Stable aqueous formulation and use

Details Stable aqueous formulation and use Stable aqueous formulation and use

1995-12-18

2001-10-23

Kulkosky, Peter F. (Department: 1615)

Drug, bio-affecting and body treating compositions

Preparations characterized by special physical form

Biocides; animal or insect repellents or attractants

C514S373000

Reexamination Certificate

active

06306413

ABSTRACT:

This application claims benefit of international application PCT/GB94/01155, filed May 27, 1994.
The present invention relates to a stable aqueous formulation of 1,2-benzisothiazolin-3-one which is substantially free from organic solvents. 1,2-benzisothiazolin-3-one (hereinafter referred to as BIT) is an established industrial biocide and is particularly effective in protecting aqueous media against microbiological spoilage. It is particularly effective as a bactericide and is especially suited to the protection of latices. Thus, one of its major uses is as an in can preservative for the preservation of acrylic and acrylate paint emulsions.
BIT has low aqueous solubility and can cause sensitisation in some individuals. Consequently, for ease of handling and to reduce the risk of sensitisation,.BIT is generally formulated as a liquid composition. These compositions include stable solutions of BIT in an amine solvent as disclosed in UK 1,191,253 and UK 1,330,531, and also solutions of BIT in propylene glycol or diethylene glycol. None of these compositions are ideal and have never been wholly successful in commercial terms.
Because of the low aqueous solubility of BIT, an alternative approach to stable aqueous solutions has been to form the alkali metal salt of BIT, especially the sodium or lithium salt. The lithium salt of BIT is disclosed in U.S. Pat. No. 4,871,754 as having an aqueous solubility above 16% by weight which is approximately twice that of the sodium salt of BIT. The lithium salt of BIT is, however, more expensive to manufacture. Other approaches to increasing the aqueous solubility of the sodium salt of BIT is to include co-solvents such as dipropylene glycol as disclosed in U.S. Pat. No. 4,188,376 or urea as disclosed in U.S. Pat. No. 4,751,311. The formulation containing dipropylene glycol has become extremely important commercially. However, formulations containing the alkali metal salt of BIT exhibit relatively high pH which is a disadvantage in some applications. Furthermore, there is an every increasing demand for formulations containing a low concentration of volatile organic compounds (hereafter VOC). Hence, formulations containing solvents such as glycols are becoming less acceptable.
Because of its low aqueous solubility, BIT has also been formulated as a dispersion wherein the BIT is generally dispersed by means of a non-ionic or anionic surface active agent. Aqueous dispersions containing 33% by weight BIT are known, but tend to be unstable under storage at elevated temperature resulting in gels which are difficult to handle. Improved dispersions have been attempted by incorporating solvents such as propylene glycol, but such dispersions tend to layer and separate on storage at elevated temperature and the BIT consequently aggregates and forms lumps. Alternatively, mineral clays have been included in the formulation to structure the aqueous phase with the objection of inhibiting separation. This tends to reduce aggregation of the BIT but the formulation again separates on storage at elevated temperature. As with the formulations containing solvents, the formulations containing clays require rehomogenising prior to use and this can be difficult and expensive. Failure to ensure uniform distributon of the BIT throughout the formulation can given rise to errors in metering and subsequent reduction, or even loss, of microbial protection in the media to be preserved.
Xanthan gum is a polysaccharide thickener which forms a structured network of entangled molecules in water which aids the suspension of particulate matter, and can reduce sedimentation. Aqueous dispersions containing 33% by weight BIT have been prepared containing both a Xanthan gum and propylene glycol as a cosolvent. Again such formulations tend to separate and the BIT tends to aggregate and form lumps. The addition of glycols such as mono- and dipropylene glycol to aqueous formulations generally increases the viscosity of the formulation as disclosed in Examples 16 to 21 of UK Patent Application No. 9300936.3. which relates to aqueous solutions of the sodium salt of BIT. The more dipropylene glycol is added, the higher the viscosity. We have now surprisingly found that when the propylene glycol is removed from aqueous formulations containing BIT dispersed in the presence of Xanthan gum and the glycol, the viscosity actually increases. This observation is contrary to the effect of the glycol observed in the formulations disclosed in UK Patent Application No. 9300936.3. As a result, we have now found it possible to make a stable aqueous formulation of BIT in the presence of a Xanthan gum which is substantially free from organic solvents.
According to the present invention there is provided a stable aqueous formulation comprising from 5 to 30% by weight microbiologically active agent containing at least 50% BIT, from 1 to 4% dispersant and from 0.1 to 0.5% by weight Xanthan gum, which formulation is substantially free from organic solvents.
The remainder of the aqueous formulation is preferably wholly water but may comprise other materials, such as inorganic salts. The formulation, is however, preferably, completely free from organic solvents.
Preferably, the amount of microbiologically active agent in the formulation is at least 7% and more preferably at least 9%, for example 10% by weight of the formulation. The amount of microbiologically active agent is also preferably less than 25% and more preferably less than 22%, for example 20% by weight of the formulation.
The dispersant is preferably either non-ionic or anionic, or a mixture thereof, but is especially anionic. Examples of suitable nonionic dispersants are condensates of ethylene oxide or propylene oxide including block co-polymers of ethylene oxide and propylene oxide. Examples of suitable anionic agents are sodium lignin sulphonate and the sodium salt of naphthalene sulphonic acid/formaldehyde condensates. Mixtures of anionic and non-ionic dispersants may also be used. Preferably the amount of dispersant is at least 1.2% and especially at least 1.5% by weight relative to the total formulation. It is preferred that the amount of dispersant is less than 3.5%, for example 3% by weight of the total formulation.
The amount of dispersant is commonly calculated on the amount of microbiologically active agent in the formulation. Thus, the ratio of dispersant to microbiologically active agent is preferably 1:20, more preferably 2:20 and especially 3:20.
The amount of Xanthan gum is preferably at least 0.2%, more preferably at least 0.3% and especially at least 0.35% relative to the total weight of the formulation. It is also preferred that the amount of Xanthan gum is less than 0.45%, for example 0.4 relative to the total weight of the composition.
The pH of the formulation may be from 1 to 8 but is preferably above 3, more preferably above 5 and especially above 6. It is especially preferred that the pH is about neutral, i.e. from 6.5 to 7.5 but more preferably is not greater than 7.
As noted hereinbefore, the exclusion of the glycol solvent from formulations of BIT containing a dispersant, Xanthan gum and propylene glycol results in an increase in viscosity. The formulations of the present invention preferably exhibit a viscosity of at least 1000, preferably at least 1200 and especially at least 1500 centipoise as measured by Brookfield viscometer using Spindle No. 2 and rotational speed of 10 rpm. The viscosity is preferably less than 3,500 and especially less than 3000 centipoise.
We have obtained a particularly stable dispersion containing about 20% by weight.BIT, about 3% anionic dispersant and 0.3 to 0.4% Xanthan gum relative to the total weight of the formulation, the remainder being water.
The formulation preferably contains BIT as the only microbiologically active agent, but it may contain one or more further microbiologically active agent. The further microbiologically active agent is preferably one which extends the spectrum of activity against micro-organisms. When the composition contains more than one microbiologically active

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