Reports

Waterborne Urethane Coatings For Film Application
By:  Tim Hlabse, Technical Director

Waterborne coatings based on polyurethane dispersions have proven useful for many industrial applications in which non-metallic substrates are being painted.  For instance, makers of vinyl or fiberglass lineals are using paints based on polyurethane dispersions for decorative and functional reasons.  Manufacturer's of fiberglass poles, from designer light poles to high tension power line poles, are using polyurethane dispersion based coatings to protect and beautify their products.  These products are also used on medical carts, vinyl fencing and wood/plastic composite housing accessories.

Functionally, waterborne urethane coatings adhere well to a variety of plastics. Besides beautifying with color they have excellent abrasion resistance, high elongation and outstanding weatherability.  Environmentally, they are low VOC products which are safe to handle and do not result in hazardous waste.  These paints can be applied by a wide variety of applications methods such as spray, dip and vacuum coating.

Kalcor 870 Line of Waterborne Urethane Coatings

Kalcor has developed a line of coatings based on polyurethane dispersion resins and modifications of those resins.  Many of these coatings have been formulated for vacuum coater application which requires a paint with excellent defoaming properties, fast flow and leveling and quick dry.  These formulation characteristics suggest that these coatings can also be applied by gravure and roll coating onto a paper or plastic web.

For the vinyl window industry these coatings have been formulated to satisfy the requirements of the American Architectural Manufacturers Association (AAMA).  A currently published document is AAMA 613-93, Organic Coatings on Plastic Profiles.  Table One lists the pertinent requirements and performance characteristics of Kalcor's 870 line of waterborne urethane enamels.

TABLE 1
AAMA 613 Tests

For many plastic substrates cleaning is the only requirement to enable good adhesion of coating to the substrate.  For some substrates is may be necessary to corona treat or flame treat the surface to achieve the best results.

Application to Plastic Film

Several applications for use on films have been developed.  In the personal, small bandage industry plastic film is printed with color or design to increase consumer appeal.  The 870 line of coatings provides several advantages over solvent based inks.  The first benefit is environmental.  The VOC content of these coatings is low, generally less than two pounds per gallon less water.  The urethane dispersions are fully reacted and do not impact health and safety.  The coating for bandages has been evaluated in skin contact tests which show no tendency to cause allergic reactions.  The coating is applied by roll coater onto a web, dried and re-rolled in one continuous operation.  The coating applies uniformly, dries in minutes and is block resistant immediately upon drying.  Other advantages are the ability to apply continuous paint films as low as 0.2 mil with precise color control batch to batch.

In the label industry these coatings can be used for several purposes.  A white coating can be used as the base coat.  It provides a durable medium which accepts both solvent and water based inks readily.  The waterborne urethane base is not affected by heat normally generated in electrical or mechanical equipment so that labels will not darken or yellow in these environments.  Flexibility and adhesion are also maintained for long product  life.

Another practical application involves the use of waterborne urethane coatings in the outdoor sign industry.  The use of vinyl sheet is becoming common for this use, where a sign is printed on the large sheet, rolled up and installed easily on billboards, buildings, etc.  The urethane coating provides and ideal medium for this application for the reasons mentioned above and because of the superior weathering characteristics of the aliphatic isocyanate resins used for this purpose.  Stripping old ink and recoating the vinyl sheet with waterborne paint allows for re-using the sheet with no loss of appearance or quality.

These products provide the ability to bridge the gap between decorative inks and protective coatings; making it possible to do the job of both with one application.