THIN FILM IWASTE MANAGEMENT Outcomes
This research has resulted in several improvements to contact cleaning efficiency while at the same time reducing the risk of damage and improving processability particulary in sheet form. Increasing the operational window of contact cleaning to remove submicron particles through surface modification. Nanocleen elastomer was designed particles down to 25nm in size from film surfaces during wide web coating. The
surface of a standard F3 roller is shown in Fig 1 while for comparison the surface of Nanocleen is shown in Fig 2
Figure 4. Diecut edge of a structured film after cleaning Autoflex – No Roller
Cleaning of small particles from Structured film . Contrast enhancement films used in LCD screen often have a grooved surface which can trap particles. Fig 3 shows the edge of a structured film which has been die cut to shape. A significant amount of particles remain both on the surface and within the grooves of the film. Fig 4 is the same section of film having been cleaned using a Teknek special elastomer roller.
Contact cleaning which does not reduce wettability. History has shown that many contact cleaning rollers reduce the surface energy of a film after cleaning. Teknek’s Nanocleen elastomer actually reduces the contact angle and actually increases wettability by removing the small particles. Contact angles for a polyester film before and after cleaning are shown in Figures 5 and 6.
Highest level of cleaning of 20 micron sheets of gloss /gloss TAC film without damage to or wrapping of films at speeds up to 40 m/min.
Figure 5. Polyester film before cleaning Autoflex + Nanocleen
types of forces involved in small particle adhesion including van der Waals and its associated forces, Electrostatic forces including coulombic and dielectrophoretic forces and molecular level forces such as hydrogen bonding. The equations defining each of these forces can be readily found in the literature. Each force involves several variables and the resulting model of a contact cleaning system is extremely complex.
In order to reduce the complexity, over the last few years Teknek have carried out a significant amount of empirical research into the key parameters highlighted by the theoretical work. We have developed our own test method to assess the ability of elastomers to detach particles from a surface that we call the Particle Pick Up (PPU) test. There was no industry standard test available to quantify this parameter. This test employs calibrated particles of different sizes, types and morphology and is used to monitor improvements in the cleaning performance of elastomers. This test, in addition to the standard analysis techniques of SEM, EDX and GCMS, is used on different formulations of elastomer to correlate properties both physical and chemical with cleaning performance.
By using in depth research into the theory of adhesion forces affecting small particles during deposition, substrate contact and detachment Teknek have been able to construct a model of a contact cleaning system. This model is supported by empirical research into the PPU of elastomers which enables the cleaning system to be tailored to optimise specific performance parameters for specific applications.
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Figure 6. Polyester film after cleaning with Nanocleen
REFERENCES 1 Kohli, R, Adhesion of small particles and innovative methods for their removal,Particles on Surfaces 7, Ed K L Mittal, 2002, VSP BV Utrecht. 2 Mittal, K.L., Ed Particles on Surfaces – Detection, Adhesion and Removal, 1995,Marcel Dekker, New York
3 Mittal, K.L., Ed Particles on Surfaces – Detection, Adhesion and Removal 5&6, 1999, VSP BV Utrecht 4 Mittal, K.L., Ed Particles on Surfaces – Detection, Adhesion and Removal 9, 2006, VSP, Leiden 5 Cardona, C and Giraldo, J, Ed, Thin Films and Small Particles, 1988, World Scientific Publishing Co, Singapore
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