Non-destructive methods in the study of IJ ink – substrate interaction
Muck, Lozo, Otahalova, Drzkova, Kaplanova
Introduction
The quality of ink-jet prints depends to a large degree on the interaction between printing
substrate and Ink-Jet ink. The penetration of printing ink should be low in order to retain high
optical colour density (1, 2). The surface of the paper also plays an important role: the
absorption capacity for printing inks should be controlled. It should not dust and should have
a suitable level of smoothness as well as other properties necessary for good operability and
printability (3, 4).
The scope of the study was to find non-destructive methods that can give a rapid and accurate
insight into the Ink-Jet ink penetration in z-direction of the substrate.
The aim of the study was to investigate the radial and vertical distribution of Ink-Jet printing
ink, both on and beneath the paper surface, on different types of papers, as well as to
determine the impact of the paper surface on print quality.
Materials and methods
The following analytical techniques were used in the study:
Penetration - Dynamics Analyser (PDA) is an analytical instrument designed for the
investigation of penetration dynamics of liquids into solid samples, such as papers. The
analytical technique employed is based on recording the change of intensity of ultrasonic
signals transmitted by solid samples while one of their sides is in contact with a liquid
(sample is immersed into the water bath).
Slit - Scanning Densitometer is used in qualitative and quantitative evaluation of thin layer
chromatograms. It was used for investigation of both radial and vertical distribution of
different spots of printing ink by measurements in reflection mode (for the wavelengths of
580 nm). We used Ink Jet printer Canon BJC 8500, printing resolution 600 dpi and the colour
intensity 100%.
Confocal Laser Scanning Microscopy (CLSM) represents a non-conventional method for
non-destructive study of interaction of Ink-Jet inks and printing substrate. It was used in the
investigation of tree-dimensional paper structure, the determination of pore volume (5, 6) and
the evaluation of ink penetration in z-direction (7).
The spots of printing ink were observed and measured with the Confocal laser scanning
microscope. The scan area was 460 µm × 460 µm, air objective with numerical aperture 0.6,
laser beam wavelength 458 nm and resolution in z-direction 2.7 µm. The sample preparation,
i.e. cutting the samples in z-direction was done virtually, by computer software.
The vertical distribution was made by observing the border of the ink spot with CLSM and
subsequently by using software for cutting the slices in z-direction. This software calculated
the number of slices necessary to pass from the most fluorescent to the non-visible part of the
dot.
Photoacoustics and photoacoustic spectroscopy are non-destructive methods for the study
of optical and thermal properties of a printed area at different depths beneath the sample
surface. This implies the examination of ink penetration into the paper structure. The physical
principles of indirect photoacoustic effect and its possible applications in the field of graphic
arts are already well established (8, 9, 10, 11).
Cross section analysis of prints was made by microtome (slice thickness 30 µm). The slices
were then examined by Optical Microscopy (OM). This is a destructive method which
enables a detailed access to the undersurface migration of printing ink through the inside
layers of the printing substrate.
At this point of the study we assessed the relevance of information obtained by different, nondestructive and destructive measurement techniques. Each of these methods, and their
limitations, are important in the study of ink – paper interactions, as well as in the impact of
substrate on print quality.
Therefore, several completely different types of paper were used as printing substrate: Z –
Zweckform Photo Paper, recommended for Ink-Jet prints, one-side coated, high glossy, (130
g/m2, 170 μm), K – Carton board, one-side coated multilayered white board, (300 g/m2, 430
μm), I – ICP Permanent Paper made at the Pulp & Paper Institute in Ljubljana, which
corresponds to standard ISO 9706, no surface treatment, (70 g/m2, 110 μm), T – Three-ply
tissue paper with a low percentage of secondary fibres, (60 g/m2, 185 μm).
Papers with wide range of quality characteristics were used to define the limits of each
measuring method.
Up till now the T sample (tissue paper) could not be measured by Photoacoustics (it splits
during the sample preparation); the K sample (carton board) could not be cut by microtome
(unsuitable caliper) and therefore Optical microscopy could not be done either; all analysed
samples caused various difficulties in Cross section analysis (as the magenta dye ink is water
soluble, the microcopy evaluation of the prints should be done in as short a time as possible
from the sample preparation).
Comment
Results obtained in this large study enable us to draw two goups of conclusions. The results of
non-destructive methods (Slitt Scanning Densitometer , CLSM, Photoacoustic spectroscopy)
correlate among themselves in the analysis of ink penetration in z-direction. The most
significant finding of all is that the data obtained by these measurements overlap with those
obtained by the destructive method (Cross section analysis by microtome and Optical
microscopy). Analysed cross sections of Ink-Jet prints are taken to represent objective truth in
the matter of ink penetration. Therefore, correlation of results of non-destructive methods
with these data proves their usability and reliability.
In this view we can conclude that the study fulfilled its purpose. We believe that nondestructive methods provide trustworthy, quick and exact methods of print analysis.
Key words: Ink jet, penetration, Photoacoustics, CLSM
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Authors:
PhD Tadeja Muck, University of Ljubljana, Faculty of Natural Sciences and Engineering,
Chair of Information and Graphic Technology, Snežniška ul. 5, SI-1000, Ljubljana, Slovenia
tel.: +386 1 2003284, fax.: +386 1 4253175
MSc Branka Lozo, University of Zagreb, Faculty of Graphic Arts, Getaldićeva 2, 10 000
Zagreb, Hrvatska
tel.: +385 1 2371080, fax.: +385 1 2371 077
Ing. Lenka Otáhalová, Ing. Markéta Držková, Prof. RNDr. Marie Kaplanová CSc.
Universtity of Pardubice, Faculty of Chemical Technology, Department of Graphic Arts and
Photophysics, Studentská 95, 532 10 Pardubice, Czech Republic
tel.: 466 038 031, fax: 466 038 031