Ondrej PANÁK
CREATE 2010
ondrej.panak@upce.cz
8—11 June 2010, Gjøvik, Norway
Thermochromic inks


The basic function of thermochromic (TC) ink is the
ability to change the colour due to the
temperature change.
The use of TC inks:
 Foodstuff
industries
 Security print
 Special design
Thermochromic inks


The offset thermochromic Inks are composites of
TC pigment and a vehicle.
TC pigment is commonly
a leucodye-developer-solvent system,
encapsulated in polymer envelope (melamine
formaldehyde or epoxy resin).
Thermochromic inks

The colour former (leucodye) can by a
sopirolactone molecule, for example Crystal Violet
Lactone.

Phenols are used as developers.
Solvents can be alcohols, esters, amides and acids
with long chain aliphatic character.

Thermochromic inks
Thermochromic inks



The phase separation plays the major role in the process.
When the solvent is melted the developer and the colour
former are dissolved and the environment is relatively
non-polar.
On cooling the colour former and developer separate from
the solution and the dye experiences a more polar
environment, the ring opens and the pigment becomes
coloured.
Thermochromic inks




The encapsulation is done using interface or insitu
polymerization.
The vehicle consist of varnishes, reducers, driers
and other additives, but neutral pH is needed to be
neutral.
The use of nonpolar solvents
is recommended.
Carefully adjusted dampening
solution.
Experiment

Two sets of TC offset inks:
CTI
– magenta (31 °C), red (31 °C), black (31 °C)
 SICPA
– pink (35 °C), blue (27 °C), gray (25 °C)
 Conventional offset magenta ink
 Offset varnish


Experiments:
Rheological properties
(rotational rheometer with
cone plate system)
 Pigment particle size distribution

Rheological properties
 F A
  v h
   
Rheological properties
Flow curves at 30 °C
η – shear viscosity
τ – shear stress
γ – shear rate
Viscosity curves at 30 °C
   / 
Rheological properties
T [°C]
   c  c
  c  
Casson model – τc [Pa]
Ostwald model – p
CTI
black
CTI
mag.
CTI
red
Sicpa varnis conv. CTI
pink
h
offset black
p
CTI
mag.
CTI
red
Sicpa varnis conv.
pink
h
offset
20
80.79 26.10 45.32 64.78
14.26 307.7
0.85
0.91
0.88
0.88
0.88
0.72
25
43.03 30.25 38.34 50.65
16.18 285.3
0.88
0.91
0.89
0.86
0.89
0.70
30
32.99 18.69 25.82 54.70
13.86 93.71
0.90
0.93
0.90
0.87
0.89
0.75
35
20.01 12.06 11.06 46.12
13.62 109.7
0.91
0.93
0.93
0.87
0.91
0.74
40
11.12
5.12
0.93
0.94
0.93
0.87
0.92
0.75
7.01
11.35 27.66
86.06
Rheological properties
Viscosity curves of SICPA gray TC ink
Particle size distribution
CTI black
0.6
0.4
0.2
0
0.1 0.45 0.95 1.45 1.95 2.45 2.95 3.45 3.95
0.8
0.6
0.4
0.2
0
1
CTI magenta
0.8
median
0.6
CTI black
1.34
0.4
CTI magenta
1.21
0.2
CTI red
1.29
0
SICPA gray
3.36
SICPA pink
2.66
SICPA blue
2.63
0.6
0.4
0.2
0
0.1 0.45 0.95 1.45 1.95 2.45 2.95 3.45 3.95
1
0.8
CTI red
0.6
SICPA pink
1
0.8
SICPA blue
0.6
0.4
0.4
0.2
0.2
0
SICPA gray
0.1
0.7
1.7
2.7
3.7
4.7
5.7
6.7
7.7
8.7
9.7
10.7
11.7
12.7
13.7
1
Particle size
distribution
[μm]
0.8
0
0.1 0.45 0.95 1.45 1.95 2.45 2.95 3.45 3.95
0.1
0.7
1.7
2.7
3.7
4.7
5.7
6.7
7.7
8.7
9.7
10.7
11.7
12.7
13.7
0.8
1
0.1
0.7
1.7
2.7
3.7
4.7
5.7
6.7
7.7
8.7
9.7
10.7
11.7
12.7
13.7
1
Conclusions

CTI TC inks behave similar to offset varnish.

TC inks needs much smaller force to start flow than
conventional offset ink.

The blue and grey Sicpa inks exhibited unexpected
depression in a specific region, and it seems to be
temperature dependent.
What next?

Prepare pigment with
combined effects
Acknowledgments
Marie KAPLANOVÁ
Marta KLANJŠEK GUNDE
Mojca FRIŠKOVEC
CREATE 2010
ondrej.panak@upce.cz
8—11 June 2010, Gjøvik, Norway