Seminar on
Process Parameters affecting Printability in Gravure Printing
By
Mr. Rugved Upadhye
Under the Guidance of
Prof. Dr. Akshay V. Joshi
Pune Vidyarthi Griha’s College of Engineering and Technology,Pune
Academic Year 2020-21
Copyright © specterkorea co,ltd. All rights reserved.
Factors affecting
gravure printability include Ink viscosity, cell angle, screen ruling, printing
speed, impression pressure, surface properties (smoothness, levelness, ink
absorbency, cleanliness, gloss, finish, etc.) and structural properties (bulk
or thickness, weight, pick resistance, dimensional stability, etc.).[2] A
material with high printability will produce a high-quality print, with sharp,
clean print and high print accuracy which we get from the gravure printing process.[5] Gravure ink has
the lowest viscosity among all the printing processes. Gravure requires a
liquid ink (h = 0.05–0.2 Pa·s), which can fill the image forming cells of the
gravure cylinder at a high printing speed. In order to ensure a good transfer
effect and long-time printing, it is advisable to adjust the printing ink
viscosity into 11-15S/Zahn #3 Cup.[4]
Doctor Blade is often referred to as the
“soul” of gravure printing. It controls the amount of ink transfer from the
image cylinder onto the substrate. For better print quality, it is recommended
to have a minimal doctor blade pressure (0.5-1.0 bar). The lamella tip-shaped blade gives the best results.[6] The cell is the engraved image carrier used in gravure
printing. The volume and shape of engraved cells are important to the
performance of the gravure printing process. The impression cylinder forms a
nip with the gravure cylinder through which the substrate passes. A wrap of
120º is typical, but it may vary according to the substrate and the diameter of
the roller. A 4:6-inch diameter roller will typically have a wrap of greater
than 90º; a larger diameter roller and less wrap is desirable for heavier
stock.[3]
To increase productivity and to decrease the
manufacturing cost in lightweight electronic devices and fabricating flexible
materials such as radio frequency identification tags (RFID), sensors, solar
cells, and flexible displays, mostly requires gravure printing over large-areas
on flexible plastic substrates at low temperatures. Other methods such as
gravure-offset6 and flexographic7 printing have been used for high-resolution
pattern printing. Due to the deformation of a blanket and line widths smaller
than 20 µm, this process is arguably one of the most significant techniques for
building patterns at high resolutions. The nip force plays a significant role in high-resolution gravure printings. The adhesive force-based ink transfer
model is developed. The model explains why the ink transfer ratio increased as
the nip force increased. The ratio of ink transfer is a function of the contact
length. As the nip force increases the contact length also increases and therefore,
the ink transfer ratio also increases. A high nip force of 754 N could increase
the ink transfer ratio and was found to be favorable for compensating the
over-doctoring case. It also showed that low nip forces (251 N) is preferred to
obtain high-resolution images and a better fidelity of the printed pattern for ηD
≈ 1.[8]
The ink uniform thickness and dot gain is affected by ink transfer, so it is required to optimize the parameter of the plate
making of gravure. Unlike letterpress and offset printing, for gravure
printing, color and gradation reproduction of image rely on not only dot area
coverage but also thickness of ink film, it transfers ink by a cell structure,
which rely on different dwell volume to achieve reproducible. By investigating
the influence of screen ruling and engraving needle tip angle on ink transfer,
the conclusions can be done such as: The vary curve of ink transfer is
different for different screening ruling and the amount ink transfer doesn’t
always increase with screening ruling increasing ( more cells in unit area ) ,
but it is better with more amount of ink transfer. The value of ink transfer
doesn’t always increase with screening ruling decreasing and cell deeper. It is
required to select the best screen ruling. While comparing different screen
rulings, the highlight and middle tone area, the ink transfer is not good,
irrespective of screen rulings . But in the darkened part, amount of ink
transfer decreases with the screen ruling increasing, so it is better for ink
transfer. For the same screen ruling, the amount of ink transfer increases with
engraving needle tip angle increasing, and the opening of cells have a major
impact on the ink transfer.[9]
Gravure printing is an intaglio printing process in
which the image is engraved on the surface of the gravure cylinder. The printing
ink is filled in the engraved cells of cylinder during printing and the rest of
the ink is stripped by a blade and separated for reuse. The efficiency and the
print quality is high in gravure printing and it is also possible to print on
different substrates. The ink viscosity, surface properties of substrate
material, and cell structures on the gravure cylinder are the main factors that
determine the print quality. Appropriate inks are chosen depending upon the
material to be printed and the finished product. Mostly solvent-based inks are
used. The printability is better than polyethylene since the printing substrate
with the lowest surface energy is polypropylene. As ethyl acetate dries faster
than other alcohol-based inks, ink density and dot growth are better in terms
of printability. Ethyl acetate gives the best results in terms of color and
gloss. However, it is highly corrosive to the ethyl acetate engraving cylinder.
For this reason, it is not recommended to use it for a long time and in large
quantities. For this reason, it is more suitable to be mixed with either
isopropyl or ethyl 36 alcohol. When examine in terms of price, the solvent with
the lowest unit cost is isopropyl alcohol. For this reason, when it is
necessary to choose among alcohols, isopropyl alcohol is a suitable solvent. It
is recommended to use a mixture of ethyl acetate-isopropyl alcohol for both
substrates in gravure printing.[10]
With the enhanced awareness of environmental
protection, as water-based ink does not contain volatile organic solvents, and is
non-combustible, and has some other advantages, it would be an
environment-friendly printing ink with a good future. But the plastic water-based
gravure ink could not meet the requirements of printability in proofing density,
dryness, and adherence, therefore the application of water-based ink on plastic is
not been promoted. Hence, the printability
of Plastic Water-based Gravure Ink is being studied in various labs. Pigment/binder
ratios are influenced by the viscosity and adherence of the inks. Inks have a
good printability both on PET and BOPP when the pigment/binder ratio is 2:1.
Inks have a good printability both on PET and BOPP when adding 0.7% of
dispersant of 750 and 0.7% of dispersant of 760. Inks prepared by single resin do not satisfy
the need of printability. In order to get the better overall performance of
inks, the method of mixing different resins is used. The optical formulation of
mixed resin both on the PET and BOPP was 3808:1437: 2640 = 1:0:1. Addition of
isopropanol in the inks would increase the proofing density. Inks have a good printability
on both PET and BOPP when the dosage of isopropanol was 1%.[11]
References
1. Handbook of Print Media | SpringerLink. Retrieved
from - https://link.springer.com/book/10.1007/978-3-540-29900-4
2. Gravure printing - Rotogravure printing process |
BOBST. Retrieved from - https://www.bobst.com/usen/products/gravure-printing/process/
3. Characterization of Gravure Cylinders. Retrieved
from - https://www.printing.org/taga-abstracts/t010001
4. Gravure Printing Ink - Gravure Ink – Castle Ink.
Retrieved from- https://castleink.com/blogs/printer-help/gravure-printing-ink-gravure-ink
5. What Is: Printability? | Print Peppermint.
Retrieved from- https://www.printpeppermint.com/glossary/printability/
6. DOCTORBLADESFORPRINTI NG - Daetwyler USA.
Retrieved from- https://www.daetwyler-usa.com/library/Daetwyler-Gravure.pdf
7. S. Elsayad F.M &S. El-Sherbiny, E.A. (2002).
Some factors affecting ink transfer in gravure printing. Pigment & Resin
Technology, Vol. 31 Iss 4 pp. 234 – 240 .Retrieved from http://dx.doi.org/10.1108/03699420210432429
8. Ho Anh Duc Nguyen, K.S, and Changwoo Lee. (2015.
Effect of Nip Force on Ink Transfer in High Resolution Roll-to-Roll Printing.
INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING Vol. 16, No.
3, pp. 517-523. Retrieved from https://link.springer.com/article/10.1007/s12541-015-0070-9
9. Deng Pujuna , Z.G & Wang Yu and F.W (2011).
Influence of screen ruling and engraving needle tip angle on ink transfer for
gravure. Advanced Materials Research Vol 174 (2011) pp 215-218. Retrieved from https://www.scientific.net/AMR.174.215
10. Arif Ozcan and Rasim Zulfigaroglu (2020). An
investigation on printability of different solvent based inks by gravure
printing onto various substrates. Journal of Graphic Engineering and Design ·
July 2020. Retrieved from https://www.researchgate.net/publication/342946643
11. CHEN Yue-tao, W.X & HUANG Bei-qing (2014).
Study about Influencing of Printing Process on Gravure Printing Ink Transfer.
Applied Mechanics and Materials Vol 469 (2014) pp 301-304. Retrieved from https://www.scientific.net/AMM.469.30
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