Technical Field

This invention relates to preservatives. The invention has particular but not exclusive application to fungicidal and insecticidal preservatives for wood and to methods for their production. Particular reference will be made in this specification to pellets, tablets and shaped rods for insertion in bores drilled in timber. However it will be realised that the invention relates to preservatives which have not been pelletised or otherwise shaped and to preservation of materials other than wood.

Background of Invention

Borate treatment of timber is well known and documented. Australian patent application 14840/92 in the name of Saneish Pty Ltd discloses a cylindrical pellet used as a wood preservative comprising at least one boron and one fluorine compound. However fluorine compounds are toxic and their use as a wood preservative, whilst common, is undesirable for use in window frames, pergolas etc, and in other timbers in buildings.

US patent 4661157 discloses the use of boron compounds bound with water by hydration and formed into tablets, but having certain disadvantages described as being overcome in the invention of the above-mentioned Australian application by the addition of the fluorine compound. The production process employed involves forming a dry mixture of the hydratable boron compound and a fluorine compound, adding water to make a paste, extruding or otherwise shaping the paste to a desired shape and allowing the paste to set.

Summary of Invention

The present invention aims to provide an alternative to known preservatives and an alternative to known processes for the production of a preservative.

This invention in one aspect resides broadly in a process for the production of a preservative, the process including:- preparing a dry mixture of a hydrated boron compound and a non-hydrated boron compound, and heating the mixture to form a slurry.

The slurry may be utilised as a preservative for external application to timber, but it is preferred that the preservative be such as can be utilised internally within timber such as, for example, by being located in a bore drilled in the timber. Accordingly it is preferred that the process includes forming the slurry into a predetermined shape. In a preferred embodiment the slurry is formed into the predetermined shape by extrusion.

The hydrated boron compound can be chosen from a range of suitable compounds and is preferably a sodium boron complex. Suitably the sodium boron complex is disodium tetraborate and preferably is disodium tetraborate decahydrate. The non-hydrated boron compound is preferably boric acid.

The hydrated boron compound and the non-hydrated boron compound are mixed in a ratio in accordance with the desired physical properties of the slurry. Thus if it is desired that the slurry be relatively thin and free flowing a relatively higher proportion of hydrated boron compound is used, whereas if a thicker slurry is required for extrusion a relatively lesser proportion of the hydrated compound is used. If the compounds are disodium tetraborate decahydrate and boric acid the compounds are mixed in a ratio of between 1:1 and 6:1 respectively. It is preferred that the ratio is substantially 3:1.

Preferably the mixture is heated such that the boron compounds are not fully dissolved. The mixture may be heated to a lower temperature sufficient to form a thick slurry. Alternatively the mixture may be heated until the boron compounds are fully dissolved to form the slurry which may then thickened if required by mixing a

hydrated boron compound and/or a non-hydrated boron compound with the slurry.

Suitably the mixture is heated to a temperature of between approximately 65 and 85 degrees Celsius. More preferably the mixture is heated to a temperature of between approximately 77 and 81 degrees Celsius. Most preferably the mixture is heated to a temperature of approximately 79 degrees Celsius.

The mixture may be heated by any suitable means such as in an oven, on a hotplate or in a heat-jacketed conduit during a flow processing operation. The mixture can be formed into a slurry in much less time if heated by microwave means such as in a microwave oven and this is preferred. In another aspect this invention resides broadly in a preservative produced by heating a dry mixture of a hydrated boron compound and a non-hydrated boron compound. Preferably the preservative is produced by a process as defined above.

Description of preferred embodiment of Invention

In order that this invention may be more easily understood and put into practical effect, reference will now be made to the following example which describes a preferred embodiment of the invention.

Three parts by weight disodium tetraborate decahydrate was mixed with one part by weight boric acid to form a dry mixture. The mixture was heated in a microwave oven to a temperature of approximately 79 degrees Celsius. The boron compounds were not fully dissolved and the mixture formed a thick slurry which was fed to an extrusion device and extruded to form a continuous length which was then cut to length to form cylindrical tablets or pellets. It was unnecessary for the extruded material or the tablets to be racked or stored to allow time for setting as it was found that the material acquired the majority of its set during the extrusion process and within a matter of minutes formed a

white crystalline solid. The tablets are approximately 9 millimeters in diameter and approximately 25 millimeters in length although other sizes can be utilised. The tablet contains approximately 14.8% boron. Rods for use in the preservation of wooden power and light poles can also be produced. The rods are approximately 14 millimeters in diameter and approximately 130 millimeters in length.

In another example the above mixture was heated on a hot plate to a temperature of approximately 80 degrees Celsius at which the boron compounds were fully dissolved and formed a slurry. A quantity of the dry mixture was mixed with the slurry to thicken it to a consistency suitable for extrusion. It has been found that a suitable temperature range to which the mixture is to be heated is between 65 and 85 degrees Celsius. Within this range, a preferred range is between 77 and 81 degrees Celsius. It has been found that the preferred temperature to which the mixture is to be heated is approximately 79 degrees Celsius.

It has been found that if the mixture is heated excessively to a temperature much above 85 degrees Celsius, the mixture will quickly become a crystalline solid unable to be extruded. Correspondingly if the mixture is only heated to a temperature much below 65 degrees Celsius, the mixture will not form a slurry or, if the temperature is sufficient to form a slurry, will only do so after an unsuitably long period of time.

Once the slurry has been produced, known extrusion techniques may be utilised to produce the tablets. Thus the extruder may have a variable diameter die to produce extrusions of differing diameter and the extruded length can be fed onto a conveyor belt in known manner and conveyed to a cutting station for severing into tablet lengths.

In use a tablet or rod is inserted in a hole drilled in the end grain of timber and is suitable for use in window frames, pergolas, decks, power and light poles and

other exposed timbers. The boron compounds processed in accordance with the invention form a diffusible chemical which diffuses through the timber in dependence on the moisture content of the timber. The production process in accordance with the invention has been found to produce an effective preservative utilising little heat input. Without the addition of water to the dry mixture a slurry is produced which sets quickly thereby simplifying production methods and reducing the time required for production.

A preservative produced in accordance with the invention does not have the toxicity of preservatives including fluorine derivatives and depending on the dampness of the environment of use should have an active life of up to 10 years before having to be replaced. A tablet made in accordance with this invention has a very stable shelf life and is odourless and non-inflammable.

It will of course be realised that whilst the above has been given by way of an illustrative example of this invention, all such and other modifications and variations hereto, as would be apparent to persons skilled in the art, are deemed to fall within the broad scope and ambit of this invention as is hereinafter claimed.