Today, plastic bottles are the package that offers dairy manufacturers the largest possible options with regard to economic, environmental and market-oriented objectives. Firstly, polystyrene (PS) or polypropene (PP) sheet reels and polyethylene terephthalate (PET) preforms can be considered as complementary materials to high-density polyethylene (HDPE) resins for either cheaper, lighter or brighter bottles.
Secondly, bottles can more easily be manufactured in-house with solutions tailored to low and medium volumes. Thirdly, bottle thermoforming (Roll N Blow), a brand new forming technique, opens new opportunities for bottle and energy cost reduction.
With this variety of solutions available, manufacturers might feel disoriented when trying to decide which one is the most suited to their specific project. Below is a step-by-step decision-making process derived from practical experience of the chilled dairy drinks market with a focus on drinking yoghurts and probiotics.
Preservation Against The Environment
The main criteria that guides the choice of a plastic bottle on the dairy drink market is its ability to protect the product against light. To simply summarise the market, chilled dairy drinks can be separated into three groups:
- Extended shelf-life milks (with a shelf-life of 20 to 30 days in cold chain)
- Pasteurised milks, flavoured milks (with a shelf-life of 7 to 15 days in cold chain)
- Fermented products (such as drinking yoghurts, probiotics and sour milk drinks with a shelf-life of maximum 30 days in a cold chain)
HDPE resin remains the most common raw material on these market segments, but the industry can also now consider the specific benefits of PET preforms, as well as PS and PP sheet reels which have long proven their value for dairy products packed in cups.
PS sheet reels can be used for pasteurised milks, but are also ideal for use with fermented products. It is often the preferred material for yoghurts in cups and a good option for drinking yoghurts and probiotics packed in bottles. Alternatively, sheets of PP can also be used and it naturally provides a good barrier against moistures.
Similarly, the development of new PET preforms allows this material to be used for any chilled dairy drink provided that the bottle is white for ESL milk. No additional barrier is required for extended shelf-life milk of 20 to 30 days inside the cold chain.
Material choice might also depend on specific additional requirements assigned to the bottle, such as the appearance or purpose. A gloss finish can, for example, be obtained with both PET preforms and PS/PP sheet reels, but PET is the only solution if perfect transparency is required, whereas for bottles that need to be sterilised, hot-filled or withstand microwave use, PP would certainly be the better option due to its excellent temperature resistance.
Each material must also be compared on the environmental aspect: PET preforms and PS/PP sheets will allow reduced bottle weight whereas PS/PP bottle thermoforming reduces the energy bill.
A definitive choice between two possible materials can be made by assessing their respective costs, which can vary significantly from one country to another and are directly linked with production volumes, or by favouring the one which is most easily available.
In-House Bottle Manufacturing
While purchasing ready-made bottles seems a natural option for manufacturers who have just started with this packaging, in-house manufacturing offers many benefits when volumes grow and product range expands.
Purchasing preforms or plastic rolls, instead of blown bottles, drastically reduces the transported volumes as well as the risk of having bottles scratched or deformed, while on-demand production avoids wasting money on storage.
In-house manufacturing also gives more flexibility on packaging lines by offering the possibility to produce different packaging shapes or sizes on the same line. Finally, in-house manufacturing provides higher safety against bottle pollution.
However, considering its implementation cost, in-house bottle manufacturing was up to now reserved for high-volume productions. Recent developments opened the doors of in-house bottle manufacturing to mid-sized dairy manufacturers, with blow-fill-cap single block units tailored to outputs of under 12,000 bottles per hour and a brand new technology derived from flat thermoforming, which can produce bottles from plastic reels at outputs ranging from 3,000 to 10,000 bottles per hour.
Three main techniques are available to form a dairy plastic bottle: extrusion blow moulding, stretch blow moulding and bottle thermoforming. These three technical options must be compared by taking into account several criteria such as: maximum bottle volume available, output constraints, level of investment and technical knowledge required.
Additional considerations include the peripheral equipment needed (such as unscramblers, conveyors and storage tanks), capping and sealing requirements and energy consumption.
Extrusion blow moulding is well-known in the dairy industry. It uses resin as a raw material to produce bottles and requires quite a high level of expertise from operators. This technique is best suited to large volume markets.
Stretch blow moulding of PET preforms has been entering the dairy market over the past few years. It should develop further in the future as new solutions which are dedicated to the low to medium output needs of niche and emerging markets as well as of mid-sized dairy manufacturers become available.
High precision stretch blow moulding also provides new opportunities for design innovation in single-serve packaging. By controlling precisely the heating process of preforms and maximising time allocated to heating and blowing, it is indeed possible to stretch light weight preforms up to their limits with consistent bottle thickness and no risk of neck deformation.
As a demonstration of what can be achieved with high precision PET stretch blow moulding, a blow-fill-cap unit is capable of producing 50 g yoghurt portions presented in an attractive fruit-shaped PET flask. The unit is operating in Brazil and blows flasks from PET preform of only 2.3 g in weight, with nearly half of the mass concentrated at the neck. High precision stretch blow moulding has allowed an expansion rate of 16 times (four times in both length and width), which is quite remarkable in this industry.
Bottle thermoforming might also soon revolutionise bottle manufacturing on the dairy market. This technique requires a lower level of plastic processing skills from operators and a lower level of investment. This technology is simpler to implement and less energy consuming than other options. This solution is suited for low outputs (from 3,000 to 10,000 bottles per hour), representing an opportunity for dairy manufacturers to benefit from in-house bottle manufacturing advantages in niche markets.
Inspired by conventional flat thermoforming, the bottle thermoforming technology (Roll N Blow) has been specifically designed to produce bottles from PS or PP sheet reels that are identical to blow moulded ones.
Innovation lies in a vertical thermoforming process that first forms the plastic sheet into a pipe before heating and blowing the bottle into a mould. As a result, bottle designs are not limited to large necks and small heights and can be shaped totally round.
Bottles also show a better resistance to vertical compression than with flat thermoforming. A secondary benefit of the vertical thermoforming process is the compact footprint of the packaging line.
Designed as a light solution for on-site bottle manufacturing, the bottle forming technology requires less equipment than a conventional moulding unit. Storage tanks and unscramblers can be avoided, as the bottle goes straight from the thermoforming unit to the filler. Even sleeve applicators are no longer an absolute necessity since the equipment can process pre-printed plastic sheets.
Finally, the bottle thermoforming technology is far less energy consuming than other blowing systems, as bottles are blown at low pressure (less than six bars) and at a low temperature (under 150 deg C).
Since the process requires no melting of plastic, very little expertise in plastics processing is required and the unit can be easily started and shut down to accommodate filling constraints. The use of plastic sheets ensures a uniform distribution of the material without having to monitor advanced parameters in the heating and blowing process.
Very similar to the manufacturing of pouches from plastic foils or carton packages from carton reels, the bottle thermoforming technology is very simple to operate even without the experience of bottle manufacturing. It is therefore an attractive option for dairy companies willing to diversify their product range and upgrade their container range with small and medium bottle packaging.
A comparison between this technology and HDPE extrusion and PET stretch blow moulding highlights the benefits that vertical bottle thermoforming can provide.
The analysis has been carried out for a drinking yoghurt with 30 days of shelf-life that is produced in Europe.
The reference packaging was a 250 ml white mono-layer bottle with a neck diameter of 38 mm and the output considered was 6,000 bottles per hour. PS thermoforming was able to produce the lowest bottle weight, raw material cost and energy consumption. This solution therefore seems to be particularly appropriate for manufacturers interested in entering the drinking yoghurt market.
Based on these considerations, bottle thermoforming has already been adopted by manufacturers, in Eastern Europe and Maghreb, for dairy drinks packed in 170, 200 and 300 g bottles. The products have been well received by consumers and millions of bottles have already been sold on the market.
The wind of technology is definitely blowing on the dairy drink market, fostering product innovation through smart packaging solutions.