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Title: The physical and structural changes throughout the drying of solvent based inks
Author: Chapman, Christopher
Awarding Body: Swansea University
Current Institution: Swansea University
Date of Award: 2011
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Drying is a critical step within the printing process of a solvent-based ink. This provides the means of generating a solid film from the fluid which has been printed. The drying process can determine the rate of evaporation and has a definitive effect upon the quality of the final film. Previous research has provided a qualitative understanding of polymer-solvent systems, but now that boundaries are being pushed, driven by practical and commercial applications, a (quantitative understanding of the processes is required. The work reported here is designed to provide an understanding of the physical and structural processes involved within a drying solvent-polynier- pigment system. The research focuses upon the conventional solvent systems but the techniques and methodologies could be applied to water-based systems. The work has attempted to observe and analyse the structural changes, such as the gelation process, throughout the drying system by means of rheological tests, as well as the physical changes (eg. solvent loss) by use of Fourier Transform Infrared Spectroscopy (FTIR) and Multi Speckle Diffusing Wave Spectroscopy (MS-DWS). A number of parameters were varied to understand their influence on the processes, in particular the polymer resin (polyamide and nitrocellulose). The system was also tested with and without pigment and over a range of initial resin content. The polyamide system was a single solvent system, whereas the nitrocellulose system was a multiple solvent system. Using the results from the experiments carried out, combined plots of diffusion coefficient, viscoelasticity and molecular movement for the polyamide and nitrocellulose systems are produced describing the complete process of drying in solvent- based ink systems. The two systems show fundamental differences in the way the structure changes throughout drying, with polyamide maintaining a fluidic structure throughout the drying process, gelating rapidly at higher polymer concentrations. The nitrocellulose system had a more gradual gelation process which in turn effects the diffusion process. Skinning is seen to occur rapidly, at a much earlier polymer concentration. The lots show the decrease in diffusion coefficient with the increase in viscoelasticity. The rate at which this happens is greater for the surface than the bulk. The concentration at which this begins, decreases with increased capillary number, due to the film becoming dominated by viscous forces rather than surface tension. The polyamide system, with an extended period of low viscoelasticity (low Ca) allows a longer period for potential mass transfer of solute, whereas nitrocellulose does not. The increase in capillary number also reflects an increase in the rate of skinning at the surface, increasing the gap in polymer concentration required for a viscoelastic change to occur in the surface and bulk. It was found that the structural changes due to the gelation process of the polymer are critical to the physical changes, such as solvent loss, throughout the drying system. The polymer used within the system had a fundamental effect upon the process, with a different gelation process a critical factor. This gelation process occurs at different rates dependent on the initial resin concentration, especially at the surface. Increased resin concentration, increases the amount of skinning that occurs, hindering the solvent loss. The addition of a small percentage of pigment to the process does not have a substantial influence upon the gelation process within the bulk, but increases the effect of skinning further and hindering solvent loss. These results and values are able to provide data to he applied to a (quantitative model to increase the knowledge and understanding of the processes involved throughout drying and the parameters that influence the process.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available