printing as a means of paper testing

Printing as a Means of Paper TestingPetter Kolseth

28 Octoberl 2009 Printing for Paper Testing / Petter Kolseth 2

The structure of paperInk on matt-coated fine paper

Ink film thickness of 1-2 µm on ~15 µm coating


Ink film thickness on coated fine paper

Silk

Matt


Runnability in sheet-fed offsetFull-scale trial on low-grammage coated


Different types of print

• Newspapers• Magazines• Special interest magazines• Manuals• Books• Art books, coffee table prints• Corporate communication, Annual reports• Sales promotion• Direct mail

• Paper testing

Reproduction of text and images to please the reader, advertiser or artist

ExpectationsTotal impressionPrint quality

Reproduction of technical areas that reveal the potential of the paper


• Print mottle– 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

What should we include in print quality potential?

Today’s presentation


• 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

How to determine print quality potential?


Sheet offset on coated woodfreeStandardised 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)

Scanning densitometer Print layoutGretag Spectrolino


A print layout for print quality potential: K-C-M-Y-C

Print Mottle

No back-trapInk SettingTone Curves

2nd unit No back-trap

5th unitNo back-trap

Print Evenness

C50 + M50 C80C + M40M

CMY

RGB

400 KK40

Ink setting and drying

2nd unit

K40

C100Print gloss 400%Ink scuffing

Print gloss Black

C100

C100 K40


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 formedby collapsing ink filaments(higher print density in black after back trap)


Four-colour offset printing

Black inkBlanket to paper

Cyan inkBlanket to paper

Black inkPaper to blanket

Magenta inkBlanket to paper


Cyan inkPaper to blanket

Yellow inkBlanket to paper


Cyan inkPaper to blanket

Magenta inkPaper to blanket


Five-cylinder configuration with chain transfer systems

M2,5 s

KC0,25 s

Y0,25 s


Back-trap equilibrium is more easily disturbed for the first inks down

1,00

1,20

1,40

1,60

1,80

2,00

Printing order

Prin

t den

sity

equilibrium equilibriumequilibrium

paper with slow

ink settingchange to paper with

medium ink-setting rateback to paper with

slow ink setting

paper with slowink setting

paper with medium ink-setting rate



Immobilisation of a setting ink film

0,1 s 1 s 3 s 10 s 30 s 1 min 3 minInk setting time

immobilisation front moves upwards through ink film


Shift of ink split position after changing to a faster setting paper

non-immobilized inkimmobilized inkpaper coating

back-trap ink on last blanket 50%

50%

splitting of non-immobilized ink film

non-immobilized inkimmobilized inkpaper coating


The effect is highly dependent on ink-setting rate

1,00

1,20

1,40

1,60

1,80

2,00

2,20

Printing order

Prin

t den

sity

equilibrium equilibriumequilibrium

paper with slow

ink settingchange to paper with fast ink-setting rate

back to paper with slow ink setting


paper with fast ink-setting rate



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

2nd unit 5th unit

burnoutGloss-coated 250 gsm


Disturbed ink transfer after excessive fount supply in four printing units

2nd unit 5th unit

burnoutSilk-coated 250 gsm


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 gainYule-Nielsen shadows

Stefan Gustavson, LiU 1998


Optical dot gainEffect on tone value and colour

after Matthieu Bossan, Creo, 2002

AM

FM



coating

base sheet



Lost light ray due to lateral light scattering in base sheet


Halftone mottle correlates to coat weight variations

Coat-weight variations (burnout test)

Print mottle in 40% black

0.0 2.5 5.0 7.51.0

1.2

1.4

1.6

1.8

2.0

Further evidence:SEM images show that

Dark regions have thin coating(more Yule-Nielsen shadow from base paper)

No significant difference in physical(mechanical) tone between dark and light regions


Burn out – Coat weight variations

Halftone mottle = 1,51Coat weight = 18 gsm

Halftone mottle = 0,94Coat 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

864200

2

4

6

8

10

Print evenness

Quality index, Fruit


Print evennessGloss mottle – Print gloss homogeneity

Mikael Lindstrand, STFI


Print evennessthree different surfaces on a curved sample holder

Mikael Lindstrand, STFI

plastic film good WFC poor LWC

1 mm


Print evenness – Surface roughness

1

2

3

4

5

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

Surface roughness

Prin

t eve

nnes

s

Gloss-Coated 200 – 350 gsm


Print evenness – Paper gloss


1

2

3

4

5

55 60 65 70 75 80 85

Paper gloss

Prin

t eve

nnes

s


Print evenness – Print gloss 400


1

2

3

4

5

75 80 85 90 95

Print gloss 400%

Prin

t eve

nnes

s

Paper shadeLudovic Coppel, Innventia

Paper shade


Print substrate colour and glossISO 12647-2: Offset lithography

• Five typical paper types and their shade/colour and gloss: Paper type L* a* b* gloss1. Gloss-coated, woodfree 93(95) 0(0) -3(-2) 652. Matte-coated, woodfree 92(94) 0(0) -3(-2) 383. Gloss-coated, web 87(92) -1(0) 3(5) 554. Uncoated, white 92(95) 0(0) -3(-2) 65. Uncoated, slightly yellowish 88(90) 0(0) 6(9) 6Tolerance ±3 ±2 ±2 ±5----------------------------------------------------------------------------------------------------------------------------------------------------------------------------

– Black backing to allow for showthrough from reverse printValues in brackets refer to white backingSubstrate backing (white) is standard in paper industry

– D50 illuminant, 2° observer, 0/45 or 45/0 geometryD65/10° or C/2° and d/0° geometry is standard in paper industry


Print substrate used for proofingISO 12647-2: Offset lithography

• Five typical paper types and their shade/colour and gloss: Paper type L* a* b* gloss1. Gloss-coated, woodfree 93(95) 0(0) -3(-2) 652. Matte-coated, woodfree 92(94) 0(0) -3(-2) 383. Gloss-coated, web 87(92) -1(0) 3(5) 554. Uncoated, white 92(95) 0(0) -3(-2) 65. Uncoated, slightly yellowish 88(90) 0(0) 6(9) 6Tolerance ±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


-10

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

-5 -4 -3 -2 -1 0 1 2 3 4 5

CIELAB-a*

CIE

LAB

-b*

Paper shade – Elrepho D65/10°Paper Type 1 – 90-250 gsm

Measurements according to paper industry standard

All products out-of-range


-10

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

-5 -4 -3 -2 -1 0 1 2 3 4 5

CIELAB-a*

CIE

LAB

-b*

Paper shade – Elrepho D65/10°Paper Type 2 – 90-250 gsm

Measurements according to paper industry standard

All except one products out-of-range


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

Measurements according to "indoor whiteness" standard

Some products in the box

-10

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

-5 -4 -3 -2 -1 0 1 2 3 4 5

CIELAB-a*

CIE

LAB

-b*


-10

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

-5 -4 -3 -2 -1 0 1 2 3 4 5

CIELAB-a*

CIE

LAB

-b*

Paper shade – Spectrolino D50/2°Paper Type 1 – 90-250 gsm

Measurements according to printing industry standard

UV content not known

Most products in the box


Paper shade – D65/10° - D50/2° - i1 D50/2°Paper Type 2 – Silk-coated fine paper

-20

-15

-10

-5

0

5

10

15

20

-20 -15 -10 -5 0 5 10 15 20

a*

b*

D50 i1D50 D65

Moderate fluorescence

The D65 UV setting high enough to offset the b*


Paper shade – D65/10° - D50/2° - i1 D50/2°Paper Type 3 – Uncoated fine paper

-20

-15

-10

-5

0

5

10

15

20

-20 -15 -10 -5 0 5 10 15 20

a*

b*

D50 i1D50 D65

Strong fluorescence

The D65 UV setting gives even larger offset in b*


Paper shade – D65/10° - D50/2° - i1 D50/2°Paper Type 4 – Uncoated WoodFree without OBA

-20

-15

-10

-5

0

5

10

15

20

-20 -15 -10 -5 0 5 10 15 20

a*

b*

D50 i1D50 D65

No fluorescence

D65 and D50 quite close, but D50 slightly more red

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 SecondariesAndreas Paul, FOGRA

Primaries and Secondaries


Colour gamut – Spectrolino D50/2°Paper Type 1 and 2, gloss/matt/silk 90-250

-100

-80

-60

-40

-20

0

20

40

60

80

100

-100 -80 -60 -40 -20 0 20 40 60 80 100

a*-a*

-b*

b*GlossMatt/Silk

Target valuesAll prints rather close to target colour CMYRGBOriginal RGB targets


Colour gamut – Spectrolino D50/2°Paper Type 1 and 2, gloss/matt/silk 90-250

-100

-80

-60

-40

-20

0

20

40

60

80

100

-100 -80 -60 -40 -20 0 20 40 60 80 100

a*-a*

-b*

b*All prints very close to target colour CMYRGBAfter the 2004 Amendment


Ten inks on gloss, silk and matt paperColour gamut – Elrepho C/2°

-100

-80

-60

-40

-20

0

20

40

60

80

100

-100 -80 -60 -40 -20 0 20 40 60 80 100

CIE a*CIE -a*

CIE b*

CIE -b*

Ten inks on Gloss paperTen inks on Silk paperTen inks on Matt paper 30 ink-paper

combinations but almost identical results

Conclusions – Primaries and Secondaries

No (or very small) influence of paper brand

Target colours can be reached with standard inks

Paper fluorescenceLudovic Coppel, Innventia

Paper fluorescence


Fluorescence – CIE Whiteness (D65)


10

20

30

40

50

60

70

100 110 120 130 140 150

CIE Whiteness (D65/10°)

Fluo

resc

ence

(D65

/10°

)


CIE Whiteness – CIELAB-b* (D65)


100

110

120

130

140

150

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

CIELAB-b* (D65/10°)

CIE

Whi

tene

ss (D

65/1

0°)


Primaries and Secondaries – Elrepho D65/10°Paper Type 2 – Silk-coated fine paper

-60

-40

-20

0

20

40

60

80

100

-80 -60 -40 -20 0 20 40 60 80

a*

b*

Elrepho D65/10°


Primaries and Secondaries – i1 D50/2°Paper Type 2 – Silk-coated fine paper

-60

-40

-20

0

20

40

60

80

100

-80 -60 -40 -20 0 20 40 60 80

a*

b*


Primaries and Secondaries – D50/2°Paper Type 2 – Silk-coated fine paper

-60

-40

-20

0

20

40

60

80

100

-80 -60 -40 -20 0 20 40 60 80

a*

b*

Elrepho D50/2°


Primaries and Secondaries – D50/2° UV excludedPaper Type 2 – Silk-coated fine paper

-60

-40

-20

0

20

40

60

80

100

-80 -60 -40 -20 0 20 40 60 80

a*

b*

Elrepho D50/2° UV excluded


Spectral power and Relative UV contentIlluminants D65, C, D50, A

0

50

100

150

200

250

300

350 400 450 500 550 600 650 700 750

Wavelength, nm

Spec

tral P

ower

D65 C D50 A

Relative to 560 nm (max colour vision)

0,00

0,25

0,50

0,75

1,00

1,25

1,50

1,75

2,00

340 360 380 400 420 440 460 480 500 520 540 560

Wavelength, nmSp

ectra

l Pow

er

D65rel Crel D50rel Arel

Relative to 440 nm fluorescence peak

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

Ludovic Coppel, Innventia, 2008300 350 400 450 500 550 600 650 700 7500

0,5

1

1,5

2

Wavelength (nm)

Rel

ativ

e Po

wer

D50D655000K CCT5000K CCT + UV

300 350 400 450 500 550 600 650 700 7500

0,5

1

1,5

2

Wavelength (nm)

Rel

ativ

e Po

wer




-14,0

-12,0

-10,0

-8,0

-6,0

-4,0

-2,0

0,0

2,0

4,0

6,0

-2,0 -1,5 -1,0 -0,5 0,0 0,5 1,0 1,5 2,0 2,5 3,0

CIELAB-a*

CIE

LAB

-b*

Proof substrates from one supplierx-rite iOne – a*-b* data

Red symbols denote certified proof substrates

Green symbols denote production paper PT2 and PT4

Type 2

Type 4

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 CyanPaper Type 1 – 90-250 gsm

Black and Cyan Dot Gain are both within tolerance

0%

5%

10%

15%

20%

25%

30%

0% 20% 40% 60% 80% 100%

Nominal tone

Bla

ck T

one

Valu

e In

crea

se

20% +/- 4

0%

5%

10%

15%

20%

25%

30%

0% 20% 40% 60% 80% 100%

Nominal tone

Cya

n To

ne V

alue

Incr

ease

20% +/- 4


Optical dot gainEffect on tone value and colour

after Matthieu Bossan, Creo, 2002

AM

FM


Reflectance histograms of K100, K40 and paper white13,2% TVI(40)

0,0

0,5

1,0

1,5

2,0

2,5

0 20 40 60 80 100

Reflectance, %

Freq

uenc

y, %

0,0

5,0

10,0

15,0

20,0

25,0

<K40> <BLACK> <WHITE>



0,0

0,5

1,0

1,5

2,0

2,5

0 20 40 60 80 100

Reflectance, %

Freq

uenc

y, %

0,0

5,0

10,0

15,0

20,0

25,0



0,0

0,5

1,0

1,5

2,0

2,5

0 20 40 60 80 100

Reflectance, %

Freq

uenc

y, %

0,0

5,0

10,0

15,0

20,0

25,0



Solid black

Halftone dots Between dots

Unimaged paper


0,0

0,5

1,0

1,5

2,0

2,5

0 20 40 60 80 100

Reflectance, %

Freq

uenc

y, %

0,0

5,0

10,0

15,0

20,0

25,0



Solid black

Halftone dots

Between dots

Unimaged paper


Black halftone seen in the microscope


Thresholding between peaks in histogram


Tone Value comparisonDensitometer readings vs. microscopy

46

48

50

52

54

56

50 52 54 56 58 60 62 64

Densitometer Tone Value

Mic

rosc

opy

Tone

Val

ue


0,0

2,0

4,0

6,0

8,0

10,0

-20 -15 -10 -5 0

Reduction in paper reflectance between dots

Opt

ical

TVI

Optical Tone Value Increase Tone Values by microscopy

Single-coat matt

multicoat gloss multicoat silk

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

Stay in control…

printing as a means of paper testing

Technology

structure of paper ink

paper blanket

blanket paper

cyan ink cyan ink paper

paper withback

unit ink

paper testing petter

paper testing petter