Why does Scuffing Sometimes Occur on Polypropylene (PP) Closures?

Mallaig Range with Pipettes & PP Closures | richmondcontainers.com

Closures are so often the finishing touch to your packaging for your product. However, sometimes scuffing happens on caps. Scratched caps can be so impractical and blemish the look of your premium beauty product, especially on the gloss surface of large jar caps when there is no top label. Polypropylene caps are particularly susceptible to this, so in this article we are going to look at the reasons for this, at why PP is so widely used, and at alternatives which are also available.

What is a scuff mark on a polypropylene (PP) closure?

Scuff marks are visual imperfections which are seldom deep enough to feel but can look unsightly. They happen when one cap rubs against another cap or against a hard surface and the gloss surface becomes marked.

Why does scuffing occur on PP caps?

PP is usually injection moulded and as the caps come out of the mould they can become scuffed as they tumble into the box, unless they are either hand-packed or robotically packed, which is rare. Most scuffing happens at this point as the caps are still hot and very susceptible to marking, but scuffing could happen thereafter at any point of the process, such as during wad-insertion or decoration. Layer-packing does not fully solve the problem, unless it is performed at every stage of the process. This is why Richmond's quality control for all PP closures and their manufacturing methods is geared towards minimising the appearance of any marks, reducing the size and frequency of them.

What do we do to reduce this?

We minimise scratching in production by keeping handling to a minimum especially when warm. Where possible we also use conveyors to allow for additional cooling before they fall into the box. We also separate any sprues or waste if applicable at the machine rather than as a secondary operation so as to eliminate any potential scratches from the sprues, which are particularly sharp.

Any marks that are consistent in nature which would evidence there being a particular issue in our production causing this would not be considered acceptable.

Range of ROJ Jars and Caps | richmondcontainers.com

Do some PP materials scratch worse than others?

Yes, indeed. Some types and grades of PP seem to show scuffing more easily than others. Wherever possible, Richmond optimises the grade of polymer and additives used in the moulding to produce caps which are as scuff resistant as possible. We have noticed that dark colours such as black show scuffing more readily and recycled grades can be particularly susceptible to scuffing. (If the cap has a top label, in most cases, this won’t be an issue as it will hide any imperfections – but don’t forget to use a PP label to ensure your cap is still fully recyclable.) Gloss surfaces tend to be less forgiving and we also offer many of our PP caps with the option of a matt finish. This seems to hide blemishes much more successfully and also looks very attractive.

If PP is susceptible to marking, what are the alternatives?

If a super-premium look is a requirement, you may need to sacrifice recyclability for a material such as urea or acrylic. Or, you may consider aluminium which is readily recyclable but is a more expensive material.

There are also metal-shelled options available, whilst not generally able to be recycled, these provide an unrivalled super-premium appearance and finish to your container.

So, why use PP?

This is a fair question. The fact is that PP is easily recyclable, is available in 100% recycled grades, is economical, easily moulded, not brittle and readily available. It can be moulded in a custom-colour with a relatively low MOQ and the range available is very comprehensive. It is still a great option, and it is a relatively sustainable choice, being easily and widely recycled including all UK household recycling schemes.

Overall, PP caps are currently the best choice on the market, offering quality, economy and sustainability.

Take a look at the choice

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Black Caps | richmondcontainers.com