WOOD PRESERVATIVE

Abstract: The invention relates to preservative compositions for treating timber comprising a boron-containing preservative characterised in that the composition further comprises a thickening agent.

Description: This invention relates to compositions and methods for the treatment of timber, and in particular to compositions and methods which involve the diffusion of one or more treatment chemicals into the timber. The invention has particular application to compositions and methods including inorganic boron-containing salts and compounds, and use of the same in timber treatment. A method of treating timber is known which typically involves a preservative composition being applied to timber, the preservative composition thereafter diffusing into the timber. Methods of application include immersion, multiple dipping, soaking, rolling, spraying or painting. Up until this time it has often been necessary to prepare a solution for the treatment of timber by providing heating facilities to a tank to dissolve boron salts, such as for example a mixture of boric acid and borax, the solution thereafter being maintained at a predetermined temperature during treatment, to maintain a relatively high solution concentration. such a process has been found to be relatively expensive and requires specialised equipment. In the treatment of certain woods and timbers, such as for example Pinus radiata , it has been possible to utilise boron-containing preservatives using diffusion techniques. However, the treatment of refractory species (for example hardwoods such as eucalyptus) with boron-containing solutions has not been practical. Hot working solutions have tended to leach wood sugars out of timber, creating strong acids and causing precipitation of the preservative from the working solution. On the other hand, cold solutions have not generally contained sufficiently high boron concentrations to achieve required preservative retention levels in the timber. Compositions and methods of treating timber with a boron-containing preservative, wherein the preservative is applied to the timber as a solution or suspension of the boron-containing preservative together with a thickening agent, have previously been known and used. However, it has previously been found that in order to render preservative salts into a soluble state, substantial heating or mixing is necessary. Australian patent application no. 8433827 discloses preservative compositions comprising a colloidal micro-crystalline suspension of boron salts and a thickening agent. Of the thickening agents disclosed in this specification, the only polysaccharides are carboxymethyl celluloses. It is an object of this invention to provide compositions and methods for treating timber which go some way towards meeting the needs of the public and the industry. According to one aspect of the invention, there is provided a preservative composition for treating timber comprising: (i) an inorganic boron-containing preservative compound present as a micro-crystalline suspension; and (ii) a thickening agent comprising the polysaccharide xanthan gum. The thickening agent optionally contains one or more further polysaccharides. It should be appreciated that compositions may contain one or more further thickening agents. Examples include other water-soluble polymers such as polyethylene oxides, acrylic emulsions and acrylic emulsion copolymers, and methyl vinyl ethers, along with proprietory formulations such as NALCATROL, (Trade Mark of Nalco Inc.), CARBOPOL (Trade Mark of B.F. Goodrich Company), FINNIFIX (Trade Mark of Metsaliitron Teollisuus Oy) and MAGNAFLOC (Trade Mark of Allied Colloids). By way of example, it has been found that polyacrylamides such as NALCATROL II (Registered Trade Mark), ALFLOC (Registered Trade Mark), or MAGNAFLOC (Registered Trade Mark) are particularly useful. By way of example, it has been found that natural polysaccharides or polysaccharide containing compositions such as KELZAN (Trade Mark of Kelco) are useful thickening agents which may be used in the compositions in accordance with the invention. Another useful natural polysaccharide is RHODOPOL (Trade Mark of Rhone-Poulenc). An active ingredient of KELZAN and RHODOPOL is xanthan gum. The amount of thickening agent or polymer used may be substantially increased or decreased over that previously known and used, and this has been found to at least assist in imparting into a composition according to the present invention increased properties of solution uptake and diffusion rate. One or more fluorosurfactants may optionally be added to the composition. Thus, it has been found that by adding into some compositions of the present invention one or more surface active agents, preferably fluorosurfactants, compositions of the present invention may exhibit increased properties which allow for an increase in surface wetting and diffusion rate. It has also been found that by increasing the amount of thickening agent or polymer, with or without a fluorosurfactant, the resultant composition has increased properties of both solution uptake and diffusion rate. Referring now to preferred surfactants, it has been found that fluorosurfactants are particularly advantageous in some compositions and methods of the present invention, in that the addition of such fluorosurfactants has been found in some compositions to aid in surface wetting and to decrease surface energy. This allows for the composition and thus boron-containing salts to be more readily and effectively absorbed by and diffused by the timber, in some cases. It has been found therefore that the addition of one or more fluorosurfactants at least assists in increasing the rate of diffusion, in some cases. It has been found desirable to use fluorosurfactants having the general formulae: R CH₂CH₂SCH₂CO₂ (Li, Na, K) (RCH₂CH₂O) v R O (ONH₄) w , v = 1 or 2, and w = 1 or 2 (RCH₂CH₂O) x P (OH) y , x = 1 or 2 and y = 1 or 2 RCH₂CH₂O(CH₂CH₂O) z H,z = 1 or 2 RCH₂CH₂SCH₂CH₂N(CH₃)₃ + CH₃SO₄ - RCH₂CH₂(OCOCH₃)CH₂N(CH₃)₂CH₂CO₂- wherein R = F₂(CF₂CF₂) n , n = 2-8. Generic terms defining suitable surfactants include the following: ammonium potassium or amine per fluoroalkyl sulphonates; ammonium potassium or sodium fluorinated alkyl carboxylates; fluorinated alkyl quaternary ammonium iodides; fluorinated alkyl polyoxyethylene ethanols; and fluorinated alkyl alcohoxylates, ethers or esters. By way of example, and in one form of the invention, it is particularly advantageous to use a fluorosurfactant selected from the group known as ZONYLs (Registered Trade Mark), having the formula: F(CF₂CF₂) m CH₂CH₂O(CH₂CH₂O) n H, wherein m = 1-8 and n = 2-8, and particularly having the formula F(CF₂CF₂)₃CH₂CH₂O(CH₂CH₂O)₆H, The above are by way of example only and it should be appreciated that fluorosurfactants of other formulae can be used. For example FLUORADs (Registered Trade Mark), may be used successfully. In another preferred form of the invention organic phosphate surfactants may be used. The present invention provides compositions and methods whereby the boron-containing salts are held in a micro-crystalline suspension, in which state they have been found to be sufficiently and readily soluble. Normal crystals have often presented problems insofar as solubility and storage stability are concerned. By way of example, examination of micro-crystals of boron-containing salts of the present invention have shown that the size of such micro-crystals may be in the order of between approximately 10 to 30 microns, whereas the size of normal crystals of precipitated salts are found to be in the order of from about 2 to 3 millimeters. This is however by way of example only, and compositions including crystals of larger size are also effective. The micro-crystalline suspensions have been found to be relatively stable, with no tendency for precipitation of the preservative salts to occur, even on long standing. Thus, on the addition of water they are readily soluble and are able to be easily applied to and diffused into the timber. By way of example, a composition formed by the method referred to hereinbefore, may be as follows: Boric Acid From 2.500 to 25.000% (w/w) Borax From 2.954 to 29.500% (w/w) Water From 4.335 to 43.356% (w/w) Polymer From 0.2 to 3.0% (w/w) Fluorosurfactant Up to 0.040% (w/w) Fungicide (stain/mould inhibitor) From 0.02 to 2.0% (w/w) Water Up to 90.02% (w/w) The advantages of the present invention result from the addition of an agent or polymers. The addition of one or more fluorosurfactants, in some forms of the invention, may also provide advantages over previously known compositions. The use of a composition according to the present invention, including both the increased amount of thickening agent or polymer and with or without one or more fluorosurfactants, tends to decrease the surface energy of the composition and renders the composition into a state or form in which it is able to be more readily absorbed by and diffused into the timber. Thus, compositions of the present invention, and methods of treating timber using such compositions allow for the boron-containing preservative salts to be more effectively and rapidly absorbed by diffusion into the timber. If desired, one or more additional additives such as fungicides and the like can be added, to further act upon and treat the timber and to stop fungal degradation during the subsequent diffusion period. The following are examples of antisapstain additives which may be used : sodium pentachlorophenoxide, captafol, copper-8 quinolinolate, TCMTB 2-(thiocyanomethylthio benzothiazole), methylene bisthiocyanate, TCMTB/methylene bisthiocyanate, carbendazim, IPBC (3-iodo-2-propynyl butyl carbamate), alkyl ammonium compounds and amine salts or mixtures of these, IPBC and one or more alkyl ammonium compounds, TCMTB and IPBC, carbendazim plus IPBC, sodium tetrachlorophenate, sodium tribromophenate, methylene bisthiocyanate and one or more alkylammonium compounds, TCMTB and one or more alkylammonium compounds, isothiazoline compounds e.g. n-octyl isothiazolin -2-one and mixtures containing these compounds, diiodomethyl-p-tolyl sulphone, diiodomethyl-p-tolyl-sulphone plus one or more alkyl ammonium compounds, inorganic fluorides e.g. potassium flouride, folpet, thiophanate methyl plus chlorothalonil and mixtures thereof. In some forms of the present invention, a suitable solvent may be used, which acts as a dispersion agent for the thickening agent. In some forms of the invention, a solvent such as methanol is added, while in other forms of the invention a suitable solvent is included in the proprietory formulations of the thickening agents used, and thus extra solvent need not be added. It should be appreciated, however, that the inclusion of a solvent is preferable, but not essential to the invention. In order to render the composition of the present invention into a usable commercial state, desired or predetermined amounts of water can be added and the diluted composition then applied to the timber so that the diluted composition and boron-containing micro-crystalline salts may be diffused into the timber for the treating of the timber. For example, compositions according to the present invention may comprise: from 2.5 to 25.0% (w/w) boric acid; from 2.954 to 29.500% (w/w) borax from 42.5 to 94.346% (w/w) water; and from 0.25 to 3.0% (w/w) polysaccharide. The present invention has been found to provide most satisfactory rates of absorption and diffusion. The compositions according to the invention may, for example, be prepared by the following process, which process constitutes a further aspect of the invention: i) heating water and adding thereto predetermined amounts of boric acid and borax; ii) stirring or agitating said solution; iii) cooling and stirring said solution; and iv) adding a thickening agent comprising xanthan gum and optionally adding a fluorosurfactant. A preferred process comprises; i) heating from 7.4 to 29.5% (w/w) water ii) adding thereto from 6.25 to 25% (w/w) boric acid and from 7.4 to 29.5% (w/w) borax; iii) stirring or agitating said solution; iv) cooling and stirring said solution; v) adding from 0.5 to 5.0% (w/w) polysaccharide; and vi) adding from 78.45 to 0% (w/w) water. One form of preparing a composition according to the present invention, and which is given by way of example only, firstly involves heating a predetermined amount of water, to a predetermined temperature. For example, the predetermined amount of water may be heated up to approximately 50 o C. Thereafter, a predetermined amount of borax is added and the mixture stirred. A predetermined amount of boric acid is then added. The mixture is preferably further stirred or agitated. If desired, following or immediately prior to the addition of the boric acid, the temperature may be increased. The addition of the borax and boric acid to the heated water, together with any stirring or agitation necessary, results in the borax and boric acid being dissolved into the water. Such stirring or agitation continues until such time as the borax and boric acid have fully dissolved into the solution. Thereafter, the solution is cooled, preferably rapidly cooled to a predetermined temperature. For example, the solution may be cooled to approximately 20 o C, or lower if desired. The temperature to which the solution may be lowered depends to some extent on local climatic conditions. For example, 10 o C may be a more suitable temperature in Canada, Finland and the United Kingdom. Thereafter further stirring or agitation continues in order to prevent or minimise the formation of large crystals during re-crystallisation. A thickening agent comprising xanthan gum is then added. One or more surfactants, such as for example a fluorosurfactant may be added, in one preferred form of the invention. This is, however, by way of example only, and it should be appreciated that the addition of a fluorosurfactant is not necessary in all forms of the invention. An amount of water is then added, if necessary. The resulting composition has a high viscosity and the boron-containing salts are held in a micro-crystalline suspension which is particularly suitable for transportation and storage. Further, given the micro-crystalline suspension of the boron-containing salts, the composition is able to be diluted in water in a straightforward manner, if necessary with the aid of stirring or pumping at ambient temperature, so as to result in a solution of a usable and acceptable concentration necessary to meet the appropriate solution strengths and viscosity for the application method used. In one form of the invention, dilution of the composition according to the present invention is made, such that the resulting composition includes a polysaccharide concentration of approximately 0.2%(w/w). This is by way of example only, however. According to a further aspect of the invention there is provided a method of treating timber which comprises applying a composition as defined above to the timber. A preferred method of treating timber which comprises applying to said timber a preservative composition including a colloidal micro-crystalline suspension of boron-containing salts and a thickening agent comprising xanthan gum; and allowing said composition to diffuse into said timber. The invention is further illustrated by the following examples: COMPARATIVE EXAMPLE 1 : The composition contains: Boric Acid From 18.75%(w/w) Borax (H₂O) From 22.14% (w/w) Water From 34.11% (w/w) Nalcatrol II (80% Kerosene) 1.3% (w/w) Magnafloc E24 0.5% (w/w) Water 23.11% (w.w) Methanol 0.1% (w.w) The composition is formed using the following procedure: 1. Water is heated to 50 o C and borax is added and agitated. The temperature is increased to approximately 60 o C and boric acid is added. Further heating may be required (to approximately 65-70 o C) until the solution is clear (water white). The solution is then crash-cooled to 25 o C, with continuous agitation. 2. The thickener, NALCATROL II (80% dispersion in kerosene) is then added to the boron salt solution as it crystallises. In a separate vessel MAGNAFLOC E24, methanol and water are combined then mixed into the boron salt solution. 3. The antisapstain formulation is then added to the thickened composition. COMPARATIVE EXAMPLE 2 : A further formulation is as for Comparative Example 1, but substitutes NALCATROL II with 1.0% ALFLOC 622, a different polyacrylamide. The fluorosurfactant used is 0.003% Zonyl FSN 100. The differences in percentage from the above example are made up with water. EXAMPLE 3 : the composition contains: Boric Acid 18.75% (w.w) Borax 22.50% (w/w) Kelzan S 0.5% (w/w) Methanol 0.5% (w/w) Zonyl FSN 100 0.003% (w/w) Water 57.49% (w/w) Antisapstain additive 0.257% (w/w) The composition of this example is formed using substantially the same method as described in Comparative Example 1, with the polysaccharide being pre-swelled and mixed in with the methanol. The fluorosurfactant is then added to the slurry formed by the polysaccharide and the methanol, and the whole composition is added to the boron salt composition.

Claims: A preservative composition for treating timber comprising: (i) an inorganic boron-containing preservative compound present as a micro-crystalline suspension; and (ii) a thickening agent comprising the polysaccharide xanthan gum. A composition as claimed in claim 1 wherein the thickening agent contains one or more further polysaccharides. A composition as claimed in claim 1 or claim 2 which contains one or more further thickening agents. A composition as claimed in any one of the preceding claims wherein the inorganic boron-containing preservative compound is present as a colloidal micro-crystalline suspension. A composition as claimed in any one of the preceding claims which further contains a fluorosurfactant. A composition as claimed in claim 5 wherein the fluorosurfactant is selected from: RCH₂CH₂SCH₂CO₂(Li,Na,K); (RCH₂CH₂O) v R O(ONH₄) w ,v=1 or 2, and w = 1 or 2; (RCH₂CH₂O) x P(OH) y ,x = 1 or 2, and y = 1 or 2; RCH₂CH₂O(CH₂CH₂O) z H,z = 1 or 2; RCH₂CH₂SCH₂CH₂N(CH₃)₃ ⁺CH₃SO₄ ⁻; and RCH₂CH₂(OCOCH₃)CH₂N(CH₃)₂CH₂CO₂⁻; wherein R = F₂(CF₂CF₂) n , n=2-8 A composition as claimed in claim 5 wherein the fluorosurfactant is selected from: ammonium potassium or amine per fluoroalkyl sulphonates; ammonium potassium or sodium fluorinated alkyl carboxylates; fluorinated alkyl quaternary ammonium iodides; fluorinated alkyl polyoxyethylene ethanols, and fluorinated alkyl alcohoxylates, ethers or esters. A composition as claimed in claim 7 wherein the fluorosurfactant is a compound of formula F(CF₂CF₂) m CH₂CH₂O(CH₂CH₂O) n H, wherein m = 2-8 and n = 2-8. A composition as claimed in claim 8 wherein the fluorosurfactant comprises F(CF₂CF₂)₃CH₂CH₂O(CH₂CH₂O)₆H. A preservative composition as claimed in claim 1 comprising: from 2.5 to 25.0% (w/w) boric acid; from 2.954 to 29.500% (w/w) borax; from 42.5 to 94.346% (w/w) water; and from 0.25 to 3.0% (w.w) polysaccharide including xanthan gum. A composition as claimed in any one of the preceding claims, containing an additional fungicide. A composition as claimed in claim 11, wherein the fungicide is selected from: sodium pentachlorophenoxide, captafol, copper-8 quinolinolate, 2-(thiocyanomethylthio benzothiazole), methylene bisthiocyanate, 2-(thiocyanomethylthio benzothiazole)/methylene bisthiocyanate, carbendazim, 3-iodo-2-propynyl butyl carbamate, alkyl ammonium compounds and amine salts or mixtures of these, 3-iodo-2-propynyl butyl carbamate and one or more alkyl ammonium compounds, 2-(thiocyanomethylthio benzothiazole) and 3-iodo-2-propynyl butyl carbamate, carbendazim plus 3-iodo-2-propynyl butyl carbamate, sodium tetrachlorophenate, sodium tribromophenate, methylene bisthiocyanate and one or more alkylammonium compounds, 2-(thiocyanomethylthio benzothiazole) and one or more alkylammonium compounds, isothiazoline compounds or mixtures thereof, including n-octyl isothiazolin-2-one, diiodomethyl-p-tolyl sulphone, diiodomethyl-p-tolyl-sulphone plus one or more alkyl ammonium compounds, inorganic fluorides including potassium fluoride, folpet, thiophanate methyl plus chlorothalonil and mixtures thereof. A composition as claimed in claim 1, wherein said composition comprises: Boric Acid From 2.500 to 25.000% (w/w) Borax From 2.954 to 29.500% (w/w) Thickening agent From 1.950 to 2.064% (w/w) Fluoro Surfactant Up to 0.040% (w/w) Water To 100% (w/w) A process for the preparation of a composition as claimed in claim 1 comprising: i) heating water and adding thereto predetermined amounts of boric acid and borax; ii) stirring or agitating said solution; iii) cooling and stirring said solution; and iv) adding the thickening agent. A process as claimed in claim 14 further comprising adding a fluorosurfactant. A process for the preparation of a composition as claimed in claim 1 comprising: i) heating from 7.4 to 29.5% (w/w) water; ii) adding thereto from 6.25 to 25% (w/w) boric acid and from 7.4 to 29.5% (w/w) borax; iii) stirring or agitating said solution; iv) cooling and stirring said solution; v) adding from 0.5 to 5.0% (w/w) polysaccharide including xanthan gum; and vi) adding from 78.45 to 0% (w/w) water. A concentrate of a composition as claimed in any one of claims 1 to 13 adapted to be diluted with water before it is applied to timber. A method of treating timber comprising applying a composition as claimed in any one of claims 1 to 13 to the timber.

Inventors: EVANS, DAVID LLOYD
Applicants: HICKSON INTERNATIONAL PLC
Application year: 1988
Main classification: B27K3
IPC codes: B27K3