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Infiltration and dimensional scaling of inkjet droplets onpapers with different surface chemistry
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. SP Technical Research Institute of Sweden, Sweden.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. SP Technical Research Institute of Sweden, Sweden.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. SP Technical Research Institute of Sweden, Sweden .
(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: urn:nbn:se:kth:diva-152902OAI: oai:DiVA.org:kth-152902DiVA: diva2:751955
Note

QS 2014

Available from: 2014-10-02 Created: 2014-10-02 Last updated: 2014-10-02Bibliographically approved
In thesis
1. Spontaneous imbibition and colloidal aspects of inkjet printing
Open this publication in new window or tab >>Spontaneous imbibition and colloidal aspects of inkjet printing
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:nbn:se:kth:diva-152904 (URN)978-91-7595-272-7 (ISBN)
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

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