Flexible packaging: an introduction

Materials used for flexible packaging may be paper or paper-based materials, metallic foils, plastics films, regenerated cellulose film, or composite structures incorporating multi-layers, coatings, metalization, lamination and impregnation that provide specific barrier properties to gases, moisture, fats, light, oders, etc. New flexible packaging materials and constructions continue to evolve.

The first processing stage in the manufacture and use of flexible packaging (after origination and pre-press) will usually be printing on a web-fed reel-to-reel  flexo or gravure press - mainly in multiple colors. There is also some use of web offset litho and screen process and, in recent years, the use of narrower web presses and digital printing for shorter runs, versions and variations. Around 60 percent of flexible packaging is printed direct onto the substrate surface; the other 40 percent is printed on the reverse of the substrate and laminated.

Apart from the printing process itself, flexible packaging substrates may be surface coated or treated to provide a moisture or vapor barrier, withstand lamination, sterilization, pasteurization or irradiation, provide strength, or make the pack sealable. They can also be shaped to match function, brand and appeal for a wide variety of packaging applications and markets.

A wide range of filling equipment for the flexible packaging market has been developed over the years, from simple manual machines for small packaging operations up to high-speed, fully-automated form, fill and seal lines for large volume packaging.

Rapid growth in flexible packaging in recent years has also been driven by a wide array of innovative new origination, print image carrier and conventional wide and narrow-web analogue and digital printing press technologies, as well as developments in flexible packaging substrates which have seen quality decorated films become ever more attractive in a consumer-driven world.
So where did flexible packaging have its early origins?

EVOLUTION OF FLEXIBLE PACKAGING
Flexible packaging using multiwall and laminated paper bag and sack constructions has been used for many decades, while the use of paper for the manufacture of flour and sugar bags can be originally traced back even further. Indeed salt, flour, rice and sugar bags have been in use for well over one hundred years, with the first patent for a machine to manufacture single-wall paper bags being granted way back in 1852.

Barrier paper constructions using multiple plies for strength and vapor-barrier performance, the addition of foil and plastic layers for moisture, gas, flavor and oder protection, and heat-sealing polyethylene layers were already coming into use by the mid-20th century. Even today, paper-based flexible packaging is still widely used and has attained growing interest as being more sustainable than some of the newer flexible packaging materials.

Outside of paper-based flexible packaging, the use of aluminum foil for flexible packaging developed rapidly after World War II when large quantities of aluminum foil became available for commercial use. Being compatible with foods and health products - offering superior flavor retention and a longer shelf life than other available flexible packaging materials - the use of aluminum foil soon found new applications and markets.

Flexible foil lids used to close and seal yogurt and cream pots and cheese dips were introduced in the United States in the mid-1960s. These provided a more reliable seal, improved shelf life, greater protection and tamper-evidence. Probably the only other material found in regular use for flexible packaging prior to the middle of the 20th century was regenerated cellulose film (RCF).

However, from the 1950s and 1960s, plastics started to play an increasing role in the world of packaging and, particularly, in the whole area of flexible packaging. It was from this time that (thin) plastics, biaxially-orientated films, extrusion coatings, film lamination, polymer adhesives and heat-seal coatings all evolved, along with new developments in converting equipment, flexographic and gravure printing machinery, ancillary materials, electronic pre-press and, more recently, digital printing, that has seen flexible packaging become one of the worldÕs largest packaging types.

Today, depending on country or region, some 70 percent, or so, of overall flexible packaging industry revenue comes from polymer materials, especially Polyethylene (PE), Low Density Polyethylene (LDPE), High Density Polyethylene (HDPE), Biaxially-Orientated Polyethylene (BOPP) and Biaxially-Oriented Polyethylene terephthalate (BOPET). The remaining materials used for flexible packaging are paper or paper-based substrates, and aluminum foils and foil laminates.

THE FLEXIBLE PACKAGING MARKET
With more than a dozen market research and consultancy companies regularly undertaking studies of the global, regional or national markets for flexible packaging, there is certainly no shortage of data available. Unfortunately, there seems to be quite large variances between these companies on what is included as flexible packaging, in the value of the market, the volume of materials used and the forecast growth of the market up to 2022 or 2024. All of which prove somewhat inconclusive.

Growth forecasts set out by the majority of the industry studies currently available range from as low as +4.3 percent per annum up to as high as +5.2 percent per annum. For the purposes of this particular article a consensus average growth of 4.9 percent per annum has been used. Highest growth forecasts for flexible packaging are for the Asia Pacific region at +6 percent per annum (India on its own at up to +10 percent per annum), with Europe and North America at around 3.2 to 3.5 percent per annum.

To try and achieve some level of consensus on the current and future size of the global flexible packaging market the Label Academy has analyzed the majority of the currently available studies to produce its own market analysis based on an average overall figure. The results can be seen in the chart shown in Figure 1.1. As can be seen, the value of the global flexible packaging market by 2024 (based on the average of all the studies) is forecast to be in excess of 225.50 billion USD.

With different products requiring different types of protection it means that some flexible packaging is made from a single layer material while, in other cases, multi-layer materials are required to provide the appropriate barrier and protection. In multiple-materials packaging, each layer performs a different function in protecting and preserving the product. By using materials with properties geared toward specific performance, manufacturers can meet customers' varying needs including product protection, contamination prevention, extended freshness, puncture, tear and burst resistance, tensile strength, and seal strength

In addition to these multi-material constructions, coatings and surface treatments have been developed to provide special barrier or resistance properties, add low temperature performance, increase durability and provide sealability. The emergence of biodegradable and bioplastic films has also been a key factor in the growth of flexible packaging.

As narrow-web printers move into flexible packaging they must also understand the requirements of sealant layers and make sure they understand how the film will be sealed, and which side seals to which side, so that they can purchase the appropriate films. Most flexible packaging films are heat sealed, but not all sealant layers are compatible. Generally sealant layers will always be compatible with themselves.

Substantial barrier properties can be achieved through coatings or metalization. Film manufacturers have been applying these for years. However, converters today do have the opportunity to apply their own barrier to film. Newer types of coatings are available which allows gravure and standard flexo converters to achieve the highest levels of barrier in a flexible coating that is not subject to flex cracking. The only word of caution is that the converter then becomes responsible for the barrier and the protection of the product in the package, and there is a risk of very high claim levels if the film underperforms.

While there are a range of flexible packaging materials and constructions that are available and widely used, it is plastics (polymer) films which now dominate the market and are said to currently account for over 70 percent of the industryÕs revenue. Commonly used plastic films include Polyethylene, Polypropylene, Poly Vinyl Chloride, Polyamide and Ethylene Vinyl Alcohol. Again, this range of basic filmic flexible packaging materials - and some of their variations - can be shown in a simplified flow chart format, as shown in Figure 1.3.

The choice of flexible packaging material, the number of layers to be used, the specific laminate construction, the use of barrier or protective coatings, the need for a sealer, etc., will be determined by the specific pack properties that are required and the demands that will be placed on the material when it used for specific goods or applications. Light, moisture and oxygen can hugely effect a productÕs flavor and freshness, so protecting it from these elements is also important.

In general, the selection of a flexible packaging material is most likely to be related to what it is to be used for. This is indicated in a simplified form in the examples shown in Figure 1.4.

TYPES OF FLEXIBLE PACKAGING
The manufacturers of all kinds of products and goods   - whether consumer or industrial - expend a vast amount of time and effort in researching, designing, manufacturing and packaging their goods, so will be looking for the best packaging solution to take those goods to market, to provide protection in transit and in store, to keep the products fresh and long-lasting, and to display them in the best possible way with optimum shelf impact.

The printing of films, some often quite thin, means that presses may require sophisticated tension control, perhaps heat management systems, static control, corona treating and registration, etc.

Typical converting operations found in flexible packaging production include varnishing or lacquering, surface treating, heat-seal or adhesive coating, priming, laminating and sealing. Coatings are often used to enhance the aesthetic appeal of the substrate, to protect the substrate and printed image, or to improve slip characteristics. Typical stages in the converting of flexible packaging are shown in Figure 1.9.

A barrier coating or sealing coat can be applied to prevent migration of ink, adhesive, or other substances through the face material. With flexible packaging, an anti-fog coating may be required to provide a specific barrier protection, such as moisture resistance or protection against light.

Laminating is the process through which two or more flexible packaging webs are joined together using a bonding agent to improve the appearance and barrier properties of the substrate.

Inks and varnishes obviously play a key role in not only providing the decorative and information performance of flexible packing, but also in adding the required barrier and sealing properties, coatings and seals. As most flexible packaging is used for food or for sensitive applications (body-care, cigarettes, etc.) it is important that neither the materials nor the inks should be able to contaminate the product by odor, migration or trace particles. Testing and test procedures are therefore important.

Most countries have quite complex standards and regulations which determine which label and packaging materials may come into direct contact with food-stuffs and human skin, as well as a whole host of other food labeling requirements (see Figure 1.10). These products are prohibited along with those where there may be some transfer or migration of substances to food. The label user and/or label manufacturer are held liable for any failure on their part to comply with standards.

Before leaving this section, mention should perhaps be made regarding pouches. The majority of pouch manufacturing has historically been undertaken with form-fill seal machinery, which provides simultaneous pouch production, filling, and sealing on one piece of equipment. However, as pouches have become more complex, some packaged goods companies are turning to preformed pouches that are purchased direct from the printer/converter. Packaging machinery makers are adding features that can make two-part pouches, laminate multiple layers of films, and handle technologically advanced substrates.

When designing and manufacturing flexible packaging for sachets and pouches for liquids, testing is a key in preventing sachet or pouch failures. Throughout the stages of package engineering, packaging film manufacturing, and sachet/pouch printing and converting, the supplier should subject the pouches and packs to various types of testing, which may include:

• Product/package compatibility testing Compression testing
• Seal testing
• Puncture resistance testing
• Water bath testing
• Tensile testing
• Burst testing
• Drop testing.

Each type of testing plays a critical role in ensuring that the final package will function optimally. For example, when forming pouches, frequently performing water bath testing (a test using external pressure) and internal pressure testing throughout each pouch converting run can immediately detect any leaks or weak seals.

WHAT IS FLEXIBLE PACKAGING USED FOR?
With the introduction of ever-more filmic materials since the 1960s, as well as advances in coatings, surface treatments and seals, sachets and pouches, the range of applications and markets for flexible packaging has grown dramatically and now includes packaging for many different and varied markets. An indication of just how diverse flexible packaging has now become can be seen in the following, non-exhaustive, list of market applications:

• Food
  • Dairy and cheese produce
  • Frozen foods and ready meals
  • Meat, fish and poultry
  • Dehydrated and dry food -soup and sauce packets, rice, food mixes
  • Coffee and tea
  • Chips (crisps), snack and nuts
  • Ice cream novelties, ice lollies
  • Fresh fruits and vegetables
  • Spice foods
  • Bread and bakery products - cookies (biscuits) and cakes, baking ingredients
  • Chocolates, sweets
• Personal care
  • Toiletries and hygiene, shampoo, liquid soaps, creams, lotions, gels
  • Cosmetics
  • Beauty products, wipes, mud packs
  • Pharmaceutical, nutraceutical, veterinary, medical
  • Pharmaceutical
  • Nutritional
  • Animal care and veterinary products
  • Medical devices
• Home and garden
  • Lawn care and grass seed
  • Bark
  • Fertilizer
  • Laundry detergents
  • Paints, pastes, plaster
  • Household items
• Animal care
  • Pet foods and nutrition options
  • Pet care products
• Beverages
• Automotive
• Agriculture

Traditional flexible packaging run lengths continue to trend downwards as wide-web converters struggle to print the smaller run lengths economically. There are however many narrower web in-line style printing presses (servo-driven machines in narrow-web widths) and new automated control systems that are now able to handle the shorter runs with a high degree of flexibility in terms of color sequence, configuration and available printing technologies. Servo drives and controls have also helped overcome the main challenges that have historically plagued the wide-web flexo market, such as gear marking.

Narrow-web flexo pre-press cost and quality can undoubtedly now successfully compete with more expensive wide-web solutions, and offer the possibility to combine printing of pressure-sensitive labels with unsupported film. Combination presses (flexo, offset, gravure), plus the possibility to add finishing processes like in-line lamination or cold foil raise the spectrum of printable products

As already mentioned, some 60 percent of flexible packaging is printed direct onto the (film) surface, with the remaining 40 percent printed on the reverse and laminated. Where narrow-web and digital printing is undertaken this is most usually undertaken on mono-layer flexible packaging materials, rather than on wider format complex multi-layer, laminating and sophisticated converting lines designed to provide a moisture and vapor barrier or withstand sterilization, pasteurisation and thermo-sealing.

When printing by any one of the conventional analogue printing processes the main stages in the whole design to print operation can be seen in Figure 1.8.

The life cycle attributes of flexible packaging demonstrate many sustainable advantages. Flexible   packaging starts with less material and less waste in the first place. Of all the packaging materials, flexible packaging has the smallest percentage weight -typically less than two percent -of the finished pack than other packaging materials (glass, cans, cardboard and corrugated), is easy to handle and greatly reduces landfill discards.

Innovation and technology have enabled flexible packaging manufacturers to use fewer natural resources in the creation of their packaging, and improvements in production processes have reduced water and energy consumption, greenhouse gas emissions and volatile organic compounds. Even more, lighter-weight flexible packaging results in less transportation-related energy and fossil fuel consumption, and environmental pollution. 

With its flexibility and versatility, custom qualities, efficiency in conserving resources, and sustainability, itÕs not surprising that flexible packaging has experienced rapid growth in recent years, and is forecast to continue good . above GDP -growth levels for at least the next five, or more, years.

Flexible packaging is undoubtedly at the forefront of important packaging trends in product protection, packaging design and performance, consumer convenience, and sustainability which positively impacts the environment, consumers and businesses.

To summarize the benefits and advantages enjoyed by users of flexible packaging this article ends with a tabular review (Figure 1.13).

Quite simply, flexible packaging makes thousands of consumer and industrial products more convenient, enjoyable, and safer to use, enhanced by the commitment to innovation, technology, and sustainability that are the hallmark of flexible packaging suppliers.