basics of offset printing and other printing techniques
TRANSCRIPT
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Basics of offset printing & other printing methods
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XXNewspapers
XXXBooks
XXXPackages, wrappers
XXXXXDirect marketing
XXBrochures, annual reports etc.
XXXMagazines, catalogues
ColdsetHeatsetSheet-fed
DigiFlexoGravure
Offset
XXNewspapers
XXXBooks
XXXPackages, wrappers
XXXXXDirect marketing
XXBrochures, annual reports etc.
XXXMagazines, catalogues
ColdsetHeatsetSheet-fed
DigiFlexoGravure
Offset
Products
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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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SummaryOffset 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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Placement of printing methods
100 1 000 10 000 100 000 1 000 000 10 000 000
Run length
Qu
alit
y
Lo
wM
ediu
mH
igh Ink-jet
Electro photo-graphy
GravureHeatset offsetSheet-fed offset
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SummaryOffset printing
What is colour ?Principle of offset printingSheet-fed offset printingHeat-set web offset printing
Other printing methodsConventional methods
GravureFlexographySilk screen
Digital printing methodsLaser (electro photography)Ink jet
Conclusion
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What is colour ?
ColourWithout light, no object has a colour
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What do we need to see colours ?A light source (Sunlight, Light Bulb, Candle)
An object to interact with the light source
A receiver and processor (eye + brain)
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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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Spectrum of electromagnetic radiation waves
400 500 600 700
nm
Radio
0,001
UVX-rayGamma
0,01 0,1 1,0 10 10³100
IR Radar
104 105 10101010106 10 11
12 13Wavelength
nm
violet blue green yellow orange red
Spectrum of the visible light
400 - 500 nm = blue 500 - 600 nm = green 600 - 700 nm = red
different wavelengths = different colours
photon
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How to create colours ? : 2 methods
SubtractiveAdditive
MagentaCyan
Yellow
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How to create colours : additive method
Additive Lights : Red + Blue + Green = White
For example a Television or a Computer Monitor
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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 reflects green light
blue + green = cyan ink
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How to create colours : subtractive method
Selective absorption of certain wavelength by the ink layer.
Magenta inkreflects redreflects blueabsorbs green
Cyan inkabsorbs redreflects bluereflects green
Yellow inkreflects redabsorbs bluereflects green
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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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SummaryOffset printing
What is colour ?
Principle of offset printing
Sheet-fed offset printing
Heat-set web offset printing
Other printing methods
Conventional methods
Gravure
Flexography
Si lk screen
Digital printing methods
Laser (electro photography)
Ink jet
Conclusion
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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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How do we get printed and unprinted areas?
Function of the offset plate
NON-IMAGEIMAGE
Ink = hydrophobic Water = hydrophilic
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How do we get printed and unprinted areas?
Magnified (15x) of an offset plate
Image
Non-Image
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How do we get printed and unprinted areas?
Magnified (1000X) picture of an offset plate
Image
Non-Image
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How do we get printed and unprinted areas?
Function of the offset plate
NON-IMAGE IMAGE
= direct transfer
Substrate
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How do we get printed and unprinted areas?
Function of Rubber blanket = indirect transfer
NON- IMAGEIMAGE
Rubber Rubber
1st transferSubstrate
2nd transfer
IMAGE NON-IMAGE
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Offset printing unit
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The printing plate
Light sensitive coating
Aluminium oxide coating
Grained aluminium base
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The printing plate
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Basic composition of offset inkPigments ~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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Offset blankets
Oil-resistant synthetic
elastomers attached to
textile fabrics
Reproduction properties
Release properties
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The fountain solutionSurface 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
surface energy of non-image area, 50 mJ/m2
water + 6% IPA,45 mN/m
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Screening
One half-tone image may contain thousands of different shades………
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Different screening
Conventional screening
distance between the centers of
the dots is constant
Stochastic screening
tone is formed by altering dot position and spacing, number of dots
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Stochastic screen
Standard dot size, but the amount of them vary.
Dot size and amount of dots vary.
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Screen ruling – conventional screening
Tonal value 75%
Tonal value 25%
Tonal value 50%
Tonal value 100%
Screening ruling (L/cm or L/inch)
Light tones ~ small dotsDark tones ~ bigger dots
The dots are so small that the human eye sees them as a single colour.
40l/cm
60l/cm
80l/cm
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Strongly magnified screen surfaceNormal screen surface
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.
Human eye
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Print densityPrint density (darkness) is created by increasing the inked area
(halftone percentage)
Black 20% Black 40% Black 60% Black 80%
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Print colourPrint colour (tone) is created by mixing halftone percentages of process colours
C80%/M20% C60%/M40% C40%/M60% C20%/M80%
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Examples of screening methods
Staccato 25µm Conventional 60 l/cm
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SummaryOffset printing
What is colour ?Principle of offset printingSheet-fed offset printingHeat-set web offset printing
Other printing methodsConventional methods
GravureFlexographySilk screen
Digital printing methodsLaser (electro photography)Ink jet
Conclusion
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Sheet fed offset press
Anti set-off powder system
Margin - FeederInk rollers & Damping rolls
Settings of pressure
and register
Delivery of the printed
sheets
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After the 4 printing units
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Sheet fed presses5 colour units + 1 varnish unit
FeederDelivery Varnish Ink units
4/4 colour units, change of the printing side of the sheet in the perfecting system
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Different formats
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Feeder
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Ink Rollers
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Sheet Transfer
Transfer cylinder
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Spray powderto avoid ink set-off
distance holder between the sheets.
increases the amount of oxygen to improve the oxidative drying process.
Spray 10 to 80 micronscalcium carbonateorganic, vegetable based powder of natural starch
300x - CaCo3
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Varnish Why ?
More gloss
Protect
Less drying time before converting
Sometimes two varnish unitsHigh gloss and matt varnish at the same runPremier and UV- varnish when using conventional inksBetter gloss than one unit applying
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SummaryOffset printing
What is colour ?Principle of offset printingSheet-fed offset printingHeat-set web offset printing
Other printing methodsConventional methods
GravureFlexographySilk screen
Digital printing methodsLaser (electro photography)Ink jet
Conclusion
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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
reelstand
infeedprinting units
dryer
chill rolls
siliconization unit
folder
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Heatset presses - different designs
additional colour varnishing unit (offset varnish)
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Operating pressDriving the press
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Infeed
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Heatset press – an example
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Plate cylinder
Blanket cylinder
Plate cylinder
Blanket cylinderPaper web
Paper web in one unit
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Oven
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Oven
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Heatset dryerWeb 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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Temperature profiles in the dryerWeb exit temp. usually 100-140 C (90-180)
Usually declining temperature profileweb temperature rises faster and solvent evaporation starts earlier
1st 2nd 3rd 4th
°C
100
200
300
130°C
195°C
255°C
165°C
drying air temp
web temp
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Chill rollsThermoplastic 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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Silicone application
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Center Cut
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Aligning ribbons
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Different kind of folders
Former fold
Cylinder/Jaw folder
Chopper folder
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Example of fold 16 pages
Formerfold
Jaw foldChopper/jaw fold
630 mm
880 mm
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Folding possibilities
310 x 440 mm
310 x 220 mm
155 x 110 mm
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Imposition and plate makingImposition
Done usually at the printerDepends on what press is used
16/32/48/64 pagesSpecial software used
Plate makingFrom imposition layout
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Press layouts
Run length
Pag
inat
ion
8-page
16-page
24-pageSingle perimeter
Double perimeter32-page
48/64-page
72/80-page
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Manual delivery
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Post-press
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Perfect bindingOperations
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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Saddle stitcherOperations
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 paginationunder 96 pages
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SummaryOffset printing
What is colour ?Principle of offset printingSheet-fed offset printingHeat-set web offset printing
Other printing methodsConventional methods
GravureFlexographySilk screen
Digital printing methodsLaser (electro photography)Ink jet
Conclusion
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Gravure
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Gravure
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Gravure - applications
Packaging & convertingFlexible packagingLabels & wrappersGift wrapsWall coveringsVinylDecorative laminatesFloor coveringsTissue productsStamps
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SummaryOffset printing
What is colour ?Principle of offset printingSheet-fed offset printingHeat-set web offset printing
Other printing methodsConventional methods
GravureFlexographySilk screen
Digital printing methodsLaser (electro photography)Ink jet
Conclusion
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Flexography
paper
sleeve
Counter pressure cylinder
blade
ink
Double face tape
plate
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Applications
• Plastic bags
• Paper sacks • Milk carton• Pocket Books
• Labels• Aluminium • Corrugated Board • Carton cups • Napkins • Tissue • Envelope • Bussinessforms • News Papers • Flexible packaging • Pocket Books
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SummaryOffset printing
What is colour ?Principle of offset printingSheet-fed offset printingHeat-set web offset printing
Other printing methodsConventional methods
GravureFlexographySilk screen
Digital printing methodsLaser (electro photography)Ink jet
Conclusion
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Silk screen
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SummaryOffset printing
What is colour ?Principle of offset printingSheet-fed offset printingHeat-set web offset printing
Other printing methodsConventional methods
GravureFlexographySilk screen
Digital printing methodsLaser (electro photography)Ink jet
Conclusion
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What is digital printing ?
DIGITAL printing means printing directly from digital dataoriginal is in digital formno films are neededno plates are needed
Slide 81
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Pro or Contra digital printing ?Pro
easily changeable infodesign and colourstext
no make-ready-> small runs with reasonable costspersonalisationversioningon-demand printingdecentralised printingeasy 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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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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SummaryOffset printing
What is colour ?Principle of offset printingSheet-fed offset printingHeat-set web offset printing
Other printing methodsConventional methods
GravureFlexographySilk screen
Digital printing methodsLaser (electro photography)Ink jet
Conclusion
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Electro photographic principle
1. Photoconductor is charged
++
+
+
-+
-
---
--
- --- - -- - -
---
- -
---
++ ++
4. Toner (image) is transferred to the paper in electric field, opposite charge
attracts
5. Toner is fixed to the paper by heat = fusing
6. Remaining toner
is wiped off
2. Latent image is
formed by discharging the drum by laser or
LED
3. Latent image is
developed by toner
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SummaryOffset printing
What is colour ?Principle of offset printingSheet-fed offset printingHeat-set web offset printing
Other printing methodsConventional methods
GravureFlexographySilk screen
Digital printing methodsLaser (electro photography)Ink jet
Conclusion
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Ink jet : continuous1. 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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Ink jet : drop on demand2. Drop-on-demand, DOD
every drop is printing
high resolution
lower speed
e.g. Aprion
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SummaryOffset printing
What is colour ?Principle of offset printingSheet-fed offset printingHeat-set web offset printing
Other printing methodsConventional methods
GravureFlexographySilk screen
Digital printing methodsLaser (electro photography)Ink jet
Conclusion
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Print definition depends on paper quality
Coated Fine,70l/cm
SC,54l/cm
LWC,60l/cm
Newsprint,48l/cm
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Different printing process, different results
Flexography(20%, 60 l/cm)• Ink is pressed to
edges, print density inside dot varies
• Edges are smooth• Shadow in the edge
of text
Gravure(~20%, 100 l/cm)• Broken shape of dots and
missing dots are typical for light tones
• Doughnut shaped dots• Text is screened, serrated
edge
Offset(20%, 75 l/cm)• Dots are uniformly
covered with ink• Edges are ragged
(uncoated papers)• Uniform text
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Examples of halftone dots and text
Inkjet(20%)• Dots are quite uniformly covered with ink• Dot is formed by using several
droplets• Edges are ragged or even
depending on paper• Satellites, escaped droplets
Electrophotography(~20%)• Dots are quite uniformly covered with toner• Edges are ragged• Separate toner particles
(dry toner methods)• Uniform text
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Questions ??Will be happy to answer your technical questions :
Françoise Accou, +32 492.582.287, [email protected]