The 19th INTERNATIONAL DAAAM SYMPOSIUM
"Intelligent Manufacturing & Automation: Focus on Next Generation of Intelligent Systems and Solutions"
22-25th October 2008
THE INFLUENCE OF THE TONER STRUCTURE ON
THE QUALITY OF BLACK-WHITE DIGITAL PRINTING
MAJNARIC, Igor; BOLANCA, Stanislav & BOLANCA MIRKOVIC, Ivana
Abstract: The actual black-white digital printing techniques
have been analyzed in this article. It is to assume, that different
composition and structure of black ink will establish different
thicknesses of ink film on identical printing substrate, namely it
enables different quality of monochromatic prints. For the
analyses the representative digital printing techniques have
been used: Electrophotography, Inkjet, Digital Screen Printing
and Digital Waterless Offset. The ability of the black toner
adhering to the printing substrate has been analyzed by the
measurements of the optic inking density (X-rite) which is
supplemented by the image analysis (Personal IAS). The results
show that EA toner allows maximum quality establishing the
thickest ink film (D=2,14) and the smallest oscillation (1,41
µm) of the defined line.
Key words: digital printing, density, ink, image analysis
1. INTRODUCTION
In recent times, the majority of the digital printing machines
development has been reduced to the investigation of the new
formulation and the finest possible toner structures which result
in better printing properties and higher productivity. The aim of
this work is the analysis of the quality of the black-white digital
printing and recognizing how different toner types adhere to the
non absorbent printing substrate. Indirect determination of
thickness of the ink film is based on the optical density
measurement. Optical density (D) is defined in form of
logarithmic ratio: D=log1/=log Io/I. Reflectance factor () is
the ratio of light intensity, (I) of light remitted by the ink film in
relation to the intensity of light (Io) remitted by the blank paper.
2. THEORETICAL PART
The digital printing techniques are characterized by the
unique digital input data which define the contents of the future
printing form, i.e. the elements of the final print. The digital
printing has been developed into two directions: Computer to
Press and Computer to Print (Goldmann, 2004). The
characteristic of the black–white digital printing, is achieving
the coloration by different types of coloration carriers. They are
polymerised toners and new colorants, pigment dispersion,
encapsulated pigment technology and dye. (Williams, 2001).
In the digital waterless offset black pigments are tiny particles
of carbon black or pure elementary carbon (20-150µm) whose
share is 10-30%. The basis of black–white digital screen
printing ink is soy oil (>6%), petroleum solvent (<10%),
glycerol (<5%), black pigment (<10%), alkid resins and water.
The particles of the carbonate black toner are less than 1µm.
The basic principle of EP (electrohotoraphy) is founded on
photoelectric effect (Bolanča et al., 2005). In 80% of the cases
the toners are powders. Two component toner of 1st generation
is a mixture which contains: resins (80–90%), coloured
pigments (5-15%), substances for charge control (1-3%) and
additives (Thompson, 2004). Toner of the 2 nd generation is
based on process EA (emulsion aggregation). The process of
EA enables exact position control of waxes within the toner
particles. The printer fusers melt the toner particles by heating,
making it sticky and able for adhering to paper even on the
lower fusing temperatures (Suzuki et al, 2003). The pigment
particles of the liquid EP toners have star like shapes (1-2µm).
For directed movement of ElectroInk, the uniformly dispersed
agents (polar molecules) for increasing the electric conductivity
are responsible (Majnarić et al., 2007). Ink Jet more recent
pigment dispersions are made on the basis of uncapsulated
technology where each pigmented particle is comprised with
the oil coating adapted for good penetration into the printing
substrate. In this way the corresponding surface smooth coating
is obtained which increases the optical reflectance of the
printed layer (Larson et al., 2002).
3. EXPERIMENTAL PART
In this work, the printing quality of black–white digital
printing systems which is applied in office business and editing
has been investigated. The digital printing machines have been
compared for that: EP (Hp Indigo Turbostream, Xerox 250, HP
LaserJet 9050), Piezo Ink Jet-a (Epson 2400 photo), digital
screen printing (RISO RZ 970 E) and digital offset printing
(Heidelberg Quickmaster 46 DI). They all use especially
composed ink. For the needs of investigation, the special
printing form in PDF was generated. It contains: the standard
achromatic illustration, wedge with 99 patches (in the range
from 1 to 100%) positive and negative micro elements, and
positive and negative lines of the standard thickness of 650 µm.
By means of the densitometer X-rite DTP 41 the optical inking
density of the printed ink layer was determined, which directly
showed the binding of toner to the printing substrate, i.e. the
possibility of printing the broadest possible range of the
achromatic inking. With the system for image analysis
(Personal IAS) the dimensional exactness of the printed
reproduction. The calendering natural paper substrate with the
high degree of whiteness, designed for digital printing was used
for printing (Splendogel EW 115 g/m2).
4. RESULTS AND DISCUSSION
In figure 2 the curves of the dependence of the inking density
(D) on total screen value (1-100% screen value), have been
presented. All the curves have the increasing form which is
uniform. The adapted printing substrate for the digital printing
has the greatest inking density on Xerox (DMAX=2,14). Indigo
TS in greatest part (1-90% screen value) has the smallest inking
density. The exception is Epson 2400 which gets the maximal
inking density at 85% screen value (D85%RTV=0,89) but it does
not succeed to keep it in higher tones.
Fig. 1. Schematic presentation of the performed experiment
Table 1. The thickness of the reproduced positive and negative
650 µm lines
Fig. 2. Dependence of the inking density (D) on screen value
for the printing substrate in the range from 1-100% screen value
The liquid pigment inks (Epson 2400) in great layers cause
the opposite effect, i.e. too big ink penetration into the substrate
which causes the capillary blooding and closing the darkest
screen values. The quality of the surface layer is emphasized
which is visible at low screen values. The greatets inking
density is achieved by HP 9050 (D10%RTV=0,26), after that
follow Riso, Epson, Xerox and Heidelberg. In these printers,
the growing trend in dependence curves D/RTV1-10% is visible,
which means that there are differences in creation of the lighter
tones. On Indigo there is no difference in inking density and the
areas 1-15% screen value are unchanged. Such characteristic
movement in value can be explained by the usage of the
software linear LUT, by which propositions the dot gain is
eliminated. In reproduction of high screen values, the
impressions of Xerox stand out more considerably. The nearest
to it are the impressions of HP 9050 DN. It is characteristic fot
the darker tone areas, that the smallest inking density has Epson
2400. On the formed layer in the zone of the medium quality
there are the digital machines Riso, Indigo, Heidelberg QM,
which have the maximal inking densities in the area between
D=1,23 and D=1,36. In relation to the linear curves, only Xerox
realizes the increase, i.e. the possiblity of the more qualitative
reprodcution of darker tones. By the image analyses Personal
IAS positive and negative lines are increased and measured.
Results are presented in table 1.
In relation to the desired positive original line, the increase of
reproduction was noticed at: Indigo TS (d=35,35 µm) and
Epson 2400 (d=40,81µm). The other printers generate the
decrease of the e.g. Xerox (d=-1,41µm) Heidelberg QM 46
(d=-17,87µm), HP 9050 (d=-23,89 µm) and RISO (d=83,44 µm). For the reproduction of the negative lines the
decrease of the desired size is applicable. The smallest change
appears at Heidelberg QM 46 (d=-33,31 µm), while the
greatest one at Epson 2400 (d=-127,93 µm), Riso (d=-136
µm) and Indigo TS (d=-173,95 µm).
5. CONCLUSION
The investigations have shown their justification in the
scientific sense and in application. The different types of digital
black white machines generate different ink layers on the
adapted non coated printing substrate for digital printing by the
application of the specific toners. The liquid toner based on the
uncapsulated pigment, will realize the different deviations in
the inking density on different screen values (in the range from
10% screen value). For the same screen areas, the black liquid
EP ink realizes minimal deviations within the light and medium
tones (D1-10%=0,01; D45-55%=0,04), but great deviations in
dark areas as well (D91-100=0,36). Paste offset ink realizes
identical deviation in inking density in lighter and medium
tones (D1-10%=0,06; D45-55%=0,06), while in the darker areas
it grows for 100% (D91-100%=0,12). The inking densities of the
water-oil black emulsion toner behave according to the whole
screen value. With the increase of the screen value, the range of
inking densities constantly grows; for the light areas (D110%=0,10), medium areas (D45-55%=0,13) and for the dark areas
(D91-100=0,21). In relation to the tested toners, the powder two
component toner will oscillate greatly in its light areas (D110%=0,15). In the middle area, the oscillation is also important
(D45-55%=0,19), while in the darkest area the saturation and
constancy appear (D91-100=0,02). The toner obtained by EA
enables the highest quality in black white printing. The inking
density deviation grows proportionally with the increase of the
screen value (D1-10%=0,07; D45-55%= 0,24; D91-100%=0,41).
In this way the thickest ink coating is achieved (Dmax=2,14)
while the tone values remain open. The densitometric results
are confirmed by the image analysis. Liquid inks do not
succeed the preciseness of the defined printing elements, so the
small gain of the positive printed elements was noticed, i.e. the
greater decrease of negative printing elements. The positive
elements printed with powder toner reproduce smaller line, and
only the toner obtained by emulsion aggregation corresponds
most closely to ideal width. Algorithm of printing elements
formation influences that movement. The constructions of
simple single coloured units have lower resolution in relation to
the multicoloured ones. Riso printed lines oscillate multi
dimensionally. The tolerance threshold in quality is very low
which enables the printing of black white applications with
lower demands.
6. REFERENCES
Bolanča, S.; Majnarić, I. & Pigac, S. (2005) Digital Printing
with Increased Ink Layers, Graphic Arts Technology design
comunications: Z. Bolanča, M. Mikota, (Ed.) 131- 142,
University of Zagreb Faculty of Graphic Arts, ISNB 95396020-3-3, Zagreb.
Goldmann, G. (2004) The World of Printers, Oce Printing
Systems GmbH, ISBN 3-00-001081-5, Dusseldorf.
Larson, J. R.; Gipson, G. A. & Schmidt, P. S. (2002) Liquid
Toner Materials, HandBook of Imaging Materials, 2nd edition,
A.D. Diamond and D. S. Weiss (Ed.). ISNB 0-8247-8903-2
Majnarić, I.; Bolanča, S. & Golubović, K. (2007). The
Influence of ElectriInk Pigmentation on the Quality of Indirect
Digital Printing, Proceedings of 11th International Conference
on Printing, Design and Graphic Communications, Z. Bolanča
(Ed.), p.p. 85-89, ISBN 978-953-96020-7-7, Zadar, Croatia.
Suzuki, C.; Takagi, M. & Inoue, S. (2003) Toner
Characteristics and Xero Interactive Performance of EA
Particles with Specific External Additives, Proceedings of
International Conference on Digital Printing Technologies NIP
19, IS&T, p.p.134-137, ISBN 0-89208-247, New Orleans,
Louisiana, USA.
Thompson, B. (2004). Printing Materials: Science and
Technology, Pira International, ISBN 1 85802 981 3, Surrey.
Williams, C. (2001). Printing Inks, Digital Demand: The
Journal of Printing and Publishing Technology 6(1), (Pira
International) 40-47, ISBN 1471-5694