Details:
Summary:
White light interferometry is a non-contact technique for the characterization of surface topography. As it is a non-contact and non-destructive method it can be used for all types of materials (solids, liquids, rubbery, sticky, etc.). The instrument is based on the light interference principle. The light from the single source passes through the beam splitter and is directed to the sample surface and the reference mirror. The beams of reflected light from those two surfaces recombine and form the pattern of interference "fringes". The maximum fringe contrast for each point of the sample occurs when the surface is at the best focus. During the vertical scanning the light interference signal from each point of the sample is recorded by the computer. The fringe signal is demodulated by the appropriate advanced computer algorithms and translated into the information about the surface topography of the sample.
The instrument and software (Wyko NT1100 Optical Profiler, by Veeco, USA) allow for quick and accurate characterization of surfaces. Among the surface characterization options and parameters that can be obtained are the surface topography - 2D and 3D images, virtual cross-sections, surface roughness, surface area, volume, line width, step height and much more. The instrument is well suited to be used for R&D as well as problem solving in the Graphic Arts Industry. For example, surface topography determines a number of important properties such as print quality, print density, gloss and visual appearance. The optical profilometry provides a unique view which can quickly resolve surface contributions to print performance. Several examples of surface characterization of the model systems and real samples will be presented in this paper.
To demonstrate the capability of the white light interferometry the following properties of the selected samples were characterized using the Wyko NT1100 Optical Profiler:
- Surface topography, roughness and the virtual cross-sections of different samples
- Surface area of smooth (glass) and rough (paper) samples
- Volume calculations - calibration standard vs. the flexographic anilox roller
- Line width and height - the flexographic print on the plastic film
- Step height - calibration standard vs. the gravure print and adhesive film
- Ink film thickness measurement - step technique - limitations of the method and possible errors while measuring prints on the transparent film.
In addition, the examples of practical application of white light interferometry for problem solving (selected case studies) were also presented:
- Characterization of surface (sample/air interface) and the interface (clear film/substrate) of the sample coated with transparent film
- Identification of the root cause of "skipped" dots in the gravure printing
The experimental data presented in this paper shows very clearly that the white light interferometry is a very useful and powerful (quick and accurate) method for the characterization of surface topography of the samples. One can anticipate that this new technique will find wide application in the Graphic Arts Industry in the coming years.