EoW January 2009

technical article

The relative dose per unit length was calculated by first multiplying the lamp power per unit length in each lamp by the corresponding residence time in that lamp. Then the doses per unit length were summed over the lamps in the system. The actual dose is significantly lower and is a function of the overall UV power conversion efficiency plus the size and distribution of the energy within the lamp sweet spot. For an equivalent UV dose, the DX-1000 series had the

Figure 4 ▲ ▲ : Comparison of ink viscosities

Figure 3 ▲ ▲ : Coloring tension vs speed

highest cure. The 751 inks had cure levels above 84% for ribbon applications up to 2,500m/min. The DX series had excellent cure at 3,000m/min with either two or three lamps, thus demonstrating its faster cure performance. In addition, DSM also performed MEK double rub tests to check actual ink cure performance. All samples survived more than 200 rubs, even when the RAU was 80%, again demonstrating excellent cures. In summary, a maximum colouring speed of 3,000m/min was achieved, while as reported in previous trials [4] , the maximum 0.9mm up-coat product speed was 900m/min. 2.3 Line drives To improve the responsiveness and accuracy of critical motors at high speeds, a separate motion controller is used to control the capstan, the dancer-spool rotation loops and the traverse motor, which controls the winding pitch and spool reversals. A PLC provides overall line coordination via Siemens Profibus or Allen-Bradley DeviceNet™ for the motion controller, the UV lamp system, the coater and other components. The result is a 10 to 1 improvement in control response times, which is critical during rapid ramps and to assure precise fibre winding. In addition, an automatic turning point correction is provided at reel flanges. An algorithm varies both pitch and reversal points to assure level winding.

nitrogen flow rate, the oxygen level, and the UV intensity through the centre tube to signal the need for centre tube changes to assure proper cure. At 3,000m/ min, three 10 inch long 600 W/inch lamps were used with type D lamps to provide excellent depth of cure. Optionally, an H bulb can be substituted for one D bulb to improve surface cure. The use of 3 separate lamps also allows a 10 to 1 range in UV power level during ramp up to match the required UV dose with speed. A single centre tube is inserted from above through all 3 UV lamps, which are mounted together on a slide that moves outwards to facilitate tube changes. The UV design was verified via extensive testing and curing level measurements using the DSM 751 and DX-1000 series inks. FTIR cure measurements were provided by DSM Desotech Inc for samples that were made over a range of speeds using two or three 600W/Inch Fusion lamps at full power. The Percent Reacted Acrylate Unsaturation (ie % RAU) results presented in Figure 6 are an average of several colours, because the ±3% accuracy of individual readings. These results demonstrate the high-speed capability of the acrylate coating-curing process. The UV cure is a function of the relative UV dose, which in turn is a function of the lamp power levels, the number of lamps and the line speed.

To allow optimisation of the internal die dimensions, a one dimensional die flow model was created. The model assumes Newtonian flow at any given cross-section, but allows the viscosity to vary with the average shear rate at that section. A Carreau-Yasuda model in combination with an Arrhenius equation was utilised to define viscosity as a function of tempera- ture and shear rate. The fibre tension and the pressure within the die are then calculated as illustrated in Figure 5 for a given coloured fibre diameter, line speed and temperature. Note the extra tension build-up within the exit die as the fibre accelerates the acrylate creating high pressure, which provides centering forces to assure a uniform coating. The manifold length was shorter than used in fibre coating, but longer than used in a typical colouring die to enhance ink recirculation, temperature uniformity and to create moderate fibre tension at high speeds. The maximum 1.7 N tension at 3,000m/min only exposes the fibre to 0.14 GPa [20 kpsi] stress, which is 20% of typical 0.69 GPa [100 kpsi] proof test levels. This moderate tension minimises the amplitude of fibre vibrations within the UV lamp system. The simple design also facilitates die cleaning and string-up. 2.2 UV curing

Development focused upon inert atmosphere control and the tracking of an efficient powerful UV curing lamp system. The new Fusion UV Systems Light Hammer® 10 electronic power supplies provide continuously variable DC power from 35% to 100%. improved magnetron and lamp life plus significantly reduced power supply weight to facilitate maintenance. Instrumentation is provided to measure the The result is

Figure 5 ▼ ▼ : Die characteristics

Figure 6 ▼ ▼ : Percent cure via FTIR vs relative dose

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EuroWire – January 2009