1.
Basics of offset printing & other
printing methods
1

2.
Products
Offset
Sheet- Heatset Coldset
Gravure Flexo Digi
fed
Magazines,
catalogues X X X
Brochures, annual
reports etc. X X
Direct marketing
X X X X X
Books
X X X
Newspapers
X X
Packages, wrappers
X X X
2

3.
Why ?
A better understanding of the first end
use of our products (to be printed) will
allow you to better advise your
customers and thus give added value to
your sales
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4.
Summary
Offset printing
What is colour ?
Principle of offset printing
Sheet-fed offset printing
Heat-set web offset printing
Other printing methods
Conventional methods
Gravure
Flexography
Silk screen
Digital printing methods
Laser (electro photography)
Ink jet
Conclusion
4

5.
High Placement of printing methods
Ink-jet
Sheet-fed offset
Heatset offset Gravure
Quality
Medium
Electro photo-
graphy
Low
100 1 000 10 000 100 000 1 000 000 10 000 000
Run length
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6.
Summary
Offset printing
What is colour ?
Principle of offset printing
Sheet-fed offset printing
Heat-set web offset printing
Other printing methods
Conventional methods
Gravure
Flexography
Silk screen
Digital printing methods
Laser (electro photography)
Ink jet
Conclusion
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7.
What is colour ?
Colour
Without light, no object has a colour
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8.
What do we need to see colours ?
A light source (Sunlight, Light Bulb, Candle)
A receiver and processor
(eye + brain)
An object to interact with the light source
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9.
Human eye
• light enters the eye through the lens and is focused on the retina
There, an array of photoreceptor cells respond to light and pass the
signals on to the brain which translates into colour sensation
There are 2 types of cells :
-> rods = black & white -> cones = colours
3 different types of cone cells sensitive to the
wavelength of
=> red light
=> green light
=> blue light
Cells light stimulates the eye three
dimensionally!!
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10.
Spectrum of electromagnetic radiation waves
Gamma X-ray UV IR Radio Radar
Wavelength 0,001 0,01 0,1 1,0 10 100 10³ 10 4 10 5 10 6 1010 1011 10 12 10 13 nm
Spectrum of the visible light
photon
violet blue green yellow orange red
nm
400 500 600 700
different wavelengths = different colours
400 - 500 nm = blue 500 - 600 nm = green 600 - 700 nm = red
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11.
How to create colours ? : 2 methods
Additive Subtractive
Yellow
Cyan Magenta
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12.
How to create colours : additive method
Additive Lights : Red + Blue + Green = White
For example a Television or a Computer Monitor
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13.
How to create colours?
Based on this (Green + Blue = CYAN, Green + Red = YELLOW, Blue + Red = MAGENTA),
we can reproduce every colour based on 3 selected colorants
Each colorant will have to act on a primary colour of the spectrum (Red, Green or Blue)
For example to act on Red, we need a colorant which absorbs only Red and not Green and
not Blue. This is the CYAN
Ink which
absorbs red light
reflects blue light blue + green = cyan ink
reflects green light
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14.
How to create colours : subtractive method
Selective absorption of certain wavelength by the ink layer.
Magenta ink Cyan ink Yellow ink
reflects red absorbs red reflects red
reflects blue reflects blue absorbs blue
absorbs green reflects green reflects green
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15.
Primary colours in printing
Mixing the 3 primary colours theoretically results in black.
=> In practice the result is brown!
=> To remedy this, blacK is used as the fourth primary colour.
CMY blacK CMYK
CMY Black CMYK
+ =
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16.
Summary
Offset printing
What is colour ?
Principle of offset printing
Sheet-fed offset printing
Heat-set web offset printing
Other printing methods
Conventional methods
Gravure
Flexography
Silk screen
Digital printing methods
Laser (electro photography)
Ink jet
Conclusion
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17.
Principle of offset printing
On a printing plate there are two areas:
• Areas accepting ink and being repellent to water
= Image areas (= hydrophobic)
• Areas accepting water
= Non-Image areas (= hydrophilic).
The areas are occupied by water.
Due to the different surface tension water and ink do not mix.
The behaviour of the image and non-image areas
is caused by a complex chemistry.
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18.
How do we get printed and unprinted areas?
Ink = hydrophobic Water = hydrophilic
IMAGE NON-IMAGE
Function of the offset plate
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19.
How do we get printed and unprinted areas?
Image
Non-Image
Magnified (15x) of an offset plate
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20.
How do we get printed and unprinted areas?
Non-
Image
Image
Magnified (1000X) picture of an offset plate
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21.
How do we get printed and unprinted areas?
Substrate
= direct transfer
IMAGE NON-IMAGE
Function of the offset plate
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22.
How do we get printed and unprinted areas?
Rubber Rubber
1st transfer 2nd transfer
Substrate
IMAGE IMAGE NON-IMAGE
NON- IMAGE
Function of Rubber blanket = indirect transfer
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23.
Offset printing unit
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24.
The printing plate
Light sensitive coating
Aluminium oxide coating
Grained aluminium base
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25.
The printing plate
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26.
Basic composition of offset ink
Pigments ~10-20 %
organic and inorganic
Binders ~30-50 %
Hard resins
Alkyds
Vegetable oils
Solvents ~20-30 %
Mineral oils
Vegetable oils
Additives ~0-5 %
waxes, rheology modifiers, antioxidants, fillers...
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27.
Offset blankets
Oil-resistant synthetic
elastomers attached to
textile fabrics
Reproduction properties
Release properties
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28.
The fountain solution
Surface tension of liquid has to be lower than surface energy of solid to
ensure quick spreading
•Water 85-98 %
•IPA (Isopropanol) 0-20 %
•Additives 2-4 %
weak organic acid(s), buffers, film formers, surfactants, chelating (sequestering) agents,
biocides, anti-foams, humectants, glycols, corrosion inhibitors
pure water,
72 mN/m water + 6% IPA,
45 mN/m
surface energy of non-image area, 50 mJ/m 2
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29.
Screening
One half-tone image may
contain thousands of
different shades………
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30.
Different screening
Conventional screening Stochastic screening
 distance between the centers of  tone is formed by altering dot position
the dots is constant and spacing, number of dots
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31.
Stochastic screen
Standard dot size, Dot size and
but the amount of amount of dots
them vary. vary.
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32.
Screen ruling – conventional screening
Light tones ~ small dots The dots are so small that the human eye
Dark tones ~ bigger dots sees them as a single colour.
Tonal value 75%
Tonal value 25%
40l/cm
Tonal value 50%
60l/cm
80l/cm
Tonal value 100%
Screening ruling (L/cm or L/inch)
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33.
Human eye
In case of the 4-colour printing the colours are mixed in the eye when
looking at them, as the eye cannot differ between the small, close
picture elements.
Normal screen surface Strongly magnified screen surface
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34.
Print density
 Print density (darkness) is created by increasing the inked area
(halftone percentage)
Black 20% Black 40% Black 60% Black 80%
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35.
Print colour
 Print colour (tone) is created by mixing halftone percentages of
process colours
C80%/M20% C60%/M40% C40%/M60% C20%/M80%
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36.
Examples of screening methods
Staccato 25µm Conventional 60 l/cm
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37.
Summary
Offset printing
What is colour ?
Principle of offset printing
Sheet-fed offset printing
Heat-set web offset printing
Other printing methods
Conventional methods
Gravure
Flexography
Silk screen
Digital printing methods
Laser (electro photography)
Ink jet
Conclusion
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38.
Sheet fed offset press
Margin -
Ink rollers & Damping rolls Feeder
Anti set-off
powder
system
Delivery of
the printed
sheets Settings of
pressure
and register
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39.
After the 4 printing units
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40.
Sheet fed presses
5 colour units + 1 varnish unit
Delivery Varnish Ink units Feeder
 4/4 colour units, change of the printing side of the sheet in the perfecting system
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41.
Different formats
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42.
Feeder
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43.
Ink Rollers
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44.
Sheet Transfer
Transfer cylinder
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45.
Spray powder
to avoid ink set-off
distance holder between the sheets.
increases the amount of oxygen to improve the oxidative drying process.
Spray
10 to 80 microns
calcium carbonate
organic, vegetable based powder of natural starch
300x - CaCo3
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46.
Varnish
Why ?
More gloss
Protect
Less drying time before converting
Sometimes two varnish units
High gloss and matt varnish at the same run
Premier and UV- varnish when using conventional inks
Better gloss than one unit applying
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47.
Summary
Offset printing
What is colour ?
Principle of offset printing
Sheet-fed offset printing
Heat-set web offset printing
Other printing methods
Conventional methods
Gravure
Flexography
Silk screen
Digital printing methods
Laser (electro photography)
Ink jet
Conclusion
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48.
Basic design of heatset press
Web widths: ~50- (over) 200 cm
Web speed: ~4-15 m/s
Web tension: ~600-800 N/m
Drying (web temp): ~110-140 °C
Folding: usually on-line
siliconization unit
reelstand dryer
printing units
infeed chill rolls
folder
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49.
Heatset presses - different designs
additional colour varnishing unit (offset varnish)
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50.
Operating press
Driving the press
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51.
Infeed
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52.
Heatset press – an example
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53.
Paper web in one unit
Plate cylinder
Blanket cylinder
Paper web
Blanket cylinder
Plate cylinder
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54.
Oven
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55.
Oven
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56.
Heatset dryer
Web delay in the dryer is ~1 s
dryer length is determined by the press speed (10 m/s  10 m)
Dryer has multiple modules
Hot air from the nozzles carries the web through the dryer
Exhaust air is either circulated back or is let to atmosphere through treatment
(e.g. afterburner)
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57.
Temperature profiles in the dryer
Web exit temp. usually 100-140 C (90-180)
Usually declining temperature profile
web temperature rises faster and solvent evaporation starts earlier
°C
300
255°C
195°C
200
165°C
130°C
100
drying air temp
web temp
1st 2nd 3rd 4th
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58.
Chill rolls
Thermoplastic ink binder is in soft form after the dryer
chill rolls cools down the web and solidifies the binder (better rub resistance)
Steel cylinders (3 - 6) with cold water pumped through
Web tension has to be high enough to ensure good contact
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59.
Silicone application
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60.
Center Cut
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61.
Aligning ribbons
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62.
Different kind of folders
Cylinder/Jaw folder
Former fold
62 Chopper folder

63.
Example of fold 16 pages
Former
fold
Jaw fold
880 mm Chopper/
jaw fold
630 mm
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64.
Folding possibilities
310 x 440 mm
310 x 220 mm
155 x 110 mm
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65.
Imposition and plate making
Imposition
Done usually at the printer
Depends on what press is used
16/32/48/64 pages
Special software used
Plate making
From imposition layout
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66.
Press layouts
72/80-page
48/64-page
Pagination
32-page
Double perimeter
Single perimeter
24-page
16-page
8-page
66 Run length

67.
Manual delivery
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68.
Post-press
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69.
Perfect binding
Operations
 signatures are collated together in conveyor belt
 signatures travels down the belt to the saw
 saw trims off of the bind edge of so the binding
glue can be applied between the individual
pages
 magazine travels to the covering station
 magazine is trimmed with 3-knife cutting
Separate cover is needed
Long grain
=MD
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70.
Saddle stitcher
Operations
 signatures are pulled open and dropped in proper order onto a moving "saddle".
 assembled signatures receive a cover in the same manner and then pass under
the stitching heads where wire staples are applied
 magazine is trimmed with 3-knife cutting
Usually used only product with pagination
under 96 pages
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71.
Summary
Offset printing
What is colour ?
Principle of offset printing
Sheet-fed offset printing
Heat-set web offset printing
Other printing methods
Conventional methods
Gravure
Flexography
Silk screen
Digital printing methods
Laser (electro photography)
Ink jet
Conclusion
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72.
Gravure
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73.
Gravure
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74.
Gravure - applications
Packaging & converting
Flexible packaging
Labels & wrappers
Gift wraps
Wall coverings
Vinyl
Decorative laminates
Floor coverings
Tissue products
Stamps
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75.
Summary
Offset printing
What is colour ?
Principle of offset printing
Sheet-fed offset printing
Heat-set web offset printing
Other printing methods
Conventional methods
Gravure
Flexography
Silk screen
Digital printing methods
Laser (electro photography)
Ink jet
Conclusion
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76.
Flexography
paper
plate
Double face tape
Counter pressure cylinder
ink
sleeve
blade
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77.
Applications
• Paper sacks
• Milk carton
• Pocket Books
• Plastic bags
• Labels
• Aluminium
• Corrugated Board
• Carton cups
• Napkins
• Tissue
• Envelope
• Bussinessforms
• News Papers
• Flexible packaging
• Pocket Books
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78.
Summary
Offset printing
What is colour ?
Principle of offset printing
Sheet-fed offset printing
Heat-set web offset printing
Other printing methods
Conventional methods
Gravure
Flexography
Silk screen
Digital printing methods
Laser (electro photography)
Ink jet
Conclusion
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79.
Silk screen
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80.
Summary
Offset printing
What is colour ?
Principle of offset printing
Sheet-fed offset printing
Heat-set web offset printing
Other printing methods
Conventional methods
Gravure
Flexography
Silk screen
Digital printing methods
Laser (electro photography)
Ink jet
Conclusion
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81.
What is digital printing ?
DIGITAL printing means printing directly from digital data
original is in digital form
no films are needed
no plates are needed
Slide
81
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82.
Pro or Contra digital printing ?
Pro
easily changeable info
design and colours
text
no make-ready
-> small runs with reasonable costs
personalisation
versioning
on-demand printing
decentralised printing
easy to operate vs. offset
”unlimited” repeat length
Contra
 Print quality still lower than in offset
 Low printing speed compared to conventional presses
 Format limitations (small reels/sheets)
 Limited or non-existing spot colours and metallic
 Conventional further converting
 Costs (toners etc)
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83.
Applications
Production variable data
 direct marketing
 individualized statements
 customized catalogues,
brochures etc
Commercial printing
 on-demand and short run
books
 short run brochures
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84.
Summary
Offset printing
What is colour ?
Principle of offset printing
Sheet-fed offset printing
Heat-set web offset printing
Other printing methods
Conventional methods
Gravure
Flexography
Silk screen
Digital printing methods
Laser (electro photography)
Ink jet
Conclusion
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85.
Electro photographic principle
1. Photoconductor is charged
2. Latent image is
formed by discharging - -
- - - - -- - -
- -
the drum by laser or --
--
LED +
++ 6. Remaining toner
--
-
+
-
-+
is wiped off
--
-
3. Latent image is
developed by toner 5. Toner is fixed
to the paper by
heat = fusing
+ ++
+
4. Toner (image) is transferred to the
paper in electric field, opposite charge
attracts
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86.
Summary
Offset printing
What is colour ?
Principle of offset printing
Sheet-fed offset printing
Heat-set web offset printing
Other printing methods
Conventional methods
Gravure
Flexography
Silk screen
Digital printing methods
Laser (electro photography)
Ink jet
Conclusion
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87.
Ink jet : continuous
1. Continuous stream, CS, CIJ
printing droplets are selected from the continuous stream by charging them selectively
droplets have similar size
high speed
e.g. Scitex VersaMark
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88.
Ink jet : drop on demand
2. Drop-on-demand, DOD
every drop is printing
high resolution
lower speed
e.g. Aprion
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89.
Summary
Offset printing
What is colour ?
Principle of offset printing
Sheet-fed offset printing
Heat-set web offset printing
Other printing methods
Conventional methods
Gravure
Flexography
Silk screen
Digital printing methods
Laser (electro photography)
Ink jet
Conclusion
89

90.
Print definition depends on paper quality
LWC, Newsprint,
60l/cm 48l/cm
Coated Fine, SC,
70l/cm 54l/cm
90

91.
Different printing process, different results
Offset Flexography Gravure
(20%, 75 l/cm) (20%, 60 l/cm) (~20%, 100 l/cm)
• Dots are uniformly • Ink is pressed to • Broken shape of dots and
covered with ink edges, print density missing dots are typical for
• Edges are ragged inside dot varies light tones
(uncoated papers) • Edges are smooth • Doughnut shaped dots
• Uniform text • Shadow in the edge • Text is screened, serrated
of text edge
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92.
Examples of halftone dots and text
Inkjet
(20%) Electrophotography
• Dots are quite uniformly (~20%)
• Dots are quite uniformly
covered with ink
• Dot is formed by using several covered with toner
• Edges are ragged
droplets
• Edges are ragged or even • Separate toner particles
depending on paper (dry toner methods)
• Satellites, escaped droplets • Uniform text
92

93.
?
Will be happy to answer your technical questions :
Questions ?
Françoise Accou, +32 492.582.287, francoise.accou@sappi.com
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