Screen-printing is one of the oldest printing processes, yet its market share remains very limited due to its slower printing speeds compared to the other available processes. This is mainly because of the reciprocating motion of the squeegee upon the printing screen. In order for screen-printing to become more competitive, the concept of a high-speed continuous belt screen-printing press was developed. However, this will produce an increase in squeegee wear and friction of the squeegee upon the screen. For this reason, this work investigated the use of a roller squeegee that could rotate across the screen. It has been proven that screen-printing with a roller squeegee can be successfully achieved. Additionally, in terms of density and tone gain, these images were comparable to those produced with traditional blade squeegees. A numerical model has been developed to simulate the characteristics that will be encountered within the ink film when printing with a roller squeegee. Numerical simulations were run where the settings corresponded to the parameters utilised in experimental trials. Here, it was discovered that an increase in squeegee diameter will increase the ink film on the squeegee and will also increase the contact width of the screen upon the substrate. This will have the effect of increasing the pumping capacity of the squeegee, which will therefore increase the ink deposit. This was confirmed in the experimental trials. It was also shown that the locking of the squeegee increased the shear mechanism within the ink film, resulting in a reduction in the ink viscosity within the nip contact region. This had the effect of reducing the ink film thickness on the squeegee, which reduces the pumping capacity of the squeegee, thus producing a reduced ink deposit. Additionally, this work is the first method that has been able to estimate the height of the ink deposit for a range of halftone open areas where the results correspond almost identically to the actual printed heights of the prints obtained in experimental studies. This work has improved the fundamental understanding of the mechanics and the process physics within the ink transfer mechanism in the screen-printing process. Use of experimental and numerical models has resulted in new theories being developed that will further the knowledge of the process. This has led to the design and manufacture of a high-speed rotary screen-printing press that will enable high-speed, continuous screen-printing.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:637001 |
| Date | January 2002 |
| Creators | Fox, Ian James |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://cronfa.swan.ac.uk/Record/cronfa42565 |
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