Printing as a Means of Paper Testing

Printing as a Means of Paper Testing
Petter Kolseth

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

Ink film thickness on coated fine paper

Silk

Matt


Runnability in sheet-fed offset
Full-scale trial on low-grammage coated


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

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


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

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


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


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


Print Mottle

Solid Cyan Blue halftones C+M 40% black


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)


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

Five-cylinder configuration
with chain transfer systems

0,25 s 2,5 s 0,25 s
Y M C K


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


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


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


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


Print on sheet with uneven ink-setting characteristics

sheet with ”slow-setting spots” gets mottled after back-trap

The memory effect
Uneven print also on next sheet

”spotless” sheet gets mottled print due to back-trap

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


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)


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)


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)


Disturbed ink transfer after excessive
fount supply in four printing units
burnout
Gloss-coated 250 gsm

2nd unit 5th unit


Disturbed ink transfer after excessive
fount supply in four printing units
burnout
Silk-coated 250 gsm

2nd unit 5th unit


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


Optical dot gain
Yule-Nielsen shadows

Stefan Gustavson, LiU 1998


Optical dot gain
Effect on tone value and colour

AM

FM

after Matthieu Bossan, Creo, 2002


Optical dot gain

coating

base sheet


Optical dot gain

Lost light ray due to
lateral light scattering
in base sheet


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


Burn out – Coat weight variations

Halftone mottle = 1,51
Coat weight = 18 gsm

Halftone mottle = 0,94
Coat weight = 22 gsm


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


Print evenness is important in heavy images

Quality index, Fruit
10

8

6

4

2

0
0 2 4 6 8
Print evenness


Print evenness
Gloss mottle – Print gloss homogeneity

Mikael Lindstrand, STFI


Print evenness
three different surfaces on a curved sample holder

plastic film good WFC poor LWC

1 mm
Mikael Lindstrand, STFI


Print evenness – Surface roughness

5

4
Print evenness

3

2

1
0,40 0,60 0,80 1,00 1,20 1,40

Surface roughness Gloss-Coated 200 – 350 gsm


Print evenness – Paper gloss

5

4
Print evenness

3

2

1
55 60 65 70 75 80 85

Paper gloss Gloss-Coated 200 – 350 gsm


Print evenness – Print gloss 400

5

4
Print evenness

3

2

1
75 80 85 90 95

Print gloss 400% Gloss-Coated 200 – 350 gsm


Paper shade

Ludovic Coppel, Innventia

Paper shade

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

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

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*


Paper shade – Elrepho D65/10°

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*


Paper shade – Elrepho C/2°
Paper Type 1 – gloss 90-250 gsm

0

-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*


Paper shade – Spectrolino D50/2°

0

-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*


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*


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*


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*


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

Primaries and Secondaries

Andreas Paul, FOGRA

Primaries and Secondaries

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


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


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*


Conclusions – Primaries and Secondaries

No (or very small) influence of paper brand

Target colours can be reached with standard inks

Paper fluorescence

Ludovic Coppel, Innventia

Paper fluorescence

Fluorescence – CIE Whiteness (D65)

70

60
Fluorescence (D65/10°)

50

40

30

20

10
100 110 120 130 140 150

CIE Whiteness (D65/10°) Gloss-Coated 200 – 350 gsm


CIE Whiteness – CIELAB-b* (D65)

150

140
CIE Whiteness (D65/10°)

130

120

110

100
-14 -12 -10 -8 -6 -4 -2 0

CIELAB-b* (D65/10°) Gloss-Coated 200 – 350 gsm


Primaries and Secondaries – Elrepho D65/10°
Elrepho D65/10°
100

80

60

40
b*

20

0

-20

-40

-60
-80 -60 -40 -20 0 20 40 60 80
a*


Primaries and Secondaries – i1 D50/2°

100

80

60

40
b*

20

0

-20

-40

-60
-80 -60 -40 -20 0 20 40 60 80
a*


Primaries and Secondaries – D50/2°
Elrepho D50/2°
100

80

60

40
b*

20

0

-20

-40

-60
-80 -60 -40 -20 0 20 40 60 80
a*


Primaries and Secondaries – D50/2° UV excluded
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*


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


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


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*


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

Tone Value Increase

Tone Value Increase

Tone Value Increase: Black and Cyan

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


Optical dot gain
Effect on tone value and colour

AM

FM

after Matthieu Bossan, Creo, 2002


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>


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, %



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, %



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, %



Black halftone seen in the microscope


Thresholding between peaks in histogram


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


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


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

Printing as a Means of Paper Testing

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