Keep a drink delicious and fresh!
A carbon coating that evolves PET bottled beverages.

Photograph of DLC coating equipment

Tea, alcoholic drinks, and carbonated drinks are sold in PET bottles! The DLC coating inside the bottles is now an ever-present part of daily life.

PET bottled beverages are sold in convenience stores, supermarkets, and just about everywhere else. They are now ubiquitous, living in many of our refrigerators and day bags.

Did you know that the inside of the PET bottle is coated with a thin carbon film to keep the beverage delicious?

The DLC (note) coating is an innovative technology to protect beverage quality. Why do PET bottles need to be coated? Let's think about the reason.

  • A type of carbon with properties similar to diamond
Scenic photograph of a woman purchasing a PET bottled beverage


Can air easily permeate a PET bottle?

PET bottles were first used as soft drink containers in around 1982, when Japan’s Food Sanitation Act was amended. Glass-bottled juice was common at the time, but the new PET bottles offered advantages such as a sturdiness, a light weight, good portability, and caps with distinct designs. Consumers everywhere began to choose PET bottles for convenience.

Yet PET bottles are more permeable to oxygen and carbon dioxide than cans or glass bottles. Oxygen can therefore easily flow into a PET bottle, and carbon dioxide gas or water can easily flow out. The gas permeability of the plastic material made it difficult to use the bottles for tea, carbonated drinks, and alcoholic drinks like wine.

Scenic photograph of a woman purchasing a PET bottled beverage

A PET bottle that inoxidizes or retains its contents was born.

To solve this problem, Mitsubishi Heavy Industries Machinery Systems (MHI-MS) developed its Mitsubishi DLC Coating Equipment jointly with a leading beverage manufacturer.

DLC is an acronym for diamond-like carbon. The material has a molecular structure similar to diamond, a gemstone. The DLC used for DLC coating is composed of carbon and hydrogen, and can flexibly follow the deformation of a PET bottle. It therefore retains a high gas barrier performance to block oxygen, carbon dioxide, and gas without reducing the transparency of the bottle material.

How can a thin film be coated on the inside of a PET bottle?

In the food packaging industry at that time, it was considered difficult to deposit a DLC film onto a PET resin (note) bottle.

We tackled the challenge by devising our Mitsubishi DLC Coating Equipment, a technology to deposit film coatings capable of reducing gas permeability to less than one-tenth of that of the original bottle material. Below we summarize the steps to develop the technology and the epoch-making technical points we discovered along the way.

  • The petroleum-derived resin commonly known as PET (Polyethylene Terephthalate) excels in strength and transparency but performs poorly in resisting heat.

DLC coating step

Step1 : Evacuate the air from inside the electrode chamber containing the PET bottle with a vacuum device.

Illustration of the DLC coating step

Step2 : Dispense an acetylene gas composed of carbon and hydrogen into the PET bottle

Illustration of the DLC coating step

Step3 : The gas molecules are decomposed by applying a high-frequency wave to the electrode chamber to produce an ionized plasma.

  • Converting a substance into an ionized plasma state with a high-frequency wave.

Step4 : Decomposed gas molecules in a plasma state fly around inside the PET bottle at high speed, forming a film by hitting against the inner surface. A DLC film coating of 10 to 40 nm in thickness is thus deposited.

DLC films are being formed.
DLC films are being formed.

High barrier performance to retain carbon dioxide gas and water inside while blocking out oxygen.

The Mitsubishi DLC coating system was completed three years after the technical principle was conceived. The system achieves high productivity by depositing DLC film coatings in as little as 6 seconds per bottle, or from 12,000 to 18,000 bottles per hour.

With the advent of the system, DLC bottles came to be used for various other beverages and also non-beverage liquids previously sold in other types of containers. DLC-bottled hot green tea (350 ml) was released on the market, and DLC bottles of different sizes followed. DLC coatings are now applied in bottles containing products such as cooking oil and carbonated drinks (500 ml). In short, DLC technology has become indispensable in daily life.

Graph of the oxygen barrier performance of a DLC coating; graph of the carbon dioxide barrier performance of a DLC coating

The emergence of DLC bottles drastically changed supermarket shelf spaces.

Many may wonder, “Can we tell a DLC bottle at a glance?” Most people cannot tell the difference. If you want to see what a DLC bottle looks like, go to a supermarket and look at the wine shelves. DLC coatings are used to guard the quality of most of the Japan-made wines bottled in plastic.

The wines in Japanese supermarkets used to be sold mostly in glass bottles or cartons. When DLC wine bottles appeared in 2010, these containers were changed to DLC bottles. The DLC wine bottle blocks oxidation and retains aroma and carbon dioxide gas. It also can be shaped into upscale designs that attract many beverage manufacturers.

In addition to full size 720 ml wine bottles, a 1.5 liter bottle is now on the market. This offers a significant advantage to retailers, as a glass bottle for the same volume would be too heavy. DLC bottles greatly contribute to the development of new products.

Illustration of wine shelves in the supermarket

Make your life more fun and affluent with evolving diversified beverages

DLC coating technology is being applied to an expanding field of containers for products such as FOSHU (food for specified health use) beverages using tea catechin, Japanese sake, and coffee beans with appealing aromas.

The light weight and strength of PET bottles also offer logistic advantages. A new generation of 3-liter DLC PET bottles is now being developed to put those advantages to use.

Beverages with novel tastes and restaurant-quality flavors are emerging day after day, year after year. The carbon films in the DLC coatings protect these beverages as they flow through the supply chain to the everyday consumer.

Technological innovations from MHI-MS continue to spur the creation of delicious and joyful new beverages.

Strategic Innovation