Hello again packaging professionals,
In this blog entry I will discuss the importance of cleaning glue flaps on folding cartons in order to achieve reliable, repeatable bonding results.
In the finishing area of a typical folding carton facility, you will often encounter multiple methods and products used to achieve bonding characteristics of all types of cartons. These can include the use of multiple types of glue (i.e. special glue for poly coated material, hotmelt etc…) in addition to other mechanical modifications to the glue flap (i.e. glue assists, skiving, knocking out the coating in the glue flap area – by cutting the printing blankets). All of these methods and materials have been developed to achieve good bonding performance that meets the end users requirements. However, even the most diligent practices can sometimes lead to bonding failure and thus the potential for rejected pieces by the end user. Providing a consistently clean and activated surface prior to gluing can help avoid claims and costs associated with failures.
All substrates, coatings and laminations contain internal contaminants – these could be things such as plasticizers that are used to engineer a product or materials such as fillers. These contaminants tend to migrate to the top of a surface and hence will impede the ability of a material to be effectively bonded. Plasma treatment can remove these contaminants allowing for a true chemical bond of the glue to the glue flap itself.
Presenting a perfectly clean surface to a glue applicator will help avoid many bonding failures. An inline plasma treatment will accomplish just this. Electrons and oxygen ions in the plasma beam itself allow for this type of cleaning. The high kinetic and thermal energy of the electrons allow them to sever covalent bonds of contaminants that are typically present on the very top of substrates – this will break down those contaminants into smaller, more volatile molecules. Oxygen ions in the plasma will then vaporize the remaining molecules into CO2 and water, leaving a perfectly clean surface to be bonded.
If such a plasma treatment is not utilized then there is always the risk that bonding could be compromised. One such case would be if printed cartons are stored for too long. When cartons are stored for longer time periods than normal, more contaminants in the coatings or substrate will migrate to the top of the surface. Over time these will be much more difficult to remove than cartons processed in a timely manner. This is the time when failures can easily occur and is a big motivating factor for customers to use a plasma treatment to achieve perfectly clean glue flaps every time.
Please stay tuned – next entry will discuss activation of the clean glue flap.
That’s it for now.