papers designed for high speed ink-jet printing · paper suitable for high-speed ink-jet printing...

Papers designed for high speed ink-jet printing

Erik Blohm, Peter Åslund

2004

According to Innventia Confidentiality Policy this report is public since 2010



S T F I R E P O R T

CW 248 D E C E M B E R 2 0 0 4

C O N T R A C T W O R K

8


STFI CW 24



S T F I R E P O R T

CW 248 D E C E M B E R 2 0 0 4

C O N T R A C T W O R K

According to STFI's Confidentiality Policy this report is assigned category 1

Papers designed for high speed ink-jet printing CW 248

Acknowledgements Vinnova is thanked for its financial support for the project. All the participating companies are gratefully thanked for the extensive work performed. Posten ePP, Metso Paper and Södra Cell are specially thanked for the extensive work performed in the pilot trials and for the pulp used in the papermaking trials.



Papers designed for high speed ink-jet printingCW 248

Contents Page

1 Summary 1

2 Introduction 3

3 Materials and methods 5 3.1 Commercial paper grades 5 3.2 Pilot-scale papers 5 3.2.1 Papermaking 5 3.2.2 Surface treatment 6 3.3 Printing 7 3.4 Evaluation of results 8 3.4.1 Paper testing methods 8 3.4.2 Print evaluation methods 8

4 Results and discussion 9 4.1 Trials with commercial papers 9 4.1.1 Paper properties 9 4.1.2 Print evaluation 11 4.1.3 Liner trials 14 4.2 Trials with pilot manufactured papers 14 4.2.1 Paper properties 15 4.2.2 Print evaluation 18 4.3 Runnability 22

5 Conclusions 23

6 References 24

STFI Database information 25



Papers designed for high speed ink-jet printing 1CW 248

1 Summary The work was performed in order to identify the requirements on paper raised by the development of high-speed ink-jet printing machines. The goal was to identify important parameters to create a cost-efficient paper with optimised properties for water-based high-speed ink-jet printing. This was done by pilot-scale papermaking trials, and full-scale printing with a high-speed ink-jet press.

Eight commercially available paper grades suitable for ink-jet printing were used in a prestudy to identify the most critical parameters. Papers were manufactured on the EuroFEX experimental paper machine and surface treated with pigment or surface sized in a metering size press. The printing was performed in a Scitex Versamark high-speed ink-jet printing press. The paper properties and the print quality were determined and evaluated after the printing.

The results of the trials showed that: A hydrophilic surface minimizes mottling effects but can, on the other hand, increase print through and decrease print sharpness. A higher colour gamut volume is achieved with the specially formulated PCC grade used in the surface-treatment trials than with GCC, which elucidates the influence of the pigment properties. A surface sizing modified with styrene acrylate improved keeps the ink colorants in the surface and can almost be compared to surface coating. Stratified forming gives more fine material in the top layer and forms a barrier that also captures the ink colorants, and tends to increase the colour gamut volume. Further, the paper structure should have a good dimensional stability during moisture exposure.

The results show that it is possible to design a slightly coated or pigmented paper suitable for high-speed ink-jet printing and giving an acceptable colour gamut volume. The main obstacle is the dimensional stability of the paper structure during the printing process due to the large amount of water transferred through the printing ink.



2 Papers designed for high speed ink-jet printing CW 248

Sammanfattning Syftet med arbetet var att identifiera de krav på egenskaper hos papper som ställs av utvecklingen av höghastighets ink-jet tryckpressar. Målet var att identifiera betydelsefulla parametrar för att skapa ett kostnadseffektivt papper med optimerade egenskaper för vattenbaserad höghastighets ink-jet tryckning. Detta genomfördes med papperstillverkning i pilotskala och fullskaletryckning i en höghastighets ink-jet tryckpress.

Åtta kommersiellt tillgängliga papperskvaliteter lämpliga för ink-jet tryckning utvärderades i en förstudie för att identifiera de mest kritiska parametrarna. Papper tillverkades på forskningspappersmaskinen EuroFEX och ytbehandlades med pigmenterad bestrykning eller ytlimmades i en limpress. Tryckningen genomfördes i en Scitex Versamark höghastighets ink-jet tryckpress. Pappersegenskaperna och tryckkvaliteten analyserades och utvärderades efter tryckningen.

Försöken visade att: En hydrofil pappersyta minimerar flammigheten i trycket men kan å andra sidan öka genomtrycket och minska tryckskärpan. En större färgrymd uppnås med den speciella PCC kvaliteten som användes vid ytbehandlingsförsöken än med GCC, vilket belyser inflytandet av pigmentegenskaperna. En ytlimning modifierad med styrenakrylat håller kvar färgpigmentet i ytan och kan nära nog jämföras med pigmenterad ytbehandling. Flerskiktsformning ger mer finmaterial i ytskiktet och skapar en barriär som fångar färgpigmentet och tenderar att öka färgrymden. Pappersstrukturen ska vidare ha god dimensionsstabilitet vid fuktpåföring.

Resultaten visar att det är möjligt att formulera ett lättbestruket papper lämpligt för höghastighets ink-jet tryckning som uppnår en acceptabel färgrymd. Det största problemet är dimensionsstabiliteten hos pappersstrukturen under tryckprocessen på grund av de stora vattenmängderna som överförs med tryckfärgen.




2 Introduction Over the years, the printing industry has seen major revolutions that have completely altered the prerequisites for the entire industry. Desktop publishing totally eliminated the typesetting profession some fifteen years ago. Now, the rapid growth of digital printing and the convergence of digital and offset printing tend to make new demands on the finances of the printing industry.

This rapid growth is a result of technological developments. Only a few years ago, offset printing and gravure were unchallenged when high demands were placed on print quality and speed. Today, both ink-jet printing and electrophotographic printing are capable of high speeds and high print quality. This means that the areas in which the various printing processes are financially feasible are beginning to overlap, and it is not obvious whether a certain print job should be run on offset or on one of the available digital printing processes. The possibility of making every copy unique makes digital printing more flexible than conventional printing techniques.

In the near future, rapid growth is foreseen for digital printing. However, it is believed that a fast technical development in the digital printing processes will have to be matched by a corresponding development in the printing substrate, i.e. the paper. Today, the volumes of paper being used in electrophotographic printing are much greater than the volumes of paper used in high-speed ink-jet printing. However, several reports predict a very rapid growth for ink-jet paper grades (Romano 2004). This can also be expected for packaging materials. These predictions justify efforts to study the physics and chemistry involved in the extremely fast ink-jet processes that are forecast to prevail in the future and to design an optimised substrate accordingly.

Ink-jet printing technology is based on microscopic ink drops emitted under pressure from a jet onto a substrate (Andreottola 1991). Ink-jet printing raises new demands on the properties of printing paper. An optimum uncoated surface is said to consist of a mat of fibres with an evenly distributed gradient of sizing, additives and fillers. When the sizing and fillers are distributed unevenly on the surface, aqueous inks tend to wick along the exposed paper fibres, significantly degrading the quality of the ink-jet print. A coating provides a homogeneous surface for ink penetration, overcoming the difficulties of wicking, and also provides a bright surface and yields a high print contrast (Bares 1991). The surface of inkjet papers should further be engineered to be a highly absorbent interface that at the same time exhibits micro-capillarity on a defined scale (Babinsky 1998). The influence of the paper structure on the ink-jet drop impact and spreading must be considered (Oliver 1984). New papermaking technologies regarding internal sizing and surface sizing systems will make it possible to enhance




the colour gamut volume and the print sharpness on the paper (Ranson and Varnell 2002). In order to achieve a high print sharpness, care should further be taken not to have too high a liquid penetration rate in the paper (Bares and Rennels 1990).

The aims of this work were (a) to identify the future demands on paper properties resulting from the development of high-speed ink-jet printing presses, (b) to design an improved and cost-efficient paper with optimised properties for water-based high-speed ink-jet printing and (c) to test the validity of the design strategies using pilot-scale papermaking trials, test printing and follow-up evaluation.




3 Materials and methods Two series of printing trials were performed, one with commercial paper grades and one with pilot-scale manufactured paper.

3.1 Commercial paper grades In the prestudy, 8 commercially available paper grades were chosen. These papers were divided into three groups with different quality levels for comparison:

• High quality, coated or slightly coated papers specially designed for ink-jet printing, here denoted H1 and H2.

• Medium quality, papers adapted for ink-jet printing, denoted M1 and M2.

• Standard quality, standard copy papers, denoted S1, S2, S3 and S4.

In addition, five liner grades were investigated in the prestudy in order to evaluate the possibility of using liner as a substrate for high-speed ink-jet printing.

3.2 Pilot-scale papers

3.2.1 Papermaking The papers were manufactured on the EuroFEX research paper machine at STFI-Packforsk. A schematic drawing of the machine is shown in Figure 1.

Figure 1. Schematic drawing of the EuroFEX res arch paper machine.

e

The pulp used in the trials was a bleached kraft pulp containing 30% softwood and 70% hardwood. Two forming methods were used: Roll-Blade forming and Stratified forming. The filler used was 20% PCC, CaCO3. The papers were internally sized with two sizing systems: ASA and AKD. This was done to reach three levels of hydrophobicity: 25, 30-35 and 80 Cobb60.




The grammage of the papers was 80 g/m2. The paper was dried off-line in the EuroFEX dryer.

3.2.2 Surface treatment The surface treatment trials were performed at Metso Paper in Järvenpää, Finland. The papers were pre-calendered before the surface sizing/coating trials and post calendered after the surface treatment. The configuration of the calendering equipment during the pre-calendering trials is shown in Figure 2.

Figure 2. The pilot cal nder at Metso Paper. Courtesy of M tso Paper. e e

The calendering line load in the pre-calendering trials was 110 kN/m while the calendering load during the post-calendering trials was 25 kN/m.

The Optisizer was used both in the coating and surface sizing of the paper. The equipment is shown in Figure 3.

Figure 3. The pilot coater and surface sizing equipment at Me o Paper. Courtesy of Metso Paper.

ts

Two pigmented coating systems and two pure surface-sizing systems were used in the trials. The formulations of the systems are shown in Table 1.




Table 1. Fo mulation of the surface treatment systems used in the trials r

1) GCC (C90) 100 parts dry Starch Cerestar SP05855 25 parts dry Styrene Acrylate Eka Jetsize CE 420 4 parts dry

2) PCC Astra Jet 5200 100 parts dry Starch Penford Gum 290 25 parts dry Cationic Polymer Nalcolyte 7135 6 parts dry

3) Starch Cerestar SP05855 (88% solids content) 94% dry Styrene Acrylate Eka Jetsize CE 420 (25% solids content) 6% dry

4) Starch Cerestar SP05855 (88% solids content) 100% dry alternative Raisamyl 302

The systems were applied with an amount of 4 g/m2 on each side of the paper in the case of the pigment coating systems 1 and 2, and with 1 g/m2 on each side in the case of surface-sizing systems 3 and 4.

3.3 Printing The high-speed ink-jet printing was performed at Posten ePP in Stockholm on a Scitex Versamark printing press. The printing press is shown in Figure 4.

Figure 4. Scitex Versama k High-Speed ink-jet printing press. r

The paper printing trials were performed at a printing speed of 100 m/min for the commercial papers and at a speed of 25 m/min for the pilot-scale papers. The lower speed was chosen due to runnability problems. The liner grades were printed at a speed of 25 m/min, the reason for this low speed being that the machine was not adapted to print liner grades.




The three test print forms used in the trials are shown in Figure 5.

Figure 5. The three test p int f rms used in the trials. The machine dir ction is upwards.

r o e

3.4 Evaluation of results

3.4.1 Paper testing methods The filler content of the papers was determined by a Metso Paper layering and ash-content analysis method. The water absorption was measured as Cobb60 according to SCAN-P12:64. The wettability was measured as contact angle with FIBRO 1100 DAT. The formation was measured with the Ambertec Beta Formation Tester. The paper surface roughness (PPS-10) was measured according to ISO 8791-4. The opacity was measured with an Elrepho instrument according to ISO 2471.

3.4.2 Print evaluation methods The subjective print quality was evaluated by a panel of observers. The samples were ranked according to print quality by the panellists. The print mottle was analysed according to STFI Mottling BA0041. The colour gamut was measured with an X-Rite Spectrophotometer. The print through was measured with a Spectrophotometer. The line width was evaluated with a desktop scanner and adherent software at DPC.




4 Results and discussion

4.1 Trials with commercial papers Eight commercially available papers were evaluated. The papers were divided in three groups according to the quality level: High quality (H1 and H2), Medium quality (M1 and M2) and Standard quality (S1, S2, S3 and S4). In addition, five liner grades were evaluated to study the possibility of using liner in ink-jet printing.

4.1.1 Paper properties The differences between the papers with respect to surface roughness and formation were small. The filler contents in the papers are shown in Figure 6. It is evident that the paper grades ranked as higher quality grades have more filler in the surface region. This is especially accentuated in paper H2. This is because the paper is slightly coated, and the coating pigment is presented as filler in the analysis.

0

10

20

30

H1 H2 M1 M2 S1 S2 S3 S4

Amou

nt o

f fil

ler

(%)

TopTotal

Figure 6. Filler distribution at the top of the paper and the total amount of filler in the paper.




The hydrophobicity of the papers was investigated with a number of methods. The Cobb60 method gives a measure of the static water absorption by the paper. Figure 7 shows Cobb60 results. Here, the papers with the lowest quality grade had the lowest Cobb60 value, i.e. they were more heavily sized.

0

40

80

120

160

H1 H2 M1 M2 S1 S2 S3 S4

g/m

2

Figure 7. Cobb60 value o the papers. f

Since high-speed ink-jet printing is a fast process, it is of interest to determine the dynamic water absorption of the papers. One measure representative of this is the time-dependence of the contact angle. Figure 8 shows the change in contact angle for these papers with time. The contact angle decreases rapidly on the papers of the higher quality grades, paper H1 absorbing the applied water most rapidly.




0

30

60

90

120

0,1 0,3 0,5 0,7 0,9 1,1

Time [s]

Cont

act

angl

e [d

egre

e]

H1

S3

M1S1S4

H2

M2

S2

Figure 8. Change in contact angle with time.

It is difficult to draw any further conclusions from the trials with commercially available papers since no further information about these papers was available. The filler distribution differed among the papers, as well as the hydrophobic properties.

4.1.2 Print evaluation The print evaluation showed relatively large differences between the papers. Figure 9 shows the subjective print quality ranking.

0

1

2

3

H1 H2 M1 M2 S1 S2 S3 S4

Subj

ectiv

e pr

int

qual

ity

Figure 9. Subjective evaluation of the print quality. There are clear differences between the papers that roughly follow the assigned quality levels H, M and S. The best result was achieved with paper H2, a single-side coated paper. This paper grade was included in the study for comparison with a high quality paper.




One significant parameter affecting the print quality is print mottle. Figure 10 shows results of the STFI print mottle analysis in the wavelength band 1-8 mm for the printed papers.

0

1

2

3

4

5

H1 H2 M1 M2 S1 S2 S3 S4

COV

Figure 10. Print mottle in the wavelength band 1 8 mm. The print mottle was measured on full- tone areas printed with cyan ink. Low values means low mottle.

-

The print mottle was significantly lower for papers from the high and medium quality levels, probably due to the higher water absorption rates in the surfaces of these paper grades.

The achievable colour gamut is another important parameter for a paper for the reproduction of coloured images. Figure 11 shows the colour gamut volume for these papers.




0

1

2

3

4

H1 H2 M1 M2 S1 S2 S3 S4

x105

Figure 11. Colour gamut volume o the evaluated papers. fThe colour gamut volume is only slightly larger for the papers with the higher quality levels, except for H2 which has a significantly larger colour gamut due to its coated surface.

The most important parameter for the subjective print quality seemed to be the mottle. Figure 12 shows the subjective print quality plotted against the print mottle.

H1

M2

H2

S1M1

S3S4

S2

0

1

2

3

0 1 2 3 4 5

COV

Subj

ectiv

e pr

int

qual

ity

Figure 12. Subjective print quality vs. print mottle.

The subjective print quality correlated well with the degree of print mottle. The high print quality on paper H2 is probably an effect of the large colour gamut volume in addition to the low/moderate mottle. Figure 13 shows the print mottle plotted against the contact angle after 0,2 seconds.




H1

M2

H2S1

M1

S3

S4S2

0

1

2

3

4

5

40 60 80 100 120

Contact angle at 0,2 s [degrees]

COV

Figure 13. Print mottle vs. contact angle at 0,2 second.

A high wettability and water absorption seems to decrease the print mottle. The water absorption may thus be important for the print quality as long as it affects the print mottle. A hydrophilic surface was therefore considered to be desirable in the subsequent pilot-scale papermaking trials. The continuing work in this study was therefore focused on the hydrophilic properties of the paper and on the surface structure.

4.1.3 Liner trials The evaluation of the print results from the trials on liner grades gave no results of interest. One reason for this was that the surface properties of the evaluated liner grades were not adapted to ink-jet printing. Another reason was that the printing press was not adapted for substrates with high grammages such as liner grades. However, the most interesting region is the top layer of the liner and the results from the finepaper trial can be used to formulate the white top layer of the liner. The runnability properties of liner will probably be better than those of fine paper because of the higher grammage of the liner.

4.2 Trials with pilot manufactured papers Papers were manufactured on the pilot paper machine EuroFEX at STFI-Packforsk. The papers were calendered and surface treated at Metso Paper in Järvenpää. The trials resulted in 14 different trial points, see Table 2.




Table 2. Pilot-scale papermaking and surface treatment trial points. SA=styr n acrylate. e e

Code Forming Sizing Cobb60 Surface treatment 636 Stratified AKD 33 GCC 637 Stratified ASA 69 GCC 638 Stratified ASA 32 GCC 639 Stratified ASA 25 GCC 641 Roll-Blade ASA 34 PCC 642 Roll-Blade AKD 32 GCC 643 Roll-Blade AKD 26 GCC 644 Stratified ASA 32 SA 645 Roll-Blade ASA 34 Starch 646 Roll-Blade ASA 34 SA 647 Roll-Blade ASA 25 GCC 648 Roll-Blade ASA 32 GCC 649 Roll-Blade ASA 72 GCC 650 Roll-Blade ASA 34 GCC

4.2.1 Paper properties The formation of the papers was evaluated, and the formation index is shown in Figure 14. It can be noted that the formation index does not differ substantially, in spite of the fact that the papers were manufactured with different forming methods.

2

3

4

5

636 637 638 639 641 642 643 644 645 646 647 648 649 650

Form

atio

n in

dex

Figure 14. Ambertec formation index.

Figure 15 shows the PPS surface roughness. The values were in the range 3,7-4,4 µm, which is within the desired range.




3

3,5

4

4,5

5

636 637 638 639 641 642 643 644 645 646 647 648 649 650

[µm

]

Figure 15. PPS surface roughness.

The paper surfaces were studied with SEM. Figure 16 shows two samples of the surface-treated papers. The left-hand image shows a paper surface sized with starch and the right-hand image a paper coated with GCC. The figure shows that the pigment particles were evenly distributed on the paper surfaces, and thus that the surface treatment was successful.

Figure 16. SEM images of the paper surfaces. To the left a paper surface siz d with starch, and to the right a pap r coated with GCC pigment.

ee

The opacity of the papers is shown in Figure 17. As expected, the opacity level was roughly the same for all the coated samples, whereas the opacity of the surface-sized samples (644 - 646) was on a lower level.




82

84

86

88

90

92

636 637 638 639 641 642 643 644 645 646 647 648 649 650

R o/R

oo

Figure 17. Opaci y of the paper samples. t

The Cobb60 values after the surface treatment are shown in Figure 18, together with the values measured directly after the papermaking. The differences are effects of the surface treatments, but they can also be effects of time-dependent changes in the hydrophobicity of the base papers. The high value of sample 641 can be noted.

0

20

40

60

80

100

636 637 638 639 641 642 643 644 645 646 647 648 649 650

[g/m

2 ]

after paper manufacturingafter surface treatment

Figure 18. Cobb60 values measured after paper manufacturing and after surface treatment.




Figure 19 shows the time-dependence of the contact angle on the paper samples. The papers with a contact angle below 90º can be assumed to have a more rapid water absorption.

30

60

90

120

0 2 4 6 8 10

Time [s]

Cont

act

angl

e [d

egre

e]

641

650

647

637

636

644646

649645

639648638

642

643

Figure 19. Contact angle as a function of time.

4.2.2 Print evaluation The print result was evaluated by a panel of judges. The result is shown in Figure 20, where it can be seen that the hydrophilic papers (exhibiting the lowest contact angle), 641, 647 and 650, show better results than the other papers. In general, the more hydrophilic papers were judged to be better regarding perceived print quality. Not unexpectedly, the surface sized papers 644, 645 and 646 showed a somewhat lower perceived print quality, even though the results were surprisingly good compared to the coated samples. The results must however be treated with caution since the print quality on some of the samples was poor due to runnability problems in the printing press.




Figure 20. Subjectively evaluated print quality.

0,4

0,8

1,2

1,6

636 637 638 639 641 642 643 644 645 646 647 648 649 650

Subj

ectiv

e pr

int

qual

ity

Figure 21 shows the colour gamut volumes. Sample 641 showed the largest volume, which could be a factor explaining the good result of the subjective evaluation. The uncoated samples had, as expected, a somewhat smaller colour gamut. In this context, it is of interest to note that the papers treated with a surface size containing styrene acrylate showed a fairly good result compared to the light coated grades. The colour gamut volume for the best, lightly coated papers was in the same range as that of the commercial papers. This indicates that the pilot-scale manufactured papers are in the proper quality range.

0,8

1

1,2

1,4

1,6

1,8

636 637 638 639 641 642 643 644 645 646 647 648 649 650

x105

Figure 21. Colour gamut volume.




The print through values for the samples are shown in Figure 22. The highest values were recorded for the uncoated samples, 644, 645 and 646. As expected, the most hydrophobic samples, 642 and 643 showed somewhat lower print through, although the differences are small.

0,00

0,02

0,04

0,06

0,08

0,10

0,12

636 637 638 639 641 642 643 644 645 646 647 648 649 650

KC+M

Figure 22. Print through.

An important measure of print quality, particularly with water-based inks and large amounts of ink is the print mottle. Figure 23 shows the print mottle in the 1-8 mm wavelength band on full tone areas printed with magenta ink. The best results were noted for the hydrophilic papers with high Cobb60 values and with a low contact angle. Rapid water absorption thus seems to minimise the mottling tendency.




1

1,5

2

2,5

3

3,5

636 637 638 639 641 642 643 644 645 646 647 648 649 650

COV

Figure 23. Print mottle in the wavelength band 1-8 mm. The print mottle was measured on full-tone areas printed with magenta ink.

Figure 24 shows the relation between print mottle and contact angle. There is a significant linear correlation although it is weak. A low contact angle which implies good wettability is beneficial for low print mottle, presumably because the ink flows on the surface.

Figure 24. Print mottle vs. contact angle at 0,1 second.

641

650

647

638 648639 636

645

644

637

642

649643

646

1,5

1,9

2,3

2,7

3,1

40 60 80 100 120

Contact angle at 0,1 s [degrees]

COV

To obtain an estimate of print sharpness, the printed line width was evaluated. Due to runnability problems which caused misregister in the high-speed press, these tests were performed on a desk-top sheet-fed printer. Figure 25 shows the results of the measurements. Papers with a high hydrophilicity, 641 and 650, show slightly larger line width values. The




differences are however very small, in the range of 0,01 mm. Significant differences are in the range of 0,1 mm.

1,31

1,32

1,33

1,34

636 637 638 639 641 642 643 644 645 646 647 648 649 650

Line

wid

th [

mm

]

K/WK/Y

Figure 25. Line width. K/W are black print on white background. K/Y are black print on yellow. The readings are m an values MD/CD. e

4.3 Runnability It is, in general, difficult to measure runnability and in these trials, the difficulty was accentuated by the fact that the runnability conditions in the printing press were not totally under control. Large printing areas or high amounts of ink increase the runnability problems to a great extent. The dimensional stability of the paper structure during water exposition is important due to the large amount of water transferred through the printing ink combined with high printing speed and high web tension. Runnability is one of the most important parameters for high-speed ink-jet printing. In general, the papers manufactured with stratified forming showed a somewhat inferior runnability.




5 Conclusions This work was performed in order to identify requirements on paper raised by the development of high-speed ink-jet printing machines. The goal was to identify important parameters to create a cost-efficient paper with optimised properties for water-based high-speed ink-jet printing. The study included pilot-scale papermaking trials, and full-scale printing in a high-speed ink-jet press.

The work was divided in two parts: -Pre-study trials with commercial papers -Pilot-scale papermaking and surface treatment trials.

The trials with commercial papers showed that:

• The wettability is of great importance.

• The paper structure should have a good dimensional stability during moisture exposure.

The pilot-scale papermaking and surface treatment trials showed that:

• A hydrophilic surface minimizes mottling but it can, on the other hand, increase print through and decrease print sharpness. The latter two effects are however small and probably of less importance.

• A larger colour gamut volume is achieved on coated papers with the specially formulated PCC grade than on papers with GCC. This elucidates the importance of choosing the proper pigment.

• Styrene-acrylate addition to the surface sizing keeps the ink colorant on the surface and the paper can almost be compared to pigmented paper grades.

• Stratified forming tends to increase the colour gamut volume, which can be explained by the occurrence of more fine material in the top layer, which forms a barrier that captures the ink colorant.

• The main problem is the dimensional stability of the paper structure during the printing process, due to the large amount of water transferred through the printing ink combined with high printing speed and high web tension.

The results show that it is possible to design a lightly coated paper suitable for high-speed ink-jet printing which gives an acceptable colour gamut volume. During high-speed ink-jet printing, large amounts of water are applied to the paper in a short time. This means that the paper must be able to absorb the water to avoid print disturbances such as print mottle and also have a good dimensional stability.




6 References Andreottola M. A. (1991) Ink Jet Ink Technology Handbook Of Imaging Materials, pp 527-544

Babinsky V. (1998) Ink Jet Pap r Development Intertech Conferences: Speciality & Technical Papers 98, San Fransisco, California, 12 pp.

e

Bares S.J. (1991) Papers and Films for Ink Jet Printing Handbook Of Imaging Materials, pp 546-562

Bares S. J., Rennels K.D. (1990) Paper compatibility with next generation ink-jet printers Tappi Journal, (73) Jan 1990, pp 123-125

Oliver J. F. (1984) Initial stages of ink jet drop impaction, spreading, and wetting on paper Tappi Journal, (67) 10 Oct 1984, pp 90-94

Ranson B. W., Varnell D. F. (2002) The challenge to uncoated paper mills – laser performance from inkjet printing Paper Technology, March 2002, pp 31-35

Romano F. (2004) Status report on digital color printing Presentation at GFF Seminar, Stockholm 2004-05-27




STFI Database information

Title: Papers designed for high-speed ink-jet printing

Author(s): Erik Blohm, Peter Åslund

Abstract: The work was performed in order to identify the requirements on paper raised by the development of high-speed ink-jet printing machines. The goal was to identify important parameters to create a cost-efficient paper with optimised properties for water-based high-speed ink-jet printing. This was done by pilot-scale papermaking trials, and full-scale printing with a high-speed ink-jet press.

Eight commercially available paper grades suitable for ink-jet printing were used in a prestudy to identify the most critical parameters. Papers were manufactured on the EuroFEX experimental paper machine and surface treated with pigment or surface sized in a metering size press. The printing was performed in a Scitex Versamark high-speed ink-jet printing press. The paper properties and the print quality were determined and evaluated after the printing.

The results showed that: A hydrophilic surface minimizes mottling effects but can, on the other hand, increase print through and decrease print sharpness. A higher colour gamut volume is achieved with the specially formulated PCC grade used in the surface-treatment trials than with GCC, which elucidates the influence of the pigment properties. A surface sizing modified with styrene acrylate improved keeps the ink colorants in the surface and can almost be compared to pigmented surface coating. Stratified forming gives more fine material in the top layer and forms a barrier that captures the ink colorants, this will tend to increase the colour gamut volume. Further, the paper structure should have a good dimensional stability during moisture exposure.

The results show that it is possible to design a lightly coated or pigmented paper suitable for high-speed ink-jet printing and giving an acceptable colour gamut volume. The main obstacle is the dimensional stability of the paper structure during the printing process due to the large amount of water transferred through the printing ink.

Keywords: Ink-jet paper, ink-jet printing, paper making, print quality, printing test, surface sizing, surface treatment, water absorption

Classification: 620, 640, 730

Type of publication: STFI-Packforsk report

Report number: CW 248

Publication year: 2004

Language: English


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