AU2017202684A1 - Formulation and method for the treatment of timber - Google Patents

Abstract

Abstract According to the present invention there is provided a formulation and method for treating timber. The formulation comprises one or more preservatives and a water carrier. When combined, the preservative/s and the water provide for a protective "envelope" of preservative/s within the treated wood. The present invention also provides a method of effecting treatment of wood using such a formulation, a concentrate of the one or more preservatives and a kit comprising same.

Description

FORMULATION AND METHOD FOR THE TREATMENT OF TIMBER

Related Application

This application claims priority from AU 2010903965 (3 September 2010), the content of which is incorporated herein by reference in its entirety.

Field of the Invention

The present invention relates to preservative treatment of timber building materials and particularly, to formulations and methods for delivering a protective envelope of said preservative to said timber.

Those skilled in the art will appreciate that although the invention has been described with reference to specific examples, it may be embodied in many other forms.

Background of the Invention

Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.

Wood is a staple construction material used throughout the world. However, it is prone to degradation from elements including the natural environment, weather events, insects, rot and fire.

For instance, in countries such as Australia, timber is especially susceptible to termite attack. This has been counteracted to some degree by the treatment of wood with preservatives in the form of insecticides. Accordingly, a range of chemical treatments has been developed to improve the durability and available working lifetime of wooden structures. Application methods and approved chemicals vary significantly throughout the world.

The treatment of timber or timber products with preservative compounds involves the introduction of stable chemicals into the cellular structure of the timber. This, in turn, protects the timber from hazards such as fungi, insects and other wood-destroying organisms. The active chemical agent is usually dissolved in a solvent and the solutions generally are of relatively low viscosity in order to facilitate the penetration of the treatment solution. However, the preservative may also be present in the carrier as an emulsion. Preservative treatments may also include the introduction of chemicals that improve resistance to degradation by fire.

Softwood timbers such as pinus radiata, pinus elliotti, and pinus carribea used as framing timber in Australia are especially susceptible to termite attack. Changes in Government regulations have limited the use of soil poisoning agents (e.g., banning of organochloride insecticides). This has unfortunately led to a higher incidence of termite attack in timber-framed houses. Accordingly, many countries continue to seek suitable cost-effective methods to combat this ever-increasing risk of termite attack.

One of the strategies to combat termite attack of softwood frames is the treatment of the timber with insecticides or more broad-spectrum wood preservatives. To this end, timber is often impregnated with a preservative such as a fungicide or insecticide. The preservative is typically present in a carrier, with the mixture being applied to the surface of the timber, for example by dipping, spraying, brushing or pressure-treatment, such that the carrier and preservative are absorbed into the timber.

Examples of commonly used insecticides include synthetic pyrethroids. These are axonic poisons that work by keeping the sodium channels open in the neuronal membranes of insects. The sodium channel is a small hole through which sodium ions are permitted to enter the axon and cause excitation. As the nerves cannot then de-excite, the insect is rendered paralysed. Examples of commercial pyrethroids include allethrin, bifenthrin, cypermethrin, cyphenothrin, deltamethrin, permethrin, prallethrin, resmethrin, sumithrin, tetramethrin, tralomethrin, transfluthrin and imiprothrin.

(1)

Permethrin (1) is an especially preferred preservative according to the present invention. It is known to be an effective insecticide, acaricide, and insect repellent. It functions as a neurotoxin, as related above. However, it generally has a low mammalian toxicity and is poorly absorbed by skin.

In Australia, the treatment of timber is covered by the Australian standard series “AS 1604-2010”. The present invention is especially applicable to Hazard classes HI, H2 and H2F. Of these, Hazard class H2 is defined for borer and termites. Although the present invention is exemplified with respect to H2F requirements, it will be readily appreciated by those skilled in the art that the invention is equally applicable to HI and H2 requirements and penetration standards. The approved chemicals are shown in the following table (retention is measured in w/w [% m/m]).

Table 1 - Minimum preservative retention in the penetration zone, H2

Table 2 - Minimum preservative retention in the penetration zone, H2F (H2F)

aPenetrated from each surface, excluding ends “Penetration” is defined under the standard as:

All preservative-treated wood shall show evidence of distribution of the preservative in the penetration zone in accordance with the following requirements: (a) If the species of timber used is of natural durability class 1 or 2, the preservative shall penetrate all the sapwood. Preservative penetration of the heartwood is not required. (b) If the species of timber used is of natural durability class 3 or 4, the preservative shall penetrate all of the sapwood and, in addition one of the following requirements shall apply: (i) Where the lesser cross-sectional dimension is greater than 35 mm, the penetration shall be not less than 8 mm from any surface. Where the lesser cross-sectional dimension is equal or less than 35 mm, the penetration shall be not less than 5 mm from any surface. (ii) Unpenetrated heartwood shall be permitted, provided that it comprises less than 20% of the cross-section of the piece and does not extend more than halfway through the piece from one surface to the opposite surface and does not exceed half the dimension of the side in the cross-section on which it occurs”.

In order to provide for penetration of the preservative, a carrier must be used. As shown in the Australian standard (see, Tables 1 and 2, above), the carriers presently available can be characterised as “waterborne” or “solvent-bome” systems. A carrier must provide sufficient penetration of a preservative into the wood, thereby to provide an effective barrier against infestation. Other considerations in the choice of carrier include the desired rate of penetration, the cost and environmental and health and safety considerations. Increased penetration of a preservative solution can also be achieved by diffusion, which despite involving less expensive equipment does require a longer time period and greater levels of stock holding. Diffusion time is also influenced by the initial wood moisture content and often requires a pre-drying step so as to create a preferential diffusion gradient along which the preservative/carrier formulation may migrate.

The preservatives commonly used in timber treatment can be characterised according to the carrier solvent used as the vehicle to carry preservatives into the timber, and by the active chemicals that provide the protection against the various hazards that compositions such as that of the present invention seek to counter. The fmal step in the preservation process is that the solvent (which may include water) must then be removed before the timber is made available for use.

Waterborne carriers swell wood and hence need to be re-dried prior to use in service. Building codes specify the maximum moisture content of pine framing; this level is around 15-18% w/w moisture content. The general process sequence is: i) dry the wood; ii) water treat the wood; and iii) re-dry the wood. This additional re-drying step adds complexity and expense to the treatment process and results in additional costs being passed on to the consumer. By comparison, solvent-borne preservatives do not raise the moisture content and hence do not swell the wood because they are non-polar. Thus, the process sequence is: i) dry the wood; and ii) solvent treat the wood.

Although the use of solvent-borne preservatives mitigates against the need for the re-drying step, the principal disadvantages of this treatment system are the relatively high cost of solvents (cf. water) and the potential environmental concerns with, e.g. volatile organic compounds being released into the atmosphere.

As mentioned above, the application of the preservative/carrier to the wood is often carried out by a batch process involving a pressure vessel. For waterborne preservatives, a vacuum pressure process (Bethell or full cell) is used. This facilitates complete sapwood penetration and adequate heartwood penetration, if required.

Copper, chromium and arsenate (FFAsCU ), “CCA”, is a leach-resistant wood preservative that has been used for some time to treat solid wood in external applications. CCA impregnates the timber in a water/salts carrier and is designed to react with the wood cell components so that the active elements copper, chromium and arsenic are “fixed” into the wood’s structure. The arsenic component protects the sapwood from insect attack; the copper and arsenic from degradation due to fungi, whilst the chromium component chemically locks the elements into the timber, offering a relatively high resistance to leaching. Following such treatment, in order to give the treated timber dimensional stability, it must be re-dried. This process can decrease the strength of the timber, and invariably adds to the cost. However, due to environmental health and safety issues - and toxicity concerns relating to the constituent metals, especially arsenic, CCA is coming under increasing regulation and is thus becoming a less desirable treatment on both commercial and environmental bases.

Inorganic boron compounds have been commonly used in Australia to protect the sapwood of susceptible hardwoods against lyctid or “powder post” borers. Such treatment consists in soaking freshly-sawn unseasoned timber in solutions of boron salts. The salts diffuse through the timber, thereby treating it; following such treatment, the timber is allowed to dry. However, boron salts are readily soluble in aqueous solutions and can be leached relatively easily from the wood once treated. This largely restricts boron-treated timber to interior uses such as flooring or joinery, wherein it is protected from the external environment.

Light Organic Solvent-borne Preservatives (LOSPs) comprise a light organic solvent, typically white spirit, to carry the preservative chemicals into the timber. White spirit is a mixture of saturated aliphatic and alicyclic C7-C12 hydrocarbons with a w/w content of about 15-20% aromatic C7-C12 hydrocarbons. The solvent is drawn out in the final stages of treatment, with the preservative remaining within the wood. Such preservatives are typically fungicides, having copper, tin, zinc, azoles and pentachlorophenols (PCPs) as major toxicants. One principal advantage of LOSP treatment is that the treated timber does not swell, making such treatment quite suitable for treatment of finished items such as mouldings and joinery. The majority of LOSPs used in wood treatment also contain insecticides and/or waxes so as to give the surface water repellent properties. However, odour and exposure to volatile organic compounds (VOCs) are significant environmental and occupational health and safety issues associated with the use of LOSPs in the timber treatment industry. Accordingly, whilst effective, such treatments are becoming increasingly undesirable.

Alkaline Copper Quat (ACQ) contains copper and a quaternary ammonium compound. It is used to protect timber against decay, fungi and insects. ACQ is applied as a water-borne preservative using an external pressure process. It is free of arsenic and is used to treat external timber applications.

Copper azole is another of the new generation of arsenic-free preservative treatments that can be used in water-borne pressure treatment processes. It is a preservative that contains copper, boric acid and tebuconazole. Copper azole has been used in Australia as a replacement for CCA for treatments having external end applications.

Creosote and pigment emulsified creosote (PEC) are commonly-used oil-borne preservatives that are painted onto timber surfaces, but can also be applied in a pressure-based process for better penetration. These compounds have volatile components and hence, a characteristic odour. This makes creosote and PEC only really suitable for use in external or industrial applications.

As the use of water-based carriers has been found to increase the moisture content of the timber, resulting in undesirable swelling of the wood, and necessitating a further drying processes after treatment, many current methods of treating and protecting wood, for H2 and H3 end uses, rely on using non-aqueous solvents. Further, pressure plants are expensive to construct, and being batch processes, conventional treatments do not match well with continuous sawmill production and require a high level of operator control to maintain costs. US 7,361,215 discloses the use of a drying oil in combination with a high flash point solvent carrier to transport an insecticide into the wood. This formulation promotes the formation of a well-defined “envelope” of preservative, thereby treating and preventing infestations of termites and other insects. A preferred embodiment of this invention is a mixture of pale boiled linseed oil (PBLO) and narrow cut kerosene (NCK). This solution, when combined with a pyrethroid preservative has proven effective in giving the required protective envelope at low uptake (12 to 15 L/m3). However, of late, the cost of both PBLO and NCK has risen as a result of the commodity boom and cost of mineral oil. US 5,846,305 discloses a liquid wood preservative solution including copper metal, liquid amine solvent, a boron compound and a glycol. Glycol has been used as a replacement for water in ancient timber restoration, or for dimensional stability in a technique known as “bulking” for many years. Boron is highly miscible in glycol and thus the movement of a glycol/boron solution into the wood is due to diffusion. Due to the length of time required for adequate diffusion into the wood, this type of preservative is required to be forced into the wood by vacuum pressure and is unsuitable for effective use in more time-effective techniques such as brushing, dipping or spraying. US 2004/0146733 relates to a method for the protective treatment of wood by means of thermal treatment at 60-250 °C and additional treatment using an amine and/or amine derivative and/or salt thereof. The wood treated according to such method has good resistance even to harmful organisms that cannot be reliably controlled by means of only a heat treatment. The method is carried out without compounds containing heavy metals and the wood treated in this way has no impact on the environmental either during the use or during the disposal thereof. However, it will be appreciated that the initial heat-treatment step is relatively undesirable for cost-energy reasons. WO 2004/050783 summarises known methods for glue, glue line resin systems and wood products incorporating glues with bifenthrin. The glues, when combined with bifenthrin are purported to be effective in preserving engineered wood products, with or without additional surface sprays. The bifenthrin is delivered to the wood in a water-based formulation by spraying.

Herein and throughout the specification and claims, the term “permethrin” should be taken to mean any one or more of its four stereoisomers (two enantiomeric pairs), arising from the two stereo genic centres in the cyclopropane ring; the trans-enantiomeric pair is often termed “transpermethrin”, e.g.,

trans-enantiomer/s cis-enantiomer the other cis-enantiomer

It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

It is an object of an especially preferred form of the present invention to provide for a water-based composition and method for the preservative treatment of timber products that is preferably effective in providing for an approximate 5 mm envelope of preservative within the treated wood.

Despite the many and varied techniques for the treatment of wood, there remains a need to satisfy the “dry after” requirement for treated timber, having less than 15% moisture content, whilst achieving the required penetration of active compounds into the wood. Additionally, remains a need for a material for treating wood that has relatively low odour, relatively minimal VOC emissions, and relatively less reliance on mineral spirits, whilst at once providing relatively good dimensional stability to the treated wood.

Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.

Although the invention will be described with reference to specific examples it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

Summary of the Invention A preferred embodiment of the present invention may be represented, at least in the Australian marketplace, by the registered trademark “Vacsol® T”.

According to a first aspect of the present invention there is provided a water-based preservative formulation for treating wood, said formulation comprising a biocidally-effective concentration of one or more preservatives within said water, wherein upon application to said wood, protective envelope of said preservative is formed.

In one embodiment, the protective envelope is approximately five millimetres deep within said wood.

In one embodiment, the one or more preservatives are selected from the group consisting of insecticides, termiticides, fungicides, mouldicides, organochlorine compounds, organophosphates, pyrethroids, neonicotinoids and biological insecticides - and mixtures thereof.

In another embodiment, the pyrethroids are selected from the group consisting of: allethrin, bifenthrin, cypermethrin, cyphenothrin, deltamethrin, permethrin, prallethrin, resmethrin, sumithrin, tetramethrin, tralomethrin, transfluthrin, imiprothrin and mixtures thereof.

In another embodiment, the neonicotinoids are selected from the group consisting of: acetamiprid, clothianidin, dinotefuran, imidacloprid, nitenpyram, thiacloprid, thiamethoxam and mixtures thereof. Most preferred are thiacloprid or imidacloprid in a w/w ratio with permethrin of about 1:4.

In another embodiment, the preservative is a fungicide or mouldicide selected from the group consisting of iodopropynylbutylcarbamate (IPBC), organic tin compounds such as tributyltin naphthenate (TBTN), organic copper compounds such as copper-8-quinolinolate and copper naphthenate, organic zinc compounds, quaternary ammonium compounds, tertiary ammonium compounds, isothiazolones, triazoles such as tebuconazole, boron compounds and mixtures thereof.

The practical limits of the preservative concentration applied to the invention is a function of the preservative itself - for instance, in the case of permethrin, about 5 g/L is likely to be the practical limit. However, generally, the preservative concentration in the formulation applied to the wood is less than about 100 g/L. Preferably, the concentration is less than about 20 g/L. More preferably, the preservative concentration is about 5 g/L. More preferably still, the preservative concentration is about 1 g/L.

In an embodiment, the migration of said preservative within said wood is along the grain of the wood and/or across the grain of the wood. It is believed that substantial migration across the grain of the wood has not yet been observed in respect of water-based preservative formulations, when applied to dry timber either via dip, spray, brushing or momentary immersion.

In another embodiment, the preservative is emulsified or dispersed in said water. Emulsions are generally cheaper and simpler. In another embodiment, the formulation comprises one or more surfactants. In another embodiment, the formulation is adapted for application to said wood by means selected from the group consisting of: spraying, dipping, brushing, rolling, painting, pressure application, autoclave, and combinations/variations thereof.

In another embodiment, the approximate five millimetre envelope retains a concentration of at least about 0.020% m/m permethrin for a period of at least ten years, which consequently renders said wood substantially resistant to insect and/or/fungal and/or mould attack for a period of at least ten years.

In an especially preferred embodiment, the preservative is an emulsion of approximately 5 to 7 g/L permethrin in water, and is preferably applicable to the wood by dipping for a period of around ten to sixty seconds.

According to a second aspect of the present invention there is provided a method for treating wood, said method comprising the step of contacting said wood with a water-based preservative formulation defined according to the first aspect of the present invention.

In an embodiment, the contacting step is effected by means selected from the group consisting of: spraying, dipping, rolling, painting, brushing, pressure application, autoclave, and combinations/variations thereof.

In another embodiment, the method further comprises a post-application drying step wherein at least some of the water is evaporated from the treated wood.

In another embodiment, the method further comprises a preliminary conditioning step wherein said wood is pre-conditioned to facilitate subsequent application of said preservative formulation.

In another embodiment, the wood is dipped in said preservative formulation from between a few seconds up to several minutes. More preferably, the wood is dipped in said preservative formulation from around 5 seconds up to about 60 seconds.

In an embodiment, the wood is contacted with a sufficient quantity of preservative and carrier to provide an uptake of between 5 to 100 L/m3. Preferably, the wood is contacted with a sufficient quantity of preservative and carrier to provide an uptake of between 10 to 100 L/m3.

In another embodiment, the method is applied to radiata pine heartwood and sapwood, slash pine (pinus elliottii) heartwood and sapwood, pinus caribaea heartwood and sapwood, FI hybrid heartwood and sapwood (pinus elliottii/caribaea hybrid), maritime pine (pinus pinaster) heartwood or sapwood, southern yellow pine heartwood and sapwood (group of species including loblolly, longleaf, shortleaf, and slash pines) and/or Douglas fir (pseudotsuga menziesii) heartwood and sapwood.

In another embodiment, the method is applied to wood composites/engineered wood products including particle board, plywood, laminated veneer lumber (LVL), plywood or oriented strand board (OSB).

According to a third aspect of the present invention there is provided treated wood, when so-treated by a method according to the second aspect of the invention.

According to a fourth aspect of the present invention there is provided a concentrate comprising one or more preservatives, wherein following dilution with a predetermined volume of water and subsequent application to wood, a protective envelope comprising a biocidally-effective concentration of said one or more preservatives is formed within said wood.

When diluted with an appropriate volume of water, the concentrate defined according to the fourth aspect of the invention gives rise to a formulation as defined according to the first aspect of the invention.

According to a fifth aspect of the present invention there is provided a method of preparing a formulation for treating wood as defined according to the first aspect of the present invention, said method comprising the step of adding to a concentrate as defined according to the fourth aspect of the present invention, a predetermined volume of water and optionally agitating or mixing.

According to a sixth aspect of the present invention there is provided a kit comprising a concentrate defined according to the fourth aspect of the present invention; and instructions pertaining to diluting said concentrate with water and/or applying the subsequently diluted concentrate to wood, thereby to provide for a protective envelope comprising a biocidally-effective concentration of one or more preservatives within said wood. In an embodiment, the kit further comprises application means such as a sprayer, brush, roller, vessel for dipping, or the like. A wide variety of preservatives may also be used in combination with the carrier. Various insecticides and termiticides known in the art may be mixed with the carrier composition. Such insecticides and termiticides include synthetic pyrethroids such as permethrin, cypermethrin, etc., and imidacloprid.

Fungicides and mouldicides may also be used, e.g. iodopropynylbutyl carbamate (IPBC), tributyltin naphthenate (TBTN) and the class of mouldicides known as isothiazolones. Other fungicides and mouldicides applicable to the present invention include iodopropynylbuthylcarbamate (IPBC), organic tin compounds such as tributyltin naphthenate, organic copper compounds such as copper-8-quinolinolate and copper naphthenate, organic zinc compounds, quaternary ammonium compounds, tertiary ammonium compounds, isothiazolones, triazoles such as tebuconazole, boron compounds such as trimethyl borate.

The Applicant has found that the above-disclosed formulation comprising a mixture of one or more preservatives and carrier provides an effective wood preservative which has the sought “envelope” effect. Migration/penetration of the preservative system occurs in both radial and tangential directions forming an envelope around the treated wood to an effective depth which is typically observed to be of the order of 5 mm. Such penetration in the tangential direction does not generally occur with waterborne preservatives when applied by low pressure methods. Further, such migration ensures a consistency of the envelope around the surface of the treated wood. The envelope may be formed in both the heartwood and the sapwood. It will be appreciated that the present invention provides an alternative to conventional preservative techniques.

In another embodiment, the present invention provides a method of treating wood comprising contact the wood with the inventive formulation. The treatment step can be conducted using conventional pressure application techniques such as existing vacuum pressure systems known in light organic solvent plants. Alternatively, the Applicant has also found the inventive composition can be applied without the need for pressure application. Treatment can be accomplished by spraying, dipping, brushing, etc., which, unlike previous conventional batch systems, is ideal for use on continuous production line facilities such as saw mills.

Brief Description of the Figures A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying figures, which show the effect of an inventive treatment of permethrin/water on radiata sapwood, as follows:

Figure 1 is a photograph of a representative field trial specimen after exposure to C. acinaciformis for 9 months; the wood is untreated and has been substantially destroyed by the termites.

Figure 2 is a photograph of a representative field trial specimen after exposure to C. acinaciformis for 9 months; the wood is treated with a formulation defined according to the present invention prior to termite exposure. As can be seen, the wood has been substantially undamaged by the termites.

Figure 3 shows moisture content (“M.C”) change as a function of sides of a section of 90 mm x 35 mm framing, and depth from the surface, with treatment. The respective moisture contents were determined by oven drying. The core gives the moisture content of the section before treatment. The moisture content of the outer 2 mm zone increased from approximately 10 to between 17 to 19% upon treatment with a water-based formulation of permethrin. The moisture content of the 3 to 5 mm zone was however essentially unchanged from that of the core, yet surprisingly, chemical analysis has shown that permethrin indeed penetrated into the 3 to 5 mm zone.

Figure 4 is a photograph of the observations made in respect of Example 7, which demonstrates heartwood penetration. Radiata pine (“R4”) and slash pine (“16B”) were sprayed with heartwood indicator; the indicated (arrowed) colour demonstrates the presence of heartwood. The heartwood/sapwood boundary is shown with a dashed line.

The Applicant has also found that the inventive formulation and method provides more than adequate protection without the need for complete sapwood penetration. The present invention rather uses an envelope-type protection rather than penetration throughout the sapwood. This protective envelope is a move away from conventional techniques but still provides adequate protection for treated timber (cf., e.g., Figures 1 and 2).

The following Examples should be viewed as representative only, and in no way limiting of the scope of the claims or efficacy of the present invention. Tests were conducted to verify the efficacy of the inventive formulation.

As applied herein throughout the remainder of the specification, “Formulation A” is a comparative oil-bome/solvent-borne preservative formulation (optionally of permethrin), sold commercially by the Applicant as Tanalith® T (see, US 7,361,215). One skilled in the art will appreciate that any of solvent-borne, oil-borne and waterborne preservative formulations may be preferable depending on the specific circumstances of the required treatment scenario.

Example 1

The formulation defined according to the present invention can be applied to timber via conventional means, e.g., momentary immersion in treatment solution. The proprietary formulation of permethrin/water used in Example 1 forms an approximate 5 mm preservative envelope.

To test the efficacy of the envelope formed by the inventive formulation, a field trial was carried out by the Commonwealth Scientific and Industrial Research Organisation (CSIRO, Australia), in accordance with the Protocols for Assessment of Wood Preservatives. The details of the trial are summarised in Table 3, below. In this Example, the formulation comprised permethrin (c. 520 g/L), ionic surfactant (< 100 g/L), non-ionic surfactant (< 100 g/L) and hydrocarbon solvent (balance).

Table 3 - Summary of details of CSIRO field trial

The field trial specimens were treated in 400 mm lengths, then docked to 200 mm. Sections of the leftover material were retained, and submitted to the Chemical Laboratory at Department Primary Industries and Fisheries, Queensland, Australia, for chemical analysis. The results are given in Table 5, below. Zone analysis was also undertaken to confirm formation of the 5 mm penetration zone.

As reflected in Table 3, the inventive formulation used was an emulsifiable concentrate of permethrin (500 g/L), which was diluted with water prior to use to give a preservative solution having a permethrin concentration of approximately 5 g/L. Permethrin, like many synthetic pyrethroids (e.g., bifenthrin), has low solubility in water. However, it is able to be introduced to the wood as an emulsion (e.g., microemulsion). It will be appreciated that within the context of the present invention, alternative formulation types are also applicable. For instance, permethrin can be solubilised in water through addition of clathrating agent such as a cyclodextrin; other variants include dispersions, etc.

After a period of nine months’ exposure at CSIRO’s field test site in the Northern Territory of Australia, all of the specimens in the six replicate drums showed evidence of contact by Coptotermes acinaciformis. There was little evidence of any remaining Eucalyptus regnans bait wood, and the untreated controls in each of the six drums had been destroyed by termites. The grading system used by CSIRO (see, Table 3, above) assigns a rating of between 8 (“sound”) and 1 (“destroyed”) to each of the specimens, where a rating of 7 or 8 must be achieved for an envelope treatment to be considered “successful”.

The results are summarised in Table 4, below. The untreated controls were all rated 1 (mass loss > 90%), demonstrating the substantial termite pressure achieved in each of the replicate drums. In contrast, specimens treated with the inventive formulation were each sound, with each specimen rated 8.

Table 4 - Summary of field test results for envelope treatments

Formulation A was included as a reference preservative. These specimens also all achieved ratings of 8. Images of an untreated specimen and a treated specimen at the completion of the field trial are shown in the respective Figures 1 and 2.

According to the present invention, the formulation can be applied via any means. In particular, the most applicable and preferable of the methods known in the art include dip, spray, autoclave treatment, etc., and variations thereof.

The Applicant’s intention was to treat only the outer portion of the wood (e.g., the outer 5 mm region) and achieve at least 0.020% m/m permethrin retention in the penetration zone. According to AS 1604 (see, Table 2, above), the concentration of permethrin required to prevent termite attack is 0.02% m/m.

Accordingly, it can be seen that the inventive formulation provides not only adequate protection but does so in a more efficient and cost effective manner than conventional techniques.

According to the experimental data attained, the C. acinaciformis termites damaged only untreated and solvent test blocks and feeder blocks. All treatments appeared to protect the test blocks. The severity of the test protocol is evidenced by the amount of termite damage to the control blocks. The termite foraging pressure was severe and conditions suitable for sustained termite foraging.

Table 5 - Analysis of envelope treated field trial specimens

These results demonstrate the efficacy of a preservative envelope delivered from a waterborne carrier to protect timbers from attack by C. acinaciformis. A further surprising feature of the invention was the discovery that timber treated with the waterborne permethrin formulation was less contacted by termites than timber treated with Formulation A, an oil/solvent-borne formulation of permethrin. The CSIRO researchers noted that the specimens treated with the waterborne permethrin formulation were only lightly mudded (see, Table 4) with an average coverage of 18%. In comparison, the Formulation A treated specimens were heavily mudded, with an average coverage of 73%. Although the timber specimens are vacuum oven dried to remove residual solvent prior to exposure in the field, it can be seen in Table 4 that the oil/solvent carrier in Formulation A does provide some deterrence to termite feeding. The oil/solvent control specimens (i.e., those treated only with the oil/solvent carrier) in general suffered less attack than the untreated specimens. It is therefore surprising that the specimens treated with the waterborne permethrin formulation, where there is no contribution to feeding deterrence from the carrier, were substantially less mudded than the Formulation A treated specimens. From this observation, which has been made on several occasions in different field trials, it can be concluded that the inventive permethrin formulation renders treated timber more repellent to termite attack than Formulation A treated timber.

Example 2

In addition to timber, per se, the inventive formulation is suitable for engineered/composite wood products (EWPs). Treatment trials have been carried out with various EWPs including particle board, plywood, oriented strand board (OSB) and laminated veneer lumber (LVL). In all cases, a protective envelope of preservative was observed within the EWP, which maintained an active concentration of at least about 0.020% m/m preservative for a period of at least one year.

Example 3

Additives such as non-ionic surfactants can also be added to the inventive formulation. It has been found that such formulations gave results similar to those achieved in Examples 1 and 2, above. The advantage in using one or more surfactants is that the formulation as applied to the wood is relatively homogeneous in its preservative concentration/dispersion throughout the water carrier, thereby facilitating a more homogeneous dispersion in the treated wood.

Example 4

The present invention also provides for a combination (i.e., one or more) of preservatives within the water carrier. Example 4 employs two such preservatives, permethrin (a pyrethroid repellent) and thiacloprid (a neonicotinoid toxicant/contact repellent) in water.

To test the efficacy of the envelope formed by the inventive formulation, a field trial was carried out by the Commonwealth Scientific and Industrial Research Organisation (CSIRO, Australia), in accordance with the Protocols for Assessment of Wood Preservatives. The experimental details of the trial are summarised in

Table 6. The field trial specimens were treated in 200 mm lengths. Sections of the leftover material were retained, and submitted to the Chemical Laboratory at Department Primary Industries and Fisheries, Queensland, Australia, for chemical analysis. The results are given in Table 7, below. Zone analysis was also undertaken to confirm formation of the 5 mm penetration zone.

Table 6 - Summary of details of CSIRO field trial

Table 7 - Results for thiacloprid &amp; thiacloprid/permethrin combinations

# Several penetrations of the envelope were observed.

It will be appreciated that the data provided in Tables 6 and 7 illustrate the benefits of combining more than one preservative within the inventive formulation. Thiachloprid alone suffered several penetrations of the treatment envelope, however, the use of thiacloprid and permethrin in combination provided satisfactory protection of the timber from termite attack.

Subsequent chemical analysis again demonstrated the formation of an approximate 5 mm envelope (see, Table 8, below).

Table 8 - Analysis of specimens treated with permethrin/thiacloprid

The above results demonstrate the efficacy of the preservative envelope to protect softwood framing timbers from attack by C. acinaciformis.

Example 5

In Example 5, samples of 90 mm x 35 mm radiata pine were dip treated in an emulsion of permethrin in water. Selected samples were sectioned and submitted for chemical analysis, the results of which clearly demonstrate envelope formation.

Table 9 - The dependence of uptake on envelope formation

Example 6

This Example demonstrates heartwood penetration. Radiata pine (90 x 45 mm in cross section) containing a significant proportion of heartwood (20 to 100%) was dip-treated in a water solution containing emulsified permethrin (5.6 g/L). Each sample was weighed before and after treatment to determine the uptake of preservative. After treatment, the specimens were sectioned and the outer 5 mm envelope of each specimen analysed for permethrin. The results are summarised in Table 10, below. The average permethrin retention in the envelope penetration zone was 0.039% m/m, and the lowest individual retention 0.026% m/m. Given the results of field testing that have demonstrated that 0.02% m/m permethrin in a 5 mm penetration zone is an effective treatment for preventing attack of framing timbers by subterranean termites, the results shown here further demonstrate the utility of the present invention.

Those specimens that contained 100% heartwood in the penetration zones were studied in greater detail. For these specimens, the inner 3 to 5 mm portion of the penetration zone was analysed separately for permethrin. The results of these analyses are also shown in Table 10, below. A substantial proportion of permethrin was found in the inner portion of the penetration zone. These results demonstrate that while a gradient is present, permethrin does penetrate the inner portion of the penetration zone, even when the penetration zone is comprised of heartwood.

Table 10 - Results from Example 6

denotes not tested

Example 7

This Example further demonstrates heartwood penetration. Specimens from the large scale experimental trial (see, Example 6, above) containing heartwood were selected for detailed analysis. With reference to Figure 4 of the accompanying drawings, sections were taken from two specimens (90 x 35 mm), one radiata pine (“R4”) and the other slash pine (“16B”), and sprayed with heartwood indicator. In the resultant image, the indicated (arrowed) colour demonstrates the presence of heartwood. The heartwood/sapwood boundary is shown with a dashed line. The inner 2 mm zone (depth 3 to 5 mm of penetration zone) was removed from the wide face that contained the most heartwood and analysed for permethrin. The results are given in Table 11, below.

Table 11 - Analysis of Example 7

Example 8 A large scale experimental trial was carried out. Mini-packs containing forty framing timbers (1800 x 90 x 35 mm) were dip-treated in a water solution containing emulsified permethrin (4.2 g/L) and a blue colorant. Individual specimens, as well as the mini-packs, were weighed before and after treatment.

Table 12 - Results from Example 8

denotes not tested

Two timber species were included in the trial, i.e., two packs were radiata pine (A, B), while the other two packs were slash pine (C, D). The uptakes for the four packs (A to D) were similar, irrespective of the species (17.6, 17.6, 16.4 and 17.5 L/m3). The preservative penetrated throughout the pack and there was no substantial difference in uptake of specimens in different locations within the packs. The distribution of individual specimens across the four packs was largely in the 11 to 20 L/m3 range.

Specimens were selected at random for chemical analysis. Eight radiata pine and seven slash pine specimens were taken, sectioned and a 5 mm outer zone analysed for permethrin retention. The results are shown in Table 12, above.

Example 9

This Example demonstrates an exemplary treatment and analysis according to the present invention. In this Example, samples of 90 x 35 mm radiata pine were dip treated in emulsion of permethrin/water. Selected samples were sectioned and submitted for chemical analysis. The results (see, Table 13, below) demonstrate envelope formation.

Table 13 - Results from Example 9

denotes not tested Industrial Applicability

It can be seen that the present invention provides an industrially-significant means with which to counter, in particular, termite infestation of timber. Although the invention has been described with reference to specific examples it will be appreciated by those skilled in the art that the invention may be embodied in many other forms. For instance, although the present invention specifically targets the protection of wood from insect attack, primarily termites, it also includes combining a mouldicide for preventing mould on damp timber, and also a colorant (e.g., a pigment or dye) for identification purposes.

Claims (44)

1. THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:-

   1. A water-based preservative formulation for treating wood, said formulation comprising a biocidally-effective concentration of one or more preservatives within said water, wherein upon application to said wood, a protective envelope of said preservative is formed within said wood.
2. 2. A formulation according to claim 1, wherein said protective envelope of said preservative is formed to a depth of up to about 5 mm.
3. 3. A formulation according to claim 1 or claim 2, wherein said protective envelope maintains said biocidally-effective concentration of said one or more preservatives for a predetermined time.
4. 4. A formulation according to claim 3, wherein said predetermined time is from about one year to more than ten years.
5. 5. A formulation according to any one of the preceding claims, wherein said one or more preservatives are selected from the group consisting of: insecticides, termiticides, fungicides, mouldicides, organochlorine compounds, organophosphates, pyrethroids, neonicotinoids, biological insecticides and mixtures thereof.
6. 6. A formulation according to claim 5, wherein said pyrethroids are selected from the group consisting of: allethrin, bifenthrin, cypermethrin, cyphenothrin, deltamethrin, permethrin, prallethrin, resmethrin, sumithrin, tetramethrin, tralomethrin, transfluthrin, imiprothrin and mixtures thereof.
7. 7. A formulation according to claim 5, wherein said neonicotinoids are selected from the group consisting of: acetamiprid, clothianidin, dinotefuran, imidacloprid, nitenpyram, thiacloprid, thiamethoxam and mixtures thereof.
8. 8. A formulation according to claim 5, wherein said fungicides and mouldicides are selected from the group consisting of: iodopropynylbutylcarbamate (IPBC), organic tin compounds such as tributyltin naphthenate (TBTN), organic copper compounds such as copper-8-quinolinolate and copper naphthenate, organic zinc compounds, quaternary ammonium compounds, tertiary ammonium compounds, isothiazolones, triazoles such as tebuconazole, boron compounds and mixtures thereof.
9. 9. A formulation according to any one of the preceding claims, wherein the concentration of each of said one or more preservatives in said formulation is less than about 20 g/L.
10. 10. A formulation according to any one of the preceding claims, wherein the concentration of each of said one or more preservatives in said formulation is less than about 5 g/L.
11. 11. A formulation according to any one of the preceding claims, wherein the concentration of each of said one or more preservatives in said formulation is less than about 1 g/L.
12. 12. A formulation according to any one of the preceding claims, wherein said one or more preservatives are emulsified or dispersed in said water.
13. 13. A formulation according to any one of the preceding claims, wherein said biocidally-effective concentration of one or more preservatives within said water is an emulsion of approximately 5 to 7 g/L permethrin in said water.
14. 14. A formulation according to any one of the preceding claims, wherein penetration of said one or more preservatives within said wood is along the grain of the wood and/or across the grain of the wood.
15. 15. A formulation according to any one of the preceding claims, further comprising one or more surfactants.
16. 16. A formulation according to any one of the preceding claims, adapted for application to said wood by means selected from the group consisting of: spraying, dipping, brushing, rolling, painting, pressure application, autoclave, and combinations/variations thereof.
17. 17. A formulation according to any one of the preceding claims, wherein said one or more preservatives comprise a combination of at least one toxicant and at least one repellent.
18. 18. A formulation according to any one of claims 5 to 17, wherein said one or more preservatives comprise a combination of at least one pyrethroid and at least one neonicotinoid.
19. 19. A formulation according to any one of claims 5 to 18, wherein said at least one pyrethroid comprises permethrin and at least one neonicotinoid comprises thiacloprid or imidacloprid.
20. 20. A formulation according to claim 19, wherein said permethrin and said thiacloprid or imidacloprid are combined in a ratio ranging from about 100:1 to about 1:100.
21. 21. A formulation according to claim 19 or claim 20, wherein said permethrin and said thiacloprid or imidacloprid are combined in a ratio of about 4:1.
22. 22. A formulation according to any one of the preceding claims, wherein said protective envelope retains a concentration of at least about 0.020% m/m of preservative for a period of between about one and about ten years.
23. 23. A formulation according to any one of the preceding claims, which when applied, renders said wood substantially resistant to insect and/or/fungal and/or mould attack for a period of between about one and about ten years.
24. 24. A method for treating wood, said method comprising the step of contacting said wood with a water-based preservative formulation defined according to any one of the preceding claims.
25. 25. A method according to claim 24, wherein said contacting is effected by means selected from the group consisting of: spraying, dipping, rolling, painting, brushing, pressure application, autoclave, and any combination or variation thereof.
26. 26. A method according to claim 24 or claim 25, further comprising a postapplication drying step wherein at least some of said water is evaporated from the treated wood following formation of said protective envelope.
27. 27. A method according to any one of claims 24 to 26, further comprising a preliminary conditioning step, wherein said wood is pre-conditioned to facilitate subsequent application of said preservative formulation.
28. 28. A method according to any one of claims 24 to 27, wherein said wood is dipped in said preservative formulation for a period of between a few seconds to several minutes.
29. 29. A method according to any one of claims 24 to 28, wherein said wood is dipped in said preservative formulation for a period of around five seconds to about sixty seconds.
30. 30. A method according to any one of claims 24 to 29, wherein the wood is contacted with a sufficient quantity of preservative and carrier to provide an uptake of between 5 to 100 L/m3 of said wood.
31. 31. A method according to any one of claims 24 to 30, wherein the wood is contacted with a sufficient quantity of preservative and carrier to provide an uptake of between 10 to 100 L/m3 of said wood.
32. 32. A method according to any one of claims 24 to 31, wherein the method is applicable to radiata pine heartwood and sapwood, slash pine (pinus elliottii) heartwood and sapwood, pinus caribaea heartwood and sapwood, FI hybrid heartwood and sapwood (pinus elliottii/caribaea hybrid), maritime pine (pinus pinaster) heartwood or sapwood, southern yellow pine heartwood and sapwood (group of species including loblolly, longleaf, shortleaf, and slash pines) and/or Douglas fir (pseudotsuga menziesii) heartwood and sapwood.
33. 33. A method according to any one of claims 25 to 33, wherein the method is applicable to wood composites/engineered wood products including particle board, plywood, laminated veneer lumber (LVL), plywood or oriented strand board (OSB).
34. 34. Treated wood, when so-treated by a method according to any one of claims 24 to 33.
35. 35. A concentrate comprising one or more preservatives, wherein following dilution with a diluents comprising a predetermined volume of water and subsequent application to wood, a protective envelope comprising a biocidally-effective concentration of said one or more preservatives is formed within said wood.
36. 36. A method of preparing a formulation for treating wood as defined according to claim 1, said method comprising the step of adding to a concentrate as defined according to claim 35, a diluents comprising a predetermined volume of water and optionally agitating or mixing.
37. 37. A kit comprising a concentrate defined according to claim 35; and instructions pertaining to diluting said concentrate with a diluents comprising water and/or applying the subsequently diluted concentrate to wood, thereby to provide for a protective envelope comprising a biocidally-effective concentration of one or more preservatives within said wood.
38. 38. A kit according to claim 37, further comprising application means in the form of a sprayer, brush, roller, vessel for dipping, or the like.
39. 39. A water-based preservative formulation for treating wood, said formulation substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples.
40. 40. A method for treating wood, said method substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples.
41. 41. Treated wood, when so-treated by a method substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples.
42. 42. A concentrate comprising one or more preservatives, said concentrate substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples.
43. 43. A method of preparing a formulation for treating wood, said method substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples.
44. 44. A kit substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples.