NZ215154A - Copper containing and chromate containing salt mixture for wood preservation - Google Patents

Description

New Zealand Paient Spedficaiion for Paient Number £15154 NO DRAWING V Priority Oate(s). .. }k T.^-.

Complete Specification F:ted:' ?*•. & Oasa: v ccK*&3|.ik.., ' 5 OMAR 1988 Publication Date: P.O. Journal. No: . !3X>. :86 215 15 4 if 13FEB m \<p SUBSTlTPIii* Of WliCAUT lMKB&::iUkZ< ■ c^c.i- -wwO liC^ Zu Patents form No.5 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION -v \ "COPPER-CONTAINING AND CHROMATE-CONTAINING SALT MIXTURE FOR WOOD PRESERVATION" —i,WE —WOLMAN GMSH—a German limited liability Company, organised and existing under the laws of the Federal Republic of Germany with a registered office at 757 3 Sinzheim, Federal Republic of Germany, hereby declare the invention, for which -I-/we pray that a patent may be granted to -me/us, and the method by which it is to be performed, to be particularly described in and by the following statement (followcd by page I A.) 21 r ' - 1A- 0.2. 0975/00035 Copper-containing and chromate-containing salt mixture for wood preservation The present invention relates to a copper-containing and chronate-containing salt mixture for wood preservation, 5 which is used by the accelerated fixing method.

It is known that wood can be protected from wood-destroying organisms by using inorganic preservative salt »ixtures which are introduced into the wood in the form of aqueous solutions by means of pressure differences 10 of by diffusion- To preserve wood under particular conditions (permanent contact with earth, water or weather), the composition of the protective salt mixtures must be such that they react with the wood to form water-insoluble, biocidal compounds which are resistant to Leaching- This 15 process is referred to as fixing. For the vast majority of conventional preservative salt mixtures, a content of hexavalent chromium (chromate) is absolutely essential for a fixing reaction. The duration of fixing is about 5-10 days for the conventional preservative salt formu-20 lations.

It is known that this time can be reduced to about 1-2 hours by supplying energy from outside (accelerated fixing), for example by supplying heat, eg. steam (superheated steam) or by generating a hi^h-frequency a.c. 25 voltage field (HF, microwaves).

Examples of conventional salt mixtures are the following mixtures: TABLE 1 CCB salts = chromium copper boron salts 30 CCF salts = chromium copper fluorine salts CCA salts = chromium copper arsenic salts CC salts = chromium copper salts.

Other chromate-containing formulations are also known, for example mixtures containing zinc compounds, 35 cadmium compounds, mercury compounds, tin compounds or lead compounds.

The usefulness of a formulation is determined by 215154 - 2 - O.Z. 0975/00035 the degree of fixing of the preservative in the wood.

The prior art shows that the presence of hexavalent chromium is absolutely essential for the initiation and continuation of the fixing process.

The hexavalent chromium has the following functions: 1. pH shift in the wood (increase in pH), 2. intermediate formation of complexes and sparingly soluble compounds containing hexavalent chromium (intermediate stage of fixing), 3. final formation of complexes and sparingly soluble compounds containing trivalent chromium (final stage of fixing), 4. initiation of redox processes in which the constituents of the wood participate (increase in the strength of the bond between the preservative and the wood substance), and . corrosion protection (passivation of the metallic implements) and stabilizer for the preservative solutions.

To ensure that the individual reactions take place efficiently, the contents of hexavalent chromium in the salt mixture must not fall below certain values; the conventional contents (in 2 by weight) of chromium and copper are given in the table below.

TABLE 2 CCB salts CCF salts CC salts CCA salts C u 6 - 122 6 - 122 6 - 152 6 - 162 Crxx 9 - 182 15 - 302 12 - 302 9 - 24% Cu: C r 1 1 1 1 XXX 1.5 2.5 2 1.5 x X X XXX based on the copper content based on the content of hexavalent chromium mean weight ratio of copper to chromium The table shows that the weights of chromium substantially exceed those of copper.

The compositions of three typical salt mixtures 2 1515 4 o - 3 - O.Z. 0975/00035 as shown in Table 2 are reproduced below: CCB salt: 34.002 by weight of CuSO^.S HjO Mixture 1 38.002 by weight of NagCrgO/^ HgO Cu:Cr = 1:1.5 25.002 by weight of H3BO3 3.002 by weight of water CCF salt: 37.002 by weight of CuSiF6.6 H20 63.002 by weight of (^4)2^267 Mixture 2 Cu:Cr = 1:3.5 CCA salt: 35.002 by weight of CUSO4.5 H2O 45.002 by weight of <2^207 20.002 by weight of AS2O5.2 H2O Mixture 3 Cu:Cr = 1:1.8 Chromium does not contribute to the biological activity of the wood preservative but serves merely for fixing the active preservative components (eg. copper) in the wood.

It is an object of the present invention to pro vide mixtures which permit the chromium content to be decreased without the degree of fixing of, for example, the copper being reduced.

We have found that this object is achieved, and 20 that inorganic copper-containing and chromium-containing salt mixtures for use in wood preservation effect good fixing of the copper, if they are used by the accelerated fixing method and the weight ratio of copper to chromium is higher than 1:1. A ratio of copper to chromium of 25 from 1.1:1 to 2:1, in particular from 1.1:1 to 1.75:1, is preferred.

It is surprising that, in spite of the lower chromium content of the salt mixture, the copper is fixed permanently in the wood.

For example, good fixing is achieved using salt mixtures having roughly the following compositions: 4 c; - 4 - 0.2. 0975/000375 TABLE 3 Cu* C r * * - -.XXX C u : C r CCB salts 12 - 182 8 - 122 1.50: 1 CCF salts - 152 8 - 122 1.25: 1 CC salts 14 - 212 8 - 122 1.75: 1 CCA salts - 202 7 - 132 1.50: 1 based on the copper content based on the content of hexavalent chroaiun mean weight ratio of copper to chromium.

The Table shows that the weights of copper sub stantially exceed those of chromium.

The compositions of three typical novel salt mixtures aS shown in Table 3 are reproduced below.

CCB salt: 43.001 by weight of CuSO^.S H£0 Example 1 26.002 by weight of Na^Cr?07.2 H?0 Cu:Cr = 1.2:1 26.002 by weight of Na 0^07.2 HjO 25.00? by weight of H3BO3 6.002 by weight of water CCF salt: 70.002 by weight of CuSiF^.6 HjO 30.002 by weight of (^4)2^207 Example 2 C u:C r = 1.14:1 CCA salt: 58.002 by weight of C u S 0 4 . 5 H2O 25.002 by weight of *2^207 17.002 by weight of AS2O5.2 H2O Example 3 Cu : Cr = 1.117:1 Fixing with the supply of energy from outside (accelerated fixing) and simultaneous reduction of the 25 chromate content of the salt mixture coupled with an increase in the biologically active components, in particular copper, have the following advantages: 1. substantial increase in the effectiveness against wood-destroying organisms, 2. reduction in the toxicity and the effect on the environment. <5, - 5 - O.Z. 0975/00035 Description of experimental procedures In general, the conventional and novel preservative salt formulations are used in the form of aqueous solutions having a concentration of from 0.5 to 10, pre-5 ferably from 2 to 6, 2 by weight.

Application is effected in pressure kettles or open tanks in order to achieve very deep penetration of the solution, and hence afford overall protection.

In tests to determine the resistance to leaching, 10 fixing is carried out (storage under cover for 5-50 days in the case of conventional mixtures and accelerated fixing for the mixtures according to the invention), followed by accelerated washout with water. To make the test more stringent, it is usual also to convert the 15 treated woods to chips in order to improve the access of the washout water.

Testing the resistance of conventionally treated and fixed woods to washing out is carried out by the usual methods.

For this purpose, 10 impregnated wood samples are stored in a fixing vessel at normal temperature (15 ° C), for A weeks, chipped when fixing is complete, and washed out six times in 600 ml of water each time. The contents of active ingredient in the washout water are determined, and ex-25 pressed as a percentage by weight of the amount of preservative absorbed during impregnation.

For accelerated fixing by treatment with external energy, the wood samples are either stored in an autoclave into which steam flows under atmospheric pressure (100°C) 30 for 60 minutes, of are exposed to a HF field for 10 minutes.

The resistance to washing out is then determined as described above.

A preservative is sufficiently resistant to the stresses caused by contact with earth, water and weather 35 only if not more than 8% of the total amount of copper and chromium introduced are dissolved out as a result of the washout procedure. • 215 154 - 6 - O.Z. 0975/00035 This is the case for the conventional preservative salt formulations stated in Table 2.

Table 4 compares the amounts absorbed (in g) and the washout rates (in 2) for the conventional salt mix-5 tures with those of the salt mixtures according to the i nvent i on.

In each case, ten wood samples were impregnated with a 42 strength aqueous preservative salt solution, fixed by the accelerated fixing method with the supply 10 of energy from outside (with the exception of experiment C 1) and then subjected to a washout procedure.

Claims (7)

2151 o r> - 7 - O.Z. I 0975/00035 TABLE 4 Amount of salt Amount washed out (X) absorbed (g) Cu C r Total A 1 5.587 2.422 0. 154 2.576 A 2 5.302 4. 147 0.371 4.518 A 3 5.629 3.925 0.278 4.203 B 1 5.417 3.875 00 «— • o 4.023 B 2 5. 19B 6 . 174 0.436 6.610 B 3 5.499 4 .623 0.241 4.864 C 1 5.243 4 1.832 0.314 42.146 A 1 A 2 A 3 = CCB salt according to Mixture 1, accelerated steam fixing = CCF salt according to Mixture 2, accelerated steam fixing = CCB salt according to Mixture 1, accelerated fixing by HF field B 1 = CCB salt according to Example 1, accelerated steam fixing B 2 = CCF salt according to Example 2, accelerated steam fixing B 3 = CCB salt according to Example 1, accelerated fixing by HF field conventional mixtures acccord-ing to the invention CCB salt according to Example 1, standard fixing procedure (4 weeks) (not according to the invention) 3.1 S1 ■s O.Z. 0975/00035 elaimt- WHAT ^/WE CLAIM IS-.

1. An inorganic copper-containing and chromate-containing salt mixture for use in wood preservation by means of accelerated fixing, wherein the weight ratio of copper to chromium is greater than 1:1.

2. A mixture as claimed in claim 1, wherein the weight ratio of copper to chromium is from 1.1:" to 2:1.

3. A mixture as claimed in claim 1, which contains, as further components, boron compounds, fluorine compounds, arsenic compounds, zinc compounds, cadmium compounds, mercury compounds, tin compounds or lead compounds, individually or as a mixture.

4. A method for preserving wood, wherein the wood is treated by an accelerated fixing procedure with a copper-conta in ing and chromate-containing salt mixture in which the weight ratio of copper to chromium is greater than 1:1.

5. A method as claimed in claim U, wherein an aqueous solution of the salt mixture is used.

6. An inorganic copper-containing and chromate-containing salt mixture as claimed in claim 1 substantially as herein described with reference to Table 3 or Table 4.

7. A method of preserving wood as claimed in claim 4 substantially as herein described with reference to the Experimental Procedure. BALDWIN, SOU F< CAREY Of- Qj. \ d\My ATrnhnrYP ion run /MTLir/rn? fT f