According to AkzoNobel ReColour report, 13% of paint is wasted every year and 99% of that paint is either burnt or buried in landfills. 

There has been a lot of effort by the industry to find ways to reuse or recycle paint and to reduce the amount of product thrown away to a minimum. For now, any packaging that has been in contact with paint is classified as hazardous waste and is sent to incineration in most of the countries. To help reduce the amount of contaminated packaging, Rapak (UK), a global packaging manufacturer with 40 years of experience, has designed a Bag-in-Box solution for paint, coatings and varnishes that was revealed at the EU Coatings Show in March 2019.

Sustainability benefits

In the Bag-in-Box packaging format, the only point of contact with the product is a thin and resistant flexible bag, which is 50% lighter than tin cans and uses 76% less plastic than HDPE jerrycans of the same size. The bag is surrounded by an outer cardboard box that protects the bag during the transport and handling. The outer carton box can be made of recycled material, it is stackable when full, foldable when empty and can be recycled. 

In terms of CO2 emissions, the new packaging represents only a 10% carbon footprint when compared to aluminium cans of the same size, drastically optimising the logistics thanks to its flat bottom and modular shape.

The innovative Bag-in-Box packaging format also tackles the issue of paint waste directly as the air-tight bag prevents the paint, varnish or coating from drying out. Rapak trials have shown that the paint can last for as long as 2 or more years after opening, depending on the product composition. This allows consumers to dispense the right amount and store the unused product without the risk of a crust forming on the top of the container. Rapak’s bag design allows up to 99% product evacuation, which means that all content can be used until the last drop. When empty, the flexible bag takes very little space, reducing disposal effort and cost. Bag-in-Box packaging can be equipped with a handy dispensing system for a user-friendly single-handed serving with no product leaks, splashing or glugging. 

Increased market demand

Given the established sustainability credentials of Bag-in-Box packaging, Rapak has detected an increase in the demand for products that are traditionally packed in HDPE bottles and/or rigid plastic containers and require an additional shipping carton for transportation. Good examples are chemicals such as paints, varnish and oils – both motor and lubricating.

The current trend to move from HDPE rigid plastic formats to Bag-in-Box can drastically reduce the environmental impact of packaging.

Challenges to meet chemicals & coatings product requirements

Designing and developing the right bag for chemicals can be a challenge when considering the range of the chemical content of the products and the many variations in viscosity. To develop optimal bags that meet the demands of this sector, Rapak was required to take a much closer look at the base material grades that were used to contain the product, as well as to keep its integrity secure. 

In the classic Bag-in-Box format, chemicals require a barrier film capable of retaining the odours and volatiles within the product through a range of environments as well as the flexibility and performance to function over long transit distances. 

Bag-in-Box bags are typically comprised of two separate plies of similarly based polyethylene film that protects either side of the liquid product and improves bag’s capability of handling a large amount of flexing that is inherent in Bag-in-Box packaging. 

To ensure that the materials can properly contain the chemical products, these structures required specific modifications, while still allowing fabrication on the traditional Bag-in-Box manufacturing machines.

Bags testing 

A higher density polyethylene film, compared to the Low Linear Density that is typically used, was tested to produce a bag with an advanced resiliency to volatiles present in many chemical products.

This required changes to manufacturing process and allowance for the reduced flexibility of these types of materials. Prior to accepting any products for testing, the MSDS sheets were studied to identify any aggressive ingredients with a known packaging risk.   

To test the film materials, Rapak used a standard compatibility process test involving samples of seams being immersed in the product to be tested at 40◦C. This gave an accelerated indication of life effect with nominally one week of lab test equating to four weeks in the field.

The samples used were of a standard seam construction produced on existing equipment to represent normal production properties. They were tested using a traditional tensile tester with a 15mm wide section cut at 90˚ to the seal. Both the inner and outer layer of the bag were captured in the jaws of the machine to replicate the load placed on the total bag perimeter seal during filling and loading. Three samples were taken per seam and the average value attained was used to measure the affects that the product had on the strength of the bag.

Rapak generally compares the tensile strength (shown on below chart), but elongation is also measured and recorded on the Tensile Test equipment. This same test can also determine if any de-lamination is taking place. Under the influence of this type of stress, the barrier material usually separates into its base layers. The aim is to determine at what value the figures level off at to predict the market life-end.  Acceptance is judged by looking at the percentage of strength lost. Once the values have stopped reducing, the maximum effect is achieved. 

To ensure that the products themselves are stable in the packaging, small sample bags of nominally 1L in size are constructed with a central filling port. Product is filled in these bags and stored at 40C˚. These bags are designed to give an accelerated result given that the surface area to volume ratio is double that seen in a 10L bag. Periodic visual inspections and weight checks are carried out to determine if there is any product leakage from the bag or if there are visual indications of any effect to either the bag film, its seals or the product itself.

The below image shows the effect of an aggressive product on the right causing the inner PE film to ‘wrinkle’ and exhibit some weight loss after only a short time of immersion (0.2% loss after 13 days).

Further structural changes to the film are underway to reduce the effect seen here. Rapak proposed an option to change the type barrier layer to give a better resistance. During this testing, it was also identified that the seal performance needed a different set of criteria for internal production testing to more closely represent the penetrative nature of the product. Any area of non-chemical bonding is immediately targeted by this family of products and the seams can begin to de-laminate, leading to physical leakage. Similar forms of failure were experienced with bags to be used in Hot Filling as the high temperature product seeks out any bond weakness’s leading to failure of the weld. To overcome this risk, Rapak has instigated additional testing during production and utilised modified parameter setting on the production machines.

For varnishes and oils, Rapak will instigate similar bag machine parameters and testing to eliminate the risk of any seam weakness leading to failure. 

Combining these revised materials and enhanced bag production capabilities, Rapak is confident that the bag quality can meet the requirements of this product sector including paints, varnishes, coatings and a variety of industrial oils and chemicals.