PRINCIPLES OF GRAVURE PRINTING PROCESS

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PRINCIPLES OF GRAVURE PRINTING PROCESS

2 August 2018

In this type of printing, the printing areas are in recess – that is, on a lower level than
the non-printing surface. The recesses are filled with ink and surplus ink is removed from the
non-printing surface by doctor blade. The substrate is then pressed against the printing
cylinder to transfer the ink onto it – see Figure. The main examples of gravure printing are
Rotogravure printing and, in the area of arts and crafts, copper plate engraving and diestamping
(also security printing).
Gravure is the process which uses the intaglio principle. The shortest ink train is
found in the gravure process as the gravure cylinder actually revolves in a bath of ink. The
doctor blade removes excess ink, but leaves ink in the thousands of engraved cells in the
copper cylinder.

The distinctive feature of gravure printing technology is the fact that the image
elements are engraved into the surface of the cylinder. The non-image areas are at a
constant, original level. Prior to printing, the entire printing plate (non-printing and printing
elements) is inked and flooded with ink. Ink is removed from the non-image (by a wiper or
blade) before printing, so that ink remains only in the cells. The ink is transferred from the
cells to the printing substrate by a high printing pressure and the adhesive forces between
printing substrate and ink.
Rotogravure printing is used for the economical production of long print runs.
Gravure printing forms are usually cylindrical. A special feature of industrial rotogravure
printing is the fact that a whole cylinder is used per color separation. This means that in a
four-color press four separate cylinders have to be changed for each new job. Consequently,
a company that has a lot of repeat jobs is forced to store a large number of cylinders.
Depending on the printing format, gravure printing cylinders are generally rather heavy and
require special conveying and handling gear systems
INTAGLIO / GRAVURE PROCESS
In this process a metal plate usually copper is used as a image carrier. Here, copper
etching or hand engraving is carried out to form an image. Ink is applied over the image
areas, excess inks are wiped off. A sheet is laid over the plate and pressure is applied. Ink
from recessed area is transferred to paper according to the width and depth of engraved
lines.
Photogravure:
Photogravure is an intaglio process. Image areas are deeply etched below the
surface of the copperised surface of printing cylinder. Liquid ink is filled in the recessed
image areas and a doctor blade wipes the surface clean free from surplus ink. The cylinder
is pressed on paper or other material for transferring the inked image.
Gravure Printing:
Gravure is the photographic version of the original “Intaglio” process and Gravure is a
process which follows the intaglio principle.
In Gravure process, the printing image is engraved into a cylinder in the form of cells.
The engraved cells are filled with ink and excess ink on the cylinder surface is wiped off by
doctor blade. Printing is achieved by passing the substrate between the gravure cylinder and
an impression roller under pressure.

Gravure processes has a much wider application than letterpress or offset as it
prints, from a low viscosity liquid ink. Coating, varnish, adhesive, hot carbon or anything that
will flow on a cylinder can be printed by gravure. Plastic sheeting, curtains, linoleum,
upholstery metallic foils, paper and boards can be printed. The finished materials can be
passed through in-line machines for punching, cutting, folding, etc. Gravure has advantages
in carton making.
Thick film of gold ink can be printed. Deep brilliant glossy solids by the slide of
delicate tones of postal shades can be laid down by gravure. Printing with 100, 120, 150,
175, 225, 300 lines screens are possible. Printing using 175 line screen is popular. The
greatest etching depth is 1 to 2 / 1,000 of an inch or 25 / 1000 to 50 / 1000 mm. The ratio of
cell wall thickness to cell width 1:2.25 or 1:2.5 for paper and board and 1:3 for solid areas on
foil and plastic is recommended. Width increases with cell depth and cell wall becomes
thinner. Ink from deep cell spreads more. The dense areas merge into one another screen
pattern. Highlight cells accept little ink.

ADVANTAGES, LIMITATIONS (DISADVANTAGES) AND CHARACTERISTICS OF
GRAVURE PROCESS
Advantages of Gravure:
1) The final printed images are of excellent visual quality. Due to its intaglio
character, the closeness of the printing areas and different thickness of ink,
gravure print displays the pleasing effect of a continuous tone image.
2) Photogravure is an exceptionally fast printing method on almost all kinds of
paper and materials. Press speed attainable in web-fed presses for paper:
1,000 fpm (Feet Per Minute) ; Film and Foil: 300 to 600 fpm. Sheet-fed
presses: 3000 sheets per hour.
3) The printed sheet is usually dried, when it leaves the press, due to the
volatility of the fluid ink.
4) Gravure cylinders yield very large number of impressions and under proper
handling even yield several millions copies. Chrome-plated copper cylinder
can print 1.5 million revolutions without re-chroming; and can print 12 to 20
million revolutions before making new cylinders, depending on material
printed.
5) Rotogravure ink, based on, fluid ink can be formulated for printing on a,
variety of printing stocks – paper, paperboard, plastic films, metal foils,
textiles, etc.
6) The supplementary operations like cutting, punching, creasing and stripping
are done “In-line”, the end product are fabricated at the same speed at which
printing press runs.
7) Cheaper paper stock can be used on gravure presses compared with other
processes.
8) Quality reproductions at low cost is possible.
9) Large presses with a web width of 144inch are used for printing of vinyl floor
covering.
10) Virtually, there is no make-ready involved while printing on a Gravure press.

Limitations of Gravure :
1) Length of time to prepare and etch a cylinder. Generally, it required between
three and four hours from the time resist has been applied to the copper
surface until the printing form is ready to be proofed.
2) The high initial cost incurred in the cylinder preparation.
3) Type, Text matter and fine line illustrations do not reproduce as sharply in
gravure as it is reproduced in offset chiefly because the rotogravure screen
gives a “sawtooth” edge to vertical lines and horizontal lines while using
gravure screens.
4) Minimum economical run is said to be 50,000 copies.
5) Once the cylinder has been prepared, very limited alterations or revisions
alone can be made without having to prepare a new cylinder.
6) Air conditioning of the plant is necessary due to the inherent nature of the
process.
Characteristics :
1) All gravure text matter as well as pictures must be screened.
2) Generally the gravure cylinder itself is etched and acts as the image carrier.
3) Gravure prints from a design below the surface of the plate or cylinder.
4) Gradations of tone are obtained by etched cells to different depths, so that
more or less ink is carried by the cells and transferred to the paper according
to their depth.
5) The use of the “Doctor blade” in the printing press (to remove ink from nonprinting
areas).
6) An interesting possibility of gravure press is the fact that a simple basic
principle allows the use of cylinders of different diameters, without complicate
changes in the unit gearings.
7) A continuous tone positive is used for exposing on the carbon tissue.

MAIN SECTIONS OF GRAVURE PRINTING MACHINE:
All gravure machines consist of following main sections:
1) Unwind section
2) Printing section
3) Drying section
4) Rewind section

a. Ink Duct
In olden days open ink trough was used. There is no control of solvent evaporation
and ink is not well agitated, it was unsuitable for high speed machines. Where there is a
pump which continuously agitate the ink and pump it to the ink trough in which printing
cylinder rotates. Excess ink is returned back to the tank from ink trough.
Due to this enclosed system solvent evaporation is reduced. This enclosed system
also employs viscosity control of the ink. In this system whenever the ink is returned from ink
trough, it is filtered and solvent is added to maintain the viscosity of ink.
Further to this enclosed inking system a spray system is also used for very high
speed machines, where ink pump delivers the ink to nozzles pointing at the cylinder. The
nozzle surface is always kept wet. It will never dry out. This system also fully enclosed.

b. Printing Cylinder:
Basically, a gravure press is still the simplest of the printing machines. Publication
presses have cylinders as big as 102 inch with a diameter of about 17 inch. Generally
publication presses are not built to permit inserting of cylinders varying in the diameter.
Presses for package printing can handle cylinder varying in their diameter within a
given range. When variable diameter cylinders are customary, the nature of the jobs controls
the dimension. Cylinders for packaging vary greatly in size from the very small, about 7 inch
long by 2 or 3 inch diameter up to massive cylinder length of 80 inch or more long with a
diameter of about 17 inch.
Presses with a printing width of 200 inch (5 meters) and above are used for speciality
printing, like printing of vinyl floor covering.

Copper Plates
Gravure plates are made from rolled copper. The ends of the plate must be carefully
bent to fit in to the clamps on the cylinder. The plate covers only parts of the cylinder
circumference since the plate cylinder must house the clamping system. This uncovered
section must be filled in with a “gap cover” or “segment” to provide a bearing surface for the
doctor blade. These type of presses (using a gravure plate) are becoming absolete.
Copper Cylinder
Gravure cylinders can be made of iron, steel, copper or aluminium. Ends are usually
fabricated with steel bar and plate, or steel shaft pressed through the cylinder body. Sleeves
cylinders are metal tubes housed in the machine on mandrels. It is only necessary to
produce a sleeve or tube with this system, for subsequent mounting on a machine mandrel.
The sleeve is generally made of steel base and deposited with copper, to a diameter slightly
larger than the required size. It is then turned and polished in a lath to obtain the correct
diameter and perfect stage. This system is not recommended for multi-unit web-fed presses
and for large-run package printing.
In the Ballard process, a thin skin deposit of copper is loosely adhered to the bulk of
the cylinder surface, but is firmly attached at the bar ends. After printing, the copper skin is
removed by cutting and then pulling off. The advantages of Ballard process are elimination
of grinding of the old etching and allowing exact size cylinders for color works. The thin film
of copper is approximately 0.006 inch thick and is deposited in about one and a half hours.
This type of cylinder is used for printing of short-run magazine and packing. On an average,
to deposit one square foot of copper for 0.001 inch thick, the requirements of copper is 0.74
oz