Quality Control: What Converters Need to Know About Sustainable Coatings

Published: June 1, 2026, By Trevor

By Tom Kerchiss, Chairman of RK PrintCoat Instruments Ltd

In simpler times glass, steel and sometimes aluminium were used for holding, protecting, transporting and displaying foods of varying types that were delicate, easily perishable or needed to be stored away for intermittent use, for example: dried goods, pasta, flour, etc. Product developers, chemists and food scientists seldom discussed barrier properties because the traditional materials axiomatically blocked the passage of liquids, gases and other spoilers.

While these materials were and still are effective for some products, they consume vast amounts of energy to produce, occupy a lot of space, both in the retail environment and in the home, are costly in bulk to transport, difficult to recycle, almost impossible to reuse and provide fewer product differentiation opportunities for brand owners and marketers. Generally, once opened many of these packaging mediums are difficult to reseal and depending upon content can spoil quickly.

Protective coatings and internal liners improve barrier resistance, but some can jeopardize paper and paperboard recyclability. © billtster - stock.adobe.com

Paper and Board Packaging

Every packaging medium has a downside. Paper and board on its own are permeable to water, water vapour, fatty esters, oxygen, carbon dioxide and nitrogen. Poor barrier resistance makes some products packed in paper and paperboard materials susceptible to volatiles, flavor scalping and aroma issues.

Custom formulated coatings and internal liners and the protective coating of the base material with specific polymers improve barrier resistance, but jeopardize paper and paperboard’s positive environmental credentials and ease of recyclability.

Barrier Resistant Properties

Food does not stay fresh forever. Many foods deteriorate when exposed to oxygen. While not perhaps immediately obvious, fats can be oxidized resulting in tainted food, which is unpalatable. Red meat turns grey and brown and develops an off-smell. Bread goes moldy. Packaging technologists tread carefully to ensure that the permeability or barrier resistant properties of the packaging material is appropriate.

Light, including both visible and UV, can trigger oxidative reactions. For certain foods a barrier must be in place to prevent light induced changes that can affect the nutritional value of foods and produce off-flavors.

Controlling Moisture Content

The moisture content of many foods needs to be monitored and controlled. Wheat products: pasta, flour and dried goods are hygroscopic, moisture content changes according to humidity and changes in temperature. An increase in moisture content encourages the growth of microorganisms, bacteria and molds. For some food items, such as leavened bread, tortillas, fruitcake and panettone, humidity or lack of moisture can be problematic.

Too dry an environment will shorten the shelf life and impact on the quality of goods such as pasta. Pasta, particularly shaped pasta can become brittle and crumble. Pasta is also prone to discolour due to moisture and/or humidity.

Pasta, rice and multigrain foods are often packed in flexible packaging. High quality leak free seals and welds are critical for flexible packaged foods. Vacuum and MAP ranks highly for many foods. With MAP the packaging can be passive or an active process whereby the internal compartmentalised atmosphere of a pack is regulated in order to slow down microbial contamination.

Sustainable Packaging Developments

Environmental compliance, statements of intent such as the aim to recycle and to manufacture, print, coat and convert from sustainable resources are no longer phrases banded about to mollify environmentalists, the media and concerned consumers. Every industrial process is to some degree under the spotlight. Industrialists of most persuasions recognize the need to develop new processing strategies and where possible use consumables, substrates and other materials responsibly that at the end-of-life cycle can be disposed of safely.

Fuelled by anti-plastic sentiment and the fact that packaging and labelling is ever present and highly visible in our every-day lives, the processes and the materials and consumables used come in for more than its fair share of criticism. Packaging producers, converters of paper, film, foil and other materials and ink, adhesives, coatings and chemistries have made notable progress towards addressing the various concerns of critics.

Some of the most interesting developments is in the area of bio-based or plant-based polymers and bio-degradable chemistries. Bio-plastics are derived from a renewable biomass such as corn, starch, pea starch and even casein protein from sources such as milk bound together with clay. Not all bio-materials meet circularity requirements. Cutin, a water repellent bio-polymer derived from tomato peel, can be combined with other bio-polymers or with the binder pectin to create hydrophobic films and coatings. Formulated with other chemistries Cutin may confer food packaging, medical textiles and many other products with barrier resistant properties. Research is on-going,

Choosing the Right Coatings

Coatings may be chosen for a variety of reasons; coatings may be passive; they may be active or they may incorporate traceability devices and condition monitoring components. QR codes and other devices are referred to as smart coatings. Regardless of application and materials and components used, success is to a large degree dependent upon preparation and on how well the process fundamentals are understood and process variables controlled.

Controlling costs without compromising on product performance has encouraged coating practitioners and the industries they serve to experiment and look at different ways of doing things. Down gauging, going thin is not confined to applications such as flexible packaging. One only has to look around and see that manufacturers across many industries have replaced heavier gauged materials with lighter gauge materials and not just for reasons of cost. Printable electronics and smart phones, even conformable tapes and die cut pieces for fuel cells and LCD displays cannot function effectively unless their components: the coatings, etc., are formulated correctly and applied ultra-thin.

Web Handling and Control Systems

Thinner webs challenge drive systems and other devices associated with web handling and control. Tension ranges and tolerances may be tighter, which in turn makes inconsistencies more noticeable. If a coater is at the edge of its performance envelope or if the coating applicator is mismatched for the task in hand there will be a noticeable rise in waste and in quality and in downtime.

Some otherwise perfectly good coating techniques will not work so well when coat weight is reduced. Conventional knife-over-roll coating cannot cope well when going ultra-thin. On the other hand:   gravure works well. Reverse gravure with its large wet coat range offers key benefits such as uniformity and freedom from pinholes. Absence of pinholes is critical as they impact on the effectiveness of any barrier put in place.

Quality Control and Product Development Systems

The frenetic pace of change taking place in materials, substrates and product development tests many existing processes. The move to water-based coatings with lower solids content often requires modifications to processing equipment such as dryers. It is essential that quality control and product development systems are in place and are appropriately optimised for the application. Pilot coating systems capable of undertaking small scale production of different materials using selectable coating and print and laminating technologies may be the way forward for many converters and for the manufacturers and producers of bio based and other materials.

About the Author

Tom Kerchiss is the chairman of sample preparation system and print/coat/laminating technology specialist RK PrintCoat Instruments Ltd. The company supplies printing ink manufacturers, both large and small, as well as printers, converters and other businesses with color communication devices for all of the major print disciplines. For more information, contact This email address is being protected from spambots. You need JavaScript enabled to view it. www.rkprint.com and visit: https://www.rkprint.com