Thixotropic index

The thixotropic property of an adhesive may be defined by its thixotropic index, the ratio of viscosities measured at two shear rates, generally a decade apart, for example. 

Viscosity 6.2 Report viscosity and thixotropic index (0.5/5 rpm) measure per ASTM D2556... 

Thixotropy may also be expressed as the thixotropic index (TI) which is the ratio of viscosities measured at speeds that have a ratio of 1 10 rpm, for example at 2 rpm... 

Adhesive Viscosity (cps) Thixotropic Index (1 10) Pot Life Cure Schedule... 

A property related to viscosity is the thixotropic index, ameasure of the dependence ofviscosify on shear-rate. The thixotropic index (TI) is the ratio of viscosities measured at speeds that have aratio of 1 10 rpm, for example, at 2 rpm and 20 rpm. For non-Newtonian materials used in automated dispensing, shear thinning is apparent from TI values of 2-6. In general, capillary-flow underfills have thixotropic indices of 1, or close to 1. 

In addition to viscosity and thixotropic index, yield value (also known as yield point or yield stress) is measured. Yield value is the minimum foree required to start the adhesive moving. Yield value may be measured by two methods. First, the yield value may be obtained from the eurve of shear stress to shear rate.f The curve is extrapolated to give the shear stress at... 

Incoming raw materials, specifically the matrix constituents and the fibre rovings and mats, should be inspected. Basic inspection includes checking the delivery notes and the labels of containers when the materials arrive. Visual inspection of raw materials is also recommended resins can be inspected for colour and the presence of contamination and gel particles (Evans, 2000) reinforcements can be checked for the presence of knots in the rovings, while simple mass measurements can be made for mats or fabrics. Some pultrusion companies have quality control and/or research and development laboratories where material characterisation tests can be performed (most often such control is executed by raw material suppliers). Fibre reinforcements can be subjected to tensile tests. The moisture content of the constituents (particularly the reinforcements and the fillers) can also be determined. The quality of incoming resins can be tested by means of thermal analysers (resin reactivity) and viscometers (resin viscosity and thixotropic index) (Owens Coming, 2003). 

The ODF sealant is dispensed by a dispensing machine after mixing with gap material and conductive material and filled in a syringe under vacuum by the LCD manufacturer. The viscosity and the thixotropic index of the ODF sealant depend largely on dispensing properties, and the optimal combinatirHi of resin and fillers is important, too. 

Frequently, the flow properties of adhesives and sealants are measined with a Brookfield viscometer at two different spindle speeds at a rotation ratio of 10 1. The ratio of the low spindle speed viscosity to the high spindle speed viscosity is termed the Shear Thinning or Thixotropic Index and is a measine of shear sensitivity (pseudoplasticity) see Figure 3. 

Viscosity is measured with cone and plate (circa 2.S poise) and with roto thinner (circa 5.0 poise) This gives a thixotropic index which is important with this type of formulation where such a degree of hold up is required in the spatter coat. 

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