Come on – It’s Just a Plastic Closure!

What might look simple from the outside reveals tremendous work of development if you look at it more closely. But before going into details of the closure product requirements we shall take a look at three major steps in the life of a closure and what makes developing them so difficult in each section. Firstly, we talk about manufacturing of closures, secondly, we talk about the application of closures and thirdly, we talk about the usage by consumers.

ROBUST ENOUGH TO TOLERATE VARIABILITY

Obviously, a beverage closure is a mass product. Hundreds of billions of beverage closures only for PET containers are being used per year. This scale – together with standardization of neck finishes – gives our industry the chance to reach very high efficiency levels. The result is high cavity molds with short cycle times. The challenge is not to manufacture one hundred closures every two seconds on one line but to manufacture one hundred ‘good’ closures every two seconds. Requirements for a ‘good’ closure design start with robustness. If we only take a look at material diversity as an example: we have sampled more than a hundred different organoleptic HDPE resin grades with our closure designs over the last couple of years. And a multiple of this number for color masterbatches. A ‘good’ closure design should manage to result in ‘good’ closures with the vast majority of these resin and masterbatch grades. A ‘good’ closure design also needs to be robust enough to balance variations of manufacturing equipment like different injection or compression molding machines and the various types of up- and downstream equipment.

PRECISE ENOUGH TO GUARANTEE HIGH SPEEDS

If we follow the value stream of beverage closures, the next set of requirements stems from application of the closure on the bottling lines. Bottling lines handling more than 2’000 bottles per hour per capping head have become frequent sights rather than lighthouse examples. High speeds usually mean tolerances for processed parts become tighter. Especially as allowable reject rates – naturally – have not been increased along with the challenges. So even though everything around the closure design can change, closures need to be reproducible in vast quantities. In other words, the first cap must look and perform exactly like the last.

PERFORMANCE AT THE LIMIT

So far we have only talked about requirements stemming from manufacturing and application of the closure. Most closure functions aim at fulfilling requirements of the final product – the filled bottle. These requirements can be categorized as follows: safety requirements (e.g. secure venting, tamper evidence), tightness requirements (e.g. sealing against inside and outside), ergonomic requirements (e.g. easy opening and reclosing), environmental requirements (e.g. withstanding temperature, mechanical impacts) and design requirements (e.g. give brand owners a chance for differentiation). corvaglia performs forty different laboratory tests to validate a closure or closure design against requirements of the final product. Passing forty different tests while being identical in vast numbers and robust enough to tolerate that everything around it can change. Not bad for a simple piece of plastic, is it?

Now with proposed EU directive procedure 2018/0172/COD the industry might even face a source of requirements that had not been very important in the past: legislative requirements that might limit or stipulate certain design features.

Most of the requirements and challenges discussed are valid for the complete beverage package (i.e. bottle + closure) but it is important to state and understand that most of the functions of the package are defined by the closure and not the bottle.

The part of the bottle that interacts with the closure (the neck finish) is more or less standardized in certain categories. The closure needs to take care that all the functions at the interface between bottles and closures are guaranteed.