservative according to the invention is evident for instance from the following: A salt mixture was prepared from 50% sodium fluoride, 45% potassium bichromate and 5% dinitrophenol. A 2% solution was prepared from' the mixture and logs of sound, clean pinewood-were fully saturated with the solution. In carrying out the saturation it was accurately determined how much solution or preservative was introduced into the wood. After saturation the logs were dried by leaving them in the open air and when dry were cut up to the size of matches. The out up wood was exposed tothe leaching action of water at ordinary temperature. This was done by shaking 100 grins. cut up wood in a glass flask of aboutllitre capacity with 600 ccms. water firstfor 2 hours, then with another .600 ccms. water for 4h'ours and then with a further 600 ccms. water for 8 hours on a shaking machine.

The shaking with 600 ccms. water for 8 hours in each case was repeated five times more, so that in all 8 shakings with 8x600 ccms. water took place in the whole 54 hours. A continued washing showed that further washing waters contained practically no moreimpregnating materials, so

that the whole amount of impregnated salt, capable of being washed out was removed from the wood by the 8 shaking processes. The washing liquors were tested for their content of leachedthat after the n 8 shaking processes had been carried out, there out constituents, and it was found was still 365% of the preservative introduced into the wood, remaining therein.

The salts of the other light and heavy metals were tested in a similar way, but proved however in some cases less economical and in some cases they gave less favourable results than the chromium salts.

. What we claim is:

1. A water soluble preservative for wood fibre consisting essentially of a water soluble salt of hydrofluoric acid to which a water soluble chromium salt is added as a fixative, the two beingin about equal quantities so that'more' than 30% of the preservative will be fixed on the wood fibres and will not wash out.

2. A water soluble preservative for wood fibre consisting essentially of equal parts of a water soluble salt of hydro-fluoric acid and a water soluble salt of arsenic'to which a water soluble salt of chromium has been added as a fixative in quantity equal to about two-thirds of'the amount of the preservative, so that more than 30% of the preservative will be fixed on the wood fibres and willnot wash out.

3. A water soluble preservative for wood fibre consisting of about 40% of a water soluble salt of hydrofluoric acid, about 40% of water soluble'