Paper

Many different types of paper are manufactured by varying the fibre properties, by further processing such as bleaching, and by treating the fibre matt with additional materials (e.g. clay fillers, wet strength additives, whitening agents). Multilayer paper-based systems are increasingly common, such as the metallised papers for visual or containment effect and also barrier layer papers used in the packaging of sensitive materials. Other specialist papers include labels (paper + adhesive layer) and release papers (paper + release agent).

Properties of Papers

As paper is essentially a non-homogeneous surface (it is not an engineered product) its characterisation is not always straightforward under a microscope, especially if the surface properties are to be quantified and compared. The chemical and topographical analysis of a paper surface is therefore critical both for production quality control and in product and process developments. Several paper parameters depend on the surface topography:

• printability
• laminating properties
• adhesive uptake
• aesthetic appearance.

Applications for Papers

Non-contact 3D surface profiling (3DP) is rapidly becoming the “norm” in paper topography analysis. 3DP combines both highly quantified surface data with visual representations of the surface. Being a non-contact technique, it is suitable for use on all paper types (including tissue). Understanding the different surface features of different grades of paper can provide invaluable information as to their performance parameters (printing, adhesion, “feel”). The differences in print surface roughness can be compared with that from the unprinted substrate. For a heavily coated product, the features are typical of those from a chemical coating rather than showing evidence of the cellulose fibres. Both macro scale features (100s of microns) and micro topography (1 to 10 microns) can be clearly seen. In addition to a rich array of quantified data, the main advantage of 3DP over traditional techniques is the high resolution images of the paper surface which can be produced. Properties including fibre diameter, roughness, void volume, can be compared.