Paint, non-drip

Non-drip paints Thixotropic Thick in the tin, thin on the brush... 

Many modem materials are time dependent, also referred to as thixotropic materials. These samples will slowly build in viscosity at rest, but under shear will break down at a rate that is appreciably faster than the rebuild rate. This will result in a hysteresis effect if a flow curve where the stress or shear rate is increased is followed by a flow curve where the same parameter is decreased. Highly filled materials with a viscous suspending phase are prone to this effect, as are latices and plastisols. Sometimes this effect is deliberately encouraged in a formulation to improve its properties in use. An example of this would be non-drip paint, where the recovery of viscosity prevents the paint from dripping from the substrate or running off the bmsh or roller. 

Today also much attention is paid to the rheologic behaviour of wet paints and the flow during the wet stage of a drying paint just before its ultimate film formation. Typical examples are thixotropic, non-drip ... 

A final modification, sometimes practised, is to introduce a measure of non-drip property into the paint. This is done by incorporating a small amount of a special polyamide into the alkyd, with which it is only partly compatible. These polyamides are derived from dimerized unsaturated fatty acids and diamines. 

Structured paint n. Paint having a gel-like consistency which breaks down under the kind of shear exerted during brushing or roller application and re-forms when the shearing force is removed. When there is a time lag between the removal of the shearing force and the start of gel re-formation, the paint is said to be thixotropic. The thixotropic structure can vary from a very light gel to the fully gelled thixotropic paints of the non-drip type. 

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