Matching pigments and pumps

Transcription

1 Seite/Page: 1 Matching pigments and pumps The relationship between the effect pigment in a concentrate for a tinting scheme and the pump technology used in the dispenser is important. The right choices must be made to ensure a correct final colour. The functionality of effect pigment concentrates in dispensing machines Minna Hilkos* Viveca Lönnberg Eija Karjalainen Peter Wissling Demand for metallic effects has risen strongly since the end of the last decade. After a period of simplicity and minimalism in design, the millennium started a mega boom in elaborate trends, using innovative materials and special effects. Despite recent developments in the global economic climate, this taste for rich and decorative effects still has a strong influence. At present, there is a significant move towards softer tones with glowing and luminous effects. In today s dynamic and globalising markets, professional contractors and consumers alike are better informed and more demanding than ever. When selecting products and paints, consumers not only expect the latest trends in colours, but also demand a much wider choice to enable them to create many shades. And more and more important today, they expect to be able to choose from a wide range of materials and surfaces. This goes as far as requiring the addition of special effects into the colourant system in a dispensing machine. Tinting systems A tinting system is a tool for the rationalisation of colour management. In tinting-system design, the consumption of all colourants needs to be taken into account. Those used very little are not easily added into the system. They create practical challenges in dispensers in the long run. Commonly used in solid colours, these kinds of small consumption colourants are related to special colour-tone areas, such as reddish blue, bright orange, orange yellow, violet, Bordeaux and magenta. The special nature of these colourants needs to be considered when designing the colour system. Various special effects may today be added in a similar way, such as metallic, pearlescent, gold, silver and copper. The special colour-tone areas are dependent on the consumer s colour preferences and the paintapplication field.most commonly-used are metallic effects with aluminium pigments (used in automotive and industrial coatings applications) or pearlescent effects, with many hues such as gold, silver and bronze (used in decorative, plastic, leather and textile applications). One of the challenges with effect pigments is their sensitivity to shear forces. For example, mixing or pumping too intensively can easily damage these special pigments. If the particle is broken down during stirring and recirculation in the tinting machine, the final colour will not come out as expected. Variety of pump technologies The actual behaviour of the effect-pigment concentrates in various dispensing-machine technologies was tested and analysed. These machines are commonly based on gear, piston or bellow pump technologies; all these pump technologies were used in the tests. In total, six commonly used effect-pigment concentrates were tested. Two of these were concentrates producing an aluminium effect: one with finer aluminium pigment particles giving a smoother metallic effect and another with coarser aluminium pigment particles giving a rougher metallic effect. A further two were concentrates producing a silver or pearlescent effect, made with mica platelets coated with a semi-transparent layer of titanium dioxide and/or iron oxide. The last two were concentrates producing a bronze-gold effect: one made with copper powder and another made with mica platelet coated with titanium dioxide and metallic oxide pigment. Each effect pigment tested has its own characteristic particle-size distribution, as shown in Table 1. The performance of these effect-pigment concentrates in dispensing machines was tested over several months. Different parameters such as colour-shade performance, particle-size distribution, particle size and shape, viscosity change, rheological performance and dosing accuracy, were analysed during this time. An important part of the evaluation was a visual follow-up of the concentrate and its behaviour during testing in dispensing machines. The influence of the pigment concentrate on the lifetime of the pumps and parts of the dispenser was also evaluated. Colour performance The evaluation of colour performance was made before and after the testing in a dispenser using three colours: full shade, a mixture with magenta, and a mixture with blue. The colour difference was evaluated by de and colour-strength values. The aluminium-pigment concentrates showed clear differences in colour shade performance between the various pump technologies (see Figure 1 for de and Figure 2 for colour-strength values). The aluminium concentrates performed well in piston and bellow pump technologies without major differences in colour change between them. In all aluminium concentrates tested, de was below 0.5 and colour strength was below +2.5 %. In gearpump technologies, the aluminium concentrates created clear colour differences, with de reaching 2 and colour strength +23 %. The colour difference was less pronounced in mixtures with magenta and blue, where the colour difference decreased to a level of +4-7 %. The testing of the coarser aluminium-pigment concentrate was stopped in gear pump technologies some time after the start of the test, as the properties of the concentrate prevented the gear

2 Seite/Page: 2 pump from working properly. No test results are therefore reported in this case. The performance of the two pearlescent-pigment concentrates varied with pump technology. With the Pearlescent-A concentrate, de remained below 0.4 and colour strength below +7.5 % with the full-shade colour and below +1 % with magenta and blue mixtures. This shows that even if the pure pearlescent concentrate has been slightly harmed in all machines, the final colour may still be correctly produced due to other pigments in the final-colour formula. The Pearlescent B concentrate showed clear de and colour-strength differences when used in the piston-pump technology. In the bellow pump technology, Pearlescent B did not function very well, so we did not get a reliable test result. The Pearlescent B concentrate performed best in the gear-pump technology (see Figure 3 for de and Figure 4 for colour-strength values of Pearlescent-pigment concentrates). With the gold-bronze concentrate, all de values were below 1 and the colour difference was below +3 %. The de values for the gold concentrate were below 0.9 and colour strength was below +3 %. For the gold-bronze concentrate, the piston technology produced the best colouristic performance. With the bellow" technology, the gold concentrate did not work properly, so the test was not completed. From a colouristic-performance point of view, the best performing pump technology for the gold concentrate was the gear pump. Particle size distribution Particle-size distributions seemed to change slightly during the testing in dispensers. The number of small particles increased slightly after the testing. The change was least in the piston-pump technology and most in the gear-pump technology. Effect pigments can be damaged when shear forces that are too strong are applied to them. This can occur by using stirring blades with sharp edges or at too high a stir speed.shear force is also applied to effect pigments in dispensing machines when the concentrates are stirred during storage time. Storage can be quite long, so there is a potential for damage to the effect-pigment flakes. However, investigations in different dispensing-machine technologies have now revealed that the shear force applied to effect pigments is below the stated critical limit, so effect pigments are not damaged at all. This can be seen in a series of microscope images of a coarse aluminium pigment, which is known to be very sensitive to shear forces. Figure 5 shows the coarse aluminium before dispenser testing and Figure 6 after testing in the piston-pump technology. On the other hand, tests have shown that, in the longterm storage of effect-pigment concentrates in various dispensing machines, the rheology profile changes. This is possibly due to interactions between concentrate components and the surface chemistry of the effect pigment. Depending on the chemistry and interaction, wide variations in rheology change are possible. It has to be considered here also that effect pigments" particle sizes, the so-called d50 values, vary greatly. It is common to use effect pigments with d50 values lying between 10 µm and 45 µm. The differing surface areas then influence the potential chemical interactions. It is assumed that the higher the surface area (i.e. small d50 value) the greater the potential for chemical interaction and vice versa for small surface area (i.e. high d50 value). A change in the rheology has an impact on effect-pigment alignment and subsequently on colour performance. For effect pigments, colour is normally measured with multi-angle colorimeters. Angles of 25, 45 and 75 are considered to be important in the industry to allow the angle-dependant colour change to be judged. Lightness L* (for gold-bronze, gold and pearlescent pigments also a* and b*) differences below one unit at all angles are generally accepted as being invisible to the naked eye. Under these conditions it was found that the effect-pigment concentrates usually showed good colour stability. Viscosity change Viscosity change after testing in dispensers is an indicator of stability changes in the concentrate. If there was no change in viscosity, the result was good. If there was some viscosity change, problems such as drying or dripping were created. If the viscosity change was severe, the use of that dispenser was not recommended. The viscosity of the aluminium-pigment concentrates did not change in piston or bellow pump technologies. In the gearpump technology, the fine-aluminium concentrate caused dripping problems in the nozzles. The coarse aluminium could not be tested in the gear-pump technology.the Pearlescent-A concentrate performed well without viscosity change in the piston-pump technology. In the gear-pump technology, a dripping problem, caused by viscosity, was seen. In the bellow pump technology, Pearlescent A also created some viscosity changes. The gold concentrate had major viscosity problems. It was only possible to pump it in the gear-technology dispenser. The gold-bronze concentrate performed well without any viscosity changes in both piston and gear pump technologies and performed quite well in the bellow pump technology. Different pump technologies The overall behaviour of the concentrates not only takes the reported test results, such as colour shade performance, particle size distribution and viscosity change into account, but also the visual evaluation of them during the whole testing period. Thus the overall behaviour summarises the performance of the various effect-pigment concentrates in the different pump-technology dispensers. The overall behaviour of the effect-pigment concentrates tested in different pump technologies is illustrated in Figure 7. The comment Good behaviour, but needs attention means for example that the rheology is challenging and therefore recirculation is needed or that the dosing of the smallest amounts is inaccurate. Some problems occurred means for example that drying occurred, which can be solved in most cases with a well-functioning humidifier system. The gold and gold-bronze concentrates performed excellently in the gear-pump technology. As this technology has a recirculation system, it is appropriate for the Pearescent-B technology. Due to the risk of drying in nozzles, the Pearlescent-A and fine-aluminium concentrates can create dispensing problems when the gear-pump technology is used. The use

3 Seite/Page: 3 of coarse aluminium in the gear-pump technology is not recommended. Both the fine-aluminium and Pearlescent-A concentrates showed superior performance in the piston-pump technology. The coarse-aluminium and gold-bronze concentrates behaved well in the piston-pump technology. When using the gold bronze concentrate, it was important to take good care of the humidifier system, in order to avoid the drying of the nozzles. Pearlescent-B and gold-concentrates can also be used in the piston-pump technology, but effective performance cannot be guaranteed. Both aluminium concentrates performed without problems in the bellow pump technology. Pearlescent-A and goldbronze concentrates can also be used in the bellow pump technology, but they need some attention. The accuracy of dispensing small amounts of gold-bronze concentrate was not good. Pearlescent A easily dried in the nozzles and required the use of a humidifier system. Pearlescent-B and gold concentrates cannot be recommended for use in the bellow pump technology. Performance differences exist between various effectpigment concentrates in dispensers with differing pump technologies. The choice of effect pigment depends on the pump technology being used. Fine aluminium concentrate is at its best in piston and bellow pump technologies. A coarse aluminium concentrate is best suited for bellow pump technology. For the Pearlescent-A concentrate, piston-pump technology is the best. Pearlescent B, gold and gold-bronze concentrates all work well in gear-pump technology. Drying of the concentrates is also an important issue, so an effective humidifier system is a must with many of the effectpigment concentrates. Results at a glance» Design trends are demanding the increased use of effect pigments.» A study was made to find out the performance of a range of effect pigment concentrates with the different pump technologies used in the dispensers.» The different characteristics and behaviour of the concentrates makes it often necessary to match effect pigment and pump technology.» In the commercial use of effect-pigment concentrates as part of a retail-tinting system, other parameters such as colour matching, matching software and colour cards need to be taken into consideration. * Corresponding Author:Minna Hilkos, CPS Color Oy Tel minna.hilkos@cpscolor.com

4 Seite/Page: 4 Pigment concentrate Particle size distribution (µm) Fine aluminium Coarse aluminium Pearlescent A Pearlescent B Gold bronze Gold

5 Seite/Page: 5 Figure 7: the behaviour of various effect-pigment concentrates in different pump technologies

6 Seite/Page: 6 Figure 1: de values of fine and coarse Al in different pump technologies

7 Seite/Page: 7 Figure 2: colour strength % of fine and coarse Al in different pump technologies

8 Seite/Page: 8 Figure 3: de values of Pearlescent A and B in different pump technologies

9 Seite/Page: 9 Figure 4: colour strength % of Pearlescent A and B in different pump technologies

10 Seite/Page: 10 Figure 5: coarse Al before testingsource: Eckart GmbH, Peter Wissling

11 Seite/Page: 11 Figure 6: coarse Al after testingsource: Eckart GmbH, Peter Wissling