One of the most hotly contested issues in the packaging world involves the delta between the application and the removal torque of the Nalgene container. Nalgene diagnostic bottles are small volume bottles for sampling, storage, and shipping and are guaranteed leak proof, often making them good for packaging reagents. The “leak proof” nature of the Nalgene containers can lead to challenges if overlooked, especially in cap/container combinations where deformation happens to ensure that the container is “leak proof.” By design, the application torque for a Nalgene container is specified at a level 25 – 45% greater than what is typically required for standard caps. On the one end – you have the long list of people that come before the end user, the designers, the engineers, the technicians, & the packaging equipment manufacturer who all have input to the creation of the primary packaging. And, on the other end, you have the end user – who may simply judge the quality of the package by how easy/hard it is to open.
Typically, when a customer comes to us and wants to process either pre-sterilized or standard Nalgene containers, we spend a fair amount of time delving into this issue with them. Filamatic’s servomotor-operated torqueing function does provide precise control of the application torque that is applied to the caps. However, the determining factor of the removal torque for each cap is a function of the fit/finish between the inner surface of the cap and the outer surface of the neck of the container.
In my experience, the first thing is that too little attention is paid to the Nalgene Cap tightness issue during bottle cap design. During this early phase, the main focus of the cap tightness issue should be if the seal achieved by a specific application torque is going to be sufficient between the cap and the bottle throughout the container life cycle, and then as applied can the cap be removed by the end user? Focus on these two criteria when determining the specific application torque for each of the cap container combinations and then make sure that your packaging equipment can provide those application torques in a repeatable manner. Any other approach or lack of attention to these two simple criteria , seal tightness and the ergonomics of cap removeability, will cost everybody a significant amount of time and energy.