Paint & Coatings Industry - February 2009 - (Page 37) Abrasion Resistance Testing was conducted as per ASTM D 4060 on wood panels. Pairs of panels are finished with three coats of the test subject and aged seven days at ambient conditions. Actual Taber testing is performed in a climatecontrolled environment (70 °F/50% RH). Test panels are conditioned to this environment for 16 to 24 hours before testing. Taber test is performed using CS17 wheels. Each test panel is weighed initially and after each 250 cycles on a scale that measures to four units to the right of the decimal point. Each panel is run for a total of 1000 cycles. Taber abrasion values are expressed as milligrams weight loss per 1000 cycles (averaged over the pair of panels). for a 24-hour time period before being tested for swell. Solvent swell was determined by measuring the diameter of the swollen film in a petri dish containing some of the solvent using digital calipers and double checked with a standard metric ruler. Discussion of Results Chemical Resistance For adequate protection against commonly used cleaners, food stuff and alcohol-based materials, floor coatings need to have excellent resistance properties in order to prevent unsightly stains and blemishes to the coating as well as the substrate. A number of materials expected to be potentially encountered in residential and commercial applications that are known to be aggressive toward coatings were evaluated on the selfcrosslinking PUD and compared against two commercial 2K-crosslinked controls based on polyaziridine and polyisocyanate crosslinkers. The exposure time of the coatings to the substance is given in parentheses next to the substance. The results shown in Table 1 illustrate the SCL PUD performs favorably compared to the commercial 2K controls in the gloss compositions that were tested. In particular, the performance of the 1K PUD is particularly impressive toward alcohol resistance where common thermoplastic PUDs tend to be weak. Moreover, the water resistance is excellent for the 1K SCL PUD, which was found to be a weakness for ketoneamine self-crosslinked PUDs.8 Scratch Resistance The test coatings are prepared by making 6-mil draw-downs on Mylar sheets (typically scrub charts). The scratch resistance of the coatings is determined by subjecting the coating to 200 double rubs with a Scotch-Brite sponge weighted with 350 g. The sponge is rotated by 180º after 100 double rubs to attain a more uniform scratch/abrasion. The coatings are analyzed for final gloss at 20, 60 and 85 and compared to the starting gloss at the same area. Results are reported as percent gloss retention. Test Floor Evaluation Each coating to be tested is prepared by applying three coats of similar weight to four separate oak panels that are cured for 7 days at ambient conditions before assembly into the test floor. The test floor evaluates up to 24 coatings at one time. There are four statistically determined varied positions for each test coating that allows for equal foot traffic and wear patterns for each coating and statistical analysis of the data. Five gloss readings are taken of each coating at each position on the test floor. 60° gloss readings are taken initially when the floor is installed and once a month after that. A template is used for placing the gloss meter on the test positions to ensure that the same location is read each time a reading is taken. Monthly readings are usually discontinued after about five month’s usage. Most gloss loss occurs in the first two months of usage. About one to two thousand people cross this floor every workday. Each coating at each location on the floor is also monitored for black heel marking and other damage that may occur to the finish (high heel indentions as an example). Solvent Swells Another way to look at how effective crosslinking is in a polymer based on an objective measurement is through solvent swell experiments. The main drawback is that they do not take into consideration the adhesion or discoloration of the coating on a wood substrate being subjected to chemical attack. As mentioned in the experimental section, cured films of known dimenTABLE 2 | Solvent swell results. Cure Time at RT- Solvent 1 Day RT Cure 1K SCL PUD (% Increase) 2K NCO (% Increase) 2K Aziridine (% Increase) Thermoplastic PUD (% Increase) 8 (moderate white) 30 dissolved dissolved 8 (moderate white) 30 highly deteriorated dissolved IPA MEK Methanol NMP 7 Day RT Cure IPA MEK Methanol NMP 6 12 10 64 10 (slight white) 24 (slight white) 20 (slight white) 62 6 18 8 46 Solvent Swell Data generated for solvent swells were based on dispersions at ~30% solids drawn-down 10-mil wet on Mylar film that was pre-coated with a Teflon release coating. The resulting films (~2-mils dry) are cured for a given time period (1 day or 7 days) at ambient conditions, after which time a 25-mm diameter circular film is punched out using a die. The 25-mm circular film sample is then submerged in the solvent being tested in a small glass jar 6 12 10 64 9 (slight white) 24 (slight white) 12 (slight white) 52 6 17 8 40 PA I N T & C O A T I N G S I N D U S T R Y 37
For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.