Guidelines for Using Polyolefin Adhesion Promoters
Polyolefin Adhesion Promoters
Eastman's polyolefin adhesion promoters are modified polypropylene polymers used to improve the adhesion of coatings, inks, and adhesives to low surface energy plastics, such as TPO, polypropylene, and polyethylene. While Eastman's polyolefin adhesion promoters are often used in primer formulations, they can also be added directly to coating, ink, and adhesive formulations to boost the adhesion of one-step systems to untreated plastic surfaces.
Several formulators have benefitted from Eastman's polyolefin adhesion promoters. They have enabled coating and adhesive formulators to provide the automotive industry with superior products that apply more evenly on various plastic parts on a vehicle’s exterior and interior. Ink and adhesive formulators have also used these adhesion promoters to increase adhesion to difficult-to-adhere-to plastic films used in packaging applications.
This article explores Eastman's polyolefin adhesion promoters in several parts: a mechanism of action, a selection guide, and a use guide.
Adhesion Failure on Polyolefin Surfaces
Polyolefin substrates are difficult to adhere to for three main reasons:
Low Surface Energy
The surface tension of the polyolefin substrate is often lower than the surface tension of the coating. This makes the surface difficult to wet.
Polarity
Polyolefins are nonpolar. This means that there are no active sites for hydrogen bonding or cross-linking.
Solvent Resistance
Polyolefin plastics are highly resistant to solvents. This prevents the coating from diffusing into the substrate properly.
How Eastman Polyolefin Adhesion Promoters Work
Eastman's polyolefin adhesion promoters are polyolefin polymers that have been functionalized with polar groups, which are typically chlorine or maleic anhydride. When applied to a polyolefin substrate, the nonpolar backbone of the adhesion promoter interacts with the nonpolar surface of the polyolefin substrate via Van der Waals forces. The polar head groups of the adhesion promoter are then free to interact with polar functional groups in the coating, ink, or adhesive film, thus creating a strong bond between the film and the substrate. The image below outlines this process in a simplified manner.
Selecting the Proper Polyolefin Adhesion Promoter
Eastman's polyolefin adhesion promoters come in a variety of grades that provide unique benefits suited to different end-use applications. The table below lays out the various commercially available grades and highlights which grades are recommended based on application and performance and regulatory attributes.
When selecting a grade, the following items that should be considered:
Substrate type
Whether or not a primer or a blend-in additive is preferred
Compatibility with other formulation parts, such as resins
Environmental regulations regarding VOCs, banned chemicals, and recyclability
Necessary attributes to provide optimal performance
ChemPoint has product specialists standing by to help you. Contact us today to discuss your application and find the grade best suited for you.
How to Use Eastman Polyolefin Adhesion Promoters
Primer Applications
The successful use of polyolefin adhesion promoters depends on the proper combination of adhesion promoter, substrate, film thickness, and coating system. The polyolefin adhesion promoter is typically spray applied as a thin mist and then allowed to dry thoroughly prior to the application of further coatings onto the substrate. The steps for applying a primer made from Eastman's polyolefin adhesion promoters are listed below.
Clean the substrate of all contamination with an appropriate cleaning solution, then dry completely.
Prepare primer by diluting the adhesion promoter to 5%–10% solids using an appropriate diluent.
Apply the primer to the substrate at 0.1–0.2 mil (dry film thickness) by spraying, wiping, or other means.
Allow the primer to dry; drying times vary but are typically anywhere from 3 to 10 minutes at 21°C.
Topcoats can be applied once the primer is completely dry.
Additive Applications
Typically, the best adhesion is achieved by applying Eastman Polyolefin Adhesion Promoters directly to the substrate as a primer. However, in certain applications it is necessary to avoid this priming step. In these applications it may be possible to Eastman's Polyolefin Adhesion Promoters as an additive to the formulation to improve adhesion. In these cases, formulators must test the compatibility of the adhesion promoter with the other components in the formulation to ensure this approach is feasible. The guidelines for utilizing Eastman Polyolefin Adhesion Promoters as an additive are listed below.
Clean the substrate of all contamination with an appropriate cleaning solution, and dry thoroughly.
Add the adhesion promoter to the formulation at 2.5% solids to the unreduced coating, ink, or adhesive and mix thoroughly.
For example, add 10 wt% CP-343-25% Xylene to a 100 wt% coating, ink, or adhesive.
Test the formulation for compatibility and the effect on dry film properties.
If the target adhesion is not achieved, increase the amount of adhesion promoter while continuing to monitor the effects on dry film and other properties.
ChemPoint has product specialists standing by to help you. Contact us below today to discuss your application and find the grade best suited for you.
