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New polymers sustain powder growth
FOCUS ON P O W D E R C O AT I N G S A MONTHLY REPORT FROM SID HARRIS JANUARY 2004
NEW POLYMERS SUSTAIN POWDER GROWTH
In this issue
TECHNICAL
2-5
Selective diisocyanate building blocks Novel UV curable powder coatings Low temperature curing polyurethane powder coatings
INDUSTRY NEWS
5-7
Distribution agreement: DuPont targets UK and Ireland market Tigerwerk invests €14 M in powder coatings R&D centre Akzo Nobel Coatings remains in Feuerbach
MARKETS
7
CEPE: stable markets in Asia A profile of the Italian paint industry
EVENTS
AN INTERNATIONAL NEWSLETTER MONITORING TECHNICAL AND COMMERCIAL DEVELOPMENTS IN POWDER COATINGS ISSN 1364–5439
7-8
Developments at DSM extend beyond the routine tasks of improving the performance of existing commercial powder grade polyesters and the first abstracted article describes an interesting exercise in polymer architecture, whereby hydroxylated polyesters are endcapped with primary and tertiary isocyanate groups, to give a fast and simple method of producing polycarbamate/urea dendrimers suitable for use in powder coatings. While the results of the tests outlined in the article were not entirely successful they point the way to the potential of polymer systems with designed structures, in powder coatings. It seems that most of the technical papers and articles published in the past few months have related to some aspect of polymer development and much of this is concerned with UV curing powder systems. In the continuing work to reduce the cost of UV curable binders, the use of allylic rather than acrylic compounds has received considerable attention. The second abstracted article describes systems produced from combinations of unsaturated polyesters and allylic ethers. My own early experiences with allylic compounds have caused me to
treat them with considerable caution due to their lachrymatory effect. In the work described it is claimed that the formation of unpleasant by-products, such as acrolein, can be prevented by control of reaction conditions. The end products are suitable for use in powder coatings giving good low temperature cure and good storage stability. The third abstract is another step in the development of low temperature curing polyurethane powder coatings. Researchers at Bayer have produced a new powder grade isocyanate crosslinker that is blocked by diethyl malonate. It is claimed that curing temperatures as low as 130°C are possible, although no reference is made to its ease of processing nor to its storage stability. The final abstract relates to the causes of breakdown in reinforced concrete structures strengthened by steel bars coated with fusion bonded epoxy powder coatings. I found this paper to be interesting because it sought to explain the reasons why I experienced problems in some severe environments, during the mid eighties. I am still convinced that the basic fault lies in the poor resistance of bis-A epoxies to dilute mineral acids and water
POWDER COATINGS POWDER COATINGS POWDER COATINGS POWDER COATINGS
F O C U S which are most corrosive in the hot, humid marine environments that prevail in the Gulf States and Southern Florida, and I prefer systems that employ epoxy novolacs. I would draw readers’ attention to the call for papers for the formulators’ technical conference to be held in conjunction with Powder Coating 2004 during September. Although time is short to meet the deadline for submission of abstracts, I will assist any interested authors to comply with the organizer’s conditions. According to a CEPE report many European coatings manufacturers are moving their facilities to the growth areas of Eastern Europe and Asia. There is also a trend to move into the Russian market. It is often claimed that the reason for the poor profitability of European coating producers is the high cost of labour. I do not believe that this is the prime factor. The pressure from bureaucrats in Brussels has had a far more devastating effect on company profits and efficiency by forcing them to employ an army of supervisory staff, to instigate and enforce restrictive legislation that erodes profitability to a much greater extent than the cost of employing gainful production workers. Sid Harris
TECHNICAL Selective diisocyanate building blocks New perspectives for dendrimers and coating binders are outlined in a recent paper describing the research and development carried out by Benthem et al at DSM. Using zirconium (IV) salts as catalyst, the reaction of a diisocyanate carrying one tertiary
2
O N
POWDER
and one primary isocyanate group (IMCI, DIMP) with alcohols can be conducted with complete regioselectivity. This unique selectivity enables the use of a diisocyanate building block in unprecedented ways. Incomplete regioselectivity of diisocyanates, as commonly encountered in currently commercial types, like IPDI and TDI, inevitably leads to polydisperse products in reaction with polyols. The ultimate monodisperse polymer architecture, dendrimers, can now be made in a facile, straightforward manner using IMCI as the ideal diisocyanate building block. Coating applications of this unique building block are not restricted to these perfect branching polymers, but also include isocyanatefunctional coating resins. Without any increase in polydispersity, hydroxyl-functional polyesters can be end-capped with the IMCI diisocyanate and subsequently serve as a crosslinker in powder coatings. A difference in the reactivity between two isocyanate groups is required for a number of reasons: efficient use of the building block would reduce cost; decreasing the polydispersity of polyurethane resins would improve performance; while a decrease in the level of isocyanate volatiles in end products would ensure safer handling. Controlling the reactivity of each isocyanate group at each reaction stage when using the diisocyanate as a building block is termed regioselectivity, and ideally the first isocyanate group should be introduced in a first reaction under controlled conditions that suppress the reaction of the second isocyanate group. The second group could then be used in a separate reaction under different control conditions. In practice, however, there is no ideally selective diisocyanate and control of one reaction will inevitably lead to some reaction by the other group. An example of this is the use of
C OAT I N G S diisocyanates in crosslinking hydroxyl functional polyesters or polyacrylates under heat curing conditions. In these cases, the volatility of the diisocyanates usually prohibits their direct use, and the diisocyanates are commonly first trimerized to isocyanurates, which are much less volatile. This trimerization adversely affects the cost since about half of the costly isocyanate groups are sacrificed in this process. Additionally, in reaction with hydroxyl groups some diisocyanate molecules will react twice while others will not react at all. These doubly reacted diisocyanate molecules lead to higher molar mass or broader molecular weight distribution while unreacted diisocyanate molecules may pose a possible health threat. A commonly used cycloaliphatic diisocyanate has been widely examined with respect to its regioselectivity to alcohol addition reaction. Isophorone diisocyanate consists of two stereoisomers and both isomers have one primary and one secondary isocyanate group. These show little difference in their rate of reaction with primary alcohols and, to achieve higher regioselectivity, widely different reactivity rates are required in the diisocyanate molecules. This study was, therefore, based upon IMCI (3,4-isocyanatomethyl-1methyl-cyclohexylisocyanate), which was introduced by Bayer in the early 1990s for use as an unblocked powder coating crosslinker in trimerized form. IMCI has a predominant isomer with an accessible primary isocyanate group and a low reactivity tertiary isocyanate which prompted Bayer to consider the use of trimerized IMCI as a powder coating crosslinker in unblocked form that was largely unaffected during hot melt extrusion. Another diisocyanate, DIMP (1,4-diisocyanato-4-methylpentane) was synthesized for this study and represents one of the
JANUARY 2004
NEW POLYMERS SUSTAIN POWDER GROWTH
In this issue
TECHNICAL
2-5
Selective diisocyanate building blocks Novel UV curable powder coatings Low temperature curing polyurethane powder coatings
INDUSTRY NEWS
5-7
Distribution agreement: DuPont targets UK and Ireland market Tigerwerk invests €14 M in powder coatings R&D centre Akzo Nobel Coatings remains in Feuerbach
MARKETS
7
CEPE: stable markets in Asia A profile of the Italian paint industry
EVENTS
AN INTERNATIONAL NEWSLETTER MONITORING TECHNICAL AND COMMERCIAL DEVELOPMENTS IN POWDER COATINGS ISSN 1364–5439
7-8
Developments at DSM extend beyond the routine tasks of improving the performance of existing commercial powder grade polyesters and the first abstracted article describes an interesting exercise in polymer architecture, whereby hydroxylated polyesters are endcapped with primary and tertiary isocyanate groups, to give a fast and simple method of producing polycarbamate/urea dendrimers suitable for use in powder coatings. While the results of the tests outlined in the article were not entirely successful they point the way to the potential of polymer systems with designed structures, in powder coatings. It seems that most of the technical papers and articles published in the past few months have related to some aspect of polymer development and much of this is concerned with UV curing powder systems. In the continuing work to reduce the cost of UV curable binders, the use of allylic rather than acrylic compounds has received considerable attention. The second abstracted article describes systems produced from combinations of unsaturated polyesters and allylic ethers. My own early experiences with allylic compounds have caused me to
treat them with considerable caution due to their lachrymatory effect. In the work described it is claimed that the formation of unpleasant by-products, such as acrolein, can be prevented by control of reaction conditions. The end products are suitable for use in powder coatings giving good low temperature cure and good storage stability. The third abstract is another step in the development of low temperature curing polyurethane powder coatings. Researchers at Bayer have produced a new powder grade isocyanate crosslinker that is blocked by diethyl malonate. It is claimed that curing temperatures as low as 130°C are possible, although no reference is made to its ease of processing nor to its storage stability. The final abstract relates to the causes of breakdown in reinforced concrete structures strengthened by steel bars coated with fusion bonded epoxy powder coatings. I found this paper to be interesting because it sought to explain the reasons why I experienced problems in some severe environments, during the mid eighties. I am still convinced that the basic fault lies in the poor resistance of bis-A epoxies to dilute mineral acids and water
POWDER COATINGS POWDER COATINGS POWDER COATINGS POWDER COATINGS
F O C U S which are most corrosive in the hot, humid marine environments that prevail in the Gulf States and Southern Florida, and I prefer systems that employ epoxy novolacs. I would draw readers’ attention to the call for papers for the formulators’ technical conference to be held in conjunction with Powder Coating 2004 during September. Although time is short to meet the deadline for submission of abstracts, I will assist any interested authors to comply with the organizer’s conditions. According to a CEPE report many European coatings manufacturers are moving their facilities to the growth areas of Eastern Europe and Asia. There is also a trend to move into the Russian market. It is often claimed that the reason for the poor profitability of European coating producers is the high cost of labour. I do not believe that this is the prime factor. The pressure from bureaucrats in Brussels has had a far more devastating effect on company profits and efficiency by forcing them to employ an army of supervisory staff, to instigate and enforce restrictive legislation that erodes profitability to a much greater extent than the cost of employing gainful production workers. Sid Harris
TECHNICAL Selective diisocyanate building blocks New perspectives for dendrimers and coating binders are outlined in a recent paper describing the research and development carried out by Benthem et al at DSM. Using zirconium (IV) salts as catalyst, the reaction of a diisocyanate carrying one tertiary
2
O N
POWDER
and one primary isocyanate group (IMCI, DIMP) with alcohols can be conducted with complete regioselectivity. This unique selectivity enables the use of a diisocyanate building block in unprecedented ways. Incomplete regioselectivity of diisocyanates, as commonly encountered in currently commercial types, like IPDI and TDI, inevitably leads to polydisperse products in reaction with polyols. The ultimate monodisperse polymer architecture, dendrimers, can now be made in a facile, straightforward manner using IMCI as the ideal diisocyanate building block. Coating applications of this unique building block are not restricted to these perfect branching polymers, but also include isocyanatefunctional coating resins. Without any increase in polydispersity, hydroxyl-functional polyesters can be end-capped with the IMCI diisocyanate and subsequently serve as a crosslinker in powder coatings. A difference in the reactivity between two isocyanate groups is required for a number of reasons: efficient use of the building block would reduce cost; decreasing the polydispersity of polyurethane resins would improve performance; while a decrease in the level of isocyanate volatiles in end products would ensure safer handling. Controlling the reactivity of each isocyanate group at each reaction stage when using the diisocyanate as a building block is termed regioselectivity, and ideally the first isocyanate group should be introduced in a first reaction under controlled conditions that suppress the reaction of the second isocyanate group. The second group could then be used in a separate reaction under different control conditions. In practice, however, there is no ideally selective diisocyanate and control of one reaction will inevitably lead to some reaction by the other group. An example of this is the use of
C OAT I N G S diisocyanates in crosslinking hydroxyl functional polyesters or polyacrylates under heat curing conditions. In these cases, the volatility of the diisocyanates usually prohibits their direct use, and the diisocyanates are commonly first trimerized to isocyanurates, which are much less volatile. This trimerization adversely affects the cost since about half of the costly isocyanate groups are sacrificed in this process. Additionally, in reaction with hydroxyl groups some diisocyanate molecules will react twice while others will not react at all. These doubly reacted diisocyanate molecules lead to higher molar mass or broader molecular weight distribution while unreacted diisocyanate molecules may pose a possible health threat. A commonly used cycloaliphatic diisocyanate has been widely examined with respect to its regioselectivity to alcohol addition reaction. Isophorone diisocyanate consists of two stereoisomers and both isomers have one primary and one secondary isocyanate group. These show little difference in their rate of reaction with primary alcohols and, to achieve higher regioselectivity, widely different reactivity rates are required in the diisocyanate molecules. This study was, therefore, based upon IMCI (3,4-isocyanatomethyl-1methyl-cyclohexylisocyanate), which was introduced by Bayer in the early 1990s for use as an unblocked powder coating crosslinker in trimerized form. IMCI has a predominant isomer with an accessible primary isocyanate group and a low reactivity tertiary isocyanate which prompted Bayer to consider the use of trimerized IMCI as a powder coating crosslinker in unblocked form that was largely unaffected during hot melt extrusion. Another diisocyanate, DIMP (1,4-diisocyanato-4-methylpentane) was synthesized for this study and represents one of the
JANUARY 2004