русский
Español
FrançaisIndustry News
After slurry viscosity drops, flow during application may look better, but filtration efficiency does not necessarily improve with it. Particle agglomeration, fine impurities, filter media clogging and the dispersion state of the slurry can all affect filtration. To analyse difficult filtration, judge viscosity, particle distribution and filter media condition together.
ViscosityLower flow resistance under a given test condition
AgglomeratesSoft agglomerates can still be present
Fine particlesMay deposit in pores or form a dense cake
Filter mediaPore size, area and pressure matter too
Introduction
In producing new-energy materials, conductive slurries and functional coatings, viscosity is an indicator watched constantly when adjusting a formulation. When slurry viscosity is high, technicians often adjust the dispersant level, optimise the grinding process or change the system composition in the hope of improving flow.
In production, though, a seemingly contradictory case sometimes appears: viscosity has dropped, but filtration speed has not risen, and the screen may even clog or the filtration pressure difference may increase.
This shows that viscosity and filtration performance are not simply positively related. Viscosity mainly reflects the flow resistance of the slurry under specific test conditions, while filtration is also affected by particle size, particle shape, agglomeration state and filter media structure.
Why filtration stays difficult after viscosity drops
| Large particles and soft agglomerates remain | A lower viscosity does not directly prove that the particles are fully dispersed. In some systems the continuous phase flows better while pigment, conductive material or other powder is still agglomerated. When these agglomerates reach the screen they may be held on the filter surface or at pore entrances and gradually form a filter cake, making it ever harder for later slurry to pass. Soft agglomerates in particular may not be obvious during stirring or viscosity testing, yet gather, deform or bridge and block pores during filtration. So slurry state should not be judged by the viscosity value alone; also watch particle distribution and changes before and after filtration. |
|---|---|
| More fine particles can worsen clogging | After grinding or dispersion adjustment, some formulations have fewer large agglomerates but a higher proportion of fine particles. Fine particles do not necessarily pass straight through the filter. Some enter the pores and gradually deposit inside; others form a dense filter cake together with other particles and reduce throughput. So even when the slurry flows more easily overall, it may not pass smoothly through a screen of a given pore size. The result also depends on how particle size distribution matches the filter pore size. |
| A changed dispersion state can change filtration behaviour | Dispersants influence the interaction between particles, but adding more does not necessarily improve filtration. When the type, level or sequence of addition of the dispersant changes, the adsorption state on particle surfaces, system stability and particle interactions may all change. If the dispersion system does not match, flocculation or re-agglomeration may still occur during storage or filtration. A viscosity drop may also come from a change in the properties of the continuous phase rather than better dispersion, so simply adding dispersant to lower viscosity may not solve screen clogging. |
| Filter media and process matter as well | Difficult filtration does not come entirely from the slurry. Screen pore size, media structure, filtration area, filtration pressure and the filter cake formed on the media surface all affect actual speed. A smaller pore size helps hold back large particles but may clog more easily; a higher filtration pressure may compact the cake further and raise later resistance. If the media is already partly blocked, swapping in a lower-viscosity slurry may not improve speed noticeably. |
How to investigate slurry filtration problems
When viscosity has dropped but filtration is still difficult, check step by step in these directions.
| Check particle state | Compare particle size distribution before and after grinding, and before and after filtration, and look for agglomerates or abnormally coarse particles. |
|---|---|
| Compare the residue | Look at what is retained on the screen and distinguish large agglomerates, fine particle deposition and foreign impurities. |
| Verify the dispersion system | Check dispersant type, level and sequence of addition, and use storage stability to judge whether re-agglomeration occurs. |
| Recheck filtration conditions | Compare filter pore size, filtration area, pressure changes and throughput per unit time, to judge whether clogging is mainly on the media surface or inside the pores. |
During investigation, run comparison tests at the same temperature, with the same filter media, filtration area and pressure, so that a change in process conditions is not mistaken for a formulation effect.
Frequently Asked Questions
Does a lower viscosity guarantee faster filtration?
No. A lower viscosity only means the flow resistance changed under a specific test condition. It does not show better particle state or guarantee a faster filtration speed.
Why can soft agglomerates still block the screen?
They may not show up during stirring or viscosity testing, but during filtration they may gather, deform or bridge across pores.
Will adding more dispersant solve clogging?
Not necessarily. A larger amount does not mean filtration improves, and a viscosity drop may come from a change in the continuous phase rather than better dispersion.
How should comparison tests be run?
Keep temperature, filter media, filtration area and pressure the same, so that process changes are not mistaken for formulation effects.
Closing summary
A lower slurry viscosity only shows that flow resistance has changed under specific test conditions. It does not directly show a better particle state, nor does it guarantee a faster filtration speed.
To improve filtration, analyse viscosity, particle distribution, dispersion stability and the filtration process together. For systems that use dispersants, what deserves more attention is whether the particles are fully dispersed, whether the system stays stable and whether the dispersion state matches later filtration requirements, rather than simply chasing a lower viscosity.
