1. Fluidity of ink
The fluidity of ink is a parameter to
measure the relationship between fluid shear stress and shear rate. In book
printing process, gravure printing ink belongs to the swelling fluid in the
fluid, that is, the flow characteristic of the fluid is that the apparent
viscosity increases with the increase of shear rate, that is, the shear
thickening. Another part of gravure printing ink belongs to pseudoplastic
fluid, that is, the apparent viscosity decreases with the increase of shear
rate, that is, shear thinning.
2. Viscosity
Viscosity is a property to prevent the flow
of liquid, which is internal friction. It is the resistance to the relative
movement of molecules caused by the interaction between the molecular forces of
fluid. The unit of viscosity is Pascal. Gravure ink can be considered as
Newtonian fluid of low viscosity ink, belongs to pseudoplastic fluid, its
characteristic is that the apparent viscosity decreases with the increase of
shear rate, that is shear thinning. Generally, all high polymer melts and
concentrated solutions belong to this category. The reason for the thinning of
the cutter is that the entanglement between the molecules is untied due to the
effect of shear force, and the molecules break away from different flow
velocities to the same layer when flowing.
3. Coloring power
Colorability test is to test the
concentration between the sample ink and the standard color sample.
Colorability indicates the concentration and purity of the ink. The greater the
coloring power, the brighter the ink color. When testing, add a certain
multiple of standard white ink into the ink sample and standard ink, and then
compare and determine.
4. Fineness
Ink fineness refers to the size and
dispersion of solid particles such as pigments and fillers mixed in binder.
Small particles dispersed well, the ink reflects a delicate, smooth, smooth
feeling. If the particles are not dispersed well, they will feel rough,
unsmooth and unsmooth. Ink fineness is a very important factor and index in
printing quality. Usually, high-precision printing products with thin screen
require high ink fineness. On the contrary, poor ink fineness, large and rough
pigment particles will cause many printing failures. Gravure printing ink in book
printing, due to large pigment particles and sedimentation. Fineness is not
only related to the performance of the ink, but also related to the rheology of
the ink.
5. Suitability of ink printing operation
The printability parameters of ink refer to
the printability of printing press in the process of dynamic printing. The
parameters tested under this condition have practical significance in
production. Generally, the printability can be measured by a printability
tester. Standard ink and standard substrate are used to establish standard test
conditions, and then the ink samples are measured and compared to evaluate the
printability of the samples.
6. Ink resistance
Ink resistance refers to the cured ink film
in the invasion of external factors process,
keep the film color, graphics clear and a variety of unchanged performance.
After the ink is transferred to the substrate material to become printed
matter, it is often applied to various environments, so the ink should have
certain resistance, such as gloss, light resistance, friction resistance, water
resistance, solvent resistance, acid and alkaline resistance, grease
resistance, etc. Printed matter in book printing can be selected,
evaluated and analyzed according to its use.
7. Rheology and leveling
Gravure printing ink should have good
rheology and leveling. Due to the characteristics of gravure printing, it
requires low viscosity, small thixotropy and low yield value. Under the action
of pressure and shear force, the rheological properties of ink should not be
changed too much. It should be able to meet the requirements of normal pressure
and shear force.
8. Adhesion
Ink should be suitable for the substrate
requirements of adhesion, for the film, the ink should be wetted before
adsorption, that is, the surface tension of the ink is less than the surface
tension of the material, or the cohesion of the ink is less than the adhesion
between the ink and the material, so that the contact angle between the two is
less than 90 °� The wettability of the ink is good; Secondly, the polar traction
between ink molecules and film molecules should be as large as possible, and
the adhesion of ink is good.
9. Dryness of ink
After the ink is transferred to the
substrate through the printing plate, the film becomes a solid or quasi-solid
film through a series of physical or chemical changes, which is called dryness.
After the ink is transferred to the substrate, the drying speed should meet the
requirements of the printing conditions, otherwise there will be pulverization,
adhesion and other failures. On the one hand, the dryness of ink is affected by
the types and properties of its solvents, on the other hand, it is affected by
the machine drying device.
10. Viscoelasticity
On the printing press of book printing,
under the action of dynamic stress, the ink produces both viscous and elastic
reactions. With the increase of printing speed, the elastic reaction is more
obvious. The viscoelastic reaction of ink is very important for the separation
process of ink on printing press.
Gravure printing press printing speed is
fast, ink stress relaxation time is long, it is not easy to draw in printing,
that is, the ink section breaks in an instant, unable to show viscous flow, but
in the ink cohesion, it shows good resilience.
