In multilayer flexible packaging structures, a chemical primer is usually needed to improve bonds between a substrate and a coating, such as an extrudate, or ink. Primers can also help to enhance barrier properties, aesthetics, and overall performance of the finished structure. Water-based primers are a common choice because they provide superior performance on a vast array of substrates. They are also a safer and more sustainable choice when compared to solvent-based primers. Water-based primer chemistries and functions can vary. There are several factors to consider when choosing the appropriate water-based primer for your application.
Water-based primers can aid in the manufacture of multilayer structures in both the extrusion lamination and extrusion coating processes. The way the structure is created and the materials used in that process will be important factors in the selection process.
To determine the best primer for your application, consider the product’s end-use and the exposures that it needs to withstand during its lifecycle. For example, if you are interested in creating a commercially compostable structure, it is important to ensure that all of the materials in the structure provide the performance and compostability requirements at the end of its life. Something else to consider is what contents the end-use package or container is protecting. For instance, contents that are oily will need different containment properties than a package holding dry or dehydrated ingredients.
The chemistry type, manufacturing process, and raw materials of extrusion primers vary greatly. Knowing the target bond strengths and/or bond requirements, and the specific substrates and/or extrudates you need to adhere to will be paramount in determining the correct type of primer for your application. Some primers also offer barrier, surface modification, or other properties in addition to adhesion. Understanding the benefits and limitations of your materials will help you understand the properties your primer needs to provide.
Regulatory compliance for water-based primers can vary. Consider whether the primer will need direct or indirect food compliance. Depending on the final structure, it may also need to be REACH registered, Halal certified, or free of Substances of Very High Concern and/or Prop 65 components. Prior to finalizing your selection, verify that the primer you choose has all the regulatory requirements you need.
Application methods may vary depending on the process and materials used. The primer recommendation may change depending on whether the application method is via smooth roll, gravure cylinder, Meyer rod, spray coating, or a flexographic printing press. Also, applying the primer inline versus offline may also play a part in your selection. For example, if you are applying primer offline on film, and the film is then rolled up and stored until the next step of the converting process, you will need a non-blocking primer that does not transfer to the other side of the rolled substrate.
Water-based products are complex. To ensure optimal bond strengths, water-based primers need pre-treatment and proper drying conditions. It is also important to regularly monitor and adjust line speeds, the time in the air gap, and dilution formulas as applicator rolls wear. Understanding the level of technical support, you need, and what your primer supplier can provide, is paramount to ensuring long-term success.
Need more assistance choosing the optimal primer for your unique application? Mica can help. We have more than 50 years of experience helping our customers through the primer selection process to the commercialization phase, and everything in between.