Abstract
We have studied the surface structure of tamper-proof paper with positive and negative watermarks at different scales ‒ from a micrometer to a nanometer level, by using the methods of contact profilometry and atomic force microscopy. Experimental research has confirmed that the structural parameters of the tamper-proof paper's surface differ at regions with and without watermarks.The results of measurements by a contact profilometer have made it possible to trace a correlation between values of the profile's mean arithmetic deviation and the presence of watermarks. It was determined that the value for the profile's largest height does not depend on a measurement region, which could be related to the chaotic arrangement of fibers and particles of the filler in the paper bulk that protrude above the profile's line.By analyzing the value of the profile's mean arithmetic deviation obtained by using a method of atomic-force microscopy, it was found that for regions with negative watermarks it is larger than that for regions with positive watermarks. The dependence of the profile's largest height on measurement region is not clearly observed. This may be due to that the size of the examined region (3,000×3,000 nm) covers only part of the pulp fibers.Thus, the results of our analysis allow us to argue that both methods are suitable for estimating the characteristics of paper's surface, and determine the character of interaction between a given type of paper and printing inks during printing process. In particular, it has been established that the method of profilometry makes it possible to determine parameters of the paper's surface profile, formed in a certain way, while the atomic force microscopy method allows analysis of the morphology of its components, located at the surface (fibers, filler's particles, etc.). The availability of information on the structural properties of paper makes it possible to predict the quality of printing reproduction, specifically clearness of reproduction of thin guilloche lines on watermarks, which is relevant because it prevents flaws in printing products for special purposes.
Highlights
One of the key factors for ensuring quality in high-quality printing of protected printed products is the manner in which paper and ink manifest their physical and technical properties.Paper represents a complex structure consisting of interlaced fibers, particles from the filler, and supporting supplements
Given the heterogeneity of the paper canvas, it is a relevant task to undertake a research aimed at identifying the structural differences of its adjacent areas, which would make it possible to predict the quality of printing reproduction
Results from the reported methods were intercorrelated, which allowed the authors to argue about the possibility of using atomic force microscopy (AFM) for operative control over the processes of surface treatment of paper
Summary
One of the key factors for ensuring quality in high-quality printing of protected printed products is the manner in which paper and ink manifest their physical and technical properties. Structural properties of paper directly affect the quality of printing reproduction, thereby largely determining the interaction with inks. Most types of paper for intended for printing of documents of strict accountability and securities include watermarks (WM) formed on a paper canvas in the process of its production. The presence of watermarks leads to heterogeneity of the surface and volumetric characteristics of paper, which can affect the optical density and color of the imprint, clarity of reproduction of fine guilloche lines. Given the heterogeneity of the paper canvas, it is a relevant task to undertake a research aimed at identifying the structural differences of its adjacent areas, which would make it possible to predict the quality of printing reproduction
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