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A New Coating Nano-technology with Unique Characteristics to Improve Print Density

Dr. M. Patricia Wild – Eka Chemicals Inc, USA Ylva Wildlock – Eka Chemicals AB, Sweden Kjell Andersson – Eka Chemicals AB, Sweden Erik Lindgren – Eka Chemicals AB, Sweden

Eka Chemicals 2008 Silica Inkjet Coating

Existing silica based coatings: zConventional technology for high quality inkjet zThree main ingredients „Silica pigments (such as fumed, gel, colloidal) „Binder (PVOH, PVA) „Cationic (PolyDADMAC) Silica Particles

z Silica is porous and hydrophilic z Capable of taking up large volumes of ink z Inter and intra particle pores makes silica very absorbent z High internal porosity silica requires large amounts of binders

Silica Gel (micro scale range) Binders

z Hold together small silica particles z Binder level and type is a compromise because: „High volumes plasticize coating , but reduce the ink receptivity „Low levels give good pigmented ink compatibility, but poor physical properties (rub-off, chalking, debris) Existing Limitations

Limitations of Existing Silica Coatings:

z Low (maximum 25%)

zRequires intense drying zNeeds slow coating speed, therefore, limits commercial application Existing Limitations (cont.)

z High binder requirements (>40 wt.%) zSwellable vs. Capillary system „Slows down rate of ink absorption „Limits ink load „Decreases print density and gamut Existing Limitations (cont.) Cost zHigh raw material costs: „Fumed silica (if used) „Addition of high amount of binders zCost in time „Slow drying due to low solids „On site preparation of formulations Nano Particle Coating (NPC)

In contrast to existing silica coatings, the new silica nano-particle coating technology (NPC) has the following attributes: •• HighHigh SolidsSolids (up(up toto 50%)50%) •• NoNo organicorganic binderbinder •• GoodGood runnabilityrunnability •• ReadyReady toto useuse NPC Binding Mechanism

z Nano silica particles contain a high number of surface active silanol groups due to large surface area z Binding is by condensation of silanol groups bridging between the silica particles z Strong covalent bonds formed between the silica particles z Colloidal silica is a binder (used in ceramic industry) (mח Colloidal Silica (nano scale range from 2 to 100 NPC Formulation

z NPC is a nano structured porous pigment z Porous silica network capable to absorb ink vehicle rapidly z 2 μm average secondary particle size z Pigment is slightly cationic z Charge optimized for aqueous inkjet inks compatibility z Rheology optimized for excellent runnability NPC Properties

NPC Coating Properties

zBrookfield : 300 to 500 cps

zWater retention value: <80 g/m2

zpH slightly acidic NPC Micrographs

Uncoated base paper Thin layer of NPC

z Left: uncoated base sheet z Right: same base sheet coated with NPC z NPC follows the contour of the paper z Does not penetrate into the base sheet NPC Micrographs (cont.)

Pre-coated (GCC) paper Pre-coated and NPC top coated paper

z Left: pre-coated with GCC and starch zFills the voids on the surface of the paper z Right: pre-coated & top coated with NPC zCreates smooth surface to receive ink Results: Gloss

70 70 bar 75 bar 60

50

40 30

20

Gloss measured at 75° 10

0 0 102030405060 No of calender Nips

Single coated w ith NPC Precoated + NPC Higher gloss obtained with fewer calender nips when using pre-coated paper NPC Pilot and Mill Trials

NPC tested on mill trials zTwo mill trials „rod metering and „puddle size press Ink – NPC Coating Interaction

Ink solvent NPC Coating Ink dye

Paper z Silica’s cationic groups fix ink dye to surface z Ink solvent absorbs within the NPC nano structure NPC Applications

Versatility in Application: z Coating Equipment z From size press to coaters z Coat Weight Range: 1.5 to 20 g/m2 z Multiple Aqueous Printers: z SOHO or Industrial applications z Narrow or wide format z HP, Epson, Canon z Base Sheet Grammage: 65 to 230 g/m2 Study

Coating A NPC z Silica gel based z Nano silica based z Primary particle size: z Primary particle size: 20 ηm 35 ηm z Secondary particle size: z Secondary particle size: 9 μm 2 μm z Solids content: 25% z Solids content: 48% z 100 pph PVOH binder z No organic binder added Case Study: Gamut Results

Gamut Volume Comparison

300000

250000

200000 Coating A with 100 pph binder 150000 Coating NPC -

Gamut Volume Gamut 100000 NO binder

50000

0 Epson Canon HP Printers Similar Gamut between Coatings A and NPC Case Study: Ink Absorption

Coating Layer Stereoscope image of Epson ink on the with Yellow surface of paper single coated with and Blue Inks NPC (RIT)

Paper

Coating NPC: Inkjet ink stayed on the surface of the paper Results: Kodak Versamark Data

%Water Optical Cockle Fast %Wet Paper Name Grammage Density 1-10 Test %Bleed Rub (High is (Low is (High is (Low is (Low is (g/m2 ) Better) Better) Better) Better) Better) Targets 1.20 3 99 10 10 NPC (WMU11) 78 1.23 3 104 7 6 Image Grip VIP 20# 76 1.17 6 104 26 13 Dataspeed Inkjet Pro 92 1.16 5 97 20 10 Z-Plot 650 90 1.15 5 103 0 0 HSIJ 24# 93 1.17 5 101 11 12 Pixelle Bond VM 91 1.03 7 107 7 17 Ultra White Ink Jet 88 1.09 7 102 1 2

Source: Kodak Versamark Transactional Data posted on Kodak webpage and NPC Test Results Provided by Kodak Results: Optical Density

Coat Weight Influence on Optical Density

1.5 1.45 1.45 1.42 1.4 1.38

1.35 1.3 1.25 1.25 1.2 1.18

Optical Density 1.15

1.1 1.05 1 0 4.6 6.5 10.6 11.7 Coat Weight (g/m^2) NPC coated papers printed at Kodak on the Versamark printer showed significant optical density increase as NPC coat weight increased Results: Line Bleed Comparison

Black on Yellow Line Bleed for HP 5650 Printer (Low value is better) Horizontal 0.12 Line Bleed

0.1 Vertical Line Bleed 0.08

0.06

Line Bleed Line 0.04

0.02

0 Source: RIT NPC Matte Photo Brochure

z NPC coated papers were sent to RIT for printing, testing, and comparison to the OEM benchmark z NPC paper performed better than the matte photo paper and similar to brochure paper Results Summary

Lab studies, pilot, and mill trials show that NPC has good: zRunnability zPrint quality zColor gamut zWater permanence zColor performance zDimensional stability Future Work

z Work will be performed to determine metrics for:

zImage Permanence

zVisual Appearance Conclusions

Nano Particle Coating (NPC) Technology: z Ready to use z Good runnability in spite of having: z No organic binder z High solids z Suitable for mills or coating facilities z Similar or better inkjet printing properties than the benchmark (print density, gamut) z Suitable for matte and semi gloss paper grades Thank you!

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