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Is fundamental research being overlooked?
FOCUS ON P O W D E R C O AT I N G S A MONTHLY REPORT FROM SID HARRIS
IS FUNDAMENTAL RESEARCH BEING OVERLOOKED?
SEPTEMBER 2013 In this issue
TECHNICAL
2-3
New Schiff base epoxy resins Local impedance spectra of organic coatings
INDUSTRY NEWS
3-5
Argex strengthens collaboration with PPG MBG Metallbeschichtung Gerstungen converts waste coating powders into heat PPG delivers record 2Q 2013 results
NEW PRODUCTS
5-6
Interpon low solar absorption powder coatings Scientists develop new colour for British Army
MARKETS
6-8
Latin American paint and coatings market rebounds Global green solvents & bio solvents market to reach $6.5 bn by 2018: MarketsandMarkets
EVENTS
AN INTERNATIONAL NEWSLETTER MONITORING TECHNICAL AND COMMERCIAL DEVELOPMENTS IN POWDER COATINGS ISSN 1364–5439
8
It has long been a contention of researchers in academic institutions that industry is reluctant to adopt their new developments until it is forced to by economic factors or increasing environmental pressures. Nowhere is this reluctance more apparent than in the coatings industry and most particularly in the field of industrial coatings. This is typified by the fact that solvent-based coatings are still widely entrenched in applicators’ workshops, despite criticisms of fire hazard, toxicity, high overspray wastage, and the everincreasing disposal costs of wastage. There appears to be no logical reason why these products are still widely used. Could it be that the alternative water-based liquid coatings have failed to fulfil their promise to offer a viable alternative, or is it simply a reluctance on the part of paint producers to let go of their longstanding industrial practices? Perhaps an example of this is to be found in the first abstracted article relating to Schiff base epoxy resins (p 2). More than fifty years ago, epoxy resins, which were developed during the war years as adhesives, became a target of the coatings industries. One of the first industrial applications was their use in food can linings where protection was provided against interaction with food, which contained chemicals
capable of attacking the tin protective layer on the steel can. It was soon apparent that this was a two-way transfer, with bisphenol A residues being leached from the protective film into the food, and thereby posing another human health hazard. In spite of this well documented criticism, more than 90% of all epoxy resins are still based on bisphenol A. The use of Schiff based replacement for bisphenol A is not only feasible as a potential safe alternative to BPA, but it also offers considerable improvements in both mechanical and chemical resistance properties. However, I am doubtful that industry will make much effort to introduce these new epoxy resins. Examination of the breakdown of coatings by electrochemical impedance spectroscopy has been widely used for locating the points where faults occur in a protective coating. There is, however, a problem when measurements are carried out in an electrolytic solution because this technique only locates through-the-coating faults when the bare metal is exposed to the electrolyte and the breakdown points are usually pinhole defects. A new technique (p 2-3) makes it possible to provide a wider investigation by introducing atomic force microscopy to locate weak points in the coatings structure, providing a useful new tool for the examination of polymer breakdown.
POWDER COATINGS POWDER COATINGS POWDER COATINGS POWDER COATINGS
FOCUS The usual batch of end of year reports are presented at this time of the calendar (p 3-5), and it appears that all of the major coatings producers had better returns in 2012 than in the previous year. A significant factor in their industrial finishes segment was the better than average growth of powder coatings, which out-performed all other industrial coatings technologies including water-borne finishes. Are we seeing the light at last? Sid Harris
TECHNICAL New Schiff base epoxy resins Epoxy resins are an important component of thermoset coatings, and 90% of the world’s epoxy resin production is based on the products of reaction between bisphenol A (BPA) and epichlorohydrin (ECH). Unfortunately, BPA can adversely affect human health and it has been found to leach from the internal coating of canned foods. An additional drawback of these resins is their poor thermal stability and flame resistance, which limits their applications in demanding areas, such as aerospace and the electronics industry. In recent years there has been a move away from the use of BPA, and the use of Schiff bases is an interesting development. It has been found that the presence of the azomethine group in a resin molecule improves adhesion of the coating to metal substrates and increases thermal stability. In addition, Schiff bases are good corrosion resistance inhibitors and act as good passivation agents for steel, copper and aluminium. It has also been found that epoxy resins which contain a complex metal ion in their structure have better thermal stability and very good mechanical properties while maintaining low processing temperatures. Antimicrobial 2
ON
POWDER
activity against various bacteria, yeast and fungi is a further property of Schiff base polymers. There are some drawbacks to epoxies containing azomethine linkages characterized by lack of toughness, high melting temperatures and brittleness, which make them unsuitable for many applications. Modifications to these resins have been found to improve these shortcomings without detracting from their desirable properties. There are various ways to do this, including: introduction of substituents into the mesogenic units, such as introducing a flexibility spacer between these units, or introducing a flexibility spacer which decouples the reactive end-functional group from the rigid mesogenic group; and the curing reaction of rigid-rod mesogenic epoxy monomers with aliphatic dicarboxylic acids. An article in Progress in Organic Coatings describes the work of researchers to obtain flexible, organic coatings with very good physical, mechanical and thermal properties by using synthesized Schiff base epoxy resins. The substances used to synthesize these Schiff base epoxy resins were: salicylaldehyde; 4,4’-diaminodiphenylether; 4,4’-diaminodiphenylmethane and benzyltrimethylammonium chloride (TEBA) used as a catalyst. Epichlorohydrin was added after distillation to remove solvents formed in the reactions. Properties of the synthesized resins were compared with a commercial epoxy EP6 and an amine hardener Epikure 3115. The article describes the preparation of both Schiff base compounds and the epoxy resins containing azomethine groups. This is followed by details of a wide range of test methods including NMR, DSC, Epoxy Equivalent EE, electrospray ionisation mass spectroscopy ESIMS, together with mechanical tests on the coatings. The coatings were then tested by applying them to glass to test hardness and steel to test
C O AT I N G S adhesion, flexibility and impact resistance. The tests showed that the coatings based on synthesized epoxy resins have very good adhesion to metal substrates. Cross-cut adhesion gave zero removal but the results of the pull-off testing varied with the structure of the Schiff base used and the final processing method. The best results were observed in the coating containing epoxy groups and many free hydroxyl groups. All other mechanical properties were good and comparable to the best of the standard epoxy systems. Additionally, these coatings have good thermokinetic properties. Article entitled “Organic Coatings Based on New Schiff Base Epoxy Resins” by researchers at Polish Universities and Engineering Institutes. Original Source: Progress in Organic Coatings, Jul-Aug 2013, 76 (7-8), 1040-1045 (Website: http://www.sciencedirect.com) © Elsevier BV 2013
Local impedance spectra of organic coatings A brief article on the use of an atomic force microscope (AFM) based approach to local impedance spectroscopy of organic coatings is another evaluation by researchers in Poland. Electrochemical impedance spectroscopy became one of the main tools for non-destructive evaluation of organic coatings making it possible to follow the changes occurring within the film as well as those occurring at the film/substrate interface. However, many of these tests have to be carried out in an electrolyte, which is not always convenient when they are only able to record through coating to bare metal defects, such as pinholes in the film. The researchers performed their investigation on an epoxy coating deposited on a carbon steel substrate and cured by UV radiation. Tests were carried out in topographical profile to compare impedance methods with and without the support of the AFM set-up. SEPTEMBER 2013
IS FUNDAMENTAL RESEARCH BEING OVERLOOKED?
SEPTEMBER 2013 In this issue
TECHNICAL
2-3
New Schiff base epoxy resins Local impedance spectra of organic coatings
INDUSTRY NEWS
3-5
Argex strengthens collaboration with PPG MBG Metallbeschichtung Gerstungen converts waste coating powders into heat PPG delivers record 2Q 2013 results
NEW PRODUCTS
5-6
Interpon low solar absorption powder coatings Scientists develop new colour for British Army
MARKETS
6-8
Latin American paint and coatings market rebounds Global green solvents & bio solvents market to reach $6.5 bn by 2018: MarketsandMarkets
EVENTS
AN INTERNATIONAL NEWSLETTER MONITORING TECHNICAL AND COMMERCIAL DEVELOPMENTS IN POWDER COATINGS ISSN 1364–5439
8
It has long been a contention of researchers in academic institutions that industry is reluctant to adopt their new developments until it is forced to by economic factors or increasing environmental pressures. Nowhere is this reluctance more apparent than in the coatings industry and most particularly in the field of industrial coatings. This is typified by the fact that solvent-based coatings are still widely entrenched in applicators’ workshops, despite criticisms of fire hazard, toxicity, high overspray wastage, and the everincreasing disposal costs of wastage. There appears to be no logical reason why these products are still widely used. Could it be that the alternative water-based liquid coatings have failed to fulfil their promise to offer a viable alternative, or is it simply a reluctance on the part of paint producers to let go of their longstanding industrial practices? Perhaps an example of this is to be found in the first abstracted article relating to Schiff base epoxy resins (p 2). More than fifty years ago, epoxy resins, which were developed during the war years as adhesives, became a target of the coatings industries. One of the first industrial applications was their use in food can linings where protection was provided against interaction with food, which contained chemicals
capable of attacking the tin protective layer on the steel can. It was soon apparent that this was a two-way transfer, with bisphenol A residues being leached from the protective film into the food, and thereby posing another human health hazard. In spite of this well documented criticism, more than 90% of all epoxy resins are still based on bisphenol A. The use of Schiff based replacement for bisphenol A is not only feasible as a potential safe alternative to BPA, but it also offers considerable improvements in both mechanical and chemical resistance properties. However, I am doubtful that industry will make much effort to introduce these new epoxy resins. Examination of the breakdown of coatings by electrochemical impedance spectroscopy has been widely used for locating the points where faults occur in a protective coating. There is, however, a problem when measurements are carried out in an electrolytic solution because this technique only locates through-the-coating faults when the bare metal is exposed to the electrolyte and the breakdown points are usually pinhole defects. A new technique (p 2-3) makes it possible to provide a wider investigation by introducing atomic force microscopy to locate weak points in the coatings structure, providing a useful new tool for the examination of polymer breakdown.
POWDER COATINGS POWDER COATINGS POWDER COATINGS POWDER COATINGS
FOCUS The usual batch of end of year reports are presented at this time of the calendar (p 3-5), and it appears that all of the major coatings producers had better returns in 2012 than in the previous year. A significant factor in their industrial finishes segment was the better than average growth of powder coatings, which out-performed all other industrial coatings technologies including water-borne finishes. Are we seeing the light at last? Sid Harris
TECHNICAL New Schiff base epoxy resins Epoxy resins are an important component of thermoset coatings, and 90% of the world’s epoxy resin production is based on the products of reaction between bisphenol A (BPA) and epichlorohydrin (ECH). Unfortunately, BPA can adversely affect human health and it has been found to leach from the internal coating of canned foods. An additional drawback of these resins is their poor thermal stability and flame resistance, which limits their applications in demanding areas, such as aerospace and the electronics industry. In recent years there has been a move away from the use of BPA, and the use of Schiff bases is an interesting development. It has been found that the presence of the azomethine group in a resin molecule improves adhesion of the coating to metal substrates and increases thermal stability. In addition, Schiff bases are good corrosion resistance inhibitors and act as good passivation agents for steel, copper and aluminium. It has also been found that epoxy resins which contain a complex metal ion in their structure have better thermal stability and very good mechanical properties while maintaining low processing temperatures. Antimicrobial 2
ON
POWDER
activity against various bacteria, yeast and fungi is a further property of Schiff base polymers. There are some drawbacks to epoxies containing azomethine linkages characterized by lack of toughness, high melting temperatures and brittleness, which make them unsuitable for many applications. Modifications to these resins have been found to improve these shortcomings without detracting from their desirable properties. There are various ways to do this, including: introduction of substituents into the mesogenic units, such as introducing a flexibility spacer between these units, or introducing a flexibility spacer which decouples the reactive end-functional group from the rigid mesogenic group; and the curing reaction of rigid-rod mesogenic epoxy monomers with aliphatic dicarboxylic acids. An article in Progress in Organic Coatings describes the work of researchers to obtain flexible, organic coatings with very good physical, mechanical and thermal properties by using synthesized Schiff base epoxy resins. The substances used to synthesize these Schiff base epoxy resins were: salicylaldehyde; 4,4’-diaminodiphenylether; 4,4’-diaminodiphenylmethane and benzyltrimethylammonium chloride (TEBA) used as a catalyst. Epichlorohydrin was added after distillation to remove solvents formed in the reactions. Properties of the synthesized resins were compared with a commercial epoxy EP6 and an amine hardener Epikure 3115. The article describes the preparation of both Schiff base compounds and the epoxy resins containing azomethine groups. This is followed by details of a wide range of test methods including NMR, DSC, Epoxy Equivalent EE, electrospray ionisation mass spectroscopy ESIMS, together with mechanical tests on the coatings. The coatings were then tested by applying them to glass to test hardness and steel to test
C O AT I N G S adhesion, flexibility and impact resistance. The tests showed that the coatings based on synthesized epoxy resins have very good adhesion to metal substrates. Cross-cut adhesion gave zero removal but the results of the pull-off testing varied with the structure of the Schiff base used and the final processing method. The best results were observed in the coating containing epoxy groups and many free hydroxyl groups. All other mechanical properties were good and comparable to the best of the standard epoxy systems. Additionally, these coatings have good thermokinetic properties. Article entitled “Organic Coatings Based on New Schiff Base Epoxy Resins” by researchers at Polish Universities and Engineering Institutes. Original Source: Progress in Organic Coatings, Jul-Aug 2013, 76 (7-8), 1040-1045 (Website: http://www.sciencedirect.com) © Elsevier BV 2013
Local impedance spectra of organic coatings A brief article on the use of an atomic force microscope (AFM) based approach to local impedance spectroscopy of organic coatings is another evaluation by researchers in Poland. Electrochemical impedance spectroscopy became one of the main tools for non-destructive evaluation of organic coatings making it possible to follow the changes occurring within the film as well as those occurring at the film/substrate interface. However, many of these tests have to be carried out in an electrolyte, which is not always convenient when they are only able to record through coating to bare metal defects, such as pinholes in the film. The researchers performed their investigation on an epoxy coating deposited on a carbon steel substrate and cured by UV radiation. Tests were carried out in topographical profile to compare impedance methods with and without the support of the AFM set-up. SEPTEMBER 2013