Brushstrokes - October 2011 - Surface Coatings Association of New ...

Recommendations

Info

Table 2. WB2K formulations. Component Raw material Weight Clear varnish White paint Polyol emulsion 51.41 36.37 Wetting additives 0.52 0.36 Base High shear thickener 2.70 1.91 Defoamer variable variable Hardener Diluents Properties Demineralized water 13.73 11.86 Mill base HDI/IPDI - 27.11 based hydrophilic isocyanate HDI based 9.85 6.97 hydrophilic isocyanate 8.66 6.12 Co-solvents* 5.82 4.12 Demineralized water 7.31 5.18 Density (kg/l) 1.04 1.22 Volume solids (%) 38.9 38.9 Weight solids (%) 42.3 50.5 VOC ready to use (g/l) 87 73 NCO/OH ratio 1.25 1.25 * co-solvent mixture consisting of butyl acetate:dipropylene glycol dimethyl ether:butyldiglycol acetate in a ratio of 13/74/13. In the base for the clear varnish formulation given in table 2, a number of different defoamer types were added at different concentration levels. All varnish samples were subjected to a foam test that is carried out as follows: the coating is applied with a pipette to the white part of a black-white paper contrast chart. After that, Table 3. Results for the foam test in a clear varnish. 14 SURFACE COATINGS ASSOCIATION OF NEW ZEALAND coating is applied to half of the black part of the chart using a brush. The varnish on the white chart is stipulated intensively with the brush to incorporate a lot of air. This varnish is then brushed over the second half of the black part of the chart. The amount of foam in the two black parts of the chart is judged after drying overnight according to a scale of one (bad) to five (good). Also the clarity of the varnish applied onto glass was judged after drying. The results are given in table 3. In the foaming test the defoamers based on a mixture of hydrophobic solids and polysiloxanes and the polyether siloxane defoamer perform well both at high and low addition levels. However the first type does introduce a strong orange peel effect in the dried film, even at low concentrations. Also this defoamer has a negative influence on the clarity of the film. The polyether siloxane defoamer also introduces a slight orange peel effect, but at low concentrations this is judged to be acceptable. The defoamer based on the mixture of polymers and hydrophobic solids is somewhat less effective but has no effect on gloss and haze. At the lower addition level, no negative effect on the leveling properties was observed. In order to verify if these defoamers also worked in pigmented systems, additional tests were performed using the defoamers at the lowest addition level. Gloss and haze values were measured for both brush and roller application and are given in Defoamer Addition level Before After Orange peel Clarity on glass Gloss* (20°) None none 2 1 none OK 84 24 Mixture of hydrophobic solids and polysiloxanes Mixture of polymers and hydrophobic solids Polyether siloxane copolymer * applied by brush low=0,17 wt%, high=0,34 wt% Figure 4. Gloss and haze values for different defoamer types. Haze* low 5 5 yes NOK 76 93 high 5 5 yes NOK 82 39 low 4 4 none OK 84 20 high 5 4.5 none OK 83 28 low 5 5 slight OK 84 22 high 5 5 yes OK 84 24
figure 4. Based on these result a final selection was made for the defoamer based on the polyether siloxane copolymer. Additional tests have been performed on the final clear varnish and white paint formulations. The coatings were applied on glass panels at a wet film thickness of 120 microns and dried at 22 °C and 50% relative humidity: drying and hardness development were measured. Household chemical resistance according to the DIN 68861-1A (on oak veneered panels two coats of respectively 175 and 125 microns wet film thickness) and resistance against methyl ethyl ketone (MEK) were measured after 1 week of drying. Results are given in table 4. Results at a glance Waterborne acrylic polyols having mixed carboxylic and sulfonic stabilization can be used to formulate hand applied two pack varnishes and paint that show good esthetical properties (gloss, flow and levelling). Proper selection of the defoamer in the formulation is essential to get smooth, defect free coatings. Evaluation of drying time, hardness build-up and resistance properties show that these are on the same level of conventional solventborne polyurethane coatings. These products open up a whole new range of end-use applications for environmentally friendly high performance coatings where previously only the use of high VOC-systems was a viable option. Email address: adriaan.sanderse@nuplexresins.com References 1. M. Melchiors, C. Kobusch, K. Noble, M. Sonntag, H. Casselmann. ‘Aqueous Two-Component Polyurethane (2C-PUR) Coatings: An Evolving Technology’, presented at the International Waterborne, High Solids and Powder Coatings Symposium, New Orleans, LA, February 10, 1999. 2. R. Hombach, H. Reiff, M. Dollhausen, US4663377 to Bayer AG. 3. J. Akkerman, R. Hall, D. Mestach and P. Vandevoorde, sixth Nürnberg Conference, 2001, 17. 4. D. Otts, M. Urban, Polymer 46 (2005), 2699. 5. D. Otts, K. Pereira, W. Jarret and M. Urban, Polymer 46 (2005), 4600. Table 4. Testing of optimized clear varnish and white paint. Clear Varnish White Paint Persoz hardness (s) 1 day 107 105 7 days 284 234 BK drying (min) phase I 15 15 phase II 195 210 phase III 360 270 phase IV 570 810 MEK resistance double rubs 68 57 Household chemical resistance (according to DIN 68861-1A) Exposure 5 = no visual damage, 0 = severe damage ammonia (25 %) 16 h 3 5 ammonia (25 %) 2 m 5 5 50 % ethanol 16 h 5 5 red wine 16 h 5 2 coffee 16 h 5 3 water 16 h 5 5 acetone 16 h 5 5 olive oil 16 h 5 5 mustard 16 h 5 3 black ink 16 h 5 3 cleaning solution 16 h 5 3 SURFACE COATINGS ASSOCIATION OF NEW ZEALAND 15
Page 1 and 2: www.scanz.org.nz OCTOBER 2011 Cryst
Page 3 and 4: This edition was intended to have T
Page 5 and 6: Fig. 2 Some white pigment sales. Fi
Page 7 and 8: A Naturally Occurring Sub-Micron Ti
Page 9 and 10: Table 4a - test results for 7% TiO2
Page 11 and 12: the shrinkage factor) and is thus i
Page 13 and 14: Bridging the gap in performance def
Page 15: the flow and levelling properties a
Page 19 and 20: FRANK JOSEPH AITKEN-SMITH One of th
Page 21 and 22: Evonik Tego wins “Ringier Technol
Page 23 and 24: Rohm and Haas New Zealand Ltd • P

Brushstrokes - October 2011 - Surface Coatings Association of New ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?