Choosing the Correct Adhesive or Coating
Choosing the correct coating or adhesive is much like following a roadmap—there are many twists, turns and decision points along the way. Often multiple options exist and the correct choice must be based on existing assets and asset utilization. At a high level, we can think about the decision process in the three components Fit, Form, and Function. Fit and Form focus on available equipment assets (adhesive supplied in water, solvent or a solventless system) while function is driven by product chemistry and performance needs. Another consideration is that often multiple package items are produced having their own unique set of requirements so finding the product that may have the broadest performance often allows coating &/or adhesive consolidation.
The first decision should be the type of product needed. Is the requirement for a laminating adhesive, heat-seal coating or other functional coating? A laminating adhesive is used to bond two or more flexible substrates together to form the structure. These substrates may be films, foils, paper, or even cloth. After the adhesive is applied to the web, rolls are allowed to cure in a “master roll” form prior to next converting step. A heat-seal coating is a non-blocking coating that is applied to a flexible substrate and again rolled up into a “master roll”. This coated film or lamination is then subsequently sealed using heat and pressure to a rigid or semi rigid cup or container forming the lid. The lid is then peel-able to open the container making the contents available. A functional coating with a specific function can also be applied to a flexible web. It may act as a primer allowing the surface to be more receptive to another applied coating, or it may add barrier properties for oxygen or moisture vapor to the film, or it could modify the base substrate for gloss, abrasion, or to add heat resistance.
Once the type of product has been determined the next step is to decide how it needs to be supplied—in water, solvent as a carrier or solvent-less. This is predicated on primarily the type of equipment available in your facility and the end performance requirements. If multiple types of converting equipment are available, the next consideration might be to decide which has the greatest excess capacity or suites the process the best with web width, line speeds, etc. Additionally, one may need to consider emission control capabilities such as incineration or solvent capture. Some products are available in HAPS free/VOC free options. Many adhesives and heat-seal coatings can be available in different of carriers—in water, solvent-based or solventless options. The chemistry may not be the same, but the ultimate end-use performance can be. This gives converters options to decide what fits their manufacturing footprint the best.
Lastly and arguably the most critical decisions are end-use performance needs—if the product needs to meet an FDA or EU standard and which standard is required. At Dow, FDA opinions are available in clear and concise formats for each product with no ambiguity. It is important to consider which substrates are to be laminated or coated because while many products have adhesion to a broad variety of substrates, others do not. It is also important to consider what will be packaged in the converted structure and what the storage requirements are. Chemical resistance of each product varies and this design input is critical to making the best product selection.
Finally, we need to consider how the product going to be sealed to make the package. If working with an adhesive it’s important to consider the sealing parameters and if a zipper will be inserted because adhesives’ heat resistance can vary. If working with a heat-seal coating, what are the seal parameters for time, temperature and dwell. Each coating has a somewhat different optimum seal window. Is there a bond strength requirement and/or peel style needed? These also can vary by product. Often various package types are produced at the same facility. The converter of course has the option to run multiple products that fit each end use, or may choose a product that meets the highest end-use requirement so adhesives products can then be used in the lower performing end needs as well.
As one can see choosing the correct adhesive or coating is indeed like following a road map. By understanding all the needed design inputs upfront, finding your destination does not have to be difficult. Involving your supplier early and having an open discussion helps to simplifies the process. Chempoint and Dow have developed a series of streamlined processes that asks many of the relevant questions posed above. Knowing these design inputs will help both parties make the best decision. Lastly the Dow Pack Studios network coating and laminating facilities allows for early prototype testing making the qualification step quicker for the converter.