In Depth: Cosmetic Dropper Pipettes (Part 2 of 3)

The Pipette Collar

So, what do we even mean by the collar, or holecap as it's sometimes called?

In simple terms, it is the part of the pipette which screws onto the neck of the bottle, ensuring that none of the contents spill or leak. The tube and the bulb are held together by the collar, which more often than not, is made of plastic (often polypropylene). However, there can be some variations to this, which we will discuss later.

What does the holecap do?

It's quite simple - it holds the pipette together, and keeps it on the bottle. So in a bit more detail the tube part (usually clear, usually made of glass) is inserted into the soft bulb (the subject of our next blog in this series!) and then the holecap holds it all together. The holecap is designed to fit securely onto the bottle with which the pipette is to be used. In this industry, this is usually a global standard bottle neck type, allowing the largest possible choice of bottles. Within Richmond, we have focused in on two common types of bottle neck types - the GL18 (18mm diameter) and the 20/410 (20mm diameter). These have very tightly controlled specifications, which means you have the best possible chance of creating a really good seal between the bottle neck and these pipettes (you may be sick of hearing us say this, but 'always test first' - brands do physical tests for a great reason even when everything is tightly specified - usually for 12 weeks as well!)

The collar needs to be tightened (torqued) down during application to ensure a good seal between bottle and cap. The sealing surface is normally the soft underside of the bulb which creates a soft gasket between the collar and the top of the neck of the glass bottle (see diagram). Therefore, having all the correct tolerances between collar, bulb/gasket and bottle neck to create the correct amount of compression of the gasket material is key to creating a great seal and ensuring your product doesn't leak - even when upside-down in your consumer's handbag!

There is another reason dropper bottles often leak (other than incorrect screwing-on torque or mismatch between collar-bulb and bottle). This is a phenomenon known as “back-off” and is the process of a pipette collar unscrewing of it’s own accord (seems crazy but it can happen!). This can be complex to diagnose correctly and our packaging technologists can help if you suspect you have this issue. Safe to say though, the most common reason for it is that the threads of the bottle have become wet with product. This lubricates them, resulting in loss of friction and encouraging the cap to become loose. The most important solutions to this issue are:

1. Ensure the neck is kept totally clean and dry during filling.
2. Ensure the neck is kept clean and dry during use after opening. This is easier said than done, without the help of a wiper seal. This is a neat little component that fits inside the neck of the bottle and wipes the surface of the pipette tube clean as it is extracted. Without this, any liquid clinging to the sides of the tube will almost certainly come into contact with the top surface of the bottle during re-insertion - resulting in the product running down the side of the neck, lubricating the threads.