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New photoluminuscent UV cured powder coatings
FOCUS ON P O W D E R C O AT I N G S A MONTHLY REPORT FROM SID HARRIS
THE WAY AHEAD?
APRIL 2010 In this issue
TECHNICAL
1-5
New photoluminuscent UV cured powder coatings Electrostatic properties of powder coatings
INDUSTRY NEWS
5-7
PPG reports 4Q 2009 financial results Grace announces sustainability policy Industrial Nanotech Inc announces large order from Saudi Arabia distributor for Nansulate coatings Loss of €60 M for AkzoNobel in 4Q 2009 NEW PRODUCTS 7-8 New brilliance in coatings design: Paliocrom Brilliant Orange from BASF Arkema offers new Rilsan grades for outdoor furniture
MARKETS
8
Updated profile of Russia paint industry released EVENTS
AN INTERNATIONAL NEWSLETTER MONITORING TECHNICAL AND COMMERCIAL DEVELOPMENTS IN POWDER COATINGS ISSN 1364–5439
8
Although we are subjected to daily statistics implying that the long awaited economic recovery is under way there is little tangible evidence from manufacturing industries to support these reports. It has been claimed that manufacturing industry has been strengthened by cost cutting and improvements in process efficiency during the economic downturn – but what is the reality? The increasing burden of escalating raw material and higher energy costs has not diminished and the coatings industry has done little to develop cost effective products and processes. Powder coating producers still offer their customers the same out-moded thermoset products in the belief that lower temperature curing cycles will resolve the problem of energy costs. They seem determined to avoid any commitment to UV curable powder coatings, despite the evidence that savings on conversion to this technology would repay the cost of the capital investment within one year. There will never be a better time to press for a significant technology change! If there is any encouraging news to emerge from the annual report figures of the major coatings producers it is contained in the profits resulting from their Asian or Middle Eastern investments. How long will these
markets continue to prosper before the Governments in these regions of high expansion decide to give preference to their own industries? I have already seen this trend in the Middle East, and China is rapidly moving in this direction. The fallacy of cheap labour benefits accruing from the vast transfer of manufacturing industry will be exposed within five years. What will be our alternative – capitulation or renewed investment within our own borders? New technology is the key! Sid Harris
TECHNICAL New photoluminuscent UV cured powder coatings UV curable powder coatings are an attractive choice due to the combination of the properties of powder coatings and UV curing, which can be described as being VOC-free technology, with low energy consumption, capable of overspray recycling and possessing relatively fast cure compared to conventional powder coatings. A recent article by researchers at AIDO, Valencia, describes the development of a new formulation for a photoluminescent powder coating applied to metallic
POWDER COATINGS POWDER COATINGS POWDER COATINGS POWDER COATINGS
F O C U S substrates, and cured by UV irradiation. This technology can also be applied to the coating of heat sensitive substrates, used in emergency safety signs. The fast UV curing process was shown to be efficient on thermo-sensitive panels. The UV curing technique is an interesting polymerization process: it is an environmentally friendly technique, which allows the polymerization reaction to occur rapidly. Photoluminescent pigments have been used in liquid coatings, but in the case of powder coatings, the main problem with this process has been to determine the extruder and mill parameters to prevent the loss of photoluminescent properties and darkening of the product. Coatings were formulated using an unsatured polyester resin; a photoluminescent pigment based on strontium aluminate (SrAl2O4) and a photoinitiator, 1-4-[(2hydroxyethoxy)-phenyl]-2-hydroxy2-methyl-1-propane-1-one. Benzoin, used as a degassing agent and flow agent (BYK 360P, acrylate additive), was added to the mixtures. This flow agent is a typical standard anti-crater and leveling additive for pigmented powder coatings. It Improves leveling of powder coating systems and prevents orange peel. Additionally, it prevents surface defects specific to powder coatings such as pinholes and fisheyes. Powder coatings were prepared containing 2% photoinitiator, 0.2% benzoin, 0.8% flow agent and photoluminescent pigment content (from 30 to 90% in weight ratio to resin). Samples were pre-mixed and the material was extruded in a twin screw extruder with a controlled screw speed setting and heating zones set at 95°C and 100°C. The cooled extrudate was ground in an ultra-centrifugal mill and sieved at 10 microns. The powder coating was applied to aluminium substrates. Test panels were degreased and
2
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POWDER
coated with white powder coating. After application, the panels were placed in an air-circulated oven for 2 min at 160°C to melt the powder particles and then cured by UV irradiation. Photoluminescent powder coating was characterized by luminance and decay time, according to UNE 23035-1:2003. This standard describes decay time parameter as the time for the luminance emitted by the photoluminescent sample to reach 0.3 mcd/m2 after the excitation light over the sample is removed and, because decay time can be so long, describes a method to estimate it by extrapolation. A salt spray test, according to ISO 9227:2006 was carried out for 96 h and the decay time was measured again. If the difference between the values is not greater than 5%, the coatings are deemed to pass the test. Luminance and decay time measurements were carried out on samples using a LMT B510 L photometer, with heads for illuminance and luminance measurements. The light source used to excite the photoluminescent sign was a non-diffusing, unfiltered, continuous short-arc xenon lamp of 180 W, providing a mean illuminance value of 1000 lx on the surface of each sample. Distance between the signal and the diffuser must be enough to give a luminance value at the centre of the illuminated area of 1000 lx. This area must be 5 cm in diameter, which is similar to that of the luminance head photometer. In order to confirm the luminance homogeneity over this area, test patches for measurements of luminance were positioned in the centre of the area of the test specimen and at each of the four points 90° on the outer rim of the surface of the test specimen. After checking the homogeneous illumination over the testing surface, the signal was located at the centre of this area and was stimulated for 5 min. Immediately after the lamp
C OAT I N G S was switched off, the luminance was measured. It was observed that illuminance increases with the quantity of pigment used up to 70%, and then decreases. The values after accelerated salt fog spray test decrease by 5%. Both values, according to UNE 23035-4:2000, establish that the coatings will be classified as B category, provided that the time taken for the luminance to decrease to 0.3 mcd/m2 when tested under the excitation conditions was ≥840 min, and the decrease on the initial values of luminance was lower than 5% after 96 h of exposition. It can also be seen that the decay time varies significantly with photoluminescent pigment concentration. It is probable that, as a consequence of these results, when photoluminescent pigment increases, the critical pigment concentration has been reached. Above this critical value, there is not enough resin to cover the pigment surface and an important amount of the polymer is absorbed in the pigment. There are void structures in the film due to insufficient polymer, but the pigment particles can still be thought of as being continuously connected. A new phase, air, is now present in the film and its properties drastically affect those of the film, especially with regard to density, mechanical, thermal, transport and optical properties. The formulation conditions of coatings are decisive to the results. In the experimental development some difficulties were experienced; possibly due to chemical structure, morphology and particle size of pigment. Extruder conditions are important, the dwell time of pigment in the barrel is critical, and it is necessary to control screw speed to avoid discolouration of the coating. Ultra-centrifugal mill conditions are important too. If the size of sieve is not suitable, the
APRIL 2010
F O C U S photoluminescent pigment will not pass through the sieve, reducing the percentage in the coating and, therefore, the luminescence values. Thickness also is a significant factor. A chart shows decay time of coatings formulated with 60% of photoluminescent pigment concentration at different thickness values. Maximum decay time is observed when coating thickness is over 100 μm and this is lowered when the thickness is reduced. The article provides full experimental details of the research programme. Optical characteristics (such as illuminance and decay time) of these coatings prepared at different photoluminescent pigment levels and applied with variable thickness, were studied. Powder coatings offer important advantages compared to liquid coatings in relation to VOC reduction and maximizing material utilization by recycling of the overspray, and the application of thicker coating layers in a single coat process. Compared to conventional coatings, UV powder coatings offer high cure speed and economic advantages together with the capability to coat thermo sensitive materials such as plastic or wood. Article entitled “Development of Photoluminescent Powder Coatings by UV Curing Process” by researchers at AIDO, Valencia, Spain, published in Progress in Organic Coatings, Feb 2010, 67 (2), 92-94
Electrostatic properties of powder coatings Powder handling operations lead most often to electrostatic charging of products due to collisions with surfaces of a different material type (particle/particle or particle/wall contacts). Although electrostatic phenomena play an important and ever emerging role in many industrial applications (eg powder coating, xerography, and pharmaceutical processing) they are regarded by many as a
APRIL 2010
O N
POWDER
trouble and a hazard source. In fact, numerous processes such as pneumatic conveying, sieving, fluidization and mixing, result on tribo-charging of powders. The electrostatic charges acquired by particles can thus affect the behaviour of handled products and their quality. Typical examples are poor flowability, pipe fouling and electrostatic discharge that can ignite flammable dust clouds or organic vapours. Factors affecting charging properties include particle size and shape, nature and work function of the contacting surface and the particulate material, area and frequency of contacts, surface purity, and atmospheric conditions. However, electrostatics and the associated charge generation mechanisms in such systems are multifaceted and not fully understood. In order to better understand and control the electrostatic consequences, it is important to develop laboratoryscale equipments allowing the proper measurement of triboelectric charging of powders. Among all manufacturing processes for automotive production, the painting operation contributes most to direct environmental emissions. As a consequence of recent restrictions in European legislation concerning the volatile organic compounds (VOC) emissions, the trend in almost every finisher industrial field is to replace the conventional solvent-borne paints by new lowemission paint systems, including powder coating systems. Powder paints are very finely divided solvent-free polymer coatings, which present large advantages over conventional paints from ecological and economical points of view. PSA Peugeot-Citroën was the first car manufacturer to use multi-colour powder primers and extend henceforth the use of this technology for new plants. In the electrostatic powder coating process, the powder paint is fluidized and transported through
C OAT I N G S a pipe to a special charging corona bell. In the corona bell, the powder is electrostatically charged and sprayed toward the grounded work piece. The adhered powder is then heated, melts and cross-links to form a uniform layer over the work piece. In addition, unlike the liquid paint systems in which non-deposited paint is lost, the over sprayed powder during the electrostatic application process can be reused. Two powder primers were used as the basis of this work, supplied by two different manufacturers. The mean particle size of both products measured by laser diffraction analysis (Malvern, Mastersizer) was about 25 μm and their true density was 1350 kg m-3 (Micromeritics, Accupyc 1330). According to these properties the powders belong to the cohesive group-C powders of the Geldart classification. Both products were polyester/epoxy thermosetting hybrid resins but contained different types of flow conditioners. The powder designated A contained 0.2% of fumed silica and the primer B the same amount of another flow conditioner (fumed alumina). Note that flow conditioners (also called Glidants) are nano-sized powdery additives used to improve the flowability of powders by coating the particles and decreasing interparticle forces. The use of flow conditioners in powder paints used in automotive industry is almost unavoidable because of small and narrow size distribution of particles that make them very cohesive. These particle size characteristics are necessary for the high-grade appearance requested in car manufacturing. Despite the similar physical properties and chemical nature, the application of the two powders A and B revealed that they behave differently in the industrial unit. In particular, the film thickness and the deposition efficiency (ie mass ratio of deposited and sprayed powder)
3
THE WAY AHEAD?
APRIL 2010 In this issue
TECHNICAL
1-5
New photoluminuscent UV cured powder coatings Electrostatic properties of powder coatings
INDUSTRY NEWS
5-7
PPG reports 4Q 2009 financial results Grace announces sustainability policy Industrial Nanotech Inc announces large order from Saudi Arabia distributor for Nansulate coatings Loss of €60 M for AkzoNobel in 4Q 2009 NEW PRODUCTS 7-8 New brilliance in coatings design: Paliocrom Brilliant Orange from BASF Arkema offers new Rilsan grades for outdoor furniture
MARKETS
8
Updated profile of Russia paint industry released EVENTS
AN INTERNATIONAL NEWSLETTER MONITORING TECHNICAL AND COMMERCIAL DEVELOPMENTS IN POWDER COATINGS ISSN 1364–5439
8
Although we are subjected to daily statistics implying that the long awaited economic recovery is under way there is little tangible evidence from manufacturing industries to support these reports. It has been claimed that manufacturing industry has been strengthened by cost cutting and improvements in process efficiency during the economic downturn – but what is the reality? The increasing burden of escalating raw material and higher energy costs has not diminished and the coatings industry has done little to develop cost effective products and processes. Powder coating producers still offer their customers the same out-moded thermoset products in the belief that lower temperature curing cycles will resolve the problem of energy costs. They seem determined to avoid any commitment to UV curable powder coatings, despite the evidence that savings on conversion to this technology would repay the cost of the capital investment within one year. There will never be a better time to press for a significant technology change! If there is any encouraging news to emerge from the annual report figures of the major coatings producers it is contained in the profits resulting from their Asian or Middle Eastern investments. How long will these
markets continue to prosper before the Governments in these regions of high expansion decide to give preference to their own industries? I have already seen this trend in the Middle East, and China is rapidly moving in this direction. The fallacy of cheap labour benefits accruing from the vast transfer of manufacturing industry will be exposed within five years. What will be our alternative – capitulation or renewed investment within our own borders? New technology is the key! Sid Harris
TECHNICAL New photoluminuscent UV cured powder coatings UV curable powder coatings are an attractive choice due to the combination of the properties of powder coatings and UV curing, which can be described as being VOC-free technology, with low energy consumption, capable of overspray recycling and possessing relatively fast cure compared to conventional powder coatings. A recent article by researchers at AIDO, Valencia, describes the development of a new formulation for a photoluminescent powder coating applied to metallic
POWDER COATINGS POWDER COATINGS POWDER COATINGS POWDER COATINGS
F O C U S substrates, and cured by UV irradiation. This technology can also be applied to the coating of heat sensitive substrates, used in emergency safety signs. The fast UV curing process was shown to be efficient on thermo-sensitive panels. The UV curing technique is an interesting polymerization process: it is an environmentally friendly technique, which allows the polymerization reaction to occur rapidly. Photoluminescent pigments have been used in liquid coatings, but in the case of powder coatings, the main problem with this process has been to determine the extruder and mill parameters to prevent the loss of photoluminescent properties and darkening of the product. Coatings were formulated using an unsatured polyester resin; a photoluminescent pigment based on strontium aluminate (SrAl2O4) and a photoinitiator, 1-4-[(2hydroxyethoxy)-phenyl]-2-hydroxy2-methyl-1-propane-1-one. Benzoin, used as a degassing agent and flow agent (BYK 360P, acrylate additive), was added to the mixtures. This flow agent is a typical standard anti-crater and leveling additive for pigmented powder coatings. It Improves leveling of powder coating systems and prevents orange peel. Additionally, it prevents surface defects specific to powder coatings such as pinholes and fisheyes. Powder coatings were prepared containing 2% photoinitiator, 0.2% benzoin, 0.8% flow agent and photoluminescent pigment content (from 30 to 90% in weight ratio to resin). Samples were pre-mixed and the material was extruded in a twin screw extruder with a controlled screw speed setting and heating zones set at 95°C and 100°C. The cooled extrudate was ground in an ultra-centrifugal mill and sieved at 10 microns. The powder coating was applied to aluminium substrates. Test panels were degreased and
2
O N
POWDER
coated with white powder coating. After application, the panels were placed in an air-circulated oven for 2 min at 160°C to melt the powder particles and then cured by UV irradiation. Photoluminescent powder coating was characterized by luminance and decay time, according to UNE 23035-1:2003. This standard describes decay time parameter as the time for the luminance emitted by the photoluminescent sample to reach 0.3 mcd/m2 after the excitation light over the sample is removed and, because decay time can be so long, describes a method to estimate it by extrapolation. A salt spray test, according to ISO 9227:2006 was carried out for 96 h and the decay time was measured again. If the difference between the values is not greater than 5%, the coatings are deemed to pass the test. Luminance and decay time measurements were carried out on samples using a LMT B510 L photometer, with heads for illuminance and luminance measurements. The light source used to excite the photoluminescent sign was a non-diffusing, unfiltered, continuous short-arc xenon lamp of 180 W, providing a mean illuminance value of 1000 lx on the surface of each sample. Distance between the signal and the diffuser must be enough to give a luminance value at the centre of the illuminated area of 1000 lx. This area must be 5 cm in diameter, which is similar to that of the luminance head photometer. In order to confirm the luminance homogeneity over this area, test patches for measurements of luminance were positioned in the centre of the area of the test specimen and at each of the four points 90° on the outer rim of the surface of the test specimen. After checking the homogeneous illumination over the testing surface, the signal was located at the centre of this area and was stimulated for 5 min. Immediately after the lamp
C OAT I N G S was switched off, the luminance was measured. It was observed that illuminance increases with the quantity of pigment used up to 70%, and then decreases. The values after accelerated salt fog spray test decrease by 5%. Both values, according to UNE 23035-4:2000, establish that the coatings will be classified as B category, provided that the time taken for the luminance to decrease to 0.3 mcd/m2 when tested under the excitation conditions was ≥840 min, and the decrease on the initial values of luminance was lower than 5% after 96 h of exposition. It can also be seen that the decay time varies significantly with photoluminescent pigment concentration. It is probable that, as a consequence of these results, when photoluminescent pigment increases, the critical pigment concentration has been reached. Above this critical value, there is not enough resin to cover the pigment surface and an important amount of the polymer is absorbed in the pigment. There are void structures in the film due to insufficient polymer, but the pigment particles can still be thought of as being continuously connected. A new phase, air, is now present in the film and its properties drastically affect those of the film, especially with regard to density, mechanical, thermal, transport and optical properties. The formulation conditions of coatings are decisive to the results. In the experimental development some difficulties were experienced; possibly due to chemical structure, morphology and particle size of pigment. Extruder conditions are important, the dwell time of pigment in the barrel is critical, and it is necessary to control screw speed to avoid discolouration of the coating. Ultra-centrifugal mill conditions are important too. If the size of sieve is not suitable, the
APRIL 2010
F O C U S photoluminescent pigment will not pass through the sieve, reducing the percentage in the coating and, therefore, the luminescence values. Thickness also is a significant factor. A chart shows decay time of coatings formulated with 60% of photoluminescent pigment concentration at different thickness values. Maximum decay time is observed when coating thickness is over 100 μm and this is lowered when the thickness is reduced. The article provides full experimental details of the research programme. Optical characteristics (such as illuminance and decay time) of these coatings prepared at different photoluminescent pigment levels and applied with variable thickness, were studied. Powder coatings offer important advantages compared to liquid coatings in relation to VOC reduction and maximizing material utilization by recycling of the overspray, and the application of thicker coating layers in a single coat process. Compared to conventional coatings, UV powder coatings offer high cure speed and economic advantages together with the capability to coat thermo sensitive materials such as plastic or wood. Article entitled “Development of Photoluminescent Powder Coatings by UV Curing Process” by researchers at AIDO, Valencia, Spain, published in Progress in Organic Coatings, Feb 2010, 67 (2), 92-94
Electrostatic properties of powder coatings Powder handling operations lead most often to electrostatic charging of products due to collisions with surfaces of a different material type (particle/particle or particle/wall contacts). Although electrostatic phenomena play an important and ever emerging role in many industrial applications (eg powder coating, xerography, and pharmaceutical processing) they are regarded by many as a
APRIL 2010
O N
POWDER
trouble and a hazard source. In fact, numerous processes such as pneumatic conveying, sieving, fluidization and mixing, result on tribo-charging of powders. The electrostatic charges acquired by particles can thus affect the behaviour of handled products and their quality. Typical examples are poor flowability, pipe fouling and electrostatic discharge that can ignite flammable dust clouds or organic vapours. Factors affecting charging properties include particle size and shape, nature and work function of the contacting surface and the particulate material, area and frequency of contacts, surface purity, and atmospheric conditions. However, electrostatics and the associated charge generation mechanisms in such systems are multifaceted and not fully understood. In order to better understand and control the electrostatic consequences, it is important to develop laboratoryscale equipments allowing the proper measurement of triboelectric charging of powders. Among all manufacturing processes for automotive production, the painting operation contributes most to direct environmental emissions. As a consequence of recent restrictions in European legislation concerning the volatile organic compounds (VOC) emissions, the trend in almost every finisher industrial field is to replace the conventional solvent-borne paints by new lowemission paint systems, including powder coating systems. Powder paints are very finely divided solvent-free polymer coatings, which present large advantages over conventional paints from ecological and economical points of view. PSA Peugeot-Citroën was the first car manufacturer to use multi-colour powder primers and extend henceforth the use of this technology for new plants. In the electrostatic powder coating process, the powder paint is fluidized and transported through
C OAT I N G S a pipe to a special charging corona bell. In the corona bell, the powder is electrostatically charged and sprayed toward the grounded work piece. The adhered powder is then heated, melts and cross-links to form a uniform layer over the work piece. In addition, unlike the liquid paint systems in which non-deposited paint is lost, the over sprayed powder during the electrostatic application process can be reused. Two powder primers were used as the basis of this work, supplied by two different manufacturers. The mean particle size of both products measured by laser diffraction analysis (Malvern, Mastersizer) was about 25 μm and their true density was 1350 kg m-3 (Micromeritics, Accupyc 1330). According to these properties the powders belong to the cohesive group-C powders of the Geldart classification. Both products were polyester/epoxy thermosetting hybrid resins but contained different types of flow conditioners. The powder designated A contained 0.2% of fumed silica and the primer B the same amount of another flow conditioner (fumed alumina). Note that flow conditioners (also called Glidants) are nano-sized powdery additives used to improve the flowability of powders by coating the particles and decreasing interparticle forces. The use of flow conditioners in powder paints used in automotive industry is almost unavoidable because of small and narrow size distribution of particles that make them very cohesive. These particle size characteristics are necessary for the high-grade appearance requested in car manufacturing. Despite the similar physical properties and chemical nature, the application of the two powders A and B revealed that they behave differently in the industrial unit. In particular, the film thickness and the deposition efficiency (ie mass ratio of deposited and sprayed powder)
3