Frequently Asked Questions Regarding Dispensing of Adhesives

The following are some of the more common questions when dispensing adhesives and a few tips.

Question

When dispensing adhesive around the opening of a large plastic container, an operator found that adhesive had somehow splattered on the inside of the bottle in some of the assemblies. What could be causing this?

Answer

There are two main possible causes for this situation, the first of which is due to static electricity. Dry conditions cause static electricity and could cause the line of adhesive to briefly jump to the other side of the bottle rather than continue to drop directly below the dispensing needle. The second possible cause is due to stringing, which is where the adhesive doesn’t stop coming out when the pressure from the dispensing needle stops, and this last little string of adhesive may then be free-falling into the wrong side of the container.

Question Dispensing Different Viscosity/Rheology

After changing raw materials, a business needed to change its adhesive so that it would bond to the new raw material. However, despite both adhesives being of the same viscosity, the new adhesive ran all over the various parts of the machinery. How can two materials with the same viscosity act so differently?

Answer

Materials can have the same viscosity but differ greatly in their rheology, which is effectively their rate of flow. There are two main types of materials when it comes to flow rate: Newtonian fluids and thixotropic. Newtonian fluids flow the same when the shear is fast or slow. Thixotropic materials will have a high viscosity when stirred slowly and a low viscosity when stirred quickly.

Question Dispensing Different Types of Adhesives

If a dispensing system has been used previously for a UV-curable adhesive, is it possible to use the same dispenser on a new application using cyanoacrylate adhesives?

Answer

It depends on what your dispenser is made of. But chances are good that you will be able to reuse your dispense for this new application. To be sure, it is wise to check with the manufacturer of the dispenser.

Question – Dispensing Adhesive Tips

What is the best type of dispenser tip to use to prevent clogging when dispensing adhesive through an automatic pressure pot system?

Answer

Generally speaking, you are best to use plastic tips to avoid clogging. These will normally be made from polypropylene or polyethylene. But it all depends on the type of adhesive you are using.

The following tips will help to prevent the dispenser tips for your adhesives from becoming clogged.

1. If you are using a UV curable adhesive, make sure your dispenser tip is able to block the light. Whether it is metal or plastic makes little difference.
2. For cyanoacrylate adhesive dispensing tips – either remove the tips and place them in a solvent to clean and reuse them or replace the tips after idle periods.
3. Avoid using metal tips when dispensing an anaerobic adhesive.
4. Single part epoxies will cure with heat, so slowly, heat tips to just above room temperature to remove clogging.
5. Two component epoxies start setting as soon as they are mixed. Refer to the adhesive’s pot life to know exactly how long you have before replacing the dispensing tip.