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Predicting performance by analytical techniques
FOCUS reduction or texturing the film surface and adjustments may have to be made to compensate for possible reduction in mechanical properties. Coating flexibility will change inversely to film thickness, and close control of film thickness is important especially, on parts that are post formed. Changing the composition of the reactants in the main binder resin can alter the properties of powder coating films. Polyester resins, for example, can be formulated with a wide range of difunctional acids and glycols. Terephthalic acid reacts with glycols to give long chain linear molecular structures that impart flexibility to the binder system. Replacing terephthalic acid by its isomer, isophthalic acid, the molecular symmetry is altered to form ring structures that give greater protection against the effect of UV radiation, but conversely have an adverse effect on flexibility and impact resistance. This is a prime reason for the poorer mechanical properties of super durable polyester powder systems. There are a number of resin components that can influence the properties of the polyester resin and achieving the required mechanical properties is dependent upon balancing the correct choice of components to optimize performance. It is claimed in the paper that the use of additives can improve performance, and surfactants are said to be beneficial in promoting pigment and filler wetting to improve flow and levelling, or promoting substrate wetting during cure, which improves adhesion and corrosion resistance. Other additives, such as micro spheres that are coreshell polymers, have been shown to improve the impact resistance of super durable powder coatings. Improved flexibility can be achieved by modifying the curative. These can include the use of more linear curatives, or
JANUARY 2005
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even the addition of uretdione curative to a super durable polyester containing TGIC as a curative, is claimed to improve impact resistance and flexibility. Reduction of pigment/filler content can be a contributory factor since flexibility and adhesion will be highest in a clear powder coating, and the addition of too much filler will adversely affect film performance. The emphasis on improving flexibility of powder coatings is aimed at expanding existing markets in applications where blank metal sheet is powder coated and subsequently post formed into the casing of a domestic appliance. There are many more outlets under consideration where powder coated blanks and coil could be applied to post forming operations if the required flexibility could be achieved. Paper entitled “Formulating for Improved Flexibility and Impact Resistance” by Chuck Danick of Danick Specialties and Support presented at Powder Coating 2004, Formulator’s Technical Conference in Charlotte NC on 20-21 Sep 2004. Bound copies of the conference papers available from the organizers: The Powder Coating Institute, 2121 Eisenhower Avenue, Suite 401, Alexandria, VA 22314, USA
Predicting performance by analytical techniques Various natural and accelerated testing procedures are used in the coatings industry to ensure the service life of the coated article. Artificial weathering machines attempt to predict outdoor exposure performance, with varying degrees of success. In some cases, this can give misleading results, and in all cases, considerable time and expense is incurred in formulation and testing laboratories. Within the powder coatings industry, there is significant diversity in the choice of testing protocols used, and the particular test choice usually depends on the expected use of the product, the
C OAT I N G S environment in which it will be employed, and the historical confidence in a particular test. The demand to reduce product development cycles and speed the introduction of next generation products into the market highlights the need for improved prediction tools. Service life of coated articles is dependent upon the combination of environmental attack factors, substrate preparation and coating application conditions. It is known that the prime reasons for coatings failure are humidity and high temperature, and this has made the South Florida testing regime the favoured natural weathering site. A paper by Eric Dumain examines the possibility of using analytical techniques at the beginning of development programmes, particularly the use of UV visible spectroscopy, as a useful tool in speeding up product development, and when properly used it might be possible to correlate this test to outdoor weatherability data. This paper concentrates only on mono-layer polyester powder coatings. A brief description of UV visible spectroscopy is included in the paper and two aspects of this method of testing are considered. Can powder coating accelerated weathering results be reasonably correlated to UV visible testing of polyester resins? What weathering results should be expected if small monomer changes are made to optimize resin performance, based on UV visible spectra? Six polyester resins of known formulation were converted to either 30% white powder coatings or 2% black powder coatings by conventional laboratory procedures. It is well known that polyesters containing a predominant amount of isophthalic acid have high weatherability and are referred to as super durable. Polyester resins based on terephthalic acid have excellent flexibility but only modest
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FOCUS weatherability characteristics. The choice of polyol is also an important factor in promoting exterior durability. In accelerated weathering tests, the comparative gloss retention of the powders based on different aromatic acids, are shown. The superior performance of the IPA rich polyester compared to the TPA rich polyester is apparent but the researcher must wait ten days for a difference in gloss retention to be observed. UV absorbance plots for the resins used in these coatings are tabulated. While the TPA rich polyester exhibits only slightly higher maximum absorbance at the shortest wavelength (280 nm), it does show a much higher peak absorbance at 310 nm than the IPA rich polyester. This higher absorbance in the UVB region would be expected to contribute to poorer weathering performance. It also displays slightly higher absorbance values in the UVA range greater than 335 nm, and the curves crossover in the 320-335 nm range. In this example, a roughly 2X increase in UV absorbance at 310 nm translates to a 4X decrease in gloss retention after 600 hours Weatherometer. The assessment was taken further by comparing two polyesters with small differences in aromatic acid composition. In the QUV-A 340 test, two IPA-rich 30% white polyesters cured with blocked isocyanates, achieved nearly 2500 test hours before changes in gloss retention were observed. The polyesters contained all IPA in the first sample and 9:1 IPA:TPA in the second sample. These small monomer changes showed the same trend under UV visible absorbance testing, although the differences were less pronounced. The weak link in the polyester chain gives the resin overall higher absorbance in the UVB range and is manifested by slightly poorer accelerated test
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performance. Tabulating the test results, shows the crossover point near 320 nm, and the all IPA resin actually shows slightly higher absorbance in the UVA range. The biggest difference between the two polymers occurs at 310 nm where the TPA polyester has 25% higher absorbance. It is difficult to correlate this higher absorbance to QUV-A gloss retention, since the all IPA resin has not changed after 5000 hours of testing. Nevertheless, the gloss retention trends and the 310 nm absorbance can give a rank ordering of test performance. Comparison of polyesters with small differences in glycol ratios were carried out on two black pigmented polyurethane powder coatings using TPA-rich polyesters with different NPG/EG ratios. It was expected that the higher NPG content would improve weathering performance, and the test results confirmed that with higher NPG the base resin gave slightly better durability. In this test the more severe QUV-B 313 was used to shorten the exposure cycle. The powder coating with the enhanced ratio of NPG showed 5% lower absorbance at 310 nm and there was no crossover point for the two curves. More work is required to confirm the trend of lower 310 nm absorption and better gloss retention. While this technique will not replace natural testing because of the importance and complex effects on weathering of substrate types, surface preparation, intercoat adhesion in multiple coat systems, it should be seen as an additional screening tool for the powder coatings development chemist. Paper entitled “Use of Analytical Techniques to Predict and Correlate Powder Coating Weatherability” by Eric Dumain of Reichhold Inc, presented at Powder Coating 2004, Formulator’s Technology Conference, in Charlotte, NC, on 20-21 Sep 2004. Bound copies of the conference papers available from the organizers: The Powder Coating Institute, 2121 Eisenhower Avenue, Suite 401, Alexandria, VA 22314, USA
C OAT I N G S
INDUSTRY NEWS Return to profits for DuPont in 3Q 2004 For 3Q 2004 DuPont posted net profits of $331 M (compared with losses of $873 M for 3Q 2003) on sales of $6.4 bn (+10% excluding changes to parameters which included the sale of Investa to Reliance). Given unchanged parameters, sales were down by 7% but operating profits rose by 67% to $603 M before exceptional elements. Excluding the Coatings and Colour Technologies division, all divisions registered a strong increase in turnover: 21% for the Agriculture and Nutrition division to $969 M; 12% for the Electronics and Communication Technologies division to $815 M; 29% for the Performance Materials division to $1.6 bn; and 19% for the Safety and Protection division to $1.18 bn. However the group’s president warns that early signs of a global slowdown have been noted, mainly because of the rapid rise in raw material costs during 3Q. DuPont expects these conditions to continue until end 2004 but is still predicting net share profits of $2.25-2.35 for the year as a whole. Chimie Pharma Hebdo, 2 Nov 2004, (274), 10 (in French)
Akzo Nobel 3Q 2004: Coatings – clearly up due to growth and acquisitions For its 3Q 2004 (ends 30 Sep 2004), the Coatings Division of Akzo Nobel NV has reported total sales of €1381 M (€1323 M for its 3Q 2003), operating income of €137 M (€125 M), EBITDA of €170 M (€159 M), capital expenditures of €33 M (€25 M), and headcount of 29,310. There is extensive analysis/discussion of
JANUARY 2005
JANUARY 2005
ON
POWDER
even the addition of uretdione curative to a super durable polyester containing TGIC as a curative, is claimed to improve impact resistance and flexibility. Reduction of pigment/filler content can be a contributory factor since flexibility and adhesion will be highest in a clear powder coating, and the addition of too much filler will adversely affect film performance. The emphasis on improving flexibility of powder coatings is aimed at expanding existing markets in applications where blank metal sheet is powder coated and subsequently post formed into the casing of a domestic appliance. There are many more outlets under consideration where powder coated blanks and coil could be applied to post forming operations if the required flexibility could be achieved. Paper entitled “Formulating for Improved Flexibility and Impact Resistance” by Chuck Danick of Danick Specialties and Support presented at Powder Coating 2004, Formulator’s Technical Conference in Charlotte NC on 20-21 Sep 2004. Bound copies of the conference papers available from the organizers: The Powder Coating Institute, 2121 Eisenhower Avenue, Suite 401, Alexandria, VA 22314, USA
Predicting performance by analytical techniques Various natural and accelerated testing procedures are used in the coatings industry to ensure the service life of the coated article. Artificial weathering machines attempt to predict outdoor exposure performance, with varying degrees of success. In some cases, this can give misleading results, and in all cases, considerable time and expense is incurred in formulation and testing laboratories. Within the powder coatings industry, there is significant diversity in the choice of testing protocols used, and the particular test choice usually depends on the expected use of the product, the
C OAT I N G S environment in which it will be employed, and the historical confidence in a particular test. The demand to reduce product development cycles and speed the introduction of next generation products into the market highlights the need for improved prediction tools. Service life of coated articles is dependent upon the combination of environmental attack factors, substrate preparation and coating application conditions. It is known that the prime reasons for coatings failure are humidity and high temperature, and this has made the South Florida testing regime the favoured natural weathering site. A paper by Eric Dumain examines the possibility of using analytical techniques at the beginning of development programmes, particularly the use of UV visible spectroscopy, as a useful tool in speeding up product development, and when properly used it might be possible to correlate this test to outdoor weatherability data. This paper concentrates only on mono-layer polyester powder coatings. A brief description of UV visible spectroscopy is included in the paper and two aspects of this method of testing are considered. Can powder coating accelerated weathering results be reasonably correlated to UV visible testing of polyester resins? What weathering results should be expected if small monomer changes are made to optimize resin performance, based on UV visible spectra? Six polyester resins of known formulation were converted to either 30% white powder coatings or 2% black powder coatings by conventional laboratory procedures. It is well known that polyesters containing a predominant amount of isophthalic acid have high weatherability and are referred to as super durable. Polyester resins based on terephthalic acid have excellent flexibility but only modest
5
FOCUS weatherability characteristics. The choice of polyol is also an important factor in promoting exterior durability. In accelerated weathering tests, the comparative gloss retention of the powders based on different aromatic acids, are shown. The superior performance of the IPA rich polyester compared to the TPA rich polyester is apparent but the researcher must wait ten days for a difference in gloss retention to be observed. UV absorbance plots for the resins used in these coatings are tabulated. While the TPA rich polyester exhibits only slightly higher maximum absorbance at the shortest wavelength (280 nm), it does show a much higher peak absorbance at 310 nm than the IPA rich polyester. This higher absorbance in the UVB region would be expected to contribute to poorer weathering performance. It also displays slightly higher absorbance values in the UVA range greater than 335 nm, and the curves crossover in the 320-335 nm range. In this example, a roughly 2X increase in UV absorbance at 310 nm translates to a 4X decrease in gloss retention after 600 hours Weatherometer. The assessment was taken further by comparing two polyesters with small differences in aromatic acid composition. In the QUV-A 340 test, two IPA-rich 30% white polyesters cured with blocked isocyanates, achieved nearly 2500 test hours before changes in gloss retention were observed. The polyesters contained all IPA in the first sample and 9:1 IPA:TPA in the second sample. These small monomer changes showed the same trend under UV visible absorbance testing, although the differences were less pronounced. The weak link in the polyester chain gives the resin overall higher absorbance in the UVB range and is manifested by slightly poorer accelerated test
6
ON
POWDER
performance. Tabulating the test results, shows the crossover point near 320 nm, and the all IPA resin actually shows slightly higher absorbance in the UVA range. The biggest difference between the two polymers occurs at 310 nm where the TPA polyester has 25% higher absorbance. It is difficult to correlate this higher absorbance to QUV-A gloss retention, since the all IPA resin has not changed after 5000 hours of testing. Nevertheless, the gloss retention trends and the 310 nm absorbance can give a rank ordering of test performance. Comparison of polyesters with small differences in glycol ratios were carried out on two black pigmented polyurethane powder coatings using TPA-rich polyesters with different NPG/EG ratios. It was expected that the higher NPG content would improve weathering performance, and the test results confirmed that with higher NPG the base resin gave slightly better durability. In this test the more severe QUV-B 313 was used to shorten the exposure cycle. The powder coating with the enhanced ratio of NPG showed 5% lower absorbance at 310 nm and there was no crossover point for the two curves. More work is required to confirm the trend of lower 310 nm absorption and better gloss retention. While this technique will not replace natural testing because of the importance and complex effects on weathering of substrate types, surface preparation, intercoat adhesion in multiple coat systems, it should be seen as an additional screening tool for the powder coatings development chemist. Paper entitled “Use of Analytical Techniques to Predict and Correlate Powder Coating Weatherability” by Eric Dumain of Reichhold Inc, presented at Powder Coating 2004, Formulator’s Technology Conference, in Charlotte, NC, on 20-21 Sep 2004. Bound copies of the conference papers available from the organizers: The Powder Coating Institute, 2121 Eisenhower Avenue, Suite 401, Alexandria, VA 22314, USA
C OAT I N G S
INDUSTRY NEWS Return to profits for DuPont in 3Q 2004 For 3Q 2004 DuPont posted net profits of $331 M (compared with losses of $873 M for 3Q 2003) on sales of $6.4 bn (+10% excluding changes to parameters which included the sale of Investa to Reliance). Given unchanged parameters, sales were down by 7% but operating profits rose by 67% to $603 M before exceptional elements. Excluding the Coatings and Colour Technologies division, all divisions registered a strong increase in turnover: 21% for the Agriculture and Nutrition division to $969 M; 12% for the Electronics and Communication Technologies division to $815 M; 29% for the Performance Materials division to $1.6 bn; and 19% for the Safety and Protection division to $1.18 bn. However the group’s president warns that early signs of a global slowdown have been noted, mainly because of the rapid rise in raw material costs during 3Q. DuPont expects these conditions to continue until end 2004 but is still predicting net share profits of $2.25-2.35 for the year as a whole. Chimie Pharma Hebdo, 2 Nov 2004, (274), 10 (in French)
Akzo Nobel 3Q 2004: Coatings – clearly up due to growth and acquisitions For its 3Q 2004 (ends 30 Sep 2004), the Coatings Division of Akzo Nobel NV has reported total sales of €1381 M (€1323 M for its 3Q 2003), operating income of €137 M (€125 M), EBITDA of €170 M (€159 M), capital expenditures of €33 M (€25 M), and headcount of 29,310. There is extensive analysis/discussion of
JANUARY 2005