Abstract
The focus of this thesis is to establish the timescale of
interactions, physical and chemical, during dye-based
inkjet ink imbibition into calcium carbonate (CaCO3)
pigmented coatings. Comparison is made between
conventional offset quality CaCO3, and special inkjet
qualities in the form of either modified or precipitated
CaCO3 combined with swelling diffusion driving or
non-swelling diffusion-inert binder. The selection of
pigment is based on the control of pore volume, pore size
distribution and connectivity of the coating layer.
Pigments with nano-size pores (intra-particle) are
primarily exemplified. The final coating layers display
discrete pore size bimodality in relation to the
intra-particle and inter-particle pores. Polyvinyl
alcohol (PVOH) is used as the diffusion sensitive binder
and styrene acrylate latex (SA) as the bulk
diffusion-inert binder. By changing the coating
structures and using the contrasting binders, the roles
of liquid diffusion, capillary pressure and permeation
flow are clarified both in the short and long timescale
imbibition. The wetting force within the finest
capillaries drives the ink into the porous structure,
whilst the viscous drag within the structure resists the
movement. The nano-size capillaries initiate absorption
of the ink vehicle, though typical impact pressure of an
inkjet droplet is shown to provide forced wetting. During
the flow, the hydrophilic binder swells, acting to close
the smallest pores and reduce the remaining pore
diameters. The total pore volume decrease competes with
the initial capillarity. The diffusion is shown to have a
marked effect on the polar liquid absorption rate into
the PVOH-containing coatings over different timescales.
The swelling opens the polymer matrix so that the
colorant fits into the binder structure and can either
hydrogen bond or become mechanically trapped. The
diffusion coefficient of water in PVOH and on SA latex
films is shown to be similar, despite the difference in
geometry. Colorant fixing is enhanced mainly by the ionic
interaction between the colorant and surface, and there
is an optimal rate beyond which the colorant has
insufficient time to translate under the Coulombic
attraction toward the cationic adsorption sites or to
respond to the binder matrix diffusion potential. The
competing mechanisms of liquid flow and ab/adsorption are
seen as crucial to developing a high quality print. High
speed inkjet print density depends on the colorant
location in the structure and the optical properties of
the whole coated paper. Intercolour bleeding is also
dependent on the coating absorption capacity at an
adequately high rate in competition with colorant
spreading.
Original language | English |
---|---|
Qualification | Doctor Degree |
Awarding Institution |
|
Supervisors/Advisors |
|
Award date | 4 May 2012 |
Place of Publication | Espoo |
Publisher | |
Print ISBNs | 978-951-38-7455-1 |
Electronic ISBNs | 978-951-38-7456-8 |
Publication status | Published - 2012 |
MoE publication type | G5 Doctoral dissertation (article) |
Keywords
- diffusion
- absorption
- permeability
- porosity
- ionic charge
- coating binder
- coating
- inkjet printing