Each year, when the weather cools, we get a call or two from our customers that goes something like this, "We are using the same jar, lid, equipment and operation we have always used but a few jars are not holding a vacuum." When we ask more questions, we find the lids are stored in an unheated area until ready to use and not allowed to warm before applying. Naturally, as the weather outside gets colder, the lids get colder and closure sealing problems become more pronounced.
What is Going On? The lips of all glass bottles and jars have variations that look rough under a microscope. The Plastisol liner needs to be warm to flex and fill the "rough" surface of the neck finish. If the Plastisol is cold, it will not flex and the lid will not hold a seal. If you try to compensate with extra tightening, the lid will strip before a good seal can be made. Twist lids were made to be applied with automated capping machines. Most automated cappers blast steam under the lids before applying to clean, kill bacteria and warm the Plastisol liner. If you apply lids by hand, it is especially important to warm the lids before applying them.
What Should You Do? So how warm is warm enough? How should the lids be warmed? These are questions you should determine based on your operations and local health officials. Some of our customers use a space heater to heat a couple of hundred lids at a time while others use a hot bath. Most Plastisol in the caps we supply should not be heated above 180F or it will melt. Flipping the jars over after the lid has been applied is too late to warm the liner. The lids need to be warmed before they are applied.
There are many other problems that might keep your jars/lids from holding vacuum and we will be happy to help you find the solution to your problem if you will contact us.
Warranty: The above remarks are offered only as suggestions relating to the causes of packaging problems and as comments that may help you to make good decisions on your packaging process. No warranty is expressed or implied. You are responsible for testing your products and your processes to be sure that they are compatible with our products and their accessories.