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How are plastic bottles made?

As a plastics bottle manufacturer, many new customers that approach us are interested in how plastic bottles are actually made. At B&I Polycontainers, we really enjoy taking these customers through our factory and showing them the entire process.

However, many people who do not visit us directly don’t have the time or demographical opportunity to visit us and check out how our factory actually turns plastic into plastic bottles for everyday use. That’s why this blog will explain exactly how our bottles are made in a very basic and easy to understand way.

If you would like a more detailed explanation and to see the bottle making process in action for yourself, please feel free to contact us. We will be happy to give you a full tour of the process.

For now, let’s begin by taking a look at the plastic bottle making process.

 

STEP ONE – Raw Materials

Every plastic bottle you see begins life as a plastic pellet – or rather, hundreds of thousands of plastic pellets. These pellets are the resit derived from petroleum hydrocarbons. The supplier of these pellets creates long chains of plastic molecules through a process called polymerization, and then mixes the material with several chemical compounds. They cut the resin into small pellets and send it on to us. 

Sometimes, we mix the resin pellets with “regrind” – recycled plastic that has been reduced to flakes. Plastic loses some of its physical properties when repeatedly heated, so we often limit the amount of regrind we use, typically capping this ingredient at 10% of the total mix. Unless producing clear bottles, dyes are introduced to the mix as well.

 

STEP TWO – Heating and Compressing

This is where the production diverges a little based on whether we’re making PET bottles or other products.

PET bottles must first be made into a preform before we move onto the next step. Currently, this is taken care of by a third party who we then buy the preforms from. We then use the preform for the next step,
For other forms of plastic, we heat the pellets and regrind mix at temperatures of about 260 degrees Celsius. A screw inside the extruder compresses the mix and injects the nearly molten material into moulds. 

 

STEP THREE – Moulding, Cooling and Trimming

Finally, this molten mix is pushed down into the mould, which is compressed with extreme pressure and cooled. This forces the molten mix to become the basic form of a plastic container, but this blow molding process must happen quickly in order to maintain the bottle’s integrity and consistent shape.

The bottle must be cooled almost instantly or it will lose its shape when gravity causes it to creep downward in its malleable, heated state. Some manufacturers cool the bottle by circulating cold water or liquid nitrogen through the mould, while others elect to fill it with a shot of air at room temperature. The mold typically yields a clean bottle, but some flashing may occur at the bottle seams, where the two mould halves meet. If so, operators trim away the excess material and add it to the regrind.

In terms of PET bottles, the preforms are preheated and then blown to shape using compressed air.

 

STEP FOUR – Quality Control and Packaging

The above process is continued for each plastic bottle created, but that isn’t the end of the plastic bottle manufacturing process.

Quality control measures are conducted throughout the manufacturing process, and a final check is performed before the bottles are packed to specification, stamped and marked for storing.

 

See it first hand

While it is great to find out how plastic bottles are made, nothing can compare to seeing it first hand in the factory of its origin. From PET bottles to PVC, B&I Polycontainers makes thousands of bottles every day, and each of them undergoes the same rigorous process above.
If you’d like to see how a plastic bottle is produced first hand, contact B&I Polycontainers today and we’ll gladly give you a full tour of our factory. Alternatively, check out our products here, to find your ideal bottle today.

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Choosing the Right Plastic Bottle Mould

We’ve covered how we make plastic bottles in a previous blog post that you can check out here, but a big part of making a plastic bottle is the mould that shapes the plastic itself.

These moulds have a huge impact on the quality of the bottle, the scrap rate, the unit production price of each bottle and the speed of production for the plastic bottle. However, few people know about making a plastic mould and what about the mould that makes the bottle cheaper or of a better quality.

This blog post will briefly go into this and other questions surrounding moulds to help you better understand this vital aspect of plastic bottle production.

STEP ONE – DESIGN 

Own the mould, own the bottle

The first thing you have to do when creating your plastic bottle mould is decide on the design.

If you take a look at our generic bottles, you’ll notice that they can be purchased by anyone. Of course, the different companies will apply their own product, branding and labels to the bottle, but the shape itself will not be unique. 

In order for you to own the shape of a bottle, you have to produce and buy a plastic bottle mould. Whether you decide to keep the mould or let B&I Polycontainers hold the mould for you, no one else can use that bottle shape without your permission.

Different moulds are used for blow-moulding and injection-blow moulding. In addition to this, you can order in-mould labelling moulds that give the bottle a unique texture and look by melding the label into the plastic. In terms of price, injection blow moulding moulds are more expensive than regular blow-moulding moulds. If you would like to find out more about injection blow-moulds, contact us and we’ll be happy to help discover your needs.

 

While complex shapes and functions that are built into the mould will require some substantial capital investment, you’ll be able to design a truly unique bottle that you can use for your business.

STEP TWO – CAVITIES

More cavities, more production, more money

Once you have the design in place, it’s time to decide how many cavities you’d like in the mould itself. Cavities refer to how many bottle-shaped indents are located in the mould, which results in how many bottles you can make per machine cycle.

Usually, the lower the amount of cavities, the cheaper the mould – however, it’s important to note that the less amount of cavities a mould has, the more expensive each individual bottle will be. This is because the amount of bottles that are produced with a double cavity are two times the amount a single cavity will produce in the same amount of time.

The amount of cavities in a mould is one of the most influential aspects when estimating the price of a mould. Single cavity blowmoulds can be anywhere between R35 000.00 and R60 000.00, while double cavities and more go beyond the R80 000.00  mark.

 

STEP THREE – STEEL

The harder the steel, the longer it lasts

Moulds, like anything, have a lifetime. They’re often used under such extreme conditions and by such heavy-duty machines that they eventually wear out. This causes problems with the resulting plastic bottle such as bad split lines, deformation and more.

In order for your mould to have a long lifespan, you’ll want to use quality materials, or steel, to ensure it lasts. Examples of steel that can be used range from steel that doesn’t ensure a long lifespan, like H-13, typical pre-hardened mould steel like P-20 and finally quality mould steel like 420 Stainless Steel.

Of course, you will want to select the steel appropriate for the runtime of your plastic bottle project. The staff at B&I can help you establish which steel would be appropriate for your project.

 

STEP FOUR – PROVIDER

The art is in the work

Different mould providers offer different levels of experience, and not every provider is made equally. 

Just as the materials, form and function of the mould contribute to the overall quality, so does the maker itself. There are many mould-makers in South Africa that you can approach with your design, as well as some international options – but ultimately, you pay for what you get.

If you would like guidance in finding the right mould-maker for your project, B&I Polycontainers has a contact list of approved providers who can help you with your specific needs. Contact B&I today and we’ll find the right fit for you.

 

Fit the Mould

Finding the right mould can be a lot of work and an expensive process. Many moulds vary from as inexpensive as R30 000.00 all the way into the hundreds of thousands. However, this process is important for anyone who would like to obtain their own unique plastic bottle.

If you would like to find out more information on this, or would just like some guidance in creating your own mould, contact B&I Polycontainers for assistance. We make thousands of bottles every day, and complete special orders for our customers around South Africa. Alternatively, check out our products here, to find your ideal generic bottle, today.