Introduction to printing and finishing

Introduction to Printing and Finishing
Hugh Speirs

Published by

Pira International Ltd
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Surrey K T22 7RU
UK
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www.piranet.com


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publication are obtained from
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reliable. However, we accept no
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information contained therein
nor conclusions drawn by any
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permission of the Copyright
owner.
© Copyright
Pira International Ltd 2003
ISBN 1 85802 906 6
Publisher
Annabel Taylor

Head of publications
and events
Philip Swinden

Customer services manager
Denise Davidson

T +44 (0) 1372 802080

Typeset in the UK by
Pantek Arts Ltd, Maidstone, Kent

Pira International Ltd acknowledges product, service and company names referred to in this
book, many of which are trade names, service marks, trade marks or registered trade marks.


Contents

List of tables vi
List of figures vii

1

Conventional printing processes 1
Introduction 1
Basic principles of the main conventional
printing processes 1
Planographic printing 1
Relief printing 2
Intaglio printing 2
Stencil printing 3
The main conventional printing processes
outlined 4
Lithography 4
Offset lithographic printing 4
Sheetfed offset lithographic printing 5
Sheetfed offset lithographic press sizes 6
Sheetfed offset litho press
configurations 8
Lithographic make-ready and printing 13
Inking systems 14
Damping systems 15
Feeding and delivery mechanism 16
Remote control/press management
systems 17
Press sophistication and automation 18
Waterless litho 18

Web offset 20
Web offset press configurations 21
Blanket-to-blanket web presses 21
Common impression web presses 22
Blanket-to-impression web presses 23
Heatset and coldset presses 24
Narrow-width web offset presses 30
Book web offset presses 32
Commercial web offset presses 32
Flexography 33
Letterpress 38
Gravure 39
Screen 44

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2

Digital printing processes 49
Background to the development of
digital printing 49
Preflight checking of files 50
Workflows 50
Data preparation for print 51
Digital printing 51
Digital printing processes 53
Toner 56
Substrates 56

Outline of digital printing systems 56
Digital printing systems: 57

3

Inks, toners, varnishes and
coatings 73
Ink drying 73
Properties and uses of printing inks 74
Properties and uses of toners 75
Anti set-off spray powder 75
Accelerated ink drying 76
Ink mixing and matching 77
Colour matching systems 78
Printing ink terms 80
Varnishes and coatings 81

4

Substrates 83
Furnish of paper and board 83
Raw materials 83
Main ingredients of paper and board 85
Papermaking 86
Preparation of the raw materials 86
Treatment of the fibres and mixing of
the ingredients 86


Introduction to Printing and Finishing

Contents

Papermaking machine 86
Finish of paper and board 88
Supercalendered papers 89
Coated papers 89
Engine-sized and tub-sized papers 90
Embossed and other finishes 91
General characteristics of paper and
board 91
Different types of substrate and their
uses 95
Paper 95
Specialist papers 100
Boards 101
Specialist boards, including noncellulose-based materials 102
Dimensions and weights of paper and
board 103
International paper and board sizes 104
Traditional UK paper and board imperial
sizes 106
US paper and board sizes 106
Sub-divisions of UK and US traditional
imperial paper and board sizes 107
Supply and purchase of paper and
board 108
Paper and board specifications 109
Description of papers and boards 109
Paper in web and reel form 109
Weight and price calculations 111

Printing processes and paper/board 112

5

Print finishing, binding and
warehousing 115
Offline finishing operations 116
Binding 125
Stitching 125
Perfect or adhesive binding 128
Burst, slot or notch binding 129
Automated binding lines 129
General finishing operations 131
Varnishing and laminating 136

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Inline finishing 137
Inline webfed folding 137
Additional inline webfed finishing 140
Magazine binding and bookbinding 140
Bookbinding 145
Print finishing operations associated with
different types of printed work 148
General or jobbing work 148
Specialist work 149
Digital/electronic work 150

6

Printing processes and products,
compared and contrasted 153
Comparisons between the different
conventional printing processes 153
Advantages and limitations of the main
printing processes 154
Offset lithography 154
Flexography 154
Letterpress 155
Photogravure 155
Screen 156
Visual characteristics of the main printing
processes 156
Offset lithography 158
Flexography 158
Letterpress 158
Gravure 158
Screen 158
The suitability of printing processes to
different classes of work 159
Offset lithography 159
Flexography 160
Letterpress 160
Gravure 160
Screen 160
Other printing and print finishing related
processes 161
Digital/electronic 161

Pad printing 161
Diestamping 162


Introduction to Printing and Finishing
Contents

Copperplate 162
Digital stencil duplicating 162
Thermography 163
Foil blocking 163

7

Developments in printing and
finishing 165
Integration between MIS, printing
processes and equipment 165

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© Copyright Pira International Ltd 2003

Printing equipment manufacturers and
suppliers developments 167
MIS supplier developments 168
CIP4 168
Developments in press automation 169
Developments in inline facilities 171
Web sheeting and feeding equipment 173

Varnishing and coating 175
Glossary 177


List of tables

1.1
1.2
2.1

2.2
4.1

4.2
4.3

Page vi

Range of sheetfed offset litho press
sizes 7
Representative range of available
heatset web offset press sizes 27
Projected market share change of
different printing processes over
time 50
Main types of digital printing 52
Multiples and subdivisions covering
the A, B and C range of sizes
in mm 105
Selection of A, RA, SRA and B

range of sizes in mm 106
Range of sizes in mm representing
the metric range of traditional UK
paper and board imperial system 106

© Copyright Pira International Ltd 2003

4.4

4.5

6.1

US paper grades, sizes and basis
weight range in lbs per ream of
500 sheets 107
US paper grades, using the basis
weight for book papers as the
reference grade, highlighted in
italics, along with the equivalent
weight in lbs per ream of 500
sheets for the other paper grades,
plus overall gsm 107
Projected market share change of
printing processes over time 154


List of figures

1.1

1.2
1.3
1.4
1.5
1.6

1.7

1.8

1.9

1.10

1.11

1.12

1.13

1.14

1.15

The planographic principle of
printing 2
The relief principle of printing 2
The intaglio principle of printing 3
The stencil principle of printing 3
The offset principle of offset litho

printing 5
Schematic drawing of a single-colour
Heidelberg Printmaster GTO 52-1,
B3 small offset press (1/0) 9
Schematic drawing of a two-colour
Heidelberg Printmaster PM74-2P,
B2 offset press, with conversion
option (2/0 and 1/1) 10
Illustration of the Komori Lithrone
440SP four-over-four B1 perfector
offset press 12
Schematic drawing of a two-colour
Ryobi 522HXX, A3+ offset press,
with common impression cylinder
construction 13
Schematic drawing of a typical
inking system used on a sheetfed
offset litho press 14
Schematic drawing of a damping
system used on an offset litho press,
showing the pan or trough of
damp, which is enclosed when an
alcohol-based solution is used 15
Schematic drawing of Heidelberg
Quickmaster DI 46-4, waterless
SRA3+ four-colour satellite
computer-to-press machine 19
Schematic drawing of a four-unit
blanket-to-blanket heatset web
press with the web travelling in a

horizontal direction 22
Schematic drawing of a four-unit
common impression satellite-type
coldset web press unit 23
Schematic drawing of a single-unit
blanket-to-impression web press
section 23

Page vii © Copyright Pira International Ltd 2003

1.16
1.17
1.18

1.19

1.20

1.21

1.22

1.23
1.24
1.25
1.26
1.27

1.28
1.29

1.30

Schematic drawing of a single web
four-unit heatset web press 25
Schematic drawing of a twin-web
eight-unit heatset web press 25
Schematic drawing of a 32-page
long-grain heatset web press
cylinder configuration 27
Schematic drawing of a 32-page
short-grain heatset web press
cylinder configuration 28
Single web two-unit coldset
H-shaped blanket-to-blanket print
unit module used on the Cromoman
four-page newspaper press, with
the web travelling in a vertical
direction 29
Schematic drawing of a highspecification four-unit narrow-width
web offset press, showing web
paper specifications and inline
finishing operations 31
Schematic drawing of a typical
single flexographic printing unit
with ink feed via a fountain roller
system 33
Chambered doctor blade inking
system 34
Common impression/satellite
multicolour flexographic press 35

Edale eight-colour Beta flexographic
and combination press 36
Cooper single-colour Flexopress
model 1500 37
Schematic drawings of letterpress
platen and flatbed cylinder
presses 38
Schematic drawing of a two-colour
gravure press 40
Comprehensive schematic drawing
of the gravure printing process 41
Schematic drawing of a KBA eightunit rotogravure TR 10 B/352
press 43


Introduction to Printing and Finishing
List of figures

1.31

Schematic drawing of a single
colour basic screen press 44
1.32 A Svecia five-colour SAMX fully
automatic screen printing press 46
2.1
Xerox Docuprint digital
monochrome copier/printer
system 58
2.2
Minolta MicroPress cluster printing

system 59
2.3
VersaMark printing system 62
2.4
Inca Eagle 44 64
2.5
Océ CPS700 seven-colour colour
copier/printer, showing the straight
paper path around one common
imaging drum 66
2.6
Schematic drawing of the
DocuColor iGen3 digital colour
production press 67
2.7
Schematic drawing of the NexPress
digital colour production press 69
2.8
B2 sheetfed b7000 HP-Indigo
digital colour production press 70
2.9
Xeikon DCP 320 D digital colour
webfed production press showing
the one-pass duplex printing
operation 71
3.1(a) The ‘neck’ of the delivery unit of a
sheetfed press showing the position
of an infrared drying unit, and (b)
the radiant heat coming from the
infrared unit 76

3.2
DuPont Eurostandard colour
bar 80
4.1
Schematic drawing of Fourdrinier
papermaking machine – from the
wet end to the dry end of the
machine 88
4.2
Stack of calender rolls as used on a
supercalender unit 89
4.3
Paper fibres aligning with the
machine direction during
papermaking 92
4.4
Illustration of how paper fibres and
sheets of paper stretch and expand
more in the cross-grain direction 94

Page viii © Copyright Pira International Ltd 2003

4.5
4.6
4.7

4.8

4.9

5.1
5.2
5.3

5.4

5.5
5.6
5.7
5.8

5.9
5.10

5.11
5.12

Watermark and laid wires on a
dandy roll 95
Construction of a whitelined
chipboard 102
The ISO series of A, B and C sizes
are proportionate to each other,
shown by the dotted line passing
through the apex indicated by each
size range 104
The range of A sizes obtained by
halving or doubling the size above
or below in the range from
A0 to A7 105

Sub-divisions of UK and US
traditional imperial paper and
board sizes from quad to 32mo 108
Heidelberg Polar cutting
system 6 118
Different types of fold, including
right angle, parallel and cross 119
Schematic drawing of the knife
action of folding used on folding
machines 120
Schematic drawing of the buckle
action of folding used on folding
machines 121
Examples of common fold
configurations 122
Illustration showing sections being
gathered 124
Illustration showing sections being
insetted 124
Collating or back step marks used
to identify visually any miscollated
sections 125
(a) Saddle-wire stitching and
(b) side-wire stitching 126
Müller Martini Bravo Plus
gather/inset, saddle stitch, trim
(GST) machine 127
Müller Martini Acoro perfect binding
gather, adhesive, trim machine 130
Müller Martini Ventura book

sewing machine 131


Introduction to Printing and Finishing
List of figures

5.13
5.14
5.15
5.16
5.17

5.18

5.19
5.20
5.21
5.22
5.23
5.24
5.25

5.26

5.27

Page ix

Operation of flatbed die cutter
cutting label to shape 134

Atlas automated label production
line 134
SP 104-E Autoplaten die-cutter/
cutting-and-creasing press 135
SP 102-BMA Foilmaster foil
stamping press 136
Schematic drawing showing former
and ribbon web folding
operation 138
Examples of page and size
configurations on a web offset
press fitted with a single chopper
combination folder 139
Examples of different cover
styles 141
Cover glued at the spine only, i.e.
wrappered 142
Cover glued at the spine and
hinged 142
Covering with endpapers glued
in 143
Plastic comb binding 144
Standard spiral wire binding 144
Wire-O binding, allowing alignment
on page spreads to be
maintained 145
Schematic drawings indicating the
typical sequence of a soft cover
adhesive bound book 146
Schematic drawings indicating the

typical sequence of a hard cover,
adhesive-bound book block 147

© Copyright Pira International Ltd 2003

5.28

5.29

5.30

5.31

6.1
7.1
7.2
7.3
7.4

7.5
7.6

Schematic drawings indicating the
typical sequence of a hard cover,
thread-sewn-bound book block 147
Schematic drawings indicating the
typical sequence of book block
processing 148
HP-Indigo webfed digital press with
printed product being cut and

folded inline 151
Horizon online binding system
linked to sheetfed digital printing
system 152
Visual characteristics of different
printing processes 157
Printcafé’s integrated Logic MIS in
schematic form 166
Flow diagram of a typical CIP4 and
MIS link-up 169
Speedmaster 74 DI digital imaging
sheetfed offset litho press 171
Schematic drawings illustrating
inline finishing of cutting, creasing
or perforating set-up on sheetfed
offset litho machines with the
preparation of blanket and
impression cylinder 172
Heidelberg CutStar sheeter and
feeder device 173
Rolls Systems DocuSheeter LS
connected to a Heidelberg
Digimaster 9110 digital printing
system 174



Conventional printing processes

Introduction

1

Lithography, letterpress, flexography, gravure and screen are the five main conventional
machine printing processes. Each of these processes is separate and distinct. This is due to
the different operation of the planographic, relief, intaglio and stencil types of printing.
All conventional printing processes follow the same initial stages in order to
convert the original matter, which can be of conventional or digital origin, into an image
carrier – such as a plate, cylinder or stencil – that produces the finished printed form.
In conventional (otherwise known as traditional) graphic reproduction, the
printing elements of type matter and graphics are converted into an intermediate film
stage of negatives or positives. These are then assembled, planned and approved before
image carriers for each of the printing processes are produced.
Image carriers, in the form of plates, cylinders or stencils, can be created either by
exposing the assembled films onto a light-sensitive image area which is then processed, or
by laser engraving, digital or chemical transfer.
All printing processes are identified and categorised by the way they create
printed images. Printing image carriers have two separate surfaces: image or printing areas
and non-image or non-printing areas. Printing areas accept the ink by physical or chemical
means of transfer. Non-printing areas do not accept or retain ink.

Basic principles of the
main conventional
printing processes

In planographic printing, the printing and non-printing areas are, to all intents and
purposes, on the same plane. This means that the substrate, such as paper or board,
is pressed into contact with the whole surface.
The processed plate is treated, so that the printing areas, when they receive ink

Planographic printing

from the inking rollers, transfer it to the substrate. The non-printing areas then reject ink,
having previously been wetted with a dampening solution.
Figure 1.1 (overleaf) illustrates the side view of a planographic plate. The ink,
represented by the solid areas, and the damping solution, seen here as wavy lines,
show the printing and non-printing areas respectively. In addition, a face-on view of
a planographic plate is shown, indicating the printing areas in the form of the words
‘offset litho printing’ and the blank non-printing areas.
Lithography is an example of the planographic printing process.

Page 1 © Copyright Pira International Ltd 2003


Introduction to Printing and Finishing
Conventional printing processes

FIGURE 1.1 The planographic principle of printing

Water accepting/ink repelling
non-image areas that do not print
Ink receptive image areas

Non-image wetted with
font solution

Offset litho
printing plate

OFFSET LITHO

PRINTING

Ink accepting/water
repelling image
areas that print

Source: Pira International Ltd

Relief printing

In relief printing, the printing areas are raised above the non-printing areas. These printing
areas receive the ink that is then transferred to the substrate when it is pressed against the
printing areas. The ink rollers and the substrate come into contact only with the raised
printing areas.
Figure 1.2 illustrates the side view of a relief plate, showing the raised solid inked
areas and the non-printing areas (below the surface). The face-on view of a relief plate is
also shown with the words ‘flexographic printing’.
Flexography and letterpress are examples of relief printing processes.
FIGURE 1.2 The relief principle of printing

Raised inked image areas
Raised image areas only
receive ink and print

Non-image areas

Non-image areas not in
relief do not receive ink
and therefore do not print

Source: Pira International Ltd

Intaglio printing

In intaglio printing, the printing areas are the reverse of that in relief printing, i.e. they
are recessed and on a lower level than the non-printing areas. The recessed printing areas
are filled with ink and then the surplus ink is removed from the non-printing areas. The
substrate is then pressed against the printing cylinder to transfer the ink onto it.
Figure 1.3 (opposite) illustrates the side view of a gravure cylinder showing the
recessed printing areas filled with ink and the non-printing, flush surface areas of the
cylinder. The face-on view of an intaglio cylinder is shown with the words ‘gravure printing’.
Gravure is an example of the intaglio printing process.

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© Copyright Pira International Ltd 2003


1

Introduction to Printing and Finishing
Conventional printing processes

FIGURE 1.3 The intaglio principle of printing

Recessed/intaglio image areas

Recessed image areas
only retain ink and print

Cylinder surface
non-image areas

Surface non-image areas
do not retain ink and
therefore do not print

Source: Pira International Ltd

Stencil printing

In stencil printing, the printing and non-printing areas are carried on a mesh screen,
with the printing areas being open, or unblocked, in the form of a stencil. The nonprinting areas are formed by blocking out the appropriate areas of the mesh.
During the printing process, the substrate is placed in contact with the
prepared mesh screen. Ink is then forced through the open, unblocked printing areas
to meet the substrate.
Figure 1.4 illustrates the side view of a processed screen stencil, showing the
weave of the mesh as thin, diagonally striped columns. The clear areas indicate the
unblocked areas through which the ink is forced onto the substrate.
Screen printing is an example of the stencil printing process.

FIGURE 1.4 The stencil principle of printing

Image areas clear to receive ink
which passes through unprotected
mesh
Squeegee
Ink

Printed substrate with

inked areas corresponding
to the clear/unblocked
areas of the stencil mesh

Processed stencil
diagonal lines indicate mesh
with solid areas representing
blocked off non-image areas,
clear areas represent image
areas though which ink
penetrates onto the substrate

Source: Pira International Ltd

Page 3 © Copyright Pira International Ltd 2003

Non-image areas blocked off
across the mesh to prevent ink
passing through


Introduction to Printing and Finishing
Conventional printing processes

The main
conventional printing
processes outlined

Lithography, based on the planographic process, is the most widely used printing process.
This is due to its versatility, speed, quality and cost-effectiveness across a wide range of

printed products.
The basic principle of lithography is essentially that of a chemically-based process

Lithography

that grease or oil and water do not mix. Printing areas are created that are oleophilic (oil
attracting) and water repelling, and non-printing areas created are hydrophilic (water
attracting) and oil repelling. A notable exception to this basic principle is waterless litho,
an explanation of which follows later in this chapter.
When viewing a litho plate, such as the one seen in the face-on image in Figure
1.1, printing and non-printing areas can be clearly identified. No physical difference can be
detected, however, if for example a hand is run over the plate surface.
Flexible litho printing plates made from paper, polyester, plastic or metal have
replaced the rigid, thick porous stones that typified the early days of the lithographic
process. Each of these materials is processed and treated to acquire the properties needed
to meet the requirements of the lithographic process.

Offset lithographic
printing

Offset lithographic printing gradually replaced direct litho printing from the early 1900s.
In offset litho printing the right-reading printed plate is not transferred directly onto the
substrate, but is initially offset, or transferred, wrong-reading onto an intermediate surface
of a rubber blanket. From there the printed image becomes right-reading again when the
substrate receives the image from the blanket cylinder (Figure 1.5, opposite).
The offset litho process was first used for tin printing before paper, board and
virtually all other substrates adopted it. It is the only major conventional process that does
not print directly onto the substrate. The offset rubber blanket offers many advantages to
the litho process. These include the ability to print very fine resolution detail, and on a
wide range of substrates including relatively thin gauge metal and plastics.

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© Copyright Pira International Ltd 2003


1

Introduction to Printing and Finishing
Conventional printing processes

FIGURE 1.5 The offset principle of offset litho printing
Inking system

Damp/font
solution
OFFSET LITHO
PRINTING

Plate cylinder

OHTIL TESFFO
GNITNIRP

Arrows indicating
direction of
paper path

Printed sheet
of paper

Blanket cylinder

Impression
cylinder
Plain paper
feed unit

OFFSET LITHO
PRINTING
Delivery cylinder

Offset litho single-colour printing unit
Printed paper
delivery unit
Source: Pira International Ltd

Offset lithographic presses are designed to print sheetfed, reelfed or webfed on a wide
range of substrates. Sheetfed presses are more flexible and numerous than webfed ones,
but both are popular depending on a company’s target print market.
The simple schematic drawing of a sheetfed offset press in Figure 1.5 illustrates
the arrangement of the three main printing cylinders: plate, blanket and impression, plus
the auxiliary delivery cylinder.

Sheetfed offset
lithographic printing

A series of machine lays and grippers control the exact position of the sheet by a sheetfed
offset lithographic press on the substrate. Irrespective of the size of sheet being printed,
three lays are used, two front and one side lay. The front lays are set and adjusted to

square up the printing on the substrate and are also used to fine tune the image position
on multi-pass work.
The side lay fits on to the press’s feed board, across which it can be set in any
position. It can also be removed and placed the other way round. This will allow the same
Page 5

© Copyright Pira International Ltd 2003


Introduction to Printing and Finishing
Conventional printing processes

edge of the sheet to be fed to it when printing the second side. An example of this is when
a job is printed by the work-and-turn method.
When the sheet is moved forward by the feeder mechanism to the front and
side lays on the feed board, the front edge of the sheet overhangs to allow it to be taken
by the grippers that carry it around the cylinder for printing. The purpose of the lays,
therefore, is to position the sheet correctly for gripping, after which it is held in that
position during printing operations.
The printing plate is clamped around the plate cylinder and, as the cylinder
revolves, the damping rollers apply the damp solution. The quality of printing largely
depends on the correct balance of damp solution and ink being applied to the plate.
To bring it into register, the position of the plate may be adjusted on the plate
cylinder. This can also be achieved by micro-adjustment of the front or side lays to which
the sheet is presented prior to being taken into the press.
Lithographic blankets are usually made of a fabric-backed material with a surface
coating of synthetic rubber. They are available in a range of shore hardness to suit the type
of work being undertaken.
Printers of general commercial work tend to favour a compressible rubber
blanket. The blanket material must be treated carefully as any indentations will leave

corresponding non-printed areas on the substrate. However, with care, it should last for
a reasonable time.
The blanket does not normally need to be changed when the printing plate
is changed, unless it has been damaged or badly worn on the previous print run.
The image is cleaned from the blanket with a suitable solvent, leaving the
blanket clean to receive the image from the next plate. Cleaning must be done carefully
and regularly to ensure that the blanket does not become contaminated.
During its life the blanket material is constantly under pressure due to coming
into contact with the plate cylinder and impression cylinder. In addition, it is regularly
washed and cleaned with solvent and other agents, which often results in a surface glaze
that has to be removed. During a print run the operator will regularly stop the press to
clean the blanket and remove an accumulation of unwanted particles such as loose fibres,
dust and ink particles, which will adversely affect the print quality.
The impression cylinder, as its name suggests, provides pressure to ensure the
substrate comes into contact with the blanket cylinder to create the printed result. It is
important that the correct amount of even pressure is applied between the two cylinders to
ensure the overall required print quality is achieved. If too much pressure is applied, there
will be a heavier printed result than required, including dot gain – and vice versa when not
enough pressure is applied.

Sheetfed offset
lithographic press sizes

Sheetfed offset lithographic presses are made in a variety of sizes. Typically, these equate
to just above the B range of the International Standards Organisation (ISO). Some presses,

Page 6

© Copyright Pira International Ltd 2003

1

Introduction to Printing and Finishing
Conventional printing processes

however, are manufactured to just above the SRA sizes, with rounding up and down
resulting in a wide range of press sizes.
Printers seldom buy trimmed, finished size paper and board such as A3, A2 or
A1. During the printing and finishing process several allowances for the overall sheet size
have to be made, such as trim or bleed, gripper allowance and colour bar, etc. Without
these additional allowances the printer could not achieve the quality and overall finished
sizes required.
In the UK, printed products are generally based on A sizes and their derivatives.
The relationship between the different sizes can be seen by comparing the size A1, which is
594 x 841mm, with SRA1, which is 640 x 900mm and B1, using the accepted rounded up
figures of 720 x 1020mm or 720 x 1040mm. More detail is included on paper and board
sizes in Chapter 4.
TABLE 1.1 Range of sheetfed offset litho press sizes
Maximum sheet size
340 ×
450mm
370 ×
520mm
508 ×
686mm
530 ×
740mm
720 × 1,020mm
820 × 1,120mm

890 × 1,260mm
920 × 1,300mm
1,020 × 1,420mm
1,200 × 1,620mm

Equivalent stock size
SRA3+
B3+
SRA2+
B2+
B1+

SRA0+
B0

Source: Pira International Ltd

Table 1.1 outlines a range of sheetfed offset litho press sizes. However, it should be noted
that the list only covers some of the available press sizes.
Press sizes typically based around SRA3 and B3 are often referred to as small
offset presses. They are available in up to at least six print units and as portrait or
landscape presses. With a portrait press the short edge of the sheet is fed into the front
lays. In the case of a landscape press, it is the long edge.
Feeding a sheet in by the long edge, i.e. landscape, gives greater sheet control
and is used in sheetfed presses of SRA2, B2 and above. Small offset presses are used to
print relatively small format, small quantity and fast turnaround work, including stationery,
such as letterheads, compliment slips, business cards and leaflets.
Medium format size presses, based around SRA2 and B2, are available in up to at
least ten colours. They are used for a range of commercial printing, mainly of larger format
size than SRA3 and B3 presses and/or typically longer print runs.

Large-format size presses, based around SRA1 and B1, are available in up to at
least 12 colours. Again, they are used for a wide range of commercial printing, including

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Introduction to Printing and Finishing
Conventional printing processes

short- to medium-range, high-pagination work such as magazines, journals, brochures, etc.
Plus they are used for specialist work such as cartons and wet gummed labels.
Extra large format size presses, based around SRA0, B0 and above, are available
in up to at least 12 colours and are not as prolific as the other sizes in terms of the number
of presses sold. They tend to be used for more specialised work, including large-format
posters of medium to large print runs. Book printers use them to produce large pagination
signatures (folded sections), or large format publications. Plus, they are used by carton
printers producing large print runs and/or large-format cartons.
With print runs in general getting smaller, there has been a move towards smaller
press sizes, at least in terms of the volume of presses sold. However, all the press sizes
mentioned are supported in the different sectors of sheetfed offset litho.

Sheetfed offset litho
press configurations

Sheetfed presses are available in a range of configurations, including single-, two-, four-,
five- and six-colour, up to at least 12-colour.
All printing presses are made up of three main parts:
ᮣ

A feed unit that feeds the substrate into the press;

ᮣ

A print unit, or series of print units, depending on the number of print heads
on the press;

ᮣ

A delivery unit that delivers the printed sheets into the delivery mechanism.

Most offset litho presses are constructed of modular, i.e. unit-based, printing units,
between each of which the sheet travels on transfer cylinders or chain grippers. Each
printing unit consists of impression, blanket and plate cylinders, together with the
necessary inking and damping rollers. Figure 1.6 illustrates a schematic drawing for a
single-colour B3 press, showing the three elements of the sheet feed unit, one printing unit
and the delivery unit.

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1

Introduction to Printing and Finishing
Conventional printing processes

FIGURE 1.6 Schematic drawing of a single-colour Heidelberg Printmaster GTO 52-1, B3

small offset press (1/0)
6 5 4

10

9

8

3

2

1

1
2
3
4
5
6
7
8
9
10

Sheet feeder unit
Sheet control system
Damping system
Inking system

Plate cylinder
Blanket cylinder
Impression cylinder
Anti-set off spray unit
Delivery unit
Press control console

7

Source: Heidelberg

Standard multicolour presses are constructed so that they can print one side only in one
press pass. These are known as straight printing presses. Other multicolour presses are
constructed so that they are able to convert from printing one side only. These are called
convertible printing presses.
On convertible presses a conversion unit is fitted between the selected printing
units. The printed sheet is turned over by the conversion mechanism that changes the
direction the sheet is travelling. This results in the sheet being presented tail end and
opposite side first to complete printing on the non-printed side of the sheet.
An example of a convertible press is the two-colour press shown in Figure 1.7. This
has been constructed so that it can either print two colours on one side of the sheet, or be
changed over to a perfecting mode to print one colour on both sides, depicted as 2/0 and
1/1. Impression cylinders on convertible presses that are either side of the conversion unit
normally have a grained surface. Or they can be coated with a material to prevent them
taking up ink from newly printed sheets.
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Introduction to Printing and Finishing
Conventional printing processes

FIGURE 1.7 Schematic drawing of a two-colour Heidelberg Printmaster PM74-2P, B2 offset

4

2

3

1

1 Sheet feeder unit
2 Print units (2)
3 Optional conversion unit
for straight or perfected
printing
4 Delivery unit

press, with conversion option (2/0 and 1/1)

Source: Heidelberg

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Introduction to Printing and Finishing
Conventional printing processes

1

Most sheetfed presses are built on the blanket-to-impression principle, as illustrated in
Figure 1.5 (page 5). However, specialist dedicated perfectors, i.e. presses that are only
designed to print both sides of the sheet in one pass, are ideally suited to work that needs
to be printed both sides. Heatset perfector presses are built on the blanket-to-blanket
principle as illustrated in Figure 1.12 (page 19) The top blanket cylinder also acts as the
impression cylinder, the bottom blanket cylinder printing on the reverse of the sheet.
Due to the success of convertible presses, which give the printer the option of
straight and perfected printing on a wide range of multicolour presses, sheetfed perfector
presses are aimed at a niche market – such as book and journal printers that specialise
in monochrome (single-colour) publications.
An interesting innovation and development in perfected printing is the Komori
Super Perfector (SP) range of multicolour, two-sided sheetfed presses. The 440SP model, for
example, is built on a four-over-four unit basis, rather than the four-back-four basis used by
other eight-colour convertible presses.
Lithrone SP presses have a very small footprint and are therefore efficient in
terms of the floor space they take up. Overall, the presses occupy around a third less space
than that occupied by the equivalent multi-unit, straight-line convertible presses. A further
feature of SP presses is that the same grip edge of the sheet is used throughout the
printing operation, whereas convertible perfecting presses grip on different sheet edges.

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© Copyright Pira International Ltd 2003


Source: Komori

3

FIGURE 1.8 Illustration of the Komori Lithrone 440SP four-over-four B1 perfector offset press

2

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© Copyright Pira International Ltd 2003

1

1 Press control console
2 Enlarged section showing double-size
impression cylinders and stacked print
unit construction
3 Delivery unit based on flat sheet
transport without conventional
swan neck

Introduction to Printing and Finishing
Conventional printing processes


1

Introduction to Printing and Finishing
Conventional printing processes

Multicolour sheetfed offset presses can be of modular or single unit construction.
Alternatively, they can be of common impression construction, with one impression cylinder

serving two or more blanket cylinders. These have become relatively uncommon. The feed
and delivery systems of all presses are similar in construction, irrespective of the number of
units in the press.
Figure 1.9 illustrates a two-colour sheetfed offset litho press with two sets of plate
and blanket cylinders, plus a common impression, double diameter cylinder. Common
impression cylinder sheetfed offset litho presses, typically built in five cylinder, two-colour
print units, are a relative niche market where space saving is an important consideration.
This is due to the smaller footprint of common impression presses. They also allow highquality register, two-colour printing without sheet transfer via gripper change between
units. Although these presses are available in up to at least six print units.
FIGURE 1.9 Schematic drawing of a two-colour Ryobi 522HXX, A3+ offset press, with common
impression cylinder construction
4

2

1

1
2
3
4

Common impression cylinder
Plate cylinders (2)
Blanket cylinders (2)
Semi-automatic
plate change facility

3
Source: Ry-Offset

Lithographic
make-ready and
printing

The time taken for make-ready (or setting up) a sheetfed press depends on the type
of work being printed, the standard of production required and the degree to which the
press is automated.
The main press make-ready operations include the setting up of the feed and
delivery units, along with the path of the substrate through the press. The inking system
has to be set to supply more ink to heavy print coverage areas than to light ones, and the
damping system must be set to deliver the correct amount of damp for each job.

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Introduction to Printing and Finishing
Conventional printing processes

Printing plates also have to be correctly positioned, with the cylinder pressures set to suit
the stock being printed and give the correct print length.
The average net output speeds of sheetfed offset litho presses vary from 3000 to
12,000 sheets per hour. This depends on the length of run, type of material being printed
and the sophistication of the press type, with maximum press speeds of up to 18,000
sheets per hour. It can take up to one hour to make-ready a single-colour basic press, and
over two hours on a four-colour basic press. On a highly automated press these times can
be reduced to 20 minutes or less and 40 minutes or less respectively.

Inking systems

On sheetfed offset litho presses, ink is generally applied to the printing plate by three or
more plate rollers. These rollers are at the end of the inking system that starts with the ink
duct. A typical example of an inking system is shown in Figure 1.10. The ink duct is a
reservoir for holding a supply of ink ready to be fed into the inking system.
Ink flow from the duct is controlled in two ways. One method is to control a
specific area, or areas, across the width of the system by loosening or tightening a series
of thumbscrews, or keys, that act on the duct blade. They thereby release more or less ink
at the particular points the ink duct keys apply or reduce pressure to the blade. An
alternative way of controlling the ink across the full width of the rollers is to adjust the
dwell, or length of time the ink feed roller remains in contact with the main distributor
roller. A longer dwell would result in more ink and a shorter dwell less ink.

FIGURE 1.10 Schematic drawing of a typical inking system used on a sheetfed offset
litho press
U
F
D

R
D

D

U
F
D
R
P

D
D

D

D

Duct roller
Feed roller
Distributor roller
Rider roller
Plate roller

D
P

P

P
Plate cylinder

Source: Pira International Ltd

Offset litho printing ink rollers are made of various materials. Plate rollers that come
into direct contact with the printing plate are usually coated with synthetic rubber,
polyurethane or other suitably compressible material. Other rollers used in the inking

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1

Introduction to Printing and Finishing
Conventional printing processes

system may be coated in steel and have a water-repellent coating. Inking rollers are often
made to oscillate from side to side to ensure better and more even ink distribution and
improve the coverage of larger printing areas.
Where ink flow is controlled from a console, i.e. remotely controlled rather than
manually adjusted by the operator, keyless ducts are used where conventional
thumbscrews and duct blades are replaced by wedges, cams or other devices to feed
the ink to the inking system. Automatic wash up of the inking system is now generally
available on presses of all sizes.

Damping systems

The damping system of offset litho presses is designed to apply an even film of moisture
to the plate while the press is running.
Conventional damping systems have two plate damping rollers, which are
covered with fabric and driven by a metal distributing roller. The damping solution is
transferred to the metal roller via a cloth-covered feed roller that moves alternately from
contact with the metal roller to contact with the fountain roller. This then rotates in
damping solution in the fountain pan or trough. As the feed roller revolves against the
metal distributing roller, it passes on some of the damp solution it has picked up.
As the amount of ink that is applied is controlled by the amount of dwell the
feed roller and other rollers have by coming into contact, so the same basic principle
applies with the application of the damp solution.

FIGURE 1.11 Schematic drawing of a damping system used on an offset litho press,
showing the pan or trough of damp, which is enclosed when an alcohol-based solution is used
Fabric-covered feed rollers
Metal distributing rollers
Plate
cylinder

Damp/font solution

Source: Pira International Ltd

Alternative damping systems to that covered by Figure 1.11 are brush feed – replacing the
feed roller – and an air mist system which replaces damping rollers altogether. Further
examples include an integrated, or continuous, method of damping and inking, via the
inking rollers, which is popular on small offset presses. This is also used on larger machines
in some special alcohol-based damping systems.
Damping solutions used by offset litho printers are seldom water alone, due to
the fact that, ironically, water on its own is not a particularly good wetting agent. Also, the
quality of water, in terms of the different treatments it is subjected to and the additives put
into it to make it suitable for drinking, varies from area to area. As a result, to improve the
‘wet ability’ and print quality of the water-based damp solution, additives and buffers are

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© Copyright Pira International Ltd 2003