Technical Bulletin Performance of several Talc Grades in a Water-Borne 2 Pack Epoxy Primer

Transcription

1 Technical Bulletin 1203 Performance of several Talc Grades in a Water-Borne 2 Pack Epoxy Primer

2 Contents Introduction Summary Experimental structure and preparation of samples Grades tested Assessment of results Results and Discussion Further investigations Mercury porosity SEM pictures Conclusions Physical values Formulations Table 2: Results at a Glance Introduction Water-borne paints are increasing their market share. To find out how the performance of such paints can be influenced by the talc grade used, several talc grades were compared in a 2 pack water-borne epoxy system. In total 9 fine and coarse talc grades at 3 different pigment volume concentrations (PVC) were tested (table 1). Experimental Structure and Preparation of Samples Grades Tested Table 1: Talc Grades Tested Summary This study showed clear differences in paint performance depending on the talc grade used. Tests were carried out at various PVCs and dry film thicknesses (DFT). The primers were applied to sand-blasted steel panels. The results obtained led to the conclusion that the degree of lamination of the extenders had the greatest impact on the corrosion resistance. This was substantiated by the poor results of the nodular magnesitecontaining AT grades and the failure of WESTMIN D30E at higher PVCs. Hydrophobicity seemed to be of secondary importance since the more hydrophilic chlorite-containing grades achieved average to good protection. Very interesting and surprising were the results at higher PVCs with the FINNTALC grades. The surface dried out very quickly after removal from the salt spray chamber. The PLUSTALC C325 grade, similar in morphology and talc content did not perform equally well. The SEM cross-section photo of this paint film showed a concentration of talc particles in the bottom of the paint. Consequently this caused failure of the paint at the high PVC test. To clarify if there was something wrong with this formulation the trial will be repeated in a later study. To check the influence of the varying composition of the grades with different oil absorptions, comparisons were carried out at 3 different pigment volume concentrations (PVCs). For the low oil absorption grade WESTMIN D30E - AW testing was extended to 5 PVCs. Also, one trial was repeated 7 times to check on the reliability of the results. The paint formulations are given in the attachment. Due to the experience gained in a 2 pack solventborne system, sand-blasted steel substrates (degree of sand-blasting acc. ISO : SA 3) were used. Three panels per trial were tested. Each primer was air-sprayed directly after mixing with the second component at varying dry film thicknesses (DFT). The aim was to obtain panels with DFTs of 60 µm, 80 µm and about 100 µm. Because of limited paint volumes and varying solid contents this target was only partially achieved. However, there was always one panel in the range of 80 µm. The DFT was measured at least at 10 points on the panels and the lowest and highest values were noted and the mean was calculated. After the drying time of 21 days at 23 C and 50 % r. H. the panels were scored and tested according to ISO 7253 (neutral salt spray fog, photo 1). To get more information about the relation of the particle size distribution and the oil absorption to the corrosion resistance at different pigment volume concentrations, fine to coarse talc grades were tested. The grades were based on Finnish, Norwegian, Chinese and Australian raw materials. Additionally, one competitor grade with 95 % chlorite content was included. This grade had showed very different behaviour in previous solvent-borne anti-corrosion tests and is therefore suitable to check the method. The detailed physical values of the talc grades can be found in table 9. 2 Mondo Minerals OY. Technical Bulletin 1203 Mondo Minerals OY. Technical Bulletin

3 Photo 1: Neutral Salt Fog Spray Photo 2: Panel 563 First defects: 312 h Duration: 528 h Creep-rusting: 2 mm Degree of blistering : m2(g3) Resistance Index: 11 poor Photo 3: Panel 551 First defects: 1008 h Duration: 1320 h Creep-rusting: 2 mm Degree of blistering : m1(g5) Resistance Index: 21 Table 3: Tests and Point System for the Assessment Assessment of Results All panels were checked at regular intervals during the test. As soon as the first defects appeared, the time was noted. When a panel showed serious defects, the salt spray exposure was stopped. Defects were considered as serious when there was evident loss of protection. To enable a numeric ranking for the degree of blistering (according to ISO ) the index numbers for the amount and the size are added up, for example a m1(g2) degree of blistering becomes a 3. When the degree of blistering sum exceeded 5, or intense rust was formed, the salt spray test was terminated. This is very subjective and therefore counted less than the first defects evaluation, which is easier to determine. In the final evaluation, the creep-rusting and the degree of blistering were determined. All cross-cut tests showed a very good adhesion (value of Gt 0) and were not taken into account. The table below shows how the parameters of this resistance index were ranked: average Photo 4: Panel 522 First defects: 1872 h Duration: 2016 h Creep-rusting: 4 mm Degree of blistering : m1(g2) Resistance Index: 34 good The resistance index points were categorised in three groups with a colour code points were considered as poor, points as average and points as good. Photos 2-4 show the typical appearance of panels listed in these categories. 4 Mondo Minerals OY. Technical Bulletin 1203 Mondo Minerals OY. Technical Bulletin

4 Results and discussion In table 4 the standard trials are listed. Usually a higher dry film thickness resulted in better protection. The results proved that there is a necessary minimum DFT of around 60 µm. The performance drops markedly below this limit. Therefore only panels with an average DFT over 60 µm were recorded in the final summary (table 2). If only the values above the limit are considered, a mean of 34 with a standard variation of ± 2 attests good reproducibility. The results at the lowest PVC didn't show much difference (see Table 5). A trend is visible concerning the MICRO-TALC AT grades. They seemed to perform slightly worse than the other grades. Panel no. 468 (MT AT 200) showed a good result but this is most probably caused by its high dry film thickness. Table 4: Results of Standard Trial Table 5: Comparison of Results of 25 % PVC 6 Mondo Minerals OY. Technical Bulletin 1203 Mondo Minerals OY. Technical Bulletin

5 By increasing the PVC to 31 % the general performance was slightly reduced. Nevertheless most grades showed acceptable protection. The grade MICRO-TALC AT EXTRA failed the test. Also Chlorite talc 95 showed inferior protection in direct comparison to e.g. FTA M15. (Panel 1051 compared to panel 522). Table 7: Comparison of Results of 37 % PVC Table 6: Comparison of Results of 31 % PVC By increasing the PVC by another 6 %, the paint performance changed markedly. Most grades tended to fail. Also, with increasing PVC, the minimum dry film thikkness level has to be increased to obtain a good result. MICRO-TALC AT 1 and MT AT 200 grades showed only average performance, the PLUSTALC grade failed completely although it had a good/average result at 31 % PVC. At first sight, the best performing grades were FTA M05N and FTA M30 and Chlorite talc 95. A closer examination of panel 853 of Ct 95 led to the conclusion that the relatively good first defects value was not deserved. The blisters in the top area of the specimen (see photo 5) had not been detected at first due to their small size. The total performance of this trial was therefore to be considered just as average. Surprisingly the very fine grade FTA M05N showed good protection (photo 6). It was expected that the higher oil absorption would create more porosity and that the paint would protect less well. However, the FINNTALC trial with the extremely high PVC of 47 % brought relatively good results (see table 8). Photo 5 (left): Panel 853 (Ct 95 37% PVC) Photo 6 (right): Panel 726 (FTA M05N 37% PVC) 8 Mondo Minerals OY. Technical Bulletin 1203 Mondo Minerals OY. Technical Bulletin

6 Table 8: Comparison of Results Higher than 37 % PVC To check if any rust formed under the paint, panel 923 (same trial but lower DFT) was partially stripped. Photos 8 and 9 proved that no such rust formation occurred. All visible defects on the steel were due to defects in the paint. FINNTALC M15 (table 8: panel 926) shows the best result at the highest PVC. This result was unexpected since WESTMIN D30E has significantly lower oil absorption and should therefore cause less porosity in a paint film. But the WESTMIN D30E panel 836 with a similar DFT failed completely. The explanation for this exceptional behaviour could be observed on the paint surface of the specimen 926 directly after testing - it dried very quickly. The same effect was observed with FINNTALC M05N, 37 % PVC trials. Photo 7 was taken directly after the salt spray test was terminated. The droplets on the standard formulation are clearly visible whereas the surface of panel 926 was already nearly dry. Droplets on standard formulation Photo 7: Fast Drying Panel 926 (FINNTALC M15, 47 % PVC) Photo 8: Panel 923 (FINNTALC M15 47%) Further Investigations Mercury porosity measurements were carried out to find out if there were any differences in the amount and size of pores in the different paint films. Additionally cross-section SEM pictures were taken to determine the distribution of talc particles in the paint film. Photo 9: Panel 923, Partially Stripped Compressibility measurements were however carried out on all the paint samples. These curves are shown in figure 1. Paint 9/2 FTA M15 47% had a slightly lower compressibility. This paint has lower binder content. The other coatings showed no differences. Mercury Porosity Dry surface Porosimetry cannot be used to measure the internal structure of the paint films since no actual intrusion into the sample itself takes place, but the sample is compressed under the high pressure and it then relaxes again as the pressure is reduced. Observation of the sample pieces after the measurement also indicated that there had been no mercury intrusion into the structure. This confirms that the film is effectively "filled" with binder as expected at such relatively low pigment volume concentrations. 10 Mondo Minerals OY. Technical Bulletin 1203 Mondo Minerals OY. Technical Bulletin

7 Figure 1: Mercury Intrusion Curves of the Paint Film Samples Photo 10: SEM - MT AT 1 PVC 37 % Photo 11: SEM - FTA M15 PVC 37 % SEM Pictures Conclusions The energy dispersive x-ray method (EDS)-analysis determines the chemical elements of a sample and can show the position of the elements in the sample. In the pictures below all detected magnesium has been coloured yellow. The morphologies of the particles are clearly visible. MT AT 1 and WM D30E (photos 10, 12) show a more nodular shape whereas FTA M15 and PT C325 (photos 11+13, 14) are more platy. All samples save PT C325 show homogeneously dispersed talc particles. There is a significantly higher talc concentration at the bottom of sample PT C325 PVC 37 %. It is possible that this weakened the paint in its protection function. To clarify if there was something wrong with the formulation this trial will be repeated in a subsequent study. Photo 15 shows the rough surface of trial FTA M15 PVC 47 %. A higher dry film thickness resulted in better protection. With increasing pigment volume concentration, the average dry film thickness has to be increased to obtain good protection. The binder system shows good salt spray resistance. Therefore all extenders show good performance at lower PVCs, where the binder has the greatest influence on the result. With increasing PVC, two FINNTALC based grades gave the best results in this binder system. Very interesting and surprising were the results at the higher PVCs with the FINNTALC grades. The surface dried out quickly as soon as the test was stopped. It is difficult to explain why the Chinese grade, with similar morphology and talc content did not perform equally well. To clarify if there was something wrong with the formulation this trial will be repeated in a later study. Also these results are only valid for this system and further investigations are necessary to check if they can be confirmed in other water-borne binder systems. Photo 12: SEM - WM D30E PVC 37 % Photo 13: SEM - FTA M15 PVC 47 % Photo 14: SEM - PT C325 PVC 37 % Photo 15: SEM - Surface of FTA M15 PVC 47 % 12 Mondo Minerals OY. Technical Bulletin 1203 Mondo Minerals OY. Technical Bulletin

8 Table 9: Physical Values Table 10: Formulation Appendix: Formulations This formulation is a laboratory formulation and meant for the comparison of talc grades and to maximize the differences. Too many additives may reduce the differences and so make it difficult to interpret the results. However some additives are recommended from the binder producer if the formulation is used in daily life. Especially when applied with low film thickness Byk-348 can be recommended for substrate wetting and to avoid craters. Also, there is an alternative thickening system possible: a combination of 0.3 % Aerosil R927, 0.3 % Optigel WX and 0.5 % Byk-420. All paint samples were prepared using a high speed mixer with a toothed disc. Preparation note: usually 500 g of base component were prepared in a conical vessel (Ø top 90 mm; Ø bottom 75 mm, 110 mm high) by stirring with a 50 mm diameter toothed disc at 4000 rpm (10.5 m/s radial speed). Disclaimer The information contained in this Technical Bulletin relates only to the specific tests designated herein and does not relate to the use of products in combination with any other material or in any process. The information provided herein is based on technical data that Mondo Minerals believes to be reliable, however Mondo Minerals makes no representation or warranty as to the completeness or accuracy thereof and Mondo Minerals assumes no liability resulting from its use for any claims, losses, or damages of any third party. Recipients using this information must exercise their own judgement as to the appropriateness of its use, and it is the user's responsibility to assess the materials suitability (including safety) for a particular purpose prior to such use. 14 Mondo Minerals OY. Technical Bulletin 1203 Mondo Minerals OY. Technical Bulletin

9 MONDO MINERALS OY. Kasarmikatu 22. FI Helsinki. Phone Fax The information contained in this Technical Bulletin relates only to the specific tests designated herein and does not relate to the use of products in combination with any other material or in any process. The information provided herein is based on technical data that Mondo Minerals believes to be reliable, however Mondo Minerals makes no representation or warranty as to the completeness or accuracy thereof and Mondo Minerals assumes no liability resulting from its use for any claims, losses, or damages of any third party. Recipients using this information must exercise their own judgement as to the appropriateness of its use, and it is the user's responsibility to assess the materials suitability (including safety) for a particular purpose prior to such use.