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Offset printing inks come with different formulas and properties. Since printing is done on a variety of materials, printing ink is also presented with different variety and characteristics, the properties of which vary based on the type of printed form, printing machine and finishing methods.
Inks can vary in terms of transparency, varnishing, resistance to heat, light, chemicals and solutions, and there are different types of composites and different formulas, each designed with a specific formula for printing a specific paper and special conditions of press and post press. There is no ink that can be the best type to do all kinds of print jobs. Ink that is suitable for printing different types of paper cannot be the best for any other printed work. Print houses should be in close contact with manufacturers and suppliers of inks and provide the most suitable composite according to their printed work requirements.
The ink should be tightened on the printed form immediately after printing to avoid staining or other damage to the printed image while moving the sheet and during the supplementary stages.
The ink is dried in the following ways:
Physical drying (absorption)
Chemical drying, oxidative (reaction with oxygen)
Combined drying (absorption and reaction with oxygen)
Chemical drying through high-energy radiation (UV = ultraviolet radiation)
Physical drying / absorption
Some inks penetrate the printed form and paste the pigment. Parts of the ink evaporate. Physical drying is relatively fast, drying time varies from minute to hour.
Inks that dry through absorption never quite tighten on the surface. Like: newspaper.
Such inks can only be used on absorbent paper.
Inks have little resistance to scratches or abrasions.
Modern printing inks usually use a combination of these drying methods to ensure good and fast ink drying on the printed form.
Chemical drying, oxidative
Some inks react with ambient oxygen and dry slowly, forming a hard layer on the surface of the paper.
This type of drying is slow, the drying time varies from hours to days (approximately 48 hours).
Chemically dried paints are suitable for less absorbent and non-absorbent layers such as aluminum paper, foils, parchment paper, metallic chromoly.
Additives that accelerate the drying process can reduce drying time to a few hours.
Inks that dry through oxidation form form a hard layer on the printed form and are resistant to scratches and abrasions.
When using these inks, you should take steps to prevent the ink from drying on the rollings when the machine stops.
The oxidative drying process generates heat. The texture of the paper will be heated.
Combined drying
The composition of printing inks is that part of the ink is physically dried (through absorption) and the other part is chemically (through oxidation, heat, radiation).
Be careful when using new ink. This ink can prolong the drying time!
Inks are dried by absorption (physically) and oxidation (chemically) on uncavailated paper, just like coated and casting layers.
Drying through energetic radiation (UV)
There are certain inks whose components react to radiation (UV radiation).
UV drying can be used on any printed form.
UV drying requires comprehensive and expensive modifications of printing machines: UV lamps, air extraction systems, UV-resistant escape protection, metal parts and non-corrosive pens, UV-resistant rollers.
The printing ink is composed of pigment dispersion (pigment) in a liquid called a carrier. Its color is determined by pigment and determines its transparency or opaqueness. The carrier provides the ink lubrication feature so that it can flow easily on composite rolls and uniformly give to the composite plate. In the printing phase and after the composite layer is placed on the printed surface, the carrier is changed from liquid to solid state, thereby sticking the pigment to the printed surface.
Two main factors cause problems in drying.
First, using inappropriate ink, second using extra water (high relative humidity) and excess acid (low pH). Offset ink should work along with moisture. Always some of the moisture in the water penetrates the compound during printing. But the compound should not be filled with water and become pasty or brittle or mixed with water. Ink mixed with fountain solution is transferred to the machine's water system, resulting in the transfer to all white parts without printing paper.
Ink manufacturers provide suitable characteristics for its proper function by selecting pigments and carriers and adjusting the concentration.
The factors affecting in the inking and printing of offsets are very high. Machine Offset encounters problems caused by compound performance that require knowledge and experience to solve it. Close cooperation between printing houses and composite manufacturers is necessary to prepare a suitable compound. Therefore, always consult and cooperate with a vendor who is familiar with the formula for making print ink and using the right additives to solve print problems.
The Drawbacks of Ink in Offset Printing
ink offset printing