Low temperature cure powders based on DEM based crosslinker

FOCUS the 4% black formulations from around 30 for the control without additive to just above 35 at the 4% additive level. A marked increase in gloss to around 70% is shown when the additive level is raised to 5.3%. The haze level falls with additive dosage from 540 for the control to 440 at 3.5% additive, and down to around 150 at the 5.3% additive dosage. Jetness increases from around 245 for the control to almost 290 at the 5.3% dosage level. Equivalent jetness can be achieved at 1% pigment, which illustrates the difference in pigment wetting performance between the polyester resin and the polymeric dispersant. The trend to lower film thickness in powder coating gives problems of hiding power, particularly with white pigmented formulations. This has proved to be a limitation in matching the opacity of some solvent based paints. A series of tests were carried out on polyester based white powder coatings using the same binder system employed in the previous tests. An alternative dispersant was employed in these tests. Two different pigment loadings were considered with control systems containing 32.5% and 50% pigment. These controls show a big difference in yield point and plastic viscosity indicating the poor flow and levelling that is likely to occur at 50% pigment loading. The yield point of the 50% titanium dioxide control with added dispersant showed a very similar result to that of the 32.5% control and in practice much improved flow and levelling. Opacity measurements at different film thickness for the two formulations show that the highly pigmented formula has more hiding power for a given film thickness. Gloss, haze and levelling results also reinforce the requirement to optimize the dosage and pigment loading depending on the target specifications. Powder coating formulators have found that replacing lead FEBRUARY 2005

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chrome yellow pigments has given problems with regard to matching colour strength, hiding power, and gloss properties. This has prompted research into new pigments to provide alternative solutions to the problems. In this paper formulations were evaluated using a yellow pigment based on bismuth vanadate/organic yellow used as a lead chrome replacement for RAL 1003 shade. Although it is usual to involve combinations of pigments to achieve the required colour effect, these trials evaluated a single pigment to optimize the dispersion properties so that the formulating window could be broadened to cover two different crosslinking systems. The two binder systems were polyesters using crosslinker Araldite PT 910 and Primid XL552. Pigment was incorporated at 25%, 35% and 40% of total charge and the polymeric dispersant used in the black tests was added at levels ranging from 1.25% to 2.8%. It is necessary to incorporate the bismuth vanadate pigment at 25% pigment content to achieve full hide at 85 microns, which is a much higher level than that required for chrome yellow and typically leads to poor flow and levelling. Pigment content can be increased from the control 25% to 40% using the polymeric dispersant due to the viscosity reduction achieved in the extrusion process. Measurements of gloss properties show that a consistent increase in gloss is achieved at the lower pigment loadings. Significant improvements in levelling, opacity, and haze reduction were evidenced at higher pigmentation and thinner film build. The improvements were noted in both binder systems. Paper entitled “Improving Problem Formulations with the use of Polymeric Dispersants” by ID Maxwell, K Siddiqui and DN Cartidge of Noveon Specialty Additives, presented at ICE 2004 in Chicago on 27-29 Oct 2004. The proceedings are available on disc from the Federation of Societies for Coating Technology, 492 Norristown Road, Blue Bell, PA 19422-2350, USA. Fax: +1 610 940 0292

C O AT I N G S Low temperature cure powders based on DEM based crosslinker In a paper published twelve months ago, Bayer Material Science, reviewed a wide range of blocked isocyanates and more recent alternatives to the standard high temperature systems based on ε-caprolactam. At that time, the use of diethyl malonate was given only a brief mention as a material capable of deblocking at temperatures below 140°C. Diethyl malonate (DEM) has been employed for some time in liquid coatings to achieve low temperature cure with improved adhesion on various substrates. Recently Bayer has managed to develop a solid urethane crosslinker based on DEM. This unique new material is interesting due to the transesterification of the hydroxyl functional resins with the pendant ester groups present in the DEM crosslinker. The DEM blocked H12MDI crosslinker is supplied as off white flakes with a Tg of 54°C. In contrast to other blocking agents, DEM does not thermally deblock from the isocyanate, and when used as the sole curative for polyols the transesterification mechanism produces ethanol as a by-product, giving a textured finish caused by outgassing. The most promising outlet for the DEM blocked isocyanate crosslinker is as a fortifying agent in epoxy polyester hybrid powder coatings and in conjunction with other epoxy based curatives such as TGIC. A paper presented at Powder Coating 2004 describes the efforts by Bayer Material Sciences to utilize this material in low temperature thermal cure systems at addition levels of 1 and 2%. They show that the gel time is reduced progressively with increasing addition of the DEM crosslinker and there is an appreciable improvement in MEK rubs resistance and impact resistance. This trend is noticeable in both systems and it is implied that this additive may 3

FOCUS lower curing temperatures and times. Paper entitled “Formulating Low Temperature Cure Powder Coatings Using Diethyl Malonate Based Crosslinker” by Ramesh Subramanian, Thomas Facke, Eric Vidra and Larry Smedley of Bayer Material Science LLC, presented at Powder Coating 2004, held in Charlotte, NC on 20/21 September 2004. Bound copies of the conference papers are available from the organizers: The Powder Coating Institute, 2121 Eisenhower Avenue, Suite 401, Alexandria, VA 22314, USA

INDUSTRY NEWS Interpon launches revamped website Akzo Nobel’s Interpon Powder Coatings business has revamped its global website. The new-look site offers expanded content and increased options, as well as enhanced navigation and usability. In redesigning the website (www.interpon.com), the main objective was to improve the structure and navigation system to make information easier to find, while also adapting the new look to fit in with corporate guidelines. There is now a homepage for each of the business’ eight market sectors, allowing visitors to easily find information on each product, as well as the supporting technical information (datasheets, performance graphs and so on) which are now all contained in a single pdf document. The site also offers both a concise and complete guide to powder coatings, along with a coverage calculator, a special video and links to Interpon’s country specific sites (Full text). Akzo Nobel News and Views, 3 Dec 2004, (Akzo Nobel nv, PO Box 9300 6800 SB Arnhem, the Netherlands. Tel: +31 26 3665760. Fax: +31 26 3665850. Website: http://newsandviews.akzonobel.com)

DSM raise prices DSM Coating Resins has posted a 12% price increase for its Uralac line of polyester powder coating resins due to the rising 4

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cost of global feedstock, particularly NPG and PTA. The increase will take effect immediately. Feedstock prices are also expected to continue to escalate along with the aggressive demand.

only a full range of powder coatings but also technical and application support. It also operates the Powder Coating Academy programme, which gives users of powder coatings theoretical and practical training.

PPCJ, Polymers, Paint, Colour Journal, Nov 2004, 194 (4482), 4

DuPont Magazine, Dec 2004, (4), 4 (DuPont Magazine, DuPont de Nemours International SA, 2 Chemin du Pavillon, PO Box 50, CH1218 Grand-Saconnex, Geneva, Switzerland, Tel: +41 22 717 51 11, Website: http://www.dupont.com)

Jotun Powder Coatings registers price increases Jotun Powder Coatings has imposed a price hike of up to 9% for polyester-based products, 17% for epoxy-based products and 10% for epoxy-polyester hybridbased products in the Middle East and South East Asia markets, effective immediately. Its prices in Europe for epoxy-based products will be 12%, epoxypolyester hybrid-based products 7% and up to 4% for polyesterbased products. PPCJ, Polymers, Paint, Colour Journal, Nov 2004, 194 (4482), 4

Powder coatings. DSM invests in China DSM Eternal Resins plans to expand the production capacity for polyester powder coatings at the facility in Kunshan in China. Additional capacity is scheduled to come on-stream in 2H 2005. DSM aims to double turnover in China by 2008. Farbe und Lack, Dec 2004, 110 (12), 67 (in German)

Powder coating acquisition: DuPont Poland DuPont Poland has acquired Pol-sver Lakiery Proszkowe, located in Lodz. Pol-sver has been the distributor of DuPont Powder Coatings (DPC) products for over a decade and is today the leading importer in the Polish market. Poland is today the biggest powder coatings market in Central and Eastern Europe and will play an even more strategic role in the future through the recent European Union expansion. Pol-sver offers not

German Ecology award: DuPont Performance Coatings DuPont Performance Coatings was one of eight German companies and institutes awarded the Ecology Prize 2004 by the Federation of German Industry in the eco-friendly technologies category. The group joined forces to form a network called Thermoface to develop an innovative pretreatment for highquality medium-density fibreboard (MDF) under the leadership of the Institute for Wood Technology in Dresden. The ecologically compatible and user-friendly method allows the MDF surface to be smoothed and pretreated without dust prior to being coated with newly developed powder coatings, which cure at a low temperature. This significantly reduces workers’ exposure to sanding dust and makes possible the uniform application of coating, even on the edges. DuPont Magazine, Dec 2004, (4), 6 (DuPont Magazine, DuPont de Nemours International SA, 2 Chemin du Pavillon, PO Box 50, CH1218 Grand-Saconnex, Geneva, Switzerland, Tel: +41 22 717 51 11, Website: http://www.dupont.com)

NEW PRODUCTS New Engelhard pigments offer powder coater’s value, flexibility, new styling options Engelhard Corporation is selling an improved pigment, Cyclo, for powder coating formulations. This FEBRUARY 2005