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Spontaneous imbibition and colloidal aspects of inkjet printing
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Water-based inkjet is one of the most abundant and versatile digital printing technologies. The subject of this thesis work is processes that take place once an inkjet drop lands on the surface of a porous printing media, with focus on liquid penetration due to capillary action (spontaneous imbibition) and aggregation of ink components. Knowing the details of these two sub-processes would allow optimization of printing processes as well as prediction of the final print result, based on material properties.

The dynamics of drops as they land on different surfaces is captured at adequate time and length-scales by an optical imaging system coupled to an inkjet dispensing unit. The evaporation rate of drops is quantified and distinguished from imbibition, and their spreading behavior on porous substrates is characterized. A set of paper grades is used as examples to conclude that the events are captured accurately. Scaling laws for imbibition are derived from Darcy’s law for liquid flow through dimensional analysis and it is shown that the imbibition rate of drops is related to dimensionless volume and time groups, defined by the volume of the drop, porosity and permeability of the substrate, viscosity of the liquid and the Laplace capillary pressure that drives the imbibition. The approach is applied for two types of systems, one that includes simple liquids imbibing homogeneous and isotropic porous glass and the other that includes complex liquids imbibing heterogeneous and anisotropic paper.

The addition of simple divalent salts to the paper surface is widely used to increase the print quality of water-based pigmented inkjet inks. Salt ions quickly diffuse into the inkjet droplets as they land on the paper and cause the ink to aggregate. This effect leads to the accumulation of colorant-pigments close to, or even on, the surface of the paper. Two salts, CaCl2 and MgCl2, are used to aggregate inkjet inks and their components. The interactions between the aggregated compounds are investigated by a set of experimental measurements that include sedimentation, confocal Raman microscopy, turbidity, rheology and electrophoretic mobility. It is concluded that the salt induced aggregation is led by a non-color polymeric ink component used as a pigment dispersant, and that CaCl2 induces stronger interactions between polymeric carboxylate groups compared to MgCl2. This ion specific effect cannot be explained by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory for electrostatic interaction in colloidal systems.

Place, publisher, year, edition, pages
Stockholm,Sweden: KTH Royal Institute of Technology, 2014. , xx, 69 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2014:39
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-152904ISBN: 978-91-7595-272-7 (print)OAI: oai:DiVA.org:kth-152904DiVA: diva2:751976
Public defence
2014-10-24, Q2, Osquldas Väg 10, KTH, Stockholm, 11:56 (English)
Opponent
Supervisors
Note

QC 20141002

Available from: 2014-10-02 Created: 2014-10-02 Last updated: 2014-10-02Bibliographically approved
List of papers
1. Imbibition and Evaporation of Water Droplets on Paper and Solid Substrates
Open this publication in new window or tab >>Imbibition and Evaporation of Water Droplets on Paper and Solid Substrates
2011 (English)In: Journal of Imaging Science and Technology, ISSN 1062-3701, E-ISSN 1943-3522, Vol. 55, no 1, 010201- p.Article in journal (Refereed) Published
Abstract [en]

Imbibition and evaporation of picoliter (pL) sized water droplets on paper media commonly used for inkjet printing is measured using high speed imaging system. Three types of uncoated and coated paper samples were chosen: multipurpose uncoated paper (80 g/m(2)), matte coated paper (230 g/m2), and gloss coated paper (240 g/m(2)). As a reference, the rate of the evaporation process was quantified by using three impermeable solid substrates with different wetting characteristics, i.e., silicon, glass, and hydrophobized glass. It is shown that for water droplets of about 60 pL, imbibition is the dominant phenomenon on the matte and gloss coated paper leading to a total drying time (imbibition plus evaporation) of 10-15 ms for gloss coated paper and 30-150 ms on the matte coated paper. In the latter sample, different regimes in the imbibition process were correlated with the layered structure of the sample. The drying process on the multipurpose paper is dominated by evaporation, with initial drying rate of 0.4-0.6 pL/ms.

Keyword
CAPILLARY RISE, POROUS-MEDIA, PENETRATION, ABSORPTION, KINETICS
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-31330 (URN)10.2352/J.ImagingSci.Technol.2011.55.1.010201 (DOI)000287563500002 ()2-s2.0-84857859785 (Scopus ID)
Funder
Knut and Alice Wallenberg Foundation
Note
QC 20110318Available from: 2011-03-18 Created: 2011-03-14 Last updated: 2017-12-11Bibliographically approved
2. Infiltration and dimensional scaling of inkjet droplets on thick isotropic porous materials
Open this publication in new window or tab >>Infiltration and dimensional scaling of inkjet droplets on thick isotropic porous materials
2014 (English)In: Microfluidics and Nanofluidics, ISSN 1613-4982, E-ISSN 1613-4990, Vol. 17, no 2, 413-422 p.Article in journal (Refereed) Published
Abstract [en]

We study the imbibition of picoliter (pL)-sized inkjet droplets on controlled pore glass membranes (CPG), as a suitable model for isotropic three-dimensional porous materials. We do so using a variety of liquids, i.e., water, formamide and diiodomethane, and measure the evolution of the imbibition process using high-speed digital imaging. Here, experiments were conducted on 2-280 nm CPG membranes with drops with initial volumes ranging from 100 to 600 pL. We derive scaling laws for imbibition through dimensional analysis and advance the argument that the rate of absorption is related to two-dimensionless groups where v(t) is the imbibed volume, as determined from experiments, t is the time, v (tot) the total liquid volume, the porosity, mu the liquid viscosity, k the permeability, and p (c) the Laplace capillary pressure. We show this scaling to well describe the system at intermediate T values and report that V alpha T-0.8.

Keyword
Imbibition, Capillarity, Scaling, Inertia, Isotropic porous material, Inkjet
National Category
Natural Sciences Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-152862 (URN)10.1007/s10404-013-1313-7 (DOI)000339886000015 ()2-s2.0-84904822647 (Scopus ID)
Note

QC 20141002

Available from: 2014-10-02 Created: 2014-10-02 Last updated: 2017-12-05Bibliographically approved
3. Infiltration and dimensional scaling of inkjet droplets onpapers with different surface chemistry
Open this publication in new window or tab >>Infiltration and dimensional scaling of inkjet droplets onpapers with different surface chemistry
(English)Manuscript (preprint) (Other academic)
Abstract [en]

We investigate experimentally and theoretically the spontaneous imbibition of complex inkjet formulations utilizing paper capillary rise and imbibition of inkjet drops. We compare two commercially available papers of the same structure but with different chemistry, one of them surface treated with CaCl. This additive is known to improve print quality when water based pigmented inkjet inks are used by rapidly aggregating the colorant pigments close to, or even on, the surface of the paper. In a previous publication we showed that the key components in the destabilization mechanism of the ink are the dispersing polymers that contain carboxylate groups which interact specifically with the Ca2+ cation. Here we demonstrate the impact of this destabilization effect on the spontaneous imbibition of ink formulations comprised of these polymers, and find that on large scale and long time the imbibition rate is slower in the CaCl2 containing paper compare to the CaCl2 free paper, as shown in paper capillary rise experiments, but on a much smaller scale and shorter times relevant for single inkjet drops no significant differences are observed. We approximate the paper structure to a two dimensional anisotropic porous material, and using Darcy’s law as a base derive dimensionless groups that scale drop imbibition.. This derivation is an expansion of the previously published dimensional scaling of drop imbibition on thick isotropic porous material. We obtain the average global system properties required, by performing sets of drop imbibition experiments where drops are impinged on random paper locations, and use the results to calculate the average volume loss of a single imbibing drop. This averageing procedure is then used in the dimensional scaling.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-152902 (URN)
Note

QS 2014

Available from: 2014-10-02 Created: 2014-10-02 Last updated: 2014-10-02Bibliographically approved
4. Aggregation of inkjet ink components by Ca and Mg ions in relation to colorant pigment distribution in paper
Open this publication in new window or tab >>Aggregation of inkjet ink components by Ca and Mg ions in relation to colorant pigment distribution in paper
Show others...
2014 (English)In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 456, 92-99 p.Article in journal (Refereed) Published
Abstract [en]

Papers coated with salts containing divalent cations exhibit superior inkjet print quality, which has been suggested to be due to fast aggregation of the colorant pigments close to, or even on, the surface of the paper. In this work we show the pivotal role of the carboxylic acid containing dispersing polymer. We report a series of aggregation and sedimentation experiments with commercial inks, generic ink formulations and specific ingredients comprising these formulations, and find differences in their response to the presence of MgCl2 or CaCl2. In particular, flocs and sediments formed in the presence of MgCl2 are denser than those formed in the presence of CaCl2. These differences are not predicted by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. We suggest that ion specific interactions occurring between Mg2+ or Ca2+, and charged carboxylate groups residing on the dispersing polymers, provoke the observed behavior.

Keyword
Inkjet, Pigment based inks, Confocal Raman microscopy, Aggregation, Dispersing polymer, Rheology
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-150517 (URN)10.1016/j.colsurfa.2014.05.023 (DOI)000340318000013 ()2-s2.0-84901642565 (Scopus ID)
Note

QC 20140915

Available from: 2014-09-15 Created: 2014-09-05 Last updated: 2017-12-05Bibliographically approved

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