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Consistency in metallic powder coatings
F O C US technique gives an understanding of how the matting technology responds to the chosen binder system, how small changes in matting agent affect the gloss level, and the matting agent level above which no noticeable reduction in gloss is observed. Hybrid formulations are given for a 50:50 hybrid and 60:40 polyester:epoxy unpigmented system using levels of 2,4,6 and 8% weight percent additions of matting agent. It is possible to prepare graphs showing the curves of gloss and gel time as a function of matting agent concentration. At the 50:50 ratio, an addition level of 4 – 5%, achieves a minimum at 40 sec gel time at 180°C with a gloss level of around 20%. When the 60:40 hybrid film is examined the gel time is again 40 sec at 180°C but the gloss level is only reduced to 20% at the 6% addition level. In the gloss range 30-80%, careful weighing control is necessary since a small change in matting agent level will produce a dramatic change in gloss. Although the gel times are faster as the level of matting agent is increased, this does not affect the overall smooth appearance of the cured coating. Tests have been carried out in different regions using local raw materials and different extruders and the results obtained were similar. Similar results were obtained when the stoving schedule of 200°C for 10 minutes was changed to 180°C for 15 minutes, and since the reactivity of the hybrid system is influenced by the reactivity of the selected polyester resin it is also possible to cure as low as 160°C. The storage stability of powder coatings containing the new matting additive was also evaluated. The initial gloss was compared with a sample stored at 40°C for four weeks and a sample stored at room temperature for one year. There NOVEMBER 2002
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were no deviations from the expected gloss levels. Paper entitled “New Matting Agent for Epoxy/Polyester Hybrids” by Todd Antenucci, Mae C Grant, Klaus Hoffmann and Carmelina Grob of Vantico Inc, presented at Powder Coating 2002 in Indianapolis on 23-24 Sep 2002. Bound copies of the conference papers available from the organizers, The Powder Coating Institute, Alexandria, VA, USA
Consistency in metallic powder coatings A cautionary account of the problems that can arise in the manufacture of powder coatings where metallic effects are incorporated is given in a paper by Richard Sammel of Morton Powder Coatings. Metals and metallic effect pigments that can be included in powder coatings are: aluminium; brass; stainless steel; copper, mica and zinc. Incorporating the metal into the powder coating is not easy if the aesthetics of the metallic effect are to be maintained. Metallic effect pigments are typically flat platelets with a particle size from 5 to 20 microns. When these are incorporated into liquid coatings, the platelets orient horizontally to provide the metallic effect. If these metallic pigments are added prior to the extrusion or fine grinding stages of powder coating manufacture they lose their lustre and the metallic effect is diminished, due to the fragility of the flat platelets and the high shear forces generated during extrusion and fine grinding. The most common method to incorporate metallic pigments is to dry blend them with a fine powder coating base. This dry blend process is relatively simple and inexpensive and gives a coating with an attractive metallic finish. They do, however, give problems during application, exhibiting dry edges; inconsistent colour and appearance in Faraday cage areas; colour drift during a production run or at shift change; colour shift in the reclaim,
C O AT I N G S and smearing of the pigment on application equipment. In addition, sparking can occur with the risk of fire. During electrostatic application the charge delivered to each component differs and so does the trajectory of these particles due to their shape and specific gravity. These are all problems associated with the heterogeneous blending of an organic powder coating and an inorganic pigment. While these dry blends can be used they are generally sprayed to waste to ensure consistent colour and appearance. A recommended method for improving the consistency of metallic powder coatings is to physically attach or bond the pigment platelets to the powder coating particles. This is achieved by intensive mixing at a temperature near to the softening point of the powder coating. It seems that these bonded particles possess a single, consistent set of properties for both specific gravity and chargeability which is insensitive to changes in application variables, and the powder can be reclaimed. There does seem to be some inconsistency with this bonding process and some powders which claim to be bonded are found to be not entirely suitable. The paper describes tests carried out on three samples of identical composition but different methods of incorporation. Each sample was sent through a cyclone and then tested for opacity compared to the virgin material to determine the amount of metallic pigment lost in the cyclone. The dry blended material lost 15% opacity while the correctly bonded powder showed no loss of opacity. The third sample which claimed to be bonded lost 4% of opacity. A similar evaluation was carried out with a chrome-like powder coating and the differences were measured by variation in the Distinctness of Image test. The differences 5
F O C U S between the three samples were again apparent. It is concluded that there are significant differences even between products that are claimed to be fully bonded and the end user should be made aware of possible variations in quality of products from different suppliers. Paper entitled “Reaching Quality and Consistency in Metallic Powder Coatings” by Richard Sammel of Morton Powder Coatings, USA, presented at PCE 2002 in Nuremberg on 15-17 Jan 2002. Bound copies of the conference papers available from the organizers: Vincentz Verlag, Schiffgraben 43, 30175 Hannover, Germany
Modern pretreatment of aluminium and other metals While powder coatings are recognized as environmentally safe coatings it is just as important to ensure that these materials are applied to surface treatments that are themselves environmentally compatible. The need for pretreatment on metal substrates, particularly over mixed metal parts, is essential to optimize the highest corrosion resistance on parts used in the automotive and architectural fields. It is also necessary that the pretreatment systems should not be carcinogenic nor have toxic potential, so that the use of chromating systems is prohibited in most major regions. Henkel have developed a range of chrome-free systems for the treatment of aluminium and zinc coated steel and these are described in a paper by Ulrich Juptner. Zinc phosphate treatment is considered the normal method for most metal substrates but is not entirely adequate for certain mixed metal applications. The modern systems for mixed metal applications are based on complex titanium and/or zirconium fluorides. On light metal surfaces a conversion coating is formed containing insoluble titanium and/or zirconium oxides. These systems also contain an organic component.
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A typical chrome-free pretreatment for aluminium is an eight stage process comprising: alkaline cleaning; alkaline etch cleaning; rinse; deoxidizing; rinse; conversion; rinse and drying with hot air. At one plant this treatment is applied to some 40,000 pieces of automotive components during a 3-shift process followed by application of a high gloss powder coating, which is highly sensitive to surface defects and marks in the pretreatment. The quality check includes adhesion testing and stone chip resistance and is shown to be equivalent to chromating. The process is also used to pre-treat more than 3000 aluminium wheels per day. An advantage of the new process over chromating is appearance since the pretreatment layer is not visible on the metallic surface, and additionally the process is cheaper. Architectural applications is another outlet for chrome-free pretreatment which has received Qualicoat, GSB compliance certification. A chrome-free pretreatment has also been designed for zinc surfaces in both the automotive and architectural industries and has been shown to give excellent corrosion protection. Magnesium components are widely used in the automotive industry and these conversion coatings offer a realistic alternative to standard yellow chromating. The conversion coating is also suitable for post passivation after zinc phosphating in the pretreatment of mixed metal components. Examples are given of recommended pretreatment systems for each of the applications described in the paper. Paper entitled “Environmental Compatible Pre-treatment of Aluminium and other Metals for Powder Painting” by Ulrich Juptner of Henkel KGaA, Germany, presented at PCE 2002 in Nuremberg on 15-17 Jan 2002. Bound copies of the conference papers available from the organizers: Vincentz Verlag, Schiffgraben 43, 30175 Hannover, Germany
C O AT I N G S
INDUSTRY NEWS IG Pulvertechnik improves distribution in Hungary Swiss company IG Pulvertechnik improved the distribution conditions in Hungary and signed a contract with local company Agrohid which envisages the sale of IGP products across Hungary. Prior to this the powder coatings were primarily sold in Greater Budapest. Farbe und Lack, Oct 2002, 108 (10), 10 (in German)
Akzo Nobel Coatings in Spain The Spanish subsidiary of Akzo Nobel Coatings predicts a growth rate of between 3-4% for 2002. The company achieved a turnover of €185 M in 2001 and operates 3 factories near Barcelona. Farbe und Lack, Oct 2002, 108 (10), 11 (in German)
Govesan America withdraws powder coatings US company Govesan America recently committed itself to withdrawing those powder coatings which were falsely promoted to be free of heavymetals. Lead, cadmium and hexavalent chromium were detected in Govesan’s powder coatings. Around 5% of all powder coatings imported by Govesan will be affected by the measure. Farbe und Lack, Oct 2002, 108 (10), 11 (in German)
Powder coatings. Slovenian manufacturer plans to build factory in Germany Slovenian powder coatings manufacturer Color Powder
NOVEMBER 2002
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POWDER
were no deviations from the expected gloss levels. Paper entitled “New Matting Agent for Epoxy/Polyester Hybrids” by Todd Antenucci, Mae C Grant, Klaus Hoffmann and Carmelina Grob of Vantico Inc, presented at Powder Coating 2002 in Indianapolis on 23-24 Sep 2002. Bound copies of the conference papers available from the organizers, The Powder Coating Institute, Alexandria, VA, USA
Consistency in metallic powder coatings A cautionary account of the problems that can arise in the manufacture of powder coatings where metallic effects are incorporated is given in a paper by Richard Sammel of Morton Powder Coatings. Metals and metallic effect pigments that can be included in powder coatings are: aluminium; brass; stainless steel; copper, mica and zinc. Incorporating the metal into the powder coating is not easy if the aesthetics of the metallic effect are to be maintained. Metallic effect pigments are typically flat platelets with a particle size from 5 to 20 microns. When these are incorporated into liquid coatings, the platelets orient horizontally to provide the metallic effect. If these metallic pigments are added prior to the extrusion or fine grinding stages of powder coating manufacture they lose their lustre and the metallic effect is diminished, due to the fragility of the flat platelets and the high shear forces generated during extrusion and fine grinding. The most common method to incorporate metallic pigments is to dry blend them with a fine powder coating base. This dry blend process is relatively simple and inexpensive and gives a coating with an attractive metallic finish. They do, however, give problems during application, exhibiting dry edges; inconsistent colour and appearance in Faraday cage areas; colour drift during a production run or at shift change; colour shift in the reclaim,
C O AT I N G S and smearing of the pigment on application equipment. In addition, sparking can occur with the risk of fire. During electrostatic application the charge delivered to each component differs and so does the trajectory of these particles due to their shape and specific gravity. These are all problems associated with the heterogeneous blending of an organic powder coating and an inorganic pigment. While these dry blends can be used they are generally sprayed to waste to ensure consistent colour and appearance. A recommended method for improving the consistency of metallic powder coatings is to physically attach or bond the pigment platelets to the powder coating particles. This is achieved by intensive mixing at a temperature near to the softening point of the powder coating. It seems that these bonded particles possess a single, consistent set of properties for both specific gravity and chargeability which is insensitive to changes in application variables, and the powder can be reclaimed. There does seem to be some inconsistency with this bonding process and some powders which claim to be bonded are found to be not entirely suitable. The paper describes tests carried out on three samples of identical composition but different methods of incorporation. Each sample was sent through a cyclone and then tested for opacity compared to the virgin material to determine the amount of metallic pigment lost in the cyclone. The dry blended material lost 15% opacity while the correctly bonded powder showed no loss of opacity. The third sample which claimed to be bonded lost 4% of opacity. A similar evaluation was carried out with a chrome-like powder coating and the differences were measured by variation in the Distinctness of Image test. The differences 5
F O C U S between the three samples were again apparent. It is concluded that there are significant differences even between products that are claimed to be fully bonded and the end user should be made aware of possible variations in quality of products from different suppliers. Paper entitled “Reaching Quality and Consistency in Metallic Powder Coatings” by Richard Sammel of Morton Powder Coatings, USA, presented at PCE 2002 in Nuremberg on 15-17 Jan 2002. Bound copies of the conference papers available from the organizers: Vincentz Verlag, Schiffgraben 43, 30175 Hannover, Germany
Modern pretreatment of aluminium and other metals While powder coatings are recognized as environmentally safe coatings it is just as important to ensure that these materials are applied to surface treatments that are themselves environmentally compatible. The need for pretreatment on metal substrates, particularly over mixed metal parts, is essential to optimize the highest corrosion resistance on parts used in the automotive and architectural fields. It is also necessary that the pretreatment systems should not be carcinogenic nor have toxic potential, so that the use of chromating systems is prohibited in most major regions. Henkel have developed a range of chrome-free systems for the treatment of aluminium and zinc coated steel and these are described in a paper by Ulrich Juptner. Zinc phosphate treatment is considered the normal method for most metal substrates but is not entirely adequate for certain mixed metal applications. The modern systems for mixed metal applications are based on complex titanium and/or zirconium fluorides. On light metal surfaces a conversion coating is formed containing insoluble titanium and/or zirconium oxides. These systems also contain an organic component.
6
O N
POWDER
A typical chrome-free pretreatment for aluminium is an eight stage process comprising: alkaline cleaning; alkaline etch cleaning; rinse; deoxidizing; rinse; conversion; rinse and drying with hot air. At one plant this treatment is applied to some 40,000 pieces of automotive components during a 3-shift process followed by application of a high gloss powder coating, which is highly sensitive to surface defects and marks in the pretreatment. The quality check includes adhesion testing and stone chip resistance and is shown to be equivalent to chromating. The process is also used to pre-treat more than 3000 aluminium wheels per day. An advantage of the new process over chromating is appearance since the pretreatment layer is not visible on the metallic surface, and additionally the process is cheaper. Architectural applications is another outlet for chrome-free pretreatment which has received Qualicoat, GSB compliance certification. A chrome-free pretreatment has also been designed for zinc surfaces in both the automotive and architectural industries and has been shown to give excellent corrosion protection. Magnesium components are widely used in the automotive industry and these conversion coatings offer a realistic alternative to standard yellow chromating. The conversion coating is also suitable for post passivation after zinc phosphating in the pretreatment of mixed metal components. Examples are given of recommended pretreatment systems for each of the applications described in the paper. Paper entitled “Environmental Compatible Pre-treatment of Aluminium and other Metals for Powder Painting” by Ulrich Juptner of Henkel KGaA, Germany, presented at PCE 2002 in Nuremberg on 15-17 Jan 2002. Bound copies of the conference papers available from the organizers: Vincentz Verlag, Schiffgraben 43, 30175 Hannover, Germany
C O AT I N G S
INDUSTRY NEWS IG Pulvertechnik improves distribution in Hungary Swiss company IG Pulvertechnik improved the distribution conditions in Hungary and signed a contract with local company Agrohid which envisages the sale of IGP products across Hungary. Prior to this the powder coatings were primarily sold in Greater Budapest. Farbe und Lack, Oct 2002, 108 (10), 10 (in German)
Akzo Nobel Coatings in Spain The Spanish subsidiary of Akzo Nobel Coatings predicts a growth rate of between 3-4% for 2002. The company achieved a turnover of €185 M in 2001 and operates 3 factories near Barcelona. Farbe und Lack, Oct 2002, 108 (10), 11 (in German)
Govesan America withdraws powder coatings US company Govesan America recently committed itself to withdrawing those powder coatings which were falsely promoted to be free of heavymetals. Lead, cadmium and hexavalent chromium were detected in Govesan’s powder coatings. Around 5% of all powder coatings imported by Govesan will be affected by the measure. Farbe und Lack, Oct 2002, 108 (10), 11 (in German)
Powder coatings. Slovenian manufacturer plans to build factory in Germany Slovenian powder coatings manufacturer Color Powder
NOVEMBER 2002