Gel formulation

Details Gel formulation Gel formulation

1997-07-22

2003-11-18

Webman, Edward J. (Department: 1617)

Drug, bio-affecting and body treating compositions

Preparations characterized by special physical form

Matrices

C424S405000

Reexamination Certificate

active

06649190

ABSTRACT:

The present invention relates to a water dispersible agrochemical gel formulation.
Gels comprising a surfactant, an agrochemical, an acrylic acid polymer or copolymer and water are disclosed in W092/01377.
The present invention provides a water dispersible gel comprising (a) an effective amount of an ionic, water soluble agrochemical, (b) an effective amount of a crosslinked polyacrylic acid, (c) water, and (d) an amount of a base sufficient to cause a mixture of (a), (b) and (c) to gel.
The water dispersible gels of the present invention are suitable for packaging in standard containers or for containment in a water-soluble or water dispersible bag. The gels of the present invention are able to be dispersed in water, and the rate of dispersion depends on the degree agitation the gel water mixture is subjected to and also the amount of water present.
The ionic, water soluble agrochemical, is, for example, a herbicide (such as a paraquat salt (for example paraquat dichloride or paraquat bis(methylsulphate), a diquat salt (for example diquat dibromide or diquat alginate) or glyphosate or a salt or ester thereof (such as glyphosate isopropylammonium, glyphosate sesquisodium or glyphosate trimesium (also known as sulfosate)), an insecticide or a fungicide. It is preferred that the ionic, water soluble agrochemical is paraquat dichloride, diquat dibromide, glyphosate isopropylammonium or glyphosate trimesium (also known as sulfosate).
Crosslinked polyacrylic acids preferably have a molecular weight in the range 5×10
5
to 5×10
6
, especially in the range 1×10
6
to 4×10
6
. They are available commercially, for example as CARBOPOLs marketed by B F Goodrich (such as CARBOPOLs 5984, 2984, 940, 5984, 910, 941, 934, 934P or ETD 2050).
Suitable bases include ammonium or alkali metal (such as sodium or potassium) hydroxides, carbonates or bicarbonates (for example sodium hydroxide, sodium carbonate or sodium bicarbonate); or amines of formula R
1
R
2
R
3
N (wherein R
1
, R
2
and R
3
are, independently, hydrogen or C
1-6
alkyl [optionally substituted by C
1-6
alkoxy, hydroxy, halogen, C
1-6
haloalkoxy (such as OCF
3
), C
1-6
hydroxyalkexy (such as HOCH
2
CH
2
O) or C
1-4
alkoxy(C
1-6
)alkoxy (such as CH
3
O (CH
2
)
2
O or CH
3
O(CH
2
)
5
O] such as HOCH
2
CH
2
). It is preferred that R
1
, R
2
and R
3
are, independently, C
1-6
alkyl or C
1-6
alkyl monosubstituted with hydroxy. An amine of formula R
1
R
2
R
3
N is, for example, triethylamine or triethanolamine.
Alkyl and the alkyl part of alkoxy groups are straight or branched chain and preferably contains from 1 to 4 carbon atoms. It is, for example, methyl, ethyl, n-propyl, iso-propyl, n-butyl or tert-butyl.
In one aspect the present invention provides a water dispersible gel comprising (a) 1-60% (especially 5-60%) by weight of an ionic, water soluble agrochemical, (b) 1-4% by weight of a crosslinked polyacrylic acid, (c) 30-80% by weight of water, and (d) 2-20% by weight of a base.
In another aspect the present invention provides a water dispersible gel comprising (a) 20-60% by weight of an ionic, water soluble agrochemical, (b) 1-4% by weight of a crosslinked polyacrylic acid, (c) 30-80% by weight of water, and (d) 2-20% by weight of a base.
In a further aspect the present invention provides a water dispersible gel comprising (a) 20-60% by weight of an ionic, water soluble agrochemical, (b) 1-4% by weight of a crosslinked polyacrylic acid, (c) 30-80% by weight of water, (d) 2-20% by weight of a base, and (e) 1-40% of an electrolyte.
When a gel of the present invention is going to be held in a water-soluble or water dispersible sachet and when the ionic strength of said gel is low it is preferred that said gel comprises a suitable electrolyte in addition to the ionic agrochemical present. The electrolyte helps to improve the insolubility of the material from which the sachet is made in the gel. (See Polyvinyl Alcohol—Properties and Applications pages 38-43, edited by C. A. Finch, published by J Wiley & Sons in 1973 and EP-A1-0518689.) Suitable electrolytes may, for example, comprise a cation or mixtures of cations selected from the list comprising: ammonium, copper, iron, potassium and sodium; and an anion or mixture of anions selected from the list comprising: sulphate, nitrate, fluoride, chloride, bromide, iodide, acetate, tartrate, ammonium tartrate, benzenesulphonate, benzoate, bicarbonate, carbonate, bisulphate, bisulphite, sulphate, sulphite, borate, borotartrate, bromate, butyrate, chlorate, camphorate, chlorite, cinnamate, citrate, disilicate, dithionate, ethylsulphate, ferricyanide, ferrocyanide, fluorosilicate, formate, glycerophosphate, hydrogenphosphate, hydroxostannate, hypochlorite, hyponitrite, hypophosphite, iodate, isobutyrate, lactate, laurate, metaborate, metasilicate, methionate, methylsulphate, nitrite, oleate, orthophosphate, orthophosphite, orthosilicate, oxalate, perborate, perchlorate, phosphate, polyfluoride, polychloride, polyiodide, polybromide, polysulphide, polysulphate, polysulphite, salicylate, silicate, sorbate, stannate, stearate, succinate or valerate. Preferred electrolytes are ammonium sulphate, sodium sulphate, potassium sulphate, copper sulphate, ammonium nitrate, sodium nitrate, potassium nitrate, sodium chloride or potassium chloride.
It is preferred that sufficient base is added to cause the pH of the water dispersible gel to be in the range 6 to 10, especially 6 to 8. If too much base is added the pH of the mixture will be too high and the gel formed will break down. Thus, in another aspect the present invention provides a water dispersible gel comprising (a) an effective amount of an ionic, water soluble agrochemical, (b) an effective amount of a crosslinked polyacrylic acid, (c) water, and (d) an amount of a base sufficient to cause the pH of the resulting gel to lie in the range 6 to 10 (especially 6 to 8, particularly 6 to 7).
In a further aspect the present invention provides a water dispersible gel which comprises 2-5% by weight of an alkali metal hydroxide, carbonate or bicarbonate.
A Bohlin VOR rheometer may be used to measure the elasticity and viscosity of the gel formulation of the present invention under low shear conditions. Here a sinusoidally varying strain (at a frequency of 1 Hz) is applied to a sample of a formulation maintained at 25° C. The resultant stress, which also varies sinusoidally with time, is observed. The ratio of the maximum stress to the maximum strain is known as the complex modulus (G*). By using the phase shift, &dgr;, between the stress and strain wave forms the complex modulus may be split into two components—the storage (elastic) modulus (G′) and the loss (viscous) modulus (G″). The storage and loss moduli are a measure of the energy stored and the energy lost respectively, in an oscillatory cycle. The relative magnitude of the loss and storage moduli (G″/G′=Tan &dgr;) provides information on the elasticity of the gel. The lower the value of Tan &dgr; the greater the degree of gelation. Similarly, gels are characterised by their non-Newtonian flow behaviour, exhibiting, for example, yield values and shear thinning. Yield values can be measured using a Haake Rotovisco RV20 under high shear conditions.
In a still further aspect the present invention provides a water dispersible gel as hereinbefore described having a storage modulus (G′) in the range 1-1000 Pa, preferably 20-500 Pa, more preferably in the range 100-200 Pa.
In another aspect the present invention provides a water dispersible gel as hereinbefore described having a tan &dgr; (ratio of loss modulus to storage modulus) of less than 1, preferably less than 0.5, more preferably less than 0.2, especially less than 0.1. (Rheological measurements are carried out at a temperature of 25° C. Oscillation measurements are carried out within the linear viscoelastic region as determined by strain sweep measurements made at a frequency of 1 Hz (6.28 rad/s)).
In another aspect the present invention provides a water dispersible ge

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