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Understanding the importance of pretreatment in corrosion prevention
FOCUS ON P O W D E R C O AT I N G S A MONTHLY REPORT FROM SID HARRIS
UNDERSTANDING THE IMPORTANCE OF PRETREATMENT IN CORROSION PREVENTION
DECEMBER 2011 In this issue
TECHNICAL
2-3
Properties of polyester powder coatings on phosphated steel
INDUSTRY NEWS
3-6
Extra performance for liners for oven pans made from renewable materials Dow Chemical expands GMA capacity Univar adds new territories to Dow Corning Coatings distribution agreement Duranar powder coatings by PPG for Norman Y Mineta International Airport Spolchemie coating resins
MARKETS
AN INTERNATIONAL NEWSLETTER MONITORING TECHNICAL AND COMMERCIAL DEVELOPMENTS IN POWDER COATINGS ISSN 1364–5439
6-8
Leap in prices for paints and coatings industry Arkema strengthens its Rilsan pipe coating solution with new working partnership with RMB Products Inc Polyurethane: a dynamic market – overview of growth forecasts and challenges in the polyurethane market
In this month’s technical section I was pleased to abstract an article that assessed the corrosion protection of a powder coating when applied over untreated, but clean, steel panels and the same powder applied over ironphosphated steel, with and without an accelerator added to the phosphated bath. It gives me an opportunity to stress the importance of pretreatment on mild steel objects prior to powder coating, particularly so when these items are destined to withstand severe corrosive environments. While the work programme involved in preparing this article is quite comprehensive in detailing the testing procedures, it did miss one important factor, which is essential to optimizing the overall performance of the system. The researchers did not record the thickness of the deposited pretreatment layers! In the early 1970s we were supplying an epoxy based powder coating for the added protection of galvanized steel bus chassis’, pretreated online with an accelerated zinc phosphate pretreatment. There were complaints from the customer that poor adhesion of the coating was affecting the mechanical properties – a fault that was not shown in our own laboratory trials. Eventually, we were able to trace the problem to an excessive film thickness of zinc phosphate on the
galvanized steel components and, by reducing the quantity of sodium nitrite accelerator, we achieved a much lower thickness for the pretreatment and a return to the excellent mechanical and chemical resistance properties. In the latest work programme all pretreatments were carried out at the same temperature and time of immersion in the pretreatment bath, which would inevitably result in higher deposition of the accelerated iron phosphate pretreatment. Despite my comments, I consider that this work is commendable because its purpose is to provide added value to the application procedure. It is refinements like this that can help to off-set the current burden on applicators, of rising costs in raw materials and energy. This is the time to refine both formulations and processing conditions in order to press home the advantages to be gained by using powder coatings. In this economic climate the benefits of 100% powder utilization, reduced waste and waste disposal costs, one-coat applications, energy savings and environmental compliance, all converge to emphasize the positive advantages of powder coatings when compared to alternative liquid industrial coatings. It was inevitable that the coatings industry would be one of
POWDER COATINGS POWDER COATINGS POWDER COATINGS POWDER COATINGS
FOCUS the first industries to suffer from the economic decline. The financial results of Akzo Nobel, the largest global coatings producer, provide stark evidence of this by reporting a 10% decline in operating profits, although its sales remain at a reasonable level, due largely to overseas investments in the buoyant Asian markets. There are, however, some indications that even these lucrative new markets are struggling to maintain their expected growth forecasts, for they are also subject to rising raw material and energy costs, and not surprisingly, to increasing labour costs as living standards improve and the needs of the workforce become a dominant factor. In the early days of this century I warned, in my editorial comments, of the pitfalls that would arise if the needs of the labour force in the developed countries were subjugated to a globalization policy based only on the acquisition of cheap labour. My comments at that time were founded upon my own experiences of joint venture operations during the 1990s in both China and India. In both countries, I learned that the social infrastructure of these economies required urgent attention before they could become capable of handling rapid industrial growth. The dominance of China now seems be declining and investors are impetuously turning to India and South American economies to repeat the same ill-advised growth policies. In Europe and North America, industrial demand has fallen drastically and governments need to realize that only a strong workforce can remedy this global imbalance. If I could conclude this editorial on a lighter note I would do so. The problems are not about the strength of this or that currency. It is simply their uneven distribution! Sid Harris
2
ON
POWDER
TECHNICAL Properties of polyester powder coatings on phosphated steel It has been found that zinc phosphate pretreatments on low carbon steel surfaces provide better corrosion resistance than the lower cost alternative of iron phosphate pretreatments. However, there are many applications where iron phosphate pretreatment could provide adequate under-film protection for the subsequent top coating, with savings in pretreatment costs and process time. A study conducted at the University of Belgrade, has examined ways in which the performance of iron phosphate pretreatment could be improved to optimize the qualities of a polyester powder coating applied to mild steel substrates. The advantages of iron phosphate pretreatments are the simpler and low cost equipment and easier waste water treatment. Most phosphating processes require high temperatures in the region of 60°C to 70°C or higher, but it is possible to phosphate at lower temperatures, which takes a longer time unless the process can be speeded up by the addition of an accelerator. The most commonly used accelerators are nitrates and nitrites. The role of the accelerator is the main purpose of this study. There are many factors that influence the correct deposition of a pretreatment layer, including the composition of the deposition bath, the operating temperature, and the deposition time, in addition to the influence of the additives. The corrosion resistance of the coated pretreated panels was examined in this study by electrochemical impedance spectroscopy (EIS) and, to reduce the time of exposure in order to evaluate the various pretreated panels more accurately, they were coated with a low film thickness of the polyester powder coating.
C O AT I N G S Panels were prepared by simple abrading, followed by degreasing, and rinsing in distilled water. The iron phosphate coating was produced by immersion in a deposition bath at 50°C for five minutes. The influence of small additions of sodium nitrite was examined. The powder coating was applied at a coatings thickness of 30 ± 2μm and cured according to the manufacturers instructions. The corrosion rates of steel and phosphated coating on steel were determined by polarization measurements in a 3 wt% NaCl solution. The method used for the EIS measurements is fully described in the article. The adhesion tests were performed by standard pull-off methods and solvent (NMP). These resistance tests were carried out on all panels. Finally, microscopic techniques were used at regular intervals to examine for signs of corrosion degradation. In the polarization tests the current densities for bare steel and steel phosphated with and without sodium nitrite (NaNO2) were evaluated. The conclusion was drawn that the lower current densities associated with the nitrite containing pretreatment inferred that the presence of the nitrite was indicative of better corrosion stability. The EIS tests on the coated steel panels showed that the coatings applied over both mild steel and phosphated steel from the sodium nitrite-free bath, exhibited the best protective properties. The onset of under-film corrosion of the coated steel with NaNO2 added phosphate pretreatment, began after 14 days. On the untreated steel, under-film corrosion began after 24 days, while the NaNO2-free phosphated panels began to corrode after 122 days of corrosive exposure. The dry adhesion tests including the NMP test gave better results for the NaNO2 containing pretreatment when DECEMBER 2011
UNDERSTANDING THE IMPORTANCE OF PRETREATMENT IN CORROSION PREVENTION
DECEMBER 2011 In this issue
TECHNICAL
2-3
Properties of polyester powder coatings on phosphated steel
INDUSTRY NEWS
3-6
Extra performance for liners for oven pans made from renewable materials Dow Chemical expands GMA capacity Univar adds new territories to Dow Corning Coatings distribution agreement Duranar powder coatings by PPG for Norman Y Mineta International Airport Spolchemie coating resins
MARKETS
AN INTERNATIONAL NEWSLETTER MONITORING TECHNICAL AND COMMERCIAL DEVELOPMENTS IN POWDER COATINGS ISSN 1364–5439
6-8
Leap in prices for paints and coatings industry Arkema strengthens its Rilsan pipe coating solution with new working partnership with RMB Products Inc Polyurethane: a dynamic market – overview of growth forecasts and challenges in the polyurethane market
In this month’s technical section I was pleased to abstract an article that assessed the corrosion protection of a powder coating when applied over untreated, but clean, steel panels and the same powder applied over ironphosphated steel, with and without an accelerator added to the phosphated bath. It gives me an opportunity to stress the importance of pretreatment on mild steel objects prior to powder coating, particularly so when these items are destined to withstand severe corrosive environments. While the work programme involved in preparing this article is quite comprehensive in detailing the testing procedures, it did miss one important factor, which is essential to optimizing the overall performance of the system. The researchers did not record the thickness of the deposited pretreatment layers! In the early 1970s we were supplying an epoxy based powder coating for the added protection of galvanized steel bus chassis’, pretreated online with an accelerated zinc phosphate pretreatment. There were complaints from the customer that poor adhesion of the coating was affecting the mechanical properties – a fault that was not shown in our own laboratory trials. Eventually, we were able to trace the problem to an excessive film thickness of zinc phosphate on the
galvanized steel components and, by reducing the quantity of sodium nitrite accelerator, we achieved a much lower thickness for the pretreatment and a return to the excellent mechanical and chemical resistance properties. In the latest work programme all pretreatments were carried out at the same temperature and time of immersion in the pretreatment bath, which would inevitably result in higher deposition of the accelerated iron phosphate pretreatment. Despite my comments, I consider that this work is commendable because its purpose is to provide added value to the application procedure. It is refinements like this that can help to off-set the current burden on applicators, of rising costs in raw materials and energy. This is the time to refine both formulations and processing conditions in order to press home the advantages to be gained by using powder coatings. In this economic climate the benefits of 100% powder utilization, reduced waste and waste disposal costs, one-coat applications, energy savings and environmental compliance, all converge to emphasize the positive advantages of powder coatings when compared to alternative liquid industrial coatings. It was inevitable that the coatings industry would be one of
POWDER COATINGS POWDER COATINGS POWDER COATINGS POWDER COATINGS
FOCUS the first industries to suffer from the economic decline. The financial results of Akzo Nobel, the largest global coatings producer, provide stark evidence of this by reporting a 10% decline in operating profits, although its sales remain at a reasonable level, due largely to overseas investments in the buoyant Asian markets. There are, however, some indications that even these lucrative new markets are struggling to maintain their expected growth forecasts, for they are also subject to rising raw material and energy costs, and not surprisingly, to increasing labour costs as living standards improve and the needs of the workforce become a dominant factor. In the early days of this century I warned, in my editorial comments, of the pitfalls that would arise if the needs of the labour force in the developed countries were subjugated to a globalization policy based only on the acquisition of cheap labour. My comments at that time were founded upon my own experiences of joint venture operations during the 1990s in both China and India. In both countries, I learned that the social infrastructure of these economies required urgent attention before they could become capable of handling rapid industrial growth. The dominance of China now seems be declining and investors are impetuously turning to India and South American economies to repeat the same ill-advised growth policies. In Europe and North America, industrial demand has fallen drastically and governments need to realize that only a strong workforce can remedy this global imbalance. If I could conclude this editorial on a lighter note I would do so. The problems are not about the strength of this or that currency. It is simply their uneven distribution! Sid Harris
2
ON
POWDER
TECHNICAL Properties of polyester powder coatings on phosphated steel It has been found that zinc phosphate pretreatments on low carbon steel surfaces provide better corrosion resistance than the lower cost alternative of iron phosphate pretreatments. However, there are many applications where iron phosphate pretreatment could provide adequate under-film protection for the subsequent top coating, with savings in pretreatment costs and process time. A study conducted at the University of Belgrade, has examined ways in which the performance of iron phosphate pretreatment could be improved to optimize the qualities of a polyester powder coating applied to mild steel substrates. The advantages of iron phosphate pretreatments are the simpler and low cost equipment and easier waste water treatment. Most phosphating processes require high temperatures in the region of 60°C to 70°C or higher, but it is possible to phosphate at lower temperatures, which takes a longer time unless the process can be speeded up by the addition of an accelerator. The most commonly used accelerators are nitrates and nitrites. The role of the accelerator is the main purpose of this study. There are many factors that influence the correct deposition of a pretreatment layer, including the composition of the deposition bath, the operating temperature, and the deposition time, in addition to the influence of the additives. The corrosion resistance of the coated pretreated panels was examined in this study by electrochemical impedance spectroscopy (EIS) and, to reduce the time of exposure in order to evaluate the various pretreated panels more accurately, they were coated with a low film thickness of the polyester powder coating.
C O AT I N G S Panels were prepared by simple abrading, followed by degreasing, and rinsing in distilled water. The iron phosphate coating was produced by immersion in a deposition bath at 50°C for five minutes. The influence of small additions of sodium nitrite was examined. The powder coating was applied at a coatings thickness of 30 ± 2μm and cured according to the manufacturers instructions. The corrosion rates of steel and phosphated coating on steel were determined by polarization measurements in a 3 wt% NaCl solution. The method used for the EIS measurements is fully described in the article. The adhesion tests were performed by standard pull-off methods and solvent (NMP). These resistance tests were carried out on all panels. Finally, microscopic techniques were used at regular intervals to examine for signs of corrosion degradation. In the polarization tests the current densities for bare steel and steel phosphated with and without sodium nitrite (NaNO2) were evaluated. The conclusion was drawn that the lower current densities associated with the nitrite containing pretreatment inferred that the presence of the nitrite was indicative of better corrosion stability. The EIS tests on the coated steel panels showed that the coatings applied over both mild steel and phosphated steel from the sodium nitrite-free bath, exhibited the best protective properties. The onset of under-film corrosion of the coated steel with NaNO2 added phosphate pretreatment, began after 14 days. On the untreated steel, under-film corrosion began after 24 days, while the NaNO2-free phosphated panels began to corrode after 122 days of corrosive exposure. The dry adhesion tests including the NMP test gave better results for the NaNO2 containing pretreatment when DECEMBER 2011