Porous Ξ- Al2O3flake powder as dye-fixing materials for inkjet printing paper

Article abstract of DOI:10.1111/j.1551-2916.2012.05271.x

Cationic additives are generally used in coated inkjet printing paper to improve water fastness. This study develops a coating for photographic inkjet printing paper that achieves good water fastness without cationic additives. Porous Ξ- Al₂O₃flake powder, which has high porosity, high specific surface area, and positive surface charges, is used as a pigment in the coating. The water fastness of prints is evaluated using an immersion method combined with the measurement of light absorbance of the water used for immersion. The results indicate that water fastness can be improved by introducing Ξ- Al₂O₃powder into the coating pigments. The intrinsic crevices and pores of Ξ- Al₂O₃provide concave sites for dye colorants and enhance the sorbtion of liquid phase of inks, but stick the dye colorants on the pigment surface. Furthermore, the positive surface charge of Ξ- Al₂O₃provides cationic sites for the fixation of dye on the coating surface via electrostatic interactions.

Full text of DOI:10.1111/j.1551-2916.2012.05271.x

J. Am. Ceram. Soc., 1–3 (2012)
DOI: 10.1111/j.1551-2916.2012.05271.x
© 2012 The American Ceramic Society
ournal
J
Porous v-Al2O3 Flake Powder as Dye-Fixing Materials for Inkjet Printing Paper
Pei-Ching Yu,‡ Chih-I Chen,‡ Rung-Je Yang,‡ Fu-Su Yen,‡,† and Shih-Tsung Max Yen§
‡Department of Resources Engineering, National Cheng Kung University, Tainan 70101, Taiwan
§College of Engineering, Technology, and Computer Science, Indiana University-Purdue University Fort Wayne, Fort Wayne,
Indiana 46805
Cationic additives are generally used in coated inkjet printing
paper to improve water fastness. This study develops a coating
for photographic inkjet printing paper that achieves good water
fastness without cationic additives. Porous v-Al2O3 flake pow-
der, which has high porosity, high specific surface area, and
positive surface charges, is used as a pigment in the coating.
The water fastness of prints is evaluated using an immersion
method combined with the measurement of light absorbance of
the water used for immersion. The results indicate that water
fastness can be improved by introducing v-Al2O3 powder into
the coating pigments. The intrinsic crevices and pores of v-
Al2O3 provide concave sites for dye colorants and enhance the
sorbtion of liquid phase of inks, but stick the dye colorants on
the pigment surface. Furthermore, the positive surface charge
of v-Al2O3 provides cationic sites for the fixation of dye on the
coating surface via electrostatic interactions.
effective charged-based fixation, because aqueous anionic-
dye-based inks are mostly used in inkjet printing. However,
poly-DADMAC is a widely used cationic additive in inkjet
printing coatings currently. Pigments such as kaolin,6 calcium
carbonate,5–11 silica,5–7 alumina,1,7 and aluminum hydrate7,12
are commonly used in coatings. The best inkjet print quality
is generally achieved with coated paper that contains silica
and/or alumina as pigments.1,6,8 Different pigments usually
require the use of different binders.8 The most common bin-
der is polyvinyl alcohol (PVOH) due to its hydrophilic nat-
ure, stability in shear and temperature, and ability to
increase the surface strength of the coating layer.4 Donigian
et al.5 reported that PVOH provides some sites for dye bind-
ing at high concentration. Lamminmaki et al.8 investigated
the role of PVOH and styrene acrylate latex as binder in the
formation of the coating structure for inkjet printing. They
found that the chemical nature of the binder affects ink
movement. PVOH becomes concentrated within the fine
pores of the structure and absorbs water and ink dye into its
polymer matrix.
The pore-size distribution and network structure of the
coating layer determines how much and how quickly ink
penetrates into the available pore volume. During the ink set-
ting process on coated papers, pores in the coating structure
provide a penetration layer and capillaries which force the
liquid phase of the ink into the pore structures; the ink colo-
rants remain on the surface of the coating. Larger and finer
pores are considered beneficial for ink penetration and capil-
laries, respectively.9–11,13 Donigian et al.5 found that finer
pores are useful for separating ink components; they hold
dye colorants and allow the fluid phase to pass through.
Coating layers with an appropriate porous structure for
the sorbtion of the liquid phase of inks and with sufficient
cationic sites for the fixation of dyes are essential for excel-
lent inkjet printing quality. In general, cationic additives in
the coating are responsible for the water fastness of inks.
This study develops a coating for photographic inkjet print-
ing paper that does not contain cationic additives while
achieving good water fastness. Porous v-Al2O3 flake pow-
der,14,15 which has high porosity, high specific surface area,
and positive surface charges, is used as a pigment in the coat-
ing. The intrinsic crevices and pores of the flake alumina
powder and the nature of the cationic surface enhance the
sorbtion of the liquid phase of inks and provide cationic sites
for the fixation of dye on the coating surface. The influence
of v-Al2O3 on water fastness and the interaction between dye
colorants and v-Al2O3 powder are investigated.
I. Introduction
OLOR inkjet printers are widely used in the office and
home due to their lower price, higher printing speed,
C
greater resolution, easier operation, and improved conve-
nience compared with those of traditional printing. Advance-
ments in inkjet printing have increased need for inkjet paper.
Inkjet papers can be classified into four major categories,
including plain or surface-sized paper, coated matte paper,
coated glossy paper, and cast-coated paper and resin-coated
paper.1 Photographic coated paper with good water fastness
is the highest quality paper due to its high resolution and
high resistance to smearing. This kind of paper is manufac-
tured by coating a base paper with special pigments, binders,
and cationic additives.
Inkjet printing quality greatly depends on the composition
and structure of the coating layers of the paper.1,2 Coatings
mainly consist of pigments, binders, and cationic additives.
For high-quality image reproduction, the colorant of the ink
must be retained and fixed on the surface of the coating
layer. The electrostatic interaction between the anionic color-
ant and cationic sites of the coating layer plays a key role in
fixing the dye colorants and improving water fastness.2–6 To
achieve this, extensive studies have been investigated. Aziri-
dine monomer chemistry,2 polydiallyl dimethyl ammonium
chloride (poly-DADMAC),3,4 ammonium zirconium carbon-
ate,3 zirconium acetate,3 and styrene maleic anhydride imide
resin4 have been used as cationic additives for providing
B. Yoldas—contributing editor
II. Experimental Procedure
Porous v-Al2O3 flake powder was obtained via the calcina-
tion of gibbsite16 (Al(OH)3, M010, The Beaming Co., Ltd,
Hsinchu, Taiwan) at 700°C for 1 h with a ramping rate
10°C/min followed by cooling to room temperature. The
Manuscript No. 31214. Received March 19, 2012; approved April 14, 2012.
†Author to whom correspondence should be addressed. e-mail: yfs42041@mail.
ncku.edu.tw
1

2
Rapid Communications of the American Ceramic Society
alumina powder was delaminated utilizing a Perl Mill appa-
ratus (Drais, PML-H/V, Uzwil, Switzerland) and mixed with
commercial silica powder (Syloid ED 5, W. R. Grace GmbH,
Columbia, MD), which is usually used as a pigment for
matte coated photo paper, as the coating pigment. Table I
shows the coating formulae employed in this study. The bin-
der used in the coating was PVOH, which has a degree of
hydrolysis of 78.5%–81.5%. The pigment slurries and PVOH
binder, both with 15 wt% solid content, were mixed well for
the coating process.
The crystalline phase of the alumina powder was identified
by X-ray diffraction (XRD, MiniFlex; Rigaku, Tokyo, Japan)
using Cua radiation in the 2h range of 20–80° with a scan rate
of 4°/min. A porosimeter (Micromertics 2020, Norcross, GA)
was utilized to measure the specific surface area and pore vol-
ume of the alumina. The microstructures of the porous alu-
mina flake powder with and without dye colorants were
observed using a transmission electron microscope (TEM,
HF-2000; Hitachi, Tokyo, Japan).
Commercial polypropylene-based synthetic paper with a
primer (Nan Ya Plastics Corporation, Taipei, Taiwan) was
used as the base sheets for coating. The coatings were
applied to the base sheets by a coating rod (RDS coating rod
#75). The coated sheets were then dried in an oven at 110°C
for 5 min to obtain the final paper.
III. Results and Discussion
(1) Porous Alumina Flake Powder
The phase of the alumina used in this study was v-Al2O3,
which is one of the transition phases of a-Al2O3 when gibb-
site (Al(OH)3) is used as the precursor.16 The XRD pattern
of the porous v-Al2O3 flake powder is shown in Fig. 1(a).
Gibbsite experiences a pseudomorphic transformation14,15
during thermal treatment; its outward morphology is pre-
served when it transforms into v-Al2O3. The porous structure
of v-Al2O3 results from a dehydration reaction from Al
(OH)3 to v-Al2O3 during thermal treatment. Flake powders
are usually efficient for coating processes. Delamination pro-
cesses were employed to obtain porous v-Al2O3 flake powder
as a coating pigment [Fig. 1(b)]. Table II shows the physical
properties of the v-Al2O3 powder used in this study.
v-Al2O3 shows a positive surface charge for pH values of
below 9. The electrostatic interaction between the anionic
colorant and cationic sites of the coating layer is considered
to play an important role in fixing the dye colorants and
improving water fastness. Therefore, the pH value of the
slurries for paper coating was adjusted to be around 5.0.
Images with bars of four solid colors (cyan, magenta,
yellow, and black) were printed on the coated paper using an
inkjet printer (Stylus Photo R290; Epson, Long Beach, CA)
with model dye-based inks. The quality inkjet printing mode
was used. Water fastness was evaluated by immersing a
printed page into water for 30 min, after which the paper
was removed and dried at room temperature. The water used
for immersion was collected and its light absorption was
measured using a photometer (Spectroquant NOVA 60;
Merck, Whitehouse Station, NJ) to represent the concentra-
tion of colorants desorbed from the coating surface. The
concentration was obtained using Beer’s law (Absorbance
A = Àlog(I/I0), which has a linear relationship with the con-
centration of colorants) and used to measure the degree of
water fastness of the paper. A high light absorbance indicates
a low degree in water fastness. Light wavelengths from 400
to 700 nm were used in the light-absorption measurements.
(2) Printed Images and Water Fastness of the Prints
Photographs of bars of four solid colors (cyan, magenta,
yellow, and black) printed on the coated paper are shown in
Fig. 2(a). All samples exhibit sharp edges and a high resolu-
tion. Figure 2(b) shows photographs of the samples taken
after the water fastness tests. An increase in the proportion of
Al2O3 in the coating pigments resulted in a lower amount of
colorants desorbed from the coating surfaces (i.e., the water
was clearer) [Fig. 2(c)]. Only a small amount of colorants
appeared in the water when the ratio of SiO2: v-Al2O3 was
50:50 (sample A50); the water was perfectly clear for sample
A100. To quantify the water fastness of the prints, the light
absorbance of the water after the immersion process was
Table I. Coating Formulae Employed in This Study
Formulae (wt%)
SiO2: Al2O3
ratio
Solid content
(wt%)
Sample
SiO2
Al2O3
PVOH
pH
A00
A20
A30
A50
A100
100: 0
80:20
70:30
50:50
0:100
83.0
0
17
17
17
17
17
15
5.0
66.4 16.6
58.1 24.9
41.5 41.5
0
83.0
(b)
(c)
(d)
Fig. 1. (a) XRD pattern of porous v-Al2O3 flake powder. (b) TEM micrograph of porous v-Al2O3 flake powder after delamination process. (c)
TEM micrograph of v-Al2O3 flake powder with dye colorants (d) Crevices and pores of v-Al2O3 filled with the colorants.
Table II. Physical Properties of Porous Alumina Flake Powder
Phase
Density (g/cm3)
Crystallite size (nm)
Cross-section diameter (nm)
Thickness (nm)
Specific surface area (m2/g)
Pore volume (cm3/g)
Chi (v)
3.0
<10
150–500
20–50
130–150
0.415

Rapid Communications of the American Ceramic Society
3
(3) Interaction Between Dye Colorants and v-Al2O3
Powder
(a)
(b)
To determine the interaction between the colorants and the
crevices and pores of alumina, the microstructures of porous
v-Al2O3 flake powder with [Fig. 1(c)] and without [Fig. 1(b)]
dye colorants were observed. The TEM micrographs reveal
that dye colorants occupied the crevices and pores of the
v-Al2O3 flake powder. The intrinsic crevices and pores of
v-Al2O3 flake powder provide concave sites for dye colorants
and enhance the sorbtion of liquid phase of inks but stick the
dye colorants on the pigment surface. Furthermore, the posi-
tive surface charge of v-Al2O3 provides cationic sites for the
fixation of dye on the coating surface via electrostatic interac-
tions. SiO2 particles usually have negative surface charges;
therefore, increasing the v-Al2O3 proportion in the coating
pigments effectively increases the number of cationic sites of
the coating layers, resulting in improving water fastness.
(c)
IV. Conclusion
Fig. 2. Photographs of four solid colors printed on coated paper
(a) before and (b) after immersion into water. (c) Water used for
immersion of corresponding samples.
Porous v-Al2O3 flake powder was added to coating pigments
to improve the dye-fixing ability of photographic inkjet print-
ing paper. Coated paper with porous v-Al2O3 flake powder as
a pigment achieved excellent water fastness without cationic
additives. The intrinsic crevices and pores of v-Al2O3 flake
powder provide concave sites for dye colorants and enhance
the sorbtion of liquid phase of inks, but stick the dye colo-
rants on the pigment surface. Furthermore, the positive sur-
face charge of v-Al2O3 provides cationic sites for the fixation
of dyes on the coating surface via electrostatic interactions.
Acknowledgment
This study was supported by the Ministry of Economic Affairs, Taiwan,
R.O.C., under grant 98-EC-17-A-08-S1-023.
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