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Gravure Printing Ink Types
With the development of printing technology, the variety of gravure printing ink is increasing, and there are many classification methods.
The printability of the ink refers to the performance of the ink that matches the printing conditions and is suitable for the printing operation. Mainly include viscosity, adhesion, thixotropy, dryness and so on.
1. Ink viscosity
The internal friction characteristics of the ink in the flow are called the viscosity of the ink, and the physical quantity that measures the viscosity of the ink is called the viscosity of the ink.
The viscosity of the ink can be measured with a viscometer. The commonly used viscometers include parallel plate viscometers, rotational viscometers, and Laray viscometers.
The faster the printing press, the greater the fluidity of the ink and the smaller the viscosity.
The viscosity of the ink can be adjusted with varnish or ink thinner.
2. Adhesion of ink
When the ink is transferred from the ink fountain to the ink roller, printing plate, (blanket) surface of the substrate, the ink film first splits and then transfers. The ability of the ink film to resist the rupture of the ink film in this dynamic process is called ink stickiness. A physical quantity that measures the adhesion of ink, is called the Tack value of the ink.
The Tack value of the ink can be measured with an ink tack meter.
During the printing process, if the adhesion of the ink does not match the performance of the substrate and the printing conditions, there will be printing failures such as paper powder loss, lint loss, poor ink overprinting, and printing plate dirt.
The adhesion of the ink can be adjusted with a detackifier or ZY ink additive.
3. Thixotropy of ink
At a certain temperature, after the ink is stirred or applied with mechanical external force, the fluidity is improved and the viscosity decreases; after standing, the fluidity becomes poor again and the viscosity increases. This property is called the thixotropy of the ink.
During the printing process, if the thixotropy of the ink is poor, there will be printing failures such as "poor ink delivery", uneven ink transfer, and serious expansion of dots. In order to prevent the occurrence of the above failures, it is necessary to use an ink shovel to stir the ink in the ink fountain frequently or install an ink agitator in the ink fountain to block the ink from time to time.
4. Drying of ink
The drying of ink is more complicated, mainly in the following three forms.
1) Penetrate dry.
A part of the binder in the ink penetrates into the substrate, and the other part is fixed on the surface of the substrate together with the pigment and dried. The non-thermosetting rotary inks used in high-speed web printing machines are generally based on penetration drying, mainly in printing newspapers and periodicals.
2) Oxidative polymerization drying.
The binder in the ink and the oxygen in the air undergoes a polymerization reaction to form a film on the surface of the substrate and dry. Offset glossy resin ink, bright color, good gloss, mainly oxidative polymerization drying, used for printing high-grade and fine offset products.
3) Evaporate and dry.
Part of the binder in the ink is volatilized into the air, and the remaining binder and the pigment are fixed on the surface of the substrate and dried. Gravure printing inks use volatile solvents as binders, and the binders used are benzene and xylene, which are harmful to the human body. At the beginning of the twentieth century, water-based inks using water as a solvent have been developed for gravure and flexographic printing, which reduces environmental pollution and has great prospects for development. Volatile drying inks are especially suitable for printing non-absorbent film materials, such as plastic films, metal foils, etc.
In addition, the drying of ink has various forms such as ultraviolet, infrared, and thermal curing.
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