An experimental & analytical investigation of screen printing process fundamentals

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Mitchell, M.C., 1998. An experimental & analytical investigation of screen printing process fundamentals. PhD, Nottingham Trent University.

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Abstract

The screen printing process has been around for centuries dating back to its use in ancient China for producing patterned silks. The same principle is used today to manufacture a diverse range of products from different areas of industry, including electronics, textiles, pharmaceuticals, packaging and graphics. Despite its age, the screen printing process is difficult to control because it is poorly understood at a fundamental level. Several attempts to model the process over the last 30 years have been reviewed here and it is concluded that, to date, none has successfully described the process and that further work is required to provide parameter relationships.

The complex nature of screen printing is confirmed in this thesis using factorial analysis to examine just a few of the many variables involved in the process. The findings are that factorial experimentation contributes minimal benefit when trying to establish process control.

As a consequence, the basic fundamentals of the process related only to filling of the screen mesh have been researched here. For the first time, the pressure required for flow through the mesh to occur has been experimentally established and this has shown that existing process models are lacking or wrong. In addition, the assumption that the screen printing process is governed by hydrodynamic lubrication theory is brought into debate, because the hydrodynamic pressure generated within the ink roll is recorded to be a factor of 25 smaller than the pressure required to ensure flow through the mesh.

This work has proposed that an adaptation of elastohydrodynamic lubrication (EHL) theory is a viable alternative on which to base a screen printing process model. Predictions of the minimum speed required to achieve the first acceptable print for a given set of parameters including mesh, squeegee and ink characteristics have been provided. This theory has been evaluated experimentally for two different squeegee types. The results show excellent agreement between theory and experiment for the softer squeegee tested, which industrially is the most common squeegee employed. The harder squeegee results follow the qualitative trend predicted by the theory but are a factor of 10 larger. It was concluded from these results that no single theory governs the screen printing process, but that a combination of theories must be sought.

This thesis provides a successful representation of the screen printing process and can be used as a basis for development of a generic model to control the screen printing process. It is, however, concerned predominantly with the filling of mesh apertures, and thus recommends that further work explore the effect of increased squeegee speeds and changes in mesh tension. In addition, deposit characterisation techniques should be reviewed and developed to allow improved assessment of the print quality.

Item Type:

Thesis

Creators:

Mitchell, M.C.

Date:

1998

ISBN:

9781369313215

Identifiers: