What is the best dispensing tip for a thin fluid?

Low-viscosity fluids like solvents and varnishes are used in many manufacturing processes. However, choosing the right dispense tip for thin fluids presents unique challenges.

What are the challenges of dispensing thin fluids?

When it comes to dispensing, thin fluids present two primary issues: dripping and wicking.

Dripping is primarily a function of unsuitable vacuum pullback settings on the dispenser, as well as using an unsuitable piston. Dripping can decrease accuracy and cause quality issues.

Wicking occurs when capillary action draws thin fluids up the outer diameter of the dispensing tip, reducing deposit accuracy.

How do I choose the right dispensing tip for my low-viscosity fluid?

Here are our “rules of thumb” for choosing the best dispense tip for a thin fluid dispensing application:

How to prevent dripping when dispensing thin fluids*

• Look for a crimped cannula
  A dispense tip with a crimped cannula is the best choice for dispensing a low-viscosity fluid. The crimp reduces the flow rate of low-viscosity fluids. A better controlled overflow rate reduces the possibility of dripping.
• Choose a slightly larger cannula than you think you need
  Choosing a narrow cannula diameter is generally beneficial for low-viscosity fluid dispensing, but only to a point. If the diameter is too narrow, it can introduce capillary action that can lead to fluid retention, and dripping. Choosing a cannula diameter slightly larger than minimum can lead to smoother flow that is not disrupted by capillary action.

* For additional information on drip control, see What kind of pistons should I use for thin fluids and cyanoacrylates?

How to prevent wicking when dispensing thin fluids

• Use a PTFE-coated tip to prevent wicking
  Polytetrafluoroethylene (PTFE, or Teflon) is a stable, hydrophobic nonstick coating (see Figure 2). PTFE-coated dispense tips help disrupt capillary action, preventing thin fluids climbing up the outside of the cannula.

   

  

  Figure 2: Designed for micro deposits of low-viscosity fluids, Nordson EFD’s Optimum PTFE-Coated dispensing tips stop wicking to prevent dripping.

• Try a chamfered tip to reduce wicking
  

  A chamfered dispense tip can help prevent wicking. These dispensing tips feature tapered outer diameters (ODs), reducing surface area (see Figure 3). The shape inhibits wicking, giving better control of the dispensing process.

   

  

  Figure 3: Optimum Chamfered dispense tips from Nordson EFD feature tapered outer diameters at the ends to discourage wicking.