Beyond Sealing: Making the Bottom End the "Invisible Guardian" of Paint Packaging

While most people think of paint packaging, they talk about the label design or think about how thick of the metal sheet is applied to their cans. Very few talk about what part is at the very bottom. But the “bottom end” actually plays an important part in the whole tin can as the “invisible guardian” of paint.

We are a Chinese factory, located at Foshan, Guangdong. We have been producing Tin Can Bottom Ends for 30 years. Today I want to share what a bottom end can do.

Sealing is the Basics

Let us state the obvious. A bottom end has the very first requirement of sealing — keeping the paint in and the air out. If it cannot do that, forget the rest of this blog post. We put in a lot of effort to get this part right. First, curling. The entire perimeter of the curl must have a smooth full arc — no burrs, no cracks. Second, the bead of sealing compound. We use food grade PVC and PU materials forming a bead inside the curl, then sending the whole package into an oven to cure into an elastic sealing layer. The width and location of the compound bead must be controlled. Too wide or too narrow and the seal fails. But to be honest, if in 30 years of production we still could not get sealing right, we really should be doing something else. Where we really feel we are adding value is where we go beyond sealing.Corrosion Defence

Peel-open a tin of paint and you’ll smell the different chemicals that go in — some are acidic, some alkaline, others contain strong solvents. Left in contact with metal, any of these can corrode, and if a bottom end rusts, a spot even a pinprick in size can ruin the whole can of paint.

We’ve done a lot of work on material choice and surface preparation to resolve this issue. For standard tinplate bottom ends, we apply a passivation coating to improve Corrosion Resistance. For water-based paints, where greater rust protection is required, we have an epoxy coating solution of our own. It’s like putting the bottom end in a suit of armour! We get salt spray test results of 72 hours plus before red rust starts to develop. That’s pretty tough by anyone’s standards.

Compatibility

Most paint factories run extremely high capacity filling lines. A seaming machine will close dozens or hundreds of cans a minute, and at this speed accuracy of dimension of the bottom end dictates that there will be no such thing as a good fit.

We had a customer who had started buying high-speed seamers from imports. The seamer kept jamming with the bottoms we supplied. A little investigation suggested the problem didn’t lie so much with the bottom ends. The seamer’s jaws were worn and needed to be set at a lower tolerance of dimensional variation for a snug grip. We helped establish the right parameters, and at the same time reduced our outer diameter tolerance from ±0.15mm to ±0.08mm. Since then the machine has run without a jam.This example illustrates that a good bottom end supplier does not just sell components. We need to understand our customers’ equipment and practices. Our technical team often takes trips to customer site to observe their filling lines and what model of seamer they are using, and adjusts our product parameters accordingly. This ‘service mind’ distinguishes us from an ordinary Chinese factory‘.

Customization: Every Customer Is Different

The paint industry is highly diversified. Architectural coatings, industrial anticorrosive paints, wood finishes, automotive refinish paints – each of them different in viscosity, volatility, corrosiveness. Of course, their requirements for packaging differ too.

Some customers want pull-ring bottom ends for easy to peel-off opening. Some need a Rieke-style lid for their upside-down dispensing design. Other want a special barrier coating on the internal face of the bottom to prevent ingredients that will react badly with metals from making contact with them. We service all these requests.

Sample turnaround is fast – often within one week of drawing confirmation. Once the sample is approved by the customer, we move directly into mass production. Our normal capacity is around half a million bottom ends per day, and we can warm up production lines during busy seasons.

Environmental Responsibility: A New Dimension

In the last few years, we cannot avoid looking into the aspect of environmental responsibility. Nowadays, customers, especially brands selling in Europe and North America, ask questions like: how recyclable are your bottom ends? Do you have procedures to deal with emissions when you process? Is there BPA or another restricted substances in your paints coating film?

We have answers to those questions. Tinplate bottom ends are 100% recyclable, and scrap metal is recovered and recycled on our customers’ premises. Waste water generated in production is treated to make sure that nothing discharges to the environment, and is recycled within the company! Coating material is implicit with EU REACH regulations and RoHS directives – heavy metals? Prohibited substances? None.

In Conclusion

Let us return to the title. Beyond Sealing. A bottom end must not just be thought of as a leak-proof entity. It is also a corrosion barrier. It is also a mechanical part of precision that ensure automation lines runs smoothly. It is ready-made for customization. And in an increasing way, it can be labeled as a environmentally interested product.

As a firmly rooted Chinese factory, we don’t seek to perform any earth shattering things. We just want to make every bottom end so right, that it can afford to sit at the bottom of a can and then shut up about it and jeweled with guarded every drop of paint inside. That’s what we think of as being an invisible guardian.