Optimising barrier coating on paper

As the demand for sustainable packaging solutions grows, understanding how to optimise these coatings becomes crucial for meeting specific end-use requirements whilst maintaining environmental responsibility.

Requirements are coming from EU’s PPWR regulation (Packaging and Packaging Waste Regulation) for recyclability and material sustainability. Demands for eco-friendly packaging arising also from consumers.

Understanding barrier coatings: fundamentals and performance parameters

Different packaging need different barrier properties. Most typical barrier types are needed against moisture, oxygen and oil/grease.

MVTR (Moisture Vapour Transmission Rate) indicates how much water vapor passes through a material over time. Expressed in g/m²·d. Test conditions greatly affect results:

• European: 23°C / 50% humidity
• Tropical: 38°C / 90% humidity
• Combined: 23°C / 85% humidity

OTR (Oxygen Transmission Rate) measures oxygen permeability (in cm³/m²·d·bar). Oxygen exposure can lead to oxidation, spoilage, or degradation in food and pharmaceuticals.

OGR (Oil and Grease Resistance) assesses resistance to fat/oil penetration (measured via KIT or TAPPI tests). Crucial for packaging fatty foods like fast food or baked goods.

The coating options available include polymer-based solutions, which offer excellent barrier properties; bio-based alternatives, which are derived from renewable resources; and hybrid systems, which combine the best of both worlds. Each type has its own niche in a variety of applications, ranging from food packaging that requires specific barrier levels, to medical packaging that demands sterile barriers, to industrial uses where chemical resistance is paramount.

The relationship between coating composition, application methods, and substrate characteristics determines the final barrier properties. A coating’s effectiveness depends not only on its chemical formulation but also on how it interacts with the paper surface and the method used to apply it.

Existing packaging often exceeds required barrier levels, which may result in unrealistic benchmarks when designing sustainable alternatives. The development of barrier papers should consider the actual product needs, minimum shelf-life (regulated in the EU), supply chain and market cycle length, food waste prevention vs. eco-optimization

How do testing protocols evaluate coating effectiveness?

Standardised testing methods provide the foundation for evaluating barrier coating performance. ASTM and ISO standards guide laboratory procedures for measuring water vapour permeability, oxygen permeability, and oil resistance. These protocols ensure consistent, comparable results across different laboratories and development stages.

Beyond basic barrier measurements, comprehensive testing includes mechanical property evaluation, accelerated ageing tests to predict long-term performance, and migration testing for food contact applications. Environmental conditioning protocols simulate real-world storage and transport conditions, revealing how coatings perform under stress.

“The bridge between laboratory success and industrial reality lies in pilot-scale testing, where coating formulations meet the challenges of commercial production speeds and equipment.”

KCL coating testing and piloting services provide this crucial link, enabling customers to validate laboratory results at production-relevant scales before committing to full industrial implementation.

Material choices for different barrier coatings

Suitable barrier coating materials against water vapor (MVTR) are wax or paraffin-based systems (e.g. PE wax, carnauba wax); also acrylate or polyurethane systems.

Against oxygen (OTR) the feasible coating materilas are PVOH (polyvinyl alcohol) and EVOH (ethylene vinyl alcohol copolymer), both hydrophilic and requiring protective MVTR coatings.

For optimum barrier properties a multilayer barrier structure is commonly used. Typical barrier system contains three layers: first MVTR barrier, then OTR barrier and further another MVTR barrier layer.

There are technical and regulatory limitations for barrier coatings. Technical limitation is related to layer thickness of barrier coating. Thicker coating reduce flexibility and may crack or show “missing dots,” compromising barrier performance. Regulatory limits relate to materilas used and recyclability. For example in Germany there is 95/5 rule — at least 95% of a package’s weight must be recyclable. Other countries the rules vary (e.g. 70/30, 50/50).

What optimization strategies improve barrier performance?

Enhancing barrier coating performance requires a systematic approach addressing multiple variables. Formulation adjustments might involve modifying polymer ratios, incorporating functional additives, or exploring novel bio-based components. Application parameters – including coat weight, drying temperature, substrate and surface properties and line speed – significantly impact final properties.

Substrate preparation techniques, such as surface treatment or primer application, can dramatically improve coating adhesion and uniformity. Multi-layer coating strategies offer opportunities to combine different functionalities, whilst coating weight optimisation balances performance with cost efficiency.

Common coating defects like pinholes, uneven coverage, and poor adhesion often stem from process variables rather than formulation issues. Troubleshooting these challenges requires comprehensive analysis of both material and process factors. Throughout optimisation, balancing performance requirements with sustainability goals remains critical, as the industry moves towards more environmentally friendly solutions.

Implementing sustainable coating solutions in production

Scaling optimised barrier coatings from pilot to industrial production presents unique challenges. Equipment requirements vary significantly between laboratory coating devices and commercial coating lines. Process control parameters that worked perfectly at small scale may need adjustment for industrial speeds and volumes.

Quality assurance protocols become critical when implementing new coating solutions. Continuous monitoring of barrier properties, coat weight, and visual quality ensures consistent product performance. For paper packaging solutions targeting circular economy goals, recyclability and compostability considerations influence coating selection and application strategies.

Regulatory compliance adds another layer of complexity, particularly for food contact applications. Certification processes require extensive documentation and testing to demonstrate safety and performance. 

Key takeaways for barrier coating optimization success

Current development progress in the market is strong and makes barrier papers important packaging option for many sectors. Barrier paper, especially when developed with realistic barrier needs in mind, is well-positioned to replace plastics in many applications. With ongoing innovations, it holds clear potential to transform sustainable packaging.

Successful barrier coating optimization relies on comprehensive testing throughout the development process. A systematic approach reduces technical risks and accelerates time to market. Professional testing and piloting services play a vital role in this development journey. KCL provides the technical infrastructure, expertise, and confidentiality that innovation requires. Our flexible approach accommodates diverse customer needs, from small-scale feasibility studies to extensive pilot production runs.