What are the specific requirements for rheology of latex paint?

1. Viscosity and Viscometer

The fluid’s resistance to flow is called viscosity, expressed in η, defined as the ratio of shear stress to shear rate, in Pa seconds (Pa . s), the former unit is poise (P), 1Pa s=10P , 1mPa·s=1cP.

Latex paint Latex paint is a non-Newtonian fluid whose viscosity changes with shear stress. The test ranges of the three commonly used viscometers in the industry are roughly as follows:

The Brookfield viscometer generally tests the viscosity at a shear rate above 10 ^-2 ~10s ^-1 , the Stormer viscometer generally tests the viscosity at a shear rate above 10~10 ² s ^-1 , and the ICI viscometer Generally test the viscosity at a shear rate of about 10 ⁴ s ^{-1 .}

2. Rheological requirements of latex paint

Latex paint often encounters different shear rates from production, storage, construction to film formation. According to Barton, during the manufacturing process, the shear rate near the dispersing disc of the high-speed disperser is about 1000~10000s ^-1 , while at the top of the container, the shear rate is only 1~10s ^-1 , and the coating close to the container wall It is actually stationary. After the latex paint is pumped into the storage tank or filled into the bucket, the shear rate drops to 0.001～0.5s ^-1 . During construction, the shear rate when dipping paint is estimated to be 15-30s ^-1 , while the shear rate when brushing is about 1000-10 000s ^-1 which is similar to that of high-speed dispersion . After application, latex paint will produce leveling, sagging and penetration, and the typical shear rate at this time is below 100s ^-1 . In order to improve productivity and obtain excellent products, different rheological requirements are proposed, see Table 5-11 for details.

Rheological requirements of latex paint

Figure 1 is a graph based on the average of 12 latex paints, showing suitable ranges for yield value, pre-application viscosity, dip paint viscosity, and application viscosity. The curves are typical viscosity distribution curves of unsheared and sheared coatings.

The relationship between the shear rate logarithm and the viscosity logarithm of Fig. 1 latex paint