PARALOID™ AU-608S

These products are typically used as high-performance topcoats. They have exceptional gloss and tint retention with very good resistance properties. As topcoats, they can be used over many primers. A typical system consists of an inorganic zinc-rich primer, a high-build epoxy polyamide midcoat with an acrylic urethane coating based on any AU-608 grade being used as the topcoat. In other applications, PARALOID™ AU-608B is the choice if one needs a HAPS-free solvent system.

The two-component formulations given herein are recommended for initial evaluation of PARALOID™ AU-608S or PARALOID™ AU-608X. The recommended ratio (solids basis) for PARALOID™ AU-608S or PARALOID™ AU- 608X/aliphatic isocyanate is 75/25 weight percent. This corresponds to a slight excess of isocyanate resin (1.0/1.05 meq hydroxyl/isocyanate). For best pot life, polyurethane grade solvents are recommended and contamination with water should be avoided. The following formulating suggestions are offered:

Isocyanate
Aliphatic (hexamethylenediisocyanates; HMDI) isocyanates are recommended for best weathering properties. The isocyanates of HMDI, such as Desmodur N-3300 and Luxate HT 2000, impart better appearance durability in PARALOID AU-608S urethane coatings than the biurets of HMDI, such as Desmodur N-75 (see exposure data in Table 3). Either Desmodur N-3300 or Luxate HT 2000 can be substituted on an equal solids basis for Desmodur N- 75 in the formulations given herein.

Catalyst Suggestions
Coatings using PARALOID™ AU-608S or PARALOID™ AU-608X develop properties more rapidly with the use of a tin catalyst such as MetacureTM T-12 (dibutyltin dilaurate). In practice, we recommend levels of 0.01 to 0.05% based on vehicle solids. The lower level appears to be better for chemical resistance properties and extended pot life, while the higher provides very rapid dry times.

Flow Aid
In many formulations, the addition of a flow aid is beneficial. Either SF-1023 Silicone or BYKTM 300 can be tried in this application at a maximum of 0.1% on total resin solids.

UV Absorbers
The addition of UV absorbers (1% each of TinuvinTM 328 and Tinuvin 292 on total resin solids) can enhance the weathering properties of acrylic urethane coatings.

Colorants
Most colors can be produced using a sand or media mill grind in PARALOID AU-608S and PARALOID™ AU-608X. In some instances, it may be preferable to use a grinding medium such as PARALOID™ DM-55. If predispersed colorants are preferred, we recommend the use of acrylic-based colorants such as the Colortrend™ 844 Series.

Solvents
If faster hardness development is required for PARALOID™ AU-608S based coatings, we recommend the use of nbutyl acetate as a partial or total replacement for PM acetate in the suggested starting point formulation.

Defoamer
Dehydran™ ARA-7219 has been found to be an effective air release agent at 0.1 to 0.2% (on total paint weight) to minimize foam, particularly in airless spray applications.

Acrylic urethane coatings based on PARALOID™ AU-608B resins demonstrate excellent performance properties which allow these coatings to perform well in highly corrosive atmospheres. The following tables demonstrate the performance obtainable with the suggested starting point formulation based on PARALOID™ AU-608S resin listed in this literature.