When it comes to screwing on a continuous thread Plastic Caps(KEXON) of any kind, application and removal torque should be properly measured to ensure a proper engagement of a threaded closure to a bottle or jar. It is a common misconception that the tighter you apply a closure to the bottle or jar, the less likely it will leak, but in reality it is quite the opposite. Over-tightening of the cap, commonly referred to by the packaging industry as excessive torque, can cause the cap to shear from the body, thread "jumping", or stripping, or even cracking the closure. On the other hand, closures that are screwed on too loose, with insufficient torque, can lead to closure "rattling" and product leakage.
Proper application of screw-on caps to bottles or jar, aka application and removal torque, should always be measured to ensure proper function of these screw cap, it's liners, and the bottle or jar. So let's first look at what application and removal torque is, how to measure it, and common recommendations from closure manufacturers.
Definition - Application Torque
Application torque is the rotational force with which a closure is applied to a bottle or jar. Measured in lb / in, rule of thumb for application torque measurement half (50%) of the diameter of the closure. For example, a 43mm closure should have an application torque of between 21 to 22 lb /in.
Since application torque cannot be measured directly on any automatic capping machines; the only way to really tell the screw cap was applied properly is to measure the removal torque. Removal torque is the maximum force required to remove or unscrew a closure. Generally speaking, removal torque should be between 40 to 60% of the application torque 24 hours after the closure has been applied.
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