2. The structure of paper
Ink on matt-coated fine paper
Ink film thickness of 1-2 µm on ~15 µm coating
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 2
3. Ink film thickness on coated fine paper
Silk
Matt
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 3
4. Runnability in sheet-fed offset
Full-scale trial on low-grammage coated
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 4
5. Different types of print
• Newspapers Reproduction of text and
• Magazines images to please the
reader, advertiser or
• Special interest magazines
artist
• Manuals
Expectations
• Books
Total impression
• Art books, coffee table prints Print quality
• Corporate communication, Annual reports
• Sales promotion
• Direct mail
• Paper testing Reproduction of technical areas
that reveal the potential of the paper
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 5
6. What should we include in print quality potential?
• Print mottle Today’s presentation
– back-trap, water-induced, halftone, gloss
• Colour gamut
• Tone Value Increase
• Print evenness
– Potential to carry dark and heavily inked images
• Ink drying and ink setting
• Trapping values
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 6
7. How to determine print quality potential?
• Full-scale print trials
– Lab prints are not enough
• Controlled print run
– Target densities
– Standard settings (impression, speed…)
– Controlled climate
– Standard supplies (inks, plates, blankets…)
• Calibrated press
– Ink roller settings
– Fount roller settings (use FOGRA’s test form!)
• Dedicated print layout
– Technical areas
– No images
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 7
8. Sheet offset on coated woodfree
Standardised Print
• Market follow-up on 50 European papers
– Paper Type 1 and 2
• Comparison of 10 inks on three papers
– Gloss, silk, matt (Type 1 and 2)
Gretag Spectrolino Scanning densitometer Print layout
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 8
9. A print layout for print quality potential: K-C-M-Y-C
Print Mottle Print gloss Black
Ink scuffing
C50 + M50 C80C + M40M Print gloss 400%
C100 C100 Ink setting and drying
5th unit
No back-trap 2nd unit
C100 K40
2nd unit Ink Setting
No back-trap No back-trap
Tone 400 K40 K
K40 Curves
B G R
Print
Evenness Y M C
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 9
10. Different types of mottled print
• Back-trap mottle
– Uneven ink films and transparent inks
• Water-induced mottle
– Uneven ink transfer
– Ink refusal where excess fount can’t be accommodated in coating
• Paper optics
– Halftone mottle – Yule-Nielsen effects in screen tones
– Gloss mottle
• Ink trap mottle
– Uneven trapping of second ink
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 10
11. Print Mottle
Solid Cyan Blue halftones C+M 40% black
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 11
12. What is back trap?
• ’Trapping’ is when ink is transferred to a wet ink film on the paper
– (e.g. magenta on cyan)
• Back trap is when the wet ink is transferred from the paper to the
following blanket
– (e.g. cyan onto magenta blanket)
• Ideally, an equilibrium ink-film thickness is formed on back-trap blankets
• Subsequent ink-film splits in back trap level out the unevenness formed
by collapsing ink filaments
(higher print density in black after back trap)
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 12
13. Four-colour offset printing
Black ink Cyan ink Magenta ink Yellow ink
Blanket to paper Blanket to paper Blanket to paper Blanket to paper
Black ink Black ink Black ink
Paper to blanket Paper to blanket Paper to blanket
Cyan ink Cyan ink
Paper to blanket Paper to blanket
Magenta ink
Paper to blanket
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 13
15. Back-trap equilibrium is more easily disturbed
for the first inks down
2,00
1,80
equilibrium equilibrium equilibrium
Print density
1,60
paper with
1,40 slow
ink setting
paper with
1,20 slow change to paper with back to paper with paper with
ink setting medium ink-setting rate slow ink setting medium
ink-setting rate
1,00
paper with
Printing order slow
ink setting
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 15
16. Immobilisation of a setting ink film
immobilisation front moves
upwards through ink film
0,1 s 1s 3s 10 s 30 s 1 min 3 min
Ink setting time
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 16
17. Shift of ink split position after changing
to a faster setting paper
back-trap ink
on last blanket 50% splitting of non-
immobilized ink film
non-immobilized ink non-immobilized ink 50%
immobilized ink immobilized ink
paper coating paper coating
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 17
18. The effect is highly dependent on ink-setting rate
2,20
2,00
Print density
1,80
equilibrium equilibrium equilibrium
1,60
paper with
slow
1,40 ink setting
paper with paper with
1,20 slow change to paper with back to paper with fast
ink setting fast ink-setting rate slow ink setting ink-setting rate
1,00
paper with
Printing order slow
ink setting
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 18
19. Print on sheet with uneven ink-setting characteristics
sheet with ”slow-setting spots” gets mottled after back-trap
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 19
20. The memory effect
Uneven print also on next sheet
”spotless” sheet gets mottled print due to back-trap
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 20
21. Water-induced print mottle
• Printing on pilot-coated paper
• Low coating porosity resulting in unwanted hold-out of fount
• Excessive feed of fount in all print units
• Ink refusal where coated surface was too wet
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 21
22. Increasing the fount supply results
in white spots in the solid print
low fount supply high fount supply
Solid areas printed without pre-damp but with back-trap
(10 pts SB-latex)
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 22
23. Back-trap will improve print quality
in areas with excessive pre-damp
no back-trap with back-trap
70% areas printed with pre-damp
(15 pts PVAc-latex)
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 23
24. Excessive pre-damp may ruin
print quality of high binder content coatings
no pre-damp with pre-damp
70% areas printed with back-trap
(20 pts SB-latex)
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 24
25. Disturbed ink transfer after excessive
fount supply in four printing units
burnout
Gloss-coated 250 gsm
2nd unit 5th unit
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 25
26. Disturbed ink transfer after excessive
fount supply in four printing units
burnout
Silk-coated 250 gsm
2nd unit 5th unit
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 26
27. Mottle in black screen tones
• High contrast between black dots and surrounding white paper
• Total reflectance is average of unprinted white and (non-reflecting)
black dots
• Ink film density not very important
• Yule-Nielsen shadows in white areas is a major contribution
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 27
28. Optical dot gain
Yule-Nielsen shadows
Stefan Gustavson, LiU 1998
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 28
29. Optical dot gain
Effect on tone value and colour
AM
FM
after Matthieu Bossan, Creo, 2002
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 29
30. Optical dot gain
Yule-Nielsen shadows
coating
base sheet
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 30
31. Optical dot gain
Yule-Nielsen shadows
Lost light ray due to
lateral light scattering
in base sheet
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 31
32. Halftone mottle correlates to coat weight variations
Print mottle in 40% black
2.0
1.8
1.6 Further evidence:
SEM images show that
1.4 Dark regions have thin coating
(more Yule-Nielsen shadow from
1.2 base paper)
1.0 No significant difference in physical
0.0 2.5 5.0 7.5
(mechanical) tone between dark and
Coat-weight variations (burnout test)
light regions
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 32
34. Ink-trap mottle and more…
Blue halftones (Cyan+Magenta)
• Blue halftones combine ink-trap mottle and
the two basic types of mottle:
– the halftone character showing dot gain
variation
– the transparent ink film showing ink film
thickness variation
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 34
35. Print evenness is important in heavy images
Quality index, Fruit
10
8
6
4
2
0
0 2 4 6 8
Print evenness
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 35
36. Print evenness
Gloss mottle – Print gloss homogeneity
Mikael Lindstrand, STFI
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 36
37. Print evenness
three different surfaces on a curved sample holder
plastic film good WFC poor LWC
1 mm
Mikael Lindstrand, STFI
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 37
41. Paper shade
Ludovic Coppel, Innventia
Paper shade
42. Print substrate colour and gloss
ISO 12647-2: Offset lithography
• Five typical paper types and their shade/colour and gloss:
Paper type L* a* b* gloss
1. Gloss-coated, woodfree 93(95) 0(0) -3(-2) 65
2. Matte-coated, woodfree 92(94) 0(0) -3(-2) 38
3. Gloss-coated, web 87(92) -1(0) 3(5) 55
4. Uncoated, white 92(95) 0(0) -3(-2) 6
5. Uncoated, slightly yellowish 88(90) 0(0) 6(9) 6
Tolerance ±3 ±2 ±2 ±5
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
– Black backing to allow for showthrough from reverse print
Values in brackets refer to white backing
Substrate backing (white) is standard in paper industry
– D50 illuminant, 2° observer, 0/45 or 45/0 geometry
D65/10° or C/2° and d/0° geometry is standard in paper industry
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 42
43. Print substrate used for proofing
ISO 12647-2: Offset lithography
• Five typical paper types and their shade/colour and gloss:
Paper type L* a* b* gloss
1. Gloss-coated, woodfree 93(95) 0(0) -3(-2) 65
2. Matte-coated, woodfree 92(94) 0(0) -3(-2) 38
3. Gloss-coated, web 87(92) -1(0) 3(5) 55
4. Uncoated, white 92(95) 0(0) -3(-2) 6
5. Uncoated, slightly yellowish 88(90) 0(0) 6(9) 6
Tolerance ±3 ±2 ±2 ±5
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
• Print substrate used for proofing – identical to that of the production
• If not possible – close match in colour, gloss, surface grammage
• Press proofing on closest match to five typical paper surface types
• Proof substrate to conform … to attributes in Table 1 of the paper type
representing the production paper
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 43
44. Paper shade – Elrepho D65/10°
Paper Type 1 – 90-250 gsm
0
-1
Measurements according
-2 to paper industry
-3 standard
CIELAB-b*
-4
-5
All products out-of-range
-6
-7
-8
-9
-10
-5 -4 -3 -2 -1 0 1 2 3 4 5
CIELAB-a*
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 44
45. Paper shade – Elrepho D65/10°
Paper Type 2 – 90-250 gsm
0
-1 Measurements according
-2 to paper industry
-3 standard
CIELAB-b*
-4
-5
All except one products
-6 out-of-range
-7
-8
-9
-10
-5 -4 -3 -2 -1 0 1 2 3 4 5
CIELAB-a*
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 45
46. Paper shade – Elrepho C/2°
Paper Type 1 – gloss 90-250 gsm
0
-1 Measurements according
-2 to "indoor whiteness"
-3 standard
CIELAB-b*
-4
-5
Some products in the box
-6
-7
-8
-9
-10
-5 -4 -3 -2 -1 0 1 2 3 4 5
CIELAB-a*
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 46
47. Paper shade – Spectrolino D50/2°
Paper Type 1 – 90-250 gsm
0
-1 Measurements according
-2 to printing industry
-3 standard
CIELAB-b*
-4 UV content not known
-5
Most products in the box
-6
-7
-8
-9
-10
-5 -4 -3 -2 -1 0 1 2 3 4 5
CIELAB-a*
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 47
48. Paper shade – D65/10° - D50/2° - i1 D50/2°
Paper Type 2 – Silk-coated fine paper
20
Moderate fluorescence
15
The D65 UV setting high
10
enough to offset the b*
5
b*
0
-5
-10
-15
D50 i1D50 D65
-20
-20 -15 -10 -5 0 5 10 15 20
a*
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 48
49. Paper shade – D65/10° - D50/2° - i1 D50/2°
Paper Type 3 – Uncoated fine paper
20
Strong fluorescence
15
The D65 UV setting gives
10
even larger offset in b*
5
b*
0
-5
-10
-15
D50 i1D50 D65
-20
-20 -15 -10 -5 0 5 10 15 20
a*
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 49
50. Paper shade – D65/10° - D50/2° - i1 D50/2°
Paper Type 4 – Uncoated WoodFree without OBA
20
No fluorescence
15
D65 and D50 quite close,
10
but D50 slightly more red
5
b*
0
-5
-10
-15
D50 i1D50 D65
-20
-20 -15 -10 -5 0 5 10 15 20
a*
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 50
51. Conclusions – Paper Shade
A matter of taste – forget "ISO compliant"
ISO does not specify allowed shades
Should be determined with dedicated equipment
Most papers are within a narrow range of shades
53. Colour gamut – Spectrolino D50/2°
Paper Type 1 and 2, gloss/matt/silk 90-250
100
Gloss b*
Matt/Silk 80
All prints rather close to
Target values
60
target colour CMYRGB
40
Original RGB targets
20
-a* a*
0
-100 -80 -60 -40 -20 0 20 40 60 80 100
-20
-40
-60
-80
-b*
-100
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 53
54. Colour gamut – Spectrolino D50/2°
Paper Type 1 and 2, gloss/matt/silk 90-250
100
b*
80
All prints very close to
60
target colour CMYRGB
40
After the 2004 Amendment
20
-a* a*
0
-100 -80 -60 -40 -20 0 20 40 60 80 100
-20
-40
-60
-80
-b*
-100
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 54
55. Ten inks on gloss, silk and matt paper
Colour gamut – Elrepho C/2°
100
Ten inks on Gloss paper CIE b*
Ten inks on Silk paper 80
Ten inks on Matt paper 30 ink-paper
60 combinations but almost
identical results
40
20
CIE -a* 0
CIE a*
-100 -80 -60 -40 -20 0 20 40 60 80 100
-20
-40
-60
-80
-100
CIE -b*
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 55
56. Conclusions – Primaries and Secondaries
No (or very small) influence of paper brand
Target colours can be reached with standard inks
60. Primaries and Secondaries – Elrepho D65/10°
Paper Type 2 – Silk-coated fine paper
Elrepho D65/10°
100
80
60
40
b*
20
0
-20
-40
-60
-80 -60 -40 -20 0 20 40 60 80
a*
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 60
61. Primaries and Secondaries – i1 D50/2°
Paper Type 2 – Silk-coated fine paper
100
80
60
40
b*
20
0
-20
-40
-60
-80 -60 -40 -20 0 20 40 60 80
a*
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 61
62. Primaries and Secondaries – D50/2°
Paper Type 2 – Silk-coated fine paper
Elrepho D50/2°
100
80
60
40
b*
20
0
-20
-40
-60
-80 -60 -40 -20 0 20 40 60 80
a*
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 62
63. Primaries and Secondaries – D50/2° UV excluded
Paper Type 2 – Silk-coated fine paper
Elrepho D50/2° UV excluded
100
80
60
40
b*
20
0
-20
-40
-60
-80 -60 -40 -20 0 20 40 60 80
a*
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 63
64. Spectral power and Relative UV content
Illuminants D65, C, D50, A
Relative to 560 nm (max colour vision) Relative to 440 nm fluorescence peak
300 2,00
1,75
250
1,50
Spectral Power
200
Spectral Power
1,25
150 1,00
0,75
100
0,50
50
0,25
0 0,00
350 400 450 500 550 600 650 700 750 340 360 380 400 420 440 460 480 500 520 540 560
Wavelength, nm Wavelength, nm
D65 C D50 A D65rel Crel D50rel Arel
Relative power of A is almost twice that of C between 340 and 380 nm
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 64
65. Illumination is NOT same as Illuminant
Illumination 5000K and Illuminant D50
D50
2 D65
5000K CCT
5000K CCT + UV
Relative Power
1,5
1
0,5
0
300 350 400 450 500 550 600 650 700 750
Wavelength (nm) Ludovic Coppel, Innventia, 2008
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 65
66. Proof substrates from one supplier
x-rite iOne – a*-b* data
6,0
Red symbols denote
4,0 certified proof substrates
2,0
Green symbols denote production
0,0 paper PT2 and PT4
CIELAB-b*
-2,0
Type 2
-4,0
-6,0
Type 4
-8,0
-10,0
-12,0
-14,0
-2,0 -1,5 -1,0 -0,5 0,0 0,5 1,0 1,5 2,0 2,5 3,0
CIELAB-a*
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 66
67. Conclusions – Paper Fluorescence
Fluorescence make papers whiter (more blue)
Effect is very dependent on illumination
Fluorescence shines through all print
Matching proof to print with proper choice of
proof substrate and illumination
69. Tone Value Increase: Black and Cyan
Paper Type 1 – 90-250 gsm
30% 30%
25% 25%
Black Tone Value Increase
Cyan Tone Value Increase
20% 20% +/- 4 20% 20% +/- 4
15% 15%
10% 10%
5% 5%
0% 0%
0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100%
Nominal tone Nominal tone
Black and Cyan Dot Gain are both within tolerance
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 69
70. Optical dot gain
Effect on tone value and colour
AM
FM
after Matthieu Bossan, Creo, 2002
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 70
71. Reflectance histograms of K100, K40 and paper white
13,2% TVI(40)
2,5 25,0
2,0 20,0
Frequency, %
1,5 15,0
1,0 10,0
0,5 5,0
0,0 0,0
0 20 40 60 80 100
Reflectance, %
<K40> <BLACK> <WHITE>
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 71
72. Reflectance histograms of K100, K40 and paper white
20,1% TVI(40)
2,5 25,0
2,0 20,0
Frequency, %
1,5 15,0
1,0 10,0
0,5 5,0
0,0 0,0
0 20 40 60 80 100
Reflectance, %
<K40> <BLACK> <WHITE>
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 72
73. Reflectance histograms of K100, K40 and paper white
13,2% TVI(40)
2,5 25,0
Halftone dots Between dots
2,0 20,0
Frequency, %
1,5 15,0
Unimaged
Solid black
paper
1,0 10,0
0,5 5,0
0,0 0,0
0 20 40 60 80 100
Reflectance, %
<K40> <BLACK> <WHITE>
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 73
74. Reflectance histograms of K100, K40 and paper white
20,1% TVI(40)
2,5 25,0
Halftone dots
2,0 20,0
Unimaged
Frequency, %
paper
1,5 15,0
Between
Solid black
dots
1,0 10,0
0,5 5,0
0,0 0,0
0 20 40 60 80 100
Reflectance, %
<K40> <BLACK> <WHITE>
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 74
75. Black halftone seen in the microscope
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 75
77. Tone Value comparison
Densitometer readings vs. microscopy
56
Microscopy Tone Value
54
52
50
48
46
50 52 54 56 58 60 62 64
Densitometer Tone Value
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 77
78. Optical Tone Value Increase
Tone Values by microscopy
10,0
Single-coat matt
8,0
Optical TVI
multicoat
6,0
gloss multicoat silk
4,0
2,0
0,0
-20 -15 -10 -5 0
Reduction in paper reflectance between dots
28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 78
79. Conclusions – Tone Value Increase
Mechanical TVI is small (in the ideal case)
Optical TVI is quite large
Optical TVI is an inherent paper property
(but not related to brand)
TVI variations are mechanical due to press settings