Choosing the Right Nozzle

Nozzles direct the flow of ink as it exits the cartridge onto your substrate. They are a critical component of the dispensing system, and control many aspects of the quality of your output. For that reason, choosing the right nozzle for the job will help ensure you get the best possible print quality.

Nozzle anatomy and types

All nozzles have the following components:

1. The hub - the Luer fitting, usually made of plastic, that attaches the nozzle to the dispenser. These are usually just molded plastic.

2. The barrel - the portion that directs the fluid to the tip. It can usually be tapered, conical, or straight. The barrel will usually determine how much resistance there is to printing; straight or narrow barrels will require more pressure, while tapered / conical or wide barrels will require less.

3. The tip or orifice - in straight-barrel nozzles, this is just the end of the barrel. The inner diameter (ID) of the tip determines the minimum print size, but smaller IDs will also limit the inks you can use depending on their particle size, and require higher pressures.

4. The material - while not strictly a labeled component on a chart, the nozzle’s material can make a big difference in performance. Material options are covered below in nozzle types.

Nozzle types

Nozzle types are usually defined by their barrel types and materials. For a good selection of diverse nozzle types, consider looking through Nordson EFD’s optimum catalog.

Barrel Shapes

As mentioned above, the most common barrel shapes are straight-barrel, tapered, or conical. When choosing a barrel type, consider the trade-offs below:

• Intended viscosity:

  • Conical nozzles are specifically made for precision dispensing with higher-viscosity materials. The conical barrel provides a gentle gradient, allowing NOVA to dispense through a high-resolution nozzle without requiring extremely high pressures. Tapered nozzles are similar, but are usually plastic and have larger nozzle orifices.

  • Straight-barrel nozzles are better suited for low-viscosity inks, where the added friction from the long barrel allows for better dispensing control. If you find your ink is extremely sensitive to pressure changes, even with the small nozzle orifice, try a straight-barrel nozzle!

• Robustness: Conical nozzles are typically quite robust, and as long as the tip is not damaged, can be handled easily and withstand interacting with NOVA’s XYZ calibration switch. Straight barrel nozzles are generally decently robust, but at smaller IDs, they will start to deflect, bend, or break with little applied force.

NOTE: Straight-barrel nozzles also have a variety of barrel length options. Longer barrels have more friction and so require higher dispensing pressures, while shorter barrels require less pressure.

Material Options

The nozzle Luer hub material doesn’t have much impact on the print quality, but there are a variety of material options for barrels and coatings.

Barrel materials are usually either metal (such as stainless steel) or plastic (usually polyethylene, sometimes polypropylene). In some specialty cases, there are also glass, ruby-tipped, or ceramic nozzles, but we won’t cover these options in this guide. When choosing barrel materials, consider the tradeoffs below:

• Cost: Cost is dramatically different between plastic and metal. While plastic nozzles can cost a few cents, metal nozzles can range from less than $1 for simple ‘general purpose’ straight-barrel nozzles, up to $10 or even more than $100 for certain precision tapered nozzles.

• Nozzle orifice / ID: Plastic nozzles can have an inner diameter as small as 200µm, while metal nozzles can generally be made available in sizes down to 50µm. Specialty material nozzles can offer even smaller orifices if necessary.

• Barrel options: Plastic nozzles are mostly restricted to tapered barrels, while metal barrels can be straight, tapered, conical, or even follow other exotic profiles like oval-shaped or chamfered orifices.

• Solvent stability: Plastic nozzles don’t have the same solvent resistance as metal. It’s helpful to check solvent compatibility tables if your material has particularly aggressive solvents.

• Nozzle outer diameter and adhesion: Plastic nozzles usually have thicker walls than metal nozzles, which means they have a larger outer diameter (OD). This gives more surface area for ink to stick to during dispensing, and can lead to ink pulling up along with the nozzle, which we call ‘stringing’. This can still happen with metal nozzles, which is where coatings come in.

Coating materials are an option with some precision conical nozzles. The purpose of coatings is usually to reduce adhesion between the nozzle OD and the ink, allowing for smoother flow and eliminating stringing when lifting away from the substrate. Coating materials are usually some type of low-surface-energy fluoropolymer, like PTFE. While coatings will add cost, they can be worth the added cost if your ink is prone to stringing.

Nozzle suppliers

Precision nozzles are more niche and more expensive, while simple plastic or straight-barrel dispensing tips can be found from many suppliers. Some example dispensing tip supplier options include:

• Nordson EFD - for a variety of general purpose, plastic, and precision nozzles

• Jensen, Subrex - for precision nozzles

• Amazon, Fisnar - for plastic dispensing nozzles

Choosing Nozzles

Now that you know more about the types of nozzles available, you should be able to select an appropriate nozzle. Here are some helpful rules of thumb:

1. Nozzle diameters - the rule of ten (or, rule of six): If you know your material’s particle size distribution, choose a nozzle inner diameter so that the 6 particles at D80 particle size will fit across. If you don’t know the distribution, play it safe and make it 10 particles at the average (or known) particle size. While particle size isn’t always the limiting factor with high viscosity materials, this can help prevent clogs. For example - if you have an average particle size of 3µm (common for silver flake inks), you should have a nozzle diameter of at least 30µm.

2. For low viscosity materials use a straight barrel nozzle. The added wall friction will give more precise control over the flow rate when using more water-like materials.

3. For high viscosity materials, use conical or tapered nozzles. Conical nozzles let you dispense high-viscosity inks at high resolution; if a small nozzle ID is not required, tapered nozzles can give you a similar option at lower cost.

When to switch nozzle types

If you start with the wrong nozzle, you will usually run into issues quite quickly. Maybe no ink flows at all, or maybe it flows too much, or is too sensitive to small pressure changes to adequately get your target trace width, or you are seeing excessive amounts of stringing and need a coated nozzle.

In any case, don’t be afraid to try something new if your nozzle isn’t working — just make sure you calibrate again when changing nozzle types.