PROPERTIES OF PRINTING INKS

 

 

PROPERTIES OF PRINTING INKS  

TACK:

It is stickiness of the ink. Tack may be done describe as the ability of the ink to act as an adhesive. It is by definition the force required to split an ink film between two rollers. Tack can be judged from a bite of ink between the finger- tips. To measure tack precisely, tack meters are employed. There are several instruments, but they all resemble the inking system of a printing machine. Typical tack meter (drag movements). The tackier the ink is, the force pulling the rider will be.

Tack is given in arbitrary units, which depend on the instrument and the methods used. Tack is an important property in the inking system as well as in the interaction between ink and paper and between in the inks. High tack is generally described, but too high tack will result in picking, that is: fibres are pulled out of the paper. Tack also plays an important role in ink trapping in four-colour printing. As a rule, the ink printed first should have a higher tack than the next one. Both tack and viscosity strongly depend on temperature.

VISCOSITY:

The speed at which various liquids flow will vary widely will search the light point more quickly than a linseed oil, this different in the speed is due to the difference in the resistance of the liquid to the force trying to move them, and this resistance to flow is known as viscosity. It is also defined as the ratio of sharing stress to sharing rate. Liquid that shows the ideal viscous behaviours are called Newtonian liquids. The most common type of increments use to measure the viscosity are “falling rod visco” meter and the “con & plate.”

TIXO-TROPY:

Lithographic ink are generally Tixotropy. In general inks thickness on standing and theis structure can be down by stirring. It is solid which can be broken down and made to flow by mechanical agitation. It is a solid body which can be broken down and made to flow by mechanical agitation.

Tixotropy is not reduced by an increase in temperature.

BODY:

It refers to the consistency stiffness or softness of the ink. Ink consistencies vary widely from very stiff inks to very sorted fluid inks for gravure &flexography conventional letter press and offset inks are shear thinning. They set to fairly, stiff mass in can. But when worked on a slab with an ink knife become quite fluid & flow freely this is why ink rollers are needed on letterpress & offset printing.

 

LENGTH:

It is a property associated with the ability of an ink to flow and form long filament. Newsprint inks characterized with this property have the consistency with poor flow property & have tendency to dump on rollers.

 

TRANSPARENCY & OPACITY:

To achieve the desire visual appearance inks have varying degree of transparency depending upon the light. Opaque’s pigments are used to when an image is to cover a substrate while the transparent pigments are used to allow background material to be seen. The choice of color at and the degree to which it has been dispersed are measure influence on this property. It depend on the particle size & reflective index of the pigment.