Evaluation of Stain Blocking Primer Coatings with Low Volatile Organic Compound (VOC) Content and Effects of Drying Conditions on the Properties of Water Reducible Coatings for Polypropylene
Available at: https://digitalcommons.calpoly.edu/theses/482
Date of Award
MS in Polymers and Coatings
Chemistry & Biochemistry
Raymond H. Fernando
The California Air Resources Board (CARB) plans to reduce the volatile organic compound (VOC) limit of specialty primers, sealers, and undercoaters (SPSU), also referred to as stain blocking primers, from 350 g/L to 100 g/L in January of 2012. These coatings are primarily used as stain blocking primers over a variety of substrates, such as wood and drywall. Currently the stain blocking primers that are considered most effective are solvent based primers that contain VOC levels much higher than 100 g/L. The goal of this study is to determine if primers on the market today with a VOC content of 100 g/L or less can provide acceptable performance in comparison to primers with a VOC content greater than 100 g/L. This project had four milestones: 1) survey currently available SPSU coatings and related literature, 2) substrate and stain characterization, 3) benchmark testing of existing formulated commercial products, and 4) prepare a final report.
This report: 1) describes the preliminary work performed in preparation of a more systematic and comprehensive study to evaluate the performance of paints sold for the SPSU market, 2) describes the final results of selected test methods for all primers, and 3) discusses the future steps required for the completion of this project.
In preliminary testing, six primers, both waterborne and solvent based, were selected for testing and comparison. Basic primer characterization was completed, including sag, leveling, contrast ratio, and density, as was preliminary stain blocking testing, including stains by various common markers and tannin staining from dark wood. From the tests conducted during this portion of the project, and through input from an industrial advisory panel, a total of 15 commercially available primers, 7 solvent based and 8 water based, were tested. Acceptable test methods representing both the physical properties and the stain blocking capabilities of the SPSU primers were also selected from the preliminary testing and industry counsel.
As a result of the data obtained from stain blocking testing, conclusions were drawn regarding the stain blocking capabilities of both categories of primer and also about each primer individually. Although it cannot be said that all stain blocking primers, both waterborne and solvent based, perform equally, it can be said that there are waterborne primers that perform as well or nearly as well as solvent based primers in several of the stain blocking tests.
Part B of this report addresses the characterization of a water reducible coating for polypropylene. The solvent retention of the paint with varying drying times and film thicknesses is analyzed using thermogravimetric analysis (TGA). Solvent retention affects the production and shipment of coated polypropylene siding. When solvent is retained within the coating, adhesion can be reduced, and stacking or movement of the product may result in adhesion failure.
Corona treatment of polypropylene was used to increase the surface tension of the substrate and improve adhesion. It was hoped that the surface tension would rise to 60 dynes/cm, however this could not be accomplished. An increase in surface tension to 38 dynes/cm was achieved and proved to be effective at significantly increasing the adhesion of the coating to the substrate.